Research On Giant Magnetostrictive-Piezoelectric Precision Drive Mechanism And Control Technology

Along with the increasing cognition of people to microcosmos, people raise much higher standers to the processing and control precision in machinery industry. The mechanical and electrical products are developed in the direction of miniaturization and micromation. Having high precision and resolution, the actuator technology has become the bases and key in the leading edge of modern manufacture, such as procession and high-procession processing, micro-machining, micron/nano-meter technology and so on, of which the level of technology can reflect the levels of economy integration and technology. Therefore, a variety of precision actuators have come into existence and become the focus of study by national and international scholars. Basing on giant magnetostrictive material, various kinds of microdisplacement actuator have the advantages of big displacement, strength, high resolution, quick response, high reliability, small drift, low driving voltage, no fatigue phenomenon and being easy to control. It has been paid high attention by people in national defense, military industry, the industry of aerial navigation and aerospace industry, electric industry, automatic control, marine science, machinery, weaving, automobile industry, petroleum, medical service, optics and other fields. In order to further increase the displacement output of precision actuator, various inchworm stepping actuators appear successively.Giant magnetostrictive stepping precision actuator overcomes the disadvantage of small working travel of direct drive and displacement amplification types. It does not only meet the request of large travel, but also micro-displacement output of small travel. After analyzing the characteristics of giant magnetostrictive materials and giant magnetostrictive displacement actuator, this thesis proposes a research plan of new giant magnetostrictive piezoelectric precision actuator , which takes giant magnetostrictive actuator as displacement driving mechanism and piezoelectric stack as clamping mechanism by combining with flexure hinge, pointing to the research status and existing problems of inchworm actuator, and conducts the research on and analysis of mechanical design, driving power, control system and other aspects of different mechanisms.1. Basic theoretical research of giant magnetostrictive materialGiant magnetostrictive material is in the varying magnetic field. It can conduct elongating and shortening movements in axial direction. By utilizing this characteristic of material, we can develop actuators for various purposes. As the driving element of giant magnetostrictive precision actuator, the performances of giant magnetostrictive material directly decide the output of actuator. Therefore, further research on and analysis of giant magnetostrictive material shall be conducted. Under study , the output of giant magnetostrictive material relates to the applied magnetic field strength, compressive stress, working temperature and other factors, meanwhile the output precision is restricted by electromechanical coupling degree of actuator, hysteresis, eddy current loss, and△E effect of materials. For the convenience of control, a bias magnetic field shall be applied to make it operate in linear area as a result of phenomenon of multi-frequency. This thesis researches on and analyzes the design theory of magnetic circuit for giant magnetostrictive actuator, forms the equation of magnetic circuit and provides design principles and methods of actuator and theoretical basis for structure design and performance analysis for displacement driving mechanism of giant magnetostrictive precision actuator.2. Structure design and analysis of giant magnetostrictive precision actuator.This thesis deeply researches on the design for driving mechanism, clamping mechanism, regulating unit and driving control system of giant magnetostrictive precision actuator and working principles and performances of various parts, and conducts tests. Apply home made GMM rod (φ8×35mm) and two piezoelectric stack (8×8×40mm) to compose inchworm micro-displacement mechanism; compose giant magnetostrictive micro-displacement actuator, of which the magnetic circuit of driving mechanism (driving coil and bias coil), working structure and temperature control system has been analyzed. It takes the way of power optimization for the coil and the water cooling with double water chamber to decrease the effect of the displacement accuracy due to the rise or change of operating temperature of the coil.; Piezoelectric clamping mechanism is another important component ensuring the output precision of actuator. The clamping strength, selection, assembly precision and symmetry of flexure hinge, the stiffness of connecting parts on clamping and driving mechanisms will have influences on the entire performance of actuator. This thesis conducts systematic analysis the designs of these mechanisms, researches on the stepping process and control time sequence of inchworm giant magnetostrictive precision actuator, designs generation system of time sequence controller, establishes the dynamic models of driving and clamping mechanisms and conducts analysis of theory. Through testing the sample of actuator, while prestress is 10MPa and the driving current change from 0 to 2A,the static displacement of the actuator has well linearity; The maximum fluctuation of the output displacement is 0.02μm in the water cooling state. The developed precision displacement mechanism can achieve bidirectional controllable movement. The maximum displacement of single step proceeding is 20.12μm, resolution of single step displacement can be 0.032μm, the maximum force of clamp is 110N, the maximum driving force is 101N, and maximum velocity is 60μm/s. Control the displacement of single step by regulating the driving current to meet the requirement of precision positioning.3. Design of and research on driving power and systemBased on the research of process of step motion and the time sequence of control for the inchworm giant magnetostrictive precision actuator. A generators of time sequence controller is designed for controlling the motion process of this actuator after the computer set parameters. In order to improve the precision of power supply and the stability of output, reduce the output ripple of power supply, this thesis researches on and designs a digital constant current power supply according to the magnetic strength of giant magnetostriction materials-the driving characteristic of striction quantity on the basis of analysis of driving characteristics of giant magnetostriction precision displacement actuator and the requirement to driving power supply. This digital constant current power supply has the feature of wide range, high precision, low ripple, quick frequency response and continuous adjustable regulation. And it can close loop to control output voltage in case of continuous changes of load. The output circuit is composed of serial 12-bit DACs Max531, low-noise high-speed precision operational amplifiers OP27 and driving circuit. It provides current from 0 to 2.048A with 0.5mA step value. Two fully differential input channels 16-bit, sigma-delta ADCs AD7705 collects output current in feedback loop. Current ripple is controlled under 0.25mA through using homemade high-performance linear power. The result shows that the driving power with characteristic of high stability and fast response meets the needs of driving of Giant Magnetostrictive Accurate–motion.4. Design of control system and research on control strategyGiant magnetostrictive actuator is the significant component achieving traveling motion to mixing precision actuator. Its control performance have a direct impact on the displacement accuracy of his actuator. Therefore, this paper studies the control strategies and control methods of the actuator system; firstly proposes using auto-disturbance rejection control method for control strategies; has studied the establishment of auto-disturbance rejection controller in further theoretical research; establishes the mathematical model of a giant magnetostrictive actuator system; and constructs auto-disturbance rejection controller of the actuator.Aiming at setting multiple parameters of control algorithm,this paper proposes a new setting method based on the parameters change, whith setting the system parameters of the auto-disturbance rejection controller. The method simplifies the tedious process of setting the parameters of a class of control objects quickly and efficiently. Simulation results show that, auto-disturbance rejection controller used in actuator control system model , measured values have a good degree of coincidence with the givens; the system has a very small overshoot magnitude; control effect is better than traditional PID control. Interference simulation proved that the auto-disturbance-rejection system has excellent anti-jamming effect. When the time parameter of the controlled object changes within a certain range, the system still obtains good control effects. It shows the auto-disturbance rejection control have strong robustness.5. Research on performance test of driving systemAfter establishing the closed loop auto-disturbance rejection control system of the hybrid actuator, the system uses computer to calculate by auto-disturbance rejection algorithm and real-time regulates and controls the driver according to the position deviation of the displacement. The control systems in wired and wireless are builded respectively. The results of these two kind of system are approximately equal, and the maximum of absolute error in location is 0.04μm. It achieves the objectives of precision control.Inchworm giant magnetostrictive precision actuator has the advantages of long travel, large driving force and high resolution. This mechanism can be applied to the system needing precision positioning. It is fixed on the coarse adjustment unit, through which the long travel can be achieved to accomplish precision positioning. It has a bright application future to high-processing machine tool, work bench for precision positioning, and aerial navigation and aerospace industries.