Motion control of electromechanical actuators at sub-micron precision

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Motion control of electromechanical actuators at sub-micron precision


Author: Chow, Hoi Wai
Title: Motion control of electromechanical actuators at sub-micron precision
Degree: Ph.D.
Year: 2012
Subject: Motion control devices.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Electrical Engineering
Pages: 211 leaves : ill. ; 30 cm.
Language: English
InnoPac Record:
Abstract: High precision linear motion has attracted much attention in the manufacturing industry. To fulfill the requirements of demanding industrial applications, high precision motion system should be accurate, fast responding, and inexpensive. Various types of linear motion systems have been developed, but few of them can fulfill all of the above requirements. A linear motion system usually suffers from external environmental influences, such as friction, erratic external forces, and load variations. This project aims to investigate and propose several motion-control methodologies, so that a fast and high precision linear motion down to submicron level can be achieved. Under this goal, a high precision position encoder based on laser interferometric method has been developed. A resolution increasing circuit has been developed and a fusion algorithm has been utilized so that the speed and accuracy of the motion sensing can be improved. In addition, a prototype of high precision linear motion system based on a permanent magnet linear motor, with an adaptive intelligent control algorithm has been developed. Both the simulation results and the experimental results validate the usefulness of the proposed methods. This project develops a high precision low cost linear motion sensor based on the optical interferometer with a 3 x 3 fiber coupler. The simulation results and the experimental measurements from a prototype linear motion sensor have demonstrated that a successful linear motion sensing system with low cost, long measurement range, and high accuracy can be achieved by using the novel optical interferometric method.
Optical linear incremental encoder is widely employed in high precision linear motion control because of its high accuracy characteristic. However, the maximum measurement speed of this incremental encoder is usually limited by the clock frequency boundary in the decoder circuitry. To make the incremental encoder more useful in high speed motion control applications, the speed limitation of linear incremental encoder have been overcome by developing a novel enhancement circuit. This circuit is responsible for increasing the resolution of sensor outputs, so that the measurement speed can be improved. The velocity information from the optical linear incremental encoder and the velocity output of the resolution increasing circuit are combined by the data fusion algorithm, so that an accurate position sensing system with higher measurement speed range can be developed. The feasibility of the idea is verified by experiments. Developing a high precision linear motion system with a direct-drive linear motor is a difficult task because this motion system usually suffers from many non-linear characteristics, such as friction, ripple-force, variation of parameter. A high precision motion control algorithm with a modified disturbance compensator and the internal model reference control is proposed and implemented. Satisfactory experimental results have been obtained. The proposed controller is capable of achieving high speed and high accuracy (with position error less than 0.1 μm). Compared with the performance of the conventional disturbance compensator, the response speed to the position command and the external disturbance is much faster when modified disturbance compensator is adopted.

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