Posture Control of a 6-DOF Parallel Hydraulic Manipulator and Washout Filter Design for Virtual Reality Application
Date Issued
2011
Date
2011
Author(s)
Chen, Sung-Hua
Abstract
The vehicle simulator is an integrated system which is a synthesis of motion platform system, computer graphs, 3-dimensional physics, and a motion cueing algorithm. This dissertation investigates the nonlinear control issues of a hydraulic actuated Stewart platform used as the motion platform in the vehicle simulator system, and the motion cueing algorithm.
In first part of this dissertation, an observer-based forward kinematics solution of a 6-6 Stewart platform is proposed and this algorithm is applied to implement an output feedback sliding mode control. The conventional forward kinematics solutions take too much computational load or are too complex to be carried out in the on-line control scheme. With the proposed solution, 6-DOF posture control of the moving platform can be achieved without installation of any external sensor after applying an output feedback control. In contrast with the conventional control scheme which aims to control individual leg length in actuator domain, the output feedback controller is proposed here to control the posture in Cartesian coordinates directly. The stability is proved to ensure convergence of the tracking errors.
After that, a backstepping control strategy is proposed to control the 6-DOF parallel hydraulic manipulator while incorporating the observed-based forward kinematics solver. Different from conventional control methods, the proposed control considers not only the platform dynamics but also the dynamics of the hydraulic actuators. The objective of controller design is to drive the moving platform such that its posture tracks a given trajectory. The stability of the whole system is thoroughly proved to ensure convergence of the tracking errors. Simulations and experimental results of the output feedback control in first part and the backstepping control are presented to validate the effectiveness of the design.
The realistic motion of the vehicle simulator is produced by the motion cueing algorithm. An optimal washout filter, taking into account the limitation of the simulator’s workspace, is applied here to minimize human’s perception error in order to provide realistic behavior. The filtering algorithm compares the human’s perception of driving simulator with that driving actual vehicle obtained based on the human vestibular model. The cost function accounting for both the pilot’s sensation error and the range of platform motion is minimized. To compensate the drawback of fixed parameters in optimal washout filter, the fuzzy control rules of motion perception are applied to online adjust the filtered signals. The simulation results verify the efficient utilization of the platform workspace and less sensation error in comparison with that obtained by the classical washout filter.
Subjects
Nonlinear Observer
Stewart Platform
Forward Kinematics
Backstepping Control
Hydraulic Actuator
Motion Cueing Algorithm
Sensation Error
Type
thesis
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