INJECTION MOLDED PROSTHETIC LIMB SYSTEM AND RELATED METHODS

Abstract

Injection molded prosthetic limb systems and related methods are disclosed. Example prosthetic hands include a plurality of segments, wherein each segment is comprised of an injection molded plastic.

Claims

1. A prosthetic hand comprising a plurality of segments, wherein each segment is comprised of an injection molded plastic.

2. The prosthetic hand as defined in claim 1, comprising a spool connected to one or more of the segments via corresponding flexion cables in the one or more segments.

3. The prosthetic hand as defined in claim 2, wherein the spool is configured to rotate in a first direction to flex the segments and to rotate in a second direction to release the segments.

4. The prosthetic hand as defined in claim 2, wherein at least one of the flexion cables is routed through at least one of the segments of a finger and is coupled to a first spring at a distal end of the one of the finger.

5. The prosthetic hand as defined in claim 4, wherein the spring and the one of the flexion cables are configured to provide compliance of the corresponding member.

6. The prosthetic hand as defined in claim 4, wherein at least one of the segments of the finger comprises a second spring biased to extend the finger.

7. The prosthetic hand as defined in claim 2, further comprising a motor configured to actuate the spool.

8. The prosthetic hand as defined in claim 2, further comprising a Bowden cable configured to actuate the spool.

9. The prosthetic hand as defined in claim 7, wherein the spool has a first diameter where the flexion cables are coupled to the spool and a second diameter where the Bowden cable is coupled to the spool.

10. The prosthetic hand as defined in claim 1, wherein at least one of the segments is a thumb finger that is manually positionable.

11. The prosthetic hand as defined in claim 1, further comprising metallic joints configured to pivotally couple two or more of the segments corresponding to a same finger.

12. The prosthetic hand as defined in claim 1, wherein the prosthetic hand is voluntary opening or voluntary closing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1A illustrates an example powered hand prosthesis including flexion cables attached to a spool that is driven by a motor, in accordance with aspects of this disclosure.

[0018] FIG. 1B illustrates an example body-powered hand prosthesis including flexion cables attached to a spool that is driven by a an actuation (Bowden) cable.

[0019] FIG. 2 shows the example hand prosthesis of either of FIG. 1A of FIG. 1B having an adaptive grasp of a plastic toy.

[0020] FIG. 3 illustrates an example spool that may be used to implement the hand prostheses of FIGS. 1A and 1B.

[0021] FIG. 4 illustrates an example body-powered hand prosthesis having a spool with an enlarged diameter where a Bowden cable is attached to the spool, to increase the pulling force of the Bowden cable on the spool.

[0022] FIG. 5 illustrates the example hand prosthesis of any of FIG. 1A, 1B, or 4, executing a pinch grasp.

[0023] FIG. 6 displays a distal structure of an example finger for any of the example hand prostheses disclosed herein, with a fused, flexed distal interphalangeal joint at 20 degrees.

[0024] FIG. 7 displays a cross-section of an example finger for any of the example hand prostheses disclosed herein, including a flexion cable routing through a spring and a flat spring at the rear of the finger.

[0025] FIG. 8 displays another example individual finger, showing steel joints at the metacarpophalangeal and proximal interphalangeal locations.

[0026] The figures are not necessarily to scale. Where appropriate, similar or identical reference numbers are used to refer to similar or identical components.

DETAILED DESCRIPTION

[0027] Upper-limb amputees need prostheses that can effectively replace lost function, enabling them to return to work and participate actively in society. As detailed below, we have developed a hand with a novel and innovative under-actuated mechanism that can be used with either body-powered or motorized actuation. This hand is robust, has good cosmesis without a glove, and enables compliant, adaptive grasps. The hand may be manufactured using molds so that stronger injection-molded plastics can be used for the final product, enabling inexpensive large-scale manufacture of a robust hand at low cost. This hand is more aesthetically pleasing and more functional than body-powered hand options currently available to US consumers, and its low cost makes it potentially accessible to users around the world.

[0028] There is an urgent need for robust, functional, and inexpensive upper limb prosthetic hands that look more natural, with a thin palm, a wrap-around grasp, and articulation of the finger MCP and PIP joints. These devices should be robust, lightweight, and ideally simple enough serviced or repaired without having to go back to the manufacturer. Finally, as highlighted above, they need to be much less expensive than current options to meet the both needs of individuals in the US and the much larger global population. These hands would also be transformational for individuals in developing countries whose prosthetic options are even more severely limited by cost and access to technology and clinical care.

[0029] We have developed a hand, embodiments of which are shown in FIGS. 1A and 1B with a novel and highly innovative underactuated mechanism that can be used with either body-powered or motorized actuation. This hand is robust, has good cosmesis without a glove, enables compliant, adaptive grasps, and can be manufactured inexpensively in large quantities using low-cost materials and production methods.

[0030] Our hand design can use either body-powered or motorized actuation. FIG. 1A displays a powered hand 100 showing flexion cables 102a-102d attached to spool 104 that is driven by a motor 106. FIG. 1B displays a body-powered hand design 110 showing an actuation (Bowden) cable 112 attached to a spool 114. In both example hands 100, 110, the palm cover has been removed and is not shown. Each of the example hands 100, 110 includes fingers 116a-116d and a thumb 118. Replication may be taken advantage of where possible to reduce the number of unique parts. In the embodiment shown in FIG. 1A, the hand is made up of unique plastic parts (identical parts are indicated by identical letters in FIG. 1A); some parts are reused for multiple hand components, for example, the distal links (b) for the index, middle and ring fingers may all use the same part. This can be done where it poses no mechanical drawback and anthropomorphic appearance is not compromised.

[0031] The fingers 116a-116d are driven by the flexion cables 102a-102d (similar to the flexion tendons in the human hand) and bend through an anatomic range of motion at the MCP and PIP joints. One aspect of the example prosthetic hands 100, 110 is that that these flexion cables 102a-102d wrap around a single, space-efficient spool 104, 114 in the palm of the hand 100, 110. Force exerted through the Bowden cable 112 turns the spool to flex the fingers to provide a forceful flexion grasp. For instance, in FIG. 2, the hand 110 is shown having an adaptive grasp of an awkwardly shaped plastic toy 200. A motorized hand would work in essentially the same manner, with a single motor drive spool rotation. Extension is provided with a contoured leaf-spring on the back of each finger that defines how the PIP and MCP flex with a given actuation force. This allows for natural-appearing and consistent movement of the fingers. Compliance is provided by springs in series with the cables of the 4.sup.th and 5.sup.th digits 112a, 116b (e.g., ring and little fingers), which enables them to conform around the object being graspedboth a functional and aesthetic feature. The 2.sup.nd and 3.sup.rd digits 116c, 116d (e.g., index and middle fingers) are not compliant, enabling an effective 3 jaw chuck to be achieved. The thumb 118 is manually rotated by the user and opens fully for a flat palm posture. When the thumb 118 is positioned opposite the index finger 116d, the hand 110 can close in a form of power grasp around an object, with the 4.sup.th and 5.sup.th digits 116a, 116b conforming to the object shape (see FIG. 2). The thumb 118 can be aligned to oppose the index finger 116d to achieve a fine pinch grasp, or placed in its most adducted position to achieve a strong and reliable 3-jaw chuck grasp.

[0032] The hands 100, 110 may be comprised of injection molded plastic components together with metal hinges. Molds are relatively expensive to build; however, once the molds are made, the parts become very inexpensive to manufacture, and the plastic is much stronger. Also the color of a batch of parts can easily be changed, thus the hands 100, 110 can be made in any color to match a large variety of skin tones. Injection-molded plastic can be made very strong with certain techniques, such as incorporating carbon fiber strands in the plastic. The plastic is easily cleaned (compared to rubber or silicone gloves). Since the color of the part is not just surface paint, the color does not scratch off, and any scratches or marks that come with use can be sanded or buffed out, making these hands very durable. In various embodiments, the hand may include additional cosmetic details, such as finger nails and some skin lines to enhance realism, thus no gloves are needed (reducing costs and weight further). Another attribute in the simplicity of the design is that the hand should be relatively easy to service by an ordinary person with some skill in tools and repair (perhaps using an instructional video on the internet such as a YouTube video). If a cable 102a-102d breaks, a new one can be installed; if a finger 116a-116d, 118 breaks, a new finger can be installed. Finger joints are common failure points in prosthetic hands. In a preferred embodiment, stainless steel joints that clip into the plastic fingers may be used to connect segments of the fingers 116a-116d. A hand may also use exact copies of a single metal joint design for all MCP and PIP joints on all fingers, which reduces cost and simplifies the design to facilitate repair.

[0033] The example prosthetic hands can be very light. Even with its additional functions of a wrap-around grasp and moveable thumb, an embodiment weighs about the same as other body-powered hands. In an embodiment, the body-powered hand weighs approximately 321 g with a standard thread bolt for coupling.

[0034] The example hands 100, 11 may be voluntary opening (VO) or voluntary closing (VC). A VC hand has a cosmetically appealing resting state in what appears to be a relaxed hand open positionthus it may have a preferred cosmesis compared to a VO hand that has a default closed position. Also an open hand is still a very useful posture for the user, as it can be used to hold or support objects.

[0035] The hand 110 may have cable-actuated fingers 116a-116d, all driven by a single Bowden cable 112. The hand may comprise a spool 114, as shown in FIG. 3. The example spool 114 has through holes 302, such as the four holes shown in FIG. 3, to attach the flexion cables 102a-102d. The spool 114 may be turned by user-generated force through the Bowden cable 112, winding the flexion cables 102a-102d around the spool 114 to flex the fingers 116a-116d.

[0036] The thumb may be manually positioned and locked into predefined orientations to facilitate up to three separate grasps. The size and shape of the hand may be modeled on the dimensions for the 50.sup.th percentile male, because over 70% of upper limb amputees are male, both in the US and in other countries. A single finger can exert 10 N of force, which is adequate for most activities of daily living. Different size hands can be obtained by varying finger length and palm size. Creating two additional palm sizes, for example, based on the 25.sup.th percentile male and the 25.sup.th percentile female would be reasonable and would cover most of the US amputee population. A variety of finger and palm sizes would enable the building of hands that fit a very wide range of body sizes. Certain fingers could be used for multiple size hands, reducing the overall the number of plastic parts needed for different sized hands, thus three more distal structures and three more proximal structures should result in enough finger combinations to make the two additional hand sizes. Different thumb sizes may be used for each hand size.

[0037] The spool-driven design allows force adjustments to be made by increasing the diameter of the spool 114 where the Bowden cable attaches. FIG. 4 shows a display of a spool-driven prosthetic hand 400, with an enlarged diameter 402 where the Bowden cable 112 is attached to the spool 404 in order to increase the pulling force of the cable 112 on the spool 404, and a smaller diameter 406 in other locations whether the flexion cables 102a-102d are attached to the spool 404. This will allow the user additional grip force if desired, and enable simple modification of the hand design to meet different user needs.

[0038] Power and fine pinch grasps are achievable through a manually positioned thumb 118. A 3-jaw chuck grasp is also shown, at FIG. 5.

[0039] Finger flexion can be driven by the flexion cables 102a-102d attached to each individual finger end. The cables 102a-102d are routed through the fingers 116a-116d such that, when the cable 102a is tensioned, the corresponding finger 116a flexes inward towards the palm of the hand 100, 110, 400. Both the proximal interphalangeal (PIP) joints and the metacarpophalangeal (MCP) joints bend. The cable tension is driven by a spool 114, such as the spool shown at FIG. 3 with the through holes 302 to allow attachment of all of flexion cables 102a-102d. The spool 114 is rotated as the user pulls on the Bowden cable 112, winding the flexion cables 102a-102d around the spool 114.

[0040] The distal interphalangeal joint (DIP) of each finger 116-116d may have a fixed angle of flexion, as shown in FIG. 6. For instance, the fixed angle of flexion may be 20 degrees. Fingers can be set in the frontal plane of the hand and may be splayed for aesthetic reasons. FIG. 6 displays a distal structure of a finger 602 with a fused, flexed DIP at 20 degrees.

[0041] Extending the fingers back to the straight position may be achieved using springs. Flat springs 702 can be seen in FIG. 7, which also displays a cross-section of an individual finger 700 showing the flexion cable 704 routing through a distal spring 706 and the flat spring 702 at a rear side 708 of the finger 700. The flat spring 708 can be inserted into the backhand side of each of the finger 700. The flat spring 70 are bent as the fingers are flexed inward. When the tension in the flexion cable is released, the springs regain their shape and straighten the finger joints. The springs are pre-tensioned such that the MCP joint flexes completely before the PIP joint flexes. This allows for a secure three jaw chuck grip (shown in FIG. 5) and ensures that a wide grasp can be achieved.

[0042] Compliance in each finger may be useful, in order to create a stable hand grasp. This is because the cables that drive the fingers to flex all rotate about the spool equally. Without compliance, when one finger contacts a solid object and stops, the others immediately stop as well. The result would be that only one finger really grasps the object. Including compliance allows the fingers to flex further and allows multiple fingers to grasp an object. Individual finger compliance is achieved by inserting the distal spring 706 into the ends of each of the fingers 700. The flexion cables 704 are each attached to a ferrule 710 at the end of the fingers. As the flexion cables 704 are tensioned and a finger 700 grasps a rigid object, the ferrule 710 compresses the distal spring 706, allowing the cables 704 to be further wound on the spool 104, 114, 404. Final grasp position occurs when one of the distal springs 706 has compressed fully and the cable 704 can no longer be wound by the actuation cable 112. The routing of the flexion cable 704 through the distal spring 706 and ferrule 710 can be seen in FIG. 7.

[0043] Maintaining a grasp requires continuous force exertion in a VC device, which can be tiring or inconvenient. A locking mechanism can be added so that once an object is grasped, the user can lock the device and no longer needs to exert force to maintain the grasp. The grasp can be released by unlocking the mechanism.

[0044] The thumb 118 will be manually positioned and locked into predefined orientations by the user. A simple notch and ball-nosed plunger may be used to hold the thumb 118 securely in position. The thumb is hinged such that the force acting upon the thumb tip is perpendicular to the axis of rotation, thus resisting rotation during use.

[0045] Reliability

[0046] The flexion cables will see a variety of loads and will be sliding across plastic surfaces. Therefore it is important that a very resilient cable be chosen. Spectra 400 Ultra can be used for its high tensile strength (400 lbs or approximately 1760N), its abrasion resistance, and its low coefficient of friction. It is fifteen times stronger than steel by weight and does not corrode. The individual flexion cables should see no more than 160N of force, which is well below the tensile strength of the Spectra cable. Teflon liners can be used to mitigate any impact of abrasion or friction.

[0047] FIG. 8 displays an individual finger 800, showing steel joints 802 at the MCP and PIP locations. The finger joints in this design will see moderate loads with relatively small rotation angles and speeds. The joints 802 may be machined into high strength plastic fingers and hand. An additional low cost option is to use steel bushings that can be inserted into the joint and make it more resilient. These inserts can be extended as far as needed into the finger parts for added strength. The hinge pins can be removable so that fingers can easily be removed and replaced if necessary. The steel inserts can be pressed into the finger parts for quick and reliable manufacturing. The same steel hinge on all finger joints 802 may be used, to keep the hand simple and low cost.

[0048] Resistance to backhand impact can be achieved through compliance. Many prosthetic hand designs use linkages to flex individual fingers. Those designs are susceptible to incidental impacts from the backhand side. During such an impact, the rigidity of finger linkages puts a high load on hinges and may cause damage. The compliance of the cable-driven finger design allows for resilience against backhand side impacts, as the fingers would merely close into the palm without damaging any of the components. The springs then straighten the fingers out once the force is removed.

[0049] The flat springs that straighten the fingers will see many load cycles. High strength, constant force, stainless steel springs can be used to resist wear. They are rated for 4,000 cycles, but if these are determined to be insufficient, higher cycle-life springs are available.

[0050] The compression springs that are used to allow for compliance in the individual fingers will only be exposed to compressive forces and should not yield.

[0051] The material that will make up the vast majority of the prosthetic hand will be a high strength plastic, which, generally speaking, is a low cost material. Injection molding allows for more diverse material options at a low per-part cost. Glass-filled nylon, for example, is a high strength option that can be manufactured in an injection mold.

[0052] Using injection molded plastics for manufacturing will allow us to have the higher quality plastic at a cost that is even lower than the original in house printed parts. We estimate that plastic fabrication method would be below $100. Further cost savings can be found in purchasing the other parts in high quantities for an expected cost per hand of below $100, for example the metal hinges. Once the initial cost of the injection molds has been met, the individual part cost will be extremely low. Either aluminum or steel molds may be employed.

[0053] Cosmetic gloves contribute significantly to the overall weight of prostheses, and can reduce performance, so disclosed example prosthetic hands may be designed for use without a glove.

[0054] While the present method and/or system has been described with reference to certain implementations, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from its scope. For example, systems, blocks, and/or other components of disclosed examples may be combined, divided, re-arranged, and/or otherwise modified. Therefore, the present method and/or system are not limited to the particular implementations disclosed. Instead, the present methods, apparatus, and/or systems include all implementations falling within the scope of the appended claims, both literally and under the doctrine of equivalents.