Research On Position And Attitude Control System Of Parallel Lifting Platform Based On Permanent Magnet Synchronous Linear Motor Cooperative Motion

With the successful commercial applications of Stewart Platforms,there is a great upsurge of parallel mechanism research including mechanism design and control strategy development.The parallel lifting platform is a kind of parallel mechanism,which plays an important role in the motion simulation platform and the parallel machine tool.Especially,the accuracy of position and attitude control can directly affect the user experience of the simulation platform and the machining accuracy of the parallel machine tool.Therefore,the position and attitude control of the lifting platform is of great significance.At present,most of the driving mechanisms of the parallel lifting platform adopt hydraulically or screw drive motor.Although this driving mechanism can provide enough load capacity,the response speed and accuracy of position and attitude control are low,which is difficult to meet the needs of high precision and rapid response to these applications.In this paper,the permanent magnet synchronous linear motor(PMSLM)is used as the driving mechanism of the parallel lifting platform,which has the advantages of simple structure,fast response,and high precision.Compared with the traditional parallel lifting platform,the position and attitude control have the characteristics of faster speed and higher precision.In order to effectively avoid the complex dynamic modeling and controller design of the parallel lifting platform,the position and attitude control adopt the space control strategy based on the kinematic model.At the same time,in order to reduce the complexity of control,the position first and attitude second control method is used to achieve the independent control of position and attitude.Therefore,the research contents of this paper are as follows: firstly,analysis of the mapping relationship between the position and attitude of platform and motion positon of each PMSLM is carried out.Secondly,modeling the vertical permanent magnet synchronous linear motor,the parameters of the servo controller is designed in combination with the actual motor and driver parameters,and the gravity compensation scheme on the current loop is directly designed.At the same time,the fuzzy controller is designed on the speed loop to increase the anti-interference performance in the process of position tracking.Then,aiming at the problem that the synchronous performance among multiple motors affects the position tracking accuracy of the parallel lifting platform and the attitude tracking error exists in the attitude open-loop control,the deviation coupling control structure and the attitude deviation compensation algorithm are designed.At last,the experimental setup of the position and attitude control system is built.The experiments on position tracking of the single vertical permanent magnet synchronous linear motor and position and attitude tracking of the parallel lifting platform are carried out.The experimental results are as follows: Firstly,under the control framework of servo system of "position loop(proportional control P)+ speed loop(fuzzy proportional integral PI)+ current loop(proportional integral PI)",the absolute value of position tracking forward(up)error and negative(down)error without gravity compensation current is 0.75 mm and 0.45 mm respectively.After the gravity compensation scheme is implemented,the absolute error from either upward or downward direction can be controlled not greater than 5 μm,which indicates that PMSLM can achieve high-precision position tracking under servo control in a vertical motion,and adding gravity compensation current can reduce the impact of gravity on position tracking error inconsistency.Secondly,under the space control strategy of the fulcrum point,compared with adding the deviation coupling control and attitude deviation compensation algorithm,experimental results demonstrate that the position error of the parallel lifting platform can be reduced from 18 μm to 9 μm and the attitude tracking error is reduced from 1.5 degrees to 1.2 degrees,which means the accuracy of position tracking and attitude are successfully improved by 50% and 20%,respectively.It shows that the deviation coupling control and attitude compensation can effectively improve the attitude tracking accuracy.