JP2020131429A - Image formation apparatus and image formation method - Google Patents

Abstract

To reduce the density unevenness due to the difference in the light amount between the writing start and the writing end.SOLUTION: An image formation apparatus includes: first optical sensor and second optical sensor arranged on the upstream side and on the downstream side in the scanning direction of the light with respect to an image carrier; a calculation unit which calculates a correction parameter of the light amount with respect to the light emission time of a light source on the basis of the change between a first detection signal output by the first optical sensor and a second detection signal output by the second optical sensor; a determination unit which determines the light emission time at which the light source should emit the light on the basis of object image data; and a control unit which controls the light amount of the light emitted from the light source with respect to the determined light emission time on the basis of the correspondence between the light emission time and the correction parameter of the light amount.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus and an image forming method.

In multifunction devices and printers, in order to record images on recording materials at high speed, laser beams from multiple laser light sources (for example, laser diode: LD) are used to capture images of multiple lines on a photoconductor in a single scan. By writing, an image is formed on the photoconductor. By repeating this image formation in the sub-scanning direction, one page of image formation is performed. However, the amount of light of the laser light source is attenuated according to the light emission time due to the drooping characteristic (droop).

For example, Patent Document 1 discloses a technique for controlling the amount of light from a laser light source based on the pulse width of the output waveform of a sensor in order to suppress a change in the amount of light due to a change in ambient temperature.

Japanese Unexamined Patent Publication No. 2012-228837

However, the laser light source itself is also a heat source, and heat is generated with the light emission time, and the amount of light changes. Therefore, in the technique focusing on the ambient temperature described in Patent Document 1, the amount of light at the start of writing can be kept constant, but the amount of light at the end of writing is not constant. As described above, in laser light emission, the amount of light at the start of writing and at the end of writing differs depending on the drooping characteristic caused by the heat generation of the laser light source itself even if one line is emitted. For this reason, uneven charging occurs in the electrostatic latent image formed on the photoconductor, and uneven density occurs in the developed image.

From the above situation, there has been a demand for a method for reducing image density unevenness due to a change in the amount of light from the start of writing to the end of writing.

In order to solve the above problems, the image forming apparatus of one aspect of the present invention is based on a light source, a scanning unit that scans the light emitted from the light source in the main scanning direction, and the light scanned by the scanning unit. An image carrier on which an image is formed, and a first optical sensor that is arranged upstream of the image carrier in the scanning direction of light and outputs a first detection signal according to the amount of received light. A second optical sensor, which is arranged downstream of the image carrier in the scanning direction of light and outputs a second detection signal according to the amount of received light, is provided. Further, the image forming apparatus includes a calculation unit that calculates a correction parameter of the amount of light with respect to the emission time of emitting light from the light source based on the change between the first detection signal and the second detection signal. A storage unit that stores the correspondence between the light intensity correction parameter with respect to the light emission time, a discrimination unit that determines the light emission time that the light source should emit light based on the image data of the image formation target, and a storage unit that stores the light source. A control unit that controls the amount of light emitted from the light source with respect to the light emission time determined by the discrimination unit is provided based on the correspondence between the light emission time and the correction parameter of the light amount.

According to at least one aspect of the present invention, it is possible to suppress a change in the amount of light from the start of writing to the end of writing, and reduce uneven density of an image due to the change in the amount of light.
Issues, configurations and effects other than those described above will be clarified by the description of the following embodiments.

It is schematic cross-sectional view which shows the structural example of the image forming apparatus which concerns on one Embodiment of this invention. It is a figure which shows the structural example of the exposure apparatus which concerns on one Embodiment of this invention, and its periphery. It is explanatory drawing about the exposure method by a plurality of lights. It is a figure which shows the relationship between the 1st optical sensor and the 2nd optical sensor arranged near the writing start position and the writing end position of the photoconductor, the light amount data, and the actual light amount. 6 is a graph showing the relationship between the amount of light detected by each of the first optical sensor and the second optical sensor and the pulse width. It is explanatory drawing which shows the difference of the pulse width based on the change of the light amount detected by the 1st optical sensor, and the light amount detected by a 2nd optical sensor. It is a block diagram which shows the structural example of the controller of the image forming apparatus which concerns on one Embodiment of this invention. It is a graph which shows the relationship example of the pulse width and light emission time which concerns on one Embodiment of this invention. It is a figure which shows the relationship example of the image data which concerns on one Embodiment of this invention, the actual light amount when there is no correction, and the correction light amount command value. It is a flowchart which shows the procedure example of the calculation processing and the storage processing of the correction parameter by the controller which concerns on one Embodiment of this invention. It is a flowchart which shows the procedure example of the printing process which concerns on one Embodiment of this invention.

Hereinafter, examples of embodiments for carrying out the present invention (hereinafter, referred to as “embodiments”) will be described with reference to the accompanying drawings. In the present specification and the accompanying drawings, components having substantially the same function or configuration are designated by the same reference numerals, and duplicate description will be omitted.

[Configuration of image forming apparatus]
First, a configuration of an embodiment of an image forming apparatus using the present invention will be described with reference to FIG.

FIG. 1 is a schematic cross-sectional view showing a configuration example of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 10 shown in FIG. 1 is a multifunction digital image forming apparatus (MFP: Multi Function Peripherals) having a plurality of functions such as a print function, a copy function, a facsimile function, and a scan function. The image forming apparatus 10 forms an image on the paper P based on the image data obtained by reading the image from the original or the image data (print data) received from an external device such as the terminal device 30. The image forming apparatus 10 to which the present invention is applied may have at least a printing function.

The image forming apparatus 10 includes an image reading unit 12, an image forming unit 13, an operation panel 15, a manual feed tray T1, a paper feed tray T2, and a paper output tray T3.

The image reading unit 12 scans and exposes an image of a document placed on a platen or an automatic document feeder (ADF) (not shown) by an optical system of a scanning exposure apparatus, and scans and exposes the reflected light by a line image sensor. Read, thereby obtaining an image signal. This image signal is input to the controller 32 (see FIGS. 2 and 7) described later as image data after being subjected to processing such as A / D conversion, shading correction, and compression. The image data input to the controller 32 is not limited to the data read by the image reading unit 12, and may be, for example, received from an external device via a network interface (not shown).

The image forming unit 13 has four of cyan (C), magenta (M), yellow (Y), and black (K), depending on the pixel values of the four colors of each pixel in the image-processed original image (image data). An image composed of one or more of the colors is formed on the paper P. As shown in FIG. 1, the image forming unit 13 includes four writing units 131Y, 131M, 131C, 131K, an intermediate transfer belt 132, a secondary transfer roller 133, a fixing device 134, and the like. Hereinafter, the writing units 131Y, 131M, 131C, and 131K may be collectively referred to as the writing unit 131, or when not particularly distinguished.

The four writing units 131Y, 131M, 131C, 131K are arranged in series (tandem) along the belt surface of the intermediate transfer belt 132 to form images of each color of C, M, Y, and K. Each writing unit 131 has the same configuration except that the color of the image to be formed is different. As shown in FIG. 1, the writing unit 131 includes an exposure device 131a, a photoconductor 131b (an example of an image carrier), a developing unit 131c, a charging unit 131d, a cleaning unit 131e, and a primary transfer roller 131f. There is.

During the image forming process, in each writing unit 131, the outer peripheral surface of the drum-shaped photoconductor 131b is charged by the charging unit 131d, and then the light beam (light beam) emitted by the exposure device 131a based on the original image is used to charge the photoconductor 131b. The outer peripheral surface is scanned to form an electrostatic latent image. In this state, when a coloring material such as toner is supplied by the developing unit 131c for development, an image is formed on the outer peripheral surface of the photoconductor 131b.

The images formed on the photoconductors 131b of the four writing units 131 are sequentially superimposed and transferred (primary transfer) on the intermediate transfer belt 132 by the corresponding primary transfer rollers 131f. As a result, an image composed of each color is formed on the intermediate transfer belt 132. The intermediate transfer belt 132 is an image carrier that is wound around a plurality of rollers and rotates. After the primary transfer, the cleaning unit 131e removes the coloring material remaining on the photoconductor 131b.

The image forming unit 13 feeds paper from the manual feed tray T1 or the paper feed tray T2 at the timing when the image on the rotating intermediate transfer belt 132 reaches the position of the secondary transfer roller 133. The secondary transfer roller 133 constitutes one of a plurality of rollers in which one pair of rollers presses against the intermediate transfer belt 132 and the other winds the intermediate transfer belt 132. The image is transferred (secondary transfer) from the intermediate transfer belt 132 onto the paper by pressure welding of the secondary transfer roller 133.

After that, the paper is conveyed to the fixing device 134, the paper is fixed in the fixing device 134, and the paper is discharged to the paper ejection tray T3. The fixing process is a process of heating and pressurizing the paper with the fixing roller 134a to fix the image on the paper. When forming an image on both sides of the paper, the paper is conveyed to the reversing path 135 to invert the paper surface, and then the paper is fed again to the position of the secondary transfer roller 133.

[Structure of exposure equipment]
FIG. 2 is a diagram showing a configuration example of the exposure apparatus 131a in FIG. 1 and its surroundings. The exposure apparatus 131a shown in FIG. 2 is an exposure apparatus for the writing unit 131Y, and the exposure apparatus for other writing units has the same configuration. Hereinafter, an example in which one light source (laser diode) used for one scanning is used will be described.

As shown in FIG. 2, the exposure apparatus 131a includes a light source unit 21, an optical system 22a, a polygon mirror 23, an optical system 22b, a first optical sensor 24, a second optical sensor 25, a detection circuit 31, and a controller 32. Be prepared.

The light source unit 21 has a laser diode 21L and a driver circuit 21D. The laser diode 21L (an example of a light source) is a light source that emits laser light. The spot diameter of the laser beam emitted from the laser diode 21L and scanned increases as the ambient temperature of the laser diode 21L decreases, and decreases as the ambient temperature of the laser diode 21L increases.

The optical system 22a is a group of various lenses arranged between the laser diode 21L and the polygon mirror 23. The optical system 22b is a group of various lenses arranged between the polygon mirror 23, the photoconductor 131b, the first optical sensor 24, and the second optical sensor 25. For the optical systems 22a and 22b, for example, an fθ lens or the like is used.

The polygon mirror 23 (an example of a scanning unit) is an element having an axis perpendicular to the axis of the photoconductor 131b, a cross section perpendicular to the axis having a polygonal shape, and a side surface thereof as a mirror. The polygon mirror 23 rotates about its axis and scans the laser beam emitted from the laser diode 21L along the axial direction (main scanning direction) of the photoconductor 131b.

The first optical sensor 24 is a sensor that receives the laser light scanned by the polygon mirror 23 in order to generate the main scanning synchronization signal. The first optical sensor 24 is arranged at a position upstream of the photoconductor 131b on the line on which the laser beam is scanned (upstream in the scanning direction). When the laser beam is incident, the first optical sensor 24 induces an output voltage corresponding to the amount of light (for example, lm · S) and outputs it as a first detection signal. The first optical sensor 24 can detect the timing at which the spot of the laser light passes through the position.

The second optical sensor 25 is arranged at a position downstream of the photoconductor 131b on the line on which the laser beam is scanned (downstream in the scanning direction). When the laser light is incident, the second optical sensor 25 induces an output voltage according to the amount of light and outputs it as a second detection signal. The second optical sensor 25 can detect the timing at which the spot of the laser light passes through the position. The first optical sensor 24 and the second optical sensor 25 have the same specifications. The first detection signal and the second detection signal may be collectively referred to as a detection signal.

The driver circuit 21D is a circuit that drives the laser diode 21L. The driver circuit 21D controls the laser diode 21L to emit laser light based on a drive signal (light intensity command value) for image formation input from the controller 32. For example, the driver circuit 21D controls the amount of light of the laser diode 21L by an automatic power control circuit (APC circuit) or an automatic current control circuit (ACC circuit) based on a reference voltage.

Although FIG. 2 shows a light source unit 21 having one laser diode 21L and one driver circuit 21D, in reality, the light source unit 21 may include a plurality of laser diodes 21L. In this case, the polygon mirror 23 scans each of the plurality of laser beams (spot light) emitted from the plurality of laser diodes 21L at different positions in the sub-scanning direction in the main scanning direction by one scanning.

[Exposure of multiple laser beams]
FIG. 3 is an explanatory diagram of an exposure method using a plurality of laser beams. For example, assume that the light source unit 21 includes eight laser diodes 21L and the positions of the laser beams (spots) emitted from the eight laser diodes 21L are different in the sub-scanning direction. In this case, as shown in FIG. 3, the exposure apparatus 131a scans each of the eight laser beams emitted from the eight laser diodes 21L at different positions in the sub-scanning direction in the main scanning direction in one scan. can do. In other words, the exposure apparatus 131a can scan eight scanning lines L1 to L8 at a time by moving eight laser beams in different positions in the sub-scanning direction and simultaneously in the main scanning direction. ..

[Light intensity data and actual light intensity]
FIG. 4 is a diagram showing the relationship between the first optical sensor 24 and the second optical sensor 25 arranged near the writing start position and the writing end position of the photoconductor 131b, the light amount data, and the actual light amount. Is. In one scanning cycle, the laser beam is incident on the first optical sensor 24 near the writing start position in the previous scanning, and then the laser beam is incident on the first optical sensor 24 near the writing start position in the next scanning. Up to. This one cycle corresponds to the scanning range of the polygon mirror 23.

In the ideal amount of laser light emitted by the laser diode 21L, the amount of light data (amplitude of the detection signal) output by the first light sensor 24 and the second light sensor 25 is the same. That is, the amount of light emitted is the same at the writing start position and the writing end position. However, in reality, since the laser diode 21L generates heat from the laser diode 21L itself, the actual amount of light decreases during scanning from the writing start position to the writing end position.

[Light intensity and pulse width]
FIG. 5 is a graph showing the relationship between the amount of light detected by each of the first optical sensor 24 and the second optical sensor 25 and the pulse width when the laser diode 21L is made to emit light as shown in FIG. .. The Gaussian distribution of the laser light changes as shown in FIG. 5 according to the amount of light. The first optical sensor 24 and the second optical sensor 25 detect the laser beam when the amount of light exceeds the threshold (broken line).

FIG. 6 shows the difference in pulse width based on the change in the amount of light detected by the first optical sensor 24 and the amount of light detected by the second optical sensor 25. The single arrow in the figure indicates the scanning direction of the laser beam. The size of the circle represents the size of the amount of laser light (spot light). The sensitivities of the first optical sensor 24 and the second optical sensor 25 do not change. Therefore, the pulse widths of the first detection signal output by the first optical sensor 24 and the second detection signal output by the second optical sensor 25 change according to the amount of light. In the examples of FIGS. 5 and 6, a difference W is generated between the pulse width of the first detection signal of the first optical sensor 24 and the pulse width of the second detection signal of the second optical sensor 25. are doing.

[Control system of image forming apparatus]
FIG. 7 is a block diagram showing a configuration example of the controller 32 of the image forming apparatus 10. The controller 32 includes a correction parameter calculation unit 321, a discrimination unit 322, a storage unit 323, and a control unit 324.

The correction parameter calculation unit 321 (an example of the calculation unit) is a laser diode based on a change between the first detection signal of the first optical sensor 24 and the second detection signal of the second optical sensor 25. The correction parameter of the amount of light with respect to the light emission time for emitting 21 L of laser light is calculated. For example, the correction parameter calculation unit 321 calculates the correction parameter of the amount of light based on the amount of change in the pulse width of the second detection signal with respect to the pulse width of the first detection signal. Then, the correction parameter calculation unit 321 outputs the correction parameter of the amount of light with respect to the light emission time of the laser diode 21L to the storage unit 323.

The determination unit 322 determines the light emission time at which the laser diode 21L should emit the laser light based on the image data of the image formation target. For example, the discrimination unit 322 determines the length of the light emission period of the light emission pattern corresponding to the actual image data as the light emission time of the laser diode 21L. The determination unit 322 discriminates the light emission pattern (writing start timing, writing end timing) for each scanning line with respect to the image data, and calculates the length of the light emitting period from the writing start timing and the writing end timing. Thereby, the light emission time can be determined based on the image data. Then, the discrimination unit 322 outputs the information of the light emission time discriminated from the image data to the storage unit 323.

The storage unit 323 stores the correspondence between the light emission time calculated by the correction parameter calculation unit 321 and the correction parameter of the amount of light. Further, the storage unit 323 stores information on the light emission time determined from the image data by the determination unit 322.

The control unit 324 controls each block constituting the controller 32. Further, the control unit 324 controls the amount of laser light emitted from the laser diode 21L with respect to the light emission time based on the correspondence between the light emission time stored in the storage unit 323 and the correction parameter of the light amount. That is, the control unit 324 adjusts the light amount by correcting the drive signal (light amount command value) supplied to the driver circuit 21D by this correction parameter.

When the correction parameter calculation unit 321 calculates the correction parameter of the amount of light, the control unit 324 emits light from the laser diode 21L while the polygon mirror 23 scans from the first optical sensor 24 to the second optical sensor 25. Control to keep emitting. The drooping characteristic of the light amount of the laser diode 21L can be measured by scanning with the light amount command value at the start of writing until the end of writing based on a constant light amount command value.

When the light source unit 21 has a plurality of laser diodes 21L, the correction parameter calculation unit 321 calculates a correction parameter for the amount of light with respect to the light emission time for each laser diode 21L. Further, the discrimination unit 322 discriminates the light emission time for each laser diode 21L based on the image data. Then, the control unit 324 controls the amount of light for each laser diode 21L with respect to the light emission time determined by the discrimination unit 322, based on the correspondence between the light emission time for each laser diode 21L and the correction parameter for the amount of light.

As shown in FIG. 11 to be described later, when the image forming apparatus 10 satisfies a predetermined condition, the correction parameter calculation unit 321 in the present embodiment recalculates the correction parameter of the amount of light and stores it in the storage unit 323. An example of a predetermined condition is that the elapsed time after the correction parameter calculation unit 321 calculates the correction parameter of the amount of light is equal to or longer than the predetermined time. Further, another example of the predetermined condition is that the number of prints after the correction parameter calculation unit 321 calculates the correction parameter of the light amount becomes the set number or more.

[Pulse width and emission time]
FIG. 8 is a graph showing an example of the relationship between the pulse width and the light emission time according to the embodiment. The horizontal axis (X axis) of FIG. 8 represents the light emission time, and the vertical axis (Y axis) represents the pulse width. The light emission time on the horizontal axis is based on the time when the laser beam is incident on the first optical sensor 24 (elapsed time is zero).

In FIG. 8, when the light emission time is “0”, the pulse width of the first detection signal in the first optical sensor 24 is “B ₁ ”, and when the light emission time is “A ₁ ”, the pulse width in the second optical sensor 25 is the second. The pulse width of the detection signal of ₂ is "B ₂ ". Further, when the light emission time of the next cycle is “A ₂ ”, the pulse width of the first detection signal in the first optical sensor 24 is “B ₃ ”. The magnitude relationship between B _{1 to} B ₃ is B ₁ > B ₃ > B ₂ .

Therefore, the broken line from the light emission time "0" to the light emission time "A ₁ " represents the attenuation rate, and the alternate long and short dash line from the light emission time "A ₁ " to the light emission time "A ₂ " represents the recovery rate. The amount of light of the laser diode 21L returns according to the stop time due to heat dissipation during stop. The stop time is the time between continuous writing processes, that is, the time from the writing end timing of the previous writing process to the writing start timing of the next writing process. The solid line from the light emission time "0" to the light emission time "A ₁ " represents the attenuation correction factor (correction amount), and the solid line from the light emission time "A ₁ " to the light emission time "A ₂ " is the return correction factor. Represents (correction). To maintain the amount of light over the light emission time "A _1" from the light-emitting time "0" constant, the pulse width of the second of the second detection signal from the light sensor in the light emission time "A _1" is "B 1 ₊ ( It is necessary to be "B _1- B ₂ )".

From the difference between the pulse width of the first detection signal of the first optical sensor 24 and the pulse width of the second detection signal of the second optical sensor 25, the correction parameter of the light amount (correction amount Y'at recovery, attenuation). The hour correction amount Y) is obtained by the equations (1) and (2).

(Correction amount Y'at return)

(Attenuation correction amount Y)

The correction parameter calculation unit 321 calculates the correction parameter for each amount of laser light using the equations (1) and (2). By calculating the correction parameter for each amount of laser light, it is possible to apply an appropriate correction parameter for each amount of light used. Here, when correcting the amount of light for the first writing process (emission), the term of the amount of correction Y'at the time of restoration on the right side of the equation (2) can be deleted.

In this embodiment, as shown in the equations (1) and (2), the attenuation correction amount Y reflects the recovery amount of the light amount (return correction amount Y') according to the stop time of the laser diode 21L. However, the configuration may be such that the correction amount Y'at the time of restoration is not taken into consideration even in the second and subsequent writing processes. However, by calculating the attenuation correction amount Y in consideration of the recovery correction amount Y', more accurate light amount correction can be realized.

[Image data, actual light amount, and corrected light amount]
Next, a method of obtaining the corrected light amount will be described using actual image data as an example.
FIG. 9 shows an example of the relationship between the image data according to one embodiment, the actual light amount when there is no correction, and the corrected light amount command value. The horizontal axis (X-axis) in FIG. 9 represents the light emission time. The image data has a light emitting time a and a light emitting time b to be emitted by the laser diode 21L in a period corresponding to the image region, and has a stop time c between the light emitting time a and the light emitting time b. The correction amount of the amount of light at each of the light emission time a, the light emission time b, and the stop time c is calculated by the following equations (3) to (5).

(A) In the light emission time a, the light emission time a is turned on and the light amount is attenuated by the amount of the light amount Ya.

(C) In the stop time c, after the above (A), the stop time c is turned off and the light amount is restored by the amount of light Y'c.

(B) In the light emission time b, after the above (C), the light emission time b is turned on and the light amount is attenuated by the amount of the light amount Yb.

The control unit 324 supplies the driver circuit 21D with a drive signal (correction light amount command value) that complements the attenuation amount of the light amount by using each correction parameter calculated by the correction parameter calculation unit 321. That is, by reflecting the attenuation (correction parameter) of the amount of laser light from the start of writing to the end of writing in the light amount command value at the start of writing (adding the attenuation according to the light emission time), at the start of writing. Align the amount of light at the end of writing. By correcting the light amount command value in this way, the control unit 324 can adjust so that the light amount of the laser light becomes constant at the start of writing and at the end of writing. Further, in the present embodiment, the correction parameter is reflected in the light amount command value at the start of the second writing (adding the return amount according to the stop time), so that the light amount command value and the laser light actually irradiated are measured. The amount of light can be adjusted.

[Calculation and storage of correction parameters]
Next, the processing of the controller 32 after the power of the image forming apparatus 10 is turned on will be described.
FIG. 10 is a flowchart showing a procedure example of the correction parameter calculation process and the storage process of the controller 32.

First, when the control unit 324 of the controller 32 detects that the power supply to the image forming apparatus 10 has been started (power ON), the control unit 324 shifts to the test mode (S1). Generally, in the test mode, the presence or absence of defects such as nozzle clogging is checked. In this embodiment, the correction parameter of the amount of light is calculated in this test mode.

Next, the control unit 324 starts the correction parameter calculation process by the correction parameter calculation unit 321 (S2). Here, when the control unit 324 calculates the correction parameter of the light amount in the correction parameter calculation unit 321, the constant light amount command value is constant while the polygon mirror 23 scans from the first light sensor 24 to the second light sensor 25. It is controlled so that the light is continuously emitted from the laser diode 21L based on the above. Then, the correction parameter calculation unit 321 uses the equations (1) and (2) to indicate the pulse width of the second detection signal of the second optical sensor 25 with respect to the pulse width of the first detection signal of the first optical sensor 24. Based on the amount of change in, the correction parameter of the amount of light with respect to the emission time of emitting the laser light of the laser diode 21L is calculated.

Next, the correction parameter calculation unit 321 stores each calculated correction parameter in the storage unit 323 (S3). After the process of step S3 is completed, the process of this flowchart is completed.

[Printing procedure]
FIG. 11 is a flowchart showing an example of a printing procedure by the image forming apparatus 10.
First, when a print command (print job) is input to the image forming apparatus 10, the control unit 324 of the controller 32 shifts to the print mode, and is it necessary to readjust the correction parameters stored in the storage unit 323? It is determined whether or not (S11). For example, after calculating the correction parameter according to the procedure of FIG. 10, the necessity of readjustment is determined based on whether or not a preset time (threshold value) has elapsed. If the set time elapses after calculating the correction parameter, it is determined that readjustment is necessary.

Next, when it is not necessary to readjust the correction parameters (NO in S11), the determination unit 322 determines the image data to be image-formed included in the print job (S12). The determination unit 322 discriminates the image data included in the print job on a page-by-page basis, and stores the light emission time of the light source unit 21 with respect to the image data in the storage unit 323 as a result of the determination.

On the other hand, when it is necessary to readjust the correction parameter in step S11 (YES in S11), the control unit 324 recalculates the correction parameter by the correction parameter calculation unit 321 according to the procedure of FIG. 10 (S17). Then, the correction parameter calculation unit 321 updates the correction parameter stored in the storage unit 323 to the newly calculated correction parameter (S18).

Next, the correction parameter calculation unit 321 reads the correction parameter from the storage unit 323 and stores it in the storage unit 323 (S13). Next, the control unit 324 starts printing the designated n-th page (for example, the first page) by using the correction parameter stored in the storage unit 323 (S14). The control unit 324 uses the read-out correction parameter to control so that the amount of laser light emitted from the laser diode 21L becomes constant at the start and end of writing out the light emission time.

Then, the control unit 324 determines whether or not the correction parameter stored in the storage unit 323 needs to be readjusted (S15). The control unit 324 determines whether or not readjustment is necessary depending on whether or not the usage state of the image forming apparatus 10 satisfies a predetermined condition. For example, when the number of prints after the power is turned on or after the start of printing is equal to or more than a preset number (threshold value), it may be determined that readjustment is necessary. Alternatively, if a preset time has elapsed after calculating the correction parameter, it may be determined that readjustment is necessary. In this way, by updating the correction parameters according to the usage state of the image forming apparatus 10, the correction accuracy of the amount of light can be maintained at a certain level or higher.

When it is not necessary to readjust the correction parameter (YES in S15), the control unit 324 executes the processes of steps S17 and S18, recalculates the correction parameter, and stores the correction parameter in the storage unit 323. To update. After the process of step S18, the process proceeds to step S13.

On the other hand, when it is not necessary to readjust the correction parameter in the determination process in step S15 (NO in S15), the control unit 324 determines whether or not printing of all pages is completed (S16), and printing is performed. If it is not completed (NO in S16), the return next page (n + 1 page) of the process in step S14 is printed. When the printing of all pages is completed (YES in S16), the processing of this flowchart ends.

Although the light emission time is determined for each page of the image data in step S12, the determination process and the storage process may be repeated for each scanning line within one page.

According to the above-described embodiment, the first optical sensor 24 and the second optical sensor 25 are arranged near the scanning start side and the scanning end side of the photoconductor 131b, respectively, according to the equations (1) and (2). Calculate the correction parameter of the amount of light. Then, using this correction parameter, the light emission of the laser diode 21L is controlled so that the amount of light at the start of writing and at the end of writing is constant with respect to the light emission time of the laser diode 21L. In this way, the drooping characteristic of the light amount of the laser diode 21L is measured by using the first light sensor 24 and the second light sensor 25, and by feeding back to the light amount control, the change in the light amount is changed from the start to the end of the writing. It can be suppressed. Therefore, it is possible to reduce the density unevenness of the image caused by the change in the amount of light and to form an image with less density unevenness.

Furthermore, the present invention is not limited to the above-described embodiments, and it goes without saying that various other application examples and modifications can be taken as long as the gist of the present invention described in the claims is not deviated. ..

For example, the above-described embodiment describes in detail and concretely the configurations of the image forming apparatus 10 and the controller 32 in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those including all the components described. .. It is also possible to add, delete, or replace other components with respect to a part of the configuration of each embodiment.

In addition, each of the above configurations, functions, processing units, and the like may be realized by hardware, for example, by designing a part or all of them with an integrated circuit. Further, each of the above components, functions, and the like may be realized by software by the processor interpreting and executing a program that realizes each function. Information such as programs, tables, and files that realize each function can be placed in a semiconductor memory, a hard disk, a recording device such as an SSD (Solid State Drive), or a recording medium that uses magnetism or light.

10 ... Image forming apparatus, 21 ... Light source unit, 21L ... Laser diode (light source), 21D ... Driver circuit, 23 ... Polygon mirror (scanning unit), 24 ... First optical sensor, 25 ... Second optical sensor, 31 ... detection circuit, 32 ... controller, 131a ... exposure device, 131b ... photoconductor (image carrier), 321 ... correction parameter calculation unit, 322 ... discrimination unit, 323 ... storage unit, 324 ... control unit

Claims (11)

Light source and
A scanning unit that scans the light emitted from the light source in the main scanning direction,
An image carrier on which an image is formed based on the light scanned by the scanning unit, and
A first optical sensor, which is arranged upstream of the image carrier in the scanning direction of the light and outputs a first detection signal according to the amount of received light,
A second optical sensor, which is arranged downstream of the image carrier in the scanning direction of the light and outputs a second detection signal according to the amount of received light,
Based on the change between the first detection signal and the second detection signal, a calculation unit that calculates a correction parameter of the amount of light with respect to the emission time of the light emitted from the light source, and a calculation unit.
A storage unit that stores the correspondence between the light emission time and the correction parameter of the amount of light,
A discriminator that determines the emission time for the light source to emit the light based on the image data of the image formation target.
A control unit that controls the amount of light emitted from the light source with respect to the light emission time determined by the discrimination unit based on the correspondence between the light emission time stored in the storage unit and the correction parameter of the light amount. An image forming apparatus comprising. When calculating the correction parameter of the light amount, the light source emits the light based on a constant light amount command value while the scanning unit scans from the first light sensor to the second light sensor. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the calculation unit calculates a correction parameter for the amount of light based on the amount of change in the pulse width of the second detection signal with respect to the pulse width of the first detection signal. The image forming apparatus according to claim 1, wherein the discrimination unit determines the length of the light emission period of the light emission pattern corresponding to the image data as the light emission time of the light source. The image forming apparatus according to claim 1, wherein the calculation unit calculates a correction parameter of the light amount for each light amount. The image forming apparatus according to claim 1, wherein the calculation unit recalculates the correction parameter of the amount of light and stores it in the storage unit when the usage state satisfies a predetermined condition. The image forming apparatus according to claim 6, wherein the predetermined condition is that a predetermined time elapses after the calculation unit calculates the correction parameter of the amount of light. The image forming apparatus according to claim 6, wherein the predetermined condition is that the number of printed sheets after the calculation unit calculates the correction parameter of the amount of light becomes the set number of sheets or more. Equipped with multiple light sources
The scanning unit scans each of a plurality of lights emitted from the plurality of light sources at different positions in the sub-scanning direction in the main scanning direction by one scanning.
The calculation unit calculates a correction parameter for the amount of light with respect to the light emission time for each light source.
The discrimination unit discriminates the light emission time for each light source based on the image data, and determines the light emission time.
The control unit controls the amount of light for the light emission time determined by the discrimination unit for each light source based on the correspondence between the light emission time for each light source and the correction parameter for the light amount. The image forming apparatus described. The image forming according to any one of claims 1 to 9, wherein when calculating the correction parameter of the light amount, the calculation unit reflects the return amount of the light amount according to the stop time of the light source in the correction parameter. apparatus. An image forming apparatus comprising a light source, a scanning unit that scans light emitted from the light source in the main scanning direction, and an image carrier that forms an image based on the light scanned by the scanning unit. It is an image formation method
The image forming apparatus outputs a first detection signal according to the amount of received light, which is output by a first optical sensor arranged on the upstream side of the image carrier in the scanning direction of the light, and the image. It was calculated based on the change between the second detection signal output by the second optical sensor arranged on the downstream side of the carrier in the scanning direction of the light and the second detection signal according to the amount of the received light. A storage unit for storing a correction parameter of the amount of light with respect to the emission time of the light source to emit the light is provided.
A process of determining the light emission time at which the light source should emit the light based on the image data of the image formation target, and
Image formation including a process of controlling the amount of light emitted from the light source with respect to the determined light emission time based on the correspondence between the light emission time stored in the storage unit and the correction parameter of the light amount. Method.

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