JPH05270050A - Electronic adjustment of slow scan image registration in image recording apparatus - Google Patents

Abstract

PURPOSE: To provide a circuit for minimizing registration error of a recording apparatus of xerography. CONSTITUTION: An image recording system, which utilizes an LED image bar, with associated circuitry for recognizing which of LED's comprising the print bar 10 are out of registration in the slow scan, process direction 17 of a moving photoreceptor 16 upon which the image is to be recorded. Modification of the drive circuits 44 to the individual LED's results in energization signals being delayed to the identified, misregistered LED's resulting in an exposure line which is in correct slow scan registration.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION The present invention relates to a xerographic (electrophotographic) recording apparatus for line-by-line exposure of a surface of a moving photoconductor, and more specifically, to a sagittal (slow scan) direction. Circuit for minimizing registration errors in.

Image printing bars used in xerographic recording systems are well known in the art. The image printing bar generally consists of a linear array of a plurality of discrete light emitting sources. Light emitting diode (LED) arrays are suitable for many recording applications. In order to achieve high resolution, a large number of light emitting diodes or pixels are arranged in a linear array,
Means are provided between the linear array and the photoconductor to provide a scanning operation of the linear array over the surface of the photoconductor. Thus, the photoconductor is LE
As the D array is stepped over the photoreceptor in a continuous or stepped manner, it is exposed to provide a row of the desired image. Each LED of the linear array is used to expose the corresponding pixel on the photoreceptor to a value determined by the image-defining video data information.

300 spots per inch (300 sp
i) 50 at 84.67 micron center as a print bar with a resolution of (118 spots per cm).
It can be said that a pixel size of × 50 microns is a typical shape. In xerographic applications where an 8.5 inch (21.6 cm) wide information line is exposed, approximately 2550 pixels arranged in a single row would be required. (If two or more parallel staggered LED arrays are used, the space between adjacent LEDs can be increased while the cost increases.) One of the conventional printing bars. The problem is the difficulty of aligning all the LED pixels in the linear direction of the array and in the sagittal plane. The sagittal surface supports slow scan or process direction motion of the photoreceptor.
Current chip technology allows for very precise pixel placement in the linear direction, but is misplaced in the sagittal direction when formed on the same chip as individual pixels or more commonly grouped pixels. there is a possibility. This will lead to registration errors in subsequent printing of the recorded image. The significance of this type of registration error becomes significant when multiple image bars are used, for example, in a color printing system where accurate registration of simultaneous line exposures of each color is required.

No prior art discloses how to identify individual pixels or sub-arrays of pixels within a large array that are misaligned with respect to other pixels or to correct the misalignment or misregistration. According to this embodiment, first a circuit and method are provided to first align the print bar to match the pixels to the misregistration of the pixels, and then drive to these misregistered pixels. It delays the signals and delays their excitation to ensure that they are registered with the rest of the LEDs to be in proper registration. More particularly, the present invention relates to an imager for line-by-line exposure of a surface of a photoreceptor moving in a slow scan process direction, which includes at least one linear printing bar having multiple light emitting elements and a slow scan direction. Including some of the elements misregistered in, the apparatus including; a drive circuit for exciting the light emitting element and a continuous supply of an input data signal to the drive circuit during a line information period. Generated by said light emitting element by selectively providing a delay tolerance signal to said drive circuit coupled to said circuit means and said light emitting element or grouped light emitting elements to be excited during the line information period. Includes permissive circuit means for ensuring that the exposed line is in linear registration. They are out.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram of an image system incorporating a pixel registration correction circuit of the present invention.

FIG. 2 shows the linear print bar of FIG. 1 with pixel groups misaligned in the sagittal direction.

FIG. 3 shows a group of selected pixels with one pixel out of registration.

FIG. 4 shows a time chart for a 16 pixel segment of the image bar of FIG.

FIG. 5 is a time chart of the segment of FIG. 4 when one pixel is out of registration.

FIG. 6 illustrates a raster output scanning system (ROS) that forms an image with multiple image bars.

FIG. 7 shows the exposure scan lines produced by the ROS system of FIG.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, an image recording system is shown in which a linear printing bar 10 is positioned on a surface 14 of a photoreceptor web 16. The linear printing bar 10 includes a plurality of LEDs 12 (FIG. 2) arranged side by side, and the photoreceptor web 16 is moved in the slow scan process direction as indicated by arrow 17. Web surface 14
Are charged to a predetermined potential as is known in the art. The individual LEDs are selectively energized as described below to match the image video data signal generated by the video data source 18 to expose the charged surface 14. Areas of the web that are exposed are discharged while areas that are not exposed retain their original state of charge. The latent image thus formed is subsequently developed, and the developed image is transferred and fixed on an output medium such as paper. All these xerographic processing steps are well known in the art.

Still referring to FIG. 1, an ESS controller 30 is shown, and the ESS controller 30 is shown.
Controls the excitation of the LEDs including the printing bar 10 via the LED drive circuit 31 which includes logic and storage elements. Included in the controller 30 is a crystal clock 32 and a delay memory storage circuit 34. The drive circuit 31 includes a shift register 42 and a latch register 44.
In addition, the drive circuit 46 is incorporated. In that operation, the binary video data signal from the data source 18 is loaded into the shift register 42 under the control of the clock signal generated by the crystal clock 32. Upon receipt of the last incoming binary bit, the data bits are shifted in parallel by the latch signal into the latch register 44, where they are temporarily stored. These signals are again shifted in parallel to the drive circuit 46 with the receipt of the latch signal generated by the detection of the end of line condition. The drive circuit includes a plurality of drive transistors, each transistor being coupled to an individual LED or group of LEDs. According to the present invention, the drive circuits are selectively addressed under the control of the controller 30 by an allow signal generated from the delay memory 34. These delayed signals are delayed in time with respect to the excitation signal supplied to the LEDs already in proper registration. The delay time of the signal applied to the misregistered pixel is determined by the method as best described with reference to FIGS.

It is assumed that the print bar 10 has a group of approximately 2550 LEDs (pixels) arranged in a line, and is to perform a line exposure of 8.5 inches (21.6 cm). In addition, the pixels are linearly registered, but one or a few more are out of alignment in the sagittal or slow scan directions (misregistration condition). Figure 2 shows bar 10
Of the pixel groups 10A, 10
B, 10C, 10D, 10N, some of which are misregistered within the sagittal dimension for a given centerline. Each group includes a plurality of LEDs 12, each LED being registered with the other LEDs of the group to which it belongs, but not necessarily with the LEDs of the other groups. For the purpose of explanation, the LED group 10B will be replaced by another group 10B.
It is shown as out of registration with A, 10C, 10D. The latter three groups are assumed to be in proper registration. The misregistration situation is shown in more detail in FIG.
There, the group 10B is the other pixel group 10
They are arranged at a distance D _d from A, 10C and 10D. In the following description, this distance D _d is a delay distance, that is, the distance from the leading end of the group 10B (misregistration group) in the moving direction to the leading end of the other three groups (properly registered groups) in the moving direction. Referred to as the delay distance defined in.
The light receiving web 14 moves at a constant speed V _pr , and a distance on the web corresponding to the distance from the moving direction tip of the pixel group 10B (right end in the figure) to the moving direction tip of the pixel groups 10A, 10C, and 10D. The time required for one point to pass is given as the delay time T _{d by the} following equation. T _d = D _d / V _pr (1)

In order to correct the misregistration condition shown in FIG. 2, the signal of the drive circuit 46 for exciting a particular pixel group needs to be delayed by a period T _d . The required timing delay can best be understood with reference to FIGS. FIG. 4 is a time chart showing the operation of the 16-pixel LED print bar. The actual duty cycle of the print bar is the ratio of the LED ON period to the total line time T ₁ . When transferred to physical space, this line time (T ₁ ) is typically the photoconductor 16
The (moving speed V _pr ) is set to be equal to the time required to move the slow scan resolution distance of the system.
_Operates at a V _pr of 10 inches (25.4 cm) per second 30
In the system of 0 × 300 spi, the line time T
_One equals 333.3 microseconds. Since at least 16 clock counts are required for all data on one serial data input line, the minimum clock frequency required for this simple virtual system would be 48 kHz. If the pixel placement of the first four pixels represented in group 10B of FIG. 3 and the timing sequence as shown in FIG. 4 is used, pixel group 10B misses the delay distance D _d on the photoreceptor. Will be registered. To correct this, pixel group 10B
The admissible signal for is delayed by the value determined by the expression given in equation (1). A timing sequence incorporating this concept is shown in FIG. By extrapolation, each pixel or group of pixels in the print bar 10 is individually addressed, if that pixel or group of pixels is excited (switched ON) for a partial line scan, and , If the pixel or pixel group has previously been identified as previously misregistered, then the excitation signal of the single or multiple groups is Generated to be delayed.

Each print bar is exposed to unique misregistration conditions. Therefore, according to another aspect of the invention, individual print bars are pre-measured to identify the LEDs of the print bars that are misregistered, and also these misregistration states. An appropriate registration correction (permissive signal) for the LED is generated and stored. This measurement is achieved by the following procedure. Fixing equipment with a built-in CCD camera array
It is attached to a precision linear scanning mechanism located parallel to the LED bar at the image plane. The fixing fixture is scanned under the LED bar and the position of each pixel in the slow scan direction is measured and stored. The position data obtained by the post processing that is subsequently performed is the ESS controller 30.
Is input to the correction logic of. Information is transferred by computer diskette, E-PROM or direct data transfer. An alternative method is to create a bar code of the measured position information and fix it directly to the LED bar where it was measured. And the position correction data is LE
It can be scanned during ESS when D-bar is attached.

Although the above description is directed to the particular problem of correcting misregistration between pixels that occurs along a linear print bar, this delayed pixel excitation method also serves other purposes. Can be used. As one example, the ROS shown in FIG.
/ Consider a bar-type hybrid scanning system for printing. The intent of this system is to produce a color print from the input video data,
Photosensitive belt 50 using OS scanning system
The first latent image is formed on the surface of, and subsequently the LEDs 70, 72 form a registered latent image with the first ROS latent image. The latter latent image corresponds to a particular color that is later developed with the appropriate toner. The system operates as follows. The laser diode 51 serves as a source of high intensity coherent light beam output. The laser power is self-adjusted and the light beam power is adjusted to match the information contained in the video signal. The conditioned beam is expanded and focused by optical elements in pre-polygon optical assist system 52. As is known in the art, the output beams 54A, 54B are formed to impinge directly on the facets 56 of the rotating polygon polygon 58. The rotation axis of the polygon 58 is provided so as to be orthogonal or substantially orthogonal to the plane in which the light beam propagates. The polygonal surface of the polygon 20 is finished as a mirror surface that reflects incident light. By rotating the polygon 20 in the direction shown by the arrow, the light beam is reflected from the irradiation facet 56 and is deflected to the scanning angle for flying spot scanning. The beam portion 60 reflected from the facet 56 is fθ
It passes through the lens 62. The fΘ lens 62 is adapted to focus along a linear focal plane so as to eliminate the arc given to the beam when reflected along the facet. Then, the beam is projected through the cylindrical lens 64 having a power only in the sagittal direction (orthogonal to the scanning direction).

The focused beam 60 is reflected by the arrow 34.
It is moved across the surface of the belt 50 as the scan line 66 in the direction indicated by. Belt 50 is rotated in the process direction as shown. Also, what forms the latent image on the surface of the belt 50 are the printing bars 70 and 72, which are provided by a video data signal provided in the same manner as described above according to the circuit of FIG. Be excited. Each line is fθ lens 6
It is conventional to linearize the scan line by 2 so as to reduce the curvature of the scan line due to the spot reflection from the facet of the rotating polygon. However, in some systems, this linearization can still leave some irregularities in the scanline. This irregular line can be characterized and plotted, and subsequent print bars can be scaled to print the line being registered with the irregular ROS scan line.

For example, as shown in FIG. 7, ROS scan line 66 is shown to include two segments. That is, the pixels in segment A are linearly registered, while the pixels in segment B lie along a portion of the arc or curve. The print bars 70, 72 are first measurement enabled and the shape of their characteristic scan lines is determined using any of the measurement support procedures described in the above description. These characterized lines are then matched to line 66 in FIG. 7 to determine the proper tolerable delay signal to be provided to each group of pixels.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an image system incorporating a pixel registration correction circuit of the present invention.

FIG. 2 shows the linear print bar of FIG. 1 with pixel groups misaligned in the sagittal direction.

FIG. 3 shows a group of selected pixels with one pixel out of registration.

4 shows a time chart of a 16 pixel segment of the image bar of FIG.

FIG. 5 is a time chart of the segment of FIG. 4 when one pixel is out of registration.

FIG. 6 illustrates a raster output scanning system (ROS) that forms an image with multiple image bars.

7 shows an exposure scan line produced by the ROS system of FIG.

[Explanation of symbols]

10 Linear printing bar, 10A, 10B, 10C,
10D, 10N pixel group, 12 LEDs, 1
4 surface, 16 photoconductor web, 18 video data source, 30 ESS controller, 31 drive circuit, 32
Crystal clock, 34 Delay memory storage circuit, 4
2 shift register, 44 latch register, 46 drive circuit, 50 photoconductor belt, 51 laser diode, 52 pre-polygon optical assist system, 54A, 5
4B output beam, 56 facets, 58 polygons, 6
0 beam part, 62 fθ lens, 64 cylindrical lens, 66 ROS scan line, 70, 72 print bar

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor John A. Durbin New York, USA 14580 Webster Hunter Circle 1283 (72) Inventor William Jay Nowak, USA 14580 Webster Larkston Drive 1074 (72) Invention By Daniel W. Costanza United States New York 14580 Webster Made Stone Drive 291

Claims (2)

[Claims] 1. A surface of a photoreceptor moving in a slow scan process direction comprising at least one linear printing bar having a number of light emitting elements and some of said elements misregistered in the slow scan direction. An imager for line-by-line exposure, comprising: a drive circuit for exciting a light emitting element, for continuously supplying an input data signal to the drive circuit during a line information period Circuit means, and permissive circuit means for selectively providing a delay permissive signal to said drive circuit coupled with the light emitting elements or grouped light emitting elements to be excited during the line information period. 2. A method of line-by-line exposure of a moving photoreceptor by at least one image printing bar comprising a plurality of linearly arranged light emitting pixel elements, the method comprising the steps of: slowing the operation of said photoreceptor. Optically determining pixels or pixel groups that are out of line registration in the scanning direction and storing the coordinates of the line registration in a selected binary data format; The video binary data signal is supplied in parallel format to drive the associated circuitry, the drive circuitry associated with the pixel element to be excited for a given line exposure is enabled and in the slow scanning direction. Misregistration The driving permission signal to the pixel element identified as the state is selected for the misregistration described above so that the exposure line in which all areas are exposed by the pixel element is in the registration state in the slow scanning direction. Delay by minutes.