Patent Publication Number: US-10772787-B2

Title: Assistance apparatus, assistance method, and recording medium

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an assistance apparatus, an assistance method, and a recording medium for assisting a wearer in walking. 
     2. Description of the Related Art 
     For example, Japanese Unexamined Patent Application Publication No. 2009-213538 discloses an assistant outfit for assisting movements of joints of a user. The disclosed assistant outfit includes a thigh link to be attached to a thigh, a thigh restraint band that restrains movement of the thigh link, a lower-leg link to be attached to a lower leg, a lower-leg restraint band that restrains movement of the lower-leg link, and a knee assistant motor that changes the angle between the thigh link and the lower-leg link. Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2016-528940 discloses a soft exosuit equipped with an actuator including an operating member. In the soft exosuit, activation of the actuator generates a moment around a joint of a user wearing the soft exosuit to assist the movement of the user. 
     SUMMARY 
     A need exists to provide assistance for movements of a user in different ways in accordance with the state of the user, such as whether the user is carrying an object such as luggage. A specific method for addressing this issue is not described in Japanese Unexamined Patent Application Publication No. 2009-213538 or Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2016-528940. 
     One non-limiting and exemplary embodiment provides an assistance apparatus, an assistance method, and a recording medium that provide assistance in accordance with the state of a user. 
     In one general aspect, the techniques disclosed here feature an assistance apparatus including an upper-body belt to be worn on an upper half of a body of a user, a left knee belt to be worn on a left knee of the user, a right knee belt to be worn on a right knee of the user, a first wire that couples the upper-body belt and the left knee belt to each other on or above a front part of the body of the user, a second wire that couples the upper-body belt and the left knee belt to each other on or above a back part of the body of the user, a third wire that couples the upper-body belt and the right knee belt to each other on or above the front part of the body of the user, a fourth wire that couples the upper-body belt and the right knee belt to each other on or above the back part of the body of the user, at least one motor, a first sensor that detects at least a tension of the first wire and a tension of the third wire, and a control circuit. In first assistance for assisting the user in walking without an object, the control circuit controls the at least one motor to generate (i) a tension greater than or equal to a first threshold value in the first wire during a first period, the first period being a period of 35% or more and 90% or less of a gait phase of a left leg of the user, (ii) a tension greater than or equal to the first threshold value in the second wire during a second period, the second period being a period of 0% or more and 25% or less and 65% or more and less than 100% of the gait phase of the left leg, (iii) a tension greater than or equal to the first threshold value in the third wire during a third period, the third period being a period of 35% or more and 90% or less of a gait phase of a right leg of the user, (iv) a tension greater than or equal to the first threshold value in the fourth wire during a fourth period, the fourth period being a period of 0% or more and 25% or less and 65% or more and less than 100% of the gait phase of the right leg, (v) a tension less than a second threshold value in the first wire during a fifth period, the fifth period being a period of 0% or more and less than 100% of the gait phase of the left leg, except the first period, (vi) a tension less than the second threshold value in the second wire during a sixth period, the sixth period being a period of 0% or more and less than 100% of the gait phase of the left leg, except the second period, (vii) a tension less than the second threshold value in the third wire during a seventh period, the seventh period being a period of 0% or more and less than 100% of the gait phase of the right leg, except the third period, and (viii) a tension less than the second threshold value in the fourth wire during an eighth period, the eighth period being a period of 0% or more and less than 100% of the gait phase of the right leg, except the fourth period. The first threshold value is larger than the second threshold value. The control circuit detects at least a break in the first wire and a break in the third wire based on a sensor value of the first sensor. In response to detection of a break in the first wire, the control circuit controls the at least one motor to generate a tension in the second wire during the second period that appears first after a timing of the break in the first wire, the tension being less than a tension of the second wire in a period during which no break occurs in the first wire. In response to detection of a break in the third wire, the control circuit controls the at least one motor to generate a tension in the fourth wire during the fourth period that appears first after a timing of the break in the third wire, the tension being less than a tension of the fourth wire in a period during which no break occurs in the third wire. 
     It should be noted that general or specific embodiments may be implemented as a system, an apparatus, a method, an integrated circuit, a computer program, a computer-readable recording medium such as a recording disk, or any selective combination thereof. The computer-readable recording medium includes a non-volatile recording medium such as a compact disc-read only memory (CD-ROM). 
     An assistance apparatus and so on according to aspects of the present disclosure can provide assistance in accordance with the state of a user. Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a user wearing an assistance apparatus according to an embodiment, as viewed from the front; 
         FIG. 2  is a back view of the user wearing the assistance apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a block diagram illustrating a functional configuration of the assistance apparatus according to the embodiment; 
         FIG. 4  is a diagram schematically illustrating the arrangement of constituent elements of the assistance apparatus illustrated in  FIG. 1 ; 
         FIG. 5  is a diagram illustrating example motions of the right leg of the user, which are assisted by the assistance apparatus; 
         FIG. 6A  is a diagram illustrating a case where the assistance apparatus according to the embodiment assists flexion of the hip joint of the left leg of the user; 
         FIG. 6B  is a diagram illustrating a case where the assistance apparatus according to the embodiment assists flexion of the hip joint of the right leg of the user; 
         FIG. 7A  is a diagram illustrating a case where the assistance apparatus according to the embodiment assists extension of the hip joint of the left leg of the user; 
         FIG. 7B  is a diagram illustrating a case where the assistance apparatus according to the embodiment assists extension of the hip joint of the right leg of the user; 
         FIG. 8  is a diagram illustrating an example of an input section of an input device included in the assistance apparatus according to the embodiment; 
         FIG. 9  is a diagram illustrating the arrangement of sensors and so on that are attached to the body of the user; 
         FIG. 10A  is a diagram illustrating a relationship between contact sensors and the hands of the user; 
         FIG. 10B  is a diagram illustrating an example of a signal of a contact sensor; 
         FIG. 11  is a diagram illustrating an example of a signal of a pressure-sensitive sensor; 
         FIG. 12  is a diagram illustrating an example of a signal of an acceleration sensor of an inertial measurement unit; 
         FIG. 13  is a perspective view of a user wearing an assistance apparatus according to a modification of the embodiment, as viewed obliquely from the front; 
         FIG. 14  is a front view of the user wearing the assistance apparatus illustrated in  FIG. 13 ; 
         FIG. 15  is a back view of the user wearing the assistance apparatus illustrated in  FIG. 13 ; 
         FIG. 16  is a diagram schematically illustrating the arrangement of constituent elements of the assistance apparatus illustrated in  FIG. 13 ; 
         FIG. 17  is a block diagram illustrating a functional configuration of the assistance apparatus illustrated in  FIG. 13 ; 
         FIG. 18  is a diagram illustrating a modification of the arrangement of wires in the assistance apparatus illustrated in  FIG. 13 ; 
         FIG. 19  is a diagram illustrating a modification of the arrangement of wires in the assistance apparatus illustrated in  FIG. 13 ; 
         FIG. 20  is a diagram illustrating a modification of the arrangement of wires in the assistance apparatus illustrated in  FIG. 13 ; 
         FIG. 21  is a diagram illustrating a modification of the arrangement of wires in the assistance apparatus illustrated in  FIG. 13 ; 
         FIG. 22A  is a diagram illustrating a case where the assistance apparatus according to the modification assists flexion of the hip joint of the left leg of the user; 
         FIG. 22B  is a diagram illustrating a case where the assistance apparatus according to the modification assists flexion of the hip joint of the right leg of the user; 
         FIG. 23A  is a diagram illustrating a case where the assistance apparatus according to the modification assists extension of the hip joint of the left leg of the user; 
         FIG. 23B  is a diagram illustrating a case where the assistance apparatus according to the modification assists extension of the hip joint of the right leg of the user; 
         FIG. 24  is a flowchart illustrating an example overall flow of an operation of the assistance apparatus according to the embodiment for assisting a user; 
         FIG. 25  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment for assisting a user in walking forward without an object; 
         FIG. 26  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment for assisting a user in walking forward with an object; 
         FIG. 27  is a flowchart illustrating an example flow of an operation of the assistance apparatus according to the embodiment when a wire is broken; 
         FIG. 28  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in a third pattern when a wire is broken during an operation in a first pattern in which no object is carried; 
         FIG. 29  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in the third pattern when a wire is broken during the operation in the first pattern in which no object is carried; 
         FIG. 30  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in the third pattern when a wire is broken during an operation in a second pattern in which an object is carried; 
         FIG. 31  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in the third pattern when a wire is broken during the operation in the second pattern in which an object is carried; 
         FIG. 32A  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in a fourth pattern when a wire is broken during the operation in the first pattern in which no object is carried; 
         FIG. 32B  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in the fourth pattern when a wire is broken during the operation in the first pattern in which no object is carried; 
         FIG. 33A  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in the fourth pattern when a wire is broken during the operation in the first pattern in which no object is carried; 
         FIG. 33B  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in the fourth pattern when a wire is broken during the operation in the first pattern in which no object is carried; 
         FIG. 34  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in the fourth pattern when a wire is broken during the operation in the second pattern in which an object is carried; and 
         FIG. 35  is a diagram illustrating an example operation of the assistance apparatus according to the embodiment in the fourth pattern when a wire is broken during the operation in the second pattern in which an object is carried. 
     
    
    
     DETAILED DESCRIPTION 
     Underlying Knowledge Forming Basis of the Present Disclosure 
     The inventors of the present disclosure, or the present inventors, have studied the techniques described in Japanese Unexamined Patent Application Publication No. 2009-213538 (hereinafter referred to as “Patent Literature 1”) and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2016-528940 (hereinafter referred to as “Patent Literature 2”) mentioned in the “BACKGROUND” section and have examined techniques for supporting, or assisting, a user in walking. The present inventors have focused on changing states of a user, who is a wearer of an assistance apparatus. For example, it is necessary that an assistance method for a user who is carrying an object such as luggage be different from an assistance method for a user who is carrying no object. 
     First, the present inventors have examined an assistance apparatus that assists a user in walking by applying forces generated by motors to the user through wires. To enable various kinds of assistance on the legs of a user, the present inventors have developed an assistance apparatus including wires, each of which is to be placed so as to extend across one of the front of the hip joint of the left leg of the user, the back of the hip joint of the left leg of the user, the front of the hip joint of the right leg of the user, and the back of the hip joint of the right leg of the user. The present inventors have further developed a configuration in which the wires are each coupled to an upper-body belt and a left knee belt or a right knee belt, which are to be attached to the body of the user, and are accordingly attached to the body of the user. Thus, the present inventors have devised an assistance apparatus having a simple configuration. 
     For example, Patent Literature 1 discloses an assistant outfit including a rod-shaped thigh link that is attached to a side portion of a thigh, and a rod-shaped lower-leg link that is attached to a side portion of a lower leg. The thigh link and the lower-leg link are coupled to a knee assistant motor. The knee assistant motor is driven to change the angle defined by the thigh link and the lower-leg link, and accordingly the assistant outfit assists flexion and extension of the knee of the user. The thigh link, the lower-leg link, and the knee assistant motor are attached to each of the side portion of the right leg of the user and the side portion of the left leg of the user, resulting in the assistant outfit disclosed in Patent Literature 1 having a structure that is large-scale and complicated for the user. Thus, the assistant outfit places a heavy burden on the user. 
     In Patent Literature 2, tension is applied to connection elements of the soft exosuit, which is worn on a part of the body of the user from the waist to a thigh and a lower leg, through a cable placed at the front part of the thigh of the user, thereby assisting flexion and extension of the knee of the user. In the soft exosuit disclosed in Patent Literature 2, the connection elements and so on, which are attached to the body of the user, are large-scale and complicated for the user. Thus, the soft exosuit places a heavy burden on the user. 
     In addition, none of Patent Literatures 1 and 2 discloses the details of a method for providing assistance in accordance with the state of a user. Accordingly, the present inventors have devised the following technique for providing assistance in accordance with the state of a user by using the assistance apparatus having a simple configuration described above. 
     An assistance apparatus according to an aspect of the present disclosure includes an upper-body belt to be worn on an upper half of a body of a user, a left knee belt to be worn on a left knee of the user, a right knee belt to be worn on a right knee of the user, a first wire that couples the upper-body belt and the left knee belt to each other on or above a front part of the body of the user, a second wire that couples the upper-body belt and the left knee belt to each other on or above a back part of the body of the user, a third wire that couples the upper-body belt and the right knee belt to each other on or above the front part of the body of the user, a fourth wire that couples the upper-body belt and the right knee belt to each other on or above the back part of the body of the user, at least one motor, a first sensor that detects at least a tension of the first wire and a tension of the third wire, and a control circuit. In first assistance for assisting the user in walking without an object, the control circuit controls the at least one motor to generate (i) a tension greater than or equal to a first threshold value in the first wire during a first period, the first period being a period of 35% or more and 90% or less of a gait phase of a left leg of the user, (ii) a tension greater than or equal to the first threshold value in the second wire during a second period, the second period being a period of 0% or more and 25% or less and 65% or more and less than 100% of the gait phase of the left leg, (iii) a tension greater than or equal to the first threshold value in the third wire during a third period, the third period being a period of 35% or more and 90% or less of a gait phase of a right leg of the user, (iv) a tension greater than or equal to the first threshold value in the fourth wire during a fourth period, the fourth period being a period of 0% or more and 25% or less and 65% or more and less than 100% of the gait phase of the right leg, (v) a tension less than a second threshold value in the first wire during a fifth period, the fifth period being a period of 0% or more and less than 100% of the gait phase of the left leg, except the first period, (vi) a tension less than the second threshold value in the second wire during a sixth period, the sixth period being a period of 0% or more and less than 100% of the gait phase of the left leg, except the second period, (vii) a tension less than the second threshold value in the third wire during a seventh period, the seventh period being a period of 0% or more and less than 100% of the gait phase of the right leg, except the third period, and (viii) a tension less than the second threshold value in the fourth wire during an eighth period, the eighth period being a period of 0% or more and less than 100% of the gait phase of the right leg, except the fourth period. The first threshold value is larger than the second threshold value. The control circuit detects at least a break in the first wire and a break in the third wire based on a sensor value of the first sensor. In response to detection of a break in the first wire, the control circuit controls the at least one motor to generate a tension in the second wire during the second period that appears first after a timing of the break in the first wire, the tension being less than a tension of the second wire in a period during which no break occurs in the first wire. In response to detection of a break in the third wire, the control circuit controls the at least one motor to generate a tension in the fourth wire during the fourth period that appears first after a timing of the break in the third wire, the tension being less than a tension of the fourth wire in a period during which no break occurs in the third wire. 
     In the configuration described above, the tension generated in the first wire can apply an assistance force for flexion to the left leg of the user, and the tension generated in the third wire can apply an assistance force for flexion to the right leg of the user. The tension generated in the second wire can apply an assistance force for extension to the left leg of the user, and the tension generated in the fourth wire can apply an assistance force for extension to the right leg of the user. In response to detection of a break in the first wire, the assistance apparatus reduces the tension to be generated in the second wire during the initial second period thereafter to a level smaller than that in a period during which no break occurs in the first wire. In response to detection of a break in the third wire, the assistance apparatus reduces the tension to be generated in the fourth wire during the initial fourth period thereafter to a level smaller than that in a period during which no break occurs in the third wire. Accordingly, the assistance apparatus weakens the assistance force for extension to be applied for the first time after a wire break to a leg for which a wire for assisting flexion is broken, compared with that before the wire break. If a wire break suddenly stops exerting an assistance force on the left or right leg, the user is likely to disrupt the balance between the movements of the left and right legs and can fall. Weakening the assistance force to be applied for the first time after the break to a leg of the user having a broken wire may prevent the user from disrupting the balance between the movements of the left and right legs. Thus, the assistance apparatus can provide assistance to the user in accordance with the state of the user. The first threshold value may be a tension value that allows the user to recognize that the movement of a leg is promoted by a tension generated in a wire, and may be 40 newtons (N), for example. The second threshold value may be a tension value that is not perceivable by the user. The second threshold value may be a tension value that prevents a wire from loosening, and may be a value that is 0.2 to 0.4 times the first threshold value or 10 N, for example. 
     In the assistance apparatus according to the aspect of the present disclosure, in second assistance for assisting the user in walking with an object, the control circuit may control the at least one motor to generate (i) a tension less than the second threshold value in the first wire during the fifth period, (ii) a tension greater than or equal to the second threshold value in the second wire during the sixth period, (iii) a tension less than the second threshold value in the third wire during the seventh period, and (iv) a tension greater than or equal to the second threshold value in the fourth wire during the eighth period. The tension of the second wire in the sixth period during the second assistance may be greater than the tension of the second wire in the sixth period during the first assistance. The tension of the fourth wire in the eighth period during the second assistance may be greater than the tension of the fourth wire in the eighth period during the first assistance. 
     In the configuration described above, the assistance apparatus generates a tension greater than or equal to the first threshold value in the first wire during the first period in the gait phase of the left leg to assist flexion of the left leg, and generates a tension greater than or equal to the first threshold value in the third wire during the third period in the gait phase of the right leg to assist flexion of the right leg, thereby assisting the user in walking. Further, the assistance apparatus sets the tension of the first wire to be less than the second threshold value during the fifth period in the gait phase of the left leg and sets the tension of the third wire to be less than the second threshold value during the seventh period in the gait phase of the right leg to weaken assistance for flexion or stop assisting flexion, thereby reducing an influence on extension of the legs. Further, the assistance apparatus generates a tension greater than or equal to the first threshold value in the second wire during the second period in the gait phase of the left leg to assist extension of the left leg, and generates a tension greater than or equal to the first threshold value in the fourth wire during the fourth period in the gait phase of the right leg to assist extension of the right leg, thereby assisting the user in walking. Further, the assistance apparatus sets the tension of the second wire to be greater than or equal to the second threshold value during the sixth period in the gait phase of the left leg to assist extension of the left leg, and sets the tension of the fourth wire to be greater than or equal to the second threshold value during the eighth period in the gait phase of the right leg to assist extension of the right leg. This may keep the center of gravity of the body of the user, who is carrying an object, at the position in the upright posture of the user. Thus, the assistance apparatus can assist a user in walking with an object while keeping the user in a stable posture. In addition, the assistance apparatus weakens, also for a user walking with an object, the assistance force for extension to be applied for the first time after a wire break to a leg for which a wire for assisting flexion is broken, compared with that before the wire break. 
     In the assistance apparatus according to the aspect of the present disclosure, the control circuit may control the at least one motor to generate (i) a tension in the second wire during the second period that appears second after the timing of the break in the first wire, the tension being equal to the tension of the second wire in the period during which no break occurs in the first wire, and (ii) a tension in the fourth wire during the fourth period that appears second after the timing of the break in the third wire, the tension being equal to the tension of the fourth wire in the period during which no break occurs in the third wire. 
     In the configuration described above, the assistance apparatus sets the wire tension for extension to be applied for the second time to a leg, for which a wire for assisting flexion is broken, after a wire break occurs, that is, an assistance force, to be the same as that before the wire break. The timing at which a wire tension for extension is applied for the second time after a wire break occurs corresponds to a time point when one or more gait phases elapse after the wire break. At this time point, the user is likely to restore the balance between the movements of the left and right legs to a stable state from an unstable state immediately after the wire break has occurred. Thus, even if an assistance force for extension to be applied to a leg for which a wire is broken is returned to that when there is no wire break, such an assistance force may less affect the body balance of the user. In addition, a uniform and sufficiently strong assistance force for extension is applied to the left and right legs of the user, and thus the user can be stably and sufficiently assisted by the assistance apparatus in walking. 
     In the assistance apparatus according to the aspect of the present disclosure, the control circuit may control the at least one motor to generate (i) a tension less than the second threshold value in the third wire during the third period after the timing of the break in the first wire, and (ii) a tension less than the second threshold value in the first wire during the first period after the timing of the break in the third wire. 
     In the configuration described above, if a wire for assisting flexion of one of the left and right legs is broken, the assistance apparatus reduces the tension to be generated in a wire for assisting flexion of the other of the left and right legs to a value less than the second threshold value. This reduces the unbalance in assistance for flexion to be provided to the user between a leg for which a wire is broken and a leg for which no wire is broken. Accordingly, the assistance apparatus can provide assistance with improved balance to the left and right legs of the user. 
     In the assistance apparatus according to the aspect of the present disclosure, the left leg may shift from a stance phase to a swing phase during the first period, the left leg may shift from the swing phase to the stance phase during the second period, the right leg may shift from the stance phase to the swing phase during the third period, and the right leg may shift from the swing phase to the stance phase during the fourth period. 
     In the configuration described above, the assistance apparatus assists flexion during the first period in which the left leg shifts from the stance phase to the swing phase, and assists flexion during the third period in which the right leg shifts from the stance phase to the swing phase. Thus, the assistance apparatus can effectively assist the user in walking. Further, the assistance apparatus assists extension during the second period in which the left leg shifts from the swing phase to the stance phase, and assists extension during the fourth period in which the right leg shifts from the swing phase to the stance phase. Thus, the assistance apparatus can effectively assist the user in walking. 
     In the assistance apparatus according to the aspect of the present disclosure, in the second assistance, the tension of the first wire in the fifth period may be less than the tension of the second wire in the sixth period, and the tension of the third wire in the seventh period may be less than the tension of the fourth wire in the eighth period. 
     In the configuration described above, in the second assistance, the tension of the first wire during the fifth period in the gait phase of the left leg can be prevented from affecting assistance for extension with the tension of the second wire during the sixth period in the gait phase of the left leg. Further, the tension of the third wire during the seventh period in the gait phase of the right leg can be prevented from affecting assistance for extension with the tension of the fourth wire during the eighth period in the gait phase of the right leg. Accordingly, the assistance apparatus can effectively maintain the center of gravity of the body of the user, who is carrying an object, at the position in the upright posture of the user. 
     In the assistance apparatus according to the aspect of the present disclosure, the at least one motor may include a first motor, a second motor, a third motor, and a fourth motor. The first wire may have a first end fixed to the left knee belt. The first wire may have a second end fixed to the first motor. The second wire may have a first end fixed to the left knee belt. The second wire may have a second end fixed to the second motor. The third wire may have a first end fixed to the right knee belt. The third wire may have a second end fixed to the third motor. The fourth wire may have a first end fixed to the right knee belt. The fourth wire may have a second end fixed to the fourth motor. 
     In the configuration described above, the assistance apparatus can separately control the respective tensions of the first wire, the second wire, the third wire, and the fourth wire. Thus, the assistance apparatus can provide fine assistance. 
     The assistance apparatus according to the aspect of the present disclosure may further include a fifth wire that couples the upper-body belt and the left knee belt to each other and that extends on or above the front part of the body of the user in a direction crossing a direction in which the first wire extends, a sixth wire that couples the upper-body belt and the left knee belt to each other and that extends on or above the back part of the body of the user in a direction crossing a direction in which the second wire extends, a seventh wire that couples the upper-body belt and the right knee belt to each other and that extends on or above the front part of the body of the user in a direction crossing a direction in which the third wire extends, and an eighth wire that couples the upper-body belt and the right knee belt to each other and that extends on or above the back part of the body of the user in a direction crossing a direction in which the fourth wire extends. In the first assistance, the control circuit may control the at least one motor to generate (i) a tension greater than or equal to the first threshold value in the first wire and the fifth wire during the first period, (ii) a tension greater than or equal to the first threshold value in the second wire and the sixth wire during the second period, (iii) a tension greater than or equal to the first threshold value in the third wire and the seventh wire during the third period, (iv) a tension greater than or equal to the first threshold value in the fourth wire and the eighth wire during the fourth period, (v) a tension less than the second threshold value in the first wire and the fifth wire during the fifth period, (vi) a tension less than the second threshold value in the second wire and the sixth wire during the sixth period, (vii) a tension less than the second threshold value in the third wire and the seventh wire during the seventh period, and (viii) a tension less than the second threshold value in the fourth wire and the eighth wire during the eighth period. 
     In the configuration described above, the tensions generated in the first and fifth wires can apply an assistance force for flexion to the left leg of the user. The tensions generated in the second and sixth wires can apply an assistance force for extension to the left leg of the user. The tensions generated in the third and seventh wires can apply an assistance force for flexion to the right leg of the user. The tensions generated in the fourth and eighth wires can apply an assistance force for extension to the right leg of the user. Thus, the assistance apparatus including the first to eighth wires can provide the first assistance in a way similar to that for the assistance apparatus including the first to fourth wires. In addition, the assistance apparatus including the first to eighth wires separately controls the respective tensions of the first to eighth wires, thereby providing more types of assistance. For example, the tensions generated in the first and fifth wires may be the same or different, and a different type of assistance can be provided in each case. 
     In the assistance apparatus according to the aspect of the present disclosure, in second assistance for assisting the user in walking with an object, the control circuit may control the at least one motor to generate (i) a tension less than the second threshold value in the first wire during the fifth period, (ii) a tension greater than or equal to the second threshold value in the second wire during the sixth period, (iii) a tension less than the second threshold value in the third wire during the seventh period, and (iv) a tension greater than or equal to the second threshold value in the fourth wire during the eighth period. The tension of the second wire in the sixth period during the second assistance may be greater than the tension of the second wire in the sixth period during the first assistance. The tension of the fourth wire in the eighth period during the second assistance may be greater than the tension of the fourth wire in the eighth period during the first assistance. In the second assistance, the control circuit may control the at least one motor to generate (i) a tension less than the second threshold value in the first wire and the fifth wire during the fifth period, (ii) a tension greater than or equal to the second threshold value in the second wire and the sixth wire during the sixth period, (iii) a tension less than the second threshold value in the third wire and the seventh wire during the seventh period, and (iv) a tension greater than or equal to the second threshold value in the fourth wire and the eighth wire during the eighth period. 
     In the configuration described above, the assistance apparatus including the first to eighth wires can provide the second assistance in a way similar to that for the assistance apparatus including the first to fourth wires. 
     In the assistance apparatus according to the aspect of the present disclosure, a time point of 50% of the gait phase of the left leg may correspond to a time point of 0% of the gait phase of the right leg, and a time point of 50% of the gait phase of the right leg may correspond to a time point of 0% of the gait phase of the left leg. 
     The assistance apparatus according to the aspect of the present disclosure may further include a memory. The memory may store a program for controlling the at least one motor. The control circuit may control the at least one motor in accordance with the program. 
     The assistance apparatus according to the aspect of the present disclosure may further include a second sensor that detects a gait cycle of the user. The control circuit may calculate the gait phase of the left leg and the gait phase of the right leg based on a sensor value of the second sensor. 
     In the configuration described above, the assistance apparatus can assist the user in walking on the basis of a gait phase corresponding to a gait cycle of the user. Accordingly, the assistance apparatus can provide assistance based on actual user walking. 
     The assistance apparatus according to the aspect of the present disclosure may further include an interface device. The control circuit may accept selection of an assistance method including the first assistance via the interface device. The control circuit may control the at least one motor in accordance with the assistance method. 
     In the configuration described above, the assistance apparatus enables selection of an assistance method desired by the user. 
     An assistance method according to another aspect of the present disclosure is an assistance method for assisting a movement of a user by using wires attached to a body of the user. The assistance method include coupling, using a first wire among the wires, an upper-body belt and a left knee belt to each other on or above a front part of the body of the user, the upper-body belt being a belt to be worn on an upper half of the body of the user, the left knee belt being a belt to be worn on a left knee of the user; coupling, using a second wire among the wires, the upper-body belt and the left knee belt to each other on or above a back part of the body of the user; coupling, using a third wire among the wires, the upper-body belt and a right knee belt to each other on or above the front part of the body of the user, the right knee belt being a belt to be worn on a right knee of the user; coupling, using a fourth wire among the wires, the upper-body belt and the right knee belt to each other on or above the back part of the body of the user; in first assistance for assisting the user in walking without an object, generating a tension greater than or equal to a first threshold value in the first wire during a first period, the first period being a period of 35% or more and 90% or less of a gait phase of a left leg of the user; generating a tension greater than or equal to the first threshold value in the second wire during a second period, the second period being a period of 0% or more and 25% or less and 65% or more and less than 100% of the gait phase of the left leg; generating a tension greater than or equal to the first threshold value in the third wire during a third period, the third period being a period of 35% or more and 90% or less of a gait phase of a right leg of the user; generating a tension greater than or equal to the first threshold value in the fourth wire during a fourth period, the fourth period being a period of 0% or more and 25% or less and 65% or more and less than 100% of the gait phase of the right leg; generating a tension less than a second threshold value in the first wire during a fifth period, the fifth period being a period of 0% or more and less than 100% of the gait phase of the left leg, except the first period; generating a tension less than the second threshold value in the second wire during a sixth period, the sixth period being a period of 0% or more and less than 100% of the gait phase of the left leg, except the second period; generating a tension less than the second threshold value in the third wire during a seventh period, the seventh period being a period of 0% or more and less than 100% of the gait phase of the right leg, except the third period; generating a tension less than the second threshold value in the fourth wire during an eighth period, the eighth period being a period of 0% or more and less than 100% of the gait phase of the right leg, except the fourth period, the first threshold value being larger than the second threshold value; acquiring a sensor value of a first sensor that detects at least a tension of the first wire and a tension of the third wire; in response to detection of a break in the first wire, generating a tension in the second wire during the second period that appears first after a timing of the break in the first wire, the tension being less than a tension of the second wire in a period during which no break occurs in the first wire; and in response to detection of a break in the third wire, generating a tension in the fourth wire during the fourth period that appears first after a timing of the break in the third wire, the tension being less than a tension of the fourth wire in a period during which no break occurs in the third wire. The tension of the first wire, the tension of the second wire, the tension of the third wire, and the tension of the fourth wire are adjusted by a motor that is controlled by at least one control circuit. The assistance method according to the aspect described above can achieve advantages similar to those of the assistance apparatus according to the aspect of the present disclosure. 
     The assistance method according to the aspect of the present disclosure may further include, in second assistance for assisting the user in walking with an object, generating a tension less than the second threshold value in the first wire during the fifth period; generating a tension greater than or equal to the second threshold value in the second wire during the sixth period; generating a tension less than the second threshold value in the third wire during the seventh period; and generating a tension greater than or equal to the second threshold value in the fourth wire during the eighth period. The tension of the second wire in the sixth period during the second assistance may be greater than the tension of the second wire in the sixth period during the first assistance. The tension of the fourth wire in the eighth period during the second assistance may be greater than the tension of the fourth wire in the eighth period during the first assistance. 
     The assistance method according to the aspect of the present disclosure may further include generating a tension in the second wire during the second period that appears second after the timing of the break in the first wire, the tension being equal to the tension of the second wire in the period during which no break occurs in the first wire; and generating a tension in the fourth wire during the fourth period that appears second after the timing of the break in the third wire, the tension being equal to the tension of the fourth wire in the period during which no break occurs in the third wire. 
     The assistance method according to the aspect of the present disclosure may further include generating a tension less than the second threshold value in the third wire during the third period after the timing of the break in the first wire; and generating a tension less than the second threshold value in the first wire during the first period after the timing of the break in the third wire. 
     In the assistance method according to the aspect of the present disclosure, the left leg may shift from a stance phase to a swing phase during the first period, the left leg may shift from the swing phase to the stance phase during the second period, the right leg may shift from the stance phase to the swing phase during the third period, and the right leg may shift from the swing phase to the stance phase during the fourth period. 
     In the assistance method according to the aspect of the present disclosure, in the second assistance, the tension of the first wire in the fifth period may be less than the tension of the second wire in the sixth period, and the tension of the third wire in the seventh period may be less than the tension of the fourth wire in the eighth period. 
     In the assistance method according to the aspect of the present disclosure, a first end of the first wire may be fixed to the left knee belt, a second end of the first wire may be fixed to a first motor among the at least one motor, a first end of the second wire may be fixed to the left knee belt, a second end of the second wire may be fixed to a second motor among the at least one motor, a first end of the third wire may be fixed to the right knee belt, a second end of the third wire may be fixed to a third motor among the at least one motor, a first end of the fourth wire may be fixed to the right knee belt, and a second end of the fourth wire may be fixed to a fourth motor among the at least one motor. 
     The assistance method according to the aspect of the present disclosure may further include coupling, using a fifth wire among the wires, the upper-body belt and the left knee belt to each other, the fifth wire extending on or above the front part of the body of the user in a direction crossing a direction in which the first wire extends; coupling, using a sixth wire among the wires, the upper-body belt and the left knee belt to each other, the sixth wire extending on or above the back part of the body of the user in a direction crossing a direction in which the second wire extends; coupling, using a seventh wire among the wires, the upper-body belt and the right knee belt to each other, the seventh wire extending on or above the front part of the body of the user in a direction crossing a direction in which the third wire extends; coupling, using an eighth wire among the wires, the upper-body belt and the right knee belt to each other, the eighth wire extending on or above the back part of the body of the user in a direction crossing a direction in which the fourth wire extends; in the first assistance, generating a tension greater than or equal to the first threshold value in the first wire and the fifth wire during the first period; generating a tension greater than or equal to the first threshold value in the second wire and the sixth wire during the second period; generating a tension greater than or equal to the first threshold value in the third wire and the seventh wire during the third period; generating a tension greater than or equal to the first threshold value in the fourth wire and the eighth wire during the fourth period; generating a tension less than the second threshold value in the first wire and the fifth wire during the fifth period; generating a tension less than the second threshold value in the second wire and the sixth wire during the sixth period; generating a tension less than the second threshold value in the third wire and the seventh wire during the seventh period; and generating a tension less than the second threshold value in the fourth wire and the eighth wire during the eighth period. 
     The assistance method according to the aspect of the present disclosure may further include, in second assistance for assisting the user in walking with an object, generating a tension less than the second threshold value in the first wire during the fifth period; generating a tension greater than or equal to the second threshold value in the second wire during the sixth period; generating a tension less than the second threshold value in the third wire during the seventh period; generating a tension greater than or equal to the second threshold value in the fourth wire during the eighth period, the tension of the second wire in the sixth period during the second assistance being greater than the tension of the second wire in the sixth period during the first assistance, the tension of the fourth wire in the eighth period during the second assistance being greater than the tension of the fourth wire in the eighth period during the first assistance; in the second assistance, generating a tension less than the second threshold value in the first wire and the fifth wire during the fifth period; generating a tension greater than or equal to the second threshold value in the second wire and the sixth wire during the sixth period; generating a tension less than the second threshold value in the third wire and the seventh wire during the seventh period; and generating a tension greater than or equal to the second threshold value in the fourth wire and the eighth wire during the eighth period. 
     In the assistance method according to the aspect of the present disclosure, a time point of 50% of the gait phase of the left leg may correspond to a time point of 0% of the gait phase of the right leg, and a time point of 50% of the gait phase of the right leg may correspond to a time point of 0% of the gait phase of the left leg. 
     The assistance method according to the aspect of the present disclosure may further include acquiring a sensor value of a second sensor that detects a gait cycle of the user; and calculating the gait phase of the left leg and the gait phase of the right leg based on the sensor value of the second sensor. 
     The assistance method according to the aspect of the present disclosure may further include accepting selection of an assistance method including the first assistance via an interface device; and generating a tension in the first wire, the second wire, the third wire, and the fourth wire in accordance with the assistance method. 
     A recording medium according to still another aspect of the present disclosure is a recording medium storing a control program for causing a device including a processor to execute a process. The recording medium is a non-volatile, computer-readable medium. A first wire couples an upper-body belt and a left knee belt to each other on or above a front part of a body of a user, the upper-body belt being a belt to be worn on an upper half of the body of the user, the left knee belt being a belt to be worn on a left knee of the user. A second wire couples the upper-body belt and the left knee belt to each other on or above a back part of the body of the user. A third wire couples the upper-body belt and a right knee belt to each other on or above the front part of the body of the user, the right knee belt being a belt to be worn on a right knee of the user. A fourth wire couples the upper-body belt and the right knee belt to each other on or above the back part of the body of the user. The process includes when assisting the user in walking without an object, causing at least one motor to generate a tension greater than or equal to a first threshold value in the first wire during a first period, the first period being a period of 35% or more and 90% or less of a gait phase of a left leg of the user; causing the at least one motor to generate a tension greater than or equal to the first threshold value in the second wire during a second period, the second period being a period of 0% or more and 25% or less and 65% or more and less than 100% of the gait phase of the left leg; causing the at least one motor to generate a tension greater than or equal to the first threshold value in the third wire during a third period, the third period being a period of 35% or more and 90% or less of a gait phase of a right leg of the user; causing the at least one motor to generate a tension greater than or equal to the first threshold value in the fourth wire during a fourth period, the fourth period being a period of 0% or more and 25% or less and 65% or more and less than 100% of the gait phase of the right leg; causing the at least one motor to generate a tension less than a second threshold value in the first wire during a fifth period, the fifth period being a period of 0% or more and less than 100% of the gait phase of the left leg, except the first period; causing the at least one motor to generate a tension less than the second threshold value in the second wire during a sixth period, the sixth period being a period of 0% or more and less than 100% of the gait phase of the left leg, except the second period; causing the at least one motor to generate a tension less than the second threshold value in the third wire during a seventh period, the seventh period being a period of 0% or more and less than 100% of the gait phase of the right leg, except the third period; causing the at least one motor to generate a tension less than the second threshold value in the fourth wire during an eighth period, the eighth period being a period of 0% or more and less than 100% of the gait phase of the right leg, except the fourth period, the first threshold value being larger than the second threshold value; acquiring a sensor value of a first sensor that detects at least a tension of the first wire and a tension of the third wire; in response to detection of a break in the first wire, generating a tension in the second wire during the second period that appears first after a timing of the break in the first wire, the tension being less than a tension of the second wire in a period during which no break occurs in the first wire; and in response to detection of a break in the third wire, generating a tension in the fourth wire during the fourth period that appears first after a timing of the break in the third wire, the tension being less than a tension of the fourth wire in a period during which no break occurs in the third wire. The recording medium according to the aspect described above can achieve advantages similar to those of the assistance apparatus according to the aspect of the present disclosure. 
     It should be noted that the general or specific aspects described above may be implemented as a system, an apparatus, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a recording disc, or any selective combination thereof. Examples of the computer-readable recording medium include a non-volatile recording medium such as a CD-ROM. 
     Embodiment 
     The following specifically describes an assistance apparatus and so on according to an embodiment of the present disclosure with reference to the drawings. The following embodiment describes general or specific examples. Numerical values, shapes, constituent elements, arrangement positions and connection forms of the constituent elements, steps, the order of the steps, and so on in the following embodiment are merely examples and are not intended to limit the present disclosure. The constituent elements mentioned in the following embodiment are described as optional constituent elements unless they are specified in independent claims that define the present disclosure in its broadest concept. The following description of the embodiment may include expressions with the term “approximately”, such as approximately parallel or approximately perpendicular. For example, the expression “approximately parallel” is used to mean not only the state of being exactly parallel but also the state of being substantially parallel, that is, the state of being parallel with an error of several percent, for example. This also applies to other expressions with “approximately”. In addition, the drawings are illustrative and are not to scale. In the drawings, substantially the same constituent elements are given the same numerals and will not be repeatedly described or will be described in brief. 
     In this embodiment, an assistance apparatus  100  will be described as an assistance apparatus that assists a user wearing the assistance apparatus  100  in walking. Specifically, the assistance apparatus  100  according to the embodiment will be described as an assistance apparatus that actively supports flexion and extension of the hip joints of the user to allow the user to walk. In this embodiment, the term “actively supporting” may refer not only to supporting flexion and extension forces, which are required for the hip joints, during flexion and extension of the hip joints of the user to walk in the direction of travel but also to applying a force for causing flexion and extension of the hip joints and to physically controlling the amount of flexion and extension of the hip joints to the desired amount of flexion and extension, that is, physically controlling movements of the hip joints of the user. As used herein, the term “assisting the user” by the assistance apparatus  100  is used to include both actively supporting the movement of the user and supporting the movement of the user in an auxiliary manner. 
     1. Configuration of Assistance Apparatus According to Embodiment 
     The assistance apparatus  100  according to the embodiment will be described with reference to  FIG. 1  to  FIG. 3 .  FIG. 1  is a front view of a user  1  wearing the assistance apparatus  100  according to the embodiment, as viewed from the front.  FIG. 2  is a back view of the user  1  wearing the assistance apparatus  100  illustrated in  FIG. 1 .  FIG. 3  is a block diagram illustrating a functional configuration of the assistance apparatus  100  according to the embodiment. 
     As illustrated in  FIG. 1  to  FIG. 3 , the assistance apparatus  100  includes an upper-body belt  111 , a left knee belt  112   a , a right knee belt  112   b , and wires  110 . The assistance apparatus  100  further includes motors  114 , force sensors  115 , and a control unit  120  that controls the operation of the motors  114 . The assistance apparatus  100  may include a power supply  130  for supplying electric power to the motors  114  and so on. The power supply  130  may be, for example, a primary battery, a secondary battery, or the like. 
     The wires  110  include wires  110   a   1  to  110   a   4 . Each of the wires  110  is coupled to the upper-body belt  111  and the left knee belt  112   a  or coupled to the upper-body belt  111  and the right knee belt  112   b.    
     The motors  114  include motors  114   a   1  to  114   a   4 . The wire  110   a   1  is coupled to the motor  114   a   1 . The wire  110   a   2  is coupled to the motor  114   a   2 . The wire  110   a   3  is coupled to the motor  114   a   3 . The wire  110   a   4  is coupled to the motor  114   a   4 . 
     The force sensors  115  include force sensors  115   a   1  to  115   a   4 . The force sensor  115   a   1  is disposed on the wire  110   a   1 . The force sensor  115   a   2  is disposed on the wire  110   a   2 . The force sensor  115   a   3  is disposed on the wire  110   a   3 . The force sensor  115   a   4  is disposed on the wire  110   a   4 . 
     The upper-body belt  111  is worn on the upper half of the body of the user  1 . The upper-body belt  111  has a band shape, for example. The upper-body belt  111  includes, near an end portion thereof, a fixing member. Examples of the fixing member include a hook-and-loop fastener such as a Velcro (registered trademark) tape, a fastener such as a hook or a buckle, and a tape. For example, the upper-body belt  111  is wrapped around the waist of the user  1  and is kept wrapped around the waist of the user  1  by using the fixing member. Thus, the upper-body belt  111  is worn on the waist of the user  1 . The fixing position of the fixing member is adjusted to change the inner diameter of the wrapped upper-body belt  111 . Since the length of the upper-body belt  111  can be adjusted, various users  1  with different waist circumferences can wear the upper-body belt  111 . The upper-body belt  111  is made of a non-extensible material, for example. Thus, the upper-body belt  111  is less deformable when pulled by the wires  110 . The term “upper half of the body”, as used herein, is used to include a portion of the body of the user from the shoulder to the waist. The upper-body belt  111  illustrated in  FIG. 1  and  FIG. 2  has a configuration of a waist belt to be worn on the waist of the user  1 . The upper-body belt  111  may be worn on, for example, the waist of the user  1  and/or the shoulder of the user  1  and/or the chest of the user  1 . 
     The upper-body belt  111  may have a tubular shape. In this case, the tubular-shaped upper-body belt  111  may have a larger circumference than the waist circumference of the user  1 . The upper-body belt  111  has an adjustment mechanism for adjusting the length of the upper-body belt  111  so that the upper-body belt  111  fits the waist of the user  1 . The adjustment mechanism is, for example, a hook-and-loop fastener and may be configured such that a portion of the hook-and-loop fastener having a hook surface is located on an outer periphery of the tubular shape in such a manner as to branch from the outer periphery and a loop surface of the hook-and-loop fastener is located on an outer peripheral surface of the tubular shape. That is, the upper-body belt  111  folds back at the portion of the hook-and-loop fastener, and the inner diameter of the tube formed by the upper-body belt  111  changes in accordance with the amount of fold-back. 
     The left knee belt  112   a  is worn on the left leg of the user  1  in the vicinity of the left knee, and the right knee belt  112   b  is worn on the right leg of the user  1  in the vicinity of the right knee. The left knee belt  112   a  may be worn on any portion of the left leg in a region extending from below the knee to the thigh. The right knee belt  112   b  may be worn on any portion of the right leg in a region extending from below the knee to the thigh. That is, the term “knee”, as used herein, may be used to include a region extending from below the knee to the thigh. 
     Each of the knee belts  112   a  and  112   b  has a band shape, for example, and includes, near an end portion thereof, a fixing member. The knee belts  112   a  and  112   b  are the knee left belt  112   a  and the right knee belt  112   b . Examples of the fixing member include a hook-and-loop fastener such as a Velcro (registered trademark) tape, a fastener such as a hook or a buckle, and a tape. Each of the knee belts  112   a  and  112   b  is worn on a corresponding one of the thighs of the user  1  or above a corresponding one of the knees of the user  1 . For example, each of the knee belts  112   a  and  112   b  is wrapped around the corresponding one of the thighs or the like of the user  1  and is kept wrapped around the corresponding one of the thighs or the like of the user  1  by using the fixing member. Thus, the knee belts  112   a  and  112   b  are worn on the thighs or the like of the user  1 . The fixing positions of the fixing members are adjusted to change the respective inner diameters of the wrapped knee belts  112   a  and  112   b . Since the lengths of the knee belts  112   a  and  112   b  can be adjusted, various users  1  having different leg circumferences can wear the knee belts  112   a  and  112   b . The knee belts  112   a  and  112   b  may not necessarily be worn over the knee joints. The human thigh has a feature in that the diameter of the thigh becomes larger gradually from the knee toward the hip. Thus, the knee belts  112   a  and  112   b , which are worn on the thighs, namely, above the knees, slip just a little even under tensile forces of the wires  110  when the knee belts  112   a  and  112   b  are tightly fastened. In addition, the knee belts  112   a  and  112   b  are made of a non-extensible material, for example. Thus, the knee belts  112   a  and  112   b  are less deformable when pulled by the wires  110 . 
     Each of the knee belts  112   a  and  112   b  may have a tubular shape. In this case, the tubular-shaped knee belts  112   a  and  112   b  may have larger circumferences than the thighs of the user  1 . The knee belts  112   a  and  112   b  have each an adjustment mechanism for adjusting the length of the corresponding one of the knee belts  112   a  and  112   b  so that the knee belts  112   a  and  112   b  fit the thighs or the like of the user  1 . Each of the adjustment mechanisms is, for example, a hook-and-loop fastener and may be configured such that a portion of the hook-and-loop fastener having a hook surface is located on an outer periphery of the tubular shape in such a manner as to branch from the outer periphery and a loop surface of the hook-and-loop fastener is located on an outer peripheral surface of the tubular shape. That is, the knee belts  112   a  and  112   b  each fold back at the portion of the hook-and-loop fastener, and the inner diameter of the tube formed by each of the knee belts  112   a  and  112   b  changes in accordance with the amount of fold-back. 
     The motors  114  are arranged on the upper-body belt  111  in a fixed manner. In this embodiment, the motors  114  include four motors  114   a   1  to  114   a   4 . For example, the motors  114   a   1  to  114   a   4  may be accommodated in hollow containers  111   a   1  to  111   a   4  included in the upper-body belt  111 , respectively. The containers  111   a   1  to  111   a   4  may be integrated with the upper-body belt  111  or may be removably attached to the upper-body belt  111 . The containers  111   a   1  to  111   a   4  may be disposed in the manner illustrated in  FIG. 1  and  FIG. 2 . In the example illustrated in  FIG. 1  and  FIG. 2 , the containers  111   a   1 ,  111   a   2 ,  111   a   3 , and  111   a   4  are located on the left side of the front part, the left side of the back part, the right side of the front part, and the right side of the back part of the body of the user  1 , respectively. The motors  114   a   1 ,  114   a   2 ,  114   a   3 , and  114   a   4  are accommodated in the containers  111   a   1 ,  111   a   2 ,  111   a   3 , and  111   a   4 , respectively. The motor  114   a   1  changes the length of the wire  110   a   1  between the upper-body belt  111  and the left knee belt  112   a  to adjust the tension of the wire  110   a   1 . The motor  114   a   2  changes the length of the wire  110   a   2  between the upper-body belt  111  and the left knee belt  112   a  to adjust the tension of the wire  110   a   2 . The motor  114   a   3  changes the length of the wire  110   a   3  between the upper-body belt  111  and the right knee belt  112   b  to adjust the tension of the wire  110   a   3 . The motor  114   a   4  changes the length of the wire  110   a   4  between the upper-body belt  111  and the right knee belt  112   b  to adjust the tension of the wire  110   a   4 . 
     In this embodiment, each of the motors  114   a   1  to  114   a   4  includes a pulley, a drive shaft for rotating the pulley, and an electric motor for driving the drive shaft to rotate. The pulley of each of the motors  114   a   1  to  114   a   4  has a corresponding wire among the wires  110   a   1  to  110   a   4  wound therearound. The motors  114   a   1  to  114   a   4  and the wires  110   a   1  to  110   a   4  have a one-to-one correspondence. The respective pulleys, drive shafts, and electric motors of the motors  114   a   1  to  114   a   4  are accommodated in the containers  111   a   1  to  111   a   4 , respectively. Each of the motors  114   a   1  to  114   a   4  may include an electric motor, but may include no pulley or drive shaft. Alternatively, the upper-body belt  111  may include pulleys and drive shafts, each pulley and drive shaft being associated with one of the motors  114   a   1  to  114   a   4 . In this case, a rotating shaft of the electric motor is coupled to the drive shaft for the pulley in such a manner that a rotational driving force can be transmitted to the drive shaft. Instead of the motors  114   a   1  to  114   a   4 , for example, a device capable of adjusting the lengths of the wires  110   a   1  and  110   a   2  between the upper-body belt  111  and the left knee belt  112   a  and the lengths of the wires  110   a   3  and  110   a   4  between the upper-body belt  111  and the right knee belt  112   b , such as a linear actuator or a pneumatic or hydraulic piston, may be used. In the assistance apparatus  100  having the configuration described above, the wound portions of the wires  110   a   1  to  110   a   4  and the motors  114   a   1  to  114   a   4  are located on the upper-body belt  111 , and the wires  110   a   1  to  110   a   4  and the knee belts  112   a  and  112   b  are located below the upper-body belt  111 . Accordingly, the assistance apparatus  100  achieves a simple and compact configuration. 
     In this embodiment, the wires  110  include four wires  110   a   1  to  110   a   4 . The motor  114   a   1  is coupled to the wire  110   a   1 , the motor  114   a   2  is coupled to the wire  110   a   2 , the motor  114   a   3  is coupled to the wire  110   a   3 , and the motor  114   a   4  is coupled to the wire  110   a   4  so as to individually adjust the lengths of the wires  110   a   1  to  110   a   4 . 
     Each of the wires  110   a   1  and  110   a   2  has one end fixed to the left knee belt  112   a . The wire  110   a   1  has another end coupled to the motor  114   a   1 , and the wire  110   a   2  has another end coupled to the motor  114   a   2 . That is, the other end of the wire  110   a   1  and the other end of the wire  110   a   2  are fixed. The wire  110   a   1  couples the left knee belt  112   a  and the motor  114   a   1  to each other, and the wire  110   a   2  couples the left knee belt  112   a  and the motor  114   a   2  to each other. 
     Each of the wires  110   a   3  and  110   a   4  has one end fixed to the right knee belt  112   b . The wire  110   a   3  has another end coupled to the motor  114   a   3 , and the wire  110   a   4  has another end coupled to the motor  114   a   4 . That is, the other end of the wire  110   a   3  and the other end of the wire  110   a   4  are fixed. The wire  110   a   3  couples the right knee belt  112   b  and the motor  114   a   3  to each other, and the wire  110   a   4  couples the right knee belt  112   b  and the motor  114   a   4  to each other. 
     In this embodiment, each of the motors  114   a   1  to  114   a   4  rotates the pulley in the forward or reverse direction to wind or unwind the corresponding wire among the wires  110   a   1  to the  110   a   4  around the pulley. The wires  110   a   1  to  110   a   4  described above are fixed to the waist of the user  1  by the upper-body belt  111  and are fixed to the left and right thighs or the like of the user  1  by the knee belts  112   a  and  112   b.    
     As described above, each of the wires  110   a   1  to  110   a   4  couples the upper-body belt  111  to the left knee belt  112   a  or the right knee belt  112   b . The wires  110   a   1  to  110   a   4  may be coupled to the upper-body belt  111  directly or indirectly. Each of the wires  110   a   1  to  110   a   4  may be coupled to the left knee belt  112   a  or the right knee belt  112   b  directly or indirectly. In the example described above, the one end of each of the wires  110   a   1  to  110   a   4  is fixed to, or is directly coupled to, the left knee belt  112   a  or the right knee belt  112   b , and the other end of each of the wires  110   a   1  to  110   a   4  is fixed to, or is indirectly coupled to, the upper-body belt  111  via the corresponding one of the motors  114 . However, each of the wires  110  may be coupled to the upper-body belt  111  and each of the wires  110  may be coupled to the left knee belt  112   a  or the right knee belt  112   b  by using the following configuration, for example. 
     Specifically, the one end of each of the wires  110  may be indirectly coupled to the left knee belt  112   a  or the right knee belt  112   b  via the corresponding one of the motors  114 , and the other end of each of the wires  110  may be directly coupled to the upper-body belt  111 . Alternatively, both ends of each of the wires  110  may be directly coupled to the upper-body belt  111  and to the left knee belt  112   a  or the right knee belt  112   b , and a motor, a linear actuator, or a pneumatic or hydraulic piston may be disposed in the middle of each of the wires  110  to adjust the length of the wire  110 . 
     Alternatively, the one end of each of the wires  110  may be directly coupled to the left knee belt  112   a  or the right knee belt  112   b , and the other end of each of the wires  110  may be indirectly coupled to the left knee belt  112   a  or the right knee belt  112   b  via the corresponding one of the motors  114  in such a manner that each of the wires  110  is arranged to reciprocate between the left knee belt  112   a  or the right knee belt  112   b  and the upper-body belt  111 . Alternatively, the one end of each of the wires  110  may be directly coupled to the upper-body belt  111 , and the other end of each of the wires  110  may be indirectly coupled to the upper-body belt  111  via the corresponding one of the motors  114  in such a manner that each of the wires  110  is arranged to reciprocate between the upper-body belt  111  and the left knee belt  112   a  or the right knee belt  112   b.    
     Alternatively, both ends of each of the wires  110  may be coupled to the corresponding one of the motors  114  and may be arranged to form a ring through the motor  114 . In this case, each of the wires  110  is arranged to reciprocate between the upper-body belt  111  and the left knee belt  112   a  or the right knee belt  112   b , and each of the motors  114  changes the length of the circumference of the ring of the corresponding one of the wires  110 . 
     In any of the configurations described above, each of the wires  110  is coupled to the upper-body belt  111  and the left knee belt  112   a  or the right knee belt  112   b  so that the tension thereof is supported by the upper-body belt  111  and the left knee belt  112   a  or the right knee belt  112   b . Thus, when each of the motors  114   a   1  to  114   a   4  pulls the corresponding wire among the wires  110 , tension that causes the upper-body belt  111  and the left knee belt  112   a  or the right knee belt  112   b  to come into close proximity to each other is generated in the corresponding wire. 
     The force sensors  115  include four force sensors  115   a   1  to  115   a   4 . The force sensor  115   a   1  detects the tension of the wire  110   a   1  and outputs the detected tension to the control unit  120 . The force sensor  115   a   2  detects the tension of the wire  110   a   2  and outputs the detected tension to the control unit  120 . The force sensor  115   a   3  detects the tension of the wire  110   a   3  and outputs the detected tension to the control unit  120 . The force sensor  115   a   4  detects the tension of the wire  110   a   4  and outputs the detected tension to the control unit  120 . The force sensor  115   a   1  is disposed on the wire  110   a   1  in the left knee belt  112   a . The force sensor  115   a   2  is disposed on the wire  110   a   2  in the left knee belt  112   a . The force sensor  115   a   3  is disposed on the wire  110   a   3  in the right knee belt  112   b . The force sensor  115   a   4  is disposed on the wire  110   a   4  in the right knee belt  112   b . The force sensors  115   a   1  to  115   a   4  may be located in the upper-body belt  111 . Each of the force sensors  115   a   1  to  115   a   4  may be capable of detecting the tension of the corresponding wire among the wires  110   a   1  to  110   a   4 , and may be a strain gauge force sensor or a piezoelectric force sensor, for example. The force sensors  115   a   1  to  115   a   4  and the wires  110   a   1  to  110   a   4  have a one-to-one correspondence. The force sensors  115   a   1  to  115   a   4  are examples of a first sensor. 
     Each of the wires  110   a   1  to  110   a   4  may be a metallic wire or a non-metallic wire. Examples of the non-metallic wire include a fiber wire and a fiber belt. A fiber wire or fiber belt is made of a material such as polyester fiber, nylon fiber, acrylic fiber, para-aramid fiber, ultrahigh molecular weight polyethylene fiber, poly-p-phenylenebenzobisoxazole (PBO) fiber, polyarylate fiber, or carbon fiber. In this embodiment, four coupling belts  111   b   1  to  111   b   4  are arranged along the wires  110   a   1  to  110   a   4 , respectively, and each of the coupling belts  111   b   1  to  111   b   4  extends from the upper-body belt  111  to the left knee belt  112   a  or the right knee belt  112   b . The coupling belts  111   b   1  to  111   b   4  and the wires  110   a   1  to  110   a   4  have a one-to-one correspondence. As a non-limiting example, the coupling belts  111   b   1  to  111   b   4  are each integrated with the upper-body belt  111  and the left knee belt  112   a  or the right knee belt  112   b  and are made of a material similar to that of the belts  111 ,  112   a , and  112   b . For example, the upper-body belt  111 , the knee belts  112   a  and  112   b , and the coupling belts  111   b   1  to  111   b   4  may form a single suit having an assistance function that is wearable by the user  1 . Each of the coupling belts  111   b   1  to  111   b   4  contains and covers the corresponding wire among the wires  110   a   1  to  110   a   4 . The coupling belts  111   b   1  to  111   b   4  may be collectively referred to as coupling belts  111   b.    
     The arrangement configuration of the wires  110   a   1  to  110   a   4  will be described in detail with reference to  FIG. 1 ,  FIG. 2 , and  FIG. 4 .  FIG. 4  schematically illustrates the arrangement of the constituent elements of the assistance apparatus  100  illustrated in  FIG. 1 . The wire  110   a   1  couples the upper-body belt  111  and the left knee belt  112   a  to each other via the motor  114   a   1  on or above the front part of the body of the user  1 . The wire  110   a   1  extends upward from the left knee belt  112   a  on or above the front part of the body of the user  1 . The wire  110   a   2  couples the upper-body belt  111  and the left knee belt  112   a  to each other via the motor  114   a   2  on or above the back part of the body of the user  1 . The wire  110   a   2  extends upward from the left knee belt  112   a  on or above the back part of the body of the user  1 . The wire  110   a   3  couples the upper-body belt  111  and the right knee belt  112   b  to each other via the motor  114   a   3  on or above the front part of the body of the user  1 . The wire  110   a   3  extends upward from the right knee belt  112   b  on or above the front part of the body of the user  1 . The wire  110   a   4  couples the upper-body belt  111  and the right knee belt  112   b  to each other via the motor  114   a   4  on or above the back part of the body of the user  1 . The wire  110   a   4  extends upward from the right knee belt  112   b  on or above the back part of the body of the user  1 . In this manner, the wire  110   a   1  is located on or above the front part of the left leg of the user  1 , the wire  110   a   2  is located on or above the back part of the left leg of the user  1 , the wire  110   a   3  is located on or above the front part of the right leg of the user  1 , and the wire  110   a   4  is located on or above the back part of the right leg of the user  1 . The wires  110   a   1  to  110   a   4  are pulled individually to apply forces in different directions to the left and right legs. 
     In the example illustrated in  FIG. 1 ,  FIG. 2 , and  FIG. 4 , the wires  110   a   1  and  110   a   3  do not cross each other on or above the front part of the body of the user  1 . However, the wires  110   a   1  and  110   a   3  may cross each other on or above the front part of the body of the user  1 . In the example illustrated in  FIG. 1 ,  FIG. 2 , and  FIG. 4 , the wires  110   a   2  and  110   a   4  do not cross each other on or above the back part of the body of the user  1 . However, the wires  110   a   2  and  110   a   4  may cross each other on or above the back part of the body of the user  1 . 
     The motors  114   a   1  to  114   a   4  pull the wires  110   a   1  to  110   a   4  to apply tensions to the wires  110   a   1  to  110   a   4 , respectively, and the tensions are transmitted to the left and right legs of the user  1  via the upper-body belt  111  and the knee belts  112   a  and  112   b . To effectively transmit the tensions of the wires  110   a   1  to  110   a   4  to the left and right legs of the user  1 , the upper-body belt  111  and the knee belts  112   a  and  112   b  may have rigidity so as not to be deformable and have inflexibility so as not to be extensible. As described above, examples of the material of the upper-body belt  111  and the knee belts  112   a  and  112   b  include a non-extensible material. The upper-body belt  111  and the knee belts  112   a  and  112   b  described above are worn by the user  1  in such a manner as to tightly fit the body of the user  1 , thus efficiently transmitting the driving forces of the motors  114   a   1  to  114   a   4  to the legs of the user  1  through the wires  110   a   1  to  110   a   4  and effectively assisting movements of the legs of the user  1 . The term “assisting”, as used herein, is used to include supporting the movement of the user in order to allow the user to perform a predetermined motion and forcing the body of the user to perform the predetermined motion to induce movements of the body. 
     A further description will be given of a relationship between tensions applied to the wires  110   a   1  to  110   a   4  by the assistance apparatus  100  and motions of the user that are assisted with the tensions. For example,  FIG. 5  illustrates example motions of the right leg of the user, which are assisted by the assistance apparatus  100 . In the example illustrated in  FIG. 5 , the assistance apparatus  100  applies an assistance force to the right leg during the swing phase of gait. The assistance apparatus  100  may apply an assistance force to the right leg during the stance phase of gait. The assistance apparatus  100  also enables the left leg of the user to perform motions similar to those of the right leg. As illustrated in  FIG. 5 , the assistance apparatus  100  can apply an assistance force for flexion and extension to the hip joint of the right leg of the user. The flexion of the hip joint is a motion of moving the thigh forward, and the extension of the hip joint is a motion of moving the thigh backward. 
     Further, a relationship between motions of the user, which are induced, or assisted, by the assistance apparatus  100 , and assistance forces given to the user through the wires  110   a   1  to  110   a   4  will be described with reference to  FIG. 6A  to  FIG. 7B .  FIG. 6A  illustrates a case where the assistance apparatus  100  according to the embodiment assists flexion of the hip joint of the left leg of the user, and  FIG. 6B  illustrates a case where the assistance apparatus  100  according to the embodiment assists flexion of the hip joint of the right leg of the user. In  FIG. 6A , to flex the left leg, the control unit  120  drives the motor  114   a   1  to increase the tension of the wire  110   a   1 , that is, to generate a tension in the wire  110   a   1 . In  FIG. 6B , to flex the right leg, the control unit  120  drives the motor  114   a   3  to increase the tension of the wire  110   a   3 . The control unit  120  may control the tensions of the wires  110  in accordance with the detection results of the force sensors  115   a   1  to  115   a   4  or in accordance with the amount of driving of the motors  114   a   1  to  114   a   4 . The details of the control unit  120  will be described below. 
     In this embodiment, as a non-limiting example, a tension is applied to each of the wires  110   a   1  to  110   a   4  in a normal state before flexion. The tension may be applied so as to prevent the corresponding one of the wires  110   a   1  to  110   a   4  from loosening and may be less than or equal to 10 N or less than or equal to 5 N, for example. To flex the left leg and the right leg, the tensions of the wires  110   a   1  and  110   a   3  are each increased to, for example, a value greater than or equal to 40 N and less than or equal to 100 N. An example for the left leg will be described. A tension greater than or equal to 40 N is exerted on the wire  110   a   1  for a user, who is a healthy adult male in 20 s to 40 s. At this time, the user is able to clearly recognize that a force in a flexing direction acts on the left leg and promotes flexion of the left leg. When a tension over 80 N is exerted on the wire  110   a   1 , the left leg of the user is raised in the flexing direction. When the tension exerted on the wire  110   a   1  is less than or equal to 20 N, the user continues the current motion without substantially perceiving the resistance caused by the tension of the wire  110   a   1 . The tension values described above are examples. The tension values may be changed, as desired, in accordance with the age, gender, body size, or physical activity level of the user, the type of motion of the leg, the degree of assistance on the leg, and so on. 
       FIG. 7A  and  FIG. 7B  illustrate cases where the assistance apparatus  100  according to the embodiment assists extension of the hip joints of the left and right legs of the user, respectively. In  FIG. 7A , the control unit  120  increases the tension of the wire  110   a   2  to extend the left leg. In  FIG. 7B , the control unit  120  increases the tension of the wire  110   a   4  to extend the right leg. The tensions of the wires  110  during extension may be similar to those during flexion. 
     In the foregoing description, the control unit  120  increases the tension of one wire to assist one motion of one leg. At this time, the control unit  120  may control the motors corresponding to the other three wires in accordance with the motion of the user so that the tensions of the other three wires are kept in the current states, and adjust the tensions of the other three wires. The control unit  120  may control the motors corresponding to the other three wires so as not to exert tension on the three wires. For example, the control unit  120  may stop the operation of the motors corresponding to the other three wires. 
     The assistance apparatus  100  described above is capable of assisting the user in walking by applying assistance torques, which are assistance forces in flexing and extending directions, to the user in accordance with torques generated during the stance phase and swing phase of the leg of the user while the user is walking. 
     Further, the configuration of the control unit  120  of the assistance apparatus  100  will be described with reference to  FIG. 3 . The control unit  120  controls the overall operation of the assistance apparatus  100 . The control unit  120  determines operations to be individually applied to the wires  110   a   1  to  110   a   4  and controls assistance for the hip joints of the user  1 . The operations to be individually applied to the wires  110   a   1  to  110   a   4  are operation patterns of the wires  110   a   1  to  110   a   4 , including the timings of applying tensions to the wires  110   a   1  to  110   a   4 , the magnitudes of the tensions, and periods during which the tensions are applied. 
     The control unit  120  acquires an instruction entered by the user  1  or the like from an input device  140  included in the assistance apparatus  100  or from a terminal device  150  external to the assistance apparatus  100 , and controls the assistance apparatus  100  to start and stop assistance in accordance with the acquired instruction. The input device  140  of the assistance apparatus  100  may be a button, a switch, a key, a touch pad, a microphone of an audio recognition device, or any other suitable device. The terminal device  150  may be a terminal device carried by the user  1  wearing the assistance apparatus  100 , and examples of the terminal device  150  include a smartphone, a smartwatch, a tablet, and a personal computer. The control unit  120  may communicate with the input device  140  and the terminal device  150  in a wired or wireless way. The wireless communication may be implemented using a wireless local area network (LAN) such as wireless fidelity (Wi-Fi (registered trademark)), or may be short-range wireless communication such as Bluetooth (registered trademark) or ZigBee (registered trademark), or any other type of wireless communication. The wired communication may be any existing wired communication. The control unit  120  may include a wired or wireless communication circuit. The wired or wireless communication circuit included in the assistance apparatus  100  may be used to perform wired communication or wireless communication. The input device  140  and the terminal device  150  are examples of an interface device. 
     For example,  FIG. 8  illustrates an example input section of the input device  140  included in the assistance apparatus  100  according to the embodiment. The input device  140  includes four physical buttons that accept input. The four buttons include an “ON” button for starting the assistance apparatus  100 , an “OFF” button for stopping the operation of the assistance apparatus  100 , a “normal walking” button for selecting a normal walking mode among operation modes of the assistance apparatus  100 , and an “object transport walking” button for selecting an object transport walking mode among the operation modes of the assistance apparatus  100 . When the input section of the input device  140  is implemented as a touch panel, the buttons may be icons. 
     In this embodiment, furthermore, as illustrated in  FIG. 9 , a contact sensor  301  and at least one of a pressure-sensitive sensor  302  and an inertial measurement unit  303  are attached to the body of the user  1 .  FIG. 9  illustrates the arrangement of sensors and so on to be attached to the body of the user  1 . The contact sensor  301 , the pressure-sensitive sensor  302 , and the inertial measurement unit  303  output detection results to the control unit  120 . The contact sensor  301  is attached to each of the hands of the user  1 . Specifically, the contact sensor  301  is attached to a finger tip or the like of gloves worn by the user  1 . The contact sensor  301  may be attached to each of both hands of the user  1  or to either hand of the user  1 . The contact sensor  301  detects a direct contact and an indirect contact between the hand of the user  1  and an object. Examples of the contact sensor  301  include a contact detection sensor, a touch sensor, a proximity sensor, and a sensor similar to the pressure-sensitive sensor  302 . The contact sensor  301  may be attached to each of the arm, chest, abdomen, and so on of the user  1 , which may come into contact with an object when the user  1  holds the object. 
     The pressure-sensitive sensor  302  is attached to each of the soles of the feet of the user  1 . Specifically, the pressure-sensitive sensor  302  is attached to each of the bottoms or the like of shoes worn by the user  1 . The pressure-sensitive sensor  302  may be attached to each of both feet of the user  1  or to either foot of the user  1 . The pressure-sensitive sensor  302  detects a pressure acting on each of the soles of the feet of the user  1 , that is, a load. Examples of the pressure-sensitive sensor  302  include a capacitive pressure sensor, a piezoelectric pressure sensor, and a strain gauge pressure sensor. The inertial measurement unit  303  is attached to a portion of the body of the user  1  that moves along with the movement of the user  1 , such as the waist in the upper half of the body of the user  1 . Specifically, the inertial measurement unit  303  is attached to the upper-body belt  111 . The inertial measurement unit  303  includes an acceleration sensor and a gyro sensor (also referred to as an “angular velocity sensor”). The inertial measurement unit  303  may include an acceleration sensor, but may include no gyro sensor. The inertial measurement unit  303  may further include a geomagnetic sensor. The inertial measurement unit  303  detects, on the basis of a detected acceleration and angular velocity, the acceleration of the user  1  in each direction, and the movement direction, movement speed, and movement distance of the user  1 . The pressure-sensitive sensor  302  and the inertial measurement unit  303  are examples of a second sensor. 
     The contact sensor  301 , the pressure-sensitive sensor  302 , and the inertial measurement unit  303  exchange information with the control unit  120  via wired communication or wireless communication. The wired communication and wireless communication may be any of the wired communication and wireless communication described above. 
     As illustrated in  FIG. 3 , the control unit  120  includes a grasp recognition unit  121 , a drive control unit  122 , a gait timing detection unit  123 , a wire tension recognition unit  124 , and a storage unit  125 . The grasp recognition unit  121 , the drive control unit  122 , the gait timing detection unit  123 , and the wire tension recognition unit  124 , which are constituent elements of the control unit  120 , may be implemented by a computer system including a processor such as a central processing unit (CPU) or a digital signal processor (DSP) and a memory such as a random access memory (RAM) and a read-only memory (ROM). Some or all of the functions of the constituent elements described above may be achieved by the CPU or the DSP executing a program recorded on the ROM by using the RAM as a work memory. Alternatively, some or all of the functions of the constituent elements described above may be achieved by a dedicated hardware circuit such as an electronic circuit or an integrated circuit. The functions of some or all of the constituent elements described above may be implemented by a combination of the software functions described above and a hardware circuit. The program may be provided as an application by communication via a communication network such as the Internet, communication conforming to a mobile communication standard, communication via any other wireless or wired network, broadcasting, or the like. A computer system and/or a hardware circuit constituted by the control unit  120  may be mounted on the upper-body belt  111 , accommodated in the containers  111   a   1  to  111   a   4  together with the motors  114   a   1  to  114   a   4 , or embedded in the upper-body belt  111  at a different location from the motors  114   a   1  to  114   a   4 , for example. The control unit  120  is an example of a control circuit. 
     The storage unit  125  is capable of storing information, and the stored information is retrievable from the storage unit  125 . The storage unit  125  stores computer programs in accordance with which the constituent elements of the control unit  120  execute processes, threshold values described below, input profiles of wire tensions described below, and so on. The storage unit  125  is implemented as a storage device, for example, a semiconductor memory such as a ROM, a RAM, or a flash memory, a hard disk drive, or a solid state drive (SSD). In this embodiment, the storage unit  125  is included in the control unit  120 . Alternatively, the storage unit  125  may be disposed separately from the control unit  120 . The storage unit  125  is an example of a memory. 
     The grasp recognition unit  121  detects a grasp of an object by the user  1  with their hands. The grasp recognition unit  121  determines whether the user  1  is holding an object with their hands on the basis of a change in sensor value, which is acquired from the contact sensor  301 . For example, as illustrated in  FIG. 10A  and  FIG. 10B , the contact sensor  301  is a piezoelectric sensor. In this case, the grasp recognition unit  121  detects a time point at which a voltage value corresponding to a sensor value detected by the contact sensor  301  becomes less than a predetermined value, as a time point at which the hands of the user  1  touch an object, that is, as a time point at which the user  1  grasps the object. For example, in the example illustrated in  FIG. 10B , the predetermined value is represented by “VA”.  FIG. 10A  illustrates a relationship between contact sensors  301  and the hands of the user.  FIG. 10B  illustrates an example of a signal of a contact sensor  301 . The grasp recognition unit  121  outputs a detection result to the drive control unit  122 . 
     The gait timing detection unit  123  detects a gait timing to determine a timing of assisting the user  1 . The gait timing may include a timing of starting assisting the user  1  during walking, and a timing of determining phases such as a stance phase and a swing phase in a period during which the user  1  takes one step. The drive control unit  122  determines a timing of assisting the user  1  from the gait timing detected by the gait timing detection unit  123  and controls the operation of the motors  114 . 
     Specifically, the gait timing detection unit  123  estimates a gait cycle of the user  1  wearing the assistance apparatus  100 , predicts gait phases in the next one step on the basis of the estimation result, and outputs assistance timings based on the predicted gait phases to the drive control unit  122 . A gait cycle is a time interval from heel strike of one leg to the next heel strike of the same leg. The gait cycle is constituted by a period of a stance phase and a period of a swing phase. The gait cycle may be sequence of motions occurring from heel strike of one leg to the next heel strike of the same leg. 
     The gait timing detection unit  123  detects a timing of heel strike of the user  1  on the basis of a sensor value acquired from the pressure-sensitive sensor  302  or on the basis of sensor values acquired from the acceleration sensor and the gyro sensor of the inertial measurement unit  303 , and estimates a gait phase for each step, or a gait cycle, of the user  1  in real time. The gait cycles and the steps may be in a one-to-one relationship. Each step of the user  1  is a step with either of the left and right legs. For example, each step of the user  1  corresponds to a period from when the left leg touches the ground to when the left leg touches the ground again. The gait timing detection unit  123  predicts, based on the estimated gait cycle, a gait phase for the next step and a starting time and duration of each of the stance phase and swing phase for the next step, and outputs the prediction results to the drive control unit  122 . When the terminal device  150  carried by the user  1  includes an inertial measurement unit, the gait timing detection unit  123  may acquire a sensor value of an acceleration sensor and a sensor value of a gyro sensor from the terminal device  150 . 
     Gait phases represent temporal timings of gait states during a single step taken by the user  1 . A time point at which one leg of the user  1  touches the ground corresponds to a time point at which a gait phase is 0%, and a time point at which the same leg of the user  1  touches the ground again corresponds to a time point at which a gait phase is 100%. In a gait phase, timings of gait states of the user  1  are represented in the range of 0% to 100%. For example, a value of 0% to 100% of a gait phase may correspond to the time elapsed from when one leg of the user  1  touches the ground to when the same leg of the user  1  touches the ground again. Specifically, when the time period from when one leg of the user  1  touches the ground to when the same leg of the user  1  touches the ground again is 1 second, the gait phase at the point in time at which a period of 0.5 seconds elapses from the time when the leg of the user  1  touches the ground is represented by 50%. 
     More specifically, the gait timing detection unit  123  determines a time point at which the leg of the user  1  touches the ground on the basis of the sensor value of the pressure-sensitive sensor  302  in such a manner that, for example, as illustrated in  FIG. 11 , a time point at which the voltage value corresponding to the pressure sensor value of the pressure-sensitive sensor  302  becomes less than a predetermined value is detected as a timing of heel strike.  FIG. 11  illustrates an example of a signal based on signals of the pressure-sensitive sensors  302 . For example, the predetermined value is represented by “VB” in  FIG. 11 . A period during which the pressure-sensitive sensor  302  measures a pressure value greater than or equal to a predetermined value corresponds to a period of heel contact. The pressure-sensitive sensor  302  is placed at each of the feet of the user  1 . The gait timing detection unit  123  acquires a timing at which the shoe touches the ground using the pressure-sensitive sensor  302 , rather than a timing that is based on the inertial measurement unit  303  located in the upper-body belt  111  or the like. Thus, the gait timing detection unit  123  can more reliably estimate a gait cycle. 
     When the inertial measurement unit  303  is used, the gait timing detection unit  123  determines a time point at which the foot of the user  1  touches the ground on the basis of information obtained by the acceleration sensor. For a method for estimating a time point at which a foot touches the ground by using an acceleration sensor, see, for example, IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 52, NO. 3, 2005, p. 488, FIG. 1, p. 489, FIG. 2. When estimating a gait cycle on the basis of a sensor value of the inertial measurement unit  303 , the gait timing detection unit  123  may estimate a gait cycle by using signal waveforms obtained from the acceleration sensor and the gyro sensor. For example, a gait cycle can be estimated by using a signal waveform obtained from the acceleration sensor, as illustrated in  FIG. 12 . In the example illustrated in  FIG. 12 , the signal waveform obtained from the acceleration sensor can be used to estimate a time point at which the foot of the user  1  touches the ground, and a gait cycle can be estimated accordingly.  FIG. 12  illustrates an example of a signal of the acceleration sensor of the inertial measurement unit  303 . 
     The user  1  may wear an angle sensor (also referred to as a “tilt sensor”). In this case, the angle sensor is attached to, for example, a thigh of the user  1 . The gait timing detection unit  123  acquires the angle of the hip joint of the user  1  as gait information. The gait timing detection unit  123  calculates a gait phase on the basis of a cycle of change in the angle of the hip joint of the user  1 . 
     Regardless of which of the pressure-sensitive sensor  302  and the inertial measurement unit  303  is used, for example, the gait timing detection unit  123  may estimate, based on a sensor value of the pressure-sensitive sensor  302  or a sensor value of the inertial measurement unit  303  for the latest three steps of the user  1 , an elapsed time of 0% to 100% of a gait phase for each step and may calculate an average value of the three elapsed times. Then, the gait timing detection unit  123  may predict the point in time corresponding to 100% of the gait phase for the next step on the basis of the average value of the elapsed times. Further, the gait timing detection unit  123  may estimate the start timings of the stance phase and the swing phase during the gait phase for each step on the basis of the signal waveform of the sensor and calculate an average value of the start timings for the three steps. Then, the gait timing detection unit  123  may predict, based on the average value, the start timings of the stance phase and the swing phase for the next one step. 
     Alternatively, the gait timing detection unit  123  may estimate, based on a sensor value of the pressure-sensitive sensor  302  or a sensor value of the inertial measurement unit  303  for the last one step of the user  1 , an elapsed time of 0% to 100% of the gait phase for the one step and may predict the point in time corresponding to 100% of the gait phase for the next step on the basis of the estimated elapsed time. Further, the gait timing detection unit  123  may estimate the start timings of the stance phase and the swing phase during the one step on the basis of the sensor values for the last one step of the user  1 , and may predict the start timings of the stance phase and the swing phase for the next one step. 
     The wire tension recognition unit  124  detects the tensions generated in the wires  110   a   1  to  110   a   4 . The wire tension recognition unit  124  detects the tensions of the wires  110   a   1  to  110   a   4  on the basis of sensor values acquired from the force sensors  115   a   1  to  115   a   4 . The wire tension recognition unit  124  outputs the detected tensions of the wires  110   a   1  to  110   a   4  to the drive control unit  122 . 
     The drive control unit  122  controls the motors  114   a   1  to  114   a   4 , which respectively adjust the tensions of the wires  110   a   1  to  110   a   4 , on the basis of information on a predicted gait phase of the user  1 , which is acquired from the gait timing detection unit  123 , and on the basis of information indicating whether the user  1  is carrying an object, which is acquired from the grasp recognition unit  121 . The drive control unit  122  starts the motors  114   a   1  to  114   a   4 , stops the operation of the motors  114   a   1  to  114   a   4 , and controls the amount by which the wires  110   a   1  to  110   a   4  are respectively pulled by the motors  114   a   1  to  114   a   4  and the pulling tensions of the wires  110   a   1  to  110   a   4 . The drive control unit  122  controls the amount of rotation of each of the motors  114   a   1  to  114   a   4  and adjusts the rotation torque of each of the motors  114   a   1  to  114   a   4 , thereby enabling control of the amount by which the corresponding wire among the wires  110  is pulled and the pulling tensions of the corresponding wire. 
     Specifically, the drive control unit  122  determines a type of assistance to be provided to the user  1  on the basis of the prediction result of the gait timing acquired from the gait timing detection unit  123 . Examples of the type of assistance include motions of the leg on which assistance is to be provided to the user  1 , such as flexion and extension. In accordance with the type of assistance, the drive control unit  122  further determines a wire to be pulled to assist a motion of the user  1  among the wires  110   a   1  to  110   a   4 , a tension to be applied to the wire, and a timing of pulling the wire. 
     Further, the drive control unit  122  changes the relationship between the tension of a wire and the timing of pulling the wire even for the same type of assistance on the basis of information acquired from the grasp recognition unit  121  indicating whether the user  1  is carrying an object. 
     An assistance correspondence, which is a relationship between the gait timing acquired from the gait timing detection unit  123  and the type of assistance, is set in advance and is stored in, for example, the storage unit  125 . A wire-tension relationship, which is a relationship between a wire to be pulled, a tension of the wire, and a timing of pulling the wire, is set in advance in accordance with the type of assistance and information indicating whether the user  1  is carrying an object, and is stored in, for example, the storage unit  125 . The wire-tension relationship may be updated on the basis of the achievement of assistance-based control by the assistance apparatus  100 . On the basis of information on the assistance correspondence and the wire-tension relationship, which are stored in the storage unit  125 , the drive control unit  122  determines a type of assistance to be provided to the user  1  and determines control of wires corresponding to the determined type of assistance. The drive control unit  122  controls the motors linked to the determined wires, in accordance with tensions to be applied to the wires and timings of pulling the wires. 
     Further, the drive control unit  122  controls the operation of the motors  114   a   1  to  114   a   4  on the basis of information on the tensions of the wires  110   a   1  to  110   a   4 , which is acquired from the wire tension recognition unit  124 , so that the tensions of the wires  110   a   1  to  110   a   4  have predetermined levels. In addition, the drive control unit  122  may change the wire-tension relationship on the basis of, in addition to the information acquired from the grasp recognition unit  121 , the gait timing detection unit  123 , and the wire tension recognition unit  124 , information on the user  1 , such as age, gender, body size, and physical activity level, the degree of assistance on the leg, and so on, and may use the changed wire-tension relationship. 
     2. Modification of Assistance Apparatus 
     In the assistance apparatus  100  described above, the upper-body belt  111  is coupled to the knee belts  112   a  and  112   b  by using the four wires  110   a   1  to  110   a   4 . However, the number of wires is not limited to that in the embodiment. For example, as illustrated in  FIG. 13  to  FIG. 17 , eight wires may be used.  FIG. 13  is a perspective view of a user  1  wearing an assistance apparatus  200  according to a modification of the embodiment, as viewed obliquely from the front.  FIG. 14  is a front view of the user  1  wearing the assistance apparatus  200  illustrated in  FIG. 13 .  FIG. 15  is a back view of the user  1  wearing the assistance apparatus  200  illustrated in  FIG. 13 .  FIG. 16  is a diagram schematically illustrating the arrangement of constituent elements of the assistance apparatus  200  illustrated in  FIG. 13 .  FIG. 17  is a block diagram illustrating a functional configuration of the assistance apparatus  200  illustrated in  FIG. 13 . 
     As illustrated in  FIG. 13  to  FIG. 17 , the assistance apparatus  200  according to the modification includes an upper-body belt  111 , knee belts  112   a  and  112   b , and eight wires, namely, first to eighth wires  110   a   1  to  110   a   8 . The assistance apparatus  200  further includes a motor  114   a   1  linked to the first wire  110   a   1 , a motor  114   a   2  linked to the second wire  110   a   2 , a motor  114   a   3  linked to the third wire  110   a   3 , a motor  114   a   4  linked to the fourth wire  110   a   4 , a motor  114   a   5  linked to the fifth wire  110   a   5 , a motor  114   a   6  linked to the sixth wire  110   a   6 , a motor  114   a   7  linked to the seventh wire  110   a   7 , a motor  114   a   8  linked to the eighth wire  110   a   8 , a force sensor  115   a   1  disposed on the first wire  110   a   1 , a force sensor  115   a   2  disposed on the second wire  110   a   2 , a force sensor  115   a   3  disposed on the third wire  110   a   3 , a force sensor  115   a   4  disposed on the fourth wire  110   a   4 , a force sensor  115   a   5  disposed on the fifth wire  110   a   5 , a force sensor  115   a   6  disposed on the sixth wire  110   a   6 , a force sensor  115   a   7  disposed on the seventh wire  110   a   7 , a force sensor  115   a   8  disposed on the eighth wire  110   a   8 , and a control unit  120 . 
     The upper-body belt  111  includes containers  111   a   1 ,  111   a   2 ,  111   a   3 , and  111   a   4  so as to correspond to the front part, left side part, back part, and right side part of the body of the user  1 , respectively. The motors  114   a   1  and  114   a   3  are accommodated in the container  111   a   1 , the motors  114   a   5  and  114   a   6  are accommodated in the container  111   a   2 , the motors  114   a   2  and  114   a   4  are accommodated in the container  111   a   3 , and the motors  114   a   7  and  114   a   8  are accommodated in the container  111   a   4 . 
     The first wire  110   a   1  and the fifth wire  110   a   5  are arranged to extend in directions crossing each other on or above the front part of the body of the user  1 , and, more specifically, are arranged to cross each other. Each of the first wire  110   a   1  and the fifth wire  110   a   5  has one end fixed to the left knee belt  112   a . The first wire  110   a   1  has another end coupled to the motor  114   a   1 , and the fifth wire  110   a   5  has another end coupled to the motor  114   a   5 . That is, the first wire  110   a   1  couples the left knee belt  112   a  and the motor  114   a   1  to each other, and the fifth wire  110   a   5  couples the left knee belt  112   a  and the motor  114   a   5  to each other. 
     The second wire  110   a   2  and the sixth wire  110   a   6  are arranged to extend in directions crossing each other on or above the back part of the body of the user  1 , and, more specifically, are arranged to cross each other. Each of the second wire  110   a   2  and the sixth wire  110   a   6  has one end fixed to the left knee belt  112   a . The second wire  110   a   2  has another end coupled to the motor  114   a   2 , and the sixth wire  110   a   6  has another end coupled to the motor  114   a   6 . That is, the second wire  110   a   2  couples the left knee belt  112   a  and the motor  114   a   2  to each other, and the sixth wire  110   a   6  couples the left knee belt  112   a  and the motor  114   a   6  to each other. 
     The third wire  110   a   3  and the seventh wire  110   a   7  are arranged to extend in directions crossing each other on or above the front part of the body of the user  1 , and, more specifically, are arranged to cross each other. Each of the third wire  110   a   3  and the seventh wire  110   a   7  has one end fixed to the right knee belt  112   b . The third wire  110   a   3  has another end coupled to the motor  114   a   3 , and the seventh wire  110   a   7  has another end coupled to the motor  114   a   7 . That is, the third wire  110   a   3  couples the right knee belt  112   b  and the motor  114   a   3  to each other, and the seventh wire  110   a   7  couples the right knee belt  112   b  and the motor  114   a   7  to each other. 
     The fourth wire  110   a   4  and the eighth wire  110   a   8  are arranged to extend in directions crossing each other on or above the back part of the body of the user  1 , and, more specifically, are arranged to cross each other. Each of the fourth wire  110   a   4  and the eighth wire  110   a   8  has one end fixed to the right knee belt  112   b . The fourth wire  110   a   4  has another end coupled to the motor  114   a   4 , and the eighth wire  110   a   8  has another end coupled to the motor  114   a   8 . That is, the fourth wire  110   a   4  couples the right knee belt  112   b  and the motor  114   a   4  to each other, and the eighth wire  110   a   8  couples the right knee belt  112   b  and the motor  114   a   8  to each other. 
     Further, the first wire  110   a   1  and the second wire  110   a   2  extend upward and toward the right side of the body of the user  1  from the left knee belt  112   a . Specifically, the first wire  110   a   1  and the second wire  110   a   2  extend to the right side of the body of the user  1  while extending upward from the left knee belt  112   a , and, for example, extend upward and diagonally to the right from the left knee belt  112   a . The fifth wire  110   a   5  and the sixth wire  110   a   6  extend upward and toward the left side of the body of the user  1  from the left knee belt  112   a . Specifically, the fifth wire  110   a   5  and the sixth wire  110   a   6  extend to the left side of the body of the user  1  while extending upward from the left knee belt  112   a , and, for example, extend upward and diagonally to the left from the left knee belt  112   a . The third wire  110   a   3  and the fourth wire  110   a   4  extend upward and toward the left side of the body of the user  1  from the right knee belt  112   b . Specifically, the third wire  110   a   3  and the fourth wire  110   a   4  extend to the left side of the body of the user  1  while extending upward from the right knee belt  112   b , and, for example, extend upward and diagonally to the left from the right knee belt  112   b . The seventh wire  110   a   7  and the eighth wire  110   a   8  extend upward and toward the right side of the body of the user  1  from the right knee belt  112   b . Specifically, the seventh wire  110   a   7  and the eighth wire  110   a   8  extend to the right side of the body of the user  1  while extending upward from the right knee belt  112   b , and, for example, extend upward and diagonally to the right from the right knee belt  112   b.    
     Extending of two wires in directions crossing each other is equivalent to crossing of directions in which the two wires extend. Further, crossing of directions in which the two wires extend is equivalent to extending of the two wires in directions that are not parallel to each other. The directions may cross each other at an intersection, or may have no intersection therebetween and may not cross each other. Thus, the two wires may actually cross each other at an intersection or may not actually cross each other. Such two wires extending in directions crossing each other may or may not cross each other when the user  1  is viewed from outside the user  1 . When the two wires do not cross each other, as illustrated in  FIG. 18  and  FIG. 19 , the two wires may extend to form a V shape, for example, or may extend away from each other.  FIG. 18  and  FIG. 19  illustrate modifications of the arrangement of the wires  110  in the assistance apparatus  200  illustrated in  FIG. 13 . 
     In this modification, furthermore, eight coupling belts  111   b   1  to  111   b   8  are arranged along the first wire  110   a   1  to the eighth wire  110   a   8 , respectively, and each of the eight coupling belts  111   b   1  to  111   b   8  extends from the upper-body belt  111  to the left knee belt  112   a  or the right knee belt  112   b . The coupling belts  111   b   1  to  111   b   8  and the first wire  110   a   1  to the eighth wire  110   a   8  have a one-to-one correspondence. 
     In this modification, as a non-limiting example of pairs of two wires extending in directions crossing each other, two wires in each pair of wires cross each other to form an X shape. The first wire  110   a   1  to the eighth wire  110   a   8  may have any other arrangement configuration. As illustrated in  FIG. 18 , for example, the first wire  110   a   1  and the fifth wire  110   a   5  may be arranged to form a V shape. In this case, the first wire  110   a   1  and the fifth wire  110   a   5  may form a tapered shape that becomes wider toward the top from the left knee belt  112   a . In addition, on the left knee belt  112   a , the first wire  110   a   1  and the fifth wire  110   a   5  may be arranged in close proximity to each other in the manner illustrated in  FIG. 18  or may be arranged away from each other in the manner illustrated in  FIG. 19 . The same applies to the other pairs of wires. 
     Alternatively, as illustrated in  FIG. 20 , for example, the first wire  110   a   1  and the fifth wire  110   a   5  may be arranged to form an inverted V shape. In this case, the first wire  110   a   1  and the fifth wire  110   a   5  may form a tapered shape that becomes narrower toward the top from the left knee belt  112   a . In addition, on the upper-body belt  111 , the first wire  110   a   1  and the fifth wire  110   a   5  may be arranged in close proximity to each other in the manner illustrated in  FIG. 20  may be arranged away from each other in the manner illustrated in  FIG. 21 . The same applies to the other pairs of wires.  FIG. 20  and  FIG. 21  illustrate modifications of the arrangement of the wires  110  in the assistance apparatus  200  illustrated in  FIG. 13 . 
     In  FIG. 13  to  FIG. 15 , the first wire  110   a   1  and the third wire  110   a   3  extending from the container  111   a   1  form an inverted V shape, the fifth wire  110   a   5  and the sixth wire  110   a   6  extending from the container  111   a   2  form an inverted V shape, the second wire  110   a   2  and the fourth wire  110   a   4  extending from the container  111   a   3  form an inverted V shape, and the seventh wire  110   a   7  and the eighth wire  110   a   8  extending from the container  111   a   4  form an inverted V shape. However, the arrangement of the first wire  110   a   1  to the eighth wire  110   a   8  on the upper-body belt  111  is not limited to the arrangement described above. For example, a wound portion of the first wire  110   a   1  and a wound portion of the third wire  110   a   3  may be arranged away from each other so that the two wires  110   a   1  and  110   a   3  do not cross each other or may be arranged so that the two wires  110   a   1  and  110   a   3  cross each other to form an X shape. A wound portion of the fifth wire  110   a   5  and a wound portion of the sixth wire  110   a   6  may be arranged away from each other so that the two wires  110   a   5  and  110   a   6  do not cross each other or may be arranged so that the two wires  110   a   5  and  110   a   6  cross each other to form an X shape. A wound portion of the second wire  110   a   2  and a wound portion of the fourth wire  110   a   4  may be arranged away from each other so that the two wires  110   a   2  and  110   a   4  do not cross each other or may be arranged so that the two wires  110   a   2  and  110   a   4  cross each other to form an X shape. A wound portion of the seventh wire  110   a   7  and a wound portion of the eighth wire  110   a   8  may be arranged away from each other so that the two wires  110   a   7  and  110   a   8  do not cross each other or may be arranged so that the two wires  110   a   7  and  110   a   8  cross each other to form an X shape. 
     In the assistance apparatus  200  described above, for example, the motor  114   a   1  generates a tension in the first wire  110   a   1 , and the motor  114   a   5  generates a tension in the fifth wire  110   a   5 . The assistance apparatus  200  drives the motor  114   a   1  to increase the tension of the first wire  110   a   1 . Thus, a force is exerted on the leg of the user  1  in a direction in which the distance between the knee and the heel is reduced to assist a motion of the ankle of the user  1  during walking. The assistance apparatus  200  drives the motor  114   a   5  to increase the tension of the fifth wire  110   a   5 . Thus, a force is exerted on the leg of the user  1  in a direction in which the distance between the knee and the heel is reduced to assist a motion of the ankle of the user  1  during walking. Further, by setting the tensions of the first wire  110   a   1  and the fifth wire  110   a   5  to different values, the assistance apparatus  200  can generate a moment of force regarding a left or right tilt of the heel of the user  1  and can assist a motion of the ankle of the user  1  during walking. 
     The assistance apparatus  200  can apply an assistance force to the hip joint of the left leg and the hip joint of the right leg of the user  1  to flex and extend the hip joints. Referring to  FIG. 22A , a case is illustrated in which the assistance apparatus  200  according to the modification assists flexion of the hip joint of the left leg of the user  1 . Referring to  FIG. 22B , a case is illustrated in which the assistance apparatus  200  according to the modification assists flexion of the hip joint of the right leg of the user  1 . In  FIG. 22A , to flex the left leg, the drive control unit  122  drives the motors  114   a   1  and  114   a   5  to increase the tensions of the first wire  110   a   1  and the fifth wire  110   a   5 . In  FIG. 22B , to flex the right leg, the drive control unit  122  drives the motors  114   a   3  and  114   a   7  to increase the tensions of the third wire  110   a   3  and the seventh wire  110   a   7 . In this modification, the tensions of the first wire  110   a   1  and the fifth wire  110   a   5  are assumed to be equivalent, but may be different. In this modification, the tensions of the third wire  110   a   3  and the seventh wire  110   a   7  are assumed to be equivalent, but may be different. 
     Referring to  FIG. 23A , a case is illustrated in which the assistance apparatus  200  according to the modification assists extension of the hip joint of the left leg of the user  1 . Referring to  FIG. 23B , a case is illustrated in which the assistance apparatus  200  according to the modification assists extension of the hip joint of the right leg of the user  1 . In  FIG. 23A , to extend the left leg, the drive control unit  122  increases the tensions of the second wire  110   a   2  and the sixth wire  110   a   6 . In  FIG. 23B , to extend the right leg, the drive control unit  122  increases the tensions of the fourth wire  110   a   4  and the eighth wire  110   a   8 . The tension of the second wire  110   a   2  for extension may be similar to the tension of the first wire  110   a   1  for flexion. The tension of the sixth wire  110   a   6  for extension may be similar to the tension of the fifth wire  110   a   5  for flexion. The tension of the fourth wire  110   a   4  for extension may be similar to the tension of the third wire  110   a   3  for flexion. The tension of the eighth wire  110   a   8  for extension may be similar to the tension of the seventh wire  110   a   7  for flexion. 
     In the foregoing description, the drive control unit  122  increases the tensions of two wires among the wires  110  to assist one motion of one leg. In this case, the drive control unit  122  may control the motors  114  to adjust the tensions of the wires  110  in accordance with a motion of the user  1  while keeping the tensions of the other six wires at the current value, or may stop the motors corresponding to the six wires so as not to exert the tensions on the six wires. 
     3. Operation of Assistance Apparatus 
     3-1. Overall Operation of Assistance Apparatus 
     Next, the overall operation flow of an assistance apparatus will be described. Since the assistance apparatus  100  according to the embodiment and the assistance apparatus  200  according to the modification are similar in terms of the overall operation flow of an assistance apparatus, the operation of the assistance apparatus  100  according to the embodiment will be described, with no description given of the operation of the assistance apparatus  200  according to the modification.  FIG. 24  is a flowchart illustrating the overall flow of an operation of the assistance apparatus  100  for assisting the user  1 . 
     As illustrated in  FIG. 3  and  FIG. 24 , in step S 001 , the control unit  120  of the assistance apparatus  100  determines the operation mode of the assistance apparatus  100  in accordance with an operation mode instruction received from the user  1 . Specifically, the drive control unit  122  receives an instruction for an operation mode to be performed by the assistance apparatus  100  from the input device  140  of the assistance apparatus  100  or from the terminal device  150 . Examples of the operation mode include a normal walking mode in which a user walks without an object such as an item like luggage, and an object transport walking mode in which a user walks with an object. For example, the user  1  is able to select an operation mode through their decision-making on the basis of not only whether the user  1  is carrying an object but also, when the user  1  is carrying an object, the weight of the object, if necessary. 
     In step S 002 , the control unit  120  determines whether the instruction indicates the object transport walking mode. If the instruction indicates the object transport walking mode (Yes in step S 002 ), the control unit  120  proceeds to step S 003 . If the instruction does not indicate the object transport walking mode (No in step S 002 ), the control unit  120  proceeds to step S 004 . 
     In step S 003 , the grasp recognition unit  121  of the control unit  120  determines whether the user  1  is carrying an object. The grasp recognition unit  121  detects whether the user  1  is carrying an object on the basis of a sensor value acquired from the contact sensor  301  that the user  1  wears on their hand, and outputs a detection result to the drive control unit  122 . If the grasp recognition unit  121  determines that the user  1  is carrying an object (Yes in step S 003 ), the process proceeds to step S 005 . If the grasp recognition unit  121  determines that the user  1  is carrying no object (No in step S 003 ), the process proceeds to step S 006 . 
     In step S 005 , the drive control unit  122  acquires a gait phase predicted by the gait timing detection unit  123 . Further, in step S 007 , the drive control unit  122  controls the motors  114   a   1  to  114   a   4  on the basis of the acquired gait phase to generate tensions in the wires  110   a   1  to  110   a   4  of the assistance apparatus  100  with input profiles corresponding to the state of walking with an object. That is, by generating tensions in the wires  110   a   1  to  110   a   4 , the drive control unit  122  assists the user  1  in flexing and extending the left and right legs. In this case, the drive control unit  122  controls the tension of the wire  110   a   1  on the basis of the tension of the wire  110   a   1 , which is acquired from the force sensor  115   a   1 , controls the tension of the wire  110   a   2  on the basis of the tension of the wire  110   a   2 , which is acquired from the force sensor  115   a   2 , controls the tension of the wire  110   a   3  on the basis of the tension of the wire  110   a   3 , which is acquired from the force sensor  115   a   3 , and controls the tension of the wire  110   a   4  on the basis of the tension of the wire  110   a   4 , which is acquired from the force sensor  115   a   4 . Accordingly, the assistance apparatus  100  assists the user  1  in walking with an object. The input profiles corresponding to the state of walking with an object will be described in detail below. 
     Each input profile includes a timing at which a tension is generated in a wire during a gait cycle of the left leg, a period during which a tension is generated in the wire, the value of the tension of the wire during the period, a timing at which a tension is generated in a wire during a gait cycle of the right leg, a period during which a tension is generated in the wire, and the value of the tension of the wire during the period. The input profiles are set in advance and are stored in the storage unit  125 . While receiving assistance provided by the assistance apparatus  100 , the user  1  may adjust the timing of generation of a wire tension, the period of generation of the wire tension, and the value of the wire tension via the input device  140  or the terminal device  150 . The drive control unit  122  may reflect the adjustment results to change the input profile, and may store the changed input profile in the storage unit  125 . The drive control unit  122  may control the wire tension by using the changed input profile. 
     Then, in step S 008 , the drive control unit  122  determines whether a stop instruction for stopping assistance provided by the assistance apparatus  100  has been acquired from the user  1 . If the stop instruction has been acquired (Yes in step S 008 ), the drive control unit  122  stops the operation of the assistance apparatus  100  and terminates the series of processes. If no stop instruction is acquired (No in step S 008 ), the process returns to step S 003 . The stop instruction may be an instruction for changing the operation mode. 
     In step S 006 , the drive control unit  122  acquires a gait phase predicted by the gait timing detection unit  123 . Further, in step S 009 , the drive control unit  122  controls the motors  114   a   1  to  114   a   4  on the basis of the acquired gait phase to generate tensions in the wires  110   a   1  to  110   a   4  of the assistance apparatus  100  with input profiles corresponding to the state of walking without an object. The drive control unit  122  controls the tension of the wire  110   a   1  on the basis of the tension of the wire  110   a   1 , which is acquired from the force sensor  115   a   1 , controls the tension of the wire  110   a   2  on the basis of the tension of the wire  110   a   2 , which is acquired from the force sensor  115   a   2 , controls the tension of the wire  110   a   3  on the basis of the tension of the wire  110   a   3 , which is acquired from the force sensor  115   a   3 , and controls the tension of the wire  110   a   4  on the basis of the tension of the wire  110   a   4 , which is acquired from the force sensor  115   a   4 , to assist the user  1  in flexing and extending the left and right legs. Accordingly, the assistance apparatus  100  assists the user  1  in walking without an object. The input profiles corresponding to the state of walking without an object will be described in detail below. After the processing of step S 009 , the drive control unit  122  proceeds to step S 008 . 
     In step S 004 , the drive control unit  122  acquires a gait phase predicted by the gait timing detection unit  123 . Further, in step S 010 , the drive control unit  122  controls the motors  114   a   1  to  114   a   4  on the basis of the acquired gait phase to generate tensions in the wires  110   a   1  to  110   a   4  of the assistance apparatus  100  with input profiles corresponding to the state of walking without an object. The input profiles in step S 010  may be equal to the input profiles in step S 009 . The drive control unit  122  controls the tension of the wire  110   a   1  on the basis of the tension of the wire  110   a   1 , which is acquired from the force sensor  115   a   1 , controls the tension of the wire  110   a   2  on the basis of the tension of the wire  110   a   2 , which is acquired from the force sensor  115   a   2 , controls the tension of the wire  110   a   3  on the basis of the tension of the wire  110   a   3 , which is acquired from the force sensor  115   a   3 , and controls the tension of the wire  110   a   4  on the basis of the tension of the wire  110   a   4 , which is acquired from the force sensor  115   a   4 , to assist the user  1  in flexing and extending the left and right legs. Accordingly, the assistance apparatus  100  assists the user  1  in walking without an object. 
     Then, in step S 011 , the drive control unit  122  determines whether a stop instruction for stopping assistance provided by the assistance apparatus  100  has been acquired from the user  1 . If the stop instruction has been acquired (Yes in step S 011 ), the drive control unit  122  stops the operation of the assistance apparatus  100  and terminates the series of processes. If no stop instruction is acquired (No in step S 011 ), the process returns to step S 004 . The stop instruction may be an instruction for changing the operation mode. 
     As described above, the assistance apparatus  100  assists a user in walking in accordance with the normal walking mode or the object transport walking mode, which is selected by the user. In the object transport walking mode, the assistance apparatus  100  changes the input profiles of tensions, each of which is generated in one of the wires  110   a   1  to  110   a   4 , in accordance with whether the user is carrying an object, and assists the user in accordance with the state of the user. 
     3-2. Description of Operation of Assistance Apparatus in First Pattern 
     The operation of an assistance apparatus in a first pattern will be described. The operation in the first pattern is an operation of an assistance apparatus for assisting a user in walking when the user walks forward while neither carrying nor holding an object such as an item. A description will be given of a relationship in the operation in the first pattern between a wire for which a tension is to be increased and the timing of increasing the tension of the wire in assistance for flexion and extension of each of the left and right legs of a user who is walking forward. The operation of the assistance apparatus  100  according to the embodiment and the operation of the assistance apparatus  200  according to the modification are the same, except that the number of wires in which tensions are to be generated for assistance for flexion and extension and maximum tension values are different. Thus, the following describes the operation of the assistance apparatus  100  according to the embodiment, with no description given of the operation of the assistance apparatus  200  according to the modification. The operation in the first pattern, that is, assistance for forward walking of a user who is carrying no object, is an example of first assistance. 
     The drive control unit  122  of the assistance apparatus  100  determines, based on a wire-tension relationship for a type of assistance, namely, either of flexion and extension, wires in which tensions are to be generated, pulling tensions of the wires, and the timing at which and the period during which the tensions of the wires are generated, and assists motions of the user. For example,  FIG. 25  illustrates an example operation of the assistance apparatus  100  for assisting a user in walking forward without an object. 
     In  FIG. 25 , a relationship is illustrated among a gait state of a user, a gait phase of each leg, and the swing phase and stance phase of each leg. In the illustration of  FIG. 25 , the gait phase of each leg, wires in which tensions are to be generated, and the states of the tensions of the wires, that is, the input profiles of wire tensions, are associated with each other. An input profile of a wire tension represents the ratio of a wire tension to a maximum tension to be generated in each wire (also referred to as tension gain). For example, when the tension gain of each wire is 100 N, a tension to be actually generated is represented by an expression of a tension value stipulated in the input profile×tension gain. During a period of 0 to 100% of a gait phase, the assistance apparatus  100  produces a wire tension while changing the wire tension, with a maximum tension being 100 N. 
     In the example illustrated in  FIG. 25 , the assistance apparatus  100  assists both flexion and extension of the left and right legs of the user. As described above, the assistance apparatus  100  generates a tension in the wire  110   a   1  to apply an assistance force for flexion to the left leg, and generates a tension in the wire  110   a   2  to apply an assistance force for extension to the left leg. The assistance apparatus  100  generates a tension in the wire  110   a   3  to apply an assistance force for flexion to the right leg, and generates a tension in the wire  110   a   4  to apply an assistance force for extension to the right leg. The assistance apparatus  100  may assist either flexion or extension of the left and right legs of the user, instead of both flexion and extension of the left and right legs of the user. 
     In  FIG. 25 , the gait phase of the right leg is used as a reference gait phase. In the gait phase of the right leg, heel strike of the right leg occurs at 0%, and heel strike of the left leg occurs at 50%. In this embodiment, as a non-limiting example, a time point of 0% of the gait phase of the right leg corresponds to a time point of 50% of the gait phase of the left leg. In the example illustrated in  FIG. 25 , the gait phase of the right leg is used as a reference gait phase, for convenience of illustration. The gait phase of either leg may be used as a reference gait phase, and the gait phase of one leg need not be used as a reference gait phase. 
     The stance phase of the right leg is a period of 0% or more and 60% or less of the gait phase of the right leg, and the swing phase of the right leg is a period of more than 60% and less than 100% of the gait phase of the right leg. 
     The swing phase of the left leg is a period of more than 60% and less than 100% of the gait phase of the left leg, and the stance phase of the left leg is a period of 100% or more and 160% or less of the gait phase of the left leg. In the gait phase of the left leg, a period of more than 60% and less than 100% of the gait phase of the left leg, which is the swing phase of the left leg, is included in a first gait cycle of the left leg, and a period of 100% or more and 160% or less of the gait phase of the left leg, which is the stance phase of the left leg, is included in a second gait cycle of the left leg, which is subsequent to the first gait cycle of the left leg. That is, a period of 100% or more and 160% or less of the gait phase of the left leg corresponds to a period of 0% or more and 60% or less of the second gait phase of the left leg. In the following description, a gait phase represented using a value greater than or equal to 100% means a gait phase subsequent to a gait phase represented using a value of 0% to 100%. In  FIG. 25 , furthermore, a gait phase represented using a value over 100% may be converted into a value of 0% to 100% and represented using the value of 0% to 100%. 
     When assisting the user in walking forward, for example, the assistance apparatus  100  applies an assistance force for flexion to the left leg at a timing of about 40% of the gait phase of the left leg. A timing of about 40% of the gait phase of the left leg is included in the stance phase of the left leg and the swing phase of the right leg. Specifically, a timing of about 40% of the gait phase of the left leg is a timing immediately before the right leg touches the ground during the swing phase. At this time, the center of gravity of the body of the user shifts forward. When assisting the user in walking forward, for example, the assistance apparatus  100  applies an assistance force for flexion to the right leg at a timing of about 40% of the gait phase of the right leg. A timing of about 40% of the gait phase of the right leg is included in the swing phase of the left leg and the stance phase of the right leg. Specifically, a timing of about 40% of the gait phase of the right leg is a timing immediately before the left leg touches the ground during the swing phase. At this time, the center of gravity of the body of the user shifts forward. 
     Further, the assistance apparatus  100  applies an assistance force for extension to the left leg at a timing of about 75% of the gait phase of the left leg, for example. A timing of about 75% of the gait phase of the left leg is included in the swing phase of the left leg and the stance phase of the right leg. Specifically, a timing of about 75% of the gait phase of the left leg is a timing in the middle of moving the left leg of the user forward during the swing phase and is included in the period during which the center of gravity of the body of the user shifts from backward to forward. Further, the assistance apparatus  100  applies an assistance force for extension to the right leg at a timing of about 75% of the gait phase of the right leg, for example. A timing of about 75% of the gait phase of the right leg is included in the stance phase of the left leg and the swing phase of the right leg. Specifically, a timing of about 75% of the gait phase of the right leg is a timing in the middle of moving the right leg of the user forward during the swing phase and is included in the period during which the center of gravity of the body of the user shifts from backward to forward. 
     When assisting the user in walking forward, the assistance apparatus  100  generates a tension greater than or equal to a first threshold value in each of the wires  110   a   1  to  110   a   4 . In the example illustrated in  FIG. 25 , the respective tensions of the wires  110   a   1  to  110   a   4  are 100 N, for example. The first threshold value may be a tension value that allows the user to recognize that flexion or extension is promoted by a tension generated in a wire. The first threshold value is, for example, 40 N, which is 40% of 100 N. In the example illustrated in  FIG. 25 , the assistance apparatus  100  generates a wire tension in each of the wires  110   a   1  to  110   a   4  in such a manner that the wire tension gradually increases, reaches a maximum tension, and then gradually decreases during the period of generation of the wire tension. The input profiles of the wire tensions generated in the wires  110   a   1  to  110   a   4  by the assistance apparatus  100  each exhibit a waveform that is convex curve. In this example, the maximum tension is 100 N. 
     To assist flexion of the left leg, for example, the assistance apparatus  100  continuously generates a tension in the wire  110   a   1  during the entirety of a first period, which is a period of 40% or more and 85% or less of the gait phase of the left leg. Then, the assistance apparatus  100  generates a tension greater than or equal to the first threshold value in the wire  110   a   1  during at least a portion of the first period. In the first period, the left leg shifts from the stance phase to the swing phase. Applying an assistance force for flexion to the left leg in the shift from the stance phase to the swing phase allows the user to easily raise the left leg and ensures that the user can easily walk. 
     In the example illustrated in  FIG. 25 , the assistance apparatus  100  generates no tension in the wire  110   a   1  during a fifth period, which is a period other than the first period. The fifth period may be a period of 0% or more and less than 40% of the gait phase of the left leg and a period of more than 85% and less than 100% of the gait phase of the left leg. However, the assistance apparatus  100  may generate a tension during the fifth period. For example, the assistance apparatus  100  may generate a tension less than a second threshold value in the wire  110   a   1  during the fifth period. The second threshold value is a tension value that is smaller than the first threshold value and that is not perceivable by the user, for example. For example, the second threshold value may be a tension value that prevents the wire  110   a   1  from loosening. The second threshold value is a value that is 0.2 to 0.4 times the first threshold value or is 10 N, for example. In the specification and the appended claims, generation of a tension smaller than the second threshold value means generation of a tension greater than or equal to 0 and less than the second threshold value and includes generation of a tension of 0. 
     The start timing of the first period may be included in a period of 35% or more and 55% or less of the gait phase of the left leg. The end timing of the first period may be included in a period of 80% or more and 90% or less of the gait phase of the left leg. In the example illustrated in  FIG. 25 , the wire tension is maximum at a timing of 65% of the gait phase of the left leg. However, the wire tension may be maximum at a time during a period of 60% or more and 70% or less of the gait phase of the left leg. Thus, the first period may be a period of 35% or more and 90% or less of the gait phase of the left leg. 
     To assist extension of the left leg, for example, the assistance apparatus  100  continuously generates a tension in the wire  110   a   2  during the entirety of a second period, which is a period of 75% or more and 120% or less of the gait phase of the left leg. Then, the assistance apparatus  100  generates a tension greater than or equal to the first threshold value in the wire  110   a   2  during at least a portion of the second period. In the second period, the left leg shifts from the swing phase to the stance phase. Applying an assistance force for extension to the left leg in the shift from the swing phase to the stance phase allows the left leg of the user to touch the ground stably and ensures that the user can easily walk. In the example illustrated in  FIG. 25 , the assistance apparatus  100  generates no tension in the wire  110   a   2  during a sixth period, which is a period other than the second period. The sixth period may be a period of more than 20% and less than 75% of the gait phase of the left leg. However, the assistance apparatus  100  may generate a tension less than the second threshold value during the sixth period. 
     The start timing of the second period may be included in a period of 65% or more and 90% or less of the gait phase of the left leg. The end timing of the second period may be included in a period of 110% or more and 125% or less of the gait phase of the left leg. In the example illustrated in  FIG. 25 , the wire tension is maximum at a timing of 100% of the gait phase of the left leg. However, the wire tension may be maximum at a time during a period of 85% or more and 100% or less of the gait phase of the left leg. Thus, the second period may be a period of 65% or more and 125% or less of the gait phase of the left leg, that is, may include a period of 0% or more and 25% or less of the gait phase of the left leg and a period of 65% or more and less than 100% of the gait phase of the left leg. 
     To assist flexion of the right leg, for example, the assistance apparatus  100  continuously generates a tension in the wire  110   a   3  during the entirety of a third period, which is a period of 40% or more and 85% or less of the gait phase of the right leg. Then, the assistance apparatus  100  generates a tension greater than or equal to the first threshold value in the wire  110   a   3  during at least a portion of the third period. In the third period, the right leg shifts from the stance phase to the swing phase. In the example illustrated in  FIG. 25 , the assistance apparatus  100  generates no tension in the wire  110   a   3  during a seventh period, which is a period other than the third period. However, the assistance apparatus  100  may generate a tension less than the second threshold value during the seventh period. The seventh period may be a period of 0% or more and less than 40% of the gait phase of the right leg and a period of more than 85% and less than 100% of the gait phase of the right leg. 
     The start timing of the third period may be included in a period of 35% or more and 55% or less of the gait phase of the right leg. The end timing of the third period may be included in a period of 80% or more and 90% or less of the gait phase of the right leg. In the example illustrated in  FIG. 25 , the wire tension is maximum at a timing of 65% of the gait phase of the right leg. However, the wire tension may be maximum at a time during a period of 60% or more and 70% or less of the gait phase of the right leg. Thus, the third period may be a period of 35% or more and 90% or less of the gait phase of the right leg. 
     To assist extension of the right leg, for example, the assistance apparatus  100  continuously generates a tension in the wire  110   a   4  during the entirety of a fourth period, which is a period of 75% or more and 120% or less of the gait phase of the right leg. Then, the assistance apparatus  100  generates a tension greater than or equal to the first threshold value in the wire  110   a   4  during at least a portion of the fourth period. In the fourth period, the right leg shifts from the swing phase to the stance phase. In the example illustrated in  FIG. 25 , the assistance apparatus  100  generates no tension in the wire  110   a   4  during an eighth period, which is a period other than the fourth period. However, the assistance apparatus  100  may generate a tension less than the second threshold value during the eighth period. 
     The start timing of the fourth period may be included in a period of 65% or more and 90% or less of the gait phase of the right leg. The end timing of the fourth period may be included in a period of 110% or more and 125% or less of the gait phase of the right leg. In the example illustrated in  FIG. 25 , the wire tension is maximum at a timing of 100% of the gait phase of the right leg. However, the wire tension may be maximum at a time during a period of 85% or more and 100% or less of the gait phase of the right leg. Thus, the fourth period may be a period of 65% or more and 125% or less of the gait phase of the right leg, that is, may include a period of 0% or more and 25% or less of the gait phase of the right leg and a period of 65% or more and less than 100% of the gait phase of the right leg. 
     As described above, during the entirety of a period corresponding to each input profile of a wire tension, the assistance apparatus  100  continuously generates a tension in the wire corresponding to the input profile. However, the embodiment is not limited to this. The assistance apparatus  100  may temporarily stop the generation of the tension in the wire during the period corresponding to the input profile. In this case, a load imposed on the leg of the user by the assistance apparatus  100  is reduced, and the load felt by the user on which the assistance apparatus  100  acts is reduced. 
     The input profiles of wire tensions illustrated in  FIG. 25  are set so that the tension of each wire rises earlier than a desired time point by several percent (%) of the gait phase in consideration of a time delay from when the drive control unit  122  outputs a signal to the corresponding motor to when a tension is actually generated in the wire. For example, in the example illustrated in  FIG. 25 , input profiles of wire tensions are created so that the tension of each wire rises earlier than a desired time point by approximately 5%. For assistance for flexion, the assistance apparatus  100  provides assistance so that the assistance for flexion is completed immediately before the heel strikes the ground. Thus, input profiles of wire tensions are created so that assistance for flexion ends at a time during a period of 80% or more and 90% or less of the gait phase of the each leg in order to complete assistance for flexion at a timing of about 100% of the gait phase of each leg in consideration of a delay of output of the tension of each wire. 
     3-3. Description of Operation of Assistance Apparatus in Second Pattern 
     The operation of the assistance apparatus  100  in a second pattern will be described. The operation in the second pattern is an operation of the assistance apparatus  100  for assisting a user in walking when the user walks forward while carrying an object. For example,  FIG. 26  illustrates an example operation of the assistance apparatus  100  for assisting a user in walking forward with an object. In the example illustrated in  FIG. 26 , the assistance apparatus  100  assists both flexion and extension of the left and right legs of the user. The assistance apparatus  100  produces a wire tension while changing the wire tension, with a maximum tension being 100 N. The operation in the second pattern, that is, assistance for forward walking of a user who is carrying an object, is an example of second assistance. 
     When assisting flexion of a user during forward walking with an object, the assistance apparatus  100  generates wire tensions in the wire  110   a   1  of the left leg and the wire  110   a   3  of the right leg in a way similar to that for a user during forward walking without an object described above. 
     When assisting extension of the left leg, for example, the assistance apparatus  100  continuously generates a tension in the wire  110   a   2  during the entirety of a second period, which is a period of 75% or more and 120% or less of the gait phase of the left leg. Then, the assistance apparatus  100  generates a wire tension greater than or equal to the first threshold value in the wire  110   a   2  during at least a portion of the second period. Then, the assistance apparatus  100  continuously generates a tension greater than or equal to the second threshold value and less than or equal to a fourth threshold value in the wire  110   a   2  during the entirety of a sixth period, which is a period other than the second period. The sixth period may be a period of more than 20% and less than 75% of the gait phase of the left leg. The tension of the wire  110   a   2  in the sixth period is greater than the tension of the wire  110   a   1  in the fifth period and is greater than the tension of the wire  110   a   2  in the sixth period during the operation in the first pattern. Then, the assistance apparatus  100  continuously generates a tension greater than the wire tension in the sixth period in the wire  110   a   2  during the entirety of the second period. Thus, the assistance apparatus  100  continuously generates a tension greater than or equal to the second threshold value in the wire  110   a   2  during an entire period including the second period and the sixth period. The fourth threshold value is a value less than the maximum wire tension. The fourth threshold value is, for example, a value given by an expression of maximum tension×0.6. 
     When assisting extension of the right leg, for example, the assistance apparatus  100  continuously generates a tension in the wire  110   a   4  during the entirety of a fourth period, which is a period of 75% or more and 120% or less of the gait phase of the right leg. Then, the assistance apparatus  100  generates a wire tension greater than or equal to the first threshold value in the wire  110   a   4  during at least a portion of the fourth period. Then, the assistance apparatus  100  continuously generates a tension greater than or equal to the second threshold value and less than or equal to the fourth threshold value in the wire  110   a   4  during the entirety of an eighth period, which is a period other than fourth period. The eighth period may be a period of more than 20% and less than 75% of the gait phase of the right leg. The tension of the wire  110   a   4  in the eighth period is greater than the tension of the wire  110   a   3  in the seventh period and is greater than the tension of the wire  110   a   4  in the eighth period during the operation in the first pattern. Then, the assistance apparatus  100  continuously generates a tension greater than the wire tension in the eighth period in the wire  110   a   4  during the entirety of the fourth period. Thus, the assistance apparatus  100  continuously generates a tension greater than or equal to the second threshold value in the wire  110   a   4  during an entire period including the fourth period and the eighth period. 
     As described above, a tension greater than or equal to the second threshold value is generated in the wires  110   a   2  and  110   a   4 , which are located on or above the back part of the body of the user, during the entirety of a period over which the assistance apparatus  100  provides assistance. Thus, the user is subjected to the action such that the left and right legs are pulled backward all the time during walking. When the user is holding an object in the front part of the body, the center of gravity of the body of the user tends to be moved forward. Thus, the user, who is holding an object in the front part of the body, is subjected to the action such that the tensions of the wires  110   a   2  and  110   a   4  cause the user to walk forward with the center of gravity of the body being kept at the center of gravity position in the upright posture. This enables the user to walk with a stable posture. Accordingly, the user is able to transport an object with comfort. In the fifth period, the tension of the wire  110   a   1  for assisting flexion of the left leg is small, and thus the action exerted by the tension of the wire  110   a   2  is achieved while being less affected by the tension of the wire  110   a   1 . In the seventh period, the tension of the wire  110   a   3  for assisting flexion of the right leg is small, and thus the action exerted by the tension of the wire  110   a   4  is achieved while being less affected by the tension of the wire  110   a   3 . 
     3-3. Description of Operations of Assistance Apparatus in Third and Fourth Patterns 
     The operations of the assistance apparatus  100  in a third pattern and a fourth pattern will be described. The operation in the third pattern and the operation in the fourth pattern are operations performed by the assistance apparatus  100  when any one of the wires  110   a   1  to  110   a   4  is broken. Specifically, the operation in the third pattern is an operation performed by the assistance apparatus  100  when at least one of the wires  110   a   1  and  110   a   3  is broken during the operation in the first or second pattern. The operation in the fourth pattern is an operation performed by the assistance apparatus  100  when at least one of the wires  110   a   2  and  110   a   4  is broken during the operation in the first or second pattern. For example,  FIG. 27  is a flowchart illustrating an example flow of the operation of the assistance apparatus  100  when a wire is broken. In the example illustrated in  FIG. 27 , the assistance apparatus  100  assists both flexion and extension of the left and right legs of the user. At this time, the assistance apparatus  100  produces a wire tension while changing the wire tension, with a maximum tension being 100 N. 
     The overall operation of the assistance apparatus  100  when at least one of the wires  110   a   1  to  110   a   4  is broken will be described with reference to  FIG. 27 . In step S 101 , the control unit  120  of the assistance apparatus  100  acquires signals, that is, detection values that are sensor values, from the force sensors  115   a   1  to  115   a   4 . At this time, the assistance apparatus  100  assists the user by using the operation in the first or second pattern. 
     Then, in step S 102 , the control unit  120  determines whether the wire  110   a   1  for assisting flexion of the left leg is broken. The wire tension recognition unit  124  of the control unit  120  calculates the tensions of the wires  110   a   1  to  110   a   4  from the signals of the force sensors  115   a   1  to  115   a   4 , respectively. When the tension of the wire  110   a   1  decreases or becomes 0 although the motor  114   a   1  is driven, the drive control unit  122  of the control unit  120  determines that the wire  110   a   1  is broken. The drive control unit  122  can determine whether each of the wires  110   a   2  to  110   a   4  is broken by using a method similar to the method for determining whether the wire  110   a   1  is broken. If the wire  110   a   1  is broken (Yes in step S 102 ), the drive control unit  122  proceeds to step S 103 . If the wire  110   a   1  is not broken (No in step S 102 ), the drive control unit  122  proceeds to step S 104 . 
     In step S 103 , the drive control unit  122  controls the tensions of the wires  110   a   1  to  110   a   4  in accordance with the content of the operation in the third pattern stored in the storage unit  125 . The operation in the third pattern will be described in detail below. 
     In step S 104 , the drive control unit  122  determines whether the wire  110   a   3  for assisting flexion of the right leg is broken by using a method similar to the determination method of step S 102 . If the wire  110   a   3  is broken (Yes in step S 104 ), the drive control unit  122  proceeds to step S 103 . If the wire  110   a   3  is not broken (No in step S 104 ), the drive control unit  122  proceeds to step S 105 . 
     In step S 105 , the drive control unit  122  determines whether the wire  110   a   2  for assisting extension of the left leg is broken by using a method similar to the determination method of step S 102 . If the wire  110   a   2  is broken (Yes in step S 105 ), the drive control unit  122  proceeds to step S 106 . If the wire  110   a   2  is not broken (No in step S 105 ), the drive control unit  122  proceeds to step S 107 . 
     In step S 106 , the drive control unit  122  controls the tensions of the wires  110   a   1  to  110   a   4  in accordance with the content of the operation in the fourth pattern stored in the storage unit  125 . The operation in the fourth pattern will be described in detail below. 
     In step S 107 , the drive control unit  122  determines whether the wire  110   a   4  for assisting extension of the right leg is broken by using a method similar to the determination method of step S 102 . If the wire  110   a   4  is broken (Yes in step S 107 ), the drive control unit  122  proceeds to step S 106 . If the wire  110   a   4  is not broken (No in step S 107 ), the drive control unit  122  proceeds to step S 108 . 
     In step S 108 , the drive control unit  122  controls the tensions of the wires  110   a   1  to  110   a   4  in accordance with the operation in the first or second pattern, which is currently being performed. 
     The control unit  120  repeatedly performs the series of processing operations of steps S 101  to S 108  to detect which of the wires  110   a   1  to  110   a   4  is broken, and controls the tensions of the wires  110   a   1  to  110   a   4  in accordance with the operation in a pattern selected on the basis of the detection result. 
     Next, the operation in the third pattern will be described in detail. For example,  FIG. 28  illustrates an example operation of the assistance apparatus  100  in the third pattern when the wire  110   a   1  is broken during the operation in the first pattern in which no object is carried. 
     As illustrated in  FIG. 28 , upon detection of a break in the wire  110   a   1  at a time point F in a period of 0 to 100% of a gait phase of the left leg, the drive control unit  122  decreases the maximum value of the tension of the second wire  110   a   2  during a second period in the gait phase of the left leg that appears first at and after the break time point F, which is the timing at which the wire  110   a   1  is broken. In the example illustrated in  FIG. 28 , the break time point F corresponds to a time point of approximately 65% of the gait phase of the left leg. Thus, the drive control unit  122  determines a period of 75 to 120% of the gait phase of the left leg as the initial second period. 
     Then, the drive control unit  122  changes the input profile of the wire tension of the wire  110   a   2  during the determined second period to an input profile whose maximum tension is reduced. Specifically, the maximum wire tension of the wire  110   a   2  is changed to a maximum tension that is 0.4 to 0.8 times the original maximum tension. For example, in the example illustrated in  FIG. 28 , the original maximum tension, e.g., 100 N, in a period during which no break occurs in the wire  110   a   1  is changed to a maximum tension that is 0.6 times, namely, to 60 N. The drive control unit  122  uses the input profile of the wire tension corresponding to the changed maximum tension. The duration over which a tension is generated using the changed input profile is equal to the duration over which a tension is generated using the original input profile. As illustrated in  FIG. 28 , furthermore, the waveform of the original input profile may be similar to the waveform of the changed input profile. The changed input profile may be created in advance and stored in the storage unit  125 , or may be created by the drive control unit  122  in accordance with the changed maximum tension. 
     When the break time point F is included in a period more than 20% and less than 75% of the gait phase of the left leg, the drive control unit  122  determines a second period, which is a period of 75 to 120% of the gait phase of the left leg, as the initial second period. The initial second period does not include the break time point F. Then, as described above, the drive control unit  122  changes the entire input profile of the wire tension of the wire  110   a   2  in the initial second period to an input profile whose maximum tension is reduced. In this way, the assistance apparatus  100  weakens the assistance force for extension to be applied for the first time at and after the break time point F to the left leg, for which the wire  110   a   1  for assisting flexion is broken, compared with that in the second period before the break in the wire  110   a   1 . 
     When the break time point F is included in a period of 0% or more and 20% or less of the gait phase of the left leg or in a period of 75% or more and 100% or less of the gait phase of the left leg, the drive control unit  122  uses a different wire tension input profile than that described above. During these periods, the drive control unit  122  generates a tension in the wire  110   a   2 . When the break time point F is included in a period of 0% or more and 20% or less of the gait phase of the left leg, the drive control unit  122  determines a second period starting from the break time point F and ending at a time point of 20% of the gait phase of the left leg as the initial second period. When the break time point F is included in a period of 75% or more and 100% or less of the gait phase of the left leg, the drive control unit  122  determines a second period starting from the break time point F and ending at a time point of 120% of the gait phase of the left leg as the initial second period. In these cases, the initial second period includes the break time point F. During the initial second period, the drive control unit  122  does not generate a tension greater than the tension generated at the break time point F in the wire  110   a   2 . In the initial second period, the tension generated at the break time point F is the greatest tension at and after the break time point F. 
     When a second period starting from the break time point F and ending at a time point of 20% of the gait phase of the left leg is the initial second period, the drive control unit  122  gradually decreases the tension of the wire  110   a   2  from the tension generated at the break time point F to a tension generated at the time point of 20% of the gait phase of the left leg over an entire period from the break time point F to the time point of 20% of the gait phase of the left leg. When a second period starting from the break time point F and ending at a time point of 120% of the gait phase of the left leg is the initial second period, the drive control unit  122  gradually decreases the tension of the wire  110   a   2  from the tension generated at the break time point F to a tension generated at the time point of 120% of the gait phase of the left leg over an entire period from the break time point F to the time point of 120% of the gait phase of the left leg. To prevent the user from feeling a rapid change in the level of assistance, the tension may be reduced slowly and smoothly. Accordingly, the drive control unit  122  uses an input profile in which the tension of the wire  110   a   2  is reduced in a period from the break time point F to the end time point of the initial second period. The assistance apparatus  100 , which performs the operation described above, weakens the assistance force for extension to be applied for the first time at and after the break time point F to the left leg, for which the wire  110   a   1  for assisting flexion is broken, compared with that before the break in the wire  110   a   1 . 
     Further, the drive control unit  122  reduces a tension to be generated in the wire  110   a   3  at and after the break time point F to a level smaller than the second threshold value. For example, in the example illustrated in  FIG. 28 , the drive control unit  122  generates a tension of 0 in the wire  110   a   3 . Thus, in all third periods at and after the break time point F within the gait phase of the right leg, the drive control unit  122  does not assist flexion of the right leg using a tension greater than or equal to the first threshold value. When the break time point F is included in a third period, the drive control unit  122  may reduce the tension to be generated in the wire  110   a   3  to a level smaller than the second threshold value during a third period next to the third period including the break time point F and during the following third periods. Alternatively, the drive control unit  122  may reduce the tension to be generated in the wire  110   a   3  to a level smaller than the second threshold value stepwise over two or more third periods. The two or more third periods may include the third period next to the third period including the break time point F and the third period coming after the next third period. 
     Further, in a second period that appears next to the initial second period at and after the break time point F within the gait phase of the left leg, that is, during the second-appearing second period, the drive control unit  122  returns the input profile of the wire tension of the wire  110   a   2  to the original input profile, which is used in a period during which no break occurs in the wire  110   a   1 . For example, in the example illustrated in  FIG. 28 , the drive control unit  122  generates a tension in the wire  110   a   2  during the second-appearing second period in accordance with an input profile whose maximum tension is 100 N. In the second- and subsequently-appearing second periods, the drive control unit  122  controls the tension of the wire  110   a   2  in accordance with an input profile used in a period during which no wire break occurs. 
     The drive control unit  122  controls the wire tension for the wire  110   a   4  at and after the break time point F illustrated in  FIG. 28  in a way similar to that in a period during which no break occurs in the wire  110   a   1 . That is, the drive control unit  122  does not change tension control for the wire  110   a   4  before and after the break time point F. 
       FIG. 29  illustrates an example operation of the assistance apparatus  100  in the third pattern when the wire  110   a   3  is broken during the operation in the first pattern in which no object is carried. In the example illustrated in  FIG. 29 , a break in the wire  110   a   3  is detected at a time point F in a period of 0 to 100% of a gait phase of the right leg. Specifically, the break time point F is a time point of approximately 65% of the gait phase of the right leg. Also in this case, the drive control unit  122  performs tension control on the wire  110   a   4  in a way similar to that on the wire  110   a   2  in the example illustrated in  FIG. 28 . That is, in the initial fourth period at and after the break time point F within the gait phase of the right leg, the drive control unit  122  controls the tension of the wire  110   a   4  in accordance with an input profile having a lower maximum tension. In the second- and subsequently-appearing fourth periods at and after the break time point F, the drive control unit  122  controls the tension of the wire  110   a   4  in accordance with the original input profile, which is used before the break in the wire  110   a   3 . Further, the drive control unit  122  performs tension control on the wire  110   a   1  in a way similar to that on the wire  110   a   3  in the example illustrated in  FIG. 28 . That is, the drive control unit  122  reduces the tension of the wire  110   a   1  at and after the break time point F to a level lower than the second threshold value. Further, the drive control unit  122  performs tension control on the wire  110   a   2  in a way similar to that on the wire  110   a   4  in the example illustrated in  FIG. 28 . That is, the drive control unit  122  does not change tension control for the wire  110   a   2  before and after the break time point F. 
     As described above, when the wire  110   a   1  for assisting flexion of the left leg is broken, the drive control unit  122  generates a wire tension in the wire  110   a   2  during the initial second period. The wire tension in the wire  110   a   2  during the initial second period is smaller than that in a period during which the wire  110   a   1  is unbroken. The wire  110   a   2  for assisting extension and the broken wire  110   a   1  are provided to assist the same lag in the situation. Then, the drive control unit  122  generates the same wire tension as that when there is no wire break in the wire  110   a   2  during the second- and subsequently-appearing second periods after the break time point F within the gait phase. Further, the drive control unit  122  reduces the tension of the wire  110   a   3 , which is not broken, to a level smaller than the second threshold value at and after the break time point F. 
     As described above, when the wire  110   a   3  for assisting flexion of the right leg is broken, the drive control unit  122  generates a wire tension in the wire  110   a   4  during the initial fourth period. The wire tension in the wire  110   a   4  during the initial fourth period is smaller than that in a period during which the wire  110   a   3  is unbroken. The wire  110   a   4  for assisting extension and the broken wire  110   a   3  are provided to assist the same lag in the situation. Then, the drive control unit  122  generates the same wire tension as that when there is no wire break in the wire  110   a   4  during the second- and subsequently-appearing fourth periods after the break time point F within the gait phase. Further, the drive control unit  122  reduces the tension of the wire  110   a   1 , which is not broken, to a level smaller than the second threshold value at and after the break time point F. 
     Accordingly, when the wire  110   a   1  for assisting flexion of the left leg is broken, the assistance apparatus  100  weakens the assistance force for extension of the left leg to be applied for the first time at and after the break time point F, compared with the assistance force for extension of the left leg which is applied before the break in the wire  110   a   1 . For example, if a wire break suddenly stops exerting an assistance force for flexion on the left leg, the user is likely to disrupt the balance between the movements of the left and right legs and can fall. When the wire  110   a   1  for assisting flexion of the left leg is broken, the assistance force to be applied for the first time at and after the break time point F to the left leg is weakened, which may prevent the user from disrupting the balance between the movements of the left and right legs. 
     When the wire  110   a   3  for assisting flexion of the right leg is broken, the assistance apparatus  100  weakens the assistance force for extension of the right leg to be applied for the first time at and after the break time point F, compared with the assistance force for extension of the right leg which is applied before the break in the wire  110   a   3 . For example, if a wire break suddenly stops exerting an assistance force for flexion on the right leg, the user is likely to disrupt the balance between the movements of the left and right legs and can fall. When the wire  110   a   3  for assisting flexion of the right leg is broken, the assistance force to be applied for the first time at and after the break time point F to the right leg is weakened, which may prevent the user from disrupting the balance between the movements of the left and right legs. 
     When the wire  110   a   1  for assisting flexion of the left leg is broken, furthermore, the assistance apparatus  100  makes the assistance forces for extension to be applied to the left leg for the second and following times, among assistance forces for extension to be applied to the left leg at and after the break time point F, equal to the assistance force for extension that is applied to the left leg before the break in the wire  110   a   1 . The timing at which an assistance force for extension is applied to the left leg for the second and following times corresponds to a time point when one or more gait cycles elapse after the break time point F. At this time point, the user is likely to restore the balance between the movements of the left and right legs to a stable state from an unstable state immediately after a wire break has occurred. Thus, when the wire  110   a   1  for assisting flexion of the left leg is broken, the assistance force for extension to be applied to the left leg less affects the body balance of the user even if the assistance force is made equal to an assistance force for extension to be applied to the left leg in a period during which no wire break occurs. Further, the assistance apparatus  100  applies a uniform and sufficiently strong assistance force for extension to the left and right legs of the user. 
     When the wire  110   a   3  for assisting flexion of the right leg is broken, furthermore, the assistance apparatus  100  makes the assistance forces for extension to be applied to the right leg for the second and following times, among assistance forces for extension to be applied to the right leg at and after the break time point F, equal to the assistance force for extension that is applied to the right leg before the break in the wire  110   a   3 . The timing at which an assistance force for extension is applied to the right leg for the second and following times corresponds to a time point when one or more gait cycles elapse after the break time point F. At this time point, the user is likely to restore the balance between the movements of the left and right legs to a stable state from an unstable state immediately after a wire break has occurred. Thus, when the wire  110   a   3  for assisting flexion of the right leg is broken, the assistance force for extension to be applied to the right leg less affects the body balance of the user even if the assistance force is made equal to an assistance force for extension to be applied to the right leg in a period during which no wire break occurs. Further, the assistance apparatus  100  applies a uniform and sufficiently strong assistance force for extension to the left and right legs of the user. 
     Further, the assistance apparatus  100  reduces the tension of the wire  110   a   1 , which is broken, and the tension of the wire  110   a   3 , which is not broken, to values less than the second threshold value. This prevents unbalanced assistance for flexion of the left and right legs from being provided to the user and allows the user to maintain the balance between the movements of the left and right legs. The assistance apparatus  100  reduces the tension of the wire  110   a   3 , which is broken, and the tension of the wire  110   a   1 , which is not broken, to values less than the second threshold value. This prevents unbalanced assistance for flexion of the left and right legs from being provided to the user and allows the user to maintain the balance between the movements of the left and right legs. 
     As described above, when the wire  110   a   1  is broken, the assistance apparatus  100  controls the tensions of the wires  110   a   1  to  110   a   4  in accordance with the input profiles of the wire tensions illustrated in  FIG. 28 . Further, for example, if the wire  110   a   3 , which is not broken, is broken after the wire  110   a   1  has been broken, the assistance apparatus  100  may continuously control the tensions of the wires  110   a   1  to  110   a   4  in accordance with the input profiles of the wire tensions illustrated in  FIG. 29  or may stop assistance. 
     As described above, when the wire  110   a   3  is broken, the assistance apparatus  100  controls the tensions of the wires  110   a   1  to  110   a   4  in accordance with the input profiles of the wire tensions illustrated in  FIG. 29 . Further, for example, if the wire  110   a   1 , which is not broken, is broken after the wire  110   a   3  has been broken, the assistance apparatus  100  may continuously control the tensions of the wires  110   a   1  to  110   a   4  in accordance with the input profiles of the wire tensions illustrated in  FIG. 28  or may stop assistance. 
       FIG. 30  illustrates an example operation of the assistance apparatus  100  in the third pattern when the wire  110   a   1  is broken during the operation in the second pattern in which an object is carried. In this case, the drive control unit  122  also controls wire tension in a way similar to that in the example illustrated in  FIG. 28 . 
     Specifically, the drive control unit  122  decreases the maximum value of the tension of the wire  110   a   2  during a second period in the gait phase of the left leg that appears first at and after the break time point F at which the wire  110   a   1  is broken. In the initial second period, the drive control unit  122  controls the tension of the wire  110   a   2  by using an input profile whose maximum tension matches the changed maximum tension. In the second- and subsequently-appearing second periods at and after the break time point F within the gait phase of the left leg, the drive control unit  122  controls the tension of the wire  110   a   2  by using the input profile used in a period during which no break occurs in the wire  110   a   1 . Further, during a sixth period in the gait phase of the left leg, the drive control unit  122  continuously generates a tension greater than or equal to the second threshold value and less than or equal to the fourth threshold value in the wire  110   a   2 , regardless of whether the wire  110   a   1  is broken. That is, before and after the break time point F, the drive control unit  122  continuously generates a tension greater than or equal to the second threshold value and less than or equal to the fourth threshold value in the wire  110   a   2 . 
     Further, the drive control unit  122  reduces a tension to be generated in the wire  110   a   3  at and after the break time point F to a level smaller than the second threshold value. Further, the drive control unit  122  controls the wire tension for the wire  110   a   4  at and after the break time point F in a way similar to when no break occurs in the wire  110   a   1 . That is, the drive control unit  122  does not change tension control for the wire  110   a   4  before and after the break time point F. 
       FIG. 31  illustrates an example operation of the assistance apparatus  100  in the third pattern when the wire  110   a   3  is broken during the operation in the second pattern in which an object is carried. Also in this case, the drive control unit  122  performs tension control on the wire  110   a   4  in a way similar to that on the wire  110   a   2  in the example illustrated in  FIG. 30 . That is, in the initial fourth period at and after the break time point F within the gait phase of the right leg, the drive control unit  122  controls the tension of the wire  110   a   4  in accordance with an input profile having a lower maximum tension. In the second- and subsequently-appearing fourth periods at and after the break time point F, the drive control unit  122  controls the tension of the wire  110   a   4  in accordance with the original input profile, which is used before the break in the wire  110   a   3 . Further, the drive control unit  122  performs tension control on the wire  110   a   1  in a way similar to that on the wire  110   a   3  in the example illustrated in  FIG. 30 . That is, the drive control unit  122  reduces the tension of the wire  110   a   1  at and after the break time point F to a level lower than the second threshold value. Further, the drive control unit  122  performs tension control on the wire  110   a   2  in a way similar to that on the wire  110   a   4  in the example illustrated in  FIG. 30 . That is, the drive control unit  122  does not change tension control for the wire  110   a   2  before and after the break time point F. 
     Further, for example, if the wire  110   a   3 , which is not broken, is broken after the wire  110   a   1  has been broken, the assistance apparatus  100  may continuously control the tensions of the wires  110   a   1  to  110   a   4  in accordance with the input profiles of the wire tensions illustrated in  FIG. 31  or may stop assistance. 
     For example, if the wire  110   a   1 , which is not broken, is broken after the wire  110   a   3  has been broken, the assistance apparatus  100  may continuously control the tensions of the wires  110   a   1  to  110   a   4  in accordance with the input profiles of the wire tensions illustrated in  FIG. 30  or may stop assistance. 
     The assistance apparatus  100 , which performs the operation described above, assists a user in walking with an object with the center of gravity of the body of the user being kept at the center of gravity position in the upright posture of the user while preventing the user from disrupting the balance between the movements of the left and right legs due to a break in the wire  110   a   1  or  110   a   3 . 
     The operation in the fourth pattern will now be described in detail. For example,  FIG. 32A  and  FIG. 32B  illustrate an example operation of the assistance apparatus  100  in the fourth pattern when the wire  110   a   2  is broken during the operation in the first pattern in which no object is carried. 
     As illustrated in  FIG. 32A  and  FIG. 32B , upon detection of a break in the wire  110   a   2  at a time point F in a period of 0 to 100% of a gait phase of the left leg, the drive control unit  122  decreases the maximum value of the tension of the wire  110   a   1  during a first period in the gait phase of the left leg that appears first at and after the break time point F, which is the timing at which the wire  110   a   2  is broken. In the illustrated example, the break time point F corresponds to a time point of approximately 100% of the gait phase of the left leg. Thus, the drive control unit  122  determines a period of 140 to 185% of the gait phase of the left leg as the initial first period. 
     The drive control unit  122  changes the input profile of the wire tension of the wire  110   a   1  during the determined first period to an input profile whose maximum tension is reduced. Specifically, the maximum wire tension of the wire  110   a   1  is changed to a maximum tension that is 0.4 to 0.8 times the original maximum tension. In the initial first period at and after the break time point F within the gait phase of the left leg, the drive control unit  122  controls the tension of the wire  110   a   1  by using an input profile whose maximum tension matches the changed maximum tension. In the second- and subsequently-appearing first periods at and after the break time point F within the gait phase of the left leg, the drive control unit  122  controls the tension of the wire  110   a   1  by using the input profile used in a period during which no break occurs in the wire  110   a   2 . 
     When the break time point F is included in a period of 0% or more and less than 40% of the gait phase of the left leg, the drive control unit  122  determines a first period, which is a period of 40 to 85% of the gait phase of the left leg, as the initial first period. When the break time point F is included in a period of more than 85% and 100% or less of the gait phase of the left leg, the drive control unit  122  determines a first period, which is a period of 140 to 185% of the gait phase of the left leg, as the initial first period. In these cases, the initial first period does not include the break time point F. Then, as described above, the drive control unit  122  changes the entire input profile of the wire tension of the wire  110   a   1  in the initial first period to an input profile whose maximum tension is reduced. In this way, when the wire  110   a   2  for assisting extension of the left leg is broken, the assistance apparatus  100  weakens the assistance force for flexion to be applied for the first time at and after the break time point F to the left leg, compared with the assistance force for flexion to be applied to the left leg during the first period before the break in the wire  110   a   2 . 
     When the break time point F is included in a period of 40% or more and 85% or less of the gait phase of the left leg, the drive control unit  122  uses a different wire tension input profile than that described above. During this period, the drive control unit  122  generates a tension in the wire  110   a   1 . When the break time point F is included in a period of 40% or more and 85% or less of the gait phase of the left leg, the drive control unit  122  determines a first period starting from the break time point F and ending at a time point of 85% of the gait phase of the left leg as the initial first period. In this case, the initial first period includes the break time point F. During the initial first period, the drive control unit  122  does not generate a tension greater than the tension generated at the break time point F in the wire  110   a   1 . The greatest tension at and after the break time point F is the tension generated at the break time point F. The drive control unit  122  gradually decreases the tension of the wire  110   a   1  from the tension generated at the break time point F to a tension generated at the time point of 85% of the gait phase of the left leg over an entire period from the break time point F to the time point of 85% of the gait phase of the left leg. To prevent the user from feeling a rapid change in the level of assistance, the tension may be reduced slowly and smoothly. Accordingly, the drive control unit  122  uses an input profile in which the tension of the wire  110   a   1  is reduced in a period from the break time point F to the end time point of the initial first period. The assistance apparatus  100 , which performs the operation described above, weakens the assistance force for flexion to be applied for the first time at and after the break time point F to the left leg, for which the wire  110   a   2  for assisting extension is broken, compared with that before the break in the wire  110   a   2 . 
     Further, the drive control unit  122  reduces a tension to be generated in the wire  110   a   4  at and after the break time point F to a level smaller than the second threshold value. That is, in all fourth periods at and after the break time point F within the gait phase of the right leg, the drive control unit  122  reduces a tension to be generated in the wire  110   a   4  to a level smaller than the second threshold value. For example, in the example illustrated in  FIG. 32A  and  FIG. 32B , the drive control unit  122  generates a tension of 0 in the wire  110   a   4 . When the break time point F is included in a fourth period, the drive control unit  122  may reduce the tension to be generated in the wire  110   a   4  to a level smaller than the second threshold value during a fourth period next to the fourth period including the break time point F and during the following fourth periods. Alternatively, the drive control unit  122  may reduce the tension to be generated in the wire  110   a   4  to a level smaller than the second threshold value stepwise over two or more fourth periods. The two or more fourth periods may include the fourth period next to the fourth period including the break time point F and the fourth period coming after the next fourth period. 
     Further, the drive control unit  122  performs tension control on the wire  110   a   3  at and after the break time point F in a way similar to when no break occurs in the wire  110   a   2 . That is, the drive control unit  122  does not change tension control for the wire  110   a   3  before and after the break time point F. 
       FIG. 33A  and  FIG. 33B  illustrate an example operation of the assistance apparatus  100  in the fourth pattern when the wire  110   a   4  is broken during the operation in the first pattern. In the example illustrated in  FIG. 33A  and  FIG. 33B , a break in the wire  110   a   4  is detected at a time point F in a period of 0 to 100% of a gait phase of the right leg. Specifically, the break time point F is a time point of approximately 100% of the gait phase of the right leg. Also in this case, the drive control unit  122  performs tension control on the wire  110   a   3  in a way similar to that on the wire  110   a   1  in the example illustrated in  FIG. 32A  and  FIG. 32B . That is, in the initial third period at and after the break time point F within the gait phase of the right leg, the drive control unit  122  controls the tension of the wire  110   a   3  in accordance with an input profile having a lower maximum tension. In the second- and subsequently-appearing third periods at and after the break time point F, the drive control unit  122  controls the tension of the wire  110   a   3  in accordance with the original input profile, which is used before the break in the wire  110   a   4 . Further, the drive control unit  122  performs tension control on the wire  110   a   2  in a way similar to that on the wire  110   a   4  in the example illustrated in  FIG. 32A  and  FIG. 32B . That is, the drive control unit  122  reduces the wire tension at and after the break time point F to a level lower than the second threshold value. Further, the drive control unit  122  performs tension control on the wire  110   a   1  in a way similar to that on the wire  110   a   3  in the example illustrated in  FIG. 32A  and  FIG. 32B . That is, the drive control unit  122  does not change tension control before and after the break time point F. 
     Further, for example, if the wire  110   a   4 , which is not broken, is broken after the wire  110   a   2  has been broken, the assistance apparatus  100  may continuously control the tensions of the wires  110   a   1  to  110   a   4  in accordance with the input profiles of the wire tensions illustrated in  FIG. 33A  to  FIG. 33B  or may stop assistance. 
     As described above, when the wire  110   a   2  for assisting extension of the left leg is broken, the drive control unit  122  generates a wire tension in the wire  110   a   1  during the initial first period. The wire tension in the wire  110   a   1  during the initial first period is smaller than that in a period during which the wire  110   a   2  is unbroken. The wire  110   a   1  for assisting flexion and the broken wire  110   a   2  are provided to assist the same lag in the situation. Then, the drive control unit  122  generates the same wire tension as that when there is no wire break in the wire  110   a   1  during the second- and subsequently-appearing first periods after the break time point F within the gait phase. Further, the drive control unit  122  reduces the tension of the wire  110   a   4 , which is not broken, to a level smaller than the second threshold value at and after the break time point F. When the wire  110   a   4  for assisting extension of the right leg is broken, the drive control unit  122  generates a wire tension in the wire  110   a   3  during the initial third period. The wire tension in the wire  110   a   3  during the initial third period is smaller than that in a period during which the wire  110   a   4  is unbroken. The wire  110   a   3  for assisting flexion and the broken wire  110   a   4  are provided to assist the same lag in the situation. Then, the drive control unit  122  generates the same wire tension as that when there is no wire break in the wire  110   a   3  during the second- and subsequently-appearing third periods after the break time point F within the gait phase. Further, the drive control unit  122  reduces the tension of the wire  110   a   2 , which is not broken, to a level smaller than the second threshold value at and after the break time point F. 
     Accordingly, also in the operation in the fourth pattern, as in the operation in the third pattern, the assistance apparatus  100  assists the user in walking while preventing the user from disrupting the balance between the movements of the left and right legs due to a break in the wire  110   a   2  or  110   a   4 . In addition, after the user restores the balance between the movements of the left and right legs to a stable state from an unstable state immediately after a wire break has occurred, the assistance apparatus  100  applies a uniform and sufficiently strong assistance force for flexion to the left and right legs of the user. Moreover, the assistance apparatus  100  reduces the tensions of the wires  110   a   2  and  110   a   4  to values less than the second threshold value at and after the break time point F, and thus does not provide unbalanced assistance for extension to the left and right legs of the user. 
       FIG. 34  illustrates an example operation of the assistance apparatus  100  in the fourth pattern when the wire  110   a   2  is broken during the operation in the second pattern in which an object is carried. As illustrated in  FIG. 34 , upon detection of a break in the wire  110   a   2  at a time point F during the operation in the second pattern, the drive control unit  122  stops the operation of the assistance apparatus  100 . That is, the drive control unit  122  generates no tension in the wires  110   a   1 ,  110   a   3 , and  110   a   4 , which are not broken, at and after the break time point F. In the operation in the second pattern, the assistance apparatus  100  assists a user in walking with an object. In this case, to assist the user with the center of gravity of the body of the user, which tends to be moved forward, being kept at the center of gravity position in the upright posture of the user, the drive control unit  122  continuously generates a tension greater than or equal to the second threshold value and less than or equal to the fourth threshold value in the wires  110   a   2  and  110   a   4 . However, due to the break in the wire  110   a   2 , the assistance apparatus  100  is unable to continuously provide the assistance described above, and thus the drive control unit  122  stops the assistance apparatus  100  from providing assistance. For example, when the assistance apparatus  100  continuously provides assistance for flexion by using the wires  110   a   1  and  110   a   3  without generating a tension in the wires  110   a   2  and  110   a   4 , the load imposed on the user may increase. 
       FIG. 35  illustrates an example operation of the assistance apparatus  100  in the fourth pattern when the wire  110   a   4  is broken during the operation in the second pattern in which an object is carried. In  FIG. 35 , as in  FIG. 34 , upon detection of a break in the wire  110   a   4  at a time point F during the operation in the second pattern, the drive control unit  122  stops the operation of the assistance apparatus  100 . That is, the drive control unit  122  generates no tension in the wires  110   a   1 ,  110   a   3 , and  110   a   2 , which are not broken, at and after the break time point F. 
     Accordingly, when the wire  110   a   2  or  110   a   4  for assisting extension of a user who is walking with an object is broken, the assistance apparatus  100  stops providing assistance to the user. 
     3-4. Modification of Operation of Assistance Apparatus 
     In the respective operations of the assistance apparatuses  100  and  200  according to the embodiment and the modification, the same input profile of wire tension and the same maximum wire tension are set for all the wires  110  for assisting flexion and extension. However, the present disclosure is not limited to the embodiment and the modification described above. Since the moment arms of the hip joints and the lengths of the legs differ from one user to another, the assistance torque exerted on the hip joint differs depending on the user even when the same tension is applied to the same wire. The assistance torque is determined by an expression of wire tension×moment arm. Thus, different tensions may be applied to wires in accordance with the user. A fatter user has a larger moment arm of the hip joint than a thinner user. Thus, for example, the maximum wire tension may be set to 60 N for a fat user with a girth of 100 cm or more, whereas the maximum wire tension may be set to 120 N for a thin user with a girth or 70 cm or less. This may make assistance torques exerted on a fat user and a thin user equivalent. 
     In addition, the wire tension may change in accordance with the lengths of the legs of the user. In assistance for flexion and extension, since a vertical, or upward and downward, force component of wire tension is more largely exerted on a user with longer legs, the wire tension for a user with longer legs may be reduced. Adjusting the wire tension for each user in accordance with the body type and the leg length enables a comfortable assistance torque to be applied to each user. 
     In addition, the wire tensions on the front and back sides of the legs of the user are set to the same value. However, the present disclosure is not limited to the embodiment and the modification described above. For example, the tensions of the wires located on the front side of the legs may be greater than the tensions of the wires located on the back side of the legs. Since the wires on the back side pass through the buttocks of the user, the moment arm on the back side of the body of the user is greater than that on the front side of the body of the user. Accordingly, the assistance torque exerted on the hip joints on the back side of the body of the user is greater than that on the front side of the body of the user. Thus, by increasing the tension of the wires on the front side, the assistance apparatuses  100  and  200  can assist flexion and extension of the user on the front and back sides in a well-balanced manner. 
     The periods during which wire tensions are generated in the wires  110  for assistance for flexion and extension are equal to each other. However, the present disclosure is not limited to the embodiment and the modification described above. For example, in the example illustrated in  FIG. 25 , the period during which a wire tension for assisting flexion is generated and the period during which a wire tension for assisting extension of the same leg is generated overlap. To reduce the overlap period, the length of either of the periods may be reduced. In particular, the periods may be adjusted such that the period in which a wire tension greater than or equal to the first threshold value is generated during assistance for flexion does not overlap the period in which a wire tension greater than or equal to the first threshold value is generated during assistance for extension. This also applies to the examples illustrated in  FIG. 26  to  FIG. 35 . This prevents the user from being confused by the simultaneous feeling of assistance for flexion and assistance for extension. The relationship between the period during which a wire tension for assisting flexion is generated and the period during which a wire tension for assisting extension is generated may be determined in accordance with the flexion and extension ability of the user. 
     In  FIG. 25 ,  FIG. 26 , and  FIG. 28  to  FIG. 35 , the waveforms of the input profiles of wire tensions are convex curve. However, the present disclosure is not limited to the illustrated examples. The waveforms of the input profiles illustrated in  FIG. 25 ,  FIG. 26 , and  FIG. 28  to  FIG. 35  are waveforms obtained through experiments, which are waveforms that allow users to feel effective and comfortable when enjoying the benefits of assistance provided by the assistance apparatus  100 . The input profiles of the wire tensions may be each created using, for example, a rectangular waveform, a trapezoidal waveform, a triangular waveform, a Gaussian waveform, or the like. When a rectangular waveform is used, the assistance apparatus  100  continuously generates a maximum tension during an entire period over which a wire tension is generated. When a trapezoidal waveform is used, the assistance apparatus  100  continuously generates a maximum tension during an entire period over which a wire tension is generated, except the initial and terminal periods. When each input profile is created using a waveform that is quadrangle such as a rectangular waveform and a trapezoidal waveform, a steep rise or a steep fall of the wire tension may occur. Such a change in tension may cause a user to feel uncomfortable during assistance. Thus, for example, when the waveform of each input profile is triangular, a rise of the wire tension to the maximum tension may be changed to a gentler one, with the wire tension changing gradually. Accordingly, the assistance apparatus  100  can carefully assist movements of the legs of the user, resulting in a reduction in the risk of falling of the user due to a steep change in wire tension. 
     In actual human walking, flexion and extension torques produced by the legs smoothly and continuously change. Thus, the waveform of each input profile may be implemented as a Gaussian waveform. The Gaussian waveform may be a waveform created by, for example, adding together, or superposing, Gaussian functions by using a Gaussian function given by Equation (1) below. In this case, among superposition methods of Gaussian functions, a superposition method that is closest to the waveform of a torque of the legs in actual human walking is found and applied to the generation of a waveform of an input profile. Finding such a method is also referred to as Gaussian fitting. Accordingly, assistance torques can be applied to realize walking similar to actual human walking, and more natural assistance can be achieved. 
     
       
         
           
             
               
                 
                   
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     Specifically, a Gaussian function has a pair of variables μ and σ (also referred to as parameters), and the waveform of the Gaussian function depends on the two parameters. The time indicating a peak of a wave of the Gaussian function depends on the variable μ, and the width of the wave of the Gaussian function depends on the variable σ. Thus, various Gaussian functions may be generated by using various combinations of values of the two parameters. 
     A function obtained by multiplying an amplitude of a torque generated in a leg during human walking by a Gaussian function forms a waveform that shows time (in seconds) on the horizontal axis and torque (in Nm) on the vertical axis. Examples of the amplitude include a maximum torque of a leg during human walking, and the amplitude is, for example, 20 Nm. Gaussian functions are superposed to find a superposition method that is closest to the torque-time waveform of the leg during actual human walking. At this time, Gaussian fitting is performed on actual human gait data by using n Gaussian functions f 1 (x), f 2 (x), . . . , and f n (x) having various values of the two parameters μ and σ to obtain Gaussian functions. The obtained Gaussian functions are further superposed to obtain a new Gaussian function. By adjusting the two parameters μ and σ of the new Gaussian function, an input profile of a wire tension can be created. 
     Further, the assistance apparatus  100  may change a maximum tension to be generated in a wire in accordance with the time of year when the user wears the assistance apparatus  100 . For example, in summer when the user wears light clothes, the user&#39;s moment arm is shorter than in winter when the user wears thick clothes. Accordingly, even when the assistance apparatus  100  applies the same tension to a wire, the torque exerted on the leg of the user in summer is smaller than that in winter. Thus, for example, the assistance apparatus  100  may increase the tension to be applied to each wire in summer to, for example, 1.2 times that in winter. 
     The operation of the assistance apparatus  200  according to the modification illustrated in  FIG. 13  to  FIG. 21  is also similar to that of the assistance apparatus  100  according to the embodiment. For the operations described above, the wire tension control for the first wire  110   a   1  and the wire tension control for the fifth wire  110   a   5  of the assistance apparatus  200  are similar to the wire tension control for the wire  110   a   1  of the assistance apparatus  100 . The wire tension control for the second wire  110   a   2  and the wire tension control for the sixth wire  110   a   6  of the assistance apparatus  200  are similar to the wire tension control for the wire  110   a   2  of the assistance apparatus  100 . The wire tension control for the third wire  110   a   3  and the wire tension control for the seventh wire  110   a   7  of the assistance apparatus  200  are similar to the wire tension control for the wire  110   a   3  of the assistance apparatus  100 . The wire tension control for the fourth wire  110   a   4  and the wire tension control for the eighth wire  110   a   8  of the assistance apparatus  200  are similar to the wire tension control for the wire  110   a   4  of the assistance apparatus  100 . 
     When assisting flexion or extension, the assistance apparatus  200  generates tensions in two wires of the same leg at the same timing. Thus, the maximum tension to be generated in the first wire  110   a   1  and the maximum tension to be generated in the fifth wire  110   a   5  of the assistance apparatus  200  may be different from the maximum tension to be generated in the wire  110   a   1  of the assistance apparatus  100  and may be smaller than the maximum tension to be generated in the wire  110   a   1  of the assistance apparatus  100 , for example. The maximum tension to be generated in the second wire  110   a   2  and the maximum tension to be generated in the sixth wire  110   a   6  of the assistance apparatus  200  may be different from the maximum tension to be generated in the wire  110   a   2  of the assistance apparatus  100  and may be smaller than the maximum tension to be generated in the wire  110   a   2  of the assistance apparatus  100 , for example. The maximum tension to be generated in the third wire  110   a   3  and the maximum tension to be generated in the seventh wire  110   a   7  of the assistance apparatus  200  may be different from the maximum tension to be generated in the wire  110   a   3  of the assistance apparatus  100  and may be smaller than the maximum tension to be generated in the wire  110   a   3  of the assistance apparatus  100 , for example. The maximum tension to be generated in the fourth wire  110   a   4  and the maximum tension to be generated in the eighth wire  110   a   8  of the assistance apparatus  200  may be different from the maximum tension to be generated in the wire  110   a   4  of the assistance apparatus  100  and may be smaller than the maximum tension to be generated in the wire  110   a   4  of the assistance apparatus  100 , for example. 
     The relationship between the maximum tension to be generated in the first wire  110   a   1  and the maximum tension to be generated in the fifth wire  110   a   5  of the assistance apparatus  200  and the maximum tension to be generated in the wire  110   a   1  of the assistance apparatus  100  changes in accordance with the angle between the direction in which the wire  110   a   1  of the assistance apparatus  100  extends and the direction in which the first wire  110   a   1  of the assistance apparatus  200  extends and in accordance with the angle between the direction in which the wire  110   a   1  of the assistance apparatus  100  extends and the direction in which the fifth wire  110   a   5  of the assistance apparatus  200  extends, and can be determined in accordance with the angles. The relationship between the maximum tension to be generated in the second wire  110   a   2  and the maximum tension to be generated in the sixth wire  110   a   6  of the assistance apparatus  200  and the maximum tension to be generated in the wire  110   a   2  of the assistance apparatus  100  changes in accordance with the angle between the direction in which the wire  110   a   2  of the assistance apparatus  100  extends and the direction in which the second wire  110   a   2  of the assistance apparatus  200  extends and in accordance with the angle between the direction in which the wire  110   a   2  of the assistance apparatus  100  extends and the direction in which the sixth wire  110   a   6  of the assistance apparatus  200  extends, and can be determined in accordance with the angles. The relationship between the maximum tension to be generated in the third wire  110   a   3  and the maximum tension to be generated in the seventh wire  110   a   7  of the assistance apparatus  200  and the maximum tension to be generated in the wire  110   a   3  of the assistance apparatus  100  changes in accordance with the angle between the direction in which the wire  110   a   3  of the assistance apparatus  100  extends and the direction in which the third wire  110   a   3  of the assistance apparatus  200  extends and in accordance with the angle between the direction in which the wire  110   a   3  of the assistance apparatus  100  extends and the direction in which the seventh wire  110   a   7  of the assistance apparatus  200  extends, and can be determined in accordance with the angles. The relationship between the maximum tension to be generated in the fourth wire  110   a   4  and the maximum tension to be generated in the eighth wire  110   a   8  of the assistance apparatus  200  and the maximum tension to be generated in the wire  110   a   4  of the assistance apparatus  100  changes in accordance with the angle between the direction in which the wire  110   a   4  of the assistance apparatus  100  extends and the direction in which the fourth wire  110   a   4  of the assistance apparatus  200  extends and in accordance with the angle between the direction in which the wire  110   a   4  of the assistance apparatus  100  extends and the direction in which the eighth wire  110   a   8  of the assistance apparatus  200  extends, and can be determined in accordance with the angles. 
     The term “same timing” is used to include not only exactly the same timing but also different timings or timings with a difference. The difference may be less than 10% or may be 5% or less in terms of the value of the gait phase. For example, when the difference is 5% or less, the values at all timings in the gait phase are included in a range of values of the gait phase, which is within ±5% from an average value of values at the timings in the gait phase. 
     If both the wires  110   a   1  and  110   a   5  are broken or both the wires  110   a   3  and  110   a   7  are broken during the operation in the first or second pattern, the assistance apparatus  200  may perform the operation in the third pattern. For example, if both the wires  110   a   1  and  110   a   5  are broken, the assistance apparatus  200  controls wire tension for the pair of wires  110   a   2  and  110   a   6 , the pair of wires  110   a   3  and  110   a   7 , and the pair of wires  110   a   4  and  110   a   8  in a way similar to that for the wires  110   a   2 ,  110   a   3 , and  110   a   4  illustrated in  FIG. 28  or  FIG. 30 , respectively. If both the wires  110   a   3  and  110   a   7  are broken, the assistance apparatus  200  controls wire tension in a way similar to that illustrated in  FIG. 29  or  FIG. 31 . 
     If either of the wires  110   a   1  and  110   a   5  is broken or either of the wires  110   a   3  and  110   a   7  is broken during the operation in the first or second pattern, the assistance apparatus  200  may continuously perform the operation in the first or second pattern or may perform the operation in the third pattern. Even if one of a pair of wires is broken, the assistance apparatus  200  can assist flexion of the left and right legs of the user by using the wire that is not broken. When performing the operation in the third pattern, the assistance apparatus  200  reduces the tension of an unbroken wire that is paired with a broken wire to a level smaller than the second threshold value at and after a break time point and controls wire tension in a way similar to that illustrated in  FIG. 28  to  FIG. 31 . 
     If both the wires  110   a   2  and  110   a   6  are broken or both the wires  110   a   4  and  110   a   8  are broken during the operation in the first or second pattern, the assistance apparatus  200  may perform the operation in the fourth pattern and stop assistance. If either of the wires  110   a   2  and  110   a   6  is broken or either of the wires  110   a   4  and  110   a   8  is broken during the operation in the first or second pattern, the assistance apparatus  200  may continuously perform the operation in the first or second pattern or may perform the operation in the fourth pattern. 
     4. Example 
     An experiment was made for the assistance operation using the assistance apparatus  100  according to the embodiment in three patterns for comparison and verification. The operation in the first pattern, the operation in the second pattern, and an operation in a new fifth pattern were compared. 
     In the operation in the fifth pattern, the assistance apparatus  100  controlled wire tension for the wires  110   a   1  and  110   a   3  in a way similar to that for the operation in the first pattern and the operation in the second pattern. Further, the assistance apparatus  100  continuously generated a maximum tension in the wires  110   a   2  and  110   a   4  during the entire duration of the assistance. Thus, strong assistance forces for extension were continuously applied to both legs of the wearer of the assistance apparatus  100  all the time during the entire duration of the assistance. 
     In the operation in the second pattern, the tension to be generated in the wire  110   a   2  was set to 20% of the maximum tension during the sixth period in the gait phase of the left leg. Further, the tension to be generated in the wire  110   a   4  was set to 20% of the maximum tension during the eighth period in the gait phase of the right leg. The maximum tension to be generated in the wire  110  was set to 100 N in the operation in the first pattern, the operation in the second pattern, and the operation in the fifth pattern. 
     The experiment was conducted on four subjects, namely A to D. The subjects A, C, and D were males, and the subject B was female. All the subjects A to D wearing the assistance apparatus  100  received three types of assistance based on the operation in the first pattern, the operation in the second pattern, and the operation in the fifth pattern, while walking forward with luggage in both hands in front of the body. Then, the subjects A to D selected one optimum operation, which was the most comfortable walking operation, from among the operations in the three patterns. The selection results are given in Table 1 below. Table 1 indicates that the operation in the second pattern is the most effective to assist the wearer in walking forward while carrying luggage. Table 1 also indicates that the operation in the first pattern is also effective to assist the wearer in walking forward. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Evaluation results of assistance based on operations in patterns 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Subject 
                 First pattern 
                 Second pattern 
                 Fifth pattern 
               
               
                   
                   
               
               
                   
                 A 
                   
                 Optimum 
                   
               
               
                   
                 B 
                   
                 Optimum 
               
               
                   
                 C 
                   
                 Optimum 
               
               
                   
                 D 
                 Optimum 
               
               
                   
                   
               
            
           
         
       
     
     5. Other Embodiments 
     While an assistance apparatus and so on according to one or more aspects have been described in conjunction with an embodiment and a modification, the present disclosure is not limited to the embodiment and modification. Applications of various modifications conceived of by persons skilled in the art to this embodiment and modification and embodiments based on combinations of constituent elements in different embodiments and modifications may also be encompassed in the scope of one or more aspects as long as such applications or embodiments do not depart from the gist of the present disclosure. 
     For example, in the assistance apparatuses  100  and  200  according to the embodiment and modification, the timings at which the control unit  120  activates the motors  114  to generate tensions in the wires  110  and values of the gait phase regarding the input profiles of the tensions are not limited to the values described in the embodiment and modification. The timings and the values of the gait phase regarding the input profiles of the tensions may be different from those described in the embodiment and modification. For example, an error of several percent in terms of gait phase may occur. 
     In the assistance apparatuses  100  and  200  according to the embodiment and modification, each of the wires  110  is provided with a motor. However, the present disclosure is not limited to the embodiment and modification. One motor may be coupled to wires. For example, in the assistance apparatus  200 , one motor may pull the wires  110   a   1  and  110   a   5 . That is, the assistance apparatus  200  may include, for example, four motors so that one motor is provided for two wires. 
     In the assistance apparatuses  100  and  200  according to the embodiment and the modification, four wires or eight wires are used to couple the upper-body belt  111  to the knee belts  112   a  and  112   b . That is, two wires or four wires are coupled to each knee belt. However, the number of wires to be coupled to each knee belt is not limited to that described above. Any number of wires more than one may be coupled to each knee belt. For example, the numbers of wires to be coupled to the front part and the back part of each knee belt may be different. Flexion of the left leg may mean flexion of the hip joint of the left leg. Flexion of the right leg may mean flexion of the hip joint of the right leg. Extension of the left leg may mean extension of the hip joint of the left leg. Extension of the right leg may mean extension of the hip joint of the right leg. 
     The present disclosure is applicable to an apparatus for assisting a user in changing direction.