Automatic Compensation System for Small Absolute Optical Encoders

Subdivision errors and long-period errors are the main components of small absolute optical encoder error. When the external environment changes or the encoder operates for a long time, the subdivision error will increase. In this study, a stepper motor and high-precision encoder are used to develop a system that automatically measures the long-period error and subdivision error of a small optical encoder. The error data are fitted and stored in the program memory of the encoder in the form of an error data table. During the displacement calculation, the encoder collects the peak and valley values of fine-coded two-channel moiré fringe signals in real time, normalizes the moiré fringe signal data, and compensates for the subdivision error and long-period error by looking up data in the table. A 16-bit small encoder was tested using the developed system, and the mean square errors of the encoder before and after compensation were <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$43.3^{\prime \prime }$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$11.7^{\prime \prime }$ </tex-math></inline-formula>, respectively. Therefore, the algorithm proposed herein can significantly improve the measurement accuracy of small optical encoders.