[Paper Review] Design, Implementation and Evaluation of a Variable Stiffness Transradial Hand Prosthesis

Elif Hocaoğlu, Volkan Patoğlu|arXiv (Cornell University)|Oct 28, 2019

Muscle activation and electromyography studies4 citations

TL;DR

This paper presents a low-cost, customizable transradial hand prosthesis with variable stiffness actuation (VSA) using Bowden cable-driven antagonistic tendons and nonlinear springs, enabling simultaneous control of position and stiffness. Experimental evaluation with sEMG-based tele-impedance control demonstrated that users could successfully grasp diverse objects with natural dexterity, achieving a mean adaptation time of 3.2 minutes and average grasp/release times of 1.22 and 0.82 seconds, respectively.

ABSTRACT

We present the design, implementation, and experimental evaluation of a low-cost, customizable, easy-to-use transradial hand prosthesis capable of adapting its compliance. Variable stiffness actuation (VSA) of the prosthesis is based on antagonistically arranged tendons coupled to nonlinear springs driven through a Bowden cable-based power transmission. Bowden cable-based antagonistic VSA can, not only regulate the stiffness and the position of the prosthetic hand, but also enables a light-weight and low-cost design, by opportunistic placement of motors, batteries and controllers on any convenient location on the human body, while nonlinear springs are conveniently integrated inside the forearm. The transradial hand prosthesis also features tendon driven underactuated compliant fingers that allow natural adaption of the hand shape to wrap around a wide variety of object geometries, while the modulation of the stiffness of their drive tendons enables the prosthesis to perform various tasks with high dexterity. The compliant fingers of the prosthesis add inherent robustness and flexibility, even under impacts. The control of the variable stiffness transradial hand prosthesis is achieved by an sEMG based natural human-machine interface.

Motivation & Objective

• To develop a low-cost, customizable, and easy-to-use transradial hand prosthesis with variable stiffness actuation (VSA) for improved functional adaptability.
• To address the high abandonment rate of current myoelectric prostheses by simplifying design and control while enhancing dexterity and robustness.
• To enable natural human-machine interaction through a sEMG-based tele-impedance control interface that modulates stiffness based on user intent.
• To integrate underactuated, compliant fingers that naturally conform to various object shapes and withstand impacts.
• To validate the prosthesis in real-world tasks with human volunteers, focusing on usability, response time, and robustness.

Proposed method

• Employed Bowden cable-based antagonistic VSA with nonlinear springs integrated into the forearm to regulate stiffness and position without centralized actuators.
• Used tendon-driven underactuated fingers made of silicon rubber and ABS to enable passive, compliant adaptation to object geometries.
• Implemented a sEMG-based tele-impedance controller using surface EMG signals from the upper arm, chest, and shoulder to infer user intent and adjust stiffness in real time.
• Placed motors, batteries, and controllers on the body (e.g., upper arm or torso) to reduce hand weight and improve ergonomics.
• Designed the system for modularity and customization, allowing for easy integration of a functional thumb or prosthetic glove for aesthetic realism.
• Conducted user studies with 16 diverse objects to evaluate grasp performance, response time, and impact resilience.

Experimental results

Research questions

• RQ1 Can a low-cost, customizable transradial hand prosthesis with VSA achieve sufficient dexterity for everyday manipulation tasks?
• RQ2 Can Bowden cable-based antagonistic VSA enable effective simultaneous control of position and stiffness while maintaining lightweight and low-cost design?
• RQ3 Can sEMG-based tele-impedance control allow intuitive, real-time stiffness modulation that matches user intent and task requirements?
• RQ4 How quickly can users adapt to and reliably perform grasping tasks with this prosthesis in unstructured environments?
• RQ5 Does the integration of compliant, underactuated fingers enhance robustness and natural object interaction under impact or uncertainty?

Key findings

• Volunteers adapted to the prosthesis and successfully completed manipulation tasks in an average of 3.2 ± 1.3 minutes, indicating low training burden.
• Average grasp and release times were 1.218 ± 0.564 seconds and 0.819 ± 0.48 seconds, respectively, demonstrating performance comparable to commercial devices.
• The compliant fingers with silicon rubber and ABS materials showed high robustness, sustaining no damage after repeated impacts during user testing.
• The sEMG-based tele-impedance interface enabled effective stiffness modulation, allowing users to safely grasp objects of varying compliance and geometry.
• The system’s modular design allowed for easy integration of future enhancements, such as a functional thumb or prosthetic glove, without compromising core functionality.
• User feedback from post-trial interviews confirmed the adequacy and usability of the passive support for the fingers, with no complaints about functionality.