| 摘要 |
PURPOSE:To correct position deviations of pattern dots highly accurately with simple and inexpensive circuits by measuring and storing the light beam scanning time of each mirror surface of a rotary polyhedral mirror and controlling character- controlling clock frequencies according to the values thereof. CONSTITUTION:When scanning is started, the beam scanning time at the scanning of the N times before is read out from the memory address indicated by a counter 19. The light beam scanning time having been read out from a memory 20 is converted to an analog value by a D/A converter 14. This analog value is inputted to an analog multiplier 16. On the other hand, at the same instant of scanning starting, a function generator 15 generates the function value of cos<2>theta and inputs the output thereof to the analog multiplier 16. The output of the analog multiplier 16, i.e., the control voltage of a voltage control pulse generator 17 is proportional to the product of cos<2>theta and the light beam scanning time. Hence, the clock period having been corrected of the fluctuations of the light beam scanning speed and the fluctuations of the light beam scanning time by plane accuracy errors of each mirror surface may be applied. |
