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 & tables
Fig. 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.
Fig. 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.
Fig. 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.
Fig. 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.
Fig. 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.
Fig. 6: Impact of splay adjustment and wrist motion on user behavior and compensatory movements. (a) Average splay levels selected by users across experimental conditions, showing preference for increased finger spacing when wrist motion is restricted (level 1 = parallel fingers, level 5 = full spacing). Error bars represent standard error across eleven users. (b) Elbow and wrist displacement rate during keyboard typing and piano playing tasks across three conditions: fixed parallel fingers (no splay, no wrist), adjustable finger spacing (with splay, no wrist), and full control (with splay and wrist). Results demonstrate progressive reduction in compensatory movements, with keyboard typing showing greater improvement than piano playing when both splay adjustment and wrist motion are available. Displacement rate is computed as distance traveled divided by key-pressing motion duration, averaged across all users.
Fig. 7: Representative example of a user operating the DigiArm during keyboard typing. The user starts with an open hand (1) and flexes the index finger to instruct the robotic hand to mimic the action and presses the keyboard (2). Then, the user lifts and extends the finger, followed by performing a wrist instruction to move the hand to the left (3 and 4). Finally, the user flexes the middle finger to press the keyboard once again and extend the finger back to its original position (5 and 6).
Fig. 8: Grasping versatility for various everyday objects. The examples show successful grip adaptation for cylindrical objects (electric screwdriver, beverage can), a glass cup, a pen, a banana, and a tomato (spherical object). The hand accommodates different geometries in precision and power grips, maintaining a stable hold across varying materials, including metal, glass, and foods.
Fig. 9: Mechanical analysis diagrams. (Left) Wrist torque analysis for ulnar/radial deviation and pronation/supination. (Right) Force analysis for finger and thumb actuation.
All authors are with the School of Engineering Mathematics and Technology, and Bristol Robotics Laboratory, University of Bristol, Bristol, BS8 1UB, U.K.
Department of Mechanical Engineering, Zhejiang University, Hangzhou, China. · Department of Mechanical Engineering, National University of Singapore, Singapore.