| 摘要 |
PURPOSE:To perform accurate focusing control by irradiating a projector, and moving the relative position of a lens to an image formation surface from one limit to the other limit and stopping the movement when a lens position signal coincides with the ratio of the quantities of light to two photodetectors. CONSTITUTION:An oscillation circuit 8 operates by the closure of a switch 7 and one-shot multivibrator circuits 9-11 generate pulses phi1-phi4. Amplifying circuits 4 and 5 are reset by the pulse phi1. A light emitting element 1 is driven by the pulse phi3 after the pulse phi2 is generated to project light for a specific time. Its reflected light is photodetected by photodetecting elements 2 and 3, whose outputs are processed by division 12 through circuits 4 and 5 to output a light quantity ratio signal O3. Then, when the pulse phi4 is generated, a magnet 19 is driven and a stopper 20 operates to release a lever 17. The output voltage VA of a reference voltage source 21 rises associatively and when it coincides with the level of the signal O3, the stopper 16 is operated by the output of a comparator 13 to perform accurate focusing control. |
