CCD assembly error and eccentricity error compensation method for single-track absolute photoelectric encoder
Abstract This paper proposes a linear CCD assembly error and grating eccentricity error compensation technique for single-track absolute angular encoder, to improve its measurement accuracy and reduce manufacturing cost. For the first time, to the best of our knowledge, the harmonic characteristics and an error correction model for Linear CCD assembly errors are presented.Firstly, the error sources of single-track absolute angular encoders are analyzed by exploring mechanisms of CCD assembly error and eccentricity error. Appropriate mathematical models for both errors are established and the harmonic characteristics of them are analyzed. Secondly, based on the harmonic characteristics of above two errors, the proposed error correction method using least squares harmonic fitting eliminates both errors. Finally, the proposed correction method is applied to a single-track absolute encoder for testing. Experiment results indicate that the proposed technique reduces the standard deviation of the angular displacement measurement error from 7.5'' to 2.6 '' with single reading head, making it significantly cost-effective.