Model-Based Control of Planar Piezoelectric Inchworm Soft Robot for Crawling in Constrained Environments

Soft robots have drawn significant attention recently for their ability to achieve rich shapes when interacting with complex environments. However, their elasticity and flexibility compared to rigid robots also pose significant challenges for precise and robust shape control in real-time. Motivated by their potential to operate in highly-constrained environments, as in search-and-rescue operations, this work addresses these challenges of soft-robots by developing a model-based full-shape controller, validated and demonstrated by experiments. A five-actuator planar soft robot was constructed with planar piezoelectric layers bonded to a steel foil substrate, enabling inchworm-like motion. The controller uses a soft-body continuous model for shape planning and control, given target shapes and/or environmental constraints, such as crawling under overhead barriers or “roof” safety lines. An approach to background model calibrations is developed to address deviations of actual robot shape due to material parameter variations and drift. Full experimental shape control and optimal movement under a roof safety line are demonstrated, where the robot maximizes its speed within the overhead constraint. The mean-squared error between the measured and target shapes improves from ~ 0.05 cm²without calibration to ~ 0.01 cm²with calibration. Simulation-based validation is also performed with various different roof shapes.

I. Introduction

Soft robots have gained attention due to their abilities to take on richer shapes than their traditional rigid counterparts. Particularly, electrostatic soft robots, using piezoelectric actuators, enable flexible construction/integration, small form factors [1], and fast response times [2], [3]. Further, a planar form factor enables piezoelectric-based soft robots to move within space-constrained environments, as expected in search-and-rescue applications, where a robot may be needed to squeeze into collapsed construction gaps or around barriers from damage/debris. In this work, we demonstrate inchworm-like robot crawling movement on a surface, under height constraints from the environment. We place an overhead barrier with various bottom contours (referred to later as a “roof”) on top of the robot, and require the robot to crawl with maximum speed while avoiding collision with the roof.