Upper extremity prosthetic with energy return system

An upper-extremity prosthetic is adapted to engage with an athletic ball. The prosthetic includes one or more springs that provide energy return as a user is throwing the ball using the prosthetic. The springs can have a conductivity that changes in relation to an amount of strain or deformation of the spring. The change in conductivity can be used to provide haptic feedback to the user so the user can sense the amount of force being applied to throw the ball. In some embodiments, the springs are made by a multi-material 3D printing (additive manufacturing) process and include a first material that is electrically non-conductive and a second material that electrically conductive. In some embodiments, the prosthetic also includes one or more cantilevered springs that are also adapted to engage with the ball and to provide energy return while throwing the ball.

TECHNICAL FIELD

This disclosure generally relates to prosthetics.

BACKGROUND

3D printing is a widely used manufacturing technique for both commercial products and research across many industries with emerging research areas in multi-material 3D printing, metamaterials, and 3D printed electronics. Because of the high customizability and accessibility 3D printing offers, more mechanisms such as prosthetics are being 3D printed. However, conventional 3D printed prosthetics do not allow for the same function and control that a natural limb provides. For example, a natural limb allows a person to feel how hard they are grasping an object.

As of 2020, there are roughly two million people living in the USA with limb loss. Of those, there are over ten times as many lower limb amputations as there are upper limb amputations leading to a large number of lower extremity prosthetic solutions. The upper extremity, and specifically the hand, is responsible for the vast majority of high dexterity and fine control tasks performed by an individual. The high dexterity required makes designing a functional prosthetic hand significantly more complex. Upper extremity prosthetics offer a range of fine motor control, but the majority are only designed for grasping tasks. Existing prosthetics are limited in their functionality because they don't give positional or force feedback which are critical features for sports specific prosthetics.

Athletes who play sports have few options for sport specific prosthetics and those that exist do not provide the high degree of dexterity and control that allows an individual to excel. Research shows that athletes or individuals who return to playing sports after an amputation have improved psychological health. Basketball is the most common ball sport played and the seventh most common recreational sport. In addition, the force applied from wrist and finger flexion on a basketball is extremely important to control the speed, direction and spin of the ball. For these reasons, a basketball prosthetic hand is helpful.

SUMMARY

In general, an aspect of the subject matter described in this specification may involve a prosthetic. The prosthetic includes a coil spring that provides energy return and that has a conductivity that varies in relation to an amount of strain on the spring. In some embodiments, the springs are made by multi-material 3D printing (additive manufacturing). Such springs made by multi-material 3D printing may include a first material that is electrically non-conductive (insulative) and a second material that electrically conductive. The extent of the deformation or strain of the spring may be determined or estimated by measuring the conductivity or resistivity of the electrically conductive material portion of the spring. A haptic feedback generator may generate haptic feedback to the user proportionate to the conductivity (and the deformation) of the coil spring. Accordingly, the energy returned by the coil spring may help a wearer of the prosthetic perform a task with less energy, and the haptic feedback may help the wearer perform the task with more fine-tuned control.

Some inventive aspects described herein include, but are not limited to: (i) an upper-extremity prosthetic that is adapted to engage with an athletic ball, (ii) springs that provide energy return as a user is throwing the ball using the prosthetic, (iii) the springs can have a conductivity that changes in relation to an amount of strain or deformation of the spring, and (iv) the change in conductivity can be used to provide haptic feedback to the user so the user can sense the amount of force being applied while throwing the ball.

In some embodiments, the prosthetic devices described herein can be made by a 3D printing (additive manufacturing) process. In particular embodiments, one or more of the springs of the prosthetic devices are made by a multi-material 3D printing process and include a first material that is electrically non-conductive and a second material that electrically conductive. In some embodiments, the prosthetic also includes one or more cantilevered springs that are also adapted to engage with the ball and to provide energy return while a user of the prosthetic is throwing the ball.

The use of one or more springs with integrated strain sensing capabilities for the prosthetic described herein may reduce the number of electronic components, reduce the steps for assembly after fabrication, and reduce the weight and overall cost in comparison to other techniques such as the use of a traditional accelerometer or pressure sensor.

In some aspects, this disclosure is directed to an upper-extremity prosthetic. Such an upper-extremity prosthetic includes a first member having a surface adapted to engage with an athletic ball and a first spring coupled to the first member. The first spring is arranged to absorb energy and to provide energy return in response to movement of the first member. The first spring has a conductivity that changes in response to deflection of the first spring. The upper-extremity prosthetic also includes electrical circuitry configured to detect the conductivity of the first spring and to output a signal responsive to the conductivity.

Such an upper-extremity prosthetic may optionally include one or more of the following features. The upper-extremity prosthetic may also include a base member coupled to the first spring and pivotably coupled to the first member. In some embodiments, pivoting the first member relative to the base member deflects the first spring. The upper-extremity prosthetic may also include a sleeve coupled to the base member and defining an interior space configured to receive a residual limb of a user of the prosthetic. The upper-extremity prosthetic may also include a haptic device arranged to receive the signal responsive to the conductivity from the electrical circuitry. The haptic device may be a vibratory motor arranged to vibrate against a residual limb in the interior space. The upper-extremity prosthetic may also include a first cantilever spring coupled to the first member and including a surface arranged to engage with an athletic ball engaged with the first member. The upper-extremity prosthetic may also include a first cantilever spring coupled to the first member and a second cantilever spring coupled to the first member. The second and third springs may each include a surface arranged to engage with an athletic ball engaged with the first member. The surfaces of the first member, the first cantilever spring, and the second cantilever spring may each be contoured to engage with an athletic ball. The first spring may be a multi-material 3D printed device. In some embodiments, the first spring and the first member are 3D printed in a single print process.

In another aspect, this disclosure is directed to an upper-extremity prosthetic that includes a first member having a surface adapted to engage with an athletic ball, a first spring coupled to the first member and arranged to deflect and to provide energy return in response to movement of the first member, and a first cantilever spring extending from the first member and having a surface adapted to engage with an athletic ball while the athletic ball is also engaged with the surface of the first member.

Such an upper-extremity prosthetic may optionally include one or more of the following features. The upper-extremity prosthetic may also include a second cantilever spring extending from the first member and having a surface adapted to engage with an athletic ball while the athletic ball is also engaged with the surface of the first member. The upper-extremity prosthetic may also include a second spring coupled to the first member and arranged to deflect and to provide energy return in response to movement of the first member. The first and second springs may each be coil springs. The upper-extremity prosthetic may also include a base member coupled to the first spring and pivotably coupled to the first member. Pivoting the first member relative to the base member may deflect the first spring. The upper-extremity prosthetic may also include a sleeve coupled to the base member and defining an interior space configured to receive a residual limb of a user of the prosthetic. The base member, the first member, the first spring, and the first cantilever spring member may each be 3D printed in a single print process. In some embodiments, the first spring is a multi-material 3D printed device and includes: a first 3D printed material; a second 3D printed material integrated with the first 3D printed material and having an electrical conductivity that is greater than an electrical conductivity of the first 3D printed material; a first electrical contact connected to the second 3D printed material; and a second electrical contact connected to the second 3D printed material. The first spring may be configured to have an electrical conductivity between the first and second electrical contacts that changes in response to deformation of the spring. The upper-extremity prosthetic may also include electrical circuitry configured to detect the electrical conductivity of the first spring between the first and second electrical contacts, and to output a signal responsive to the electrical conductivity. The upper-extremity prosthetic may also include a haptic device arranged to receive the signal responsive to the electrical conductivity from the electrical circuitry, and wherein the haptic device is a vibratory motor arranged to vibrate against a limb of a user of the prosthetic.

The details of one or more implementations are set forth in the accompanying drawings and the description, below. Other potential features and advantages of the disclosure will be apparent from the description and drawings, and from the claims.

DETAILED DESCRIPTION

Referring toFIGS.1and2, an example upper-extremity prosthetic100can be worn by a user1(e.g., an amputee) to, for example, shoot a basketball10into a basketball goal12. As described further below, in some embodiments the prosthetic100includes one or more springs, and can include a haptic feedback system that provides the user1with a physical sensation that is proportional to the amount of force applied to the basketball10via the prosthetic100during the shot. Accordingly, the energy returned by the spring(s) may help the user1shoot the basketball10while using less energy, and the haptic feedback may help the user1shoot the basketball10with more fine-tuned control.

While the scenario depicted here is a basketball shot, the design aspects of the prosthetic100described below can also be applied for prosthetics adapted for use in other contexts. For example, the concepts described herein can be applied in prosthetics adapted for purposes such as, but not limited to, throwing a football, throwing an item such as a baseball or softball, throwing a flying disc, dribbling a ball, and the like, without limitation.

Referring toFIGS.3-5, the prosthetic100includes a first member110, a first spring120, a second spring130, a first cantilever spring140, a second cantilever spring150, a base member160, a socket170, electrical circuitry180, and a haptic device190. At least the following components of the prosthetic100are optional and not included in some embodiments of the prosthetic100: the second spring130, the second cantilever spring150, the socket170, the electrical circuitry180, and the haptic device190. For example, in some embodiments the prosthetic100can include just the first member110, the first spring120, the first cantilever spring140, and the base member160.

The first member110has a surface that is adapted to engage with an athletic ball (in this example, the basketball10). In some embodiments, the surface of the first member110is contoured with a concavity that matches the outer spherical surface curvature of the basketball10. The surface of the first member110can be textured in some embodiments. Depending on the particular type of object to be engaged with the first member110, the surface can be adapted in various ways in order to correspond to the shape and size of the particular object.

The first spring120is coupled to the first member110. The first spring120is also coupled to the base member160. Accordingly, as described further below, when the first member110pivots in relation to the base member160(such as during shooting the basketball10using the prosthetic100) the first spring120will deform or deflect. Initially during the shooting motion, the first spring120will become compressed. Then later during the shooting motion, the first spring120will provide energy return. In other words, the potential or stored energy of the compressed first spring120will be released as the first spring120extends.

In some embodiments, as described further below, the first spring120is constructed to have an electrical conductivity that changes in response to the deflection of the first spring120. While in the depicted embodiment the first spring120is a coil spring, in some embodiments the first spring120can be another type of spring such as, but not limited to, a platform leaf spring, a multi-segment platform leaf spring, a bow spring, a cantilever spring, a torsion spring, a variable rate spring, a constant force spring, a constant rate spring, and the like, without limitation.

In the depicted embodiment, the first cantilever spring140and the second cantilever spring150are not constructed to have an electrical conductivity that changes in response to their deflection or force applied to them. However, in some embodiments one or both of the first cantilever spring140and/or the second cantilever spring150can be constructed to have an electrical conductivity that changes in response to the deflection(s) thereof. In some such embodiments, the first spring120also has such a capability (i.e., to have an electrical conductivity that changes in response to the deflection). Alternatively, in some such embodiments the first spring120does not include such a capability.

In some embodiments (such as the depicted embodiment), the prosthetic100also includes the second spring130. The second spring130is coupled to the first member110and to the base member160(like the first spring120). During the basketball shooting motion using the prosthetic100, the second spring130becomes compressed and then rebounds to provide energy return in the same manner as the first spring120.

The prosthetic100also includes the first cantilever spring140. The first cantilever spring140is attached to and extends from the first member110. The cantilever spring140is deflectable in relation to the first member110. As described further below, the cantilever spring140deflects in relation to the first member110and provides energy return during the motion of shooting the basketball10using the prosthetic100. The first cantilever spring140has a surface that is arranged to engage with the basketball10while the basketball10is also engaged with the first member110. In some embodiments, the surface of the first cantilever spring140is contoured with a concavity that matches the outer spherical surface curvature of the basketball10.

In some embodiments (such as the depicted embodiment), the prosthetic100also includes the second cantilever spring150. The second cantilever spring150can be attached to and extend from the first member110like the first cantilever spring140. Also like the first cantilever spring140, the second cantilever spring150is deflectable in relation to the first member110, and it deflects in relation to the first member110and provides energy return during the motion of shooting the basketball10using the prosthetic100. The second cantilever spring150also has a surface that is arranged to engage with the basketball10while the basketball10is also engaged with the first member110. In some embodiments, the surface of the second cantilever spring150is contoured with a concavity that matches the outer spherical surface curvature of the basketball10.

The prosthetic100also includes the base member160. The first spring120and the second spring130are coupled to the base member160. As described further below, the first member110is pivotably coupled to the base member160. The base member160also provides a connection point to releasably connect the socket170to the base member160.

The socket170defines an interior space configured to receive a residual limb of the user1. For example, if the arm of the user1is amputated below the elbow, the interior space of the socket170can be configured to receive a portion of the forearm of the user1. The socket170can be any type of sleeve used by amputees. In some embodiments, the socket170includes a connection member configured to releasably connect the socket170to the base member160. For example, in some embodiments the socket170includes a threaded rod that can be used to attach the base member160to the end of the socket170.

In some embodiments (such as the depicted embodiment), the prosthetic100also includes the electrical circuitry180. The electrical circuitry180can be in one or more housings coupled to the socket170and/or the base member160, in some embodiments.

The electrical circuitry180can comprise solid state circuitry (e.g., integrated circuits, transistors, diodes, etc.) and/or analog electrical circuitry. In some embodiments, the electrical circuitry180can comprise one or more processors. In some embodiments, the electrical circuitry180is programmable. The electrical circuitry180can include a power source such as a battery. The electrical circuitry180can be configured to receive one or more inputs (such as from electrical connections to measure the conductivity of the first spring120). The inputs can be digital and/or analog. The electrical circuitry180can be configured to provide one or more outputs (such as to the haptic device190). The outputs can be digital and/or analog. In some embodiments, the outputs can be responsive to the inputs. For example, in the depicted embodiment the output to the haptic device190provided by the electrical circuitry180can be responsive to the input to the electrical circuitry180from the conductivity measurements of the first spring120. In particular embodiments, an analog output to the haptic device190provided by the electrical circuitry180can be proportional to an analog input to the electrical circuitry180from the conductivity measurements of the first spring120.

In some embodiments, the circuitry180can include a wireless connection such as WiFi, BT, BLE or ANT+ radio that communicates from the arm prosthetic100to a smartphone, smartwatch, tablet computer, or another device running an application to provide to the user1real-time feedback or post-activity analysis and improvement suggestions. In some embodiments, the application can also include a training tool for the user1to visualize how much strain is being applied to each spring of the prosthetic100during a shot.

In some embodiments (such as the depicted embodiment), the prosthetic100also includes the haptic device190. In some embodiments, the haptic device190can be coupled to the socket170. In particular embodiments, the haptic device190can be coupled to a sock or liner that is worn on a residual limb of the user1. In still other embodiments, the haptic device190can be coupled to other areas of the user1or items worn by the user1.

The haptic device190can be various types of devices such as, but not limited to, a vibratory motor, a device that outputs a variable amount of force, an electrotactile device, and the like, without limitation. In some embodiments, the haptic device190can be a vibratory motor coupled to the socket170and arranged to vibrate against a residual limb of the user1within the interior space of the socket170.

While not required in all embodiments, in some embodiments the prosthetic100is made by 3D printing. For example, in some embodiments at least the first member110, the first spring120, the second spring130, the first cantilever spring140, the second cantilever spring150, and the base member160are all made by 3D printing. In some embodiments, at least the first spring120is made by a multi-material 3D printing process, as described further below. In particular embodiments, the prosthetic100is made by a single 3D printing process.

In some embodiments, the components of the prosthetic100are made by one or more various types of processes (e.g., machining, molding, forming, 3D printing, etc.), and the components are then assembled to form the prosthetic100.

FIGS.6-8are a series of illustrations depicting the deflections of the springs of the prosthetic100during the process of shooting the basketball10using the prosthetic100. The cantilever springs140/150and the coil springs120/130act as the energy return components. The coil springs120/130represents the force generated from wrist flexion, and the cantilever springs140/150represents the force generated from finger flexion. Because the index and middle fingers are the last two points to make contact with the basketball10in a traditional basketball shot, the prosthetic100has two cantilever springs140/150, corresponding to two fingers. The cantilever springs140/150may be curved to match the contour of the first member110and the contour of the basketball10.

A staged deformation between the coil springs120/130and the cantilever springs140/150may be achieved so the energy return system can closely replicate the biomechanics of a traditional basketball shot. The main upwards force applied by the user1goes directly through the center of the coil springs120/130, and the cantilever springs140/150are offset from the main load path. The coil springs120/130may be additionally printed with a curved track (as described further below in reference toFIGS.12and13) instead of a linear prismatic joint to match the angle of rotation about the integrated hinge between the first member110and the base member160(as described further below in reference toFIGS.9-11).

As depicted inFIG.6, the basketball shooting motion using the prosthetic100causes compression of the first spring120(and compression of the second spring130if the prosthetic100includes the second spring130). The compression of the first spring120is caused by the pivoting of the first member110in relation to the base member160. The pivoting of the first member110in relation to the base member160is caused by the weight of the basketball10(and the first member110) as the prosthetic100is being accelerated upward during the basketball shooting motion using the prosthetic100.

As described further below, the extent of the compression of the first spring120can be detected by monitoring the electrical conductivity of the first spring120. For example, the electrical circuitry180(FIGS.3and4) can be configured and operable to measure/monitor the electrical conductivity of the first spring120as the first spring120is being compressed during the basketball shooting motion using the prosthetic100. In some embodiments, the electrical circuitry180can provide an output to the haptic device190that corresponds (e.g., a proportional output) to the measured/monitored electrical conductivity of the first spring120. Accordingly, the user of the prosthetic100can receive a physical sensation that is indicative of the mount of force being exerted on the basketball10during the basketball shooting motion using the prosthetic100.

As depicted inFIG.7, the basketball shooting motion using the prosthetic100also causes deflection of the first cantilever spring140(and deflection of the second cantilever spring150if the prosthetic100includes the second cantilever spring150). The deflection of the first cantilever spring140is caused by the weight of the basketball10as the prosthetic100is being accelerated forward during the basketball shooting motion using the prosthetic100.

As depicted inFIG.8, the basketball shooting motion using the prosthetic100also includes the release of energy (energy return) from the rebound of the first spring120(and from the second spring130, if included) and from the rebound of the first cantilever spring140(and from the second cantilever spring150, if included). The release of the energy provides a basketball shot from the prosthetic100that closely simulates a normal basketball shot resulting from the motions of the hands, wrists, and arms of normal shot by a person having all of his/her body parts. For example, the energy return from the first cantilever spring140(and from the second cantilever spring150, if included) provides the last force to the basketball10, and generates a backspin of the basketball10like a natural shot.

As can be now more readily understood in the context of the sequence ofFIGS.6-8, it can be said that the prosthetic100includes springs that are arranged in series. That is, the first spring120and the first cantilever spring140are arranged in series, with the first member110arranged between the first spring120and the first cantilever spring140.

FIGS.9-11depict an example type of pivotable mechanical connection that can be used between the first member110and the base member160. In the depicted embodiment, the first member110includes two opposing conical protrusions112. The base member defines two opposing conical recesses162. The conical protrusions112movably reside within the conical recesses162. The interface between the conical protrusions112and the conical recesses162provide a revolute joint by which the first member110is pivotably coupled to the base member160.

Other arrangements can be used for the pivotable mechanical connection between the first member110and the base member160. For example, in some embodiments the conical protrusions112can extend from the base member160and the conical recesses162can be defined by the first member110. The conical shape is not required in all embodiments. For example, in some embodiments a cylindrical shape or semi-spherical can be used for the protrusions and recesses.

The pivotable mechanical connection between the first member110and the base member160can be created during the 3D printing of the first member110and the base member160, if a 3D printing process is used to make the first member110and the base member160. For example, in some embodiments the conical protrusions112can be 3D printed within the conical recesses162that are defined by 3D printing. In other words, in some embodiments the pivotable mechanical connection between the first member110and the base member160can be created during a single process/run of 3D printing that creates the first member110and the base member160.

FIGS.12-15illustrate additional features of the first spring120(which can also be representative of the second spring130, if included). The depicted first spring120includes a coil made of a first material122and a second material124that are integrated with each other. The first spring120also includes a shaft121and a guide sleeve123. The shaft121is attached to one end of the first spring120and the guide sleeve123is attached to the opposite end of the first spring120.

The shaft121movably slides within an internal space defined by the guide sleeve123. In some embodiments, including the shaft121and the guide sleeve123can advantageously prevent the first spring120from buckling when compressed. These components, while beneficial in some embodiments, are optional. In some embodiments, a dampener is included as part of the assembly of the shaft121and the guide sleeve123. In particular embodiments, the dampener is adjustable so that the user1can adjust the amount of dampening.

In the depicted embodiment, the shaft121has a polygonal cross-sectional shape and the cross-sectional shape of the internal space defined by the guide sleeve123has a corresponding shape (to create a sliding fit therebetween). The polygonal cross-sectional shapes prevent rotations of the shaft121relative to the guide sleeve123. In the depicted embodiment, the polygonal cross-sectional shape is rectangular. However, other polygonal cross-sectional shapes and non-polygonal cross-sectional shapes (e.g., circular) can also be used in some embodiments of the first spring120.

In some embodiments (e.g., as depicted inFIGS.12and13), the shaft121can be curved, and the internal space defined by the guide sleeve123can have a corresponding curve. Alternatively, in some embodiments the shaft121and the internal space defined by the guide sleeve123can be linear (e.g., as depicted inFIGS.14and15).

Referring in particular toFIGS.14and15, in some embodiments the first spring120can be configured to have an electrical conductivity that changes in response to deformations of the first spring120. In other words, the first spring120can provide an integrated strain sensing capability in addition to providing energy return.

In the depicted embodiment, the first spring120is made of at least two different materials. For example, the coil of the first spring120includes the first material122and the second material124. The first material122and the second material124have differing electrical properties. For example, in some embodiments the second material124has an electrical conductivity that is greater than an electrical conductivity of the first material122. In some embodiments, the first material122is an electrical insulator and the second material124is an electrical conductor.

The first spring120is a coil spring and a compression spring. It should be understood, however, that the strain sensing concepts described herein in the context of the first spring120(which is a coil compression spring) can also be implemented in many other types of springs. For example, the concepts described herein can be implemented in other types of springs such as, but not limited to, extension springs, torsion springs, cantilevered springs, leaf springs, variable rate springs, constant force springs, constant rate springs, and the like, without limitation.

The first spring120can be configured to have any desired spring property including, but not limited to, spring rate, numbers of coils, coil member diameter, pitch, inner and outer diameter of the spring coils, free length, solid length, end types, and the like. Moreover, the first spring120can be tuned to generate different desired spring rates and/or force profiles by changing the properties of the first spring120as defined by Hooke's Law and Castigliano's theorem. For example, by changing the cross-sectional thickness, the spring diameter, and/or the number of turns (which affect the spring's Young's modulus and shear modulus of a coil spring), the properties of the first spring120can be changed. Accordingly, the first spring120has the potential to be tuned for a specific end use including, but not limited to, the prosthetic100.

The first spring120also includes a first electrical contact126and a second electrical contact128. The first electrical contact126and the second electrical contact128are each in electrical communication with the second material124. At least a portion of the second material124extends between the first electrical contact126and the second electrical contact128. In some embodiments, an entirety of the second material124extends between the first electrical contact126and the second electrical contact128. In particular embodiments (such as the depicted embodiment), the first electrical contact126and the second electrical contact128are made of the same type of material as the second material124. In such a case, the second material124and the contacts122and124are made as a continuous unitary member. In some embodiments, the first electrical contact126and/or the second electrical contact128are made of a different type of material than the second material124.

In some embodiments, the first spring120is, or comprises, a 3D printed spring or a multi-material 3D printed spring. For example, the first material122can be a first 3D printed material, and the second material124can be a second 3D printed material that is integrated with the first 3D printed material. In some cases, during at least some portions of the multi-material 3D printing process to make the first spring120, the first material122and the second material124are deposited concurrently or simultaneously.

3D printing is a manufacturing technique with emerging areas of research in multi-material 3D printing, metamaterials, and 3D printed electronics. Such techniques can be used to form the first spring120. The high customizability of a multi-material 3D printing process can make such a process well suited to making the first spring120and other components of the prosthetic100.

A multi-material 3D printed object (e.g., such as the first spring120with its first material122and second material124) may refer to an object printed with multiple materials by a multi-material 3D printer. Multi-material 3D printers are capable of consistently printing with multiple materials in the same print. When printing, the material properties of a part are at least somewhat dictated by the material properties of the materials it is printed with.

Metamaterials expands on this capability by allowing parts printed with only one material to have different material properties in multiple sections of the part. This is possible by changing the geometry and internal structure of the print. Metamaterials can enable printing compliant mechanisms and deformable structures without the need for multiple parts. A key application of 3D printed deformable objects is tunable 3D printed helical springs, such as the first spring120. 3D printing springs introduces the possibility of printing not only deformable objects, but objects with energy return properties.

In some implementations, such as the first spring120, a conductive material (e.g., from a carbon-based filament) is printed at the same print as traditional material(s) (e.g., from non-conductive filaments). For example, in some embodiments the first spring120can be formed by using a multi-material 3D printing process where the first material122is made from one or more non-conductive materials and the second material124is made from one or more conductive materials (e.g., from one or more carbon-based conductive PLA filaments, silver filaments, graphene filaments, etc.).

As described further below, the first spring120is capable of integrated strain sensing, and can be used in combination with the electrical circuitry180(FIGS.3and4). The strain-related data from the first spring120can be used as either a digital signal or an analog signal.

The first spring120is made for absorbing compression and for providing energy return as the first spring120rebounds from being compressed as described above. When the first spring120is compressed, its coils elastically deform. The deformations of the coils naturally result in stresses and strains in the materials of the coils of the first spring120(i.e., the first material122and the second material124). In the depicted embodiment of the first spring120, both the first material122and the second material124deform when the first spring120is compressed.

The electrical resistance of a conductive material (e.g., the second material124in this example) varies with changes in strain of the material. Accordingly, the electrical circuitry180can be used to determine or estimate the extent of the deformation of the first spring120by monitoring the electrical resistance (or conductivity) of the second material124, which is strained as the first spring120is compressed and/or rebounds from being compressed. In some embodiments, the changes of the electrical resistance/conductivity of the second material124in response to the deformation of the first spring120are proportional to the extent of deformation of the first spring120.

The first electrical contact126and the second electrical contact128are in electrical communication with the second material124. While the first electrical contact126and the second electrical contact128are at the ends of the second material124in the depicted embodiment, in some embodiments first electrical contact126and/or the second electrical contact128is/are at locations along the second material124. At least a portion of the second material124(in the coils of the first spring120) extends between the first electrical contact126and the second electrical contact128. In some embodiments, the first electrical contact126, the second material124, and the second electrical contact128are all 3D printed from the same material.

The second material124inherently has a certain conductivity or resistivity. That conductivity or resistivity varies as the second material124is strained or deformed. Accordingly, it follows that the first spring120is configured to have an electrical conductivity/resistivity between the first electrical contact126and the second electrical contact128that changes in response to deformation of the first spring120. It also follows that by measuring or monitoring the electrical conductivity between the first electrical contact126and the second electrical contact128using the electrical circuitry180, the extent of the deformation of the first spring120can be determined or estimated.

The materials that make up the 3D printed first spring120can be configured in many different ways. In some embodiments, the cross-sectional configuration of the material(s) of the first spring120is consistent all along the coils of the first spring120. In particular embodiments, the cross-sectional configuration of the material(s) of the first spring120varies along the coils of the first spring120(e.g., the material(s) can be arranged in two of more differing configurations at separate locations along the coils of the first spring120). Multiple sensor architectures can be used for different applications. Printing with a triangle infill over lines may yield a stiffer spring, and both mechanical and electrical properties may be optimized further to achieve the most elastic response from the coil first spring120and the largest and most predictable reading from the integrated strain gauge. This may be made possible by printing the core of a spring with a conductive material that has one infill pattern and density, then a traditional PLA or other material as a shell with a different infill pattern and density for advantageous mechanical properties.

In some embodiments, the coil of the first spring120is 3D printed exclusively using the second material124(the conductive material) and 100% infill. That is, in some embodiments only the second 3D printed material124is between the first electrical contact126and the second electrical contact128. This configuration works well for the highest conductivity to transmit a signal, but may experience little or no change in resistance under loading/strain/deformation. Resistance may increase if the infill percentage is lowered, due to a smaller cross sectional area of conductive material. These implementations may provide more of a digital than an analog output. Because the carbon-based PLA (the second material124) has such high conductivity, the first spring120may not produce a change in resistance throughout the full range of compression. Instead, a change in resistance may only be detected when the first spring120is fully compressed.

In some embodiments, to protect the conductive trace of the second 3D printed material124from external elements, the conductive trace is printed inside the walls of the first material122(e.g., inside the walls of the traditional PLA filament). In other words, the second 3D printed material124is encapsulated within the first 3D printed material100at one or more locations (or entirely) between the first electrical contact126and the second electrical contact128. By changing the infill density and pattern of the conductive PLA filament (the second 3D printed material124), the stiffness or spring constant of the first spring120can be adjusted.

In some embodiments, the printing of the conductive material (the second 3D printed material124) comprises an outer portion/segment of the coil, and the rest of the coil is printed with the first 3D printed material110(e.g., traditional PLA). In other words, the second 3D printed material124between the first electrical contact126and the second electrical contact128comprises a portion of an outer surface of the first spring120. In the depicted embodiment (seeFIG.15), the second material124comprises about 20% of the outer surface of the coil, and the first material122comprises the other 80%. In some embodiments, the second material124comprises a majority of the outer surface of the coil. In some embodiments, the first material122comprises a majority of the outer surface of the coil. This configuration may be desirable for transmitting a signal through the second material124of the coil first spring120(e.g., to act as a strain gauge) while retaining the mechanical material properties of the first material122(the other non-conductive material) for desired spring characteristics.

In some embodiments, to generate a more analog response (e.g., where the change in resistivity/conductivity of the second material124is more directly proportional to the deformation of the first spring120), conductive PLA filament may be embedded not only in the coil spring, but in other locations such as in the prismatic joint between the first member110and the base member160. By placing the strain sensor in the revolute or prismatic joint, the mechanical material properties of the coil first spring120may be tuned to exactly what the application calls for while reading cleaner signals from the sensor. Inspiration may be taken from metamaterials, but by designing open linkages.

FIG.16illustrates that deformations of the first spring120that cause a change in the conductivity/resistivity of the second material124can be used to provide an electrical signal for various useful purposes including, but not limited to, providing feedback via the haptic device190of the prosthetic100.

In this example, variances of the electrical signal (in response to variances in the deformation of the first spring120) are shown in a plot280. The x-axis of the plot280is time and the y-axis is a signal output from the first spring120that is responsive to, and indicative of, the deformations of the first spring120.FIG.16shows the change in resistance of the coil first spring120during a cycle of relaxation, compression, and relaxation.

In some embodiments, the electrical circuitry180can include a Wheatstone bridge used in conjunction with the first spring120to provide a variable voltage output from the first spring120that is responsive or proportional to the strain of the second material124(and responsive or proportional to the deformation of the first spring120).

Strain may be measured through a change in resistance of the conductive coil (the second material124) of the first spring120. In some embodiments, the resistance may be read through the analog input of an Adafruit Metro Mini 328 microcontroller and smoothed using a moving average filter with a window size of 10, for example.