Transparent coating thickness measuring device for printed material

摘要

The thickness measuring device involves measuring thickness of a lacquer or laminate coating on a printed item by comparing the distance of a light path reflecting off the surface of the coating (3) with that involving an additional refracted path (11,12) which reaches down to and reflects off the surface (2) of the printed material (1) underneath. A beam of light (5) is transmitted through a linear polariser (8) to the test object at an oblique angle. The beams reflected (10,13) strike a double-image prism (16) and are transmitted to a diffraction mirror (19), which reflects them to an opto-electronic analyser (24). Half the light from the print surface (13) is also transmitted through the prism to a second analyser (25). This acts as a check in comparing the distances between the incidence of the beams on the receiving plane (26) from which the thickness of the coating can be measured.