JP2008233401A - Image forming apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image forming method by which light beams are multiple-emitted. <P>SOLUTION: The image forming apparatus 100 includes: an optical unit 110 wherein a multi-beam light source 206 to emit light beams L including a plurality of beams is disposed; a photoreceptor drum 122 that is irradiated with the light beams L so as to form an electrostatic latent image; a control means 202 to adjacently scan the surface of the photoreceptor drum with the spot-diameter light beams L including a plurality of scanning lines, to integrate the irradiation hysteresis related to a pixel included in the scanning line older by the number of set lines, then, to control the irradiation light amount related to the current scanning pixel; and a light modulating means 204 to modulate the light beam L in response to the control of the irradiation light quantity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus and an image forming method for irradiating multiple light beams.

  For the purpose of providing a high-definition image by electrophotographic printing, an image forming method using multi-beam irradiation is known. The multi-beam adjacent scanning optical element mainly uses a combination of a plurality of laser diodes (LD), a laser diode array (LDA) in which a plurality of LDs are built in one chip, a surface emitting laser diode (VCSEL). The writing is performed with several to several tens of lasers.

  It is also known that when an image is formed by multi-beam adjacent scanning, the exposure amount for a predetermined pixel of the photosensitive drum is relatively increased, and an image defect due to a reciprocity failure is generated in the image forming technical field. Yes. The reciprocity failure is considered to be caused by a phenomenon that the charge transport efficiency on the photosensitive drum loses linearity in a region where the exposure amount is higher than the exposure amount. It is known that the influence of reciprocity failure caused by multi-beam scanning causes a reduction in image quality referred to as so-called banding on a created image.

  So far, various proposals have been made to improve density unevenness due to reciprocity failure and to improve image quality. For example, in Japanese Patent No. 2585346 (Patent Document 1), image data for one line of the pre-scan is stored, and in relation to the image data of the first line of the current scan, in the pre-scan or the current scan The light quantity of at least one of the adjacent LDs is adjusted. In Patent Document 1, only the image data for one line of the previous line and the first image data of the current scan are to be detected, and the light amount adjustment of only 1 LD is not sufficient as a countermeasure for high density writing.

  Japanese Patent Laid-Open No. 2003-182139 (Patent Document 2) discloses that the light amount is adjusted by selecting the end LD. However, when a higher resolution image is formed and the writing density is increased, it is affected by a wider range of laser beams, and the degree of influence of reciprocity failure varies depending on the image formation pattern, which is insufficient as a countermeasure.

  Further, in Japanese Patent Application Laid-Open No. 2003-205642 (Patent Document 3), although the influence of reciprocity failure is reduced by writing using an auxiliary light source, it is difficult to flexibly cope with different patterns. Japanese Patent Application Laid-Open No. 2004-20911 (Patent Document 4) discloses that interlaced scanning is performed with an interval between LDs, but the exposure efficiency is lowered, and as a result, productivity is lowered. Will occur.

In addition, Japanese Patent Laid-Open No. 2004-077714 (Patent Document 5) discloses that the influence of reciprocity failure is suppressed by performing interlaced scanning and multiple exposure. However, even with the method disclosed in Patent Document 5, the exposure efficiency is lowered, resulting in another problem that productivity is lowered. Similarly, in Japanese Patent Application Laid-Open No. 2004-109680 (Patent Document 6), although interlaced scanning by light emission LD switching is performed, a new problem of reducing productivity is generated in the same manner.
Japanese Patent No. 2865346 JP 2003-182139 A JP 2003-205642 A JP 2004-20911 A JP 2004-0777714 A JP 2004-109680 A

  The present invention has been made in view of the above problems. A multi-beam light source that emits a plurality of light beams, a photosensitive drum that is exposed by the light-modulated light beam to form an electrostatic latent image, and the electrostatic drum In the technology to form images by developing latent images with developer, images that satisfy both of the conventional characteristics that have a trade-off relationship between high-density writing and reduced productivity, and perform image formation with high efficiency and high image quality. An object of the present invention is to provide a forming apparatus and an image forming method.

  In the present invention, when overlapping a target pixel with a laser beam irradiated from a multi-beam light source, a pixel position and an image of the pixel position are already detected for the pixels of the scanning line (previous line scanning) that have already been irradiated. Using the irradiation history corresponding to the presence or absence of the laser beam, the light quantity of the laser beam of the scanning line (current scanning line) irradiated in the second half is controlled.

  The irradiation history of the previous scan line changes the area of the laser beam that is irradiated while being superimposed on the target pixel of the current scan line. When the target pixel of the current scan line is irradiated with a laser beam, the irradiation amount to be irradiated on the current scan line is calculated using the pixel irradiation history data of the previous scan line calculated in advance for the amount of light irradiated to the target pixel. Give feedback to the calculation of light intensity.

  In the present invention, in parallel with the process of driving the multi-beam light source corresponding to the image data of the previous scan line, the control device prefetches the image data that does not exceed the set number of current scan lines, and from the current scan line Is also used to control the amount of light applied to the pixels irradiated thereafter. The number of set lines can be set to be equal to or less than the number of beams constituting the light beam in the sub-scanning direction, and is preferably determined as (n-1) lines where n is the number of beams.

  Pattern detection is performed on the pre-fetched image data using an irradiation history table that is used as a mapping table in which pixel positions of pixels that integrate the amount of irradiation light on the target pixel are mapped. The pattern detection result is logically ANDed with a value indicating whether or not the pixel registered in the irradiation history table has been irradiated, and used to create irradiation history data. The light amount correction amount is calculated in advance using the irradiation history data, and is stored in the register memory until the target pixel of the corresponding current scanning line is irradiated.

  For this reason, irradiation history data and a light amount correction amount are prepared when scanning of the subsequent scanning line is started, and when scanning the target pixel of the current scanning line, a delay for performing light amount correction, thinning of the light beam, and the like are prevented. In addition, it is possible to determine the irradiation light amount of the target pixel of the current scanning line with a minimum time delay.

  In the present invention, by using the above-described processing, it is possible to prevent image degradation due to reciprocity failure while performing efficient laser beam irradiation without performing processing such as thinning out irradiation light, and high productivity and It is possible to provide an image forming apparatus and an image forming method for improving the image quality trade-off and performing image formation with high efficiency and high image quality.

That is, according to the present invention,
A multi-beam light source that emits a light beam including a plurality of beams;
A photosensitive drum irradiated with the light beam to form an electrostatic latent image;
The surface of the photosensitive drum is adjacently scanned with the light beam having a spot diameter including a plurality of scanning lines, the irradiation history for the pixels included in the previous scanning line corresponding to the set number of lines is integrated, and irradiation is performed on the current scanning line. Control means for controlling the amount of light applied to the current scan pixel;
Light modulating means for modulating the light beam in response to the control of the irradiation light amount;
An image forming apparatus is provided.

In the present invention, pattern detection means for calculating irradiation history data by performing a specific pattern detection from the image data of the previous scanning line, the irradiation light quantity of the current scanning pixel being less than the set number of lines,
A light amount correction amount calculating means for calculating a light amount correction amount for irradiating the current scanning pixel based on the result of the pattern detection;
Light amount adjustment control means for holding the current scanning pixel and instructing an irradiation light amount for the current scanning pixel using the light amount correction amount by the light amount correction amount calculating means.

  The light quantity adjustment control means may be PWM modulation using the light quantity correction amount or laser power modulation using digital / analog conversion of the light quantity correction quantity. The control means holds an image pattern of the previous scan line and a mapping table for calculating the light amount correction amount, and an irradiation history for calculating the light amount correction amount of the current scan pixel is stored in the previous scan line. The image pattern and the mapping table can be used for calculation. In order to perform the pattern detection for the current scanning pixel, a pre-acquisition acquisition unit that pre-acquires image data corresponding to the set number of lines is provided, and the pattern detection unit calculates the light amount correction amount for the current scanning pixel. After completion, the pixel data of the current scan pixel can be read from the prefetch acquisition means to create the irradiation history for the post scan line. The control means is configured such that the distance from the spot center of the first line of the current scan to the spot center of the preceding scan line corresponding to the set number of lines on the surface of the photosensitive drum is a sub-position of the spot formed on the surface of the photosensitive drum. A scanning line can be provided so as to be equal to or smaller than the spot diameter of the light beam when measured in the scanning direction.

According to the present invention,
An image forming method using a multi-beam light source that emits a light beam including a plurality of beams, and forming an electrostatic latent image on a photosensitive drum by irradiation of the light beam,
Emitting a plurality of light beams;
Scanning the surface of the photosensitive drum adjacently with the light beam having a spot diameter including a plurality of scanning lines;
Pre-fetching image data in the pre-scan line direction less than the set number of lines for the current scan pixel;
The current scanning pixel of the current scanning line is held, and the pixels included in the previous scanning line corresponding to the set number of lines are accumulated using the irradiation history generated by the pre-fetching, and should be irradiated on the current scanning line Controlling the amount of light applied to the current scan pixel;
And modulating the light beam in response to the control of the irradiation light amount.

In the present invention, performing a pattern detection of the image data acquired in advance, calculating an irradiation history;
Calculating a light amount correction amount for irradiating the current scanning pixel using the irradiation history;
Commanding an irradiation light amount for the current scanning pixel using the light amount correction amount.

  The step of calculating the irradiation history may include a step of calculating an irradiation history using presence or absence of an image at a position mapped to the mapping table in the pre-acquired image data. The step of controlling the irradiation light amount may include a step of modulating laser power by PWM modulation using the light amount correction amount or digital-analog conversion of the light amount correction amount.

Hereinafter, although the present invention is explained with an embodiment, the present invention is not limited to an embodiment. FIG. 1 shows an embodiment of an image forming apparatus. The image forming apparatus 100 can be configured as a multi-function full color digital copying machine, a color laser printer, or the like. In the embodiment of the copying machine, the image forming apparatus 100 can include an image reading unit such as an ADF (Auto Document Feeder), a facsimile processing unit, and an operation input unit. When the image forming apparatus 100 is mounted as a color printer, the image forming apparatus 100 is mounted with a parallel interface such as IEEE 1294 or USB, a serial bus interface, or a network interface for connecting to Ethernet (registered trademark). Printer
Execute image creation processing using (Job Language).

  The image forming apparatus 100 includes an optical unit 110, an image forming unit 120, and a transfer / fixing unit 130. The optical unit 110 includes a polygon mirror 102, a plurality of fθ lenses 106, and a plurality of reflection mirrors 108. The polygon mirror 102 is mounted on a spindle motor 104 or the like and is driven at a rotational speed of several thousand to several tens of thousands rpm. The polygon mirror 102 is irradiated with a plurality of light beams from a multi-beam light source (not shown) such as a laser diode array (LDA) or a surface emitting laser diode (VCSEL), and the fθ lens 106 is irradiated. The light is reflected and reflected toward the image forming unit 120 by the reflection mirror 108 through an optical system such as a WTL lens.

  The image forming unit 120 accommodates a plurality of photosensitive drums 122 corresponding to cyan (C), magenta (M), yellow (Y), and black (K), and developer of each color, and includes a developing sleeve and a developing blade. And a developing device 124 including The photosensitive drum 122 is applied with an electrostatic charge by a charger (not shown) such as a charging roller and then imagewise exposed by a plurality of light beams from a multi-beam light source to form an electrostatic latent image. .

  The formed electrostatic latent image is conveyed to the developing device 124 as the photosensitive drum 122 rotates. The electrostatic latent image is developed with a developer, and a developer image is formed on the photosensitive drum 122 and carried. The developer image is conveyed to the transfer / fixing unit 130 as the photosensitive drum 122 rotates. The transfer / fixing unit 130 includes a transport belt 132, a plurality of paper feed cassettes 146, 150, 154, a paper feed unit including a plurality of transport rollers 144, and the like. The paper feed cassettes 146, 150, and 154 contain transfer members such as high-quality paper and plastic sheets, and the transfer members are transported to the transport belt 132 by transport rollers 144, 148, and 152.

  The developer image on the photosensitive drum 122 is transferred to a transfer member electrostatically attracted to the conveyance belt 132 under a transfer bias potential, and after transferring four colors, a full color image is formed on the transfer member. The formed full color image is fixed by the fixing device 134. The printed matter after fixing is discharged onto a normal discharge tray 164. In addition, when double-sided printing is performed on the printed matter, after double-sided printing is performed by a double-sided printing unit including the separation claw 136 and the reverse feed conveyance members 140 and 142, a plurality of paper discharge rollers 162 and a switching plate 166 are printed. The image is discharged to the outside of the image forming apparatus 100 through a finisher 160 including the above.

  The finisher 160 guides the transfer member conveyed by the paper discharge unit 138 of the main body toward the paper discharge roller 162 or the staple table 172, and provides the finishing printed matter processed by the user. When the switching plate 166 is directed upward, the printed matter is discharged to the normal discharge tray 164 side via the discharge roller 162. Further, by switching the switching plate 166 downward, the transfer member is transported to the staple table 172 via the transport rollers 168 and 170, and the stapling process is performed. Each time a sheet of transfer paper loaded on the staple table 172 is discharged, the paper end surface is aligned by the paper alignment jogger 174 and is bound by the stapler 178 upon completion of copying in a partial unit. The transfer member bound by the stapler 178 is stored in the staple completion discharge tray 176 by its own weight.

  The image forming apparatus 100 illustrated in FIG. 1 is an exemplary embodiment, and the image forming apparatus is an image forming apparatus of another type such as a multi-function peripheral (MFP) or a high-speed printer. Can be implemented as

FIG. 2 is a diagram showing a schematic planar configuration 200 of the optical unit 110 of the image forming apparatus 100 including the photosensitive drum 122. The optical unit 110 includes a control device (hereinafter referred to as a CPU 202), a laser driver 204, and a multi-beam light source (hereinafter referred to as MBS: Multi) configured as a laser diode array or a surface emitting laser.
Reference as Beam Source. 206). The CPU 202 controls rotational driving of the polygon mirror 102, irradiation control of the MBS 206, synchronization control in the main scanning direction A and sub-scanning direction B, and the like.

  The light beam L including a plurality of laser beams reflected by the polygon mirror 102 is deflected to the photosensitive drum 122 by the fθ lens 106, scans the surface of the photosensitive drum 122 in the main scanning direction A, and electrostatic latent Form an image. Further, the light beam L deflected by the polygon mirror 102 is irradiated to the synchronization detection sensor 210 by the reflection mirror 208 at the start of irradiation, and the light beam control in the main scanning direction A and the sub-scanning direction B is performed. Synchronous control of a drive motor (not shown) is performed.

  With the above-described configuration, the pixel position on the photosensitive drum 122 is irradiated with the light beam L including a plurality of laser beams, and as a result, the light beam is concentrated and irradiated in a close region, so-called reciprocity failure is generated. Exposure is given. FIG. 3 shows an embodiment in which a unit pixel of a light beam irradiated on the surface of the photosensitive drum 122 is exposed. FIG. 3A shows the overlapping of the laser beams in the sub-scanning direction, and FIG. 3B shows an embodiment of the overlapping of the laser beams in the main scanning direction.

  In the embodiment shown in FIG. 3, it is assumed that 1200 dpi writing is performed with four laser beams per main scan of a single color. In this case, the scan lines are defined with an interval of about 21 μm. In the case of the embodiment shown in FIG. 3, the spot diameter of the light beam L including four laser beams obtained from the multi-beam light source on the surface of the photosensitive drum 122 is 80 μm for both main scanning and sub scanning. Suppose that Note that the spot shape and spot size can be appropriately changed in response to the characteristics of the MBS 206 used and the resolution of image formation.

  As shown in FIG. 3A, the MBS 206 irradiates the photosensitive drum 122 as a spot 300 including a plurality of pixels to be irradiated by shifting four laser beams in the main scanning direction by the scanning line width. The center of adjacent laser beams (hereinafter, in this embodiment, the intensity distribution of the laser beam is a Gaussian distribution. As shown in FIG. 3B, the overlap of the beams in the main scanning direction is A laser beam is irradiated to the spot 302 and the spot 304 while being adjacent to each other in the main scanning direction while being shifted by about 21 μm corresponding to the resolution in the same manner as in the sub-scanning direction, so that an overlapping region 306 is formed. The overlap in the main scanning direction does not necessarily have to be a value corresponding to 1200 dpi for other purposes such as scanning speed.

  The spot 300 has a distance from the center of the spot corresponding to the first line currently scanned on the surface of the photosensitive drum 122 to the center of the spot of the previous scanning line by the set number of lines on the surface of the photosensitive drum 122. When the spot to be formed is measured in the sub-scanning direction, the scanning line and the spot are defined so as to be equal to or smaller than the spot diameter, and so-called adjacent irradiation can be performed. In the embodiment shown in FIG. 3, the number of beams is four and the number of set lines is (4-1), and the distance between the head line and the number of set lines is about 61 μm. Giving. Note that the number of set lines can be appropriately set according to a specific purpose, and more generally a number obtained by subtracting the number of current scan lines from the number of scan lines included in a spot covered by the light beam. Can be set to

  FIG. 4 shows an embodiment of laser beam irradiation in the main scanning direction and the sub-scanning direction with respect to a spot including the target pixel when viewed in time series. In FIG. 4, in the case of irradiating the spot 400, the exposure state of the spot 400 to the spot 400 when the spot 400 moves in correspondence with the rotation of the photosensitive drum 122 to the third line in the sub-scanning direction. Are shown in the order of FIG. 4 (a) → FIG. 4 (b) → FIG. 4 (c). As shown in FIG. 4, the spot 400 is continuously irradiated by the spots 402, 404, and 406 while being transported in the sub-scanning direction in units of scanning lines.

  For this reason, the spot 400 is excessively exposed by the number of laser beams, and the superposition of the laser beams causes image degradation due to the influence of reciprocity failure. Here, the relationship between the spots 402, 404, and 406 formed by the laser beam and the target pixel in the spot 400 will be further examined with reference to FIG. As shown in FIG. 4, it is shown that the overlapping range of the spots 402, 404, and 406 with respect to the spot 400 becomes smaller as the spot 400 moves away in the sub-scanning direction.

  In FIG. 4, the spot position indicated by a broken line indicates a spot where there is no spot overlap with the spot 400 or the degree of overlap is considerably small. That is, it can be seen that the degree of influence of the overlapping irradiation by the laser beam spot differs depending on the relative position of the spot 400 and the spots 402 to 406 along the sub-scanning direction. In the case of the embodiment shown in FIG. 4, it is determined that the influence of the beam superimposition is significant for the pixels in the spot indicated by a predetermined number of lines from the spot 400, that is, three lines.

  FIG. 5 shows an embodiment of an irradiation history table 500 used when the light amount is controlled using the degree of superimposition for each scanning line from the relative relationship between the spots 402, 404, and 406 shown in FIG. 4 and the spot 400. . The irradiation history table 500 designates the pixel positions in the main scanning direction and the sub scanning direction of the pixels that affect the target pixel included in the spot 400 among the pixels in the already scanned line, and includes them in the light amount correction calculation. Can be registered in the CPU 202 or other control device.

  FIG. 5 shows pixels that have already been scanned, when the predetermined target pixel is irradiated, the pixels included in the previous scan line. The already irradiated pixels are related to whether or not an image exists, and are irradiated when there is an image, and not irradiated when there is no image.

  On the other hand, among the pixels shown in the previous scan, for the target pixel X of the first line, the irradiation history or irradiation history of the previous three lines and the irradiation light amount are required to determine the exposure amount of the target pixel. For this reason, in order to feed back the exposure amount of the target pixel X in consideration of the overlap from the previous scan line, it is necessary to calculate the irradiation history of 15 pixels from A to O.

  On the other hand, for the target pixel Y, when the history is acquired in relation to the previous scan line, referring to the overlapping degree shown in FIG. 4, C, E, F, H, I, K, M, N It can be seen that a history of 8 pixels is required. Furthermore, for the target pixel Z, as shown in FIG. 4C, it is necessary to register the history of three pixels of F, I, and M in the previous scan. FIG. 6 schematically shows the influence of the pixel irradiation history in the previous line scan on the exposure amount control of the target pixel currently being scanned.

  In FIG. 6A, when irradiation is performed for all pixels in the previous line scan in relation to the spot 600, it is shown that the region 602 of the spot 600 is irradiated twice. On the other hand, as shown in FIG. 6B, only pixels C, H, K, F, I, and M of FIG. The region 604 will be irradiated twice. In addition, the area W1 in FIG. 6A shows the area with the highest overlap where the 10 beams are subjected to overlapping irradiation, and the area W2 in FIG. As shown in FIG. 6, the intensity of the laser beam to be irradiated on the pixels included in the spot 600 can be effectively controlled by using the irradiation history of the scanning line that was irradiated last time.

  FIG. 7 is a functional block diagram of the CPU 202 that performs the exposure control described above in the present embodiment. As shown in FIG. 7, the CPU 202 includes a main scanning counter 700 and a sub-scanning counter 702, and registers the pixels irradiated with the laser beam in a register memory or the like as the data structure shown in FIG. Further, the CPU 202 includes a pattern detection unit 704 and a data delay unit 708 that functions as a prefetch acquisition unit for image data. The pattern detection unit 704 uses the data of the image data 1 to the image data 3, and the image irradiation pattern for three lines of the scanning line at that time (corresponding to the data of the previous line scanning in FIG. 5), Registration is performed corresponding to the values of the main scanning counter 700 and the sub scanning counter 702.

  In the illustrated embodiment, the data delay unit 708 prefetches the values of the already-scanned pixels necessary for calculating the degree of superimposition and passes them to the pattern detection unit 704 as data for irradiation of the next scan line. The data delay unit 708 delays data for three lines of image data of the current scanning line and inputs the delayed data to the pattern detection unit 704, which corresponds to image data 2, image data 3, and image data 4 in FIG. The delayed image data is passed to the pattern detection unit 704 in correspondence with the timing for controlling the output level for the post-scan line.

  In the embodiment shown in FIG. 7, it is shown that the image data of the current scanning line is input to the pattern detection unit 704. For example, when this is the first line of the image area, Since there is no data of already irradiated pixels, when the data is transferred to the pattern detection unit 704 and reflected in subsequent processing, or when irradiation history data is lost due to a shift in processing timing, for subsequent processing When the irradiation history data and the light amount correction data are normally stored and used to create the irradiation history, the pattern inspection unit 704 does not accept input. In FIG. 7, the description will be made assuming that the three image data of the current scanning line are input to the data delay unit 708. However, the number of image data of the current scanning line to be delayed in accordance with a specific image formation size is as follows. It can be set arbitrarily.

  Further, the transfer of the image data can be processed in units of 4 scanning lines as in the embodiment shown in FIG. 7, or the image forming apparatus 100 mounted in units of 8 lines, 16 lines, 32 lines, or the like. This can be set as appropriate according to the setting and the number of beams constituting the light beam. In addition, the pattern detection unit 704 and the data delay unit 708 can change the number of input lines accordingly.

  Further, the CPU 202 includes a light amount correction amount calculation unit 706 and a light amount adjustment control unit 710. The light amount correction amount calculation unit 706 calculates the irradiation light amount for the target pixel to be irradiated in the next scan using the irradiation history data registered by the pattern detection unit 704. The irradiation light amount is calculated by reading the irradiation history data registered in the register memory or the like by the CPU 202 by the light amount correction calculation unit 706 before performing irradiation of the next scanning line, and calculating the light amount correction amount. This is executed by passing the correction amount to the light amount adjustment control unit 710.

  The light amount adjustment control unit 710 controls the laser power by driving the laser driver 204 by PWM (Pulse Width Modulation) control or control of the control voltage value by analog conversion, and performs light amount adjustment.

  The CPU 202 buffers image data used for subsequent correction in parallel with the process of driving the laser driver 204 corresponding to the image data of the previous scan line, and controls the amount of image data of the current scan line. It is possible to prepare irradiation history data and light amount correction data. For this reason, when image data 5, image data 6 and image data 7 (none of which are shown) of the subsequent scanning line have been transferred, the light quantity correction data already created is within the line scanning interval. The light amount adjustment control unit 710 can be passed, and the irradiation light amount of the target pixel on the current scan line can be controlled with a minimum time delay.

  Hereinafter, an embodiment of the light amount correction amount calculation performed by the light amount correction amount calculation unit 706 will be described. The light amount correction amount calculation unit 706 gives the correction amounts x, y, and z of the target pixels X, Y, and Z by the following expression (1) using the irradiation history data shown in FIG. Note that correction coefficients (including the amount of light) corresponding to the pixels A to O are defined by variables a to o in the equation, and the variables A to O indicate the presence or absence of image data used as image presence information. Binary value etc.

  In the above formula, px, py, and px are normalization constants corresponding to the case where all the pixels to be used are irradiated. Since all the pixels related to the correction coefficient related to the target pixel X are subject to calculation, px is not required if a value obtained by normalizing the sum of a to o in advance to 1 is used (1 And omitted.)

  However, as an effective means for reducing the influence of the reciprocity failure, it is known to reduce the amount of light when forming an image across the scans, so that the correction coefficients a to are given by the following equation (2). o can also be set in advance.

  Since the process of the above formula (1) is performed using the irradiation history table shown in FIG. 5, various methods are possible. For example, the irradiation history data used for the above equation (1) is obtained by using the irradiation history table 500 registered as pixel positions (main scanning counter value, sub-scanning counter value) used for calculation by the pattern detection unit 704. Multiply by a binary value (represented by value = 1 with image, value = 0 without image) whether or not an image exists at the corresponding pixel position referenced by the scan counter value and sub-scan counter value Irradiation history data can be created and registered in the register memory.

  The correction coefficients a to o can be used as a look-up table (LUT) that the CPU 202 registers in a nonvolatile memory such as an EEPROM, EPROM, or ROM. FIG. 8 shows an embodiment of an LUT that can be used by the CPU 202.

  In the LUT 800 shown in FIG. 8A, correction coefficients are directly registered, the CPU 202 calculates a light amount correction value, and passes the value as a control value to a light amount adjustment control unit 710 including a DAC or the like. This is an embodiment that is preferably used in some cases. Further, as indicated by the LUT 802, the CPU 202 can also be an embodiment in which control data set at 16 levels for performing PWM modulation corresponding to the correction value is registered. The LUT 802 is used when controlling the spot diameter of the laser beam at the corresponding correction coefficient. Further, the LUT 804 is an embodiment in which, when a DA converter is used as the light amount adjustment control unit 710, an output level set with 16-bit resolution is registered corresponding to a correction coefficient.

  When the correction coefficients a to o are the LUT 800 of FIG. 8, assuming that the light amount correction amounts of the target pixel X shown in FIGS. 6A and 6B are x1 and x2, respectively, x1 = 0. 8, x2 = 0.935. By setting py and pz in the same manner, the light amount correction amounts y and z of the target pixels Y and Z shown in FIG. 5 can be obtained in the same manner.

  In another embodiment, in the embodiment in which the amount of light at the beam spot on the exposure surface has a Gaussian distribution and the amount of laser light emission forming the peripheral pixels including the pixels is considered to be substantially constant, the irradiation history of FIG. The correction coefficients applied to the table 500 can be A = J, B = L, C = K, D = O, E = N, F = M, and the coefficients can be reduced. When the beam spot is approximated by a Gaussian distribution, the above equation (1) is given as the following equation (3).

上記式（３）中、式（２）で説明した関係が適用できるので、走査を跨いで照射を行う場合、下記式（４）で与えられる設定とすることが好ましい。

In the above equation (3), the relationship described in equation (2) can be applied. Therefore, when irradiation is performed across the scan, it is preferable to set the following equation (4).

  Hereinafter, an embodiment of the light amount correction amount calculation processing corresponding to the change with time of the MBS 206 and the change of the laser beam intensity will be described. A semiconductor laser widely used as a light source for electrophotographic printing is known to have a characteristic that the amount of light decreases as it continues to emit light. In addition, the photoconductor widely used as a recording medium also undergoes characteristic changes such as a change in charging potential due to deterioration over time. When such a characteristic change due to a change with time of the image forming apparatus occurs, an image with uniform quality can be obtained by controlling to increase or decrease the amount of light. Increasing the light intensity of the laser beam with a Gaussian distribution on the exposure surface deepens the electrostatic latent image formation, increasing the influence on the surroundings. Conversely, decreasing the laser light intensity reduces the electrostatic latent image. It is known that the formation becomes shallower and the influence on the surroundings becomes weaker.

  In FIG. 4, the spot indicated by the broken line has been excluded because it has not been affected by the reciprocity failure until now. However, for example, by increasing the amount of laser beam, it is necessary to consider the beam spot at the broken line. . An embodiment of processing corresponding to an increase in the amount of laser beam will be described with reference to FIG. As shown in FIG. 9, the range of light amount correction amount calculation is expanded to the A ′, B ′, D ′, J ′, L ′, and O ′ pixels for each target pixel X, Y, and Z, and an enlarged irradiation history table 900. It is possible to cope with the case where the light amount is adjusted by providing a corresponding correction coefficient.

  When dealing with changes in the intensity of the laser beam, the correction coefficients corresponding to the pixels A ′, B ′, D ′, J ′, L ′, O ′ are a ′, b ′, d ′, j ′, l ′, If o ′ and A ′, B ′, D ′, J ′, L ′, and O ′ are image data that is image presence information of each pixel, the light amount correction amounts x and y of the target pixels X, Y, and Z , Z is given by the following formula (5) using the above formula.

上記式（５）では、下記式（６）の条件を満足するように、補正係数ａ〜ｏを設定することが好ましい。

In the above equation (5), it is preferable to set the correction coefficients a to o so as to satisfy the condition of the following equation (6).

  For example, when the beam spot diameter on the image plane is reduced by changing the optical system, the degree of superposition of the spots 1002, 1004, and 1006 on the spot 1000 changes as shown in FIG. In this case, as shown in FIG. 11, an irradiation history table with a narrow range when the light amount correction amount is derived is selected, and pattern search is executed.

  Similarly, correction coefficients corresponding to C, E, F, H, I, K, M, and N pixels are c, e, f, h, i, k, m, and n, and C, E, F, H, When I, K, M, and N are image data that is image presence information of each pixel, the light amount correction amounts x and y of the target pixels X and Y are expressed by the following formula (7) by correcting the above formula. Can do.

上記式（７）では、補正係数ａ〜ｏは、下記式（８）の条件を満足するものとすることが好ましい。

In the above formula (7), it is preferable that the correction coefficients a to o satisfy the condition of the following formula (8).

  Further, in the case of narrowing down the spot diameter on the contrary, it is possible to cope with this by simply reducing the pixel range to be used for the light amount calculation using the reduced irradiation history table 1100 shown in FIG. When the spot diameter is reduced and the light quantity is increased at the same time, the spots 1002, 1004, and 1006 indicated by broken lines may be included in the light quantity correction calculation with respect to the spot 1000 in FIG. In addition, a plurality of irradiation history tables are registered in advance for the light amount and the spot diameter of the laser beam, and the irradiation history table to be used is read or selected by referring to the light amount and the spot diameter at that time. The detection unit 704 can be used for processing.

  An embodiment of processing executed by the image forming apparatus 100 will be described with reference to FIGS. 12 and 13. The image forming method of the image processing apparatus 100 starts from step S1200. In step S1201, it is determined that the image area has been reached, and in step S1202, it is determined whether the scanning is for the first line. When scanning is the first line (yes), the process branches to step S1206, and image data of N lines is acquired in advance from the (N-M + 1) line on which image formation is performed at that time, and buffered. In step S1207, the preliminarily acquired image data is used for laser irradiation to form a latent image.

  On the other hand, if it is not the first line scan in step S1202 (no), the process branches to step S1203 to calculate the light amount correction amount using the irradiation history data and the correction coefficient. In step S1204, the light amount correction amount data is received and image data with the light amount controlled is calculated. Further, in step S1205, it is determined whether or not it is the final scanning line. If it is the final line (yes), laser beam irradiation of the final line is executed in step S1207, and the process is terminated in step S1208. On the other hand, if it is not the last scanning line in step S1205 (no), in step S1206, image data of N lines from (N−M + 1) lines where image formation is performed at that time is held and buffered. Thereafter, in step S1207, the image area is irradiated with a laser beam to form an electrostatic latent image until it exits the image area, and the process ends in step S1208.

  FIG. 13 shows an embodiment of the process when the condition is changed during the image forming process. The processing in FIG. 13 starts from step S1300, and in step S1301, it is determined whether or not the conditions at the time of image formation, such as the spot diameter, laser beam intensity, and dpi value, have been changed. If the imaging condition is changed in step S1301 (yes), the process branches to step S1302, and the value M of the prefetched image data is set to a positive integer value α so as to correspond to the correction or change of the imaging condition. In steps S1304 to S1310, the processing described with reference to FIG. 12 is executed, and the printing processing is executed while preventing image quality deterioration due to reciprocity failure.

  The present invention has been described with the embodiment. However, the present invention is not limited to the embodiment, and other embodiments, additions, modifications, deletions, and the like can be conceived by those skilled in the art. Any of the embodiments is included in the scope of the present invention as long as the operations and effects of the present invention are exhibited.

1 is a diagram illustrating an embodiment of an image forming apparatus. FIG. 2 is a diagram illustrating a schematic planar configuration of an optical unit of an image forming apparatus including a photosensitive drum. The figure which showed embodiment in the case of exposing the unit pixel of the light beam irradiated on the surface of a photoreceptor drum. The figure which showed embodiment of the laser beam irradiation in the main scanning direction with respect to a spot at the time of seeing in time series, and a subscanning direction. FIG. 5 is a diagram showing an embodiment of an irradiation history table used when the light amount is controlled using the degree of superimposition for each scanning line from the relative relationship between the spots 402, 404, and 406 shown in FIG. The figure which showed roughly the influence which the pixel irradiation log | history in the previous line scanning has on the exposure amount control of the object pixel which is performing the present line scanning. The functional block diagram of CPU which performs the exposure control mentioned above in this embodiment. The figure which showed embodiment of LUT which CPU can use. The figure explaining embodiment of the process corresponding to the light quantity increase of a laser beam. The figure which showed the relationship between spots when the beam spot diameter on an image surface becomes small by changing an optical system. The figure which showed embodiment of the irradiation history table which narrowed the range at the time of derivation | leading-out of correction amount. 6 is a flowchart of a first embodiment of processing executed by the image forming apparatus. 10 is a flowchart of a second embodiment of processing executed by the image forming apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 102 ... Polygon mirror, 104 ... Spindle motor, 106 ... f (theta) lens, 108 ... Reflection mirror, 110 ... Optical unit, 120 ... Image forming unit, 130 ... Transfer / fixing unit, 122 ... Photoconductor drum, 124: Developing unit, 132: Conveying belt, 134: Fixing device, 136: Separation claw, 146, 150, 154 ... Paper feeding cassette, 144, 148, 152 ... Conveying roller, 160 ... Finisher, 162 ... Discharge roller, 164 ... Normal discharge tray, 166 ... Switching plate, 168, 170 ... Conveyance roller, 172 ... Staple table, 174 ... Jogger, 176 ... Staple completion discharge tray, 178 ... Stapler, 202 ... Control device (CPU), 204 ... Laser Driver 206 ... Multi-beam light source (MBS) 300, 302, 304 ... Sport 306 ... superimposed area 400, 402, 404, 406 ... spot, 500 ... irradiation history table, 600 ... spot, 602, 604 ... area, 700 ... main scanning counter, 702 ... sub-scanning counter, 704 ... pattern detection , 706... Light amount correction amount calculation unit, 708... Data delay unit, 710... Light amount adjustment control unit, 800, 802, 804 ... Look-up table (LUT), 900 ... Extended irradiation history table, 1000, 1002, 1004, 1006 ... Spot, 1100 ... Reduced irradiation history table

Claims (10)

A multi-beam light source that emits a light beam including a plurality of beams;
A photosensitive drum irradiated with the light beam to form an electrostatic latent image;
The surface of the photosensitive drum is adjacently scanned with the light beam having a spot diameter including a plurality of scanning lines, the irradiation history for the pixels included in the previous scanning line corresponding to the set number of lines is integrated, and irradiation is performed on the current scanning line. Control means for controlling the amount of light applied to the current scan pixel;
Light modulating means for modulating the light beam in response to the control of the irradiation light amount;
An image forming apparatus. Pattern detection means for calculating irradiation history data by performing a specific pattern detection from the image data of the previous scanning line, the irradiation light quantity of the current scanning pixel being less than the set number of lines;
A light amount correction amount calculating means for calculating a light amount correction amount for irradiating the current scanning pixel based on the result of the pattern detection;
2. The image forming apparatus according to claim 1, further comprising: a light amount adjustment control unit that holds the current scanning pixel and uses the light amount correction amount by the light amount correction amount calculation unit to command an irradiation light amount for the current scanning pixel. .   The image forming apparatus according to claim 1, wherein the light amount adjustment control unit is PWM modulation using the light amount correction amount or laser power modulation using digital / analog conversion of the light amount correction amount.   The control means holds an image pattern of the previous scan line and a mapping table for calculating the light amount correction amount, and an irradiation history for calculating the light amount correction amount of the current scan pixel is stored in the previous scan line. The image forming apparatus according to claim 2, wherein calculation is performed using the image pattern and the mapping table.   In order to perform the pattern detection for the current scanning pixel, a pre-acquisition acquisition unit that pre-acquires image data corresponding to the set number of lines is provided, and the pattern detection unit calculates the light amount correction amount for the current scanning pixel. 3. The image forming apparatus according to claim 2, wherein after completion, the pixel data of the current scanning pixel is read from the prefetching means in order to create the irradiation history for the post-scanning line.   The control means is configured such that the distance from the spot center of the first line of the current scan to the spot center of the preceding scan line corresponding to the set number of lines on the surface of the photosensitive drum is a sub-position of the spot formed on the surface of the photosensitive drum. The image forming apparatus according to claim 1, wherein a scanning line is provided so as to be equal to or smaller than a spot diameter of the light beam when measured in a scanning direction. An image forming method using a multi-beam light source that emits a light beam including a plurality of beams, and forming an electrostatic latent image on a photosensitive drum by irradiation of the light beam,
Emitting a plurality of light beams;
Scanning the surface of the photosensitive drum adjacently with the light beam having a spot diameter including a plurality of scanning lines;
Pre-fetching image data in the pre-scan line direction less than the set number of lines for the current scan pixel;
The current scanning pixel of the current scanning line is held, and the pixels included in the previous scanning line corresponding to the set number of lines are accumulated using the irradiation history generated by the pre-fetching, and should be irradiated on the current scanning line Controlling the amount of light applied to the current scan pixel;
Modulating the light beam in response to the control of the irradiation light quantity. Performing pattern detection of the image data acquired in advance and calculating an irradiation history;
Calculating a light amount correction amount for irradiating the current scanning pixel using the irradiation history;
The image forming method according to claim 7, further comprising: commanding an irradiation light amount for the current scanning pixel using the light amount correction amount.   The step of calculating the irradiation history includes a step of calculating an irradiation history using presence or absence of an image at a position mapped to the mapping table in the pre-acquired image data. Image forming method.   The image forming apparatus according to claim 7, wherein the step of controlling the irradiation light amount includes a step of modulating laser power by PWM modulation using the light amount correction amount or digital-analog conversion of the light amount correction amount.

Images