JP2001150731A - Method for reducing print head signature, image drawing engine, and method for processing image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved novel technology for reducing print head signature. SOLUTION: A signature output intensity response is determined for each scanning line of a print head and a different tune reproduction curve is determined for each scanning line of that print head. The different tune reproduction curve is determined such that a desired output intensity response is generated for each scanning line when that tune reproduction curve is applied in relation to the signature output intensity response of a corresponding scanning line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to print image processing and drawing. The invention has particular application in connection with inkjet printers and will be described with particular reference to inkjets. However, the invention is applicable to other similar applications, such as thermal transfer printers, pin-dot-matrix printers, impact printers, and other similar drawing engines that use a printhead to draw multiple scan lines by way of traversing a recording medium. It should be understood that this is also applicable. The present invention is also directed to electrophotographic technology that uses a plurality of imaging elements to expose a photosensitive drum, such as, for example, a light emitting diode (LED) bar or an electrophotograph using a multi-beam laser raster output scanner (ROS). Applicable.

[0002]

2. Description of the Related Art In general, a printhead includes an array of marking devices or mechanisms that are oriented substantially parallel to the direction of travel of the recording medium and substantially perpendicular to the direction of travel of the printhead. For example, in an ink jet device, a marking device usually has a nozzle that accelerates or discharges a droplet of ink substantially linearly toward a recording medium along a trajectory substantially perpendicular to the recording medium. is there. Thus, each marking device has the function of drawing a corresponding scan line as the printhead passes over the recording medium, and the corresponding array of scan lines as a whole tract or output. Print width (sw
ath).

[0003] However, due to incorrect manufacturing tolerances or other similar conditions, the physical characteristics of the marking devices (eg, nozzles of an inkjet printhead) that produce the individual scan lines are not all the same. That is, in order to obtain a uniform output intensity response, the marking devices are ideally identical to one another, but in practice they are often somewhat irregular. For example, the marking device may be out of position, out of direction, large or small, or near or far from the recording medium. As a result, to obtain a similar need or target output intensity,
The amount of ink or other marking material placed on the recording medium is not uniform between scan lines. For example, due to the physical characteristics of the marking device, the printhead prints at a larger spot than prints a scan line adjacent to one scan line, so that one scan line is more likely to print than its adjacent scan line. May also appear dark. Similarly, the printhead prints with a smaller spot than it does on a scan line adjacent to one scan line, so
A scan line may appear thinner than its adjacent scan line.

[0004] The aforementioned artifacts are nominally printhead signatures (signatures).
Called. Because printhead signatures result from irregularities in certain physical properties of the printhead and, in particular, the marking device, its artifacts do not change over time.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a new and improved technique for mitigating printhead signature artifacts that overcomes the above-referenced problems and others.

[0006]

In accordance with one aspect of the present invention, a method for reducing printhead signatures comprises a print engine having a printhead that depicts a plurality of scan lines by each path of the printhead across a recording medium. For use in The method includes determining a signature output intensity response for each scan line of the printhead, and determining an individual tone reproduction curve (TRC) for each scan line of the printhead.
The separate tone reproduction curves are determined such that a desired output intensity response is generated for each scan line when the tone reproduction curve is applied in conjunction with the signature output intensity response of the corresponding scan line. The desired output intensity response is substantially equal between scan lines.

[0007] In accordance with another aspect of the present invention, an image rendering engine is provided. It comprises a printhead that draws multiple scan lines with each path across the recording medium.
Each of the scan lines has a signature output intensity response. The corrector provides a separate tone reproduction curve for each scan line so that when the tone reproduction curve is applied in conjunction with the corresponding scan line signature output intensity response, the desired output intensity response occurs for each scan line. give. The desired output intensity response is substantially equal between scan lines.

According to another aspect of the present invention, there is provided a method of image processing. The method includes determining signature intensity responses of a plurality of imaging elements, each responsible for rendering a corresponding portion of an image being processed, and determining a tone reproduction curve for each imaging element. And steps. The tone reproduction curve is determined such that when the tone reproduction curve is applied with respect to the signature intensity response of the corresponding imaging element, a substantially uniform intensity response occurs for each portion.

One advantage of the present invention is that it efficiently reduces printhead signatures.

[0010] Further advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the preferred embodiments of the invention.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, in a preferred embodiment of the present invention, an image rendering engine, such as the illustrated ink jet printer 10, has a single line nozzle or nozzle array 15 and is integrated. A disposable ink supply cartridge 12a having a printhead 14 mounted and mounted is provided. In another usage and / or rendering engine, as is known in the art, other imaging elements or marking devices similar to the nozzle 15 may be used for rendering portions (eg, lines) of the image being processed. Play a role. In any event, for the inkjet embodiment, the combination of ink cartridge and printhead is removably mounted on a movable carriage 20. During the printing operation,
The carriage 20 reciprocates back and forth on a guide rail 22 in a first direction (indicated by an arrow 23) across a recording medium 24 such as a sheet of paper, a transparent sheet, a mailing label, or the like. This first direction preferably has a direction substantially perpendicular or perpendicular to the line or array of nozzles 15.

The distance traveled from carriage to carriage 20 and the printhead 14 on the carriage 20 from end to end is shown as distance B. The carriage 20 is driven back and forth across the entire length of the cylindrical platen 16 in a conventional manner, for example, by a cable and pulley system or a drive system (not shown) having a reversible motor mounted on a screw drive shaft. Is done. In this way, the print head 14 moves back and forth in the first direction across the recording medium 24.

The recording medium 24 is mounted on the platen 16. Platen 16 has a diameter of 10-20 cm,
For example, the drive shaft 13 </ b> A preferably includes an outer sleeve 17 having an end cap 13, and preferably extends through the end cap 13. A pulley 33 is attached to one end of the drive shaft 13A. The pulley 33 is driven by a motor (not shown) via a belt 32 or other strand-like thing. The drive shaft 13A that drives the platen 16 is driven by driving the pulley 33. The platen 16 is connected to the frame side surface 2 including both ends of the guide rail 22 if desired.
Preferably, it is rotatably mounted on one. Since the recording medium 24 is held by the platen 16, when the platen 16 rotates, the recording medium 24 passes through the print head 14 and is substantially perpendicular to the first direction, i.e., in a second direction perpendicular to the first direction (arrow 19). ).

In operation, when the print head 14 moves in the first direction, the platen 16
4 is preferably retained. Periodically, i.e., between printhead passes, the platen 16 is driven to advance the recording medium 24 through the printhead 14 in the second direction. The image is drawn by the ink supply cartridge 1
This is performed by supplying ink from 2a to the print head 14 and selectively ejecting ink from the nozzles 15. That is, at each relative position of the print head 14 with respect to the recording medium 24, a drop of ink is selectively and substantially linearly from the nozzle 15 to the recording medium 24 along a trajectory substantially perpendicular to the recording medium 24. Accelerated or ejected.

More specifically, a complete image is drawn on recording medium 24 with the spread or width created by the plurality of scan lines. In other words, the print heads 14 are arranged such that the plurality of drawn scan lines form a spread or a width by each path.
Passes through the recording medium 24 back and forth in the first direction, each nozzle 15 draws a corresponding scanning line. Between passes of the printhead, the platen 16 rotates, causing the recording media 24 to move the printhead 14 such that the next (preferably adjacent or overlapping) spread or print width is drawn in the next printhead path. Pass through the second
In the direction of.

Prior to rendering the image, printhead 14 is calibrated to reduce printhead signatures. That is, while drawing an image, the response of the output intensity obtained from each scan line or nozzle 15 may not be uniform between scan lines or nozzles, and the print head 14 may be configured to reduce this non-uniformity. Calibrated. If necessary, this calibration is performed only before the first use of the image rendering engine. Alternatively, changes in environmental conditions, changes in the printhead 14, or changes in the physical properties of the drawing engine (eg, wear due to repeated use, accumulation of debris or dry ink, damage to parts, movement or repositioning of the drawing engine, etc.). Before each use of the image rendering engine, before each rendering of the desired image, before each rendering of a single desired image or print width, During the flight, recalibration is performed at predetermined intervals and / or as desired or selected.

With further reference to FIG. 2, in a preferred embodiment, the calibration process 100 begins at step 110. Next, at step 120, the signature output intensity responsiveness is determined for each individual nozzle 15 and / or for each individual scan line of the printhead 14. The signature output intensity response is a function or curve 200 (best shown in FIG. 3) that correlates or maps the required or input target intensity with the actual measured output intensity obtained accordingly. ). Thus, the signature output intensity responsiveness for each separate scan line or nozzle 15 is preferably determined by measuring the actual output intensity and comparing it to the input target intensity used to generate them.

Next, at step 130, a separate tone reproduction curve (TRC) for each scan line or nozzle 15 is determined. The TRC is a function or curve 210 that correlates or corresponds the target input intensity to a corrected or adjusted intensity that achieves the desired output intensity response from the scan line or nozzle 15.
(Best shown in FIG. 3). That is, when the TRC is applied to the target input intensity, the target input intensity is corrected or adjusted to produce an adjusted intensity. Contrary to the target input intensity, which achieves a signature output intensity response, the adjusted intensity achieves a predetermined, selected, or desired output intensity response. Thus, in a preferred embodiment, a separate TRC for each scan line or nozzle 15 is determined, so that the output intensity response achieved is substantially the same between scan lines or nozzles. In this way, the resulting output intensity responsiveness for each scan line or nozzle 15 is substantially the same throughout the printhead 14 regardless of substantially irregular or different physical properties therebetween. Or become uniform. As a result, printhead signatures are reduced. Next, at step 140, the calibration process 100 is completed.

If for each scan line or nozzle 15 its respective TRC is applied in relation to its respective signature output intensity response, the corresponding output power response obtained is the curve 220 (FIG. 3). (Shown most often). In order to obtain such a linear response, curve 210 (ie, TRC) is
(Ie, a curve showing the signature output intensity response). That is, curve 210 is a mirror image of curve 200 with respect to line or curve 220 (ie, a curve exhibiting the desired linear response). Further, the linear response preferably adapts or corresponds to the target intensity to substantially the same output intensity.

In a preferred embodiment, the TRC for each scan line or nozzle 15 determines its separate TRC based on the signature output intensity responsiveness for that particular scan line or nozzle 15 and the desired output intensity responsiveness. Determined individually by calculating or generating. Alternatively, a fixed number of representative TRCs are available. Representative TRC
Includes a range of unspecified signature output intensity responses that are expected to be encountered across multiple scan lines or nozzles 15 of printhead 14. In this alternative case, for each scan line or nozzle 15, one of the representative TRCs for applications related to the signature output intensity response, such that the resulting output intensity response is closest to the desired one. Is designated or selected. Since the number of available representative TRCs is constant, any one of the representative TRCs is
One or more scan lines or nozzles 15 can be specified or selected.

Still referring to FIG. 4, in a preferred embodiment, the TRC is stored in a storage device 300, such as, for example, a look-up table (LUT), random access memory (RAM), optical or magnetic storage. During image rendering, an input signal indicating the target intensity for each scan line of the spread or print width to be rendered is applied to the signal processor 3.
10 from an input signal source 320. The signal processor 310 is generated from the storage device 300,
Access the specified or determined TRCs and apply them to each signal for the corresponding scan line. T
The RC correction or adjustment signal is then sent to the printhead 14, which controls or adjusts its respective scan line output intensity or nozzle 15.

To further enhance the reduction of printhead signatures, in a preferred embodiment, adjacent spreads or print widths are drawn in overlapping fashion. The spread or print width drawn by each printhead path preferably overlaps half. That is, between each drawing path of the print head 14 traversing the recording medium 24 in the first direction, the recording medium 24
Is advanced in a second direction past the printhead 14 by half the length of the printhead in that direction. In this embodiment, only one portion of the width of the printhead 14 is drawn in one pass, and the remaining portion is drawn in the return pass or immediately following pass. The portion drawn in each successive path is preferably a complementary portion of the checkerboard pattern with each row of the checkerboard pattern corresponding to a scan line. In this manner, the plurality of nozzles 15
Or a similar marking device is used to draw each single scan line. Therefore, the printhead signature is further averaged in the area where the print widths overlap.

In a preferred embodiment, the image rendering engine is a full color device. For example, referring again to FIG. 1, an additional disposable ink having an integrally mounted printhead (not shown) having a single nozzle or nozzle array or other similar marking device (not shown). Supply cartridges 12b to 12d are provided. Each ink supply cartridge 12a-12b is a source of a different color ink and is used to draw its corresponding color separation (eg, cyan, yellow, magenta, and black) image, and each color separation image It undergoes a process similar to that described in the specification.

Regarding the preferred xerographic embodiment,
Multiple imaging elements (eg, LEDs on LED bars, multi-beam laser ROS, etc.) that play a role in drawing different parts or lines of the image being processed in a manner similar to the embodiment using a printhead. For each of the signature strength responses. Thereafter, a separate TRC is specified or determined for each imaging element to correct for the fluctuating signature, and is uniformly applied to each part or line independent of the imaging element responsible for rendering each part or line of the image. A strong intensity response.

[Brief description of the drawings]

FIG. 1 is a partial cutaway view illustrating an inkjet printer as an exemplary embodiment of an image rendering engine used in accordance with aspects of the present invention.

FIG. 2 is a flowchart illustrating a printhead calibration process used in accordance with aspects of the present invention.

FIG. 3 shows an exemplary signature output intensity response in which the horizontal axis represents the target intensity and the vertical axis represents the actual uncorrected output intensity generated accordingly, and the horizontal axis represents the input intensity and the vertical axis corresponds thereto. 5 is a graph of a combination, expressed in arbitrary units, representing an exemplary tone reproduction curve showing the adjusted intensity and the desired linear response showing the input intensity on the horizontal axis and the desired output intensity on the vertical axis.

FIG. 4 is a flowchart illustrating an image drawing process according to an aspect of the present invention.

[Explanation of symbols]

 Reference Signs List 10 inkjet printer 12a ink supply cartridge 12b ink supply cartridge 12c ink supply cartridge 12d ink supply cartridge 14 print head 16 platen 15 nozzle 20 carriage 22 guide rail 24 recording medium

Claims (3)

[Claims] 1. A method for reducing a printhead signature for use in a drawing engine having a printhead that depicts a plurality of scan lines by each path of the printhead across a recording medium, the method comprising: (a) B) determining a signature output intensity responsiveness for each scan line of the print head; and b) determining a separate tone gradation curve for each scan line of the print head. Reduced printhead signatures when tone reproduction curves are applied in relation to their corresponding scan line signature output intensity response, resulting in substantially the same desired output intensity response for each scan line. how to. 2. A printhead that describes a plurality of scan lines along each path across a recording medium, each of said scan lines having a signature output intensity response, and a separate tone reproduction curve for each scan line. Wherein the tone reproduction curve produces a desired output intensity response for each of the scan lines when applied in conjunction with a signature output response of the corresponding scan line, wherein the desired output intensity is The responses are substantially equal to each other, the image rendering engine. 3. A method comprising: (a) determining a signature intensity responsiveness of a plurality of image forming elements, each element playing a role in rendering a corresponding portion of an image being processed; Determining a separate tone reproduction curve for each imaging element, wherein the tone reproduction curve is substantially equal for each portion when applied in relation to the signature intensity responsiveness of the corresponding imaging element. An image processing method that produces an intensity response of