DENSITOMETER

Abstract: The present invention relates to a densitometer having a light source (2) by means of which a light beam (4) is directed upon a printed web of paper (6) as well as a photo electric cell (8) measuring the amount of light reflected by the paper (6) said desintometer having an air jet nozzle (7) by means of which a jet of air can be directed to the spot (5) where the light beam (4) hits the paper (6) said jet preferably being perpen­ dicular to the paper-plane said densitometer allowing a method to control the ink supply to the ink roller of the printing press which press can have a plurality of densitometers each controlling one or more of a number of ink supply members located side by side.

Description: Densitometer The invention relates to a densitometer comprising a photoelectric cell and a light source, said photo-electric cell and light source are arranged in a housing with respect to each other such that in positioning said housing above a reflecting surface such as a printed web of paper, the light,beam of the light source impinges on a point of said surface beneath the measuring cell and the lighttbeam reflected by said surface is received by the measuring cell measuring the intensity thereof. Such densitometers are generally knowmAmong others, they are used to measure whether the quantity of ink transferred to a substrate meets a desired value. If said quantity differs from the desired value then also the quantity of the reflected light varies which is an indication that the ink supply should be adjusted. In present-day measuring methods in a web printing press a web is taken from the stack at intervals and thereafter measured with a hand densitometer. This results in that the check carried out with the hand densitometer and the correction to be performed eventually in consequence thereof takes place too late. For executing the measurement the web should lie stable on an underground. The usual hand densitometers measurements at a moving paper section or a moving paper web in á printing press are not possible. The object of the invention is to aTovide a densitometer by if SQ desired wnicfltflisispossibie and the measurement can take place for each web so that corrections can be performed much quicker. According to the invention, said object is achieved by providing the densitometer with an air jet nozzle the jet of which impings on the measuring point. Thereby it is achieved that the moving web is pressed well so that a measurement is reliable. Moreover, one obtains thereby that the meter itself needs not be in contact with the web so that spreading or soiling of the ink being not entirely dry needs not to be feared. Such a densitometer may be arranged at a suitable location in the printing press and may perform measurements at any desired moment. Preferably, the air jet nozzle comprises a tube directed perpendicular to the surface to be measured and in which the photo-electric cell has been provided. Such a densitometer has the advantage not to make filthy. Particles flying around such as paper fibers, ink mist and anti-soil powder etc. cannot reach the light-sensitive cell so that the constant quality of the measurement is assured. -Now, the invention facilitates also a method for controlling the ink supply in a printing press by fixing the densitometer near the impression cylinder having the measuring point in the plane of the web coming from the press and using the measured value delivered by the densitometer for controlling the ink supply to the ink roller. The invention relates also to a device for using the method, in which device the ink supply to the ink roller is subdivided in wnlcn in a number of ink sutlv members located side bv side andnarallel been to the impression cylinder a beamha?provided on which the same been number of densitometers as the number of ink supply members hasV positioned and each densitometer can control the ink supply member lying in its range. The densitometer according to the invention which needs no longer to have a housing to be placed on the paper can have small dimensions so that a high number of densitometers distributed over the width of the paper may be placed each of which controls a narrow area of the width of a printed web. By making the number of densitometers equal to the number of zones in which the ink supply is subdivided it is possible to obtain printed matter having equal quality over the entire width and for each web. Whereafter the invention will be explained by reference to the drawing showing in cross-section the densitometer according to the invention. The densitometer shown in the drawing comprises a housing 1 in which is provided a light source 2 not shown in details and directing a light beam bounded by the lines 4 on a surface 5 of the web 6 through a lens 3. Perpendicular to the surface 5 a tube 7 is provided having in it the photo-electric cell 8 and connected to said tube ic a conduct or hose 9 through which may be blown air adapted to stream along the photocell 8 and along the infrared filter 10 and being directed onto the measured surface 5 and pressing it against the underground not shown. - claims

Claims: CLAIMS 1. Densitometer comprising a photo-electric cell and a light source, said photo-electric cell and light source are arranged in a housing with respect to each other such that in placing said housing above a reflecting layer such as a printed web of paper, the light beam of the light source impinges on a measuring point of the layer beneath the measuring cell and the light reflected by the layer is received by the measuring cell measuring the intensity thereof, char a c t e r i z e d in that the densitometer is provided with an air jet nozzle the jet of which is directed to the measuring point. 2. Densitometer according to claim 1, c h a r a c t e r i ze d in that the air nozzle consists of a tube perpendicular to the layer and in which the photo-electric cell is provided. 3. Method for controlling the ink supply in a web printing press, c h a r a c t e r i z e d in that a densitometer according to claim 1 or 2 is fixed near the impression cylinder having the measuring point in the plane of the web coming from the press and the measured value delivered by the densitomete is used for controlling the quantity of ink to the ink roller. 4. Device for using the method according to claim 3, c h a r a c t e r i z e d in that the ink supply to the ink roller is subdivided in a number of ink supply members that located side by side andnparallel to the impression cylinder a been beashasprovided on which the same number of densitometers as been the number of ink supply membershasoplaced and each densitometer controls individually the ink supply member lying in its range.

Inventors: LAANE, ALBERTUS WILLEM, VAN DOMSELAAR, JAN
Applicants: REPROTEST B.V.
Application year: 1981
Main classification: G01N21
IPC codes: G01N21