Wirelessly-Controlled Untethered Piezoelectric Planar Soft Robot Capable of Bidirectional Crawling and Rotation

TL;DR

This paper tackles the challenge of untethered control for electrostatic soft robots by integrating on-board high-voltage electronics and wireless control into a five-actuator piezoelectric planar robot with a scalable fabrication approach. The device, powered by 3.7-V batteries and a flexible HV electronics stack, demonstrates frequency-dependent locomotion and turning driven by the interaction of mass distribution and vibrational modes, achieving forward/backward crawling up to ~0.6 cm/s and in-place rotation up to ~1.1 deg/s (and up to 6 cm/s with payload optimization). The mechanism is validated through experiments with a bare robot to isolate weight-distribution effects and through simulations of traveling waves, highlighting the critical role of nonuniform mass in motion control. The work advances practical untethered soft robotics by showing a compact, wireless platform capable of complex motions, with clear directions for quantitative modeling and optimization.

Abstract

Electrostatic actuators provide a promising approach to creating soft robotic sheets, due to their flexible form factor, modular integration, and fast response speed. However, their control requires kilo-Volt signals and understanding of complex dynamics resulting from force interactions by on-board and environmental effects. In this work, we demonstrate an untethered planar five-actuator piezoelectric robot powered by batteries and on-board high-voltage circuitry, and controlled through a wireless link. The scalable fabrication approach is based on bonding different functional layers on top of each other (steel foil substrate, actuators, flexible electronics). The robot exhibits a range of controllable motions, including bidirectional crawling (up to ~0.6 cm/s), turning, and in-place rotation (at ~1 degree/s). High-speed videos and control experiments show that the richness of the motion results from the interaction of an asymmetric mass distribution in the robot and the associated dependence of the dynamics on the driving frequency of the piezoelectrics. The robot's speed can reach 6 cm/s with specific payload distribution.

Figures (13)

• Figure 1: (a) Separated and (b) assembled views for battery-powered wirelessly-controlled robot structure, 500 mm long and 20 mm wide. Five "B"-shape hollow foam feet are attached on the bottom side, under the middle of each actuator. (c) Bending mechanism of a single actuator made of PZT fibers bonded on steel foil substrate. When voltage is applied, the $\text{d}_{33}$-type ($\text{d}_{31}$-type) PZT composite layer tries to extend (contract), while the substrate does not. As a result, the whole structure bends concave down (up).
• Figure 2: Pictures of the robot: (a) top view including power converters, Bluetooth module, microcontroller, and batteries; (b) side view showing foam feet attached to the robot's bottom side.
• Figure 3: Snapshots of the robot's frequency-controlled lateral movement over time: (a) forward motion, when driven at 13 Hz; (b) backward motion, when driven at at 14 Hz.
• Figure 4: Frequency dependence of the lateral speed. Positive numbers mean that the robot moves forward.
• Figure 5: Motion examples in the time domain for: (a) lateral forward (rightward) movement, when driven at 11 Hz; (b) side-view pictures for the forward motion (along x direction) over 3 seconds.