Research And Application Of Multiple Degrees-of-freedom Error Motions Measurement System For Precision Rotary Tables

Rotary motion is one of the most basic motion in mechanism kinematics,which is widely applied in industrial robots,precision machine tools,laser tracker,coordinate measuring machines,etc.However,due to the assembly,manufacturing,design of rotary tables,there are always position dependent geometric errors and position independent geometric errors inherently in the rotating motion.Error prevention method and error compensation method are the most commonly used methods to improve the rotating accuracy of precision machining and measuring instruments.Compared with the error prevention method,the error compensation method does not need to improve the manufacturing and assembly accuracy of parts and components,and the related mathematical model is established through theoretical analysis to compensate for errors,and further improve the processing and measurement accuracy of the instrument.This thesis focuses on the measurement and separation of the geometric error motion of the rotary tables,puts forward to the two measurement methods on-line and off-line calibrated geometric errors of rotating motion firstly,establishes the separation and compensation model of the geometrical error motions secondly,and finally carries on the measurement comparison and verification experiment of rotary tables' error motions.In this thesis,a laser off-line measurement system for 5-DOF geometric error motions of precious rotary tables is proposed.Based on the homogeneous coordinate transformation model,the geometric relationship between the position independent geometric errors of the misalignment between the reference axis and the rotary axis,the installation errors of the measuring instruments,and the inherent multi-degrees-of-freedom position dependent geometric errors of the rotary axis were analyzed.The least square circle(LSC)was used to analyze the measurement error motion,and the installation error of the measuring instrument is separated.Meanwhile,the five-degrees-of-freedom position dependent geometric error of the precision rotary tables and the position independent geometric error of the misalignment error of the rotary axis were decoupled.Finally,the precision rotary table was measured clockwise(CW)and counter clockwise(CCW)for several times,and the results were compared with the photoelectric autocollimator,which successfully verified the feasibility and effectiveness of the rotary table's multi-degrees-of-freedom error motion measurement system.At present,including the methods proposed in this paper,the multiple-degrees-of-freedom geometric error motion identification of rotary table mostly belongs to off-line measurement.However,in the actual rotating motion,there is inevitably a load in the rotary tables.Due to the real-time change of the load,the position dependent geometric error motions of the rotary table were inconsistent with the model of off-line quasi-static error measurement,which leads to the error motions compensation effect of off-line quasi-static measurement is not ideal in on-line motion.Therefore,this paper proposes a multi degrees of freedom measurement system for online geometric error motion of precision rotary table with double grid discs.The dual grid discs can be embedded in the rotating spindle of precision rotary tables.The geometric error motions of grid discs were analyzed based on Fast Fourier Transform(FFT),and the M-DOF position dependent geometric errors and position independent geometric errors of precision rotary tables were successfully separated.Finally,compared with a linear variable differential transformer(LVDT)measuring the roundness errors,the feasibility and effectiveness of the on-line measurement system are verified.Based on the above-mentioned on-line multi-DOF real-time measurement system with embedded dual grid discs,a precision rotary table with on-line self-calibration of geometric error motion was successfully designed.The radial error motions are within ±1.5?m,and the tilt error motions are with ±2arcsec,Through the static analysis and modal analysis of the selfcalibration rotary table,the performance indexes of the self-calibration rotary table satisfy the designed demand.