Replicated multi-channel sensors for decucing ink thicknesses in color printing devices

Abstract

A method and computing system are proposed for deducing ink thickness variations from solid-state multi-sensor measurements performed online on a printing press or printer. The computed ink thickness variations enable controlling the ink deposition and therefore the color accuracy. Ink thickness variations are expressed as ink thickness variation factors incorporated into an ink thickness variation and sensor response enhanced spectral prediction model. The ink thickness variation computing system comprises multi-channel sensor devices (e.g. red, green, blue, near infra-red), a processing module, and a computing system. The multi-channel sensor devices are replicated over the width of the print sheet. Preferably embodied by Single Photon Avalanche Diodes (SPADs), due to their high-speed acquisition capabilities, they provide responses according to the reflectance of small area segments within a print sheet. The processing module accumulates the digital sensor responses and forwards them to the computing system, which deduces the ink thickness variations.

Description

[0001] The present patent application is a continuation-in-part of U.S. patent application Ser. No. 10 / 631743, Prediction model for color separation, calibration and control of printers, inventors R. D. Hersch, P. Emmel, F. Collaud, filed Aug. 1, 2003.BACKGROUND OF THE INVENTION [0002] The present invention relates to the field of color printing and more specifically to the control of color printer actuation parameters. It discloses a new concept of non-expensive replicated illuminating and sensor devices placed on the printer in face of the moving paper sheets as well as a spectral prediction model extension adapted to the proposed set of illuminating and sensor devices. [0003] Color control in printing presses is desirable in order to ensure that effectively printed colors correspond to the desired colors, i.e. the colors expected by the prepress color separation stage. Color consistency is desirable both across consecutive sheets of a multi-sheet print job and also from print job...

AI Technical Summary

Benefits of technology

The present invention proposes a method and a computing system for deducing ink thickness variations in real-time during printing or printing. This allows for real-time control of the ink deposition process, which ensures high color accuracy from print sheet to print job. The invention uses multi-channel sensors to measure ink thickness and sensor responses, which are then used to compute ink thickness variations and sensor response enhanced spectral prediction models. The models predict the ink thickness variations based on the superposition conditions of the inks. The invention can be calibrated and can be used with different printer operating conditions. It also takes into account the influence of paper reflectance and ink thickness variation factors. The invention enables online control of the ink deposition process, improving color accuracy and stability.

Problems solved by technology

Due to the large number of parameters which need to be taken into account, this solution seems complex and costly.

Such high order polynomials are known to oscillate between the known values of input / output variables and therefore do not always provide a correct mapping between sensor input variables and ink dot size output variables.

Since these two conversion tables are deduced from experiments which may have been performed under different printing conditions (temperature, settings of the press, etc.), the control of the ink aperture is not precisely adapted to the current operating conditions of the press.

In addition, experience shows that it is very difficult to control the ink feed of 4 inks (c,m,y,k) with a 3-sensor system only.

That method does not consider controlling the ink feed rate according to sensor responses of illuminated polychromatic halftones.

It is known that the Kubelka-Munk model only works on uniformly diffuse layers and is therefore not applicable to halftones.

But due to the uncertainty between joint variations in the ink thicknesses of cyan, magenta, and yellow and a variation in thickness of black, the method does not work well for the set of cyan, magenta, yellow and black inks.

In addition, that method does not teach how to calibrate the prediction model with halftones that are an integral part of a printed document page delivered to a customer.

This patent application does neither teach how to obtain ink thickness control parameters from polychromatic halftone patches nor from halftones being part of the actual printed document pages.

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