Piezoelectric Soft Robot Inchworm Motion by Tuning Ground Friction through Robot Shape: Quasi-Static Modeling and Experimental Validation

Abstract

Electrically-driven soft robots based on piezoelectric actuators may enable compact form factors and maneuverability in complex environments. In most prior work, piezoelectric actuators are used to control a single degree of freedom. In this work, the coordinated activation of five independent piezoelectric actuators, attached to a common metal foil, is used to implement inchworm-inspired crawling motion in a robot that is less than 0.5 mm thick. The motion is based on the control of its friction to the ground through the robot's shape, in which one end of the robot (depending on its shape) is anchored to the ground by static friction, while the rest of its body expands or contracts. A complete analytical model of the robot shape, which includes gravity, is developed to quantify the robot shape, friction, and displacement. After validation of the model by experiments, the robot's five actuators are collectively sequenced for inchworm-like forward and backward motion.

Figures (25)

• Figure 1: Inchworm motion inchwormpictures and analogous robot motion of contract and extend cycles in 4 steps. The robot consists of five thin-film piezoelectric actuators (each shown in a different color) on a common substrate. Raising the actuator on one end increases the friction on that end relative to the opposite end, enabling crawling motion.
• Figure 2: Mechanism of bending. Type P1 PZT devices bend concave down with positive applied voltage and type P2 devices bend concave up.Smartmaterial
• Figure 3: Cross-section of a five-actuator soft robot prototype, 500 mm long and 25 mm wide. Each actuator includes a piezoelectric device made of a lead zirconate titanate (PZT) fiber composite, controlled by voltage signals wired from off-robot voltage supplies. All PZT devices are attached to a common 50-µ m-thick steel foil substrate.
• Figure 4: Robot setup: (a) top view; (b) side view when the central three actuators are turned on. The 5-actuator robot is sitting on a rigid acrylic base, wired to high-voltage supplies with thin gold wires. Zheng2022 (c) System setup: the system is in a Faraday cage and contains the robot prototype and the power and control electronics.
• Figure 5: One-actuator setup on the ground with the left end clamped. A negative voltage is applied to make the actuator bend up. One part of it ($L_{\text{FLAT}}$) lies flat on the ground due to gravity, the other part ($L_{\text{SUS}}$) is suspended in the air.