JP2009214454A - Multi-beam scanning apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LSU (laser scanning unit) which is equipped with a light source having a plurality of light emitting parts, and can make two image data to be objects for image processing to be adjoining lines without depending on the inputted image data even when the scale of the circuit is small. <P>SOLUTION: The LSU 20 is equipped with an LD (laser diode) 1 having two light emitting parts 1a and 1b, and image data buffers 28 and 29 into which the image data are written on every line in accordance with respective light emitting parts 1a and 1b, and forms latent images by performing modulation control of the LD 1 based on the image data successively read out from the image data buffers 28 and 29. The LSU 20 is equipped with an image processing part 30 which compares the image data successively read out with the adjoining pixel and corrects them. When the image data of the same line are written into the image data buffers 28 and 29, the LSU 20 writes the data of a white image to the image data buffer 28(29) of an odd number line in a period before the image data of the first line are written. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multi-beam scanning apparatus that performs light scanning by condensing a beam from a plurality of light emitting points of a laser light source as a light spot on a photoconductor in one scan.

  2. Description of the Related Art Image forming apparatuses such as copying machines and printers perform printing using a laser scanning device called a laser scanning unit (LSU). In the LSU, a polygon mirror having a plurality of reflecting surfaces is rotated by a motor, laser light is reflected by the polygon mirror, and the photosensitive member is scanned with the reflected light to form an electrostatic latent image on the photosensitive member. . As this LSU, in order to increase the printing speed and the printing resolution, a laser light source having a plurality of light emitting points (light emitting portions) is used to scan a plurality of lines in one scan. (For example, refer to Patent Document 1).

For example, the LSU can acquire image data from a circuit that processes image data from a scanner or the like in the image forming apparatus, and can control the laser light source based on the acquired image data.
The LSU control circuit including the laser light source control circuit has a relatively small scale. In this control circuit, the signal waveform is prevented from being disturbed when the laser light is turned on / off at high speed, and various LSU circuits are provided. There is a need to prevent the influence of noise on the signal to be controlled. In addition to these reasons, the LSU control circuit is often provided in the LSU because it is not necessary for the user or service person to touch it. On the other hand, a processing circuit for a scanner image or the like is relatively large and needs to be arranged at a position that is relatively easy to operate for function expansion after installation.
For this reason, it is desirable to transfer image data with as few signals as possible from the processing circuit such as a scanner image to the LSU control circuit, and to reduce the circuit scale of the LSU control circuit as much as possible.

  Furthermore, in recent years, there have been many developments such as a dedicated printer and a multi-function machine in which copying and FAX functions are integrated into a printer function based on one engine, and one LSU control circuit can handle a plurality of types of image data. There is a need. For example, a printer (function) is required to print based on image data having a resolution of 1200 dpi (Dot Per Inch), but a copy (function) is based on image data having a resolution of 600 dpi due to the performance of the scanner unit. Occurs when printing.

In addition, depending on the input image data, there is a case where the image data is not necessarily transmitted via the processing circuit such as the scanner image described above. The image processing needs to be executed in the LSU control circuit.
However, since the LSU control circuit needs to be accommodated in the LSU as described above, it is necessary to suppress the circuit scale as much as possible.
JP-A-10-268214

  However, on a circuit board with a reduced scale in an LSU having two light emitting units, two image data to be subjected to image processing (such as processing for reducing the density of the edge portion of the formed image) are not used regardless of input image data. It has been impossible in the past to use adjacent lines. The reason is as follows.

The control circuit of the LSU equipped with a light source (two-beam laser) having two light emitting units includes two line memories in which image data is written for each line corresponding to each light emitting unit. The light source is controlled based on the sequentially read image data.
Here, consider a case where printing is performed based on input image data having a resolution of 1200 dpi using LSUs in which light from two light emitting units is arranged on the photosensitive member at a pitch of 1200 dpi in the sub-scanning direction. In this case, in order to enable this printing, the LSU control circuit reads the image data of the adjacent lines so that the image data for the two light emitting units is always for the lines adjacent to each other. The data can be read from two line memories at the same time. Accordingly, two image data to be subjected to image processing can be set to adjacent lines without providing a separate line memory (processing with adjacent image lines is possible).

However, when printing is performed based on input image data having a resolution of 600 dpi using the same apparatus (LSU), the light from the two light emitting units is arranged at a pitch of 1200 dpi in the sub-scanning direction. In the circuit, since the same image data is printed by the two light emitting units, the image data of the same line can be simultaneously read from the two line memories. Alternatively, the conventional control circuit is configured so that printing can be performed with one light emitting unit turned off (one beam). In any case, the image data for the two light emitting units is not for adjacent lines, and the control circuit can simultaneously read the image data for the adjacent lines from the two line memories. It is not possible.
Therefore, in order to make two pieces of image data to be subjected to image processing adjacent to each other even if the input image data is 600 dpi, a line memory is conventionally added to the control circuit, and in the case of 600 dpi, It was necessary to configure the circuit to perform image processing using the added line memory.

  Further, when used in a full-color tandem engine, the conventional LSU includes, for example, four colors of two-beam lasers arranged at a 1200 dpi pitch, and if possible, the scanning positions of the respective colors are accurately matched. The scanning timing in the sub-scanning direction is adjusted. However, when the LSU has a common polygon mirror for all colors, the laser scanning timing for each color is the same for each color at the same time, so simply adjusting the scanning (printing) start timing in the sub-scanning direction makes it possible to adjust the sub-scanning direction. Can be corrected only for one scan, that is, in units of 600 dpi. For this reason, when the resolution of the input image data is 1200 dpi, it is controlled which of the two beams starts scanning the first line in the input image data so that correction can be performed in units of 1200 dpi.

  In the conventional LSU used in the above-described full-color tandem engine having a single polygon mirror, when the resolution of the input image data is 600 dpi, color misregistration correction in the sub-scanning direction is performed in units of 600 dpi. In this way, when color misregistration correction in the sub-scanning direction is performed in units lower than the high resolution when printing based on low resolution input image data with an engine capable of high resolution printing, Since there may be a difference in performance (image quality) related to color misregistration between resolution images, it is not desirable.

  Patent Document 1 describes that the writing start position of each beam is sequentially shifted in multi-beam printing. This is correction in the main scanning direction of the image, and the above-described processing in the sub-scanning direction. There is no disclosure or suggestion regarding the issues arising from.

  The present invention has been made in consideration of the above-described circumstances, and includes a light source having a plurality of light emitting units. Even if the circuit scale is small, an image can be obtained regardless of input image data. Provided is a multi-beam scanning device capable of setting two image data to be processed to be adjacent lines, and is used in a full-color tandem engine, and a light source having two light emitting units is provided for each color. And a multi-beam scanning device which is provided with a common polygon mirror for all colors and can always perform color misregistration correction in the sub-scanning direction in the same unit as the high resolution. Objective.

  In order to solve the above-described problem, the first technical means of the present invention includes a light source having a plurality of light emitting units that can be independently controlled, and image data corresponding to each of the plurality of light emitting units. A plurality of image data buffers written for each, and a multi-beam that forms a latent image on a photoconductor by modulating the light source with image data sequentially read from the plurality of image data buffers in which the image data is written The scanning device includes an image processing unit that compares and corrects image data sequentially read from the plurality of image data buffers with adjacent pixels, and when writing image data of the same line to the plurality of image data buffers, A white image is stored in the image data buffer for odd lines in the period before the image data for the first line is written in the image data buffer. Data is obtained by and writes the.

  A second technical means is characterized in that, in the first technical means, modulation control of the light source by the image data of each line corrected by the image processing unit is prohibited with respect to one of an odd line and an even line. Is.

  A third technical means corresponds to full color in the first technical means, and includes the light source, the plurality of image data buffers, and the image processing unit for each color, and is the same as the plurality of image data buffers. When writing line image data, at least one color image data is written with white image data into the odd line image data buffer before writing the first line image data into the plurality of image data buffers. Thus, color misregistration is prevented.

  According to a fourth technical means, in any one of the first to third technical means, the light source includes two light emitting units, and an image having a predetermined resolution and a resolution twice the predetermined resolution as printing conditions. It is used for an image forming apparatus corresponding to the above image.

According to the multi-beam scanning device of the present invention, even if the circuit scale is small, two image data to be subjected to image processing can be of adjacent lines regardless of input image data.
Further, according to the multi-beam optical scanning device of the present invention, the device is used in a full-color tandem engine, a light source having two light emitting units is provided for each color, and a polygon that is common to all colors Even if a mirror is provided, color misregistration correction in the sub-scanning direction can always be performed in the same unit as the high resolution.

FIG. 1 is a schematic diagram illustrating a configuration example of a mechanism unit of an LSU that is an example of a multi-beam scanning device according to the present invention.
The LSU mechanism includes a semiconductor laser (LD) 1 that is a “light source” of the present invention, a collimator lens 2, a cylindrical lens 3, a polygon mirror 4, fθ lenses 5 and 6, and an aperture 8. A photoconductor (drum) 7 provided outside the unit is scanned with light (laser beam) from the LD 1. The LD 1 includes, for example, two light emitting units 1a and 1b (see FIG. 2) on a single chip, and emits laser beams modulated according to image data from the light emitting units 1a and 1b. The two emitted beams are collimated by a collimator lens 2, an aperture, and a cylindrical lens 3, and the beam cross section is shaped into a predetermined shape, and is irradiated to a polygon mirror 4 constituting a polygon motor.

  More specifically, the two beams are converted into parallel light beams by the collimator lens 2 and then shaped by the aperture 8 having a slit having a predetermined size. The shaped parallel light beams are condensed by the cylindrical lens 3 so that each beam for image writing in the main scanning direction has a predetermined size on the surface of the photoconductor (drum) 7 and is condensed on the polygon mirror 4. Irradiated.

Since the polygon mirror 4 is continuously rotated at a constant speed by the motor of the polygon motor, the beam incident on the polygon mirror 4 is periodically deflected and travels on the photoconductor 7 in the main scanning direction (the axial direction of the photoconductor 7). ) Is repeatedly scanned. At this time, the beam deflected by the polygon mirror 4 is converted from an equiangular motion to a constant velocity motion by the fθ lenses 5 and 6, and is imaged on the surface of the photoreceptor 7 with a predetermined beam diameter.
The collimator lens 2, the cylindrical lens 3, the polygon mirror 4, and the fθ lenses 5 and 6 constitute an optical system O (see FIG. 3) from the LD 1 to the photoconductor 7.

  The beam immediately before scanning on the photosensitive member 7 passes through the BD sensor 10 via the synchronous mirror 9 provided in the optical path on the main scanning start point side outside the writing region in the main scanning direction on the photosensitive member. The BD sensor 10 is for defining the start timing (position) of one scan in the main scanning direction, and outputs a Low signal (BD signal) when a beam is incident. Various timing signals and the like are generated based on the BD signal.

Note that the LD 1 has a predetermined resolution in the sub-scanning direction (the rotation direction of the photosensitive member 7) on the photosensitive member 7 so that the beams from the two light emitting units have a predetermined pitch (positional difference). Provided. FIG. 2 is a diagram showing an irradiation shape on the photoconductor 7 of the beam from the LD 1 of FIG.
The LD 1 having two light emitting portions at a predetermined interval is arranged so as to be inclined so that the scanning line interval (sub-scanning pitch) in the sub-scanning direction of the two beams on the photoconductor 7 becomes a predetermined value. In this example, it is assumed that the sub-scanning pitch is adjusted to one line of 1200 dpi, that is, about 21.2 μm.

  In a color image forming apparatus equipped with the LSU as described above for each color, for example, an electrostatic latent image corresponding to image data is formed on the surface of the photoreceptor 7 corresponding to each color. In the color image forming apparatus, the electrostatic latent image is developed with toner of each color, and the toner image is sequentially transferred onto the (intermediate) transfer belt by the transfer device and superimposed (synthesized). Then, the superimposed color toner images are transferred onto the recording paper conveyed by the paper conveying device and thermally fixed by the fixing device, and the recording paper on which the color image has been thermally fixed is discharged out of the device by the paper conveying device. Is done.

  FIG. 3 is a diagram illustrating a configuration example of a main part of an LSU control system of a multifunction peripheral (MFP) that is an example of a color image forming apparatus including the above-described LSU. In the example of this figure, it is assumed that the MFP includes the same LSU and photoconductor for each color. Therefore, the LSU and the photoconductor are described together. The MFP can operate in various modes. Here, an example in which the MFP operates in the copy mode or the printer mode will be described.

  As illustrated, the MFP 20 includes, for example, an LSU 21 that exposes the photoconductor 7 based on input image data, an image control unit (ICU) 22 that generates input image data, and a scanner unit S that reads a document. Is provided. Although not shown, the MFP 20 further includes a main control unit that controls the entire MFP 20, an input unit that receives an operation from a user, a page memory and a sheet leading edge detection unit, which will be described later, and the like.

In the copy mode, the MFP 20 reads an image of the document set on the document table with the scanner unit S and sends it to the scanner processing unit 23 of the ICU 22. Then, by performing image processing in the scanner processing unit 23, RGB (Red / Green / Blue) data from the scanner processing unit 23 is converted into YMCK (Yellow / Magenta / Cyan / blackK) data for each print color. Conversion is performed to generate input image data.
In the printer mode, the MFP 20 acquires printing data from a personal computer (hereinafter referred to as a personal computer) P connected to an external interface (not shown), and sends it to the printer processing unit 24 of the ICU 22. Then, the printer processing unit 24 performs image processing to generate YMCK data (input image data) for each print color.
Since the ICU 22 is connected to the personal computer P via an interface such as a network or USB, the ICU 22 is arranged on the rear surface of the MFP casing and can be accessed relatively easily by service personnel and users.

The switching unit (switching circuit) 25 switches input image data to be transmitted to the LSU 21 according to the mode. The switching unit 25 allows the MFP 20 to transmit one of the input image data generated by the scanner processing unit 23 and the input image data generated by the printer processing unit 24 from the ICU 22 to the LSU control unit 26 of the LSU 21. . During this transmission, the ICU 22 also transmits a synchronization signal SY1 indicating the start of one line.
In the MFP 20, the resolution of the input image data generated by the scanner processing unit 23 (that is, the input image data in the scanner mode) is a predetermined resolution (in this example, 600 dpi due to the document reading sensor of the scanner unit S). The resolution of the input image data generated by the printer processing unit 24 (that is, the input image data in the print mode) is twice the predetermined resolution (1200 dpi in this example).

  In addition to the above-described LD1 and optical system O, the LSU 21 has an LSU control unit (corresponding to the “drive control unit” of the present invention) 26 that controls the LD1 based on input image data. The LSU control unit 26 includes an ICU interface (hereinafter, ICU I / F) 27, first and second image data buffers 28 and 29, an image processing unit 30, a timing generation unit 31, and the like.

  The ICU I / F 27 performs control to receive the image data from the ICU 22 and write it to the first and second image data buffers 28 and 29. In the MFP 20, in the print mode (in the case of 1200 dpi input image data), the image data is alternately written to the first and second image data buffers 28 and 29 for each line by the ICU I / F 27. In the case of the mode (in the case of 600 dpi input image data), the image data of the same line can be written into the first and second image data buffers 28 and 29. That is, when the resolution of the input image data in the sub-scanning direction is one half of the resolution corresponding to the pitch of the LD1 beam in the sub-scanning direction (hereinafter referred to as the resolution at the time of image formation). The ICU I / F 27 functions as a data writing unit that writes the same image data into the two image data buffers 28 and 29. With this configuration, the number of signals for transferring image data is reduced between the LSU 21 and the ICU 22.

  The ICU I / F 27 has the following functions as characteristic functions of the present invention. That is, in the MFP 20, the first and second image data are determined by the ICU I / F 27 in a predetermined case (when the resolution in the sub-scanning direction of the input image data is half of the resolution at the time of image formation). Before writing the first line of the input image data in the buffers 28 and 29, the image data of the white image for one line can be written in the image data buffer corresponding to the light emitting unit that forms the latent image of the odd lines. Whether or not it is a predetermined case can be determined based on, for example, the operation mode of the apparatus. By writing the white image, the MFP 20 has the same resolution as that at the time of image formation even when input image data having a resolution that is half the resolution at the time of image formation is input, as will be described later. Similar to the case where input image data is input (even when the resolution of the input image data is 600 dpi, as in the case of 1200 dpi), image processing can be performed on adjacent image lines.

The first (second) image data buffer 28 (29) is used to write image data for the first (second) light emitting unit 1a (1b), and has a ring buffer configuration. As described above, when the resolution of the input image data is 1200 dpi, the MFP 20 alternately writes the data of adjacent lines in the input image data into the first and second image data buffers 28 and 29. On the other hand, in the case of 600 dpi, one line of white image data is written into one of the first and second image data buffers 28 and 29, and then the same line data in the input image data is stored in both of the data buffers. Write simultaneously.
Further, the reading of the image data from the first (second) image data buffer 28 (29) can be performed independently of the writing of the image data into the buffer. Reading from the first and second image data buffers 28 and 29 is performed simultaneously.

The image processing unit 30 sequentially acquires the image data written in the first and second image data buffers 28 and 29 at a predetermined interval during image formation, and a predetermined image is obtained with respect to the acquired image data. Execute the process.
FIG. 4 is a diagram illustrating an example of predetermined image processing executed by the image processing unit 30. In the figure, reference numerals 1-1 to 1-5 denote pixels of image data to be recorded (printed) by the first light emitting unit 1a (that is, image data read from the first image data buffer 28). Reference numerals -1 to 2-5 denote pixels of image data (that is, image data read from the second image data buffer 29) to be recorded by the second light emitting unit 1b.
The two image data to be subjected to image processing in the image processing unit 30 are image data read from the first and second image data buffers 28 and 29, and each image data is actually in the main scanning direction. However, the image processing unit 30 sequentially performs image processing using the target pixel (1-3 in FIG. 4) and the surrounding 2 lines × 3 pixels. In this image processing, for example, by calculating the difference in print density between the pixels indicated by the arrows in the figure and reducing the print density of the pixel of interest when the difference is greater than or equal to a certain value, I try to lower the concentration.

  As will be described later, the image data acquired by the image line processing unit 30 at the same time is from the first image data buffer 28 and from the second image data buffer 29 unless the function of the present invention is used. In some cases, the original input image data has different lines and the same input lines. As is clear from FIG. 4, the image processing for reducing the density of the edge portion of the image is effective because the difference in the print density is large when the line is in the different line. In some cases, the difference in the print density is small, so it is not effective.

  The image processing unit 30 further generates a modulation signal for each of the first light emitting unit 1a and the second light emitting unit 1b based on the input image data subjected to image processing. The LSU 21 drives the LD 1 with the generated modulation signal, thereby scanning the photoconductor 7 with a beam from the LD 1 via the optical system O and forming an electrostatic latent image.

The timing generation unit 31 generates an operation timing signal for each unit based on a one-scan reference timing signal (BD signal) input from the BD sensor 10. The timing generation unit 31 generates a synchronization signal SY2 for image transfer. The synchronization signal SY2 is transmitted to the ICU I / F 27 and the ICU 22. The synchronization signal SY2 for image transmission includes a synchronization signal for each line (synchronization signal in the main scanning direction) synchronized with the BD signal and a synchronization signal (synchronization signal in the sub scanning direction) indicating the start of data transfer for one page. ) Note that the synchronization signal in the sub-scanning direction can be generated based on the sheet leading edge detection signal. The paper leading edge detection signal is a paper leading edge detection signal that is output when the leading edge detection unit of the MFP 20 detects the leading edge of the paper. Further, the synchronization signal in the sub-scanning direction may be input from the main control unit of the MFP 20.
In the MFP 20, the synchronization signal SY1 from the ICU 22 is controlled to synchronize with the synchronization signal in the main scanning direction.

  The LSU control unit 26 further includes an LD ENB circuit 34 and buffers 32 and 33, which will be described later.

  Next, the operation of the MFP 20 when printing based on 1200 dpi input image data in the printer mode will be described with reference to FIG. FIG. 5A is a timing chart in this case, and FIG. 5B is a diagram showing a configuration of an image (latent image on the photoconductor 7) formed by this operation. In the following drawings, L1, L2,... Indicate image data of the first line, second line,..., Or an image (latent image) corresponding thereto in the input image data. In the MFP 20, the synchronization signal is composed of a signal indicating the start of transfer for one page (sub-scanning) and a signal indicating the start of one line (main scanning), and in order to prevent a shift due to a response delay of the circuit, the ICU 22 Is configured to return only the main scanning direction in response to the synchronization signal from the LSU control unit 26. However, in the following figures, since the difference in the reciprocation of the synchronization signal is very small, both are substituted with one waveform.

As shown in FIG. 5A, when the MFP 20 prints based on 1200 dpi input image data, the timing generation unit 31 generates two main scanning direction synchronization signals based on one BD signal.
Then, the MFP 20 clears each image data buffer when the sub-scanning direction synchronization signal is input, and during the subsequent image transfer period (until an EOP signal described later is input), the main-scanning direction synchronization signal. The input image data is sequentially transferred from the ICU 22 to the ICU I / F 27 line by line. In the MFP 20, among the input image data transferred in order, odd-numbered ones that are transferred in synchronization with a synchronization signal in the main scanning direction closer to the original BD signal are preferred for forming an odd-line latent image. The image data buffer corresponding to the LD is written (stored), and for the even lines, the image data buffer corresponding to the other LD is written (stored). In this way, writing to the first image data buffer 28 and writing to the second image data buffer 29 are performed alternately.

  As a result, one image data buffer (first image data buffer 28 in the example of FIG. 4) stores the odd-numbered line data in the input image data in order from the first line, and the other image data buffer (( In the example of FIG. 4, the second image data buffer 29)) can store the data of even-numbered lines in the input image data in order from the second line.

  Further, in synchronization with the BD signal, the MFP 20 reads out one line from both the first and second image data buffers 28 and 29 simultaneously, and sequentially outputs them to the image processing unit 30. As a result, as shown in FIG. 5B, in the nth scan, the image (latent image) corresponding to the 2n-1th line of 1200 dpi input image data and the 2nth line of the same input image data. A latent image corresponding to the object can be formed simultaneously. As a result, a latent image in which each line is arranged in the same order as the input image data, as indicated by I1 in FIG. 5B, can be obtained.

  In the case of FIG. 5, in the image processing unit 30, the two data acquired from the image data buffer are those of adjacent lines (different lines) in the input image data. In other words, in this case, the two image data to be subjected to image processing are adjacent lines, and the image processing executed by the image processing unit 30 is effective.

  Next, operations of the MFP 20 and the MFP of the comparative example when printing based on 600 dpi input image data in the copy mode will be described with reference to FIGS. 6 and 7. FIG. 6 is a timing chart in each MFP in this case, and FIG. 7 is a diagram showing a configuration of a latent image on the photoconductor 7 formed by the operation of each MFP. Note that the MFP of the comparative example is one that does not implement the present invention in the MFP 20, in other words, before writing the first line data in the input image data, the image data buffer corresponding to the light emitting unit for odd lines This is an MFP having an LSU that does not write image data of a white image for one line (does not write a white image in advance). W in the figure indicates white image data or a latent image corresponding thereto.

  As shown in FIG. 6, when printing is performed based on 600 dpi input image data, the input image data required for one scanning (period from the input of the BD signal to the next input) is one line. It is. Accordingly, in both the MFP of the comparative example and the MFP 20, the timing generator 31 adjusts so that the period of the synchronization signal in the main scanning direction used for reading from the ICU 22 is the same as the period of the BD signal (that is, the timing The generation unit 31 generates one main scanning direction synchronization signal based on one BD signal.)

  In the MFP of the comparative example, the image data buffers 28 and 29 are cleared when the synchronization signal in the sub-scanning direction is input, and synchronization in the main scanning direction is performed during the subsequent image transfer period as shown in FIG. In synchronization with the signal, the input image data is sequentially transferred from the ICU 22 to the ICU I / F 27 line by line. In the MFP 20, the ICU I / F 27 simultaneously writes image data of the same line in the original input image data to the first and second image data buffers 28 and 29 based on the transferred input image data. . Thereby, in the MFP of the comparative example, the input image data can be stored in order from the first line in both the first and second image data buffers 28 and 29.

  In the MFP of the comparative example, one line is simultaneously read from both the first and second image data buffers 28 and 29 in synchronization with the BD signal and sequentially output to the image processing unit 30. As a result, as shown in FIG. 7A, two latent images corresponding to the nth line of 600 dpi input image data can be formed simultaneously at a 1200 dpi pitch in the nth scan. As a result, a latent image as indicated by I2 in the figure can be obtained.

  However, in the case of the MFP of the comparative example, in the image processing unit 30, the two data acquired simultaneously from the first and second image data buffers 28 and 29 are on the same line in the input image data. That is, in this case, since the two image data to be subjected to image processing are not adjacent lines, the adjacent image line processing executed by the image processing unit 30 is not effective.

  On the other hand, as shown in FIG. 6B, the MFP 20 uses an image data buffer corresponding to a light emitting unit for forming an odd-numbered latent image (in the example shown, a first image corresponding to the first light emitting unit 1a). The data buffer 28) operates as follows so that the white image data W for one line can be stored before the input image data (so that the white image can be written in advance).

That is, the MFP 20 clears the first image data buffer 28 before inputting the synchronization signal in the sub-scanning direction (that is, before starting the transfer of the input image data on the first line), and writes to this buffer. Start. The ICU 22 outputs white image data for one line in synchronization with the synchronization signal in the main scanning direction outside the image transfer period (period from the input of the synchronization signal in the sub-scanning direction to the input of the EOP signal). Therefore, a white image for one line is written in the first image data buffer 28.
The EOP signal is a signal representing an image area in the sub-scanning direction of the scanning beam (a signal representing an image area in one page), and this EOP signal is generated by, for example, the main control unit of the MFP 20. In addition, the operation timing signal for clearing the first image data buffer 28 and starting writing to the buffer can be generated by the timing generation unit 31 based on, for example, the BD signal and the paper leading edge detection signal.

  After writing the white image, the MFP 20 clears the second image data buffer 29. During the subsequent image transfer period, the input image data is sequentially transferred line by line from the ICU 22 to the ICU I / F 27 in synchronization with the synchronization signal in the main scanning direction, as in the comparative MFP. In the data, the image data of the same line is simultaneously written in the first and second image data buffers 28 and 29. Thus, in the MFP 20, the first image data buffer 28 can store the input image data in order from the first line after the white image data, and the second image data buffer 29 can store the input image data. Can be stored in order from the first line.

  The MFP 20 also reads out one line from both the first and second image data buffers 28 and 29 simultaneously and sequentially outputs them to the image processing unit 30 as in the comparative example MFP. As a result, as shown in FIG. 7B, a white image data latent image and a latent image corresponding to the first line of 600 dpi input image data can be simultaneously formed in the first scan. In the nth and subsequent scans, an image (latent image) corresponding to the n-1th line of 600 dpi input image data and a latent image corresponding to the nth line of the input image data are simultaneously formed. it can. As a result, a latent image as indicated by I3 in the figure can be obtained.

  In this case, in the image processing unit 30, the two data (two read image data) acquired from the image data buffer are always composed of adjacent lines in the input image data. In other words, in this case, the two image data to be subjected to image processing are adjacent lines, and the image processing executed by the image processing unit 30 is effective.

  As described above, in the MFP 20 including the LSU 21, even when the light emitting units are provided at a 1200 dpi pitch, when the resolution of the input image data is 600 dpi, the image processing target is the same as when the resolution is 1200 dpi. Two pieces of image data can be adjacent lines, and effective image processing can be executed. Therefore, the MFP 20 can reduce the density of the edge portion of the image, and as a result, the consumption of toner during printing can be suppressed.

  Next, the LD ENB circuit 34 and the buffers 32 and 33 included in the LSU 21 of FIG. 3 will be described with reference to FIG. In FIG. 8, I4 and I5 indicate latent images (images) formed (or can be formed) by the light emitting unit 1a and the light emitting unit 1b of the MFP 20, respectively, and the image data that is the source of I4 and I5 is the input image. The same line in the data.

  When forming a latent image on the basis of 600 dpi input image data using both the light emitting units 1a and 1b in the MFP 20 of FIG. 3, as shown in FIG. When substantially the same (that is, when the beam diameter is substantially the same as the width of one line of 1200 dpi), the width H in the sub-scanning direction of the latent image formed based on the input image data of one line is 600 dpi. Is substantially the same as the width of one line.

  However, the laser beam usually has a certain spread, and the diameter of the beam irradiated onto the photoconductor 7 is larger than the size determined by the printing resolution. In this case, as shown in FIG. 8B, the width H in the sub-scanning direction of the latent image formed based on one line of input image data is larger than that shown in FIG. Specifically, in FIG. 8B, the beam diameter is substantially the same as the width of one line of 600 dpi, and the skirts of a plurality of beams overlap, so the width H is 1 of 400 dpi. It is almost the same as the line width.

Although there is no problem with the latent image shown in FIG. 8B, if the beam diameter on the photoconductor 7 in the MFP 20 is substantially the same as the width of one line of 600 dpi, the latent image shown in FIG. As shown in the figure, when the latent image formation by the beam from one light emitting portion is prohibited, a latent image equivalent to the more preferable FIG. 8A can be obtained, so the output from one of the light emitting portions is prohibited. It is preferable if possible.
Even when the output from the light emitting unit is prohibited, it is necessary not to prevent the execution of the adjacent image line processing.
Therefore, the LSU 21 prohibits / permits the output of the on / off signal (modulation signal) output from the image processing unit 30 to the first or second light emitting unit 1a, 1b, respectively. , 33. Further, the LSU 21 includes an LD ENB circuit 34 that transmits a laser output permission signal to the first and second buffers 32 and 33. The first and second buffers 32 and 33 operate based on the presence / absence of a permission signal.

When a latent image is formed based on 1200 dpi input image data, or when both light emitting units are used as shown in FIG. 8B when a latent image is formed based on 600 dpi input image data, the LD ENB circuit 34 outputs a permission signal, and based on that, the first and second buffers 32 and 33 permit the modulation signal to be output to the first and second light emitting units 1a and 1b.
On the other hand, when the operation of one light emitting unit is used as shown in FIG. 8C when forming a latent image based on 600 dpi input image data, depending on which light emitting unit 1a, 1b is used. The LD ENB circuit 34 outputs a permission signal to one of the buffers 32 and 33. Based on this, the first and second buffers 32 and 33 prohibit / permit output of modulation signals to the first and second light emitting units 1a and 1b.
Note that which light emitting unit is used is arbitrary, and may be selected by a user or a service person.

  As described above, even if the operation is performed so that the output from one light-emitting unit can be prohibited, in the above-described configuration, the output prohibition (operation prohibition) of the light-emitting unit is performed at the subsequent stage of the image processing unit 30. Thus, effective adjacent image line processing in the image processing unit 30 can be executed in the same manner as described above.

  In the MFP 20, the input image data is transferred from the ICU 22. However, the input image data may be transferred from a built-in hard disk connected to a page memory (not shown) via the page memory. In this case, if the configuration is such that the white image data can be transferred from the page memory, as described above, even if the input image data is 600 dpi, the MFP 20 can perform image processing on adjacent lines.

FIG. 9 is a diagram illustrating another configuration example of the main part of the LSU control system of the MFP, which is an example of a color image forming apparatus including the LSU of FIG. 9, the same components as those of the MFP 20 in FIG. 3 are denoted by the same reference numerals as those in FIG. 3, and the description thereof is omitted.
The MFP 20 ′ in FIG. 9 is an example of an image forming apparatus using the multi-scan apparatus of the present invention, and has a so-called full-color tandem configuration that includes an LSU control unit, a laser, and the like for each color of K, Y, M, and C. Is. In the following, reference numbers (symbols) of the respective members are given reference symbols K, Y, M, and C indicating the respective colors, and the reference symbols are omitted when collectively described. In FIG. 9, for the colors whose components are not changed for each color, the illustration of colors other than K is simplified.

  The MFP 20 'in FIG. 9 includes one LSU 21', ICU 22, and scanner unit S, and a photoreceptor 7 for each color of KYMC. The MFP 20 ′ can also drive the LD 1 with the LSU 21 ′ based on the input image data transferred from the ICU 22 to form a latent image on each color photoconductor 7. The LSU 21 ′ of the MFP 20 ′ in FIG. 9 includes an LD 1 having two light emitting units 1a and 1b, an LSU control unit 26 ′, and an optical system O for each color of KCMY, and further, a polygon mirror 4 (FIG. 9) common to all colors. 1) and one BD sensor 10. Detection of the BD sensor 10 is performed by a laser from the LD 1K. In this example as well, the two light emitting portions 1a and 1b of the LD 1 are provided so that the beams from them have a 1200 dpi pitch. Further, the MFP 20 ′ includes an image data transfer signal line for each color between the LSU control unit 26 ′ and the ICU 22, and although not illustrated, a synchronization signal line is provided for each color.

  The LSU control unit 26 'is different from the LSU control unit 26 in that prior white image writing is performed when the resolution of the input image data is 600 dpi and there is a color shift. By performing prior white image writing in this way, as described later, even when the resolution of the input image data is 600 dpi, the MFP 20 'can perform color misregistration adjustment in the sub-scanning direction.

  Color misregistration adjustment between black (K) and cyan (C) when the MFP 20 'performs printing based on 600 dpi input image data will be described with reference to FIG. Here, in order to facilitate understanding, it is assumed that the input image data for even-numbered lines is white image data, and the even-numbered lines in the image to be formed are free of toner. That is, here, a pattern in which lines in the main scanning direction for one scan are drawn every other scan, that is, a pattern in which lines are drawn at a pitch of 600 dpi is formed. In the figure, K1 to K5 indicate input image data of the first to fifth lines of K or a toner image corresponding thereto, and C1 to C5 indicate input image data of the first to fifth lines of C or input image data thereof. The corresponding toner image is shown.

  In MFPs having a full color tandem configuration, such as the MFP 20 ', a latent image is formed by irradiating the K photoconductor 7K with a laser beam, as shown in FIG. The toner image T1 based on the formed latent image is conveyed in the direction of the arrow in the figure, further transferred to the transfer belt 40, and conveyed to just below the C photoconductor 7C. A toner image T2 is formed for C as well as K. Then, the toner image T2 is combined with the K toner image T1. After that, the combined image is further combined with the remaining M and Y toner images.

In the MFP 20 ′, when the input image data is 600 dpi, the number of delay lines from the start of black printing to the start of cyan printing is adjusted in one scan unit of LD1 (ie, 600 dpi unit). In other words, the MFP 20 ′ performs color misregistration correction in the sub-scanning direction in units of 600 dpi.
Here, it is assumed that the MFP 20 ′ reads the same line of image data simultaneously to the two light emitting units K and Y 1K and 1Y and prints them simultaneously in one scanning period, as in the conventional MFP.

  Even under this assumption, if the distance L between the K photoconductor 7K and the C photoconductor 7C is exactly a multiple of 600 dpi pitch (a multiple of one pixel size of 600 dpi), K and When the C toner image is synthesized, as shown in FIGS. 10B and 10C, various timings are set so that the K toner image T1 and the C toner image T2 overlap each other (no color misregistration). Can be adjusted.

  On the other hand, under this assumption, when the distance L is not a multiple of the 600 dpi pitch and a fraction of 0.5 lines is generated in the distance L from the multiple of the 600 dpi pitch, for example, FIG. ), The toner image T1 of the toner K and the toner image T2 of the C are shifted by 0.5 scan, that is, 1200 dpi pitch. Even if the adjustment is performed in units of one scan of LD1 from here, the adjustment amount of C (that is, the delay amount from the printing of K to the printing of C) is reduced by one scanning (600 dpi). ), (G), color misregistration exists.

  In the MFP 20 ′, when the resolution of the input image data corresponds to the pitch of the light emitting unit (when it is 1200 dpi), which of the two light emitting units starts scanning the first line in the input image data. Is controlling. Therefore, even when the distance L is a multiple of 600 dpi pitch, the distance L is not a multiple of the 600 dpi pitch, and the distance L may be a fraction of 0.5 lines from a multiple of the 600 dpi pitch. There can be no deviation.

  Similarly, in order to prevent color misregistration even when the resolution of the input image data is 600 dpi (to perform color misregistration correction in the sub-scanning direction with an accuracy of 1/2 unit of one scan), When the distance L is a multiple of 600 dpi pitch, as shown in FIG. 10C, it is necessary to print image data for one line of 600 dpi using both light emitting units in one scanning period. . When the distance L is not a multiple of the 600 dpi pitch and a fraction of 0.5 lines is generated from the multiple of the 600 dpi pitch in the distance L, for example, as shown in FIG. It is necessary to print input image data for one line of 600 dpi over two scanning periods.

  Here, looking at the latent image I2 shown in FIG. 7A, both the K and C toner images in FIG. 10C are formed by the operation shown in the timing chart of FIG. 6A. It is clear that the toner image corresponds to the above. Similarly, looking at the latent images I2 and I3 shown in FIGS. 7A and 7B, the K toner image in FIG. 10H is a toner image corresponding to the latent image I2, and FIG. It is obvious that the C toner image of H) is a toner image corresponding to the latent image I3 formed by the operation shown in the timing chart of FIG.

Based on this, even when the resolution of the input image data is 600 dpi, there is no color misregistration (so that color misregistration correction can be performed) as in the case where the resolution of the input image data is 1200 dpi. For this purpose, the LSU control unit executes either one of the operation shown in the timing chart of FIG. 6A and the operation shown in the timing chart of FIG. 6B in accordance with the amount of deviation of each color in the sub-scanning direction. What is necessary is just to control by 26 '.
As described above, in the MFP 20 ′ having the full color tandem configuration using the LSU 21 ′, even when the print resolution is switched according to the printer mode or the copy mode, the color misregistration correction in the sub-scanning direction can always be performed in the same unit as the high resolution. , Improve the image quality.

  Note that the LSU 21 ′ may also include the buffers 32 and 33 and the LD ENB circuit 34 described above. However, in the LSU 21 ′, which light-emitting unit is used when performing control using the LD ENB circuit 34 may be set according to the adjustment amount in the sub-scanning direction.

It is the schematic explaining the structural example of the mechanism part of LSU which is an example of the multi-beam scanning apparatus of this invention. It is a figure which shows the irradiation shape on the photoconductor 7 of the beam from LD1 of FIG. FIG. 2 is a diagram illustrating a configuration example of a main part of an LSU control system of an MFP, which is an example of a color image forming apparatus including the LSU of FIG. 1. It is a figure explaining an example of the predetermined image processing performed with the image processing part 30 of FIG. FIG. 4 is a diagram for explaining the operation of the MFP 20 in FIG. 3 when printing is performed based on 1200 dpi input image data in the printer mode. 6 is a timing chart in the MFP 20 and a comparative example MFP when printing is performed based on 600 dpi input image data in a copy mode. FIG. 10 is a diagram illustrating a configuration of a latent image formed by the operation of the MFP 20 and a comparative example MFP when printing is performed based on 600 dpi input image data in the copy mode. FIG. 3 is a diagram for explaining an LD ENB circuit and buffers 32 and 33; FIG. 7 is a diagram for explaining another configuration example of a main part of an LSU control system of an MFP including the LSU of FIG. 1. FIG. 10 is a diagram for describing color misregistration adjustment between black (K) and cyan (C) when printing is performed based on 600 dpi input image data with the MFP 20 ′ in FIG. 9.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser (LD), 1a ... 1st light emission part, 1b ... 2nd light emission part, 2 ... Collimator lens, 3 ... Cylindrical lens, 4 ... Polygon mirror, 5, 6 ... f (theta) lens, 7 ... Photoconductor 8 ... Aperture, 9 ... Synchronous mirror, 10 ... BD sensor, 20, 20 '... MFP (MFP), 21,21' ... LSU, 22 ... ICU, 23 ... Scanner processing unit, 24 ... Printer processing unit, 25 ... switching unit, 26, 26 '... LSU control unit, 27 ... ICU I / F, 28 ... first image data buffer, 29 ... second image data buffer, 30 ... image processing unit, 31 ... timing generation unit, 32, 33... Buffer, 34... LD ENB circuit, 40.

Claims (4)

A light source having a plurality of light emitting units that can be controlled independently, and a plurality of image data buffers corresponding to each of the plurality of light emitting units, in which image data is written for each line, are written. In a multi-beam scanning apparatus that forms a latent image on a photoconductor by modulating and controlling the light source by image data sequentially read from the plurality of image data buffers,
An image processing unit that compares and corrects image data sequentially read from the plurality of image data buffers with adjacent pixels;
When writing the image data of the same line to the plurality of image data buffers, the white image data is written to the image data buffer of the odd lines in the period before the first line of image data is written to the plurality of image data buffers. A multi-beam scanning device.   The multi-beam scanning device, wherein modulation control of the light source by image data of each line corrected by the image processing unit is prohibited for one of an odd line and an even line.   In the case of corresponding to full color, each color having the light source, the plurality of image data buffers, and the image processing unit, and writing image data of the same line in the plurality of image data buffers, at least one color The color shift is prevented by writing white image data to the odd-numbered image data buffer in a period before writing the first-line image data to the plurality of image data buffers. The multi-beam scanning device according to claim 1.   The light source includes two light emitting units, and is used in an image forming apparatus corresponding to an image having a predetermined resolution and an image having a resolution twice the predetermined resolution as printing conditions. 4. The multi-beam scanning device according to any one of 3.

Images