Abstract:
In a walking assistance device ( 10 ) including a main frame ( 22 ) supporting a power generator ( 26, 28 ) and worn on a pelvic part of a user, the main frame is provided with an opening ( 23 ) in a middle part thereof, and an electronic unit ( 25 ) is received in the opening. As the electronic unit is placed in the middle part of the main frame which is relatively free from deformation, the electronic unit is protected from deformation or stress that could impair the reliability of the electronic unit. To achieve both an easy access to the electronic unit, and an attractive appearance, the opening may be provided with a lid ( 24 ) that selectively closes the opening from a side adjacent to the user, and the lid may be formed as a back support member for supporting a back part of the user. As the lid serves the dual purposes, the weight and cost of the device can be minimized. For the convenience of the handling of the lid, the lid may be supported by the main frame via a hinge ( 121 ) provided adjacent to an upper or lower part of the opening.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a walking assistance device, and in particular to a walking assistance device including a femoral support member configured to be worn on a femoral part of a user to apply thereto a walking assistance force generated by a power generator. 
       BACKGROUND OF THE INVENTION 
       [0002]    Previously proposed is a walking assistance device that includes a power generator such as an electric motor to apply a working assistance force to a lower limb of a user for the purposes of assisting the walking movement of the user, and/or rehabilitating the walking impairment of the user by helping the user to regain the motor coordination that is required for the user to walk. 
         [0003]    Such a walking assistance device typically includes a pelvic frame consisting of a C-shaped main frame configured to be worn on a pelvic part of the user and extending from a lower back part of the user to either side of the pelvic part of the user and an abdominal belt for securing the main frame to the pelvic part of the user, a pair of power generators mounted on either lateral end of the pelvic frame (at parts corresponding to the hip joints of the user) and a pair of femoral support members for transmitting the power generated by the power generators to the corresponding femoral parts of the user. See patent document 1 (Japanese patent laid-open publication JP2009-95645A). 
         [0004]    A walking assistance device of this kind requires an electronic control unit and a battery for executing the required control action and providing the electric power to the power generator. It is most convenient if such electronic/electric units can be mounted on the pelvic frame. However, because the pelvic support assembly is worn closely on the body of the user, and is limited in space, there is some difficulty in placing the electronic/electric units on or in the pelvic frame. 
         [0005]    Also, the pelvic frame is configured to support the load (weight and reaction force) of the walking assistance device, and is given with an adequate mechanical strength, but inevitably undergoes some deformation during use. If the deformation of the main frame is transmitted to the electronic/electric units, the durability and reliability of the electronic/electric units may be impaired. This problem can be overcome by increasing the stiffness of the main frame, but it adds to the weight and cost of the main frame. 
         [0006]    It is also important that the electronic/electric units are placed in such a part of the walking assistance device that can be readily accessed in view of the need to service the electronic/electric units and replace a component thereof from time to time. 
         [0007]    The electronic/electric units often generate heat in operation, and there may be a need to insulate the user from the heat. 
         [0008]    It is known to provided a back support member on a middle part of the main frame facing a lower back part of the user for the purpose of evenly distributing the load (weight and reaction force) of the walking assistance device uniformly over the body of the user and maximize the comfort of the user. See patent document 2 (Japanese patent laid-open publication JP2005-000634A). The inventors have realized that the back support member can be used not only for supporting a lower back part of the user but also as a part of the enclosure for receiving electronic/electric units and prevent the transmission of heat from the electronic/electric units of the user. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    In view of such problems of the prior art and the recognition of the inventors, a primary object of the present invention is to provide a walking assistance device that is configured to store an electric/electronic unit free from stress without increasing the overall weight of the walking assistance device. 
         [0010]    A second object of the present invention is to provide a walking assistance device that can store an electric/electronic unit so as to be readily accessible. 
         [0011]    A third object of the present invention is to provide a walking assistance device that can store an electric/electronic unit so as to shield the user from the heat generated by the electric/electronic unit. 
         [0012]    According to the present invention, such objects can be accomplished by providing a walking assistance device configured to apply a walking assistance force to a femoral part of a user, comprising: a pelvic support assembly configured to be worn on a pelvic part of a user to support a power generator and a femoral support assembly configured to transmit a walking assistance force generated by the power generator to a femoral part of the user; wherein the pelvic support assembly comprises a main frame configured to be worn on a pelvic part of the user and extending from a lower back of the user to either side of the pelvic part of the user forming a C-shape in plan view, at least one free end of the main frame being configured to support the power generator at a position corresponding to a hip joint of the user, and an abdominal belt attached to the main frame at base ends thereof, extending along an inner periphery of the main frame and configured to be detachably passed along an abdominal part of the user; and wherein the main frame is provided with an opening in a middle part thereof, and an electronic unit is received in the opening. 
         [0013]    The electronic unit as used herein includes, not exclusively, an electric circuit, an electronic circuit, a control circuit, a power circuit, a battery, a telecommunication unit or the like. As the electronic unit is placed in the middle part of the main frame which is relatively free from deformation, the electronic unit is protected from deformation or stress that could impair the reliability of the electronic unit. 
         [0014]    According to a preferred embodiment of the present invention, the opening is passed through a thickness of the middle part of the main frame and a bottom plate closes an end of the opening facing away from the user. Preferably, the electronic unit is incorporated in the bottom plate, and the bottom plate is formed with a receptacle for receiving a battery therein in a detachable manner. 
         [0015]    If the electronic unit is secured to the main frame at a laterally central part of the electronic unit, the transmission of the deformation of the pelvic frame to the electronic unit can be minimized. To ensure a secure and stable attachment of the electronic unit to the main frame, the electronic unit may be secured to the main frame at an upper and lower laterally central part of the electronic unit. To insulate the electronic unit from the deformation of the main frame, the electronic unit may be secured to the main frame via a resilient member. 
         [0016]    When the main frame is provided with an opening in a middle part thereof, and an electronic unit is received in the opening, an electric cable extending from the electronic unit to the power generator may be passed inside the main frame so as to ensure a high reliability and conceal the lead wire from view. 
         [0017]    To achieve both an easy access to the electronic unit, and an attractive appearance, the opening may be provided with a lid that selectively closes the opening from a side adjacent to the user. According to a particularly preferred embodiment of the present invention, the lid is formed as a back support member for supporting a back part of the user. As the lid serves the dual purposes, the weight and cost of the device can be minimized. For the convenience of the handling of the lid, the lid may be supported by the main frame via a hinge provided adjacent to an edge of the opening. 
         [0018]    To enhance the capability of the back support member to conform to the body of the user, and to minimize the transmission of heat from the electronic unit to the user, the back support member may be provided with a plurality of vertical slots arranged along a lateral direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Now the present invention is described in the following with reference to the appended drawings, in which: 
           [0020]      FIG. 1  is a perspective view of a walking assistance device embodying the present invention; 
           [0021]      FIG. 2  is an exploded perspective view of a pelvic support assembly of the walking assistance device; 
           [0022]      FIG. 3  is a sectional view of a middle part of a main frame of the pelvic support assembly; 
           [0023]      FIG. 4  is a fragmentary exploded perspective view of a hinge assembly of the main frame; 
           [0024]      FIGS. 5A and 5B  are fragmentary perspective views showing how an electronic unit is received in an opening formed in the middle part of the main frame and how the opening is closed by a lid; 
           [0025]      FIGS. 6A and 6B  are perspective views showing how a battery is received in a receptacle formed in a bottom plate; and 
           [0026]      FIG. 7  is a vertical sectional view showing how the battery is retained in the receptacle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    An embodiment of the walking assistance device of the present invention will now be described in the following with reference to  FIG. 1 . In the following description, the direction of the walking assistance device will be based on the directional arrows shown in each of the drawings. When the device is worn by the user, the front and back directions of the walking assistance device coincide with the coronal axis, while the left and right directions coincide with the sagittal axis. 
         [0028]    The walking assistance device  10  is provided with a pelvic support assembly  20 . The pelvic support assembly  20  is configured to be worn on the pelvic part of the user, and includes a main frame  22  that extends outwardly from a lower back part of the user to either side of the pelvic part to form a C-shape when viewed in plan view. The main frame  22  is formed with molded plastic material such as polyamide resin, glass fiber reinforced plastic material, carbon fiber reinforced plastic material or other material having a high stiffness and mechanical strength. 
         [0029]    A middle part  22 A of the main frame  22  is formed with a storage opening ( FIG. 2 ) passed across the thickness thereof for receiving an electronic unit including a control unit and a battery. A back support member  24  is attached to the inner side of the middle part  22 A of the main frame  22 . The back support member  24  is made of a plastic plate member having a high resiliency, and is formed with a number of vertical slots  24 A arranged laterally at a regular interval for promoting air permeability and enhancing resiliency with the aim of improving the comfort of the user. 
         [0030]    A left end part  22 B and a right end part  22 C on either side of the main frame  22  are positioned outwardly on either side of the user, and are each provided with a power generator mainly consisting of a motor unit  26 ,  28 . The upper end of each motor unit  26 ,  28  is connected to the corresponding end part  22 B,  22 C of the main frame  22  via a hinge having a hinge axis extending in the coronal axis (front/back directional axis) of the user so that the motor unit  26 ,  28  is suspended from the upper end part, and can rotate around the hinge axis within a prescribed angular range. 
         [0031]    Along the inner side of the main frame  22  extends an abdominal belt  30 , which is wrapped around the abdominal part of the user. The abdominal belt  30  of this embodiment includes a left side belt  36 , a right side belt  38  and a front belt  40 . These parts  36 ,  38  and  40  are each made of flexible materials such as fabric and leather. 
         [0032]    The left side belt  36  is passed through an opening  51 B of a left engagement piece  51 , and the two ends of the left side belt  36  are attached to an upper and lower part of the inner side of the middle part  22 A of the main frame  22 , respectively, so as to form a loop. Therefore, the left side belt  36  is reversed over in the shape of letter V at the left engagement piece  51 . The length of the left side belt  36  can be adjusted by using a belt length adjustment buckle (not shown in the drawings) provided in a middle part of the belt. The left hook engagement piece  51  is made of plastic or metallic material, and is further provided with a left hook shaped part  51 A. 
         [0033]    Similarly, the right side belt  38  is passed through an opening  52 B of a right engagement piece  52 , and the two ends of the right side belt  38  are attached to an upper and lower part of the inner side of the middle part  22 A of the main frame  22 , respectively, so as to form a loop. Therefore, the right side belt  38  is reversed over in the shape of letter V at the right engagement piece  52 . The length of the right side belt  38  can be adjusted by using a belt length adjustment buckle (not shown the drawings) provided in a middle part of the belt. The right engagement piece  52  is made of plastic or metallic material, and is further provided with a right hook shaped part  52 A. 
         [0034]    In the illustrated embodiment, each of the left and right engagement pieces  51  and  52  is made of a flat plate member having a slightly greater width than the belts  36  and  38 . 
         [0035]    Each end of the front belt  40  is fitted with a buckle  56 ,  58  provided with an opening  56 A,  58 A configured to receive the hook shaped part  51 A,  52 A of the corresponding engagement piece  51 ,  52 . Each of the buckles  56 ,  58  is provided with a pair of rectangular openings  56 B and  58 B separated by a lateral bar for passing the corresponding end of the front belt  40  in a length adjustable manner. The left and right buckles  56  and  58  are each made of a flat plate member having a slightly greater width than the front belt  40 . 
         [0036]    Therefore, the front belt  40  can be detachably connected to the left and right side belts  36  and  38  by engaging the hook shaped parts  51 A and  52 A of the engagement pieces  51  and  52  with the openings  56 A and  58 A of the corresponding buckles  56  and  58 . When the three parts of the abdominal belt  30  are connected to one another as described above, the abdominal belt  30  forms a loop that surrounds the abdominal part of the user. By suitably adjusting the length of each part of the abdominal belt  30  and snugly wrapping the abdominal belt  30  around the abdominal part of the user, the main frame  22  can be securely fitted to the pelvic part of the user without causing discomfort to the user. 
         [0037]    The pelvic support assembly  20  further comprises a left supporter piece  44  and a right supporter piece  46 . Each supporter piece  44 ,  46  is made of relatively stiff sheet member having a vertical width greater than the combined width of the two runs of the corresponding abdominal belt  36 ,  38  extending along the outer surface of the supporter piece  44 ,  46 . Each supporter piece  44 ,  46  has a base end located between the back support member  24  and corresponding side belt  36 ,  38 , and is jointly secured to the main frame  22 , and extends along the inner surface of the side belt  36 ,  38 . To impart a suitable stiffness to each supporter piece  44 ,  46 , a resilient plastic or metallic wire  44 A,  46 A may be incorporated in the supporter piece  44 ,  46 , for instance, along the outer periphery thereof. 
         [0038]    Thus, the supporter pieces  44  and  46  are flexible enough to conform to the contour of the pelvic part of the user but stiff enough to distribute the pressure from the left and right side belts  36  and  38  over a large area of the body of the user so that the comfort of the user may be enhanced. Also, in order to increase the air breathability, and ensure the comfort to the user in a warm weather, the supporter pieces  44  and  46  may be at least partly made of a mesh type fabric or other air permeable material. 
         [0039]    The base end of the left supporter piece  44  is secured to the middle part  22 A of the main frame  22 , and extends between the back support member  24  and left abdominal belt  36  as mentioned earlier. The free end of the left supporter piece  44  terminates at a point adjacent to the left engagement piece  52  in the illustrated embodiment, but may also extend slightly beyond the left engagement piece  52 . 
         [0040]    Similarly, the base end of the right supporter piece  46  is secured to the middle part  22 A of the main frame  22 , and extends between the back support member  24  and right abdominal belt  38 . The free end of the right supporter piece  46  terminates at a point adjacent to the right engagement piece  54  in the illustrated embodiment, but may also extend slightly beyond the left engagement piece  52 . The right supporter piece  46  extends along the side of the user in a similar fashion as the left supporter piece  44 . 
         [0041]    A stabilizer member  53 ,  54  is connected to each end part  22 B,  22 C of the main frame  22 . Each stabilizer member is made of an elongated, relatively stiff plastic member having a base end pivotally attached to the inner side of the corresponding end part  22 B,  22 C via a pivot member so as to be rotatable around a pivot axis substantially in parallel with the sagittal axis or so as to be rotatable in the vertical direction. 
         [0042]    Each stabilizer member  53 ,  54  has a free end  53 A,  54 A formed with a passage  53 B,  54 B through which the two runs of the corresponding side belt  36 ,  38  are passed. The passage  53 B,  54 B has a certain length so that the stabilizer member  53 ,  54  may evenly engage a corresponding length of each run of the belt. The free end  53 A,  54 A of each stabilizer member  53 ,  54  is attached to a free end part of the corresponding supporter piece  44 ,  46  via a cushioning member  55 ,  57  such as a foamed plastic piece. 
         [0043]    The stabilizer members  53  and  54  are made of a relatively stiff molded elastomeric material such as vulcanized rubber. The main part of each stabilizer member  53 ,  54  consists of a strip member having a relatively large width as compared to the thickness thereof and having a major plane extending along the outer contour of the abdominal part of the user. Therefore, the stabilizer members  53  and  54  are compliant in the direction to conform to the outer contour of the abdominal part of the user, but is relatively stiff against the bending deformation in the vertical direction. 
         [0044]    As the abdominal belt  30  is fastened around the abdominal part of the user, and is tightened, the stabilizer members  53  and  54  deflect inwardly against the body or the user, and the free ends  53 A and  54 A thereof are placed adjacent to or slightly above the anterior superior iliac spine of the user. 
         [0045]    Each electric motor unit  26 ,  28  is positioned so as to coincide with the corresponding hip joint of the user, and is provided with an angular sensor (not shown in the drawings). To the output end of each electric motor unit  26 ,  28  on the exterior side thereof is releasably attached a base end part  60 A,  62 A of a swing arm  60 ,  62  in a torque transmitting relationship. 
         [0046]    Each swing arm  60 ,  62  is made of highly stiff and strong material such as aluminum, glass fiber reinforced plastic material, and carbon fiber reinforced plastic material. The main part of each swing arm  60 ,  62  consists of a hollow member having an elliptic cross section as illustrated in  FIG. 2 . The cross section of each swing arm  60 ,  62  is highly elongated along a major plane extending perpendicularly to the sagittal axial at the base end  60 A,  62 A thereof. Each swing arm  60 ,  62  is generally twisted so that the major plane of the free end  60 B,  62 B, which is located adjacent to a lower end of the femoral part, extends perpendicularly to the coronal axis. 
         [0047]    The free end  60 B,  62 B of each swing arm  60 ,  62  is fitted with a front femoral support member  68 ,  70  via a coupling  64 ,  66  that permits angular movement of the femoral support member  68 ,  70  relative to the free end  60 B,  62 B of the swing arm  60 ,  62 . Each front femoral support member  68 ,  70  is formed of a substantially rectangular plate member made of plastic material, and is curved in the shape of a part-cylindrical surface so as to conform to the outer contour of the lower femoral part of the user. Each front femoral support member  68 ,  70  is formed with a number of vertical slots  68 A,  70 A arranged laterally at a regular interval for promoting air permeability and enhancing resiliency with the aim of improving the comfort of the user. 
         [0048]    Each femoral support member  68 ,  70  is fitted with a femoral belt  73 ,  74  for retaining the femoral support member  68 ,  70  to the femoral part of the user as shown in  FIG. 1 . Each femoral belt  73 ,  74  includes a main belt portion  83 ,  85  that surrounds the femoral part of the user in cooperation with the corresponding femoral support member  68 ,  70 , and an auxiliary belt portion  84 ,  86  integrally bifurcated from an intermediate part of the main belt portion  83 ,  85 . The two femoral belts  73  and  74  are mirror images of each other. 
         [0049]    The femoral support assembly is now described in the following. As the two femoral support assemblies are mirror images of each other, only the right femoral support assembly is described in the following. A first end  83 A of the main belt portion  83  is secured to a belt engaging bar  68 B extending vertically on one lateral side of the femoral support member  68 , and a second end  83 B of the main belt portion  83  is fitted with a tongue piece  75 . The tongue piece  75  includes four lateral bars and a pair of longitudinal bars connecting the corresponding ends of the lateral bars. The femoral belt  73  is passed through an opening  75 B defined between the second and third lateral bars from inside to outside, and is then passed through the opening defined between the first and second lateral bars from outside to inside, the lateral bars being counted from the end adjacent to the femoral belt  73 . Thus, the free end of the femoral belt  73  is passed between the first lateral bar and the remaining part of the femoral belt, from outside to inside. Thus, the femoral belt  73  is frictionally engaged against loosening when fastened while enabling the femoral belt  73  to be tightened by pulling the free end of the femoral belt  73 . In the illustrated embodiment, a surface fastener  87  is attached to the outer side of the free end of the femoral belt  73  so that the parts of the femoral belt overlying each other near the base end of the tongue piece  75  can be joined to each other, and the femoral belt  73  is positively prevented from slackening during use. 
         [0050]    If desired, the surface fastener may also be applied to the abdominal belt  30  or in particular the front belt  40  for the purpose of preventing the loosening or slackening of the abdominal belt  30 . 
         [0051]    The femoral support member  68  is formed with a hook portion  71  on the opposite lateral side thereof. The hook portion  71  is formed on the front side of the femoral support member  68  so as to define a hook opening facing away from the adjacent lateral edge of the femoral support member  68 . Thereby, the tongue piece  75  can be secured to the femoral support member  68  by engaging the hook portion  71  in the opening defined between the first and second lateral bars of the tongue piece. 
         [0052]    The free end of each auxiliary belt part  84  is fitted with a grommet  84 C, and is connected to an intermediate part of the corresponding swing arm  62  via a pivot pin  88  fixedly secured to the swing arm  60  and rotatably received in the grommet  84 C. 
         [0053]    Thus, the main belt portion  83  is wrapped around the femoral part of the user by securing the base end of the main belt portion  83  to the belt engaging bar  68 B of the femoral support member  68  and engaging the tongue piece  75  with the hook portion  71  provided on the opposite lateral end of the femoral support member  68 . 
         [0054]    The main belt portions  83  and  85  as well as the auxiliary belt portions  84  and  86  may be made of any flexible material such as fabric and leather, and may be at least partly made of mesh material as denoted in numerals  73 B and  74 B. Resilient plastic wires  73 A,  73 B are incorporated along the lateral edges of the mesh material  73 B,  74 B so that the femoral belt  73 ,  74  may maintain a curved shape so that the handling of the femoral belt  73 ,  74  may be improved during the fastening and releasing of the femoral belt. 
         [0055]    In the illustrated embodiment, the auxiliary belt portions  84  and  86  are at least partly incorporated with elastic rubber belts  84 B and  86 B so that the variation in the build of the user may be accommodated by the extension and contraction of the auxiliary belt portions  84  and  86 , and the comfort of the user may be improved. 
         [0056]    Each femoral belt  73 ,  74  including the main belt portion  83 ,  85  and auxiliary belt potion  84 ,  86  assumes an inverted frustoconical shape when the free end of the main belt portion  83 ,  85  is connected to the femoral support member  68 ,  70  via the belt buckle including the tongue piece  75 ,  76  and the hook portion  71 ,  72  so as to conform to the outer contour of the lower femoral part of the user. Thus, each femoral belt  73 ,  74  may be shaped three-dimensionally by using the draping technique so as to optimally conform to the femoral part of the user. 
         [0057]    Thus, the free end of each swing arm  60 ,  62  can engage the lower part of the corresponding femoral part of the user by passing the femoral belt  73 ,  74  around the femoral part of the user, and engaging the hook-shaped part  71 ,  72  with the opening  75 A,  76 A of the corresponding tongue piece  75 ,  76 . By appropriately tightening the femoral belt  73 ,  74  by using the tension adjusting feature of the tongue piece  75 ,  76 , the femoral part of the user can be securely but releasably engaged by the free end of the swing arm  60 ,  62 . 
         [0058]    By actuating the motor units  26  and  28  in dependence on the walking effort made by the user (which can be detected by using suitable load sensors not shown in the drawings), the user is assisted in the effort to walk not only by the assisting power provided by the motor units  26  and  28  but also by the gait or pace also provided by the motor units  26  and  28  for the purpose of helping the user regain the motor coordination required for walking. The motor units  26  and  28  are provided with angular sensors so that the angular movements of the motor units  26  and  28  may be accurately controlled by feedback control. 
         [0059]    Referring to  FIGS. 2 to 4 , the electronic unit  25  comprises a unit main body  100  which is received in an opening  23  having an elliptic cross section and passed across the thickness of the main frame  22 . In particular, the unit main body  100  is loosely fitted in the opening  23  as will be discussed hereinafter. The unit main body  100  is formed as a bottom plate that closes the opening  23  from the side remote from the user, and is internally provided with an electronic control unit (not shown in the drawings). The electronic control unit may be molded or otherwise sealed within the unit main body  100 . The side of the unit main body  100  facing the user is formed with a rectangular receptacle  102  that receives a battery  101  in a detachable manner. The battery  101  provides the electric power required for the operation of the control unit in the unit main body  100  and the electric motor units  26  and  28 . An upper threaded hole  103  and a lower threaded hole  104  are passed centrally at an upper and lower end of the unit main body  100 , respectively. 
         [0060]    A pair of grommets  105  made of elastomeric material are fitted on either lateral end of the unit main body  100 . Electric cables  106  are passed through these grommets  105 , and then into holes  107  formed in the lateral wall defining the opening  23 . The electric cables  106  are passed through the hollow interior of the main frame  22 , and connect the motor units  26  and  28  with the electronic unit  25  for exchanging electric signals and feeding the electric power to the motor units  26  and  28 . 
         [0061]    An upper engagement piece  111  projects from the upper wall defining the opening  23 , and a lower engagement piece  113  similarly projects from the lower wall defining the opening  23 . These engagement pieces  111  and  113  are centrally located with respect to the lateral direction. 
         [0062]    The unit main body  100  is fixedly secured to the main frame  22  by using a pair of threaded bolts  114  which are passed through holes  111 A and  113 A formed in the engagement pieces  111  and  113 , and threaded into the upper and lower threaded holes  103  and  104 , respectively. A rubber bush  115 ,  116  is interposed between each threaded bolt  114  and the corresponding holes  111 A,  113 A. 
         [0063]    During use, the main frame  22  may undergo some twisting deformation around the middle part  22 A thereof as indicated by arrows A and B in  FIG. 2  due to the reaction of the electric motors  26  and  28  applying a walking assistance force to the femoral parts of the user. As the unit main body  100  is loosely fitted in the opening  23 , is located centrally of the main frame  22 , and is supported therein via resilient members such as the rubber bushes  115  and  116 , the deformation of the main frame  22  is prevented from being transmitted to the unit main body  100 . In particular, the unit main body  100  is supported via the upper and lower engagement pieces  111  and  113  which are located centrally with respect to the lateral direction, and this is particularly beneficial in deformation free support of the unit main body  100 . 
         [0064]    The back support member  24  is connected to the main frame  22  via a hinge assembly  121 . As best shown in  FIG. 4 , the lower engagement piece  113  is connected to the main frame  22  via a coronal extension  112  extending from the part of the main frame  22  immediately below the lower central edge of the opening  23 . The lateral sides of the coronal extension  112  are provided with pivot holes  124  disposed in a coaxial relationship. The lower end of the back support member  24  on the side facing away from the user is provided with a pair of elastic projections  122  laterally opposing each other, and provided with pivot pins  123  projecting toward each other in a coaxial relationship. These pivot pints  123  are placed in the corresponding pivot holes  124  of the coronal extension  112  by resiliently forcing the elastic projections  122  away from each other, and releasing the elastic projections  122  to the initial positions once the pivot pints  123  are received in the pivot holes  124 . The lateral sides of the coronal extension  112  in which the pivot holes  124  are formed are given with a tapering surfaces so that the pivot pints  123  can be easily received in the pivot holes  124  by pushing the coronal extension  112  into the gap between the two elastic projections  122  as indicated by an arrow C in  FIG. 2 . 
         [0065]    The lower end of the unit may body  100  was connected with the part of the main frame  22  adjacent to the central part of the lower edge of the opening  23  via the hinge assembly  121 , but it is also possible to connect the upper end of the unit main body  100  with the part of the main frame  22  adjacent to the central part of the upper edge of the opening  23  via a similar hinge assembly as can be readily appreciated by a person skilled in the art. It is even possible to provide a hinge assembly on a lateral edge of the opening  23 . 
         [0066]    The upper end of the back support member  24  is provided with a pair of engagement portions  125  on the side of the back support member  24  facing away from the user. The engagement portions  125  comprises permanent magnet pieces that cooperate with associated engagement portions  126  made of iron and provided on the main frame  22 . The associated engagement portions  126  are configured so as to come into engagement with the engagement portions  125  and get magnetically attached thereto when the back support member  24  is swung upward around the hinge assembly  121 , and closes the opening  23  from the side of the user. Thus, the back support member  24  is enabled to close the opening  23  when desired, and can be held in the closed position by the magnetic attraction between the engagement portions  125  and associated engagement portions  126 . 
         [0067]    Owing to the structure of the back support member  24  discussed above, the user can easily gain access to the electronic unit  25  simply by opening the back support member  24  via the hinge assembly  121 . 
         [0068]    When the opening  23  is exposed by swinging the back support member  24  downward around the hinge assembly  121 , the battery  101  can be placed into the receptacle  102  and taken out of the receptacle  102  as required, as illustrated in  FIGS. 5A and 5B . As shown in  FIGS. 6 and 7 , the upper central part of the battery  101  is provided with a U-shaped sheet spring  131  having a pair of engagement claws  132 , and the upper wall of the receptacle  102  is provided with a pair of engagement recesses  134  configured and positioned so as to receive the engagement claws  132 . The lower end of the battery  101  is provided with a pair of projections  133  configured to be received by a pair of corresponding recesses  135  formed in the lower wall of the receptacle  102 . 
         [0069]    Therefore, by placing the projections  133  in the recesses  135  formed in the lower wall of the receptacle  102 , and pushing the battery  101  into the receptacle  102 , the engagement claws  132  are resiliently engaged in the corresponding recesses  134  formed in the upper wall of the receptacle  102 . This snap fit action is facilitated because the side  133 A of each projection  133  facing the user is tapered, and the corresponding side wall  135 A of the corresponding recess  135  is given with a complementary taper. 
         [0070]    When the battery  101  is fully received in the receptacle  102 , battery terminals  141  ( FIG. 6A ) provided centrally in the lower end of the battery  101  are electrically connected to unit terminals  142  provided centrally in the lower wall of the receptacle  102 . The battery  101  can be recharged by using a battery recharger (not shown in the drawings) which is configured to recharge the battery  101  via the battery terminals  141 . 
         [0071]    The removal of the battery  101  can be accomplished in an equally simple manner. By depressing the U-shaped sheet spring  131  downward, the engagement between the engagement claws  132  and engagement recesses  134  can be released, and the battery  101  can be taken out of the battery receptacle  102  by tilting it around the lower end thereof. 
         [0072]    As shown in  FIG. 2 , the side of the back support member  24  facing away from the user is provided with a pair of vertically extending ribs  151  that are configured to be pushed against the opposing surface of the battery  101  at free ends  151 A thereof when the back support member  24  is closed. If desired, the vertically extending ribs  151  may be made of elastomeric or other resilient material. 
         [0073]    As the back support member  24  is used as a lid for the battery receptacle  102 , the access to the battery  101  is facilitated, and the need for special members that are dedicated for the retaining of the battery  101  can be eliminated. As the battery  101  is detachably received in the unit main body  100 , the battery  101  or in particular the battery terminals  141  are prevented from being affected by the deformation of the main frame  22  during use. 
         [0074]    The back support member  24  was provided with vertically extending slots  24 A in the illustrated embodiment, but may be perforated or otherwise given with an air permeable property for affording a favorable resiliency or flexibility to the back support member  24 . Also, the electronic unit  25  may generate heat during use. Particularly when the back support member  24  is given with an air permeable property, it can shield the heat generated from the electronic unit  25  to the user. 
         [0075]    Although the present invention has been described in terms of a preferred embodiment thereof. It is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims. 
         [0076]    The contents of the original Japanese patent applications on which the Paris Convention priority claim is made for the present application are incorporated in this application by reference.