Closed-Loop Control Through Self-Sensing of a Joule-Heated Twisted and Coiled Polymer Muscle

Abstract

The twisted and coiled polymer muscle has two major benefits: low weight and low cost. Therefore, this new type of actuator is increasingly used in robotic applications where these benefits are relevant. Closed-loop control of these muscles, however, requires additional sensors that add weight and cost, negating the muscles' intrinsic benefits. Self-sensing enables feedback without added sensors. In this paper, we investigate the feasibility of using selfsensing in closed-loop control of a Joule-heated muscle. We use a hardware module capable of driving the muscle, and simultaneously providing sensor measurements based on inductance. A mathematical model relates the measurements to the deflection. In combination with a simple force model, we can estimate both deflection and force, and control either of them. For a muscle that operates within deflections of [10,30] mm and forces of [0.32,0.51] N, our self-sensing method exhibited a 95% confidence interval of 2.14 mm around a mean estimation error of-0.27 mm and 29.0 mN around a mean estimation error of 7.5 mN, for the estimation of respectively deflection and force. We conclude that self-sensing in closed-loop control of Jouleheated twisted and coiled polymer muscles is feasible and may facilitate further deployment of such actuators in applications where low cost and weight are critical.

Recent Advances in Perceptive Intelligence for Soft Robotics

“…Twisted self-sensing is usually based on twisted and coiled actuators or artificial muscles using Joule heating for actuation and sensing. The actuation principle is represented by twisted and coiled polymer muscles (TCPMs) [77,78] and twisted string actuators (TSAs). [79] They are known for their low weight, low cost, high-energy efficiency, and large linear strain and stress outputs.…”

“…[ 80 ] The principle of twisted self‐sensing is precisely to create twist actuators using conductive functional materials and to indirectly measure twists by detecting the relationship between the electrical parameters of the twist actuator construction and the deflection. For example, Ding et al [ 78 ] reported a facile preparation method for self‐sensing magnetically anisotropic films, in which magnetic and conductive materials can be predesigned. In this method, magnetically active films of various shapes with complex chain‐like oriented structures, are used to achieve advanced driving functions.…”

“…e) Self-sensing magnetically anisotropic films. Reproduced with permission [78]. Copyright 2021, American Chemical Society (ACS).…”

Realization of a Simultaneous Position-Stiffness Controllable Antagonistic Joint Driven by Twisted-Coiled Polymer Actuators Using Model Predictive Control

“…The behavior of the actuator can be predicted using both phenomenal models and physics-based models that have been proposed [5], [20]- [23]. Considering its high non-linearity, various position controllers [21], [24]- [26] and force controllers [27] have been developed for this type of actuator. Thanks to those achievements, soft SCP actuators have become a reliable actuation method for many bionic applications such as rehabilitation and prosthesis devices [9]- [11], [13].…”

Artificial stepper tensile actuator using Joule-heated twisted and coiled polymer muscles

“…Instead electrical impedance of the coil that is dependent to coil length is used as a displacement sensor. In another work Weijde et al completed the self-sensing method using closed-loop control of Joule-Heated TCPM [11]. They proposed a closed loop system that could control displacement and force with 95 % confidence.…”