Control Of Bilateral Teleoperation Systems Research Articles

Adaptive control of bilateral teleoperators with convergent parameter estimation and guaranteed compliance

Although adaptive control has been studied for teleoperation systems in the past decades, the convergence of parameter estimation is generally difficult to claim in the existing methods, and thus only specific scenarios (e.g., free motion) and partial operation performance (e.g., synchronization) have been addressed. In this paper, we found that the convergence of parameter estimation is crucial for bilateral teleoperation systems to retain the guaranteed operation performances, including compliance in the tracking motion and transparency in the contact motion. Accordingly, this paper suggests an alternative adaptive control for bilateral teleoperation systems, where a new adaptive law with the estimation errors as leakage terms is developed to obtain finite-time convergence of the parameter estimation. This convergent property allows to compensate for the undesired dynamics (e.g., gravity) in the closed-loop system so as to achieve ideal compliance and transparency. The control system’s stability and performances under constant time delays are analyzed for three scenarios: free motion, tracking motion, and contact motion. The quantitative relationship between the joint velocities and the human torques in the tracking motion is also studied, and the transparency is addressed in the contact motion. Simulations and experiments on a Baxter robot all showcase the effectiveness and superiority of the developed approach.

Position and Force Control of Bilateral Teleoperation Systems With Time-varying Delays Based on Force Estimation

Position and Force Control of Bilateral Teleoperation Systems With Time-varying Delays Based on Force Estimation

A USDE-Based Control for Bilateral Teleoperation Systems With Time-Varying Delays

A USDE-Based Control for Bilateral Teleoperation Systems With Time-Varying Delays

Observer-based fuzzy integral sliding mode control for bilateral teleoperation systems with time-varying delays

This paper aims to examine the stability and tracking performance of a bilateral teleoperation system. The Takagi–Sugeno fuzzy method is utilized, through which the nonlinear master–slave dynamics is converted as a fuzzy-based system. The state observers are designed for the linearized fuzzy teleoperation systems, and the corresponding estimation errors are formulated. Importantly, a novel observer-based fuzzy integral sliding mode control is developed by deliberately introducing the delay term into the sliding surfaces. As such, advanced delay-product type of Lyapunov–Krasovskii functionals are constructed for the augmented state vectors, in order to acquire the additional delay information. In addition, the Wirtinger-based integral inequality along with an extended reciprocally convex matrix inequality is applied to the Lyapunov derivatives to establish the delay-dependent stability conditions. Numerical results are provided to demonstrate efficacy of the developed control mechanism.

The PID in the Control of Bilateral Teleoperation System with Time-Varying Delays: An Experimental Approach

The control of bilateral teleoperation systems with time-varying delays is a challenging problem that is usually dealt with advanced control techniques. The well-known controllers, such as PD or PID, are scarcely employed and usually in conjunction with other approaches or at least with gravity compensation. In this contribution we intend to show, experimentally, that the standard PID controller exhibits good performance and robustness in position control for teleoperators with variable delays. The results obtained are compared with a well-known algorithm used for teleoperator control.

Design of Synchronization Tracking Adaptive Control for Bilateral Teleoperation System with Time-Varying Delays.

The performances of position synchronization and force interaction of the teleoperation system provide a safe and efficient way for operators to perform tasks in remote, hazardous environments. In practice, however, communication delays and dynamic uncertainties can impair the performance of position synchronization controls. Under the above factors, it is necessary to study and design appropriate bilateral control methods to achieve stable and effective position synchronization control. In this paper, a new adaptive control architecture based on velocity feedback filter and radial basis function neural network is proposed. In the proposed control scheme, only the position signal is transmitted during the communication process, and the speed feedback filter and compensation method are designed and adopted to avoid the use of acceleration signals. In addition, a new auxiliary variable with a tracking error integral term is used to reduce the steady-state error of position tracking under nonzero external environmental forces. Using the Lyapunov–Krasovskii method, the stability of closed-loop remote operating systems is demonstrated. In the simulation and experiment sections, the algorithm was verified separately and compared with other algorithms. The results of a master–slave robot system verify the tracking performance of our proposed control scheme.

Adaptive event‐triggered synchronization control for bilateral teleoperation system subjected to fixed‐time constraint

SummaryThe time‐constrained positional synchronization control problem for a class of bilateral teleoperation systems is investigated and a novel fixed‐time event‐triggered control scheme is developed. Different from existing methods, the controller is triggered in a nonperiodic manner, which reduces considerably the triggering frequency of control devices. This not only saves communication resource, but also extends the lifespan of system devices because of the reduction of switching times. The control settling time is further considered by introducing a fixed‐time stability theorem. Theoretical analysis as well as a simulation example verifies that the proposed control method can reduce remarkably the amount of control signals transmitted between the master and slave while ensuring that the system output tracking error converges to a small neighborhood close to zero within a fixed‐time frame.

Adaptive Practical Fixed-Time Synchronization Control for Bilateral Teleoperation System With Prescribed Performance

In this brief, an adaptive practical fixed-time synchronization control scheme for position tracking of a bilateral teleoperation system with prescribed performance is proposed. A prescribed performance function (PPF) is incorporated into the fixed-time control framework such that the synchronization errors will converge into a residual set in a fixed time and the upper bound of setting time is regardless of the initial states. The upper bound of system uncertainties is estimated via adaptive technique such that the adverse effect induced by system uncertainties can be attenuated. Simulation studies and experiments demonstrate the effectiveness and practicality of the proposed control scheme in terms of both transient and steady-state performance.

Finite-Time Synchronization Control for Bilateral Teleoperation Systems With Asymmetric Time-Varying Delay and Input Dead Zone

In this article, the synchronization control problem of bilateral teleoperation systems with time-varying delays and input dead zones is addressed. A novel radial basis function network (RBFN)-based adaptive finite-time synchronization control scheme is proposed, where system uncertainties, asymmetric time-varying delays, and dead-zone phenomena are considered simultaneously. Specifically, an RBFN is designed to approximate system uncertainties and unknown nonlinearities. The approximation error as well as the time-associated uncertainty and the nonlinear margin of the dead zone is compensated by an adaptive compensator. Using a Lyapunov-Krasovskii function and the finite-time stability criteria, the system is proved to be semiglobally practically finite-time stable. The theoretical analysis is given to prove the stability of the closed-loop system. The tracking performance of the designed controller is demonstrated by comparative simulation studies and experiment results.

Adaptive quantisation synchronisation control for bilateral teleoperation systems with communication delays

In this paper, the quantisation synchronisation control problem of bilateral teleoperation systems with communication delays is investigated. The inaccurate modelling problem including the system uncertainties and the unknown disturbances are compensated by using the radial basis function networks (RBFN). By introducing the hysteretic quantiser, the control signals are quantised to a set of discrete values to ease the accuracy requirement for actual physical systems and the requirement for communication rate. The position synchronisation of joint variables between the master and slave manipulators is achieved by using the designed control signals and adaptive parameters. Simulation results verify that the synchronisation tracking errors gradually converge to a small neighbourhood around zero.

Prescribed performance output feedback synchronisation control of bilateral teleoperation system with actuator nonlinearities

This work investigates output feedback synchronisation control of uncertain bilateral teleoperation system with synchronisation error constraints, time-varying delay, actuator backlash-like hysteresis and unknown control direction. The constrained system is transformed into unconstrained one via the output error transformation. A Prescribed-Performance Function (PPF) is proposed to ensure that all the outputs with predefined transient and steady states' performances converge to a predefined set. In addition, a radial basis function neural network (RBFNN) is utilised to estimate the uncertain dynamics. Moreover, a Nussbaum-type function is introduced to tackle the loss of control direction due to the actuator backlash-like hysteresis. By Lyapunov stability analysis, all the closed-loop signals are guaranteed to converge to a small neighbourhood of the origin. Finally, simulation results are provided to demonstrate the effectiveness of the proposed method.

Composite Adaptive Guaranteed Performances Synchronization Control for Bilateral Teleoperation System With Asymmetrical Time-Varying Delays.

This article studies the guaranteed performance synchronization control problem for networked bilateral teleoperation systems with system uncertainties. The communication channel connecting the master and the slave is subject to asymmetrical varying time delays with unknown upper bounds. The first result on prescribed performance synchronization control for the bilateral teleoperation system under such a weak assumption on the communication time delays is provided. Moreover, a novel composite adaptive control algorithm is proposed under a much weaker interval-excitation (IE) condition. More specifically, parameter adaptive estimation accuracy and speed are quantificationally ensured by employing a composite technique. Therefore, both steady-state performance and transient-state performance are achieved for the position synchronization and parameter estimation with the proposed control strategy. The Lyapunov function and the multidimensional small-gain framework are utilized to derive system stability criteria. It demonstrates that the allowable maximal derivatives of the transmission delays can be easily computed with the given parameters of the control algorithm and the nonlinear performance functions. Finally, both simulation and experimental results are provided to demonstrate the feasibility and superiority of the proposed composite adaptive strategy.

Force feedback control for bilateral teleoperation system with unknown Prandtl-Ishlinskii hysteresis

Hysteresis nonlinearity is a common phenomenon in mechanical actuators. Specially, it appears when the direction of motion of mechanical actuated joint is reversed in robotic manipulator. This paper focuses on the force feedback control problem for bilateral teleoperation system with unknown Prandtl-Ishlinskii (PI) hysteresis. First, an improved sliding mode observer with adaptive gains is provided for estimating the external force signals acting on the manipulators. This removes the need for force sensors and reduces hardware-cost. Next, to improve transparency and guarantee the passivity of the communication network, a four-channel wave variable transformation scheme including force information is introduced. Then, an adaptive switching-based control framework is proposed to deal with Prandtl-Ishlinskii hysteresis dynamics. Finally, the theoretical findings are supported by simulation and experiment results.

Neuro-fuzzy control of bilateral teleoperation system using FPGA

This paper presents an adaptive neuro-fuzzy controller ANFIS (Adaptive Neuro-Fuzzy Inference System) for a bilateral teleoperation system based on FPGA (Field Programmable Gate Array). The proposed controller combines the learning capabilities of neural networks with the inference capabilities of fuzzy logic, to adapt with dynamic variations in master and slave robots and to guarantee good practical robustness against the disturbances, by adjusting neuro-fuzzy network output parameters in a short time, thanks to the computing power of FPGA and its high sampling frequency. The design methodology adopted to design the control algorithm aims to minimize the hardware resources used by the FPGA in order to optimize the execution and the design times, and this by using the Fixed-Point Tool and HDL Coder features of MATLAB-Simulink. The proposed controllers were experimentally validated on a teleoperation system comprising a pair of one degree of freedom. The experimental results clearly show that the proposed ANFIS control algorithm significantly outperformed the conventional control methods (PID).

Composite adaptive control for bilateral teleoperation systems without persistency of excitation

Composite adaptive control schemes, which use both the system tracking error and the prediction error to drive the updating law, have become widespread in achieving an improvement of system performance. However, a strong persistent-excitation (PE) condition is required to guarantee the convergence of the parameter estimation errors. This paper proposes a novel composite adaptive control for nonlinear teleoperation systems with dynamic uncertainties and time-varying communication delays, by which the parameter convergence is achieved without the PE condition. The novelty lies in the construction of the prediction errors by designing lower-bounded gain matrices of the prediction errors. The stability criteria of the closed-loop teleoperation system are given in terms of linear matrix inequalities. Simulation studies are given to show the effectiveness of the proposed method.

Synchronization control for bilateral teleoperation system with position error constraints: A fixed-time approach

In this work, a novel exponential-type Barrier Lyapunov Function (EBLF) is proposed to address the synchronization control issue for a class of bilateral teleoperation systems with system uncertainties, external disturbances, and constraint requirement. The most prominent feature of the EBLF is that it can be used in a unified scheme, which deals with full state constrained and output constrained problems. Moreover, a novel control strategy is incorporated with the EBLF to achieve fixed-time convergence into a small set while the synchronization position tracking errors are guaranteed to never exceed the predefined constraints through the “adding a power integrator” technique, and the estimated settling time is shown to be independent of initial values. Simulation results demonstrate the effectiveness of the proposed control scheme.

Force Reflecting Control for Bilateral Teleoperation System Under Time-Varying Delays

In this paper, the force reflection control problem is addressed for a bilateral teleoperation system with time-varying delays. A dynamic gain force observer is proposed to obtain the force information for the force reflection control scheme. In virtue of the adaptive law, the internal uncertainties can be estimated based on the prescribed performance functions. The corrective wave variable method is utilized such that the bilateral teleoperation system could achieve a satisfactory control performance. A number of practical experiments are implemented on the bilateral teleoperation system to demonstrate the validation of the proposed methodology.

Adaptive finite‐time control for bilateral teleoperation systems with jittering time delays

SummaryIn this paper, we present a robust adaptive control algorithm for a class of bilateral teleoperation systems with system uncertainties and jittering time delays. The remarkable feature of jittering delays is that time delays change sharply and randomly. Conventional controllers would fail because jittering time delays introduce serious chattering. To address the jittering issue, a novel jittering‐free scheme is developed by relaxing and extending the frequently used constant upper bound. Moreover, an adaptive law was incorporated with the Chebyshev neural network to deal with the system uncertainties. To obtain finite‐time synchronization performance, a fast terminal sliding mode controller is proposed through the technique of “adding a power integrator.” With the proposed control scheme, the robust finite‐time convergence performance is guaranteed. The settling time can be further calculated with the controller parameters. The simulation and experiment results have demonstrated the effectiveness of the proposed method.

Hybrid Analog/Digital Control of Bilateral Teleoperation Systems

Hybrid analog/digital control of bilateral teleoperation systems can lead to superior performance (transparency) while maintaining stability compared to pure analog or digital control methods. Such hybrid control is preferable over pure analog control, which is inflexible and not ideal for realizing complex teleoperation control algorithms, and pure digital control, which restricts teleoperation performance due to a well-known stability-imposed upper bound on the product of the digital controller's proportional gain and the sampling period. In this paper, a hybrid controller combining a Field programmable analog array (FPAA) based analog controller and a personal computer-based digital controller is compared in terms of performance and stability to its analog and digital counterparts. A stability analysis indicates that the addition of analog derivative term widens the range of teleoperation controls gains that satisfy the stability conditions, paving the way for improving the teleoperation performance. We also show how the hybrid controller leads to better teleoperation performance. To this end, we study the human's performance of a switch flipping task and a stiffness discrimination task in the teleoperation mode. In both tasks, the hybrid analog/digital controller allows the human operators to achieve the highest task success rates.

Stabilisation for teleoperation systems with sampled-data information feedback

ABSTRACTThis paper considers sampled-data control of bilateral teleoperation systems in the presence of time-varying delay. The assumptions on continuous-time position/force signal transmission are removed and the proposed control strategy is more realistic. By constructing a novel delay-dependent Lyapunov functional, the relationship is established among the control parameters, the delay bounds and the upper bounds of the sampling periods. The tracking performance can be achieved with the designed controller. Simulations and experiments are both provided to verify the effectiveness and benefits of the proposed approach.