Application of Ultraprecision Microgrooving to Manufacturing Diffraction Grating for a Small Encoder

• Published in: Transactions of the Japan Society of Mechanical Engineers Series C Vol. 66; no. 648; pp. 2846 - 2851
• Main Authors: SAWADA, Kiyoshi, ODAKA, Shun'ichi, KAWAI, Tomohiko, TAKEUCHI, Yoshimi, SATA, Toshio
• Format: Journal Article
• Language: Japanese
• Published: The Japan Society of Mechanical Engineers 2000
• Subjects: Diamond Endmill; Micrograting; Micromachining; Rotary Encoder; Ultraprecision Milling Machine
• ISSN: 0387-5024; 1884-8354
• DOI: 10.1299/kikaic.66.2846

This study deals with the manufacture of a small high-resolusion rotary encoder for a feed-back sensor of small actuators to move a small robot arm in the near future. A laser diffraction grating is desirable to exert the diffraction efficiency. Thus, the encoder with 32786 V-shaped grooves radiately around a track of 10 mm in diameter is designed to obtain a resolution of two million pulses for a rotation. Smooth and correct V-shaped grooves are created by means of ultraprecision micromachining technology, where a rotational diamond cutting tool is fed on an ultraprecision milling machine having 1 nm positioning accuracy. In order to obtain a good encoder, diamond tool wear was monitored, servomotors were tuned to reduce the tracking error, and the master encoder was compensated to eliminate the periodical positioning error. However, a phase mismatch took place at the point, where the cutting starts and finishes. This is mainly due to the thermal disturvance since it takes about ten hours to complete the cutting. Thus, the cutting order was modified so as to make the influence of thermal disturbance uniformly distribute around the track of encoder. As a result, it is proved that the way of cutting enables the encoder to have enough optical performance.