Stability of Bilateral Teleoperators with Projection-Based Force Reflection Algorithms

Abstract-A general stability result for force-reflecting teleoperator systems with projection-based force reflection algorithms is established. It is shown that the closed-loop system's gain can be assigned arbitrarily by an appropriate choice of certain weighting function of the projection-based force reflection algorithm. In particular, this allows to achieve stability of the force-reflecting teleoperator system in presence of timevarying irregular delays for arbitrarily large force-reflecting gain and arbitrarily low damping and stiffness of the master. The proposed approach solves, to some extent, the trade-off between stability, manoeuvrability, and high force reflection gain in force-reflecting teleoperator system with network-induced communication constraints

Experimental Evaluation of the Projection-based Force Reflection Algorithms for Haptic Interaction with Virtual Environment

Haptic interaction with virtual environments is currently a major and growing area of research with a number of emerging applications, particularly in the field of robotics. Digital implementation of the virtual environments, however, introduces errors which may result in instability of the haptic displays. This thesis deals with experimental investigation of the Projection-Based Force Reflection Algorithms (PFRAs) for haptic interaction with virtual environments, focusing on their performance in terms of stability and transparency. Experiments were performed to compare the PFRA in terms of performance for both non-delayed and delayed haptic interactions with more conventional haptic rendering methods, such as the Virtual Coupling (VC) and Wave Variables (WV). The results demonstrated that the PFRA is more stable, guarantees higher levels of transparency, and is less sensitive to decrease in update rates

Control of Cooperative Haptics-Enabled Teleoperation Systems with Application to Minimally Invasive Surgery

Robot-Assisted Minimally Invasive Surgical (RAMIS) systems frequently have a structure of cooperative teleoperator systems where multiple master-slave pairs are used to collaboratively execute a task. Although multiple studies indicate that haptic feedback improves the realism of tool-tissue interaction to the surgeon and leads to better performance for surgical procedures, current telesurgical systems typically do not provide force feedback, mainly because of the inherent stability issues. The research presented in this thesis is directed towards the development of control algorithms for force reflecting cooperative surgical teleoperator systems with improved stability and transparency characteristics. In the case of cooperative force reflecting teleoperation over networks, conventional passivity based approaches may have limited applicability due to potentially non-passive slave-slave interactions and irregular communication delays imposed by the network. In this thesis, an alternative small gain framework for the design of cooperative network-based force reflecting teleoperator systems is developed. Using the small gain framework, control algorithms for cooperative force-reflecting teleoperator systems are designed that guarantee stability in the presence of multiple network-induced communication constraints. Furthermore, the design conservatism typically associated with the small-gain approach is eliminated by using the Projection-Based Force Reflection (PBFR) algorithms. Stability results are established for networked cooperative teleoperator systems under different types of force reflection algorithms in the presence of irregular communication delays. The proposed control approach is consequently implemented on a dual-arm (two masters/two slaves) robotic MIS testbed. The testbed consists of two Haptic Wand devices as masters and two PA10-7C robots as the slave manipulators equipped with da Vinci laparoscopic surgical instruments. The performance of the proposed control approach is evaluated in three different cooperative surgical tasks, which are knot tightening, pegboard transfer, and object manipulation. The experimental results obtained indicate that the PBFR algorithms demonstrate statistically significant performance improvement in comparison with the conventional direct force reflection algorithms. One possible shortcoming of using PBFR algorithms is that implementation of these algorithms may lead to attenuation of the high-frequency component of the contact force which is important, in particular, for haptic perception of stiff surfaces. In this thesis, a solution to this problem is proposed which is based on the idea of separating the different frequency bands in the force reflection signal and consequently applying the projection-based principle to the low-frequency component, while reflecting the high-frequency component directly. The experimental results demonstrate that substantial improvement in transient fidelity of the force feedback is achieved using the proposed method without negative effects on the stability of the system

Sensorless force feedback joystick control for teleoperation of construction equipment

This paper aims to develop an innovative approach named sensorless force feedback joystick control for teleoperation of construction equipment. First, a force sensorless supervisory controller is designed with two advanced modules: a neural network-based environment classifier to estimate environment characteristics without requiring a force sensor and, a fuzzy-based force feedback tuner to generate properly a force reflection to the joystick. Second, two local robust adaptive controllers are simply built using neural network and Lyapunov stability condition to ensure desired task performances at both master and slave sites. A teleoperation system is setup to demonstrate the applicability of the proposed approach

Force reflecting joystick control for applications to bilateral teleoperation in construction machinery

This paper presents a simple and effective force reflecting joystick controller for applications to bilateral teleoperation in construction machinery. First, this controller is a combination of an advanced force reflecting gain tuner and two local adaptive controllers, master and slave. Second, the force reflecting gain tuner is effectively designed using recursive least square method and fuzzy logics to estimate directly and accurately the environmental characteristics and, consequently, to produce properly a force reflection. Third, the local adaptive controllers are simply designed using fuzzy technique and optimized using a smart leaning mechanism to ensure that the slave follows well any given trajectory while the operator is able to achieve truly physical perception of interactions at the remote site. An experimental master-slave manipulator is setup and real-time control tests are carried out under various environmental conditions to evaluate the effectiveness of the proposed controller

Projection-based force reflection algorithm for stable bilateral teleoperation over networks

The problem of stable force-reflecting teleoperation is addressed where the communication between the master and the slave is subject to multiple time-varying,

Projection-based force reflection algorithm for stable bilateral teleoperation over networks

The problem of stable force-reflecting teleoperation is addressed, where the communication between the master and the slave is subject to multiple time-varying, discontinuous, and possibly unbounded communication delays. A new force reflection (FR) algorithm is proposed, which improves the stability of the system without decreasing its transparency. Based on the estimate of human forces provided by the high-gain input observer, the proposed algorithm restricts the reflected force in such a way that it eliminates the motion of the master induced by the FR signal without changing the human perception of the environmental force. It is shown that the proposed FR algorithm allows us to achieve stability of the system for an arbitrarily high FR gain and arbitrarily low damping and stiffness of the master manipulator. The stability analysis is based on the input-to-output stability small-gain theorem for systems with multiple time-varying communication delays

Projection-Based Force Reflection Algorithms for Teleoperated Rehabilitation Therapy

Abstract-The problem of designing of a haptics-enabled teleoperated rehabilitation system in the presence of communication delays is addressed. In a teleoperated rehabilitation system, communication delays introduce phase shift which may result in the task inversion phenomenon. To overcome the task inversion, a new type of projection-based force reflection algorithm is proposed which is suitable for assistive/resistive therapy in the presence of irregular communication delays. Additionally, algorithms for augmented therapy are introduced which combine the projection-based force reflection with a delay-free local virtual therapist. A small-gain design is developed which guarantees stability of the proposed schemes for both assistive and resistive modes of the therapy. Simulations and experimental results are presented which confirm the improvement achieved by the proposed methods