The present exemplary embodiments relate generally to duplex printing and overprinting, and more particularly to image to paper (IOP) registration of image one to image two error compensation. The present exemplary embodiments relate to media (e.g., document or paper) handling systems and systems for printing thereon and is especially applicable for a printing system comprising xerographic devices or other marking engines such as inkjet.
As conventional in the art, simplex printing includes printing or imaging only a single side of a page or sheet of media. However, duplex printing includes printing or imaging both sides of the page or sheet media. Overprinting means printing multiple images on the same side of the sheet. Both simplex and duplex printing are well known in the art of printers, copiers, facsimile devices and the like.
With duplex printing, the alignment of the images on the front and back side of the page is critical. For example, when a stack of pages is folded to make a booklet, the back side of page one will share a margin with the front side of page two. Thus, any misalignment of the front and back images will produce an undesirable visible step at the margin.
Conventional image alignment or registration technologies focus on making the registration or image placement for each side of a page correct so that the front and back images will align correctly. However, to achieve acceptable simplex registration so that the duplexed pages are also acceptably aligned is prohibitively complex and expensive.
In addition, increasing the consistency of the simplex registration to improve the duplex registration cannot compensate for small errors in paper size. Since the duplex process flips the page to image the second side, both edges of the page (relative to the media processing direction in the imaging device) are used for positioning the page in the printer. Thus, when transferring the image to the paper varies during transfer, the front and back side images will be shifted by the amount of the page alignment error. Although a paper alignment error may be small, such small errors in front to back image alignment are very visible.
As explained for duplex printing, the same is also true for overprinting when printing a second image on the same side of the page which already has an image.
Accordingly, an object of the present invention is to provide a method to reduce the misalignment between the image one and image two, printed either on the different sides of the same sheet or on the same side of the same sheet. The final error (skew, process and cross-process) between the actual sheet orientation and the desired orientation during the transfer of image one is measured and recorded. When the same sheet comes for imaging the second time either on the same side or on side two, the error recorded during image one printing is retrieved and used to compensate the desired angular, process and cross-process registration of the sheet for image two printing so that the alignment of image one and image two are improved in comparison to systems that register the sheet without considering image one imaging errors.
There is provided a method of aligning images in an image forming device wherein a sheet has first image formed on a first side thereof and second image formed on an opposing second or same side thereof, the method comprising: forming the first image on the first side of the sheet with the image forming device; sensing skew and cross process alignment of the sheet while in the state of receiving the first image along at least one sheet edge approximately parallel with the process direction and storing a first skew and cross process alignment value; sensing process alignment of the sheet while in the state for receiving the first image along at least one sheet edge approximately parallel with the cross process direction and storing a first process alignment value; these errors (skew, process and cross-process) becomes the new reference for image two; transporting the sheet into the image forming device for the second image; re-sensing the skew, process and cross-process error in the sheet orientation and evaluating them with respect to the new reference; and positioning the sheet using these skew, process and cross process alignment errors to adjust desired position and orientation of the sheet before forming the second image on the opposing or same side thereby substantially minimizing relative first image to second image mis-registration.
With reference to the drawings wherein the showings are for purposes of illustrating alternative embodiments and not for limiting same.
The marking engines 12, 14 shown in
Referring to
Referring to
α is the angle between the orientation read by the sensor pair 132 and 134 and the desired orientation at the time of transfer.
ey is the error in Cross-Process alignment of the sheet at the CM as read by sensor pair 132 and 134.
ex is the error in Process alignment of the sheet at the CM as read by sheet lead edge process sensor 126.
When the same sheet comes for imaging image two, the errors (α, ex and ey) recorded during side one printing is retrieved and used by the media registration device controller to compensate the desired angular, process and cross-process orientation for image two so that the misalignment of image one and image two is improved in comparison to the systems that register the sheet without considering image one imaging errors.
Prior to reaching the transfer zone for printing the second image which could be with the marking engine 12 or in marking engine 14, sheet is re-registered with media registration device controller in a similar manner as discussed supra in regard to image one. However, media registration device controller uses the skew, process and cross-process alignment errors in image one to adjust desired position and orientation of the sheet before forming the second image thereby substantially minimizing relative first image to second image mis-registration.
In one embodiment in combination with media registration device controller reregistering the sheet, media registration device controller can also send the skew correction factor and the process and cross-process alignment correction factor to the image controller so that second image alignment is altered during formation of the image produced by marking element 318 or 320.
It is to be appreciated that a control system suitable for use in the exemplary embodiments is used in conjunction with the drive motors and sensors. A controller controls operations of the reproduction machine, or a portion thereof, as is well known in the art of reproduction machine control, and may be comprised of a microprocessor capable of executing control instruction in accordance with a predetermined sequence, and subject to sensed parameters, and producing a controlling output in response thereto. For the exemplary embodiments, an 8-bit microcontroller is a satisfactory microprocessor for control of, for example, a sheet registration subsystem of a reproduction machine. Other alternatives are, of course, available.
The exemplary embodiments have been described with reference to the specific embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiments be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.