Stable Haptic Interaction and Control

Haptic feedback involves direct physical interaction between a human and the haptic device. Therefore, particular importance must be attached to stable control. Violating stability may result in uncontrollable oscillations that make any reasonable interaction impossible, and moreover, can even harm the human operator. We research on stable haptic control, not only to understand the influence of involved system parameters, but rather to get the best out of our haptic devices and make the interaction with a virtual reality or during telemanipulation applications as realistic and effective as possible.

Our fundamental stability analysis of haptic systems takes into account:

• Time delay, e.g. caused by communication or haptic force computation
• Mixed-time (hybrid) systems, composed of discrete- and continuous-time elements
• Model of the human operator with uncertain parameters

This analysis reveals several useful results for controlling haptic devices:

• The virtual wall stiffness depends quadratically on time delay
• The human operator has an overall stabilizing effect on impedance-controlled haptic devices
• Passivity-based control approaches are only limited suitable for haptic rendering
• Optimal control parameter pairs exhibit less than 50% of the maximum stable stiffness

Selected Publications

• T. Hulin: A Practically Linear Relation between Time Delay and the Optimal Settling Time of a Haptic Device, IEEE Robotics and Automation Letters (RA-L) & IEEE ICRA 2017, May 2017, Singapore
• T. Hulin: Control of Hybrid Systems Affected by Time Delay with Application in Haptic Rendering, Dissertation, Leibniz Universität Hannover, April 2017
• T. Hulin, A. Albu-Schäffer, G. Hirzinger: Passivity and Stability Boundaries for Haptic Systems with Time Delay, IEEE Transactions on Control Systems Technology, Volume 22, Issue 4, July 2014
• T. Hulin, R. González, A. Albu-Schäffer: Optimal Control for Haptic Rendering: Fast Energy Dissipation for Step Response, IROS2013, Nov. 2013, Tokio, Japan
• J.J. Gil, E. Sanchez, T. Hulin, C. Preusche, G. Hirzinger: Stability Boundary for Haptic Rendering: Influence of Damping and Delay, Journal of Computing and Information Science in Engineering, Volume 9, Issue 1, Mar. 2009