Case study of a rapid prototyping method for optimizing soft gripper structures with integrated piezoresistive sensors

Closed-loop control systems and monitoring the activities of soft robots in the natural environment require sensing elements in soft actuator modules. In this study, additive manufacturing is used for sensorized soft actuator modules to investigate the influence of the Shore hardness and design aspects of an open-source tendon-based gripper structure, in a time-efficient way. Additionally, the placement of the piezoresistive sensing element (tension or compression side on the bending soft gripper) was investigated. A user-friendly method, based on thermoplastic material extrusion, has been explored to improve the future design optimization in of active soft robotic structures successfully. A higher Shore hardness resulted in a higher total deflection and a higher force to bend the gripper structure. By increasing the geometrical stiffness of the gripper printed with low Shore hardness, the total deflection was increased, but the force needed to activate the movement was higher in comparison to high Shore hardness and low geometrical stiffness. Moreover, the sensing element on the substrate of higher Shore hardness, leads to low drift, monotonic response, with good sensitivity, independent of the sampling rate. The gripper of higher Shore hardness had a larger functional range, being capable of gripping small and larger objects.面向自然环境下软体机器人（soft robot）的闭环控制系统（closed-loop control systems）搭建与行为监测，需在软体驱动模块（soft actuator modules）中集成传感元件。本研究采用增材制造（additive manufacturing）技术制备集成传感功能的软体驱动模块，以高效省时的方式，探究邵氏硬度（Shore hardness）与开源绳驱式机械手爪结构（open-source tendon-based gripper structure）的设计参数对其性能的影响。此外，本研究还探究了压阻式传感元件（piezoresistive sensing element）在弯折式软体机械手爪受拉侧与受压侧的布置方案。本研究同时探索了一种基于热塑性材料挤出成型（thermoplastic material extrusion）的便捷方法，以成功助力未来主动式软体机器人结构（active soft robotic structures）的设计优化工作。研究结果表明，邵氏硬度越高，机械手爪的总变形量越大，弯折该结构所需的作用力也越高。对于采用低邵氏硬度材料打印的机械手爪，提升其几何刚度（geometrical stiffness）可增大总变形量，但相较于高邵氏硬度且低几何刚度的结构，其触发运动所需的作用力更高。此外，搭载高邵氏硬度基材的传感元件，输出漂移低、响应呈单调特性且灵敏度优异，且不受采样速率（sampling rate）的影响。高邵氏硬度的机械手爪拥有更宽的作业量程，能够抓取尺寸各异的小型与大型物体。