Design and experimental study of a passive power-source-free stiffness-self-adjustable mechanism

Yuwang Liu,Jinguo Liu,Dongqi Wang,Guangbo Hao,Shangkui Yang

doi:10.1007/s11465-020-0604-4

Abstract

Passive variable stiffness joints have unique advantages over active variable stiffness joints and are currently eliciting increased attention. Existing passive variable stiffness joints rely mainly on sensors and special control algorithms, resulting in a bandwidth-limited response speed of the joint. We propose a new passive power-source-free stiffness-self-adjustable mechanism that can be used as the elbow joint of a robot arm. The new mechanism does not require special stiffness regulating motors or sensors and can realize large-range self-adaptive adjustment of stiffness in a purely mechanical manner. The variable stiffness mechanism can automatically adjust joint stiffness in accordance with the magnitude of the payload, and this adjustment is a successful imitation of the stiffness adjustment characteristics of the human elbow. The response speed is high because sensors and control algorithms are not needed. The variable stiffness principle is explained, and the design of the variable stiffness mechanism is analyzed. A prototype is fabricated, and the associated hardware is set up to validate the analytical stiffness model and design experimentally.

Highlights

Even in traditional industrial production, robots are no longer limited to structured environments; they have gradually become free of closed operating spaces by cooperating with humans and working with them in unstructured environments
When directly used in cooperative and unstructured environments, such robots can collide with the surrounding objects and people; the robot body may become damaged by the strong collision, and the surrounding users may suffer from fatal injuries [1]
According to the previous design and analysis, the greater the external force applied at the end of the arm is, the greater the distance the external force point moves and the smaller the deflection angle of the joint is

Summary

Introduction

Even in traditional industrial production, robots are no longer limited to structured environments; they have gradually become free of closed operating spaces by cooperating with humans and working with them in unstructured environments. The German Aerospace Center proposed the concept of active variable stiffness and successfully applied it to a KUKA robot [2]. This method uses an algorithm to simulate an elastic element that does not exist in the joint, making the joint actively flexible. The disadvantages are high energy consumption, severe impacts, and inability to store energy effectively. This method requires a complex sensor system to detect external information, and the real-time response capability of joint stiffness variation is limited due to the constraint in system bandwidth. The slow response leads to a high probability of non-compliant cooperation and collisions in unstructured environments

Methods

Results

Conclusion