Error Analysis And Compensation Of Angle Measurement Of Turntable

Precision rotary table is widely applied in many kinds of instruments and equipment,such as roundness instrument,inertial test equipment and angle measuring equipment.It plays an extremely fundamental and important role in the field of industry.Error compensation is the important approach to improve the angle measuring accuracy of turntable.It not only can eliminate most systematic error in turntable,but also gain a higher accuracy within a lower cost.Based on the harmonic analysis of angle error,this paper compensates the turntable’s long period angle measurement error by using autocollimator and optical polygon.The specific research content is as follows:(1)The composition and principle of angel measurement system of turntable are analyzed.And many kinds of error sources in the turntable are summarized.Based on the principle of homogeneous coordinate transformation,the angle measurement error caused by mounting eccentricity and inclination of divided circle are deduced.The results indicate that eccentricity of grating’s center leads to first harmonic angle error.The inclination of the grating with respect to rotation axis leads to second harmonic angle error.There is some coupling influence between each other.The coupling error is the sum of first and third harmonic,which is always ignored realistically because its amplitude is very small.Two methods for angle calibration,equal division averaged method and autocollimator measurement method,are analyzed.Two methods for compensating turntable’s angle measurement error,cam method and software method,are introduced.(2)The errors such as inclination of table(adjustment error),inclination of rotation axis(mounting error),etc,are analyzed.Inclination of table,is coupling with the mirror perpendicularity and mirror azimuth,leads the angle error which is sum of first harmonic and second harmonic.Leveling can eliminate the systematic error caused by tilt of table.A leveling method based on planer vector analysis is studied.The tilt status is measured by autocollimator firstly,then the table can be leveling according to the tilt status.The leveling experiments demonstrate that the standard deviation of table tilt angle is about 0.6″.The table tilt angle can be adjusted to be less than 2.0" after twice leveling and the error caused by tilt is eliminated.(3)Turntable’s angle measurement error is compensated by the high precision autocollimator.In-2000″ ~ 2000″,short period error of turntable is calibrated by comparing turntable against autocollimator.And in 0°~360°,we apply the principle of single closure to calibrate long period error of turntable.Compensation results shows that the short period error is bigger,whose peak-to-peak value is a little less than 2.0″.The long period error of turntable,whose peak-to-peak value is a little less than 1.4″.If the zero position of turntable not changes,the minimum compensation value of long period error is located at about 230°,and the maximum is located at about 315°.