Abstract
Soft robots and devices exploit deformable materials that are capable of changes in shape to allow conformable physical contact for controlled manipulation. While the use of embedded sensors in soft actuation systems is gaining increasing interest, there are limited examples where the body of the actuator or robot is able to act as the sensing element. In addition, the conventional feedforward control method is widely used for the design of a controller, resulting in imprecise position control from a sensory input. In this work, we fabricate a soft self-sensing finger actuator using flexible carbon fibre-based piezoresistive composites to achieve an inherent sensing functionality and design a dual-closed-loop control system for precise actuator position control. The resistance change of the actuator body was used to monitor deformation and fed back to the motion controller. The experimental and simulated results demonstrated the effectiveness, robustness and good controllability of the soft finger actuator. Our work explores the emerging influence of inherently piezoresistive soft actuators to address the challenges of self-sensing, actuation and control, which can benefit the design of next-generation soft robots.
Highlights
Soft robots are defined as “soft systems” that use materials with elastic moduli comparable to soft biological materials (104 –109 Pa) and are capable of autonomous behaviour
Two main challenges have been found in fabricating piezoresistive self-sensing actuators in our research [8]: (i) The addition of a filler should not reduce the compliance of the soft actuator and affect its performance. (ii) The composite must remain conductive and manufacturable to form soft actuators
The finger consists of two layers; (i) an upper pure silicone teeth layer fabricated using pure silicone to allow maximum mechanical flexibility and deformation and (ii) a lower carbon fibre-rich composite layer fabricated using 15 vol% carbon fibres mixed with silicone to create a piezoresistive layer to provides an inherent sensing capability to the finger
Summary
Soft robots are defined as “soft systems” that use materials with elastic moduli comparable to soft biological materials (104 –109 Pa) and are capable of autonomous behaviour. The fabrication process of this form of multi-functional sensing element is relatively complex, and the application is more sensor-based, such as the creation of an e-skin which can be integrated onto the surface of soft actuators, but is challenging to use and to manufacture. 3D-printing technology has been successfully used for piezoresistive sensor fabrication, Liu et al presented a fully printed accelerometer with a piezoresistive carbon paste-based strain gauge printed on its surface, which can be manufactured at low cost and with high efficiency. The combination of inherent sensing and dual feedback control can significantly benefit the design of the actuator system, since any disturbances introduced by the external sensor characteristics and measurement can be eliminated, which could otherwise lead to instability of controller This new approach, provides a solution to the current sensing and instrumentation challenges we are facing when design untethered soft actuators or robots
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