On-line angle self-correction strategy based on a cobweb-structured grating scale

Installation eccentricity of the grating scale is the main source of error for rotary optical encoders in practical applications. In this paper, an on-line angle self-correction strategy for rotary optical encoders is proposed. Firstly, the eccentricity error model is described, which explains the numerical relationship between the eccentricity error and the eccentric parameters including eccentric distance and eccentric angle. Then, a bioinspired cobweb-structured grating scale is adopted as the measurement standard of the rotary optical encoder. This grating scale allows the rotary optical encoder to sense the rotary angle and the radial displacement simultaneously. The eccentric parameters can be determined in real time from the rotary angle and the radial displacement information. Thus, the measured rotary angle can be on-line corrected by applying the eccentric parameters to the eccentricity error model. The feasibility and effectiveness of the proposed strategy have been confirmed from the experimental results.