Patent Publication Number: US-2021177687-A1

Title: Skiing exoskeleton control method and system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional of and claims the benefit of U.S. Provisional Application No. 62/948,069, filed Dec. 13, 2019, entitled “POWERED DEVICE TO BENEFIT A WEARER DURING SKIING,” with attorney docket number 0110496-007PR0. This application is hereby incorporated herein by reference in its entirety and for all purposes. 
     This application is also a non-provisional of and claims the benefit of U.S. Provisional Application 63/030,586, filed May 27, 2020, entitled “POWERED DEVICE FOR IMPROVED USER MOBILITY AND MEDICAL TREATMENT” with attorney docket number 0110496-010PR0. This application is hereby incorporated herein by reference in its entirety and for all purposes. 
     This application is also a non-provisional of and claims the benefit of U.S. Provisional Application 63/058,825, filed Jul. 30, 2020, entitled “POWERED DEVICE TO BENEFIT A WEARER DURING TACTICAL APPLICATIONS” with attorney docket number 0110496-011PR0. This application is hereby incorporated herein by reference in its entirety and for all purposes. 
     This application is also related to U.S. patent application Ser. No. 15/082,824, filed Mar. 28, 2016 entitled “LOWER-LEG EXOSKELETON SYSTEM AND METHOD” with attorney docket number 0110496-001US0. This application is hereby incorporated herein by reference in its entirety and for all purposes. 
     This application is also related to U.S. patent application Ser. No. 15/823,523, filed Nov. 27, 2017 entitled “PNEUMATIC EXOMUSCLE SYSTEM AND METHOD” with attorney docket number 0110496-002US1. This application is hereby incorporated herein by reference in its entirety and for all purposes. 
     This application is also related to U.S. patent application Ser. No. 15/887,866, filed Feb. 02, 2018 entitled “SYSTEM AND METHOD FOR USER INTENT RECOGNITION,” having attorney docket number 0110496-003US0. This application is hereby incorporated herein by reference in its entirety and for all purposes. 
     This application is also related to U.S. patent application Ser. No. 15/953,296, filed Apr. 13, 2018 entitled “LEG EXOSKELETON SYSTEM AND METHOD” with attorney docket number 0110496-004US0. This application is hereby incorporated herein by reference in its entirety and for all purposes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 and 2  are example illustrations of an embodiment of an exoskeleton system being worn by a user while skiing. 
       FIG. 3  is a front view of an embodiment of a leg actuation unit coupled to one leg of a user. 
       FIG. 4  is a side view of the leg actuation unit of  FIG. 3  coupled to the leg of the user. 
       FIG. 5  is a perspective view of the leg actuation unit of  FIGS. 3 and 4 . 
       FIG. 6  is a block diagram illustrating an example embodiment of an exoskeleton system. 
       FIG. 7  illustrates a user interface disposed on a strap of a backpack in accordance with one embodiment. 
       FIG. 8 a    illustrates a side view of a pneumatic actuator in a compressed configuration in accordance with one embodiment. 
       FIG. 8 b    illustrates a side view of the pneumatic actuator of  FIG. 8 a    in an expanded configuration. 
       FIG. 9 a    illustrates a cross-sectional side view of a pneumatic actuator in a compressed configuration in accordance with another embodiment. 
       FIG. 9 b    illustrates a cross-sectional side view of the pneumatic actuator of  FIG. 9 a    in an expanded configuration. 
       FIG. 10 a    illustrates a top view of a pneumatic actuator in a compressed configuration in accordance with another embodiment. 
       FIG. 10 b    illustrates a top of the pneumatic actuator of  FIG. 10 a    in an expanded configuration. 
       FIG. 11  illustrates a top view of a pneumatic actuator constraint rib in accordance with an embodiment. 
       FIG. 12 a    illustrates a cross-sectional view of a pneumatic actuator bellows in accordance with another embodiment. 
       FIG. 12 b    illustrates a side view of the pneumatic actuator of  FIG. 12 a    in an expanded configuration showing the cross section of  FIG. 12   a.    
       FIG. 13  illustrates an example planar material that is substantially inextensible along one or more plane axes of the planar material while being flexible in other directions. 
    
    
     It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are generally represented by like reference numerals for illustrative purposes throughout the figures. It also should be noted that the figures are only intended to facilitate the description of the preferred embodiments. The figures do not illustrate every aspect of the described embodiments and do not limit the scope of the present disclosure. 
     DETAILED DESCRIPTION 
     The following disclosure includes example embodiments of the design of novel exoskeleton devices for use during skiing activities. Exoskeletons have been conceived and evaluated for a variety of applications, however, the use of exoskeleton devices for recreational activities such as skiing is yet unexplored. This disclosure describes various embodiments of an exoskeleton used for skiing activities and methods of operating an exoskeleton in conjunction with the operator. 
     In one aspect, this disclosure teaches the method for developing various embodiments of an exoskeleton for use during recreational skiing. Various preferred embodiments include: a leg brace with integrated actuation, a mobile power source, and a control unit that determines the output behavior of the device in real-time. 
     A component of an exoskeleton system that is present in various embodiments is a body-worn, lower-extremity brace that incorporates the ability to introduce torque to the user. One preferred embodiment of this component is a leg brace that is configured to support the knee of the user and includes actuation across the knee joint to provide assistance torques in the extension direction. This embodiment can connect to the user through a series of attachments including one on the boot, below the knee, and along the user&#39;s thigh. This preferred embodiment can include this type of leg brace on both legs of the user. 
     The present disclosure teaches example embodiments of a fluidic exoskeleton system that includes one or more adjustable fluidic actuator. Some preferred embodiments include a fluidic actuator that can be operated at various pressure levels with a large stroke length in a configuration that can be oriented with a joint on a human body. 
     As discussed herein, an exoskeleton system  100  can be configured for various suitable uses. For example,  FIGS. 1 and 2  illustrate an exoskeleton system  100  being used by a user  101  during skiing. As shown in  FIGS. 1 and 2  the user  101  can wear the exoskeleton system  100  and a skiing assembly  190  that includes a pair of ski boots  191  and pair of skis  192 .  FIGS. 3 and 4  illustrate a front and side view of an actuator unit  110  coupled to a leg  102  of a user  101  and  FIG. 5  illustrates a side view of an actuator unit  110  not being worn by a user  101 . 
     As shown in the example of  FIGS. 1 and 2 , the exoskeleton system  100  can comprise a left and right leg actuator unit  110 L,  110 R that are respectively coupled to a left and right leg  102 L,  102 R of the user. In various embodiments, the left and right leg actuator units  110 L,  110 R can be substantially mirror images of each other. 
     As shown in  FIGS. 1-5 , leg actuator units  110  can include an upper arm  115  and a lower arm  120  that are rotatably coupled via a joint  125 . A bellows actuator  130  extends between the upper arm  115  and lower arm  120 . One or more sets of pneumatic lines  145  can be coupled to the bellows actuator  130  to introduce and/or remove fluid from the bellows actuator  130  to cause the bellows actuator  130  to expand and contract and to stiffen and soften, as discussed herein. A backpack  155  can be worn by the user  101  and can hold various components of the exoskeleton system  100  such as a fluid source, control system, a power source, and the like. 
     As shown in  FIGS. 1-4 , the leg actuator units  110 L,  110 R can be respectively coupled about the legs  102 L,  102 R of the user  101  with the joints  125  positioned at the knees  103 L,  103 R of the user  101  with the upper arms  115  of the leg actuator units  110 L,  110 R being coupled about the upper legs portions  104 L,  104 R of the user  101  via one or more couplers  150  (e.g., straps that surround the legs  102 ). The lower arms  120  of the leg actuator units  110 L,  110 R can be coupled about the lower leg portions  105 L,  105 R of the user  101  via one or more couplers  150 . 
     The upper and lower arms  115 ,  120  of a leg actuator unit  110  can be coupled about the leg  102  of a user  101  in various suitable ways. For example,  FIGS. 1-4  illustrates an example where the upper and lower arms  115 ,  120  and joint  125  of the leg actuator unit  110  are coupled along lateral faces (sides) of the top and bottom portions  104 ,  105  of the leg  102 . As shown in the example of  FIGS. 1-4 , the upper arm  115  can be coupled to the upper leg portion  104  of a leg  102  above the knee  103  via two couplers  150  and the lower arm  120  can be coupled to the lower leg portion  105  of a leg  102  below the knee  103  via two couplers  150 . 
     Specifically, upper arm  115  can be coupled to the upper leg portion  104  of the leg  102  above the knee  103  via a first set of couplers  250 A that includes a first and second coupler  150 A,  150 B. The first and second couplers  150 A,  150 B can be joined by a rigid plate assembly  215  disposed on a lateral side of the upper leg portion  104  of the leg  102 , with straps  151  of the first and second couplers  150 A,  150 B extending around the upper leg portion  104  of the leg  102 . The upper arm  115  can be coupled to the plate assembly  215  on a lateral side of the upper leg portion  104  of the leg  102 , which can transfer force generated by the upper arm  115  to the upper leg portion  104  of the leg  102 . 
     The lower arm  120  can be coupled to the lower leg portion  105  of a leg  102  below the knee  103  via second set of couplers  250 B that includes a third and fourth coupler  150 C,  150 D. A coupling branch unit  220  can extend from a distal end of, or be defined by a distal end of the lower arm  120 . The coupling branch unit  220  can comprise a first branch  221  that extends from a lateral position on the lower leg portion  105  of the leg  102 , curving upward and toward the anterior (front) of the lower leg portion  105  to a first attachment  222  on the anterior of the lower leg portion  105  below the knee  103 , with the first attachment  222  joining the third coupler  150 C and the first branch  221  of the coupling branch unit  220 . The coupling branch unit  220  can comprise a second branch  223  that extends from a lateral position on the lower leg portion  105  of the leg  102 , curving downward and toward the posterior (back) of the lower leg portion  105  to a second attachment  224  on the posterior of the lower leg portion  105  below the knee  103 , with the second attachment  224  joining the fourth coupler  150 D and the second branch  223  of the coupling branch unit  220 . 
     As shown in the example of  FIGS. 1-4 , the fourth coupler  150 D can be configured to surround and engage the ski boot  191  of a user. For example, the strap  151  of the fourth coupler  150 D can be of a size that allows the fourth coupler  150 D to surround the larger diameter of a ski boot  191  compared to the lower portion  105  of the leg  102  alone. Also, the length of the lower arm  120  and/or coupling branch unit  220  can be of a length sufficient for the fourth coupler to  150 D to be positioned over a ski boot  191  instead of being of a shorter length such that the fourth coupler  150 D would surround a section of the lower portion  105  of the leg  102  above the ski boot  191  when the leg actuator unit  110  is worn by a user. 
     Attaching to the ski boot  191  can vary across various embodiments. In one embodiment, this attachment can be accomplished through a flexible strap that wraps around the circumference of ski boot  191  to affix the leg actuator unit  110  to the ski boot  191  with the desired amount of relative motion between the leg actuator unit  110  and the strap. Other embodiments can work to restrict various degrees of freedom while allowing the desired amount of relative motion between the leg actuator unit  110  and the boot  191  in other degrees of freedom. One such embodiment can include the use of a mechanical clip that connects to the back of the ski boot  191  that can provide a specific mechanical connection between the device and the ski boot  191 . Various embodiments can include but are not limited to the designs listed previously, a mechanical bolted connection, a rigid strap, a magnetic connection, an electro-magnetic connection, an electromechanical connection, an insert into the user&#39;s boot, a rigid or flexible cable, or a connection directly to a ski  192 . 
     Another aspect of the exoskeleton system  100  can be fit components used to secure the exoskeleton system  100  to the user  101 . Since the function of the exoskeleton system  100  in various embodiments can rely heavily on the fit of the exoskeleton system  100  efficiently transmitting forces between the user  101  and the exoskeleton system  100  without the exoskeleton system  100  significantly drifting on the body  101  or creating discomfort, improving the fit of the exoskeleton system  100  and monitoring the fit of the exoskeleton system  100  to the user over time can be desirable for the overall function of the exoskeleton system  100  in some embodiments. 
     In various examples, different couplers  150  can be configured for different purposes, with some couplers  150  being primarily for the transmission of forces, with others being configured for secure attachment of the exoskeleton system  100  to the body  101 . In one preferred embodiment for a single knee system, a coupler  150  that sits on the lower leg  105  of the user  101  (e.g., one or both of couplers  150 C,  150 D) can be intended to target body fit, and as a result, can remain flexible and compliant to conform to the body of the user  101 . Alternatively, in this embodiment a coupler  150  that affixes to the front of the user&#39;s thigh on an upper portion  104  of the leg  102  (e.g., one or both of couplers  150 A,  150 B) can be intended to target power transmission needs and can have a stiffer attachment to the body than others couplers  150  (e.g., one or both of couplers  150 C,  150 D). Various embodiments can employ a variety of strapping or coupling configurations, and these embodiments can extend to include any variety of suitable straps, couplings, or the like, where two parallel sets of coupling configurations are meant to fill these different needs. 
     In some cases the design of the joint  125  can improve the fit of the exoskeleton system  100  on the user. In one embodiment, the joint  125  of a single knee leg actuator unit  110  can be designed to use a single pivot joint that has some deviations with the physiology of the knee joint. Another embodiment, uses a polycentric knee joint to better fit the motion of the human knee joint, which in some examples can be desirably paired with a very well fit leg actuator unit  110 . Various embodiments of a joint  125  can include but are not limited to the example elements listed above, a ball and socket joint, a four bar linkage, and the like. 
     Some embodiments can include fit adjustments for anatomical variations in varus or valgus angles in the lower leg  105 . One preferred embodiment includes an adjustment incorporated into a leg actuator unit  110  in the form of a cross strap that spans the joint of the knee  103  of the user  101 , which can be tightened to provide a moment across the knee joint in the frontal plane which varies the nominal resting angle. Various embodiments can include but are not limited to the following: a strap that spans the joint  125  to vary the operating angle of the joint  125 ; a mechanical assembly including a screw that can be adjusted to vary the angle of the joint  125 ; mechanical inserts that can be added to the leg actuator unit  110  to discreetly change default angle of the joint  125  for the user  101 , and the like. 
     In various embodiments, the leg actuator unit  110  can be configured to remain suspended vertically on the leg  102  and remain appropriately positioned with the joint of the knee  103 . In one embodiment, coupler  150  associated with a ski boot  191  (e.g., coupler  150 D) can provide a vertical retention force for a leg actuator unit  110 . Another embodiment uses a coupler  150  positioned on the lower leg  105  of the user  101  (e.g., one or both of couplers  150 C,  150 D) that exerts a vertical force on the leg actuator unit  110  by reacting on the calf of the user  101 . Various embodiments can include but are not limited to the following: suspension forces transmitted through a coupler  150  on the ski boot (e.g., coupler  150 D) or another embodiment of ski boot attachment discussed previously; suspension forces transmitted through an electronic and/or fluidic cable assembly; suspension forces transmitted through a connection to a waist belt; suspension forces transmitted through a mechanical connection to a backpack  155  or other housing for the exoskeleton device  610  and/or pneumatic system  620  (see  FIG. 6 ); suspension forces transmitted through straps or a harness to the shoulders of the user  101 , and the like. 
     In some embodiments, it can be desirable to verify that the fit of the leg actuator unit  110  on the leg  102  of the user  101  is within suitable operating parameters to enable ideal operation and performance of the exoskeleton system  100 . One embodiment can include the use of an external fit jig that can be held up to the leg  102  of the user  101  with the leg actuator unit  110  donned to determine where the fit of the leg actuator unit  110  is outside of allowable tolerances. In some examples, such a mechanical jig can be used upon initial donning of one or more leg actuator units  110  or periodically throughout use of the one or more leg actuator unit  110  to determine whether the fit of the leg actuator unit  110  is outside of allowable tolerances. Various embodiments include but are not limited to the following: external mechanical jig; the exoskeleton device  610  tracking performance of the exoskeleton system  100  to identify proper or improper fit; visual inspection tools that analyze one or more images of the exoskeleton system  100  on the user  101  (e.g. an application on a smartphone); a laser-guided fit system, and the like. 
     In various embodiments, a leg actuator unit  110  can be spaced apart from the leg  102  of the user with a limited number of attachments to the leg  102 . For example, in some embodiments, the leg actuator unit  110  can consist or consist essentially of three attachments to the leg  102  of the user  101 , namely via the first and second attachments  222 ,  224  and the  215 . In various embodiments, the couplings of the leg actuator unit  110  to the lower leg portion  105  can consist or consist essentially of a first and second attachment on the anterior and posterior of the lower leg portion  105 . In various embodiments, the coupling of the leg actuator unit  110  to the upper leg portion  104  can consist or consist essentially of a single lateral coupling, which can be associated with one or more couplers  150  (e.g., two couplers  150 A,  150 B as shown in  FIGS. 1-5 ). In various embodiments, such a configuration can be desirable based on the specific force-transfer for use during skiing. Accordingly, the number and positions of attachments or coupling to the leg  102  of the user  101  in various embodiments is not a simple design choice and is specifically selected for the application of skiing. 
     While specific embodiments of couplers  150  are illustrated herein, in further embodiments, such components discussed herein can be operably replaced by an alternative structure to produce the same functionality. For example, while straps, buckles, padding and the like are shown in various examples, further embodiments can include couplers  150  of various suitable types and with various suitable elements. For example, some embodiments can include Velcro hook-and-loop straps, or the like. 
     Additionally, in various embodiments, it can be desirable for the exoskeleton system  100  to be configured for coupling over the clothing of a user  101  and without modification or addition of hardware to a skiing assembly  190  such as to ski boots  191 . For example, as shown in the embodiments of  FIGS. 1-5 , the fourth coupler can be configured to couple to the ski boot  191  of a user  101  without modification of the ski boot  191  or addition of hardware to the ski boot  191 . In other words, a user can don clothing and ski gear as they would normally and then don the exoskeleton system  100  over their normal clothing and ski gear. Such a configuration can be desirable so that users  101  can quickly and easily switch out or use different ski gear without need to modify or change hardware on the ski gear to use the exoskeleton system  100 . Additionally, such a configuration can allow multiple users  101  to easily use the same exoskeleton system  100  interchangeably. 
       FIGS. 1-4  illustrate another example of an exoskeleton system  100  where the joint  125  is disposed laterally and adjacent to the knee  103  with a rotational axis of the joint  125  being disposed parallel to a rotational axis of the knee  103 . In some embodiments, the rotational axis of the joint  125  can be coincident with the rotational axis of the knee  103 . In some embodiments, a joint can be disposed on the anterior of the knee  103 , posterior of the knee  103 , inside of the knee  103 , or the like. 
     In various embodiments, the joint structure  125  can constrain the bellows actuator  130  such that force created by actuator fluid pressure within the bellows actuator  130  can be directed about an instantaneous center (which may or may not be fixed in space). In some cases of a revolute or rotary joint, or a body sliding on a curved surface, this instantaneous center can coincide with the instantaneous center of rotation of the joint  125  or a curved surface. Forces created by a leg actuator unit  110  about a rotary joint  125  can be used to apply a moment about an instantaneous center as well as still be used to apply a directed force. In some cases of a prismatic or linear joint (e.g., a slide on a rail, or the like), the instantaneous center can be kinematically considered to be located at infinity, in which case the force directed about this infinite instantaneous center can be considered as a force directed along the axis of motion of the prismatic joint. In various embodiments, it can be sufficient for a rotary joint  125  to be constructed from a mechanical pivot mechanism. In such an embodiment, the joint  125  can have a fixed center of rotation that can be easy to define, and the bellows actuator  130  can move relative to the joint  125 . In a further embodiment, it can be beneficial for the joint  125  to comprise a complex linkage that does not have a single fixed center of rotation. In yet another embodiment, the joint  125  can comprise a flexure design that does not have a fixed joint pivot. In still further embodiments, the joint  125  can comprise a structure, such as a human joint, robotic joint, or the like. 
     In various embodiments, leg actuator unit  110  (e.g., comprising bellows actuator  130 , joint structure  125 , and the like) can be integrated into a system to use the generated directed force of the leg actuator unit  110  to accomplish various tasks. In some examples, a leg actuator unit  110  can have one or more unique benefits when the leg actuator unit  110  is configured to assist the human body or is included into a powered exoskeleton system  100 . In an example embodiment, the leg actuator unit  110  can be configured to assist the motion of a human user about the user&#39;s knee joint  103 . To do so, in some examples, the instantaneous center of the leg actuator unit  110  can be designed to coincide or nearly coincide with the instantaneous center of rotation of the knee  103  of a user  101 . In one example configuration, the leg actuator unit  110  can be positioned lateral to the knee joint  103  as shown in  FIGS. 1-4 . In various examples, the human knee joint  103  can function as (e.g., in addition to or in place of) the joint  125  of the leg actuator unit  110 . 
     For clarity, example embodiments discussed herein should not be viewed as a limitation of the potential applications of the leg actuator unit  110  described within this disclosure. The leg actuator unit  110  can be used on other joints of the body including but not limited to one or more elbow, one or more hip, one or more finger, one or more ankle, spine, or neck. In some embodiments, the leg actuator unit  110  can be used in applications that are not on the human body such as in robotics, for general purpose actuation, animal exoskeletons, or the like. 
     Also, while example embodiments herein can relate to skiing, further embodiments can be used for or adapted for various other suitable applications such as tactical, medical, or labor applications, and the like. Examples of such applications can be found in U.S. patent application Ser. No. 15/823,523, filed Nov. 27, 2017 entitled “PNEUMATIC EXOMUSCLE SYSTEM AND METHOD” with attorney docket number 0110496-002US1 and U.S. patent application Ser. No. 15/953,296, filed Apr. 13, 2018 entitled “LEG EXOSKELETON SYSTEM AND METHOD” with attorney docket number 0110496-004US0, which are incorporated herein by reference. 
     Some embodiments can apply a configuration of a leg actuator unit  110  as described herein for linear actuation applications. In an example embodiment, the bellows  130  can comprise a two-layer impermeable/inextensible construction, and one end of one or more constraining ribs can be fixed to the bellows  130  at predetermined positions. The joint structure  125  in various embodiments can be configured as a series of slides on a pair of linear guide rails, where the remaining end of one or more constraining rib is connected to a slide. The motion and force of the fluidic actuator can therefore be constrained and directed along the linear rail. 
       FIG. 6  is a block diagram of an example embodiment of an exoskeleton system  100  that includes an exoskeleton device  610  that is operably connected to a pneumatic system  620 . While a pneumatic system  620  is used in the example of  FIG. 6 , further embodiments can include any suitable fluidic system or a pneumatic system  620  can be absent in some embodiments, such as where an exoskeleton system  100  is actuated by electric motors, or the like. 
     The exoskeleton device  610  in this example comprises a processor  611 , a memory  612 , one or more sensors  613  a communication unit  614 , a user interface  615  and a power source  616 . A plurality of actuators  130  are operably coupled to the pneumatic system  620  via respective pneumatic lines  145 . The plurality of actuators  130  include a pair knee-actuators  130 L,  130 R that are positioned on the right and left side of a body  100 . For example, as discussed above, the example exoskeleton system  100  shown in  FIG. 6  can comprise a left and right leg actuator unit  110 L,  110 R on respective sides of the body  101  as shown in  FIGS. 1 and 2  with one or both of the exoskeleton device  610  and pneumatic system  620 , or one or more components thereof, stored within or about a backpack  155  (see  FIGS. 1 and 2 ) or otherwise mounted, worn or held by a user  101 . 
     Accordingly, in various embodiments, the exoskeleton system  100  can be a completely mobile and self-contained system that is configured to be powered and operate for an extended period of time without an external power source, such as during a skiing session, mountaineering, and the like. The size, weight and configuration of the actuator unit(s)  110 , exoskeleton device  610  and pneumatic system  620  can therefore be configured in various embodiments for such mobile and self-contained operation. 
     In various embodiments, the example system  100  can be configured to move and/or enhance movement of the user  101  wearing the exoskeleton system  100 . For example, the exoskeleton device  610  can provide instructions to the pneumatic system  620 , which can selectively inflate and/or deflate the bellows actuators  130  via pneumatic lines  145 . Such selective inflation and/or deflation of the bellows actuators  130  can move and/or support one or both legs  102  to generate and/or augment body motions such as walking, running, jumping, climbing, lifting, throwing, squatting, skiing or the like. 
     In some cases, the system  100  can be designed to support multiple configurations in a modular configuration. For example, one embodiment is a modular configuration that is designed to operate in either a single knee configuration or in a double knee configuration as a function of how many of the actuator units  110  are donned by the user  101 . For example, the exoskeleton device  610  can determine how many actuator units  110  are coupled to the pneumatic system  620  and/or exoskeleton device  610  (e.g., on or two actuator units  110 ) and the exoskeleton device  610  can change operating capabilities based on the number of actuator units  110  detected. 
     In further embodiments, the pneumatic system  620  can be manually controlled, configured to apply a constant pressure, or operated in any other suitable manner. In some embodiments, such movements can be controlled and/or programmed by the user  101  that is wearing the exoskeleton system  100  or by another person. In some embodiments, the exoskeleton system  100  can be controlled by movement of the user  101 . For example, the exoskeleton device  610  can sense that the user is walking and carrying a load and can provide a powered assist to the user via the actuators  130  to reduce the exertion associated with the load and walking. Similarly, where a user  101  wears the exoskeleton system  100  while skiing, the exoskeleton system  100  can sense movements of the user  101  (e.g., made by the user  101 , in response to terrain, or the like) and can provide a powered assist to the user via the actuators  130  to enhance or provide an assist to the user while skiing. 
     Accordingly, in various embodiments, the exoskeleton system  130  can react automatically without direct user interaction. In further embodiments, movements can be controlled in real-time by user interface  615  such as a controller, joystick, voice control or thought control. Additionally, some movements can be pre-preprogrammed and selectively triggered (e.g., walk forward, sit, crouch) instead of being completely controlled. In some embodiments, movements can be controlled by generalized instructions (e.g. walk from point A to point B, pick up box from shelf A and move to shelf B). 
     The user interface  615  can allow the user  101  to control various aspects of the exoskeleton system  100  including powering the exoskeleton system  100  on and off; controlling movements of the exoskeleton system  100 ; configuring settings of the exoskeleton system  100 , and the like. The user interface  615  can include various suitable input elements such as a touch screen, one or more buttons, audio input, and the like. The user interface  615  can be located in various suitable locations about the exoskeleton system  100 . For example, in one embodiments, the user interface  615  can be disposed on a strap of a backpack  155  as shown in  FIG. 7 . In some embodiments, the user interface can be defined by a user device such as smartphone, smart-watch, wearable device, or the like. 
     In various embodiments, the power source  616  can be a mobile power source that provides the operational power for the exoskeleton system  100 . In one preferred embodiment, the power pack unit contains some or all of the pneumatic system  620  (e.g., a compressor) and/or power source (e.g., batteries) required for the continued operation of pneumatic actuation of the leg actuator units  110 . The contents of such a power pack unit can be correlated to the specific actuation approach configured to be used in the specific embodiment. In some embodiments, the power pack unit will only contain batteries which can be the case in an electromechanically actuated system or a system where the pneumatic system  620  and power source  616  are separate. Various embodiments of a power pack unit can include but are not limited to a combination of the one or more of the following items: pneumatic compressor, batteries, stored high-pressure pneumatic chamber, hydraulic pump, pneumatic safety components, electric motor, electric motor drivers, microprocessor, and the like. Accordingly, various embodiments of a power pack unit can include one or more of elements of the exoskeleton device  610  and/or pneumatic system  620 . 
     Such components can be configured on the body of a user  101  in a variety of methods. One preferred embodiment is the inclusion of a power pack unit in a torso-worn pack that is not operably coupled to the leg actuator units  110  in any manner that transmits substantial mechanical forces to the leg actuator units  110 . Another embodiment includes the integration of the power pack unit, or components thereof, into the leg actuator units  110  themselves. Various embodiments can include but are not limited to the following configurations: torso-mounted in a backpack, torso-mounted in a messenger bag, hip-mounted bag, mounted to the leg, integrated into the brace component, and the like. Further embodiments can separate the components of the power pack unit and disperse them into various configurations on the user  101 . Such an embodiment may configure a pneumatic compressor on the torso of the user  101  and then integrate the batteries into the leg actuator units  110  of the exoskeleton system  100 . 
     One aspect of the power supply  616  in various embodiments is that it must be connected to the brace component in such a manner as to pass the operable system power to the brace for operation. One preferred embodiment is the use of electrical cables to connect the power supply  616  and the leg actuator units  110 . Other embodiments can use electrical cables and a pneumatic line  145  to deliver electrical power and pneumatic power to the leg actuator units  110 . Various embodiments can include but are not limited to any configuration of the following connections: pneumatic hosing, hydraulic hosing, electrical cables, wireless communication, wireless power transfer, and the like. 
     In some embodiments, it can be desirable to include secondary features that extend the capabilities of a cable connection (e.g., pneumatic lines  145  and/or power lines) between the leg actuator units  110  and the power supply  616  and/or pneumatic system  620 . One preferred embodiment includes retractable cables that are configured to have a small mechanical retention force to maintain cables that are pulled tight against the user with reduced slack remaining in the cable. Various embodiments can include, but are not limited to a combination of the following secondary features: retractable cables, a single cable including both fluidic and electrical power, magnetically-connected electrical cables, mechanical quick releases, breakaway connections designed to release at a specified pull force, integration into mechanical retention features on the users clothing, and the like. Yet another embodiment can include routing the cables in such a way as to minimize geometric differences between the user  101  and the cable lengths. One such embodiment in a dual knee configuration with a torso power supply can be routing the cables along the user&#39;s lower torso to connect the right side of a power supply bag with the left knee of the user. Such a routing can allow the geometric differences in length throughout the user&#39;s normal range of motion. 
     One specific additional feature that can be a concern in some embodiments is the need for proper heat management of the exoskeleton system  100 . As a result, there are a variety of features that can be integrated specifically for the benefit of controlling heat. One preferred embodiment integrates exposed heat sinks to the environment that allow elements of the exoskeleton device  610  and/or pneumatic system  620  to dispel heat directly to the environment through unforced cooling using ambient airflow. Another embodiment directs the ambient air through internal air channels in a backpack  155  or other housing to allow for internal cooling. Yet another embodiment can extend upon this capability by introducing scoops on a backpack  155  or other housing in an effort to allow air flow through the internal channels. Various embodiments can include but are not limited to the following: exposed heat sinks that are directly connected to a high heat component; a water-cooled or fluid-cooled heat management system; forced air cooling through the introduction of a powered fan or blower; external shielded heat sinks to protect them from direct contact by a user, and the like. 
     In some cases, it may be beneficial to integrate additional features into the structure of the backpack  155  or other housing to provide additional features to the exoskeleton system  100 . One preferred embodiment is the integration of mechanical attachments to support storage of the leg actuator units  110  along with the exoskeleton device  610  and/or pneumatic system  620  in a small package. Such an embodiment can include a deployable pouch that can secure the leg actuator units  110  against the backpack  155  along with mechanical clasps that hold the upper or lower arms  115 ,  120  of the actuator units  110  to the backpack  155 . Another embodiment is the inclusion of storage capacity into the backpack  155  so the user  101  can hold additional items such as a water bottle, food, personal electronics, and other personal items. Various embodiments can include but are not limited to other additional features such as the following: a warming pocket which is heated by hot airflow from the exoskeleton device  610  and/or pneumatic system  620 ; air scoops to encourage additional airflow internal to the backpack  155 ; strapping to provide a closer fit of the backpack  155  on the user, waterproof storage, temperature-regulated storage, and the like. 
     In a modular configuration, it may be required in some embodiments that the exoskeleton device  610  and/or pneumatic system  620  be configured to support the power, fluidic, sensing and control requirements and capabilities of various potential configurations of the exoskeleton system. One preferred embodiment can include an exoskeleton device  610  and/or pneumatic system  620  that can be tasked with power a dual knee configuration or a single knee configuration (i.e., with one or two leg actuator units  110  on the user  101 ). Such a system  100  can support the requirements of both configurations and then appropriately configured power, fluidic, sensing and control based on a determination or indication of a desired operating configuration. Various embodiments exist to support an array of potential modular system configurations, such as multiple batteries, and the like. 
     In various embodiments, the exoskeleton device  100  can be operable to perform methods or portions of methods described in more detail below or in related applications incorporated herein by reference. For example, the memory  612  can include non-transitory computer readable instructions (e.g., software), which if executed by the processor  611 , can cause the exoskeleton system  100  to perform methods or portions of methods described herein or in related applications incorporated herein by reference. 
     This software can embody various methods that interpret signals from the sensors  613  or other sources to determine how to best operate the system  100  to provide the desired benefit to the user. The specific embodiments described below should not be used to imply a limit on the sensors  613  that can be applied to such a system  100  or the source of sensor data. While some example embodiments can require specific information to guide decisions, it does not create an explicit set of sensors  613  that an exoskeleton system  100  for outdoor applications will require. 
     One aspect of control software can be the operational control of leg actuator units  110 , exoskeleton device  610  and pneumatic system  620  to provide the desired response. There can be various suitable responsibilities of the operational control software. For example, as discussed in more detail below, one can be low-level control which can be responsible for developing baseline feedback for operation of the leg actuator units  110 , exoskeleton device  610  and pneumatic system  620 . Another can be intent recognition which can be responsible for identifying the intended maneuvers of the user  101  based on data from the sensors  613  and causing the exoskeleton system  100  to operate based on one or more identified intended maneuvers. A further example can include reference generation, which can include selecting the desired torques the system  100  should generate to best assist the user  101 . It should be noted that this example architecture for delineating the responsibilities of the operational control software is merely for descriptive purposes and in no way limits the wide variety of software approaches that can be deployed on further embodiments of a system  100 . 
     One method implemented by control software can be for the low-level control and communication of the system  100 . This can be accomplished via a variety of methods as required by the specific joint and need of the user. In a preferred embodiment, the operational control is configured to provide a desired torque by the leg actuator unit  110  at the user&#39;s joint. In such a case, the system  100  can create low-level feedback to achieve a desired joint torque by the leg actuator units  110  as a function of feedback from the sensors  613  of the system  100 . For example, such a method can include obtaining sensor data from one or more sensors  613 , determining whether a change in torque by the leg actuator unit  110  is necessary, and if so, causing the pneumatic system  620  change the fluid state of the leg actuator unit  110  to achieve a target joint torque by the leg actuator unit  110 . Various embodiments can include, but are not limited to, the following: current feedback; recorded behavior playback; position-based feedback; velocity-based feedback; feedforward responses; volume feedback which controls a fluidic system  620  to inject a desired volume of fluid into an actuator  130 , and the like. 
     Another method implemented by operational control software can be for intent recognition of the user&#39;s intended behaviors. This portion of the operational control software, in some embodiments, can indicate any array of allowable behaviors that the system  100  is configured to account for. In one preferred embodiment, the operational control software is configured to identify two specific states: Skiing, and Not Skiing. In such an embodiment, to complete intent recognition, the system  100  can use user input and/or sensor readings to identify when it is safe, desirable or appropriate to provide assistive actions for skiing. For example, in some embodiments, intent recognition can be based on input received via the user interface  615 , which can include an input for Skiing or Not Skiing. Accordingly, in some examples, the use interface can be configured for a binary input consisting of Skiing or Not Skiing. 
     In some embodiments, a method of skiing intent recognition can include the exoskeleton device  610  obtaining data from the sensors  613  and determining, based at least in part of the obtained data, whether the data corresponds to a user state of Skiing or Not Skiing. Where a change in state has been identified, the system  100  can be re-configured to operate in the current state. For example, the exoskeleton device  610  can determine that the user  101  is in a Not Skiing state such as walking, riding a chairlift or siting at a ski lodge and can configure the system  100  to operate in a Not Skiing configuration. For example, such a Not Skiing configuration can, compared to a Skiing configuration, provide for a wider range of motion; provide no torque or minimal torque to the leg actuation units  110 ; save power and fluid by minimizing processing and fluidic operations; cause the system to be alert for supporting a wider variety of non-skiing motion, and the like. 
     The exoskeleton device  610  can monitor the activity of the user  101  can determine that the user is skiing or is about to ski (e.g., based on sensor data and/or user input), and can then configure the system  100  to operate in a Skiing configuration. For example, such a Skiing configuration, compared to a Not Skiing configuration, can allow for a more limited range of motion that would be present during skiing (as opposed to motions during non-skiing); provide for high or maximum performance by increasing the processing and fluidic response of the system  100  to support skiing; and the like. When the user  101  finishes a ski run, is identified as resting, or the like, the system  100  can determine that the user is no longer skiing (e.g., based on sensor data and/or user input) and can then configure the system  100  to operate in the Not Skiing configuration. 
     In some embodiments, there can be a plurality of Skiing states, or Skiing sub-states that can be determined by the system  100 , including hard skiing, moderate skiing, light skiing, downhill, moguls, jumping, powder, ice, trees, open-slope, racing, recreational, and the like (e.g., based on sensor data and/or user input). Such states can be based on the difficulty of the skiing, skill of the user, snow conditions, weather conditions, elevation, angle of the ski slope, desired performance level, power-saving, and the like. Accordingly, in various embodiments, the exoskeleton system  100  can adapt for various specific types of skiing based on a wide variety of factors. 
     Also, it should be clear that while various examples, discussed herein relate to downhill snow skiing, such examples should not be construed as limiting and various other sports or activities are within the scope and spirit of the present disclosure including snowboarding, telemark skiing, mono-skiing, cross-country skiing, ski-jumping, freestyle skiing, ski mountaineering, ice skating, and the like. Also, it should be clear that the present disclosure is intended to cover similar sports or activities that are not necessarily performed on snow or ice, such as sand, dirt or volcano skiing, skateboarding, surfing, mountain biking, BMX biking, roller blading, rock climbing, and the like. 
     In another embodiment, operational control software can be configured to identify a variety of states and their safe transitions: skiing, standing, turning, stopping, chairlift, and the like. Identifying a given skiing state and possible transitions from the state can be desirable because it can allow the system  100  to predict, anticipate and prepare for possible transitions to provide improved performance and support for the user. For example, where the user  101  is determined to be in a chairlift state, the system  100  can predict that the next state of the user  101  will be dismounting the chairlift given that dismounting the chair lift is essentially the only possible next state for the user  101 . Accordingly, the system  100  can anticipate and prepare for dismounting the chairlift. For example, the system can  100  focusing or weighting state detection to chairlift dismounting states since other states may be extremely unlikely or impossible. Also, the system  100  can physically prepare for supporting a chairlift dismounting state by preparing the pneumatic system  620  for supporting a chairlift dismounting state, or the like. Various embodiments can include any suitable combination of specific maneuver states and it is not to be assumed that the inclusion of any added states necessarily changes the behavior or responsibility of the operational control software to complete intent recognition. 
     Additionally, the system  100  can be configured to identify crash, danger or emergency states and respond accordingly. For example, sensor data can indicate that the user is crashing or may have already crashed while skiing and can change the configuration of the leg actuation units  110  accordingly, such as releasing all torque, performing a diagnostic, and the like. For example, when a crash event is identified, the system can generate a free reference where the actuation units  110  work to maintain zero torque on the knee joint of the user  101  throughout the crash. 
     Similarly, system  100  may identify a danger or emergency of the user, such as a hard fall, crash followed by lack of movement by the user, or the like. In some examples, in response to danger or an emergency detected, the system  100  can be configured to alert authorities, activate a location beacon, activate an audio or visual alarm on the system  100 , or the like. 
     In another embodiment, an intent recognition method can identify a jump behavior where a portion of one or both of the skis  192  have left the ground during a jump. For example, were the system  100  identifies a jump state, the systems  100  can produce references to provide zero additional torque to the legs during the flight phase, but prepares to provide a large impulse of torque to brace the user  101  upon landing when a landing state is observed. In some embodiments, an amount of impulse torque to brace the user  101  can be determined based on factors such as length of time of the jump event; speed, velocity or acceleration of the user; identified snow conditions; orientation of the user  101 , and the like. Additionally, the system  100  can be configured to differentiate between a jump event and an event when a user is simply lifting a ski  192  off the ground; for example, based on data from sensors  613 . 
     In another embodiment, an intent recognition method can identify a walking maneuver. For example, when a walking maneuver is identified, the exoskeleton system  100  can generate references to free the legs  102  in an effort to provide no assistance but also not get in the user&#39;s way. Other embodiments may be configured to identify more phases of a walking gate to provide assistance during stance but not swing, for example, or extend the assistance to provide a substantial benefit while hiking in the system  100 . In another embodiment, the software can identify a sustained standing behavior and provide extension assistance at the user&#39;s knees  103  to support the body during extended standing. Various embodiments can include any one of, none of, all of, or more than these maneuvers. 
     Another method implemented by operational control software can be the development of desired referenced behaviors for the specific joints providing assistance. This portion of the control software can tie together identified maneuvers with the level control. For example, when the system  100  identifies an intended user maneuver, the software can generate reference behaviors that define the torques, or positions desired by the actuators  130  in the leg actuation units  110 . In one embodiment, the operational control software generates references to make the leg actuation units  110  simulate a mechanical spring at the knee  103  via the configuration actuator  130 . The operational control software can generate torque references at the knee joints that are a linear function of the knee joint angle. In another embodiment, the operational control software generates a volume reference to provide a constant standard volume of air into a pneumatic actuator  130 . This can allow the pneumatic actuator  130  to operate like a mechanical spring by maintaining the constant volume of air in the actuator  130  regardless of the knee angle, which can be identified through feedback from one or more sensors  613 . 
     In another embodiment, a method implemented by the operational control software can generate torques in a dual leg actuation unit  110  configuration (e.g., where left and right leg actuation units  110 L,  110 R are worn by a user  1010 ) such that the behavior is coordinated across or between the leg actuation units  110 . In one embodiment, the operational control software coordinates the behavior of the leg actuation units  110  to direct system torque away from the most bent leg  103 . In this example case, the leg actuation units  110  can operate opposite of a spring where the leg  102  receives less torque as the knee  103  is bent more, but based on the relative angles of the two knees  103 L,  103 R of the two legs  102 L,  102 R. For example, if both legs  102 L,  102 R are bent the same amount, the legs  102 L,  102 R can receive the same torque reference via the left and right leg actuation units  110 L,  110 R respectively, but if only one leg  102  is bent (e.g., if the left leg  102 L is bent), the torque applied by the actuation units  110  can skewed towards the leg  102  that is more straight (e.g., to the right leg  102 R if the left leg  102 L is bent). 
     Accordingly, a method of operating an exoskeleton system can include the exoskeleton device  610  obtaining sensor data from the sensors  610  indicating an amount of bend in the legs  102 L,  102 R of a user  101  based on the configuration of left and right leg actuation units  110 L,  110 R and determining a difference between the amount of bend in the legs  102 L,  102 R of a user  101 . Where one leg  102 L is bent more than the other leg  102 R, the more-bent leg  102 L can receive less torque than the more-bent leg  102 R, with the amount of less torque being applied based at least in part on the difference between the amount of bend in the legs  102 L,  102 R of the user  101 . 
     In another embodiment, a method implemented by the operational control software can include evaluating the balance of the user  101  while skiing and directing torque in such a way to encourage the user  101  to remain balanced by directing knee assistance to the leg  102  that is on the outside of the users current balance profile. Accordingly, a method of operating an exoskeleton system can include the exoskeleton device  610  obtaining sensor data from the sensors  610  indicating a balance profile of a user  101  based on the configuration of left and right leg actuation units  110 L,  110 R and/or environmental sensors such as position sensors, accelerometers, and the like. The method can further include determining a balance profile based on the obtained data, including and outside and inside leg, and then increasing torque to the actuation unit  110  associated with the leg  102  identified as the outside leg. 
     Various embodiments can use but are not limited to kinematic estimates of posture, joint kinetic profile estimates, as well as observed estimates of body pose. Various other embodiments exist for methods of coordinating two legs  102  to generate torques including but not limited to guiding torque to the most bent leg; guiding torque based on the mean amount of knee angle across both legs; scaling the torque as a function of speed or acceleration; and the like. It should also be noted that yet another embodiment can include a combination of various individual reference generation methods in a variety of matters which include but are not limited to a linear combination, a maneuver specific combination, or a non-linear combination. 
     In some cases where a method includes operational control software coordinating control between various legs  102 , it can be helpful to incorporate user preference to account for a variety of factors such as self-selected skiing style or skill. In such a scenario, there can be factors used to combine or scale the parameters for operating the exoskeleton system  100  while skiing. In one embodiment, the user  101  can provide input (e.g., via user interface  615 ) about the overall amount of torque desired which can be used in an operational control method to scale the output torque reference up or down based on the input from the user  101 . 
     In another embodiment, an operational control method can blend two primary reference generation techniques: one reference focused on static assistance and one reference focused on leading the user  101  into their upcoming behavior. In some examples, the user  101  can select how much predictive assistance is desired while using the exoskeleton system  100 . For example, by a user  101  indicating a large amount of predictive assistance, the system  100  can be configured to very responsive and may be well configured for a skilled skier on a challenging terrain. The user  101  could also indicate a desire for very low amount of predictive assistance, which can result in slower system performance, which may be better tailored towards a learning skier or less challenging terrain. 
     Various embodiments can incorporate user intent in a variety of manners and the examples embodiments presented above should not be interpreted as limiting in any way. For example, method of determining and operating an exoskeleton system  100  can include systems and method of U.S. patent application Ser. No. 15/887,866, filed Feb. 02, 2018 entitled “SYSTEM AND METHOD FOR USER INTENT RECOGNITION,” having attorney docket number 0110496-003US0, which is incorporated herein by reference. Also, various embodiments can use user intent in a variety of manners including as a continuous unit, or as a discrete setting with only a few indicated values. 
     At times it can be beneficial for operational control software to manipulate its control to account for a secondary or additional objective in order to maximize device performance or user experience. In one embodiment, the exoskeleton system  100  can provide an elevation-aware control over a central compressor or other components of a pneumatic system  620  to account for the changing density of air at different elevations. For example, operational control software can identify that the system is operating at a higher elevation based on data from sensors  613 , or the like, and provide more current to the compressor in order to maintain electrical power consumed by the compressor. Accordingly, a method of operating a pneumatic exoskeleton system  100  can include obtaining data indicating air density where the pneumatic exoskeleton system  100  is operating (e.g., elevation data), determining optimal operating parameters of the pneumatic system  620  based on the obtained data, and configuring operation based on the determined optimal operating parameters. In further embodiments, operation of a pneumatic exoskeleton system  100  can be tuned based on environmental temperature, which may affect air volumes. 
     In another embodiment, the system  100  can monitor the ambient audible noise levels and vary the control behavior of the system  100  to reduce the noise profile of the system. For example, when a user  101  is in a quiet public place or quietly enjoying the outdoors alone or with others, noise associated with actuation of the leg actuation units  110  can be undesirable (e.g., noise of running a compressor or inflating or deflating actuators  130 ). Accordingly, in some embodiments, the sensors  613  can include a microphone that detects ambient noise levels and can configure the exoskeleton system  100  to operate in a quiet mode when ambient noise volume is below a certain threshold. Such a quiet mode can configure elements of a pneumatic system  620  or actuators  130  to operate more quietly, or can delay or reduce frequency of noise made by such elements. 
     In the case of a modular system, it can be desirable in various embodiments for operational control software to operate differently based on the number of leg actuation units  110  operational within the exoskeleton system  100 . For example, in some embodiments, a modular dual-knee system  100  (see e.g.,  FIGS. 1 and 2 ) can also operate in a single knee configuration where only one of two leg actuation units  110  are being worn by a user  101  (see e.g.,  FIGS. 3  and  4 ) and the system  100  can generate references differently when in a two-leg configuration compared to a single leg configuration. Such an embodiment can use a coordinated control approach to generate references where the system  100  is using inputs from both leg actuation units  110  to determine the desired operation. However in a single-leg configuration, the available sensor information may have changed, so in various embodiments the system  100  can implement a different control method. In various embodiments this can be done to maximize the performance of the system  100  for the given configuration or account for differences in available sensor information based on there being one or two leg actuation units  110  operating in the system  100 . 
     Accordingly, a method of operating an exoskeleton system  100  can include a startup sequence where a determination is made by the exoskeleton device  610  whether one or two leg actuation units  110  are operating in the system  100 ; determining a control method based on the number of actuation units  110  that are operating in the system  100 ; and implementing and operating the system  100  with the selected control method. A further method operating an exoskeleton system  100  can include monitoring by the exoskeleton device  610  of actuation units  110  that are operating in the system  100 , determining a change in the number of actuation units  110  operating in the system  100 , and then determining and changing the control method based on the new number of actuation units  110  that are operating in the system  100 . 
     For example, the system  100  can be operating with two actuation units  110  and with a first control method. The user  101  can disengage one of the actuation units  110 , and the exoskeleton device  610  can identify the loss of one of the actuation units  110  and the exoskeleton device  610  can determine and implement a new second control method to accommodate loss of one of the actuation units  110 . In some examples, adapting to the number of active actuation units  110  can be beneficial where one of the actuation units  110  is damaged or disconnected during use and the system  100  is able to adapt automatically so the user  101  can still continue skiing uninterrupted despite the system  100  only having a single active actuation unit  110 . 
     In various embodiments, operational control software can adapt a control method where user needs are different between individual actuation units  110  or legs  102 . In such an embodiment, it can be beneficial for the exoskeleton system  100  to change the torque references generated in each actuation unit  110  to tailor the experience for the user  101 . One example is of a dual knee exoskeleton system  100  (see e.g.,  FIGS. 1 and 2 ) where a user  101  has significant weakness issues in a single leg  102 , but only minor weakness issues in the other leg  102 . In this example, the exoskeleton system  100  can be configured to scale down the output torques on the less-affected limb compared to the more-affected limb to best meet the needs of the user  101 . 
     Such a configuration based on differential limb strength can be done automatically by the system  100  and/or can be configured via a user interface  616 , or the like. For example, in some embodiments, the user  101  can perform a calibration test while using the system  100 , which can test relative strength or weakness in the legs  102  of the user  101  and configure the system  100  based on identified strength or weakness in the legs  102 . Such a test can identify general strength or weakness of legs  102  or can identify strength or weakness of specific muscles or muscle groups such as the quadriceps, calves, hamstrings, gluteus, gastrocnemius; femoris, sartorius, soleus, and the like. 
     Another aspect of a method for operating an exoskeleton system  100  can include control software that monitors the system  100 . A monitoring aspect of such software can, in some examples, focus on monitoring the state of the system  100  and the user  101  throughout normal operation in an effort to provide the system  100  with situational awareness and understanding of sensor information in order to drive user understanding and device performance. One aspect of such monitoring software can be to monitor the state of the system  100  in order to provide device understanding to achieve a desired performance capability. A portion of this can be the development of a system body pose estimate. In one embodiment, the exoskeleton device  610  uses the onboard sensors  613  to develop a real-time understanding of the user&#39;s pose. In other words, data from sensors  613  can be used to determine the configuration of the actuation units  110 , which along with other sensor data can in turn be used to infer a user pose or body configuration estimate of the user  101  wearing the actuation units  110 . 
     At times, and in some embodiments, it can be unrealistic or impossible for the system  100  to directly sense all important aspects of the system pose due to the sensing modalities not existing or their inability to be practically integrated into the hardware. As a result, the system  100  in some examples can rely on a fused understanding of the sensor information around an underlying model of the user&#39;s body and the system  100  the user is wearing. In one embodiment of a dual leg knee assistance system  100 , the exoskeleton device  610  can use an underlying model of the user&#39;s lower extremity and torso body segments to enforce a relational constraint between the otherwise disconnected sensors  613 . Such a model can allow the system  100  to understand the constrained motion of the two legs  102  in that they are mechanically connected through the user&#39;s kinematic chain created by the body. This approach can be used to ensure that the estimates for knee orientation are properly constrained and biomechanically valid. In various embodiments, the system  100  can includes sensors  613  embedded in the exoskeleton device  610  and/or pneumatic system  620  to provide a fuller picture of the system posture. In yet another embodiment, the system  100  can include logical constraints that are unique to the application in an effort to provide additional constraints on the operation of the pose estimation. This can be desirable, in some embodiments, in conditions where ground truth information is unavailable such as highly dynamic actions, where the system  100  is denied an external GPS signal, or the earth&#39;s magnetic field is distorted. 
     Another aspect of a method of controlling an exoskeleton system  100  can include monitoring software configured to identify geolocation based triggers for different device behavior. In one embodiment, the system  100  can determine a ski run the user  101  is about to go down and then switch to a pre-recorded or previously user-defined or system-defined set of parameters to appropriately fit the identified ski run. For example, if a user  101  is going down a low difficulty ski slope she may choose to specify a low amount of predictive assistance for the system  100 , whereas before she goes down a high difficulty ski run she may typically switch the predictive assistance to a much higher level. In future visits to the low difficulty ski run, the system can use the geolocation based monitoring to identify the upcoming run and suggest to the user or automatically switch to the lower predictive setting and do the inverse when the monitoring software identifies the user  101  is entering a high difficulty area. Various embodiments can use this capability in a variety of methods which can include but are not limited to the discrete identification of specific geolocated indicators, or the continuous monitoring of geolocated triggers with the ability to manipulate performance as the user  101  is using the device  100 . 
     Identifying location of the user  101  and/or exoskeleton system  100  can be done in various suitable way, including via GPS system of the exoskeleton device  610 ; a user device such as a smartphone or wearable device; or location tags such as an RFID, wireless signal, or the like. Identifying a given location as being associated with the beginning of a ski run, a portion of a ski run, an end of a ski run, or non-ski run location can be done in various suitable ways. In one example, an administrator can define geographic boundaries or locations for different ski runs, non-ski run locations, beginning and/or end of a ski run, or the like, and the determined location of the user  101  and/or exoskeleton system  100  can be compared to these defined boundaries or locations. Additionally, locations of different items or attributes of a location can be defined such as terrain, hazards, points of interest, or routes, which can include as open slope, trees, rocks, jumps, cliffs, crevasses, avalanche zones, chair lifts, slope angles, moguls, difficulty rating, and the like. 
     In some embodiments, local tags such as gates, beacons, or the like can identify a location and/or attributes of a location. For example, the user passing through a gate or coming within proximity of a beacon (e.g., RFID, wireless signal, or the like) can identify a location and/or attributes of a location, which can be used to configure an exoskeleton device  100 . In some embodiments, such a gate or beacon can communicate information regarding location and/or attributes of a location or such a gate or beacon can communicate an identifier, which the exoskeleton system  100  can use to lookup information corresponding to a location and/or attributes of a location. 
     For example, a user  101  with an exoskeleton system  100  can come into proximity of a beacon, pass through a gate or be geo-located at a location that can indicate that the user  101  is at the start of a black diamond ski run and the exoskeleton system  100  can be configured accordingly. Similarly, changes to the configuration of the system  100  can be based on being at the beginning of a chairlift, at the end of a chairlift, at the end of a ski run, entering a portion of a ski run with a different difficulty, entering a ski lodge, and the like. 
     In some embodiments, changes in configuration of the system  100  based location and/or location attributes can be performed automatically and/or with input from the user  101 . For example, in some embodiments, the system  100  can provide one or more suggestions for a change in configuration based location and/or location attributes and the user  101  can choose to accept such suggestions. In further embodiments, some or all configuration of the system  100  based location and/or location attributes can occur automatically without user interaction. 
     In some embodiments, tagging locations and recording location information and attributes can be initiated by a user  101 . For example, before going down a new ski run, the user can tag the current location of user as being the start of a ski run, which may or may not include ski run attributes such as difficulty level, or the like. Additionally, in some examples, the user can record activity of the system  100  during a ski run, which can be associate with that ski run. Accordingly, some embodiments allow users to generate profiles for a plurality of ski runs, which can be used to identify when the user is at the start of a given ski run, how to configure the system  100  for the ski run, how to change the configuration of the system  100  during the ski run, and the like. 
     Various embodiments can include the collection and storage of data from the system  100  throughout operation. In one embodiment, this can include the live streaming of the data collected on the exoskeleton device  610  to a cloud storage location via the communication unit(s)  614  through an available wireless communication protocol or storage of such data on the memory  612  of the exoskeleton device  610 , which may then be uploaded to another location via the communication unit(s)  614 . For example, when the system  100  obtains a network connection, recorded data can be uploaded to the cloud at a communication rate that is supported by the available data connection. Various embodiments can include variations of this, but the use of monitoring software to collect and store data about the device  100  locally and/or remotely for retrieval at a later time for a device such as this can be included in various embodiments. 
     In some embodiments, once such data has been recorded, it can be desirable to use the data for a variety of different applications. One such application can be the use of the data to develop further oversight functions on the device  100  in an effort to identify device system issues that are of note. One embodiment can be the use of the data to identify a specific exoskeleton device  100  or leg actuator unit  110  among a plurality, whose performance has varied significantly over a variety of uses. Another use of the data can be to provide it back to the user  101  to gain a better understanding of how they ski. One embodiment of this can be providing the data back to the user  101  through a mobile application that can allow the user  101  to review their day skiing on a mobile device. Yet another use of such device data can be to synchronize playback of data with an external data stream to provide additional context. One embodiment is a system that incorporates the GPS data from a companion smartphone with the data stored natively on the device. Another embodiment can include the time synchronization of recorded video with the data stored that was obtained from the device  100 . Various embodiments can use these methods for immediate use of data by the user to evaluate their own performance, for later retrieval by the user to understand behavior from the past, for users to compare with other users in-person or through an online profile, by developers to further the development of the system, and the like. 
     Another aspect of a method of operating an exoskeleton system can include monitoring software identifying of user-specific traits. For example, the system  100  can provide an awareness of how a specific skier  101  operates in the system  100  and over time can develop a profile of the user&#39;s specific traits in an effort to maximize device performance for that user. One embodiment can include the device  100  identifying a user-specific skiing type in an effort to identify the skiing style or level of the specific user. Through an evaluation of the skier&#39;s form and stability during skiing actions (e.g., via analysis of data obtained from the sensors  613  or the like), the exoskeleton device  610  in some examples can identify if the skier is highly skilled, novice, or beginner. This understanding of skill level or style can allow the system  100  to better tailor control references to the specific user. 
     In further embodiments, the exoskeleton system  100  can also use individualized information about a given user to build a profile of the user&#39;s biomechanic response to the exoskeleton system  100 . One embodiment can include the system  100  collecting data regarding the user to develop an estimate of the individual user&#39;s knee strain in an effort to assist the user with understanding the burden the user has placed on his legs  102  throughout skiing. This can allow the system  100  to alert a user if the user has reached a historically significant amount of knee strain to alert the user that he may want to stop to spare himself potential pain or discomfort. 
     Another embodiment of individualized biomechanic response can be the system collecting data regarding the user to develop an individualized system model for the specific user. In such an embodiment the individualized model can be developed through a system ID (identification) method that evaluates the system performance with an underlying system model and can identify the best model parameters to fit the specific user. The system ID in such an embodiment can operate to estimate segment lengths and masses (e.g., of legs  102  or portions of the legs  102 ) to better define a dynamic user model. In another embodiment, these individualized model parameters can be used to deliver user specific control responses as a function of the users specific masses and segment lengths. In some example of a dynamic model, this can help significantly with the devices ability to account for dynamic forces during highly challenging ski activities. 
     In various embodiments the device  100  can monitor itself in relation to a community of skiers around the user  101  and device  100  where the others skiers may or may not be wearing an exoskeleton device  100  of their own. In addition some embodiments being configured to evaluate user time or location in relation to other skiers, the device  100  in some examples can allow the user to compare and broadcast a much wider variety of information with friends and others in proximity of the user. 
     One embodiment of community monitoring can include playback or broadcast of posture data during a ski run. This can allow others to observe the body posture of another user correlated to specific locations on the ski run. In some embodiments, this information can be displayed in a strictly private mode where users can selectively share their data with selected friends, and in other embodiments the data can be broadcast with nearby users for comparison or observation. In some embodiments it can be beneficial to compare ski performance on a specific run to that of another selected user. This can be done through a comparison of a specific user to the performance of a friend, or to the performance of specified target user such as a ski professional. In another embodiment, community ski data can be aggregated to determine the specific snowy conditions of the run. In another embodiment, the system  100  can determine when a skier has had a serious crash and appears to be injured. The system  100  can then use this information to alert nearby skiers or safety personnel to check in on the user. 
     In various embodiments, the exoskeleton system  100  can provide for various types of user interaction. For example such interaction can include input from the user  101  as needed into the system  100  and the system  100  providing feedback to the user  101  to indicate changes in operation of the system  100 , status of the system  100 , and the like. As discussed herein, user input and/or output to the user can be provided via one or more user interface  615  of the exoskeleton device  610  or can include various other interfaces or devices such as a smartphone user device. Such one or more user interfaces  615  or devices can be located in various suitable locations such as on a backpack  155  (see e.g.,  FIGS. 1, 2 and 7 ), the pneumatic system  620 , leg actuation units  110 , or the like. 
     The system  100  can be configured to obtain intent from the user  101 . For example, this can be accomplished through a variety of input devices that are either integrated directly with the other components of the system  100  (e.g., one or more user interface  615 ), or external and operably connected with the system  100  (e.g., a smartphone, wearable device, remote server, or the like). In one embodiment, a user interface  615  can comprise a button that is integrated directly into one or both of the leg actuation units  110  of the system  100 . This single button can allow the user  101  to indicate a variety of inputs. In another embodiment, a user interface  615  can be configured to be provided through a torso-mounted lapel input device that is integrated with the exoskeleton device  610  and/or pneumatic system  620  of the exoskeleton system  100 . In one example, such a user interface  615  can comprise a button that has a dedicated enable and disable functionality; a selection indicator dedicated to the user&#39;s desired power level (e.g., an amount or range of force applied by the leg actuator units  100 ); and a selector switch that can be dedicated to the amount of predictive intent to integrate into the control of the system  100 . Such an embodiment of a user interface  615  can use a series of functionally locked buttons to provide the user  101  with a set of understood indicators that may be required for normal operation in some examples. Yet another embodiment can include a mobile device that is connected to the exoskeleton system  100  via a Bluetooth connection or other suitable wired or wireless. Use of a mobile device or smartphone as a user interface  615  can allow the user a far greater amount of input to the device due to the flexibility of the input method. Various embodiments can use the options listed above or combinations and variants thereof, but are in no way limited to the explicitly stated combinations of input methods and items. 
     The one or more user interface  615  can provide information to the user  101  to allow the user to appropriately use and operate the device  101 . Such feedback can be in a variety of visual, haptic and/or audio methods including, but not limited to, feedback mechanisms integrated directly one or both of the actuation units  110 ; feedback through operation of the actuation units  110 ; feedback through external items not integrated with the system  100  (e.g., a mobile device); and the like. Some embodiments can include integration of feedback lights in the actuation units  110 , of the exoskeleton system  100 . In one such embodiment, five multi-color lights are integrated into the knee joint  125  or other suitable location such that the user  101  can see the lights. These lights can be used to provide feedback of system errors, device power, successful operation of the device, and the like. In another embodiment, the system  100  can provide controlled feedback to the user to indicate specific pieces of information. In such embodiments, the system  100  can pulse the joint torque on one or both of the leg actuation units  110  to the maximum allowed torque when the user changes the maximum allowable user-desired torque, which can provide a haptic indicator of the torque settings. Another embodiment can sue an external device such as a mobile device where the system  100  can provide alert notifications for device information such as operational errors, setting status, power status, and the like. Types of feedback can include, but are not limited to, lights, sounds, vibrations, notifications, and operational forces integrated in a variety of locations that the user  101  may be expected to interact with including the actuation units  110 , pneumatic system  620 , backpack  155 , mobile devices, or other suitable methods of interactions such as a web interface, SMS text or email. 
     The communication unit  614  can include hardware and/or software that allows the exoskeleton system  100  to communicate with other devices, including a user device, a classification server, other exoskeleton systems  100 , or the like, directly or via a network. For example, the exoskeleton system  100  can be configured to connect with a user device, which can be used to control the exoskeleton system  100 , receive performance data from the exoskeleton system  100 , facilitate updates to the exoskeleton system, and the like. Such communication can be wired and/or wireless communication. 
     In some embodiments, the sensors  613  can include any suitable type of sensor, and the sensors  613  can be located at a central location or can be distributed about the exoskeleton system  100 . For example, in some embodiments, the exoskeleton system  100  can comprise a plurality of accelerometers, force sensors, position sensors, and the like, at various suitable positions, including at the arms  115 ,  120 , joint  125 , actuators  130  or any other location. Accordingly, in some examples, sensor data can correspond to a physical state of one or more actuators  130 , a physical state of a portion of the exoskeleton system  100 , a physical state of the exoskeleton system  100  generally, and the like. In some embodiments, the exoskeleton system  100  can include a global positioning system (GPS), camera, range sensing system, environmental sensors, elevation sensor, microphone, thermometer, or the like. In some embodiments, the exoskeleton system  100  can obtain sensor data from a user device such as a smartphone, or the like. 
     The pneumatic system  620  can comprise any suitable device or system that is operable to inflate and/or deflate the actuators  130  individually or as a group. For example, in one embodiment, the pneumatic system can comprise a diaphragm compressor as disclosed in related patent application Ser. No. 14/577,817 filed Dec. 19, 2014. 
     As discussed herein, various suitable exoskeleton systems  100  can be used in various suitable ways and for various suitable applications. However, such examples should not be construed to be limiting on the wide variety of exoskeleton systems  100  or portions thereof that are within the scope and spirit of the present disclosure. Accordingly, exoskeleton systems  100  that are more or less complex than the examples of  FIGS. 1-6  are within the scope of the present disclosure. 
     Additionally, while various examples relate to an exoskeleton system  100  associated with the legs or lower body of a user, further examples can be related to any suitable portion of a user body including the torso, arms, head, legs, or the like. Also, while various examples relate to exoskeletons, it should be clear that the present disclosure can be applied to other similar types of technology, including prosthetics, body implants, robots, or the like. Further, while some examples can relate to human users, other examples can relate to animal users, robot users, various forms of machinery, or the like. 
     Turning to  FIGS. 8 a , 8 b , 9 a  and 9 b   , examples of a leg actuator unit  110  can include the joint  125 , bellows  130 , constraint ribs  135 , and base plates  140 . More specifically,  FIG. 8 a    illustrates a side view of a leg actuator unit  110  in a compressed configuration and  FIG. 8 b    illustrates a side view of the leg actuator unit  110  of  FIG. 8 a    in an expanded configuration.  FIG. 9 a    illustrates a cross-sectional side view of a leg actuator unit  110  in a compressed configuration and  FIG. 9 b    illustrates a cross-sectional side view of the leg actuator unit  110  of  FIG. 9 a    in an expanded configuration. 
     As shown in  FIGS. 8 a , 8 b , 9 a  and 9 b   , the joint  125  can have a plurality of constraint ribs  135  extending from and coupled to the joint  125 , which surround or abut a portion of the bellows  130 . For example, in some embodiments, constraint ribs  135  can abut the ends  132  of the bellows  130  and can define some or all of the base plates  140  that the ends  132  of the bellows  130  can push against. However, in some examples, the base plates  140  can be separate and/or different elements than the constraint ribs  135  (e.g., as shown in  FIG. 1 ). Additionally, one or more constraint ribs  135  can be disposed between ends  132  of the bellows  130 . For example,  FIGS. 8 a , 8 b , 9 a  and 9 b    illustrate one constraint rib  135  disposed between ends  132  of the bellows  130 ; however, further embodiments can include any suitable number of constraint ribs  135  disposed between ends of the bellows  130 , including 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 50, 100 and the like. In some embodiments, constraint ribs can be absent. 
     As shown in cross sections of  FIGS. 9 a  and 9 b   , the bellows  130  can define a cavity  131  that can be filled with fluid (e.g., air), to expand the bellow  130 , which can cause the bellows to elongate along axis B as shown in  FIGS. 8 b  and 9 b   . For example, increasing a pressure and/or volume of fluid in the bellows  130  shown in  FIG. 8 a    can cause the bellows  130  to expand to the configuration shown in  FIG. 8 b   . Similarly, increasing a pressure and/or volume of fluid in the bellows  130  shown in  FIG. 9 a    can cause the bellows  130  to expand to the configuration shown in  FIG. 9 b   . For clarity, the use of the term ‘bellows’ is to describe a component in the described actuator unit  110  and is not intended to limit the geometry of the component. The bellows  130  can be constructed with a variety of geometries including but not limited to: a constant cylindrical tube, a cylinder of varying cross-sectional area, a 3-D woven geometry that inflates to a defined arc shape, and the like. The term ‘bellows’ should not be construed to necessary include a structure having convolutions. 
     Alternatively, decreasing a pressure and/or volume of fluid in the bellows  130  shown in  FIG. 8 b    can cause the bellows  130  to contract to the configuration shown in  FIG. 8 a   . Similarly, decreasing a pressure and/or volume of fluid in the bellows  130  shown in  FIG. 9 b    can cause the bellows  130  to contract to the configuration shown in  FIG. 9 a   . Such increasing or decreasing of a pressure or volume of fluid in the bellows  130  can be performed by pneumatic system  620  and pneumatic lines  145  of the exoskeleton system  100 , which can be controlled by the exoskeleton device  610  (see  FIG. 6 ). 
     In one preferred embodiment, the bellows  130  can be inflated with air; however, in further embodiments, any suitable fluid can be used to inflate the bellows  130 . For example, gasses including oxygen, helium, nitrogen, and/or argon, or the like can be used to inflate and/or deflate the bellows  130 . In further embodiments, a liquid such as water, an oil, or the like can be used to inflate the bellows  130 . Additionally, while some examples discussed herein relate to introducing and removing fluid from a bellows  130  to change the pressure within the bellows  130 , further examples can include heating and/or cooling a fluid to modify a pressure within the bellows  130 . 
     As shown in  FIGS. 8 a , 8 b , 9 a  and 9 b   , the constraint ribs  135  can support and constrain the bellows  130 . For example, inflating the bellows  130  cause the bellows  130  expand along a length of the bellows  130  and also cause the bellows  130  to expand radially. The constraint ribs  135  can constrain radial expansion of a portion of the bellows  130 . Additionally, as discussed herein, the bellows  130  comprise a material that is flexible in one or more directions and the constraint ribs  135  can control the direction of linear expansion of the bellows  130 . For example, in some embodiments, without constraint ribs  135  or other constraint structures the bellows  130  would herniate or bend out of axis uncontrollably such that suitable force would not be applied to the base plates  140  such that the arms  115 ,  120  would not be suitably or controllably actuated. Accordingly, in various embodiments, the constraint ribs  135  can be desirable to generate a consistent and controllable axis of expansion B for the bellows  130  as they are inflated and/or deflated. 
     In some examples, the bellows  130  in a deflated configuration can substantially extend past a radial edge of the constraint ribs  135  and can retract during inflation to extend less past the radial edge of the constraint ribs  135 , to extend to the radial edge of the constraint ribs  135 , or to not extend less past the radial edge of the constraint ribs  135 . For example,  FIG. 9 a    illustrates a compressed configuration of the bellows  130  where the bellows  130  substantially extend past a radial edge of the constraint ribs  135  and  FIG. 9 b    illustrates the bellows  130  retracting during inflation to extend less past the radial edge of the constraint ribs  135  in an inflated configuration of the bellows  130 . 
     Similarly,  FIG. 10 a    illustrates a top view of a compressed configuration of bellows  130  where the bellows  130  substantially extend past a radial edge of constraint ribs  135  and  FIG. 10 b    illustrates a top view where the bellows  130  retract during inflation to extend less past the radial edge of the constraint ribs  135  in an inflated configuration of the bellows  130 . 
     Constraint ribs  135  can be configured in various suitable ways. For example,  FIGS. 10 a , 10 b    and  11  illustrate a top view of an example embodiment of a constraint rib  135  having a pair of rib arms  136  that extend from the joint  125  and couple with a circular rib ring  137  that defines a rib cavity  138  through which a portion of the bellows  130  can extend (e.g., as shown in  FIGS. 9 a , 9 b , 10 a  and 10 b   ). In various examples, the one or more constraint ribs  135  can be a substantially planar element with the rib arms  136  and rib ring  137  being disposed within a common plane. 
     In further embodiments, the one or more constraint ribs  135  can have any other suitable configuration. For example, some embodiments can have any suitable number of rib arms  136 , including one, two, three, four, five, or the like. Additionally, the rib ring  137  can have various suitable shapes and need not be circular, including one or both of an inner edge that defines the rib cavity  138  or an outer edge of the rib ring  137 . 
     In various embodiments, the constraining ribs  135  can be configured to direct the motion of the bellows  130  through a swept path about some instantaneous center (which may or may not be fixed in space) and/or to prevent motion of the bellows  130  in undesired directions, such as out-of-plane buckling. As a result, the number of constraining ribs  135  included in some embodiments can vary depending on the specific geometry and loading of the leg actuator unit  110 . Examples can range from one constraining rib  135  up to any suitable number of constraining ribs  135 ; according, the number of constraining ribs  135  should not be taken to limit the applicability of the invention. Additionally, constraining ribs  135  can be absent in some embodiments. 
     The one or more constraining ribs  135  can be constructed in a variety of ways. For example the one or more constraining ribs  135  can vary in construction on a given leg actuator unit  110 , and/or may or may not require attachment to the joint structure  125 . In various embodiments, the constraining ribs  135  can be constructed as an integral component of a central rotary joint structure  125 . An example embodiment of such a structure can include a mechanical rotary pin joint, where the constraining ribs  135  are connected to and can pivot about the joint  125  at one end of the joint  125 , and are attached to an inextensible outer layer of the bellows  130  at the other end. In another set of embodiments, the constraining ribs  135  can be constructed in the form of a single flexural structure that directs the motion of the bellows  130  throughout the range of motion for the leg actuator unit  110 . Another example embodiment uses a flexural constraining rib  135  that is not connected integrally to the joint structure  125  but is instead attached externally to a previously assembled joint structure  125 . Another example embodiment can comprise the constraint rib  125  being composed of pieces of fabric wrapped around the bellows  130  and attached to the joint structure  125 , acting like a hammock to restrict and/or guide the motion of the bellows  130 . There are additional methods available for constructing the constraining ribs  135  that can be used in additional embodiments that include but are not limited to a linkage, a rotational flexure connected around the joint  125 , and the like. 
     In some examples, a design consideration for constraining ribs  135  can be how the one or more constraining ribs  125  interact with the bellows  130  to guide the path of the bellows  130 . In various embodiments, the constraining ribs  135  can be fixed to the bellows  130  at predefined locations along the length of the bellows  130 . One or more constraining ribs  135  can be coupled to the bellows  130  in various suitable ways, including but not limited to sewing, mechanical clamps, geometric interference, direct integration, and the like. In other embodiments, the constraining ribs  135  can be configured such that the constraining ribs  135  float along the length of the bellows  130  and are not fixed to the bellows  130  at predetermined connection points. In some embodiments, the constraining ribs  135  can be configured to restrict a cross sectional area of the bellows  130 . An example embodiment can include a tubular bellows  130  attached to a constraining rib  135  that has an oval cross section, which in some examples can be a configuration to reduce the width of the bellows  130  at that location when the bellows  130  is inflated. 
     The bellows  130  can have various functions in some embodiments, including containing operating fluid of the leg actuator unit  110 , resisting forces associated with operating pressure of the leg actuator unit  110 , and the like. In various examples, the leg actuator unit  110  can operate at a fluid pressure above, below or at about ambient pressure. In various embodiments, bellows  130  can comprise one or more flexible, yet inextensible or practically inextensible materials in order to resist expansion (e.g., beyond what is desired in directions other than an intended direction of force application or motion) of the bellows  130  beyond what is desired when pressurized above ambient pressure. Additionally, the bellows  130  can comprise an impermeable or semi-impermeable material in order to contain the actuator fluid. 
     For example, in some embodiments, the bellows  130  can comprise a flexible sheet material such as woven nylon, rubber, polychloroprene, a plastic, latex, a fabric, or the like. Accordingly, in some embodiments, bellows  130  can be made of a planar material that is substantially inextensible along one or more plane axes of the planar material while being flexible in other directions. For example,  FIG. 13  illustrates a side view of a planar material  1300  (e.g., a fabric) that is substantially inextensible along axis X that is coincident with the plane of the material  1100 , yet flexible in other directions, including axis Z. In the example of  FIG. 13 , the material  1100  is shown flexing upward and downward along axis Z while being inextensible along axis X. In various embodiments, the material  1300  can also be inextensible along an axis Y (not shown) that is also coincident with the plane of the material  1300  like axis X and perpendicular to axis X. 
     In some embodiments, the bellows  130  can be made of a non-planar woven material that is inextensible along one or more axes of the material. For example, in one embodiment the bellows  130  can comprise a woven fabric tube. Woven fabric material can provide inextensibility along the length of the bellows  130  and in the circumferential direction. Such embodiments can still able to be configured along the body of the user  101  to align with the axis of a desired joint on the body  101  (e.g., the knee  103 ). 
     In various embodiments, the bellows  130  can develop its resulting force by using a constrained internal surface length and/or external surface length that are a constrained distance away from each other (e.g. due to an inextensible material as discussed above). In some examples, such a design can allow the actuator to contract on bellows  130 , but when pressurized to a certain threshold, the bellows  130  can direct the forces axially by pressing on the plates  140  of the leg actuator unit  110  because there is no ability for the bellows  130  to expand further in volume otherwise due to being unable to extend its length past a maximum length defined by the body of the bellows  130 . 
     In other words, the bellows  130  can comprise a substantially inextensible textile envelope that defines a chamber that is made fluid-impermeable by a fluid-impermeable bladder contained in the substantially inextensible textile envelope and/or a fluid-impermeable structure incorporated into the substantially inextensible textile envelope. The substantially inextensible textile envelope can have a predetermined geometry and a non-linear equilibrium state at a displacement that provides a mechanical stop upon pressurization of the chamber to prevent excessive displacement of the substantially inextensible textile actuator. 
     In some embodiments, the bellows  130  can include an envelope that consists or consists essentially of inextensible textiles (e.g., inextensible knits, woven, non-woven, etc.) that can prescribe various suitable movements as discussed herein. Inextensible textile bellows  130  can be designed with specific equilibrium states (e.g., end states or shapes where they are stable despite increasing pressure), pressure/stiffness ratios, and motion paths. Inextensible textile bellows  130  in some examples can be configured accurately delivering high forces because inextensible materials can allow greater control over directionality of the forces. 
     Accordingly, some embodiments of inextensible textile bellows  130  can have a pre-determined geometry that produces displacement mostly via a change in the geometry between the uninflated shape and the pre-determined geometry of its equilibrium state (e.g., fully inflated shape) due to displacement of the textile envelope rather than via stretching of the textile envelope during a relative increase in pressure inside the chamber; in various embodiments, this can be achieved by using inextensible materials in the construction of the envelope of the bellows  130 . As discussed herein, in some examples “inextensible” or “substantially inextensible” can be defined as expansion by no more than 10%, no more than 5%, or no more than 1% in one or more direction. 
       FIG. 12 a    illustrates a cross-sectional view of a pneumatic actuator unit  110  including bellows  130  in accordance with another embodiment and  FIG. 12 b    illustrates a side view of the pneumatic actuator unit  110  of  FIG. 12 a    in an expanded configuration showing the cross section of  FIG. 12 a   . As shown in  FIG. 12 a   , the bellows  130  can comprise an internal first layer  132  that defines the bellows cavity  131  and can comprise an outer second layer  133  with a third layer  134  disposed between the first and second layers  132 ,  133 . Throughout this description, the use of the term ‘layer’ to describe the construction of the bellows  130  should not be viewed as limiting to the design. The use of ‘layer’ can refer to a variety of designs including but not limited to: a planar material sheet, a wet film, a dry film, a rubberized coating, a co-molded structure, and the like. 
     In some examples, the internal first layer  132  can comprise a material that is impermeable or semi-permeable to the actuator fluid (e.g., air) and the external second layer  133  can comprise an inextensible material as discussed herein. For example, as discussed herein, an impermeable layer can refer to an impermeable or semi-permeable layer and an inextensible layer can refer to an inextensible or a practically inextensible layer. 
     In some embodiments comprising two or more layers, the internal layer  132  can be slightly oversized compared to an inextensible outer second layer  133  such that the internal forces can be transferred to the high-strength inextensible outer second layer  133 . One embodiment comprises a bellows  130  with an impermeable polyurethane polymer film inner first layer  132  and a woven nylon braid as the outer second layer  133 . 
     The bellows  130  can be constructed in various suitable ways in further embodiments, which can include a single layer design that is constructed of a material that provides both fluid impermeability and that is sufficiently inextensible. Other examples can include a complex bellows assembly that comprises multiple laminated layers that are fixed together into a single structure. In some examples, it can be necessary to limit the deflated stack height of the bellows  130  to maximize the range of motion of the leg actuator unit  110 . In such an example, it can be desirable to select a low-thickness fabric that meets the other performance needs of the bellows  130 . 
     In yet another embodiment, it can be desirable to reduce friction between the various layers of the bellows  130 . In one embodiment, this can include the integration of a third layer  134  that acts as an anti-abrasive and/or low friction intermediate layer between the first and second layers  132 ,  133 . Other embodiments can reduce the friction between the first and second layers  132 ,  133  in alternative or additional ways, including but not limited to the use of a wet lubricant, a dry lubricant, or multiple layers of low friction material. Accordingly, while the example of  FIG. 10 a    illustrates an example of a bellows  130  comprising three layers  132 ,  133 ,  134 , further embodiments can include a bellows  130  having any suitable number of layers, including one, two, three, four, five, ten, fifteen, twenty five, and the like. Such one or more layers can be coupled together along adjoining faces in part or in whole, with some examples defining one or more cavity between layers. In such examples, material such as lubricants or other suitable fluids can be disposed in such cavities or such cavities can be effectively empty. Additionally, as described herein, one or more layers (e.g., the third layer  134 ) need not be a sheet or planar material layer as shown in some examples and can instead comprise a layer defined by a fluid. For example, in some embodiments, the third layer  134  can be defined by a wet lubricant, a dry lubricant, or the like. 
     The inflated shape of the bellows  130  can be important to the operation of the bellows  130  and/or leg actuator unit  110  in some embodiments. For example, the inflated shape of the bellows  130  can be affected through the design of both an impermeable and inextensible portion of the bellows  130  (e.g., the first and second layer  132 ,  133 ). In various embodiments, it can be desirable to construct one or more of the layers  132 ,  133 ,  134  of the bellows  130  out of various two-dimensional panels that may not be intuitive in a deflated configuration. 
     In some embodiments, one or more impermeable layers can be disposed within the bellows cavity  131  and/or the bellows  130  can comprise a material that is capable of holding a desired fluid (e.g., a fluid impermeable first internal layer  132  as discussed herein). The bellows  130  can comprise a flexible, elastic, or deformable material that is operable to expand and contract when the bellows  130  are inflated or deflated as described herein. In some embodiments, the bellows  130  can be biased toward a deflated configuration such that the bellows  130  is elastic and tends to return to the deflated configuration when not inflated. Additionally, although bellows  130  shown herein are configured to expand and/or extend when inflated with fluid, in some embodiments, bellows  130  can be configured to shorten and/or retract when inflated with fluid in some examples. Also, the term ‘bellows’ as used herein should not be construed to be limiting in any way. For example the term ‘bellows’ as used herein should not be construed to require elements such as convolutions or other such features (although convoluted bellows  130  can be present in some embodiments). As discussed herein, bellows  130  can take on various suitable shapes, sizes, proportions and the like. 
     The bellows  130  can vary significantly across various embodiments, so the present examples should not be construed to be limiting. One preferred embodiment of a bellows  130  includes fabric-based pneumatic actuator configured such that it provides knee extension torque as discussed herein. Variants of this embodiment can exist to tailor the actuator to provide the desired performance characteristics of the actuators such as a fabric actuator that is not of a uniform cross-section. Other embodiments of can use an electro-mechanical actuator configured to provide flexion and extension torques at the knee instead of or in addition to a fluidic bellows  130 . Various embodiments can include but are not limited to designs that incorporate combinations of electromechanical, hydraulic, pneumatic, electro-magnetic, or electro-static for positive power or negative power assistance of extension or flexion of a lower extremity joint. 
     The actuator bellows  130  can also be located in a variety of locations as required by the specific design. One embodiment places the bellows  130  of a powered knee brace component located in line with the axis of the knee joint and positioned parallel to the joint itself. Various embodiments include but are not limited to, actuators configured in series with the joint, actuators configured anterior to the joint, and actuators configured to rest around the joint. 
     Various embodiments of the bellows  130  can include secondary features that augment the operation of the actuation. One such embodiment is the inclusion of user-adjustable mechanical hard end stops to limit the allowable range of motion to the bellows  130 . Various embodiments can include but are not limited to the following extension features: the inclusion of flexible end stops, the inclusion of an electromechanical brake, the inclusion of an electro-magnetic brake, the inclusion of a magnetic brake, the inclusion of a mechanical disengage switch to mechanically decouple the joint from the actuator, or the inclusion of a quick release to allow for quick changing of actuator components. 
     In various embodiments, the bellows  130  can comprise a bellows and/or bellows system as described in related U.S. patent application Ser. No. 14/064,071 filed Oct. 25, 2013, which issued as U.S. Pat. No. 9,821,475; as described in U.S. patent application Ser. No. 14/064,072 filed Oct. 25, 2013; as described in U.S. patent application Ser. No. 15/823,523 filed Nov. 27, 2017; or as described in U.S. patent application Ser. No. 15/472,740 filed Mar. 29, 2017. 
     In some applications, the design of the fluidic actuator unit  110  can be adjusted to expand its capabilities. One example of such a modification can be made to tailor the torque profile of a rotary configuration of the fluidic actuator unit  110  such that the torque changes as a function of the angle of the joint structure  125 . To accomplish this in some examples, the cross-section of the bellows  130  can be manipulated to enforce a desired torque profile of the overall fluidic actuator unit  110 . In one embodiment, the diameter of the bellows  130  can be reduced at a longitudinal center of the bellows  130  to reduce the overall force capabilities at the full extension of the bellows  130 . In yet another embodiment, the cross-sectional areas of the bellows  130  can be modified to induce a desired buckling behavior such that the bellows  130  does not get into an undesirable configuration. In an example embodiment, the end configurations of the bellows  130  of a rotary configuration can have the area of the ends reduced slightly from the nominal diameter to provide for the end portions of the bellows  130  to buckle under loading until the actuator unit  110  extends beyond a predetermined joint angle, at which point the smaller diameter end portion of the bellows  130  would begin to inflate. 
     In other embodiments, this same capability can be developed by modifying the behavior of the constraining ribs  135 . As an example embodiment, using the same example bellows  130  as discussed in the previous embodiment, two constraining ribs  135  can fixed to such bellows  130  at evenly distributed locations along the length of the bellows  130 . In some examples, a goal of resisting a partially inflated buckling can be combated by allowing the bellows  130  to close in a controlled manner as the actuator unit  110  closes. The constraining ribs  135  can be allowed to get closer to the joint structure  125  but not closer to each other until they have bottomed out against the joint structure  125 . This can allow the center portion of the bellows  130  to remain in a fully inflated state which can be the strongest configuration of the bellows  130  in some examples. 
     In further embodiments, it can be desirable to optimize the fiber angle of the individual braid or weave of the bellows  130  in order to tailor specific performance characteristics of the bellows  130  (e.g., in an example where a bellows  130  includes inextensibility provided by a braided or woven fabric). In other embodiments, the geometry of the bellows  130  of the actuator unit  110  can be manipulated to allow the robotic exoskeleton system  100  to operate with different characteristics. Example methods for such modification can include but are not limited to the following: the use of smart materials on the bellows  130  to manipulate the mechanical behavior of the bellows  130  on command; or the mechanical modification of the geometry of the bellows  130  through means such as shortening the operating length and/or reducing the cross sectional area of the bellows  130 . 
     In further examples, a fluidic actuator unit  110  can comprise a single bellows  130  or a combination of multiple bellows  130 , each with its own composition, structure, and geometry. For example, some embodiments can include multiple bellows  130  disposed in parallel or concentrically on the same joint assembly  125  that can be engaged as needed. In one example embodiment, a joint assembly  125  can be configured to have two bellows  130  disposed in parallel directly next to each other. The system  100  can selectively choose to engage each bellows  130  as needed to allow for various amounts of force to be output by the same fluidic actuator unit  110  in a desirable mechanical configuration. 
     In further embodiments, a fluidic actuator unit  110  can include various suitable sensors to measure mechanical properties of the bellows  130  or other portions of the fluidic actuator unit  110  that can be used to directly or indirectly estimate pressure, force, or strain in the bellows  130  or other portions of the fluidic actuator unit  110 . In some examples, sensors located at the fluidic actuator unit  110  can be desirable due to the difficulty in some embodiments associated with the integration of certain sensors into a desirable mechanical configuration while others may be more suitable. Such sensors at the fluidic actuator unit  110  can be operably connected to the exoskeleton device  610  (see  FIG. 6 ) and the exoskeleton device  610  can use data from such sensors at the fluidic actuator unit  110  to control the exoskeleton system  100 . 
     The described embodiments are susceptible to various modifications and alternative forms, and specific examples thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the described embodiments are not to be limited to the particular forms or methods disclosed, but to the contrary, the present disclosure is to cover all modifications, equivalents, and alternatives. Additionally, elements of a given embodiment should not be construed to be applicable to only that example embodiment and therefore elements of one example embodiment can be applicable to other embodiments. Additionally, elements that are specifically shown in example embodiments should be construed to cover embodiments where that comprise, consist essentially of, or consist of such elements, or such elements can be explicitly absent from further embodiments. Accordingly, the recitation of an element being present in one example should be construed to support some embodiments where such an element is explicitly absent.