A Hierarchical Adaptive Controller with Configurable Joint Torque Constraints for Flexible LIMS Elbow Cable-Driven Mechanism
Weining Lu, and Chunting Jiao
AI summary
Problem
Existing cable-driven mechanism controllers often ignore joint torque constraints, risking cable slack and unsafe interactions, while relying on oversimplified linear transmission models that fail to capture complex cable dynamics.
Approach
The method uses a two-loop hierarchical structure: an anti-windup adaptive joint controller for tracking and a decoupled cable loop that bounds cable deformation to enforce torque limits using only motor and joint position feedback.
Key results
- Stability analysis relaxing the continuous second-derivative assumption for joint-loop controllers
- Enhanced inherent compliance and safety through configurable joint torque constraints
- Mitigation of cable slack by actively bounding cable deformation
- Experimental validation demonstrating superior tracking accuracy and compliance under varying loads and fast trajectories
Why it matters
Enables safer, sensor-free human-robot interaction in collaborative cable-driven robots by preventing cable slack and enforcing strict torque limits.
Abstract
Cable-driven mechanisms (CDMs) provide en- hanced safety for human interaction thanks to their lightweight design and inherent compliance. However, designing high- performance tracking controller for CDMs is challenging due to the complex dynamics introduced by cables’ flexibility. Existing works studied improving tracking performance for CDMs, but joint torque constraints are rarely considered, which may cause cable slack and bring additional uncertainties into system dynamics. Besides, most works modeled the actuator-to-joint transmission as a linear torsional spring, making it nontrivial to implement the controllers to CDMs with complex transmission mechanical design. To further enhance the compliance and safety and mitigate cable slackness of CDMs, we propose a novel hierarchical adaptive controller with configurable joint torque constraints for LIMS (Low Inertia Manipulator with high Stiffness and Strength) elbow CDM. The controller consists of an anti-windup adaptive joint control loop and a decoupled cable deformation control loop, which can achieve safe and compliant physical interaction without using torque/tension sensors or force/torque observers. Finally, the controller’s stability is analyzed, and its capabilities in accuracy, safety, and compliance are validated via comprehensive experiments compared to the other two baseline controllers.