Image forming device

Abstract

To reduce the number of density detection parts to be installed without deteriorating accuracy of density variation correction in comparison to a case where an exposure part is constituted by a plurality of light emission parts and a case where the density detection parts for detecting the density of the image are installed in the same number as the number of the light emission parts.SOLUTION: An exposure part is constituted by three LPH 141-143 in which a plurality of LEDs are arrayed respectively. Five density sensors 170a-170e are arranged for detecting the densities of images obtained by developing electrostatic latent images on a photoreceptor roll 152. The density sensors 170a-170c are arranged at positions corresponding to the substantially center position of each of the three LPH 141-143 being the light emission parts. The density sensors 170d, 170e are arranged at positions corresponding to an end closer to an end of the photoreceptor roll 152 of the two LPH 141, 143 arranged on an end side of the photoreceptor roll 152 out of the three LPH 141-143.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Patent document 1 discloses an image forming device that generates a composite value by combining the density unevenness values ​​for each factor corresponding to the synchronized timing for each factor from each of first density unevenness distribution information representing a two-dimensional distribution of density unevenness for each of a plurality of factors that cause density unevenness in an image, extracted in correspondence with timing synchronized for each factor, and controls image data or the exposure amount of an exposure device based on the generated composite value so that density unevenness corresponding to the timing synchronized for each factor does not occur. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-022101 A Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present invention is to provide an image forming device which, when an exposure section is composed of multiple light-emitting sections, can reduce the number of density detection sections to be installed without degrading the accuracy of density fluctuation correction, compared to a case in which the same number of density detection sections for detecting the density of an image are installed for each of the multiple light-emitting sections. [Means for solving the problem]

[0005] The image forming apparatus according to a first aspect of the present invention includes an image carrier that holds an image developed by a developer; an exposure section which has a plurality of light emitting sections, each of which has a plurality of light emitting elements arranged therein, and which is arranged so as to face the image carrier and is offset from the image carrier, and which forms an electrostatic latent image on the image carrier by exposing the image carrier to light; The image forming apparatus is provided with a plurality of concentration detection units, each of which is disposed at a position corresponding to approximately the center position of each of the plurality of light-emitting units, and at a position corresponding to the end closer to the end of the image carrier of two of the plurality of light-emitting units which are disposed on the end side of the image carrier, and which detect the concentration of an image obtained by developing an electrostatic latent image on the image carrier.

[0006] An image forming apparatus of a second aspect of the present invention is the image forming apparatus of the first aspect, further comprising a correction unit that performs gradation correction to correct output density for input pixel values ​​using density information detected by a density detection unit arranged corresponding to approximately the center position of a centrally located light-emitting unit among the plurality of light-emitting units when the number of the plurality of light-emitting units is odd.

[0007] An image forming apparatus of a third aspect of the present invention is the image forming apparatus of the second aspect, in which the correction unit performs density correction using density information detected by a density detection unit among the plurality of density detection units, the density detection unit being provided at a position corresponding to approximately the center position of each of the plurality of light-emitting units, so as to suppress density differences between the light-emitting units.

[0008] An image forming apparatus of a fourth aspect of the present invention is an image forming apparatus of the second or third aspect, in which the correction unit uses each density information detected by the multiple density detection units to correct periodic density fluctuations in a sub-scanning direction perpendicular to a main scanning direction in which the exposure unit exposes the image carrier.

[0009] An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects, wherein the density detection units arranged at positions corresponding to approximately central positions of the plurality of light emitting units among the plurality of density detection units are configured to be capable of receiving specularly reflected light and diffusely reflected light of a measurement target image; Among the multiple density detection units, the density detection unit arranged at a position corresponding to the end closer to the end of the image carrier of the two light-emitting units arranged on the end side of the image carrier is configured to receive only the specularly reflected light of the image to be measured.

[0010] An image forming apparatus of a sixth aspect of the present invention is an image forming apparatus of any one of the first to fifth aspects, wherein the multiple density detection units are arranged to detect the density of an image on an intermediate transfer body to which a developer image formed on the image carrier is transferred.

[0011] An image forming apparatus according to a seventh aspect of the present invention includes an image carrier that holds an image developed by a developer; an exposure section which has a plurality of light emitting sections, each of which has a plurality of light emitting elements arranged therein, and which is arranged so as to face the image carrier and is offset from the image carrier, and which forms an electrostatic latent image on the image carrier by exposing the image carrier to light; The exposure unit is provided with a control unit that controls the formation of multiple inspection images of the same density in succession in a sub-scanning direction perpendicular to the main scanning direction, at positions corresponding to approximately the center positions of each of the multiple light-emitting units in a main scanning direction, which is the direction in which the exposure unit exposes the image holder, and at positions corresponding to the ends of two of the multiple light-emitting units that are arranged on the end side of the image holder that are closer to the end of the image holder. Effect of the Invention

[0012] According to the image forming apparatus of the first aspect of the present invention, when the exposure section is composed of a plurality of light-emitting sections, the number of density detection sections to be installed can be reduced without deteriorating the accuracy of density fluctuation correction, compared to a case in which the same number of density detection sections for detecting the density of an image are installed for each of the plurality of light-emitting sections.

[0013] According to the image forming apparatus of the second aspect of the present invention, the amount of processing required for tone correction can be reduced compared to when tone correction is performed based on densities at a plurality of locations.

[0014] According to the image forming apparatus of the third aspect of the present invention, even when only one density detection unit is arranged for one light-emitting unit, it is possible to perform density correction that suppresses density differences between the light-emitting units.

[0015] According to the image forming apparatus of the fourth aspect of the present invention, it is possible to correct density fluctuations in the sub-scanning direction at each location where a plurality of density detection units are arranged.

[0016] According to the image forming apparatus of the fifth aspect of the present invention, it is possible to realize density fluctuation correction in the sub-scanning direction and gradation correction without requiring all density detection units to have high performance.

[0017] According to the image forming apparatus of the sixth aspect of the present invention, the density of the developer image can be detected before the image is formed on the recording medium.

[0018] According to the seventh aspect of the image forming apparatus of the present invention, the amount of developer used for density measurement can be reduced compared to when a test image for density measurement is formed over the entire area in the main scanning direction. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram showing a configuration of an image forming apparatus 10 according to an embodiment of the present invention. [Diagram 2] 2 is a diagram showing the positional relationship between a photoconductor roll 152 and a developing roll 157. FIG. [Diagram 3] 1A and 1B are diagrams for explaining the state in which the shape of the photoconductor roll 152 and the developing roll 157 themselves is distorted or warped. [Figure 4] 1 is a diagram for explaining names of directions in the layout of an image forming apparatus 10 and an image to be formed. [Diagram 5] 1 is a diagram for explaining an operation when density correction is performed by a control unit 20 in an image forming apparatus 10 according to an embodiment of the present invention. FIG. [Figure 6] FIG. 6(A) shows an example in which three concentration sensors 170 are arranged for one LPH in a printer compatible with A3 size, and FIG. 6(B) shows an example in which three concentration sensors 170 are arranged for one LPH in a printer compatible with large size. [Figure 7]1 is a diagram for explaining the positional relationship between a concentration sensor 170 and LPHs 141 to 143 in this embodiment. [Figure 8] 13 is a diagram showing an example of the arrangement of the density sensor 10 when the exposure unit 140 is composed of two LPHs. FIG. [Figure 9] 13 is a diagram showing an example of the arrangement of the density sensor 10 when the exposure unit 140 is composed of four LPHs. FIG. [Figure 10] FIG. 13 is a diagram showing an example of an arrangement in which, of five concentration sensors 170a to 170e, two types of sensors with different performance are used. [Figure 11] FIG. 13 is a diagram showing an example of the configuration of an inspection patch image 200 for detecting density unevenness when five density sensors 170a to 170e are arranged. [Figure 12] 1 is a diagram for explaining a state in which a test patch image 200 is formed only in a place where it is desired to detect a density value when an inline density sensor 170 is used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Next, an embodiment of the present invention will be described in detail with reference to the drawings.

[0021] FIG. 1 is a diagram showing a configuration of an image forming apparatus 10 according to an embodiment of the present invention.

[0022] 1, the image forming apparatus 10 includes image forming units 14K, 14C, 14M, and 14Y, an intermediate transfer belt 16, a paper tray 17, a paper transport path 18, a fixing unit 19, and a control unit 20. The image forming apparatus 10 includes a printer function for printing image data received from a personal computer (not shown) or the like.

[0023] First, to give an overview of the image forming apparatus 10, a control unit 20 is disposed on the upper part of the image forming apparatus 10. The control unit 20 performs image processing such as gradation correction and resolution correction on image data input from a personal computer (not shown) or the like via a network line such as a LAN, and outputs the image to the image forming unit 14.

[0024] Four image forming units 14K, 14C, 14M, and 14Y are arranged below the control unit 20 in correspondence with the colors constituting the color image. In this embodiment, the four image forming units 14K, 14C, 14M, and 14Y corresponding to the colors of black (K), cyan (C), magenta (M), and yellow (Y) are horizontally arranged at regular intervals along the intermediate transfer belt 16. The intermediate transfer belt 16 rotates in the direction of the arrow A in the figure as an intermediate transfer body, and these four image forming units 14K, 14Y, 14M, and 14C sequentially form toner images of each color based on image data input from the control unit 20, and transfer (primary transfer) these multiple toner images to the intermediate transfer belt 16 at a timing when they are superimposed on each other. The order of the colors of each image forming unit 14K, 14C, 14M, 14Y is not limited to black (K), cyan (C), magenta (M), and yellow (Y), but may be any order, such as yellow (Y), magenta (M), cyan (C), and black (K).

[0025] The paper transport path 18 is disposed below the intermediate transfer belt 16. The recording paper 32 supplied from the paper tray 17 is transported on the paper transport path 18, and the toner images of each color transferred in multiple layers onto the intermediate transfer belt 16 are transferred together (secondary transfer). The transferred toner images are fixed by a fixing device 19 and discharged to the outside along the arrow B.

[0026] Next, each component of the image forming apparatus 10 will be described in more detail.

[0027] The control unit 20 performs predetermined image processing such as shading correction, brightness / color space conversion, gamma correction, etc., on the input image data. For example, when the input image data is data of red (R), green (G), and blue (B) (each 8 bits), the image processing by the control unit 20 converts it into document color material gradation data of four colors, black (K), cyan (C), magenta (M), and yellow (Y) (each 8 bits).

[0028] The image forming units 14K, 14C, 14M, and 14Y (image forming means) are arranged in parallel at regular intervals in the horizontal direction, and are configured almost the same except for the colors of the images they form. Therefore, the image forming unit 14K will be described below. The configuration of each image forming unit 14 is distinguished by adding K, C, M, or Y.

[0029] The image forming unit 14K has an exposure section 140K that irradiates light in accordance with image data input from the control section 20, and an image forming device 150K in which an electrostatic latent image is formed by the laser light scanned by this exposure section 140K.

[0030] The exposure unit 140K forms an electrostatic latent image on the photoreceptor roll 152K by irradiating the photoreceptor roll 152K of the image forming device 150K with laser light corresponding to image data of black (K). The exposure unit 140K is composed of a plurality of rod-shaped LPHs (LED Print Heads) each having a plurality of LEDs, which are light-emitting elements, arranged thereon. The configuration of the exposure unit 140K will be described in detail later.

[0031] The image forming device 150K is composed of a photoconductor roll 152K that rotates at a predetermined rotation speed along the direction of the arrow A, a charging device 154K as a charging means for uniformly charging the surface of the photoconductor roll 152K, a developing device 156K that develops an electrostatic latent image formed on the photoconductor roll 152K, and a cleaning device 158K. The photoconductor roll 152K is a cylindrical image carrier that holds an image developed with a developer such as toner, and is uniformly charged by the charging device 154K, and an electrostatic latent image is formed on the photoconductor roll 152K by a laser beam irradiated by an exposure unit 140K. The electrostatic latent image formed on the photoconductor roll 152K is developed with a developer such as black (K) toner by the developing device 156K and transferred to the intermediate transfer belt 16. Note that residual toner and paper powder adhering to the photoconductor roll 152K after the transfer process of the toner image (developer image) are removed by the cleaning device 158K.

[0032] The other image forming units 14C, 14M, and 14Y similarly have photoconductor rolls 152C, 152M, and 152Y and developing devices 156C, 156M, and 156Y, respectively, and form toner images of cyan (C), magenta (M), and yellow (Y) colors, and transfer the formed toner images of each color to the intermediate transfer belt 16.

[0033] The intermediate transfer belt 16 is wound around a drive roll 164, idle rolls 165, 166, 167, a backup roll 168, and an idle roll 169 with a constant tension, and is driven to circulate at a predetermined speed in the direction of arrow A by a drive motor (not shown) rotating the drive roll 164. The intermediate transfer belt 16 is formed into an endless belt shape by forming a flexible synthetic resin film such as polyimide into a belt shape and connecting both ends of the belt-shaped synthetic resin film by welding or the like.

[0034] Further, primary transfer rolls 162K, 162C, 162M, and 162Y are disposed on the intermediate transfer belt 16 at positions facing the image forming units 14K, 14C, 14M, and 14Y, respectively, and the toner images of each color formed on the photoreceptor rolls 152K, 152C, 152M, and 152Y are transferred in multiple layers onto the intermediate transfer belt 16 by these primary transfer rolls 162. Residual toner adhering to the intermediate transfer belt 16 is removed by a cleaning blade or brush of a belt cleaning device 189 provided downstream of the secondary transfer position.

[0035] Also, a density sensor 170 is provided in the vicinity of the intermediate transfer belt 16. This density sensor 170 is a density detection unit that detects the density of the toner image transferred onto the intermediate transfer belt 16. Note that in this embodiment, a plurality of density sensors 170 are arranged, and the positions at which the density sensors 170 are arranged will be described later.

[0036] The paper transport path 18 is provided with a paper feed roll 181 that takes out the recording paper 32 from the paper tray 17, a first roll pair 182, a second roll pair 183, and a third roll pair 184 for paper transport, and a registration roll 185 that transports the recording paper 32 to the secondary transfer position at a predetermined timing.

[0037] Further, at the secondary transfer position on the paper transport path 18, a secondary transfer roll 186 is disposed in pressure contact with the backup roll 168, and the toner images of each color transferred in multiple layers onto the intermediate transfer belt 16 are secondarily transferred onto the recording paper 32 by the pressure and electrostatic force of this secondary transfer roll 186. The recording paper 32 onto which the toner images of each color have been transferred is transported to the fixing device 19 by transport belts 187 and 188.

[0038] The fixing device 19 applies heat and pressure to the recording paper 32 onto which the toner images of each color have been transferred, thereby melting and fixing the toner to the recording paper 32 .

[0039] The developing device 156K has a cylindrical developing roll (developer transport section) 157K that transports developer to the photoconductor roll 152K by rotational motion and forms a developer image on the photoconductor roll 152K. Similarly, the image forming units 14C, 14M, and 14Y that form images of other colors also have developing rolls in the developing devices 156C, 156M, and 156Y, respectively.

[0040] In the image forming apparatus 10 of this embodiment, an image is formed on a recording medium such as printing paper by the electrophotographic method configured as described above.

[0041] However, in the image forming apparatus 10 of this embodiment, since images are formed using rotating bodies such as the photosensitive roll 152 and the developing roll 157, periodic density unevenness (density fluctuation) may occur in the sub-scanning direction, which is the paper transport direction.

[0042] For example, the positional relationship between the photoconductor roll 152 and the developing roll 157 is shown in FIG.

[0043] 2, the photoconductor roll 152 and the developing roll 157 are provided facing each other with a certain gap therebetween. The developing roll 157 holds the developer on its surface by the magnetic force of a magnet provided inside, and rotates to transport the developer held in the gap formed between it and the photoconductor roll 152, thereby visually developing the electrostatic latent image formed on the surface of the photoconductor roll 152.

[0044] However, if the rotation axes of the photoconductor roll 152 and the developing roll 157 are eccentric and deviate from the ideal rotation axes, the gap between the photoconductor roll 152 and the developing roll 157 will change periodically. Also, the same problem occurs when the photoconductor roll 152 and the developing roll 157 are not arranged completely parallel to each other.

[0045] Furthermore, as shown in Fig. 3, the same problem occurs when the shape of the photoconductor roll 152 or the developing roll 157 itself is distorted or warped. Fig. 3(A) shows the case where the photoconductor roll 152 or the developing roll 157 has an ideal shape. Fig. 3(B) shows the case where the center portion of the photoconductor roll 152 or the developing roll 157 has a shape that bulges out more than the ends, and Fig. 3(c) shows the state where the photoconductor roll 152 or the developing roll 157 is warped.

[0046] Due to such causes, periodic density unevenness may occur in the formed image in the sub-scanning direction.

[0047] Here, the names of the directions in the image formed and the arrangement of the image forming apparatus 10 will be described with reference to Fig. 4. As shown in Fig. 4, the direction in which the laser light is scanned by the exposure unit 140, that is, the longitudinal direction of the photoreceptor roll 12, is referred to as the main scanning direction. The direction perpendicular to this main scanning direction, that is, the paper transport direction in which printing paper or the like is transported, is referred to as the sub-scanning direction.

[0048] Next, the operation when density correction is performed by the control unit 20 in the image forming apparatus 10 of this embodiment will be described with reference to FIG.

[0049] As described above, the control unit 20 controls the formation of an image based on the input image data on a recording medium such as printing paper. The control unit 20 also includes a density correction unit 21 for performing density correction to suppress density unevenness in the image formed on the recording medium.

[0050] The density correction unit 21 detects density unevenness in the output image based on density information such as density values ​​detected by the density sensor 170, and adjusts the amount of exposure in the exposure unit 140 or changes pixel values ​​when forming an image so as to suppress the detected density unevenness. Note that the density correction unit 21 determines the position in the image when performing such density correction based on rotation phase information such as the Z-phase signal of the photoconductor roll 152, rotation phase information such as the Z-phase signal of the developing roll 157, a page top signal, and a scanning top signal.

[0051] As described above, the density unevenness caused by the eccentricity, distortion, or bending of the photoconductor roll 152 or the developing roll 157 varies in period, phase, and amplitude depending on the position in the main scanning direction. In particular, the degree of density unevenness may vary significantly between the center and the ends in the main scanning direction.

[0052] Therefore, instead of providing only one density sensor 170 for detecting density unevenness, a plurality of density sensors 170 are used to detect density unevenness.

[0053] For example, as shown in FIG. 6A, in the case of a printer compatible with A3 size, concentration sensors 170 are arranged at three locations, namely, the center and both ends, of a photosensitive roll 152a and one LPH 141 to detect concentration.

[0054] Here, when an LPH for A3 size is converted to a printer compatible with large sizes whose main scanning direction is longer than the A3 width, multiple LPHs are arranged to expose the entire width of the photoconductor roll 152.

[0055] For example, in the image forming apparatus 10 of this embodiment, three LPHs 141 to 143 are arranged to expose the photoconductor roll 152 to light.

[0056] Here, LPHs 141 to 143 are each light-emitting units in which multiple LEDs are arranged, and are offset so as to face the photoconductor roll 152, which is an image carrier, thereby being configured to expose the entire width of the photoconductor roll 152.

[0057] FIG. 6B shows a state in which three concentration sensors 170 are arranged for each of the three LPHs 141 to 143.

[0058] 6B, when three density sensors 170 are arranged for each LPH, a total of nine density sensors 170 are required. Arranging such a large number of density sensors 170 leads to cost information of the image forming apparatus 10.

[0059] Therefore, the density sensor 170 in the image forming apparatus 10 of this embodiment is disposed at a position as shown in Fig. 7. Fig. 7 is a diagram for explaining the positional relationship between the density sensor 170 and the LPHs 141 to 143 in this embodiment.

[0060] In the image forming apparatus 10 of this embodiment, the exposure section 140 is made up of three LPHs 141 to 143. In addition, in the image forming apparatus 10 of this embodiment, five density sensors 170a to 170e are arranged.

[0061] The five density sensors 170a to 170e are arranged to detect the density of an image obtained by developing the electrostatic latent image on the photoconductor roll 152. The density sensors 170a to 170c are arranged at positions corresponding to the approximate center positions of the three LPHs 141 to 143 which are light-emitting units, and the density sensors 170d and 170e are arranged at positions corresponding to the ends of the two LPHs 141 and 143 which are arranged on the end side of the photoconductor roll 152 among the three LPHs 141 to 143 and which are closer to the end of the photoconductor roll 152.

[0062] Here, "approximately the center of the LPH" means within a range of 40 to 60% of the total length of the LPH, and "ends" means regions whose distance from both ends of the object is within a range of 0 to 10% of the object's length.

[0063] Incidentally, the density sensors 170a to 170c are disposed in the centers of the LPHs 141 to 143, respectively, so that when density unevenness occurs between the LPHs 141 to 143, the density sensors 170a to 170c can detect the density unevenness between the LPHs 141 to 143. Also, the density sensors 170d and 170e are disposed at positions where they can detect density unevenness at the ends of the photoconductor roll 152, that is, at the ends of the formed image in the main scanning direction.

[0064] For example, when the rotation axis of the photoconductor roll 152 or the developing roll 157 is tilted, or when the rotation axis of the photoconductor roll 152 and the rotation axis of the developing roll 157 are not parallel, density unevenness may occur at the ends of the formed image in the main scanning direction. Also, when the shape of the photoconductor roll 152 or the developing roll 157 is distorted or warped, the density difference between the center and the ends may become large, and density unevenness can be detected by comparing the density value of the density sensor 170b arranged in the center with the density values ​​of the density sensors 170d and 170e arranged at the ends.

[0065] When the number of multiple LPHs is odd, the density correction unit 21 performs gradation correction to correct the output density for the input pixel value, using density information detected by a density sensor 170 arranged corresponding to approximately the center position of the centrally arranged LPH among the multiple LPHs.

[0066] For example, since the number of LPHs in this embodiment is three, tone correction is performed to correct the output density for the input pixel value using density information detected by density sensor 170b arranged corresponding to LPH 142, which is arranged in the center of the three LPHs 141 to 143.

[0067] This is because the density information at the center position in the main scanning direction of the image to be formed is most likely to represent the density of the entire image, and therefore, when performing gradation correction using only one piece of density information, it is likely that the most appropriate gradation correction can be performed by using the density information from density sensor 170b, which detects the density at the center of the image.

[0068] In addition, the concentration correction unit 21 performs concentration correction so as to suppress the concentration difference between the LPHs, using concentration values ​​detected by the concentration sensors 170a to 170c, among the five concentration sensors 170a to 170e, which are provided at positions corresponding to approximately the central positions of the three LPHs 141 to 143.

[0069] In other words, the concentration values ​​detected by the three concentration sensors 170a to 170c provided at positions corresponding to approximately the center positions of the three LPHs 141 to 143 can be considered to represent the characteristics of the LPHs 141 to 143, respectively.

[0070] The density correction unit 21 then uses the density values ​​detected by the five density sensors 170a to 170e to correct periodic density fluctuations in the sub-scanning direction perpendicular to the main scanning direction in which the exposure unit 140 exposes the photoconductor roll 152.

[0071] As described above, the five density sensors 170a to 170e are arranged so as to detect the density of the image on the intermediate transfer belt 16 onto which the developer image formed on the photoconductor roll 152 is transferred.

[0072] 7 has been described as a case where each exposure section 140 is composed of three LPHs, but an example of the arrangement of the concentration sensor 10 when the exposure section 140 is composed of two LPHs is shown in Fig. 8. Fig. 8 shows a case where the exposure section 140 is composed of two LPHs, 141 and 142.

[0073] In this manner, when the exposure section 140 is composed of two LPHs 141, 142, the four concentration sensors 170a to 170d are arranged at positions corresponding to approximately the centers of the LPHs 141, 142, and at two positions corresponding to the ends closer to the ends of the photosensitive roll 152b of the two LPHs 141, 142.

[0074] That is, the concentration sensors 170a and 170b are disposed so as to correspond to approximate central positions of the LPHs 141 and 142, respectively, and the concentration sensors 170c and 170d are disposed at positions corresponding to the ends of the photoconductor roll 152b.

[0075] Next, an example of the arrangement of the density sensor 10 when the exposure section 140 is composed of four LPHs is shown in Fig. 9. In Fig. 9, the exposure section 140 is shown to be composed of four LPHs 141-144.

[0076] In this manner, when the exposure section 140 is composed of four LPHs 141-144, the six concentration sensors 170a-170f can be disposed at positions corresponding to approximately the centers of the LPHs 141-144, and at two positions corresponding to the ends of the two LPHs 141, 144 provided on the end side of the photosensitive roll 152c that are closer to the end of the photosensitive roll 152c.

[0077] That is, the concentration sensors 170a to 170d are disposed so as to correspond to approximate center positions of the LPHs 141 to 143, respectively, and the concentration sensors 170e and 170f are disposed at positions corresponding to the ends of the photoconductor roll 152c.

[0078] In the example of the arrangement of the concentration sensors 170 shown in FIG. 7, the five concentration sensors 170a to 170e all have the same performance. However, FIG. 10 shows an example of an arrangement in which two types of sensors with different performance are used.

[0079] 10, the five density sensors 170a-170e, which are arranged at positions corresponding to the approximate centers of the three LPHs 141-143, are configured to be able to receive specularly reflected light and diffusely reflected light from the image to be measured. Among the five density sensors 170a-170e, the density sensors 170d and 170e arranged at positions corresponding to the ends of the two LPHs 141 and 143 arranged on the end side of the photoconductor roll 152 that are closer to the end of the photoconductor roll 152 are configured to be able to receive only specularly reflected light from the image to be measured.

[0080] Generally, a sensor capable of receiving both specularly reflected light and diffusely reflected light is more expensive than a sensor capable of receiving only specularly reflected light.

[0081] The three density sensors 170a to 170c arranged approximately in the center of the LPHs 141 to 143 are used to suppress density variations between the LPHs 141 to 143 and correct the gradation characteristics of each, so they are required to accurately detect absolute density values.

[0082] In contrast, the two density sensors 170d, 170e arranged at the ends of the photosensitive roll 152 only need to be able to detect density unevenness in the sub-scanning direction, and therefore their purpose will be achieved if they can detect relative density changes.

[0083] For this reason, low-cost sensors are used for the two density sensors 170d, 170e arranged at the ends of the photosensitive roll 152, and high-cost sensors are used for the three density sensors 170a-170c arranged approximately in the centers of the LPHs 141-143.

[0084] By arranging the concentration sensors in this way, the overall cost can be reduced compared to a case in which all of the five concentration sensors 170a to 170e are high-cost sensors.

[0085] Next, FIG. 11 shows an example of the configuration of an inspection patch image 200 for detecting density unevenness when the density sensor is arranged in the above-mentioned state.

[0086] As shown in FIG. 11, it can be seen that the test patch image 200, which is a test image for detecting density unevenness, is formed corresponding to the positions where the density sensors 170a to 170d are disposed.

[0087] When forming such a test patch image 200, the control unit 20 controls the formation of multiple test patch images 200 of the same density in succession in the sub-scanning direction perpendicular to the main scanning direction at positions corresponding to approximately the center positions of each of the three LPHs 141 to 143 in the main scanning direction, which is the direction in which the exposure unit 140 exposes the photosensitive roll 152, and at positions corresponding to the ends closer to the end of the photosensitive roll 152 of the two LPHs 141, 143 arranged on the end side of the photosensitive roll 152 among the three LPHs 141 to 143.

[0088] In addition, in Figure 11, a case is shown in which a solid image of the same density and maximum density is formed as the inspection patch image 200, but in some cases, an image of not only the maximum density but also a half-tone image may be formed as the inspection patch image 200.

[0089] For example, when adjusting the gradation characteristics, which are the characteristics of the density of the output image relative to the input pixel value, it is necessary to form an image of not only maximum density but also intermediate density and measure the density value with the density sensor 170.

[0090] 11, the test patch image 200 is formed only at positions corresponding to the positions where the density sensors 170a-170d are arranged, but it is possible to perform density detection even if an image of the same density is formed over the entire width in the main scanning direction. However, if an image of the same density is formed over the entire width in the main scanning direction, a large amount of toner is consumed, and the toner formed in positions other than the positions where the density detection is performed is wasted. Therefore, if the test patch image 200 is formed only at positions corresponding to the positions where the density sensors 170a-170d are arranged, as shown in FIG. 11, the amount of toner consumed can be reduced.

[0091] As shown in FIG. 12, even when an inline-type density sensor 170 is used instead of density sensors 170a to 170d, the amount of toner consumed can be reduced to a minimum by forming a test patch image 200 only in the location where the density value is to be detected. [Explanation of symbols]

[0092] 10 Image forming device 14K, 14C, 14M, 14Y Image forming unit 16 Intermediate transfer belt 17 Paper Tray 18 Paper transport path 19 Fixing unit 20 Control section 21 Density correction section 32 Recording Sheet 140K exposure section 141~144 LPH 150K image forming device 152K, 152C, 152M, 152Y Photoconductor roll 154K Charging device 156K, 156C, 156M, 156Y Developing Device 158K Cleaning Device 162K, 162C, 162M, 162Y Primary transfer roll 164 Drive Roll 165, 166, 167 Idol Roll 168 Backup Roll 169 Idol Roll 170, 170a~170e Concentration sensor 189 Cleaning Equipment 168 Backup Roll 181 Paper feed roll 182, 183, 184 Roll vs. 185 Registration Roll 186 Secondary transfer roll 187, 188 Conveyor belt

Claims

1. an image carrier that holds an image developed by a developer; an exposure section which has a plurality of light emitting sections, each of which has a plurality of light emitting elements arranged therein, and which is arranged so as to face the image carrier and is offset from the image carrier, and which forms an electrostatic latent image on the image carrier by exposing the image carrier to light; a plurality of density detection units that are disposed at positions corresponding to approximately central positions of the plurality of light-emitting units and at positions corresponding to ends closer to the ends of the image carrier of two light-emitting units that are disposed on the end sides of the image carrier among the plurality of light-emitting units, and detect the density of an image obtained by developing the electrostatic latent image on the image carrier; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, further comprising a correction unit that performs gradation correction to correct output density for input pixel values ​​using density information detected by a density detection unit that is positioned corresponding to approximately the center position of a centrally located light-emitting unit among the plurality of light-emitting units when the number of the plurality of light-emitting units is odd.

3. The image forming apparatus according to claim 2, wherein the correction unit performs density correction so as to suppress density differences between the light-emitting units, using density information detected by a density detection unit among the plurality of density detection units, the density detection unit being provided at a position corresponding to approximately the center position of each of the plurality of light-emitting units.

4. 4. An image forming apparatus according to claim 2 or 3, wherein the correction unit uses the respective density information detected by the plurality of density detection units to correct periodic density fluctuations in a sub-scanning direction perpendicular to a main scanning direction in which the exposure unit exposes the image carrier.

5. Among the plurality of density detection units, density detection units arranged at positions corresponding to approximately central positions of the plurality of light emitting units are configured to be capable of receiving specular reflected light and diffuse reflected light from an image to be measured, 5. An image forming apparatus according to claim 1, wherein the density detection unit arranged at a position corresponding to the end closer to the end of the image carrier than the two light-emitting units arranged on the end side of the image carrier is configured to receive only the specularly reflected light of the image to be measured.

6. 6. The image forming apparatus according to claim 1, wherein the plurality of density detection units are arranged to detect the density of an image on an intermediate transfer body onto which the developer image formed on the image carrier is transferred.

7. an image carrier that holds an image developed by a developer; an exposure section which has a plurality of light emitting sections, each of which has a plurality of light emitting elements arranged therein, and which is arranged so as to face the image carrier and is offset from the image carrier, and which forms an electrostatic latent image on the image carrier by exposing the image carrier to light; a control unit that controls so that a plurality of inspection images of the same density are successively formed in a sub-scanning direction perpendicular to the main scanning direction at positions corresponding to approximately central positions of the plurality of light-emitting units in a main scanning direction in which the exposure unit exposes the image carrier, and at positions corresponding to ends of two light-emitting units among the plurality of light-emitting units that are disposed on the end sides of the image carrier that are closer to the end of the image carrier; and An image forming apparatus comprising:

Images