Patent Publication Number: US-2021178613-A1

Title: Clutched Joint Modules for a Robotic System

Description:
RELATED APPLICATIONS 
     This is a divisional application of U.S. application Ser. No. 15/810,101, filed Nov. 12, 2017, entitled “Clutched Joint Modules for a Robotic System” which claims the benefit of U.S. Provisional Application Ser. No. 62/421,175, filed Nov. 11, 2016, and entitled, “Tunable Energy Recovering Quasi-Passive Actuators,” each of which is incorporated by reference in its entirety herein. 
    
    
     BACKGROUND 
     A wide variety of exoskeleton, humanoid, robotic arms, and other robots and robotic systems exist, many of which seek the most efficient operation possible. One fundamental technical problem that continues to be a focus is how such systems, such as where energetic autonomy is concerned, can minimize power consumption while still providing acceptable levels of force output. Indeed, power remains an inevitable challenge in the world of robotics. Designers of such systems typically attempt to optimize operation based on the intended use or application. In many cases, either power or efficiency is sacrificed, at least to some extent. For instance, some robotic systems employ high-output power systems that can meet the force output demands of the robotic system, putting this ahead of any efficiency considerations. On the other hand, some robotic systems employ more efficient power systems in an attempt to improve efficiency, with force output being a secondary consideration. High output force or power systems, while capable of performing various tasks, can be costly. Moreover, such systems often are tethered to a power source as portable power remains limited in its capabilities. Efficient, yet low force output systems can lack practicality, inasmuch as many robotic systems are designed to assist humans in work related or other tasks that require a certain level of force in order to perform the task(s). Overall, the power issue has been a challenging obstacle with various efforts being made to maximize output while minimizing power consumption. Even small advances in this ratio of power to output energy consumption area can be highly beneficial. While much research and development is ongoing to improve power sources, another way robotic systems can improve the power to energy output ratio is through the structural build of the robotic system, namely the way various components are configured, how these are controlled, and if the systems can take advantage of naturally occurring phenomenon, such as gravity. 
     BRIEF SUMMARY OF THE INVENTION 
     An initial summary of the disclosed technology is provided here. Specific technology examples are described in further detail below. This initial summary is intended to set forth examples and aid readers in understanding the technology more quickly, but is not intended to identify key features or essential features of the technology nor is it intended to limit the scope of the claimed subject matter. 
     The present disclosure sets forth a clutched joint module for use within a robotic assembly, comprising an output member operable to couple to a first support member of a robotic system; an input member operable to couple to a second support member of the robotic system; a primary actuator operable to apply a torque to rotate the output member about an axis of rotation; and a clutch mechanism operably coupled between the input member and the output member, the clutch mechanism operable in an engaged state, a semi-engaged state, or a disengaged state, wherein the engaged state and the semi-engaged state facilitate selective, variable application of the primary torque to the output member. 
     The clutch mechanism can be operable in the engaged or semi-engaged state to generate a braking force for restricting rotation between the input and output members either with or without the primary torque. 
     The clutch mechanism can comprise a plurality of plates and an actuator operable to compress the plurality of plates to cause the clutch mechanism to function in the engaged state or the semi-engaged state. 
     The clutch mechanism can comprise a clutch axis of rotation substantially collinear with the axis of rotation. 
     The primary actuator can comprise a motor and a transmission operatively coupled between the motor and the output member. The clutch mechanism, the motor, and the transmission can be arranged along and operable about the axis of rotation. The transmission can be at least partially disposed within a central void of the motor. In one example, the motor can comprise a brushless frameless electric motor. 
     A quasi-passive elastic actuator can be coupled to the input member and arranged in parallel with the primary actuator, the quasi-passive elastic actuator being operable to store and release energy upon the clutch mechanism being engaged or semi-engaged. The quasi-passive elastic actuator can operate to generate a braking force to at least partially restrict rotation between the input and output members. The quasi-passive elastic actuator can also operate to apply an augmented torque to be combined with a primary torque generated by the primary actuator to assist in rotation of the output member. The quasi-passive elastic actuator can comprise a quasi-passive linear pneumatic actuator, wherein the quasi-passive linear pneumatic actuator is gas pressure charged to at least partially define a joint stiffness value of the clutched joint module. The quasi-passive elastic actuator can be selectively switchable in real-time between an elastic state, a semi-elastic state, and an inelastic state via the clutch mechanism. 
     The clutch mechanism can comprise a clutch housing coupled to the input member; a plurality of input plates retained by the clutch housing; a plurality of output plates rotatably supported by the clutch housing and rotatably engaged with the plurality of input plates; and an actuator operable to apply a compression force to the output plates and the input plates, upon receiving the clutch control signal, to cause the clutch mechanism to operate in the engaged state. The output member can be coupled to the plurality of output plates, such that, when the clutch mechanism is in the disengaged state, the output plates freely rotate relative to the input plates. 
     The primary actuator can comprise a motor, and the clutched joint module can further comprise a first transmission disposed at least partially within the motor and a second transmission operatively coupled between the first transmission and the clutch mechanism. 
     The clutch mechanism can alternatively comprise a clutch housing coupled to the input member; a plurality of input plates retained by the clutch housing; a plurality of output plates rotatably supported by the clutch housing and rotatably engaged with the plurality of input plates; a ball-ramp clutch device coupled to the clutch housing; and an actuator coupled to the ball-ramp clutch device and operable to rotate the ball-ramp clutch device, upon receiving a control signal, to apply a compression force to the output plates and the input plates to cause the clutched mechanism to operate in the engaged state. The clutch mechanism can further comprise an output shaft coupled to the plurality of output plates, such that, when the clutch mechanism is in the disengaged state, the output plates freely rotate relative to the input plates. The primary actuator can comprise a motor, and wherein the clutched joint module further comprises a first transmission disposed at least partially within the motor, and a second transmission operatively coupled between the first transmission and the clutch mechanism. 
     The present disclosure further sets forth a robotic system comprising a robotic limb having at least one rotatable joint, the robotic assembly comprising a plurality of support members; and a plurality of clutched joint modules defining respective joints of the robotic limb, each clutched joint module rotatably coupling together at least two of the plurality of support members, and comprising: a joint rotatable about an axis of rotation and defining a degree of freedom; a primary actuator operable to apply a primary torque to rotate the joint; and a clutch mechanism coupled to the primary actuator and operable between an engaged state, a semi-engaged state and a disengaged state, wherein the engaged state and the semi-engaged state facilitate selective application of the primary torque to rotate the joint. 
     The clutch mechanism can be operable in the engaged or semi-engaged state to generate a braking force for restricting rotation of the joint either with or without the primary torque, wherein the primary actuator comprises a motor and a transmission operatively coupled to the motor. The clutch mechanism, the motor, and the transmission can be arranged along and operable about the axis of rotation. 
     The clutched joint module can further comprise a quasi-passive elastic actuator operable with the clutch mechanism and arranged in parallel with the primary actuator, the quasi-passive elastic actuator being operable to store and release energy upon the clutch mechanism being engaged or semi-engaged. 
     The quasi-passive elastic actuator can operate to generate a braking force to at least partially restrict rotation between the input and output members. 
     The quasi-passive elastic actuator can also operate to apply an augmented torque to be combined with a primary torque generated by the primary actuator to assist in rotation of the joint. 
     One of the plurality of clutched joint modules can comprise a quasi-passive elastic actuator comprising an elastic element of a first type, and another one of the plurality of clutched joint modules can comprise a quasi-passive elastic actuator comprising an elastic element of a different type. 
     The quasi-passive elastic actuator can be selectively switchable in real-time between an elastic state, a semi-elastic state, and an inelastic state via the clutch mechanism. 
     The present disclosure further sets forth a method for operating a robotic joint of a robotic system, the method comprising operating a clutch mechanism of a clutched joint module defining a joint of the robotic system between an engaged state, a semi-engaged state, and a disengaged state, wherein the clutch mechanism is operably coupled between input and output members of the clutched joint module; and rotating a first support member of the robotic system coupled to the output member relative to a second support member coupled to the input member, thus rotating the joint about an axis of rotation. 
     Rotating the first support member relative to the second support member can comprise actuating a primary actuator of the clutched joint module with the clutched mechanism in the engaged or semi-engaged state to apply a primary torque to the output member, wherein the clutched mechanism functions to transfer at least a portion of the primary torque from the primary actuator to the output member and rotate the joint. 
     Rotating the first support member relative to the second support member can comprise passively rotating these with the clutched mechanism in the engaged or semi-engaged state in response to an external force, thereby generating a braking force operable to resist rotation of the joint. 
     The method can further comprise operating the clutch mechanism in the disengaged state, wherein the joint enters a free swing mode. 
     The method an further comprise operating a quasi-passive elastic actuator of the clutched joint module in an elastic state or semi-elastic state by selectively engaging the clutch mechanism to generate and apply an augmented torque to the output member. 
     The method can further comprise operating a quasi-passive elastic actuator of the clutched joint module in an elastic state or semi-elastic state by selectively engaging the clutch mechanism to generate a braking force within the clutched joint module. 
     The method can further comprise operating a quasi-passive elastic actuator of the clutched joint module in an inelastic state to cause the clutched joint module to enter a free swing mode. 
     The method can further comprise pre-charging the quasi-passive elastic actuator to a predetermined stiffness. 
     The present disclosure further sets forth a clutched joint module for use within a robotic assembly, comprising an output member operable to couple to a first support member of a robotic system; an input member operable to couple to a second support member of the robotic system; a primary actuator operable to apply a primary torque to the output member to rotate the first and second support members relative to one another about an axis of rotation of the clutched joint module; a quasi-passive elastic actuator coupled to the input member and operable to apply an augmented torque to the output member that combines with the primary torque applied by the primary actuator to rotate the output member about the axis of rotation; and a clutch mechanism operably coupled to the primary actuator and the quasi-passive elastic actuator, the clutch mechanism operable in an engaged state, a semi-engaged state, or a disengaged state, wherein, in the engaged state, the clutch mechanism operates to place the quasi-passive elastic actuator in an elastic state, and to facilitate application of the augmented torque. 
     The clutch mechanism and the primary actuator can each have a central axis of rotation substantially parallel to each other. 
     The quasi-passive elastic actuator can comprise a linear pneumatic actuator, wherein the elastic component further comprises a piston rod and a piston cylinder moveable in a linear motion within a housing, the piston cylinder defining, at least in part, a compression chamber and an expansion chamber. 
     The linear pneumatic actuator can comprise the input member, wherein the piston rod can be pivotally coupled to a housing of the clutch mechanism at an off-center position, such that, upon the first rotation, movement of the input member causes the piston cylinder to move to compress gas in the compression chamber to selectively store energy. 
     The primary actuator and the output member can be operatively coupled to each other by a transmission. 
     Upon the second rotation, the linear pneumatic actuator can release energy via the piston rod to apply the augmented torque to the output member in parallel with the primary torque applied by the primary actuator. 
     The primary actuator can comprise a motor and a transmission rotatably coupled to the motor, and wherein the drive transmission is at least partially disposed within a central void of the motor. 
     The clutch mechanism can comprise a clutch housing coupled to the input member; a plurality of input plates retained by the clutch housing; a plurality of output plates rotatably supported by the clutch housing and rotatably engaged with the plurality of input plates; and an actuator operable to apply a compression force to the output plates and the input plates, upon receiving the clutch control signal, to cause the clutch mechanism to operate in the engaged state. 
     The output member can be coupled to the plurality of output plates, such that when the clutch mechanism is in the disengaged state, the output plates freely rotate relative to the input plates. 
     Alternatively, the clutch mechanism can comprise a clutch housing coupled to the input member; a plurality of input plates retained by the clutch housing; a plurality of output plates rotatably supported by the clutch housing and rotatably engaged with the plurality of input plates; a ball-ramp clutch device coupled to the clutch housing; and an actuator coupled to the ball-ramp clutch device and operable to rotate the ball-ramp clutch device, upon receiving a control signal, to apply a compression force to the output plates and the input plates to cause the clutched mechanism to operate in the engaged state. 
     The clutch mechanism can further comprise an output shaft coupled to the plurality of output plates, such that, when the clutch mechanism is in the disengaged state, the output plates freely rotate relative to the input plates, the output shaft being coupled to the output member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention; and, wherein: 
         FIG. 1  illustrates two positions of a robotic assembly in the form of a lower exoskeleton having at least one clutched joint module in accordance with an example of the present disclosure; 
         FIG. 2A  is a schematic illustration of a clutched joint module in accordance with an example of the present disclosure; 
         FIG. 2B  is a schematic illustration of a clutched joint module in accordance with an example of the present disclosure; 
         FIG. 3A  is a graph illustrating human weight normalized knee joint torque vs. knee joint angle of a human gait cycle; 
         FIG. 3B  is a graph illustrating the torque required to accomplish a joint trajectory and a portion of a gait where an elastic response can be created by a clutched joint module; 
         FIG. 3C  is a graph illustrating performance of a clutched joint module in accordance with an example of the present disclosure; 
         FIG. 4A  is an isometric view of a robotic assembly, namely a wearable robotic exoskeleton, having at least one clutched joint module in accordance with an example of the present disclosure; 
         FIG. 4B  is an isometric view of the robotic exoskeleton of  FIG. 4A ; 
         FIG. 4C  is a close-up isometric view of the robotic exoskeleton of  FIG. 4A ; 
         FIG. 5A  is an isometric view of a clutched joint module in accordance with an example of the present disclosure; 
         FIG. 5B  is an exploded view of the clutched joint module of  FIG. 5A ; 
         FIG. 5C  is an exploded view of a portion of the clutched joint module of 
         FIG. 5A  showing the planet gears of the planetary transmission; 
         FIG. 5D  is an exploded view of the clutched joint module of  FIG. 5A ; 
         FIG. 5E  is an exploded view of the clutch mechanism of the clutched joint module of  FIG. 5A ; 
         FIG. 6A  is an isometric view of a clutched joint module in accordance with an example of the present disclosure; 
         FIG. 6B  is an isometric view of the clutched joint module of  FIG. 6A  from another perspective; 
         FIG. 6C  is an exploded view of the clutched joint module of  FIG. 6A ; 
         FIG. 6D  is an exploded view of the clutched joint module of  FIG. 6A  from another perspective; 
         FIG. 6E  is an exploded view of the clutch mechanism of the clutched joint module of  FIG. 6A ; 
         FIG. 6F  is an exploded view of the clutch mechanism of the clutched joint module of  FIG. 6A ; 
         FIG. 6G  is an exploded view of a portion of the clutch mechanism of the clutched joint module of  FIG. 6A ; 
         FIG. 7A  is an exploded view of a clutched joint module in accordance with an example of the present disclosure, having the clutch mechanism and quasi-passive elastic actuator of  FIG. 5A-5E  located about an axis offset from an axis of the primary actuator and coupled to the primary actuator via a torque-transferring device; and 
         FIG. 7B  is an exploded view of the primary actuator of the clutched joint module of  FIG. 7A . 
     
    
    
     Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. 
     DETAILED DESCRIPTION 
     As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result. 
     As used herein, “adjacent” refers to the proximity of two structures or elements. Particularly, elements that are identified as being “adjacent” may be either abutting or connected. Such elements may also be near or close to each other without necessarily contacting each other. The exact degree of proximity may in some cases depend on the specific context. 
     One example of a robotic assembly  100  is generically illustrated in  FIG. 1 . The robotic assembly  100  is shown in the form of an exoskeleton, and particularly a lower exoskeleton wearable by a user about the lower body. However, this is not intended to be limiting in any way as the concepts discussed herein can be applicable to and incorporated into or implemented with various types of robotic devices, such as exoskeletons (both upper and lower exoskeletons), humanoid robots or robotic devices, teleoperated robots or robotic devices, robotic arms, unmanned ground robots or robotic devices, master/slave robots or robotic devices (including those operable with or within a virtual environment), and any other types as will be apparent to those skilled in the art. 
     In the example of the robotic assembly  100 , the exoskeleton as disclosed herein can be configured as a full-body exoskeleton (i.e., similar to the exoskeleton having both a lower body portion and upper body portion, see  FIG. 4A ), or as only a lower body exoskeleton (i.e., some or all of the lower body portion), or as only an upper body exoskeleton (i.e., some or all of the upper body portion). 
     In some examples, the robotic assembly  100  can comprise left and right exoskeleton limbs. Note that only the right exoskeleton limb  102  is shown in  FIG. 1 , but it should be appreciated that the principles discussed can relate to joint modules of any exoskeleton limb of an upper body or lower body exoskeleton. The right exoskeleton limb  102  can comprise a plurality of lower body support members  104   a - d . The support members  104   a - d  can be coupled together for relative movement about a plurality of clutched joint modules  106   a - d  defining a plurality of degrees of freedom about respective axes of rotation  108   a - d . The rotational degrees of freedom about the axes of rotation  108   a - d  can correspond to one or more degrees of freedom of the human leg. For example, the rotational degrees of freedom about the axes  108   a - d  can correspond, respectively, to hip abduction/adduction, hip flexion/extension, knee flexion/extension, and ankle flexion/extension, respectively. Similarly, although not shown, rotational degrees of freedom about respective axes of rotation within an upper body exoskeleton can correspond to one or more degrees of freedom of a human arm. For example, the degrees of freedom about the axes of rotation can correspond to shoulder abduction/adduction, shoulder flexion/extension, shoulder medial/lateral rotation, elbow flexion/extension, wrist pronation/supination, and wrist flexion/extension. A degree of freedom corresponding to wrist abduction/adduction can also be included, as desired. 
     A human user or operator may use or interact with the exoskeleton robotic assembly  100  (or  101  of  FIG. 4A ) interfacing with the robotic assembly  100 . This can be accomplished in a variety of ways as is known in the art. For example, an operator may interface with the robotic assembly  100  by placing his or her foot into a foot portion of the assembly, where the foot of the operator can be in contact with a corresponding force sensor. Portions of the human operator can also be in contact with force sensors of the exoskeleton robotic assembly  100  located at various locations of the robotic assembly  100 . For example, a hip portion of the robotic assembly  100  can have one or more force sensors configured to interact with the operator&#39;s hip. The operator can be coupled to the robotic assembly  100  by a waist strap, shoulder strap or other appropriate coupling device. The operator can be further coupled to the robotic assembly  100  by a foot strap and/or a handle for the operator to grasp. In one aspect, a force sensor can be located about a hip, knee or ankle portion of the robotic assembly  100 , corresponding to respective parts of the operator. While reference is made to sensors disposed at specific locations on or about the robotic assembly  100 , it should be understood that position or force sensors, or both, can be strategically placed at numerous locations on or about the robotic assembly  100  in order to facilitate proper operation of the robotic assembly  100 . 
     As a general overview, clutched joint modules  106   a - d  can be associated with various degrees of freedom of the exoskeleton to provide forces or torques to the support members in the respective degrees of freedom. Unlike traditional exoskeleton systems and devices, the robotic assembly  100  can be configured, such that each clutched joint module is configured as either an active actuator, or a quasi-passive actuator, as further discussed below. As a quasi-passive actuator, a particular clutched joint module ( 106   a - d ) can be configured to recover energy, which can reduce complexity and power consumption of the robotic assembly  100 . For example, the clutched joint module  106   c , which defines a degree of freedom corresponding to a degree of freedom of knee flexion/extension, can be configured to recover energy during a first gait movement and then release such energy during a second gait movement to apply an augmented torque to assist a primary actuator providing a primary torque in rotation of the joint about the degree of freedom (and in parallel with the torque applied by the primary actuator of the clutched joint module  106   c , as discussed below) . The clutched joint module  106   c  can be selectively controlled, so as to be engaged (i.e., caused to enter an operating state or condition in which the elastic actuator stores and releases energy (an elastic state)) and disengaged from operation (i.e., caused to enter an operating state or condition or configuration where it neither stores nor releases energy (an inelastic state)), such that the joint “freely swings” with negligible resistance to rotate the joint as the operator walks or runs, for instance. By operating in parallel with the primary actuator (e.g., a primary motor operable to actuate the joint), the quasi-passive elastic actuator can provide or apply an augmented torque in parallel with the torque provided by the primary actuator (i.e., a torque that is added to the torque generated by the primary actuator). The quasi-passive elastic actuator can comprise a compact internal valve, such as a two-way valve, that can be controlled and operated to change the modes of the quasi-passive actuator, namely to switch between an elastic state (where the actuator acts as a spring for transient energy storage and recovery), and an inelastic state (where the actuator employs a shunting function that allows the actuator to move freely (i.e., not to store or release energy) (except for friction and movement of fluid through the valve). And, the clutched joint module  106   c  (as a quasi-passive actuator) can be “tuned” to comprise a desired stiffness, which can also be modified, as further discussed below. Thus, the magnitude of stiffness for a given joint is adjustable for mission specific payloads and terrain-specific gaits while the active valve controls exactly when that stiffness is engaged for energy recovery during the support phase and when it is disengaged during the free swinging phase. 
     As a quasi-passive actuator, the result is effectively a quasi-passive elastic mechanism that is selectively operable to recover energy (e.g., energy lost during some gait or other motions) to reduce or minimize power consumption required to actuate the joint. 
     The example elastic actuators described herein can be referred to as quasi-passive elastic actuators as they are operable in active and inactive states or modes of operation (as compared to being entirely passive elastic actuators that are always either storing energy or releasing energy during all rotational movements of a joint, or other movements of a mechanical system). In examples described herein, the passive and inactive modes or states of operation can be selectable or controllable and even dynamically selectable or controllable (e.g., selectable in real-time), as well as repeatedly switched from one state or mode to another state or mode, during operation of the robotic system. Depending upon the configuration of the clutched joint module, example quasi-passive elastic actuators can comprise a first active state (sometimes referred to herein as an “elastic state”) in which the quasi-passive elastic actuator can be actuated to store and release energy during various rotations of a joint of the robotic system, a second passive state (sometimes referred to herein as an “inelastic state”) in which the quasi-passive elastic actuator can be made inactive, such that energy is neither stored nor released during various rotations of the joint, and in some cases a third semi-active or partially active state (sometimes referred to herein as a “semi-elastic state”) in which the quasi-passive elastic actuator can be partially actuated to store and release energy during various rotations of the joint. In some example robotic systems, the quasi-passive elastic actuator can be switchable between the different modes or states of operation as needed or desired depending on, for example, needed or desired tasks and corresponding rotation movements, various torque or load requirements of the one or more joints of the robotic system, or needed or desired braking forces. 
     When combining a plurality of clutched joint modules within a robotic assembly, such as the lower body exoskeleton shown in  FIG. 1 or 4A , for example, a significant amount of energy can be recovered and utilized during movement (via hip, knee, and ankle joints), which can reduce weight, size, complexity, and power consumption of the exoskeleton. The above general overview is explained in more detail below. Moreover, each of the various joint modules in the robotic system or assembly can comprise the same type or a different type of quasi-passive elastic actuators (or in other words the same type of different types of elastic components), thus the robotic assembly can be configured for optimal performance depending upon the particular application or tasks to be carried out. As active actuators (i.e., having no quasi-passive elastic element), a particular clutched joint module can be selectively operable (i.e., via a clutch mechanism) to be engaged as an active actuator to actuate a joint, and also to provide gravity compensation, as further discussed below. 
       FIGS. 2A and 2B  each schematically illustrate clutched actuator joint modules in accordance with two examples of the present disclosure.  FIG. 2A  shows a clutched actuator joint module  120  having a primary actuator  122  operable to provide a primary torque to the clutched joint module. In one example, the primary actuator can comprise a motor  124  and a transmission or gear train  126  (e.g., a planetary transmission) operating in parallel with a clutch mechanism  128  and an elastic element or spring  128  (e.g., a quasi-passive elastic actuator, such as a rotary or linear pneumatic (air or other gas) type of quasi-passive elastic actuator). The primary actuator  122  is operable to apply a primary torque to a load (e.g., to rotate an output member coupled to a robotic support member) in parallel with an augmented torque selectively applied by the spring (quasi-passive elastic actuator)  128  to rotate a joint of a robotic assembly, as in  FIGS. 1 and 4A . The augmented torque is selectively applied by operation of the clutch mechanism  128 , which is operable between an engaged state and a disengaged state, as further described below. Note that the gear train  126  can be removed or may not be needed, or a supplemental transmission or gear train can be coupled adjacent the gear train  126  to provide a two-stage transmission from the motor  124  to the load. The examples of  FIGS. 5A-6G  are schematically represented by  FIG. 2A . Further note that the output of the spring  130  can be operatively coupled between the motor  124  and the gear train  126 , as illustrated by the dashed lines in  FIG. 2A . 
       FIG. 2B  shows a clutched joint module  121  comprising a primary actuator  123  comprising a motor  125  and a transmission or gear train  127  (e.g., a planetary transmission) operating in parallel with a clutch mechanism  129 . Here, the clutch mechanism  129  is operable between an engaged state (that facilitates actuation of a primary torque by the primary actuator  123  to the load) and a disengaged state (that allows free swing of an input relative to an output (the load)), as further described below. Note that the gear train  127  can be removed or may not be needed, or a supplemental transmission or gear train can be coupled adjacent the gear train  127  to provide a two-stage transmission from the motor  125  to the load. The examples of  FIGS. 5A-6G  are each schematically represented by  FIG. 2B , but without incorporation of a spring (e.g., removal of the quasi-passive elastic actuator  134 ,  204 ). 
       FIG. 3A  is a graph showing joint torque vs. joint position as these occur during an example gait of a human, the graph showing the torque (N-m/kg) occurring in the joint relative to or as corresponding to the angle of rotation of the joint. This particular graph is illustrative of an example torque/angular rotation relationship of a human knee (without wearing an exoskeleton), while walking approximately 3 mph on a flat surface. A first gait movement from point A to point B illustrates stance compression following heel strike, a second gait movement from point B to C illustrates stance extension, with the stance phase being completed at point D. A third gait movement between points D, E, F, and A illustrates “double support and leg swing.” Therefore, the “stance phase” is from heel strike (point A) to toe-roll/terminal stance (points A to D), where the torque-joint profile has a quasi-elastic behavior (walking and running are similar regarding this quasi-elastic stiffness). During this phase, the knee also acts as a shock absorber. The “swing phase” is from toe-off to heel strike (points E to A), and during this phase the knee exhibits a quasi-ballistic (passive dynamics) response with some damping during the final extension that occurs before heel strike (thus, the knee acts as a controlled damper or shock absorber). 
     This characteristic of the human gait is not unique to the knee joint, nor limited to the walking gait, and forms the basis for the clutched joint modules discussed herein. Indeed, when reviewing the joint torque vs. position plots of simulated cyclical exoskeleton activities, such as walking, running, and step climbing, there are periods of time during these specific gait motions where elastic energy recovery can be exploited to reduce the requirement for motor torque to run the joint. Thus, the clutched joint modules described herein can be configured to exploit the features of the natural motion of the hip, knee, and ankle, for instance, to minimize demands on powered actuators (e.g., electric-geared motors) to reduce overall power consumption within the robotics assembly. The clutched joint modules discussed herein can also be incorporated into shoulder and elbow joints, for instance, but these may be more task-specific than as with the lower body joints, as further discussed below. However, the clutched joint modules of lower joints (e.g., hip, knee, ankle) can also be configured to operate based on a specific task (e.g., lifting a load, sitting and standing, and others), rather than just a cyclical operation (e.g., walking or running). 
       FIG. 3B  is a graph showing a standard exoskeleton knee joint torque (N-m) vs. position (deg.) for walking at 3.5 mph with a 50 lb. payload. The plotted “triangular” labeled line (“joint actuation torque”) represents the required overall torque to accomplish the prescribed joint trajectory, while the plotted “circular” labeled lines (“spring reaction torque”) represents the part of the gait where an elastic response can by created by a quasi-passive elastic actuator of a clutched joint module. Thus, this spring reaction torque can be exploited to reduce power consumption to actuate a joint, as further detailed below. 
       FIG. 3C  is a graph illustrating performance of an exoskeleton having a clutched joint module with a quasi-passive elastic actuator operating in parallel with a primary actuator, the joint module having a joint stiffness of 7 N-m/degree, associated with the human knee joint, in one example. More specifically, the graph shows joint torque (N-m) vs. joint speed (deg./sec) for walking at 3.5 mph with a 50 lb. payload. The plotted “triangular” labeled line (“joint actuation torque”) represents the required overall torque to accomplish the prescribed joint trajectory (e.g., the torque required to rotate a knee), while the plotted “circular” labeled lines (“spring reaction torque”) represents the part of the gait where an elastic response can be created by engaging and disengaging the quasi-passive elastic actuator in a timely manner, as exemplified herein. 
     As illustrated by this “circular” labeled line, the resulting peak torque is substantially reduced (approximately 25 N-m) vs. the normalized torque requirement (approximately 100 N-m) of the “triangular” labeled line. That is, normally (i.e., without incorporating a clutched joint module having an elastic actuator) the torque requirement is peaked at approximately 100 N-m; however, when incorporating a clutched joint module having an elastic actuator as disclosed herein, the resulting peak torque can be only approximately 20 N-m, thus significantly reducing power requirements for the same gait cycle and operating conditions. This is because the clutched joint module stores energy during a first gait movement (via the quasi-passive elastic actuator), and then releases that energy during a second gait movement to apply an augmented torque that can be applied in parallel with a torque applied by a primary actuator (e.g., a geared motor) of the clutched joint module. Of course, other factors play a role in these results, such as weight, payload, etc. In any event, these graphs illustrate that much less on-board power is required by the powered motor to appropriately actuate a joint when used in conjunction with a selectively controllable quasi-passive elastic actuator, as further exemplified below. The use of a parallel elastic actuator effectively reduces the requirement for motor torque as the elastic actuator is engaged and disengaged in a timely manner, such as during specific phases of a gait cycle. Similar plots or graphs can be shown for hip joints, ankle joints, shoulder joints, and elbow joints. In some cases, the elastic actuator can be engaged full-time for the gait cycles of these joints. 
       FIGS. 4A-4C  show isometric views of an exemplary robotic assembly  101  in the form of an exoskeleton wearable or usable by a human operator. The robotic assembly  101  could alternatively be a humanoid robot, or other robotic assembly as discussed above. As shown, the robotic assembly  101  can be configured as a full-body exoskeleton (i.e., an exoskeleton having both a lower body portion and an upper body portion). However, this is not intended to be limiting as the exoskeleton can comprise only a lower body exoskeleton (i.e., some or all of the lower body portion), or only an upper body exoskeleton (i.e., some or all of the upper body portion). 
     The robotic assembly  101  can comprise left and right exoskeleton limbs. The right exoskeleton limb  103  can comprise a plurality of lower body support members  105   a - d . The support members  105   a - c  can be coupled together for relative movement about a plurality of respective joints  107   a - c  defining a plurality of degrees of freedom about respective axes of rotation. As described in U.S. patent application Ser. No. 15/810,108, filed Nov. 12, 2017, which is incorporated by reference in its entirely herein, the hip joint  107   a  and knee joint  107   c  can each comprise a tunable actuator joint module  109   a  and  109   c  that can comprise a tunable quasi-passive elastic actuator, as shown in  FIGS. 4A and 4B , having a rotary air spring device as an elastic element or component. Alternatively, the hip and knee joints  107   a  and  107   c  can each comprise a clutched joint module, such as described by the present disclosure. Joints  107   b  and joint  107   d  can also each comprise a clutched joint module  109   b  and  109   d , respectively, as described herein. 
     Similarly, the right exoskeleton limb  103   b  can comprise a plurality of upper body support members  105   e - h  coupled together for relative movement about a plurality of joints  107   e - h  defining a plurality of degrees of freedom about respective axes of rotation (see  FIG. 4C  for a closer view). Each joint  107   e - h  can comprise a clutched joint module  109   e - h , respectively, as described herein. Notably, as further described below, each clutched joint module can be provided in a compact form, meaning that the particular axis of rotation of the joint, joint  107   e  for instance, is substantially collinear with primary components of the clutched joint module  109   e , for instance (e.g., primary actuator, transmission(s), clutch mechanism(s), quasi-passive elastic actuator(s)), these being arranged along and configured to be operable about the axis of rotation, as further exemplified below. Thus, each clutched joint module can provide a particular high-torque output in a compact form, such as a clutched joint module that is generally cylindrical and that locates the mass of the module near to the axis of rotation. 
       FIGS. 5A-5E  illustrate a clutched joint module  130  according to an example of the present disclosure, which can be incorporated as, or in other words, can comprise a joint of a robotic assembly (e.g.,  100 ,  101 ). 
     The clutched joint module  130  can comprise a primary actuator  132 , an optional quasi-passive elastic actuator  134 , and a clutch mechanism  136  operatively coupled to each other, with the clutch mechanism  136  and the primary actuator  132  positioned or arranged along and operable about an axis of rotation  140 . As further detailed below, an input member  138   a  and an output member  138   b  ( FIG. 5B ) can be directly or indirectly coupled to respective support members of the robotic assembly, which support members are rotatable relative to each other about the axis of rotation  140  of the joint, which corresponds to an axis of rotation of a degree of freedom of a human joint. For instance, the clutched joint module  130  can be incorporated into the robotic assembly  101  as clutched joint module  109   f  of  FIG. 4C  that defines, at least in part, the joint  107   f  comprising a shoulder joint having a flexion/extension degree of freedom. Note that input and output members  138   a  and  138   b  are shown as members coupled to their respective components, but they can take many different forms and configurations of suitable input and output members or components that are coupleable to robotic support members, for instance. 
     The primary actuator  132  can comprise a motor  133  and, optionally, a transmission, such as a first planetary transmission  148  and, further optionally, a second transmission, such as second planetary transmission  170 . The motor  133  is operable to apply a primary torque to the output member  138   b  for rotation about the axis of rotation  140 , and the quasi-passive elastic actuator  134  (e.g., a quasi-passive linear pneumatic elastic actuator) is selectively operable to store energy during a rotation of the clutched joint module, and to release energy in the form of an augmented torque that can be applied to the output member  138   b  along with the primary torque applied by the motor  133  (the two torques being combined to generate an output via the output member  138   b ). 
     In one example configuration with the clutched joint module  130  comprising a quasi-passive elastic actuator  134 , the clutch mechanism  136  is operable to selectively control the quasi-passive elastic actuator  134  and the generation of the braking force or application of the augmented torque. Indeed, a braking force can be generated to restrict rotation of the joint in some operational scenarios (e.g., scenarios where the primary actuator is active or not active to produce a primary torque, but where rotation of the joint is desired), or an augmented torque can be generated and applied in combination with a primary torque to assist in rotation of the output member and the joint, as discussed below. 
     More specifically, the quasi-passive elastic actuator  134  is operable to selectively store energy or generate a braking force (when in an elastic or semi-elastic configuration or mode or state) upon a rotation of the input member  138   a  (e.g., where the rotation is either actively carried out using the primary actuator, or passively carried out, such as rotation of a joint under the influence of gravity of some other externally applied force that induces rotation) when the clutch mechanism  136  is engaged or semi-engaged, and is operable to selectively release energy (also when in the elastic or semi-elastic configuration or mode or state) upon a rotation (in the same or a different direction as the rotation for storing the energy) of the input member  138   a  when the clutch mechanism  136  is engaged or semi-engaged to apply the augmented torque to the output member  138   b  in parallel with the primary torque applied by the primary actuator  132 , in this case motor  133 . The quasi-passive elastic actuator  134  is further operable to neither store nor release energy during rotation of the joint (when in an inelastic configuration or mode or state) when the clutch mechanism  136  is selectively disengaged. In this inelastic state, the input member  138   a  is in “free swing” relative to the output member  138   b , meaning that negligible resistance is applied within the clutched joint module  130  via the quasi-passive elastic actuator  134  (so that the quasi-passive elastic actuator  134  does not have a stiffness value that would restrict rotation of the input member  138   a  relative to the output member  138   b ). The clutch mechanism  136  can also move from an engaged or semi-engaged state to a disengaged state to dissipate any stored energy (i.e., dissipate any braking force generated, such as when the braking force no longer needed). Thus, the quasi-passive elastic actuator  134  is selectively switchable between the elastic state, the semi-elastic state, and the inelastic state via operation of the clutch mechanism  136 . One advantage is that the quasi-passive elastic actuator  134  can be caused to apply, at select times, an augmented torque in parallel with the primary torque applied by the motor  133 , which applies a combined torque to the output member  138   b , thereby reducing the power requirements/demands of the primary actuator  132 . 
     With the advantage of an augmented torque, the motor  133  selected can be of a smaller size and a lower power dissipation than otherwise would be required by the robotic system without the assistance of such augmented torque applied by the quasi-passive elastic actuator  134 . 
     In examples described herein, “selective” can mean that the clutched joint module can be controlled in real-time, such as to vary a magnitude and timing of a braking force, vary a magnitude and timing of compression of the elastic component of the quasi-passive actuator and the storing and releasing of energy therein, or vary a magnitude and timing of a primary torque generated by the primary actuator depending upon different operating conditions, operating states, different demands of the robotic system, or as desired by the operator. Selective control can mean that the quasi-passive elastic actuator can be operated in conjunction with the primary actuator all or some of the time or for a desired duration of time. In addition, “selective” can mean, in examples, that one or more operating parameters or the output performance of the clutched joint module can be controlled and varied in real-time as needed or desired. Operating parameters or output performance can include, but is/are not limited to, a magnitude of the augmented torque to be applied, a magnitude of the braking force generated, the stiffness or elasticity of the elastic actuator, the zero or null point of actuation of the elastic actuator, and others. 
     In examples, “semi-engaged” can mean that the clutch mechanism is engaged, but not fully engaged nor disengaged, such that some slippage occurs within the clutch mechanism (i.e., there is a less than a 1:1 transfer of forces from the input of the clutch to the output of the clutch through the clutch mechanism, such that the clutch mechanism does not act as a rigid system). For example, in the case of the clutch mechanism having a plurality of plates, such as input and output plates, the semi-engaged state would mean that the plates are under a compression force sufficient to compress the plates together some degree, but that some relative movement (i.e., slippage) occurs between the plates (i.e., they are not completely locked up such that they rotate together and movement between them is not completely restricted) and a friction force is generated between them (e.g., a usable braking force). The term “engaged state” as used herein can include the semi-engaged state as these are also meant to describe at least a partially engaged state of the clutch mechanism, as well as to describe the clutch mechanism where the amount of slippage and thus the amount of the braking force (or augmented torque) is controllable and variable between the disengaged state where negligible braking force is generated and fully engaged where the clutch models a rigid connection member. 
     In examples where the quasi-passive actuator is caused to enter a “semi-elastic state” or mode of operation, the quasi-passive elastic actuator can be actuated to partially compress the elastic or spring component of the quasi-passive elastic actuator to store, and be enabled to release, an amount of energy or enabled to generate a magnitude of a braking force that is less than what would otherwise be achieved if the quasi-passive elastic actuator were in a fully elastic state. Stated another way, “semi-elastic” describes that state in which there is a less than 1:1 transfer of energy or forces, due to rotation of the joint, to the quasi-passive elastic actuator coupled between the input and output members (e.g., because the clutch mechanism is in the semi-engaged state). “Semi-elastic,” as used herein, is not intended to refer to the inherent elastic property (i.e., the elasticity) of the elastic component of the quasi-passive elastic actuator, but merely to a degree of compression of the elastic component. 
     In one example, the motor  133  can be a high-performance Permanent Magnet Brushless DC motor (PM-BLDC), which can be a variant of a frameless torque motor with winding optimized to achieve the desired maximum torque and speed while operating using a 48 VDC supply and a high-performance COTS controller, such as electric motor MF0127-032 marketed by Allied Motion. 
     With reference to  FIG. 5B , the motor  133  can comprise a stator  142  and rotor  144  rotatable relative to each other (in a typical fashion for commercially available frameless brushless motors). Thus, the motor  133  of the primary actuator  132  comprises a cylindrical void  146  about the central area of the rotor  144 . Advantageously, the first planetary transmission  148  can be positioned (at least partially) within the cylindrical void  146  of the motor  133 , which provides a low-profile, compact geared motor configuration as the first planetary transmission  148  and the motor  133  are packaged together, as shown and described. 
     In the present example the first planetary transmission  148  can comprise a 4:1 geared transmission. Thus, in one example, the first planetary transmission  148  can comprise an outer housing  150  attached to the rotor  144  via fasteners (not shown) through apertures  152  of the outer housing  150 . The outer housing  150  can comprise inner gear teeth  156  formed around an inner surface of the outer housing  150 . Such gear teeth  156  can be configured to engage corresponding gear teeth of each of four planet gears  158  of the first planetary transmission  148 . A sun gear  160  can be disposed centrally between the four planet gears  158  and along the axis of rotation  140 , with the sun gear  160  comprising teeth engaged to the teeth of each of the four planet gears  188  (see  FIG. 5C ). 
     With reference to  FIG. 5C , the planet gears  158  rotate about their own central axis and around the sun gear  160 . A carrier plate  162  can be fastened to four carrier pins  164  via fasteners  166 . The planet gears  158  can each comprise a hollow tubular body that rotatably receives a respective carrier pin (see carrier pins  164 ) through the hollow body of each planet gear  158 . The planet gears  158  can each be rotatably interfaced to respective carrier pins  164  via front bushings  168   a  and rear bushings  168   b . A transfer wheel  165  can be fastened to the rotor  144  via perimeter fasteners  167 , and the transfer wheel  165  can comprise a central coupling portion  169  coupled to the sun gear  160 . Therefore, upon receiving a primary control signal (e.g., from a controller operable to cause rotation of the clutched joint module), the motor  133  rotates the rotor  144  about the axis of rotation  140 , which causes the transfer wheel  165  to rotate, which thereby causes the sun gear  160  to rotate, thereby rotating the planet gears  158 . Note that the transfer wheel  165  is only shown in  FIGS. 5B and 5D . 
     The planet gears  158  can be configured to drive the second planetary transmission  170 . Specifically, the planet gears  158  can be coupled to a supplemental sun gear  172  of the second planetary transmission  170  via the carrier pins  164 . Thus, upon rotation of the supplemental sun gear  172 , planet gears  174  rotate ( FIG. 5B ), which rotates a carrier  176  ( FIG. 5D ) (i.e., the output of the second planetary transmission  170 ). Accordingly, an outer ring  178  of the second planetary transmission  170  comprises the stationary component, which can be coupled to the motor  133  via a support housing or frame (not shown). The carrier  176  can be coupled to the output member  138   b , such that rotation of the carrier  176  causes rotation of the output member  138   b.    
     Support frames, such as described regarding FIG. 5A of U.S. patent application Ser. No. 15/810,102, filed Nov. 12, 2017, which is incorporated by reference in its entirely herein, can be utilized to house and structurally support the primary actuator  132 , the secondary planetary transmission  170 , and the clutch mechanism  136 , of the present disclosure in a similar manner. 
     Planetary and other types of transmissions, such as the second planetary transmission  170 , are known and commercially available. One such example of a planetary transmission that can be incorporated into the clutched joint module is Matex&#39;s 75-4MLG12 planetary transmission, which is a 4:1 geared unit with a 2.95 inch outside diameter having a 118 N-m peak torque, weighing just 500 grams. Another benefit of providing a transmission is the fact that, in one example, the transmission (e.g.,  148 ,  170 ) can be situated to be in-line or collinear with the axis of rotation  140  of the motor  133  (and consequently of the joint module  130 ), which allows for compact mounting configurations. Other examples may locate the transmission offset from one or more other components of the clutched joint module, with the transmission being operable with the primary actuator. 
     With reference to  FIG. 5D , the output member  138   b  can be a shaft attached to a central portion of the carrier  176 , such that rotation of the carrier  176  causes rotation of the output member  138   b  about the axis of rotation  140 . This is not intended to be limiting as other output member configurations are possible and contemplated, as well as how these interface with and how these are coupled to the carrier  176 . This provides a 4:1 geared-down transmission arrangement (from the output rotation of the first planetary transmission  148  to the output rotation of the output member  138   b ). Thus, the present example provides a 16:1 final drive transmission from the motor  133  to the output member  138   b . Other planetary transmission types and gear reduction schemes can be used instead of a 4:1 transmission, such as a 3:1 planetary gear scheme. Note that output member  138   b  is shown generically as a solid body shaft, but it could take other suitable forms and configurations for interfacing with the second planetary transmission  170  and with a robotic support member, for example. 
     To reduce build height, as well as to provide other advantages, the first planetary transmission  148  can be configured to be positioned inside of the rotor of the motor  133 . Depending on the motor selected, the inside diameter of the rotor can dictate the maximum outside diameter of the planetary transmission. Once the planetary ring has been constrained by its outside diameter, there are a limited amount of options for gear ratios and output torques available. The output ratio is determined from the ratio of the number of teeth on the ring gear to the number of teeth on the sun gear. To obtain a higher reduction in the compact design of the planetary unit, the sun gear diameter can be reduced, which generally corresponds to less power transmission. The capacity to transmit higher torques is reduced with the smaller sun gear. A balance of reduction and strength can be considered for a planetary unit that will physically fit inside the motor rotor. By implementing a helical cut gear, higher forces can be transmitted on the gear teeth making the unit stronger. A wider tooth will also improve the load carrying capacity of the gear, however this increases the weight as well. Multiple stages of a planetary transmission can be cascaded (e.g.,  148  and  170 ) to produce extremely high gear reduction in a relatively compact package. In addition, the sun gear can be configured to make contact with several teeth simultaneously, wherein the contact ratio will be much higher than a conventional spur gear transmission. In some examples, a single stage planetary transmission can achieve efficiencies of around 97%. At higher RPM, gear noise can be an issue, especially for multiple stage planetary units. Another benefit of planetary gears is the fact that the transmission can be positioned in-line with the motor, which allows for compact mounting configurations within the joint module of the robot or robotic assembly. 
     Advantageously, the motor  133 , the first and second planetary transmissions  148  and  170 , and the output member  138   b  can each operate or rotate about substantially the same axis of rotation as the axis of rotation  140  of the clutched joint module  130  (i.e., the axis of rotation of the corresponding joint of the robot or robotic assembly), which axis of rotation in some cases, can also correspond to the axis of rotation of a human joint, such as an operator in an exoskeleton. Said another way, each axis of rotation of the motor  133 , the first and second planetary transmissions  148  and  170 , and the output shaft  138   b  can be arranged to be collinear or substantially collinear with the axis of rotation  140 . This locates the mass of such components close or near to the axis of rotation of a particular joint, which further minimizes power requirements by the motor  133  to actuate the joint. 
     In the illustrated example of  FIGS. 5A-5E , the output member  138   b  applies a relatively higher torque at a low speed with very little noise and backlash via the planetary transmissions  148  and  170 , all in a compact form with the planetary transmission  148  being housed within the void  146  of the motor  133 , and because of the cascading arrangement of the motor  133  and the first and second planetary transmissions  148  and  170  all arranged along, and operating about or around, the axis of rotation  140 . 
     With particular reference to  FIGS. 5B-5E , and as introduced above, the quasi-passive elastic actuator  134  is operable to apply an augmented torque to rotate the output member  138   b  along with the torque applied by the primary actuator  132 , or to generate a braking force within the clutched joint module. In one example, the quasi-passive elastic actuator  134  can be a linear pneumatic spring comprising a housing  180  and a robotic support member interface  182  coupled to the housing  180 , and pivotally coupleable to a robotic support member as part of a joint within a limb of the robot or robotic assembly (e.g.,  105   f  of  FIG. 4C ). The robotic support member interface  182  can be one or two bearings, fasteners, or other coupling device(s) that can couple the housing  180  to such robotic support member. 
     The quasi-passive elastic actuator  134  can comprise a piston rod  184  pivotally coupled, on one end, to a coupling portion  195  of the clutch mechanism  136 . On the other end, the piston rod  184  can be coupled to a piston cylinder  186  that is slidably supported within the housing  180 . Accordingly, the housing  180  can comprise a compression gas chamber  188  adjacent/above the piston cylinder  186  and an expansion chamber adjacent/below the piston cylinder, these being sealed off by the piston cylinder  186 . As shown, the piston rod  184  can be pivotally coupled to the clutch mechanism  136  off-center relative to the axis of rotation  140 . Accordingly, as further detailed below, and with the clutch mechanism  136  engaged or semi-engaged to place the quasi-passive actuator  134  in the elastic or semi-elastic state, as further discussed below, upon movement of a robotic support member (e.g.,  105   f  of  FIG. 4C ), the housing  180  can move downwardly, for instance, which causes the piston cylinder  186  to translate upwardly within the housing  180 , which causes gas in the gas compression chamber  188  to compress, thereby storing energy within the quasi-passive elastic actuator  134 . This action can also be used to generate a braking force (i.e., compression of the elastic element generates a force that can be used to restrict movement of the output member relative to the input member). Furthermore, once stored, the energy can be dissipated at any time without being used either as a braking force or to apply an augmented torque (by disengaging the clutch mechanism  136 ) or released (by keeping the clutch mechanism  136  at least partially engaged) to apply an augmented torque that can be combined with a primary torque by the motor  133 , as discussed herein. Note that the quasi-passive elastic actuator  134  is shown somewhat schematically in  FIG. 5B , but it can have other various features of known linear air spring actuators for properly compressing and releasing gas pressure energy. Furthermore, as indicated below, other types of quasi-passive elastic actuators can be incorporated, such as those comprising a pneumatic or liquid elastic element, those comprising a mechanical elastic element, and others. 
     Generally, the quasi-passive elastic actuator  134  is switchable between an elastic configuration or state (including a semi-elastic configuration or state) and an inelastic configuration or state via operation of the clutch mechanism  136  for selectively controlling application of the augmented torque applied by the quasi-passive elastic actuator  134 . In one example, with reference to  FIGS. 5B, 5D, and 5E , the clutch mechanism  136  can comprise a multi-plate clutch mechanism comprising a clutch housing  190  that includes a first support frame  192   a  and a second support frame  192   b  coupled together via fasteners  194 . Each of the first and second support frames  192   a  and  192   b  comprises a central opening to receive and allow passage of the output member  138   b  ( FIG. 5B ). A plurality of input plates  196   a  (e.g., four total) are retained by the clutch housing  190 . That is, the first support frame  192   a  can comprise perimeter retaining features  201  (e.g., slots or recesses) that receive and retain perimeter flanges  191  of each of the input plates  196   a  to restrict movement of the input plates  196   a  relative to the clutch housing  190 . A plurality of output plates  196   b  (e.g., four total) can each be slidably or frictionally interfaced (i.e., sandwiched between) with adjacent input plates  196   a , and in an alternating manner as best shown in  FIG. 5E . The output plates  196   b  can each have a curvilinear perimeter that is slidably supported within curved inner surfaces of the first support frame  192   a . Each output plate  196   b  can comprise a splined central aperture  193  that engages a splined portion  199  of the output member  138   b  ( FIGS. 5B and 5D ). 
     With reference to  FIG. 5D , an actuator  197  can be operable to switch the clutch mechanism  136  between an engaged state, a semi-engaged state and a disengaged state. In one example, the actuator  197  can comprise a type that is operable to apply a selective, variable force to the input and output plates  198   a ,  198   b . The actuator  197  can comprise an electric motor having a receiver in communication with a controller (wired or wirelessly) of a computer system that controls operation of the clutch mechanism  136  via the actuator  197 . Thus, upon receiving a clutch control signal, the actuator  197  can cause compression of the input plates  196   a  between the output plates  198   b  to restrict rotation of the output member  138   b  relative to the input member  138   a  (further detailed below). This is achieved as the input plates  198   a  are retained by the clutch housing  190 , so when the output plates  198   b  are compressed between respective the input plates  196   a , a braking friction force between adjacent input and output plates  198   a  and  198   b  restricts rotation of the output plates  196   b  relative to the input plates  198   a . In one aspect, with the clutch mechanism  136  operating in the engaged state, movement between the input plates  198   a  and the output plates  198   b  can be completely restricted (i.e., the clutch can be fully engaged). Consequently, this restricts rotation of the input member  136   a  relative to the output member  136   b  so that they rotate together in the same rotational direction and speed (because the output plates  198   b  are engaged with the output member  138   b ). In another aspect, with the clutch mechanism  136  operating in a semi-engaged state, movement between the input plates  198   a  and the output plates  198   b  can be partially restricted by the actuator  197  applying a smaller compression force to the input and output plates  198   a ,  198   b , such that some movement between the input plates  198   a  and the output plates  198   b  is facilitated or caused to occur. In the engaged or the semi-engaged state, the clutch mechanism  136  and the quasi-passive elastic actuator  134  can function as a brake, or in other words, can provide a braking force operable to dissipate energy within the joint module, or these can function to apply an augmented torque to the output member. The degree or magnitude of the compression force applied by the actuator  197  to the input and output plates  198   a ,  198   b  can be dynamically controlled in real-time by controlling or varying the amount of force generated and applied by the actuator  197 . In the disengaged state, the clutch mechanism  136  is not intended to restrict movement between the input plates  198   a  and the output plates  198   b.    
     More specifically, the actuator  197  can be configured and controlled as a binary device (i.e., the clutch is either on/engaged or off/disengaged) when applying a compression force to compress the plates together, and when removing the compression force to release compression between the plates. Alternatively, the actuator  197  can be configured and controlled as an analog device, meaning a variable force can be applied by the actuator  197  to compress the plates to a varying degree to generate a braking force and to facilitate gradually storing energy or dissipating/releasing stored energy in a more controlled manner for damping or braking purposes (i.e., the clutch mechanism  136  is in a semi-engaged state and the quasi-passive elastic actuator  134  is in a semi-elastic state). In one example operational scenario, the clutch mechanism  136  can be fully engaged or semi-engaged such that the quasi-passive elastic actuator  134  at least partially stores energy. This stored energy can function to generate a braking force that can restrict rotation of the output member (e.g., such as in the case where the primary actuator is inactive and not producing a primary torque, yet rotation of the joint is still desired or needed (e.g., rotation of the joint under the influence of gravity or in response to some externally applied force to the robotic system)), or it can be released as an augmented torque to assist the primary actuator. Furthermore, in the event of the release of the energy as an augmented torque, when the quasi-passive elastic actuator  134  is releasing energy in the elastic or semi-elastic states (e.g., during a stance extension), the actuator  197  can be operated or moved to slightly compress the plates to generate a gradual “braking force” about the plates so that the augmented torque can be discharged or applied in a controlled, gradual manner. This can help to reduce the likelihood of applying a torque within the robotic system that may actuate the joint too quickly and with too much velocity at an initial stage of actuation (which, in the case of an exoskeleton, can cause discomfort to the operator and can disrupt a desired fluid/natural movement of an exoskeleton limb). This may also be advantageous when lowering a load with the robotic system, where it is desirable to lower the load in a controlled manner by controlling the amount of braking force applied by plates of one or more clutched joint modules of the robotic system. Also in the case of an exoskeleton, this may also be advantageous when an operator wearing the exoskeleton moves from a crouching position while picking up a load, wherein the stance extension may need to be slower or more controlled. In such a case, the plates of the clutches of the hip and/or knee clutched joint modules may then be controlled as brakes to controllably dissipate stored energy released by the associated quasi-passive elastic actuators. 
     As further explanation, and to further illustrate, the multi-plate configuration of the clutch mechanism  136  can act as a brake. This is achieved by controlling the compression force applied to the input and output plates  198   a  and  198   b , thus providing a beneficial energy saving mode of operation. For instance, by controlling the braking force, the robotic system can be caused to lower a load subject to gravity by simultaneously controlling the brake force and the torque applied by the primary actuator (which in some cases can be zero), thus providing a very efficient mode of operation. The controlled braking can also be used to store energy in the elastic component of the quasi-passive elastic actuator. For example, an exoskeleton operator could lower him/herself to a squat position by letting part of his weight be supported by the exoskeleton while getting in the squat position. In this process, energy can be stored in the quasi-passive elastic actuator, while controlling the torque by controlling the braking force. At least some of the energy may then be recovered as the robotic device moves to the standing position, and additional torque may be provided, if required, by the primary actuator that would combine with the torque produced by the quasi-passive elastic actuator. In the latter example the clutch mechanism  136  can be used as a brake or as a clutch, or both. 
     With the clutch mechanism  136  in the engaged or semi-engaged state, the quasi-passive elastic actuator  134  is therefore operable in the elastic and semi-elastic states, respectively, to store or release energy upon movement of the input member  136   a  relative to the output member  136   b . Conversely, upon receiving a clutch control signal, the actuator  197  can operate to place the clutch mechanism  136  in the disengaged state. That is, the actuator  197  operates to remove or release the compression force and pressure from plates, which thereby allows the input and output plates  198   a ,  198   b  to freely rotate relative to one another. This permits “free” rotation of the input member  138   a  relative to the output member  138   b , therefore placing the quasi-passive elastic actuator  134  in its inelastic configuration where the quasi-passive elastic actuator  134  neither stores nor releases energy, but is rather passive in its function where it has no appreciable impact or influence on the operation of the joint module (a “free-swing” mode). Thus, the quasi-passive elastic actuator  134  exerts negligible resistance in this “free-swing” mode, when the clutch mechanism  136  is disengaged, so that the input and output members  138   a  and  138   b  can freely rotate relative to each other with minimal resistance. 
     It is noted that in  FIG. 5D , the actuator  197  is shown generically as a box operable with a part of the clutch mechanism  136 . This is to illustrate generally an actuator, that those skilled in the art will recognize can take many forms and configurations. For instance, the actuator  197  can comprise an electric motor having a movable member associated therewith that is actuatable by the motor to exert and remove a biasing or compression force against the input plates  196   b , such as a rotatable cam member, a ramped ring member, or other suitable movable device, in order to compress the plates  198   a  and  198   b  together to partially or completely restrict relative movement between them, as well as to facilitate their expansion to remove any compression forces. In other examples, the actuator  197  can comprise a piezoelectric actuator, a dielectric actuator, an electromagnetic actuator, or other similar low-power actuator. Thus, upon sending a clutch control signal to the actuator  197  from a controller, the actuator  197  can be caused to actuate the movable member to apply (or remove) a compression force to the plates  198   a  and  198   b . In another example, the movable member (actuatable by an electric motor of the actuator  197 ) can comprise force application devices disposed on either side of the collective plates  198   a  and  198   b  (somewhat similar to those found in a bicycle disk brake), such that actuation of the actuator  197  causes a compression force to be applied to the collection of plates  198   a  and  198   b  from both sides of the plates  198   a  and  198   b , which can help to reduce wear on the plates. In one aspect, the plates  198   a  and  198   b  can be comprised of Teflon-impregnated aluminum, composites, plastics, polymers, certain metals, and the like. 
     Accordingly, upon a first rotation of the input member  138   a  relative to the output member  138   b , the quasi-passive elastic actuator  134  stores energy (as discussed above) when the clutch mechanism  136  is engaged (i.e., the plates  198   a  and  198   b  are being compressed). Such rotational movement can be the result of a gait movement (e.g., of a lower body exoskeleton comprising one or more clutched joint modules) that causes a first robotic support member (e.g.,  104   e ) to rotate about a second robotic support member (e.g.,  104   d ), such as during a gait cycle between point B to C of  FIG. 2 . Upon a second rotation (e.g., of  104   e  and  104   d  between points A to B of  FIG. 2 ), the quasi-passive elastic actuator  134  can release its stored energy when the clutch mechanism  136  is controlled/maintained in its engaged or semi-engaged state, which facilitates application of the augmented torque to combine with the primary torque from the primary actuator to assist in the rotation of the output member  136   b , as detailed above. The first and second rotations can be in the same or different directions. 
     Concurrently (and upon the second rotation of the input member  138   a  relative to the output member  138   b ), the primary actuator  132  can be operated to apply a primary toque (along with the augmented torque of the quasi-passive elastic actuator  134 ) to rotate the output member  138   b  about axis of rotation  140  to actuate the clutched joint module  130 . Because the torque applied by the primary actuator  132  is supplemented with the torque applied by releasing stored/recovered energy via the quasi-passive elastic actuator  130 , the electric motor  132  can be selected from a group of smaller (e.g., less power dissipation) motors than would otherwise be needed in an equivalent robotic assembly not employing a quasi-passive elastic actuator, which contributes to the compact configuration of the module  130 , as discussed above. 
     At a select time, such as upon a third rotation of the input member  138   a  relative to the output member  138   b  (e.g., of  104   e  and  104   d  along points from C, D, E, F, and A of  FIG. 2 ), the clutch mechanism  136  can be switched to the disengaged state (i.e., the actuator  197  releases the applied-compression force) such that the output plates  198   b  freely rotate relative to the input plates  198   a . As a result, the quasi-passive elastic actuator  134  neither stores nor releases energy (inelastic configuration) upon rotation of the input member  138   a  relative to the output member  138   b . In this inelastic configuration, the input member  138   a  is in “free swing” relative to the output member  138   b , meaning that negligible resistance is applied via the quasi-passive elastic actuator  134  (so that the actuator  134  does not have a stiffness value restricting rotation of the input member  138   a  relative to the output member  138   b ). Thus, in this manner the quasi-passive elastic actuator  134  is switchable between the elastic configuration or state, the semi-elastic configuration or state, and the inelastic configuration or state via operation of the clutch mechanism  136  so that the quasi-passive elastic actuator  134  can be operable to either apply the augmented torque in parallel with the torque (i.e., primary torque) applied by the primary actuator  132 , thereby applying a combined torque to rotate the output member  138   b , or to function passively where the quasi-passive elastic actuator  134  neither stores nor releases energy and where the primary torque by the primary actuator  132  is not augmented by a torque from the quasi-passive elastic actuator  134 . 
     Each of such first, second, and third rotational movements of the input member  138   a  relative to the output member  138   b  (e.g., of a robotic joint) can be sensed by one or more position and/or force sensors  199  ( FIG. 5D ) associated with and/or coupled to the joint module  130  to sense a direction, speed, and/or force associated with rotation of the joint module  130 . The one or more sensors can be coupled at various locations, such as a frame support of the joint module  130 , at the input member  138   a  and/or output member  138   b , at the transfer wheel  165 , and/or other suitable locations of the joint module  130 . In one example, a particular position sensor (e.g., Hall effect sensor) can sense a relative position of the input member  138   a , and, upon the second rotation (discussed above), the position sensor can communicate a position signal to a computer system, having a central processing unit, that processes the position signal, and then ultimately transmits an appropriate clutch signal to the clutch actuator  197  to engage (or maintain engagement of) the clutch mechanism  136  (for instance), and/or transmits a primary actuator signal to the motor  133  to apply the primary torque, as discussed further herein. 
     In the example where the clutched joint module  130  is incorporated as a shoulder joint (e.g.,  109   f ) of an arm of an exoskeleton ( FIG. 4A ), assume a human operator wearing the exoskeleton desires to lift a 200 pound payload. As the operator moves the arm downwardly (e.g., the “first rotation” of the shoulder joint), the clutch mechanism  136  is controlled to the engaged state so that the quasi-passive elastic actuator  134  stores energy (gravitational forces exerted on the robotic arm can also assist to lower the arm, thereby storing energy in the quasi-passive elastic actuator  134 ). Then, as the operator grabs and begins to lift the payload (i.e., the “second rotation” of the shoulder joint), the clutch mechanism  136  can be maintained in the engaged state so that the quasi-passive elastic actuator  134  can release the stored energy to apply the augmented torque to actuate the shoulder joint module to assist to lift the payload. Concurrently, a primary control signal can be received by the motor  133  to cause the motor  133  to apply a primary torque. The primary torque, along with the augmented torque, operate together to actuate the shoulder joint module to lift the payload. And, upon releasing the payload, the clutch mechanism  136  can be controlled/switched to the disengaged state to remove any spring stiffness that may exist about the quasi-passive elastic actuator  134 , thereby placing the joint in free swing mode so that the operator can lower the arm to a desired position with minimal effort (e.g., using gravitational forces). 
     Note that spring stiffness of the quasi-passive elastic actuator  134  (and  204  of  FIG. 6A and 205  of  FIG. 6C ) is a function of chamber geometries, as well as gas pressure charge, and other geometries of the assembly. Thus, the magnitude of stiffness for a given joint module can be adjustable for mission-specific payloads and terrain-specific gaits while the clutch mechanism determines exactly when that stiffness is engaged for energy recovery during the support phase (elastic configuration), for instance, and when it is disengaged during the free swinging phase (inelastic configuration). For instance, the volume of the compression chamber  188  can be selected of a particular volume along with the density of the gas. Also, the particular joint location can be determinative of the magnitude of the selected stiffness value. For instance, the charge pressure for a knee joint and the joint speed would both be significantly larger than required from a hip joint, and the charge pressure for an elbow joint may be lower than the charge pressure for a shoulder joint. Thus, the chamber  188  can be pre-charged with a desired gas pressure to define a selected stiffness value determinative by the particular application and location of the joint on an exoskeleton, for instance. This can be anywhere from a nominal pre-charge value of 0 psi up to 1500 psi, or more, depending on the particular applications, such as the location of the joint on an exoskeleton and/or the possible tasks of the particular joint. Moreover, this stiffness value can be modified by modifying the pre-charge pressure amount. 
     It is to be specifically noted that in another example configuration of the clutched joint module  130 , the quasi-passive elastic actuator  134  may be optional (i.e., not included in or part of the clutched joint module  130 , or rather the clutched joint module  130  is configured without a quasi-passive elastic actuator). For instance, a joint (e.g., one associated with wrist rotation, or shoulder abduction/adduction), may only be configured with an active actuator (i.e., a primary actuator as discussed herein, even though the term “primary” suggests that another torque generating element exists) and without an elastic element. Accordingly, an input member (e.g., a robotic support member) can be directly coupled to the clutch housing  190  rather than to a quasi-passive elastic actuator, such as at an off center position (e.g., at coupling portion  195 ). In this configuration, the clutch mechanism  136  can still be selectively operated between the engaged state, semi-engaged state and the disengaged state to control movement between the output and input members  138   a  and  138   b . Indeed, in one aspect, the clutched mechanism  136  can be engaged or semi-engaged to restrict movement between the output and input members  138   a  and  138   b , thereby facilitating application of the primary torque to the output member by the motor  133 . In another aspect, the clutched mechanism  136  can be disengaged to facilitate free swing of the joint between the input and output members  138   a  and  138   b . To illustrate this example configuration, in one operational scenario, with the clutched joint module operating without a quasi-passive elastic actuator, and where no primary torque is applied in the clutched joint module  130  (i.e., the primary actuator is not active or actuated), the clutch mechanism  136  can be operated in the engaged or semi-engaged states to generate a braking force that can be used to restrict, to some degree, relative rotation between the input and output members  138   a ,  138   b  of the clutched joint module  130 . In another operational scenario, again with the clutched joint module  130  operating without a quasi-passive elastic actuator, and where a primary torque is to be applied to the output member  138   b  to rotate the joint, the clutch mechanism  136  can be operated in the engaged or semi-engaged states to facilitate application of the primary torque to the output member  138   b  in a controlled manner by virtue of selective, variable compression of the plates of the clutch mechanism  136 . These two operational scenarios illustrate the selective capabilities of within the clutched joint module  130  to cause the clutched joint module  130  to function as a clutch for application of a primary torque or as a brake to restrict rotation. 
       FIGS. 6A-6G  illustrate various aspects of a clutched joint module  200  according to an example of the present disclosure, which can be incorporated into any suitable robotic joint of a robotic assembly (e.g.,  100 ,  101 ). The clutched joint module  200  is similar in many respects to the clutched joint module  130  shown in  FIGS. 5A-5E . As such, the description set forth above can be applicable here where the various clutched joint modules  130  and  200  comprise the same or similar elements or perform in the same or a similar way, as will be recognized by those skilled in the art. For example, the clutched joint module  200  can be configured without a quasi-passive elastic actuator (i.e., the quasi-passive elastic actuator  204  is optional). 
     In one example configuration, the clutched joint module  200  can comprise a primary actuator  202 , an optional quasi-passive elastic actuator  204 , and a clutch mechanism  206  operatively coupled to each other, with each situated or arranged along and operable about an axis of rotation  210 . As further detailed below, an input member  208   a  and an output member  208   b  can be directly or indirectly coupled to respective support members of the robotic assembly, which support members are rotatable relative to each other about the axis of rotation  210  corresponding to a joint of the robotic assembly, which ultimately corresponds to an axis of rotation of a degree of freedom of a human joint, such as joint  107   f  associated with clutched joint module  109   f  of  FIG. 4C  for a shoulder joint having a flexion/extension degree of freedom. 
     The primary actuator  202  can comprise a motor  212  and a transmission, such as a first planetary transmission  214 . Optionally, a second transmission, such as a second planetary transmission  216 , can be coupled to the first planetary transmission  214 . The motor  212  is operable to apply a primary torque to the output member  208   b  for rotation about the axis of rotation  210  and the quasi-passive elastic actuator  204  (e.g., a quasi-passive linear pneumatic elastic actuator) is selectively operable to function similar to the quasi-passive elastic actuator  134  discussed above to generate a braking force and/or to apply an augmented torque to the output member  208   b  along with the primary torque applied by the motor  212 , or to be actuated to generate and apply a braking force. The clutch mechanism  206  is operable to selectively control the application of the augmented torque, or a braking force, as discussed herein. 
     In one example configuration with the clutched joint module  200  comprising a quasi-passive elastic actuator  204 , the clutch mechanism  206  is operable to selectively control the quasi-passive elastic actuator  204  and the generation of the braking force or application of the augmented torque. Indeed, a braking force can be generated to restrict rotation of the joint in some operational scenarios (e.g., scenarios where the primary actuator  212  is active or not active to produce a primary torque, but where rotation of the joint is desired), or an augmented torque can be generated and applied in combination with a primary torque to assist in rotation of the output member  208   b  and the joint, as discussed below. 
     More specifically, the quasi-passive elastic actuator  204  is operable to selectively store energy or generate a braking force (when in an elastic or semi-elastic configuration or mode or state) upon a first rotation of the input member  208   a  (e.g.,, where the first rotation is either actively carried out using the primary actuator, or passively carried out, such as rotation of a joint under the influence of gravity of some other externally applied force that induces rotation) when the clutch mechanism  206  is engaged or semi-engaged, and is operable to selectively release energy (also when in the elastic configuration or mode or state) upon a second rotation of the input member  210   a  when the clutch mechanism  206  is engaged or semi-engaged to apply the augmented torque to the output member  208   b  in parallel with the torque applied by the primary actuator, in this case the motor  212 . The quasi-passive elastic actuator  204  is further operable, such as upon a third rotation, to neither store nor release energy during rotation of the joint (when in an inelastic configuration or mode or state) when the clutch mechanism  206  is selectively disengaged. In this inelastic state, the input member  208   a  is in “free swing” relative to the output member  208   b , meaning that negligible resistance is applied within the clutched joint module  200  via the quasi-passive elastic actuator  204  (so that the quasi-passive elastic actuator  204  does not have a stiffness value that would restrict rotation of the input member  208   a  relative to the output member  208   b ). The clutch mechanism  206  can also move from an engaged or semi-engaged state to a disengaged state to dissipate any stored energy (i.e., dissipate any braking force generated, such as when the braking force no longer needed). Thus, the quasi-passive elastic actuator  204  is selectively switchable between the elastic state, the semi-elastic state and the inelastic state via operation of the clutch mechanism  206 . One advantage is that the quasi-passive elastic actuator  204  can be caused to apply, at select times, an augmented torque in parallel with the primary torque applied by the motor  212 , which applies a combined torque to the output member  208   b , thereby reducing the power requirements/demands of the primary actuator  202  (e.g., motor  212 ). With the advantage of an augmented torque, the motor  212  selected can be of a smaller size and lower power dissipation than otherwise would be required by an equivalent system without the assistance of the augmented torque provided by the quasi-passive elastic actuator  204 . 
     In one example, the motor  212  can be a high-performance Permanent Magnet Brushless DC motor (PM-BLDC), similar to the one discussed above. In other examples, the electric motors discussed and shown in the examples can be replaced with a suitable hydraulic actuator, pneumatic actuator, or other types of actuators or motors suitable for functioning as a primary actuator, as will be recognized by those skilled in the art. Such electric motors and alternative motors and actuators can be arranged in series or parallel to cause rotation along the same axis of rotation  140 . In a specific example, the primary actuator can be arranged to rotate the transfer wheel  165  or the sun gear  160  of the first planetary transmission  148  (e.g., see  FIG. 5B ) to effectuate application of a primary torque along with an augmented torque. 
     With reference to  FIG. 6C , the motor  212  can comprise a stator  220  and rotor  222  rotatable relative to each other (in a typical fashion for commercially available frameless brushless motors). Thus, the motor  212  of the primary actuator  202  comprises a cylindrical void  224  about the central area of the rotor  222 . Advantageously, the first planetary transmission  214  can be positioned (at least partially) within the cylindrical void  224  of the motor  212 , which provides a low-profile, compact geared motor configuration as the first planetary transmission  214  and the motor  212  are packaged together, as shown and described. A transfer wheel  226  can be coupled to the rotor  222  about the perimeter of the transfer wheel  226  via fasteners, and coupled to a sun gear  221  of the first planetary transmission  214 , as also described above regarding  FIG. 5B . 
     The motor  212 , the first and second planetary transmissions  214  and  218 , and the transfer wheel  226  can be the same or similar to, and can have the same or similar arrangement and functionality, as the like components described above regarding  FIGS. 5A-5E . As such, these will not be described in greater detail regarding the clutched joint module  200  of  FIGS. 6A-6G . 
     However, as can be appreciated from the arrangement shown in  FIGS. 6D and 6E , the rotor  222  drives/rotates the transfer wheel  226 , which drives/rotates the sun gear  221  of the first planetary transmission  214 , which drives/rotates a sun gear  223  of the second planetary transmission  218 , and which drives/rotates the output member  208   b , thereby transferring the primary torque from the motor  212  to the output member  208   b  via a two-stage transmission drive system. This provides a 16:1 geared down torque output. As with the case of  FIGS. 5A-5E , the motor  212 , the first and second planetary transmissions  214  and  218 , and the output member  208   b  can each operate or rotate about substantially the same axis of rotation as the axis of rotation  210  of the clutched joint module  200 . Said another way, each axis of rotation of the motor  212 , the first and second planetary transmissions  214  and  218 , and the output member  208   b , can be made to be collinear or substantially collinear with the axis of rotation  210 . 
     Support frames, such as those described regarding FIG. 5A of U.S. patent application Ser. No. 15/810,102, filed Nov. 12, 2017, which is incorporated by reference in its entirely herein, can be utilized to house and structurally support the primary actuator  202 , the secondary planetary transmission  218 , and the clutch mechanism  206 , of the present disclosure in a similar manner. 
     In the illustrated example of  FIGS. 6A-6G , the output member  208   b  applies a relatively higher torque at a low speed with very little noise and backlash via the planetary transmissions  214  and  218 , all in a compact form with the planetary transmission  214  being housed within the central void  224  of the motor  212 , and because of the cascading arrangement of the motor  212  and the first and second planetary transmissions  214  and  218  all arranged along, and operating about or around, the axis of rotation  210 . 
     With particular reference to  FIGS. 6A , and similar to  FIGS. 5A-5E , the quasi-passive elastic actuator  204  is operable to apply an augmented torque to rotate the output member  208   b  along with the primary torque applied by the motor  212  of the primary actuator  202 . In one example, similar to  FIG. 5B , the quasi-passive elastic actuator  204  can be a linear pneumatic spring comprising a housing  228  and a robotic support member interface  230  coupled to the housing  228  and pivotally coupleable to a robotic support member as part of a joint within a limb of the robot or robotic assembly (e.g.,  105   f  of  FIG. 4C ). The robotic support member interface  230  can be one or two bearings, fasteners, or other coupling device(s) that can pivotally couple the housing  228  to such robotic support member. 
     As with  FIGS. 5A-5E , the quasi-passive elastic actuator  202  of  FIG. 6A  can comprise a piston rod  232  pivotally coupled, on one end, to a coupling portion  234  of the clutch mechanism  206 . On the other end, the piston rod  232  can be coupled to a piston cylinder  236  that is slidably supported within the housing  228 . Accordingly, the housing  228  can comprise a compression gas chamber  238  adjacent the piston cylinder  236  and an expansion chamber, these being sealed off by the piston cylinder  236 . As shown, the piston rod  232  can be pivotally coupled to the clutch mechanism  206  off-center relative to the axis  210 . Accordingly, as further detailed below, and with the clutch mechanism engaged or semi-engaged to place the quasi-passive elastic actuator  204  in the elastic or semi-elastic state, upon movement of a robotic support member (e.g.,  105   f ), the housing  228  can move downwardly, for instance, which causes the piston cylinder  236  to translate upwardly within the housing  228 , which causes gas in the gas compression chamber  238  to compress, thereby storing energy within the quasi-passive elastic actuator  204 , which energy can be released to apply an augmented torque as discussed above. This action can also be used to generate a braking force (i.e., compression of the elastic element generates a force that can be used to restrict movement of the output member relative to the input member). Furthermore, once stored, the energy can be dissipated (by disengaging the clutch mechanism  206 ) or released (by keeping the clutch mechanism  206  at least partially engaged) to apply an augmented torque that can be combined with a primary torque by the motor, as discussed herein. Note that only  FIGS. 6A and 6B  show the linear air spring for purposes of illustration clarity of the other Figures. 
     Alternatively, as shown in  FIG. 6C , the linear air spring can be replaced with another elastic element, such as a rotary fluid spring  205  (schematically shown) comprising a rotor vane  207   a  and a stator vane  207   b  coupled to a housing  209  that define a compression chamber and an expansion chamber. The rotor vane  207   a  can be coupled to an input device, such as a robotic support member, such that a first rotation of the robotic support member causes rotation of the rotor vane  207   a  relative to the stator vane  207   b , thereby storing energy in the compression chamber in the form of fluid pressure (e.g., liquid or gas). And, upon a second rotation of the robotic support member, the rotor vane  207   a  moves in the opposite rotational direction relative to the stator vane  207   b , thereby releasing stored energy to apply an augmented torque to the input member  208   a  associated with the clutch mechanism  206 . The rotary fluid spring  205  can have the same or similar features as the linear actuators described herein (e.g.,  134 ,  204 ), such as being tunable by modifying the pre-charge fluid pressure in the compression and expansion chambers, having elastic, semi-elastic and inelastic states, and being selectively and variably controlled. rotary fluid spring configured in this manner can store and release more energy than a comparable linear spring actuator, which may be advantageous for certain joints that can benefit from such features, such as the hip and knee joints. The rotary fluid spring  205  can further be operable with a valve assembly capable of controlling in real-time the actuation of the rotary fluid spring  205 , and for facilitating selective switching between the elastic, semi-elastic and inelastic states of the rotary fluid spring  205 . The valve assembly can define a shunt circuit for the flow of the fluid between the compression and expansion chambers and a movable valve device of the valve assembly that controls the opening and the closing of the valve. 
     Generally, the quasi-passive elastic actuator  204  is switchable between an elastic configuration or state (including a semi-elastic state) (i.e., storing or releasing energy) and an inelastic configuration or state (i.e., neither storing nor releasing energy) via operation of the clutch mechanism  206  for selectively controlling application of the augmented torque applied by the quasi-passive elastic actuator  204 . In one example, with reference to  FIGS. 6E-6G , the clutch mechanism  206  can comprise a multi-plate clutch mechanism comprising a clutch housing  240  that includes a first support frame  242   a  and a second support frame  242   b  coupled together via fasteners  244  ( FIG. 6E ). A transfer component  246  is rotatably supported and surrounded by a partition plate  248  ( FIG. 6F ), which can be coupled to the second support frame  242   b  by corresponding slots or fasteners. A roller bearing device  250  comprises a plurality of roller bearings  252  that rotatably interface to the partition plate  248 . A ball-ramp clutch device  254  comprises a rotatable ball ramp frame  256  and a spring collar  258  coupled to an inner area of the ball ramp frame  256 . The ball ramp frame  256  comprises three ball ramp recesses  260  formed around the perimeter of the ball ramp frame  256 . The ball ramp frame  256  comprises a cable interface  262  that couples the ball ramp frame  256  to an actuator  264  via a cable  266 . The cable  266  can traverse along a slot formed around the perimeter of the ball ramp frame  256 . A ball support frame  268  can be disposed adjacent the ball ramp frame  256 , and can comprises a plurality of balls (e.g., see three balls  270 ) rotatably support by the ball support frame  268 . One side surface of each ball  270  can be biased to an inner surface of the second support frame  242   b , and the other side surface of the balls  270  can be slidably and rotatably interfaced about the ball ramp recesses  260  of the ball ramp frame  256 . 
     The spring collar  258 , in a nominal state, can be configured to exert a rotational biasing force in the counter clockwise direction ( FIG. 6F ) against the ball ramp frame  256 , which seats the balls  270  in respective deep pockets of the ball ramp recesses  260 , thereby placing the clutch mechanism  206  in the disengaged state (see the below discussion regarding compressing and uncompressing the plates). The actuator  264  can comprise an electric motor having a receiver in communication with a controller (wired or wirelessly) of a computer system that controls operation of the clutch mechanism  206  via the actuator  264 . Upon receiving a clutch control signal, the actuator  264  (e.g., electric motor) can operate to pull on the cable  266 , which rotates the ball ramp frame  256  in the clockwise direction ( FIG. 6F ). This causes the ball ramp recesses  260  to move clockwise relative to the seated balls  270 . Because the ball ramp recesses  260  are formed from deep pockets to shallow pockets along their profiles, the clockwise rotation of the ball ramp frame  256  results with seating the balls  270  in the shallow pocket areas of the ball ramp recesses  260 . This tends to “increase the thickness” (or axial area consumed) of the ball ramp frame  256 , which causes an axial biasing force from the ball ramp frame  256  against the collar bearing device  250 , which causes an axial biasing force against the partition plate  248 , which thereby causes an axial biasing force against a plurality of plates  272  to compress the plates  272  together. 
     With particular reference to  FIG. 6G , which configuration is similar to that shown in  FIG. 5E  and described above, the plurality of plates  272  comprises a plurality of input plates  274   a  retained and supported by the first support frame  242   a  of the clutch housing  240 . Note that only two input plates are shown on  FIG. 6G  for illustration clarity, but more than two plates are possible. Accordingly, the first support frame  242   a  can comprise perimeter retaining features  276  (e.g., slots or recesses) that receive and retain perimeter flanges  278  of each of the input plates  274   a  to restrict movement of the input plates  274   a  relative to the clutch housing  240 . A plurality of output plates  274   b  (two shown) can each be slidably or frictionally interfaced with (i.e., sandwiched between) adjacent input plates  274   a , for example in an alternating manner. The output plates  274   b  can each have a curvilinear perimeter that is slidably supported within curved inner surfaces of the support frame  242   a  of the clutch housing  240 . Each output plate  274   b  can comprise a central aperture  280   a  that allows passage of a shaft  282  of the transfer component  246 , and each output plate  274   b  can comprise openings  284   a  (e.g., six total) formed around the central aperture  280   a.    
     Each input plate  274   a  can comprise a central aperture  280   b  that rotatably supports a central support ring  287  disposed about the central aperture  280   b , and each central support ring  287  can comprise openings  284   b  (e.g., six total) formed around the support ring  287  at locations corresponding to the openings  284   a  of each output plate  274   a . The transfer shaft component  246  comprises openings  284   c  (e.g., six total) formed around the perimeter of a head of the transfer component  246  at locations corresponding to openings  284   a  and  284   b . Accordingly, the transfer component  246  can be coupled to each of the output plates  274   b  and the support rings  287  via fasteners (not shown) such as pins, nuts and bolts, threaded fasteners, etc. 
     The shaft  282  of the transfer component  246  can be coupled to the sun gear  221  of the first planetary transmission  214  (and through the central opening of the transfer wheel  226 ). Therefore, when the clutch mechanism  206  is in the disengaged state, the ball-ramp device  256  does not exert an axial biasing force against the plurality of plates  272 . Thus, the input and output plates  274   a  and  274   b  freely rotate relative to each other, such that the input member  208   a  freely rotates relative to the output member  208   b  (but with some minor resistance due to the planetary transmissions  214  and  218  coupled between the input and output members  208   a  and  208   b ). Accordingly, the quasi-passive elastic actuator  204  is caused to be in the inelastic state because of the rotational freedom between the input and output plates  274   a  and  274   b , and thus, the quasi-passive elastic actuator  204  does not store or release energy. This rotational movement of the input member  208   a  relative to the output member  208   b , where the joint module  200  is in free swing mode, can occur during a portion of a gait cycle (e.g., from points from C, D, E, F, and A of  FIG. 2 ), such as in examples where the joint module  200  is integrated with a lower body exoskeleton as one of the joints of the exoskeleton. 
     When the clutch mechanism  206  is actuated to the engaged state (as explained above), the ball-ramp device  256  exerts an axial biasing force against the adjacent input plate  274   a , which causes compression force between the output plates  274   b  and the adjacent input plates  274   a . Such compression causes the plurality of plates  272  to “bind up” together (i.e., to rotate together in the same speed/direction). Thus, upon a first rotation of the input member  208   a  relative to the output member  208   b , for example, when the input member  208   a  moves in a clockwise direction ( FIG. 6C ), the quasi-passive elastic actuator  204  stores energy about the compression gas chamber  238  ( FIG. 6A ) by virtue of upward movement of the piston cylinder  232  through the housing  228  (such first rotation can be during a shoulder joint movement, or movement of a lower exoskeleton joint (e.g., a knee joint) during a portion of a gait cycle, such as from point B to C of  FIG. 2 ). And, upon a second rotation of the input member  208   a  (e.g., a counter shoulder joint movement, or movement of a lower exoskeleton joint during another portion of a gait cycle, such as from point A to B of  FIG. 2 ), such that the input member  208  moves counter clockwise, the quasi-passive elastic actuator  204  can be caused to release its stored energy to apply an augmented torque to rotate the clutch housing  240 , which drives/rotates the plurality of plates  272 , which drives/rotates the transfer shaft component  246 , which drives/rotates the sun gear of the first planetary transmission  214 , which drives/rotates the second planetary transmission  218 , and which ultimately transfers the augmented torque to the output member  208   b . In one example, only two plates may be utilized in the clutched , that is, only one input plate  274   a  and one output plate  274   b  can be frictionally engaged to each other and configured to provide the clutch function discussed herein. This is not intended to be limiting in any way. Indeed, any number of additional input and output plates can be incorporated to account for larger torques that may be transferred via the clutch plates when the clutch is engaged. These same alternatives are true for the plates of the example of  FIGS. 5A-5E  (e.g., just two plates, or any number of additional plates). 
     Concurrently, upon receiving a primary control signal, the rotor  220  of the primary actuator (e.g., motor  212 ) exerts a primary torque to drive/rotate the transfer wheel  226 , which drives/rotates the sun gear  221  of the first planetary transmission  214 , which drives/rotates the second planetary transmission  218 , and which ultimately transfers said primary torque to the output member  208   b , along with the augmented torque concurrently applied via the quasi-passive elastic actuator  204 , to actuate a shoulder joint module of an exoskeleton, for instance. This can dramatically reduce the size and power requirements of the motor  212  that would otherwise be needed because the total output torque of the joint module  200  is supplemented with augmented torque recovered via the quasi-passive elastic actuator  204 . Note that the quasi-passive elastic actuator  204  can have the same or similar features and advantages discussed above with reference to the clutched joint module shown in  FIGS. 5A-5E . As can be seen, and as discussed above, the quasi-passive elastic actuator can be caused to switch between the elastic and inelastic states as needed or desired. 
     Each of the rotational movements (discussed above) of the input member  208   a  relative to the output member  208   b  (e.g., of a robotic joint) whether the clutch mechanism  206  is engaged or disengaged, and the quasi-passive elastic actuator in a respective elastic or an inelastic state, can be sensed by one or more position and/or force sensors  229  ( FIG. 6C ) associated with and/or coupled to the joint module  200  to sense a direction, speed, and/or force associated with rotation of the joint module  200 . The one or more sensors can be coupled at various locations, such as a frame support of the joint module  200 , at the input member  208   a  or output member  208   b , at the transfer wheel  226 , or any other suitable locations of the joint module  200 , or any combination of these. In one example, a particular position sensor (e.g., Hall effect sensor) can determine a relative position of the input member  208   a , and, upon the second rotation (as discussed above), the position sensor can communicate a position signal to a computer system, having a central processing unit, that processes the position signal, and then ultimately transmits an appropriate clutch signal to the clutch actuator  264  to engage (or maintain engagement of) the clutch mechanism  206  (for instance), or to transmit a primary actuator signal to the motor  212  to apply the primary torque, as discussed further herein, or some combination of these. 
     In one example, the clutch mechanism  206  can be arranged such as is shown in  FIG. 5A , whereby the clutch mechanism  136  of  FIG. 5A  is replaced with clutch mechanism  206 . In this manner, the augmented torque that would be applied by the quasi-passive elastic actuator  204  would be a 1:1 drive ratio (i.e., it would not be geared down by 16:1, as with  FIGS. 6A-6F ). As indicated above, in another example configuration of the clutched joint module  200 , the quasi-passive elastic actuator  204  may be optional (i.e., not included in or part of the clutched joint module  200 , or rather the clutched joint module  200  is configured without a quasi-passive elastic actuator). For instance, a joint (e.g., one associated with wrist rotation, or shoulder abduction/adduction, may only be configured with an active actuator (i.e., a primary actuator as discussed herein, even though the term “primary” suggests that another torque generating element exists) and without an elastic element. Accordingly, an input member or robotic support member can be directly coupled to the clutch housing  240  rather than to a quasi-passive elastic actuator, such as at an off center position. In this configuration, the clutch mechanism  206  can still be selectively operated between the engaged state, the semi-engaged state and the disengaged state to control and restrict movement between the output and input members  208   a  and  208   b . Indeed, in one aspect, the clutched mechanism  136  can be engaged or semi-engaged to restrict movement between the output and input members  138   a  and  138   b , thereby facilitating application of the primary torque to the output member by the motor  212 . In this manner, the actuator  264  can be variably controlled to variably move the ball ramp device  256  to apply a variable compression force to the plates  274  and  274   b , which can provide a braking function and/or gravity assist control function. 
     It is noted that the various functions and operational states described above with respect to the clutched joint module  130  are applicable to the clutched joint module  200 . As such, these are not described again here, but those skilled in the art will recognize that upon reading the description above as it pertains to  FIGS. 5A-5E , that the clutched joint module  200  can be operated in the same or a similar manner. 
       FIG. 7A  illustrates a clutched joint module  1130  in accordance with an example of the present disclosure, and  FIG. 7B  illustrates a primary actuator of the clutched actuator module  1130 . The clutched actuator joint module  1130  can comprise the clutch mechanism  136  and the quasi-passive elastic actuator  134  described with reference to  FIGS. 5A-5E  positioned off-axis relative to an axis of rotation  1203  of a primary actuator  1132 . That is, an axis of rotation  1137  of the clutch mechanism  136  can be generally parallel to, but offset from, the axis of rotation  1203  of the primary actuator  1132 . Here, the output shaft  138   b  can be coupled to a torque-transfer device, such as a transmission belt  1224 , via a splined ring gear (not shown) fastened or formed as part of the right end of the output shaft  138   b . Alternatively, the splined ring gear can be coupled to the second support frame  192   b  of the clutch mechanism  136 . In either scenario, a torque-transfer device, in this case a transmission belt  244 , can transfer a torque to the output shaft  138   b  to actuate rotation within the clutched joint module  1130 . Although not shown to scale, the left end of the output shaft  138   b  can be rotatably interfaced to and through an aperture  1152  of a support frame  1138   b , and then can be coupled to an output member that is coupled to a robotic support member, or it can be coupled directly to the robotic support member. Thus, as further detailed above regarding  FIGS. 5A-5E , rotation of the input member  138   a  via the quasi-elastic actuator  134  causes rotation of the output shaft  138   b  (when the clutch is engaged) to actuate the clutched joint module  1130 . 
     More specifically regarding this alternative configuration, the primary actuator  1132  (e.g., a geared electric motor) can be configured and operable to apply a torque to the output member  138   b  for rotation about the axis of rotation  1137 , and the quasi-passive elastic actuator  134  (e.g., a linear or rotary pneumatic actuator) can be selectively operable (via operation of the clutch) to apply an augmented torque to the output member  138   b  along with the torque applied by the primary actuator  1132  to reduce the power required to actuate rotation of the joint module, such as during a certain portion of a gait cycle by an exoskeleton (or other movement of an exoskeleton limb, such as the an upper body movement). 
     The clutch mechanism  136  can be structurally mounted to the primary actuator  1132  by a first mounting plate  1138   a  and a second mounting plate  1138   b , each positioned on either side so as to constrain the primary actuator  1132  and the clutch mechanism  136  in a “sandwich” state. Although not shown here, the first and second housings  192   a  and  192   b  of the clutch mechanism  136  can have support members extending outwardly therefrom and that support annular collar bearings that rotatably couple and support the clutch mechanism  136  to the first and second mounting plates  1138   a  and  1138   b . Other suitable means of rotatably coupling the clutch mechanism  136  to the support plates are possible as will be recognized by those skilled in the art. 
     The first mounting plate  1138   a  can be mounted to a housing mount  1140  (that supports the primary actuator  1132 ) via a plurality of fasteners  1142  (with spacers there between). The second mounting plate  1138   b  can be mounted to the other side of the housing mount  1140  via a plurality of fasteners  1151 . 
     The output shaft  138   b  (and/or an output member coupled to the shaft  138   b ) can be a load transfer component that can comprise many different shapes and forms, depending upon the particular type of robotic system and its application (e.g., exoskeleton, humanoid robot, robotic hand or arm). As such, the specific configurations shown are not intended to be limiting in any way. The output member  136   b  can comprise a robotic support member interface portion coupleable to a support structure of a robotic assembly, such as the exoskeleton of  FIG. 4A . 
     The housing mount  1140  can comprise a first mount structure  1174   a  and a second mount structure  1174   b  coupled to each other via fasteners. The first and second mount structures  1174   a  and  1174   b  can be fastened together to house and structurally support many of the components of the primary actuator  1132 . For instance, the primary actuator  1132  can comprise a motor  1178  (e.g., electric motor) that is seated in the first and second mount structures  1174   a  and  1174   b . The motor  1178  can be a high-performance Permanent Magnet Brushless DC motor (PM-BLDC). The motor described above and shown in the drawings is not intended to be limiting in any way. Indeed, other motors suitable for use as the primary actuator  1132  are contemplated herein, as are various other types of actuators, such as hydraulic or pneumatic actuators. 
     As further shown in  FIG. 7B , the motor  1178  can comprise a stator  1180  and rotor  1182  rotatable relative to each other (in a typical fashion for commercially available frameless brushless motors). Note that the view of  FIG. 7B  is rotated relative to the view initially shown in  FIG. 7A  of the primary actuator  1132 . The motor  1178  can be configured to comprise a central void  1184  about the central area of the motor  1178  and surrounded by the rotor  1182 . Advantageously, a transmission, such as a planetary transmission  1186  (or any other type of transmission), can be positioned within (entirely or partially) the central void  1184 . This provides a low-profile geared motor state with high torque output for a relatively small electric motor, as exemplified elsewhere herein. It should be appreciated that the planetary transmissions exemplified herein can be replaced (or supplemented with) other transmission types, such as harmonic, cycloidal, worm, belt/chain, crank, four-bar linkage, backhoe linkage, bell crank, and continuously variable, for instance. 
     In the present example the planetary transmission  1186  can be configured as a 4:1 geared planetary transmission. Thus, in one example the planetary transmission  1186  can comprise an outer ring  1190  engaged to four planet gears  1188  (one labeled) mounted about a carrier  1192 , whereby the four planet gears  1188  have gear teeth that engage with the gear teeth of a central sun gear (not visible from this view). In the present example, the outer ring  1190  is stationary, as it is fastened to the first mount structure  1174   a  via fasteners (not shown) through apertures around the outer ring  1190  and into threaded bores in the first mount structure  1174   a . A rotatable transfer wheel  1198  is disposed on an outer side of the primary actuator  1132  adjacent the second mount structure  1174   b , and is fastened to a drive collar  1200  via perimeter fasteners. The drive collar  1200  is fastened or fixed to the rotor  1182  of the motor  1178 . The transfer wheel  1198  is operable to transfer rotation from the rotor  1182  of the motor  1178  to the sun gear (of transmission  1186 ) about the axis of rotation  1203  ( FIG. 7A ). A spacer sleeve  1201  can be positioned adjacent the drive collar  1200  and between the outer ring  1190  of the planetary transmission  1186  and the rotor  1182  to act as a support spacer between the planetary transmission  1186  and the rotor  1182 . 
     The transfer wheel  1198  can comprise a central aperture  1204  that supports a transfer hub  1206  that is fastened to the transfer wheel  1198  via fasteners. The transfer hub  1206  can have inner gear teeth (not shown) that can be engaged with outer gear teeth of the sun gear. Therefore, upon applying an electric field to the motor  1178 , the rotor  1182  rotates about axis  1203 , which causes the transfer wheel  1198  to rotate, which thereby causes the sun gear  1194  to rotate, all in a 1:1 ratio. Upon rotation of the sun gear about axis of rotation  1203 , the planetary gears  1188  rotate around the sun gear, which causes the carrier  1192  to rotate. An output shaft  1209  is secured to a central portion  1211  of the carrier  1192 , such that rotation of the carrier  1192  causes rotation of the output shaft  1209  about axis  1203 , which provides a 4:1 geared-down transmission arrangement from rotation of the rotor  1182  to the output shaft  1209  via the planetary transmission  1186 . Other planetary transmission types and gear reduction schemes can be used instead of a 4:1 transmission, such as a 3:1 or a 5:1 (or even greater ratios) planetary gear scheme. 
     To reduce build height, the planetary transmission  1186  can be positioned inside of the rotor  1182  of the motor  1178 . Depending on the motor selected, the inside diameter of the rotor will dictate the maximum outside diameter of the planetary transmission. Once the planetary ring has been constrained by its outside diameter, there are a limited amount of options for gear ratios and output torques available. The output ratio is determined from the ratio of the number of teeth on the ring gear to the number of teeth on the sun gear. To obtain a higher reduction in the compact design of the planetary unit, the sun gear diameter can be reduced, which generally corresponds to less power transmission. The capacity to transmit higher torques is reduced with a smaller sun gear. A balance of reduction and strength can be determined for a planetary unit that will physically fit inside the motor rotor. By implementing a helical cut gear, higher forces can be transmitted on the gear teeth making the unit stronger. A wider tooth will also improve the load carrying capacity of the sun gear, however this increases the weight as well. 
     In addition, the sun gear makes contact with several teeth simultaneously so the contact ratio is much higher than a conventional spur gear transmission. Another benefit of planetary gears is the fact that the transmission is in-line with the motor, which allows for compact mounting states. Two of the 4:1 planetary units can be nested together to produce a 16:1 final drive, for instance. 
     Thus, in one example using Allied Motion&#39;s MF0127-032 motor, it has an inside diameter of 3.3 inches, which means that a planetary transmission of approximately 3.15 inches (or less) could be used and disposed in the central void of the motor. And, Matex&#39;s 75-4MLG12 planetary transmission can be incorporated, which is a 4:1 unit with a 2.95 inch outside diameter having a 118 N-m peak torque, weighing just 500 grams. Such planetary transmission could be incorporated with a brushless motor as discussed herein to generate a compact configuration. Therefore, in the illustrated example of  FIG. 7B , the output shaft  1209  applies a relatively higher torque at a low speed with very little noise and backlash via the planetary transmission  1186 , all in a compact form because the planetary transmission  1186  is housed within the void  1184  of the brushless frameless electric motor  1178 . It is noted that the specific types of motors and planetary transmissions described herein are not intended to be limiting in any way, as will be recognized by those skilled in the art. 
     With continued reference to  FIGS. 7A and 7B  a free end  1210  of the output shaft  1192  extends through an aperture  1212  of the first mount structure  1174   a . A tapered support collar  1214  surrounds and is coupled to the output shaft  1192  (a key and slot interface can be used to couple the support collar  1214  to the output shaft  1192 ). The tapered support collar  1214  has an outer tapered surface that mates to an inner tapered surface of a primary pulley  1216  (e.g., such as a Morse taper interface) to couple the output shaft  1192  to the primary pulley  1216  (a key and slot interface can be used to couple the support collar  1214  to the primary pulley  1216 ). A first collar bearing can be positioned within the aperture  1212  ( FIG. 7A ) of the first mount structure  1174   a  to rotatably support the output shaft  1192 , and a second collar bearing  218   b  can be positioned with an outer end of the primary pulley  1216  to rotatably support the free end  1210  of the output shaft  1192 . 
     In one example, a sensor plate  1220  can be fastened to an outer side of the second mount structure  1174   b , the sensor plate  1220  comprising an aperture that supports a position sensor  1222 . The position sensor  1222  can be adjacent the transfer wheel  1198 , which has an aperture through to the sun gear  1194  to allow the position sensor  1222  to determine the position of the sun gear  1194 , which can ultimately determine the rotational position of the output shaft  1209 , thereby providing the angular position of a knee or hip joint, for instance. The position sensor  1222  can be any suitable sensor, such as a 13-bit hall-effect sensor. Additional positions sensors can be coupled to the system, and utilized to ultimately determine the position of the joint. The particular position of a robotic joint is relevant in determining and controlling actuation of the clutch mechanism to switch the quasi-passive elastic actuator between the inelastic, semi-elastic and elastic states, or to dynamically vary a zero point or position of the elastic actuator. 
     Upon rotation of the output shaft  1209  (in either rotational direction) by operating the motor  1178 , the primary pulley  1216  rotates the transmission belt  1224  that is coupled to the output shaft  138   b  (or to the clutch mechanism  136 ), as discussed above, to provide a primary torque to rotate the output shaft  138   b  to actuate a robotic joint, for instance. The transmission belt  1224  can be a Gates Poly Chain GT Carbon synchronous belt, or other suitable belt. A belt tensioning device  1225  ( FIG. 7A ) can be adjustably slidably coupled to a slot of the first mounting plate  1138   a  via a fastener, which is operable by a user with a tool to slide the belt tensioning device  1225  toward or away from the belt  1224  to tighten or loosen the belt  1224 , as desired. In some examples, various other torque-transmitting devices can replace the particular configuration of the belt  1224 , such as one or more belts or linkages or gears or tendons (or combinations of such). Moreover, the transmission(s) can be arranged to have an axis of rotation that is offset (e.g., oriented in a direction along a plane that is orthogonal or at some other angle) from the axis of rotation  1203  of the primary actuator  1132  (some other position other than collinear). And, various transmissions can be arranged to provide different gear reductions from input to output, including a relatively high gear reduction (e.g., 20:1, or more), or a relatively low gear reduction (e.g., 1:1), or any gear reduction between these, depending on the particular application. In some examples, the torque-transmitting device in the form of belt  1224 , or such various alternative torque-transmitting devices, can allow the primary actuator  1132  to be remotely located away from the output (i.e., the primary actuator  1132  is located a given distance away from the output of the clutched joint module, but operably connected thereto via the torque-transmitting device), wherein the remotely located primary actuator  1132  can be actuated and its torque transferred to the output of the tunable actuatable joint module corresponding to a joint of the robotic system. 
     For instance, the primary actuator  1132  could be located at a lower back area of an exoskeleton (e.g.,  FIG. 4A ), while such alternative torque-transmitting device(s) could transfer the primary toque from the lower back area to an output member located in the clutched actuator joint module for the hip joint for actuating the hip joint. 
     It should be appreciated that the clutch mechanism  206  and the quasi-passive elastic actuator(s)  204  or  205  discussed regarding  FIGS. 6A-6B  could readily replace the clutch mechanism  136  and quasi-passive elastic actuator  134  of  FIG. 7A , and can be mounted to the mounting plates in a similar or different manner and can be operatively coupled to the primary actuator  1132  via a transmission belt (or other transmission) in a similar way as described regarding  FIGS. 7A and 7B . 
     In some examples, as shown herein, the quasi-passive elastic actuators can comprise linear pneumatic actuators (e.g.,  134 ,  204 ), but each of these can be replaced with other elastic elements, such as rotational springs (e.g., torsional springs), rotary pneumatic springs, coil springs, leaf springs, and the like. Such quasi-passive elastic actuators contemplated herein can be comprised of metal, composite, polymer, rubber, etc. In some examples, additional linkages or pivoting support members can be coupled between a particular quasi-passive elastic actuator and a particular input and/or output member, which can reduce packaging size (e.g., remotely locate the quasi-passive elastic actuators away from the joint), as well as take advantage of torque output versus the position at which the quasi-passive elastic actuator is coupled to the output member. 
     It should be appreciated that the planetary transmissions exemplified herein can be replaced (or supplemented with) other transmission types, such as harmonic, cycloidal, worm, belt/chain, crank, four-bar linkage, backhoe linkage, bell crank, and continuously variable, for instance. And, various torque-transmitting devices can be operatively coupled between the planetary transmissions (and alternative transmissions discussed), such as one or more belts or linkages or gears or tendons (or combinations of such. 
     It is noted that the various functions and operational states described above with respect to the clutched joint module  130  are applicable to the clutched joint module  1130 . As such, these are not described again here, but those skilled in the art will recognize that upon reading the description above as it pertains to  FIGS. 5A-5E , that the clutched joint module  1130  can be operated in the same or a similar manner. 
     It is further noted that rotation of the joints (i.e., relative rotation between the input and output members) defined by the various clutched joint modules discussed herein can be in any direction (e.g., the same direction, different directions) during the storing and releasing of the energy, during the generation and application of a braking force, as well as the disengagement of the clutch mechanism to facilitate free swing of the joint. In other words, the clutch mechanism can be operated to engage to store energy, to release energy, or to disengage to facilitate free swing of the joint upon rotation of an associated joint in the same direction or in various different directions. This is the case for all of the examples set forth in the present disclosure. 
     It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting. 
     Reference throughout this specification to “one example” or “an example” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one example” or “in an example” in various places throughout this specification are not necessarily all referring to the same embodiment. 
     Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
     Although the disclosure may not expressly disclose that some embodiments or features described herein may be combined with other embodiments or features described herein, this disclosure should be read to describe any such combinations that would be practicable by one of ordinary skill in the art. The user of “or” in this disclosure should be understood to mean non-exclusive or, i.e., “and/or,” unless otherwise indicated herein. 
     While the foregoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.