Shaft position measurement using dual absolute encoders

Mechatronics systems have become more accurate and compact. An accurate and compact measurement equipment is also required for this system. An encoder, specifically an absolute encoder, is a major equipment that measures the shaft position. However, the disk of the absolute encoder should be enlarged to increase its resolution, and its measurement range is usually limited to 360°. In addition, directly coupling an absolute encoder to the output shaft is still a difficult task in a mechatronics system. This paper proposes a principle that measures the position of the output shaft by combining two absolute encoders connected with the output shaft with different multiplying ratios. The output shaft position is calculated from the combinations of the measured values of the encoders and the multiplying ratios, regardless of power turn-off, interruption, or corruption from electrical transients. The multiplication of the output shaft rotation improves the resolution of the measurement and requires less space to install. Moreover, the range of measurement can be extended by the combinations of the multiplying ratios. Aside from the principle, the criterion of multiplying ratios is proposed in this paper. The simulations and experiment are conducted to verify the validity of the proposed principle.