Research On Motion Characteristics Of Two Dimensional Precise Positioning Worktable Driven By Linear Motor

As one of the three pillar industries,all countries have attached great importance to the study of materials.In addition to the material properties,its processing technology has also attracted much attention.With the progress of science and technology,people are increasingly demanding more accuracy and efficiency in materials processing.In order to meet these higher requirements,it is inseparable from the support of modern high-end equipment.As the core component of manufacturing equipment,the accuracy and range of the worktable directly determine the machining precision and ability of the manufacturing equipment.The performance of the equipment directly affects the processing quality and efficiency of the equipment.It is an important part of the processing system.The traditional driving device of the worktable is a rotary motor,which is limited by speed,acceleration and machining accuracy.It has been unable to meet the higher processing requirements.Because of the advantages of high speed and acceleration,high positioning precision and unrestricted motion stroke,linear motor will gradually replace the rotating motor as an inevitable trend in the future precision machining field.Therefore,the research of linear motor driven worktable is a hot topic in the field of precision machining in the future.This paper aims to study the motion characteristics of a two-dimensional precision positioning worktable driven by a linear motor.The main contents include the construction of the worktable,the design of the motion program,the debugging of the control system,the motion performance and the study of the precision.From the aspects of driving,guidance,detection and control,the parts of the two dimensional workbench are discussed.Finally,the U type hollow permanent magnet synchronous linear motor is selected.The control strategy adopts the compound control of the PID+ speed and acceleration compound feedforward + notch filter with PMAC control card as the carrier,and the straight line rolling guide as the guide.The system and linear grating ruler are used as detection.The effective travel time of X and Y directions is 400 mm and 300 mm respectively,and the maximum load is 10 kg.A motion program based on PMAC card is designed.The motion program is composed of linear interpolation and circular interpolation,and the track curve matching with it is obtained.The PID control method based on PMAC is adopted in the two-dimensional precision positioning worktable,and the specific control strategy is the compound control of the PID+ speed and acceleration compound feedforward + notch filter.From the classical PID control algorithm,we deduce two kinds of digital PID control algorithms,namely positional and incremental.The open loop characteristics of the system are debugged,and the stability and transient characteristics of the system are debugged by the trial and error method,and the control parameters combination of the X and Y axis of the worktable is finally obtained.Taking the Y axis as an example,two values are selected on both sides of the six control parameters of I230,I231,I232,I233,I235 and I268.The control variable method is used to study the influence of the change of each parameter on the speed,position and acceleration of the linear motor.The results show that the change of each control parameter has a certain influence on the motor performance and the influence of each parameter are different.The velocity,position and acceleration of X and Y axes were studied under the load of 0,3kg,6kg and 9kg.The results showed that the motion performance of the X and Y axis of the worktable was little influenced by the load,and the motion curve was basically coincided with the load.When the load continues to increase,in the uniform acceleration stage and at the same time,the greater the load,the smaller the speed,the uniform deceleration is just the opposite.In addition,the velocity at the end of uniform acceleration has a certain excess volume,which increases with the increase of load;The acceleration curve shows that the acceleration fluctuation is more obvious with the increase of load,which indicates that the motion process is more unstable.The control parameters are optimized by the relative average deviation of acceleration in the forward acceleration phase,and the orthogonal test is adopted in the optimization method,and the optimization results are verified.The results show that the relative mean deviation of X and Y acceleration is 8.89% and 8.26% respectively after optimization,which is smaller than that before optimization,so the optimization effect is remarkable.According to GB/T17421.2-2016,the detection results of X and Y axis positioning accuracy and repeated positioning accuracy of the worktable show that the positioning accuracy and repeated positioning accuracy of the X axis motor are 6.81 um and 6.51 um respectively,and the Y axis is 4.93 um and 4.62 um.In addition,the accuracy changes of the worktable are studied under the conditions of 0,3kg,6kg and 9kg.The results show that the positioning precision and repeated positioning precision are both high when the load is 0 and 3kg.When the load is increased to 6kg and 9kg,the precision is obviously reduced.Therefore,the comprehensive analysis can be obtained.When the load is changed in a certain range,there is no effect on the accuracy of the worktable,and the accuracy of the worktable will decrease obviously after the load is over a certain value.At the same time,the repetitive positioning accuracy of each target position of the worktable was studied when the 6kg and 9kg loads were loaded.The results showed that the precision of some position accuracy decreased obviously in the load range of the worktable,and the other position precision changed little.