Patent Publication Number: US-10786417-B2

Title: Motion assist device

Description:
TECHNICAL FIELD 
     The present invention relates to a motion assist device for assisting a motion of a user such as a walking motion of a user. 
     BACKGROUND ART 
     Various motion assist devices in the form of walking assist devices have been proposed for clinical and other purposes. In a typical walking assist device, the movement of the legs of the user is detected, and a power unit for providing a walking assist force is controlled according to the detected movement of the legs. See JP2000-166997A, for instance. 
     The walking assist device disclosed in this patent document comprises an abdominal support unit configured to be worn on the abdomen of the user, a pair of femoral support units configured to be worn on the respective femoral parts of the user, a pair of electric motors supported on the abdominal support unit, a pair of power transmission mechanisms for transmitting the power of the electric motors to the respective femoral support units and a control unit for controlling the motions of the electric motors. In this device, the angles of the femoral parts with respect to the abdomen of the user are detected by angle detectors, and the control unit controls the electric motors according to the detected angles of the femoral parts. Typically, the motors are operated so as to assist the movements of the femoral parts. When the femoral parts are simultaneous swung forward, as it may indicate that the user desires to be seated on a chair, the assistance of the electric motors are interrupted so that the user may be allowed to be comfortably seated without being hampered by any assist force. 
     JP5021574B discloses a walking assist device comprising a pelvic support unit configured to be worn on the pelvic part of the user, a pair of power units attached to the pelvic support member and each having a rotational center line coinciding with the corresponding hip joint of the user and a pair of femoral support units attached to the output shafts of the respective power units. According to this prior art, because the power units and the femoral support units are directly connected to each other, the overall power transmission structure can be simplified. 
     According to the known walking assist devices, when a torque or a force is applied to the femoral part of the user, the reaction force is transmitted from the power unit to the pelvic part or the abdominal part of the user via the corresponding support unit. This may cause some discomfort to the user. Furthermore, because of the need to withstand the reaction force, the pelvic or abdominal support unit is required to have a high torsional stiffness, and this causes an increase in weight. When the user desires to sit or crouch, the motor which is not actuated applies a resistance in the form of a cogging torque of the electric motor to the femoral support unit, and thereby hampers the movement of the user. In particular, when a gear reduction unit and/or any mechanism that prevents external torque to be transmitted to the electric motor are provided in association with the electric motor, the user may be entirely prevented from sitting or crouching. 
     In the walking assist device proposed in JP5021574B, because the power units are on either side of the pelvic part of the user, the electric motors are required to have a low profile in order not to obstruct the movement of the arms of the user, and this causes an increase in cost. Even when low profile motors are used, the motors may still obstruct the swinging movement of the arms. Also, because the electric motors are integrally incorporated in the mechanism for transmitting the output power of the electric motors to the corresponding femoral support units, when the specifications of the electric motors are changed, the entire power units have to be redesigned. 
     SUMMARY OF THE INVENTION 
     In view of such problems of the prior art, a primary object of the present invention is to provide a motion assist device which can assist the opposite phase movement of the body parts of the user such as the lower limbs and upper limbs of the user as well as the same phase movement of the body parts of the user. 
     A second object of the present invention is to provide a motion assist device which can minimize the transmission of the reaction force of the power unit to the user. 
     A third object of the present invention is to provide a motion assist device which may be based a modular design so that various component parts of the power unit may be changed without requiring corresponding changes to be made to other parts of the power unit. 
     To achieve such objects, the present invention provides a motion assist device for assisting a motion of a user, comprising: a pair of body part support units ( 3 L,  3 R) configured to be worn by two body parts of a user; a single power source ( 4 ,  70 ) for producing power; and a power transmission unit ( 20 ;  60 ;  91 ,  92 ) for transmitting the power of the power source to the body part support units as an opposite phase motion; wherein the power transmission unit includes a differential unit ( 22 ;  63 ,  64 ;  93 ,  94 ) for accommodating a same phase motion of the two body part support units. 
     Owing to the provision of the differential unit, the two body parts such as femoral parts are allowed to undergo a same phase motion while the single power source can assist the opposite phase motion of the two body parts. Also, the reaction force caused by one of the body support units is transmitted to the other body part support unit so that any other part of the user&#39;s person is prevented from experiencing any discomfort. 
     According to a preferred embodiment of the present invention, the body parts are femoral parts of the user. 
     According to a certain aspect of the present invention, the differential unit includes a differential gear mechanism, and the power transmission mechanism includes a counter gear ( 38 ) provided between an output end of the differential gear mechanism and the corresponding body part support unit. 
     Thereby, the power transmission unit and the different unit can be constructed as highly simple units. 
     According to another aspect of the present invention, the power source comprises an electric motor including an outer member ( 18 ) rotatably supported by a fixed frame and an inner member ( 19 ) rotatably supported by the outer member, and wherein the differential unit comprises a bearing ( 53 ) for rotatably supporting the outer member on the fixed frame, and the power transmission unit includes a first power transmission unit ( 20 L) for connecting the outer member with one of the body part support units and a second power transmission unit ( 20 R) for connecting the inner member with the other body part support unit. 
     This arrangement also allows the power transmission unit and the different unit to be constructed as highly simple units. 
     According to yet another aspect of the present invention, the power source includes an output shaft ( 19   a ), and the power transmission unit comprises a primary rack and pinion mechanism ( 61 ) and a pair of secondary rack and pinion mechanisms ( 62 A,  62 B), the primary rack and pinion mechanism including a primary pinion ( 61 ) attached to the output shaft and a pair of primary racks ( 62 A,  62 B) slidably supported by a fixed frame and meshing with the primary pinion so as to convert a rotational movement of the primary pinion into linear movements of the primary racks directed in mutually opposite directions, each secondary rack and pinion mechanism including a secondary pinion ( 65 ,  66 ) rotatably supported by the corresponding primary rack and a pair of secondary racks ( 67 A,  67 B,  68 A,  68 B) slidably supported by the corresponding primary rack and meshing with the secondary pinion so as to convert a rotational movement of the secondary pinion into linear movements of the secondary racks directed in mutually opposite directions, the power transmission unit including a pair of pulleys ( 35 L,  35 R) attached to the body part support units, respectively, and a pair of belts ( 69 L,  69 R) passed around the respective pulleys, two ends of each belt being connected to one of the secondary racks of one of the secondary rack and pinion mechanisms, and to one of the secondary racks of the other secondary rack and pinion mechanism. 
     According to yet another aspect of the present invention, the power source comprises a double acting displacement pump ( 70 ) including a first pump chamber ( 76   a ) and a second pump chamber ( 77   a ), and the power transmission unit includes a pair of fluid actuators ( 71 L,  71 R) provided in association with two body parts of the user, each fluid actuator including a first fluid chamber ( 82   a  L,  82   a R) and a second fluid chamber ( 83   a L,  83   a R), and a passage system ( 91 - 94 ) communicating the first pump chamber with the first fluid chamber of one of the actuators and the second fluid chamber of the other actuator, and the second pump chamber with the second fluid chamber of the one actuator and the first fluid chamber of the other actuator. 
     The present invention also provides a motion assist device for assisting a motion of a user, comprising: a pair of body part support units ( 3 L,  3 R) configured to be worn by two body parts of a user; a single power source ( 4 ,  70 ) for producing power at an output end thereof; and a power transmission unit ( 20 ;  60 ;  91 ,  92 ) for transmitting the power of the power source to the body part support units as an opposite phase motion, the power transmission unit including a differential unit ( 22 ;  63 ,  64 ;  93 ,  94 ) for accommodating a same phase motion of the two body part support units; and a control unit ( 5 ) configured to actuate the power source when the body part support units are undergoing the opposite phase motion, and to keep the output end of the power source stationary when the body part support units are undergoing the same phase motion. 
     According to this arrangement, owing to the provision of the differential unit, no power is drawn from or supplied to the power unit when the two body part support members are undergoing a same phase motion so that the two body parts can be moved without being hampered by the power unit. Meanwhile, when the two body part support members are undergoing an opposite phase motion, the power from the power source can be transmitted to the two body part support members to assist the motion of the body parts such as femoral parts of the user. Also, the reaction force caused by one of the body support units is transmitted to the other body part support unit so that any other part of the user&#39;s person is prevented from experiencing any discomfort. 
     According to the present invention, an opposite phase motion of the two body parts of the user can be assisted by the power from the power source while a same phase motion of the two body parts of the user is enabled without being hindered by the power source, and the two body part support members can be actuated by using only one power source. Furthermore, the reaction force caused by one of the body support units is transmitted to the other body part support unit so that any other part of the user&#39;s person is prevented from experiencing any discomfort. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a walking assist device given as a first embodiment of the present invention as being worn by a user indicated by imaginary lines; 
         FIG. 2  is a rear perspective see-through view showing an essential part of the walking assist device; 
         FIG. 3  is a rear view of the internal structure of the walking assist device; 
         FIG. 4  is a block diagram of a control unit for controlling the electric motor of the walking assist device; 
         FIG. 5  is a diagram defining the various angles used for describing the action of the walking assist device; 
         FIG. 6  is a diagram of a walking assist device given as a second embodiment of the present invention; 
         FIG. 7  is a diagram of a walking assist device given as a third embodiment of the present invention; 
         FIG. 8 a    is a left side view of a walking assist device given as a fourth embodiment of the present invention; 
         FIG. 8 b    is a rear view of the fourth embodiment of the present invention; 
         FIG. 8 c    is a right side view of the fourth embodiment of the present invention; 
         FIGS. 9 a  and 9 b    are diagrams showing the mode of operation of the hydraulic pump used in the fourth embodiment; 
         FIGS. 10 a  and 10 b    are diagrams showing the mode of operation of the hydraulic actuators used in the fourth embodiment; and 
         FIG. 11  is an overall diagram showing the mode of operation of the walking assist device of the fourth embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Preferred embodiments of the present invention are described in the following with reference to the appended drawings. 
     First Embodiment 
     A walking assist device  1  given as a first embodiment of the present invention is described in the following with reference to  FIGS. 1 to 5 . The walking assist device  1  is generally symmetric about the sagittal plane of the user P, and some of the components are provided on either side of the user. Such parts are denoted with numerals followed by a suffix L or R to indicate on which side (either left or right side) of the user the particular component is located. However, when such components are collectively referred to, the suffices may be omitted for the convenience of description. 
     As shown in  FIGS. 1 and 2 , the walking assist device  1  comprises a pelvic support unit  2  worn on a pelvic part of a user P, a pair of femoral support units  3 L and  3 R worn on femoral parts of the user P, respectively, a single electric motor  4  positioned in the pelvic support unit  2  to provide the power required to cause a reciprocating angular movement to each femoral support unit  3 , a control unit  5  for controlling the motion of the electric motor  4 , an angular position sensor  6  incorporated in the electric motor  4  for detecting the angular position of the electric motor  4  and a battery  7  for providing electric power to the electric motor  4  and the control unit  5 . 
     The pelvic support unit  2  is provided with a pelvic support assembly  11  positioned on the backside of the pelvic part of the user P and a pair of side frames  12 L and  12 R connected to either lateral end of the pelvic support assembly  11 . The pelvic support assembly  11  includes a pelvic frame  13  ( FIG. 2 ) made of hard plastic or any other stiff material, and the front side of the pelvic frame  13  is lined with a pad or a cover member. A pelvic belt  14  is connected to either lateral end of the pelvic frame  13  via a buckle or other device so that the user may pass the pelvic belt  14  in front of the user in a detachable manner while holding the pelvic support assembly  11  on the back side of the pelvic part of the user to keep the pelvic support assembly  11  fixed in position during operation. 
     Each side frame  12  may consist of a hollow arm member made of hard plastic formed integrally with the pelvic frame  13 , and extending from the corresponding lateral end of the pelvic frame  13  (obliquely in the forward and downward direction) to the part adjoining the hip joint of the user P. In another embodiment, each side frame  12  is provided separately from the pelvic frame  13 , and is detachably attached thereto by using a suitable fastener. Alternatively, each side frame  12  may be connected to the pad or the cover member of the pelvic support assembly  11 . 
     Each femoral support unit  3  is provided with a femoral arm member  16  having a base end supported by the free (lower) end of the corresponding side frame  12  in a rotatable manner about a laterally extending axial line and a retainer  17  attached to the free (lower) end of the femoral arm member  16  for retaining the corresponding femoral part of the user. The femoral arm member  16  is made of hard plastic, and extends substantially downward along the side of the femoral part of the user, and is configured to swing about the base end thereof in the fore and aft direction. The retainer  17  may be made of a combination of different materials so that the necessary mechanical strength and stiffness may be attained while providing a maximum comfort to the user. In the illustrated embodiment, the retainer  17  consists of a fabric belt, and is configured to be detachably wrapped around the corresponding femoral part of the user. Alternatively, the retainer  17  may include a pair of plate members that are applied to the front and rear sides of the femoral part of the user so favorably distribute the pressure the retainer  17  applies to the femoral part of the user. 
     As shown in  FIGS. 2 and 3 , the electric motor  4  includes an outer member  18  (outer stator, see  FIG. 3 ) fixed to the pelvic frame  13  and an inner member  19  (inner rotor, see  FIG. 3 ) rotatably received in the outer member  18  and provided with an output shaft  19   a  extending laterally out of the outer member  18 . The electric motor  4  is mounted on the laterally central part of the pelvic frame  13 . The electric motor  4  receives a supply of electric power from the battery  7  via the control unit  5 . Thus, the electric motor  4  rotates the inner member  19  and the output shaft  19   a  in the directions indicated by arrows A and B in  FIG. 3  under the control of the control unit  5 , and provides the required assist toque to the femoral parts of the user. 
     A power transmission mechanism  20  is provided on the pelvic frame  13  and the side frames  12  so as to transmit the power of the electric motor  4  to the femoral parts of the user P via the femoral support units  3 . 
     As shown in  FIGS. 2 and 3 , a pair of first drive shafts  25 L and  25 R are rotatably supported by the pelvic frame  13  in a mutually aligned relationship. A differential gear mechanism  22  is connected between the opposing ends of the first drive shafts  25 L and  25 R. The differential gear mechanism  22  includes a ring gear  23  serving as an input gear and three pinions  24  each consisting of a small bevel gear and supported by the ring gear  23  at a regular angular interval (at a 120 degree interval) so as to be rotatable around a radial line of the ring gear  23 , a pair of side gears  26 L and  27 R disposed coaxially with the ring gear  23  and meshing with the pinions  24  from either lateral side. The opposing ends of the first drive shafts  25 L and  25 R are connected to the corresponding side gears  26 L and  27 R, respectively. 
     A pinion  21  fitted on the output shaft  19   a  of the inner member  19  of the electric motor  4  meshes with an external gear formed on the outer circumference of the ring gear  23  of the differential gear mechanism  22 . The left end of the left first drive shaft  25 L is fitted with a small spur gear  27 L, and the right end of the right first drive shaft  25 R is fitted with a small spur gear  27 R. 
     The differential gear mechanism  22  distributes the output torque of the electric motor  4  to the two first drive shafts  25  evenly while accommodating the difference in the rotational speed between the two first drive shafts  25 . For the convenience of description, the power transmission mechanism  20  is divided into a left power transmission mechanism  20 L for transmitting power from the left first drive shaft  25 L to the left femoral support unit  3 L, and a right power transmission mechanism  20 R for transmitting power from the right first drive shaft  25 R to the right femoral support unit  3 R. 
     The left power transmission mechanism  20 L is described in the following. The left small spur gear  27 L meshes with a left large spur gear  29 L fitted on a left second drive shaft  28 L rotatably supported by the pelvic frame  13  in parallel with the left first drive shafts  25 L. 
     The left second drive shaft  28 L is connected, via a shaft coupling assembly consisting of a pair of Hook joints  31  and a left third drive shaft  32 L, to a left fourth drive shaft  33 L which is rotatably supported by the base end of the left side frame  12 L. The outer end of the left fourth drive shaft  33 L is fitted with a large pulley  34 L, and the upper end of the left femoral arm member  16 L is fitted with a small pulley  35 L. A belt  36 L is passed around the two pulleys  34 L and  35 L so that the rotation of the left fourth drive shaft  33 L is converted into the angular movement of the femoral arm member  16 L. 
     The right power transmission mechanism  20 R is described in the following. The right small spur gear  27 R meshes with a counter gear  38  rotatably supported by the pelvic frame  13 , and the counter gear  38  further meshes with a right large spur gear  29 R fitted on a right second drive shaft  28  rotatably supported by the pelvic frame  13 . The right second drive shaft  28  is connected, via a shaft coupling assembly consisting of a pair of Hook joints  31  and a right third drive shaft  32 R, to a right fourth drive shaft  33 R which is rotatably supported by the base end of the right side frame  12 R. The outer end of the right fourth drive shaft  33 R is fitted with a large pulley  34 R, and the upper end of the right femoral arm member  16 R is fitted with a small pulley  35 R. A belt  36 R is passed around the two pulleys  34 R and  35 R so that the rotation of the right fourth drive shaft  33 R is converted into the angular movement of the femoral arm member  16 R. 
     Owing to the presence of the counter gear  38 , the rotational motion of the electric motor  4  is distributed to the fourth drive shafts  33 L and  33 R as motions of opposite phases. When there is no difference between the loads of left and right femoral support units  3 L and  3 R, these two femoral arm members  16 L and  16 R move in opposite phases without causing any differential motion in the differential gear mechanism  22 . 
     More specifically, as shown in  FIG. 3 , when the output shaft  19   a  of the electric motor  4  turns in the direction indicated by arrow A, the left fourth drive shaft  33 L rotates in the same direction as indicated by arrow A. On the other hand, the right fourth drive shaft  33 R rotates in the opposite direction as indicated by arrow A owing to the inclusion of the counter gear  38 . The rotational motions of the fourth drive shafts  33 L and  33 R are converted into the pivotal movements of the femoral arm members  16 L and  16 R, respectively, of the corresponding directions owing to the transmission of power by the belts  36 L and  36 R, respectively. 
     At the same time, owing to the presence of the differential gear mechanism  22 , the left and right femoral support units  3 L and  3 R are enabled to move forward or rearward simultaneously without involving the rotation of the electric motor  4 , or in other words, can move in an same phase relationship. Furthermore, if the femoral arm members  16 L and  16 R are subjected to external loads or encounter obstructions, owing to the presence of the differential gear mechanism  22 , the femoral arm members  16 L and  16 R are given with freedom to move in any phase relationship including the same phase relationship and the opposite phase relationship. For instance, when the electric motor  4  is not powered, the user P may squat or sit down, and stand up without encountering any undue resistance. 
     For instance, when the two femoral support unit  3 L and  3 R are both swung forward (to allow the user P to squat) (a same phase motion), the left third drive shaft  32 L rotates in the direction indicated by arrow A while the right third drive shaft  32 R rotates in the direction indicated by arrow B so that the first drive shafts  25 L and  25 R are caused to rotate in the opposite directions at the same speed. The planetary pinions  24  then accommodate the mutually opposite rotations of the bevel side gears  26 L and  26 R so that the ring gear  23  remains stationary. 
     Therefore, the user is enabled to bend the lower limbs in the same direction (for sitting, for instance) or extend the lower limbs in the same direction (for standing up, for instance) without causing the rotation of the electric motor  4  (against the cogging torque of the electric motor  4 ) and without encountering any significant resistance. 
     Referring to  FIGS. 1 and 2  once again, the angular position sensor  6  is incorporated in the electric motor  4  in the illustrated embodiment, and may consist of a rotary encoder that detects the absolute angular position of the inner member  19  relative to the outer member  18  which is fixed to the pelvic frame  13 . The output signal of the angular position sensor  6  is supplied to the control unit  5 . 
     The control unit  5  which is accommodated in the pelvic support unit  2  essential consists of an electronic circuit unit including CPU, RAM, ROM and a peripheral circuit, and executes the control process for controlling the operation of the electric motor  4  or the assist force τ that is to be applied to the user P. The CPU of the control unit  5  is programmed to execute required computational processes by reading out commands and necessary data from a storage unit (memory) not shown in the drawings. 
     The battery  7  is accommodated in the pelvic support unit  2 , and supplies electric power to the control unit  5  and the electric motor  4 . The control unit  5  and/the battery  7  may also be accommodated in the femoral support units  3 , or may be provided separately from the walking assist device  1  and connected to the electric motor  4  via wiring. 
     When powered up, the control unit  5  controls the electric power supplied from the battery  7  to the electric motor  4  such that the necessary assist force (assist torque) ti as determined by the control unit  5  from the detection signal of the angular position sensor  6  is applied to the femoral parts of the user P via the femoral support units  3 . 
     The structure of the control unit  5  is described in the following. As shown in  FIG. 4 , the control unit  5  includes a differential angle computation unit  41  for computing the differential angle θ between the two femoral support units  3  or the two femoral parts of the user P and an assist force computation unit  42  for computing the assist force τ that is required to be applied to the femoral parts of the user by executing a computational process (which is discussed hereinafter) based on the differential angle θ computed by the differential angle computation unit  41 . 
     The differential angle θ is defined as the difference between the femoral part angles θL and θR of the two femoral parts of the user P which are in turn defined as the angles between the respective center lines of the femoral parts of the user P and the vertical line as projected on the sagittal plane. The femoral part angles θL and θR are positive in sign when the corresponding femoral part is swung forward (is bent), and negative in sign when the corresponding femoral part is swung rearward (is extended). Therefore, the differential angle θ obtained by subtracting one of the femoral part angles θR (right femoral part angle, for instance) from the other femoral part angle θL is positive in sign when the left leg is ahead of the right leg, and negative in sign when the right left is ahead of the left leg. 
     The differential angle θ may be directly detected by measuring the rotational angle of the inner member  19  relative to the outer member  18 . For this purpose, the detection value of the angular position sensor  6  when the differential angle θ is zero is set and stored as the zero point in the control unit  5  so that the differential angle computation unit  41  computes the differential angle θ by subtracting the zero point value from the angular position of the electric motor  4  detected by the angular position sensor  6  and multiplying a prescribed conversion factor (determined by the gear ratio) to the difference. The differential angle computation unit  41  execute this computation process at a prescribed process cycle. 
     When the user has moved the left leg ahead of the right leg from the state where the differential angle θ is zero, the rotational angle of the electric motor  4  increases from the zero point, and the differential angle computation unit  41  computes the differential angle θ as a positive value. Conversely, when user has moved the right leg ahead of the left leg from the state where the differential angle θ is zero, the rotational angle of the electric motor  4  decreases from the zero point, and the differential angle computation unit  41  computes the differential angle θ as a negative value. When the user has moved the both legs either forward or rearward at the same speed from the state where the differential angle θ is zero, the rotational angle of the electric motor  4  remains at the zero point, and the differential angle θ computed by the differential angle computation unit  41  is zero. 
     The assist force computation unit  42  computes the differential angular speed ω from the differential angle θ computed by the differential angle computation unit  41 , and by executing an inverse tangent computation, computes a differential phase angle ϕ in a phase plane of the differential angle θ and the differential angular speed ω. The assist force τ for each femoral part is computed from the obtained differential phase angle ϕ. Alternatively, the assist force computation unit  42  computes the differential angular speed ω and the walking frequency from the differential angle θ, and computes the differential phase angle ϕ in the phase plane of the differential angle θ and the differential angular speed ω. At the same time, an oscillator phase angle ϕc of a phase oscillator which oscillates in synchronism with the differential phase angle ϕ at a resonant frequency corresponding to the walking frequency is computed, and the assist force τ for each femoral part is computed from the obtained differential phase angle ϕ and the oscillator phase angle ϕc. 
     By computing the assist force τ with the assist force computation unit  42  in this manner, when the femoral parts of the user wearing the respective femoral support units  3  are undergoing an opposite phase motion, because this causes changes in the differential angle θ, the assist force τ which is either positive (bending motion) or negative (extending motion) in sign is computed, and the electric motor  4  produces the corresponding power. Conversely, when the femoral parts of the user wearing the respective femoral support units  3  are undergoing a same phase motion, because this causes no change in the differential angle θ, the assist force τ is zero, and the electric motor  4  does not produce any power. 
     As discussed earlier with reference to  FIG. 3 , the output torque of the electric motor  4  is equally distributed between the right and left femoral support units  3 L and  3 R via the differential gear mechanism  22 , and is transmitted to the right and left femoral support units  3 L and  3 R in an opposite phase relationship owing to the intervention of the counter gear  38 . Also, owing to the differential gear mechanism  22 , the rotational speed of the electric motor  4  is distributed between the right and left femoral support units  3 L and  3 R in a manner corresponding to the respective loading on the right and left femoral support units  3 L and  3 R. 
     This walking assist device  1  thus includes the single electric motor  4  serving as a power source and a power transmission mechanism  20  for transmitting the power of the electric motor  4  to the femoral support units  3  as an opposite phase motion, and the powered transmission mechanism includes the differential gear mechanism  22  for distributing the power of the electric motor  4  between the two femoral support units  3 , so that the two legs of the user P are enabled to move in an opposite phase relationship with ease, and the opposite phase assist to the two legs of the user P can be achieved by using the single electric motor  4 . The reaction force produced by one of the femoral support unit  3  in providing the assist force to the corresponding femoral part of the user is transmitted to the other femoral support unit  3  so that the reaction force is not transmitted to any part of the user except for the femoral parts of the user P. Therefore, the user is prevented from experiencing any discomfort owing to the application of the reaction force to any other part of the user&#39;s body. Also, the stiffness of the pelvic support unit  2  is not required to be unduly stiff. Furthermore, owing to the favorable arrangement of the power transmission mechanism  20 , the specifications of the electric motor  4  may be changed without causing any significant design change to any other part of the walking assist device  1 . 
     According to the power transmission mechanism  20  of the illustrated embodiment, the power of the electric motor  4  can be transmitted to the two femoral support units  3  in opposite phase by using a simple structure combining the differential gear mechanism  22  and the counter gear  38  provided between the right first drive shaft  25 R connected to one of the output ends of the differential gear mechanism  22  and the right femoral support unit  3 R. 
     Second Embodiment 
     The walking assist device  1  given as a second embodiment of the present invention is described in the following with reference to  FIG. 6 . In  FIG. 6 , the parts corresponding to those of the preceding embodiment are denoted with like numerals without necessarily repeating the discussion of such parts in the following description. 
     The power transmission mechanism  20  of the second embodiment is modified from that of the first embodiment in the structure of the power transmission mechanism  20 . In particular, a reduction gear mechanism is connected to the output shaft  10   a  of the electric motor  4 , and the electric motor  4  is incorporated in the power transmission mechanism  20 . The electric motor  4  and the reduction gear mechanism  51  jointly form an integral electric motor unit  52 . 
     The field system of the electric motor  4  may consist of either electromagnets or permanent magnets. In the case of an electromagnetic field system, either the outer member  18  or the inner member  19  may serve as the armature. When supplied with electric power, the electric motor  4  produces a torque that tends to rotate the outer member  18  and the inner member  19  relative to each other. The reduction gear mechanism  51  is not essential for the present invention, and may be omitted or may consist of any per se known speed reduction unit. 
     The electric motor unit  52  (or the outer member  18  thereof and the housing of the reduction gear mechanism  51 ) is rotatably supported by the pelvic frame  13  via a pair of bearings  53 , in a coaxial relationship to the output shaft  19   a  of the electric motor  4 . 
     A first output shaft  52   a  of the reduction gear mechanism  51  or the electric motor unit  52  extends rearward from the left end of the electric motor unit  52  to transmit the rotation of the inner member  19  of the electric motor  4 . A second output shaft  52   b  which is fixed to (or integrally formed with) the right end of the outer member  18  of the electric motor  4  extends rightward in a coaxial relationship to the first output shaft  52   a  to transmit the rotation of the outer member  18  of the electric motor  4 . 
     For the convenience of description, the power transmission mechanism  20  is divided into a left power transmission mechanism  20 L for transmitting power from the first output shaft  52   a  (on the left) to the left femoral support unit  3 L and a right power transmission mechanism  20 R for transmitting power from the second output shaft  52   b  (on the right) to the right femoral support unit  3 R. 
     In the left power transmission mechanism  20 L, the first output shaft  52   a  is rotatably supported by the pelvic frame  13  and/or the left side frame  12 L via a bearing  54 , and a left pulley  34 L is integrally attached to the left end of the first output shaft  52   a . A belt  36 L is passed around the left pulley  34 L and the left small pulley  35 L which is fixedly attached to the left femoral arm member  16 L and rotatably supported by the left side frame  12 L so that the torque of the electric motor  4  can be transmitted to the left small pulley  35 L. 
     In the right power transmission mechanism  20 R, the second output shaft  52   b  is rotatably supported by the pelvic frame  13  and/or the right side frame  12 R via a bearing  54 , and a right pulley  34 R is integrally attached to the right end of the second output shaft  52   b . A belt  36 R is passed around the right pulley  34 R and the right small pulley  35 R which is fixedly attached to the right femoral arm member  16 R and rotatably supported by the right side frame  12 R so that the torque of the electric motor  4  can be transmitted to the right small pulley  35 R. 
     The mode of operation of the power transmission mechanism  20  is described in the following. For the convenience of description, the reduction gear mechanism  51  is omitted from the following discussion. 
     When the electric motor  4  is powered, the outer member  18  and the inner member  19  are subjected to a torque which is equal in magnitude and opposite in direction. Therefore, owing to the presence of the bearings  53  that rotatably support the outer member  18  of the electric motor  4 , the electric motor  4  is provided with the function to distribute the output torque thereof between the two femoral support units  3 , and the function to transmit the torque to the two femoral support units  3  in a mutually opposite phase relationship. Owing to the presence of the bearings  53 , the power transmitted to the first output shaft  52   a  and the second output shaft  52   b  are transmitted to the two femoral support units  3  via the left power transmission mechanism  20 L and the right power transmission mechanism  20 R, respectively. 
     Furthermore, owing to the presence of the bearings  53 , the two femoral support units  3  can be moved jointly in the forward or rearward direction without rotating the electric motor  4  (or causing no relative rotation between the outer member  18  and the inner member  19 ). In other words, the two femoral parts  3  are enabled to move in a same phase relationship without being hampered. 
     More specifically, when the two femoral parts  3  are both moved forward, the outer member  18  and the inner member  19  rotate in the same direction and at the same speed relative to each other. Likewise, when the two femoral parts  3  are both moved rearward, the outer member  18  and the inner member  19  rotate in the same direction and at the same speed relative to each other. 
     Therefore, without rotating the electric motor  4  or without being hampered by the cogging torque of the electric motor  4 , the user of the walking assist device  1  is enabled to bend the both femoral parts (for sitting, for example) and to extend the both femoral parts (for standing up, for example) at the same time. 
     Thus, because the functions of the power transmission mechanism including the function of the differential unit are provided by the bearings  53  for rotatably supporting the outer member  18  of the electric motor  4  on the pelvic frame  13 , the right power transmission mechanism  20 R connecting the outer member  18  with the right femoral support unit  3 R and the left power transmission mechanism  20 L connecting the inner member  19  with the left femoral support unit  3 L, the overall structure of the power transmission mechanism  20  can be simplified. 
     Third Embodiment 
     The walking assist device  1  given as a third embodiment of the present invention is described in the following with reference to  FIG. 7  which is a developed view schematically illustrating an essential part of the walking assist device  1 . In  FIG. 7 , the parts corresponding to those of the preceding embodiments are denoted with like numerals without necessarily repeating the discussion of such parts in the following description. 
     This embodiment also differs from the preceding embodiments in the structure of the power transmission mechanism  20 . The output shaft  19   a  of the electric motor  4  which is fixedly attached to the pelvic frame  13  is fixedly fitted with a primary pinion  61 , and a pair of racks (a first primary rack  62 A and a second primary rack  62 B) extending laterally in parallel to each other are mounted on the pelvic frame  13  in a freely slidable manner along the lengthwise direction. The primary pinion  61  meshes with both of these primary racks  62 A and  62 B. The primary pinion  61  and the first and second primary racks  62 A and  62 B jointly form a primary rack and pinion mechanism  60 . Thus, when the electric motor  4  is actuated, the first and second primary racks  62 A and  62 B move laterally in mutually opposite directions in synchronism with each other. 
     Each primary rack  62  is provided with a secondary rack and pinion mechanism  63 ,  64  (a first secondary rack and pinion mechanism  63  and a second secondary rack and pinion mechanism). Each secondary rack and pinion mechanism  63 ,  64  includes a secondary pinion  65 ,  66  rotatably supported by the corresponding primary rack  62 A,  62 B having a central axial line extending in parallel with that of the primary pinion  61  and a pair of secondary racks  67 A,  67 B,  68 A,  68 B which extend in parallel with the primary racks  62 A and  62 B and supported by the corresponding rack  62 A,  62 B in a freely slidable manner along the lengthwise direction (the racks of each secondary rack and pinion mechanism may be referred to as the upper secondary rack and the lower secondary rack as shown in the drawings although the terms “upper” and “lower” may not correspond to the actual positioning of these secondary racks). 
     Each secondary pinion  65 ,  66  meshes with the corresponding pair of secondary racks  67 A,  67 B,  68 A,  68 B. Thus, in each of the secondary rack and pinion mechanisms  63  and  64 , each pair of the secondary racks  67 A,  67 B,  68 A,  68 B can only move laterally in mutually opposite directions in synchronism with each other. The first secondary pinion  65  and the second secondary pinion  66  are urged by respective biasing means such as torsion coil springs (not shown in the drawings) in the direction to move the first secondary racks  67 A and  68 A (of the two different secondary rack and pinion mechanisms) in the rightward direction and the second secondary racks  67 B and  68 B (of the two different secondary rack and pinion mechanisms) in the leftward direction. 
     A left pulley  35 L is integrally attached to the base end of the left femoral arm member  16 L forming a part of the left femoral support unit  3 L, and a left belt  69 L is passed around the left pulley  35 L. One end of the left belt  69 L is connected to the first secondary rack  67 A of the upper secondary rack and pinion mechanism  63  and the other end of the left belt  69 L is connected to the first secondary rack  68 A of the lower secondary rack and pinion mechanism  64 . 
     A right pulley  35 R is integrally attached to the base end of the right femoral arm member  16 R forming a part of the right femoral support unit  3 R, and a right belt  69 R is passed around the right pulley  35 R. One end of the right belt  69 R is connected to the second secondary rack  67 B of the upper secondary rack and pinion mechanism  63 , and the other end of the right belt  69 R is connected to the first secondary rack  68 B of the lower secondary rack and pinion mechanism  64 . 
     The mode of operation of this power transmission mechanism is described in the following. 
     The rotational output of the electric motor  4  is converted into the linear movements of the first and second primary racks  62 A and  62 B which are then transmitted to the two femoral support units  3 L and  3 R via the first and second belts  69 L and  69 R. When the loadings on the two femoral support units  3 L and  3 R are equal to each other, no differential movement is caused to the secondary rack and pinion mechanism  63  and  64 . Therefore, when the primary pinion  61  is turned in the direction indicated by arrow A, each primary rack  62  moves in the direction indicated by arrow A so that the left belt  69 L rotatively actuates the left pulley  35 L, along with the left femoral arm member  16 L, in the direction indicated by arrow A or in the forward direction while the right belt  69 R rotatively actuates the right pulley  35 R, along with the right femoral arm member  16 R, in the direction indicated by arrow A or in the rearward direction. Conversely, when the primary pinion  61  is turned in the direction indicated by arrow B, each primary rack  62  moves in the direction indicated by arrow B with the result that the left femoral arm member  16 L and the right femoral arm member  16 R are rotatively actuated in the direction indicated by arrows B. 
     Thus, the power transmission mechanism  20  of the third embodiment includes a pair of secondary rack and pinion mechanisms  63  and  64 , and the left belt  69 L which is passed around the left pulley  35 L is connected between the secondary racks  67 A and  68 A of the different secondary rack and pinion mechanisms  63  and  64  while the right belt  69 R which passed around the right pulley  35 R is connected between the secondary racks  67 B and  68 B of the different secondary rack and pinion mechanisms  63  and  64 . Therefore, the two femoral support units  3  are enabled to move simultaneously forward or rearward or to move in the opposite phase relationship without causing the rotation of the electric motor  4 . 
     More specifically, when the left femoral arm member  16 L moves forward as indicated by arrow A and the right femoral arm member  16 R moves also forward as indicated by arrow B, the primary rack and pinion mechanism  60  does not operate, and the first secondary rack  67 A of the first secondary rack and pinion mechanism  63  moves rightward (aided by the urging force of the biasing means), the first secondary rack  68 A of the second secondary rack and pinion mechanism  64  moves leftward (against the urging force of the biasing means), the second secondary rack  67 B of the first rack and pinion mechanism  63  moves leftward (aided by the urging force of the biasing means), and the second secondary rack  68 B of the second secondary rack and pinion mechanism  64  moves rightward (against the urging force of the biasing means). 
     When the left femoral arm member  16 L moves rearward as indicated by arrow B and the right femoral arm member  16 R moves also rearward as indicated by arrow A, the primary rack and pinion mechanism  60 , again, does not operate, and the first secondary rack  67 A of the first secondary rack and pinion mechanism  63  moves leftward (against the urging force of the biasing means), the first secondary rack  68 A of the second secondary rack and pinion mechanism  64  moves rightward (aided by the urging force of the biasing means), the second secondary rack  67 B of the first rack and pinion mechanism  63  moves rightward (against the urging force of the biasing means), and the second secondary rack  68 B of the second secondary rack and pinion mechanism  64  moves leftward (aided by the urging force of the biasing means). 
     Therefore, without rotating the electric motor  4  or without being hampered by the cogging torque of the electric motor  4 , the user of the walking assist device  1  is enabled to bend the both femoral parts (for sitting, for example) and to extend the both femoral parts (for standing up, for example) at the same time. 
     The third embodiment provides advantages similar to those of the preceding embodiments. 
     Fourth Embodiment 
     The walking assist device  1  given as a fourth embodiment of the present invention is described in the following with reference to  FIGS. 8 to 11 . 
     In the walking assist device  1  of the fourth embodiment, a fluid pump  70  consisting of a double acting displacement pump is attached to the pelvic frame  13  of the pelvic support unit  2 , and a pair of fluid actuators  71 L and  71 R also of a double acting type are provided in the junctions between the side frames  12 L and  12 R and the corresponding femoral support units  3 R and  3 L, respectively. In the illustrated embodiment, the fluid pump  70  uses bellows for creating chambers whose volumes can change, but may also use a regular cylinder receiving a reciprocating piston therein or any other pump elements. 
     As shown in  FIG. 9 , the fluid pump  70  is powered by an electric motor  73  fixedly attached to the pelvic frame  13 , and includes a swing arm  74  attached to the output shaft  73   a  of the electric motor  73 , a bellows rod  75  having a middle point engaged by the free end of the swing arm  74 , a pair of bellows  76  and  77  internally defining a first and a second pump chamber  76   a  and  77   a  and having moveable walls that are connected to the respective ends of the bellows rod  75 . The opposite walls of the bellows  76  and  77  are fixed to the pelvic frame  13 . The first and second pump chambers  76   a  and  77   a  are filled with suitable actuating fluid which may be either gas or liquid. Thus, when the swing arm  74  is tilted in either direction by the output shaft  73   a  of the electric motor  73 , the moveable walls of the bellows  76  and  77  are displaced in such a manner that the volume of one of the pump chambers  76   a ,  77   a  is reduced, and the volume of the other pump chamber  76   a ,  77   a  is increased by the same amount. A suitable reduction gear mechanism may be interposed between the output shaft  73   a  of the electric motor  73  and the swing arm  74 . 
     As shown in  FIGS. 8 and 10 , each fluid actuator  71  includes a housing  81  fixedly secured to the corresponding side frame  12 , and a pair of bellows  82  and  83  connected in series, and having respective fixed walls at opposite ends thereof and a common moveable wall which is connected to the femoral arm member  16 . The bellows  82  and  83  internally define first and second fluid chambers  82   a  and  83   a , respectively. Therefore, by changing the volumes of the first and second fluid chambers  82   a  and  83   a  in a complementary manner or by supplying a certain amount of fluid to one of the fluid chambers  82   a ,  83   a , and drawing the same amount of fluid from the other fluid chamber  82   a ,  83   a , the femoral arm member  16  is caused to swing in the corresponding direction. 
     As shown in  FIG. 11 , the fluid pump  70  and the two fluid actuators  71  are connected to one another by a plurality of fluid passages  91  to  94 . Specifically, the first pump chamber  76   a  is connected to the first fluid chamber  82   a  L of the left fluid actuator  71 L via a first passage  91 , and the second pump chamber  77   a  is connected to the first fluid chamber  82   a R of the right fluid actuator  71 R via a second passage  92 . The second fluid chamber  83   a L of the left fluid actuator  71 L is connected to the second pump chamber  77   a  via a third passage  93 , and the second fluid chamber  83   a R of the right fluid actuator  71 R is connected to the first pump chamber  76   a  via a fourth passage  94 . 
     In the illustrated embodiment, the first passage  91  and the fourth passage  94  are commonly connected to the first pump chamber  76   a , and the second passage  92  and the third passage  93  are commonly connected to the second pump chamber  77   a.    
     The mode of operation of the power transmission mechanism  20  of the fourth embodiment is described in the following. 
     When the loadings to the right and left femoral support units  3  are equal to each other, the rotation of the output shaft  73   a  of the electric motor  73  causes the swing arm  74  to swing in one direction, rightward for instance, as indicated by arrow A such that the volume of the first pump chamber  76   a  increases while the volume of the second pump chamber  77   a  decreases by the corresponding amount. As a result, the fluid in the second pump chamber  77   a  is equally distributed between the second passage  92  and the third passage  93  to be conducted into the first fluid chamber  82   a R of the right fluid actuator  71 R and the second fluid chamber  83   a L of the left fluid actuator  71 L. At the same time, the same amount of fluid is expelled from the second fluid chamber  83   a R of the right fluid actuator  71 R and the first fluid chamber  82   a L of the left fluid actuator  71 L flows into the first pump chamber  76   a  via the fourth passage  94  and the first passage  91 , respectively. As a result, the left arm member  16 L moves forward as indicated by arrow A, and the right arm member  16 R moves rearward as indicated by arrow A. The right and left femoral arm members  16  thus receive a same torque from the power transmission mechanism  20 . 
     Because the first passage  91  and the fourth passage  94  communicate with each other, and the second passage  92  and the third passage  93  communicate with each other, the two femoral support units  3  are enabled to move jointly forward or rearward or to perform an opposite phase motion without involving the rotation of the output shaft  73   a  of the electric motor  73 . 
     More specifically, when both the femoral arm members  16  move rearward as indicated by arrows B, there is no inflow into or outflow from either the first chamber  76   a  or the second chamber  77   a , and the actuating fluid flows from the second fluid chamber  83   a R of the right fluid actuator  71 R to the first fluid chamber  82   a L of the left fluid actuator  71 L, and from the second fluid chamber  83   a L of the left fluid actuator  71 L to the first fluid chamber  82   a R of the right fluid actuator  71 R. Also, when both the femoral arm members move forward, there is no inflow into or outflow from either the first chamber  76   a  or the second chamber  77   a , and the actuating fluid simply moves between the two fluid actuators  71 . 
     Therefore, without rotating the electric motor  73  or without being hampered by the cogging torque of the electric motor  73 , the user of the walking assist device  1  is enabled to bend the both femoral parts (for sitting, for example) and to extend the both femoral parts (for standing up, for example) at the same time. 
     In the illustrated embodiment, the first passage  91  and the fourth passage  94  were communicated with each other by branching off the first passage  91  from the fourth passage  94 , but may also be connected in different ways as long as one of the pump chambers  76   a ,  77   a  is communicated with the corresponding fluid chambers  82   a L,  83   a R,  83   a L,  83   a R of the two fluid actuators  71 L and  71 R. The same is true with the second passage  92  and the third passage  93 . 
     The fourth embodiment provides advantages similar to those of the preceding embodiments. 
     Although the present invention has been described in terms of specific embodiments, the present invention is not limited by such embodiments, but may be modified and substituted in a number of different ways without departing from the spirit of the present invention. 
     The foregoing embodiments were directed to walking assist devices  1  for assisting the walking movement of a user, but may also be constructed as devices for assisting the movement of other parts of the user during walking or in other situations. For instance, the device of the present invention may also be used for assisting the movement of the humeral parts of the user. 
     The two femoral support units  3  in the foregoing embodiments were rotatably attached to the frame part of the pelvic support unit  2 , but the pelvic support unit  2  may also consist solely of a flexible belt which directly supports the femoral support units  3  in a rotatable manner. In such a case, the drive unit and the battery  7  may be supported at any single part of the pelvic support unit  2  or may be divided into a plurality of different components so that each component may be supported by the pelvic support unit  2  at a plurality of different parts thereof. 
     Also, in any of the foregoing embodiments, it should be understood that any other controllable power sources such as hydraulic motors and pneumatic motors may be used in place of the electric motor  4 ,  73 , and the motor may be incorporated with a reduction gear unit without departing from the spirit of the prevent invention. In the first embodiment, instead of providing the counter gear  38 , one of the belts  36 L and  36 R may consist of a crossed belt so that the rotational direction may be reversed. 
     The original Japanese patent application on which the Convention priority is claimed for this application and any references mentioned in this application are hereby incorporated into this application by reference.