Sensor for water film on a plate in printing machines

• US 5,185,644 A
• Filed: 07/17/1991
• Issued: 02/09/1993
• Est. Priority Date: 07/17/1990
• Status: Expired due to Term

• Current Assignee: Mitsubishi Jukogyo Kabushiki Kaisha (Mitsubishi Heavy Industries, Ltd.)
• Original Assignee: Mitsubishi Jukogyo Kabushiki Kaisha (Mitsubishi Heavy Industries, Ltd.)
• Inventors: Shimoyama, Makoto, Ozaki, Ikuo
• Primary Examiner(s): Rosenberger, Richard A.
• Assistant Examiner(s): Pham, Hoa Q.
• Application Number:
  US07/731,656
• Time in Patent Office: 573 Days
• Field of Search: 356/367, 356/368, 356/369, 356/381, 356/382, 356/446, 356/445, 356/364, 356/365, 356/366, 250/225
• US Class Current: 356/369
• CPC Class Codes: G01B 11/065 using one or more discrete wavelengths
• CPC Class Codes: Y10S 101/45 Sensor for ink or dampening fluid thickness or density

Abstract

An on-plate water film sensor for printing machines uses a narrow-band light source, a photo modulator for chopping a light beam therefrom into p- and s-polarized beams, a collimator for making parallel the rays of the collimated beams with a given cross-sectional area for measurement, a wavelength plate for adjusting the wavefront of the parallel rays, a receiver for the light secularly reflected from a plate, and an arithmetic unit to figure out the thickness of a water film formed on the plate based on the intensities of the received beams. Water lining which usually has patterns of narrow width can be detected, and the measurement of a water film thickness can be done with high speed.

Claims

1. A sensor for measuring the thickness of a water film formed on a plate in a printing machine, comprising a narrow-band light source, a photo modulator for alternatively chopping light from the light source into p-polarized and s-polarized beams, a collimator for making rays of the chopped beams parallel to each other with a given cross-sectional area for measurement, a wave-length plate for adjusting wavefront of the collimated parallel rays and directing the parallel rays onto the water film at a selected angle of incidence, and a device for receiving light beams reflected specularly from the plate and for calculating the thickness of a water film formed on the plate.

2. The sensor as defined in claim 1, wherein said photo modulator is a chopper using an electro-optical effect.

3. The sensor as defined in claim 1, wherein the angle of incidence of the collimated parallel rays and a plane perpendicular to the plate is a Brewster angle.

4. The sensor as defined in any one of claims 1 to 3, wherein said narrow-band light source is a laser.

5. The sensor as defined in any one of claims 1 to 3, wherein said narrow-band light source is a light emitting diode (LED).