Series elastic actuator configuration for robotic prostheses

Abstract

An actuator for a prosthesis including an outer housing formed by a front cover and a back cover oriented along a rotational axis, each of the front cover and the back cover having a coaxial cutout formed therethrough; a motor positioned in the cutout of the back cover; a transmission positioned coaxially within the outer housing, the transmission including: a transmission casing encircling the rotational axis; an input element coupled to the motor; and an output element extending through the cutout of the front cover; a c-spring having a first end coupled to the transmission casing and a second end coupled to the front cover with an arcuate spring body extending therebetween, the arcuate spring body coaxially encircling a portion of the transmission casing; and an encoder positioned at the back cover and configured to detect a deflection of the c-spring around the rotational axis.

Description

NEX-19125SERIES ELASTIC ACTUATOR CONFIGURATION FOR ROBOTIC PROSTHESESCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This Application is a Patent Cooperation Treaty (PCT) Application and claims the benefit of priority to US Provisional Patent Application No. 63 / 687,877, filed on August 28, 2024, the entire contents of which are hereby incorporated by reference herein.GOVERNMENT SUPPORT

[0002] This invention was made with government support under Grant Number 1R21EB035665-01 awarded by the National Institutes of Health. The Government has certain rights in the invention.BACKGROUND OF THE DISCLOSED SUBJECT MATTER

[0003] Series elastic actuators (SEAs) and parallel elastic actuators (PEAs) have been in development for a few decades and are a preferred choice of actuator type for a wide range of powered prostheses. Elastic actuators can provide excellent torque control and protect the transmission from unexpected loads that may be experienced often in locomotion tasks. The elastic element inside these transmissions can take many forms, but common materials are spring steel, titanium, and composites, all of which have high energy storage and low hysteresis. The most efficient materials are composites, but they are not always used due to manufacturing or packaging constraints.

[0004] When composites are used, the orientation of the fibers in each layer is an important consideration, as it determines the strength of the spring. Most composite springs used in series elastic actuators are beam springs, which are easy to manufacture and machine. When rotary springs are implemented, they are made of titanium or spring steel.- 1 -FH12915382.4NEX-19125Unfortunately, beam springs can be difficult to package in actuators with size constraints, especially if linear spring behavior is desired.SUMMARY OF THE DISCLOSED SUBJECT MATTER

[0005] The purpose and advantages of the disclosed subject matter will be set forth in and apparent from the description that follows, as well as will be learned by practice of the disclosed subject matter. Additional advantages of the disclosed subject matter will be realized and attained by the methods and systems particularly pointed out in the written description and claims hereof, as well as from the appended drawings.

[0006] To achieve these and other advantages and in accordance with the purpose of the disclosed subject matter, as embodied and broadly described, the disclosed subject matter includes an actuator for a prosthesis including: an outer housing formed by a front cover and a back cover oriented along a rotational axis, each of the front cover and the back cover having a coaxial cutout formed therethrough; a motor positioned in the cutout of the back cover; a transmission positioned coaxially within the outer housing, the transmission including: a transmission casing encircling the rotational axis; an input element coupled to the motor; and an output element extending through the cutout of the front cover, each of the input element and the output element configured to rotate about the rotational axis; a c- spring having a first end coupled to the transmission casing and a second end coupled to the front cover with an arcuate spring body extending therebetween, the arcuate spring body coaxially encircling a portion of the transmission casing; and an encoder positioned at the back cover and configured to detect a deflection of the c-spring around the rotational axis.

[0007] In some embodiments, the transmission is a harmonic drive.

[0008] In some embodiments, the actuator for a prosthesis further including a movable member operatively coupled to the output element.- 2 -FH12915382.4NEX-19125

[0009] In some embodiments, the movable member is at least one of a portion of a prosthetic foot element or a portion of a prosthetic limb element.

[0010] In some embodiments, the transmission is configured to reduce rotation of the output element relative to the rotation of the input element.

[0011] In some embodiments, the transmission casing is configured to rotate about the rotational axis, thereby deflecting the c-spring.

[0012] In some embodiments, the c-spring is configured to deflect along an arc defined by the arcuate body of the c-spring.

[0013] In some embodiments, the outer housing comprises an adapter configured to couple to at least one stationary member.

[0014] In some embodiments, the c-spring comprises an internal surface spaced from an external surface, defining a thickness therebetween and the c-spring is coupled to the transmission casing on the internal surface and coupled to the front cover on the external surface.

[0015] In some embodiments, the actuator for a prosthesis further including a stabilization rod extending coaxially from the back cover to the front cover along the rotational axis.

[0016] In some embodiments, the c-spring is formed from carbon fiber.

[0017] In some embodiments, the c-spring is formed from a carbon fiber layup, comprising at least one inner layer having fibers oriented from the first end to the second end and at least one outer layer having woven fibers.

[0018] In some embodiments, the c-spring is cut from a tubular workpiece.

[0019] In some embodiments, the spring body comprises at least one cutout oriented along the arcuate spring body.- 3 -FH12915382.4NEX-19125

[0020] In some embodiments, the at least one encoder is one of a partial arc reflective incremental encoder or an absolute encoder.

[0021] In some embodiments, the transmission casing comprises a projection extending through the back cover, the projection having optical tape emplaced thereon, the encoder configured to detect the deflection of the c-spring based on a rotation of the projection around the rotational axis.

[0022] In some embodiments, the encoder is communicatively coupled to the motor and configured to transmit at least one electrical signal to the motor in response to the deflection of the c-spring.

[0023] To achieve these and other advantages and in accordance with the purpose of the disclosed subject matter, as embodied and broadly described, the disclosed subject matter includes a prosthesis system including: an outer housing formed by: a front cover having a front planar face circumscribed by an arcuate sidewall, the front planar face having a front cutout formed therethrough, defining a rotational axis; a back cover having a back planar face and a back cutout formed coaxially with the front cutout, the back cover configured to couple to the front cover along the arcuate sidewall; a motor positioned within the back cutout; a transmission positioned coaxially within the outer housing and extending between the front cutout and the motor; a c-spring positioned concentrically between the transmission and the outer housing, the c-spring comprising: a first end coupled to the transmission; a second end spaced from the first end along an arc and coupled to the arcuate sidewall of the front cover, an arcuate body extending between the first end and the second end along the arc, the arcuate body having an outer surface spaced from an inner surface, defining a thickness therebetween, an opening defined between the first end and the second end; and the first end configured to deform along the first arc relative to the second end.- 4 -FH12915382.4NEX-19125

[0024] In some embodiments, at least one cutout is formed in the arcuate body opposite the opening.

[0025] In some embodiments, the arcuate body comprises a first lateral side and a second lateral side defining a width therebetween.

[0026] In some embodiments, the width is variable along the arcuate body.

[0027] In some embodiments, the width proximate the first end and the second end is greater than the width proximate the arcuate body.

[0028] In some embodiments, the width proximate the first end and the second end is lesser than the width proximate the arcuate body.

[0029] In some embodiments, each of the first end and the second end comprise openings formed from the inner surface to the outer surface.

[0030] In some embodiments, the c-spring is formed from carbon fiber.

[0031] In some embodiments, the c-spring is formed from fiberglass.

[0032] In some embodiments, at least a portion of the c-spring is formed from a carbon fiber layup, comprising at least one inner layer having fibers oriented along the arc and at least one outer layer having woven fibers.

[0033] To achieve these and other advantages and in accordance with the purpose of the disclosed subject matter, as embodied and broadly described, the disclosed subject matter includes a method for forming a c-spring, the method including: forming a tubular workpiece having a circumference circumscribing a longitudinal axis, wherein forming the tubular workpiece comprises: laying a first woven fiber sheet over a mandrel; laying at least one unidirectional fiber sheet over the first woven fiber sheet; and laying a second woven fiber sheet over the at least one unidirectional fiber sheet to form a layup; curing the layup to harden the tubular workpiece; cutting the tubular workpiece in a predetermined path that extends at least partially around the circumference and along the longitudinal axis to form a- 5 -FH12915382.4NEX-19125 c-shaped component, wherein the c-shaped component is defined by a first end and a second end having an arcuate body extending therebetween; and the c-shaped component retains at least a portion of the circumference of the tubular workpiece.

[0034] In some embodiments, the method further includes cutting a portion of the arcuate body to form a cutout therein.

[0035] In some embodiments, the method further includes cutting a portion of the first end and the second end to form at least one opening therein.

[0036] Both the foregoing summary and the following detailed description provide examples and are explanatory only. Accordingly, the foregoing summary and the following detailed description should not be considered to be restrictive. Further, features or variations may be provided in addition to those set forth herein. For example, embodiments may be directed to various feature combinations and sub-combinations described in the detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the disclosed subject matter claimed.

[0037] It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the disclosed subject matter claimed.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] A detailed description of various aspects, features, and embodiments of the subject matter described herein is provided with reference to the accompanying drawings, which are briefly described below. The drawings are illustrative and are not necessarily drawn to scale, with some components and features being exaggerated for clarity. The drawings illustrate various aspects and features of the present subject matter and may- 6 -FH12915382.4NEX-19125 illustrate one or more embodiment(s) or example(s) of the present subject matter in whole or in part.

[0014] Furthermore, the drawings may contain text or captions that may explain certain embodiments of the present disclosure. This text is included for illustrative, nonlimiting, explanatory purposes of certain embodiments detailed in the present disclosure.

[0014] FIGS. 1A-1B are front and back perspective views of an actuator in accordance with embodiments of the present disclosure.

[0015] FIG. 2 is an exploded view of a portion of an actuator in accordance with embodiments of the present disclosure.

[0016] FIG. 3 is a section view of an actuator in accordance with embodiments of the present disclosure.

[0017] FIGS. 4A-4B are planform and perspective views of a c-spring mounted between a transmission casing and within an outer housing of an actuator in accordance with embodiments of the present disclosure.

[0018] FIGS. 5A-5B are planform and perspective views of a c-spring mounted on a transmission casing in accordance with embodiments of the present disclosure.

[0019] FIGS. 6A-6B are planform and perspective views of a c-spring mounted within the front cover of the outer housing in accordance with embodiments of the present disclosure.

[0020] FIGS. 7A-7B are perspective views of embodiments of a c-spring for an actuator in accordance with embodiments of the present disclosure.

[0021] FIGS. 8A-8B are perspective views of an actuator in the form of an ankle prosthesis in accordance with embodiments of the present disclosure.

[0022] FIG. 8C is a perspective view of an actuator in the form of an ankle prostheses in accordance with embodiments of the present disclosure.- 7 -FH12915382.4NEX-19125

[0023] FIG. 9 is a perspective view of a transmission in accordance with embodiments of the present disclosure.

[0024] FIG. 10 is a section view of a transmission with a central pass through in accordance with embodiments of the present disclosure.

[0025] FIG. 11 is a flowchart of a method for forming a c-spring configured for use in an actuator in accordance with embodiments of the present disclosure.

[0026] The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the method and system of the disclosed subject matter. Together with the description, the drawings serve to explain the principles of the disclosed subject matter.DETAILED DESCRIPTION

[0027] As a preliminary matter, it will readily be understood by one having ordinary skill in the relevant art that the present disclosure has broad utility and application. As should be understood, any embodiment may incorporate only one or a plurality of the above-disclosed aspects of the disclosure and may further incorporate only one or a plurality of the above-disclosed features. Furthermore, any embodiment discussed and identified as being “preferred” is considered to be part of a best mode contemplated for carrying out the embodiments of the present disclosure. Other embodiments also may be discussed for additional illustrative purposes in providing a full and enabling disclosure. Moreover, many embodiments, such as adaptations, variations, modifications, and equivalent arrangements, will be implicitly disclosed by the embodiments described herein and fall within the scope of the present disclosure.

[0028] Accordingly, while embodiments are described herein in detail in relation to one or more embodiments, it is to be understood that this disclosure is illustrative and exemplary of the present disclosure, and are made merely for the purposes of providing a- 8 -FH12915382.4NEX-19125 full and enabling disclosure. The detailed disclosure herein of one or more embodiments is not intended, nor is to be construed, to limit the scope of patent protection afforded in any claim of a patent issuing here from, which scope is to be defined by the claims and the equivalents thereof. It is not intended that the scope of patent protection be defined by reading into any claim a limitation found herein that does not explicitly appear in the claim itself.

[0029] Thus, for example, any sequence(s) and / or temporal order of steps of various processes or methods that are described herein are illustrative and not restrictive.Accordingly, it should be understood that, although steps of various processes or methods may be shown and described as being in a sequence or temporal order, the steps of any such processes or methods are not limited to being carried out in any particular sequence or order, absent an indication otherwise. Indeed, the steps in such processes or methods generally may be carried out in various different sequences and orders while still falling within the scope of the present invention. Accordingly, it is intended that the scope of patent protection is to be defined by the issued claim(s) rather than the description set forth herein.

[0030] Additionally, it is important to note that each term used herein refers to that which an ordinary artisan would understand such term to mean based on the contextual use of such term herein. To the extent that the meaning of a term used herein — as understood by the ordinary artisan based on the contextual use of such term — differs in any way from any particular dictionary definition of such term, it is intended that the meaning of the term as understood by the ordinary artisan should prevail.

[0031] Furthermore, it is important to note that, as used herein, “a” and “an” each generally denotes “at least one” but does not exclude a plurality unless the contextual use dictates otherwise. When used herein to join a list of items, “or” denotes “at least one of the- 9 -FH12915382.4NEX-19125 items” but does not exclude a plurality of items of the list. Finally, when used herein to join a list of items, “and” denotes “all of the items of the list”.

[0032] The following detailed description refers to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar elements. While many embodiments of the disclosure may be described, modifications, adaptations, and other implementations are possible. For example, substitutions, additions, or modifications may be made to the elements illustrated in the drawings, and the methods described herein may be modified by substituting, reordering, or adding stages to the disclosed methods. Accordingly, the following detailed description does not limit the disclosure. Instead, the proper scope of the disclosure is defined by the appended claims. The present disclosure contains headers. It should be understood that these headers are used as references and are not to be construed as limiting upon the subjected matter disclosed under the header.

[0033] Reference will now be made in detail to exemplary embodiments of the disclosed subject matter, an example of which is illustrated in the accompanying drawings. The method and corresponding steps of the disclosed subject matter will be described in conjunction with the detailed description of the system.

[0034] Referring now to FIGS. 1A-1B, front and back perspective views of an actuator 100 is shown. Actuator 100 may be utilized as a joint in a prosthesis. In various embodiments, actuator 100 may be utilized as a joint in a robotic system. In various embodiments, actuator 100 may be utilized as a robotic joint in a human prosthesis. In various embodiments, actuator 100 may be employed in a complex network of other actuators and / or robotic components, for example as two or more separate joints working in tandem, in either a human prosthesis, robot or the like. In various embodiments, actuator 100 may be coupled to a human being’s existing limb, such as a thigh, shin, arm, forearm or- 10 -FH12915382.4NEX-19125 the like. As can be seen in FIGS. 1A-1B, a human’s existing limb may be fitted with an adapter configured to couple to adapter 128 of the actuator 100. Adapter 128 of actuator 100 may fixedly couple actuator 100 to the human limb, including bearing the weight of the actuator 100 itself, including handling the electronic and sensor connection required to operate said actuator 100. Adapter 128 may be manufactured to accommodate a specific limb arrangement of an animal or human being or fitted to couple to a robotic system as necessary. One of skill in the art would appreciate that the form factor of the adapter 128 is not limited by this disclosure, and any suitable adapter may be interchanged with the shown adapter 128 to fit actuator 100 to the host, whether human or robotic or other.

[0035] With continued reference to FIGS. 1A-1B, actuator 100 may be coupled to adapter 128 via one or more mechanical fasteners, such as screws, bolts, adhesives, geometrical retaining features, rails or the like. For example, and without limitation, as shown, the actuator 100 may generally be formed as a cylindrical system or a system having an arcuate outer housing, therefore adapter 128 may include complementary geometrical features configured to mate with the outer housing such as an arcuate receiver configured with flanges provided openings for mechanical fasteners. Actuator 100 may include a front cover 104 and a back cover 108. Front cover 104 may be formed as a generally cylindrical shell having a front planar face circumscribed by an arcuate sidewall, forming an internal space therebetween. Front cover 104 may include a front cutout 105 (not labeled in FIGS. 1A-1B for clarity - front cutout 105 is shown in FIG. 2) formed as a circular opening defining a rotational axis 101 extending perpendicularly and centrally therethrough. Front opening 105 may be sized to accommodate any one of the succeeding described components, movable members fixed thereto, based on the deployed system in which the actuator 100 is used. Front cover 104 may include a polygonal sidewall or another shaped front cutout 105, such as a rectilinear opening. As will be described- 11 -FH12915382.4NEX-19125 hereinbelow, front cutout 105 may provide a passthrough from one or more internal components from an internal space of outer housing to the outer surface of the outer housing. In various embodiments, as shown in FIG. 1A, front cutout 105 may be configured to provide a passthrough for an output element 119 of a transmission or a drive train. As will be described herein, output element 119 may be driven by a motor, transmission, controller, encoder or a similar system to rotate one or more output members, such as a prosthetic foot, prosthetic limb element or a robotic end effector. Front cutout 105 may include any number of bearings to bear loads outside of the axis of rotation, such as section bearings, roller bearings, ball bearings, or the like.

[0036] With continued reference to FIGS. 1A-1B, actuator 100 may include a back cover 108. Back cover 108 may include a back cutout (shown covered by a back cap in FIG. IB). Back cover 108 may include a generally planar surface having an arcuate edge configured to mate with the arcuate sidewall of front cover 104. Back cover 108 may be configured to releasably coupled to front cover 104 via one or more mechanical fasteners fitted through corresponding openings along the arcuate edge and matching arcuate sidewalls of the back cover 108 and front cover 104, respectively. Back cover 108 may be formed to accommodate internal components such as a motor or transmission. As shown in FIG. IB, a cylindrical sidewall may extend from the back cover 108 along the rotational axis 101. One of skill in the art would appreciate the overall form factor of the back cover 108 may be adjusted to accommodate the system in which actuator 100 is employed, for example with a smooth outer wall or planar surface.

[0037] Further, as shown in FIG. IB, actuator 100 may include an encoder 124 configured to detect and / or measure a deflection of one or more internal components, such as a transmission. Encoder 124 may be coupled to back cover 108, such as a planar surface of back cover 108, and measure the deflection of a protrusion passing through the relatively- 12 -FH12915382.4NEX-19125 stationary back cover 108 from one or more moving components internally positioned within actuator 100.

[0038] Referring now to FIG. 2, an exploded perspective view of actuator 100 for a prosthesis is shown. One of skill in the art would appreciate that some components, such as bearings, fasteners, among others have been removed for clarity. Adapter 128 has been removed from clarity, and may be coupled to actuator 128 in any orientation appropriate for the system in which actuator 100 is employed, for example, adapting to a corresponding component on an existing human limb, prosthetic device, robotic system or the like. Actuator 100 is shown aligned with a centrally extending rotational axis 101. Rotational axis 101 may extend at an axial center of actuator 100 and extend from the front cover 104 to the back cover 108. Front cover 104 is shown with a planar surface having an arcuate sidewall extending parallel to the rotational axis 101, with a front cutout 105 formed as a generally circular opening concentrically positioned to the rotational axis 101. Back cover 108 is shown at the opposite end of the figure with a generally planar face having an arcuate edge matched to the arcuate sidewall of front cover 104. Back cover 108 is shown with a cylindrical sidewall extending from the planar surface parallel and radially symmetrical about the rotational axis 101. Any of front cover 104 and back cover 108 may include openings or geometrical retaining features configured to couple to adapter 128 (not shown).

[0039] With continued reference to FIG. 2, actuator 100 may include a motor 112. Motor 112 may be an electric motor. In various embodiments, motor 112 may be any powered actuator configured to actuate in response to one or more electrical signals. For example, and without limitation, motor 112 may be configured to rotate a rotor relative to a stator in response to one or more electrical signals. In various embodiments, motor 112 may be configured with a spindle-type rotor configured to rotate within a generally circular- 13 -FH12915382.4NEX-19125 stator, said rotor coaxially positioned with the rotational axis 101. Motor 112 may include one or more controllers, processors or computing nodes configured to rotate the motor 112 based on one or more electrical signals provided thereto. In various embodiments, motor 112 may be configured to receive power from one or more power sources, such as an electrochemical battery, rechargeable battery or the like. In various embodiments, motor 112 may include one or more bearings configured to transmit axial and radial loads from the rotor or shaft to a motor housing or another portion of actuator 100. In various embodiments, motor 112 may be embodied by a stepper motor, servomotor, axial rotor motor, coreless rotor motor, electrostatic motors, piezoelectric motors, brushed direct current (DC) motors, brushless DC motors, switched reluctance motors, universal motors, induction motor, or the like.

[0040] With continued reference to FIG. 2, actuator 100 may include a transmission 116. Transmission 116 may be coaxially positioned within the outer housing. In various embodiments, transmission 116 may be configured to transmit torque from the motor 112 through an input element 118 to an output element 119 (hidden from view in the perspective view of FIG. 2), and on to one or more external members, as will be described below. Transmission 116 may be configured to change speed, direction of rotation, or multiply / reduce torque from the motor 112 to output element 118. In various embodiments, transmission 116 may be configured with a fixed gear ratio, a plurality of selectable distinct gear ratios, or continuously variable gear ratios. Transmission 116 may include any number of gears in any arrangement to accomplish speed, rotation direction, or torque multiplication / reduction.

[0041] Transmission 116 may be generally formed as a cylindrical assembly extending along the rotational axis 101 within the outer housing proximate the back cover 108 to the front cover 104. Transmission 116 may include a casing 117 surrounding the- 14 -FH12915382.4NEX-19125 internal gearing, input element 118 and output element 119. Casing 117 may be an arcuate sidewall encompassing transmission 116 and encircling the rotational axis 101. Casing 117 may include at least one boss or raised feature extending radially from casing 117 providing a coupling for one or more components, such as a spring, as will be described herein below. Casing 117 may be formed from one or more metals or metal alloys, plastics, composites or another suitable material. Casing 117 may include any number of openings formed parallel to the rotational axis 101 and configured to couple to one or more components of actuator 100 within the drive train described herein. For example, casing 117 may include a plurality of openings positioned along the circumference of the casing 117 to couple to a tape mount 115. Tape mount 115 may be bolted to casing 117 with a central opening coaxially aligned with the input element 118. In this arrangement, tape mount 115 may be coupled to casing 117 while allowing input element 118 to be rotatably engaged with motor 112. Tape mount 115 may include a protrusion extending along the rotational axis 101 and through an opening in back cover 108. When assembled, tape mount 115 may align the protrusion into optical contact with encoder 124, positioned externally at the back cover 108.

[0042] With continued reference to FIG. 2, encoder 124 may be a partial arc reflective incremental or absolute encoder. In various embodiments, encoder 124 may be positioned on the outside of the transmission 116, specifically tape mount 115. In various embodiments, optical tape or a magnetic strip may be placed on tape mount 115, which extends from transmission 116, through back cover 108, and in optical communication with encoder 124. The encoder 124 will read the deflection of the transmission casing 117, which can be multiplied by the rotational stiffness of the spring to directly determine the torque of the transmission 116. In the state of the art, two encoders are usually necessary to measure the performance of the system, one before the spring and one after the spring. These encoder measurements may be subtracted from one another, and the deflection of the- 15 -FH12915382.4NEX-19125 spring may be measured for torque control. By mounting encoder 124 so it can directly measure deflection of the transmission casing 117, the same measurement can be accomplished with a single encoder.

[0043] A portion of transmission 116 may be exposed through front cutout 105 for further mechanical connections to one or more components. Transmission 116 may be coupled to motor 112. Transmission 116 may include input element 118 positioned a first end of transmission 116 and proximate the back cover 108. Input element 118 may be coupled to an output of the motor 112, such as the rotor, armature or spindle. Input element 118 of transmission 116 may be rotated by motor 112, for example rotating under the power of the rotor of motor 112. For example and without limitation, input element 118 may be fixed to the output of the motor 112 such that one rotation of the rotor of motor 112 rotates the input element 118 exactly once. Input element 118 may be coupled to motor 112 by one or more plates having corresponding openings for mechanical fasteners. In various embodiments, input element 118 may be formed as an integral component with the output of motor 112, such that motor 112 rotates input element 118 directly. Input element 118 of transmission 116 may be retained by one or more rotatable bearings, such as roller bearings, section bearings, or ball bearings, so off-axis loads are transmitted to another portion of actuator 100 instead of input element 118.

[0044] In various embodiments, transmission 116 may be embodied as a harmonic drive or strain wave gearing arrangement. In various embodiments, transmission 116 may include a flexible spline with external teeth which are deformed by a rotating elliptical cam to engage with internal teeth of an outer spline. In various embodiments, harmonic drive transmission 116 may be configured to provide no backlash, be compact and light, produce high gear ratios, high torque capacity, with coaxial input and output elements, such as shafts. Harmonic drive transmission 116 may include a wave generator, flex spline, circular- 16 -FH12915382.4NEX-19125 spline. In various embodiments, the wave generator may include an elliptical (or other shaped) cam and optionally an outer ball bearing. The cam is inserted into the bearing, forcing the bearing to conform to the shape of the cam, but allowing rotation of the cam within the outer bearing. In various embodiments, the flex spline may be formed as a deformable cup having teeth positioned externally about the sidewall. The flex spline may have the cam inserted therein, such that as the cam rotates, the shape deforms the sidewalls of the flex spline without slipping over the cam, with the ball bearing allowing the flex spline to rotate independently of the rotation of the cam’s shaft. Further, the circular spline is a ridged circular ring with internally positioned teeth. When the flex spline is inserted into the circular spline, a portion of the external teeth of the flex spline mesh with the circular spline. The flex spline may have less teeth than the circular spline, such that as the flex spline rotates, it meshes with the circular spline at certain points, and an output shaft coupled to the flex spline rotates slower than the input shaft. One of skill int eh art would appreciate that the gear ratio produced by the harmonic drive transmission 116 is a function of the teeth of the flex spline and the teeth of the circular spline. Transmission 116 may include an output element 119 (as shown in FIGS. 3, 9 and 10) coupled to the output of the flex spline, therefore the output element 119 rotates relative to the input element 118 by a predetermined gear ratio, such as reduced 1:10, 1:20, 1:30, 1:40, 1: 50, 1: 60, 1: 70, 1:80, 1:90, 1:100, 1:110, 1:120, 1:130, 1:40, 1:150, 1:160, 1:170, 1:180, 1:190 or 1:200, for example and without limitation. Transmission 116 may be configured to rotate output element 119 in the same direction as input element 118 or motor 112. In various embodiments, transmission 116 may be configured to reverse the direction of rotation of output element 119 relative to input element 118 and motor 112. In various embodiments, the output element 119 and input element 118 may be configured to coaxially rotate. In- 17 -FH12915382.4NEX-19125 various embodiments, transmission 116 may be configured to rotate output element 119 about a parallel axis to the axis of rotation of input element 118 and motor 112.

[0045] Output element 119 may be configured to mate with one or more externally movable components such as a prosthetic limb or robotic end effector. Output element 119 may be a circular plate rotatably fixed to the transmission 116. Output element 119 may rotate based on input element 118, for example a fraction of the rotation of input element 118. Output element 119 may rotate a prosthetic foot element along an arc, mimicking the dorsiflexion, plantar flexion, flexion and / or extension of a human foot. Output element 119 may rotate a prosthetic foot element along an transverse arc, mimicking the rotation of a human foot in the transverse plane, such as inversion and / or eversion of an ankle. In various embodiments, output element 119 may rotate a prosthetic limb element, mimicking abduction of a human leg, adduction of human leg, extension of a human leg, and / or flexion of a human leg. In various embodiments, when actuator 100 embodies an elbow joint, output element 119 may rotate a prosthetic limb member mimicking the flexion, extension or rotation of a human radius bone. Transmission 116 may be arranged as shown in FIGS. 9 and 10. For example, transmission 116 may include a plurality of section bearings 114 configured to bear radial loads while allowing for concentric rotations of the components of the transmission 116, shown specifically in the section view shown in FIG. 10. Further, a coaxially-positioned rod 121 may be positioned within a central cavity extending from the motor 112 to the transmission 116, the rod 121 configured to maintain relative concentric and coaxial alignment of the drive train’s rotating components, as shown in FIG. 10. Rod 121 may be formed from a metal or metal alloy, such as aluminum, steel or alloys thereof. In various embodiments, rod 121 may be formed from a composite material such as fiberglass or carbon fiber. Rod 121 may be positioned along the rotational axis 101 and- 18 -FH12915382.4NEX-19125 retained by one or more bearings, such as ball bearings, roller bearings or section bearings 114.

[0046] With continued reference to FIG. 2, actuator 100 may include a c-spring 120. C-spring 120 may have a first end and a second end, with an arcuate spring body extending therebetween. C-spring 120 may be formed in a generally cylindrical shape having an opening formed along its arc between the first end and the second end, opposite the arcuate spring body, as shown in FIG. 7B. C-spring 120 may have an inner surface having a first radius from the rotational axis 101 and an outer surface having a second radius from the rotational axis 101, where the second radius is greater than the first radius, thereby defining a thickness between the inner surface and the outer surface. The four parameters that are changed to adapt the spring to a specified strength and compliance are the height, diameter, thickness, and arc length. By increasing the height or thickness, the spring will become stiffer and stronger. Increasing the diameter will cause the spring to become less stiff. Increasing the arc length will also cause the spring to become less stiff. By adjusting the four parameters to optimize for strength and compliance subject to the constraints of the actuator 100 design, a wide variety of springs may be manufactured for a range of applications. In various embodiments, c-spring 120 may be of any dimensions and configured to fit within actuator 100. For example, and without limitation, c-spring 120 may be between 5-10 mm, such as 9 mm.

[0047] C-spring 120 may include openings formed proximate the first end and the second end, extending from the inner surface to the outer surface. By constraining the motion of the spring, more efficient energy storage solutions for this geometry can be unlocked. Squeezing both ends of the c-shape together would produce energy storage, but the stress will be concentrated in the region equidistant from the two points of load. Instead, the spring is fixed at one end, and the other end is constrained to follow a circular path of- 19 -FH12915382.4NEX-19125 the same diameter as the spring. This is accomplished by fixing the spring to a member that rotates on the same rotational axis 101 as the center of the spring. In this orientation, the large stresses are experienced near the fixture points at either end of the arc. Because of this, the energy storage of the spring is increased and some of the material furthest from the two fixture points may be removed, in various embodiments. Further, c-spring 120 may include a cutout formed in the arcuate spring body, as shown in FIG. 7A. For example, and without limitation, a cutout may be formed in the arcuate spring body opposite the gap between the first end and the second end. In various embodiments, the cutout may be formed as an oblong cutout extending along the arc of the arcuate spring body. In various embodiments, c-spring 120 may have a variable width along the arcuate spring body. For example, and without limitation, the c-spring 120 may be wider proximate the first end and the second end, and neck down distal to the first end and the second end. In various embodiments, c-spring 120 may have a lesser width proximate the first end and the second end, and widen distal to the first end and the second end. In various embodiments, c-spring 120 may be wider proximate a first end, and thinner proximate a second end. In various embodiments, the arcuate edge of the arcuate spring body may be planar, radiused, chamfered or the like.

[0048] C-spring 120 may be positioned coaxially around the rotational axis 101, extending in an arc extending at least a portion of the radial distance around rotational axis 101. C-spring 120 may extend about the rotational axis 101 more than 180 degrees. For example, and without limitation, c-spring 120 may extend about the rotational axis 101 approximately 240 degrees. For example, and without limitation, c-spring 120 may extend along an arc extending about the rotational axis 101 of more than 270 degrees. In various embodiments, c-spring 120 may surround the rotational axis 101 approximately 300 degrees. C-spring 120 may include openings formed as through holes, slots, threaded- 20 -FH12915382.4NEX-19125 openings, or the like, configured to mechanically couple c-spring 120 to one or more components at the first end and the second end. C-spring 120 may include inserts or adapters configured to bear transverse loads or reduce abrasion at the openings of the first end and second ends as the spring deflects.

[0049] In various embodiments, c-spring 120 may be coupled to transmission 116 at the first end of the c-spring and surround at least a portion of casing 117 of transmission 116, as shown in FIGS. 5A-5B. The spring geometry and motion constraints allow the c- spring to be implemented in rotary actuation systems with linear behavior (no linkages). By placing the c-spring around the transmission, and connecting the outside of the transmission to ground, a high-torque, compact elastic actuator may be developed. In various embodiments, in actuator 100, the spring is placed between the casing 117 of the transmission 116 and ground, and the load (element coupled to output element 118) and the transmission 116 are directly coupled. C-spring 120 may be mechanically fastened to the boss protruding from casing 117, but otherwise not physically contact casing 117. C-spring 120 may be spaced equally from casing 117 along its arc. C-spring 120 may be further mechanically fastened to front cover 104 at the second end of c-spring 120, as shown in FIGS. 6A-6B. Therefore, transmission 116 may be suspended within actuator 100 via the c- spring 120. C-spring 120 may be coupled to the front cover 104 and positioned within the front cover 104 between the arcuate sidewall thereof and the casing 117 of transmission116, which can be seen in FIGS. 4A-4B. In various embodiments, c-spring 120 may deflect along its arc when casing 117 rotates about rotational axis 101 within front cover 104. As motor 112 turns input element 118 of transmission 116, casing 117 of transmission 116 may also rotate in response, c-spring 120 may deflect with casing 117 and provide a restoring force to casing 117 in the opposite direction of the imparted rotation of the casing117. In various embodiments, c-spring 120 may deflect in the opposite direction, wherein- 21 -FH12915382.4NEX-19125 the gap between the first end and the second end is enlarged, thereby compressing the spring along its arc. C-spring 120 may provide a restoring force in the opposite direction, towards the c-spring rest position.

[0050] C-spring 120 may be formed from a metal or metal alloy. C-spring 120 may be formed by a composite material. C-spring 120 may be formed from a composite material formed by a layup. In various embodiments, c-spring 120 may be carbon fiber, fiberglass or the like. C-spring 120 may be formed by a series of fabrics having fibers directed in a plurality of directions. C-spring 120 may be made of a custom tube, optimized for hoop strength. At least one layer of unidirectional composite material may be sandwiched between at least one layer of twill or other weave that will prevent delamination. The unidirectional layers will provide hoop strength, which is the largest loading condition of this spring geometry. The twill or other weave pre-preg fiber sheets should be rolled onto the mandrel first, followed by the amount of unidirectional pre-preg desired, and finally the outside of the tube should be wrapped in twill or another weave. Composite materials such as carbon fiber and fiberglass have the highest energy storage by weight of any known materials, as well as low hysteresis. In applications where the width of an actuator is important, it can be extremely valuable to have a spring that has circular geometry, so that the spring may be placed in series or parallel with the system, concentric with the axis of rotation. Our spring diameter, width, height, and arc length may be adjusted to allow it to fit within a wide array of actuated systems.

[0051] C-spring 120 may be manufactured by modifying tubes, another common composite geometrical shape, to develop a spring that achieves unprecedented levels of energy storage and strength in a circular package that is manufacturable and cost-effective. By modifying tubes to form c-spring 120, the spring can achieve a larger range of strength and deflection targets compared to previously known springs. Composite tube construction- 22 -FH12915382.4NEX-19125 is a well understood, standardized method of manufacturing. By purchasing prepreg fibers, tubes may be constructed without any specialized equipment. Thus, c-spring 120 is capable of withstanding much higher stresses than other springs of similar weight. In other state-of- the-art devices, springs made of titanium or spring steel that withstand similar stresses may weigh more than five times as much as a spring made using this method. This makes the design invaluable in weight-constrained applications.

[0052] Referring now to FIG. 3, a section view of actuator 100 wherein the internal components thereof is shown. Actuator 100 may be encased generally by front cover 104 and back cover 108. Motor 112 may be positioned within a cylindrical sidewall of back cover 108. Motor 112 may include a stator and a rotor, such that the rotor is configured to rotate about the rotational axis 101 in response to electric signals received by motor 112. Motor 112 may be operatively coupled to transmission 116. Specifically, the motor 112 may be operatively coupled to input element 118 of transmission 116. Transmission 116 may transmit the torque from motor 112 to output element 119 positioned proximate the front cover 104. Transmission 116 may be a harmonic drive as described hereinabove. Transmission 116 may include a casing 117 having a cylindrical sidewall encircling the rotational axis 101 and allowed to rotate within the front cover 104 and back cover 108. The casing 117 of transmission 116 may be mounted within front cover 104 via a c-spring 120 that encircles at least a portion of the casing 117. C-spring 120 may be any c-spring as described herein. Further, c-spring 120 may be coupled to casing 117 at a first end and coupled to front cover 104 at a second end, forming an arcuate spring body therebetween that encircles at least a portion of transmission 116. C-spring 120 may be positioned within an annular space between transmission 116 and front cover 104. Actuator 100 may include an adapter 128 configured to couple to one or more components, such as a human limb, robotic arm, or the like.- 23 -FH12915382.4NEX-19125

[0053] Referring now to FIGS. 8A-8B, an embodiment of actuator 100 utilized in a prosthetic ankle is shown. Actuator 100 may be positioned with the front cover and back cover oriented laterally relative to the sagittal plane of a human body such that the actuator 100 is at its relatively thinnest orientation. The orientation of the actuator 100 in this way allows for a walking gait of the human subject to be unimpeded by the size of the actuator 100 itself. Additionally, the rotational axis would be perpendicular to the sagittal plane such that actuation of the actuator 100 would generally mimic flexion and extension of a human foot, forward and backward in the direction of a human walking. Actuation of actuator 100 would rotate the prosthetic foot element 200 about the rotational axis to mimic flexion when the actuator 100 is raised up to take a step, and extension when the prosthetic foot element 200 strikes the ground to push off from said prosthetic, like a human foot would. The orientation of actuator 100 in this configuration allows for the other leg of the human to pass forward and backward past the actuator 100 during the walking gait. Actuation of the prosthetic foot element 200 may mimic heel strikes, pushing off of the front of the prosthetic foot, as well as other tasks required during a human gait, such as climbing or descending stairs, or driving. One of skill in the art would appreciate that the actuator 100 may be embodied in other prosthetic joints, such as a knee or elbow, where actuation of actuator 100 may bend a prosthetic leg during a human gait (i.e., walking, running, jogging, etc.) or bend a prosthetic arm in a single plane. Further, actuator 100 may be used in conjunction with a number of other actuators, identical, similar, or varied in a larger prosthetic system. Further, actuator 100, as discussed herein, may be employed in a robotic arm or robotic system to actuate one or limbs or effectors in a single plane, each. As shown in FIGS. 8A-8B, actuator 100 may be self-contained, i.e., have no external moving components other than the prosthetic foot element 200 coupled thereto and the adapter- 24 -FH12915382.4NEX-19125 disposed proximate a top portion of actuator 100 for connection with one or more external components, such as a prosthetic leg, arm, or robotic system.

[0054] As shown in FIG. 8C, actuator 100 may include one or more housing components, such as struts, plates, or the like configured to bear off-axis loads. In various embodiments, the actuator 100 may include one or more open housings, such that the c- spring 120 is exposed to the environment, coupling the transmission to the housing. In the configuration shown in FIG. 8C, c-spring 120 may be coupled to the transmission as described above, and further to the housing such that rotation of the transmission is constrained to the deflection regime of the c-spring. In various embodiments, c-spring 120 may also be employed to absorb shocks or sudden loads experienced by actuator 100 during use in a human subject or a robotic system, such as a heel strike with the ground, for example.

[0055] Referring now to FIG. 11 , a method for forming a c-spring is shown in a flowchart. In various embodiments, method 1100 may be utilized to form a c-spring for use in an actuator, such as actuator 100. In various embodiments, method 1100 may be utilized to form a c-spring for other uses, or multiple c-springs for use in actuator 100. Method 1100, at step 1105, may include forming a tubular workpiece having a predetermined circumference and a longitudinal axis. The tubular workpiece may include a constant circumference along the longitudinal axis, forming a hollow right cylinder. In various embodiments, the tubular workpiece may be formed with a variable circumference along the longitudinal axis. In various embodiments, the tubular workpiece may be formed as a solid right cylinder, with the inner material cut away at a later step. In various embodiments, the tubular workpiece may be formed as a portion of a hollow right cylinder, such as with an arcuate sidewall having a first end and a second end separated by a sector.- 25 -FH12915382.4NEX-19125Forming a tubular workpiece such as in step 1105, may include a sub-method as will be described hereinbelow.

[0056] Method 1100, at step 1105a, may include forming a layup by laying a first woven fiber sheet over a mandrel. The mandrel may be a tubular tool having an arcuate wall that imparts the inner diameter of the tubular workpiece and maximum length along the longitudinal axis of the tubular workpiece. In various embodiments, the mandrel may be capable of altering its shape at various points in the disclosed method, for example, expanding to increase its diameter, or moving one or more interleaved structures to allow the layup to be removed from the mandrel, whether hardened or still pliable. In various embodiments, the first woven fiber sheet, and subsequent sheets may be referred to as plies. The first woven fiber sheet, or a plurality thereof, may be formed from fiberglass or carbon fiber sheets. Laying the first woven fiber sheet may include laying a plurality of first woven fiber sheets over the mandrel. The first woven fiber sheet may include a first portion of fibers extending along the major longitudinal axis and a second portion of fibers generally transverse to the major longitudinal axis. The second portion of fibers may extend about a circumference of the mandrel. The first woven fiber sheet may be formed by a preimpregnated, or pre-preg, fiber sheet.

[0057] Method 1100, at step 1105b, may include laying at least one unidirectional fiber sheet over the first woven fiber sheet. The method, at step 1105b may include laying a plurality of unidirectional fiber sheets over the first woven fiber sheet. In various embodiments, each of the plurality of unidirectional fiber sheet with their respective fibers parallel to one another. The at least one unidirectional fiber sheet, or a plurality thereof, may be formed from fiberglass or carbon fiber sheets. In various embodiments, each ply of the plurality of unidirectional fiber sheets may be laid with their respective fibers oriented at a predetermined angle to one another. The unidirectional fiber sheet may be configured- 26 -FH12915382.4NEX-19125 to provide optimized hoop strength, and generally extend along the circumference of the mandrel, which will be the largest loading condition of the spring. The at least one unidirectional fiber sheet may be formed by a pre-impregnated, or pre-preg, fiber sheet.

[0058] Method 1100, at step 1105c, may include laying a second woven fiber sheet over the at least one unidirectional fiber sheet to form a layup. Laying a second woven fiber sheet may include laying a plurality of second woven fiber sheets over the at least one unidirectional fiber sheet. The second woven fiber sheet, or a plurality thereof, may be formed from fiberglass or carbon fiber sheets. The second woven fiber sheet may also include a first portion of fibers extending generally along the major longitudinal axis and a second portion of fibers that extend transverse to the major longitudinal axis and extend about the circumference of the mandrel. The second woven fiber sheet may be formed by a pre-impregnated, or pre-preg, fiber sheet.

[0059] Method 1100, at step 1110, may include curing the layup to harden the tubular workpiece. In various embodiments, curing the layup may include curing the resin within the pre-impregnated fiber sheets (i.e., the first and second woven fiber sheets and the at least one unidirectional fiber sheet) to harden the layup to form a rigid tubular workpiece. Curing the layup may include applying heat to the layup to harden the resin within the fiber sheets to form a rigid tubular workpiece. Curing the layup may include applying pressure to the layup to harden the resin within the fiber sheets to form a rigid tubular workpiece. In various embodiments, both heat and pressure may be applied continuously, periodically, or alternatingly to the layup to form a rigid tubular workpiece. In various embodiments, curing the layup may include the application of one or more chemicals or compounds to the layup to harden the resin and form a rigid tubular workpiece.

[0060] Method 1100, at step 1115, may include cutting the tubular workpiece in a predetermined path that extends at least partially around the circumference and along the- 27 -FH12915382.4NEX-19125 longitudinal axis to form a c-shaped component. In various embodiments, a single c-shaped component may be cut form the tubular workpiece. In various embodiments, a plurality of c-shaped components may be cut from the tubular workpiece. In various embodiments, the predetermined cut path may be optimized to cut a maximum number of c-shaped components form the tubular workpiece. In various embodiments, the predetermined cut path may be made at a portion of the tubular workpiece that is determined to have optimal characteristics, for example, maximum strength, optimal circumference or shape, or another characteristic. The c-shaped component may include a first end and a second end, having an arcuate body extending therebetween. The arcuate body may retain at least a portion of the circumference of the tubular workpiece. Further, a portion of the c-shaped component may be cut away to form a cutout in the arcuate body or proximate the first end and the second end. The cutout may be an oblong cut out extending along the original circumference of the tubular workpiece, which now forms the arcuate body of the c-shaped component. In various embodiments, slots, holes, openings, or threaded holes may be formed in the first end and / or the second end from an outer surface of the c-shaped component to the inner surface of the c-shaped component.

[0061] While the disclosed subject matter is described herein in terms of certain preferred embodiments, those skilled in the art will recognize that various modifications and improvements may be made to the disclosed subject matter without departing from the scope thereof. Moreover, although individual features of one embodiment of the disclosed subject matter may be discussed herein or shown in the drawings of the one embodiment and not in other embodiments, it should be apparent that individual features of one embodiment may be combined with one or more features of another embodiment or features from a plurality of embodiments.- 28 -FH12915382.4NEX-19125

[0062] In addition to the specific embodiments claimed below, the disclosed subject matter is also directed to other embodiments having any other possible combination of the dependent features claimed below and those disclosed above. As such, the particular features presented in the dependent claims and disclosed above can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter should be recognized as also specifically directed to other embodiments having any other possible combinations. Thus, the foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.

[0063] It will be apparent to those skilled in the art that various modifications and variations can be made in the method and system of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents.- 29 -FH12915382.4

Claims

NEX-19125CLAIMSWhat is claimed is:

1. An actuator for a prosthesis comprising: an outer housing formed by a front cover and a back cover oriented along a rotational axis, each of the front cover and the back cover having a coaxial cutout formed therethrough; a motor positioned in the cutout of the back cover; a transmission positioned coaxially within the outer housing, the transmission comprising: a transmission casing encircling the rotational axis; an input element coupled to the motor; and an output element extending through the cutout of the front cover, each of the input element and the output element configured to rotate about the rotational axis; a c-spring having a first end coupled to the transmission casing and a second end coupled to the front cover with an arcuate spring body extending therebetween, the arcuate spring body coaxially encircling a portion of the transmission casing; and an encoder positioned at the back cover and configured to detect a deflection of the c-spring around the rotational axis.

2. The actuator for a prosthesis of claim 1, wherein the transmission is a harmonic drive.

3. The actuator for a prosthesis of claim 1, further comprising a movable member operatively coupled to the output element.- 30 -FH12915382.4NEX-191254. The actuator for a prosthesis of claim 3, wherein the movable member is at least one of a portion of a prosthetic foot element or a portion of a prosthetic limb element.

5. The actuator for a prosthesis of claim 1, wherein the transmission is configured to reduce rotation of the output element relative to the rotation of the input element.

6. The actuator for a prosthesis of claim 1, wherein the transmission casing is configured to rotate about the rotational axis, thereby deflecting the c-spring.

7. The actuator for a prosthesis of claim 1, wherein the c-spring is configured to deflect along an arc defined by the arcuate body of the c-spring.

8. The actuator for a prosthesis of claim 1, wherein the outer housing comprises an adapter configured to couple to at least one stationary member.

9. The actuator for a prosthesis of claim 1, wherein the c-spring comprises an internal surface spaced from an external surface, defining a thickness therebetween and the c-spring is coupled to the transmission casing on the internal surface and coupled to the front cover on the external surface.

10. The actuator for a prosthesis of claim 1, further comprising a stabilization rod extending coaxially from the back cover to the front cover along the rotational axis.

11. The actuator for a prosthesis of claim 1, wherein the c-spring is formed from carbon fiber.

12. The actuator for a prosthesis of claim 11, wherein the c-spring is formed from a carbon fiber layup, comprising at least one inner layer having fibers oriented from the first end to the second end and at least one outer layer having woven fibers.- 31 -FH12915382.4NEX-1912513. The actuator for a prosthesis of claim 1, wherein the c-spring is cut from a tubular workpiece.

14. The actuator for a prosthesis of claim 1, wherein the spring body comprises at least one cutout oriented along the arcuate spring body.

15. The actuator for a prosthesis of claim 1, wherein the at least one encoder is one of a partial arc reflective incremental encoder or an absolute encoder.

16. The actuator for a prosthesis of claim 1, wherein the transmission casing comprises a projection extending through the back cover, the projection having optical tape emplaced thereon, the encoder configured to detect the deflection of the c-spring based on a rotation of the projection around the rotational axis.

17. The actuator for a prosthesis of claim 1, wherein the encoder is communicatively coupled to the motor and configured to transmit at least one electrical signal to the motor in response to the deflection of the c-spring.

18. A prosthesis system, the comprising: an outer housing formed by: a front cover having a front planar face circumscribed by an arcuate sidewall, the front planar face having a front cutout formed therethrough, defining a rotational axis; a back cover having a back planar face and a back cutout formed coaxially with the front cutout, the back cover configured to couple to the front cover along the arcuate sidewall; a motor positioned within the back cutout;- 32 -FH12915382.4NEX-19125 a transmission positioned coaxially within the outer housing and extending between the front cutout and the motor; a c-spring positioned concentrically between the transmission and the outer housing, the c-spring comprising: a first end coupled to the transmission; a second end spaced from the first end along an arc and coupled to the arcuate sidewall of the front cover, an arcuate body extending between the first end and the second end along the arc, the arcuate body having an outer surface spaced from an inner surface, defining a thickness therebetween, an opening defined between the first end and the second end; and the first end configured to deform along the first arc relative to the second end.

19. The prosthesis system of claim 18, wherein at least one cutout is formed in the arcuate body opposite the opening.

20. The prosthesis system of claim 18, wherein the arcuate body comprises a first lateral side and a second lateral side defining a width therebetween.

21. The prosthesis system of claim 20, wherein the width is variable along the arcuate body.

22. The prosthesis system of claim 21, wherein the width proximate the first end and the second end is greater than the width proximate the arcuate body.

23. The prosthesis system of claim 21, wherein the width proximate the first end and the second end is lesser than the width proximate the arcuate body.- 33 -FH12915382.4NEX-1912524. The prosthesis system of claim 18, wherein each of the first end and the second end comprise openings formed from the inner surface to the outer surface.

25. The prosthesis system of claim 18, wherein the c-spring is formed from carbon fiber.

26. The prosthesis system of claim 18, wherein the c-spring is formed from fiberglass.

27. The prosthesis system of claim 18, wherein at least a portion of the c-spring is formed from a carbon fiber layup, comprising at least one inner layer having fibers oriented along the arc and at least one outer layer having woven fibers.

28. A method for forming a c-spring, the method comprising: forming a tubular workpiece having a circumference circumscribing a longitudinal axis, wherein forming the tubular workpiece comprises: laying a first woven fiber sheet over a mandrel; laying at least one unidirectional fiber sheet over the first woven fiber sheet; and laying a second woven fiber sheet over the at least one unidirectional fiber sheet to form a layup; curing the layup to harden the tubular workpiece; cutting the tubular workpiece in a predetermined path that extends at least partially around the circumference and along the longitudinal axis to form a c-shaped component, wherein the c-shaped component is defined by a first end and a second end having an arcuate body extending therebetween; and- 34 -FH12915382.4NEX-19125 the c-shaped component retains at least a portion of the circumference of the tubular workpiece.

29. The method of forming a c-spring of claim 28, further comprising cutting a portion of the arcuate body to form a cutout therein.

30. The method of forming a c-spring of claim 28, further comprising cutting a portion of the first end and the second end to form at least one opening therein.- 35 -FH12915382.4

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