Transparent Teleoperation Research Articles

Adaptive Control for State Synchronization of Nonlinear Haptic Telerobotic Systems with Asymmetric Varying Time Delays

In this paper, we introduce a new adaptive controller design scheme for nonlinear telerobotic systems with varying time delays where the delays and their variation rates are unknown. The designed controller has the ability to synchronize the state behaviors of the local and the remote robots. In this paper, asymptotic stability in the presence of varying time delays is of interest. Using the proposed controller, asymptotic stability of the bilateral telerobotic system subject to any bounded yet unknown varying delay with a bounded yet unknown rate of change can be guaranteed. Besides the varying time delay, the proposed adaptive controller has the ability to adapt to the parameter variations in the local and the remote robots' dynamics. It is shown that position and velocity errors between the local and the remote manipulators converge to the zero asymptotically, thus ensuring teleoperation transparency. Experimental and simulation results with a pair of PHANToM haptic devices and a pair of planar manipulators under varying time delays in the communication channel demonstrate the effectiveness of the proposed scheme.

Quantitative Absolute Transparency for Bilateral Teleoperation of Mobile Robots

This paper proposes a new criterion, called absolute transparency, to design control schemes applied to bilateral teleoperation of mobile robots with time-varying delay. The absolute transparency measures how and how fast the human operator and the remote system interact with each other through a teleoperation system. The absolute transparency of different control schemes is analyzed and tested through teleoperation experiments where a human operator drives a mobile robot and receives both visual and force feedback.

Stable and Transparent Time-Delayed Teleoperation by Direct Acceleration Waves

For time-delayed bilateral teleoperation systems, this paper presents a novel structure to considerably improve performance in terms of transparency and perception bandwidth, which are extremely low for passive systems, as well as force-position and velocity tracking on which delay control systems suffer both necessity for provision of identical initial conditions and drift problem. Performance improvement is carried out in three steps. The first step is the utilization of a four-channel wave-transmission structure that provides direct force and velocity feedbacks to each robot by asymmetric damping. Since the common dimension of wave variables is acceleration, the second step is the conversion of wave data into acceleration terms and the employment of acceleration control. The third step is the scaling of both the force- and position-based acceleration dimensions. Perception-bandwidth-limiting filters are used neither in wave space nor in control space. We showed the validity by experiments and superiority to previous systems by various comparative analyses.

Haptic Effects of Surgical Teleoperator Flexibility

Minimally invasive surgery systems typically involve thin and cable-driven surgical instruments. This introduces link and joint flexibility in the slave robot of a master—slave teleoperation system, reducing the effective stiffness of the slave and the transparency of teleoperation. In this paper, we analyze transparency under slave link and joint flexibility (tool flexibility). We also evaluate the added benefits of using extra sensors at the tip of the flexible robot. It is shown that tip velocity (or position) feedback improves free-space position tracking performance in the presence of robot flexibility. Also, when the interaction forces with an environment are measured by a force sensor and fed back to the user’s hand, tip velocity feedback improves hard-contact force tracking performance. During a hard contact task, tip velocity feedback can also eliminate the transmission of robot flexibility to the user’s hand.

Model-based Decentralized Control of Time-delay Teleoperation Systems

Recently, within a centralized control framework, the authors proposed a time-delay reduction method to achieve improved transparency in time-delay teleoperation. In this paper, a decentralized version of the controller is introduced that can further enhance the teleoperation transparency and robust stability by allowing the use of local delay-free measurements in local master/slave controllers. State/observation transformations are proposed that produce delay-free dynamics/measurements from the perspective of the local controllers at the master and slave stations. It is shown that the use of local suboptimal linear quadratic Gaussian master and slave controllers results in a delayed state perturbation term in the closed-loop dynamics. The stability of the system is then analyzed using a delay-dependent frequency sweeping test. The controllers employ a simple switching logic to handle large variations in the environment dynamics from free motion to rigid contact. The performance and robustness of the new decentralized controller are compared with those of the centralized controller using numerical analysis. Experimental results demonstrate the effectiveness of the proposed approach.

Stability and performance in delayed bilateral teleoperation: Theory and experiments

In the presence of communication latency in a bilaterally controlled teleoperation system, stability and transparency are severely affected. In this paper, based on a passivity framework, admittance-type and hybrid-type delay-compensated communication channels, which warrant different bilateral control architectures, are introduced. Wave transforms and signal filtering are used to make the delayed-communication channel passive and passivity/stability conditions are derived based on the end-to-end model of the teleoperation system with and without incorporating force measurement data of the master and the slave manipulators’ interactions with the operator and the remote environment in the control configuration. Based on analogies of the hybrid parameters of the teleoperation systems, it is demonstrated that using force sensor measurements about hand/master and/or slave/environment interactions in the control algorithm can significantly improve teleoperation transparency. Experimental results with a soft-tissue task for a hybrid-type architecture and for round-trip delays of 60 and 600 ms further substantiate the hypothesis that using slave-side force measurements considerably enhances the matching of the master and the slave forces and consequently the transparency compared to a position error-based configuration.

Transparent Rate Mode Bilateral Teleoperation Control

Transparent teleoperation under rate mode has proven to be difficult in terms of stability, performance and implementation. This is mainly due to the need for an exchange of derivative and integral of measured positions and forces which make transparent rate mode controllers prone to noise and abrupt contact force changes. Moreover, the performance of controllers declines in the presence of communication delays. This paper proposes two control architectures based on the use of local force feedback (LFF) and environment impedance reflection (EIR). The LFF controllers eliminate a force channel while preserving transparency under ideal conditions. In the EIR controller, the identified impedance of the environment is employed in the master controller to predict the slave position and contact force derivatives. The stability robustness and performance of these controllers are evaluated and compared to those of a benchmark controller under different operational conditions, such as noise and delay, using analytical methods and experimental results.

High-Fidelity Bilateral Teleoperation Systems and the Effect of Multimodal Haptics

In master-slave teleoperation applications that deal with a delicate and sensitive environment, it is important to provide haptic feedback of slave/environment interactions to the user's hand as it improves task performance and teleoperation transparency (fidelity), which is the extent of telepresence of the remote environment available to the user through the master-slave system. For haptic teleoperation, in addition to a haptics-capable master interface, often one or more force sensors are also used, which warrant new bilateral control architectures while increasing the cost and the complexity of the teleoperation system. In this paper, we investigate the added benefits of using force sensors that measure hand/master and slave/environment interactions and of utilizing local feedback loops on the teleoperation transparency. We compare the two-channel and the four-channel bilateral control systems in terms of stability and transparency, and study the stability and performance robustness of the four-channel method against nonidealities that arise during bilateral control implementation, which include master-slave communication latency and changes in the environment dynamics. The next issue addressed in the paper deals with the case where the master interface is not haptics capable, but the slave is equipped with a force sensor. In the context of robotics-assisted soft-tissue surgical applications, we explore through human factors experiments whether slave/environment force measurements can be of any help with regard to improving task performance. The last problem we study is whether slave/environment force information, with and without haptic capability in the master interface, can help improve outcomes under degraded visual conditions.

A Force-Reflection Algorithm for Improved Transparency in Bilateral Teleoperation With Communication Delay

The problem of stable force-reflecting teleoperation with time-varying communication delay is addressed in this paper. A new force-reflection (FR) algorithm is presented, where the environmental force reflected on the master side can be altered depending on the forces applied by the human operator. This alteration is not felt by the human operator; however, it makes the FR safe in the sense it does not destroy the stability of the teleoperator system. In particular, using input-to-output stability small gain approach, it is shown that the overall stability in the teleoperator system with the force-reflecting algorithm proposed can be achieved theoretically for arbitrarily low damping on the master side and arbitrarily high FR gain. The simulation results presented confirm that the proposed FR algorithm significantly improves the stability/performance characteristics of the force-reflecting teleoperator system in the presence of time-varying communication delays.

Adaptive force reflecting teleoperation with local force compensators

SUMMARYThis paper addresses problems to achieve transparency and contact stability for teleoperation that consists of unconstrained and constrained motions. The adaptive bilateral control with a local force compensator is developed, based on adaptive impedance control and contact force driven compensation with auto-switching functions. Without any knowledge about robotic and environment dynamics and with a communication delay, the developed method guarantees good adaptive tracking performance in unconstrained motion and reduction of oscillating contacts in constrained motion. Based on an actual haptic device and a virtual manipulator, haptic simulations are presented to demonstrate adaptive transparency and contact stability in the presence of communication delay.

Model Predictive Control for Transparent Teleoperation Under Communication Time Delay

Prior efforts in bilateral teleoperation under communication delay have mainly yielded control algorithms that sacrifice performance in order to guarantee robust stability. In contrast, this paper proposes a multimodel predictive controller that can enhance the teleoperation transparency in the presence of a known constant delay. Separate controllers are designed for free motion/soft contact and contact with rigid environments, with switching between these mode-based control laws occurring according to the identified contact mode. Performance objectives such as position tracking and tool impedance shaping for free motion/soft contact, as well as position and force tracking for contact with rigid environments, are incorporated into a multi-input/multi-output state-space representation of the system dynamics. New Artstein-type state and measurement transformations are proposed to generate delay-free dynamics suitable for output-feedback control, based on the original dynamics with delays in various input and output channels. The application of the continuous-time linear quadratic Gaussian control synthesis to the resulting mode-based delay-free dynamics yields control laws that guarantee closed-loop stability and enhanced performance in each phase of teleoperation. The robustness of the mode-based controllers with respect to parametric uncertainty is analyzed. Experimental results with a single-axis teleoperation setup demonstrate the effectiveness of the proposed approach

Development of a high-performance haptic telemanipulation system with dissimilar kinematics

This work addresses selected practical issues regarding the development of a telerobotic system for 6-d.o.f. tasks. The system consists of a hyper-redundant 10-d.o.f. haptic input device ViSHaRD10, a redundant 7-d.o.f. manipulator and a stereo vision system. The redundancy of the haptic input device is exploited to assure large convex workspaces and singularity-free operation. The anthropomorphic construction of the telemanipulator enables intuitive manipulation and increases the user-friendliness of the overall system. As a practical benchmark, an assembly experiment in 6 d.o.f. for the case of a negligible time delay was performed. Issues regarding inverse kinematics, spatial interaction control, transparency and intuitiveness of teleoperation are discussed.

Transparency and Stability of Bilateral Kinesthetic Teleoperation with Time-Delayed Communication

This paper presents a novel control approach that simultaneously ensures stability and transparency of bilateral kinesthetic teleoperation in case of communication delay. The approach rests upon a straight-forward combination of two-port lossless line theory, proper adaptation of line terminating impedance functions and situation dependent switching of adaptation filters. Application of a resulting transparency oriented control strategy to 1- or multi-DoF telemanipultion systems leads to improvements in human operator's presence feeling and task performance.

Transparency in time-delayed systems and the effect of local force feedback for transparent teleoperation

This paper first investigates the issue of transparency in time-delayed teleoperation. It then studies the advantages of employing local force feedback for enhanced stability and performance. In addition, two classes of three-channel control architectures, that are perfectly transparent under ideal conditions are introduced. The stability robustness of the proposed architectures to delays is rigorously analyzed, leading to certain bounds on force feedforward control parameters. Experimental results are included in support of the theoretical work.

Adaptive controller of a master-slave system for transparent teleoperation

This article presents an adaptive control scheme based on position-force architecture to achieve the stability and transparency for teleoperation in unknown or varying environments. Without any knowledge about the parameters of the slave robot and environment dynamics, the proposed scheme guarantees the robustness to the parameter uncertainties of the master robot as well as the stability of the whole teleoperation system. Numerical simulations are presented to demonstrate the transparency and robustness to the parameter uncertainties of the master robot. Experimental results to a master]slave system show the validity of the proposed scheme. Q 1998 John Wiley &

Stability and transparency in bilateral teleoperation

Tools for quantifying teleoperation system performance and stability when communication delays are present are provided. A general multivariable system architecture is utilized which includes all four-types of data transmission between master and slave: force and velocity in both directions. It is shown that a proper use of an four channels is of critical importance in achieving high performance telepresence in the sense of accurate transmission of task impedances to the operator. It is also shown that transparency and robust stability (passivity) are conflicting design goals in teleoperation systems. The analysis is illustrated by comparing transparency and stability in two common architectures, as well as a recent passivated approach and a new transparency-optimized architecture, using simplified one-degree-of-freedom examples. >