Theoretical And Experimental Research On The Stick-slip Precise Transportable Platform Driven By Piezoelectric Bimorph

As one of the prevail research in micromanipulation systems, the in-plane precise transportable module is indispensably. Whether used in some operations such as micromachining, micro-assembly and inosculate/separate of the cells etc., or in some locomotive modules for micro-robot. The key of the research can be summarized as below, i.e., in order to drive the transportable module, what type of actuators is suitable and how to drive the mechanism utilizing the selected actuator as well as how to control them. Recently, a lot of researching works in the world have been done and many types of precise transportable platform driven by different materials and different principle have been proposed. Among these prototypes, the piezoelectric type platforms are important ones. The present research results about platforms, however, mostly choose PZT stacks or some special component manufactured through complicated device and process. Up to now, the stick-slip type in-plane precise transportable platforms driven by common piezoelectric bimorph have not been found. In this paper, a new method that bimorph is used to drive transportable platform is proposed based on the analysis to the performance of piezoelectric bending elements. The platform has 3 actuators which work on stick-slip mode and the actuating directions are intersectant. As well known, the distinct advantages of stick-slip type of mechanism are simple structure and apt to fabricate. In such platform, the ordinary sandwiched piezoelectric bimorph is used for actuator. The basic using method of bimorph is that fixed two edges of the metal layer and output displacement as well as force in the midline. The fixed manner is expecting to augment the output force and improve the frequency response. Combined with stick-slip principle, a new kind of in-plane precise transportable platform is developed. Moreover, such proposal of combined fixing two edges and stick-slip principle can maximize the output force. In addition, the working manner of the platform is carrying load on the back, which is in favor of obviating the weakness of bimorph such as small force and weak stiffness. The main studies of this paper are as followed. In the thesis, the kinematics differential equation and the displacement differential equation of bimorph are deduced. Therefore, it provides theoretical guide to determine the structural parameters of piezo actuators (such as small dimension, high load bearing ability, large displacement and high frequency response etc.) and to improve moving ability of the platform. Because it is difficult to resolve the piezoelectric sheet while its shape is abnormity, the Finite Element Analysis method is adopted to analyze the influence to the actuator's bending characteristic of the sheet's protuberance. This provides the reference to determining the protuberance dimension. On various structural parameters, 8 pieces of typical bimorphs are made in order to confirm the main static performances of the bimorph under the condition of fixing two edges. At the same time, the contrasts among the actuator samples are also made. In order to eliminate the measuring errors as possible as we can, every index is tested repetitious, then get the average as the results. So the testing time is long and tedious. Making use of the interface function of apparatus, automatic testing software is programmed. Computer accomplishes all the testing works except putting on the mechanical load, include storage of the data, drawing the curve, etc. The testing results list below. Displacement decreases with the thickness of metal layer increases and the reverse when the thickness of piezoelectric layer increases under the condition of two edges fixed. Compared with bimorph, the loading capacity of multi-morph is improved, but the transitiontime is lengthened. The nonlinear properties are similar to that of piezoelectric stack, the hysteresis loop and creep value are in the same order. The hysteresis loop under no load are bigger than that under load. The ratio of creep value to initial displacement is less than that of stack. It has been proved that bimorph fixed two edges can satisfy precise positioning and precise driving. Based on the former works, a 2-DOF precise stick-slip type transportable platform is produced and the dynamic model of single freedom platform is established. Based on the model, some simulation analysis has also been done. The simulation results are consistent with the experimental results. It proves that the dynamic and simulation model are appropriate and could describe the kinematics character properly. These models are suitable for optimizing design parameters and guide the further research. Some tests to the 2-DOF precise stick-slip type transportable platform have been done. The experimental results prove that: ①Motion linearity of the structure seems well, the velocity within forward and backward is unanimous, the step error is about 0.05um, the excursion error is about 2%. ②Step Value of such stick-slip device is among that of the n pieces of actuators. ③Within 50V of the drive voltage, the linearity of the step-voltage curve is excellent. ④The step value of the device is decreased slowly with the increase of driving frequency, but the change is little below 50Hz, so it can be approximately considered only relate to the driving voltage. ⑤The bearing ability is well and the step is steady under the outer load of 100gf below. ⑥The device velocity can be adjusted by changing the driving voltage or the working frequency. Since the working performance and controllable property of the 2-DOF prototype have been confirmed, a 3-DOF prototype is developed Based on the kinematics analysis, the control method to the 3-DOF platform is proposed. Furthermore, a special controller that based on the 8 bits 51 serials MPU is also fabricated, which is a small bulk and high reliability. The results of experimentation prove that the performance of the controller as well as its software is excellent. The platform is able to move anywhere within a plane underthe operator's constructions. Results from the references to the experimentations, corresponding improvements to the control tactics are made. The paper's creative works are listed below. 1) Bring forward a new concept about stick-slip type platform driven by ordinary bimorph which two edges are both fixed. 2) The main static properties of bimorph are tested and made contrast. The results confirm the feasibility of application in the precise actuation field of bimorphs. 3) The prototype of this kind of machine is manufactured and the dynamic model of it is established. Furthermore, the driving controller and the control software are also developed. Experiments prove that the platform could reach any location and make precise positioning within the horizontal plane. Recently, a lot of researching works on the precise transportable platform have been done. Up to now, however, the stick-slip type ones driven by common piezoelectric bimorph have not been found. This paper proves that the feasibility of the driving principle and control method of stick-slip type platform actuated by bimorphs on both theory and experiment aspect. These works make well foundations for the miniaturized autonomous transportable platform integrated mechanical and electrical units. Many problems, however, should be still deeply researched in the future, such as location detection, autonomous motion's realization, miniaturization etc.