为了实现编码器测角精度的高精度测量，介绍了应用多面棱体和自准直仪组合测量编码器测角精度的原理和方法，建立了多面棱体坐标系和自准直仪测量坐标系，利用坐标变换的方法推导了塔差对测角精度测试结果影响的精确模型。结果表明，编码器转轴的倾斜角度和倾斜方向会影响编码器测角精度的测量结果。测量误差随编码器的倾斜角度的增大而增大，且近似成平方关系。测量误差随随编码器的倾斜方向改变，倾斜方向角为0°或180°时，测量误差最小；倾斜方向角为90°或270°时，测量误差最大。当倾斜角度为5′时，引入的测量误差为0.11″～0.48″，这对于Ⅰ~Ⅲ级编码器的测试是不能忽略的。根据被测编码器的精度等级将塔差控制在恰当的范围内，给出了不同精度等级编码器测试时塔差的控制要求。

In order to realize the high precision measurement of encoder accuracy, the principle and method to measure encoder accuracy by using polyhedron and autocollimator are introduced. The polyhedron coordinate system and autocollimator measurement coordinate system are established, and the precise mathematical model is established, which is relation with the measurement error of the encoder accuracy and pyramidal error. The simulation results show that the encoder shaft tilt angle and tilt direction will affect the measurement results of the encoder accuracy. Measurement error of encoder accuracy increases with encoder shaft tilt angle, and approximately proportional to the square. Measurement error of encoder accuracy changes with encoder shaft tilt direction. When encoder shaft tilt direction is 0°or 180°, measurement error is the smallest; When encoder shaft tilt direction is 90°or 270°, measurement error is the maximum. As encoder shaft tilt angle is 5′, the measurement errors can reach 0.11"~0.48", which cannot be ignored for encoder with 1~3 levels of precision grade. Pyramidal error should be cotrolled in the appropriate range based on the precision grade of measured encoder. Specific requirements on pyramidal error are given for encoders with different precision grades.