Patent Publication Number: US-11020307-B2

Title: Assist system, assist method, and storage medium

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an assist system, an assist method, and a storage medium, for assisting a movement of a human. 
     2. Description of the Related Art 
     Japanese Unexamined Patent Application Publication No. 2014-133121 discloses an assist tool capable of detecting a posture of a user using a sensor or the like and judging a fastening state of a corset varying depending on the posture of the user thereby allowing it to adjust the clamping force. 
     SUMMARY 
     However, in the conventional technique disclosed in Japanese Unexamined Patent Application Publication No. 2014-133121, it is difficult to prevent a belt from shifting from its correct position when the belt is not fastened tightly. 
     One non-limiting and exemplary embodiment provides an assist system that assists a movement of a person using a wire and that is capable of effectively detecting looseness or the like of a belt of the assist system. 
     In one general aspect, the techniques disclosed here feature an assist system including a first belt to be worn on an upper body of a user, a second belt to be worn on a knee of the user, a wire having a first end and a second end, a motor coupled with the first end, the motor being disposed on the first belt or the second belt, the second end being coupled with the second belt when the motor is disposed on the first belt, the second end being coupled with the first belt when the motor is disposed on the second belt, a drive controller that controls driving of the motor, a gyro sensor that is disposed on the second belt and that measures a magnitude of an angular velocity about a direction perpendicular to a longitudinal direction of the wire, and, a controller that outputs first information when a first condition is satisfied, the first condition including a condition that the magnitude is greater than or equal to a first threshold value when a first tension is applied to the wire by using the motor. 
     According to the present disclosure, it is possible to effectively detect a looseness of a belt or the like of an assist system. 
     It should be noted that general or specific embodiments may be implemented as an apparatus, a system, a method, an integrated circuit, a computer program, a computer-readable storage medium, or any selective combination thereof. The computer-readable storage medium may be a non-transitory storage medium such as a CD-ROM (Compact Disc-Read Only Memory) or the like. 
     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 
         FIGS. 1A and 1B  are schematic diagrams illustrating a manner in which an assist system according to an embodiment is used by a user; 
         FIG. 2  is a block diagram illustrating a configuration of an assist system according to an embodiment; 
         FIGS. 3A and 3B  are diagrams each illustrating an example of a method of presenting information when a user uses an assist system; 
         FIG. 4  is a diagram illustrating an example of a method of making a judgement of a looseness; 
         FIG. 5  is a graph showing a calibration signal for a case where an input pattern is a pulse wave; 
         FIG. 6  is a graph showing a calibration signal for a case where an input pattern is a triangular wave; 
         FIG. 7  is a graph showing a calibration signal for a case where another type of input pattern is given; 
         FIG. 8  is a diagram illustrating an example of determining timing of starting calibration; 
         FIG. 9  is a diagram illustrating a state in which a knee belt is shifted in a direction in which a wire is pulled; 
         FIG. 10  is a graph showing a change in acceleration at a knee belt unit in a direction along an X-axis when a first tension is applied to a wire by inputting a pulse-wave calibration signal; 
         FIG. 11  is a diagram illustrating a rotational movement of a knee belt unit about a Y-axis direction when a first tension is applied to a wire; 
         FIG. 12  is a graph showing a change in an angular velocity of a knee belt unit about a Y-axis direction when a first tension is applied to a wire by inputting a pulse-wave calibration signal; 
         FIG. 13  is a diagram illustrating a rotational movement of a knee belt unit about a Z-axis direction when a first tension is applied to a wire; 
         FIG. 14  is a graph showing an angular velocity of a knee belt unit about a Z-axis direction when a first tension is applied to a wire by inputting a pulse-wave calibration signal; 
         FIG. 15  is a diagram illustrating an example of a location of a movement measurement unit and a wire on a knee belt unit; 
         FIG. 16  is a diagram illustrating another example of a location of a movement measurement unit and a wire on a knee belt unit; 
         FIG. 17  is a diagram illustrating another example of a location of a movement measurement unit and a wire on a knee belt unit; 
         FIG. 18  is a diagram illustrating another example of a location of a movement measurement unit and a wire on a knee belt unit; 
         FIG. 19  is a diagram illustrating an example of a method of making a judgment as to a wearing position shift of a knee belt unit; 
         FIG. 20  is a diagram illustrating another example of a method of making a judgment as to a wearing position shift of a knee belt unit; 
         FIGS. 21A and 21B  are diagrams each illustrating an example of a manner in which information is presented to a user; 
         FIG. 22  is a flow chart illustrating a flow of a process performed in an assist system according to an embodiment; 
         FIG. 23  is a block diagram illustrating a configuration of an assist system according to a first modification; and 
         FIG. 24  is a diagram illustrating a manner in which a wearing state of a knee belt unit is judged for a user in a sitting state. 
     
    
    
     DETAILED DESCRIPTION 
     Underlying Knowledge Forming Basis of the Present Disclosure 
     The present inventor has found a fact that a problem described below can occur in the assist tool described above in Section “2. Description of the Related Art”. 
     In the assist tool disclosed in Japanese Unexamined Patent Application Publication No. 2014-133121, when the assist tool is worn, an actuator on the assist tool is driven to measure a clamping force of a belt thereby measuring a looseness of the belt. Based on a measured value, clamping is performed. However, in this assist tool, a shift of a belt position due to a looseness is not measured, and thus it is not possible to prevent the belt from being shifted from a correct position owing to the looseness of the belt. 
     In view of the above, the present disclosure provides improved techniques of effectively detecting looseness or the like of a belt in an assist system as described below. 
     In an embodiment of the present disclosure, an assist system includes a first belt to be worn on an upper body of a user, a second belt to be worn on each knee of the user, a wire having a first end and a second end, a motor coupled with the first end, the motor being disposed on the first belt or the second belt, the second end being coupled with the second belt when the motor is disposed on the first belt, the second end being coupled with the first belt when the motor is disposed on the second belt, a drive controller that controls driving of the motor, a gyro sensor that is disposed on the second belt and that measures a magnitude of an angular velocity about a direction perpendicular to a longitudinal direction of the wire, and a controller that outputs first information when a first condition is satisfied, the first condition including a condition that the magnitude is greater than or equal to a first threshold value when a first tension is applied to the wire by using the motor. 
     In this aspect, in the assist system that assists a person to move by using a wire, it is possible to effectively detect looseness or the like of the second belt in the assist system, and present a detection result to, for example, the user. This may prompt the user to refasten the belt securely such that the user is allowed to receive a more effective assisting force from the assist system. The first information may include information indicating that the second belt is a loose state. The first information may include information indicating whether the second belt is in a shifted state. 
     The assist system may further include an acceleration sensor, and the first condition may further include a condition that an acceleration measured by the acceleration sensor is smaller than or equal to a second threshold value. 
     Thus, in a situation in which a user is in a no-movement state, if the second belt is in a loose state or if the second belt is in a shifted state, it is possible to output information indicating such a state, which makes it possible to more effectively present information to the user as to the state. 
     The assist system may further include an acceleration sensor wherein when the acceleration measured by the acceleration sensor is smaller than or equal to the second threshold value, the drive controller may control the motor to apply the first tension to the wire. 
     Thus, in a situation in which a user is in a no-movement state, if the second belt is in a loose state or if the second belt is in a shifted state, it is possible to more effectively detect such a state. 
     In the assist system, the direction perpendicular to the longitudinal direction of the wire may be a direction that is a forward-backward direction as seen from the user and is perpendicular to the longitudinal direction of the wire, and the first information may include information indicating that the second belt is in a shifted state. 
     Thus, a user is allowed to refasten the second belt in response to the information so as to correct the wearing position of the second belt. Thus, when there is looseness of the second belt, it is possible to eliminate the looseness of the second belt. 
     The assist system may further include an accepter that accepts setting by a user, and a storage unit that stores the setting accepted by the accepter, wherein the controller may adjust the first threshold value depending on the setting stored in the storage unit and outputs, as the information, a result of judgement performed using the adjusted first threshold value. 
     According to this aspect, the first threshold value used in the judgment of the looseness or the shift of the second belt is adjusted depending on the setting performed by a user, and thus it is possible to output a result of judgment performed properly depending on the user&#39;s preference as to the looseness or the shift of the second belt. 
     Note that general or specific embodiments described above may be implemented as a method, an integrated circuit, a computer program, a computer-readable storage medium, or any selective combination thereof. 
     The assist system according to embodiments of the present disclosure is described in detail below with reference to drawings. 
     Note that each embodiment described below is for illustrating a specific example of an implementation of the present disclosure. In the following embodiments of the present disclosure, values, shapes, materials, constituent elements, locations of elements, manners of connecting elements, steps, the order of steps, and the like are described by way of example but not limitation. Among constituent elements described in the following embodiments, those constituent elements that are not described in independent claims indicating highest-level concepts of the present disclosure are optional. 
     Embodiments 
     In the following description of embodiments, it is assumed by way of example that when the upper-body belt unit and the knee belt unit of the assist system are worn on a user&#39;s body or when the user is in a no-movement state after the assist system is worn, the looseness of the knee belt unit is judged from a value output from an acceleration sensor and/or a gyrosensor of the assist system, and information is presented to the user as to a result of the judgment. 
     1.1 Configuration 
     An assist system  200  according to an embodiment is described below with reference to drawings. 
       FIGS. 1A and 1  B are schematic diagrams illustrating a manner in which an assist system according to an embodiment is used by a user, and  FIG. 2  is a block diagram illustrating a configuration of the assist system according to the embodiment. 
     As illustrated in  FIGS. 1A and 1  B and  FIG. 2 , the assist system  200  includes a controller  100 , an upper-body belt unit  110  functioning as a first belt, one or more knee belt units  120  each functioning as a second belt, and one or more wires  130 . Hereinafter, for simplify of explanation, a description “the knee belt unit  120 ” is used to describe either one of the knee belt units  120 , and a description “the wire  130 ” is used to describe either one of the plurality of wires  130  unless otherwise stated. The assist system  200  may further include a presentation unit  140  that presents information as to a wearing state determined by the controller  100 . 
     The controller  100  includes a signal input unit  101  and a judgment unit  102 . The controller  100  is disposed, for example, on the upper-body belt unit  110 . Alternatively, the controller  100  may be disposed on the knee belt unit  120 . 
     The signal input unit  101  generates a calibration signal for use in detecting the looseness of the knee belt unit  120 . 
     The judgment unit  102  judges the wearing state of the knee belt unit  120  of a user from a result of a measurement performed by a movement measurement unit  121  of the knee belt unit  120 . More specifically, when a first tension is applied by a motor  112  to the wire  130 , the judgment unit  102  determines whether an angular velocity measured by a gyrosensor  123  of the movement measurement unit  121  is greater than or equal to a first threshold value. In a case where it is determined that the angular velocity measured by the gyrosensor  123  is greater than or equal to the first threshold value, the judgment unit  102  outputs information indicating that the knee belt unit  120  is in a loose state or the knee belt unit  120  is in a shifted state. Note that the loose state refers to a state in which the knee belt unit  120  is not securely fastened to a user, and thus if a tension is applied from the wire  130  to the knee belt unit  120 , the knee belt unit  120  may move toward a thigh of the user. The shifted state refers to a state in which the knee belt unit  120  is worn in a wrong position, that is, the position of the knee belt unit  120  is deviated in one rotational direction from a correct position on a thigh of a user, wherein the correct position is such a position where two wires  130  connected to one knee belt unit  120  are correctly aligned to each other at front and backs sides of the thigh. 
     The controller  100  may be realized, for example, using a processor and a memory such that the processor executes a particular program stored in the memory. Alternatively, the controller  100  may be realized using a dedicated circuit. 
     The upper-body belt unit  110  includes a drive controller  111  and a motor  112 . The upper-body belt unit  110  is a wearing unit that is worn on an upper-body part of a user as shown in  FIG. 1A . Examples of upper-body parts of a user are a waist, shoulders, and the like. In this system, when the wire is pulled, the upper-body belt unit is pulled downward vertically (toward the knee belt unit). When the wire is pulled in this way, if the upper-body belt unit is located, for example, on a waist, the belt is prevented by a pelvis from sliding. In a case where the upper-body belt unit is worn on shoulders of a user, the upper-body belt unit can be fixed on the shoulders by carrying the upper-body belt unit in a similar manner as when carrying a backpack. 
     For example, the upper-body belt unit  110  may be formed in a long band shape like a sash such that it is allowed to be worn around a waist of a user. The upper-body belt unit  110  may include a fastener such as a hook and loop fastener that allows it to be kept fastened around the waist. The upper-body belt unit  110  may be formed using, for example, an inelastic material such that the upper-body belt unit  110  is not easily deformed when a tension is applied in an assist operation. 
     The drive controller  111  controls the driving of the motor  112  according to the received signal. The motor  112  is coupled with the wire  130  such that under the control of the drive controller  111 , the motor  112  pulls or loosens the wire  130 . The motor  112  is fixed at a particular location on the upper-body belt unit  110 . 
     The upper-body belt unit  110  may be formed in a barrel shape. In this case, the perimeter of the barrel is set to be longer than the perimeter of the waist of a user. To achieve this, the upper-body belt unit  110  may include an adjustment mechanism for adjusting the length of the upper-body belt unit  110  depending on the length of the waist of the user. For example, a hook and loop fastener may be used as the adjustment mechanism. The hook and loop fastener is provided such that a hook fastener part extending beyond an end of the belt and can be attached to a loop fastener part disposed on the opposite end of the belt. 
     The wire  130  connects between the upper-body belt unit  110  and the knee belt unit  120 . More specifically, the wire  130  connects between the motor  112  and the knee belt unit  120 . The wire  130  has a first end and a second end. The first end is connected to the motor  112 . In a case where the motor  112  is disposed on the upper-body belt unit  110 , the second end is connected to the knee belt unit  120 . In a case where the motor  112  is disposed on the knee belt unit  120 , the second end is connected to the upper-body belt unit  110 . 
     The knee belt unit  120  includes a movement measurement unit  121 . The knee belt unit  120  may be formed in the shape of, for example, a long band like the upper-body belt unit  110 . The knee belt unit  120  is worn on a thigh or a part above a knee of a user. The knee belt unit  120  does not need to be worn on a hip joint. The thigh of a human has a feature that its cross-sectional size gradually increases from the knee to the hip. Therefore, when the knee belt unit  120  is worn around a thigh&#39;s part slightly above a knee and the knee belt unit  120  is fastened securely, significant sliding of the knee belt unit  120  does not occur when it is pulled by the wire and thus it is possible to provide an efficient assist to a user. For example, after the knee belt unit  120  is worn around a thigh of a user, the two ends of the knee belt unit  120  are attached together such that the knee belt unit  120  is kept in the worn state. The knee belt unit  120  may be formed using an inelastic material that is not easily deformed when a tension is applied to the knee belt unit  120  in an assisting operation. In the present embodiment, the assist system  200  includes two knee belt units  120  to be respectively worn around two legs on a user. Note that the assist system  200  may include only one knee belt unit  120 . Note that in the following description, a description “the knee belt unit  120 ” is used to describe the only one knee belt unit  120  when there is only one knee belt unit  120 , but when there are two knee belt units  120 , it describes either one of the two knee belt units  120  unless otherwise stated. 
     The movement measurement unit  121  is disposed on the knee belt unit  120  and measures a movement of the knee belt unit  120 . More specifically, two movement measurement units  121  are disposed on the two respective knee belt units  120 . Each movement measurement unit  121  includes an acceleration sensor  122  that measures an acceleration of a corresponding one of the two knee belt units  120  in each of three different directions respectively along the X-axis, the Y-axis, and Z-axis. Each movement measurement unit  121  also includes a gyrosensor  123  that measures an angular velocity of a corresponding one of the two knee belt units  120  in each of rotational directions about the X-axis, the Y-axis, the Z-axis. Note that in the following description, the expression “the movement measurement unit  121 ” is used to describe either one of the two movement measurement units  121  unless otherwise stated. That is, the gyrosensor  123  is disposed on a front side of a corresponding one of the two knee belt units  120  and the gyrosensor  123  measures angular velocities in the respective rotational directions about the X-axis, the Y-axis, and the Z-axis where the X-axis is defined in the longitudinal direction of one of the two wires  130  that is connected to the front side of the knee belt unit  120 . The movement measurement unit  121  transmits a measurement result to the judgment unit  102  of the controller  100 . To align the X-axis of the acceleration sensor  122  so as to be coincident with the X-axis of the wire, an arrow mark indicating the X-axis of the acceleration sensor  122  may be formed on the acceleration sensor  122  of the movement measurement unit  121 , and the movement measurement unit  121  may be positioned such that the direction of the arrow mark is coincident with the direction of the wire. The Y-axis and Z-axis are defined as follows. After the X-axis defined, a direction (in a right-left direction of a user) that is horizontal and perpendicular to the X-axis is defined as the Y-axis, and another direction (in a forward-backward direction of the user) that is vertical to the X-axis is defined as the Z-axis. The three respective axes of the gyrosensor  123  of the movement measurement unit  121  are defined in a similar manner to the X-axis, the Y-axis, and the Z-axis. 
     As described above, the upper-body belt unit  110  and the knee belt unit  120  are formed using an inelastic material, and thus in a case where the knee belt unit  120  is worn securely around a leg of a user with no looseness, it is possible to easily transfer an assisting force to the user and thus it is possible to achieve more efficient assist. Note that another movement measurement unit  121  may also be disposed on the upper-body belt unit  110  to measure a movement of the upper-body belt unit  110  thereby measuring a movement of a user. 
     The presentation unit  140  presents to a user a result of the judgement made by the judgment unit  102  of the controller  100 . That is, the presentation unit  140  presents to a user information indicating whether the knee belt unit  120  is in a loose state or the knee belt unit  120  is in a shifted state. 
       FIGS. 3A and 3B  are diagrams each illustrating an example of a manner in which information is presented to a user using the assist system. 
     In a case where the knee belt unit  120  worn on a user is in a loose state, the presentation unit  140  presents, to the user, information indicating that the knee belt unit  120  is in the loose state. In a case where the knee belt unit  120  worn on a user is shifted from a correct wearing position, the presentation unit  140  presents, to the user, information indicating that the knee belt unit  120  is shifted from its correct position. For example, the presentation unit  140  may be realized by disposing a vibration actuator (not shown) on the knee belt unit  120  as shown in  FIG. 3A  such that when the knee belt unit  120  is in a loose state or/and when the knee belt unit  120  is shifted from its correct wearing position, the vibration actuator vibrates thereby notifying the user of the state. Alternatively, for example, the presentation unit  140  may be realized by disposing a vibration actuator on the upper-body belt unit  110  such that when the knee belt unit  120  is in a loose state or/and when the knee belt unit  120  is shifted from its correct wearing position, the vibration actuator vibrates thereby notifying the user of the state. Alternatively, when the knee belt unit  120  is in a loose state or/and when the knee belt unit  120  is shifted from its correct wearing position, the presentation unit  140  may transmit information indicating this state to a portable terminal  300  such as a smartphone or the like of the user such that an image or text information indicating the state is displayed on a display  301  of the portable terminal  300  as shown in  FIG. 3B . 
       FIG. 4  is a diagram illustrating an example of a method of judging looseness. 
     The assist system  200  assists a user to move his/her two legs (for example, in walking) by pulling up the knee belt units  120  from the upper-body belt unit  110  via the wires  130 . A total of four wires  130  are provided such that two are provided for a left leg and two for right leg of a user. One of each two wires is located on a front side and the other one is located on a back side of a leg. Four motors  112  are provided for the four respective wires  130 . That is, the four motors  112  are disposed on the upper-body belt unit  110  at proper locations corresponding to the front and back sides of the two knee belt units  120 . Thus, pulling forces can be applied, at four locations, to the user who wears the assist system  200 . The magnitude of the pulling force applied at each of the four locations and the timing of applying the pulling force are controlled such that the movements of the two legs of the user are properly assisted. In the assisting operation, if either one of the knee belt units  120  is in a loose state, as shown in  FIG. 4 , then this knee belt unit  120  moves along the thigh of the user, and thus the assisting force applied via the wire  130  is not effectively transferred to the thigh of the user. In this situation, a change occurs in the acceleration of the knee belt unit  120  in the longitudinal direction of the wire  130  (that is, in the X-axis direction), and, furthermore, a large change occurs in angular velocity in rotational directions perpendicular to the direction of the wire (that is, angular velocity in rotational directions about the Y-axis and the Z-axis). 
     In the assist system  200  according to the present embodiment, a calibration signal is input in order to apply a first tension to the wire  130  thereby detecting, using the phenomenon described above, whether the assist system  200  is fastened securely on a user without looseness of the knee belt unit  120 . The assist system  200  evaluates the accelerations and the angular velocities detected by the acceleration sensor  122  and the gyrosensor  123  disposed on the knee belt unit  120  thereby determining whether the knee belt unit  120  is in a loose state or not. The assist system  200  also evaluates the angular velocities detected by the gyrosensor  123  and determines whether the knee belt unit  120  is shifted from a correct wearing position or not. 
     As described above, the assist system  200  detects whether the knee belt unit  120  is in a loose state or not and/or whether the knee belt unit  120  is in a shifted state or not, and the assist system  200  outputs a detection result, and thus if the knee belt unit  120  has a looseness or a shift, a user can easily get aware of the looseness or the shift immediately after the user wears the assist system  200  or after some movement is performed wearing the assist system  200 . Therefore, the user can properly re-fasten the knee belt unit  120  such that it becomes possible to receive a more effective assist from the assist system  200  in terms of the movements of the two legs of the user. 
     Next, elements in the functional block diagram shown in  FIG. 2  are described in detail below. 
     1.1.1 Signal Input Unit 
     The signal input unit  101  is a unit that determines a signal for use in detecting whether the knee belt unit  120  is in a loose state or not when the assist system  200  is worn on a user and transmits the determined signal to the drive controller  111 . More specifically, the signal input unit  101  determines the first tension to be applied to the wire  130  for pulling the knee belt unit  120 , and then determines an input pattern for calibration based on the determined first tension, and finally transmits a calibration signal of the determined input pattern to the drive controller  111 . More specifically, the signal input unit  101  generates the calibration signal by which to drive the motor  112  to apply the first tension to the wire  130 , and outputs the generated calibration signal to the drive controller  111  described later. The signal input unit  101  may calculate the rotation angle by which the motor  112  is to be rotated to achieve the determined first tension, and then determine the input pattern for the calibration based on the calculated rotation angle, and finally transmit the calibration signal of the determined input pattern to the drive controller  111 . 
       FIG. 5  and  FIG. 6  are graphs each illustrating an example of a calibration signal.  FIG. 5  is a graph illustrating a calibration signal for a case where the input pattern is a pulse wave.  FIG. 6  is a graph illustrating a calibration signal for a case where the input pattern is a triangular wave. As shown in  FIG. 5  and  FIG. 6 , the input pattern of the calibration signal may be a pulse wave or a triangular wave. 
     In  FIG. 5  and  FIG. 6 , w denotes a signal width, and h denotes an input tension (the magnitude of the first tension). 
     First, an explanation is given for the case where the pulse wave is used as the input pattern of the calibration signal. If the input tension h is too small, then even when the knee belt unit  120  is in a loose state, the knee belt unit  120  is not slid sufficiently enough to correctly detect whether the knee belt unit  120  is in a loose state or in a shifted state. On the other hand, if the input tension h is too large, then even when the knee belt unit  120  is fastened around the thigh of a user tightly enough to sufficiently assist the movement of the two legs of the user, there is a possibility that the knee belt unit  120  is slid too much. Therefore, the magnitude of the input tension h may be determined within a predetermined range (for example, 50 to 400 N) in which the input tension h is applied when the movements of the two legs of the user are assisted. In a case where the knee belt unit  120  is shifted when the input tension within the predetermined range is applied to the wire  130 , the assisting force is not well transferred to the thigh of the user. In this case, the controller  100  determines that the knee belt unit  120  is in a loose state or the knee belt unit  120  is in a shifted state, and thus the controller  100  determines that it is necessary for the user to properly re-fasten the knee belt unit  120 . 
     Note that the pulse wave is an input pattern having a steep rising edge and a steep falling edge, and the rising time and the falling time are small enough compared with the signal width w. Therefore, when the signal width w is greater than a particular threshold value, for example, 0.1 seconds, it is possible to drive the knee belt unit  120  much enough to correctly determine whether the knee belt unit  120  is in a loose state or a shifted state. However, to quickly detect the looseness or the shift of the knee belt unit  120 , it is desirable that the signal width w be as small as allowed. Therefore, in the present embodiment, in the case where the pulse wave is used as the input pattern for the calibration signal, the signal width w may be set in range, for example, from 0.1 to 1.0 sec. 
     In a case where a triangular wave is used for the input signal, the input tension h may be set within a range substantially equal to a range (for example, from 50 to 400 N) in which the input tension is applied in the operation of assisting the movements of the two legs of the user as in the case of the pulse wave. The influence of the signal width w on the knee belt unit  120  is different depending on whether the signal width w is large or small. For example, in a case where the signal width w is as small as, for example, 0.2 sec, the input tension rises up to h and falls down to original value of 0 in a short period, and thus the waveform is similar to that of a step input like the pulse wave, which causes the knee belt unit  120  to operate in a similar manner to the case where the pulse wave is used. On the other hand, in a case where the signal width w is as large as, for example, greater than 1.0 sec, the tension of the wire increases gradually and linearly and then again decreases. Thus, it is possible to control the motor  112  so as to precisely provide the change in the tension of the wire described above. That is, in a case where the knee belt unit  120  is in a loose state, when a calibration signal with a signal width w greater than 1.0 sec is input to the drive controller  111 , the tension provided by the wire  130  increases slowly, and thus the knee belt unit  120  is pulled gradually by the wire  130 . As a result, the knee belt unit  120  shifts from its original position. After the calibration signal reaches a vertex of the triangular wave, the input tension h starts to decrease. In this case, therefore, the knee belt unit  120  has a less probability of returning to its original position during the falling down period of the triangular wave than in the case where the tension is applied by a sharp waveform. 
     That is, in the case where the calibration signal used has an input pattern of a triangular wave and has a signal width w as large as, for example, 1.0 sec or larger, the judgment unit  102  of the controller  100  calculates displacement values (displacements in the X-axis direction, the Y-axis direction, and the Z-axis direction, and amounts of rotation about the X-axis, the Y-axis, and the Z-axis) of the knee belt unit  120  from the accelerations and the angular velocities detected by the movement measurement unit  121  disposed on the knee belt unit  120 . That is, the judgment unit  102  calculates the shift of the knee belt unit  120  from its original position. If the calculated shift is greater than a predetermined threshold value (for example, 1 cm), the judgment unit  102  may judge that the knee belt unit  120  is in a loose state. 
     In the present embodiment, by way of example, the calibration signal has a predetermined one input pattern, and the looseness and/or the shift of the knee belt unit  120  is judged using the calibration signal. However, the calibration signal is not limited to this example. For example, two calibration signals respectively having the two input patterns described above may be input, and the looseness and/or the shift of the knee belt unit  120  may be judged from a combination of measured results provided by the movement measurement unit  121 . For example, when a calibration signal having an input pattern of a pulse wave is input  4  times to the drive controller  111 , if it is determined that the knee belt unit  120  is in a loose state two out of four times, it is difficult to correctly determine whether the knee belt unit  120  is in a loose state or a shifted state. In such a case, the controller  100  may further input a calibration signal having an input pattern of a triangular wave and having a large signal width w. A displacement amount of the knee belt unit  120  that occurs in response to the input calibration signal is calculated from values measured by the movement measurement unit  121 , and if the displacement amount is greater than a predetermined threshold value (for example, 1 cm), it may be determined that the knee belt unit  120  is in a loose state. 
     Calibration signals having input patterns other than those shown in  FIG. 5  and  FIG. 6 , such as those shown in  FIGS. 7( a ) to 7( d ) , may be used as calibration signals. More specifically,  FIG. 7( a )  is a graph showing an example of a calibration signal having an input pattern that causes the tension to increase linearly and then fall down steeply.  FIG. 7( b )  is a graph showing an example of a calibration signal having an input pattern that decreases in a stairstep fashion.  FIG. 7( c )  is a graph showing an example of a calibration signal having an input pattern that causes the tension to increase steeply and then decrease linearly.  FIG. 7( d )  is a graph showing an example of a calibration signal having an input pattern that causes the tension to increase in a stairstep fashion. A calibration signal having one of input patterns shown in  FIGS. 7( a ) to 7( d )  may be input, and the looseness and/or the shift of the knee belt unit  120  may be judged based on a movement of the knee belt unit  120  that occurs in response to a change in tension. 
     For example, in a case where the calibration signal shown in  FIG. 7( a )  is used, an abrupt reduction in tension causes the knee belt unit  120  to quickly return to its original position and inertia causes the knee belt unit  120  to further move beyond the original position. In a case where the calibration signal shown in  FIG. 7( b )  or  FIG. 7( c )  is used, a result is similar to that achieved when the triangular wave with large w shown in  FIG. 6  is used. In a case where the calibration signal shown in  FIG. 7( d )  is used, the shift of the knee belt unit  120  increases gradually, and thus the final shift of the knee belt unit  120  from its original position becomes great. By using various types of input patterns for the calibration signal in the judgement of the looseness and/or the shift knee belt unit  120 , it becomes possible to achieve improved accuracy in the judgement of the looseness and/or the shift knee belt unit  120 . 
     1.1.2 Drive Controller 
     The drive controller  111  is a unit that is disposed on the upper-body belt unit  110  and drives the motor  112  in accordance with a signal received from the signal input unit  101 . More specifically, the drive controller  111  calculates a necessary number of revolutions of the motor  112  from an input tension indicated by the signal received from the signal input unit, and drives the motor  112  to rotate by the calculated necessary number of revolutions. In a case where the signal received from the signal input unit  101  indicates the necessary number of revolutions, the drive controller  111  may drive the motor  112  to rotate by the number of revolutions indicated by this signal. 
     The drive controller  111  may receive, from the controller, information indicating that the acceleration measured by the acceleration sensor  122  is smaller than or equal to a second threshold value. In this case, when the drive controller  111  receives this information, the drive controller  111  may drive the motor  112  to apply a first tension to the wire  130  for performing a calibration. 
     1.1.3 Movement Measurement Unit 
     The movement measurement unit  121  is disposed on the knee belt unit  120  and measures a movement of the knee belt unit  120 . The movement measurement unit  121  transmits a measurement result in terms of the measured movement as time-series data to the judgment unit  102 . More specifically, the movement measurement unit  121  includes the acceleration sensor  122  and the gyrosensor  123 , thereby measuring a movement of the knee belt unit  120  that occurs when the knee belt unit  120  is pulled by the motor  112  via the wire  130 . In a case where the knee belt unit  120  is not fastened securely around a thigh, the amount of displacement of the knee belt unit  120  due to the pulling by the wire  130  is greater than in the case where the knee belt unit  120  is fastened securely on the thigh (hereinafter this state will be referred to simply as a tight state). In a case where the wearing position of the knee belt unit  120  is shifted from a correct position, when the knee belt unit  120  is pulled by the wire  130 , for example, a rotational force is applied to the knee belt unit  120 . Note that a more detailed description will be given later as to which values of those acquired by the movement measurement unit  121  are used in the judgment of the wearing state. 
     The assist system  200  is basically used to assist a user to move, for example, to walk. To properly providing assisting, it is necessary to judge whether the knee belt unit  120  is in a loose state or not immediately after the assist system  200  is worn or after some movement is performed wearing the assist system  200 . The timing of making the judgement of the looseness of the knee belt unit  120  is immediately after the assist system  200  is worn or after some movement is performed wearing the assist system  200 . In any case, the assist system  200  needs to perform the judgment when the user is in a no-movement state. Therefore, based on measurement values provided from the acceleration sensor  122  and the gyrosensor  123 , the movement measurement unit  121  may determine whether the user is in a no-movement state or not. If it is determined that the user is in a no-movement state, a start signal for starting the calibration may be transmitted to the signal input unit  101 . 
       FIG. 8  is a diagram illustrating an example of a process of determining the timing of starting a calibration. In a graph shown in  FIG. 8 , a horizontal axis represents time, and a vertical axis represents an acceleration which is a resultant value obtained by combining respective accelerations in the X-axis direction, the Y-axis direction and the Z-axis direction. In the example shown in  FIG. 8 , when a user stops, for example, at a traffic signal or the like during walking, accelerations are measured by the movement measurement unit  121  in the X-axis direction, the Y-axis direction, and the Z-axis direction, and a change in the resultant combined acceleration is shown. When the change in the resultant acceleration obtained by combining respective accelerations in the X-axis direction, the Y-axis direction, and the X-axis direction is measured, if the change is smaller than or equal to a second threshold value H (for example, 0.3 m/s 2 ) over a certain time period with a particular length (for example, 2 sec or longer) as with the case shown in  FIG. 8 , then the movement measurement unit  121  may determine that the user is in a no-movement state, and may transmit a start signal to the signal input unit  101 . That is, the movement measurement unit  121  determines whether it is time to start a calibration by determining whether the acceleration measured by the acceleration sensor  122  disposed on the knee belt unit  120  is smaller than or equal to the second threshold value. If the resultant acceleration obtained by combining the respective accelerations in the X-axis direction, the Y-axis direction, and the Z-axis direction is smaller than or equal to the second threshold value, the movement measurement unit  121  transmits, to the signal input unit  101 , a start signal indicating that the calibration is to be started. 
     In the example described above, the criterion for judging whether to start the calibration is, by way of example, that the time period T is 2 sec and the second threshold value H is 0.3 m/s 2  in terms of the resultant acceleration obtained by combining the respective accelerations in the X-axis direction, the Y-axis direction, and the Z-axis direction. However, the judgment criterion is not limited to this example. The time period T may be set to different values as long as it is allowed to detect whether a user is moving during walking or the like or the user in no-movement state. Therefore, for example, a walk cycle of a person is detected by the acceleration sensor  122 , and the time period T may be set to be twice the one step period determined from the detected walk cycle. For example, in a case where the one step period of a user is 1.5 sec, the time period T may be set to 3 sec. The second threshold value H in terms of the resultant acceleration obtained by combining the respective accelerations in the X-axis direction, the Y-axis direction, and the Z-axis direction may also be determined based on a magnitude of change in acceleration of a user during walking. For example, the second threshold value H may be set to one-third the change in the resultant acceleration obtained by combining the respective accelerations in the X-axis direction, the Y-axis direction, and the Z-axis direction in walking. 
     In the example described above, the movement measurement unit  121  determines that the calibration is to be started when the resultant acceleration obtained by combining the respective accelerations in the X-axis direction is smaller than or equal to the second threshold value H. However, the manner of starting the calibration is not limited to this example. For example, a start button for starting the calibration may be provided in the assist system  200 , and the calibration may be started when the start button is pressed by a user. The start button may be disposed, for example, on the controller  100  or the knee belt unit  120  such that it is allowed for a user to press the start button, for example, when the user stops at a traffic signal or the like thereby checking the looseness of the knee belt. In a case where the movement measurement unit  121  makes the judgment described above, the movement measurement unit  121  may be realized using the acceleration sensor  122 , the gyrosensor  123 , and a dedicated circuit or a processor for performing the judgment, and the like. In a case where the judgement described above is not performed, the movement measurement unit  121  may be realized using the acceleration sensor  122  and the gyrosensor  123 . 
     1.1.4 Judgment Unit 
     The judgment unit  102  is a unit that determines whether the knee belt unit  120  worn on a user is in a loose state or not based on a measurement result provided by the movement measurement unit  121 . The judgment unit  102  also functions as a unit that detect a shift of the waring position of the knee belt unit  120  worn on a user. More specifically, when the judgment unit  102  receives the calibration start signal from the signal input unit  101 , the operation mode goes into the judgment mode in which the judgement as to the looseness and/or the shift of the knee belt unit  120  is performed. After the operation mode goes into the judgment mode, the judgment unit  102  receives values in terms of accelerations and/or angular velocities from the movement measurement unit  121 , and judges whether the knee belt unit  120  is in a loose state and whether the knee belt unit  120  is in a shifted state. 
     Next, a method of judging the looseness and/or the shift of the knee belt by the judgment unit  102  is described below. 
     In a case when the knee belt unit  120  is pulled from the upper-body belt unit  110 , the judgment unit  102  first performs the judgement of the looseness of the knee belt unit  120  based on the magnitude of the change in the acceleration in the direction in which the wire  130  is pulled. 
       FIG. 9  illustrates a state in which the knee belt has a shift in a direction in which the knee belt is pulled by the wire. 
     In the following description of the present embodiment, as shown in  FIG. 9 , it is assumed that the X-axis is defined in an upward-downward direction of a user, the Y-axis is defined in a right-left direction of the user, and the Z-axis is defined in a forward-backward direction of the user where position directions thereof are defined in an upward direction, leftward direction, and forward direction, respectively. 
     In the assist system  200 , the wire  130  connected between the upper-body belt unit  110  and the knee belt unit  120  extends in the X-axis direction. Therefore, when the knee belt unit  120  is in a loose state, if the knee belt unit  120  is pulled by the wire  130 , then, in the knee belt unit  120 , first, a change occurs in the acceleration in the X-axis direction. An example of this situation is illustrated in  FIG. 10 . 
       FIG. 10  is a graph indicating a change in acceleration of the knee belt unit  120  in the X-axis direction that occurs when a calibration signal of a pulse wave with w=0.2 sec and h=100 N is input to the drive controller  111  thereby applying the first tension to the wire  130 . In the graph shown in  FIG. 10 , a horizontal axis represents time, and a vertical axis represents the acceleration in the X-axis direction. In this graph, a dash-dot line (Tight) represents an acceleration change in a state in which the knee belt unit  120  is fastened tightly, and a solid line (Loose) represents an acceleration change in a state in which the knee belt unit  120  is loose. As shown in  FIG. 10 , a greater change in the acceleration in the X-axis direction occurs in the case where the knee belt unit  120  is in the loose state than in the case where the knee belt unit  120  is fastened tightly. Therefore, when the calibration signal of the pulse wave corresponding to the first tension (for example, h=100 N) is input, if an acceleration in the X-axis direction greater than or equal to the particular threshold value (for example, 2.5 m/s 2 ) occurs, then the judgment unit  102  may determine that the knee belt unit  120  is in a loose state. 
     The judgment unit  102  may determine whether the knee belt unit  120  is in a loose state or not based on information provided from the movement measurement unit  121 , in particular, using information indicating a change in angular velocity about the Y-axis.  FIG. 11  is a diagram illustrating a rotational movement of the knee belt unit about the Y-axis that occurs when the first tension is applied to the wire. More specifically,  FIG. 11( a )  illustrates the assist system  200  seen from the Y-axis direction in a state in which the first tension is applied to the wire  130 .  FIG. 11( b )  and  FIG. 11( c )  each illustrate an enlarged view of the knee belt unit  120  shown in  FIG. 11( a ) . Each of these figures shows a manner in which the knee belt unit  120  moves when the first tension is applied to the wire  130 . 
     As shown in  FIG. 11( a )  and  FIG. 11( b ) , when the wire  130  is pulled in a situation in which the knee belt unit  120  is in a loose state, the knee belt unit  120  moves not only in the longitudinal direction of the wire  130  (in the X-axis direction) but a rotational movement about the Y-axis also occurs as shown in  FIG. 11( c ) . In particular, in the case where wires  130  are connected to the knee belt unit  120  on both front and back sides as is the case the assist system  200 , if only the wire  130  on the front side is pulled, it is possible to more easily detect a rotational movement of the loose knee belt unit  120  about the Y-axis as shown in  FIG. 11( b )  and  FIG. 11( c ) . That is, it becomes possible for the judgment unit  102  to more easily judge whether the knee belt unit  120  is in a loose state based on time-series data in terms of angular velocity about the Y-axis measured by the movement measurement unit  121  disposed on the knee belt unit  120 . 
       FIG. 12  is a graph showing, like  FIG. 10 , a change in angular velocity of the knee belt unit  120  about the Y-axis that occurs when a calibration signal of a pulse wave with w=0.2 sec and h=100 N is input to the drive controller  111  thereby applying a first tension to the wire  130 . In the graph shown in  FIG. 12 , a horizontal axis represents time, and a vertical axis represent the angular velocity about the Y-axis. In this graph, a dash-dot line (Tight) represents an angular velocity change in a state in which the knee belt unit  120  is fastened tightly, and a solid line (Loose) represents an angular velocity change in a state in which the knee belt unit  120  is loose. As shown in  FIG. 12 , a greater change in the angular velocity change about Y-axis occurs in the case where the knee belt unit  120  is in the loose state than in the case where the knee belt unit  120  is fastened tightly. Therefore, as in the case where the looseness of the knee belt unit  120  is judged based on the acceleration change in the X-axis direction, the judgment unit  102  may perform the judgement such that when the calibration signal of the pulse wave corresponding to the first tension (h=100 N) is input, if an angular velocity about Y-axis greater than or equal to the particular threshold value (for example, 1.5 rad/s 2 ) occurs, then the judgment unit  102  determines that the knee belt unit  120  is in a loose state. 
     The judgment unit  102  may perform judgement as to the looseness and/or the shift of the knee belt unit  120  based on the magnitude of the angular velocity about the Z-axis in a similar manner to the angular velocity about the Y-axis.  FIG. 13  is a diagram illustrating a rotational movement of the knee belt unit  120  about the Z-axis that occurs when the first tension is applied to the wire  130 . More specifically,  FIG. 13( a )  illustrates the assist system  200  seen from the Z-axis direction in a state in which the first tension is applied to the wire  130 .  FIG. 13( a )  and  FIG. 13( c )  each illustrate an enlarged view of the knee belt unit  120  shown in  FIG. 13( a ) . Each of these figures shows a manner in which the knee belt unit  120  moves when the first tension is applied to the wire  130 . 
     As shown in  FIG. 13( a )  and  FIG. 13( b ) , when the wire  130  is pulled in a situation in which the knee belt unit  120  is in a loose state, the knee belt unit  120  moves not only in the longitudinal direction of the wire  130  (in the X-axis direction) and rotationally about Y-axis but also moves rotationally about the Z-axis shown in  FIG. 13( c ) . 
       FIG. 14  is a graph showing, like  FIG. 10  and  FIG. 12 , an angular velocity of the knee belt unit  120  about the Z-axis that occurs when a calibration signal of a pulse wave with w = 0 . 2  sec and h=100 N is input to the drive controller  111  thereby applying a first tension to the wire  130 . In the graph shown in  FIG. 14 , a horizontal axis represents time, and a vertical axis represents the angular velocity about the Z-axis. In this graph, a dash-dot line (Tight) represents an angular velocity change in a state in which the knee belt unit  120  is fastened tightly, and a solid line (Loose) represents an angular velocity change in a state in which the knee belt unit  120  is loose. As shown in  FIG. 14 , a greater change in the angular velocity about Z-axis occurs in the case where the knee belt unit  120  is in the loose state than in the case where the knee belt unit  120  is fastened tightly. Therefore, as with the method of judging the looseness of the knee belt unit  120  based on the acceleration change in the X-axis direction or with the method of judging the looseness of the knee belt unit  120  based on the angular velocity change about the Y-axis, the judgment unit  102  may performed judgment such that when the calibration signal of the pulse wave corresponding to the first tension (h=100 N) is input, if an angular velocity about the Z-axis greater than or equal to the particular threshold value (for example, 0.4 rad/s 2 ) occurs, the judgment unit  102  may judge that the knee belt unit  120  is in a loose state. 
     In the example described above, it is assumed by way of example that the judgment unit  102  performs the judgement as to the looseness of the knee belt unit  120  by detecting the acceleration in the X-axis direction the angular velocity about the Y-axis, and the angular velocity about the Z-axis. However, the judgment method is not limited to the example described above. For example, when the acceleration about the X-axis and the angular velocity about the Y-axis are both greater than or equal to respective particular threshold values, the judgment unit  102  may determine that the knee belt unit  120  is in a loose state. Alternatively, the judgment unit  102  may check changes in the angular velocity about the Z-axis in addition to the acceleration in the X-axis direction and the angular velocity about the Y-axis, and when values output from the corresponding sensors indicate that all these three values are greater than or equal to respective particular threshold values, the judgment unit  102  may determine that the knee belt unit  120  is in a loose state. The judgment unit  102  may determine whether the knee belt unit  120  is in a loose state by determining whether at least the change in the angular velocity about the Y-axis is greater than or equal to the particular threshold value. The judgment unit  102  may determine that the knee belt unit  120  is in a loose state when the angular velocity about the Y-axis is greater than or equal to the corresponding particular threshold value and the acceleration in the X-axis direction is greater than or equal to the corresponding particular threshold value. The judgment unit  102  may determine that the knee belt unit  120  is in a loose state when the angular velocity about the Y-axis is greater than or equal to the corresponding particular threshold value and the angular velocity about the Z-axis is greater than or equal to the corresponding particular threshold value. By employing one of the judgment methods, the judgment unit  102  is capable of making high-accuracy judgement as to the looseness of the knee belt unit  120 . 
     In the above example, the judgment unit  102  judges the looseness of the knee belt unit  120  based on the acceleration change in the X-axis direction, the angular velocity change about the Y-axis, and the angular velocity change about the Z-axis such that when the calibration signal that causes a first tension (h=100 N) to be applied to the wire  130  is input, if the acceleration change in the X-axis direction, the angular velocity change about the Y-axis, and the angular velocity change about the Z-axis that occur in response to the calibration signal are respectively greater than or equal to 2.5 m/s 2 , 1.5 rad/s 2 , and 0.4 rad/s 2 , then the judgment unit  102  determines that the knee belt unit  120  is in a loose state. However, the judgement is not limited to this example. For example, when a calibration signal that causes a first tension in a range from 50 to 400 N to be applied to the wire  130  is input, if the resultant acceleration and angular velocity changes are respectively greater than or equal to 1.2 m/s 2 , 1.0 rad/s 2 , and 0.3 rad/s 2 , the judgment unit  102  may judge that the knee belt unit  120  is in a loose state. 
     Note that the value of the first tension applied by the calibration signal, and the particular threshold value in terms of at least one of the acceleration change in the X-axis direction, the angular velocity change about the Y-axis, and the angular velocity change about the Z-axis may be set depending on each user, and the judgement of the looseness and/or the shift of the knee belt unit  120  may be performed using the calibration signal and the particular threshold value set for the user. In this case, the assist system  200  may include an accepter that accepts a preference from a user. The accepter may be realized, for example, using an input interface such as a button, a switch, an input key, a touch panel or the like, and a processor, a memory, and the like. 
     For example, the fastening state and/or the feeling of the knee belt unit  120  varies depending on the user. Therefore, at the time when the assist system  200  is used for the first time and/or at proper times, periodically, after the use of the assist system  200  is started, the user may tightly re-fasten the knee belt unit  120  and values of the acceleration change and the angular velocity change of the knee belt unit  120  that occur in the state in which the knee belt unit  120  is tightly refastened may be stored. According to the stored values, the particular threshold values for use in the judgment of the looseness and/or the shift of the knee belt unit  120  may be set. For example, for a user who prefers a tightly fastened state, the particular threshold value may be set to be smaller, for example, by 5 to 20% than the initial value (the standard value). On the other hand, for a user who prefers a loosely fastened state, the particular threshold value may be set to be greater, for example, by 5 to 20% than the standard value. That is, the assist system may further include an accepter that accepts setting by a user and a storage unit that stores the setting accepted via the accepter. The controller may adjust the first threshold value according to the setting stored in the storage unit, and may output information indicating a result of the judgement performed using the adjusted first threshold value. 
     Even in a case where the fastening state varies depending on a preference of a user or the fastening state varies, even for the same user, day by day depending on clothes the user wears, it is possible to properly judge the looseness and/or the shift of the knee belt unit  120  by changing the particular threshold value for use in the judgment of the shift of the knee belt unit  120  to a proper different value depending on the difference. 
     In the present embodiment, as described above, when the wire  130  is pulled, a response to the pulling is detected not only in terms of a change in acceleration of the knee belt unit  120  in the X-axis direction but also in terms of an angular velocity change, and more specifically, angular velocity changes about the right-left direction (the Y-axis direction) and the forward-backward direction (Z-axis direction) of a user, and the determination is performed as to whether the detected changes are greater than or equal to respective corresponding threshold values thereby accurately judging the looseness and/or the shift of the knee belt unit  120 . 
     To clearly detect an angular velocity change, the movement measurement unit  121  and the wire  130  may be disposed at particular positions, and the knee belt unit  120  may be fixed by a particular method, as described below. 
     First, a description is given below as to the position of the movement measurement unit  121  for measuring the angular velocity about the Y-axis direction and the position where the wire  130  is connected to the knee belt unit  120 . 
       FIG. 15  is a diagram illustrating an example of a position of the movement measurement unit  121  and an example of a position where the wire  130  is connected to the knee belt unit  120 . 
     As shown in  FIG. 15 , the movement measurement unit  121  and a connection part  131  where the wire  130  is connected to the knee belt unit  120  having a substantially barrel shape where the movement measurement unit  121  is denoted by an open square while the connection part  131  is denoted by a solid square. As shown in  FIG. 15( a ) , the acceleration sensor  122  and the gyrosensor  123  of the movement measurement unit  121  and the connection part  131  where the wire  130  is connected to the knee belt unit  120  are all located in a lower-half area (apart in the negative X-axis direction from the center line, as seen in the X-axis direction, of the knee belt unit  120 ). In the example shown in  FIG. 15 , the location of the movement measurement unit  121  overlaps the location of the connection part  131 . In  FIG. 15 , a dash-dot line denotes the center line, as seen in the X-axis direction, of the knee belt unit  120 . In the above-described arrangement in which the movement measurement unit  121  and the connection part  131  are disposed in the lower-half area of the knee belt unit  120  as described above, when the first tension is applied via the wire  130 , if the knee belt unit  120  is in a loose state, then the lower-half area of the knee belt unit  120  moves such that it lifts upward (in the position direction of the X-axis direction). Because this arrangement makes it possible for the lower-half part of the knee belt unit  120  to easily lift up, a large angular velocity change about the Y-axis direction is obtained even in a case where the first tension applied via the wire  130  is small, and thus it becomes possible for the judgment unit  102  to easily judge the looseness of the knee belt unit  120 . 
     In the example described above, it is assumed by way of example that the location of the movement measurement unit  121  overlaps the location of the connection part  131  where the wire  130  is connected to the knee belt unit  120 . However, the locations are not limited to those in this example. The movement measurement unit  121  and the connection part  131  may be disposed at other locations, for example, below the center line of the knee belt unit  120 . 
     The movement measurement unit  121  and the connection part  131  may be disposed such that the locations thereof are closer to a lower end of the knee belt unit  120 . As the location of the connection part  131  is closer to the lower end of the knee belt unit  120 , a greater rotation is obtained about the Y-axis direction when the first tension is applied in a situation in which the knee belt unit  120  is in a loose state. As the locations of the acceleration sensor  122  and the gyrosensor  123  of the movement measurement unit  121  are closer to one of ends, in the X-axis direction, of the knee belt unit  120 , a greater rotation component is given by the knee belt unit  120 . However, the locations of the acceleration sensor  122  and the gyrosensor  123  of the movement measurement unit  121  are not involved in the actual rotation of the knee belt unit  120 . Therefore, priority may be given to the location of the connection part  131  of the wire  130 , and the connection part  131  of the movement measurement unit  121  may be determined in the lower-half area of the knee belt unit  120  after the location of the connection part  131  of the wire  130  is determined. That is, the movement measurement unit  121  and the wire  130  may be disposed on the knee belt unit  120  such that the condition described above is satisfied, for example, as shown in  FIG. 16( a ) . That is, when the location of the movement measurement unit  121  does not overlap the location of the connection part  131 , if the above-described condition is satisfied, it is possible for the judgment unit  102  to more effectively acquire the angular velocity about the Y-axis direction as shown in  FIG. 16( b ) , which makes it possible to more easily judge the looseness of the knee belt unit  120 . 
     Next, to measure the angular velocity about the Z-axis direction, the location of the movement measurement unit  121  and the location of the connection part where the wire  130  is connected to the knee belt unit  120  may be disposed as described below. 
       FIG. 17  is a diagram illustrating an example of a location of the movement measurement unit  121  and a location of the connection part where wire  130  is connected to the knee belt unit  120 . 
     As shown in  FIG. 17( a ) , the movement measurement unit  121  and the connection part  131  are disposed, on the knee belt unit  120 , on one of sides opposing each other in the Y-axis direction via the center of the knee belt. The movement measurement unit  121  and the connection part  131  may be disposed such that when the locations of the movement measurement unit  121  and the connection part  131  are seen from the Z-axis direction, the movement measurement unit  121  and the connection part  131  are rotated about a rotation center, defined by of the center axis of the circular cylinder of the knee belt unit  120 , within an angle range from 20° to 80° in one rotational direction with reference to 0° defined in the forward direction of a user (in the positive direction of the Z-axis direction). In  FIG. 17  a dash-dot line denotes the center line, as seen in the Y-axis direction, of the knee belt unit  120 . This makes it possible to obtain a greater rotation about the Z-axis direction as can be seen from  FIG. 17( b ) . Note that the location of the movement measurement unit  121  does not necessarily need to overlap the location of the connection part  131  as described above with reference to  FIG. 16 . For example, as shown in  FIG. 18( a ) , on the knee belt unit  120 , the movement measurement unit  121  may be disposed at the center as seen in the Y-axis direction, and the connection part  131  is disposed at a location shifted in the positive or negative direction from the center. This makes it possible, as shown in  FIG. 18( b ) , for the judgment unit  102  to more effectively acquire the angular velocity about the Z-axis direction, which makes it possible to more easily judge the looseness or the shift of the knee belt unit  120 . 
     Furthermore, to make it possible to more effectively judge the looseness or the shift of the knee belt unit  120 , the wire  130  and the movement measurement unit  121  may be disposed at locations that allow it to more easily measure both the angular velocities about the Y-axis and Z-axis directions. For example, as shown in  FIG. 17  and  FIG. 19 , it is desirable that, the locations, on the knee belt unit  120 , of the movement measurement unit  121  and the connection part  131  be in a lower-half area of the knee belt unit  120 . The location of the connection part  131  may be shifted from the center, as seen in the Y-axis direction, of the knee belt unit  120  in the positive or negative direction of the Y-axis direction. This makes it possible for the judgment unit  102  to more effectively acquire the angular velocity about the Y-axis direction and the angular velocity about the Z-axis direction, which makes it possible to more easily judge the looseness of the knee belt unit  120  based on the acquired two pieces of information. 
     In the present embodiment, the length of the knee belt unit  120  in the X-axis direction may be twice or greater than the size of the connection part  131  of the wire  130  or the size of the movement measurement unit  121 . This makes it possible to dispose the connection part  131  of the wire  130  and the movement measurement unit  121  such that they are located in the lower-half area of the knee belt unit  120 , which makes it possible to more effectively provide a rotational component about the Y-axis direction. 
     In the example described above, it is assumed by way of example that the judgment unit  102  uses the angular velocity about the Z-axis direction to detect the looseness of the knee belt unit  120 . However, the angular velocity about the Z-axis direction may also be used by the judgment unit  102 , for example, to detect a shift of the wearing position of the knee belt unit  120 . That is, the judgment unit  102  may determine whether the knee belt unit  120  is shifted from a correct wearing position based on the change in the angular velocity about the Z-axis direction. The assist system  200  may be realized in the form of an assist suit that assists movements of two legs (hip joints) of a user. In this case, ideally, wires  130  may be provided such that they extend between the upper-body belt unit  110  and the knee belt units  120  in the gravitational direction (that is, the X-axis direction) as shown in  FIG. 4 . 
     Next, a method of judging the wearing position shift of the knee belt unit  120  is described below with reference to  FIG. 19 . 
       FIG. 19  is a diagram illustrating an example of a method of making a judgment as to a wearing position shift of the knee belt unit  120 .  FIG. 19( a )  illustrates a situation in which a user wears the knee belt unit  120  such that the location of a wire  130  is shifted from its ideal position represented by a broken line. In the example shown in  FIG. 19( a ) , a knee belt unit  120  worn around a left knee of the user is rotationally shifted in a rightward direction as seen from the user. In this situation, if the wire  130  is pulled by applying a first tension to the wire  130 , the knee belt unit  120  has a rotation about the Z-axis direction as shown in  FIG. 19( b ) . When the rotation about the Z-axis direction is detected as in this example, the controller  100  may present information to the user to prompt that the wearing position of the knee belt unit  120  is to be rotated to the left such that the connection position where the wire  130  is connected to the knee belt unit  120  comes to the center of the front side of the user as shown in  FIG. 19( c ) . 
     In a case where the wearing position of the knee belt unit has a deviation to the left as opposed to the example described above, the judgment may be performed in a similar manner. 
       FIG. 20  is a diagram illustrating another example of a method of making a judgment as to the wearing position shift of the knee belt unit  120 .  FIG. 20( a )  illustrates a situation in which a user wears the knee belt unit  120  such that the location of a wire  130  is shifted from its ideal position represented by a broken line. In the example shown in  FIG. 20( a ) , a knee belt unit  120  worn around a left knee of the user is rotationally shifted in a leftward direction as seen from the user. In this situation, if the wire  130  is pulled by applying a first tension to the wire  130 , the knee belt unit  120  has a rotation about the Z-axis direction as shown in  FIG. 20( b ) . When the rotation about the Z-axis direction is detected as in this example, the controller  100  may present information to the user to prompt that the wearing position of the knee belt unit  120  is to be rotated to the right such that the connection position where the wire  130  is connected to the knee belt unit  120  comes to the center of the front side of the user as shown in  FIG. 20( c ) . 
     In the examples described above with reference to  FIG. 19  and  FIG. 20 , it is assumed by way of example that the judgement is performed as to the wearing position shift of the knee belt unit  120  worn on the left knee of the user. Note that the it is possible to make a judgement in a similar manner as to the wearing position shift of the knee belt unit  120  worn around the right knee of the user. 
     When the rotation of the knee belt unit  120  about the Z-axis direction is detected, there can be following two possibilities: a first possibility that the rotation is due to a looseness of the knee belt unit  120 ; and a second possibility that the rotation is due to a wrong wearing position of the knee belt unit  120 . When a rotation about the Z-axis direction is detected, the determination as to whether the rotation is due to the looseness or the wearing position shift of the knee belt unit  120  may be performed assuming that the rotation is due to the wearing position shift. More specifically, in a case where the angular velocity about the Z-axis direction (about the forward-backward direction of a user) is greater than or equal to a first threshold value, the controller  100  may output information indicating that the knee belt unit  120  is in a shifted state without outputting information indicating that the knee belt unit  120  is in a loose state. A reason for this is as follows. When a user corrects a wearing position shift, there is a high probability that the knee belt unit  120  is loosened once and then the knee belt unit  120  is refastened. Therefore, even if the rotation about the Z-axis direction is actually due to a looseness of the knee belt unit  120 , it is very likely that the looseness of the knee belt unit  120  will be eliminated when the knee belt unit  120  is refastened by the user. 
     In a case where not only the angular velocity about the Z-axis direction but also the angular velocity about the Y-axis direction and/or the angular velocity about the X-axis direction are also large, and more specifically, in a case where they are greater than or equal to corresponding particular threshold values, the controller  100  may present information to the user to prompt that the wearing position shift of the knee belt unit  120  is to be corrected and the knee belt unit  120  is to be refastened more tightly than before. 
     In a case where the angular velocity change about the Z-axis direction is greater than or equal to the particular threshold value and the angular velocity change about the Y-axis direction is smaller than or equal to the corresponding particular threshold value, the controller  100  may determine that the knee belt unit  120  is not in a loose state but the knee belt unit  120  has a wearing position shift. In a case where in addition to the above, the angular velocity change about the X-axis direction is also smaller than or equal to the corresponding particular threshold value, the controller  100  may also determine that the knee belt unit  120  is not in a loose state but the knee belt unit  120  has a wearing position shift. Conversely, in a case where the angular velocity change about the Z-axis direction is smaller than the corresponding particular threshold value and the angular velocity change about the Y-axis direction is greater than or equal to the corresponding particular threshold value or the angular velocity change about the X-axis direction is greater than or equal to the corresponding particular threshold value, the controller  100  may determine that the knee belt unit  120  is in a loose state but there is no wearing position shift. 
     1.1.5 Presentation Unit 
     The presentation unit  140  is a unit that presents to a user a result of the judgment made by the judgment unit  102  as to the looseness or the shift of the knee belt unit  120  worn on a user. More specifically, a vibration actuator may be disposed on the knee belt unit  120  to present information such that when the judgment unit  102  determines that the knee belt unit  120  is in a loose state or there is a wearing position shift, the vibration actuator is vibrated in a particular rhythm thereby informing a user that the knee belt unit  120  is in a loose state or there is a wearing position shift. That is, the presentation unit  140  may be realized using the vibration actuator. The vibration pattern may be changed depending on whether the knee belt unit  120  is loose or has a wearing position shift. 
     In a case where the knee belt unit  120  is in a loose state, there is a possibility that a user is not aware of the vibration unless the vibration actuator is vibrated with a large vibration magnitude. When the controller  100  determines that the knee belt unit  120  is in a loose state, the controller  100  may increase the tension of the wire  130 , for example, to 200 N and may vibrate the vibration actuator, for example, at 2 Hz. On the other hand, in the case where it is determined that the knee belt unit  120  has a wearing position shift, there is a possibility that there is no a looseness. Therefore, the tension of the wire  130  may be set to a value, for example, 100 N, smaller than in the case where the knee belt unit  120  is in the loose state, and the vibration actuator may be vibrated, for example, at 5 Hz. Note that the vibration patterns are not limited to the examples described above, but other vibration patterns may be employed according to user&#39;s preference. 
     In a case where the controller  100  determines that only the knee belt unit  120  worn on a right leg has a looseness or a wearing position shift, the controller  100  may vibrate only the vibration actuator disposed on the knee belt unit  120  worn on the right leg. On the other hand, in a case where the controller  100  determines that only the knee belt unit  120  worn on a left leg has a looseness or a wearing position shift, the controller  100  may vibrate only the vibration actuator disposed on the knee belt unit  120  worn on the left leg. In a case where the controller  100  determines that both knee belt units  120  worn respectively on the right and left legs have a looseness or a wearing position shift, the controller  100  may vibrate the vibration actuators disposed on both knee belt units  120 . In this way, the controller  100  may indicate which knee belt unit  120  has a looseness or a wearing position shift. The purpose of the present embodiment is to judge the looseness or the wearing position shift of the knee belt unit  120  and notify a user of the judgment result, and thus vibrating one or both of the knee belt units  120  depending on which knee belt unit  120  has a looseness or a shift is a good method of intuitively notifying the user of the judgment result. 
     In the example described above, it is assumed by way of example but not limitation that the presentation unit  140  presents information to a user using the vibration actuators provided on the respective knee belt units  120 . However, alternatively, a vibration actuator may be disposed on the upper-body belt unit  110 . For example, in a case where the looseness is so large that a user is not aware of the vibration when the knee belt unit  120  is vibrated, the user is likely not to be aware of the vibration of the actuator disposed on the knee belt unit  120 . To avoid the problem described above, a vibration actuator may be disposed on the upper-body belt unit  110  which is likely to have relatively smaller a looseness, and this vibration actuator may be vibrated to effectively notify a user of the looseness of the knee belt unit  120 . 
     In the example described above, it is assumed by way of example that the presentation unit  140  vibrates the vibration actuator disposed on the knee belt unit  120  or the upper-body belt unit  110  in response to detecting the looseness or the wearing position shift thereby presenting information to a user to notify that there is a looseness or the wearing position shift. However, the implementation of the presentation unit  140  is not limited to this example. For example, as shown in  FIG. 3B , the assist system  200  may wirelessly communicate with a portable terminal  300  such as a smartphone or the like of a user thereby presenting information on the portable terminal  300 . That is, the presentation unit  140  may be realized using an external device such as the portable terminal  300 . 
     Alternatively, when the controller  100  determines that the knee belt unit  120  has a wearing position shift, the controller  100  may display, on the portable terminal  300 , an image representing the assist system  200  to intuitively present an instruction to a user as shown in  FIGS. 21A and 21B .  FIGS. 21A and 21B  each illustrate an example of information presented to a user. More specifically,  FIG. 21A  illustrates an example of information which is presented when it is determined that the knee belt unit  120  is rotationally shifted to the right and which prompts a user to rotate the knee belt unit  120  to the left.  FIG. 21B  illustrates an example of information which is presented when it is determined that the knee belt unit  120  is rotationally shifted to the left and which prompts a user to rotate the knee belt unit  120  to the right. As described above, by presenting an instruction prompting a user to correct the wearing position to a correct position by using an image of the assist system  200 , it becomes possible for the user to intuitively understand the direction in which the knee belt unit  120  is to be rotated to adjust the wearing position. 
     1.2 Operation 
     Next, an operation of the assist system  200  is described below. 
       FIG. 22  is a flow chart illustrating a flow of a process performed in an assist system according to an embodiment. 
     From a value detected by the acceleration sensor  122 , the movement measurement unit  121  detects that a user is in a no-movement state (S 001 ). More specifically, the movement measurement unit  121  determines whether a change in the acceleration measured by the acceleration sensor  122  is smaller than or equal to the second threshold value H continuously over a time period T. In a case where the acceleration change has been smaller than or equal to the second threshold value H continuously over the time period T, it is determined that the user is in a no-movement state, but otherwise it is determined that the user is not in a no-movement state. 
     When it is detected that the user is in the no-movement state, the movement measurement unit  121  outputs a start signal to the controller  100 . As a result, the assist system  200  starts a calibration mode. 
     When the movement measurement unit  121  detects that a user is in a no-movement state (Yes in step S 001 ), the calibration mode is started. In the controller  100 , the signal input unit  101  determines a calibration signal for use in detecting a looseness and/or a shift of the knee belt unit  120 , and the signal input unit  101  transmits the determined calibration signal to the drive controller  111  (S 002 ). When this calibration signal is received by the drive controller  111 , the drive controller  111  drives the motor  112  in accordance with the calibration signal thereby pulling the wire  130  and thus applying a pulling force (first tension) to the knee belt unit  120 . 
     Next, the movement measurement unit  121  measures the movement of the knee belt unit  120  that occurs in the state in which the first tension is applied via the wire  130  (S 003 ). Note that the movement measurement unit  121  may start the operation of measuring the movement of the knee belt unit  120  in a particular time before the first tension is applied, or the movement measurement unit  121  may always measure the movement of the knee belt unit  120  as long as the assist system  200  is active. 
     The judgment unit  102  determines whether the knee belt unit  120  is in a loose state by making a comparison between an acceleration change in the X-axis direction and a corresponding particular threshold value, and/or a comparison between an angular velocity change about the Y-axis direction and a corresponding particular threshold value, and/or a comparison between an angular velocity change about the Z-axis direction and a corresponding particular threshold value. The judgment unit  102  determines whether the knee belt unit  120  has a wearing position shift by comparing the magnitude of the change in angular velocity about the Z-axis direction with a corresponding particular threshold value (S 004 ). 
     In a case where the judgment unit  102  determines that the knee belt unit  120  does not have a looseness and the knee belt unit  120  does not have a wearing position shift (Yes in S 004 ), the processing flow returns to step S 001 . 
     Conversely, in a case where the judgement by the judgment unit  102  is that the knee belt unit  120  is in a loose state and/or the knee belt unit  120  has a wearing position shift (No in S 004 ), the controller  100  presents information via the presentation unit  140  to notify a user that the knee belt unit  120  is in the loose state and/or the knee belt unit  120  is in the shifted state (S 005 ). 
     1.3 Advantageous effects 
     In the assist system  200  according to the present embodiment, when a user wears the assist system  200 , it is determined whether the knee belt unit  120  is in a loose state or whether the knee belt unit  120  is in a shifted state based on a magnitude of change in a value output from the acceleration sensor  122  or the gyrosensor  123  disposed on the knee belt unit  120 . In a case where it is determined that the knee belt unit  120  has a looseness or a shift, information indicating a determination result is presented to a user thereby prompting the user to properly refasten the knee belt unit  120 . This makes it possible to reduce the looseness and/or the shift of the knee belt unit  120  that may occur when a user wears the assist system  200 , which makes it possible for the user to receive a more effective assisting force from the assist system  200 . 
     1.4 Modifications 
     1.4.1 First modification 
     A modification of the embodiment provides an assist system  200 A further including a storage unit  150  in addition to the elements of the assist system  200  according to the embodiment described above.  FIG. 23  is a block diagram illustrating a configuration of an assist system according to a first modification. 
     Each time a user uses the assist system  200 , the storage unit  150  stores following information together: user information; a calibration signal from the signal input unit  101 ; values of accelerations and angular velocities that occur in response to the calibration signal and measured by the movement measurement unit  121 ; and a result of judgement made by the judgment unit  102 . When the assist system  200 A is used for the second time or thereafter, the judgment unit  102  may check data stored in the storage unit  150  in terms of the calibration signals, the acceleration values, the angular velocity values, and past judgement results on wearing states, and if good consistency in data is found, the judgment unit  102  may employ the same judgement as one of the past judgements. 
     Use of the storage unit  150  in the above-described manner provides a further advantageous effect as described below. Values measured by the movement measurement unit  121  for the same user are accumulated, and a new measurement result is compared with past data stored in the storage unit  150 . This makes it possible to get information, for example, as to whether the degree of looseness is great compared with the looseness in the past, or as to whether a wearing position shift occurs although the looseness is not greater than in the past. Thus, it becomes possible for the user to sensuously recognize the fastening state of the knee belt unit  120 . 
     By storing, in the storage unit  150 , patterns of measured values and fastening states of the knee belt unit  120  varying depending on conditions in terms of circumstances, clothes, and the like of the same user as described above, it becomes possible to more accurately judge the looseness of the knee belt unit  120 . Depending on the user, there is a possibility that the knee belt unit  120  is always worn in a wrong position. To handle such a situation, the storage unit  150  may learn patterns associated with wrong wearing of the knee belt unit  120 , and a warning may be given to the user each time the knee belt unit  120  is worn, which makes it possible to properly provide an assist from the beginning. 
     1.4.2 Second Modification 
     In the embodiment described above, it is assumed by way of example that the looseness of the knee belt unit  120  worn on a user is judged basically when the user is in a standing position. However, the judgement may be performed when a user is in a sitting position. For example, in a case where the assist system  200  is worn on an old user, the user is likely to wear the assist system  200  after the user sits in a chair. Therefore, in this case, when the looseness or the wearing position shift of the knee belt unit  120  is judged immediately after assist system  200  is worn, it is necessary to make the judgement in a state in which the user sits in a chair. 
       FIG. 24  is a diagram illustrating a manner in which the wearing state of the knee belt unit is judged for a user in a sitting position. 
     In the case of the standing position, the direction of the wire  130  is substantially the same as the gravitational direction, and thus if the wire  130  is pulled when the knee belt unit  120  is in a loose state, the knee belt unit  120  lifts upward once and then moves downward by the gravitational force. In this case, rotational movements about the Y-axis direction and the Z-axis direction may also occur. From values associated with these movements, the judgment unit  102  judges whether the knee belt unit  120  is in a loose state or whether the knee belt unit  120  is in a shifted state. 
     However, in the case of the sitting position, as shown in  FIG. 24 , the direction of pulling the wire  130  is different from the gravitational direction, and thus when the knee belt unit  120  is pulled by the wire  130 , the knee belt unit  120  is unlikely to move back to its original position where it is located before it is pulled. 
     In  FIG. 24 , the X-axis direction is defined in a forward-backward direction of a user, the Y-axis direction is defined in a right-left direction of the user, and the Z-axis direction is defined in an upward-downward direction of the user. In the sitting position, as shown in  FIG. 24 , lower parts of legs (thighs) of the user are in contact with a chair. Therefore, when the wires  130  located on the lower parts of the user are pulled, frictional force causes the knee belt units  120  to hardly move regardless of whether the knee belt unit  120  is in a loose state. On the other hand, the wire  130  disposed on the front side of each leg of the user is not in contact with the chair. Therefore, when the wire  130  on this side is pulled, the knee belt unit  120  can move if the knee belt unit  120  is in a loose state. However, because the gravitational direction is different from the longitudinal direction of the wire  130 , the knee belt unit  120  does not easily move back to its original position. Furthermore, in the sitting position, as shown in  FIG. 24 , when the wire  130  is pulled, the knee belt unit  120  is not pulled in a direction along the thigh but diagonally pulled in a direction toward the upper-body belt unit  110 . 
     Therefore, in the case of the sitting position, the judgment unit  102  may integrate the acceleration in the X-axis direction and the angular velocity about the Y-axis direction provided from the movement measurement unit  121  and may calculate the displacement in the X-axis direction and the displacement about the Y-axis direction. If these values are greater than or equal to respective threshold values, and more specifically, for example, if the displacement in the X-axis direction is greater than or equal to a threshold value set to 2 cm to 10 cm or the displacement about the Y-axis direction is greater than or equal to a threshold value set to 0.05 to 0.5 rad, then the judgment unit  102  may determine that there is a looseness. 
     The determination as to whether a user is in the sitting position or the standing position may be performed based on a value output from the acceleration sensor disposed in the movement measurement unit  121 . More specifically, for example, when a gravitational component is greater than or equal to 70% of the total value in the X-axis direction measured by the acceleration sensor, it may be determined that the user is in the standing position. On the other hand, if the gravitational component is greater than or equal to 70% of the total value in the Z-axis direction, it may be determined that the user is in the sitting position. 
     1.4.3 Third Modification 
     In the embodiments described above, the presentation unit  140  determines whether the knee belt unit  120  has a looseness or a wearing position shift, and presents information to a user by vibrating the knee belt unit  120  or by other methods to inform of the fact that the knee belt unit  120  has the looseness or the shift. However, what is presented is not limited to the example described above. For example, the presentation unit  140  may automatically fasten the knee belt unit  120  depending on the looseness so as to eliminate the looseness, or may rotate the knee belt unit  120  such that the wearing position shift is adjusted to its correct position. In this case, the presentation unit  140  may adjust the fastening degree of the knee belt unit  120  depending on the looseness degree measured by the movement measurement unit  121 . That is, the assist system  200  may fasten the knee belt unit  120  such that the knee belt unit  120  is not shifted and such that a user does not feel a pain due to too strong fastening. 
     1.4.4 Fourth Modification 
     In the embodiments described above, it is assumed by way of example that the determination as to whether the calibration is started is performed by the movement measurement unit  121 . However, the unit that performs the determination is not limited to the movement measurement unit  121 . For example, the judgment unit  102  of the controller  100  may perform the determination. In this case, the judgment unit  102  may receive in real time the acceleration and the angular velocity of each knee belt unit  120  from the movement measurement unit  121 , and may perform the determination based on the received acceleration and angular velocity as to whether the calibration is to be started. More specifically, for example, the judgment unit  102  may further determine whether the acceleration measured by the acceleration sensor  122  disposed on the knee belt unit  120  is smaller than or equal to the second threshold value. In a case where the acceleration measured by the acceleration sensor  122  is smaller than or equal to the second threshold value and the angular velocity measured by the gyrosensor  123  is greater than or equal to the first threshold value, the judgment unit  102  may output information indicating that the knee belt unit  120  is in a loose state or the knee belt unit  120  is in a shifted state. 
     This makes it possible for the judgment unit  102  to output information such that when a user is in a no-movement state, the information is output to notify the user that the knee belt unit  120  is in a loose state or the knee belt unit  120  is in a shifted state, which makes it possible to more effectively present to the user the information indicating the state. That is, when the user is in a no-movement state, the vibration actuator functioning as the presentation unit  140  may be vibrated to notify the user that the knee belt unit  120  is in a loose state or the knee belt unit  120  is in a shifted state more effectively than in the case where the notification is given when the user is in a moving state. 
     In a case where the acceleration measured by the acceleration sensor  122  is smaller than or equal to the second threshold value, the judgment unit  102  may output, to the drive controller  111 , information indicating that the acceleration measured by the acceleration sensor  122  is smaller than or equal to the second threshold value. 
     1.4.5 Fifth Modification 
     In the embodiments described above, it is assumed by way of example that the upper-body belt unit  110  and the knee belt units  120  are formed separately. However, the manner of implementing the upper-body belt unit  110  and the knee belt units  120  is not limited to this example. For example, the upper-body belt unit  110  and the knee belt units  120  may be connected together into the form of pants (shorts). 
     1.5 Other Embodiments 
     In each embodiment described above, each constituent element may be realized using dedicated hardware or may be realized by executing software program corresponding to the constituent element. Each constituent element may be realized by a program execution unit such as a CPU, a process or the like by reading software program stored in a storage medium such a hard disk, a semiconductor memory, or the like and executing the software program. The software that realizes the assist method according to one or more embodiments may be a program described below. 
     That is, the program causes a computer to execute an assist method in an assist system including a first belt worn on an upper body of a user, a second belt worn on a knee of the user, a wire via which the first belt and the second belt are connected, and a motor coupled with the wire, the method including (a) applying a first tension to the wire by using the motor, (b) measuring, using a gyrosensor, an angular velocity in a direction perpendicular to a longitudinal direction of the wire when the first tension is applied, (c) in a case angular velocity is greater than or equal to a first threshold value, outputting information indicating that the second belt is in a loose state or the second belt is in a shifted state. 
     In the present disclosure, all or part of units, devices, and all or part of functional blocks illustrated in  FIG. 2  or  FIG. 23  may be implemented by one or more electronic circuits including a semiconductor device, a semiconductor integrated circuit (IC), an LSI (Large Scale Integration). The LSI or the IC may be integrated on a single chip or may be realized by a combination of a plurality of chips. For example, functional blocks other than storage elements may be integrated on a signal chip. The integrated circuits called the LSI or the IC herein may be called differently depending on the integration density, and integrated circuits called a system LSI, a VLSI (Very Large Scale Integration), or a ULSI (Ultra Large Scale Integration) may also be used in the present disclosure. Furthermore, a field programmable gate array (FPGA) capable of being programmed after the LSI is produced, and a reconfigurable logic device capable of being reconfigured in terms of internal connections or capable of being set up in terms of internal circuits blocks may also be used for the same purpose. 
     Part or all of functions or operations of units, apparatuses, part of an apparatus may be realized by software. In this case, the software may be stored in a non-transitory storage medium. The non-transitory storage medium may be one of or a combination of a ROM, an optical disk, a hard disk drive, or the like. A particular function is realized by executing the software by the processor in cooperation with a peripheral device. The system or the apparatus may include one or more non-transitory storage media in which software is stored, a processor, and a hardware device such as an interface. 
     The present disclosure has been described above with reference to, by way of example, the assist system and the assist method according to embodiments. However, the present disclosure is not limited to the embodiments described above. It will be apparent to those skilled in the art that many various modifications may be applicable to the embodiments without departing from the spirit and scope of the present disclosure. Furthermore, constituent elements of different embodiments may be combined. In this case, any resultant combination also falls within the scope of the present disclosure. 
     The technique according to the present disclosure is useful in an assist system that assists, using a wire, a movement of a person and more particularly in an assist system capable of effectively detecting a looseness or the like of a belt in the assist system.