Bogdan Liacu

Some Remarks on Smith Predictor-Based Control with Distance Feedback for a 3-Dof Haptic System with Distributed Delays

Abstract This paper focuses on the construction of a Smith predictor for network-based haptic systems. Roughly speaking, the idea is to use a predictor just on the haptic side in order to compensate the viscosity effect and to provide an accurate feeling in the case of contacts. A new approach is presented by using the available information on the distance from the virtual reality simulator and introducing it in the predictor in order to maintain the similarity between the “real” and the “predicted model”. In order to validate the approach, experimental results are presented for constant and random varying delays (normal distributed and gamma with gap distributed), for a simple virtual environment and for a virtual box.

Experimental comparative study of control architectures for haptic interfaces including communication delays

The aim of this paper is to present a comparative study of control algorithms for haptic interfaces and virtual environments subject to communication delays. It is well known that the presence of delays deteriorates the overall system performance. More precisely, delays introduce a feeling of viscosity in free motion and reduce the sense of stiffness in case of hard contacts. Six methods in their basic form (classic Proportional Derivative (PD), PD with local dissipation, PD with passivity observer, PD with passive set-point modulation, wave scattering transform and Smith predictor) are analyzed and compared, using a real-time experimental platform which enables tracking the impact of delays, from the point of view of position tracking error and transparency degree.

Low-Order Controller Design for Haptic Systems under Delayed Feedback

Abstract In this paper, we consider PD controller design for haptic systems under delayed feedback. More precisely, we present a complete stability analysis of a haptic system where local dynamics are described by some second-order mechanical dynamics. Next, using two optimization techniques ( H ∞ and stability margin optimization) we propose an optimal choice for the controller gains. The derived results are tested on a three degree of freedom real-time experimental platform to illustrate the theoretical results.

Smith Predictor-Based Control with Distance Feedback for Haptic Systems Under Distributed Time-Delays

This chapter proposes a Smith predictor-based control with distance feedback until a possible collision for network based haptic systems. The main idea is to use a predictor just on the haptic side in order to compensate the viscosity effect and to provide an accurate feeling in case of contacts. The critical problem is that in haptics there are two situations: free and restricted motion, which implies a model changing on the predictor side. For solving this problem, a new approach is presented by using the available information on the distance from the virtual reality simulator and introducing it in the predictor in order to maintain the similitude between the real and the predicted model. The three most common delay distributions (uniform, gamma with gap and normal) are analyzed from the stability point of view and are tested on a 3-dof real-time experimental platform.

PD control with gain-scheduling depending on the distance for a 3-dof network based haptic system

This paper presents a Proportional Derivative (PD) controller with gain-scheduling depending on the distance for haptic interfaces and virtual environments subject to communication delays. It is well known that the presence of delays deteriorates the overall system performance. More precisely, depending on the proposed architecture as, for example, bilateral position-position coupling, time-delays introduce a feeling of viscosity in free motion and reduce the sense of stiffness in the case of hard contacts. Even in the presence of time-delays, the controller gains can be tuned in order to guarantee the desired behavior and performances for one case (free or restricted motion) with the price of the completely loss of the other case performances and behavior. To overcome this drawback, a gain-scheduling controller is designed, able to guarantee the desired behavior and performances for free and restricted motion. The experimental results obtained on a three-degree of freedom real-time experimental platform enforce the theoretical developments.

Some remarks on the fragility of transparency and stability in general 4-channel architecture for bilateral teleoperation with delay

This paper addresses the “trade-off” between transparency and stability of some specific bilateral teleoperation systems including communication time-delays. Using a geometric approach, we derive a simple method to study the fragility of the proposed controller for a general 4-channel architecture for bilateral teleoperation with time-delays such that the closed-loop stability as well as the transparency are guaranteed for the overall scheme. Illustrative examples complete the presentation.