Design and Assessment of a High Speed Low Torque Joint Transmission for Use in a Partial Hand, Powered Finger Prosthesis

Abstract

This paper presents the design and assessment results of two types of miniature, high speed, low torque transmissions to be used in a partial hand, powered finger prosthesis. Transmissions enabling torque transfer across varied flexion angles of a finger joint can allow placement of a motor and a gearbox in adjacent phalanges, significantly decreasing space requirements for partial hand prostheses. Bevel gear-based and cable-based transmission designs for a variety of flexion angles are implemented and tested in comparison with a direct cascaded motor and gearbox (benchmark) configuration. The miter-gear transmission provided consistent operation at tested flexion angles, but demonstrated reduced efficiency in comparison with the benchmark configuration. Cable transmission matched efficiency of the benchmark configuration at low flexion angles but lacked mechanical durability at high loads and flexion angles. The designs presented complementary strengths and weaknesses, with the miter-gear design demonstrating better overall mechanical reliability, while the cable transmission excelled in secondary characteristics.

Design and evaluation of a distally actuated powered finger prosthesis with self-contained transmission for individuals with partial hand loss

“…21 Both of these devices house the entire power transmission in the proximal phalanx, which limits their minimum lengths and the degree of anthropometry, despite the Vincent finger and iLimb Digits having reasonable overall lengths. 34,35 The transmission, summarized in Table 1, begins with a bevel stage adapted from Filatov et al 20 at the PIP joint. The bevel stage reorients the rotation axes for the remainder of the transmission to be parallel to the IP joints.…”

“…A major constraint in the design of powered finger prostheses is the limited volume available for housing the various actuation, power, and control components. 20 The DC motor and gearhead occupy a large portion of this available space and require an elongated proximal phalanx when fully contained within an anatomical finger. Several existing partial and full hand prostheses are 2-DOF mechanisms with a feature on the distal finger segment that provide the appearance of the distal interphalangeal (DIP) joint.…”

“…Esthetic considerations are important since it is thought that an anatomically similar artificial limb leads to greater ownership and acceptance of the device, as well as reduced phantom limb pains. 22 Filatov et al 20 explored the possibility of separating the motor and gearhead across an interphalangeal (IP) joint to potentially improve both anthropometry and minimum overall size. The IP transmissions from Filatov et al 20 showed promise for further miniaturization and integration into a powered finger.…”

“…We utilize direct laser metal sintering (DMLS) to fabricate a functional gear transmission and directly integrate it into the medial phalanx of our finger. The transmission connects to a DC motor in the proximal phalanx using elements from Filatov et al 20 These elements also allow for torque transmission across the PIP joint. Our design allows for a powered finger equivalent in size to a 50th percentile female index finger with potential for further size reductions that will improve its accessibility for amputee populations and enable the placement of its MCP joint closer to the anatomical MCP of the user.…”

“…22 Filatov et al 20 explored the possibility of separating the motor and gearhead across an interphalangeal (IP) joint to potentially improve both anthropometry and minimum overall size. The IP transmissions from Filatov et al 20 showed promise for further miniaturization and integration into a powered finger. In addition, recent advances in additive manufacturing (AM) processes for plastic and metal are enabling the development of robust production-grade parts for a variety of industries.…”