Patent Publication Number: US-2019175435-A1

Title: Muscular strength assisting apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a muscular strength assisting apparatus that is worn by a wearer so as to assist muscular strength of the wearer. 
     BACKGROUND 
     As disclosed in, for example, Japanese Patent Application Publication No. 2015-182833A, attention has been focused on a muscular strength assisting apparatus with the aim of reducing a physical and muscular load on workers engaged in agriculture, construction industry, nursing care, and so on. The muscular strength assisting apparatus includes a pair of attachment tools mounted respectively to a torso and upper arm of a human body, which are connected together via a shoulder joint, and assists muscular strength of a wearer of the muscular strength assisting apparatus by retaining the pair of attachment tools at a predetermined relative position or by actively causing the pair of attachment tools to operate relative to each other, utilizing a force output by a drive means. 
     Such a muscular strength assisting apparatus has a switching means such as a brake and a clutch, and when performing muscular strength assistance, the force output by a drive means held by one of the attachment tools is transmitted to the other of the attachment tools through the switching means. Whereas when the muscular strength assistance is not performed, the force output by the drive means is blocked by the switching means, so that the wearer&#39;s motion is not restrained by the drive means. 
     SUMMARY 
     The shoulder joint enables motions of the upper arm relative to the trunk about more than one axis, specifically flexion/extension motion, internal/external rotation motion, and adduction/abduction motion. Meanwhile, the muscular strength assisting apparatus situated in the vicinity of an upper arm of a wearer may limit movement of another upper arm of the wearer to which the muscular strength assistance is not performed, in particular, the switching means, whose size structurally tends to be large, is located in a movable range of the upper arm and interfere with the upper arm. The present invention has been made in view of the above-described circumstances, and it is an object to provide a muscular strength assisting apparatus in which limitation on wearer&#39;s motion can be reduced. 
     A first muscular strength assisting apparatus according to one aspect of the invention includes a drive means held by a first attachment tool attached to a torso, and a transmission means for transmitting a force output by the drive means to a second attachment tool attached to an upper arm. The transmission means includes an output shaft member coupled to the second attachment toot and a switching means capable of switching between transmission and interruption of the force from the drive means to the output shaft member, and the switching means is disposed on a rear, upper or laterally outer side of the output shaft member. 
     In the first muscular strength assisting apparatus according to one aspect of the invention, the switching means may be disposed on the rear side of the output shaft member. 
     In the first muscular strength assisting apparatus according to one aspect of the invention, the first attachment tool may include a center frame attached to the torso at a position facing a back, and a side frame rotatable relative to the center frame, and the switching means may be supported by the side frame. 
     In the first muscular strength assisting apparatus according to one aspect of the invention, a portion of the drive means coupled to the transmission means may be supported by the side frame. 
     In the first muscular strength assisting apparatus according to one aspect of the invention, the transmission means may further include a shaft member disposed between the output shaft member and the switching means along a force transmission path, the shaft member being rotatable about a rotation axis that is not parallel to a rotation axis of the output shaft member. 
     A second muscular strength assisting apparatus according to another aspect of the invention includes a drive means held by a first attachment tool attached to a torso, and a switching means capable of switching between transmission and interruption of a force output by the drive means to the second attachment tool. The switching means is disposed on a rear, upper or laterally outer side of a shoulder joint. 
     In the second muscular strength assisting apparatus according to one aspect of the invention, the switching means may be disposed on the rear side of the shoulder joint. 
     In the first and second muscular strength assisting apparatus, the switching means may include a first member coupled to the second attachment toot and a second member coupled to the drive means and capable of moving close to and away from the first member. The first member is held rotatably relative to the first attachment toot and the second member may be contactable with the first member from a radial direction about a rotation axis of the first member. 
     According to the aspects of the invention, it is possible to reduce restriction on motions of the wearer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a muscular strength assisting apparatus together with a wearer wearing the same for explaining one embodiment of the invention. 
         FIG. 2  is a perspective view showing the muscular strength assisting apparatus shown in  FIG. 1 . 
         FIG. 3  is a view showing, from a forward side, part of the muscular strength assisting apparatus shown in  FIG. 1 . 
         FIG. 4  is a view showing, from a lateral outer side, a part of the muscular strength assisting apparatus shown in  FIG. 1 . 
         FIG. 5  is a view showing, from a rear side, a part of the muscular strength assisting apparatus shown in  FIG. 1 . 
         FIG. 6  illustrates a drive force transmission mechanism of the muscular strength assisting apparatus shown in  FIG. 1 . 
         FIG. 7  is a view showing, from the lateral outer side, the main part of a position control device of the muscular strength assisting apparatus. 
         FIG. 8  is a view showing, from the lateral outer side, a main part of the position control device of the muscular strength assisting apparatus in a state different from the state shown in  FIG. 7 . 
         FIG. 9  is a view showing, from the lateral outer side, a main part of the position control device of the muscular strength assisting apparatus in a state different from the state shown in  FIGS. 7 and 8 . 
         FIG. 10  is a perspective view showing the muscular strength assisting apparatus  10  together with a wearer wearing the same for describing a modification example. 
         FIG. 11  is a view showing, from a front side, a part of the muscular strength assisting apparatus shown in  FIG. 10 . 
         FIG. 12  is a view showing, from the lateral outer side, a part of the muscular strength assisting apparatus shown in  FIG. 10 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, one embodiment of the present invention will be described with reference to the appended drawings.  FIG. 1  to  FIG. 12  are views for describing one embodiment of the invention and modification examples thereof. Among these drawings,  FIG. 1  and  FIG. 2  are perspective views showing a muscular strength assisting apparatus  10  in its entirety, and  FIG. 1  in particular shows a state where the muscular strength assisting apparatus  10  is worn on a human body. The muscular strength assisting apparatus  10  includes a first attachment tool  20  and a second attachment tool  25  rotatable relative to each other about a first rotation axis d 1 , and a position control device  15  that controls a relative position between the first attachment tool  20  and the second attachment tool  25 , in other words, a rotational position of the second attachment tool  25  with respect to the first attachment tool  20 . The position control device  15  includes a drive means  30  held by the first attachment tool  20 , a transmission means  35  for transmitting a force output by the drive means  30  to the second attachment tool  25 , and a control unit  16  for controlling the drive unit  30  and the transmission means  35 . As shown in  FIG. 1 , the first attachment tool  20  and the second attachment tool  25  are mounted to two parts of a human body connected together via a joint, which are a torso and an upper arm. The position control device  15  controls the relative positions of the first attachment  20  and the second attachment  25  to assist in maintaining a relative position of the upper arm with respect to the torso and/or a relative motion of the upper arm with respect to the torso. In particular, the muscular strength assisting apparatus  10  described herein is designed to reduce restriction on wearer&#39;s motion. 
     As shown in  FIG. 1 , a shoulder joint enables a flexion/extension motion in which the upper arm is rotated relative to the torso about a flexion/extension axis da, an adduction/abduction motion in which the upper arm is rotated relative to the torso about an adduction/abduction axis db, and an internal/external rotation motion in which the upper arm is rotated relative to the torso about an internal/external rotation axis dc. Further, as will be mentioned later, the muscular strength assisting apparatus  10  shown assists in retaining the upper arm at a predetermined position so as to prevent the upper arm from coming down and further assists a flexion motion in which the upper arm is lifted forward. At the same time, as will be described later, the muscular strength assisting apparatus  10  is devised so as not to restrict the adductor and abduction rotational motions and the internal and external rotation motions of the upper arm. 
     In the illustrated example, the position control device  15  has an output shaft  76  as an output member that outputs the drive force. The output shaft member  76  is rotatable relative to the first attachment tool  20  about the first rotation axis d 1 . The output shaft member  76  is connected to the second attachment tool  25 . The first rotation axis d 1  acting as the rotation axis of the output shaft member  76  is provided so as to correspond to the flexion/extension axis da of a shoulder. The second attachment tool  25  rotates relative to the first attachment tool  20  about the first rotation axis d 1 , thus enabling a flexion motion and an extension motion of the upper arm about the shoulder joint. 
     The muscular strength assisting apparatus according to the present invention is not limited to the example shown and may assist any one or more of a flexion motion, an extension motion, an adduction motion, an abduction motion, an internal rotation motion, and an external rotation motion. 
     With reference to specific examples shown in the drawings, each component will be now described. In  FIGS. 1 to 12  referred to below, in order to facilitate understanding, constituent elements shown in one drawing may be omitted in other drawings. 
     First, a description is given of the first attachment tool  20 . As shown in  FIGS. 1 and 2 , the first attachment tool  20  has a center frame  21  and a side frame  22 . The center frame  21  is provided with a belt holding portion  21   a  to which a fixing belt  11  ( FIGS. 3 to 5 ) is attached. The center frame  21  is attached via the fixing belt  11  to the torso of a wearer, for example, at a position facing the back. The side frame  22  extends outward in a transverse direction from the center frame  21 . The side frame  22  includes a rear frame portion  22   a  connected to the center frame  21  and a front extending frame portion  22   b  extending forward from the lateral outer end of the rear frame portion  22   a.  The rear frame portion  22   a  is disposed at a position facing the shoulder from the rear. The front extending frame portion  22   b  is disposed at a position facing the shoulder from the outer lateral side. The side frame  22  is connected so as to be rotatable relative to the center frame  21  about a third rotation axis d 3 . The third rotation axis d 3  is provided so as to correspond to the internal/external rotation axis dc of the shoulders. The side frame  22  rotates relative to the center frame  21  about the third rotation axis d 3 , thus enabling an internal rotation motion and an external rotation motion of the upper arm about the shoulder joint. 
     The illustrated muscular strength assisting apparatus  10  that assists movements of the upper arm(s), is configured to act on both the upper arms. Specifically, the side frame  22  is provided on each lateral side of the center frame  21 . The transmission means  35  of the position control device  15  and so on are supported on each side frame  22 . In addition, the second attachment tool  25  is provided corresponding to each side frame  22 . A pair of elements provided respectively at each side of the center frame  21  are disposed symmetrical to each other and yet may be configured in the same manner in other respects. Therefore the following description and  FIG. 3  to  FIG. 12  are based on a configuration in which the muscular strength assisting apparatus  10  acts on the right shoulder. 
     Furthermore, the terms used herein, such as “front,” “rear,” “upper,” “lower,” and “a transverse direction,” are assumed to refer to corresponding directions “front,” “rear,” “upper,” “lower,” and “a transverse direction” with reference to the wearer wearing the muscular strength assisting apparatus  10 . Moreover, a “width direction” herein refers to the “transverse direction.” 
     Next, a description is given of the second attachment tool  25 .  FIG. 3  shows the second attachment tool  25  from the front side (anterior view). The second attachment tool  25  is connected to the output shaft member  76  of the transmission means  35 , which will be detailed later. As the output shaft member  76  rotates, the second attachment tool  25  rotates about the first rotation axis d 1  that is the rotation axis of the output shaft member  76 . The second attachment tool  25  has the attachment portion  26  attached to the human body, an working portion  28  fixed to the output shaft member  76 , and a coupling portion  27  coupling the attachment portion  26  and the working portion  28 . The working portion  28  receives a force generated by the drive means  30  from the output shaft member  76  that is disposed at the most downstream (closest to the output) of the transmission means  35 . The coupling portion  27  couples the working portion  28  to the attachment portion  26  such that attachment portion  26  rotates relative to the first attachment tool  20  as the output shaft member  76  rotates relative to the first attachment tool  20 . 
     In the example shown, the attachment portion  26  is attached to the upper arm of the human body. In order to efficiently transfer a force supplied from the position control device  15  to the upper arm, preferably, the attachment portion  26  is configured such that its relative movement with respect to the upper arm in a direction of movement caused by rotation about the first rotation axis d 1  is restricted. In particular, when the muscular strength assisting apparatus assists a lifting motion (flexion motion) of an upper arm, it is preferable to effectively restrict a rearward movement of the upper arm relative to the attachment portion  26 . As is well illustrated in  FIG. 3 , the attachment portion  26  includes a belt holding portion  26   a  and an arm belt  26   b  forming a tubular portion into which an upper arm is inserted, and a bracket  26   c  connected to the coupling portion  27 . The belt holding portion  26   a  and the bracket  26   c  are made of, for example, a highly rigid resin molded product or the like. In the illustrated example, the belt holding portion  26   a  and the bracket  26   c  are integrally formed into a single body. As shown in  FIGS. 4 and 5 , the belt holding portion  26   a  is disposed at a position facing the upper arm from the rear. The arm belt  26   b  is made of a flexible belt material and is disposed at a position facing the upper arm mainly from the front. By adjusting the length of the belt holding portion  26   a,  the attachment portion  26  can stably hold the upper arm. 
     In order to transmit the force supplied from the position control device  15  to the attachment portion  26 , the coupling portion  27  connects the attachment portion  26  and the working portion  28  such that the attachment portion  26  and the working portion  28  do not rotate relative to each other about the first rotation axis d 1 . That is, since the second attachment tool  25  receives a rotational force about the first rotation axis d 1  from the position control device  15 , excepting a backlash or elastic deformation of the elements themselves, the working portion  28  that receives the rotational force from the position control device  15  and the attachment portion  26  that exerts an assisting force on the human body are disposed so as not to move relative to each other in the direction of the force input by the position control device  15 , that is, in a circumferential direction around the first rotation axis d 1 . 
     In the illustrated example, the coupling portion  27  is connected to the working portion  28  so as to be rotatable relative to the working portion  28  about the second rotation axis d 2  perpendicular to the first rotation axis d 1 . The second rotation axis d 2  is provided so as to correspond to the internal/external rotation axis db of a shoulder. The coupling portion  27  rotates relative to the working portion  28  about the second rotation axis d 2 , thus enabling the internal rotation motion and the external rotation motion of the upper arm about the shoulder joint. 
     For the purpose of reducing a wearer&#39;s restraint feeling, it is preferable that the coupling portion  27  be configured to couple the attachment portion  26  and the working portion  28  such that the distance between the first rotation axis d 1  and the attachment portion  26  is changeable in projection onto a surface orthogonal to the first rotation axis d 1 . Further, to reduce the wearer&#39;s restraint feeling, the coupling portion  27  is configured to couple the attachment portion  26  and the working portion  28  such that the second attachment tool  25  forms a mechanism having three degrees of freedom between the working portion  28  and the attaching portion  26 . As is well understood from  FIG. 3 , in the illustrated example, the coupling portion  27  includes a first link  27   a  operably coupled to the working portion  28 , and a second link  27   b  operably coupled to the first link  27   a  and the attachment portion  26 . According to this coupling portion  27  thus described, the configuration extending from the working portion  28  to the attachment portion  26  enables actions with three degrees of freedom. In other words, the attachment portion  26  can perform relative movements with three degrees of freedom relative to the working portion  28 . 
     In the example shown in  FIGS. 3 to 5 , the first link  27   a  and the second link  27   b  are connected so as to be rotatable relative to each other about a first coupling rotation axis d 2   a.  The first coupling rotation axis d 2   a  is perpendicular to the first rotation axis d 1  and is parallel to the second rotation axis d 2 . The second link  27   b  and the attachment portion  26  are connected so as to be rotatable relative to each other around a second coupling rotation axis d 2   b.  The first coupling rotation axis d 2   a  is perpendicular to the first rotation axis d 1  and is parallel to the second rotation axis d 2 . 
     Further, as shown in  FIG. 3 , in a plane orthogonal to the second rotation axis d 2 , a connection position mj (hereinafter also referred to as “intermediate connection position”) between the first link  27   a  and the second link  27   b  of the coupling portion  27  is always situated on one side with respect to a virtual straight line vsl that passes through a connection position pj (hereinafter also referred to as “proximal-side connection position”) between the coupling portion  27  and the working portion  28  and a connection position dj (hereinafter also referred to as “distal-side connection position”) between coupling portion  27  and the attachment portion  26 . Particularly in the example shown, structurally, the intermediate connection position mj is set so as to be always on one side with respect to the virtual straight line vsl passing through the proximal end side connection position pj and the distal end side connection position dj. This means that, even in a case where the coupling portion  27  is extended so that both ends thereof are maximally separated from each other, the intermediate connection position mj does not reach to the virtual straight line vsl Further, in the illustrated example, the intermediate connection position mj is located on the same side as the output shaft member  76  with respect to the virtual straight line vsl. As shown in  FIG. 3 , the intermediate connection position mj, together with the output shaft member  76 , is located on an opposite side to the human body with respect to the virtual straight line vsl. According to this configuration, it is possible to effectively avoid a situation where, when the coupling portion  27  is contracted, an intermediate portion of the coupling portion  27  makes contact with the human body. 
     In the example shown in  FIG. 3 , the coupling portion  27  has a biasing member  27   c  that serves as a bias member. The biasing member  27   c  is arranged so as to extend over the first link  27   a  and the second link  27   b.  The biasing member  27   c  lifts the second link  27   b  and the attachment portion  26  to some extent against the weight of the second link  27   b  and the attachment portion  26 , so that the first link  27   a  and the second link  27   b  are maintained in a bent state as illustrated in  FIG. 3 . From the state shown in  FIG. 3 , the coupling portion  27  is capable of bending so as to lengthen the distance between both ends thereof as well as bending so as to shorten the distance. 
     Alternatively, unlike in the example shown, when the coupling portion  27  is maximally extended, the coupling portion  27  may be located on the virtual straight line vsl, or the intermediate connection position mj may be located on either side with respect to the virtual straight line vsl. In the muscular strength assisting apparatus  10  configured as above, preferably, provided that the coupling portion  27  is maximally extended when the muscular strength assisting apparatus  10  is worn on the human body during actual use, the intermediate connection position mj is located on one side with respect to the virtual straight line vsl, particularly, on the same side as the output shaft member  76 , which is an opposite side to the human body. In this case, it is possible to effectively avoid a situation where, during use of the muscular strength assisting apparatus  10 , the intermediate portion of the coupling portion  27  makes contact with the human body. 
     Next, a description is given of the position control device  15 . As described above, the position control device  15  controls the relative positions of the first attachment tool  20  and the second attachment tool  25 . The position control device  15  includes a drive means  30  held by the first attachment tool  20 , a transmission means  35  for transmitting a force output by the drive means  30  to the second attachment tool  25 , and a control unit  16  for controlling the drive unit  30  and the transmission means  35 . The control unit  16  detects a motion of the wearer, for example, by a detection means (not shown) provided in the second attachment tool  25 , and based on the detection result or based on an external input from the wearer or the like as another example, transmits a control signal to control operations of the drive means  30  and the transmission means  35 . 
     First, the drive means  30  will be now described. The drive means  30  includes a so-called actuator to output a force to the transmission means  35 . In the illustrated example, the position control device  15  has an extendable actuator, in other words, a linear actuator  31  whose longitudinal length is changeable. As shown in  FIG. 5 , the actuator  31  is connected, at its one end, to the transmission means  35 . The actuator  31  is connected, at its other end, to an upper end of the side frame  22  (the rear frame portion  22   a ) of the first attachment tool  20 . Depending on the drive force required by the drive means  30 , a plurality of actuators  31  may be provided. 
     An expandable and contractible member under a fluid pressure can be used for the actuator  31 . As one specific example, McKibben artificial muscles known as a fluid pressure-type actuator can be used as the actuator  31 . When formed of McKibben artificial muscles, the actuator  31  is supplied inside with a fluid (typically, a gas) and thus becomes increased in diameter and contracted. As a result of the contraction, the actuator  31  generates a contraction force. In the illustrated example, the drive means  30  has a fluid source (a fluid pressure source)  32  that can supply a fluid to the actuator  31 . As shown in  FIG. 5 , the fluid pressure source  32  configured as, for example, a compressor is supported by the center frame  21  of the first attachment tool  20 . 
     Next, a description is given of the transmission means  35 . The transmission means  35  transmits a force output by the drive means  30  to the second attachment tool  25 . As shown in  FIG. 6 , the transmission means  35  described here includes a switching means  40  for switching between transmission and blocking of the force output by the drive means  30  to the second attachment tool  25 .  FIG. 6  is a perspective view showing the structure of the transmission means  35  together with the actuator  31  and the second attachment tool  25 . In  FIG. 6 , in order to facilitate understanding, the first attachment tool  20  and the like are omitted. 
     The switching means  40  includes a first member  41  and a second member  46 , and functions as a drum brake mechanism  39  as described in detail later. The first member  41  is supported by the side frame  22  of the first attachment tool  20 , in particular, the rear frame portion  22   a,  such that it is rotatable about a first intermediate rotation axis d 1   a.  The second member  46  is connected to one end of the actuator  31  that moves linearly. The first member  41  and the second member  46  can be brought close to each other and separated from each other. That is, the first member  41  and the second member  46  are capable of moving away from each other and move towards each other. In particular, in the illustrated example, the first member  41  and the second member  46  can be situated at a relative position spaced apart from one another and a relative position in contact with each other. The first member  41  can rotate without being restrained by the second member  46  at a position separated from the second member  46 . The second member  46  retains the rotational position of the first member  41  while contacting with the first member  41 . In other words, the second member  46  regulates a relative motion, in particular, a relative rotation, between the second member  46  and the first member  41  in a state of being in contact with the first member  41 . 
     In the illustrated example, the first member  41  is coupled to the second attachment tool  25 . Here, coupling of the first member  41  and the second attachment tool  25  means that the first member  41  moves in conjunction with the second attachment tool  25 , more specifically, the second attachment tool  25  moves in accordance with the movement of the first member  41 . Therefore, by adjusting the relative position between the first member  41  and the second member  46 , it is possible to maintain an upper arm of the wearer at a predetermined position via the second attachment tool  25 . Further, as will be described later, by rotating the first member  41  together with the second member  46 , it is possible to assist the wearer&#39;s upper arm&#39;s motion via the second attachment tool  25 . 
     A specific configuration of the switching unit  40  will be described later, and elements other than the switching means  40  of the transmission means  35  will be firstly described with reference mainly to  FIG. 6 . In the example shown in  FIG. 6 , the transmission means  35  includes, in addition to the switching means  40 , a first relay shaft member  71  connected to the first member  41  of the switching means  40 , a second relay shaft member  73  moving in conjunction with the first relay shaft member  71 , and the output shaft member  76  moving in conjunction with the second relay shaft member  73 . 
     The first relay shaft member  71  is held by the rear frame portion  22   a,  which is a part of the side frame  22  of the first attachment tool  20 . The first relay shaft member  71  is disposed rotatably about the first intermediate rotation axis d 1   a.  The first member  41  is fixed to the first relay shaft member  71 . Thus, the first member  41  is supported by the rear frame portion  22   a  of the side frame  22  and rotates about the first intermediate rotation axis d 1   a  in synchronization with the first relay shaft member  71 . A first transmission gear  72  is fixed to the first relay shaft member  71 . The first transmission gear  72  is, for example, a spur gear. 
     The second relay shaft member  73  is held by the front extending frame portion  22   b,  which is a part of the side frame  22  of the first attachment tool  20 . The second relay shaft member  73  is disposed rotatably about a second intermediate rotation axis d 1   b.  A second transmission gear  74  is fixed to the second relay shaft member  73 . The second transmission gear  74  is disposed in the vicinity of one end (rear end portion) of the second relay shaft member  73 . The second transmission gear  74  is engaged with the first transmission gear  72 , so that the second relay shaft member  73  is interlocked with the first relay shaft member  71 . The second transmission gear  74  has a configuration corresponding to the first transmission gear  72 , and may be configured as, for example, a spur gear. In the illustrated example, the second intermediate rotation axis d 1   b,  which is the rotation axis of the second relay shaft member  73 , is disposed parallel to the first intermediate rotation axis d 1   a  which is the rotation axis of the first relay shaft member  71 . A third transmission gear  75  is fixed in the vicinity of the other end (front end portion) of the first relay shaft member  71 . Although not shown, the third transmission gear  75  is configured as, for example, a helical gear. 
     Similarly to the second relay shaft member  73 , the output shaft member  76  is held by the front extending frame portion  22   b.  As described above, the output shaft member  76  is held so as to be rotatable about the first rotation axis d 1 . A fourth transmission gear  77  is fixed to the output shaft member  76 . The fourth transmission gear  77  is disposed in the vicinity of one end (outer end portion) of the output shaft member  76 . The fourth transmission gear  77  is threadably coupled with the third transmission gear  75  thereby the output shaft member  76  moves in conjunction with the second relay shaft member  73 , the first relay shaft member  71 , and the first member  41  of the switching means  40 . The fourth transmission gear  77  has a configuration corresponding to the third transmission gear  75 , and may be configured as, for example, a spur gear. In the illustrated example, the first intermediate rotation axis d 1   b,  which is the rotation axis of the output shaft member  76 , is disposed perpendicular to the second intermediate rotation axis d 1   b  which is the rotation axis of the second relay shaft member  73  with some offset in the height direction. The other end (inner end portion) of the output shaft member  76  is fixed to the working portion  28  of the second attachment tool  25 . 
     Next, with reference mainly to  FIGS. 7 to 9 , details of the switching means  40  will be described. In the illustrated example, the switching means  40  is held on the side frame  22  as shown in  FIG. 4 . The switching means  40  is disposed on the side opposite to the human body side of the side frame  22 , that is, on the rear side of the side frame  22 . As shown in  FIG. 4 , the switching means  40  is situated behind the output shaft  76  that is disposed on the most downstream side of the transmission means  35  and is situated on the rear side of the shoulder joint of the wearer wearing the muscular strength assisting apparatus  10 . 
     First, a description is given of the first member  41 . Referring to  FIG. 7 , the first member  41  includes a rotary drum  42  fixed to the first relay shaft member  71 . The rotary drum  42  has a disk-like outer diameter, and the central axis of the rotary drum  42  is situated on the first intermediate rotation axis d 1   a  which is the rotation axis of the first relay shaft member  71 . The rotary drum  42  is held by the rear frame portion  22   a  of the side frame  22  via the first relay shaft member  71 . The plate face of the rotary drum  42  is aligned with the planar direction of the rear frame portion  22   a.  Therefore, it is possible to effectively prevent the rotating drum  42  from largely protruding out from the body of the wearer. The rotary drum  42  has a friction layer  42   a  on its surface. The friction layer  42   a  is a portion supposed to contact with the second member  46  which will be hereunder described. The friction layer  42   a  may be formed of rubber or the like that generates a large friction force between itself and the second member  46 . 
     Next, the second member  46  and configurations related to the second member  46  and will be described. As shown in  FIGS. 7 to 9 , the second member  46  includes a first swing member  47   a  and a second swing member  47   b.  The first swing member  47   a  is connected to the actuator  31  via the bracket  48   b.  Further, the switching means  40  has a pair of support members  50  formed in a plate shape. The second member  46  (the swing members  47   a,    47   b ) is movably supported by the pair of support members  50 , more specifically, swingably supported. As shown in  FIG. 4 , the pair of support members  50  are arranged in a direction parallel to the first intermediate rotation axis d 1   a,  and the rotation drum  42  and the pair of swing members  47   a,    47   b  are disposed between the pair of support members  50 . The rotary drum  42  is rotatable relative to the support members  50  about the first intermediate rotation axis d 1   a.  That is, the rotary drum  42  is rotatable relative to the support members  50  between the pair of support members  50 . In  FIGS. 7 to 9 , the support member  50  on the near side is omitted. 
     As shown in  FIGS. 7 to 9 , the swing members  47   a  and  47   b  each have an arcuate outer shape. The swing members  47   a,    47   b  are each swingable relative to the support members  50  about one end portion thereof. The swinging axes of the swing members  47   a,    47   b  are parallel to the first intermediate rotation axis d 1   a.  In the space between the pair of support members  50 , the rotary drum  42  is disposed between the pair of swing members  47   a,    47   b.  The swing members  47   a,    47   b  face the rotary drum  42  of the first member  41  from an outer side in the radial direction about the first intermediate rotation axis d 1   a.  A large part of an outer peripheral surface of the rotary drum  42  is covered by the pair of swing members  47   a,    47   b.  The swing members  47   a,    47   b  swing relative to the support members  50  and thus can come in contact with the rotary drum  42  from the outer side in the radial direction about the first intermediate rotation axis d 1   a.  In this way, the first member  41  and the second member  46  form the drum brake mechanism  39 . The swinging members  47   a,    47   b  included in the second member  46  has an arcuate body portion  48  and a friction body  49  that forms a second contact surface  46   a  contacting with the first member  41 . The friction body  49  makes contact with the friction layer  42   a  of the rotary drum  42  and thus generates a friction force between itself and the friction layer  42   a.  The friction layer  42   a  is formed of a material that produces a sufficient frictional force, for example, rubber or the like. 
     Further, in the illustrated example, the switching means  40  further includes a bias member  52  as biasing means for urging the swing members  47   a,    47   b  to separate from the rotating drum  42 . The bias member  52  is disposed between a support base  51  fixed to the support member  50  and a bracket  48   c  of the respective swing members  47   a,    47   b.  In the illustrated example, the bias member  52  is formed by a tension spring. 
     Further, the body portion  48  including the swing members  47   a,    47   b  has timing gears  48   a.  Swinging motions of the pair of swing members  47   a,    47   b  are adjusted by the timing gears  48   a.  More specifically, the pair of timing gears  48   a  are engaged with each other and thereby the pair of swing members  47   a  and  47   b  are moved synchronously and symmetrically with respect to the rotating drum  42 . Therefore, when the first swing member  47   a  is in contact with the rotary drum  42  by an action of the actuator  31 , the second swing member  47   b  also contacts the rotary drum  42 . When the first swing member  47   a  is separated from the rotary drum  42  by an action of the actuator  31 , the second swing member  47   b  is also separated from the rotary drum  42 . 
     In the illustrated example, the support member  50  is supported by the rear frame portion  22   a  which is a part of the side frame  22  of the first attachment tool  20 . Here, the support member  50  is rotatable relative to the rear frame portion  22   a.  More specifically, the support member  50  is held rotatably relative to the first relay shaft member  71  about the first intermediate rotation axis d 1   a  and consequently it is rotatable relative to the rear frame portion  22   a.  Therefore, the second member  46  supported by the support member  50 , the support base  51  fixed to the support member  50  and the like are not fixed to the first attachment tool  20 , but they are rotatable relative to the first attachment tool  20  about the intermediate rotation axis d 1   a.    
     At the same time, the switching means  40  further includes an adjusting means  37  for restricting free rotations of the support members  50  and the second member  46 . A balance between the force supplied from the adjusting means  37  and the force supplied from the drive means  30  is used to control the states of the first member  41 , the second member  46 , and the support members  50 . In the illustrated example, the adjusting means  37  is formed as a bias member  38  for urging the support members  50  and the second member  46  in one direction. One end of the bias member  38  is attached to the rear frame portion  22   a  of the side frame  22  and the other end is attached to the bracket  48   c  of the second swing member  47   b.  In the illustrated example, the bias member  38  is formed by a tension spring which serves as the biasing means. 
     In the illustrated position control device  15 , when the actuator  31  contracts from the state shown in  FIG. 7 , the actuator  31  draws the first swing member  47   a  that forms the second member  46  as shown in  FIG. 8 . As a result, the pair of swing members  47   a,    47   b  abut against the rotary drum  42  that forms the first member  41 . In the state shown in  FIG. 8 , the second member  46  retains the first member  41 , and thus relative rotation between the second member  46  and the first member  41  is restricted. At this time, the force applied by the actuator  31  is smaller than the biasing force by the bias member  38  that serves as the adjusting means  37 . That is, the force required to swing the swing members  47   a,    47   b  included in the second member  46  relative to the support members  50  is higher than the force required to rotate the support members  50  relative to the first attachment tool  20 . Therefore, before the support members  50  rotate relative to the first attachment tool  20 , the swing members  47   a,    47   b  that form the second member  46  swing relative to the support members  50 . 
     When the actuator  31  further contracts from the state shown in  FIG. 8 , the actuator  31  tries to further draw the first swing member  47   a.  When the force output by the actuator  31  becomes larger than the biasing force generated by the bias member  38  that forms the adjusting means  37 , the actuator  31  rotates the support members  50  relative to the first attachment tool  20  against the biasing force, thereby further drawing the first swing member  47   a  as shown in  FIG. 9 . That is, the force output by the actuator  31  is larger than the force required to rotate the support members  50  relative to the first attachment tool  20 . As a result, the second member  46  rotates about the first intermediate rotation axis d 1   a  together with the support members  50  and the like. At this time, the first member  41  contacts the second member  46 , and its rotation relative to the second member  46  is restricted. Therefore, the first member  41  rotates about the first intermediate rotation axis d 1   a  in synchronization with the second member  46 . 
     Movements of the drive means  30  is controlled by the control unit  16 . In the example shown in  FIG. 1 , the control unit  16 , together with the fluid source  32 , is supported by the center frame  21  of the first attachment tool  20 . The control unit  16  controls operation of the actuator  31  by controlling supply of fluid (for example, air) from the fluid source  32  to the actuator  31  and discharge of the fluid from the actuator  31 . 
     Next, a description is given of an operation of the muscular strength assisting apparatus  10  having the above-described configuration. 
     As shown in  FIG. 1 , first, the center frame  21  of the first attachment tool  20  is attached to the torso by using the attachment belt  11 . Furthermore, the attachment portion  26  of the second attachment tool  25  is attached to the upper arm. 
     The illustrated muscular strength assisting apparatus  10  may be maintained in either the free rotation mode shown in  FIG. 7 , the rotation restrained mode shown in  FIG. 8 , or the rotation drive mode shown in  FIG. 9 . 
     First, in the free rotation mode shown in  FIG. 7 , a fluid inside the actuator  31  is discharged, and thus the actuator  31  is extended. Therefore, the swing members  47   a,    47   b  of the second member  46  are not subjected to a force generated by the actuator  31  toward the rotary drum  42  that forms the first member  41 . On the other hand, the swing members  47   a,    47   b  included in the second member  46  are urged by the bias member  52  in a direction away from the rotary drum  42  that forms the first member  41 . Thus, in the free rotation mode, rotation of the first member  41  about the first intermediate rotation axis d 1   a  is not restricted by the second member  46 , and the first member  41  can freely rotate about the first intermediate rotation axis d 1   a.    
     It is to be noted that the second member  46  and the support members  50  supporting the second member  46  receive a force that makes them rotate in the clockwise direction in  FIG. 7  by the biasing force (pulling force) of the bias member  38  which serves as the adjusting means  37 . However, the force supplied by the adjusting means  37  mainly affects the rotation of the second member  46  and the support members  50  relative to the first attachment tool  20 , and less influences the swinging of the second member  46  relative to the support members  50 . Therefore, in the free rotation mode, the first member  41  and the second member  46  are separated from each other. 
     In the free rotation mode, the second attachment tool  25  that moves in conjunction with the first member  41  is freely rotatable with respect to the first attachment tool  20 . Thus, the wearer of the muscular strength assisting apparatus  10  can freely rotate the upper arm with respect to the torso about the first rotation axis d 1 , the attachment portion  26  of the second attachment tool  25  being mounted to the upper arm. That is, the wearer can perform a flexion motion and an extension motion without being restrained by the muscular strength assisting apparatus  10 . 
     Next, in the rotation restrained mode shown in  FIG. 8 , a fluid is supplied from the fluid source  32  into the actuator  31 , and thus the actuator  31  is contracted. As the actuator  31  contracts, the drive means  30  acts on the first swing member  47   a  raw the first swing member  47   a.  Referring  FIG. 8 , the force applied by the actuator  31  to the first swing member  47   a  causes the first swing member  47   a  to move toward the rotary drum  42  of the first member  41 . Referring again to  FIG. 8 , the second contact surface  46   a  formed of the friction body  49  of the swing members  47   a,    47   b  contacts the first contact surface  41   a  formed of the friction layer  42   a  provided as the outer circumferential surface of the rotary drum  42 . The second member  46  holds the first member  41  by utilizing the friction force between the friction body  49  and the friction layer  42   a.  In this manner, the relative rotation between the second member  46  and the first member  41  is restricted, and as a result, rotations of the rotary drum  42  and the output shaft member  76  are restricted. 
     In the rotation braking mode, relative rotation of the second attachment tool  25  with respect to the first attachment tool  20  is restricted. For example, the muscular strength assisting apparatus  10  assists in maintaining the lifted upper arm at the lifted position and thus can effectively prevent the upper arm from being lowered. Although the second member  46  is connected to the adjusting member  37  and the drive means  30 , the second member  46  is still rotatable relative to the first attachment tool  20  together with the support members  50 . Thus, the wearer can further lift the upper arm from the state shown in  FIG. 6  by rotating the support members  50  against the biasing force of the adjusting means  37 . 
     In the rotation drive mode shown in  FIG. 9 , a fluid is further supplied from the fluid source  32  into the actuator  31 , and thus the actuator  31  is further contracted. As the actuator  31  is further contracted, the drive means  30  further draws the first swing member  47   a.  While the first swing member  47   a  is brought in contact with the rotary drum  42 , a force exerted from the actuator  31  on the swing member  47   a  causes the support member  50  to rotate against the biasing force of the adjusting means  37 , and the second member  46  is rotated together with the first member  41  about the first intermediate rotation axis d 1   a.  In  FIG. 9 , in a state where relative rotation between the second member  46  and the first member  41  is restricted, the second member  46  and the first member  41  rotate counterclockwise in synchronization with each other. 
     In the rotation drive mode, the second attachment tool  25  is driven to rotate relative to the first attachment tool  20  in conjunction with the rotation of the first member  41 . That is, the muscular strength assisting apparatus  10  assists, for example, to lift the upper arm. 
     To end the rotation drive mode, the drive means  30  stops applying a drive force that causes the second attachment tool  25  to rotate relative to the first attachment tool  20 . At this time, the drive means  30  may continue to supply a drive force that restricts the relative rotation between the first member  41  and the second member  46 . That is, after ending the rotation drive mode, a transition may be made to the rotation braking mode instead of the free rotation mode. 
     Meanwhile, the shoulder joint enables motions of the upper arm with respect to the torso about more than one axis. Therefore, not only the flexion/extension motion of the upper arm about the flexion/extension axis da of which the muscle force is assisted by the muscular strength assisting apparatus, but also the adduction/abduction motion of the upper arm around about the adduction/abduction axis db and the internal/external rotation motion of the upper arm around the internal/external rotation axis dc are also possible. Therefore, in a state where the muscular strength assisting apparatus is worn by the wearer, some of the components of the muscular strength assisting apparatus are situated within the movable range of the upper arms, especially within the movable range of the upper arm of which muscle force is not assisted by the apparatus, which may hamper motions of the upper arm. 
     In this respect, according to the embodiment, the muscular strength assisting apparatus  10  includes the drive means  30  held by the first attachment tool  20  mounted on the torso of a wearer, and the transmission means  35  for transmitting a force output by the drive means  30  to the second attachment tool  25  mounted on an upper arm of the wearer. The transmission means  35  has the output shaft member  76  connected to the second attachment tool  25 , and the switching means  40  capable of switching between transmission and interruption of the force from the drive means  30  to the output shaft member  76 . The switching means  40  is configured to be situated on the rear of the output shaft member  76 . Generally, a movable range of the upper arm in the flexion/extension motion, the adduction/abduction motion, and the internal/external rotation motion largely extends in the front, downward, and laterally inward of the shoulder joint. Therefore, among the components of the muscular strength assisting apparatus  10 , by disposing the switching means  40 , which tends to be made relatively large in size, on the rear, upper, or laterally outer side of the output shaft member  76 , it is possible to effectively prevent the switching means  40  from obstructing not only muscular force assisted motions but also unassisted motions of the arms. Therefore, according to the embodiment described above, the switching means  40  is situated on the rear side of the output shaft member  76 , and it is possible to avoid that the switching means  40  largely enters the movable range of the upper arm. In this way, it is possible to reduce the restrictions imposed on the wearer by attaching the muscular strength assisting apparatus  10  according to the embodiment. Further, the switching means  40  disposed on the rear side can be placed not in a position distant from the wearer but, for example, in the vicinity of the back of the wearer. In this case, since an inertial force generated during the operation of the switching means  40  can be effectively reduced, the attachment state of the muscular strength assisting apparatus  10  to the back of the wearer is stabilized, whereby the muscular strength assisting force can be stably and effectively applied on the wearer by using the muscular strength assisting apparatus  10 . 
     Further, according to the embodiment, the muscular strength assisting apparatus  10  includes the drive means  30  held by the first attachment tool  20  mounted on the torso of a wearer, and the switching means  40  capable of switching between transmission and interruption of the force output by the drive means  30  to the second attachment tool  25  mounted on an upper arm of the wearer. The switching means  40  is configured to be situated on the rear side of the output shaft member  76 . As described above, the shoulder joint situated between the torso to which the first attachment tool  20  is attached and the upper arm to which the second attachment tool  25  is attached enables motions of the upper arm relative to the torso about the axes da, db, dc, more specifically, the flexion/extension motion, the adduction/abduction motion, and the internal/external rotation motion. In many cases of such motions, a movable range of the upper arm extends in the forward, downward, and laterally inward of the shoulder joint. Therefore, by disposing the switching means  40 , which tends to be made relatively large in size, on the rear, upper, or laterally outer side of the shoulder joint, it is possible to effectively prevent the switching means  40  from obstructing not only muscular force assisted motions but also unassisted motions of the arms. According to the embodiment described above, it is possible to reduce the limitation to which the wearer is subjected. 
     Furthermore, according to the embodiment, the first attachment tool  20  includes the center frame  21  attached to the torso of the wearer at a position facing the back of the wearer, and the side frame  22  rotatable relative to the center frame  21 . The switching means  40  is supported by the side frame  22 . According to this configuration, the switching means  40  can move together with the side frame  22  in accordance with motions of the shoulder (for example, the adduction/abduction motion) other than the motion whose muscle force is assisted (the flexion motion, in the above example). Therefore, even when the upper arm performs a motion different from the motion to be assisted, it is still possible to maintain the relative positional relationships of the components from the switching means  40  to the output shaft member  76  connected to the second attachment tool  25 . Consequently, it is possible to more stably transmit a muscular strength assisting force to the second attachment tool  25  via the transmission means  35  including the switching means  40 . In addition, the switching means  40  can move in accordance with a motion of the upper arm as the side frame  22  supporting the switching means  40  rotates relative to the center frame  21 . Therefore, it is possible to more effectively prevent the switching means  40  from obstructing motions of the upper arm. 
     Furthermore, according to the embodiment, the portion of the drive means  30  connected to the transmission means  35  is supported by the side frame  22 . That is, according to this configuration, since the portion of the drive means  30  connected to the transmission means  35  and the transmission means  35  are both supported by the side frame  22 , it is possible to stably output an assisting force from the drive means  30  to the position control device  15  without being affected by the relative rotation between the side frame  22  and the center frame  21 . This makes it possible to more stably transmit the muscular strength assisting force from the drive means  30  to the second attachment tool  25  via the transmission means  35 . 
     Furthermore, according to the embodiment, the transmission means  35  includes the second relay shaft member  73  disposed between the output shaft member  76  and the switching means  40  along the force transmission path. The second relay shaft member  73  is rotatable about the rotation axis d 1   b  that is not parallel to the rotation axis d 1  of the output shaft member  76 , in particular, perpendicular to the rotation axis d 1 . By providing the second relay shaft member  73  as described above, it is possible to more effectively prevent the switching means  40  from interfering with the upper arm in motion. 
     Furthermore, according to the embodiment, the switching means  40  includes the first member  41  coupled to the second attachment tool  25 , and the second member  41  coupled to the drive means  30  and capable of moving close to and away from the first member  41 . The first member  41  is held so as to be rotatable relative to the first attachment tool  20 . The second member  46  is configured to be contactable with the first member  41  from the radial direction about the rotation axis d 1   a  of the first member  41 . The switching means  40  can function as the drum brake mechanism  39 . In this switching unit  40 , when the diameter of the first member  41  is increased, a friction force generated between the first member  41  and the second member  46  can be increased and thereby it is possible to more reliably transmit the force. In the embodiment, since the disposition of the switching means  40  is well considered, even if the first member  41  has a large diameter, it is possible to effectively prevent the switching means  40  from interfering with the upper arm in motion. Therefore, the disposition of the switching means  40  described herein is suitable for the switching means  40  that includes the first member  41  and the second member  46 . 
     While the foregoing description has been made based on one embodiment illustrating the present invention, the present invention is not limited thereto and can be implemented in various other aspects. The following describes one modification example. In the following description, parts that can be configured similarly to those in the foregoing embodiment are denoted by the same reference characters as those used for corresponding parts in the foregoing embodiment, and duplicate descriptions thereof are omitted. 
     In the above-described embodiment, the switching means  40  is disposed on the rear side of the output shaft member  76 , and the switching means  40  is situated behind the shoulder joint. As described above, the shoulder joint situated between the torso to which the first attachment tool  20  is attached and the upper arm to which the second attachment tool  25  is attached enables motions of the upper arm relative to the torso about the axes da, db, dc, more specifically, the flexion/extension motion, the adduction/abduction motion, and the internal/external rotation motion. In many cases of such motions, a movable range of the upper arm extends in the forward, downward, and laterally inward of the shoulder joint. Therefore, in addition to placing the switching means  40  on the rear side of the output shaft member  76  or the shoulder joint, or instead of placing the switching means  40  on the rear side of the output shaft member  76  or the shoulder joint, the switching means  40  may be placed on the upper or outer side of the output shaft member  76  or the switching means  40  may be placed above or on laterally outer side of the shoulder joint. Even in this modification example, in the same manner as the above-described embodiment, it is possible to effectively prevent the switching means  40  from obstructing not only muscular force assisted motions but also unassisted motions of the arm. In this way, it is possible to reduce restraint on motions of the arm of the wearer who wears the muscular strength assisting apparatus  10 . 
     In order to dispose the switching means  40  above or on the laterally outer side of the output shaft member  76  or the shoulder joint, for example, in the above-described embodiment, a force transmission belt member or the like may be provided between the first relay shaft member  71  and the second relay shaft member  73  to secure the drive force transmission, and the first relay shaft member  71  may be then shifted to the upper side or laterally outer side together with the actuator  31  and the switching means  40 .  FIGS. 10 to 12  show another example of the muscular strength assisting apparatus  10 . In the examples shown in  FIGS. 10 to 12 , the switching means  40  is disposed on the laterally outer side of the output shaft member  76  and the shoulder joint. In the muscular strength assisting apparatus  10  shown in  FIGS. 10 to 12 , the position control device  15  has the switching means  40  that includes the first member  41  and the second member  46 , and the output shaft member  76  connected to the first member  41  of the switching means  40  such that it is unrotatable relative to the first member  41 . The first member  41  is rotatable about the first rotation axis d 1 . Further, the second member  46  is swingable about the swing axis parallel to the first rotation axis d 1 . Further, the actuator  31  connected to the second member  46  and the adjusting means  37  are both disposed in the plane orthogonal to the first rotation axis d 1  together with the switching means  40 . 
     The foregoing embodiment has described the specific configuration of the switching means  40  merely as an example. While the foregoing embodiment has shown the example in which the second member  46 , together with the first member  41 , constitutes the drum brake mechanism  39 , and the swing members  47   a,    47   b  of the second member  46  are brought into contact with the rotary drum  42  of the first member  41  from the radially outer side, there is no limitation thereto. Alternatively, the rotary drum  42  may be formed in a barrel shape, and the first member  41  disposed inside the rotary drum  42  comes in contact with the rotary drum  42  from radially inner side so as to restrict the relative rotation between the first member  41  and the second member  46 . Furthermore, the switching means  40  is configured as a ratchet mechanism, and the switching means  40  may be rotated together with the first member  41  by a drive force of the drive means  30  while rotation of the switching means  40  relative to the first member  41  is restricted. 
     Furthermore, in the above-described embodiment, the drive means  30  of the muscular strength assisting apparatus  10  has the fluid source  32  for driving the actuator  31 , but the invention is not limited to this example. As the fluid source for driving the actuator  31 , the power used in a factory or the like where the muscular strength assisting apparatus  10  is used may be utilized. 
     The foregoing embodiment has described the specific configuration of the drive means  30  merely as an example. In the above-described embodiment, the drive means  30  applies a force that pulls the second member  46  to the second member  46  (the first swing member  47   a ), so that the second member  46  is brought in contact with the first member  41 . However, it is not limited to this. Alternatively, the second member  46  may be brought into contact with the first member  41  by applying a force that pushes out the second member  46  to the second member  46  (the first swing member  47   a ). In principle, it is possible to use various actuators as the drive means  30  without limiting to the drive means  30  having the above-described actuator  31 . 
     Furthermore, in the above-described embodiment, the example in which the first member  41  and the second member  46  are brought close to each other and separated from each other is realized by a swinging movement of the second member  46 , but this is not only an example. For example, such relative movements between the first member  41  and the second member  46  may be realized by causing the second member  46  to perform a motion other than swinging movement. Alternatively, by moving the first member  41  instead of the second member  46 , the first member  41  and the second member  46  may be brought close to each other and separated from each other, or by moving both the second member  46  and the first member  41 , they may be brought close to each other and separated from each other. 
     Furthermore, while the foregoing embodiment has shown an example in which, in the rotation drive mode, the muscular strength assisting apparatus  10  assists only an action of lifting an arm upward and does not assist an action of lowering the arm, there is no limitation thereto, and the muscular strength assisting apparatus  10  may be configured to assist an action of lowering an arm in the rotation drive mode. For example, while the foregoing embodiment has shown an example in which the adjusting means  37  that is formed of the bias member  38  is provided between the second member  46  and the first attachment tool  20 , there is no limitation thereto. Alternatively an auxiliary actuator that serves as the adjusting means  37  can be used in place of the bias member  38 . According to this modification example, depending on a magnitude of a force acting on the second member  46  from the drive means  30  and a magnitude of a force acting on the second member  46  from the auxiliary actuator  62 , the position at which the second member  46  remains still with respect to the first attachment tool  20  together with the rotary member  41  can be controlled with a higher degree of freedom. That is, a position at which the second attachment tool  25  is secured with respect to the first attachment tool  20  can be adjusted with a higher degree of freedom. Furthermore, it becomes also possible to assist in lowering an upper arm. 
     While several modification examples with respect to the foregoing embodiment have thus been described, needless to say, plural ones of these modification examples can be combined as appropriate, and such combinations are also applicable to the present invention.