Long Shape Memory Alloy Tendon-based Soft Robotic Actuators and Implementation as a Soft Gripper

Ji-Hyeong Lee,Hugo Rodrigue,Yoon Seop Chung

doi:10.1038/s41598-019-47794-1

Abstract

Shape memory alloy (SMA) wire-based soft actuators have had their performance limited by the small stroke of the SMA wire embedded within the polymeric matrix. This intrinsically links the bending angle and bending force in a way that made SMA-based soft grippers have relatively poor performance versus other types of soft actuators. In this work, the use of free-sliding SMA wires as tendons for soft actuation is presented that enables large increases in the bending angle and bending force of the actuator by decoupling the length of the matrix and the length of the SMA wires while also allowing for the compact packaging of the driving SMA wires. Bending angles of 400° and tip forces of 0.89 N were achieved by the actuators in this work using a tendon length up to 350 mm. The tendons were integrated as a compact module using bearings that enables the actuator to easily be implemented in various soft gripper configurations. Three fingers were used either in an antagonistic configuration or in a triangular configuration and the gripper was shown to be capable of gripping a wide range of objects weighing up to 1.5 kg and was easily installed on a robotic arm. The maximum pulling force of the gripper was measured to be 30 N.

Highlights

Soft robots present several advantages over their traditional counterparts in that they are compliant which allows them to interact adaptively and safely with their environment and with humans without requiring complex and costly control systems that can require sensors or large computational power[1,2,3]
We present the use of Shape memory alloy (SMA) wires themselves as free-sliding tendons to drive a polymeric matrix which allows the SMA length and the design of the polymeric matrix to be decoupled while allowing the compact packaging of the driving SMA wires through mechanical systems
The length of the SMA wire embedded in the actuator is approximately one meter such that the maximum tendon length is 400 mm since it functions as two wires in parallel

Summary

Introduction

Soft robots present several advantages over their traditional counterparts in that they are compliant which allows them to interact adaptively and safely with their environment and with humans without requiring complex and costly control systems that can require sensors or large computational power[1,2,3]. We present the use of SMA wires themselves as free-sliding tendons to drive a polymeric matrix which allows the SMA length and the design of the polymeric matrix to be decoupled while allowing the compact packaging of the driving SMA wires through mechanical systems This allows greater control for designing actuators based on the required bending angle and force characteristics. The effect of the length of the tendon on the bending angle is presented and compared with a quasi-static numerical model, and the effect of the tendon length on the tip force is evaluated This SMA wire tendon concept is applied to a compact and modular module using pulleys to compactly package the SMA wire which was implemented in a soft gripper that can be mounted to any robotic arm and used to grasp a wide range of objects. The gripper was tested with a wide range of object shapes and weights, tested using a tensile testing machine, and mounted on a robotic arm

Methods

Results

Discussion

Conclusion