JP2006133677A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having electrophotographic process, such as a laser beam printer. <P>SOLUTION: The surface potential of an electrostatic latent image formed on a photoreceptor is measured, the variation of the latent image by reciprocity failure is corrected, by regulating the light quantity of laser light emitted from LEDAs (501-504), LDs (901a-901d) or the like, and difference in an image, due to difference between time intervals of writing of adjacent image data in a sub-scanning direction can be reduced. Since the occurrence of reciprocity failure is detected, without outputting an image, the time required to regulate the light quantity of laser light and the consumption of toner can be reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a laser beam printer having an electrophotographic process.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a device using a semiconductor laser has been widely put into practical use as a means for forming an electrostatic latent image after first charging a photosensitive member as an image carrier.

  In recent years, latent image forming means using a multi-laser that simultaneously emits a plurality of lasers in one main scan has been put into practical use as the image forming apparatus performs high-speed printing.

  In forming a latent image using a multi-laser, there is a problem that the halftone density is different even if there is no individual difference between laser pairs. This is a new problem that the halftone image density differs when the writing position is shifted by 1 in the sub-scanning direction even in the same image pattern. This phenomenon is caused by a curve (EV curve) of the light amount E and the potential V of the photoconductor. ) Is considered to be non-linear.

  Specifically, when forming an image on a photoconductor in latent image formation using a laser beam, an image is formed by overlapping dots in the sub-scanning direction. In that case, the time interval for writing adjacent image data in the sub-scanning direction may change. For example, when an optical scanning system has a plurality of light beams and an image is formed on a photosensitive member using a polygon mirror, when writing image data adjacent in the sub-scanning direction across one surface of the polygon mirror, There are times when writing across two mirror surfaces. At this time, the writing time interval is longer when writing is performed across two surfaces than when writing is performed across only one surface.

  As a result, due to the phenomenon of reciprocity law failure, the surface potential of the formed electrostatic latent image differs, density and latent width change, and reciprocity law is established due to the difference in the writing time interval even if the light intensity of the laser beam is constant. The image is different between the part that is formed and the part that is not formed. In addition, when they are mixed, the image is disturbed. This phenomenon becomes more conspicuous as the resolution of the image is higher (1200 dpi than 600 dpi) and appears more prominently.

  Here, the reciprocity law is a law that when the intensity of the laser beam is doubled, the same surface potential can be obtained on the photoconductor if the irradiation time of the laser beam is halved. That is, a relationship in which the surface potential of the photoconductor after irradiation is constant if the total energy of the laser beams is the same is called “reciprocity law”. And the case where the relationship is not materialized is called "reciprocity failure" (shown in FIG. 13).

Patent Document 1 discloses a latent image forming apparatus capable of high-speed printing, which can obtain a stable image regardless of the writing timing of the main scanning line, even when a latent image forming unit using a multi-laser is used. A forming apparatus, a control method for an image forming apparatus, and a process cartridge have been proposed.
JP 2002-113903 A

  However, the above invention has the following problems.

  Since the invention described in Patent Document 1 detects the influence of the reciprocity failure by the density distribution of the image output from the image forming apparatus, when the reciprocity failure occurs, after adjusting the amount of laser light, Need to output the same image. Also, the output of the image must be repeated until the image quality of the output image becomes uniform, and the light quantity cannot be adjusted quickly. Furthermore, a lot of toner is used due to repeated image output.

  Therefore, the present invention corrects the change in the latent image due to reciprocity failure by measuring the surface potential of the electrostatic latent image formed on the photoconductor and adjusting the amount of laser light emitted from the LEDA, LD, etc. An object of the present invention is to propose an image forming apparatus capable of reducing the difference in image due to the difference in the writing time interval between adjacent image data in the sub-scanning direction.

  According to a first aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an electrostatic latent image on a photoconductor, wherein the multilaser for exposing the photoconductor composed of a plurality of laser diodes is formed by the multilaser. And detecting means for detecting the surface potential of the electrostatic latent image on the photoconductor, and adjusting means for adjusting the light quantity of each laser diode in accordance with the surface potential detected by the detecting means. Features.

  According to a second aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an electrostatic latent image on a photosensitive member, a multi-laser for photosensitive member exposure composed of a plurality of laser diodes, and a laser emitted from the multi-laser. A polygon mirror that causes the laser beam to be incident on the photoconductor, a detection unit that detects a surface potential of the electrostatic latent image on the photoconductor exposed by the multi-laser, and the surface detected by the detection unit And adjusting means for adjusting the light quantity of each laser diode in accordance with the potential.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the adjustment unit is configured such that the light quantity when the adjacent laser diodes emit light simultaneously is the same when the laser diodes emit light alone. It is characterized by adjusting more than the amount of light.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the multi-laser forms an electrostatic latent image continuous in the sub-scanning direction on the photoconductor. The detecting means detects the surface potential of the electrostatic latent image formed by the simultaneous emission of the adjacent laser diodes and the surface potential of the electrostatic latent image formed by the laser diodes alone. It is characterized by that.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the total amount of laser light emitted from each of the laser diodes is constant.

  A sixth aspect of the present invention is the image forming apparatus according to any one of the first to fifth aspects, wherein the electrostatic latent image is formed by the laser diode continuous in the sub-scanning direction. .

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the image forming apparatus further includes a setting unit that sets an image forming condition, and the image forming condition is set by the setting unit. The multi-laser forms the electrostatic latent image on the photoconductor.

  The present invention measures the surface potential of the electrostatic latent image formed on the photoreceptor, and corrects the change in the latent image due to reciprocity failure by adjusting the amount of laser light emitted from the LEDA, LD, etc. An image difference due to a difference in writing time interval between adjacent image data in the sub-scanning direction can be reduced. Further, since the occurrence of reciprocity failure is detected without outputting an image, it is possible to reduce the time required for adjusting the amount of laser light and reduce the amount of toner consumed.

  The configuration and operation of the image forming apparatus according to this embodiment will be described below.

  First, the configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG.

  The image forming apparatus includes an automatic document feeder (ADF) 1, a document table 2, a paper feed roller 3, a feed belt 4, a delivery roller 5, a document set detection unit 7, a first tray 8, The second tray 9, the third tray 10, the first paper feed unit 11, the second paper feed unit 12, the third paper feed unit 13, the vertical transport unit 14, the photoconductor 15, and the transport belt 16. And a fixing unit 17, a paper discharge unit 18, a developing unit 27, a contact glass 6, an exposure lamp 51, a first mirror 52, a lens 53, a CCD image sensor 54, a second mirror 55, and a third mirror 56. Read unit 50, laser output unit 58, image forming lens 59, writing unit 57 including mirror 60, switching plate 101, normal paper discharge roller 102, transport roller (1 3, 105), a finisher 100 including a normal discharge tray 104, a stapler 106, a discharge roller 107, a staple table 108, a jogger 109, and a staple completion discharge tray 110, a duplex feeding unit 111, and a reverse unit 112. And is configured.

  Next, processing operations in the image forming apparatus will be described.

  First, a document bundle placed on the document table 2 in the automatic document feeder (hereinafter referred to as ADF) 1 with the image surface of the document facing upward is pressed when the print key 34 on the operation unit 30 is pressed. The lowermost document is fed to a predetermined position on the contact glass 6 by the feeding roller 3 and the feeding belt 4. Note that the image forming apparatus has a counting function for counting up the number of originals upon completion of feeding one original.

  Next, the document fed to a predetermined position on the contact glass 6 is read by the reading unit 50 and the document data of the document on the contact glass 6 is read. The paper is discharged through the discharge roller 5. Further, when the document set detection unit 7 detects that there is a next document on the document table 2, the document is fed onto the contact glass 6 by the same processing as the above-described document. The feeding roller 3, the feeding belt 4, and the discharging roller 5 are driven by a conveyance motor.

  The transfer sheets stacked on the first tray 8, the second tray 9, and the third tray 10 are fed by the first paper feeding device 11, the second paper feeding device 12, and the third paper feeding device 13, respectively, and are vertically conveyed. The unit 14 is transported to a position where it abuts on the photoreceptor 15.

  The document data read by the reading unit 50 is written on the photoconductor 15 by the laser from the writing unit 57 and passes through the developing unit 27 to form a toner image. Then, the toner image on the photosensitive member 15 is transferred while the transfer paper is conveyed by the conveying belt 16 at the same speed as the rotation of the photosensitive member 15. Thereafter, the image is fixed by the fixing unit 17 and is discharged by the paper discharge unit 18 to the finisher 100 serving as a post-processing device.

  The finisher 100 serving as a post-processing device can be guided to the normal paper discharge tray 102 side and the staple table 108 side. By switching the switching plate 101 upward, the transfer sheet can be discharged to the normal discharge tray 104 side via the transport roller 103. Further, by switching the switching plate 101 downward, the transfer sheet can be conveyed to the staple table 108 via the conveyance rollers (105, 107).

  The transfer paper loaded on the staple table 108 is aligned by the paper jogger 109 each time it is discharged, and is bound by the stapler 106 upon completion of a partial copy. The group of transfer sheets bound by the stapler 106 is stored in the staple completion discharge tray 110 by its own weight.

  On the other hand, the normal paper discharge tray 104 is a paper discharge tray that can be moved back and forth. The copy paper that moves back and forth for each original or for each copy section sorted by the image memory is simply discharged. Will be sorted.

  When images are formed on both sides of the transfer paper, the reversing unit 112 for switching the path is used without guiding the transfer paper fed and formed from the respective paper feed trays (8 to 10) to the discharge tray 104 side. Is set on the upper side, and the transfer paper is once stocked in the duplex feeding unit 111. Then, in order to transfer the toner image formed on the photosensitive member 15 to the transfer paper stocked on the double-sided paper feed unit 111, the transfer paper stocked on the double-sided paper feed unit 111 is fed again, and the path The reversing unit 112 for switching is set on the lower side, and the transfer paper on which images are transferred on both sides is guided to the paper discharge tray 104.

  In this way, the double-sided paper feeding unit 111 is used when creating images on both sides of the transfer paper.

  Next, processing operations from the time of document reading to the time of image writing will be described.

  The reading unit 50 includes a contact glass 6 on which an original is placed and an optical scanning system. The optical scanning system includes an exposure lamp 51, a first mirror 52, a lens 53, a CCD image sensor 54, and the like. It is configured. The exposure lamp 51 and the first mirror 52 are fixed on a first carriage (not shown), and the second mirror 55 and the third mirror 56 are fixed on a first carriage (not shown).

  When reading a document image, the first carriage and the second carriage are mechanically operated at a relative speed of 2: 1 so that the optical path length does not change. This optical scanning system is driven by a scanner drive motor (not shown). The document image is read by the CCD image sensor 54, converted into an electrical signal, and processed.

  The writing unit 57 includes a laser output unit 58, an imaging lens 59, and a mirror 60. Inside the laser output unit 58, a laser diode that is a laser light source and a polygon mirror that is rotated at a constant speed by a motor. (Polygon mirror) is installed. The laser light emitted from the laser output unit 58 is polarized by a polygon mirror that rotates at a constant speed, passes through an imaging lens 59, is folded by a mirror 60, and is focused and imaged on the surface of the photoreceptor.

  The polarized laser light is exposed and scanned in the direction (main scanning direction) perpendicular to the direction in which the photosensitive member rotates, and the line-by-line recording of the image signal output from the selector 64 of the image processing unit described later is performed. An image (electrostatic latent image) is formed on the surface of the photosensitive member by repeating main scanning at a predetermined cycle corresponding to the rotational speed and recording density of the photosensitive member.

  As described above, the laser beam output from the writing unit 57 is applied to the image forming photoconductor 15. Although not shown, a beam sensor for generating a main scanning synchronization signal is disposed at a position where a laser beam near one end of the photoconductor 15 is irradiated. Based on the main scanning synchronization signal, control of image recording start timing in the main scanning direction and generation of a control signal for inputting / outputting image signals described later are performed.

  FIG. 2 illustrates a control device with a main controller as a center. The main controller 20 controls the entire image forming apparatus. A main motor 25 and various clutches 21 to 24 necessary for paper conveyance and the like are connected to the main controller 20. Further, an image processing unit (IPU) that performs display for an operator, an operation unit 30 that performs function setting input control from the operator, control of a scanner, control for writing a document image into an image memory, control for image formation from an image memory, and the like. 49, a distributed control device such as an automatic document feeder (ADF) 1 is connected. Each distributed controller and the main controller 20 exchange machine status and operation commands as necessary. A control program executed by each distributed control device is stored in a ROM inside each distributed control device. An IC card slot 27 is connected to the main controller 20, and control program data stored in an IC card outside the image forming apparatus is downloaded to the ROM inside the distributed control apparatus via the IC card slot 27 for control. It is possible to change the program.

  The configuration of the image processing unit (image reading unit and image writing unit) according to the present embodiment will be described with reference to FIG. The light emitted from the exposure lamp 51 illuminates the original surface, and the reflected light from the original surface is imaged and received by a CCD image sensor 54 with an imaging lens (not shown), and is photoelectrically converted. The digital signal is converted by the D converter 61. The image signal converted into the digital signal is subjected to shading correction 62 and then subjected to MTF correction, γ correction and the like in the image processing unit 63. In the selector 64, the destination of the image signal is switched to the writing γ correction unit 71 or the image memory controller 65. The image signal that has passed through the writing γ correction unit 71 is sent to the writing unit 57. Between the image memory controller 65 and the selector 64, an image signal can be input and output bidirectionally. Although not explicitly shown in FIG. 3, in addition to the original data input from the reading unit 50, original data supplied from the outside (for example, output from a data processing device such as a personal computer) is output to the image processing unit (IPU). A function of selecting input / output of a plurality of data so that data can be processed.

  A CPU 68 for setting the image memory controller 65 and the like and controlling the reading unit 50 and the writing unit 57, and a ROM 69 and a RAM 70 for storing programs and data thereof are provided. Further, the CPU 68 can write and read data in the image memory 66 via the memory controller 65. In addition, an HDD 73 for storing the contents of the image memory 66 is provided. The HDD 73 stores document data and the like written to the image memory 66. The RAM 70 also includes NV-RAM.

  Next, a specific configuration and operation of the writing unit 57 that is a characteristic part of the image forming apparatus according to the present embodiment will be described.

  FIG. 4 is a diagram showing a specific configuration of the writing unit 57 according to the present embodiment. The writing unit 57 includes an LD unit 400, an exhaust fan 401, a polygon motor driver 402, a polygon motor 403, an fθ lens (404, 405), a BTL lens 406, a third mirror 407, a photosensitive drum 408, a second mirror 409, and a dust proof. A glass 410, a first mirror 411, a synchronization detection sensor 412, a cylinder lens 413, an intake fan 414, and a dustproof filter 415 are provided. In this embodiment, the photosensitive member 15 is exposed to laser light using an LED array composed of LEDs 501 to 504 shown in FIG. Exposure of laser light from the LEDA 501 to 504 is controlled by an LED board (shown in FIG. 6) 600 that receives image data from an image processing unit (IPU) 49. The LED board 600 includes a power modulation 601, an LED (LED Drive) 602, an LED controller 603, and LEDA (LED Array) 501 to 504.

  The writing unit 57 uniformly charges the photoconductor 15 and forms an electrostatic latent image on the photoconductor 15 by the laser beam from the LD unit 400. The electrostatic latent image formed on the photoconductor 15 is converted into a toner image by the developing unit 27, the toner image is transferred to a transfer sheet, the image is fixed by the fixing unit 17, and the post-processing device is output by the paper discharge unit 18. The finisher 100 is discharged.

  Here, in a conventional image forming apparatus, when a horizontal line of 2 dots and 2 spaces is scanned with a multi-laser beam, portions having different densities are generated. Specifically, the density of 2 dots and 2 spaces irradiated simultaneously with two laser beam pairs in the main scanning line direction was lower than that of 2 dots and 2 spaces irradiated alternately with laser beams. This is because the spot diameter of the LED array to be used is not sufficiently small, so that the spots of the two pairs of laser beams are overlapped, and the potentials are different at the overlapping portions.

  When the beams are simultaneously irradiated, the overlapping portion of the spots is irradiated after the light amounts are combined, and holes are generated at the same time. On the other hand, when individually irradiated, holes are generated after the first beam is applied to the photoconductor, and then holes are generated after the next beam is applied to the photoconductor. That is, the total amount of light is the same in the spot overlapping portion, but if irradiated simultaneously, the strong light hits the photosensitive member only once, and if irradiated individually, weak light hits the photosensitive member twice.

  In other words, in the case of multi-beams, even when the two pairs of beams are exposed at the same time and when they are individually exposed, even if the amount of light is the same, due to the reciprocity failure of the photoconductor, the potential of the simultaneous exposure is higher than the potential of the individual exposure. Is high and sensitivity is poor.

  However, in this embodiment, the surface potential of the electrostatic latent image formed on the photoconductor 15 is statically adjusted when the laser beam is irradiated by adjusting the amount of laser light when the laser beam is alternately irradiated. By matching the surface potential of the electrostatic latent image, the image quality of the output image due to reciprocity failure is kept uniform.

  When 2 dots and 2 lines are exposed on the photoreceptor 15 in the LED array shown in FIG. 5, there are four patterns of LEDA 501 and 502, LEDA 502 and 503, LEDA 503 and 504, and LEDA 504 and 501. Here, LEDA 501 and 502, LEDA 502 and 503, and LEDA 503 and 504 are simultaneously written. However, in the case of LEDA 504 and 501, scanning by LEDA 504 and exposure by LEDA 501 are not performed at the same time. The phenomenon occurs.

  Therefore, in the image forming apparatus according to the present embodiment, the surface potential of at least one of the electrostatic latent images among the LEDA 501 and 502, the LEDA 502 and 503, and the LEDA 503 and 504 is measured, and the electrostatic potential exposed by the LEDA 504 and 501 is measured. The light quantity of the LEDA 504 or 501 is adjusted so that the surface potential of the latent image approaches the measured surface potential. In the present embodiment, the surface potential of the electrostatic latent images exposed by the LEDs 504 and 501 is adjusted by adjusting the light amount of the LEDA 501.

Specifically, a 2-dot, 2-line electrostatic latent image using LEDs 501 to 504 was formed under the following conditions.
Charging potential: -800V
Surface potential of electrostatic latent image: -100V
Resolution: 1200 dpi,
Light amount (photosensitive member surface): 0.44 μJ / cm ²
Beam diameter in the sub scanning direction: 70 μm,
Beam diameter in the main scanning direction: 55 μm,
Write time interval: simultaneous writing for LEDA 501 and 502, LEDA 502 and 503, and LEDA 503 and 504, time difference of about 1/4000 sec (photosensitive linear velocity 340 mm / sec) for LEDA 504 and 501,
Light amount adjustment value: Only when LEDA 504 and 501 are used to form a latent image (dot, line, solid, etc.), only LEDA 501 is fixed at -25% (according to PM 601).

  FIG. 7 shows an image when a 2-dot, 2-line electrostatic latent image (test pattern) is formed under the above conditions. According to FIG. 7, the widths of 2 dots and 2 lines of the LEDA 501 and 502, the LEDA 502 and 503, and the LEDA 503 and 504 that did not change the light amount were about 85 μm. On the other hand, the widths of 2 dots and 2 lines of the LEDA 504 and 501 whose light amount was changed were about 100 μm before the light amount change, but about 85 μm after the light amount change. In other words, by measuring the surface potential of the electrostatic latent image formed by exposing the laser beam at the same time and adjusting the amount of laser beam when performing laser beam exposure with a time difference, the image quality of the output image Can be kept uniform.

  In the present embodiment, the adjustment of the light amount by the four arrays has been introduced. However, since the light amount is not a fixed value and is changed only when necessary, it can be applied to two arrays. In addition, the phenomenon of reciprocity failure occurs even in an image with a resolution of 600 dpi, but since the original line width is thick, the influence of the phenomenon is small and inconspicuous. Therefore, when the resolution is low, the change amount of the light amount may be small. Further, when the time difference is shorter than 1/4000 sec, the change amount of the light amount may be small.

  In the adjustment of the light amount of the LEDA 504 and 501 described above, when the IPU 49 performs image processing, it recognizes from the coordinates whether the image is written by the LEDA 504 and 501 and suppresses the phenomenon of reciprocity failure only when necessary. Therefore, complicated control is required, and quick handling is difficult.

  Therefore, the light amounts of the LEDA 504 and 501 are uniformly reduced with respect to the standard light amount (LEDA504 = LEDA501), and the light amounts of the LEDA502 and 503 are increased with respect to the standard light amount. (LEDA502 = LEDA503) However, the decrease rate with respect to the standard light amount of LEDA501 and the increase rate with respect to the standard light amount of LEDA503 are made equal so that the total light amount of LEDA501 to 504 before and after the light amount adjustment does not change. (Before adjustment LEDA501 + LEDA502 + LEDA503 + LEDA504 = before adjustment LEDA501 + LEDA502 + LEDA503 + LEDA504)

Specifically, a 2-dot, 2-line electrostatic latent image using LEDs 501 to 504 was formed under the following conditions.
Charging potential: -800V
Surface potential of electrostatic latent image: -100V
Resolution: 1200 dpi,
Light amount (photosensitive member surface): 0.44 μJ / cm ²
Beam diameter in the sub scanning direction: 70 μm,
Beam diameter in the main scanning direction: 55 μm,
Write time interval: simultaneous writing for LEDA 501 and 502, LEDA 502 and 503, and LEDA 503 and 504, time difference of about 1/4000 sec (photosensitive linear velocity 340 mm / sec) for LEDA 504 and 501,
Light amount adjustment value: When a latent image is formed using LEDA 504 and 501 (dot, line, solid, etc.), LEDA 504 and 501 are fixed to -11% (by PM601) with respect to the standard light amount, and LEDA 502 and 503 are used. When forming a latent image (dots, lines, solids, etc.), LEDA 502 and 503 are fixed at + 11% (by PM 601) with respect to the standard light amount.

  FIG. 8 shows an image when a 2-dot, 2-line electrostatic latent image (test pattern) is formed under the above conditions. According to FIG. 8, the widths of 2 dots and 2 lines of the LEDs 501 and 502 and the LEDs 503 and 504 whose light amounts were not changed were about 85 μm. On the other hand, the widths of 2 dots and 2 lines of the LEDA 504 and 501 whose light amount was changed were about 100 μm before the light amount change, and about 92 μm after the light amount change. Further, the widths of 2 dots and 2 lines of the LEDA 502 and 503 in which the light amount was changed were about 85 μm before the light amount change, but about 91 μm after the light amount change. That is, by adjusting the light amount of the laser light emitted from each LEDA with respect to the standard light amount, it is possible to reduce degradation of the output image due to reciprocity failure without complicated control.

  Although a reciprocity failure phenomenon occurs even in an image with a resolution of 600 dpi, the original line width is thick, so the influence of the phenomenon is small and is not noticeable. Therefore, when the resolution is low, the change amount of the light amount may be small. Further, when the time difference is shorter than 1/4000 sec, the change amount of the light amount may be small.

  Next, the case where an electrostatic latent image is formed by the writing unit 57 shown in FIG. 9 will be described. A writing unit 57 shown in FIG. 9 includes a photodiode 900, an LD beam 901, an aperture 902, a collimating lens 903, and a laser diode 904. Note that the LD beam 901 includes LDs 901a to 901d. The LD array 901 is controlled by the LD board 1000 shown in FIG. The LD board 1000 includes a PWM (pulse width modulation) 1001, an LDD (LD lighting control) 1002, and an LD controller 1003.

  When exposing 2 dots and 2 lines on the photoconductor 15 with the LD beam (901a to 901d) shown in FIG. 9, exposure is performed using the LD901a and 901b, LD901b and 901c, and LD901c and 901d on the same polygon mirror surface. There are two patterns that are exposed using the LDs 901d and 901a on the two polygon mirror surfaces. Here, LD 901a and 901b, LD 901b and 901c, and LD 901c and 901d are simultaneous writing, but in the case of LD 901d and 901a, scanning by LD 901d and exposure by LD 901a are not performed simultaneously, so the reciprocity law introduced earlier. A failure phenomenon occurs.

  Therefore, in the image forming apparatus according to the present embodiment, the surface potential of at least one of the electrostatic latent images among the LDs 901a and 901b, the LDs 901b and 901c, and the LDs 901c and 901d is measured, and the electrostatic potential exposed by the LDs 901d and 901a is measured. The light amounts of the LDs 901d and 901a are adjusted so that the surface potential of the latent image approaches the measured surface potential. In the present embodiment, the surface potential of the electrostatic latent images exposed by the LDs 901d and 901a is adjusted by adjusting the light quantity of the LD 901a.

Specifically, a 2-dot, 2-line electrostatic latent image using LDs 901a to 901d was formed under the following conditions.
Charging potential: -800V
Surface potential of electrostatic latent image: -100V
Resolution: 1200 dpi,
Light amount (photosensitive member surface): 0.44 μJ / cm ²
Beam diameter in the sub-scanning direction: 70 μm
Beam diameter in the main scanning direction: 55 μm,
Write time interval: LD901a and 901b, LD901b and 901c, LD901c and 901d, simultaneous writing, LD901d and 901a, a time difference of about 1/4000 sec (photosensitive linear velocity 340 mm / sec),
Light amount adjustment value: Only when LD 901d and 901a are used to form a latent image (dot, line, solid, etc.), LD 901a only is fixed to -25% (according to PM1003).

  FIG. 11 shows an image when a 2-dot, 2-line electrostatic latent image (test pattern) is formed under the above conditions. According to FIG. 11, the widths of 2 dots and 2 lines of the LDs 901a and 901b, the LDs 901b and 901c, and the LDs 901c and 901d that did not change the light amount were about 85 μm. On the other hand, the widths of 2 dots and 2 lines of the LDs 901d and 901a in which the light amount was changed were about 100 μm before the light amount change, but about 85 μm after the light amount change. In other words, by measuring the surface potential of the electrostatic latent image formed by exposing the laser beam at the same time and adjusting the amount of laser beam when performing laser beam exposure with a time difference, the image quality of the output image Can be kept uniform.

  In the present embodiment, the adjustment of the amount of light by the four beams has been introduced. However, the amount of light is not a fixed value but is changed only when necessary, and can be applied to two beams. In addition, the phenomenon of reciprocity failure occurs even in an image with a resolution of 600 dpi, but since the original line width is thick, the influence of the phenomenon is small and inconspicuous. Therefore, when the resolution is low, the change amount of the light amount may be small. Further, when the time difference is shorter than 1/4000 sec, the change amount of the light amount may be small.

  In adjusting the light amount of the LD 901d and 901a described above, when the IPU 49 performs image processing, it recognizes from the coordinates whether the image is written by the LD 901d and 901a, and suppresses the phenomenon of reciprocity failure only when necessary. Therefore, complicated control is required, and quick handling is difficult.

  Therefore, the light amounts of the LDs 901d and 901a are uniformly reduced with respect to the standard light amount (LD901d = LD901a), and the light amounts of the LDs 901b and 901c are increased with respect to the standard light amount. (LD901b = LD901c) However, the decrease rate of the LD901a with respect to the standard light amount and the increase rate of the LD901c with respect to the standard light amount are made equal so that the total light amount of the LDs 901a to 901d before and after the light amount adjustment does not change. (Before adjustment LD901a + LD901b + LD901c + LD901d = After adjustment LD901a + LD901b + LD901c + LD901d)

Specifically, a 2-dot, 2-line electrostatic latent image using LDs 901a to 901d was formed under the following conditions.
Charging potential: -800V
Surface potential of electrostatic latent image: -100V
Resolution: 1200 dpi,
Light amount (photosensitive member surface): 0.44 μJ / cm ²
Beam diameter in the sub scanning direction: 70 μm,
Beam diameter in the main scanning direction: 55 μm,
Write time interval: LD901a and 901b, LD901b and 901c, LD901c and 901d, simultaneous writing, LD901d and 901a, a time difference of about 1/4000 sec (photosensitive linear velocity 340 mm / sec),
Light amount adjustment value: When forming a latent image using the LDs 901d and 901a (dot, line, solid, etc.), the LDs 901d and 901a are fixed at -11% (by PM1003) with respect to the standard light amount, and the LDs 901b and 901c are used. When forming a latent image (dots, lines, solids, etc.), LDs 901b and 901c are fixed at + 11% (according to PM1003) with respect to the standard light amount.

  FIG. 12 shows an image when a 2-dot, 2-line electrostatic latent image (test pattern) is formed under the above conditions. According to FIG. 12, the widths of 2 dots and 2 lines of the LDs 901 a and 901 b and the LDs 901 c and 901 d that did not change the light amount were about 85 μm. On the other hand, the widths of 2 dots and 2 lines of the LDs 901d and 901a whose light amounts were changed were about 100 μm before the light amount change, but about 92 μm after the light amount change. Further, the widths of 2 dots and 2 lines of the LDs 901b and 901c in which the light amount was changed were about 85 μm before the light amount change, but about 91 μm after the light amount change. That is, by adjusting the amount of laser light emitted from each LD with respect to the standard amount of light, it is possible to reduce degradation of the output image due to reciprocity failure without complicated control.

  Although a reciprocity failure phenomenon occurs even in an image with a resolution of 600 dpi, the original line width is thick, so the influence of the phenomenon is small and is not noticeable. Therefore, when the resolution is low, the change amount of the light amount may be small. Further, when the time difference is shorter than 1/4000 sec, the change amount of the light amount may be small.

  Note that the photoreceptor sensitivity and development γ vary with time and environment. Therefore, in the case of an image forming apparatus that performs an image forming condition adjustment operation (process control), the light amount adjustment operation of each light beam is performed subsequent to the end of the image forming condition adjustment operation, so that the photosensitive member sensitivity and development γ at that time are adjusted. Since the light amount can be set in accordance with (development characteristics with respect to the development potential), the effect is further increased.

1 is a schematic view of an image forming apparatus according to an embodiment. 2 is a block diagram illustrating a configuration of a control device of the image forming apparatus according to the present exemplary embodiment. FIG. 2 is a block diagram illustrating a configuration of an image processing unit of the image forming apparatus according to the present exemplary embodiment. FIG. It is the schematic of the writing unit which concerns on this embodiment. It is the schematic of the LED array which concerns on this embodiment. It is a block diagram which shows the structure of the LED board which concerns on this embodiment. It is an electrostatic latent image (test pattern) of 2 dots and 2 lines. It is an electrostatic latent image (test pattern) of 2 dots and 2 lines. It is the schematic of the writing unit which concerns on this embodiment. It is a block diagram which shows the structure of the LD board which concerns on this embodiment. It is an electrostatic latent image (test pattern) of 2 dots and 2 lines. It is an electrostatic latent image (test pattern) of 2 dots and 2 lines. It is a 2 dot, 2 line electrostatic latent image (test pattern) by a conventional image forming apparatus.

Explanation of symbols

400 LD unit 401 Exhaust fan 402 Polygon motor driver 403 Polygon motor 404, 405 fθ lens 406 BTL lens 407 Third mirror 408 Photosensitive drum 409 Second mirror 410 Dust-proof glass 411 First mirror 412 Synchronization detection sensor 413 Cylinder lens 414 Intake fan 415 Dust-proof filter 501, 502, 503, 504 LEDA
600 LED board 601 PM
602 LED
603 LED Controller
900 photodiode 901 LD array 901a to 901d LD
902 Aperture 903 Collimating lens 904 Laser diode 1000 LDB
1001 PWM
1002 LDD
1003 PM
1004 LD Controller

Claims (7)

In an electrophotographic image forming apparatus that forms an electrostatic latent image on a photoreceptor,
A multi-laser for exposing a photoreceptor composed of a plurality of laser diodes;
Detecting means for detecting a surface potential of the electrostatic latent image on the photoreceptor formed by the multi-laser;
An image forming apparatus comprising: an adjusting unit that adjusts a light amount of each laser diode according to the surface potential detected by the detecting unit. In an electrophotographic image forming apparatus that forms an electrostatic latent image on a photoreceptor,
A multi-laser for exposing a photoreceptor composed of a plurality of laser diodes;
A polygon mirror that causes laser light emitted from the multi-laser to enter the photoreceptor;
Detecting means for detecting a surface potential of the electrostatic latent image on the photoconductor exposed by the multi-laser;
An image forming apparatus comprising: an adjusting unit that adjusts a light amount of each laser diode according to the surface potential detected by the detecting unit. The adjusting means includes
3. The image forming apparatus according to claim 1, wherein the amount of light when the adjacent laser diodes emit light simultaneously is adjusted to be larger than the amount of light when the laser diodes emit light alone. The multi-laser forms a continuous electrostatic latent image on the photoconductor in the sub-scanning direction,
The detecting means detects a surface potential of an electrostatic latent image formed by light emission of the adjacent laser diodes simultaneously and a surface potential of an electrostatic latent image formed by light emission of the laser diodes alone. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein the total amount of laser light emitted from each of the laser diodes is constant.   The image forming apparatus according to claim 1, wherein the electrostatic latent image is formed by the laser diode continuous in a sub-scanning direction. Having setting means for setting image forming conditions;
7. The image formation according to claim 1, wherein after the image forming condition is set by the setting unit, the multi-laser forms the electrostatic latent image on the photosensitive member. apparatus.

Images