Control method improves flexible robotic arm bending accuracy
Prescribed-Time Contracting-Boundary Control of a Tendon-Driven Flexible Arm
Robotics
Summary
Controlling flexible robotic arms is tricky because they bend in complicated ways. The authors introduced a new way to measure and control the arm’s bending that avoids problems when the arm is straight. Their control method keeps the bending error within a shrinking boundary and ensures it meets a precise target within a set time. They tested this method in simulations and a small experiment, showing it improved accuracy significantly without breaking the set error limits.
What this means in practice
- •For robotic arm developers: Provide a control technique that guarantees flexible robots reach bending accuracy targets within fixed times while avoiding error boundary breaches.
- •For prosthetics manufacturers: Use the control approach to design tendon-driven prosthetic arms with improved bending precision and reliable performance timing.
Authors
Yi Lu, Chao Tang, Zhiji Han, Hongdu Wang
Abstract
This study develops a prescribed-time performance-shaping control method for curvature tracking of a single-segment flexible arm actuated by three antagonistic tendon pairs. A Cartesian curvature representation is introduced to avoid the undefined bending direction at the straight configuration and to establish an explicit six-tendon kinematic mapping. A cubic performance boundary contracts smoothly from an initially admissible error bound to a nonzero terminal accuracy bound within a prescribed time. Based on this boundary, a dual transformation combining static symmetric error scaling and time-varying behavior shaping maps the tracking error into a fixed unit box. The resulting controller guarantees boundary invariance, prescribed-time entry into the terminal accuracy region, and subsequent asymptotic convergence. Numerical evaluations with Python and OpenCR--MuJoCo, together with a supervised reduced-order experiment on a two-section, four-channel platform, provide complementary validation. Across six experimental trials, no violation of the prescribed boundary is observed, and the proposed controller reduces the mean terminal curvature RMSE by 32.5% relative to a matched baseline, with comparable terminal-band entry times. These results support the feasibility of the proposed approach in the reduced-order experimental setting.