A miniaturized polymer-based bimorph actuator with self-sensing capability

Soft actuators have recently attracted great attention in the fields of soft robots, artificial muscles, and biomimetic devices. As the size is reduced to sub-centimeter scale, most soft actuators only possess actuation capabilities without integrated sensing functions, which limits the effectiveness of device operation and control. In this study, we present a miniaturized polymer-based bimorph actuator (MPBA) that is capable of simultaneously performing the functions of actuation and sensing with two input electric terminals. The proposed device has an electrothermal bilayer structure that consists of a silicone film and a polymer-based conductive composite film, and it can be realized with a standard soft-lithography technique and a two-step vacuum filtration process. By optimizing the mass percentages of conductive fillers, the conductive composite film is capable of serving as an electrothermal heater for actuating the device, as well as serving as a piezoresistive strain gauge for detecting the motion of the device. With this self-sensing capability, closed-loop control of this MPBA can be easily achieved. The measured relationships between structure deformation and resistance change, which are stable and accurate, were employed to demonstrate the MPBA capabilities of displacement tracking and touch detection. Furthermore, a two-finger microgripper consisting of two MPBAs was implemented, and a demonstration of object grasping and moving was presented.