Flexible-Link Velocity-Bounding Proxy Based Sliding Mode Control
Hafsa Nouhi, Chaoyue Fei, Thierry Hubert, Greet Van de Perre
AI summary
Problem
Flexible-link manipulators face control challenges from reduced rigidity, causing oscillations and deflections, while existing collaborative control strategies often lack safe interaction handling or require complex dynamic models.
Approach
A nested control scheme extends velocity-bounding proxy-based sliding mode control with model-free proportional strain feedback for vibration damping and a quasi-static feed-forward term for gravity compensation, operating without a full dynamic model.
Key results
- Extends VB-PSMC to flexible-link manipulators with explicit flexural compensation
- Proves closed-loop stability via interconnected subsystem analysis
- Achieves accurate free-motion tracking with compliant physical interaction
- Reduces interaction forces by up to 32% and ensures vibration-free post-contact recovery
Why it matters
Enables safer and more precise collaborative robotics applications by addressing inherent link flexibility without relying on complex dynamic models.
Abstract
This paper proposes a control strategy for flexible link manipulators preserving high tracking accuracy in free motion, while ensuring smooth and safe behavior in scenarios involving physical interaction or large positional errors, based on the VB-PSMC. The scheme is extended to compensate for the manipulator’s flexural dynamics, resulting in a nested control scheme where damping of the induced oscillations is achieved by a model-free proportional strain feedback while gravity induced deflections are counteracted by a feed-forward term based on a quasi-static Euler-Bernoulli beam model. A convergence study on the modified sliding manifold and a stability analysis of the closed-loop system is provided. The performance of the controller was evaluated experimentally and compared against other control strategies such as PSMC and torque limited PD control. The results demonstrate the controller’s accurate end effector tracking in free motion, while achieving compliant behavior during contact, by efficiently handling the link’s inherent flexibility leading up to a 32% reduction in interaction force. In addition, studying the FL-VB-PSMC response after releasing contact demonstrated the smooth and vibration-free recovery even for large position errors.