Introducing V-Soft Pro: a Modular Platform for a Transhumeral Prosthesis with Controllable Stiffness

TL;DR

The paper introduces V-Soft Pro, a modular transhumeral prosthesis platform that uses Variable Stiffness Actuators to replicate controllable joint impedance. It details three submodules—VS-Elbow, VS-Wrist, and a SoftHand Pro/SoftHand 2 hand—integrated into two configurable configurations to balance degrees of freedom and stiffness control. Preliminary lab demonstrations show coordinated multi-joint motion and task-adaptive stiffness, suggesting enhanced safety and versatility in unstructured environments. The work highlights the potential impact on user experience and daily functioning while outlining the need for clinical trials and advanced biosignal-based control to realize practical benefits.

Abstract

Current upper limb prostheses aim to enhance user independence in daily activities by incorporating basic motor functions. However, they fall short of replicating the natural movement and interaction capabilities of the human arm. In contrast, human limbs leverage intrinsic compliance and actively modulate joint stiffness, enabling adaptive responses to varying tasks, impact absorption, and efficient energy transfer during dynamic actions. Inspired by this adaptability, we developed a transhumeral prosthesis with Variable Stiffness Actuators (VSAs) to replicate the controllable compliance found in biological joints. The proposed prosthesis features a modular design, allowing customization for different residual limb shapes and accommodating a range of independent control signals derived from users' biological cues. Integrated elastic elements passively support more natural movements, facilitate safe interactions with the environment, and adapt to diverse task requirements. This paper presents a comprehensive overview of the platform and its functionalities, highlighting its potential applications in the field of prosthetics.

Figures (3)

• Figure 1: Two configurations of the V-Soft Pro transhumeral prosthesis, customized to meet diverse user needs. Panel (a) illustrates a V-Soft Pro configuration designed to achieve a human-like weight distribution for proximal transhumeral amputations. Panel (b) shows a version of the V-Soft Pro platform adapted for users with longer residual limbs.
• Figure 2: The V-Soft Pro platform. The V-Soft Pro transhumeral prosthesis supports a modular design that can be customized to meet the diverse needs of end-users, including residual limb morphology, required dexterity, comfort with device weight, and available control inputs.
• Figure 3: Functional demonstration of two configurations of the V-Soft Pro system. Sequence (a) shows the V-SP platform performing active, simultaneous motion across all its submodules. Sequence (b) demonstrates the benefits of variable stiffness actuation within the transhumeral prosthesis. In the first scene, the prosthesis uses low joint stiffness to navigate an unstructured environment, allowing gentle contact with nearby objects without knocking them over. It then performs a tripod grasp (second scene) followed by wrist pronation. With low elbow stiffness, the prosthesis adapts to external forces without resisting (third scene). However, the V-SP system can increase its stiffness to counter external disturbances (fourth scene) and perform precision tasks (fifth scene).