| 摘要 |
<p>PURPOSE:To enable the using of the apparatus in better condition for a long time even under a bad environment loaded with much dust by covering a light transmitting part (opening) provided on the side of a surface to be measured of a cassette with an optically transparent film free to exchange at each fixed time. CONSTITUTION:Projection light from a light emitting unit 1 is reflected on a surface to be measured of a printing plate passing through an opening 3a and received with photodetecting units 2a And 2b passing through openings 3b and 3c. A new film 10 transparent optically wound on a supply roller 5 in a cassette 4 is exposed to the front of the cassette 4 via the inside of a tunnel part 11a to cover the openings 3a-3b and wound on a winding roller 6 passing through a tunnel part 11b. With the operation of a printing machine, dust builds up on the film 1 on the openings 3a-3b. When the operation of the printing machine reaches a specified set value, a motor 7 is driven to wind the film 10 on the roller 6 by a fixed length, Thus, the portion covering the openings 3a-3b is replaced with a new part yet to be soiled by dust thereby allowing the preventing of a drop in detection accuracy.</p> |
