GB1338464A - Measurement and control of ink density - Google Patents

Abstract

1338464 Measurement of ink density in printing HARRIS-INTERTYPE CORP 31 Aug 1971 [12 Oct 1970] 40557/71 Heading B6C [Also in Division G1] In an apparatus for measuring the ink density of a test patch of ink on sheet material with respect to a reference patch on said sheet a beam of light is directed on by the sheet so as to impinge on the two patches, and first and second light sensor means angularly spaced from the beam receive the reflected light and provide first and second signals which are processed to provide an output indication of the colour density of the test patch area. In a conventional sheet fed lithographic press, including an ink fountain 20 a plate cylinder 10, a blanket cylinder 12 an impression cylinder 14 and a delivery cylinder 16, a gauging apparatus G is adjustably positioned on a support bar 48 so as to monitor each sheet member 50 carried by the impression cylinder 14. Each sheet member 50 carries a test patch and a reference patch for each colour ink used and the gauging apparatus comprises an intermittently actuated Xenon lamp, which simultaneously illuminates the test and reference patches, and a pair of photodiodes TS-1, RS-1 for receiving the light refiected off the two patches. Each pair of output signals are fed to a separated gated densitometer control circuit GD-1, GD-2, GD-3, and GD-4 (if there are four colours), Fig. 5. As shown each gated densitometer control circuit output is fed to a signal recorder SR, an analogue deviation meter AM, a digital meter DM and a corresponding control meter MC1 or MC2 &c. which controls the ink flow from the ink fountain 20. The operation of the densitometer and the lamp L are synchronized with the movement of the sheet members 50 by means of a cam 52 activating a switch 56 and 58 which forms the synchronizer pick-up shown in Fig. 5, so that the lamp and the densitometer control circuit are simultaneously activated. A suitable circuit for the gated densitometer is disclosed (Fig. 6, not shown). In order to keep its lens surface and filter surface clean, the gauging apparatus C includes an air supply with tubing to direct air currents across the surfaces. A further embodiment, a conventional web fed lithographic press, Figs. 10 and 11 (not shown), is disclosed and it incorporates the gauging apparatus before monitoring test patches on the web emerging from the press. However, preceeding each set of test and reference patches is a mark which is sensed by an additional sensor (220, Fig. 11, not shown). The additional sensor replaces the cam 52 of the previous embodiment as a. means of synchronizing the lamp and the densitometer. A suitable electronic circuit for the additional densitometer is also disclosed.