JP2010069668A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device for which the beam intensity deviation of an optical spot on a scanned surface is stabilized sequentially without manufacturing a polygon mirror whose reflection factor differs partially without attaching a filter separately and without making the polygon mirror large. <P>SOLUTION: The image formation device includes a light source means for generating a luminous flux, a deflection means for performing a reflection scan of the luminous flux coming from the light source means, a scan imaging optical means for condensing the luminous flux coming from the reflection means on the scanned surface as an optical spot and makes the optical spot scan the scanned surface, a scan position sensing means for detecting the scan position of the optical spot, a memory means for memorizing a light-amount correction data of the light source means given beforehand for every section wherein all scan positions of the optical spot detected with the scan position sensing means are partitioned into a predetermined number, and a control means for controlling the light amount of the light source means corresponding to each partitioned section from the light-amount correction data stored in the memory means. In the image formation device, the light-amount correcting data given beforehand is set by adding a predetermined light-amount deviation to the correction data for correcting a shading characteristic for every partitioned section. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a beam scanning image forming apparatus such as a laser printer, a digital copying machine, and a facsimile machine.

In a beam scanning type image forming apparatus, when a beam is scanned on a surface to be scanned through constituent optical components such as a mirror or a lens, the transmittance and reflectance of each optical component varies depending on the incident angle of the beam. There was a problem that the light quantity deviation occurred on the surface.
More specifically, use of light such as reflectance and transmittance of optical elements such as a polygon mirror 28, a polygon mirror shield glass, an imaging lens, a reflection mirror, a barrel toroidal lens, and a translucent dustproof member (dustproof glass) through which a laser beam passes. Since the rate varies depending on the incident angle of light to the optical element, the intensity of the laser beam varies depending on the image height.
FIG. 9 is a diagram showing the light amount deviation on the surface to be scanned.
The laser beam intensity according to the image height is expressed on the surface to be scanned (the surface of the photosensitive drum 100) when the laser diode included in each light source of the image forming apparatus is illuminated with the same light amount at the entire image height.
In FIG. 9, the center of the photosensitive drum 100 in the main scanning direction is set to an image height of 0, the photodetection device 101 is at the position of the image height of −160, and an effective writing is performed in the range from the image height of −150 to the image height of +150. It becomes an area.
In order to solve such a problem, Patent Document 1 is given in advance corresponding to the scanning position detection means for detecting the scanning position of the light spot and the scanning position of the light spot detected by the scanning position detection means. A storage means for storing the light amount correction data of the light source, and a control means for controlling the light amount of the light source corresponding to the scanning position of the light spot based on the light amount correction data stored in the storage means. A forming apparatus is described.

FIG. 10 is a diagram showing light amount correction data in the image forming apparatus.
By controlling the light amount of the light source for each scanning position of the light spot according to the light amount correction data shown in FIG. 10, it is possible to suppress the light amount deviation between the scanning positions of the surface to be scanned.
However, when the polygon mirror is operated for a long period of time, partial fogging occurs on the mirror surface of the polygon mirror due to the influence of the wind pressure when the polygon mirror rotates, and the reflectivity of the portion where the fogging occurs is reduced. This fogging progresses with the driving time, and accordingly, the reflectivity of the mirror surface of the polygon mirror decreases. Since the conventional technology does not consider the influence of the fogging of the polygon mirror, the fogging progresses with time as the polygon mirror is operated for a long time, and the reflectance of the polygon mirror mirror surface in the cloudy part decreases. As the reflectivity decreases, the beam intensity of the light spot on the scanned surface corresponding to the cloudy position of the mirror surface of the polygon mirror decreases, and the beam intensity deviation of the light spot on the scanned surface increases. Has the problem of appearing as shading in the image.
As means for avoiding deterioration of image quality due to cloudiness of the polygon mirror, there are the following inventions.
In Patent Document 2, in a deflection scanning device that rotationally drives a polygon mirror to deflect and scan a light beam, an unused area that is not used for deflecting and scanning the light beam is provided on a part of each mirror surface of the polygon mirror. A deflection scanning device is described.
Further, Patent Document 3 is provided with a reflecting surface for reflecting a light beam, and is used for writing an electrostatic latent image and a writing area for reflecting an optical beam used for writing an electrostatic latent image. In a polygon mirror provided with a non-writing area for reflecting a non-light beam on a reflecting surface, a first portion having a first reflectance and a second portion having a second reflectance lower than the first reflectance A polygon mirror characterized by being provided in the writing area is described.
JP 2000-0771010 A Japanese Patent Application Laid-Open No. 07-199106 JP 2004-233554 A

However, as in the inventions described in Patent Documents 2 and 3, when the part of the polygon mirror where the fogging occurs is set as a non-writing area, the entire reflecting surface is secured in order to secure a necessary and sufficient writing area. The polygon mirror is enlarged. In addition, it is costly to manufacture a polygon mirror having different reflectivities on the same surface, to provide a filter for changing the reflectivity, and to provide a plurality of light emitting means.
In view of such circumstances, the present invention reduces the beam intensity deviation of the light spot on the surface to be scanned without manufacturing a polygon mirror having partially different reflectivity, providing a separate filter, or enlarging the polygon mirror. An object of the present invention is to provide an image forming apparatus stabilized over time.

In order to solve the above problems, the invention described in claim 1 is directed to a light source means for generating a light beam, a deflecting means for deflecting and scanning the light beam from the light source means, and a light beam from the deflecting means on the surface to be scanned. Scanning imaging optical means for focusing as a light spot and scanning the scanned surface with the light spot, scanning position detecting means for detecting the scanning position of the light spot, and the scanning position detecting means For each section obtained by dividing the entire scanning position of the light spot into a predetermined number, the storage unit stores light amount correction data of the light source unit given in advance, and based on the light amount correction data stored in the storage unit, And a control unit that controls the light amount of the light source unit corresponding to each divided section. The light amount correction data given in advance is further provided for each of the divided sections. To have a light amount difference, it characterized in that it is set.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the light amount deviation is a light amount deterioration amount of the light spot in a predetermined period after the start of use of the image forming apparatus in each section. It is characterized by an image forming apparatus which is substantially half.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, in the divided section, the light quantity deviation in the section where the amount of fog of the deflecting unit exceeds a predetermined value is different. It is characterized in that it is set to be larger than this section.
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the divided section is determined in accordance with the position and size of the fog of the deflecting unit.

  According to the present invention, the change in the light amount deviation between the scanning positions over time during the guarantee period of the image forming apparatus is reduced without increasing the size of the polygon mirror, and the image density due to the difference in the light amount at each scanning position. Nonuniformity can be reduced and image quality can be improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of a print control unit in the image forming apparatus of the present invention.
The print control unit is not limited to that shown in FIG. 1, but only the portion related to the present invention is shown in FIG.
First, the clock generation circuit 50 is constituted by a crystal oscillator or a PLL frequency synthesizer, and generates a print pixel clock LDCLK.
The print pixel clock LDCLK is synchronized with the timing of the synchronization detection signal (synchronization detection pulse signal) XDETP from the light detector 35 in the clock synchronization circuit 51 and becomes the laser beam modulation clock LDCLK1.
The synchronization detection pulse signal XDETP from the optical detector 35 is synchronized with the laser beam modulation clock LDCLK1 by the clock synchronization circuit 50 and becomes the main scanning start signal LCLR.
The laser beam modulation clock LDCLK1 and the main scanning start signal LCLR are output to an image input unit (not shown), and are used as a clock and a synchronization signal for synchronizing image data with image writing in the image input unit.
That is, the image input unit starts transfer of image data for one line to the print control unit by the main scanning start signal LCLR, and transfers image data to the print control unit in synchronization with the laser beam modulation clock LDCLK1. Do.
Further, the main scanning start signal LCLR from the clock synchronization circuit 50 is also output to the reset terminal of the first counter 52 to reset the first counter 52.

The first counter 52 is a so-called main scanning counter, and is a binary counter that is reset by the main scanning start signal LCLR from the clock synchronization circuit 51 and incremented by the laser beam modulation clock LDCLK1 from the clock synchronization circuit 51. The main scanning position of the laser beam can be determined from the count value.
The first counter 52 has a number of bits that does not overflow during scanning of one line.
The number of bits is 14 bits if an image is printed at 800 dpi on a printing paper with a main scanning direction of 297 mm.
Two comparators 53 and 54 are connected to the first counter 52, and the first comparator 53 generates a forced drive signal BD of the LD 59 for synchronous detection of the laser beam.
The first comparator 53 is connected to a CPU (Central Processing Unit) 55, which is a numerical value setting means for variably setting the numerical value B, via a register 56.
The first comparator 53 compares the count value A of the first counter 52 with the numerical value B preset in the first comparator 53 variably by the CPU 55, and when the set value B exceeds the set value B, The output signal BD becomes active.
The output signal BD of the first comparator 53 is logically ORed with the image data from the image input unit by the OR gate 57 as a beam detection signal, and the LD modulator 58 receives the LD (Laser) based on the output signal of the OR gate 57. Diode) 59 is driven to emit light.
Therefore, the LD 59 is forcibly driven by the forcible lighting signal from the OR gate 57 and is lit.

When a laser beam from the LD 59 that is forcibly turned on by a forcible drive signal from the OR gate 57 enters a light receiving portion of a photodetector described later, a beam detection signal (synchronous detection signal) output from the photodetector. XDETP becomes active.
The beam detection signal XDETP is synchronized with the laser beam modulation clock LDCLK1 by the clock synchronization circuit 51, is output as the main scanning start signal LCLR, and the first counter 52 is reset.
The forcible drive signal BD of the LD 59 is an output signal of the first comparator 53. The first comparator 53 compares the count value A of the first counter 52 with a numerical value B preset in a variable manner by the CPU 55. Since the output signal becomes active when the count value A is larger than the set value B, when the first counter 52 is reset, the forced drive signal BD is negated and the LD 59 is turned off.
When the first counter 52 is reset, the first counter 52 resumes counting the laser beam modulation clock LDCLK1 from the clock synchronization circuit 51. Therefore, the counting operation of the first counter 52 is performed for each surface of the polygon mirror. Will be repeated.
At this time, the forced driving timing of the LD 59 is such that the laser beam scanned on the next surface of the polygon mirror reaches the light receiving portion of the photodetector after the scanning beam from the polygon mirror passes through the effective writing area. Since it is necessary to prevent the flare from occurring, the laser beam scanned on the next surface of the polygon mirror reaches the timing just before the light receiving portion (PIN photodiode) of the photodetector. The CPU 55 sets a set value B.

The second comparator 54 generates an effective write area signal LGATE. The period during which the effective write area signal LGATE is at a high level indicates an effective write area.
The second comparator 54 is connected to a CPU 55 as a numerical value setting means for variably setting numerical values C and D via a register 56.
The second comparator 54 compares the count value A of the first counter 52 with numerical values C and D that are variably set in the second comparator 54 by the CPU 55, and the count value A is greater than or equal to the set value C. In addition, the output signal LGATE becomes active during a period that is not more than the set value D.
The CPU 55 converts the distance from the light detector to the position where the effective writing area starts and the distance from the light detector to the position where the effective writing area ends as numerical values C and D, respectively, and converts them into the number of clocks. Since writing is performed to the second comparator 54, the effective writing area signal LGATE indicates that the scanning position of the laser beam is in the effective writing area.
The effective write area signal LGATE from the second comparator 54 is applied to the second counter 60.

Further, when the count value A of the first counter 52 matches the set value C, the second comparator 54 generates a pulse signal indicating that the scanning position of the laser beam is at the start position of the effective writing area. The pulse signal is logically ORed with the output signal of the third comparator 62 by an OR gate 61.
The output signal of the OR gate 61 is applied to the reset input terminal of the second counter 60 and the count clock input terminal of the third counter 63.
The second counter 60 and the third comparator 62 constitute means for dividing the entire effective writing area into a plurality of equal intervals according to the image height.
First, the second counter 60 receives the valid write area signal LGATE from the second comparator 54 as an enable signal, and performs a count operation when the valid write area signal LGATE is negative, that is, outside the valid write area. Do not do.
The second counter 60 is reset by the output signal of the OR gate 61 when the effective write area signal LGATE from the second comparator 54 becomes active, and at the same time, modulates the laser beam from the clock synchronization circuit 51. The count of the clock LDCLK1 is started.
The count value of the second counter 60 is output to the third comparator 62, and a CPU 55, which is a numerical value setting means for variably setting the numerical value F, is connected to the third comparator 62 via the register 56. Yes.

The third comparator 62 compares the count value E of the second counter 60 with the numerical value F preset in the third comparator 62 variably by the CPU 55, and when the count value E matches the set value F A pulse signal WIDTH for dividing the effective writing area is generated.
The CPU 55 converts the width for dividing the effective writing area at equal intervals into the number of clocks LDCLK1 and writes it in the register 56 as a numerical value F in advance.
The pulse signal WIDTH from the third comparator 62 is logically ORed with a pulse signal indicating that the scanning position of the laser beam from the second comparator 54 is at the start position of the effective writing area by the OR gate 61. The output signal of the OR gate 61 is applied to the reset input terminal of the second counter 60 and the count clock input terminal of the third counter 63.
The second counter 60 is reset by a pulse signal WIDTH inputted from the third comparator 62 via the OR gate 61 and dividing the effective write area into a plurality of parts, and restarts the counting operation.
For this reason, the counting operation of the second counter 60 is repeated for each width that divides the effective writing area at equal intervals until the effective writing area signal LGATE from the second comparator 54 becomes negative. The comparator 62 generates a pulse signal WIDTH that divides the effective writing area at equal intervals.
The third counter 63 has a period during which the effective write area signal LGATE from the second comparator 54 is input to the reset input terminal and the effective write area signal LGATE from the second comparator 54 is negative, that is, 0 is output outside the valid write area.
When the effective write area signal LGATE from the second comparator 54 becomes active, the laser beam is scanned from the second comparator 54 to the count clock input terminal of the third counter 63 via the OR gate 61. A pulse signal indicating that the position is at the start position of the effective writing area is input, the third counter 63 is incremented, and the third counter 63 outputs 1.

Next, the third comparator 62 outputs the pulse signal WIDTH that divides the effective writing area while the laser beam scans the effective writing area for each width that divides the effective writing area at equal intervals. To do.
The pulse signal WIDTH from the third comparator 62 is input to the count clock input terminal of the third counter 63 via the OR gate 61, and the third counter is scanned while the laser beam scans the effective writing area. 63 is incremented by the pulse signal WIDTH.
When the scanning position of the laser beam exceeds the effective writing area, the effective writing area signal LGATE from the second comparator 54 becomes negative, and the count value of the third counter 63 returns to zero.
As described above, the count value of the third counter 63 indicates the scanning position scanned by the laser beam and the effective writing area is divided at equal intervals. The counting operation of the third counter 63 is performed by the polygon mirror 28. It will be repeated for each face.
The count value of the third counter 63 is input as an address signal to a RAM (Random Access Memory) 64 as storage means, and the address of the RAM 64 is designated by the count value of the third counter 63.

The RAM 64 stores numerical values that are variably set by the CPU 55 as a data table, and the CPU 55 controls the reading and writing of data.
The CPU 55 obtains light amount correction data corresponding to each scanning position obtained by dividing the effective writing area in advance, so that the light intensity of the light spot at each scanning position becomes substantially constant. The address is designated by the count value of the counter 63).
Here, as the light amount correction data, a predetermined light amount deviation (for example, for each scanning position, for example, data for correcting shading characteristics caused by the fact that the transmittance and reflectance of each optical component varies depending on the incident angle of the beam is used. What is necessary is just to add a value that is approximately half of the light amount deterioration amount of the light spot in a predetermined period after the start of use of the image forming apparatus.
The RAM 64 reads light amount correction data corresponding to each scanning position of the laser beam from the address designated by the count value of the third counter 63 when scanning the effective writing area with the laser beam.
This light amount correction data is digital-to-analog converted by a digital / analog converter (DAC) 65 to become an analog voltage corresponding to the light amount correction data, and is input to the LD modulation unit 58 as a light amount correction signal LDLVL through a low pass filter (LPF) 66. Is done.

The LPF 66 cuts and smoothes the high frequency component of the analog signal from the DAC 65.
Thereby, it is prevented that the intensity of the laser beam is switched due to the switching of the division of the effective writing area and a step is generated in the image density, and the step of the image density is smoothed.
The LD modulator 58 modulates and drives the LD 59 based on the modulation data from the OR gate 61.
The LD modulation driving of the LD modulator 58 is called pulse width modulation for controlling the pulse width of one dot according to the modulation data, or power modulation for controlling the light amount of one dot according to the modulation data, or the applicant of the present application. A combination of the pulse width modulation and the power modulation disclosed in Japanese Patent Application Laid-Open No. 2-243363 related to the above application may be used.
The LD modulator 58 controls the light amount of the LD 59 by controlling the drive current of the LD 59 based on the output signal of the monitor photodiode 67 that monitors the light amount of the LD 59 built in the LD unit.
Further, the LD modulation unit 58 controls the reference light amount of the LD 59 corresponding to the scanning position of the laser beam by the light amount correction signal LDLVL from the LPF 66.

FIG. 2 is a diagram showing the configuration of the photodetector in the image forming apparatus of the present invention.
As shown in FIG. 2, the photodetector 35 receives a laser beam from the barrel toroidal lens 37 and photoelectrically converts the PIN photodiode 35a as a light receiving element (light receiving portion), and an output signal of the PIN photodiode 35a. Is converted into an on / off digital signal, and when the PIN photodiode 35a receives the laser beam from the barrel toroidal lens 37, it outputs a synchronization detection signal XDETP which becomes low level.
As the photodetector, an IC in which the light receiving element 35a and the electric circuit 35b are contained in one package may be used, or the light receiving element 35a and the electric circuit 35b may be separated.
Further, the optical detector 35 may use an optical fiber that guides a laser beam from the barrel toroidal lens 37.
The synchronization detection signal XDETP from the optical detector 35 is input to the print control unit shown in FIG. 1, and the print control unit combines the image data from the image input unit (not shown) with the forced lighting signal for obtaining the synchronization detection signal. And output as modulation data of the LD 59 to the LD control unit 58.

FIG. 3 is a time chart of the synchronization detection pulse signal XDETP and the light amount correction signal LDLVL when the effective writing area is divided into 15 equal parts when the effective writing area is divided into equal intervals.
The light amount correction signal LDLVL is light amount correction data # 1 to # 15 that has the opposite characteristics to the shading characteristics in a plurality of regions obtained by dividing the effective writing region into 15 equal parts, and is constant in the regions other than the effective writing region. Light quantity correction data # 0.
In order for the light detector 35 to generate the beam detection pulse XDETP with a precise timing, the received light amount needs to be an appropriate amount.
The timing of the beam detection pulse XDETP may differ depending on the amount of received light, and the optimum amount of received light of the light detector 35 is the amount of laser beam irradiated to the photosensitive drum (C, M, Y, K) for image formation. Does not necessarily match.
Therefore, the CPU 55 sets the data to be written at address 0 of the RAM 64 independently from the data corresponding to the beam power applied to the photosensitive drum 15, and sets the data to be written at address 0 of the RAM 64 to the light detector 35. The light amount of the beam is set to an appropriate value so that the light amount becomes a constant light amount sufficient for the light detector 35 to detect the laser beam.
For this reason, the light amount correction data # 0 in the region other than the effective writing region is data that makes the light amount of the laser beam incident on the light detector 35 appropriate, and the light amount of the laser beam incident on the light detector 35 is appropriate. become.

When the power is turned on or when the LD 59 is turned off and then turned on again, the laser beam scanning position is not known until the beam detection signal is first obtained.
Therefore, the CPU 55 first obtains the beam detection signal when the laser beam scanning position is not known until the first beam detection signal is obtained, such as when the power is turned on or when the LD 59 is turned off and then turned on again. Until then, the count start value of the first counter 52 is set to a value larger than the set value D irrespective of the scanning position of the laser beam.
For this reason, since the output signal of the OR gate 57 does not become active, the light amount correction signal LDLVL becomes a level based on the light amount correction data at address 0 of the RAM 64, and the light amount of the laser beam first incident on the light detector 35 is detected by light. The light intensity is constant enough for the device 35 to detect the laser beam.
As described above, according to the present invention, as the light amount correction data, the light amount correction data is the data for correcting the shading characteristics caused by the fact that the transmittance and reflectance of each optical component varies depending on the incident angle of the beam. By writing light amount correction data obtained by adding a predetermined light amount deviation to the RAM 64 and correcting the light amount of the LD 59 based on the light amount correction data, even if the intensity of the light spot changes with time, the light on the surface to be scanned The beam intensity of the spot can be made constant.

The embodiment of the present invention will be described in more detail with reference to FIGS.
In the present invention, the beam light amount correction amount caused by the shading of the optical component for each scanning position on the photosensitive drum 6 is set for a certain period after the start of use of the image forming apparatus for each section (for example, a product warranty period). The correction amount is set by adding the amount of change in the amount of light over time due to the cloudiness of the polygon mirror surface.
In the prior art, when the beam intensity of the light spot is corrected, the deviation of the beam intensity of the light spot on the surface to be scanned is set to 0. However, as shown in FIG. .DELTA.Hn occurs in the beam intensity deviation of the light spot on the scanned surface.
In FIG. 4, as in FIG. 9, the light detector 35 has the image height 0 at the center of the photosensitive drum 6 in the main scanning direction, and the light detector 35 at the image height −160. A range from 150 to the image height +150 is an effective writing area.

Therefore, as shown in FIG. 5, in anticipation of the temporal change in light quantity ΔHn of the polygon mirror reflectivity over time, ΔHn / 2 is added to the corrected light quantity ΔPn by ΔHn / 2 (ΔPn + ΔHn / 2). ) By correcting, the beam spot deviation of the light spot on the surface to be scanned is + ΔHn / 2 before the reflectance of the polygon mirror is lowered over time, and on the surface to be scanned after the warranty period of the image forming apparatus. The beam intensity deviation of the light spot becomes −ΔHn / 2, and the change in the beam intensity deviation of the total warranty period of the image forming apparatus can be halved. Obviously, the beam intensity deviation when viewed over time is minimized when ΔHn / 2 is added.
As a result, a change in light amount deviation between scanning positions over time is reduced, and unevenness in image density due to a difference in light quantity at each scanning position is reduced. Image quality can be maintained.
In this way, the amount of light of the laser beam is corrected to a large amount in anticipation of the beam intensity change amount ΔHn of the light spot in each section of the surface to be scanned accompanying the decrease in the reflectance of the polygon mirror over time. By reducing the variation in the beam intensity deviation of the light spot at the end of the warranty period of the forming device and reducing the unevenness of the image density due to the difference in the amount of light at each scanning position, stable and good during the warranty period of the image forming device Image quality can be maintained.

Further, the light amount correction may be performed more at the end of the scanning position on the photosensitive drum 6 (outer section of the section where all scanning positions are divided into a predetermined number).
By doing so, even in a raster optical system optical scanning device with a relatively small amount of light at the scanning position end, it is possible to reduce the light amount deviation between the scanning positions over time.
In addition, by performing a large amount of light amount correction in the section corresponding to the cloudy spot of the polygon mirror, the change in light amount deviation between the scanning positions over time can be further reduced, and the image density can be reduced due to the difference in light amount at each scanning position. Uniformity can be reduced and image quality can be improved.
Further, since the scanning section on the photosensitive drum 6 is determined from the cloudiness size / position of the polygon mirror 6, the change in the light amount deviation between the scanning positions over time can be reduced with high accuracy, and for each scanning position. Image density non-uniformity due to different light amounts can be greatly reduced, and image quality can be improved.
Note that the light amount deviation ΔH between the divided sections in the light amount correction data in the above-described embodiment is a variation of the light amount due to the fogging of the polygon mirror due to the diameter, but is not limited to this. The light quantity deviation ΔH may be set in consideration of the change factor and the light quantity change caused thereby.
This makes it possible to reduce changes in the light intensity deviation between the scanning positions due to the optical system, reduce the light intensity deviation change between the scanning positions over time due to various factors, and uneven image density due to the difference in the light intensity at each scanning position. Can be reduced, and the image quality can be improved.

6 is a longitudinal side view schematically showing a color printer which is an image forming apparatus provided with a print control unit of the present invention, FIG. 7 is a plan view showing the internal structure of the optical writing device in FIG. 6, and FIG. It is a vertical side view which shows a writing device.
As shown in FIG. 6, four printer engines 3 (3Y, 3C, 3M, 3K), light beams are emitted to a substantially central portion inside the main body case 2 of the color printer 1 that is an image forming apparatus, and the light beams are emitted. An optical writing device 4 that irradiates a later-described photoconductor with a scanning line, a print control unit (control unit) Ctr as an image formation control unit, an intermediate transfer belt 5 and the like are arranged. Each printer engine 3 is a portion for forming a toner image, and is formed in the same structure. Each printer engine 3 uses a different color toner to form a different color toner image. In the description of the present specification and drawings relating to the printer engine 3 and the components of the printer engine 3, the subscripts Y, C, M, and K indicate yellow, cyan, magenta, and black, respectively. These subscripts are omitted as necessary.
The mechanical structures of the four printer engines 3Y, 3C, 3M, and 3K are the same. Each printer engine 3 includes a photosensitive drum 6 that is driven to rotate in the direction of the arrow, and a charging unit that is disposed around the photosensitive drum 6. 7, a developing unit 8, a cleaning unit 9, and the like.

The photosensitive drum 6 is formed in a cylindrical shape and is rotationally driven by a drive motor (not shown), and a photosensitive layer is provided on the outer peripheral surface. By irradiating the outer peripheral surface of the photosensitive drum 6 with the light beam emitted from the optical writing device 4, an electrostatic latent image corresponding to image data is written on the outer peripheral surface of the photosensitive drum 6.
The charging unit 7 is a conductive roller member formed in a roller shape, and a charging bias voltage is supplied to the charging unit 7 from a power supply device (not shown), so that the outer peripheral surface of the photosensitive drum 6 is uniform. Is charged.
The developing unit 8 supplies toner to the photosensitive drum 6. The supplied toner adheres to the electrostatic latent image written on the outer peripheral surface of the photosensitive drum 6, whereby the electrostatic latent image on the photosensitive drum 6 is visualized as a toner image.
The cleaning unit 9 cleans residual toner adhering to the outer peripheral surface of the photosensitive drum 6 after the toner image formed on the photosensitive drum 6 is transferred to the intermediate transfer belt 5.

The intermediate transfer belt 5 is a loop belt formed with a resin film or rubber as a base, and a toner image formed on the photosensitive drum 6 is transferred to the intermediate transfer belt 5. This intermediate transfer belt 5 is supported by rollers 10, 11, 12 and is driven to rotate in the direction of the arrow. Four transfer rollers 13 for transferring the toner image on each photosensitive drum 6 onto the intermediate transfer belt 5 are arranged on the inner peripheral surface side (inside the loop) of the intermediate transfer belt 5. The toner images formed on the respective photosensitive drums 6 are sequentially transferred onto the intermediate transfer belt 5, whereby a color toner image is carried on the intermediate transfer belt 5. On the outer peripheral surface side (outside the loop) of the intermediate transfer belt 5, a cleaning unit 14 that cleans residual toner, paper dust, and the like attached to the outer peripheral surface of the intermediate transfer belt 5 is disposed.
Below the four printer engines 3 and the optical writing device 4 in the main body case 2, a paper feeding cassette 15 in which the recording medium P is stacked and held is disposed. The recording media P stacked and held in the paper feed cassette 15 are separately fed by the paper feed roller 16 in order from the highest one.
In the main body case 2, a transport path 17 is formed through which the recording medium P separated and fed from the paper feed cassette 15 is transported. On the conveyance path 17, a registration roller 18, a transfer roller 19, a fixing unit 20, a paper discharge roller 21, and the like are arranged.

The registration roller 18 is a roller that is rotationally driven intermittently at a predetermined timing. By intermittently driving the registration roller 18, the recording medium P that has been transported to the position of the registration roller 18 and stopped is sent to a transfer position sandwiched between the intermediate transfer belt 5 and the transfer roller 19. The toner image on the intermediate transfer belt 5 is transferred to the recording medium P in the process in which the recording medium P passes this transfer position.
The fixing unit 20 is a part that applies heat and pressure to the recording medium P to which the toner image has been transferred to melt the toner and fix the toner image on the recording medium P. The recording medium P on which the toner image is fixed by passing through the fixing unit 20 is discharged onto a paper discharge tray 22 formed on the upper surface of the main body case 2 by a paper discharge roller 21.

Next, the optical writing device 4 will be described with reference to FIG.
The optical writing device 4 has an optical housing 23, and a light source that emits a light beam (laser light) corresponding to image data of different colors (Y, C, M, K) in the optical housing 23. A light source unit 24 (24Y, 24C, 24M, 24K) and various optical members (scanning imaging optical system) for irradiating the photosensitive drum 6 with a scanning line by a light beam are accommodated. The optical member accommodated in the optical housing 23 includes an aperture 25 for tilting correction, a cylinder lens 26, a mirror 27, a polygon mirror (polarizing means) 28, an imaging lens 29, and reflecting mirrors 30 and 31 (30Y, 30Y, 31Y, 30C, 31C, 30M, 31M, 30K, 31K), a synchronization detecting mirror 32, an imaging lens 33, a photoelectric element 35 (scanning position detecting means) mounted on the circuit board 34, and the like. The light source unit 24 includes a semiconductor laser (laser diode) that emits divergent light, a collimator lens that substantially collimates the divergent light emitted from the semiconductor laser, a semiconductor laser driving circuit board, and the like.
The polygon mirror 28 is connected to a polygon motor 36 and rotates at high speed. The number of rotations of the polygon mirror 28 varies, but there are, for example, those exceeding 40,000 rpm.

In this color printer 1, image data input from a document reading device (scanner) or an image data output device (a personal computer, a word processor, a facsimile receiving unit, etc.) (not shown) is color-separated, and the color-separated image data of each color is obtained. Is converted into a signal for driving each light source unit 24, and a light beam is emitted from each light source unit 24 in accordance with the signal. The light beams emitted from the respective light source sections 24 reach the polygon mirror 28 via the surface tilt correction aperture 25 and the cylinder lens 26, and are deflected and scanned in two symmetrical directions by the two light beams by the polygon mirror 28. .
The light beams deflected and scanned in two symmetrical directions by the polygon mirror 28 pass through the imaging lens 29 and are folded back by the two kinds of reflection mirrors 30 and 31 toward the photosensitive drum 6 of each printer engine 3. proceed. Then, the electrostatic beam is written on the outer peripheral surface of the photosensitive drum 6 by irradiating the outer peripheral surface of the photosensitive drum 6 with the light beam traveling toward the photosensitive drum 6 as a scanning line.

On the bottom surface of the optical housing 23, an opening Op is formed that is positioned at a position facing the photosensitive drum 6 of each printer engine 3 and that is elongated along the center line direction of the photosensitive drum 6. . A light-transmitting dustproof member 38 that allows the light beam to pass therethrough and prevents dust from entering the optical housing 23 is attached to these openings Op, and the light beam directed toward the photosensitive drum 6 is transmitted with the light-transmitting dustproof material. It proceeds through the member 38. As the translucent dustproof member 38, for example, flat glass is used.
Of the light beam that has passed through the imaging lens 29, the light beam that has passed through the preceding scanning side end of the imaging lens 29 is folded back by the synchronization detection mirror 32, passes through the imaging lens 33, and is received by the photoelectric element 35. The When the photoelectric element 35 receives light, a scanning start synchronization signal is output from the photoelectric element 35. Here, since the original meaning of the synchronization detection is to take a scanning timing, it is sufficient that the photoelectric element 35 is installed at a position where the light beam is received prior to the scanning. In order to detect a change in (or time), a photoelectric element 35 may be provided on the rear end side of the scan. In the present embodiment, a configuration is shown in which a synchronization detection mirror 32 and a photoelectric element 35 are arranged on the preceding scanning side of the imaging lens 29 and synchronization is performed before scanning.

FIG. 3 is a diagram illustrating a configuration of a print control unit in the image forming apparatus of the present invention. FIG. 3 is a diagram illustrating a configuration of a photodetector in the image forming apparatus of the present invention. The time chart of the synchronous detection pulse signal XDETP and the light quantity correction signal LDLVL when the effective writing area is divided into 15 equal parts when the effective writing area is divided into equal intervals. FIG. 6 is a diagram illustrating a beam intensity deviation of a light spot on a scanned surface after a predetermined period has elapsed after the start of use of the image forming apparatus. The figure which shows the beam light quantity correction amount in printing control in this invention. FIG. 2 is a longitudinal side view schematically illustrating a color printer that is an image forming apparatus including a print control unit according to the invention. FIG. 7 is a plan view showing an internal structure of the optical writing device in FIG. 6. FIG. 3 is a longitudinal side view showing the optical writing device. The figure which shows the light quantity deviation in the to-be-scanned surface in the conventional image forming apparatus. The figure which shows the light quantity correction data in the conventional image forming apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Color printer, 2 Main body case, 3 Printer engine, 4 Optical writing device, 5 Intermediate transfer belt, 6 Photosensitive drum, 7 Charging part, 8 Developing part, 9 Cleaning part, 10 Roller, 13 Transfer roller, 14 Cleaning part , 15 Photosensitive drum, 15 Paper cassette, 16 Paper feed roller, 17 Transport path, 18 Registration roller, 19 Transfer roller, 20 Fixing part, 21 Paper discharge roller, 22 Paper discharge tray, 23 Optical housing, 24 Light source part, 25 Aperture, 26 Cylinder lens, 27 Mirror, 28 Polygon mirror, 28a Polygon mirror shield glass, 29 Imaging lens, 30 Reflection mirror, 32 Sync detection mirror, 33 Imaging lens, 34 Circuit board, 35 Photo detector, 35a PIN photodiode, 35b 36 polygon motor, 37 barrel toroidal lens, 38 translucent dustproof member, 50 clock generation circuit, 51 clock synchronization circuit, 52 counter, 53 comparator, 54 comparator, 55 CPU, 56 registers, 57 OR gate, 58 LD modulation , 59 LD, 60 counter, 61 OR gate, 62 comparator, 63 counter, 64 RAM, 65 DAC, 66 LPF, 67 monitor photodiode, 100 photosensitive drum, 101 photodetection device

Claims (4)

Light source means for generating a light beam, deflection means for deflecting and scanning the light beam from the light source means, and condensing the light beam from the deflection means as a light spot on the scanned surface and scanning the scanned surface with the light spot Scanning image forming optical means, scanning position detecting means for detecting the scanning position of the light spot, and for every section obtained by dividing all scanning positions of the light spot detected by the scanning position detecting means into a predetermined number, Storage means for storing light amount correction data of the light source means given in advance, and control for controlling the light amount of the light source means corresponding to each of the divided sections based on the light amount correction data stored in the storage means An image forming apparatus comprising:
2. The image forming apparatus according to claim 1, wherein the light amount correction data given in advance is formed by adding a predetermined light amount deviation to correction data for correcting shading characteristics for each of the divided sections. The image forming apparatus according to claim 1.
2. The image forming apparatus according to claim 1, wherein the light amount deviation is substantially half of a light amount deterioration amount of the light spot in a predetermined period after the start of use of the image forming apparatus in each section. The image forming apparatus according to claim 1.
In the divided section, the light quantity deviation in a section where the amount of cloudiness of the deflecting means exceeds a predetermined value is set larger than that in other sections. The image forming apparatus according to claim 1.
2. The image forming apparatus according to claim 1, wherein the divided section is determined according to a cloudy position and a magnitude of the deflecting unit.

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