Development of Ultra high accuracy calibration system for rotary encoders

1.标定系统的研制：该系统由精密恒速旋转机构、分度机构、误差测量电路和计算机组成。这两个编码器都是每转36000个脉冲的光学类型，并安装了10个检测头。旋转机构由精密旋转空气轴承和直流电机组成，从1rpm到20rpm均可旋转。分度机构由旋转空气轴承、交流电机和分度用旋转编码器组成。该机构可以在任意角度位置对旋转编码器A的检测头单元进行分度。分度后，机械盘式刹车系统完美地固定了检测头单元。误差测量电路可以同时获得40个旋转编码器的相对角度位置误差，并进行高分辨率的时间换算测量。计算机控制分度和测量，并进行正田法的计算。2.实验与结果单探头相对角度位置误差的标准偏差为0.008秒。旋转编码器B和A的相对角度位置误差的标准偏差分别为0.01和0.02角秒。两个5头旋转编码器的相对角度位置误差的标准偏差为0.003角秒。通过Masuda定标法验证，两个编码器的角度位置误差为+/-0.2角秒，校准值的不确定度为0.03角秒。它发现，它的值的重复性非常高，为0.003角秒。不确定性没有达到目标的0.005秒的原因是索引精度不够。

1.Development of the calibration system.This system consists of the precise constant speed rotating mechanism mounted two standard rotary encoders A and B, the index mechanism, the error measurement circuit and the computer. Both encoders are the optical type with 36000 pulses per revolution and come to be installed with 10 detecting heads. The rotary mechanism consists of the precise rotary air bearing and the d.c.motor and it can rotate with 20rpm from 1rpm. The index mechanism consists of the rotary air bearing, the a.c.motor and the rotary encoder for indexing. The mechanism can index the detecting heads unit of the rotary encoder A at any angle position. After indexing, the mechanical disc brake system fixes the detecting head unit perfectly. The error measurement circuit can get the relative angle position errors of forty rotary encoders at the same time and does the measurement of the time conversion method with high resolution. The computer controls the indexing and the measuring and performs the computation of Masuda method.2.Experiment and ResultsThe standard deviation of the relative angle position error of the single detection head was 0.008 seconds. The standard deviations of the relative angle position error of the rotary encoder B and A were 0.01 and 0.02 arc seconds, respectively. The standard deviations of the relative angle position error of both rotary encoders with 5 heads were 0.003 arc seconds. By Masuda calibration method, it was confirmed that the angle position errors of both encoders were +/- 0.2 arc seconds and the uncertainty of the calibration values were 0.03 arc seconds. It found that the repeatability of its values were very high with 0.003 arc seconds. The cause that the uncertainty didn't reach the 0.005 seconds of the goal is insufficiency of the indexed accuracy.