Chih-Jer Lin

Identification and Compensation of Nonlinear Friction Characteristics and Precision Control for a Linear Motor Stage

The main goal of this investigation is to improve the tracking accuracy of the stage of a linear motor. A DC brushless linear motor is used to actuate a gantry stage to perform printing. To compensate for the tracking error of the gantry stage that is associated with nonlinear friction, the dynamics of the nonlinear static friction are formulated using the Hsieh-Pan model. Particle swarm optimization (PSO), genetic algorithm, and real-coded genetic algorithm-based optimization problems are investigated to evaluate the parameters of the nonlinear friction model. The use of PSO-based optimization to tune the parameters of a disturbance-observer-based variable structure controller is also discussed to improve the tracking response. To check the consistency of the proposed controller, it is implemented in real time and an improved positional accuracy better than 0.1 μm is readily achieved.

Tracking control of a biaxial piezo-actuated positioning stage using generalized Duhem model

Nonlinear hysteresis modeling is studied using a novel PZT-actuated flexure-based mechanism. To compare the performance of variant hysteresis models with respect to the tracking reference, we reformulate the Bouc-Wen model, the Dahl model and the Duhem model as a generalized Duhem model. System parameters for these three hysteresis models are formulated into nonlinear optimization problems with constraints. These optimization problems are solved by the particle swarm optimization method. Since the Duhem model includes both electrical and mechanical domains, it has a smaller modeling error compared to the other two hysteresis models. The simulation results are confirmed by modeling the proposed biaxial piezo-actuated positioning stage of these hysteresis models. Cross-coupling effects between the X- and Y-axis actuation are also alleviated by a novel feedforward compensation mechanism based on the Duhem model with crossover terms. Finally, a real-time experiment is performed to confirm the feasibility of the proposed method. The experimental results validate the capability of the proposed controller to achieve precision tracking tasks with submicron precision.

Motion planning of redundant robots by perturbation method

A redundant robot for the specific applications to trajectory tracking, singularity avoidance, and obstacle avoidance is considered in this paper. This paper also presents an optimal path planning approach to minimize the cost of moving a redundant robot manipulator along a specified geometric path subject to angle change constraints. The proposed motion planning approach using the forward kinematics and the perturbation method can be applied to solve the path planning problem with geometrical singularity and task priority requirements, such as obstacle avoidance and singularity avoidance. The solution is obtained according to the design objective using an optimization procedure. The experiments using the RV-M2 robot of MITSUBISHI are also presented.

PRECISE POSITIONING OF PIEZO-ACTUATED STAGES USING HYSTERESIS-OBSERVER BASED CONTROL

Abstract The piezo-actuated stages are composed of the piezo-electric actuator and the positioning mechanism. The positioning accuracy of the piezo-actuated stage is limited due to hysteretic nonlinearity of the PEA and friction behaviour of the positioning mechanism. To compensate this nonlinearity of piezoelectric actuator, a PI feedback control associated with feedforward compensating based on the hysteresis observer is proposed in this paper. To verify the consistency of the proposed method, the experiments are implemented by real-time control to be compared with the numerical simulation.

PSO Based PI Controller Design for a Solar Charger System

Due to global energy crisis and severe environmental pollution, the photovoltaic (PV) system has become one of the most important renewable energy sources. Many previous studies on solar charger integrated system only focus on load charge control or switching Maximum Power Point Tracking (MPPT) and charge control modes. This study used two-stage system, which allows the overall portable solar energy charging system to implement MPPT and optimal charge control of Li-ion battery simultaneously. First, this study designs a DC/DC boost converter of solar power generation, which uses variable step size incremental conductance method (VSINC) to enable the solar cell to track the maximum power point at any time. The voltage was exported from the DC/DC boost converter to the DC/DC buck converter, so that the voltage dropped to proper voltage for charging the battery. The charging system uses constant current/constant voltage (CC/CV) method to charge the lithium battery. In order to obtain the optimum PI charge controller parameters, this study used intelligent algorithm to determine the optimum parameters. According to the simulation and experimental results, the control parameters resulted from PSO have better performance than genetic algorithms (GAs).

Chaos suppression control of a coronary artery system with uncertainties by using variable structure control

Nonlinear behavior and the chaos suppression problem are studied in a coronary artery chaotic system. Based on the variable structure control (VSC) theory, the sliding mode control scheme is used to design a chaos suppression controller in this study. A suitable sliding surface is selected to ensure a sliding mode motion of error states when the proposed control law is applied. As expected, the error state drives to zero with matched external uncertainties or into a predictable neighborhood of zero with mismatched external uncertainties. Therefore, suppressing the abnormal chaotic behavior of a coronary artery system to a normal unstable periodic orbit of the nominal coronary artery system can reduce the occurrence of heart disease. A modified continuous sliding mode controller is also proposed to avoid chatter. Illustrative examples are given to demonstrate the superiority of the proposed approach.

Motion planning of redundant robots

Motion planning of robot manipulators is one of the most challenging problems encountered in the field of robotics. This article concentrates on those problems that require geometrical singularity and task priority. An alternative to the conventional approach is proposed, using a forward kinematics and optimization technique. The solution can be obtained corresponding to the design objective using an optimization procedure. The robustness of the proposed method to geometrical singularity is demonstrated. The concept of the permissible region is proposed for the motion planning problem with obstacle avoidance. Illustrated examples are also given.© 1997 John Wiley & Sons, Inc.

System Identification and Semiactive Control of a Squeeze-Mode Magnetorheological Damper

The main goal of this investigation is to establish modeling of a squeeze-mode magnetorheological (MR) damper and to design a semiactive fuzzy controller for vibration reduction. To model the MR damper, the Bouc-Wen model has been used in many past studies. However, using the Bouc-Wen model to characterize the squeeze-mode MR damper needs a lookup table of system parameters for the application with various amplitudes and frequencies. Therefore, a biviscosity model is proposed to describe this squeeze-mode MR damper. In addition, genetic-algorithm-based optimization is used to evaluate the parameters of the system. To reduce the vibration of the structure, a semiactive fuzzy controller using the MR damper is presented for the structure vibration at various frequencies. To check the consistency of the proposed fuzzy controller, the real-time implementation validated the performance of the controller.

Structural vibration control using a tunable hybrid shape memory material vibration absorber

Vibration absorber has been used as an effective tool in the vibration reduction of structure-suffered single-frequency excitation. However, for structures subjected to excitation with varying frequency, an absorber with actively tunable frequency capability may offer more powerful solution. In this study, an absorber that consisted of a spring element made of hybrid shape memory materials was proposed. A cantilevered beam fabricated by superelastic core and shape memory polymer sleeves was employed as the spring element of the absorber. By controlling the electric current through the superelastic core, and thereby the temperature of the shape memory polymer sleeves, the natural frequency of the absorber was tunable. The fabricated hybrid shape memory material absorber was capable of changing its natural frequency by more than 45%. Finally, vibration reduction of a cantilever structure subjected to different harmonic excitations was demonstrated using gain-scheduling control algorithm.

A SLIDING MODE CONTROL APPROACH TO ROBOTIC TRACKING PROBLEM

Abstract In the conventional sliding mode control, a discontinuous switching control signal is applied. It makes the system invariant to parametric uncertainty and external disturbance, but also causes actuator chattering. This paper considers a tracking control of robot manipulators using a dynamic sliding mode control, where a global invariance is achieved and the resulting control signal is chattering free. The resulting performances are illustrated by its application to the tracking problem of robot manipulators.