Exemplary non-limiting embodiments of the invention are described in the following description, read with reference to the figures attached hereto. In the figures, identical and similar structures, elements or parts thereof that appear in more than one figure are generally labeled with the same or similar references in the figures in which they appear. Dimensions of components and features shown in the figures are chosen primarily for convenience and clarity of presentation and are not necessarily to scale. In the attached figures:
In an exemplary embodiment of the invention, a photoreceptor 102 is electrified by a corotron, scorotron or other electrifying means 104. A scanning laser 106 beam or beams impinge on photoreceptor 102 and form a latent image of a particular separation thereon. A dispenser of liquid toner 108 which may be, for example, a binary ink developer (“BID”) cartridge, as described in one or more of U.S. Pat. No. 5,596,396 to Landa et al., and U.S. Pat. No. 5,610,694, to Lior et al., the disclosures of which are incorporated by reference. Optionally, a plurality of BID cartridges is used, each containing a different color toner. Alternatively, the dispenser of liquid toner is any one of the following: a spray dispenser, a series of spray dispensers or a series of slit dispensers, as known in the art, supply a liquid toner of a color corresponding to the separation. Optionally, the toner is a powder toner, applied in any manner known in the art.
The latent image is developed by the toner to form a visible image on photoreceptor 102. In some embodiments of the invention, a squeegee roller 112 compresses the image and removes excess liquid therefrom, prior to the transfer of the image to an intermediate transfer member (“ITM”) 114. The image is then transferred to a substrate 118 at a nip between ITM 114 and an impression roller 116. After transfer of the image to ITM 114, residual toner and charge on photoreceptor 102 are optionally removed by discharge and cleaning apparatus 120 which may be any of the many types that are well known in the art.
Individual separations are written (by scanning laser 106), developed and transferred to substrate 118 in seriatim. Optionally, a plurality of separations (or all the separations) may be transferred to the ITM first and then transferred as a group to the final substrate.
Unfortunately, the horizontal registration of the separations may not be perfect. Thus, in a calibration operational mode for printing apparatus 100, the image created is a calibration print output (described in more detail with respect to
Controller 122 is programmed with software to, inter alia, control the laser to write the latent image for the separations. In addition, controller 122 receives data pertaining to separation misregistration and makes corrections in the operation of printing apparatus 100 to correct the misregistration. For example, by directing scanning laser 106 to alter its latent image formation on photoreceptor 102 such that misregistration will not take place, or will be reduced to within a prescribed acceptable limit. In some embodiments of the invention, the horizontal offset and/or scaling of at least one separation is adjusted to implement at least a partial correction of misregistration. Optionally, the horizontal misregistration is corrected by adjusting the timing of the writing of the horizontal lines by scanning laser 106, for at least one separation. Optionally, the timing is adjusted dynamically, for example in response to commands received from controller 122. In an embodiment where data pertaining to separation misregistration is provided to controller 122 manually, for example by a user of printing apparatus 100, the calibration print output is produced by printing apparatus 100 and is examined by the user for perceived misregistration problems.
Printing apparatus 100 is optionally provided with a user input device 126, for example including a keyboard, with which to enter user-detected horizontal misregistration data. Examples of what and/or how the user enters data are described below with respect to
In some embodiments of the invention, data pertaining to separation misregistration is provided to controller 122 automatically. In some exemplary embodiments of the invention, the print engine is provided with at least one sensor 124, in operative communication with controller 122, for measuring at least one indicator of horizontal misregistration (and/or registration if it is determined there is only slight misregistration within prescribed acceptable limits). Optionally, an indicator is at least two rough adjustment lines (described below). Optionally, an indicator is a calibration pattern and a plurality of offset markers (described below). Optionally, the at least one sensor 124 is a densitometer provided with an appropriate resolution for carrying out the final adjustment described herein.
It should be noted that the printing apparatus configuration shown is only used to illustrate an exemplary configuration for carrying out the present invention and that other configurations could be used to achieve substantially the same effect (e.g. optionally, ITM 114 is not used).
Referring to
Calibration print output 200 is provided with at least one calibration pattern 206 optionally with a plurality of offset markers 208, shown in the calibration patterns located on the left side of calibration print output 200 in
Optionally, a visually perceptible scale 212, shown in the right side calibration patterns of
In some exemplary embodiments of the invention, at least two rough adjustment lines 202, 204 are printed as a pair on calibration print output 200, with each rough adjustment line corresponding to a separation. Optionally, rough adjustment lines are printed in more than one location on calibration print output 200, for example on the left and right sides, such as shown in
In an embodiment of the invention, each sub-pattern comprises an array of lines, generally running in the process direction and closely spaced in the horizontal direction. The lines in each sub-pattern form an angle with the process direction which is different from the angle for the other sub-pattern. Thus, the lines in the subsets cross at a fixed spacing in the process direction, given by s/(sin α), where s is the spacing between the lines and α is the angle at which the lines in the two sub-patterns cross. For small α, this reduces to s/α (α in radians)
Using this formula, a line spacing of 1 mm and an angle of 4 degrees (=4π/180 radians), the distance between crossings is about 14 mm. More importantly, when one of the sub-patterns is moved 100 micrometers (0.1 mm) horizontally with respect to the other, the crossings move about 1.4 mm in the process direction. This vertical offset is linear with the horizontal offset and measurements of the relatively large vertical offset allows for measurement, with substantial accuracy, of very small horizontal offsets.
It is understood that halfway between the crossings, each set of lines will be exactly between the lines. Thus, at the crossings a maximum unprinted area is produced and between the crossings a minimum unprinted area is produced. If the lines are half the spacing, then the contrast is a maximum. This results in alternating light and dark bands in the printed result.
These values of angle and spacing and line width are just an example and other values can be used if different sensitivity or contrast is desired.
In an exemplary embodiment of the invention, a first sub-pattern 302 is printed during the first separation using a given color. Optionally, the color is black or magenta. A second sub-pattern 304 is printed as a subsequent separation, in accordance with an embodiment of the invention. Optionally, the subsequent separation is the final separation of the image being printed. Optionally, second sub-pattern 304 is printed in a black color. Optionally, the lines in each sub-pattern are between 0.25 and 0.75 microns apart. Optionally, the lines in each sub-pattern are approximately 0.5 microns apart. In some embodiments of the invention, for example in manual embodiments, line spacing is selected for ease of perceptibility to the human eye. In some embodiments of the invention, line spacing is selected which results in a vertical offset that is readable by automatic sensors.
In an exemplary embodiment of the invention, when calibration pattern 206 comprised of the at least two overlapping sub-patterns 302, 304 is observed and magenta and black are used as the print colors, a light band 306 appears where the lines of the two sub-patterns 302, 304 touch or overlap. Where they do not touch or overlap, the calibration pattern assumes a color similar to that of the magenta separation. It is noted that if black and magenta are used then the pattern will have a reddish tint when the lines do not cross, which will disappear when they cross and the magenta is obscured by the black. Alternatively cyan or yellow could be used.
Offset markers 208 are provided to calibration pattern 206 which are detectable by a sensor, for example a densitometer. In an embodiment of the invention, offset markers 208 are arranged on calibration pattern 206 in a manner that will convey to controller 122 the approximate position of light band 306 on the calibration pattern 206. It should be understood that the sub-patterns 302, 304 are overlapped in a manner such that if first sub-pattern 302, and thus the first separation, is registered with second sub-pattern, and thus the subsequent separation, then light band 306 is centered at the “0” (offset marker 308) on the offset markers 208. In an exemplary embodiment of the invention, corresponding offset markers 208 are related to calibration pattern (for example by printing it together with one of the separations) so that slight horizontal misregistration, approx. 0.5 mm in some embodiments, of the sub-patterns 302, 304 causes light band 306 to move up or down in relation to offset markers 208 (for example as shown in
In some embodiments of the invention, the separations are configured that the white (or colorless) band is at the center of the pattern (as shown in
In addition to horizontal misregistration correction, vertical misregistration can be corrected utilizing the patterns and method shown in WO 00/43206 and WO 2004/088969, the disclosures of which are incorporated herein by reference. Alternatively, other methods, as known in the art, may be used to correct vertical misregistration. In principle, vertical misregistration should be corrected first to avoid its effect on the measurement of horizontal registration. However, since the effect of horizontal misregistration on the band position is many times greater than that of the vertical misregistration, in practice, the order may not be important.
Since the horizontal alignment mechanism described above is very sensitive, it may be necessary to perform a coarse horizontal alignment before utilizing the above described method. Any of the many methods of providing this coarse alignment can be used, for example, if two parallel arrays of lines running in the process direction are provided (for example lines 202 and 204, then the density and possibly the color of the image will be a function of the spacing between the lines. The lines to be printed are designed so that they print one top of each other when alignment is correct. When two different colors are used for the separation (such as for example black and magenta) horizontal misregistration will manifest itself in impartation of a reddish hue to the area of the lines. The direction and approximate amount of misregistration can be determined from a magnified view of the print.
Another method of performing rough adjustment is to use the same methodology as described with respect to
Alternatively, in some embodiments of the invention, a simple visual observation of a printed image may be sufficient to bring the image into rough registration.
In an exemplary embodiment of the invention, the produced (402) calibration print output 200 is used to detect and correct misregistration between the separations. Optionally, a rough adjustment performed (404) on calibration print output 200 using rough adjustment lines 202, 204, or by any other means known in the art. In some embodiments of the invention, a first rough adjustment line 202 is printed in a different color than second rough adjustment line 204 so that they can be easily discerned from one another. In some embodiments of the invention, rough adjustment (404) is performed if the fine adjustment indicator, light band 306, is far removed from the “0” of corresponding offset markers 208 or is not present within calibration pattern 206 due to being “off the scale”. Rough adjustment is optionally performed (404) if the rough adjustment lines 202, 204 do not touch or overlap each other on calibration print output 200, in an exemplary embodiment of the invention.
In some embodiments of the invention, a user of printing apparatus 100 manually inputs the misregistration data into controller 122 via user input device 126. In some embodiments of the invention, at least one sensor 124 automatically detects misregistration and communicates the misregistration data to controller 122. In a preferred embodiment of the invention, at least one sensor 124 is placed near the surface of calibration output 200 to measure the position of light band 306 and a corresponding offset marker 208 in a calibration pattern 206. Other sensors, as known in the art, may be used to measure the position of the markers 208, such that the controller can determine the relative offset of the band with respect to the markers.
In an exemplary embodiment of the invention, misregistration data includes an indication of whether first rough adjustment line 202 is to the left or right of second rough adjustment line using − or +. In addition, the instant methodology is intended to incrementally improve misregistration errors, and therefore the indication of left or right is also accompanied by a correction integer indicating how much left or right correction should be made by printing apparatus 100 in order to cause rough adjustment lines 202, 204 to touch or overlap. Optionally, the correction integer varies depending on the sensed or perceived misregistration error. Optionally, the correction integer is set depending on how precisely printing apparatus 100 can be controlled. Optionally, the correction integer is changed from one production (402) of calibration print output 200 to the next production (402), for example to make more fine adjustments.
In accordance with an exemplary methodology of the present invention, if first rough adjustment line 202 is to the left of second rough adjustment line 204, signaling that the first separation is horizontally misregistered to the left of the subsequent separation, controller 122 receives “−6” as misregistration data, where “−” indicates misregistration of the first separation to the left and the “6” indicating units, each unit comprised of 30 microns, of incremental correction to be implemented by printing apparatus 100 for the next printing. Optionally, each unit is comprised of more or fewer microns depending on the application or adjustment accuracy desired. In an exemplary embodiment of the invention, should first rough adjustment line 202 be to the right of second rough adjustment line 204, controller 122 would receive “+6” as misregistration data. In an embodiment of the invention, where the rough adjustment lines 202, 204 touch or overlap, no rough adjustment correction is to be made, thereby allowing for the input of “0” into controller 122 for rough adjustment misregistration data. In an embodiment of the invention, production (402) of calibration print outputs 200 and rough adjustment is performed (404) is repeated (406) until the incremental corrections of misregistration produce a calibration print output 200 wherein rough adjustment lines 202, 204 touch or overlap.
If a less sensitive version of the methodology of the fine adjustment is used for coarse adjustment, then this can be entered automatically, in the same way as described below.
In an exemplary embodiment of the invention, a fine adjustment is performed (408) after the optional rough adjustment (404). As described above, with respect to
In some exemplary embodiments of the invention, calibration print output 200 is provided with a plurality of calibration patterns located at various points on calibration print output 200. Calibration print output 200 depicted in
In some embodiments of the invention, the fine adjustment pattern is printed at several places across the image, or all across the image. This allows for the measurement of changes in horizontal registration across the page. While measurements taken at a border of the page are generally corrected by offsetting one separation from another, variations along the horizontal direction can be corrected by adjusting the instantaneous timing of the data along the horizontal sweep of the laser.
In the description and claims of the present application each of the verbs, “comprise” and “include” and conjugates thereof are used to convey that the object or objects of the verb are not necessarily a listing of all the components, elements or parts of the subject or subjects of the verb.
While the invention has been described with reference to certain preferred embodiments, various modifications will be readily apparent to and may be readily accomplished by persons skilled in the art without departing from the spirit and the scope of the above teachings. Various embodiments of the invention have been described having specific features. It should be understood that features of the various embodiments may be combined, where appropriate and features which are described above may be omitted, in some preferred embodiments of the invention. Therefore, it is understood that the invention may be practiced other than as specifically described herein without departing from the scope of the following claims: