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

Abstract

Partial hand loss accounts for the overwhelming majority of upper limb deficiencies. Despite this, individuals with partial hand loss have a limited number of prosthetic options at their disposal. Existing externally powered devices typically house both motor and gear transmission in the proximal phalanx, which provides function at the expense of anthropomorphism. We present a novel design for an externally powered finger prosthesis with a custom gear transmission that is capable of higher intermittent torques compared to commercial gearheads of equivalent volume. We manufacture a fully functional transmission using a high-strength maraging steel alloy and direct laser metal sintering. The transmission consists of multiple planetary and spur gear stages arranged in a stackable (or laminar) configuration and accommodates joint movement at the proximal interphalangeal joint. The powered finger is equivalent in size to a 50th percentile female index finger and is capable of generating pinch forces comparable to those of commercial powered fingers at flexion speeds that exceed those of existing devices. While there are several practical and functional improvements for future iterations, our design represents a viable option for a powered finger capable of accommodating a wide range of individuals with partial hand loss.

Design of a High-Speed Prosthetic Finger Driven by Peano-HASEL Actuators

“…A kinematic system of an eight-bar linkage, which was derived by Murali et al ( 2019 ) was adapted in this work to suit the four-bar linkage system used in the Bebionic v2 Prosthetic Hand (RSL Steeper). Figure 4 shows a crank-rocker system that is composed of binary linkages r 1 , d 1 , l 1 , r 2 , d 2 , d 3 (Norton, 2000 ).…”

“… Schematic describing the prosthetic finger (based off of commercially available prosthetic hand) represented by a crank-rocker four-bar linkage as used in the kinematic model (Murali et al, 2019 ). The proximal and distal phalanges are fused, causing the distal interphalangeal (DIP) joint to be fixed, while the metacarpal phalangeal (MCP) and proximal interphalangeal (PIP) joints are free to rotate.…”

“…First, link length l 1 is obtained based on known initial conditions using Equation 1 (Murali et al, 2019 ).…”

“…ϕ 1 , ϕ 2 , ϕ 3 , ϕ 4 are fixed, meaning they do not change value throughout flexion. The full kinematic model was developed using several equations derived by Norton (2000) and, in context of prosthetic finger design, in Murali et al (2019). Figure 5 details how various parameters of interest behave over the MCP joint (θ 1 ) flexion range which is constrained from 0 to 90 • .…”

“…The following derivation explains how these parameters of interest were determined. First, link length l 1 is obtained based on known initial conditions using Equation 1 (Murali et al, 2019).…”