Optics: measuring and testing – Of light reflection – With diffusion
Patent
1996-09-13
1999-11-09
Kim, Robert H.
Optics: measuring and testing
Of light reflection
With diffusion
356429, G01N 2145
Patent
active
059825006
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a device for measuring the surface of a print product.
Such devices are used to determine the optical density of the different printing inks applied and generally have a measuring head which can be moved over the finished print product and determines the optical density of the different colour separations.
2. Disclosure of Relevant Art
Although, in modern printing machines, the ink films of the print products are dried by exposure to heat or light radiation so that the print products do not have to be dried in racks, even after such irradiation the printing inks are still somewhat tacky, so that print products stacked on top of each other can stick together. To prevent this, the upper surface of the print product is frequently dusted over with a fine powder, which may, for example, be finely ground mineral material or finely ground starch. The quantity of the powder mass applied is set on the dusting device according to empirical values and with continuous monitoring of the dusted products. However, with a more precise knowledge of the quantity of the powder mass actually obtained on the print product, it would be possible in many cases to reduce the powder delivery on the dusting device, i.e., to work with a smaller surplus. This would be advantageous not only in terms of a saving in powder, but it would also be possible in this way to prevent powder deposits in the printing machine which can result from the delivery of excessive powder.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a device that can measure the powder mass deposited on the print product by dusting after printing.
This object is achieved, according to the invention, by a for measuring the surface of a print product, comprising a measuring head including a measuring light source and measuring light detector. The measuring light source and the measuring light detector each have a directional characteristic, the axes of which are set at different angles relative to the surface of the print product so that if the surface of the print product is ideally level and smooth, no measuring light reaches the measuring light detector. The axes of the measuring light source directional characteristic and the measuring light detector directional characteristic coincide adjacent to the print product, and both form an angle of less than 90 degrees with the surface of the print product.
The features of the invention are advantageous with respect to the largest possible variations in the sensor output signal with predefined variations in the mass of powder present on the print product.
The setting angle of the axis of the measuring light source characteristic relative to the surface of the print product is advantageously less than 45 degrees. The angle between the axes of the characteristic of the measuring light source and the measuring light detector is advantageously less than 45 degrees.
The wavelength of the measuring light source is selected to interact in different ways with the powder particles, on the one hand, and the printing ink, on the other hand. This provides for the sharpest possible differentiation between the measuring light modified by powder particles and those portions of the measuring light which are reflected by the printing base itself or by the printing ink present on the latter. The wavelength of the measuring light is preferably selected so that it is reflected by the powder particles but is absorbed by the printing ink or the printing base. Alternatively, it is possible to use a measuring light of a wavelength which releases a characteristic luminescence on the powder particles, whereas this is not the case with the printing ink and the printing base.
A device is provided for generating a flow of gas from the surface of the print product to the sensor spaced at a distance from the surface of the print product.
A device is provided for holding the flow of gas constant. Given a constant speed of flow of gas carrying the pow
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patent: 5053822 (1991-10-01), Butler
patent: 5160981 (1992-11-01), Hirashima
patent: 5216469 (1993-06-01), Yamada
patent: 5276481 (1994-01-01), Kinoshita et al.
patent: 5357335 (1994-10-01), Sparks et al.
patent: 5519497 (1996-05-01), Hubble, III et al.
Kim Robert H.
Smith Zandra V.
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