DigiArm: An Anthropomorphic 3D-Printed Prosthetic Hand with Enhanced Dexterity for Typing Tasks

TL;DR

A low-cost, lightweight, 3D-printed robotic prosthetic hand, specifically engineered for enhanced dexterity with electronic devices such as a computer keyboard or piano, as well as general object manipulation is presented.

Abstract

Despite recent advancements, existing prosthetic limbs are unable to replicate the dexterity and intuitive control of the human hand. Current control systems for prosthetic hands are often limited to grasping, and commercial prosthetic hands lack the precision needed for dexterous manipulation or applications that require fine finger motions. Thus, there is a critical need for accessible and replicable prosthetic designs that enable individuals to interact with electronic devices and perform precise finger pressing, such as keyboard typing or piano playing, while preserving current prosthetic capabilities. This paper presents a low-cost, lightweight, 3D-printed robotic prosthetic hand, specifically engineered for enhanced dexterity with electronic devices such as a computer keyboard or piano, as well as general object manipulation. The robotic hand features a mechanism to adjust finger abduction/adduction spacing, a 2-D wrist with the inclusion of controlled ulnar/radial deviation optimized for typing, and control of independent finger pressing. We conducted a study to demonstrate how participants can use the robotic hand to perform keyboard typing and piano playing in real time, with different levels of finger and wrist motion. This supports the notion that our proposed design can allow for the execution of key typing motions more effectively than before, aiming to enhance the functionality of prosthetic hands.

Figures (9)

• Figure 1: The developed robotic prosthetic hand. The system features independent finger control, adjustable finger spacing, and a 2D wrist optimized for keyboard typing and piano playing applications. All components are 3D-printed with affordable electronics and actuators.
• Figure 2: Technical snapshots of the main mechanisms of the DigiArm, with each block demonstrating the mechanism in two different states. (C1) An internal view of the 2D-wrist mechanism: ulnar-radial deviation is powered by the top motor, and pronation-supination is powered by the bottom motor. (C2) Assembled finger module showing the motor base housing, bevel gear system, and cable-driven actuation mechanism connecting to the distal phalanx. (C3) The "splay" mechanism for adjustable finger spacing showing the finger spacing while closed and opened. (C4) The Thumb module illustrating the integrated motor design and bidirectional rotational motion from extension to flexion.
• Figure 3: DigiArm control system architecture. The ESP32-based communication module receives sensor commands via WiFi and transmits them to the Teensy 4.1, which performs real-time closed-loop control of seven motors using PWM signals and SPI-based communication for encoder updates.
• Figure 4: Force measurement experiment. (a) Our experimental setup showing a finger module positioned above a 6-axis force sensor for quantifying key-press forces. (b) Force output as a function of input voltage, displaying mean with standard deviation (green) for the average force during the pressing duration and maximum values (blue) during contact events, with a maximum output of 3.6N at 6V input.
• Figure 5: Finger usage patterns during key-pressing tasks. (a) Piano key selection heatmap showing correspondence patterns between finger choice and key position, with a slight preference for thumb and finger gestures. (b) Keyboard typing heatmap revealing index finger dominance across most keys, with an interesting shift towards outer fingers (middle, ring, little) correlated with rightmost key positions, and clear thumb specialization for the space key. Results demonstrate consistent finger selection strategies across subjects during prosthetic hand operation.