Ping Sun

Robust Redundant Input Reliable Tracking Control for Omnidirectional Rehabilitative Training Walker

The problem of robust reliable tracking control on the omnidirectional rehabilitative training walker is examined. The new nonlinear redundant input method is proposed when one wheel actuator fault occurs. The aim of the study is to design an asymptotically stable controller that can guarantee the safety of the user and ensure tracking on a training path planned by a physical therapist. The redundant degrees of freedom safety control and the asymptotically zero state detectable concept of the walker are presented, the model of redundant degree is constructed, and the property of center of gravity constant shift is obtained. A controller that can satisfy asymptotic stability is obtained using a common Lyapunov function for admissible uncertainties resulting from an actuator fault. Simulation results confirm the effectiveness of the proposed method and verify that the walker can provide safe sequential motion when one wheel actuator is at fault.

A robust adaptive tracking control method for a rehabilitative walker using random parameters

ABSTRACT The present paper investigates stochastic modelling and a new nonlinear reliable tracking control method for a rehabilitative training walker. The stochastic model is constructed by considering random parameters. A new nonlinear tracking method against actuator fault is proposed based on redundant degree of freedom and a state feedback controller is designed by exploiting an adaptive control technique. It is proved that the mean square of the trajectory tracking error can be made arbitrarily small by choosing appropriate design parameters. As an application, simulation results confirm the effectiveness of the proposed method and verify that the walker with random parameters can provide safe sequential motion when one wheel actuator is at fault.

Output tracking control for an omnidirectional rehabilitative training walker with incomplete measurements and random parameters

ABSTRACT In this study, we propose a model and an output feedback tracking control for an omnidirectional rehabilitative training walker (ODW) with unmeasurable speed, incomplete measurements of position output, and random structural parameters. A stochastic model and an incomplete measurement model were proposed to describe the motion of an ODW subject to random structural parameters and to account for any incomplete data transmission phenomenon caused by possible sensor ageing or failures. A speed observer and a state observer were designed to estimate the unmeasurable speed and the incomplete measurements of position output. Moreover, a dynamic output feedback controller was constructed to ensure the exponential stability in mean square of the tracking error system. Furthermore, the results verify that the choice of appropriate design parameters can result in the mean square of the tracking error becoming arbitrarily small. A simulation example was provided to illustrate the effectiveness of the proposed design procedures.

Improvement model for omnidirectional rehabilitative training walker and tracking control

This paper is concerned with the problem of improvement model for the omnidirectional rehabilitative training walker and tracking control. The aim of the study is to obtain a model that closes to actual walker by considering motor rotation character. An asymptotically stable controller was gotten that can ensure tracking on a training path planned by a physical therapist. The controller that can satisfy asymptotic stability is obtained by constructing the Lyapunov function. The simulation results confirm the feasibility and effectiveness of the designed scheme and indicate the walker can ensure tracking motion by using the improved model.

Stochastic adaptive tracking for a rehabilitative training walker with control constraints considering the omniwheel touchdown characteristic

ABSTRACT This article investigates the improvement of trajectory tracking on an omnidirectional rehabilitative training walker (ORTW) with random shifts in the centre of gravity, control constraints, and touchdown characteristics of omniwheels. Analysis of the touchdown characteristic improved the accuracy of the dynamic ORTW model. The control constraints guarantee the safety of the omniwheels and the ORTW training process. After describing the random centre-of-gravity shifts using Wiener process, an improved stochastic dynamic model was constructed. Under trajectory tracking control with adaptive technology, the ORTW followed the trajectory designed by the rehabilitation therapist. The exponentially practical stability in mean absolute of the tracking-error system was derived from stochastic theory and Markovs inequality. The effectiveness of the proposed methods was confirmed in simulations.

Fault diagnosis and control of a cushion robot considering actuator degradation

This paper investigates fault diagnosis and control of a cushion robot considering actuator degradation. A novel fault diagnostic observer was designed to observe the value of loss of effect on the actuators, which will be used to the trajectory tracking controller. Based on Lyapunov stability theory and LaSalles invariance principle, it is proved that the designed fault diagnostic observer and the controller can make the tracking error system asymptotically stable. Simulation results demonstrate the feasibility and effectiveness of the proposed method.

Tracking control for an omnidirectional rehabilitative training walker with safety velocity performance

In this study, a new nonlinear trajectory tracking method with velocity constraints performance is proposed for an omnidirectional rehabilitative training walker. The aim is to guarantee the rehabilitee can complete rehabilitation training under the safety velocity. According to Lyapunov theory, the safety velocity controller can be designed to maintain stability in terms of solutions of linear matrix inequalities. The concept of safety velocity is given and the sufficient condition for the existence of such a controller with safety velocity constraints performance is derived. As an application, simulation results confirm the effectiveness of the proposed method and verify that the walker can provide safe training velocity.

Robust fault-tolerant compensation tracking control for omni-directional rehabilitative training walker

This paper is concerned with the problem of robust fault-tolerance tracking control on the omni-directional rehabilitative training walker. The nonlinear robust fault-tolerance compensation method is proposed when a fault occurs on one wheel actuator. The aim of the study is to design an asymptotically stable controller that can guarantee the safety of user and ensure tracking on a training path planned by a physical therapist. The controller that can satisfy asymptotic stability is obtained by constructing the energy storage function and the dissipation inequality. An evaluation signal is designed to verify the nonlinear gain performance index. Finally, the simulation results confirm the feasibility and effectiveness of the designed scheme and indicate the walker can ensure safety motion when one wheel is at fault by compensation input forces for another three wheels.