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Research Of The Planar 3PRR Parallel Positioning System Under The Micro/nano Operating Environment

Posted on:2017-04-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:J S MoFull Text:PDF
GTID:1108330503468583Subject:Mechanical and electrical engineering
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Micro/nano operation system is an important development direction in the fields of the precision operation, precision manufacturing and precision measurement. Micro/nano operating system generally includes the observer, positioning platform, operator, and controller and so on. The content of this paper is the macro part of the macro-micro combination positioning platform which uses the scanning electron microscopy(SEM) as the observer. In order to fulfill the requirements of micro/nano operation and macro-micro combination, in this paper, the planar parallel mechanism driven by ultrasonic linear motor called 3PRR has been studied. This mechanism has three links; each link has a prismatic pair as the driven joint, and 2 revolute pairs, so it is called the 3PRR mechanism. The positioning platform can meet the requirements of magnetic-field free and vacuum compatible under SEM environment. Combining with the mechanism optimization and control algorithm, the macro positioning platform is able to position in the workspace of the micro positioning platform, usually realizing the micro grade precision.The design and control of the planar 3PRR parallel mechanism have been studied in this paper, whose main contents are list below.(1) Analyze and design the planar 3PRR parallel mechanism. The forward and inverse kinematic of the 3PRR has been established and the velocity Jacobian matrix has been derived. Combining micro/nano operation workspace requirement, obtain the distribution rule of the singularity free workspace by analyzing the 3PRR workspace rule and the singularity rule. According to the precision demand of micro/nano operation,parameters optimization was carried out on the planar 3 PRR parallel mechanism, and combining with the singular workspace constraints, so the optimization parameters of the platform have been achieved. The modeling and analysis of the dynamics model of planar 3PRR parallel mechanism has been taken. The dynamic model of the planar 3PRR parallel mechanism has been established. By Compared with the software simulation results, the correction of the model has been verified. Based on the dynamic model, analyze the end-effector dynamic characteristics. Finally, the experiment prototype has been designed and produced.(2) The error transfer rule and parameter calibration method of the planar parallel mechanism has been studied. Firstly, establish error models of the planar 3PRR and 3RRR parallel mechanism; put forward a global index of the error sensitivities. Based on this index, get the main error sources of two different planar parallel mechanisms, and compare the similarities and differences. By comparing the error transfer matrix and the velocity Jacobian matrix, find that the velocity Jacobian matrix is dimension reduction form of error transfer matrix. Therefore, a generalized Jacobian matrix is defined. Through research on the parameter calibration method based on the error model, the identification methods only identify parts of the parameters. For a planar 3RRR parallel mechanism, the main error can be identified; but for the planar 3PRR parallel mechanism, the main error cannot be identified accurately. In order to make up for this method, some assistant measurement points on the mechanism have been designed. Combining with the error model identification method and the assistant measuring method, the calibration precision can be improved.(3) The singularities avoid and escape method of planar 3RRR parallel mechanism has been studied. The singular area and singularity configuration of parallel mechanism is inevitable; it is one of the most important factors influencing positioning accuracy. In order to improve the positioning precision and dexterity, strengthen the mechanism motion reliability, put forward a control strategy on avoiding and escaping the singular area of the 3PRR parallel platform. Aiming at singular area avoidance, present two control strategies for avoiding singular area, called singularity boundary avoid method and change posture avoid singularity method respectively. In terms of the singularity configuration escape, aiming at three kinds of typical singularity type of the mechanism, designs escape process respectively.(4) The drive and control algorithm of the planar 3PRR parallel positioning platform has been studied. Research on characteristics of ultrasonic linear motor, by modeling and identify the ultrasonic linear motor, the positioning control algorithm was designed. Without considering the dead zone influence caused by static friction, the model reference adaptive control(MRAC) algorithm was applied to joint space positioning control. Positioning effects compared with traditional algorithm. Because the dead zone influence caused by static friction has not been considered, trajectory tracking error is still large. In order to further improve the trajectory tracking precision, design the friction feedforward compensation control algorithm and the adaptive friction compensation control algorithm. These two algorithms can compensate the dead zone influence caused by static friction and improve the trajectory tracking precision. But the friction feedforward compensation control algorithm needs to measure the static friction dead zone size in advance, which has great limitations. But adaptive friction compensation control algorithm can carry out adaptive compensate the dead zone influence cause by static friction according to the volume of generalized deviation, which has a better applicability.(5) Experimental research, first of all, carry out the ultrasonic linear motor identification and positioning control experiment, then take the kinematics parameter calibration experiments based on the planar 3PRR parallel mechanism, finally, conduct the end-effector positioning control experiment.
Keywords/Search Tags:Micro/nano operating environment, Parallel mechanism, Precision positioning, Adaptive control, Ultrasonic linear motor
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