Infinite-Dimensional Closed-Loop Inverse Kinematics for Soft Robots via Neural Operators

TL;DR

This paper introduces an infinite-dimensional approach to closed-loop inverse kinematics for soft robots, utilizing neural operators to learn complex actuation-to-shape mappings and enabling shape-based control in infinite-dimensional spaces.

Contribution

It formulates CLIK in an infinite-dimensional setting for soft robots and employs neural operators to learn the actuation-to-shape map, extending beyond finite-dimensional models.

Findings

Successfully applied to a three-fiber soft robotic arm

Derived a Jacobian-based CLIK algorithm in infinite dimensions

Demonstrated effectiveness with neural operator learning

Abstract

For fully actuated rigid robots, kinematic inversion is a purely geometric problem, efficiently solved by closed-loop inverse kinematics (CLIK) schemes that compute joint configurations to position the robot body in space. For underactuated soft robots, however, not all configurations are attainable through control action, making kinematic inversion extremely challenging. Extensions of CLIK address this by introducing end-to-end mappings from actuation to task space for the controller to operate on, but typically assume finite dimensions of the underlying virtual configuration space. In this work, we formulate CLIK in the infinite-dimensional domain to reason about the entire soft robot shape while solving tasks. We do this by composing an actuation-to-shape map with a shape-to-task map, deriving the differential end-to-end kinematics via an infinite-dimensional chain rule, and thereby obtaining a Jacobian-based CLIK algorithm. Since this actuation-to-shape mapping is rarely available in closed form, we propose to learn it using differentiable neural operator networks. We first present an analytical study on a constant-curvature segment, and then apply the neural version of the algorithm to a three-fiber soft robotic arm whose underlying model relies on morphoelasticity and active filament theory.