JP2020052197A - Image formation device - Google Patents

Abstract

To accurately determine an amount of focus deviation of a latent image written on a photoreceptor when writing the latent image on the photoreceptor using a plurality of light source elements.SOLUTION: An image formation device comprises: a photoreceptor 1; an image writing device 2 having light source means 3 consisting of a plurality of light source elements 3a and image formation means 4 that forms an image on the photoreceptor 1 using light Bm for image formation emitted from the light source means 3; a development device 5 that develops the latent image formed on the photoreceptor 1 by the image writing device 2; drawing means 6 that draws a determination image 11 including a vertical line image 12 extending in a vertical direction along the photoreceptor 1 in its rotational direction and a lateral line image 13 extending in a lateral direction along the photoreceptor 1 in its axial direction with respect to the vertical line image 12 on the surface of the photoreceptor 1, using the image writing device 2 and the development device 5 when determining an amount of focus deviation of the latent image written by the image writing device 2; and measurement means 7 that measures an image change attributed to the amount of focus deviation generated by the image writing device 2 based on the determination image 11.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

Conventionally, as this type of image forming apparatus, for example, those described in Patent Documents 1 and 2 are already known.
Japanese Patent Application Laid-Open No. H11-163873 discloses a supply detection unit that detects that a photosensitive drum or a writing exposure unit of an image forming apparatus has been replaced. Each time the supply detection unit detects, a reference image forming unit sets a predetermined reference density as a target. A reference image is formed on the photosensitive drum under the image forming conditions determined, and the density of the reference image is detected by an optical density detecting means. There is disclosed an image forming apparatus which determines that a defocus has occurred between a photosensitive drum and a writing exposure unit by a determining unit.
Patent Document 2 discloses that an LED print head has an LED array and a rod lens array, forms first and second toner images with the same exposure pattern on a photosensitive drum, and then forms a first image with a density sensor. And the density distribution of the second toner image is obtained, and the first and second density distributions are obtained. The arithmetic circuit converts the first and second density distributions into voltage values based on the first and second voltage signals. The first and second MTFs are obtained, the position of the LED print head is adjusted by the motor drive control device, the distance between the LED print head and the photosensitive drum is adjusted so that the MTF is maximized, and further, the arithmetic circuit is Moving the other end of the exposure unit relative to the photosensitive drum with one end of the LED print head as a reference point according to the phase difference between the first and second voltage signals to correct the inclination of the LED print head. Image forming apparatus is disclosed.

JP, 2015-52645, A (Embodiment for carrying out the invention, FIG. 12) JP-A-2004-148748 (Embodiment of the invention, FIG. 1)

  A technical problem to be solved by the present invention is to accurately determine a defocus amount of a latent image written on a photoconductor when writing a latent image on the photoconductor using a plurality of light source elements.

  The invention according to claim 1 is a light source unit comprising a rotating photoreceptor, a plurality of light source elements provided to face the photoreceptor, and arranged along the axial direction of the photoreceptor, and irradiation from the light source unit. An image writing device having an image forming unit that forms the formed latent image forming light on the photoconductor, a developing device that develops the latent image formed by the image writing device on the photoconductor, When determining the amount of defocus of the latent image written by the image writing device, the image writing device and the developing device are used, and on the surface of the photoconductor in a vertical direction along the rotation direction of the photoconductor. A drawing unit that draws a vertical line image that extends toward the image and a determination image that includes a horizontal line image that extends in the horizontal direction along the axial direction of the photoconductor relative to the vertical line image, and a drawing unit that draws the determination image. From the image for determination, the image writing device Measuring means for measuring an image change due to the focus shift amount by an image forming apparatus comprising the.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image for determination is arranged in the direction of rotation of the photoconductor and the vertical line image in a stripe pattern arranged in the axial direction of the photoconductor. An image forming apparatus characterized by including the striped horizontal line image.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image for determination is an interval between images of the vertical line image and the horizontal line image arranged in a striped manner without a focus shift. Is wider than the line width of each image.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the measuring unit also serves as a detecting unit that detects a density of a developed image developed by the developing device. Image forming apparatus.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, a correction unit that corrects a defocus amount of the image writing device based on a measurement result of the measurement unit is provided. Device.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the correction unit calculates a development density change by a development device due to a defocus amount by the image writing device, and calculates the development density change. An image forming apparatus is characterized in that a developer is supplied so as to make a correction.
According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth aspect, the correction unit calculates a latent image potential change caused by a defocus amount by the image writing device, and corrects the latent image potential change. An image forming apparatus that adjusts a latent image forming condition of the image writing apparatus so as to perform the latent image forming operation.
The invention according to claim 8 is the image forming apparatus according to claim 5, wherein the correction unit adjusts a focal length of the image writing device based on a defocus amount of the image writing device. Image forming apparatus.
According to a ninth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the correction unit calculates a density change of the halftone image due to a defocus amount by the image writing device, and calculates the density change of the halftone image. An image forming apparatus is characterized in that a gradation level of the halftone image is adjusted so as to correct a density change.

According to the first aspect of the invention, when writing a latent image on a photoconductor using a plurality of light source elements, the amount of defocus of the latent image written on the photoconductor can be accurately determined.
According to the second aspect of the present invention, it is easier to determine the defocus amount of the image writing device from the determination image than when using the determination image having one vertical line image and one horizontal line image. Can be.
According to the third aspect of the present invention, even if the line width of the striped vertical line image and the horizontal line image is widened due to the focus shift by the image writing device, it is possible to make it difficult to affect the adjacent image.
According to the fourth aspect of the invention, the existing detecting means used for detecting the density of the developed image can be used as the measuring means.
According to the fifth aspect of the present invention, it is possible to reduce the deterioration of the image quality due to the defocus amount by the image writing device.
According to the sixth aspect of the present invention, it is possible to improve a change in development density caused by a defocus amount by the image writing device.
According to the seventh aspect of the invention, it is possible to improve a latent image potential change caused by a defocus amount by the image writing device.
According to the eighth aspect of the invention, it is possible to improve the image quality deterioration due to the defocus amount by the image writing device.
According to the ninth aspect, it is possible to improve the image quality of the halftone image caused by the defocus amount by the image writing device.

(A) is an explanatory diagram showing an outline of an embodiment of an image forming apparatus to which the present invention is applied, (b) is an explanatory diagram showing a beam state with no defocus and a defocus, and (c) is no defocus. 7D is an explanatory diagram showing a change when the vertical line image is out of focus, and FIG. 7D is an explanatory diagram showing a change when the horizontal line image without defocus is out of focus. FIG. 1 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to a first embodiment. (A) is an explanatory view showing a configuration example of an image writing device (in this example, an LED printer head (LPH) is used) used in the embodiment, and (b) is an arrow view as viewed from the direction B in (a). FIG. 3C is an explanatory view showing a beam irradiation state on a photoconductor without a focus shift, FIG. 4D is an explanatory view showing a beam irradiation state on a photoconductor with a focus shift, and FIG. (F) is an explanatory view schematically showing an operation process at the time of producing a vertical line image along the rotation direction of the photoconductor, and FIG. FIG. (A) is an explanatory view showing a change when a vertical stripe patch without a focus shift is out of focus, (b) is an explanatory view showing a change when a horizontal stripe patch without a focus shift is out of focus, and (c) is a vertical line FIG. 7D is an explanatory diagram showing another configuration example of the patch, and FIG. 9D is an explanatory diagram showing another configuration example of the horizontal line patch. 7A is a graph showing a relationship between a focal length deviation amount and a change in patch line width, and FIG. 6B is a graph showing a relationship between a focal length deviation amount and a patch density detection value. FIG. 3 is an explanatory diagram illustrating a control system of the image forming apparatus according to the first embodiment. 5 is a flowchart illustrating an LPH defocus measurement process used in the first embodiment. (A) and (b) are explanatory views showing a configuration example of a correction process of ΔDOF (focal length shift amount). (A) is an explanatory diagram showing a relationship between ΔDOF and a change in density sensor output, and (b) is an explanatory diagram showing a relationship between ΔDOF and a change in latent image potential. 9A is an explanatory diagram illustrating a main part of a ΔDOF correction process used in the image forming apparatus according to Embodiment 2, and FIG. 9B is an explanatory diagram illustrating an operation principle of the ΔDOF correction process. FIG. 9B is an explanatory diagram illustrating a main part of the ΔDOF correction process used in the image forming apparatus according to the third embodiment, and FIG. 10B is an explanatory diagram illustrating an operation principle of the ΔDOF correction process. FIG. 4 is an explanatory diagram illustrating a relationship between a focal length deviation amount and a patch density detection value for vertical stripe patches and horizontal stripe patches used in the image forming apparatus according to the first embodiment. FIG. 13 is a graph illustrating a result of measuring a relationship between a solid image density and a halftone image density under the conditions of no defocus and a defocus in the image forming apparatus according to the second embodiment. FIG. 13 is an explanatory diagram illustrating a relationship between ΔDOF and a density sensor output in the image forming apparatus according to the third embodiment. FIG. 14 is a graph illustrating a relationship between a halftone level and a halftone image density value under the condition of no ΔDOF and presence of ΔDOF in the image forming apparatus according to the fourth embodiment.

Outline of Embodiment FIG. 1A shows an outline of an embodiment of an image forming apparatus to which the present invention is applied.
In FIG. 1, the image forming apparatus includes a rotating photoconductor 1, a light source unit 3 including a plurality of light source elements 3 a provided to face the photoconductor 1 and arranged along the axial direction of the photoconductor 1, and a light source. An image writing unit 2 having an image forming unit 4 for forming the latent image forming light Bm emitted from the unit 3 on the photoreceptor 1, and a latent image formed by the image writing unit 2 formed on the photoreceptor 1; When determining the defocus amount of the latent image written by the image writing device 2 with the developing device 5 that develops an image, the image writing device 2 and the developing device 5 are used to apply the photosensitive material on the surface of the photoconductor 1. A determination image 11 including a vertical line image 12 extending in the vertical direction along the rotation direction of the body 1 and a horizontal line image 13 extending in the horizontal direction along the axial direction of the photoconductor 1 than the vertical line image 12 is drawn. And a determination image 1 drawn by the drawing means 6 And measuring means 7 for measuring an image change due to defocus amount by the image writing device 2 from those having a.

In such technical means, the image writing device 2 may be any light source means 3 having a plurality of light source elements 3a, and a typical example is an LPH (LED print head) using LEDs. The arrangement of the plurality of light source elements 3a may be continuously arranged in one row, or may be divided into a plurality of rows and arranged.
Since the present application deals with the LPH defocusing as a technical problem, the image writing device 2 is typically provided with an imaging unit 4. Here, when there is no defocus of the LPH, as shown in FIG. 1B, it indicates a state in which the light Bm emitted from the image writing device 2 is converged on the photoconductor 1, and there is a defocus. In the case of (1), as shown in FIG. 1B, it indicates a state in which the light emitted from the image writing device 2 is focused on a position shifted from above the photoconductor 1.
The vertical line image 12 extending in the vertical direction along the rotation direction (corresponding to the sub-scanning direction) of the photoconductor 1 is not limited to the image along the sub-scanning direction as shown in FIG. Includes those inclined at an angle of.
Further, the horizontal line image 13 extending along the axial direction (corresponding to the main scanning direction) of the photoreceptor 1 includes, as shown in FIG. Shall be considered.

Further, as a typical mode of the vertical line image 12 and the horizontal line image 13, a mode in which the vertical line image 12 and the horizontal line image 13 are arranged in a stripe pattern as described later can be cited. However, a single line can be used, and the line type is not limited to a solid line. Dot row).
Further, as the determination image 11, a vertical line image 12 and a horizontal line image 13 are required.
This is because, when there is a defocus, the horizontal line image 13 also becomes thick, and therefore, when only the vertical line image 12 is used as the determination image 11, there is a concern that it cannot be determined whether or not the thickening is caused by the defocus. It depends.
Furthermore, the measuring means 7 captures an image change (density, line width) due to the defocus of the image writing device 2 for the drawn determination image 11 (vertical line image 12 and horizontal line image 13). If possible, a suitable selection may be made.
The vertical line image 12 and the horizontal line image 13 have a larger line width as the defocus amount is larger, but the vertical line image 12 has higher sensitivity than the horizontal line image 13 and has a wider line width (w1 → w1 ′, w2 → w2 ′) appears remarkably (see FIGS. 1C and 1D). This depends on the difference in the exposure time of light by the image writing device 2, and the vertical line image 12 has more light energy than the horizontal line image 13.
Further, the measuring means 7 may be provided at an arbitrary position facing the photoconductor 1, the intermediate transfer member 8, or a recording medium (not shown) as long as the measuring image 11 can be measured. In FIG. 1A, reference numeral 9 denotes a transfer unit that transfers an image formed on the photoconductor 1 to the intermediate transfer body 8.

Next, a typical mode or a preferable mode of the image forming apparatus according to the present embodiment will be described.
First, as a typical mode of the image 11 for determination, a mode including a striped vertical line image 12 arranged in the axial direction of the photoconductor 1 and a striped horizontal line image 13 arranged in the rotation direction of the photoconductor 1 is cited. Can be In the case of one vertical line image 12 and one horizontal line image 13, it is necessary to check the respective line widths. It is possible to determine the amount of defocus of the writing device 2.
In addition, as a preferable mode of the image for determination 11, in a state where there is no defocus, the interval between the vertical line images 12 and the horizontal line images 13 arranged in stripes is wider than the line width of each image. No. In this example, the line width of the vertical line image 12 and the horizontal line image 13 arranged in stripes is selected to be wider than the interval between each image, and the phenomenon of the line width thickening due to defocus is separated from the adjacent image area. This is preferable because it can be easily performed.
Further, as a preferable embodiment of the measuring unit 7, there is an embodiment which also serves as a detecting unit (for example, an ADC (abbreviation of Analog Digital Converter) sensor) for detecting the density of the developed image developed by the developing device 5.

Further, in the present embodiment, as a preferable mode, there is provided a mode in which a correction unit 10 for correcting the defocus amount by the image writing device 2 based on the measurement result by the measurement unit 7 is provided. This embodiment is preferable in that the correction unit 10 improves image quality defects due to defocus.
The following is an example of the configuration of this type of correction means 10.
(1) As a configuration example 1 of the correcting unit 10, a change in the development density by the developing device 5 due to the defocus amount by the image writing device 2 is calculated, and the developer is supplied so as to correct the change in the development density. An embodiment is mentioned. In the present embodiment, a change in the development density (attributable to the defocus amount) is corrected by supplying the developer.
(2) As a configuration example 2 of the correcting unit 10, a latent image potential change caused by the defocus amount of the image writing device 2 is calculated, and the latent image potential of the image writing device 2 is corrected so as to correct the latent image potential change. There is an embodiment in which the image forming conditions are adjusted. In this embodiment, the latent image potential change (attributable to the defocus amount) is corrected by adjusting the latent image forming condition by the image writing device 2.

(3) As a third configuration example of the correcting unit 10, there is a mode in which the focal length of the image writing device 2 is adjusted based on the defocus amount of the image writing device 2. In the present embodiment, the focal length is directly corrected by adjusting the focal length of the image writing device 2.
(4) As a configuration example 4 of the correcting unit 10, a change in the density of the halftone image caused by the defocus amount by the image writing device 2 is calculated, and the change in the density of the halftone image is corrected. To adjust the gray level of the image. In this example, the tone level of the halftone image (corresponding to the halftone level) is adjusted to correct a change in density (due to defocus) of the halftone image.

Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.
◎ Embodiment 1
FIG. 2 shows an overall configuration of an image forming apparatus as a powder processing apparatus according to the first embodiment.
-Overall configuration of image forming apparatus-
In the figure, an image forming apparatus 20 has an image forming engine 30 capable of producing each color component image in an image forming apparatus housing 21 and a recording medium below the image forming engine 30 in the image forming apparatus housing 21. A sheet supply device 50 that supplies the sheet S as a sheet is installed, and the sheet S (see FIG. 6) supplied from the sheet supply device 50 to one side surface (corresponding to the left side in FIG. 2 in this example) of the image forming apparatus housing 21. ) Is formed in a substantially vertical direction, and a transfer device 60 that transfers an image created by the image forming engine 30 to the sheet S is provided in a portion of the transfer path 55 facing the image forming engine 30. At the same time, a fixing device 70 for fixing an image transferred to the paper S is provided downstream of the transfer device 60 in the transport direction of the paper S in the transport path 55.

-Imaging engine-
In the present embodiment, the image forming engine 30 uses, for example, an electrophotographic method to form a plurality of color component images (four in this example, yellow (Y), magenta (M), cyan (C), and black (K)). And a plurality of image forming units 31 (specifically, 31a to 31d) for producing the image data, and temporarily transferring and holding each color component image produced by each image producing unit 31 before transferring it to the sheet S. And a belt-shaped intermediate transfer body 40.
In this example, the image forming unit 31 (31a to 31d) includes a photoconductor 32, a charging device (a charging roll is used in this example) 33 for charging the photoconductor 32, and an electrostatic latent on the charged photoconductor. An image writing device (in this example, an LED writing head is used) for writing an image, a developing device 35 for developing the latent image formed on the photoconductor 32 with toner, and a toner such as toner remaining on the photoconductor 32 A cleaning device 36 for cleaning the residue.

Further, in this example, the intermediate transfer body 40 is wound around a plurality of (four in this example) tension rolls 41 to 44, and one of the tension rolls 41 to 44, for example, the driving roll 41 is driven by a driving roll. As shown in FIG.
In this example, the image forming units 31 are arranged below the intermediate transfer body 40 in a substantially horizontal direction along the rotation direction of the intermediate transfer body 40, and face the photoconductor 32 of each image forming unit 31. A primary transfer device (transfer roll is used in this example) 46 is provided on the back surface of the intermediate transfer body 40 so that each color component image formed on each photoconductor 32 is electrostatically transferred to the intermediate transfer body 40 in order. Has become.
In this example, a transfer device (corresponding to a secondary transfer device for secondary transferring an image from the intermediate transfer member 40 to the paper S in this example) 60 is installed at a portion of the intermediate transfer member 40 facing the stretching roll 42. In addition, an intermediate transfer body cleaning device 47 that cleans a residue such as toner and paper dust on the intermediate transfer body 40 is installed at a portion facing the stretching roll 41, and the stretching roll 43 It is also used as a tension adjusting roll for adjusting the tension of the body 40.

-Transfer device (secondary transfer device)-
In the present embodiment, the basic configuration of the secondary transfer device 60 is as follows. The transfer roll 61 is installed so as to face the stretching roll 42 of the intermediate transfer body 40. A transfer voltage from a transfer power source (not shown) is applied to form a transfer electric field in a transfer area between the intermediate transfer body and the transfer roll 61, so that an image on the intermediate transfer body 40 is transferred onto a sheet passing through the transfer area. Is secondary-transferred.
-Fixing device-
Further, in the present embodiment, the fixing device 70 includes a rotatable heating fixing member (a heating fixing roll is used in this example) 71 whose surface temperature is heated to a predetermined temperature by a heater as a heating source, A pressure fixing member (in this example, a pressure fixing roll is used) 72 that rolls in contact with a predetermined contact pressure along the axial direction of the heat fixing member 71, and the contact area between the fixing members 71, 72 is undecided. The unfixed image is fixed by passing the sheet S holding the received image.

-Paper transport system-
In the present embodiment, the paper transport system sends the paper S from the feeder unit 51 of the paper supply device 50 to the transport path 55, and transports the paper S from the secondary transfer area of the secondary transfer device 60 on the transport path 55. After the position of the sheet S is aligned by the position alignment roll 56 installed on the upstream side in the direction, the transfer process by the secondary transfer device 60 is performed, and the sheet that has been subjected to the fixing process by the fixing device 70 is transferred to the image forming apparatus housing. The paper is discharged by a discharge roll 57 toward a paper storage receiver 58 formed on the top of the paper 21. It is needless to say that the transport path 55 may be provided with an appropriate number of transport members (transport rolls and the like) as necessary. When the duplex image forming mode is performed, a double-sided conveyance unit (not shown) is added, and the sheet on which single-side recording has been performed is transferred through the double-sided conveyance path (not shown) before the position alignment roll 56 in the conveyance path 55. The front and back surfaces may be reversed and the image forming process may be performed on the other side of the sheet on which single-sided image formation has been performed.

-Configuration example of image writing device-
In the present embodiment, an LED printer head (LPH) is used as the image writing device 34. Here, the LPH 34 as an image writing device includes, as shown in FIG. 3A, for example, an LED array 341 in which a plurality of LEDs 342 are arranged as light source elements in a single row or a plurality of rows, and the LED array 341. And a lens array 343 that forms an image of the light Bm emitted from each of the LEDs 342 on the surface of the photoconductor 32.
Here, as a path of the light Bm emitted from the LPH 34, as shown in FIG. 3B, the light Bm emitted from each LED 342 of the LED array 341 enters the lens array 343 as parallel light, respectively. The light is focused on the photoconductor 32 according to the focal length of the lens array 343.
However, even when the lens array 343 is installed at a predetermined position when the LPH 34 is mounted at a predetermined position, for example, due to the variation in the focal length of the lens array 343, as shown in FIG. The light Bm focused at 343 is not always irradiated onto the photoconductor 32 without defocus, and as shown in FIG. 3D, the light Bm focused at the lens array 343 is There is a concern that irradiation may be performed with a defocus state above.

At this time, for example, in the case where a vertical line latent image Zt which is a vertical line image extending in the rotation direction of the photoconductor 32 (corresponding to the sub-scanning direction) is produced in a state where there is a focus shift, FIG. As described above, since the exposure time Tt required to produce the vertical line latent image Zt is long, the exposure energy for the vertical line latent image Zt is large, and the vertical line image becomes thicker than that in the case where there is no defocus. Tends to be easy.
On the other hand, when producing a horizontal line latent image Zy that is a horizontal line image extending in the axial direction (corresponding to the main scanning direction) of the photoconductor 32, as shown in FIG. Although the horizontal line latent image Zy tends to be thicker than that, the exposure time Ty required to produce the horizontal line latent image Zy is short, so that the exposure energy for the horizontal line latent image Zy is small, and the vertical line image It is understood that the degree of fatness of the horizontal line image tends to be smaller than that of the horizontal line image.

−Image for judging defocus−
In the present embodiment, when a determination image pattern for determining a focus shift is examined, a vertical stripe patch Pt as shown in FIG. 4A and a horizontal stripe patch Py as shown in FIG. Combination images have proven to be preferred.
In the present example, the vertical stripe patches Pt are arranged in a plurality (four in this example) in the axial direction of the photoconductor 32 at predetermined pitch intervals mt with respect to the vertical line images 81 extending in the rotation direction of the photoconductor 32. Things.
Here, the pitch interval mt is selected to be sufficiently wider than the line width wt of the vertical line image 81 when there is no defocus.
The pitch interval mt may be selected so that at least the adjacent vertical line images 81 do not overlap with each other in consideration of the degree of thickening of the vertical line image 81 when there is a focus shift, for example, the line width wt of the vertical line image 81 Is about 10 μm, while the pitch interval mt is about 40 to 50 μm.
On the other hand, the horizontal stripe patch Py is configured such that a plurality of (three in this example) horizontal line images 91 extending in the axial direction of the photoconductor 32 are arranged in the rotation direction of the photoconductor 32 at a predetermined pitch interval mt. .
Here, the pitch interval my is selected wider than the line width wy of the horizontal line image 91 when there is no defocus, but the pitch interval my is the degree to which the horizontal line image 91 becomes thicker when there is defocus. In consideration of the above, at least the horizontal line images 91 may be selected so as not to overlap. In particular, when there is a focus shift, the degree of fatness of the horizontal line image 91 is smaller than that of the vertical line image 81, so that the pitch interval mt of the vertical stripe patch Pt can be set narrower.

Further, in the present embodiment, the vertical stripe patch Pt is typically formed by arranging a plurality of vertical line images 81 extending in the rotation direction of the photoconductor 32, but is not limited to this. For example, FIG. ), A plurality of vertical line images 82 extending in a direction inclined by an angle α with respect to the rotation direction of the photoconductor 32 may be arranged.
On the other hand, in the present embodiment, the horizontal stripe patch Py is typically a plurality of horizontal line images 91 extending in the axial direction of the photoconductor 32. However, the present invention is not limited to this. For example, FIG. As shown in FIG. 7, a mode may be adopted in which a plurality of horizontal line images 92 extending in a direction inclined by an angle β with respect to the axial direction of the photoconductor 32 are arranged.
However, the vertical line image 82 of the vertical line patch Pt needs to be positioned closer to the direction extending in the rotation direction of the photoconductor 32 than the horizontal line image 92 of the horizontal stripe patch Py.
As for the vertical line image 82, when the component on the rotation direction side of the photoreceptor 32 is larger than the component on the axial direction side, the degree of fatness due to the focus shift of the vertical line image 82 becomes more conspicuous. Is preferably less than ± 45 °.

<Characteristics of vertical stripe patch Pt and horizontal stripe patch Py>
In the present embodiment, when the characteristics of the vertical stripe patches Pt and the horizontal stripe patches Py with respect to the shift amount of the focal length (the focus shift amount), the following characteristics were found.
(1) Change in Patch Line Width For the vertical stripe patch Pt and the horizontal stripe patch Py, the amount of defocus and the line width change of the vertical line image 81 and the horizontal line image 91 of each patch Pt and Py were examined. The result was obtained.
According to the figure, the line widths wt and wy of the vertical line image 81 and the horizontal line image 91 of the vertical stripe image Pt and the horizontal stripe image Py tend to increase as the defocus amount increases. It is understood that the fatness degree is larger than the fatness degree of the horizontal line image 91.
(2) Detected Patch Density Values The relationship between the amount of defocus and the detected density values of the patches Pt and Py was examined for the vertical stripe patches Pt and the horizontal stripe patches Py, and the results shown in FIG. 5B were obtained.
According to the figure, the density detection values of the vertical stripe patch Pt and the horizontal stripe patch Py both tend to decrease as the amount of defocus increases, but the reduction rate of the vertical stripe patch Pt is smaller than that of the horizontal stripe patch Py. Remarkable. This is based on the fact that the vertical stripe image Pt increases in the thickness of the vertical line image 81 as the defocus amount increases, so that the reflected light component from the vertical stripe patch Pt decreases accordingly.

-Drive control system of image forming apparatus-
In this embodiment, as shown in FIG. 6, reference numeral 100 denotes a control device for controlling an image forming process of the image forming apparatus, and the control device 100 is a microcomputer including a CPU, a ROM, a RAM, and an input / output interface. The switch signal such as a start switch (not shown) and a mode selection switch for selecting an image forming mode and various sensor signals are taken in through an input / output interface, and an image forming processing program stored in a ROM in advance is executed by the CPU. Then, after generating a control signal for the drive control target, the control signal is transmitted to each drive control target.
In particular, in this example, a density sensor 110 for detecting, for example, the density of each color component image is disposed in a non-contact state with the intermediate transfer body 40 at a portion of the intermediate transfer body 40 facing the stretching roll 43.
Further, the control device 100 is provided with respective processing units for executing an image forming processing program, and one of them is provided with an “LPH defocus measurement processing unit 101”, and the LPH defocus measurement processing shown in FIG. Run the program.

-LPH defocus measurement process-
Next, “LPH defocus measurement processing” by the image forming apparatus according to the present embodiment will be described.
Now, in order to execute the LPH defocus measurement processing, first, as shown in FIG. 7, the production of vertical stripe patches Pt and horizontal stripe patches Py is started.
In this example, the vertical stripe patches Pt and the horizontal stripe patches Py of the respective color components shown in FIG. 4A are respectively produced using the image forming units 31 (31a to 31d).
At this time, assuming that the LPH 34 as the image writing device of each of the image forming units 31 (31a to 31d) is installed with a defocus, the line width of the vertical line image 81 of the vertical stripe patch Pt is as shown in FIG. As shown in FIG. 4A, the line width of the horizontal stripe patch 91 of the horizontal stripe patch Py increases to wy ′ (> wy) as shown in FIG. 4B. .
The produced vertical stripe patches Pt and horizontal stripe patches Py are primary-transferred from the image forming units 31 (31a to 31d) to the intermediate transfer member 40, and then detected by the density sensor 110 as the intermediate transfer member 40 moves. Pass through the area.
In this state, the density detection operation by the density sensor 110 is performed, and the density Dt of the vertical stripe patch Pt is detected, and the density Dy of the horizontal stripe patch Py is detected.

Next, the control device 100 determines whether or not Dt> Dy, and when Dt> Dy, calculates the defocus amount ΔDOF (abbreviation for Distance Of Focus) from the density difference ΔD between the two.
In this calculation process, for example, as shown in FIG. 5B, ΔDOF may be calculated based on the characteristics of the focus shift amount and the patch density detection value.
Thereafter, the ΔDOF correction processing is performed.

<ΔDOF correction processing>
In the present embodiment, for example, the following processing is performed as the ΔDOF correction processing.
(1) Correction Process by Replenishing Toner When ΔDOF is calculated, a change in development density is calculated as shown in FIG.
At this time, as shown in FIG. 9A, a characteristic graph of ΔDOF and the output of the concentration sensor is stored in the RAM of the control device 100 in advance, and for example, when ΔDOF is assumed to be ΔLa, the characteristic graph at the time of ΔLa is assumed. a concentration sensor output DTa, obtains a density sensor output DT ₀ in the case of focus-free from the characteristic graph, the difference between them ΔDT is found that the concentration difference due to defocus. Therefore, the toner supply amount from the toner cartridge 37 may be corrected so as to correct the density difference.

(2) Correction Process Based on Latent Image Potential Condition When ΔDOF is calculated, a change in latent image potential is calculated as shown in FIG. 8B.
At this time, as shown in FIG. 9B, a characteristic graph of ΔDOF and the latent image potential is stored in the RAM of the control device 100 in advance, and for example, the latent image potential Za when ΔDOF is ΔLa and the focus The latent image potential Z _{0 in} the case where there is no shift is obtained from the characteristic graph, and it is found that the difference ΔZ between them is the latent image potential difference ΔZ caused by the focus shift. Therefore, as shown in FIG. 8B, the image output potential (corresponding to the charging potential) and the exposure amount of the LPH 34 may be corrected so as to correct the latent image potential difference ΔZ.

◎ Embodiment 2
FIG. 10A is an explanatory diagram illustrating a main part of the image forming apparatus according to the second embodiment.
In the figure, an LPH 34 as an image writing device mounts an LED array 341 and a lens array 343 on a movable holder 345 that can move up and down, and moves the movable holder 345 up and down by an elevating mechanism 346, and the lens array 343 of the LPH 34. The distance L between the photoconductor 32 and the photoconductor 32 is variably adjusted.
In this example, the lifting mechanism 346 supports both ends of a ball screw 347 extending in the vertical direction with bearings 348, is screwed into the ball screw 347, connects the movable holder 345 to the lifting table 350, and rotates the ball screw 347 by the drive motor 349. Thus, the lifting table 350 is raised and lowered by an appropriate amount, and the LPH 34 is raised and lowered via the movable holder 345.
In the present embodiment, as shown in FIG. 7, when ΔDOF is calculated, control device 100 sends a control signal to drive motor 349 so as to correct this, and rotates drive motor 349 appropriately. It was done.
As a result, assuming that the LPH 34 is out of focus by ΔL, for example, as shown in FIG. 10B, if the installation position of the LPH 34 is not adjusted so as to correct this, the LPH 34 has no defocus. The position is adjusted to the state.

◎ Embodiment 3
FIG. 11A is an explanatory diagram illustrating a main part of the ΔDOF correction processing employed in the image forming apparatus according to the third embodiment.
In the figure, in the ΔDOF correction process, when ΔDOF is calculated, the density change of the halftone image is calculated.
At this time, for example, as shown in FIG. 11B, the halftone level (hereinafter, referred to as HT level as necessary) and the density value of the halftone image (halftone image (hereinafter, referred to as HT image as necessary)) Is stored in the RAM of the control device 100 as a characteristic graph created in advance through experiments and the like under the condition of no defocus (ΔDOF = 0) and defocus (ΔDOF (i): i = 1... N). Assuming that the calculated ΔDOF is, for example, ΔDOF (i), the relationship between the HT level and the density value of the HT image is grasped based on the characteristic of ΔDOF (i) shown in FIG.
Here, for example, assuming that the HT image is displayed at an HT level of 55% (Q1 in the figure) under the condition of no defocus, it is necessary to obtain the same density value under the condition that the defocus amount is ΔDOF (i). As shown by Q2 in the figure, the HT image may be displayed at the HT level of 45%.
Therefore, in this example, the HT level of the HT image may be corrected using the characteristic of ΔDOF (i).

◎ Example 1
In this example, the image forming apparatus according to Embodiment 1 was used to examine the relationship between the focal length deviation amount (focus deviation amount) and the patch density detection value for the vertical stripe patch Pt and the horizontal stripe patch Py. The result shown in FIG. 12 was obtained.
In the figure, for example, the patch density detection values are plotted when there is no defocus (ΔDOF = 0) and when there is defocus (ΔDOF = 150 μm), and the average values are connected by a solid line and a broken line. .
According to the figure, when the amount of defocus increases in both the vertical stripe patch Pt and the horizontal stripe patch Py, the patch density detection value tends to decrease, but the vertical stripe patch Pt has a higher patch density than the horizontal stripe patch Py. It is understood that the rate of decrease in the detection value is high.

◎ Example 2
In this embodiment, the image forming apparatus according to the first embodiment is used, and the solid image density and the halftone (HT) are set under the conditions of the defocus (with ΔDOF: 200 μm in this example) and no defocus (without ΔDOF). When the relationship with the 50% image density was examined, the result shown in FIG. 13 was obtained.
According to the figure, it is understood that the tone curve characteristics when there is a defocus are different from those when there is no defocus. This is presumed to be a factor that greatly affects the image quality specifications when there is a defocus.

◎ Example 3
In this example, when the relationship between the defocus amount (ΔDOF) and the output of the density sensor was examined using the image forming apparatus according to Embodiment 1, the results shown in FIG. 14 were obtained.
In FIG. 14, the output of the density sensor is plotted under the conditions of no defocus, ΔDOF = 50 μm, and ΔDOF = 100 μm, and their average values are connected by a straight line.
According to the figure, for example, under the condition of ΔDOF = 70 μm, the density detection value by the density sensor is about 50 (corresponding to TC (Toner Concentration): 1.5 to 2.0%) as compared with the case where there is no defocus. It is understood that it decreases. For this reason, it is understood that when there is a defocus, it greatly affects the toner density control, and it is understood that the ΔDOF correction processing as described in the first embodiment is effective.

◎ Example 4
In the present example, the relationship between the halftone (HT) level and the HT image density value was examined using the image forming apparatus according to Embodiment 3 with no defocus and with defocus (ΔDOF = 200 μm). However, the result shown in FIG. 15 was obtained.
According to the figure, it is understood that the characteristic graphs of the HT level and the HT image density value are different between the case with the defocus and the case with the defocus. For this reason, it is understood that the HT image density value is higher when there is a defocus than in the case where there is no defocus, and this greatly affects the HT image specifications. Therefore, it can be seen that the ΔDOF correction processing as described in the third embodiment is effective.

  DESCRIPTION OF SYMBOLS 1 ... Photoreceptor, 2 ... Image writing device, 3 ... Light source means, 3a ... Light source element, 4 ... Imaging means, 5 ... Developing means, 6 ... Drawing means, 7 ... Measuring means, 8 ... Intermediate transfer means, 9 ... Transfer means, 10 ... Correction means, 11 ... Image for judgment, 12 ... Vertical line image, 13 ... Horizontal line image, Bm ... Light, w1 ... Line width without defocus of vertical line image, w1 '... Vertical line image Line width with defocus, w2 ... line width without defocus of horizontal line image, w2 '... line width with defocus of horizontal line image

Claims (9)

A rotating photoconductor,
A light source unit, which is provided to face the photoconductor and includes a plurality of light source elements arranged along the axial direction of the photoconductor, and forms a latent image forming light emitted from the light source unit on the photoconductor. An image writing device having an image forming means for forming an image;
A developing device for developing a latent image formed on the photoconductor by the image writing device;
When determining the amount of defocus of the latent image written by the image writing device, the image writing device and the developing device are used, and on the surface of the photoconductor in a vertical direction along the rotation direction of the photoconductor. Drawing means for drawing a vertical line image extending toward the determination image including a horizontal line image extending in the horizontal direction along the axial direction of the photoconductor than the vertical line image,
Measuring means for measuring an image change caused by a defocus amount by the image writing device from the determination image drawn by the drawing means,
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The image forming apparatus, wherein the determination image includes the striped vertical line image arranged in the axial direction of the photoconductor and the striped horizontal line image arranged in the rotation direction of the photoconductor. The image forming apparatus according to claim 1, wherein
The image forming apparatus is characterized in that, in the determination image, there is no defocus, and the interval between the vertical line image and the horizontal line image arranged in a stripe pattern is wider than the line width of each image. The image forming apparatus according to claim 1, wherein
The image forming apparatus according to claim 1, wherein the measuring unit also serves as a detecting unit that detects a density of a developed image developed by the developing device. The image forming apparatus according to claim 1,
An image forming apparatus comprising: a correction unit that corrects a defocus amount by the image writing device based on a measurement result by the measurement unit. The image forming apparatus according to claim 5,
The image forming apparatus is characterized in that the correction means calculates a change in the development density of the developing device caused by the amount of defocus by the image writing device, and supplies a developer so as to correct the change in the development density. The image forming apparatus according to claim 5,
The correction means calculates a latent image potential change caused by the defocus amount by the image writing device, and adjusts a latent image forming condition by the image writing device so as to correct the latent image potential change. The image forming apparatus is a feature. The image forming apparatus according to claim 5,
The image forming apparatus, wherein the correction unit adjusts a focal length of the image writing device based on a defocus amount of the image writing device. The image forming apparatus according to claim 5,
The correction unit calculates a density change of the halftone image caused by the defocus amount by the image writing device, and adjusts a gradation level of the halftone image so as to correct the density change of the halftone image. An image forming apparatus comprising:

Images