Adaptive Control of Bilateral Teleoperation with Time Delay

This paper presents model-based predictive controllers that achieve a high level of transparency while maintaining stability in bilateral teleoperation under known constant or variable time delay. This goal is accomplished by utilizing available information on system model and time delay within an adaptive predictive control framework. The performance objectives are delay-free position tracking between the master and slave and the establishment of virtual mass-damper tool impedance between the user and environment. The controllers adapt to parameter changes in the user, environment as well as the master and slave dynamics. Delay reduction is accomplished based on a state observer and estimates of the system parameters. Using the delay-reduced dynamics, an adaptive output regulation problem is formulated and solved to obtain the control laws. A Lyapunov analysis of the performance and stability of the resulting system is presented. The proposed controllers are evaluated experimentally under constant and variable delay conditions. DOI: 10.4018/ijimr.2012010101 2 International Journal of Intelligent Mechatronics and Robotics, 2(1), 1-27, January-March 2012 Copyright © 2012, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. and user dynamics. In most conventional control systems the unknown external disturbances must be suppressed. In teleoperation, however, the unknown user exogenous force is the main cause of motion and cannot be rejected. Teleoperation systems belong to the lager family of decentralized control systems since their sensing and actuation are distributed at the master and slave sites. While research in distributed control is extensive, many existing solutions attempt to weaken the interaction among the control sites rather than to coordinate their operation, as desired in teleoperation. Above all, the communication time delay between the master and slave sites poses a formidable challenge to achieving transparency while maintaining system stability in some applications of teleoperation. 1.1. Literature Survey Teleoperation has been subject of extensive research in the past and the reader is referred to Hokayem and Spong (2006) for a historical survey of the field. Some of the early work based on linear system analysis can be found in Hannaford (1989), Kazerooni et al. (1993), Lawrence (1993), Colgate (1993), and Yokokohji and Yoshikawa (1994) among others. Robust linear controllers based on theH¥ and m -synthesis theories have been developed to achieve robust stability and enhanced performance in the presence of dynamics uncertainty (Leung et al., 1995; Yan & Salcudean, 1996; Sirouspour, 2005). Zhu and Salcudean (2000) presented a comprehensive solution for deal-free bilateral teleoperation that considers the full nonlinear dynamics of the master and slave robots and adapts to parameter variations in the environment and user dynamics. Based on the concept of passive decomposition, Lee and Li (2005) proposed a nonlinear controller that provides useful task-specific dynamics for inertia scaling, motion guidance, and obstacle avoidance. Ryu and Kwon (2004) presented a time-domain passivity-based controller for teleoperation under a wide range of environment impedance and operation speed. Communication delay is the most challenging aspect of teleoperation control. It imposes a difficult trade-off between the conflicting requirements of stability and transparency (Lawrence, 1993; Hashtrudi-Zaad & Salcudean, 2002). Numerous efforts have been made to address time-delay related stability and performance issues in teleoperation; the reader can find a comparison of some of the existing methods in Arcara and Melchiorri (2002). The principle of passivity and the scattering theory have been instrumental in the development of a vast majority of existing time-delay teleoperation controllers (e.g., see Anderson & Spong, 1989; Niemeyer & Slotine, 1991, 1998; Ueda & Yoshikawa, 2004) among other references. The master and slave robots are energetically passive and the environment and user dynamics may also be modeled as passive elements. Passivity-based methods render the teleoperation system, including the controllers and communication channel, as an interconnection of a network of passive components. Such approach guarantees robust stability in the presence of time delay and unknown passive user and environment dynamics. This robustness, however, is gained at the expense of system transparency. Several variations of passivity-based controllers have been developed to improve their transparency. Baier (2004) proposed an adaptation of line terminating impedance functions to remedy the loss of transparency in bilateral teleoperation based on the scattering theory. Munir and Book (2002) combined a wave-based teleoperation controller with a Smith Predictor, a Kalman filter, and an energy regulator to improve its transparency. Lee and Spong (2006) employed the passivity concept in combination with a proportional-derivative controller over the delayed channel to enhance the teleoperation performance. Chopra and Spong (2004) enhanced teleoperation transparency by defining new passive outputs that include position and velocity information. Tanner and Niemeyer (2005) employed wave filtering and shaping to reduce the damping resulted from impedance matching. They also used a high 25 more pages are available in the full version of this document, which may be purchased using the "Add to Cart" button on the product's webpage: www.igi-global.com/article/adaptive-control-bilateralteleoperation-time/64216?camid=4v1 This title is available in InfoSci-Journals, InfoSci-Journal Disciplines Engineering, Natural, and Physical Science. Recommend this product to your librarian: www.igi-global.com/e-resources/libraryrecommendation/?id=2