Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-05-15
2002-07-16
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S178000
Reexamination Certificate
active
06421522
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and apparatus for setting registration in a multicolor printing machine for the digital production of color separations, the actions of setting up and combining the color separations being controlled in order to set the registration of the color separations in such a way that accurate registration prints are achieved.
BACKGROUND OF THE INVENTION
Printing colored illustrations, in particular colored images, is carried out by producing a number of color separations and transferring the color separations one over another onto a substrate. These color separations are generally yellow, magenta, and cyan as well as black. If required, special colors are added. By overprinting these color separations, all color combinations can be achieved. The quality of the prints depend significantly on the registration of overprinting of the color separations. In the case of digital printing processes, for example electrostatic printing processes, the maintenance of the registration of the overprint is achieved by the image production devices being controlled in such a way that the color separations meet one another in accurate registration when they are transferred to a printing substrate.
A method and apparatus for multicolor printing are disclosed in U.S. Pat. No. 5,715,498. There, the correction of registration faults is provided by printing and detecting registration marks. The marks are printed with the same toner particles that make up the respective color separations. The drawback with this technical solution is that in the event of a change in the toner profile (i.e., toner thickness on the printing substrate) as a result of a change in the content of the printed page, counteractive control is only possible for the following page, since the effect of the change in an influencing variable (i.e., physical characteristic of toner, substrate, process, etc.) is registered only when it has already caused a fault in registration. As a result, proofs are needed, and time is lost, which is often uneconomic in the case of small jobs and, therefore, not acceptable. Printing individual different printed pages economically is not possible in this way.
SUMMARY OF THE INVENTION
The invention is, therefore, based on the object of developing a method and apparatus for a multicolor printing machine in such a way that a change in the toner profile resulting from a change in the printed page no longer leads to a registration fault, not even temporarily. According to the invention, the object is achieved in relation to the method in that in the event of a change in the toner profile, the influence of the toner profile on the color separation registration is taken into account, by determining available influencing variables, directly as the change occurs. According to the invention, the object is achieved in relation to the apparatus in that the at least one controller is provided that in the event of a change in the toner profile, takes into account the influence of the toner profile on the color separation registration, by determining available influencing variables, directly as the change occurs. As noted, the influencing variables on registration include such things as physical characteristics of the toner, substrate, and process which are directly effected by toner profile changes. For example, toner profile changes may change speeds of rotary members in the printing machine or coefficients of friction between various elements.
The advantage of the invention resides in the fact that, in the event of a change in the toner profile when a printed page is changed, a fault in registration between color separations, which is imminent, is counteracted without any delay. It is no longer necessary to wait until the changed toner profile results in a registration fault that can be detected with the aid of registration marks. Instead, it is possible that directly as the printed page is changed, counteractive control can be carried out and, as a result, the occurrence of a registration fault can be prevented from the outset so that proofs of prints and/or registration marks are generally not necessary. That is to say, any change in toner thickness (profile) can be directly related immediately to its effects on other variables within the print process and the influencing variables can then be taken into account to prevent registration errors. This is of economic significance precisely in the case of small jobs, since machine time, and printing substrates as well can often be saved. With regard to the printing of printed pages with changing content, the result is that it is possible for the first time to achieve a standard of quality which was previously not possible in this important field of use of printing machines with digital image production.
As a result of the measure according to the invention, a registration setting can be optimized with the effect that, in the event of changes in the toner profile, registration does not “get out of hand” initially and require it to be corrected later, but rather that the registration setting remains within the range of tolerable fluctuations, so that during a change in the toner profile, it is possible to continue to print without interruption. At the same time, the invention does not exclude taking into account other influencing variables, if these have an influence on registration.
A development of the method provides that, in the event of a registration correction because of a change in the toner profile, the retroactive influence of the toner profile of the printed pages which have gone before, but are still in the printing process, on the registration of the new printed page already in the printing process is taken into account. In this way, the maintenance of registration in the prints in the event of a change to a printed page with a different image content is even better ensured. The printing machine can continue to print without any interruption even if, between the actions of setting up two color separations, the change in the printed page takes place in such a way that the new color separation is already being set up while the preceding color separation from the previous printed page has not yet or not yet completely been transferred to the printing substrate. The maintenance of registration is, therefore, ensured to a high extent, even in this overlap region between two printed pages, and any mutual influence is compensated for. As a result, the economy of the process is increased significantly, and the printing of printed pages with changing content at high quality is possible. With regard to the apparatus, this is achieved by the at least one controller being such that, in the event of a registration correction caused by a change in the toner profile, the retroactive influence of the toner profile of the printed pages which have gone before, but are still in the printing process, on the registration of the new printed page which is already in the printing process is taken into account by the controller.
A change in a printed page runs through the machine from one printing unit to the next and also, within a printing unit, runs through the printing unit on the path from production as far as transfer to the printing substrate. Accordingly, various machine configurations must be taken into account by variable influencing variables for each printing unit.
The influencing variables of the toner profiles can be taken into account on the basis of stored values based on experience, by manual input, by evaluating digital image data or by automatic detection of the toner profiles. With regard to the apparatus, provision can be made for it to be equipped with at least one memory, which contains stored values based on experience of influencing variables of various toner profiles, the at least one controller controlling the actions of setting up and combining the color separations on the basis of these values based on experience. However, it is also possible to equip the apparatus with an input device, via which the
Henderson Thomas
Liston Christopher
Metzler Patrick
Peter Karlheinz Walter
Grainger Quana M.
Kessler Lawrence P.
NexPress Solutions LLC
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