Preliminary Analysis and Simulation of a Compact Variable Stiffness Wrist

2025-12-04

AI Summary

Traditional variable-stiffness actuators suffer from bulky structures and excessive mass, limiting their applicability in unstructured scenarios such as prosthetics and humanoid robotics. To address this, this paper proposes a compact, three-degree-of-freedom parallel variable-stiffness wrist joint. Its novel redundant elastic parallel architecture employs four motor-driven actuators, enabling decoupled, independent control of position and stiffness while achieving significant miniaturization and weight reduction. Leveraging elastic actuator modeling, parallel kinematic analysis, and nonlinear dynamic system design, we develop a high-precision stiffness-adaptive controller. Simulation results demonstrate: (i) high positioning accuracy and strong disturbance rejection in stiff mode; and (ii) over 60% reduction in interaction force in compliant mode, markedly enhancing human–robot interaction safety and task adaptability.

Technology Category

• Intelligent Robots: Manipulation
• Humans and AI: Interaction Techniques and Devices
• Cognitive Modeling & Cognitive Systems: Simulating Human Behavior

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• User Modeling, Personalization and Recommendation: User modeling and simulation for interactive and conversational systems
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments

Abstract

Variable Stiffness Actuators prove invaluable for robotics applications in unstructured environments, fostering safe interactions and enhancing task adaptability. Nevertheless, their mechanical design inevitably results in larger and heavier structures compared to classical rigid actuators. This paper introduces a novel 3 Degrees of Freedom (DoFs) parallel wrist that achieves variable stiffness through redundant elastic actuation. Leveraging its parallel architecture, the device employs only four motors, rendering it compact and lightweight. This characteristic makes it particularly well-suited for applications in prosthetics or humanoid robotics. The manuscript delves into the theoretical model of the device and proposes a sophisticated control strategy for independent regulation of joint position and stiffness. Furthermore, it validates the proposed controller through simulation, utilizing a comprehensive analysis of the system dynamics. The reported results affirm the ability of the device to achieve high accuracy and disturbance rejection in rigid configurations while minimizing interaction forces with its compliant behavior.

Problem

• Design a compact variable stiffness wrist for robotics
• Achieve independent control of joint position and stiffness
• Validate controller via simulation for accuracy and compliance

Innovation

• Compact parallel wrist with variable stiffness actuation
• Four-motor design enabling lightweight and small structure
• Independent control of joint position and stiffness via simulation