Image formation apparatus

Abstract

To enable the light emission intensity of each light-emitting element to be continuously changed without having a plurality of correction values in advance.SOLUTION: An image formation apparatus includes an LED head control unit 140 which calculates a corrected light emission intensity of one LED by adding to the light emission intensity of the one LED a correction value to perform correction so as to increase the light emission intensity as the actual light emission amount of the one LED included in the plurality of LEDs deviates further from a predetermined reference average light emission amount for the plurality of LEDs, and causes the one LED to emit light at the corrected light emission intensity. The corrected light emission intensity varies according to a rate of change, which is the ratio that changes the light emission amount calculated by multiplying the predetermined light emission intensity of the one LED by the time for which the one LED is caused to emit light.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus.

Background Art

[0002] Conventionally, in an LED (Light Emitting Diode) print head used in an image forming apparatus, correction for adjusting the emission intensity of each LED has been performed in order to suppress local print density unevenness due to variations in the imaging diameter of the LEDs as light emitting elements.

[0003] Generally, since the correction amount of this emission intensity is a value optimized for a certain average emission amount, when trying to change the average emission amount to adjust the print density, new print density unevenness due to this correction amount will occur. For this reason, the image forming apparatus described in Patent Document 1 preliminarily provides a second correction value to be used when changing the average emission amount in addition to a given first correction value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since the conventional technology only has two types of correction values, the effect of correcting local print density unevenness against continuous changes in the average emission intensity is limited.

[0006] Therefore, one or more aspects of the present disclosure aim to be able to continuously change the emission intensity of each light emitting element without preliminarily providing a plurality of correction values.

Means for Solving the Problems

[0007] An image forming apparatus according to an aspect of the present disclosure includes an exposure unit including a plurality of light emitting elements, an image carrier on which an electrostatic latent image is formed by receiving exposure by the plurality of light emitting elements, an image forming unit that forms a developer image by attaching a developer to the electrostatic latent image, a transfer unit that transfers the developer image to a medium, a fixing unit that fixes the developer image to the medium, and an exposure control unit that controls the exposure unit. The exposure control unit calculates a corrected emission intensity of one of the plurality of light emitting elements by adding a correction value that greatly corrects the emission intensity as the actual emission amount of one of the plurality of light emitting elements deviates from a predetermined reference average emission amount for the plurality of light emitting elements to the emission intensity of the one light emitting element, and causes the one light emitting element to emit light with the corrected emission intensity. The corrected emission intensity changes according to a change rate that is a rate of changing the emission amount calculated by multiplying the predetermined emission intensity of the one light emitting element by the time for which the one light emitting element emits light.

Effect of the Invention

[0008] According to one or more aspects of the present disclosure, the emission intensity of each light emitting element can be continuously changed without previously preparing a plurality of correction values.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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Figure 8

Embodiments for Carrying Out the Invention

[0010] FIG. 1 is a cross-sectional view schematically showing the configuration of the image forming apparatus 100 according to the embodiment. The image forming apparatus 100 is, for example, an electrophotographic color printer.

[0011] A paper feeding mechanism for feeding paper as a medium is arranged at the lower part of the image forming apparatus 100. The paper feeding mechanism includes a paper cassette 101, a paper color measuring unit 102 as a medium color measuring unit, a hopping roller 103, and a registration roller pair 104.

[0012] The paper cassette 101 is a medium storage unit for storing paper as a medium. In addition to paper, OHP (OverHead Projector) paper, envelopes, copy paper, special paper, etc. can be used as the medium. The paper color measuring unit 102 is a medium color measuring unit for measuring the color of the paper as a medium.

[0013] The hopping roller 103 takes out a single sheet of paper from the paper cassette 101. The registration roller pair 104 regulates the skew of the taken-out single sheet of paper and conveys the single sheet of paper to the downstream side.

[0014] Downstream of the registration roller pair 104, four independent image forming units, namely image forming mechanisms 110K, 110Y, 110M, and 110C, are arranged along the insertion side to the discharge side of the single sheet of paper. In FIG. 1, a capital letter "K" is appended to the end of the reference numeral for the portion related to black, a capital letter "Y" is appended to the end of the reference numeral for the portion related to yellow, a capital letter "M" is appended to the end of the reference numeral for the portion related to magenta, and a capital letter "C" is appended to the end of the reference numeral for the portion related to cyan. Hereinafter, when there is no need to particularly distinguish and explain the colors, the capital letters "K", "Y", "M", and "C" will be omitted in the description.

[0015] One image forming mechanism 110 includes a photosensitive drum 111, a charging roller 112, a toner cartridge 113, a toner supply roller 114, a developing roller 115, and a developing blade 116.

[0016] The photosensitive drum 111 is an image carrier that carries an image. The charging roller 112 is a charging unit that uniformly charges the surface of the photosensitive drum 111.

[0017] The toner cartridge 113 is a developer storage unit that stores toner as a developer. The toner supply roller 114 is a developer supply unit that supplies toner from the toner cartridge 113 to the developing roller 115. The developing roller 115 is a developing unit that forms a toner image (developer image) of each color, which is a visible image, by attaching toner to the electrostatic latent image formed on the surface of the photosensitive drum 111. The developing blade 116 thins out the toner supplied from the toner supply roller 114 to the developing roller 115.

[0018] Above the photosensitive drum 111 in the image forming mechanism 110, an LED head 120, which is an exposure device, is provided at a position facing the photosensitive drum 111. The LED head 120 is an exposure unit that exposes the photosensitive drum 111 according to image data of each color and forms an electrostatic latent image on the photosensitive drum 111.

[0019] FIG. 2 is a perspective view showing the appearance of the LED head 120. In the LED head 120, a plurality of LEDs as a plurality of light-emitting elements are arranged in a row.

[0020] Returning to FIG. 1, as described above, the image forming mechanism 110 has a photosensitive drum 111 on which an electrostatic latent image is formed by being exposed to light by a plurality of light-emitting elements included in the LED head 120, and forms a toner image by attaching toner to the electrostatic latent image. Below the photosensitive drum 111 in the image forming mechanism 110, a transfer mechanism is arranged. The transfer mechanism includes a conveyance belt 105 and a transfer roller 106.

[0021] The conveyance belt 105 conveys a single sheet of paper from the registration roller pair 104 in the direction of arrow E shown in FIG. 1. The transfer roller 106 is arranged to face the photosensitive drum 111 via the conveyance belt 105, and is a transfer unit that transfers the toner image formed on the photosensitive drum 111 to the single sheet of paper by charging the single sheet of paper conveyed by the conveyance belt 105 to a polarity opposite to that of the toner.

[0022] A fixing device 130 is provided on the discharge side of a single sheet of paper from the conveyance belt 105. The fixing device 130 includes a heating roller 131 and a backup roller 132, and is a fixing unit that fixes the toner image to a medium.

[0023] The heating roller 131 is provided with a heater (not shown) inside and is heated by the heat generation of the heater. The backup roller 132 presses the single sheet of paper conveyed in the direction of the heating roller 131. The fixing device 130 fixes the toner image transferred to the single sheet of paper to the single sheet of paper by pressurizing and heating. On the discharge side of the fixing device 130, a discharge roller, pinch roller, paper stacker, etc. (not shown) are provided, and by these, the single sheet of paper on which the toner image is fixed is discharged to the outside of the image forming apparatus 100.

[0024] FIG. 3 is a schematic diagram showing the LED head 120 and the LED head control unit 140 that controls the LED head 120. The LED head control unit 140 is an exposure control unit that controls the LED head 120 as an exposure unit. As described above, the LED head 120 has a plurality of LEDs arranged in a substantially straight line on the substrate. The LED head 120 includes a plurality of light emission control units 121 that control the light emission of each LED. The LED head 120 also includes a correction information storage unit 122 that stores the light emission correction amount Pn for each LED as correction information.

[0025] The LED head control unit 140 reads the correction information of each LED from the correction information storage unit 122 of the LED head 120, and sets the corrected light emission intensity, which is the light emission intensity for actually causing the corresponding LED to emit light, for the light emission control unit 121.

[0026] Here, the LED head control unit 140 calculates the corrected light emission intensity of one light emitting element by adding a correction value that greatly corrects the light emission intensity of each light emitting element as the actual light emission amount P1 of each light emitting element deviates from the reference average light emission amount P, and the light emission intensity of each light emitting element optimized so that the printing density unevenness is eliminated with respect to P, to the light emission intensity of each light emitting element. Then, the LED head control unit 140 causes the one light emitting element to emit light with the corrected light emission intensity. Note that the correction value is a value that changes according to a change rate, which is a rate of changing the light emission amount calculated by multiplying the light emission correction amount Pn of one light emitting element by the time for causing the one light emitting element to emit light. Also, the actual light emission amount P1 is a value that changes depending on the temperature and humidity during printing and the printing medium.

[0027] Here, a method for calculating the light emission correction amount Pn indicated by the correction information stored in the correction information storage unit 122 will be described.

[0028] During printing, the LED head control unit 140 sequentially sends raster data to the light emission control unit 121, reads out correction information previously stored in the correction information storage unit 122, calculates the corrected light emission intensity of each light emitting element using the light emission correction amount Pn indicated by the correction information, and sequentially sends the corrected light emission intensity to the light emission control unit 121.

[0029] From this, the light emission control unit 121 selectively causes a plurality of light emitting elements of the LED head 120 to emit light according to the above raster data, and individually corrects the light emission amount of each light emitting element according to the corrected light emission intensity of each light emitting element. Then, the LED head 120 converges the LED light onto the uniformly charged photosensitive drum 111 by a lens array (not shown), and forms an electrostatic latent image corresponding to the raster data on the photosensitive drum 111.

[0030] The light emission amount of the LED can be calculated by the following formula (1). (Light emission amount) = (Light emission intensity) × (Exposure time) (1) Here, the light emission intensity mainly depends on the current (driving current) flowing through the LED which is the light emitting element, and also depends on the characteristics of the lens array (not shown). The light emission control unit 121 individually corrects the light emission amount of the LED by individually setting the driving current or the exposure time.

[0031] Here, the light emission correction amount Pn indicated by the correction information stored in the correction information storage unit 122 is a value for correcting the light emission amount of the LED so that the variation in the light emission amount of the LED and the variation in the LED exposure dot width (LED exposure dot resolution) in the direction corresponding to the screen angle of each color of black (K), yellow (Y), magenta (M), and cyan (C), which are predetermined when forming a color image with a tandem type LED color printer, are reduced. When the LED exposure dots are distorted, variations occur in the LED exposure dot width.

[0032] In a tandem type LED color printer, for each of K, Y, M, and C, a color toner image is formed by independent exposure and development processes, and an LED head 120 is arranged for each process. In such an LED color printer, if the LED exposure dots are distorted, density unevenness will occur in the color toner image.

[0033] When forming a color image with a tandem type LED color printer, the screen angles for each of the colors K, Y, M, and C are determined. Therefore, the image forming apparatus 100 sequentially exposes the photosensitive drum 111 to form a two-dimensional electrostatic latent image. At different screen angles, the arrangement of the exposure dots in the above-mentioned electrostatic latent image, and thus the arrangement of the toner dots in the toner image and the arrangement of the print dots in the printed image, are different.

[0034] Here, it is assumed that Y is printed at a screen angle of -45°, M and K are printed at a screen angle of +45°, and C is printed at a screen angle of 90°.

[0035] When printing Y over the entire surface at a screen angle of -45°, for example, in the first line, it is printed on the 1st, 3rd, 5th,... dots, and in the second line, it is printed on the 2nd, 4th, 6th,... dots. Also, when printing M or K over the entire surface at a screen angle of -45°, for example, in the first line, it is printed on the 2nd, 4th, 6th,... dots, and in the second line, it is printed on the 1st, 3rd, 5th,... dots. Furthermore, when printing C at a screen angle of 90° over the entire surface, for example, it is printed on the 1st, 3rd, 5th... dots in each line.

[0036] The procedure for obtaining the light emission correction amount Pn will be described below. As the light emission correction amount Pn, an array of correction parameters is denoted as Lcorrect, and the parameter value of the i-th dot (i = 1, 2, 3,..., i max ) of the correction parameter Lcorrect is denoted as Lcorrect(i). Here, i maxis the number of LEDs arranged in a single line.

[0037] First, obtain Pcorrect, which is a correction parameter for making the light emission amount of the LEDs constant, that is, eliminating the variation in the light emission amount of the LEDs. The parameter value of the i-th dot (i = 1, 2, 3, ···, i max ) of the parameter Pcorrect is denoted as Pcorrect(i). If the drive current is individually set according to the parameter Pcorrect, the light emission intensity of the LEDs can be made constant. Therefore, if the exposure time is set to be constant, the light emission amount of the LEDs can be made constant. Also, if the exposure time is individually set according to the parameter Pcorrect, the light emission amount of the LEDs can be made constant.

[0038] To obtain the parameter Pcorrect, for example, only one dot of the plurality of LEDs of the LED head 120 is made to emit light, and the LED light passing through the lens array is imaged from above the lens array by a CCD camera or the like. Then, the LED exposure intensity is obtained from the acquired camera image. And a parameter value for correcting this LED exposure intensity to a constant value is calculated. This parameter value is calculated for each LED.

[0039] Also, obtain WDratio, which is a parameter for making the exposure dot width in the direction along the screen angle constant, in other words, eliminating the variation in the exposure dot width. The parameter value of the i-th dot (i = 1, 2, 3, ···, i max ) of the parameter WDratio is denoted as WDratio(i).

[0040] To obtain the parameter WDratio, for example, a plurality of LEDs of the LED head 120 are caused to emit light every other dot, and the LED light that has passed through the lens array is imaged from above the lens array by a CCD camera or the like. Then, the obtained camera image is normalized so that the peak brightness becomes 1, and this normalized image is binarized with a value equal to or greater than a certain threshold value. For example, 1 / e2 (where e is the base of the natural logarithm) is generally defined as the threshold value. Next, from the above binarized image, the LED exposure dot width in the direction along the screen angle is obtained. Then, a parameter value for correcting the light emission intensity of the LED is calculated so that this LED exposure dot width becomes equal to the light emitting part pitch. This parameter value is calculated for each LED.

[0041] For example, in the case of the LED head 120 with 600 dpi, the pitch of the light emitting part is 1 / 600 mm (= 42.3 μm), and a parameter value for correcting so that the LED light emission dot width in the direction along the screen angle becomes 42.3 μm is calculated.

[0042] The LED exposure dot width WD(i) when the one-dimensional light emission intensity distribution of the LED shown in FIG. 4 is binarized with a threshold value (for example, 1 / e2), in other words, the LED exposure dot width WD(i) at the threshold value (for example, 1 / e2) of the one-dimensional light emission intensity distribution in FIG. 9 is obtained for each dot. Then, the average value WDavg of the LED exposure dot widths WD(1), WD(2), WD(3), ···, WD(i max ) can be obtained by the following formula (2).

[0043] [Equation]

[0044] Next, the ratio of the LED exposure dot width WD(i) to the average value WDavg of the LED exposure dot widths is defined as the parameter WDratio(i), and its value can be obtained by the following formula (3).

[0045] [Equation]

[0046] However, correcting the LED exposure dot width to be constant will ignore the correction for making the light emission amount of the LED constant (correction by the parameter Pcorrect). In the correction for making the LED exposure dot width constant as described above, density unevenness due to variations in the light emission amount of the LED will conversely become apparent.

[0047] Therefore, here, a parameter WDcorrect for reducing variations in the LED exposure dot width in the direction along the screen angle is obtained by multiplying a parameter WDratio for making the LED exposure dot width in the direction along the screen angle constant by a weight k (<1). A correction parameter Lcorrect for reducing both variations in the light emission amount of the LED and variations in the LED exposure dot width in the direction along the screen angle is obtained by this parameter WDcorrect and a parameter Pcorrect for making the light emission amount of the LED constant. The parameter value of the i-th dot of the parameter WDcorrect is denoted as WDcorrect(i).

[0048] The parameter WDcorrect(i) is obtained by multiplying the parameter WDratio(i) in the above formula (3) by the weight k (<1). In other words, the parameter WDcorrect(i) is obtained by the following formula (4). WDcorrect(i)=k×WDratio(i) (4) The optimal value of the weight k varies depending on the exposure / development process conditions, but around 0.2 to 0.4 is appropriate.

[0049] Then, by multiplying Pcorrect by WDcorrect considering the LED image width, variations in the LED image width can be eliminated, and density unevenness can be eliminated. The finally determined light emission correction amount Pn(i) is represented by the following formula (5). Pn(i)=Pcorrect(i)×WDcorrect(i) (5) This light emission correction amount Pn(i) is written as initial parameters in the correction information storage unit 122 at the time of factory shipment of the LED head 120.

[0050] At this time, WDcorrect is calculated for each slit, and different weights k are applied. That is, assuming the weights of the 90°, +45°, and -45° slits are k1, k2, and k3 respectively, the light emission intensity of the i-th LED is represented by the following formula (6). Pn(i) = Pcorrect(i) × WDcorrect{90(i)} × WDcorrect{+45(i)} × WDcorrect{-45(i)} (6)

[0051] Here, WDcorrect{90(i)}, WDcorrect{+45(i)}, and WDcorrect{-45(i)} are calculated by the following formulas (7) to (9) respectively from the above formula (4). WDcorrect{90(i)} = k1 × WDratio(i) (7) WDcorrect{+45(i)} = k2 × WDratio(i) (8) WDcorrect{-45(i)} = k3 × WDratio(i) (9)

[0052] Next, the operation of the image forming apparatus 100 will be described with reference to FIG. 1. First, a single sheet of paper is fed out from the papers in the paper cassette 101 by the hopping roller 103 and sent to the registration roller pair 104.

[0053] The single sheet of paper is sent from the registration roller pair 104 to the conveyance belt 105, and is conveyed to the image forming mechanisms 110K, 110Y, 110M, and 110C as the conveyance belt 105 runs.

[0054] In the image forming mechanism 110, the surface of the photosensitive drum 111 is charged by the charging roller 112. Then, by being exposed by the LED head 120, an electrostatic latent image is formed on the photosensitive drum 111.

[0055] On the electrostatic latent image, toner thinned on the developing roller 115 is electrostatically attached to form a toner image.

[0056] The toner image is transferred onto a single sheet of paper by the transfer roller 106, and a color toner image is formed on the single sheet of paper.

[0057] After the transfer of the toner image, the single sheet of paper is sent to the fixing device 130. In this fixing device 130, the color toner image is fixed onto a single sheet of paper to form a color image. The single sheet of paper on which the toner image is fixed is sandwiched between a discharge roller and pinch rollers (not shown) and discharged to a paper stacker. Through such a process, a color image is formed on the paper.

[0058] Next, a process of calculating the light emission amount of each light emitting element will be described with reference to FIG. 3. The LED head 120 includes a correction information storage unit 122 on a substrate, and the correction information storage unit 122 stores correction information indicating the light emission correction amount Pn(i) for each LED.

[0059] The LED head control unit 140 of the image forming apparatus reads the correction information from the correction information storage unit 122 and calculates the average light emission intensity Pa by averaging the light emission correction amount Pn(i). The LED head control unit 140 further calculates a correction magnification Rn(i), which is a magnification for correcting the light emission intensity of each LED, from the light emission correction amount Pn(i) and the average light emission intensity Pa using the following formula (10). Rn(i)=Pn(i)÷Pa - 1 (10)

[0060] Here, as shown in formula (10), the correction magnification Rn(i) is a value that makes it more difficult to correct the light emission intensity of the LED of the i dot as the light emission correction amount Pn(i) is closer to the average light emission intensity Pa. In other words, it is a value that makes the light emission intensity more greatly corrected as the light emission correction amount Pn(i) is farther from the average light emission intensity Pa.

[0061] Furthermore, the LED head control unit 140 calculates the emission intensity En(i) during the printing operation using the correction intensity S according to the following formula (11). En(i)=Pa×(1+Rn(i)×S) (11)

[0062] Here, formula (11) can be transformed as shown in the following formula (12). En(i)=Pa+Pa×Rn(i)×S (12) In other words, the emission intensity En(i) can be calculated by adding the correction value V represented by V = Pa×Rn(i)×S to the average emission intensity Pa. Note that the emission intensity En(i) is also referred to as the corrected emission intensity.

[0063] The LED head control unit 140 sets the calculated emission intensity En(i) as the emission intensity of the LED corresponding to the i-th dot in the corresponding emission control unit 121 mounted on the LED head 120.

[0064] Here, the correction intensity S is represented by the following formula (13) using the correction coefficient α. S=ΔPm×α+1 (13) Also, ΔPm indicates the rate of change, which is the rate of changing the emission amount. For example, for plain paper such as that used in an electrophotographic printer, ΔPm = 1; for glossy paper with a smooth paper surface, ΔPm = -0.4; for recycled paper with a rough paper surface smoothness, ΔPm = +0.4. It is a value predetermined according to the printing conditions, which are the conditions for forming an image.

[0065] When the emission control signal of the LED head 120 is transmitted by the LED head control unit 140 of the image forming apparatus 100 based on the image data, the emission control unit 121 of the LED head 120, which is an exposure device, causes the LED, which is a light emitting element, to emit light at the emission intensity En(i) set based on the emission control signal.

[0066] The imaging diameter of each LED in the LED head 120 varies depending on the state of the lens that forms the image of the LED. Therefore, in order to achieve a constant imaging diameter on the photosensitive drum 111 even when the imaging states are different, for example, for low-resolution LEDs, the light emission correction amount Pn(i) is determined so that its light emission intensity becomes smaller than the average. As a result, as shown in Fig. 5(A), the imaging diameter d at the development threshold is equal whether it is low resolution or high resolution.

[0067] However, when the change rate ΔPm of the light emission amount is changed, as shown in Fig. 5(B), a difference occurs between the imaging diameter d1 of the low-resolution LED with reduced light emission intensity and the imaging diameter d2 of the high-resolution LED with increased light emission intensity.

[0068] According to the first embodiment described above, as the change rate ΔPm of the light emission amount changes, the correction intensity S changes. Therefore, the light emission correction amount Pn(i) for the low-resolution imaging state becomes brighter, and the light emission correction amount Pn(i) for the high-resolution imaging state becomes darker. As a result, the imaging diameter difference as shown in Fig. 5(B) can be eliminated.

[0069] Fig. 6 shows the results of experimentally examining the streak level of density unevenness for each ΔPm, which is the change rate of the light emission amount, while actually changing the correction intensity S, and presenting them in a graph. As shown in Fig. 6, the peak of the printing level at the change rate of the light emission amount exists at a position different from the correction intensity S = 1. In other words, it can be seen that by adjusting the correction intensity S, the printing quality can be improved at each change rate of the light emission amount.

[0070] In this experiment, when determining the optimal correction intensity S for the rate of change in the light emission amount (here, the peak coordinates of the quadratic approximation curve for each data point in FIG. 6), as shown in FIG. 7, the best result was obtained when the correction coefficient (in other words, the slope of the approximate straight line) was changed at 0.017. Furthermore, for the streak level where the difference in density unevenness by visual inspection is not noticeable, the acceptable range of the correction coefficient α allowing a difference within 0.5 from the peak level is the intersection of the acceptable ranges of α at the rate of change in the light emission amount ΔPm = ±0.4. As shown in FIG. 7, it can be expected to exhibit a certain effect within the range of 0.005 to 0.025.

[0071] As described above, part or all of the LED head control unit 140 can be configured by, for example, a memory 10 and a processor 11 such as a CPU (Central Processing Unit) that executes a program stored in the memory 10, as shown in FIG. 8(A). Such a program may be provided through a network or may be provided recorded on a recording medium. That is, such a program may be provided, for example, as a program product.

[0072] Also, part or all of the LED head control unit 140 can be configured by a processing circuit 12 such as a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, an ASIC (Application Specific Integrated Circuit), or an FPGA (Field Programmable Gate Array), as shown in FIG. 8(B). As described above, the LED head control unit 140 can be configured by a processing circuit network. Note that the light emission control unit 121 can be configured by the processing circuit 12.

[0073] As described above, in this embodiment, the correction intensity S can be continuously changed with respect to the rate of change in the light emission amount, and the printing quality can be improved by continuously changing the correction magnification Rn(i) applied to each LED without providing a plurality of light emission correction amounts Pn(i).

Description of Symbols

[0074] 100 Image forming apparatus, 105 Conveyor belt, 106 Transfer roller, 110 Image forming mechanism, 111 Photosensitive drum, 112 Charging roller, 113 Toner cartridge, 114 Toner supply roller, 115 Developing roller, 116 Developing blade, 120 LED head, 121 Light emission control unit, 122 Correction information storage unit, 140 LED head control unit.

Claims

1. An exposure unit including a plurality of light-emitting elements, An image forming unit having an image carrier on which an electrostatic latent image is formed by receiving exposure by the plurality of light-emitting elements, and forming a developer image by attaching a developer to the electrostatic latent image, A transfer unit that transfers the developer image to a medium, A fixing unit that fixes the developer image to the medium, An exposure control unit that controls the exposure unit, and is provided with, The exposure control unit calculates a corrected emission intensity of one light-emitting element among the plurality of light-emitting elements by adding a correction value that greatly corrects the emission intensity as the actual emission amount of one light-emitting element included in the plurality of light-emitting elements deviates from a predetermined reference average emission amount for the plurality of light-emitting elements to the emission intensity of the one light-emitting element, and causes the one light-emitting element to emit light with the corrected emission intensity, The corrected emission intensity varies according to a change rate that is a rate of changing the emission amount calculated by multiplying the predetermined emission intensity of the one light-emitting element by the time for which the one light-emitting element emits light, An image forming apparatus characterized by the above.

2. When the correction value is V, the average value is Pa, the correction magnification of one light-emitting element is Rn, and a predetermined correction intensity is S, the correction value is calculated by V = Pa × Rn × S, When the predetermined emission intensity of the one light-emitting element is Pn, the correction magnification Rn is calculated by Rn = Pn ÷ Pa - 1, The image forming apparatus according to claim 1, characterized by the above.

3. When the change rate is ΔPm and a predetermined correction coefficient is α, the correction intensity S is calculated by S = 1 + ΔPm × α, The change rate ΔPm is predetermined according to the conditions for forming an image, The image forming apparatus according to claim 2, characterized by the above.

4. The correction coefficient α is a value within the range of 0.005 < α < 0.025, The image forming apparatus according to claim 3, characterized by the above.

Images