Real-Time Compliance and Position Control of a Hyper-redundant Soft Robotic Arm

2026-06-28

AI Summary

This study addresses the challenge of simultaneously achieving precise end-effector positioning and adjustable compliance for soft robots operating in unstructured environments. The authors propose a seven-link hyper-redundant compliant manipulator that integrates a rigid-joint backbone with antagonistically actuated pneumatic muscles, enabling independent control of joint angles and stiffness. By introducing a task-space compliance model and a unified iterative inverse kinematics/inverse compliance control algorithm, the work demonstrates, for the first time on a physical system, quantitative, synchronous, and real-time control of both end-effector position and compliance. Experimental results show that the approach exhibits exceptional robustness and practicality in complex contact-rich tasks—such as whiteboard writing under perturbations and inserting a key or opening a drawer with unknown misalignments—surpassing the capabilities of conventional rigid or purely soft robotic arms.

Abstract

Robots working in unstructured or partially unobservable environments must combine accurate motion with physical compliance that can passively correct contact misalignment. Soft robots provide this compliance but have struggled to precisely control their tip compliance and position. This paper presents a robot architecture designed around that control problem: a 7-link arm whose six articulated joints provide twelve independently driven revolute axes, each actuated by an antagonistic pair of pneumatic muscles, so that every axis can simultaneously change its angle and linearly adjust its stiffness. The rigid articulated backbone makes the tip compliance and position of the arm predictable enough to be commanded quantitatively in real time. The robot employs a unified iterative inverse-kinematics and inverse-compliance controller to achieve simultaneous, quantitative control of both compliance and position. The task-space compliance and kinematics models and the control law are derived and verified on both the physical arm and a matched simulation. Simulation is then used to study how the same framework extends to other arm morphologies. Finally, the arm demonstrates tasks that have been difficult for both rigid and soft arms: rejecting disturbances while writing on a moving whiteboard, and passively correcting hidden misalignment during a key-insertion and drawer-opening task. That these tasks succeed under so straightforward a controller is evidence for the advantage of this algorithm-informed structural design.

Problem

• soft robotic arm
• real-time control
• compliance control
• position control
• hyper-redundant

Innovation

• soft robotics
• compliance control
• real-time control
• antagonistic actuation
• inverse kinematics