Printing – Processes – Position or alignment
Reexamination Certificate
2001-05-15
2003-09-09
Nolan, Jr., Charles H. (Department: 2854)
Printing
Processes
Position or alignment
C101S484000, C347S116000, C358S001180, C399S301000
Reexamination Certificate
active
06615732
ABSTRACT:
The invention relations to a method for setting register on a multicolor printing machine having color printing units assigned to various printing inks, at least one image cylinder, image production equipment for producing color separations, in particular electrostatic latent color separations, on the at least one image cylinder, a carrier for printing substrates and at least one image transfer point for the transfer of the color separations to the printing substrates, an assignment of the image production points on the at least one image cylinder being carried out in order to achieve coincidence of register between the color separations in the print, by both the production of the image starts and the production of areas of the color separations being set on the basis of the print and the evaluation of register marks.
The invention also relates to apparatus for setting register in accordance with the above-mentioned method on a multicolor printing machine having color printing units assigned to various printing inks, at least one image cylinder, image production equipment for producing color separations, in particular electrostatic latent color separations, on the at least one image cylinder, a carrier for printing substrates and at least one image transfer point for the transfer of the color separations to printing substrates, sensors for measuring positions and at least one setting device for assigning the positions of the image production points on the at least one image cylinder in order to achieve coincidence of register between the color separations in the print, at least one register sensor being arranged to detect register marks, and the setting device being designed such that it initiates the printing of register marks and evaluates them in such a way that it sets the production of the image starts and the production of areas of the color separations on this basis.
The invention also relates to a multicolor printing machine having apparatus of the aforementioned type.
Printing color illustrations, in particular color images, is carried out by a number of color separations being printed over one another. These are generally the colors yellow, magenta and cyan, as well as black. If required, special colors are also added. By means of overprinting these colors, all color compositions can be achieved, the quality of the prints depending significantly on the in-register overprinting of the color separations. In the case of conventional printing processes, the printing plates are corrected by means of test prints and register marks printed together with the latter until exact overprinting, that is to say the maintenance of register in the print is achieved.
In digital printing processes, the image cylinders are written with image points by means of an item of image production equipment in each case, for example, by electrostatic charges being generated and these being provided with adhering color pigments. The color pigments are then transferred to a printing substrate. In the case of digital printing processes, maintenance of register can be achieved by the image production equipment being controlled appropriately. Since the setting of an image is carried out anew for each print, it is not necessary, as in conventional printing processes, for a one-off setting to be made. Instead, provision can be made for presetting and regulation, which makes corrections for each individual print. Of course, this applies not only to the application of electrostatic latent images but also to all other printing processes in which image points are applied by means of a digital control system.
For an electrostatic printing process of the type mentioned at the beginning, U.S. Pat. No. 5,287,162 has, therefore, proposed printing register marks, preferably onto the carrier for the printing substrates and detecting these by means of an apparatus. In this case, the times which the register marks need from the production by the image production equipment as far as a detection point are determined. These times are then used to determine the instants at which the image production equipment begins its image-setting on the individual image cylinders in order to achieve the maintenance of register after the images have been transferred to a printing substrate. Faults, which can be produced in a manner, which repeats over time, by fluctuations in the speed of the image cylinders. Faulty determinations of the position by the rotary encoders of the image cylinders or other causes are registered by means of calibration tables. On the basis of these calibration tables, compensation for the faults is carried out. Provision is made for either the regulation of the image cylinder speeds, as a function of the position of the image cylinders, or corresponding production of the lines in the image.
Although, in the above-mentioned specification, mention is made of the fact that the start of the data, that is to say, the beginning of the image setting, and then the start of each line in the image, are controlled, what is lacking is the solution to the problem of obtaining data for the image starts and lines in the image or other subareas of a color separation in such a way that a rapid correction with high quality can be achieved with a tolerable outlay.
The invention is, therefore, based on the object of developing methods and apparatus of the type mentioned at the beginning in such a way that the setting of register can be implemented with a tolerable computing effort and high accuracy and, in particular, the data can be obtained and processed with a tolerable computing effort.
With regard to the method, the object is achieved by at least one picture page being printed which has register marks and has a length differing from that of the prints whose register is to be set, and in order to determine the correction values, by the data from the register marks of the at least one picture page being measured and placed in a relationship with positions of elements that carry images and substrates, and by the image production equipment being controlled in accordance with the correction values.
With regard to the apparatus, the object is achieved by its having at least one setting device which is designed such that it initiates the printing of at least one picture page which has register marks and has a length differing from that of the prints whose register is to be set, and by the at least one setting device being designed such that, in order to determine the correction values, it places the data from the detected register marks in a relationship with positions of elements that carry images and substrates, and controls the image production equipment in accordance with these correction values.
With regard to the multicolor printing machine, the object is achieved by its being equipped with apparatus of the above-mentioned type.
The invention has the advantage that it provides a method and apparatus by means of which, with a tolerable computing effort and within a short time, the correction values can be determined from the actual and desired values, and the corrections can be made. The basic idea of the invention consists in the ability to separate the actual values of the image starts from the actual values of the areas of the color separations by means of the proposed configuration of register marks. This separation can be carried out as an intermediate step, for example, for the determination by computation of the correction values for the image productions, or separate correction values can be determined and taken into account.
To achieve the aforementioned ability to be separated, it is proposed that at least one test print be made in which a picture page is printed which has register marks and which is longer than the prints whose register is to be set, or, if a number of picture pages are set up, that these be shorter than the prints whose register is to be set. Length deviations of this type make it possible to separate the faults in the image starts, which are caused by an assignment error between the image pro
Hunold Heiko
Metzler Patrick
Kessler Lawrence P.
NexPress Solutions LLC
Nolan, Jr. Charles H.
LandOfFree
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