Disturbance observer-based control of non-linear haptic teleoperation systems

Abstract

Teleoperation systems are subject to different types of disturbances. Such disturbances, when unaccounted for, may cause poor performance and even instability of the teleoperation system. This paper presents a novel nonlinear bilateral control scheme using the concept of disturbance observer based control for nonlinear teleoperation systems. Lumping the effects of dynamic uncertainties and external disturbances into a single disturbance term enables us to design a disturbance observer in order to suppress these disturbances and alleviate their adverse effects on the teleoperation system. A disturbance observer based control law is proposed for nonlinear teleoperation systems which will guarantee global asymptotic force tracking and global exponential position and disturbance tracking when the bilateral teleoperation system is experiencing slow-varying disturbances. In the case of fastvarying disturbances, the tracking errors are shown to be globally uniformly ultimately bounded, with an ultimate bound that can be made as small as desired using the design parameters. Simulations are presented to show the effectiveness of the proposed approach.

Control of nonlinear bilateral teleoperation systems subject to disturbances

“…The previous theorem addresses the case when we have slow-varying disturbances. In tha case of fast-varying disturbances, the tracking errors will be globally uniformly ultimately bounded [12]. The next theorem states that the disturbance tracking and the position tracking errors of the teleoperation system can converge exponentially to zero under certain conditions.…”

“…Then the disturbance observer based control laws given in (4) and (5) with choices in (8), (9) and (10) (20) and (21). Proof: Proof can be found in [12]. The previous theorem addresses the case when we have slow-varying disturbances.…”

Nonlinear disturbance observer design for robotic manipulators

“…The time-delayed position/force signals are then added to the output of the disturbance observer in order to provide the master and the slave robots with estimation of the undelayed versions of the position/force signals and thus improve the teleoperation system transparency (Natori et al, 2010). In (Mohammadi et al, 2011b), the authors implemented a pair of nonlinear disturbance observers in a 4-channel bilateral teleoperation architecture to achieve full transparency in the absence of communication time delays in both free and constrained motions. In that work, however, the availability of joint acceleration measurements, which is necessary for achieving full transparency, simplified design of disturbance observers.…”

Control of nonlinear teleoperation systems subject to disturbances and variable time delays

“…In [9], a disturbance observer was used at the slave side of a nonlinear unilateral teleoperation system in order to improve the position tracking between the master and the slave while the slave robot was moving in free space. In [10], the authors implemented a pair of nonlinear disturbance observers in a 4-channel bilateral teleoperation architecture to achieve full transparency in the absence of communication time delays in both free and constrained motions.…”