Patent Publication Number: US-11654546-B2

Title: Arm supporting exoskeleton with a variable force generator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/997,742, filed on 2020 Aug. 19, which is a continuation of U.S. patent application Ser. No. 16/834,647, filed on 2020 Mar. 30, and issued as U.S. Pat. No. 10,786,896 on 2020 Sep. 29, which is a continuation of U.S. patent application Ser. No. 16/455,899, filed on 2019 Jun. 28, and issued as U.S. Pat. No. 10,639,785 on 2020 May 5, which is a continuation of U.S. patent application Ser. No. 16/242,875, filed on 2019 Jan. 8, and issued as U.S. Pat. No. 10,391,627 on 2019 Aug. 27, which claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/614,841, filed on 2018 Jan. 8. 
     U.S. patent application Ser. No. 16/242,875 is also a continuation-in-part (CIP) application, claiming priority to U.S. patent application Ser. No. 16/157,417, filed on 2018 Oct. 11, and issued as U.S. Pat. No. 10,369,690 on 2019 Aug. 6, which is a continuation of U.S. application Ser. No. 15/848,487, filed on 2017 Dec. 20, and issued as U.S. Pat. No. 10,124,485 on 2018 Nov. 13. U.S. application Ser. No. 15/848,487 is a continuation of U.S. application Ser. No. 15/158,113, filed on 2016 May 18, and issued as U.S. Pat. No. 9,889,554 on 2018 Feb. 13. U.S. application Ser. No. 15/158,113 claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application 62/162,871, filed on 2015 May 18. All of the above-referenced applications are incorporated herein by reference in their entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure pertains to the art of support devices for the human arm and, more particularly, to an arm support device configured to reduce the moment on a person&#39;s shoulder during arm elevation. The present disclosure is further directed to a variable force generator applied to an arm supporting exoskeleton capable of being selectively transitioned between at least two stiffness rates. Depending on the configuration, these stiffness rates may correspond to high and low stiffness or an on and off mode, wherein on provides a noticeable stiffness, and off provides a substantially small stiffness that just compensates for the mass and friction of the device. 
     BACKGROUND 
     Conventional passive lift devices, mounted to the torso of a person and configured to support the weight of the arm, are not able to automatically cut or substantially reduce assistance when the person intends to rest his/her upper arm at his/her side, or pick a tool from his/her tool belt. Such devices do not provide a sustained range of position where support torque automatically reduces to zero. Except for a few position points, these devices continuously apply lifting forces to a person&#39;s upper arm, potentially inhibiting motion and creating discomfort during non-working postures when assist is not desired. 
     SUMMARY 
     Methods and devices describes herein provide the person a supporting torque to raise his/her upper arm thereby reducing the human shoulder forces and torques required to raise the upper arm. However, when the person intends to rest his/her upper arm at his/her sides or pick a tool from his/her tool belt, the device here automatically reduces the lifting force to zero (or substantially small value) allowing the wearer to move her/his upper arm freely. During non-working postures, zero (or substantially small) torque is desired to allow free motion of person&#39;s upper arm or to allow person&#39;s upper arm to rest without the impedance of an applied torque from the assist device. This creates a greater overall comfort for person during non-working postures. 
     In embodiments, an arm supporting exoskeleton configured to be coupled to a person comprises: a shoulder base configured to be coupled to a trunk of the person; and an arm link mechanism configured to be coupled to the shoulder base. The arm link mechanism comprises: a proximal link and a distal link configured to rotate relative to each other about a rotating joint and along a first rotational axis substantially orthogonal to a gravity line when the person is standing upright; at least one arm-coupler adapted to couple an upper arm of the person to the distal link; a tensile force generator coupled to the proximal link at a first end of the tensile force generator and coupled to the distal link at a second end of the tensile force generator, the tensile force generator providing a torque to flex the distal link relative to the proximal link; and a protrusion located substantially at the rotating joint. When the distal link extends pasta toggle angle, the protrusion constrains the tensile force generator, and the torque provided by the tensile force generator remains substantially small, and when the protrusion does not constrain the tensile force generator, the torque has the tendency to flex the distal link relative to the proximal link, thereby reducing human shoulder forces and torques required to raise the upper arm of the person. 
     In embodiments, an arm supporting exoskeleton configured to be coupled to a person comprises: a shoulder base configured to be coupled to a trunk of the person; and an arm link mechanism configured to be coupled to the shoulder base. The arm link mechanism comprises: a proximal link and a distal link configured to rotate relative to each other about a rotating joint and along a first rotational axis substantially orthogonal to a gravity line when the person is standing upright; at least one arm-coupler adapted to couple an upper arm of the person to the distal link; and a tensile force generator coupled to the proximal link at a first end of the tensile force generator and coupled to the distal link at a second end of the tensile force generator, the tensile force generator providing a torque to flex the distal link relative to the proximal link. When the arm support exoskeleton is coupled to the person and an angle between the proximal link and the distal link is smaller than a toggle angle, the torque has the tendency to flex the distal link relative to the proximal link, thereby reducing human shoulder forces and torques required to raise the upper arm of the person and imposing reaction forces and torques on the shoulder base. When the angle between the proximal link and the distal link is larger than the toggle angle, the tensile force generator provides a substantially small torque between the proximal link and the distal link, allowing the person to move the upper arm of the person freely. 
     In one embodiment, a variable force generator is used at the tensile force generator, or torque generator, attached to an arm link mechanism of an arm supporting exoskeleton to create a torque about a rotating joint that allows for elevation of a person&#39;s arm. When a base of the arm supporting exoskeleton is attached to a person&#39;s torso and an arm of the arm supporting exoskeleton is attached to a person&#39;s arm, the torque created from the variable force generator serves to flex the person&#39;s arm and support it against the force of gravity. The variable force generator is configured to create at least two different stiffness rates. When the variable force generator creates a first stiffness, a first torque is applied to the person&#39;s arm that is substantially small and allows the person to flex and extend the upper arm with minimal inhibition from the created first torque throughout the range of motion of person&#39;s arm. When the variable force generator creates a second stiffness, a second torque is applied to the person&#39;s arm that is substantially higher than the first torque mode and serves to support the person&#39;s arm against the forces of gravity. 
     It can be appreciated that while described as a part of an arm supporting exoskeleton, the variable force generator can be applied to create forces and torques across a multitude of joints and in many different applications. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a rear perspective view of an assist device, with a person&#39;s arm outstretched. 
         FIG.  2    is a close-up view of an arm link mechanism. 
         FIG.  3    is a close up rear perspective view of an arm link mechanism. 
         FIG.  4    is a side view of an assist device, wherein a first angle is less than a toggle angle. 
         FIG.  5    is a side view of an assist device, wherein a first angle is greater than a toggle angle. 
         FIG.  6    is a front perspective view of an arm support exoskeleton, including two arm link mechanisms. 
         FIG.  7    is a front view of a person showing frontal plane and width dimensions. 
         FIG.  8    is a back view of a person showing length dimensions. 
         FIG.  9    is a side view of a person showing width dimensions. 
         FIG.  10    is a rear view of a load bearing structure including a back frame and a hip loading belt. 
         FIG.  11    is a rear view of a back frame including an upper frame and a lower frame. 
         FIG.  12    is a rear view of a back frame including a spine frame. 
         FIG.  13    is a rear view of an upper frame and a lower frame including width and depth adjusters. 
         FIG.  14    is a front perspective view of a coupling mechanism including a belt, a chest strap, and an anchor strap. 
         FIG.  15    is rear view of a coupling mechanism including a belt, a chest strap, and an anchor strap. 
         FIG.  16    is a back perspective view of a coupling mechanism including a belt, a chest strap, and an anchor strap. 
         FIG.  17    is a front perspective view of a coupling mechanism including a belt, a shoulder strap, and a sternum strap. 
         FIG.  18    is a rear view of a coupling mechanism including a belt, a shoulder strap, and a sternum strap. 
         FIG.  19    is a back perspective view of a coupling mechanism comprising a belt, a shoulder strap, and a sternum strap. 
         FIG.  20    is a front perspective view of a coupling mechanism including a belt and a vest. 
         FIG.  21    is a rear view of a coupling mechanism including a belt and a vest. 
         FIG.  22    is a back perspective view of a coupling mechanism including a belt and a vest. 
         FIG.  23    is a front perspective view of a coupling mechanism including a vest connected to a safety harness. 
         FIG.  24    is a rear perspective view of a coupling mechanism including a vest connected to a safety harness. 
         FIG.  25    is a rear perspective view of a coupling mechanism including a belt connected to a safety harness. 
         FIG.  26    is a rear perspective close up view of an assist device showing a first rotational axis aligning with a person&#39;s glenohumeral joint. 
         FIG.  27    is a rear view of an assist device showing a first rotational axis aligning with a person&#39;s glenohumeral joint. 
         FIG.  28    is a perspective view of an arm link mechanism including a second rotational axis. 
         FIG.  29    is a rear close up view of the second rotational axis of  FIG.  28    aligning with a person&#39;s glenohumeral joint. 
         FIG.  30    is a perspective view of shoulder bracket connecting a shoulder base to arm link mechanism. 
         FIG.  31    is a perspective view of a shoulder bracket showing an arm link mechanism removed from a shoulder base. 
         FIG.  32    is a perspective view of a shoulder bracket allowing shoulder width adjustment of an arm supporting exoskeleton. 
         FIG.  33    is a perspective view of a shoulder bracket, showing a scapular rotation axis. 
         FIG.  34    is a front perspective view of a person with an arm support exoskeleton in a stowed position. 
         FIG.  35    is a perspective view of an arm supporting exoskeleton in a working position. 
         FIG.  36    is a perspective view of an arm supporting exoskeleton in a stowed position. 
         FIG.  37    is a perspective view of an arm link mechanism containing an arm coupler. 
         FIG.  38    is a perspective view of an arm link mechanism wherein an arm coupler contains an arm rotation joint. 
         FIG.  39    is a perspective view of an arm link mechanism wherein an arm coupler contains a translation joint. 
         FIG.  40    is a section view of an arm coupler containing a translation joint. 
         FIG.  41    is a front view of an arm coupler containing an internal external rotation joint. 
         FIG.  42    is a side section view of a torque generator with an extension spring. 
         FIG.  43    is a schematic of a torque generator. 
         FIG.  44    is an alternative side section view of a torque generator with an extension spring. 
         FIG.  45    is a side section view of a torque generator with a compression spring. 
         FIG.  46    is an alternative side section view of torque generator with compression spring. 
         FIG.  47    is a side section view of a torque generator with an upper bracket in a raised position. 
         FIG.  48    is a side section view of a torque generator with an upper bracket in a lowered position. 
         FIG.  49    is a plot of a torque generator torque profile for two positions of an upper bracket. 
         FIG.  50    is a side section view of a torque generator with a lower bracket in an extended position. 
         FIG.  51    is a side section view of a torque generator with a lower bracket in a retracted position. 
         FIG.  52    is a plot of a torque generator torque profile for two positions of a lower bracket. 
         FIG.  53    is a side section view of torque generator with protrusion where first angle is larger than a toggle angle. 
         FIG.  54    is a close up side section view of a torque generator including a protrusion comprising a joint pin. 
         FIG.  55    is a close up side section view a torque generator including a protrusion that is part of a proximal link. 
         FIG.  56    is a plot of a torque generator torque profile without protrusion. 
         FIG.  57    is a plot of a torque generator torque profile with protrusion. 
         FIG.  58    is a side section view of a torque generator including an offset adjustment joint. 
         FIG.  59    is a side section view of a torque generator showing an offset position increased. 
         FIG.  60    is an exploded perspective view of arm link mechanism showing offset adjustment joint. 
         FIG.  61    is a plot of a torque generator torque profile for two values of an offset adjustment angle. 
         FIG.  62    is an example of a desired torque generator support torque profile compared to an arm weight torque profile. 
         FIG.  63    is an alternative example of a desired torque generator support torque profile compared to an arm weight torque profile. 
         FIG.  64    is an alternative example of a desired torque generator support torque profile compared to an arm weight torque profile. 
         FIG.  65    is a front perspective view of a back frame coupled to a lower extremity exoskeleton. 
         FIG.  66    is a front perspective view of a back frame coupled to a trunk exoskeleton. 
         FIG.  67    is a schematic of a variable force generator. 
         FIG.  68    is an axial section view of a variable force generator. 
         FIG.  69    is an axial section view of a variable force generator creating a first tensile force. 
         FIG.  70    is an axial section view of a variable force generator creating a second tensile force. 
         FIG.  71    is an axial section view of a variable force generator creating a first compressive force. 
         FIG.  72    is a radial section view of a variable force generator with constraining mechanism in first position. 
         FIG.  73    is a radial section view of a variable force generator with constraining mechanism in second position 
         FIG.  74    is a detailed section view of a variable force generator at a transition position with constraining mechanism in a second position. 
         FIG.  75    is a detailed section view of a variable force generator at a transition position with constraining mechanism in a first position. 
         FIG.  76    is a detailed section view of a variable force generator creating a second tensile force. 
         FIG.  77    is a detailed section view of a variable force generator creating a first tensile force. 
         FIG.  78    is an embodiment of a retaining ring type constraining mechanism. 
         FIG.  79    is an embodiment of a rotating type constraining mechanism. 
         FIG.  80    is an alternate embodiment of a rotating type constraining mechanism. 
         FIG.  81    is an embodiment of a hook type constraining mechanism. 
         FIG.  82    is an embodiment of an integrated constraining mechanism. 
         FIG.  83    is an embodiment of a screw type constraining mechanism. 
         FIG.  84    is an embodiment of a clamp type constraining mechanism. 
         FIG.  85    is a close up section view of an embodiment of a constraining mechanism and switch. 
         FIG.  86    is a close up section view of an alternate embodiment of a constraining mechanism and switch. 
         FIG.  87    is a close up section view of an embodiment of a constraining mechanism and wedge element. 
         FIG.  88    is a close up section view of an alternate embodiment of a constraining mechanism and wedge element. 
         FIG.  89    is a section view of a variable force generator configured to create a first torque. 
         FIG.  90    is a section view of a variable force generator configured to create a second torque. 
         FIG.  91    is a section view of an alternate embodiment of a variable force generator configured to create a second torque. 
         FIG.  92    is a section view of variable force generator configured to create a torque at a first transition angle 
         FIG.  93    is a section view of a variable force generator configured to create a torque at a second transition angle. 
         FIG.  94    is a perspective view of a variable force generator as part of an arm supporting exoskeleton. 
         FIG.  95    is a schematic of a first alternate embodiment of a variable force generator with three stiffness settings. 
         FIG.  96    is a section view of a first alternate embodiment of a variable force generator with three stiffness settings 
         FIG.  97    is a schematic of a second alternate embodiment of a variable force generator with three stiffness settings. 
         FIG.  98    is a section view of a second alternate embodiment of a variable force generator with three stiffness settings. 
         FIG.  99    is a schematic of a third alternate embodiment of a variable force generator with three stiffness settings. 
         FIG.  100    is a section view of a third alternate embodiment of a variable force generator with three stiffness settings. 
         FIG.  101    is a schematic of an alternate embodiment of a variable force generator with extension springs. 
         FIG.  102    is a section view of an alternate embodiment of a variable force generator with extension springs generating a second force. 
         FIG.  103    is a section view of an alternate embodiment of a variable force generator with extension springs generating a first force. 
         FIG.  104    is a section view of an alternate embodiment of a variable force generator with extension springs with a hook type constraining mechanism. 
         FIG.  105    is a section view of an alternate embodiment of a variable force generator with extension springs with a rotating type constraining mechanism. 
         FIG.  106    is a schematic of a first alternate embodiment of a variable force generator with series springs. 
         FIG.  107    is a section view of a first alternate embodiment of a variable force generator with series. 
         FIG.  108    is a schematic of a second alternate embodiment of a variable force generator with series springs. 
         FIG.  109    is a schematic of a third alternate embodiment of a variable force generator with series springs. 
         FIG.  110    is a schematic of a fourth alternate embodiment of a variable force generator with series springs. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    depicts an embodiment of arm support exoskeleton  100 , which may be also referred to as an assist device. Arm support exoskeleton  100  comprises shoulder base  102 , which is configured to be coupled to trunk  202  of person  200 . In some embodiments, shoulder base  102  is substantially located behind person  200 , which may be also referred to as a user. Arm support exoskeleton  100  additionally comprises at least one arm link mechanism  104  that is coupled to shoulder base  102 . Arm link mechanism  104  comprises at least proximal link  150  and distal link  152  capable of rotation relative to each other along first rotational axis  154 . In some embodiments, first rotational axis  154  is orthogonal to the gravity line  208  when person  200  in standing upright. The term “gravity line” should be understood to mean the direction in which gravity acts. First joint  151  represents a hinge, where distal link  152  rotates relative to proximal link  150 . Arm support exoskeleton  100  additionally comprises at least one arm coupler  106  that couples upper arm  204  (of person  200 ) to distal link  152  of arm link mechanism  104 . Arm coupler  106  is depicted in  FIG.  2   . Arm support exoskeleton  100  additionally comprises at least one torque generator  108  configured to create torque  280  between proximal link  150  and distal link  152 . A close up view of arm link mechanism  104  is depicted in  FIG.  3   . Torque  280  in  FIG.  1    and  FIG.  3    shows the torque imposed on distal link  152  from proximal link  150 . As shown in  FIG.  4   , first angle  193  represents an angle between proximal link  150  and distal link  152 . When first angle  193  is smaller than toggle angle  195 , as depicted in  FIG.  4   , torque generator  108  generates torque  280  that has the tendency to flex distal link  152  relative to proximal link  150 . The term “toggle angle” should be understood to mean the angle between a first position (e.g., arm is raised) in which proximal link  150  and distal link  152  are collinear, and a second position (e.g., arm is lowered) in which the proximal link  150  and distal link  152  become collinear. The term “flex” should be understood to mean a movement of distal link  152  resulting in the decrease of first angle  193 , while the term “extend” as used herein should be understood to mean a movement of distal link  152  resulting in the increase of first angle  193 . The torque  280  produces supporting force  212  (shown in  FIG.  2    and  FIG.  4   ) onto upper arm  204  by arm coupler  106 . This reduces the human shoulder forces and torques required to raise upper arm  204  and imposes set reaction force  214  and reaction torque  215  on shoulder base  102 . 
     When angle  193  is larger than toggle angle  195  as depicted in  FIG.  5   , torque generator  108  provides a substantially small torque between proximal link  150  and distal link  152 . The term “substantially small torque” should be understood to mean a torque value which does not cause substantial inhibition or discomfort of upper arm  204 . This allows person  200  to move her/his upper arm  204  freely. In the Example shown in  FIG.  5   , when upper arm  204  (of person  200 ) is lowered, a position of distal link  152  moves past a position of collinear alignment with proximal link  150 , and torque generator  108  provides substantially small torque between proximal link  150  and distal link  152  such that the person can easily maneuver their upper arm  204  in this lowered position. 
       FIG.  6    depicts another embodiment of arm support exoskeleton  100  including two arm link mechanisms  104  connected to shoulder base  102 , each including at least one torque generator  108  and at least one arm coupler  106 . In some embodiments, distal link  152  moves in such a manner that it remains substantially parallel with upper arm  204 . 
     In some embodiments, as depicted in  FIG.  6   , shoulder base  102  of arm supporting exoskeleton  100  comprises load bearing structure  112  coupled to arm link mechanism  104  and coupling mechanism  114  that attaches shoulder base  102  to trunk  202  of person  200 . Load bearing structure  112  supports reaction forces  214  and reaction torques  215  from arm link mechanisms  104 . In some embodiments, as depicted in  FIG.  10    through  FIG.  13   , reaction forces  214  and reaction torques  215  transfer to person  200 . In some embodiments, as depicted in  FIG.  65   , reaction forces  214  and reaction torques  215  transfer to a support surface (e.g., ground  310 ). Various embodiments of load bearing structure  112  and coupling mechanism  114  are described below. 
       FIGS.  7 ,  8 , and  9    are presented here to describe various dimensions used herein in the description of load bearing structure  112 .  FIG.  7    depicts a front view of person  200  including hip width  234 , shoulder width  236 , and frontal plane  250  of person  200 .  FIG.  8    depicts a back view of person  200 , including torso height  232  and upper arm length  242 .  FIG.  9    depicts a side view of person  200  including hip depth  238  and shoulder depth  240 . 
       FIG.  10    through  FIG.  13    depict various embodiments of load bearing structures  112 . As depicted in  FIG.  10   , in embodiments, load bearing structure  112  comprises back frame  130  supporting reaction forces  214  and torques  215  from arm link mechanisms  104  (not shown) and hip loading belt  131 . Hip loading belt  131  transfers at least a portion of the reaction forces  214  and reaction torques  215  to hips  220  of person  200  (shown in  FIG.  14   ), resulting in hip reaction force  221 . Back frame  130  may also transfer at least a portion of the reaction forces  214  to shoulders  224  of person  200  (depicted in  FIG.  14   ), as illustrated by shoulder reaction forces  225 . Back frame  130  can be custom made, or incrementally sized, to accommodate torso height  232 , hip width  234 , shoulder width  236 , hip depth  238 , shoulder depth  240 , or any combination thereof. In some embodiments, hip loading belt  131  and back frame  130  are constructed as one item. 
       FIG.  11    depicts a further embodiment of load bearing structure  112  wherein back frame  130  comprises upper frame  136  coupled to arm link mechanisms  104  (not shown) and lower frame  138  translationally coupled to upper frame  136  to provide desirable torso height adjustment  233  for torso height  232 . Lower frame  138  is coupled to, or part of, hip loading belt  131 . Reaction forces  214  from arm link mechanisms  104  are supported by upper frame  136 , at least a portion of which are transferred to hips  220  by hip loading belt  131  via lower frame  138 , resulting in hip reaction force  221 . Upper Frame  136  may also transfer at least a portion of the reaction forces  214  to shoulders  224 , as depicted by shoulder reaction forces  225 . Upper frame  136  can be custom made, or incrementally sized, to accommodate shoulder width  236  and shoulder depth  240 . Lower frame  138  can be custom made, or incrementally sized, to accommodate hip width  234  and hip depth  238 . 
       FIG.  12    depicts a further embodiment of load bearing structure  112  wherein back frame  130  further comprises spine frame  134  connecting upper frame  136  to lower frame  138 . Spine frame  134  is rotatably coupled to lower frame  138  on its lower end allowing for rotation of spine frame  134  relative to lower frame  138  in frontal plane  250  ( FIG.  7   ) of person  200 . Mediolateral flexion motion  260  shows the direction of movement between spine frame  134  and lower frame  138 . Spine frame  134  is rotatably coupled to upper frame  136  along spine frame axis  135 . Spinal twisting motion  262  shows the direction of movement between spine frame  134  and upper frame  136 . Upper frame  136  may also translate relative to spine frame  134  along spine frame axis  135  to provide torso height adjustment  233  for torso height  232  of person  200 . Degrees of freedom of spinal twisting motion  262  between upper frame  136  and spine frame  134  and mediolateral flexion motion  260  between lower frame  138  and spine frame  134  allow upper frame  136  to substantially move in unison with chest  222  of person  200  (depicted in  FIG.  14   ), and lower frame  138  to substantially move in unison with hips  220  of person  200 . 
       FIG.  13    depicts another embodiment of load bearing structure  112  wherein lower frame  138  further comprises lower middle bar  144  and two lower corner bars  140  wherein each lower corner bar  140  can be coupled to lower middle bar  144  at various locations on the lower middle bar  144  to provide desirable hip width adjustment  235  to accommodate hip width  234  of person  200 . Lower frame  138  may further comprise two lower side brackets  149  wherein each lower side bracket  149  can be coupled to lower frame  138  at various locations on lower frame  138  to provide desirable hip depth adjustment  239  to accommodate hip depth  238  of person  200 . Upper frame  136  further comprises upper middle bar  142  and two upper corner bars  146  wherein each upper corner bar  146  can be coupled to upper middle bar  142  at various locations on upper middle bar  142  to provide desirable shoulder width adjustment  237  to accommodate shoulder width  236  of person  200 . Upper frame  136  may also comprise two upper side brackets  148  wherein each upper side bracket  148  can be coupled to upper frame  136  at various locations on upper frame  136  to provide desirable shoulder depth adjustment  241  to accommodate shoulder depth  240  of person  200 . Upper frame  136  may also comprise hammocks  128  spanning curves in upper frame  136  to more evenly distribute respective shoulder reaction force  225  (depicted in  FIG.  13   ) to shoulders  224  of person  200  (depicted in  FIG.  14   ). Adjustment of upper side brackets, upper corner bars, lower side brackets, and lower corner bars may include the use of plunger pins, screws, clamps, friction locks, rack and pinions, or any combination thereof. 
       FIG.  14    through  FIG.  22    depict various embodiments where coupling mechanism  114  includes belt  116  that attaches to load bearing structure  112  at belt attachment points  115  and at least partially encircles hips  220  of person  200 . Belt  116  can move in unison with hips  220  of person  200 . In some embodiments, belt  116  can change length to allow secure attachment to hips  220 . 
       FIGS.  14 , 15  and  16    depict various embodiments of the shoulder base  102 .  FIG.  14    shows a front perspective view of shoulder base  102  with person  200 .  FIG.  15    shows a rear view of shoulder base  102  without person  200 .  FIG.  16    shows a rear perspective view of shoulder base  102  without person  200 . In this embodiment, a coupling mechanism  114  includes chest strap  118 . Chest strap  118  at least partially encircles chest  222  of person  200 . Chest strap  118  is mounted to load bearing structure  112  at mid-dorsal attachment points  117  approximately at the level of chest  222 . In some embodiments, coupling mechanism  114  includes at least one anchor strap  119  mounted to load bearing structure  112  at upper ventral attachment points  121  at its first end, and attaches to chest strap  118  at its second end. Chest strap  118  and anchor strap  119  move in unison with chest  222 . In some embodiments, chest strap  118  and anchor strap  119  can change length to allow secure attachment to chest  222 . In some embodiments, chest strap  118  is rigid to prevent deflection due to the tightening of anchor straps  119 . 
       FIGS.  17 , 18  and  19    depict various embodiments of the shoulder base  102 .  FIG.  17    shows a front perspective view of shoulder base  102  with person  200 .  FIG.  18    shows a rear view of shoulder base  102  without person  200 .  FIG.  19    shows a rear perspective view of shoulder base  102  without person  200 . In this embodiment, coupling mechanism  114  includes at least two shoulder straps  120 . Two shoulder straps  120  at least partially encircle shoulders  224 . Each shoulder strap  120  is mounted to load bearing structure  112  at respective upper ventral attachment points  121  on a first end and at lower dorsal attachment points  123  on a second end. In some embodiments, sternum strap  122  connects to one shoulder strap  120  at its first end and another shoulder strap  120  at its second end. Shoulder strap  120  and sternum strap  122  move in unison with chest  222 . In some embodiments, shoulder strap  120  and sternum strap  122  can change length to allow secure attachment to chest  222 . In some embodiments, shoulder strap  120  is mounted to load bearing structure  112  at upper ventral attachment point  121  on its first end and middle dorsal attachment points  117  at its second end. 
       FIGS.  20 ,  21  and  22    depict various embodiments of the shoulder base  102 .  FIG.  20    shows a front perspective view of shoulder base  102  with person  200 .  FIG.  21    shows a rear view of shoulder base  102  without person  200 .  FIG.  22    shows a rear perspective view of shoulder base  102  without person  200 . In this embodiment, coupling mechanism  114  includes vest  124  that securely attaches to chest  222 . Vest  124  can move in unison with chest  222 . In some embodiments, vest  124  is connected to shoulder base  102  by a plurality of vest attachment points  125 . In some embodiments, vest attachment points  125  attach to chest straps  118 , anchor straps  119 , shoulder straps  120 , sternum straps  122 , or any combination thereof. 
       FIG.  23    through  FIG.  25    depict embodiments of shoulder base  102  wherein coupling mechanism  114  can be coupled to safety harness  126  worn by person  200  by at least one safety harness attachment point  127  without modification of safety harness  126 .  FIG.  23    and  FIG.  24    depict an embodiment wherein vest  124  contains at least one safety harness attachment point  127 . Safety harness attachment points  127  allow vest  124  to attach to safety harness  126  without modification of safety harness  126 . Safety harness attachment points  127  may be located on the front, shoulder, or back of vest  124 .  FIG.  23    shows a front perspective view of safety harness attachment points  127  on the front and shoulders of vest  124 .  FIG.  24    depicts a close up back perspective view of the embodiment (without load bearing structure  112 ), including safety harness attachment points  127  on a back and shoulders of vest  124 . Safety harness attachment points  127  may be formed by VELCRO® loops, buttoned flaps, straps, buckles, clips, clamps, or any combination thereof.  FIG.  25    depicts an embodiment wherein belt  116  contains at least one safety harness attachment point  127 . Safety harness attachment point  127  allows safety harness  126  to be attached to belt  116  without modification of safety harness  126 . In some embodiments, safety harness attachment points  127  are located on the sides of belt  116 . Safety harness attachment points  127  may be formed by VELCRO® loops, buttoned flaps, straps, buckles, clips, clamps, or any combination thereof. 
       FIG.  26    depicts the close up view of arm link mechanism  104 . In this embodiment, first rotational axis  154  of first joint  151  approximately passes through glenohumeral joint  218  of person  200 .  FIG.  27    depicts a back view of this embodiment wherein arm support exoskeleton  100  contains two arm link mechanisms  104 . 
       FIG.  28    and  FIG.  29    depict another embodiment of arm supporting exoskeleton  100  wherein arm link mechanism  104  comprises at least one horizontal rotation joint  156 . Horizontal rotation joint  156  allows proximal link  150  to rotate relative to shoulder base  102  about second rotational axis  155 . Second rotational axis  155  is substantially orthogonal to first rotational axis  154 .  FIG.  29    shows a rear view of the arm link mechanism  104 , wherein the second rotational axis  155  is shown to substantially pass through glenohumeral joint  218  of person  200 . 
       FIG.  30    and  FIG.  31    depict an embodiment of arm support exoskeleton  100  that comprises at least one shoulder bracket  153  coupled to shoulder base  102 . Shoulder bracket  153  facilitates a quick connect and disconnect coupling between arm link mechanism  104  and shoulder base  102 .  FIG.  30    depicts shoulder bracket  153  coupling arm link mechanism  104  to shoulder base  102 .  FIG.  31    shows shoulder bracket  153  allowing arm link mechanism  104  to be removed from shoulder base  102 . 
       FIG.  32    depicts another embodiment of arm support exoskeleton  100  that comprises at least one shoulder bracket  153  coupled to shoulder base  102 . Shoulder bracket  153  can couple shoulder base  102  to arm link mechanism  104  in multiple positions to provide desirable shoulder width adjustment  237  to accommodate shoulder width  236  of person  200 , referenced in  FIG.  7   . In another embodiment not depicted, shoulder bracket  153  can couple to arm link mechanism  104  in multiple positions to provide desirable shoulder depth adjustment  241  to accommodate shoulder depth  240  of person  200 . 
       FIG.  33    depicts another embodiment of arm supporting exoskeleton  100  wherein shoulder base  102  comprises at least one shoulder bracket  153 . Shoulder bracket  153  is rotatably coupled to arm link mechanism  104  along scapular rotation axis  171 , wherein the scapular rotation axis  171  is substantially orthogonal to gravity line  208  when person  200  (not shown) is standing upright. 
       FIG.  34    through  FIG.  36    depict another embodiment of arm support exoskeleton  100 , wherein shoulder base  102  is coupled to a shoulder bracket  153 . Shoulder bracket  153  couples to arm link mechanism  104 . Shoulder bracket  153  contains stow joint  158  that allows shoulder bracket  153  to rotate relative to shoulder base  102  (stow joint  158  not depicted in  FIG.  34   ). When shoulder bracket  153  rotates about stow joint  158 , it may position arm link mechanism  104  substantially behind person  200 . Shoulder bracket  153  can be held stationary about stow joint  158  to keep arm link mechanism  104  in the desired orientation.  FIG.  34    shows person  200  wearing arm supporting exoskeleton  100  wherein arm link mechanism  104  is in a stowed position that is substantially out of workspace  230  of person. The term “workspace of person” or “person&#39;s workspace” should be understood to mean the range of motion of upper arm  204  of person  200  that may be utilized during common workplace tasks.  FIG.  35    shows perspective view of shoulder bracket  153  in a working position. In the working position arm link mechanism  104  is positioned to support upper arm  204  (not shown).  FIG.  36    shows a perspective of shoulder bracket  153  in a stowed position wherein arm link mechanism  104  is positioned substantially behind person  200  (not shown). In a stowed position, distal link  152  remains fully flexed relative to proximal link  150  due to torque generator  108  acting about first rotational axis  154 . This serves to further secure arm link mechanism  104  out of workspace  230 . It should be understood that other joints between arm link mechanism  104  and shoulder base  102  may be utilized to further secure arm link mechanism  104  out of workspace  230 . 
       FIG.  37    through  FIG.  41    depict embodiments of arm supporting exoskeleton  100  wherein arm coupler  106  further comprises a load bearing coupler  160  coupled to distal link  152  capable of imposing supporting force  212 , directed upward, on upper arm  204  (shown in  FIG.  1   ). In some embodiments, load bearing coupler  160  comprises distal link attachment  167  that attaches arm coupler  106  to distal link  152  and at least one arm cuff  168  that at least partially encircles upper arm  204  (shown in  FIG.  1   ). 
       FIG.  37    depicts an embodiment of arm support exoskeleton  100  wherein arm coupler  106  further comprises an arm coupling mechanism  162 . Arm coupling mechanism  162  is capable of coupling arm coupler  106  to upper arm  204  (shown in  FIG.  2   ). Arm coupling mechanism  162  may comprise an element or combination of elements selected from a group consisting of rigid, semi-rigid, or compliant materials preventing separation of upper arm  204  (shown in  FIG.  1   ) from arm coupler  106 . 
       FIG.  38    depicts an embodiment of arm coupler  106  wherein load bearing coupler  160  contains an arm rotation joint  164 . Arm rotation joint  164  allows arm cuff  168  to rotate with respect to distal link  152  along arm cuff rotation axis  165  substantially parallel to first rotational axis  154 . Arm rotation joint  164  allows arm cuff  168  to provide maximum contact with upper arm  204  (shown in  FIG.  1   ) or compensate for movement discrepancies between distal link  152  and upper arm  204  of person  200 . 
       FIG.  39    depicts an embodiment of arm coupler  106  wherein arm coupler  106  locations can be adjusted with respect to distal link  152 . In some embodiments, load bearing coupler  160  can translate with respect to distal link  152  at translation joint  166  to allow for arm length adjustment  243  of arm link mechanism  104  to fit length  242  of upper arm  204  of person  200  (referenced in  FIG.  7   ), or to compensate for any movement discrepancies between distal link  152  and s upper arm  204  of person  200  (depicted in  FIG.  1   ).  FIG.  40    depicts another embodiment of translation joint  166  wherein distal link  152  contains a t-slot mating with load bearing coupler  160 . Load bearing  160  contains locking pin  169  that fixes the position of load bearing coupler  160  relative to distal link  152 . 
       FIG.  41    depicts an embodiment of arm coupler  106  wherein load bearing coupler  160  allows for internal and external rotation of upper arm  204  (shown in  FIG.  1   ) with internal/external rotation joint  172 . Internal/external rotation joint  172  is located between distal link attachment  167  and arm cuff  168 . Internal/external rotation joint  172  rotates about internal external rotation axis  173 . In another embodiment not depicted, sliding contact with upper arm  204  resting in arm cuff  168  allows for rotation about internal external rotation axis  173 . 
       FIG.  42    through  FIG.  46    depict various embodiments of arm supporting exoskeleton  100  wherein torque generator  108  comprises tensile force generator  178 . Tensile force generator  178 , as shown in  FIG.  42   , is coupled to proximal link  150  from its first tensile end  176  and distal link  152  from its second tensile end  177 . The tensile force in tensile force generator  178  provides torque  280  to flex distal link  152  relative to proximal link  150  about first rotational joint  151 . In some embodiments of torque generator  108 , tensile force generator  178  comprises coil spring element  180 . In some embodiments of torque generator  108 , tensile force generator  178  comprises line element coupling coil spring element  180  to proximal link  150 . Line element  182  comprises an element or combination of elements selected from a group consisting of wire rope, rope, cable, twine, strap, chain, or any combination thereof. In some embodiments of torque generator  108 , line element  182  at least partially encircles pulley  183  coupled to distal link  152  before line element  182  is coupled to proximal link  150 . In some embodiments pulley  183  does not rotate relative to distal link  152 . In some embodiments, pulley  183  is a curved surface incorporated into distal link  152 .  FIG.  42    depicts an embodiment of torque generator  108  where coil spring element  180  is an extension spring. Coil spring element  180  is coupled to line element  182  at junction  179  and coupled to distal link  152  at second tensile end  177 . 
       FIG.  43    shows an approximate schematic of torque generator  108 . Tensile force generator  178  is coupled to proximal link  150  at first distance  272 . Tensile force generator  178  acts about distal link at second distance  270 . Tensile force generator effective length  276  is the distance between first distance  272  along proximal link  150  and second distance  270  along distal link  152 . Tensile force generator original length is the tensile force generator effective length  276  corresponding to a zero value of first angle  193 . Tensile force is a function of spring constant, spring preload, tensile force generator original length, and tensile force generator effective length  276  at a given value of first angle  193 . Torque  280  causes distal link to flex relative to shoulder base  102 . 
       FIG.  44    through  FIG.  46    depicts various embodiments of torque generator  108  wherein tensile force generator  178  comprises coil spring element  180  and line element  182 . Line element  182  at least partially encircles pulley  183  coupled to distal link  152 .  FIG.  44    depicts an embodiment of torque generator  108  where coil spring element  180  is an extension spring with a different orientation than shown in  FIG.  42   . Coil spring element  180  is coupled to line element  182  at junction  179  and coupled to distal link  152  at second tensile end  177 . In some embodiments, line element  182  at least partially wraps around pulley  183  attached to distal link  152  before attaching to proximal link  150 .  FIG.  45    depicts an embodiment of torque generator  108  where coil spring element  180  is a compression spring. Coil spring element  180  is coupled to line element  182  at junction  179  and coupled to distal link  152  at second tensile end  177 . In some embodiments, line element  182  at least partially wraps around pulley  183  attached to distal link  152  before attaching to proximal link  150 .  FIG.  46    depicts an embodiment of torque generator  108  where coil spring element  180  is a compression spring with a different orientation than shown in  FIG.  45   . Coil spring element  180  is coupled to line element  182  at junction  179  and coupled to distal link  152  at second tensile end  177 . In some embodiments, line element  182  at least partially wraps around pulley  183  attached to distal link  152  before attaching to proximal link  150 . It is understood that in all embodiments, instead of coil spring element  180 , a gas spring, air spring, elastomer, or any combination that exhibits similar behavior can be utilized. 
       FIG.  47    and  FIG.  48    depict an embodiment of torque generator  108  wherein proximal link  150  comprises an upper bracket  188  coupled to tensile force generator  178 . The location of upper bracket  188  can be adjusted along proximal link  150  to adjust torque  280  provided by tensile force generator  178 . The location of upper bracket  188  corresponds to first distance  272  in the schematic of  FIG.  43   . In some embodiments, the location of upper bracket  188  is adjusted relative to proximal link  150  by upper bracket screw  187  where upper bracket  188  incorporates a threaded feature that mates with upper bracket screw  187 . By turning upper bracket screw  187 , the location of upper bracket  188  is adjusted along proximal link  150 . In general, the farther upper bracket  188  is from first joint  151 , the larger the amplitude of torque  280  will be.  FIG.  47    depicts upper bracket  188  in an extended position relative to first joint  151 , resulting in a large first distance  272  (see  FIG.  43   ).  FIG.  48    depicts upper bracket  188  in a retracted position relative to first joint  151 , resulting in a small first distance  272  (see  FIG.  42   ).  FIG.  49    depicts two plots of torque  280  created by torque generator  108  as a function of first angle  193  for two positions of upper bracket  188  described in  FIG.  47    and  FIG.  48   . The torque profile of configuration shown in  FIG.  47    is represented by torque profile  288 . The torque profile of configuration shown in  FIG.  48    is represented by torque profile  287 . It can be seen that torque profile  288  has larger amplitude compared to torque profile  287 . 
       FIG.  50    and  FIG.  51    depict an embodiment of torque generator  108  wherein distal link  152  comprises lower bracket  190  coupled to tensile force generator  178 . The location of lower bracket  190  can be adjusted along distal link  152  to adjust torque  280  provided by tensile force generator  178 . The location of lower bracket  190  corresponds to preload of tensile force generator  178 . In some embodiments, the location of lower bracket  190  is adjusted relative to distal link  152  by lower bracket screw  189  where lower bracket  190  incorporates a threaded feature that mates with lower bracket screw  189 . By turning lower bracket screw  189 , the location of lower bracket  190  is adjusted along distal link  152 . In general, the farther lower bracket  190  is from first joint  151 , the smaller the amount of preload will be.  FIG.  50    depicts lower bracket  190  in a lengthened position relative to first joint  151 , resulting in a small tensile force generator  178  preload.  FIG.  51    depicts lower bracket  190  in a shortened position relative to first joint  151 , resulting in a large tensile force generator  178  preload.  FIG.  52    depicts two plots of torque  280  created by torque generator  108  as a function of first angle  193  for two positions of lower bracket  190  described in  FIG.  50    and  FIG.  51   . The torque profile of configuration shown in  FIG.  50    is represented by torque profile  290 . The torque profile of configuration shown in  FIG.  51    is represented by torque profile  289 . Shortened lower bracket torque profile  289  has a larger amplitude compared to lengthened lower bracket torque profile  290 . 
       FIG.  53    through  FIG.  55    depict an important characteristic where the torque  280  provided by tensile force generator  178  will automatically remain substantially small when first angle  193  is greater than or equal to toggle angle  195 . That is, when a person moves their arm from a first position wherein first angle  193  is not greater than or equal to toggle angle  195 , to a second position wherein first angle  193  is greater than or equal to toggle angle  195 , tensile force generator  178  will automatically shift from a first torque mode wherein a first torque is provided by tensile force generator  178  (at the first position of the arm), to a second torque mode (at the second position of the arm) wherein a substantially small torque will be provided by tensile force generator  178 . Likewise, when a person moves their arm back from the second position to the first position, the tensile force generator  178  will automatically shift from the second torque mode to the first torque mode. 
       FIG.  53    shows a configuration where first angle  193  is larger than 180 degrees, and arm link mechanism  104  comprises a protrusion  186  located substantially at first joint  151 . When first angle  193  becomes equal to or greater than toggle angle  195 , protrusion  186  constrains tensile force generator  178  (line element  182  of force generator  178  as shown in  FIG.  53   ) in a position substantially centered about first joint  151 . By constraining tensile force generator  178 , protrusion  186  prevents tensile force generator  178  from passing over first joint  151 . Torque  280  remains substantially zero since the force of the constrained tensile force generator  178  is substantially centered about first joint  151 . First angle  193  being greater than toggle angle  195  corresponds to situations where person  200  intends to rest his/her upper arm  204  at his/her sides, or pick a tool from his/her tool belt. In these situations, a substantially small torque  280  is desired to allow free motion of upper arm  204  of person or to allow upper arm  204  to rest without the impedance of torque  280 . This creates a greater overall comfort of person  200  during non-working postures.  FIG.  54    depicts an embodiment wherein protrusion  186  is formed by first joint pin  184  forming first joint  151 .  FIG.  55    depicts an embodiment wherein protrusion  186  is a part of proximal link  150 . 
       FIG.  56    depicts a graph of torque  280  created by torque generator  108  as a function of first angle  193  without protrusion  186 . At toggle angle  195 , torque  280  becomes negative. Negative values of torque  280  may impede movement of upper arm  204  or decrease comfort of person  200 .  FIG.  57    depicts a graph of torque  280  created by torque generator  108  as a function of first angle  193  when protrusion  186  is created. When first angle  193  becomes equal to or greater than toggle angle  195 , protrusion  186  constrains tensile force generator  178 , ensuring that the torque  280  remains substantially small (as described in  FIG.  53   ). After toggle angle  195 , torque  280  becomes substantially zero, creating neutral zone  197  for the remainder of first angle  193 . Neutral zone  197  allows upper arm  204  of person  200  to move with a substantially zero applied torque  280  within first angle  193  greater than toggle angle  195 . Neutral zone  197  allows person  200  to comfortably rest his/her upper arm in a neutral position or to preform secondary tasks such as reaching into pockets or a tool belt. 
       FIG.  58    and  FIG.  59    depict an embodiment of arm supporting exoskeleton  100  wherein the orientation of proximal link  150  can be adjusted and held in place relative to shoulder base  102 . Proximal link offset position  191  is defined as the orientation of proximal link  150  relative to gravity line  208  fixed to shoulder base  102  when person  200  is standing upright. Proximal link offset position  191  is adjusted at offset adjustment joint  159 , which rotates substantially in the plane of first joint  151 . Toggle position  194  represents the position of distal link  152  when first joint angle  193  has become equal to toggle angle  195 . By adjusting proximal link offset position  191 , toggle position  194  is adjusted relative to shoulder base  102 . Offset angle  199  represents the angle between proximal link offset position  191  and gravity line  208  when person  200  is standing upright.  FIG.  58    shows an embodiment wherein offset angle  199  is relatively small.  FIG.  59    shows an embodiment wherein offset angle  199  is increased.  FIG.  60    shows an exploded embodiment of arm link mechanism  104  comprising offset adjustment joint  159 . Offset adjustment joint  159  allows proximal link  150  to rotate relative to shoulder base  102 . Offset adjustment joint  159  can further lock the rotation of proximal link  150  relative to shoulder base  102  at a particular position. 
       FIG.  61    depicts a graph of torque  280  created by torque generator  108  as a function of angle of distal link  152  from horizon  209 . Torque profile  291  corresponds to a configuration when offset angle  199  is zero. Torque profile  292  corresponds to a configuration when offset angle  199  is fifty degrees, meaning the upward torque will not push the person&#39;s arm upward unless the angle of distal link  152  is raised relative to 40 degrees below horizon  209 . It can be observed from this graph that one can move the toggle position by adjusting offset angle  199 . Torque generator offset angle  199  may be adjusted in order to position toggle position  194  at a specific angle relative to horizon  209 . Torque generator offset angle  199  may also be adjusted in order to create a torque profile with a specific peak position at a desired angle relative to horizon  209 . When protrusion  186  is present, neutral zone  197  is formed for both curves for angles of distal link  152  past toggle position  194 . When offset angle  199  is increased, a larger range of neutral zone  197  is created relative to the range of motion of upper arm  204 . 
     In some embodiments, lower bracket  190 , upper bracket  188 , and proximal link offset position  191  can all be adjusted to create a desired support profile for torque  280 . Arm weight torque profile  198  is defined as a torque to counter the weight of upper arm  204 , forearm  206 , hand  207 , and tool  308 .  FIG.  62    depicts the profile of torque  280  where it matches arm weight torque profile  198  in angles substantially above horizon  209  and approximately cancels the arm weight torque profile  198 . Overhead welding is a good example of an activity of a person that may require such torque. When the absolute angle of the distal link  152  is below −60 degrees from horizon  209 , the profile of torque  280  enters neutral zone  197  where torque is substantially zero. This profile of torque  280  may be created with a lower bracket  190  position or upper bracket position  188  that creates torque  280  with a reduced peak amplitude compared to arm weight torque profile. Offset angle  199  may then be adjusted to shift support profile of torque  280  so that it closely matches arm weight torque profile  198  for the desired range of motion. When matched to arm weight torque profile  198 , support torque  280  of reduced amplitude corresponds to a smaller range of angles in which torque  280  matches arm weight torque profile  198  and a larger size of neutral zone  197 . 
       FIG.  63    depicts another support profile of torque  280  with values larger than the arm weight torque profile  198  at some angles above horizon  209 . This is useful when person  200  needs to apply an upward force greater than the combined weight of upper arm  204 , forearm  206 , hand  207 , and tool  308 . Drilling into a ceiling is a good example of an activity that may require such torque. When the absolute angle of the distal link  152  is below −40 degrees from horizon  209 , the profile of torque  280  enters neutral zone  197  where torque is substantially zero. This profile of torque  280  may be created with lower bracket  190  position or upper bracket position  188  that creates torque  280  with any peak amplitude compared to arm weight torque profile  198 . Offset angle  199  may then be adjusted to shift profile of torque  280  so that it exceeds arm weight torque profile  198  for the desired range of motion. When adjusted to arm weight torque profile  198 , support torque  280  of reduced amplitude corresponds to a smaller range of angles in which torque  280  exceeds arm weight torque profile  198  and a larger size of neutral zone  197 . 
       FIG.  64    depicts another possible support profile of torque  280  with values substantially equal to the arm weight torque profile  198  at all angles. Manipulating a tool throughout the entire range of motion is an example of an activity that may require such torque. This profile of torque  280  may be created with lower bracket  190  position or upper bracket position  188  that creates torque  280  with equal peak amplitude compared to arm weight torque profile  198 . Offset angle  199  may then be adjusted to align profile of torque  280  peak with the peak of arm weight torque profile  198 . Below −90 degrees of deviation from horizon  209 , torque  280  enters neutral zone  197  (not shown) where torque  280  is substantially zero. Even with the full forward range of motion supported, neutral zone  197  provides substantially zero torque when upper arm  204  extends negatively behind trunk  202  of person  200 , such as when a person&#39;s hand is reaching for a back pocket. 
       FIG.  65    depicts an embodiment wherein load bearing structure  112  comprises back frame  130  located substantially behind person  200  and lower extremity exoskeleton  304  coupled to back frame  130  and also coupled to legs  228  of person  200 . Back frame  130  is coupled to arm link mechanism  104  and supports at least a portion of reaction forces  214  and reaction torques  215  from arm link mechanism  104 . Back frame  130  transfers at least a portion of reaction forces  214  and reaction torques  215  to lower extremity exoskeleton  304 . Lower extremity exoskeleton  304  transfers at least a portion of reaction forces  214  and reaction torques  215  to ground  310 , resulting in ground reaction forces  311 . Exoskeletons can be coupled to arm supporting exoskeletons  100 , in accordance with some examples. 
       FIG.  66    depicts an embodiment wherein load bearing structure  112  comprises a back frame  130  located substantially behind person  200  and a trunk supporting exoskeleton  302  coupled to back frame  130 . 
       FIG.  94    depicts a perspective view of arm supporting exoskeleton  100  utilizing variable force generator  401  configured to create a torque about first rotational joint  431  to support gravity forces on upper arm  204  of person  200 . In some embodiments variable force generator  401  may be the same as tensile force generator  178  or torque generator  108 , and first rotational joint  431  may be designed to rotate along first rotational axis  154 . Arm coupler  106  is configured to couple to upper arm  204  and is coupled to distal link  152  or first element  406 . Shoulder base  102  is configured to transfer reaction forces and torques from arm coupler  106  to trunk  202  of person  200 , and is coupled to rotational base link  430  or proximal link  150 . In some embodiments, rotational base link  430  may the same as proximal link  150 . 
     In one embodiment, a variable force generator creates an “on” and “off” support mode of arm supporting exoskeleton  100 . In a first force mode, variable force generator  401  exhibits a substantially small first stiffness and creates a substantially small first force  402 , and a substantially small first torque  404  is applied to person&#39;s arm that compensates for the mass and friction of the arm supporting exoskeleton  100 . A substantially small first torque  404  allows free, relatively unsupported movement of upper arm  204  of person  200 . Small reaction forces and torques from first torque  404  are applied to trunk  202  of person through shoulder base  102  or are applied to a lower extremity exoskeleton  304  (not shown). This constitutes the off mode of arm supporting exoskeleton  100 . In a second force mode, variable force generator  401  exhibits a second stiffness and creates second force  403  that is substantially larger than first force  402 , and second torque  405  substantially larger than first torque  404  is applied to upper arm  204 . Second torque  405  supports upper arm  204  from gravitational forces, while reaction forces and torques from second force  403  and second torque  405  are applied to trunk  202  of person  200  through shoulder base  102 , or are applied to a lower extremity exoskeleton  304  (not shown). This constitutes the on mode of arm supporting exoskeleton  100 . 
     In one embodiment, variable force generator creates a “high” and “low” support mode of arm supporting exoskeleton  100 . In a first force mode, variable force generator  401  exhibits a first stiffness and creates first force  402 , and first torque  404  is applied to upper arm  204 , while reaction forces and torques from first force  402  and first torque  404  are applied to trunk  202  of person  200  through shoulder base  102 , or are applied to a lower extremity exoskeleton  304  (not shown). First torque  404  supports upper arm  204  from gravitational forces. This constitutes a low support mode of arm supporting exoskeleton  100 . In a second force mode, variable force generator  401  exhibits a second stiffness and creates second force  403  that is substantially larger than first force  402 , and second torque  405  substantially larger than first torque  404  is applied to upper arm  204 . Second torque  405  supports upper arm  204  from gravitational forces, while reaction forces and torques from second force  403  second torque  405  are applied to upper trunk  202  through shoulder base  102 , or are applied to a lower extremity exoskeleton  304  (not shown). This constitutes the high support mode of arm supporting exoskeleton  100 . 
     It can be appreciated that the forces and or torques applied by variable force generator  401  can be applied in a similar manner to a multitude of joints and movement mechanisms of exoskeleton, robotic, or similar applications. 
       FIG.  67    shows a schematic embodiment of variable force generator  401 . Variable force generator  401  is adaptable to exhibit two stiffness rates between first element  406  and second element  407 . In some embodiments, first element  406  may be the same as distal link  152  and second element  407  may be the same as line element  182 . Variable force generator  401  comprises first spring  408  that has first end  409  and second end  410 . First spring  408  is constrained by first element  406  from its first end  409  and by the second element  407  from its second end  410 . Variable force generator  401  further comprises second spring  411  which has first end  412  and second end  413 . Second spring  411  is constrained by first element  406  from its first end  412 . Variable force generator  401  further comprises at least one constraining mechanism  414  which is configurable to have at least a first position and a second position.  FIG.  68    shows a hardware embodiment of variable force generator  401 . 
     In operation, in the first force mode of variable force generator  401 , the constraining mechanism  414  is in its first position as shown in  FIG.  69   , second end  413  of second spring  411  is not constrained by second element  407 . This causes second spring  411  not to affect the motion between first element  406  and second element  407 . In this first position the equivalent stiffness is the stiffness of first spring  408 . 
     In the second force mode of variable force generator constraining mechanism  414  is in its second position as shown in  FIG.  70   , second end  413  of second spring  411  is constrained by second element  407 . This causes the second spring  411  to act in parallel with first spring  408 . In this second position, the equivalent stiffness is the addition of both the stiffness of first spring  408  and stiffness of second spring  411 . 
     In some embodiments, the stiffness of first spring  408  is substantially smaller than the stiffness of second spring  411 . When constraining mechanism  414  is in its first position, the motion between first element  406  and second element  407  generates a substantially small force between first element  406  and second element  407  relative to the force generated when constraining mechanism  414  is in its second position. “Substantially small force” is defined as just enough force to overcome the mass and or friction associated with the movement of variable force generator  401 . With a substantially small force applied, variable force generator  401  appears to be off, or free moving, to an observer, with little to no spring force discernable. When constraining mechanism  414  is in its second position, the motion between first element  406  and second element  407  generates a force between first element  406  and second element  407  roughly equivalent to the stiffness of second spring  411 . 
       FIG.  68   ,  FIG.  69   , and  FIG.  70    show an embodiment wherein first spring  408  further comprises first spring element  442  and first spring bracket  415 . First spring element  442  provides the stiffness of first spring  408 . First spring element  442  may take the form of a coil spring as shown in all figures, or the form of a gas spring, rubber, or any other type of resilient element with an associated stiffness. First spring bracket  415  serves to facilitate the housing, motion, or general function of constraining mechanism  414  between its first position and second position. First spring bracket  415  may be located at first end  409  or second end  410  of the first spring  408 . First spring bracket  415  may further facilitate the coupling of first spring  408  to second element  407 . First spring bracket  415  may further facilitate the motion or stabilization of first spring  408  while it is undergoing compression or extension. First spring bracket  415  transfers force between first spring  442  and second element  407 . First spring bracket  415  also transfers force between constraining mechanism  414  and second element  407  when constraining mechanism  414  is in its second position. 
       FIG.  68   ,  FIG.  69   , and  FIG.  70    show an embodiment wherein second spring  411  further comprises second spring element  443  and second spring bracket  416 . Second spring element  443  provides the stiffness of second spring  411 . Second spring element  443  may take the form of a coil spring as shown in all figures, or the form of a gas spring, rubber, or any other type of resilient element with an associated stiffness. Second spring bracket  416  serves to facilitate the housing, motion, or general function of constraining mechanism  414  between its first position and second position. Second spring bracket  416  may be located at the first end  412  or second end  413  of second spring  411 . Second spring bracket  416  may further facilitate the motion or stabilization of second spring  411  while it is undergoing compression or extension. Second spring bracket  416  transfers force between second spring element  443  and constraining mechanism  414  when constraining mechanism  414  is in its second position. 
       FIG.  69    and  FIG.  70    show an embodiment of variable force generator  401  configured to create a tensile force between first element  406  and second element  407 . To generate a tensile force, second element  407  may be made of a rigid, semi-rigid, or flexible material. In some embodiments, second element  407  comprises a flexible steel cable. 
       FIG.  69    shows variable force generator  401  wherein constraining mechanism  414  is in a first position. Second end  413  of second spring  411  is not constrained by second element  407 . Therefore, second spring  411  does not affect the motion between first element  406  and second element  407 . In this first position, the equivalent stiffness is the stiffness of first spring  408 , and variable force generator  401  produces first force  402  between first element  406  and second element  407  that is tensile. 
       FIG.  70    shows variable force generator  401  wherein constraining mechanism  414  is in a second position. Second end  413  of second spring  411  is constrained by second element  407 . This causes the second spring  411  to act in parallel with first spring  408 . In this second position, the equivalent stiffness is the addition of both the stiffness of first spring  408  and stiffness of second spring  411 , and variable force generator  401  produces second force  403  between first element  406  and second element  407  that is tensile. 
       FIG.  71    shows an embodiment of variable force generator  401  configured to create a compressive force between first element  406  and second element  407  through a re-arrangement of components. Second element  407  may be made of a rigid or semi-rigid material in order to generate a compressive force. 
     In  FIG.  71   , constraining mechanism  414  is in a first position. Second end  413  of second spring  411  is not constrained by second element  407 , so second spring  411  does not affect the motion between first element  406  and second element  407 . In this first position, the equivalent stiffness is the stiffness of first spring  408 , and variable force generator  401  produces a first force  402  between first element  406  and second element  407  that is compressive. It can be understood by one skilled in the art that the force produced by any embodiment herein may be made compressive by a similar re-arrangement of components. 
       FIG.  72    and  FIG.  73    show a radial section of an embodiment wherein first spring  408  and second spring  411  are arranged concentrically.  FIG.  72    shows variable force generator  401  wherein constraining mechanism  414  is in a first position.  FIG.  73    shows variable force generator  401  wherein constraining mechanism  414  is in a second position. 
     In the embodiment of  FIG.  72    and  FIG.  73   , second element  407  is arranged concentrically with one or a combination of the first spring  408 , second spring  411 , or first element  406 . 
     In the embodiment of  FIG.  72    and  FIG.  73   , first element  406  comprises a cylindrical opening. First spring  408  and second spring  411  are arranged concentrically within the cylindrical first element  406  while constrained by the cylindrical first element  406  from their respective first ends  409  and  412 . 
       FIG.  72    and  FIG.  73    depict a radial section of variable force generator  401  further comprising orientation sleeve  417 . Orientation sleeve  417  is configured to radially constrain first spring  408  relative to second spring  411 . The radial constraint may be used to facilitate smooth motion or a bearing surface, or to prevent contact between coils of first spring  408  and second spring  411 . 
       FIG.  74   ,  FIG.  75   ,  FIG.  76   , and  FIG.  77    depict a detailed axial section view of variable force generator  401 . Variable force generator  401  may further comprise one or more rotational orientation elements that rotationally constrain first spring  408 , second spring  411 , orientation sleeve  417 , or any combination thereof relative to first element  406 . In the embodiment of  FIG.  74   , first orientation element  418  rotationally constrains orientation sleeve  417  relative to first element  406  by means of a pin, although other configurations are possible. Additionally, second orientation element  419  rotationally constrains orientation sleeve  417  relative to first spring bracket  415  by means of a pin, although other configurations are possible. 
     In some embodiments, orientation sleeve  417  is configured to radially constrain second spring  411  relative to first element  406 . The radial constraint may be used to facilitate smooth motion or a bearing surface, or to prevent contact between coils of second spring  411  and first element  406 . 
     In some embodiments first element  406  acts to radially constrain second spring  411 . In still other embodiments, second element  407  acts to radially constrain first spring  408 . 
     In some embodiments, a number of rotational orientation elements may be used to rotationally constrain first spring  408  and or second spring  411  relative to first element  406 . Rotational constraints may be necessary to ensure proper positioning of components for the function of constraining mechanism  414  to move between its first position and second position.  FIG.  72    shows an embodiment where constraining mechanism  414  further serves to rotationally constrain second spring  411  relative to first element  406  and or orientation sleeve  417  when constraining mechanism  414  is in its first position. 
       FIG.  73    shows an embodiment wherein constraining mechanism  414  further serves to rotationally constrain second spring  411  relative to first spring  408  or orientation sleeve  417  when constraining mechanism  414  is in its second position. 
       FIG.  74    depicts an embodiment of variable force generator  401  that comprises one or more axial orientation elements that axially constrain first spring  408 , second spring  411 , orientation sleeve  417 , or any combination thereof to first element  406 . Axial constraint of first spring  408  and second spring  411  relative to first element  406  serves to remove any forces on constraining mechanism  414  due to the stiffness of first spring  408  or second spring  411 . Removing forces on constraining mechanism  414  allows for an easier transition between its first position and second position. 
     In embodiment shown in  FIG.  74   , first orientation element  418  axially constrains orientation sleeve  417 , relative to first element  406 . Furthermore, first orientation element  418  axially constrains the maximum extension of first spring  408  and second spring  411  relative to first element  406  by means of a pin, although other configurations are possible 
     In another embodiment, second orientation element  419  axially constrains orientation sleeve  417  relative to first spring  408  by means of a pin and slot configuration, although other configurations are possible. 
     The axial position of first orientation element  418  and second orientation element  419  may further be used to preload first spring  408  and or second spring  411  when axially constrained by first orientation element  418  or second orientation element  419 . The amount of preload of first spring  408  and or second spring  411  may be manipulated to alter the forces generated by variable force generator  401 . 
     In some embodiments, variable force generator  401  further comprises preload element  426 . Preload element  426  axially constrains first spring  408  and or second spring  411  relative to first element  406  to preload first spring  408  and or second spring  411  when axially constrained against first orientation element  418  and or second orientation element  419 . When axially constrained against first orientation element  418 , preload element  426  may preload first spring  408  by a different distance than second spring  411 . The amount of preload provided by preload element  426  may be used to alter the force profile of variable force generator  401 , allow for the use of varying types and or lengths of first spring  408  and or second spring  411 , or facilitate proper positioning of components. 
     In some embodiments, the axial length of first spring bracket  415  and or second spring bracket  416  act to preload first spring element  442  and or second spring element  443  when axially constrained against first orientation element  418  and or second orientation element  419   
     In some embodiments, constraining mechanism  414  is translationally coupled to second spring  411 .  FIG.  72    through  FIG.  77    show an embodiment of variable force generator  401  wherein constraining mechanism  414  is a pin or t-pin that slides though a hole within second spring  411 . Constraining mechanism  414  is configured to slide into a profile, such as a hole or slot, within first spring  408  when constraining mechanism  414  is in its second position. When the constraining mechanism  414  has slid into the hole of first spring  408 , the result is that second spring  411  is axially coupled to first spring  408 , and thus second element  407 , allowing stiffness from both first spring  408  and second spring  411  to be transferred between first element  406  and second element  407 . 
       FIG.  78    is a radial section view of an alternative embodiment of variable force  401  wherein constraining mechanism  414  is a retaining ring translationally coupled to second spring  411  and configured to lock into a groove on first spring  408  and therefore axially couple first spring  408  to second spring  411 . 
     In another embodiment (not shown) constraining mechanism  414  may similarly be translationally coupled to first spring  408  and slide into a profile, such as a hole or slot, in second spring  411 . 
       FIG.  79    is an axial section view of an alternative embodiment of variable force generator  401  wherein constraining mechanism  414  is rotatably coupled to second spring  411 . In its second position, constraining mechanism  414  is configured to couple to a profile in the first spring  408  and therefore axially couple second spring  411  to first spring  408  or second element  407 . When constraining mechanism  414  is in its second position, stiffness from both first spring  408  and second spring  411  is transferred between first element  406  and second element  407 . 
       FIG.  80    is an axial section view of an embodiment of variable force generator  401  wherein constraining mechanism  414  is rotatably coupled to first spring  408 . In its second position, constraining mechanism  414  is configured to couple to a profile in the second spring  411  and therefore axially couple second spring  411  to first spring  408  or second element  407 . When constraining mechanism  414  is in its second position, stiffness from both first spring  408  and second spring  411  is transferred between first element  406  and second element  407 . 
       FIG.  81    is an axial section view of an alternative embodiment of variable force  401  wherein constraining mechanism  414  comprises a pin translationally coupled to second spring  411  that can be selectively coupled to a hook that is coupled to or part of first spring  408 . When constraining mechanism  414  is in its first position, it cannot couple to the hook. When constraining mechanism  414  is in its second position as shown, it can couple with the hook and therefore axially couple first spring  408  to second spring  411 . In another embodiment (not shown), the pin can be rotatably coupled to second spring  411  or the pin and hook combination can be reversed between first spring  408  and second spring  411 . 
       FIG.  82    shows a radial section view of an embodiment of variable force generator  401  wherein the function of constraining mechanism  414  is embedded in the shape and rotational orientation of second spring  411  relative to first spring  408 . In the embodiment, first spring  408  comprises a number of protrusions and second spring  411  comprises a number of profiles allowing the protrusions of first spring  408  to pass through. When the protrusions of first spring  408  and profiles of second spring  411  are aligned, constraining mechanism  414  is in its first position and second spring  411  is not coupled to first spring  408 . When second spring  411  is rotated so that the protrusions of first spring  408  and profiles of second spring  411  are not aligned, constraining mechanism  414  is in its second position and first spring  408  is axially coupled to second spring  411 . In another embodiment (not shown), the protrusions are on second spring  411  and the profiles are on first spring  408 . 
       FIG.  83    shows an axial section view of an embodiment of variable force generator  401  wherein the function of constraining mechanism  414  is embedded into the first spring  408  and second spring  411 . First spring  408  and second spring  411  each comprise mating threads that allow first spring  408  to be axially coupled to second spring  411  when either is rotated in a manner that engages the threads.  FIG.  83    shows the constraining mechanism  414  in a second position wherein the threads between first spring  408  and second spring  411  are engaged. The first position of constraining mechanism  414  would correspond to no threads between first spring  408  and second spring  411  being engaged. 
       FIG.  84    shows a radial section view of an embodiment of variable force generator  401  wherein constraining mechanism  414  is a screw or cam that causes second spring  411  to clamp, or friction lock, with first spring bracket  408 . When constraining mechanism  414  is in its first position, the screw or cam is loose and first spring  408  can freely pass in and out of second spring  411 . When constraining mechanism  414  is in its second position, the screw or cam is tightened and first spring  408  is compressed within second spring  411 . This feature couples first spring  408  to second spring  411  allowing the stiffness of second spring  411  to be transferred between first element  406  and second element  407 . 
     It can be appreciated by one skilled in the art that all of the embodiments of constraining mechanism  414  presented herein can be applied to other spring arrangements described later in this text to constrain any combination of first spring  408 , second spring  411 , first element  406 , or second element  407   
     In the embodiment shown in  FIG.  74    through  FIG.  77   , first spring bracket  415  has a profile that when first spring bracket  415  is not constrained to second spring bracket  416 , the first spring bracket  415  profile moves constraining mechanism  414  out of the way of first spring bracket  415  (i.e., into first position), allowing first spring bracket  415  to reach the transition position. In the first embodiment, first spring bracket  415  has a chamfered profile but it can be appreciated that other profiles are possible to reach similar results. 
     In some embodiments constraining mechanism  414  is made of a magnetic material. 
     In the embodiment shown in  FIG.  74    through  FIG.  77   , variable force generator  401  further comprises at least one first magnet  422  coupled to first spring  408  that attracts constraining mechanism  414  into its second position when first spring  408  and second spring  411  are properly aligned with first element  406 . When first magnet  422  attracts constraining mechanism  414 , it thereby axially and/or rotationally couples first spring  408  to second spring  411 . 
     In the embodiment shown in  FIG.  74    through  FIG.  77   , variable force generator  401  further comprises at least one second magnet  423  coupled to first element  406  that attracts constraining mechanism  414  into its first position when first spring  408  and second spring  411  are properly aligned to first element  406 . When second magnet  423  attracts constraining mechanism  414 , it thereby decouples first spring  408  from second spring  411 . 
     In some embodiments, the influence of second magnet  423  on constraining mechanism  414  is stronger than the influence of first magnet  422  on constraining mechanism  414 . When first spring  408  and second spring  411  are properly positioned relative to first element  406 , constraining mechanism  414  will automatically enter a first position. 
     In the embodiment shown in  FIG.  74    through  FIG.  77   , variable force generator  401  further comprises switch  420  coupled to at least one second magnet  423  and translationally coupled to first element  406 . In another embodiment (not shown), switch  420  may be rotatably coupled for first element  406 . Switch  420  can be moved relative to first element  406  between a first position wherein the second magnet  423  does attract the constraining mechanism  414  to a second position wherein the second magnet  423  does not attract the constraining mechanism  414 . 
       FIG.  74    shows variable force generator  401  at the transition position wherein switch  420  is in its second position. Second magnet  423  does not have influence on constraining mechanism  414 ; thus, first magnet  422  attracts constraining mechanism  414  to its second position and causes it to couple first spring  408  to second spring  411 . Switch  420  can be moved to its second position for any position of first spring  408  and second spring  411 , and when first spring  408  and second spring  411  return to the transition position, constraining mechanism  414  will move it its second position. 
       FIG.  75    shows variable force generator  401  at the transition position wherein switch  420  is in its first position. Second magnet  423  attracts constraining mechanism  414  to its first position and causes it to decouple first spring  408  from second spring  411 . Switch  420  can be moved to its first position for any position of first spring  408  and second spring  411 , and when first spring  408  and second spring  411  return to the transition position, constraining mechanism  414  will move it its first position. In some embodiments first element  406  further comprises cover  421  for switch  420 . 
       FIG.  85    shows another embodiment of variable force generator  401  wherein switch  420  further comprises a holding magnet  453 . The influence of holding magnet  453  on constraining mechanism  414  is weaker than the influence of first magnet  422  on constraining mechanism  414 . Thus, when both the holding magnet  453  and first magnet  422  are exposed to constraining mechanism  414 , constraining mechanism  414  will transition to a second position. Holding magnet  453  is exposed to constraining mechanism  414  when switch  420  is at a second position. Holding magnet  453  holds constraining mechanism  414  out of the way of first spring  408 , allowing first spring  408  to reach a transition position. Thus when first spring  408  reaches the transition position, constraining mechanism  414  will automatically move to its second position. 
       FIG.  86    shows an embodiment wherein constraining mechanism  414  houses a third magnet  444  and wherein switch  420  comprises fourth magnet  445  and fifth magnet  446 . Fourth magnet  445  is configured to attract third magnet  444  housed in constraining mechanism  414 . When switch  420  is positioned so that fourth magnet  445  attracts third magnet  444 , constraining mechanism  414  moves to a first position wherein first  408  is decoupled from second spring  411 . Fifth magnet  446  is configured to repel third magnet  444  housed in constraining mechanism  414 . When switch  420  is positioned so that fifth magnet  446  repels third magnet  444 , constraining mechanism  414  moves to a second position wherein first spring  408  is coupled to second spring  411 . 
     It can be appreciated by one skilled in the art that for any of the embodiments herein, the movement of constraining mechanism  414  relative to first spring  408  or second spring  411  may be similarly biased by a spring to cause constraining mechanism  414  to move to a first position or a second position. 
       FIG.  87    shows an embodiment of variable force generator  401  further comprising wedge element  429 . Wedge element  429  forces constraining mechanism  414  into a second position in the event that constraining mechanism  414  is caught between first and second position and is therefore coupling first element  406  to second element  407 . This prevents variable force generator  401  from locking first element  406  to second element  407 . 
       FIG.  88    shows an embodiment of variable force generator  401  wherein wedge element  429  is a contoured surface of constraining mechanism  414 . 
       FIG.  89    depicts an axial section view of variable force generator  401  configured to create a torque about first rotational joint  431 . First rotational joint  431  is formed between first element  406  and rotational base link  430 . In the embodiment, variable force generator  401  further comprises pulley  432  attached to first element  406  that routes flexible second element  407  to a rotational coupling with rotational base link  430 . In the embodiment shown, constraining mechanism  414  is in a first position wherein first spring  408  is decoupled from second spring  411 . First force  402  is created between first element  406  and second element  407  and thus first torque  404  is created between first element  406  and rotational base link  430  about first rotational joint  431 . 
       FIG.  90    depicts variable force generator  401  of  FIG.  76    wherein constraining mechanism  414  is in its second position and wherein first spring  408  is coupled to second spring  411 . A second force  403  is created between first element  406  and second element  407  and thus second torque  405  is created between first element  406  and rotational base link  430  about first rotational joint  431 . 
     When the proper position (radially, axially, and/or rotationally) is achieved between first spring  408 , second spring  411 , and first element  406 , a transition position is achieved wherein there are no forces acting on constraining mechanism  414 . This allows constraining mechanism  414  to more easily transition variable force generator  401  between first force mode and second force mode. 
       FIG.  72   ,  FIG.  73   ,  FIG.  74   , and  FIG.  75    show variable force generator  401  in transition position wherein all forces acting on constraining mechanism  414  due to first spring  408  and or second spring  411  facilitate ease of motion of constraining mechanism  414 .  FIG.  73    and  FIG.  74    show constraining mechanism  414  is in its second position.  FIG.  72    and  FIG.  75    show constraining mechanism  414  in its first position. 
       FIG.  92    depicts variable force generator  401  of  FIG.  89    and  FIG.  90    at the transition position, resulting in transition angle  427  between first element  406  and rotational base link  430 . When an angle of first element  406  relative to rotational base link  430  is smaller than first transition angle  427 , flexible second element  407  goes slack and variable force generator  401  does not generate a force or torque about first rotational joint  431 . When an angle of first element  406  relative to rotational base link  430  is larger than first transition angle  427 , variable force generator  401 , depending on the position of constraining mechanism  414 , generates either first force  402  and thus first torque  404  or second force  403  and thus second torque  405 . 
     In some embodiments, it is possible to change the length of second element  407  by means of its coupling to first spring  408 . In the embodiment of  FIGS.  92  and  93   , this is done by threaded end  425  on second element  407  meshing with a female thread on first spring bracket  415 . 
       FIG.  93    depicts variable force generator  401  of  FIG.  89    at the transition position. The length of second element  407  has been increased relative to  FIG.  92    resulting in a larger transition angle  427 . It can be appreciated by one skilled in the art that the length of second element  407  may be increased or decreased to increase or decrease the transition angle  427 . 
     In other embodiments (not shown), second element  407  may have a similar screw connection with rotational base link  430  to achieve the same adjustment to transition angle  427 . In still other embodiments, second element  407  may comprise the ability to change length, such as with a turnbuckle, without an adjustable connection to first spring  408  or rotational base link  430  to achieve the same adjustment to transition angle  427 . 
       FIG.  91    depicts an axial section view of an alternative embodiment of variable force generator  401  configured to create a torque about first rotational joint  431  formed between first rotating link  434  and rotational base link  430 . First element  406  is rotatably and/or translationally coupled to first rotating link  434 , and second element  407  is rotationally and/or translationally coupled to rotational base link  430 . In the embodiment shown, constraining mechanism  414  is in its second position wherein first spring  408  is coupled to second spring  411 . Second force  403  is created between first element  406  and second element  407  and thus second torque  405  is created between first element  406  and rotational base link  430  about first rotational joint  431 . 
     In some embodiments, variable force generator  401  may be mounted to the shoulder base  102  of arm supporting exoskeleton  100  and transfer forces to the arm link mechanism  104  by means of control cables. This be done to move the mass of the arm supporting exoskeleton  100  as close to the torso as possible. The control cables may be situated as to not inhibit motion of the arm link mechanism  104  or shoulder base  102 . 
       FIG.  101    shows a schematic embodiment of variable force generator  401  designed to utilize extension springs rather than compression springs as previously shown. Variable force generator  401  is adaptable to exhibit two stiffness rates between first element  406  and second element  407 . Variable force generator  401  comprises first spring  408  that has first end  409  and second end  410 . First spring  408  is constrained by first element  406  from its first end  409  and by the second element  407  from its second end  410 . Variable force generator  401  further comprises second spring  411  which has first end  412  and second end  413 . Second spring  411  is constrained by second element  407  from its second end  413 . Variable force generator  401  further comprises at least one constraining mechanism  414  which is configurable to have at least a first position and a second position.  FIG.  102    shows a hardware embodiment of variable force generator  401 . 
     In operation, when the constraining mechanism  414  is in its first position, as shown in  FIG.  103   , first end  412  of second spring  411  is not constrained by first element  406 . This causes second spring  411  not to affect the motion between first element  406  and second element  407 . In this first position, the equivalent stiffness is the stiffness of first spring  408 . 
     When constraining mechanism  414  is in its second position as shown in  FIG.  102   , first end  412  of second spring  411  is constrained by first element  406 . This causes the second spring  411  to act in parallel with first spring  408 . In this second position, the equivalent stiffness is the addition of both the stiffness of first spring  408  and stiffness of second spring  411 . 
       FIG.  102    and  FIG.  103    depict a translational coupling arrangement of constraining mechanism  414  between second spring  411  and first element  406  similar in function to the embodiment of  FIG.  68   , the only difference being between the two components constrained by constraining mechanism  414 . 
       FIG.  104    depicts a pin and hook arrangement of constraining mechanism  414  between second spring  411  and first element  406  similar in form to the embodiment of  FIG.  81   , the only difference being between the two components constrained by constraining mechanism  414 . 
       FIG.  105    depicts a rotatable coupling arrangement of constraining mechanism  414  between second spring  411  and first element  406  similar in form to the embodiment of  FIG.  80   , the only difference being between the two components constrained by constraining mechanism  414 . 
     It can be appreciated by one skilled in the art that all of the embodiments of constraining mechanism  414  presented herein can be applied to other spring arrangements described later in this text to constrain any combination of first spring  408 , second spring  411 , first element  406 , or second element  407 . 
       FIG.  106    shows a schematic embodiment of variable force generator  401  utilizing first spring  408  and second spring  411  in series. Variable force generator  401  is adaptable to exhibit two stiffness rates between first element  406  and second element  407 . Variable force generator  401  comprises first spring  408  that has first end  409  and second end  410 . First spring  408  is constrained by first element  406  from its first end  409  and by the second spring  411  from its second end  410 . Variable force generator  401  further comprises second spring  411 , which has first end  412  and second end  413 . Second spring  411  is constrained by first spring  408  from its first end  412  and by second element  407  from its second end. Variable force generator  401  further comprises at least one constraining mechanism  414 , which is configurable to have at least a first position and a second position.  FIG.  107    shows a hardware embodiment of this embodiment of variable force generator  401 . 
     In operation, when the constraining mechanism  414  is in its first position, first end  412  of second spring  411  is not constrained by first element  406 . This causes second spring  411  to act in series with first spring  411 . In this first position, the equivalent stiffness is the stiffness of first spring  408  and second spring  411  in series. In this first position, the equivalent deflection is the deflection of first spring  408  and second spring  411  in series. When constraining mechanism  414  is in its second position, first end  412  of second spring  411  is constrained by first element  406 . This causes the second spring  411  to act alone. In this second position, the equivalent stiffness is the stiffness of second spring  411 , and the equivalent deflection is the deflection of second spring  411 . In the series combination shown, first spring  408  or second spring  411  may be compression or extension springs. 
       FIG.  108    shows an alternative embodiment of variable force generator  401  with first spring  408  and second spring  411  in series. Variable force generator  401  is adaptable to exhibit two stiffness rates between first element  406  and second element  407 . Variable force generator  401  comprises first spring  408  that has first end  409  and second end  410 . First spring  408  is constrained by second spring  411  from its first end  409  and by the second element  407  from its second end  410 . Variable force generator  401  further comprises second spring  411 , which has first end  412  and second end  413 . Second spring  411  is constrained by first element  406  from its first end  412  and by first spring  408  from its second end  413 . Variable force generator  401  further comprises at least one constraining mechanism  414 , which is configurable to have at least a first position and a second position. 
     In operation, when the constraining mechanism  414  is in its first position, second end  413  of second spring  411  is not constrained by second end  410  of first spring  408 . This causes second spring  411  to act in series with first spring  408 . In this first position, the equivalent stiffness is the stiffness of first spring  408  and second spring  411  in series. In this first position, the equivalent deflection is the deflection of first spring  408  and second spring  411  in series. When constraining mechanism  414  is in its second position, second end  413  of second spring  411  is constrained by second end  410  of first spring  408 . This causes the second spring  411  to act alone. In this second position, the equivalent stiffness is the stiffness of second spring  411 , and the equivalent deflection is the deflection of second spring  411 . 
       FIG.  109    shows an alternative embodiment of variable force generator  401  with first spring  408  and second spring  411  in series. Variable force generator  401  is adaptable to exhibit two stiffness rates between first element  406  and second element  407 . Variable force generator  401  comprises first spring  408  that has first end  409  and second end  410 . First spring  408  is constrained by second spring  411  from its first end  409  and by the second element  407  from its second end  410 . Variable force generator  401  further comprises second spring  411 , which has first end  412  and second end  413 . Second spring  411  is constrained by first element  406  from its first end  412  and by first spring  408  from its second end  413 . Variable force generator  401  further comprises at least one constraining mechanism  414 , which is configurable to have at least a first position and a second position. 
     In operation, when the constraining mechanism  414  is in its first position, second end  413  of second spring  411  is not constrained by first element  406 . This causes second spring  411  to act in series with first spring  411 . In this first position, the equivalent stiffness is the stiffness of first spring  408  and second spring  411  in series. In this first position, the equivalent deflection is the deflection of first spring  408  and second spring  411  in series. When constraining mechanism  414  is in its second position, second end  413  of second spring  411  is constrained by first element  406 . This causes the first spring  408  to act alone. In this second position, the equivalent stiffness is the stiffness of first spring  408 , and the equivalent deflection is the deflection of first spring  408 . 
       FIG.  110    shows a schematic embodiment of a variable force generator  401  utilizing first spring  408  and second spring  411  in series. Variable force generator  401  is adaptable to exhibit two stiffness rates between first element  406  and second element  407 . Variable force generator  401  comprises first spring  408  that has first end  409  and second end  410 . First spring  408  is constrained by first element  406  from its first end  409  and by the second spring  411  from its second end  410 . Variable force generator  401  further comprises second spring  411 , which has first end  412  and second end  413 . Second spring  411  is constrained by first spring  408  from its first end  412  and by second element  407  from its second end. Variable force generator  401  further comprises at least one constraining mechanism  414 , which is configurable to have at least a first position and a second position. 
     In operation, when the constraining mechanism  414  is in its first position, second end  413  of second spring  411  is not constrained by second end  410  of first spring  408 . This causes second spring  411  to act in series with first spring  411 . In this first position, the equivalent stiffness is the stiffness of first spring  408  and second spring  411  in series. In this first position, the equivalent deflection is the deflection of first spring  408  and second spring  411  in series. 
     When constraining mechanism  414  is in its second position, second end  413  of second spring  411  is constrained by second end  410  of first spring  408 . This causes the first spring  408  to act alone. In this second position, the equivalent stiffness is the stiffness of first spring  408 , and the equivalent deflection is the deflection of first spring  408 . 
       FIG.  95    shows a schematic embodiment of variable force generator  401 . Variable force generator  401  is adaptable to exhibit three stiffness rates between first element  406  and second element  407 . Variable force generator  401  comprises first spring  408  that has a first end  409  and second end  410 . First spring  408  is constrained by first element  406  from its first end  409  and by the second element  407  from its second end  410 . Variable force generator  401  further comprises two second springs  411  which have first end  412  and second end  413 . Second springs  411  are constrained by first element  406  from their first end  412 . Variable force generator  401  further comprises at least two constraining mechanisms  414  which are configurable to have at least a first position and a second position.  FIG.  96    shows a hardware embodiment of variable force generator  401 . 
     In operation, when both constraining mechanisms  414  are in their first position, second end  413  of both second springs  411  are not constrained by second element  407 . This causes second springs  411  not to affect the motion between first element  406  and second element  407 . In this first position, the equivalent stiffness is the stiffness of first spring  408 . When one constraining mechanism  414  is in its second position and one constraining mechanism  414  is in its first position, second end  413  of one second spring  411  is constrained by second element  407  and second end  413  of the other second spring  411  is not constrained by second element  407 . This causes one second spring  411  to act in parallel with first spring  408 . In this second position, the equivalent stiffness is the addition of both the stiffness of first spring  408  and stiffness of one second spring  411 . When both constraining mechanisms  414  are in their second position, second end  413  of both second springs  411  are constrained by second element  407 . This causes both second springs  411  to act in parallel with first spring  408 . In this second position, the equivalent stiffness is the addition of both the stiffness of first spring  408  and stiffness of both second springs  411 . 
     It may be appreciated by one skilled in the art that a greater number of second springs  411  may be added to increase the number of stiffness rates between first element  406  and second element  407 . 
       FIG.  97    shows a schematic embodiment of variable force generator  401 . Variable force generator  401  is adaptable to exhibit three stiffness rates between first element  406  and second element  407 . Variable force generator  401  comprises first spring  408  that has a first end  409  and second end  410 . First spring  408  is constrained by first element  406  from its first end  409  and by the second element  407  from its second end  410 . Variable force generator  401  further comprises second spring  411 , which has first end  412  and second end  413 . Second spring  411  is constrained by first element  406  from its first end  412 . Variable force generator further comprises third spring  447  which has first end  448  and second end  449 . Third spring  447  is constrained by first element  406  from its first end  448 . Variable force generator  401  further comprises constraining mechanism  414 , which is configurable to have at least a first position and a second position. Variable force generator further comprises a second constraining mechanism  452 , which is configurable to have at least a first position and a second position. 
       FIG.  98    shows a hardware embodiment of variable force generator  401  wherein first spring  408  further comprises first spring element  442  and first spring bracket  415 , second spring  411  further comprises second spring element  443  and second spring bracket  416 , and third spring  447  further comprises third spring element  450  and third spring bracket  451 . The function of each spring element is to provide the stiffness of the respective spring. The function of each spring bracket is to transfer force, facilitate the housing, motion, or general function of constraining mechanism  414  or second constraining mechanism  452 , facilitate the coupling between components, or facilitate the motion or stabilization of its respective spring. 
     In operation, when constraining mechanism  414  is in its first position, second end  413  of second spring  411  and of third spring  447  are not constrained by second element  407 . This causes second spring  411  and third spring  447  not to affect the motion between first element  406  and second element  407 . In this first position, the equivalent stiffness is the stiffness of first spring  408 . When constraining mechanism  414  is in its second position and second constraining mechanism  452  is in its first position, second end  413  of second spring  411  is constrained by second element  407  and second end  413  of third spring  447  is not constrained by second element  407 . This causes second spring  411  to act in parallel with first spring  408 . In this second position, the equivalent stiffness is the addition of both the stiffness of first spring  408  and stiffness of one second spring  411 . When constraining mechanisms  414  and second constraining mechanism  452  are in their second positions, second end  413  of second springs  411  and of third spring  447  are constrained by second element  407 . This causes second spring  411  and third spring  447  to act in parallel with first spring  408 . In this second position, the equivalent stiffness is the addition of the stiffness of first spring  408  the stiffness of second springs  411 , and the stiffness of third spring  447 . 
       FIG.  99    shows a schematic embodiment of variable force generator  401 . Variable force generator  401  is adaptable to exhibit three stiffness rates between first element  406  and second element  407 . Variable force generator  401  comprises first spring  408  that has first end  409  and second end  410 . First spring  408  is constrained by first element  406  from its first end  409  and by the second element  407  from its second end  410 . Variable force generator  401  further comprises second spring  411 , which has first end  412  and second end  413 . Second spring  411  is constrained by first element  406  from its first end  412 . Variable force generator further comprises third spring  447 , which has first end  448  and second end  449 . Third spring  447  is constrained by first element  406  from its first end  448 . Variable force generator  401  further comprises constraining mechanism  414 , which is configurable to have at least a first position, a second position, and a third position. 
       FIG.  100    shows a hardware embodiment of variable force generator  401  wherein first spring  408  further comprises first spring element  442  and first spring bracket  415 , second spring  411  further comprises second spring element  443  and second spring bracket  416 , and third spring  447  further comprises third spring element  450  and third spring bracket  451 . The function of each spring element is to provide the stiffness of the respective spring. The function of each spring bracket is to transfer force, facilitate the housing, motion, or general function of constraining mechanism  414 , facilitate the coupling between components, or facilitate the motion or stabilization of its respective spring. 
     In operation, when constraining mechanism  414  is in its first position, second end  413  of second spring  411  and of third spring  447  are not constrained by second element  407 . This causes second spring  411  and third spring  447  not to affect the motion between first element  406  and second element  407 . In this first position, the equivalent stiffness is the stiffness of first spring  408 . When constraining mechanism  414  is in its second position, second end  413  of second spring  411  is constrained by second element  407  and second end  413  of third spring  447  is not constrained by second element  407 . This causes second spring  411  to act in parallel with first spring  408 . In this second position, the equivalent stiffness is the addition of both the stiffness of first spring  408  and stiffness of one second spring  411 . When constraining mechanisms  414  is in a third position, second end  413  of second springs  411  and of third spring  447  are constrained by second element  407 . This causes second spring  411  and third spring  447  to act in parallel with first spring  408 . In this third position, the equivalent stiffness is the addition of the stiffness of first spring  408 , the stiffness of second springs  411 , and the stiffness of third spring  447 . 
     It can be understood that the various embodiments of spring element arrangements and types of spring elements described can be combined to form embodiments with multiple force modes not explicitly described herein, and that the mechanisms described herein can be modified by a rearrangement of parts to selectively couple first  406 , second element  407 , first spring  408 , second spring  411 , first spring bracket  415 , second spring bracket  416  or any combination thereof to accomplish multiple stiffness rates of the variable force generator  401  as described in through various series and parallel spring arrangements with compression and extension spring elements.