JP2009262344A - Image formation device and image correcting method - Google Patents

Abstract

An image forming apparatus and an image correction method for reducing density unevenness recognized when a printed matter after shading correction is visually observed.
An image forming apparatus 100 divides a main scanning line of a surface to be scanned in an image carrier 107 into a plurality of regions, adjusts an output light amount of a light source 15 based on light amount correction data 71 corresponding to each region, and An apparatus for correcting shading characteristics in the scanning direction, which changes the duty value of a pulse modulation signal for each region based on correction data 71, and outputs a pulse modulation signal 81 for light amount adjustment according to the changed duty value Means 46, and changing means 51 for changing the division position P of each area in the main scanning line when adjusting the output light quantity based on the pulse modulation signal 81 for adjusting the light quantity output by the output means 46. It is characterized by having.
[Selection] Figure 11

Description

  The present invention relates to a beam scanning type image forming apparatus such as a laser printer, a digital copying machine, and a facsimile machine, and more particularly to a shading correction technique.

  2. Description of the Related Art Image forming apparatuses such as laser printers, digital copiers, and facsimile machines include apparatuses that are configured to form an image by irradiating a scanned surface with a light beam and scanning the scanned surface with the light beam. For example, as an apparatus having such a configuration, a scanning unit such as a polygon mirror scans a laser beam in a main scanning direction on a surface to be scanned such as a photosensitive member, and moves the surface to be scanned in a sub-scanning direction to thereby obtain an effective image area. There is a beam scanning type image forming apparatus that writes an image for each line in an (image writing area).

  In the beam scanning image forming apparatus, the laser light is deflected at a constant angular velocity by a polygon mirror, and the scanning speed on the surface to be scanned is made constant by an fθ lens and an fθ mirror. The laser light transmitted through the fθ lens and the fθ mirror has a substantially constant scanning speed on the surface to be scanned, but the intensity of the laser light varies depending on the image height. This is because the light utilization efficiency (specifically, optical elements such as glass, lenses, mirrors, etc.) that pass between the time when the laser light is emitted from a light source such as a laser diode and reaches the surface to be scanned such as a photoreceptor. This is because, for example, the reflectance and transmittance are different depending on the incident angle of the laser light, and the thickness of the fθ lens is different depending on the image height.

  The intensity of the beam intensity depending on the image height is called a shading characteristic. The shading characteristics vary little among the image forming apparatuses and change due to the operating environment such as temperature and humidity, and are determined mainly by the characteristics and arrangement of the optical elements. Although the shading characteristic varies depending on the optical system, it is usually about 10 (%) and affects the density of the formed image. Therefore, the beam scanning type image forming apparatus is required to correct the shading characteristic.

  As a method for correcting shading characteristics (hereinafter referred to as “shading correction method”), for example, a photosensitive member is irradiated with laser light by a semiconductor laser (LD), and a latent image formed on the surface of the photosensitive member is developed with a developer. In a digital copying machine that transfers an image onto a transfer sheet, data such as sensitivity unevenness causing image density unevenness, that is, shading data is stored in a storage device provided in the apparatus, and the result is stored. A method of performing shading correction by changing the reference signal of the semiconductor laser emission power by using a PWM (Pulse Width Modulation) modulation circuit or a smoothing circuit in write control is already known. Regarding the change timing of the reference signal of the semiconductor laser emission power, the effective image area is divided into a predetermined number, and each divided area is divided. A method of changing based on shading correction data set in advance has been proposed.

For example, in Patent Document 1, an arbitrary point on the shading correction data line period is selected for the purpose of reducing density unevenness at the division position of the effective image region, and PWM corresponding to a necessary light amount at the selected point position is disclosed. The width value is set, the difference between adjacent points is calculated using an application specific integrated circuit (ASIC) for write control, and the PWM width is gradually increased in a direction to reduce the difference when moving to the next point position ( A configuration that can be varied (in units of pixels) is disclosed.
JP 2005-262509 A

  However, the above-described conventional shading correction method has a problem in that density unevenness occurs in the formed image due to an increase in the amount of change in the light amount adjustment signal of the semiconductor laser emission power at the division position of the effective image area. is there.

  For example, the method disclosed in Patent Document 1 is intended to reduce density unevenness, but is a method in which the PWM width is gradually changed in a direction to reduce the difference between adjacent points. It can not be said that the unevenness in density is sufficiently dealt with at the divided positions where the amount of change of the difference is large, that is, at the position where the difference between adjacent points is large.

  An object of the present invention is to provide an image forming apparatus and an image correction method that reduce density unevenness that is recognized when a printed matter after shading correction is visually observed.

  In order to achieve the above object, the image forming apparatus of the present invention divides the main scanning line of the surface to be scanned in the image carrier into a plurality of regions, and adjusts the output light amount of the light source based on the light amount correction data corresponding to each region. An image forming apparatus for correcting shading characteristics in the main scanning direction, wherein the pulse modulation signal for adjusting the light amount is changed according to the changed duty value by changing the duty value of the pulse modulation signal for each region based on the light amount correction data. Output means for changing the output light quantity based on the pulse modulation signal for light quantity adjustment output by the output means, changing means for changing the division position of each region in the main scanning line, It is characterized by having.

  In order to achieve the above object, in the image forming apparatus of the present invention, the changing unit changes the division position for each main scanning line so that the division position of each region is different between adjacent main scanning lines. It is characterized by that.

  In order to achieve the above object, in the image forming apparatus of the present invention, the changing unit assigns a predetermined value to the number of pixels relatively representing the division position of each area in the pixel array constituting the main scanning line. Addition is performed, and the division position of each region is changed.

  In order to achieve the above object, the image forming apparatus of the present invention stores and holds, in a predetermined storage area, a shift amount representing a direction and a moving amount of the division position on the main scanning line. And the changing means adds the shift amount held by the holding means to the number of pixels, and periodically changes the division position of each area for each of a plurality of main scanning lines. Features.

  In order to achieve the above object, the image forming apparatus of the present invention includes a control unit that periodically generates a numerical value in a predetermined range and controls the change of the division position, and the changing unit includes the number of pixels. Further, the shift amount associated with the numerical value in the predetermined range generated by the control means is added.

  In order to achieve the above object, the image forming apparatus according to the present invention includes a sub-scanning line number acquisition unit that counts sub-scanning lines and acquires the number of lines, and the sub-scanning line acquired by the sub-scanning line number acquisition unit. Dividing the number by a predetermined number of lines, and obtaining a remainder value as a calculation result, and a change value obtaining means for obtaining the remainder value obtained by the remainder value obtaining means. The shift amounts associated with each other are added.

  In order to achieve the above object, the image forming apparatus of the present invention includes a random number generation unit that generates a predetermined range of random numbers, and the changing unit adds the random number generated by the random number generation unit to the number of pixels. A value is added as the shift amount.

  In order to achieve the above object, the image forming apparatus of the present invention is characterized in that the changing unit changes the division position by a shift amount having the same value for each region.

  In order to achieve the above object, the image forming apparatus of the present invention is characterized in that the changing unit changes the division position by a shift amount having a different value for each region.

  In order to achieve the above object, the image correction method of the present invention divides the main scanning line of the scanned surface of the image carrier into a plurality of regions, and adjusts the output light amount of the light source based on the light amount correction data corresponding to each region. An image correction method in an image forming apparatus for correcting shading characteristics in the main scanning direction, wherein a duty value of a pulse modulation signal for each region is changed based on the light amount correction data, and light amount adjustment is performed according to the changed duty value An adjustment procedure for adjusting the output light amount of the light source, and a change procedure for changing the division position of each region in the main scanning line when the output light amount is adjusted by the adjustment procedure, It is characterized by having.

  According to the present invention, in the shading correction, the density unevenness recognized visually can be reduced by diffusing the occurrence position of the density unevenness in the effective image area.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention (hereinafter referred to as “embodiments”) will be described in detail with reference to the drawings.

[First Embodiment]
<Image forming operation having shading correction function>
The image forming apparatus according to the present embodiment includes an optical device that uses a laser diode (LD) as a light source, irradiates a laser beam on the surface of the photosensitive member, and forms an electrostatic latent image. The present invention can be applied to a monochrome image forming apparatus and a multi-color full-color image forming apparatus.

  First, an image forming operation of the image forming apparatus 100 according to the present embodiment will be described using a schematic diagram of the apparatus. FIG. 1 is a schematic diagram of an image forming apparatus 100 according to the first embodiment of the present invention.

  In the image forming apparatus 100 according to the present embodiment, the surface of the drum-shaped photoconductor 107 is first charged by the charger 101. The charged surface of the photoconductor 107 is irradiated with a laser beam corresponding to image data by the optical device 102 to form a latent image. The formed latent image is formed (developed) with a toner image by the developing device 103, and the formed toner image is transferred to the printing paper conveyed from the paper supply roller 104 by the transfer device 105. Thereafter, the printing paper is conveyed to a fixing unit (not shown), and the toner image is fixed on the printing paper by pressure and heat, and is discharged by a paper discharge roller 106. Finally, the cleaning device 108 cleans the surface of the photoconductor 107 and removes the toner adhering to the surface excessively.

  When forming a full-color image, a latent image is formed for each color component color (for example, for each color such as cyan (C), magenta (M), yellow (Y), and black (Bk)), and each component color The toner image is transferred while being superimposed on the printing paper.

  Next, a hardware configuration for controlling the image forming operation will be described. FIG. 2 is a diagram illustrating a hardware configuration example of the image forming apparatus 100 according to the first embodiment of the present invention.

  The image forming apparatus 100 according to this embodiment includes an image reading device 109 that reads a document image, an optical device 102 that forms a latent image based on image data on the surface of a charged photoconductor 107, and control of the entire device. A CPU (Central Processing Unit) 16, a ROM (Read Only Memory) 17 in which a control program is stored, a RAM (Random Access Memory) 18 that is temporarily read when the control program is executed, and an image reading device 109. Controller 20 having an image memory 19 for storing image data read by, various interfaces (hereinafter referred to as “I / F”) for performing data communication with an external device (not shown), and operations from the user. An operation panel 110 for receiving instructions, operating condition settings, and the like. It has become capable of transmitting and receiving on the connected bidirectionally predetermined data I. The image reading device 109 and the optical device 102 include a local I / F 2 that is an I / F for connecting each hardware to the internal system bus 1.

  The image reading device 109 includes a VPU (Visual Processing Unit) 11 that performs black offset correction, shading correction, pixel position correction, and the like by performing A (Analog) / D (Digital) conversion on the read signal, and predetermined image processing. The optical device 102 includes an ASIC 13 for writing control that performs writing control using a laser beam, an LD control unit 14 that controls a laser diode, and the surface of the photoconductor 107. And a laser diode (LD) 15 for forming electrostatic latent image data.

  Finally, the controller 20 includes, for example, a LAN (Local Area Network compliant with IEEE 802.3 and 802.11 standards), USB (Universal Serial Bus), IEEE 1394 (FireWire (i.LINK)), IEEE 1284 (printer port standard). ) And other image data sent and received according to various data communication standards such as image rotation, image composition, image scaling, etc., or by using a PDL parser (Page Description Language Parser) Print data (PDL data) received from the computer is converted into data that can be interpreted by the optical device 102.

  Next, an electrostatic latent image operation performed by the optical device 102 will be described. FIG. 3 is a diagram illustrating a configuration example of the optical device 102 and its peripheral members according to the first embodiment of the present invention.

  As described above, the image forming apparatus 100 according to the present embodiment, together with the optical device 102, the collimating lens 21 that converts the diverging light emitted from the laser diode 15 into parallel light, and a plurality of reflecting mirrors (polyhedral mirrors). ), Which is driven by a motor (not shown) and reflects and deflects a laser beam incident on a reflecting mirror, and is reflected from the polygon mirror 22 and reflected on the surface of the photoreceptor 107 in the axial direction ( The fθ lens 23 for correcting the scanning speed of the laser beam scanned in the main scanning direction to a constant value, and the laser beam that passes through the fθ lens 23 and scans the surface of the photoconductor 107 at a constant speed in the main scanning direction are detected. And a light detector 24.

  As described above, in the image forming apparatus 100, the laser beam emitted from the laser diode 15 is collimated by the collimating lens 21, then deflected by the polygon mirror 22, and then the surface of the photoreceptor 107 (uniformly by the fθ lens 23. The image is formed on the charged scanning surface. As a result, the image forming spot is repeatedly moved in the main scanning direction of the photoconductor 107 by the rotation of the polygon mirror 22, and at the same time, the photoconductor 107 is rotated.

  At this time, the light detector 24 is provided outside the area in the main scanning direction of the photoconductor 107 where a latent image can be formed (hereinafter referred to as “effective image area”), and the laser beam deflected by the polygon mirror 22 is emitted. Detect and generate a synchronization detection signal.

  The write control ASIC 13 supplies a DATA signal (information signal) from the image reading device 109 to the drive unit 28 of the LD control unit 14, and controls the timing by a synchronization detection signal from the light detector 24. The drive unit 28 instructs the light emitting unit 25 of the laser diode 15 to emit light according to the information signal from the writing control ASIC 13, and as a result, the laser beam emitted by the light emitting unit 25 is irradiated onto the charged surface of the photosensitive member 107. As a result, an electrostatic latent image is formed.

  The laser beam emitted from the light emitting unit 25 of the laser diode 15 is incident on the light receiving unit 26, and the output signal from the light receiving unit 26 is an APC (Automatic Power Control) control unit (light quantity adjustment control unit) of the LD control unit 14. ) 27.

  The APC control unit 27 controls the drive unit 28 of the LD control unit 14 in accordance with the output signal of the light receiving unit 26 and the APC signal and the light amount adjustment signal from the write control ASIC 13 so that the output light amount of the laser diode 15 is constant. (This is referred to as “APC operation”). Specifically, the output light amount of the light emitting unit 25 of the laser diode 15 is adjusted and held so as to be constant (line cycle interval).

  A write control ASIC 13 that supplies various control signals such as the DATA signal, APC signal, and light amount adjustment signal to the LD control unit 14 and controls the output of the laser beam applied to the surface of the photosensitive member 107 is shown in FIG. It has a configuration. FIG. 4 is a diagram showing a configuration example of the write control ASIC 13 according to the first embodiment of the present invention.

  The write control ASIC 13 includes a memory block 31, an image processing unit 32, and an output data control unit 33, and a memory block for image data that is input data from the IPU 12 or the controller 20 of the image reading device 109. A speed conversion or a format conversion is performed by 31, and the converted data is subjected to predetermined image processing by the image processing unit 32. As a result, the image-processed data is transferred from the image processing unit 32 to the output data controller unit 33 and supplied to the LD control unit 14 as a DATA signal.

  The output data control unit 33 counts the pixel clock, counts the main scanning counter 33a that manages the main scanning position based on the synchronization detection signal, and the number of lines in the sub-scanning direction (the driving direction of the photoconductor 107). The sub-scanning counter 33b and the period detection unit 33c for detecting the interval of the line period based on the synchronization detection signal supplied from the light detector 24, and the main scanning counter 33a. Is reset based on the detection result by the period detector 33c (count reset in synchronization with the synchronization detection signal turned on for each line in the main scanning direction).

  Further, the output data control unit 33 has a configuration shown in FIG. FIG. 5 is a diagram illustrating a configuration example of the output data control unit 33 according to the first embodiment of the present invention.

  The output data control unit 33 includes a P pattern block 41, a γ conversion block 42, an APC block 43, an LD on / off block 44, a gate signal generation unit 45, and a PWM signal generation unit 46.

  The output data control unit 33 uses the P pattern block 41 to acquire data for determining process conditions, and the data of the P sensor pattern (toner image having a predetermined density) formed on the surface of the photosensitive member 107 is converted into the image processing unit 32. Is attached to the input data, and the attached data is passed to the γ conversion block 42.

  In the γ conversion block 42, γ conversion is performed by changing the weight of the data, and the data after γ conversion is transferred to the APC block 43, and the APC block 43 keeps the output light quantity from the laser diode 15 constant. In addition, the data after the γ conversion is transferred from the APC block 43 to the LD on / off block 44 in synchronization with the timing of the APC operation.

  Finally, the LD on / off block 44 supplies light emission data for synchronization detection to the LD control unit 14 based on the data after γ conversion.

  The gate signal generation unit 45 generates a gate signal in the main scanning direction according to the main scanning counter 33a. The PWM signal generation unit 46 divides the effective image area into a predetermined number from the gate signal generation unit 45. The area information is received, and based on the received divided area information, a light amount adjustment PWM signal for adjusting the output light amount corresponding to each divided area is generated.

  The PWM signal generated at this time is output from the PWM signal generation unit 46 and then smoothed through, for example, a low-pass filter LPF shown in FIG. 6, and finally passes from the output data control 33 to the LD control unit 14. FIG. 6 is a diagram illustrating an example of a circuit that smoothes the PWM signal according to the first embodiment of the present invention.

  The circuit shown in FIG. 6 is a low-pass filter circuit that constitutes a low-pass filter LPF, which includes resistors R1 to R4, a capacitor C1, and an operational amplifier IC1. The PWM signal supplied from the PWM signal generation unit 46 is Smoothing is performed by the resistor R and the capacitor C and converted to a DC voltage, and impedance matching is performed by the operational amplifier IC (removing and smoothing the high-frequency component of the PWM signal). In the low-pass filter circuit, the voltage V1 and the values of the resistors R1 to R3 are set according to the specification of the LD light amount control analog voltage of the LD control unit 14.

  For example, a PWM signal as shown in FIG. 7 is supplied to the low-pass filter LPF. FIG. 7 is a diagram illustrating an example of an output waveform from the PWM signal generation unit 46 according to the first embodiment of the present invention.

  The PWM signal generation unit 46 performs PWM output corresponding to the light intensity of each divided area of the effective image area. More specifically, a PWM signal as shown in the figure is generated based on a duty specified in association with each divided area of the effective image area.

  FIG. 7A shows an example of the output waveform when the duty is designated as 50 (%), and FIG. 7B shows an example of the output waveform when the duty is designated as 70 (%). It is shown. The duty value to be specified (%) is, for example, an output 3.0 (output 3.0) of the output port of the PWM signal generator 46 when it is desired to obtain an output of a light amount adjustment signal of 1.5 (v) in a certain divided area. Assuming v), the duty specified in association with the divided area is “1.5 / 3.0 = 50 (%)”. As described above, if the output of the light amount adjustment signal desired to be obtained for each divided area is known in advance, the duty designated for each divided area is determined in advance. The duty value designated for each divided area can be set by, for example, the device administrator via the operation panel 110, and the duty value set in this way can be set in a predetermined storage area (for example, image formation). Held in a non-volatile storage device included in the device 100.

  FIG. 8 is a diagram showing general shading correction data. Correction data for each divided area (hereinafter referred to as “shading correction data”) that is opposite to the plurality of divided areas n in the effective image area and the shading characteristics (light intensity distribution) on the surface of the photoreceptor 107. When the voltage (v) is represented on the vertical axis and each divided area is represented on the horizontal axis, a waveform 71 as shown in FIG. 8 is obtained. That is, this waveform 71 is shading correction data.

  The effective image area shown in FIG. 8 is divided into 10 areas along the main scanning line (the entire main scanning line is divided into 10 or more areas including the ineffective image area). The position of each upper divided area is recognized by the main scanning counter 33a which is reset by the synchronization detection signal.

  The gate signal generation unit 45 performs the counting operation of the main scanning counter 33a, recognizes each divided area from the divided area 0 to the divided area n, and supplies the information regarding the recognized divided area to the PWM signal generating unit 46 as divided area information. hand over.

  As a result, the PWM signal generation unit 46 generates a PWM signal for adjusting the output light amount based on the associated duty based on the received divided area information. In addition, since the divided area 0 is an area outside the effective image area, an APC operation is performed.

  As described above, in the image forming apparatus 100 according to the present embodiment, the voltage level of the light amount adjustment PWM signal supplied from the PWM signal generation unit 46 of the write control ASIC 13 to the drive unit 28 of the LD control unit 14 is mainly set. By changing based on the duty corresponding to the divided area (scanning position on the main scanning line) recognized on the scanning line, the output light amount of the laser diode 15 is adjusted and shading correction is performed.

<Relationship between shading correction and density unevenness>
Here, the relationship between shading correction and density unevenness performed by the image forming apparatus 100 according to the present embodiment will be briefly described with reference to the drawings.

FIG. 9 is a diagram illustrating output light amount adjustment characteristics with respect to general shading characteristics. In this example, the divided area is moved from the divided area 1 to the divided area 5 along the main scanning line, and the duty value designated in each divided area is sequentially reduced, while the divided area 6 is moved to the divided area 10. By increasing the designated duty value, output light quantity adjustment characteristics approximating the shading correction data 71 corresponding to each divided area can be obtained. That is, a PWM signal for light amount adjustment (hereinafter referred to as “light amount adjustment signal”) 81n approximate to the shading correction data 71 is obtained for each divided area (reference numerals 81 ₁ to 81 ₁₀ in the figure).

  Among them, at the division position P where the division area changes (for example, the broken line circle in the figure), the light amount adjustment signal 81 changes greatly due to the switching of the duty, so that the level of the output light amount adjustment signal 81 is increased. A large level difference occurs, and density unevenness as shown in FIG. 10 occurs in the output image (printed image) after image formation (an image resulting from switching of light intensity that occurs when moving the divided area of the effective image area) Concentration steps occur).

  FIG. 10 is a diagram illustrating the relationship between the division position P and the density unevenness occurrence position 91. Since the density unevenness occurs due to the cause described above, the division position P of the effective image area coincides with the density unevenness generation position (hereinafter referred to as “density unevenness occurrence position”) 91, and the main. It always occurs at a fixed position on the scan line. For this reason, the output image after image formation is visually recognized (perceived) as streaky unevenness (hatched area in the figure) with respect to the sub-scanning line.

<Diffusion function of density unevenness during shading correction>
Therefore, in the image forming apparatus 100 according to the present embodiment, the density unevenness recognized when the output image after the shading correction is viewed is diffused by diffusing the density unevenness occurrence position 91 in the effective image area in the shading correction. It has a “density unevenness diffusion function” to reduce.

<< Configuration >>
FIG. 11 is a diagram illustrating a configuration example of the density unevenness diffusion function according to the first embodiment of the present invention. In the image forming apparatus 100 according to the present embodiment, in order to realize the density unevenness diffusion function, the writing control ASIC 13 includes a division position changing unit 51, a change cycle control unit 52, and a divided area pixel number holding unit 53. It is the composition which has. The above functional units will be briefly described.

  The division position changing unit 51 has a function of changing the division position P of each main scanning line by shifting the division position P of the division area by a predetermined number of pixels along the main scanning line.

  The change cycle control unit 52 controls the cycle (hereinafter referred to as “change cycle”) of the change pattern (shift pattern) of the division position P performed by the division position change unit 51 in a plurality of main scanning lines with a counter value. This function is realized by a counter circuit having a predetermined number of bits.

  The divided area pixel number holding unit 53 stores a predetermined number of pixels (hereinafter referred to as “divided area pixel number”) in which the division position P of the divided area is set as a relative pixel position on the main scanning line. This function is held in the area and is realized by a register.

  The image forming apparatus 100 realizes a density unevenness diffusion function by exchanging necessary data in each functional unit at a predetermined timing. Hereinafter, the operation of each functional unit will be described in detail.

<< Operation >>
First, in the image forming apparatus 100 according to this embodiment, the number of divisions of the effective image area, the number of division area pixels of each division area, and the output value of the PWM signal for adjusting the light amount of each color in each division area can be set. It has become. These values can be specified on the operation screen in the administrator mode via the operation panel 110 by, for example, a device administrator. The division number, the number of images, and the signal output value specified in this way are set in a register included in the write control ASIC.

  When the laser diode 15 causes the image of the first line of the main scanning line to be latent imaged (written) on the surface of the charged photosensitive member 107 and the APC operation of the second line is executed, the division position changing unit 51 changes the division position P of the division area.

At this time, the division position changing unit 51 changes the number of divided area pixels of the divided area 0 outside the effective image area according to the change cycle controlled by the change cycle control unit 52, and the divided area 0 and the divided area 1 are changed. shifting the division position _{P 0} between.

That is, the division position changing unit 51 adds the shift amount composed of the direction and the number of pixels to the division area pixel number of the division area 0 outside the effective image area held by the division area pixel number holding unit 53, The division position P ₀ with respect to the area 1 is changed by shifting in the main scanning direction or the opposite direction by the predetermined number of added pixels.

In split position changing section 51, since the number of divided areas of pixels is a value that indicates the relative pixel position in the main scanning line on, for example, when the division position P ₀ of the divided areas 0 want to have shifted 3 pixels in the main scanning direction If you want to shift by 3 pixels in the opposite direction, add “3” to the number of divided area pixels in the divided area 0, such as “−3”. Then, the division position P ₀ of the division area 0 is changed.

Hereinafter, an operation of changing the division position P performed by the division position changing unit 51 (an operation of shifting by a predetermined number of pixels) will be specifically described with reference to FIG. FIG. 12 is a diagram illustrating an operation example of changing the division position P according to the first embodiment of the present invention. FIG. 12 is a partially enlarged view of the divided area 0 and the divided area 1, and the reference symbol N in the figure is the number of divided area pixels in the divided area 0, that is, the divided position P ₀ between the divided area 1. The pixel position on the corresponding main scanning line is represented, and the hatched portion in the figure represents the density unevenness. FIG. 12A shows an example of a conventional output image in which density unevenness has occurred, and FIG. 12B shows an example of an output image in the present embodiment in which density unevenness has occurred.

  As can be seen from FIG. 12A, the density unevenness on each main scanning line generated in the conventional output image has the same density unevenness occurrence position 91 in all the main scanning lines. Pixel positions are arranged, and streaky density unevenness is formed along the sub-scanning. For this reason, when the user looks at the output image formed on the printing paper, the generated density unevenness is easily visually recognized (the density unevenness is easily recognized by the user).

  Compared with that, as shown in FIG. 12B, the density unevenness on each main scanning line generated in the output image according to the present embodiment has a different density unevenness occurrence position 91 in each main scanning line. The pixel position where the density unevenness is generated is shifted by a predetermined number of pixels in the main scanning line adjacent along the sub-scanning. In other words, in the present embodiment, in the output image formed on the printing paper, the pixel positions where the density unevenness is generated are diffused within a predetermined range without being aligned along the sub-scanning.

  In the image forming apparatus 100 according to the present embodiment, the diffusion of the density unevenness occurrence position 91 is realized by the following method.

(Change of division position P ₀ of division area 0)
For example, in the image forming apparatus 100, the device administrator or the like via the operation panel 110 has an effective image area division number of 10 and the division area pixel number of the division area 0 (pixel position representing the division position P ₀ ) is [ N] is set.

  When the image forming apparatus 100 starts an image forming operation in this setting state, the image of the first line of the main scanning line is latent (written) in the divided area pixel number holding unit 53, and the APC of the second line. When the operation is executed, the set number of divided area pixels [N] is held. The change cycle control unit 52 outputs the initialized count value.

  In the present embodiment, for example, the change cycle control unit 52 is a 2-bit counter circuit, and the initialized count value means that the 2-bit value is “00”. The change cycle control unit 52 is synchronized with the APC operation and counts up when the APC operation is executed. That is, when the APC operation for the second line is completed, the 2-bit value changes from “00” to “01” and is output from the counter circuit as a count value.

  In this way, when the change cycle control unit 52 is realized using a 2-bit counter circuit, the 2-bit value is counted up to the fourth line where the value is “11”, and the 2-bit value from the fifth line. Returns to “00”, which is the same as in the first line (the count value is cleared).

  When the APC operation for the second line is executed, the division position changing unit 51 sets the shift amount [+3] corresponding to the count value “01” obtained from the change cycle control unit 52 to the division area pixel number holding unit 53. Is added to the number of divided area pixels [N] held by [N + 3]. As a result, the division position P of the second line is shifted by 3 pixels in the main scanning direction. As a result, for each divided area other than the divided area 0, the division number P of the divided area does not change the number of pixels (number of divided area pixels) set as a relative pixel position on the main scanning line. The division positions Pn of the divided areas located on the second main scanning line are all shifted by three pixels in the main scanning direction on the main scanning line. That is, the division position Pn of each divided area after the divided area 0 is shifted in the main scanning direction by three pixels.

  Thereafter, the image forming apparatus 100 forms a latent image on the second line image in which the division position Pn of each of the divided areas is changed, and counts the change line control unit 52 when executing the APC operation on the third line. The count value is changed from “01” to “10”.

As described above, in the image forming apparatus 100 according to the present embodiment, the change cycle control is performed by the division position changing unit 51 to the division area pixel number of the division area 0 held by the division area pixel number holding unit 53. The division amount of each divided area on the main scanning line is changed by adding a shift amount corresponding to the count value of the section 52 and changing the relative pixel position on the main scanning line which is the division position P ₀ of the divided area 0. The position Pn is changed.

  Further, the shift amount is associated with the count value of the change cycle control unit 52 and is stored in a predetermined storage area (for example, a non-volatile storage device provided in the image forming apparatus 100). In the case of the present embodiment, four count values (four count values of “01”, “10”, “11”, and “00”) are obtained from the change cycle control unit 52. Corresponding shift amounts ([+3], [-6], [+5], [-2]) are stored in advance.

Therefore, in the image forming apparatus 100 according to the present embodiment, the division position changing unit 51 uses the shift amount different for each main scanning line in the change cycle based on the count value of the change cycle control unit 52. The division position P ₀ of ₀ is changed.

  For example, when the APC operation for the third line is executed, the division position changing unit 51 sets the shift amount [−6] corresponding to the count value “10” obtained from the change cycle control unit 52 to the previous two lines. The shift amount is added at the time of eye and added to the number of pixels (N + 3) held by the divided area pixel number holding unit 53 ((N + 3) −6 = (N−3)). As a result, the division position P of the third line is shifted in the direction opposite to the main scanning direction by three pixels.

  Similarly, in the case of the fourth line, the shift amount is added at the time of the third line, and the count value “11” is set to the number of pixels (N−3) held by the divided area pixel number holding unit 53. The corresponding shift amount [+5] is added ((N−3) + 5 = (N + 2)). As a result, the division position P of the fourth line is shifted in the main scanning direction by two pixels.

  In the case of the fifth line, the shift amount is added in the case of the fourth line, and the shift amount corresponding to the count value “00” is added to the number of pixels (N + 2) held by the divided area pixel number holding unit 53 [ -2] is added ((N + 2) -2 = (N)). As a result, the dividing position P of the fifth line is shifted in the direction opposite to the main scanning direction by two pixels, and becomes the same position as the first line.

  The image forming apparatus 100 according to the present embodiment repeatedly performs the change pattern as described above according to the change period controlled by the count value of the change period control unit 52. As a result, the image forming apparatus 100 forms an output image in which the density unevenness occurrence position 91 is diffused as shown in FIG.

  FIG. 13 is a diagram illustrating an example of a result of diffusion of the density unevenness occurrence position 91 according to the first embodiment of the present invention. In this way, when each density unevenness occurrence position 91n that coincides with the division position Pn of each divided area is diffused, it becomes difficult to visually recognize density unevenness throughout the output image, and as a result, density unevenness is reduced. can do.

<< Processing procedure >>
FIG. 14 is a flowchart illustrating an example of image forming processing according to the first embodiment of the present invention. FIG. 14 shows a processing procedure example of an image forming operation including the operations of the functional units described above (the division position changing unit 51, the change cycle control unit 52, and the divided area pixel number holding unit 53). .

  The image forming apparatus 100 according to the present embodiment includes the number of divisions of the effective image area received via the operation panel 110, the number of division area pixels of each division area, and the PWM signal for adjusting the light amount of each color in each division area. The CPU 16 sets the output value in the register of the write control ASIC 13 (steps S101, S102, and S103).

  Subsequently, in the image forming apparatus 100, image data to be image formed is input from the IPU 12 of the image reading apparatus 109 or the controller 20 to the writing control ASIC 13 and the pixel clock is turned on (shifts to a predetermined frequency) (step) S104).

  In the image forming apparatus 100, the APC control unit 27 controls the drive unit 28 of the LD control unit 14 according to the output signal of the light receiving unit 26, the APC signal from the write control ASIC 13, and the light amount adjustment signal, and the laser diode At the time of APC operation for controlling the output light quantity of 15 to be constant, a synchronization detection signal is supplied to the output data control unit 33 of the write control ASIC 13 to reset the main scanning counter 33a (step S105).

  Subsequently, in the image forming apparatus 100, based on the PWM signal for light amount adjustment, the laser diode 15 driven by the LD control unit 14 irradiates the surface of the charged photoconductor 107 with a laser beam having a predetermined output, and performs main scanning. An image for one line is formed as a latent image (step S106).

Subsequently, in the image forming apparatus 100, the division position changing unit 51 sets the number of pixels in the divided area 0 held by the divided area pixel number holding unit 53, which is a register, to the change cycle control unit 52, which is a counter circuit of a predetermined bit. By adding the shift amount corresponding to the count value and changing the relative pixel position on the main scanning line which is the dividing position P ₀ of the divided area 0, the dividing position P of the divided area is changed for each main scanning line. (Step S107).

  In the image forming apparatus 100, the output data control unit 33 determines whether or not the latent image forming operation (writing operation) is completed based on the count value of the sub-scanning counter 33b (step S108).

  When it is determined that the latent image forming operation (writing operation) has been completed (when step S108 is YES), the processing is terminated.

  If it is determined that the latent image forming operation (writing operation) has not ended (if step S109 is NO), the sub-scanning counter 33b and the counter that is the change cycle control unit 52 are counted. Up (step S109), the process proceeds to step S105.

<Summary>
As described above, according to the first embodiment of the present invention, the image forming apparatus 100 according to the present embodiment divides the divided area 0 held by the divided area pixel number holding unit 53 by the division position changing unit 51. By adding the shift amount corresponding to the count value of the change cycle control unit 52 to the number of area pixels, and changing the relative pixel position on the main scanning line that is the division position P ₀ of the division area 0, the main scanning The division position Pn of each division area on the line is changed.

  In addition, since the image forming apparatus 100 has a configuration in which different shift amounts are stored in a predetermined storage area in association with the count value of the change cycle control unit 52, the division position change pattern based on these shift amounts is changed by the change cycle control. It repeats according to the change period controlled by the count value of the unit 52.

  Accordingly, in the image forming apparatus 100, the density unevenness recognized when the printed matter after the shading correction is viewed can be reduced by diffusing the density unevenness occurrence position 91 in the effective image area in the shading correction. .

  Further, in the conventional configuration in which the PWM width is changed little by little, the processing step for controlling density unevenness in shading correction becomes complicated, the circuit scale becomes large, and the exposure speed (writing speed) to the photosensitive member 107 is increased. However, in the image forming apparatus 100 according to the present embodiment, the processing process for controlling density unevenness is complicated. In addition, since the circuit scale is not increased, it can be realized more easily than in the past.

<Modification: Part 1>
In the image forming apparatus 100 described above, the division position changing unit 51 responds to the counter value based on the counter value of the change cycle control unit 52 (2-bit counter circuit) that counts up for each main scanning line. The amount of shift to be added is added to the number of divided area pixels held by the divided area pixel number holding unit 53, and the division position P of the divided area in the main scanning line is changed, so that the shading correction can be performed within the effective image area. Although the configuration is such that the density unevenness occurrence position 91 is diffused, the present invention is not limited to the configuration of the density unevenness diffusion function.

  FIG. 15 is a diagram showing a modification (No. 1) of the density unevenness diffusion function according to the first embodiment of the present invention. In this modification, instead of the change cycle control unit 52, the count value of the sub-scanning counter 33b included in the output data control unit 33 of the write control ASIC 13 is divided by the predetermined number of main scanning lines, and the remainder value is obtained. It is the structure which includes the remainder value calculating part 54 which calculates. The residue value calculated by the residue value calculation unit 54 is passed to the division position changing unit 51 and used for specifying the shift amount to be added to the number of divided area pixels held by the divided area pixel number holding unit 53.

  For example, when performing the same control as the change cycle control unit 52 which is a 2-bit counter circuit, the remainder value calculation unit 54 sets the counter value of the sub-scanning counter 33b to “4” which is the number of main scanning lines. Divide by and calculate the remainder value. The remainder value calculated in this way becomes a value from “0” to “3”, and is obtained periodically as the counter value of the sub-scanning counter 33b is sequentially counted up in the sub-scanning direction. From this, the shift amount corresponding to each value can be specified from these four remainder values, and the division position P of the division area can be changed.

  FIG. 16 is a flowchart showing an example of the pixel number changing process according to the modification (part 1) according to the first embodiment of the present invention. FIG. 16 shows an example of the processing procedure of step S107 of FIG. 14 performed by the remainder value calculation unit 54.

  The remainder value calculating unit 54 receives the count value from the sub-scanning counter 33b, divides the received count value by a predetermined number of main scanning lines, and passes the calculated residue value to the division position changing unit 51 ( S201).

The division position changing unit 51 adds the shift amount corresponding to the received remainder value to the number of pixels in the division area 0 held by the division area pixel number holding unit 53 that is a register, and the division position P _{0 of the} division area 0 is obtained. By changing the relative pixel position on the main scanning line, the division position P of the divided area is changed for each main scanning line (step S202).

<Modification: Part 2>
FIG. 17 is a diagram showing a modification (No. 2) of the density unevenness diffusion function according to the first embodiment of the present invention. FIG. 17 shows a configuration example having a random number generation unit 55 which is a random number circuit for generating random numbers as a modification example of another density unevenness diffusion function. In addition to the modification example (part 1), Such a functional configuration may be used.

In the present modification, the divided position pixel number holding unit 53 holds the random number value generated by the random number generating unit 55 according to the counter value of the change cycle control unit 52 as the shift amount. By adding to the number of division area pixels and changing the relative pixel position on the main scanning line which is the division position P ₀ of the division area 0, the division position P of the division area is changed for each main scanning line.

  In each of the modifications described above, the same effects as those of the first embodiment can be obtained.

  So far, the present invention has been described based on the above embodiment. Among them, in the above embodiment, when changing the division position P of the divided area in the main scanning line, the division position P of each divided area in the entire main scanning line is changed based on the same shift amount. Although the density unevenness diffusion function has been described, the present invention is not limited to this method. For example, for each divided area in the main scanning line, a different shift amount may be added to each divided area pixel number to change the divided position P of the divided area, and the density unevenness occurrence position 91 in the output image is within a predetermined range. May be diffused within.

  In the above embodiment, the density unevenness diffusion function at the time of shading correction for changing the division position P of the divided area for each main scanning line has been described. However, the present invention is not limited to this method. Absent. For example, it may be a pattern in which the division positions P of a plurality of lines are changed together, such as 2 lines instead of every line. In shading correction, the occurrence position of density unevenness in the effective image area is diffused. The density unevenness may be reduced to such an extent that it cannot be visually confirmed. As described above, in the case of the method of changing the division positions P of a plurality of lines at once, the processing speed is reduced because the calculation such as the shift amount for changing is less than the change of the division position P for each main scanning line. Can be improved.

  In the above embodiment, the density unevenness diffusion function at the time of shading correction in the single-color latent image operation has been described. However, the present invention is not limited to this operation. In the case of a full-color image forming apparatus that performs an image forming operation using a plurality of constituent colors, the density unevenness diffusion function may be implemented based on the shift amount corresponding to each constituent color.

  Finally, the present invention is not limited to the requirements shown here, such as combinations of other elements with the shapes and configurations described in the above embodiments. With respect to these points, the present invention can be changed within a range that does not detract from the gist of the present invention, and can be appropriately determined according to the application form.

1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present invention. 1 is a diagram illustrating a hardware configuration example of an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the structural example of the optical apparatus which concerns on the 1st Embodiment of this invention, and its peripheral member. It is a figure which shows the structural example of ASIC for write control which concerns on the 1st Embodiment of this invention. It is a figure which shows the structural example of the output data control part which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the circuit which smoothes the PWM signal which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the output waveform from the PWM signal generation part which concerns on the 1st Embodiment of this invention. It is a figure which shows general shading correction data. It is a figure which shows the adjustment characteristic of the output light quantity with respect to a general shading characteristic. It is a figure which shows the relationship between a division position and the generation | occurrence | production position of density nonuniformity. It is a figure which shows the structural example of the density nonuniformity diffusion function which concerns on the 1st Embodiment of this invention. It is a figure which shows the operation example which changes the division position which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the result as which the density | concentration nonuniformity generation position which concerns on the 1st Embodiment of this invention was diffused. 3 is a flowchart illustrating an example of image forming processing according to the first embodiment of the present invention. It is a figure which shows the modification (the 1) of the density nonuniformity diffusion function which concerns on the 1st Embodiment of this invention. It is a flowchart which shows an example of the pixel number change process by the modification (the 1) which concerns on the 1st Embodiment of this invention. It is a figure which shows the modification (the 2) of the density nonuniformity diffusion function which concerns on the 1st Embodiment of this invention.

Explanation of symbols

1 Internal system bus 2 Local I / F
11 VPU
12 IPU
13 ASIC for write control
14 LD control unit 15 Laser diode 16 CPU
17 ROM
18 RAM
19 Image memory 20 Controller 21 Collimator lens 22 Polygon mirror 23 fθ lens 24 Photo detector 25 Light emitting unit 26 Light receiving unit 27 APC control unit 28 Drive unit 31 Memory block 32 Image processing unit 33 Output data control unit 33a: main scanning counter, 33b : Sub-scanning counter, 33c: Period detection unit 41 P pattern block 42 γ conversion block 43 APC block 44 LD on / off block 45 Gate signal generation unit 46 PWM signal generation unit 51 Division position change unit 52 Change cycle control unit (counter circuit) )
53 Divided Area Pixel Count Holding Unit (Register)
54 Remainder value calculation unit 55 Random number generation unit 61 Register 71 Shading correction data 81 Light amount adjustment signal (PWM signal for light amount adjustment)
91 Density unevenness occurrence position 100 Image forming apparatus 101 Charging device 102 Optical device 103 Developing device 104 Paper feed roller 105 Transfer device 106 Paper discharge roller 107 Photoconductor 108 Cleaning device 109 Image reading device 110 Operation panel LPF: Low-pass filter, P: Division Position, N: Number of pixels in the divided area

Claims (10)

An image forming apparatus that divides a main scanning line on a scanned surface of an image carrier into a plurality of regions, adjusts the output light amount of a light source based on light amount correction data corresponding to each region, and corrects shading characteristics in the main scanning direction. And
An output means for changing a duty value of a pulse modulation signal for each region based on the light amount correction data, and outputting a pulse modulation signal for light amount adjustment according to the changed duty value;
And changing means for changing a division position of each area in the main scanning line when adjusting the output light quantity based on the pulse modulation signal for light quantity adjustment outputted by the output means. Image forming apparatus. The changing means is
The image forming apparatus according to claim 1, wherein the division position for each main scanning line is changed so that the division position of each region is different between adjacent main scanning lines. The changing means is
3. The division position of each area is changed by adding a predetermined value to the number of pixels relatively representing the division position of each area in the pixel array constituting the main scanning line. The image forming apparatus described. The image forming apparatus is
On the main scanning line, holding means for storing and holding a shift amount representing a direction and a moving amount for moving the division position in a predetermined storage area,
The changing means is
The image according to claim 3, wherein the shift amount held by the holding unit is added to the number of pixels, and the division position of each region is periodically changed for each of a plurality of main scanning lines. Forming equipment. The image forming apparatus is
A control unit that periodically generates a numerical value of a predetermined range and controls the change of the division position,
The changing means is
The image forming apparatus according to claim 4, wherein the shift amount associated with a numerical value in a predetermined range generated by the control unit is added to the number of pixels. The image forming apparatus is
Sub-scanning line number acquisition means for counting sub-scanning lines and acquiring the number of lines;
Dividing the sub-scanning line number acquired by the sub-scanning line number acquiring unit by a predetermined number of lines, and acquiring a residual value as a calculation result,
The changing means is
The image forming apparatus according to claim 4, wherein the shift amount associated with the residue value acquired by the residue value acquisition unit is added to the number of pixels. The image forming apparatus is
Having random number generation means for generating a predetermined range of random numbers;
The changing means is
The image forming apparatus according to claim 3, wherein a random number value generated by the random number generation unit is added to the number of pixels as the shift amount. The changing means is
The image forming apparatus according to claim 1, wherein the division position is changed by a shift amount having the same value for each region. The changing means is
The image forming apparatus according to claim 1, wherein the division position is changed according to a shift amount having a different value for each region. An image in an image forming apparatus that divides a main scanning line on a scanned surface of an image carrier into a plurality of areas, adjusts an output light amount of a light source based on light amount correction data corresponding to each region, and corrects shading characteristics in a main scanning direction. A correction method,
An adjustment procedure for changing the duty value of the pulse modulation signal for each region based on the light amount correction data, outputting a pulse modulation signal for light amount adjustment according to the changed duty value, and adjusting the output light amount of the light source,
An image correction method comprising: a change procedure for changing a division position of each region in the main scanning line when the output light amount is adjusted by the adjustment procedure.

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