JP2009098356A - Image forming apparatus, control device for image forming apparatus, and control program of image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a failure on an image due to relative displacement between latent images formed by first and second latent image forming means in forming a latent image on the same image carrier using the first and second latent image forming means. <P>SOLUTION: An image forming apparatus 100 comprises: latent image formers 3-1 and 3-2 for forming a latent image on an image carrier 1; an image forming part for forming a first image by the latent former 3-1 and a second image by the latent image former 3-2 on the image carrier 1 in such a manner that the two images overlap at least in some areas, and forming an image for displacement detection, of which contrast is higher than that of the image formed by one of the latent image formers, on the image carrier 1; an information acquisition part for acquiring information showing the amount of relative displacement between the latent images by the two latent image formers, which is detected based on the image for displacement detection; and a control part for controlling the latent image formation by the latent image formers 3-1 and 3-2 so that the positions of the latent images overlap each other, based on the information showing the amount of displacement. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, a control apparatus for the image forming apparatus, and a control program for the image forming apparatus.

  In an electrophotographic image forming apparatus, an exposure apparatus that exposes the surface of a photoreceptor to form an electrostatic latent image is used.

  As one of the above-described exposure apparatuses, Patent Document 1 includes two rows of line-shaped light emitting elements, and image formation points on the photosensitive member of light emitted from the line-shaped light emitting elements in each row overlap in the main scanning direction. An optical head configured as described above is described. According to the optical head, the writing line on the photoconductor can be exposed from two locations simultaneously.

  Patent Document 2 describes an image forming apparatus using a solid scanning exposure unit such as an LED head that controls the exposure position of an image by the exposure unit using distortion data of the input exposure unit. Has been.

  Further, in a color image forming apparatus that forms a toner image of each color on a photoconductor for each color and sequentially superimposes the toner images on the photoconductor for each color on a transfer belt to form a multicolor image. A technique is known in which a toner pattern is formed on a transfer belt, and a positional deviation (that is, a color deviation) of toner images between colors is corrected based on the detection result of the toner pattern (for example, Patent Documents 2 to 8). reference).

  In Patent Document 2, in a color image forming apparatus that includes an exposure unit for each color and an image forming medium for each color that is exposed by each exposure unit to form an image, the array distortion of the exposure units using distortion data. After the correction, a resist pattern is created on the image forming medium, and control is performed so as to eliminate the positional deviation of the image based on the detection result of the resist pattern.

  In Patent Document 3, in a color image forming apparatus including an LED array for each color, data relating to the arrangement position accuracy of each light emitting element included in the LED is stored in advance and formed on the transfer belt using each LED array. In this document, color misregistration information is detected based on the resist pattern to be controlled, and the image writing timing of each color is controlled so as to eliminate the color misregistration based on the data regarding the arrangement position accuracy and the color misregistration information.

  In Patent Document 4, for example, a plurality of alignment marks obtained by sequentially shifting yellow, magenta, and black one by one dot vertically and horizontally with respect to cyan are transferred and recorded on a recording sheet, and the recorded alignment marks for each color are recorded. A technique for adjusting the image formation start position of the photosensitive drum based on this is described.

Japanese Patent Laid-Open No. 5-100555 JP 2001-301232 A JP 2002-108043 A Japanese Patent Laid-Open No. 6-238594 JP 2001-265083 A Japanese Patent Laid-Open No. 2005-91901 JP 2004-333837 A JP-A-2005-352291

  By the way, in the configuration in which the first and second latent image forming units are used to form the latent image on the same image carrier, the latent images formed by the first and second latent image forming units are relatively relative to each other. If there is a slight misalignment, a problem on the image occurs.

  In the present invention, when a latent image is formed on the same image carrier using the first and second latent image forming means, the relative relationship between the latent images formed by the first and second latent image forming means is determined. An object of the present invention is to provide an image forming apparatus capable of reducing inconveniences on an image due to a general positional shift.

  The image forming apparatus according to the present invention includes first and second latent image forming means for forming a latent image on the same image carrier, and the first image by the first latent image forming means. A second image is formed on the image carrier by the second latent image forming unit so that the first and second images overlap at least partially, and the first and second latent images are formed. An image forming means for forming on the image carrier an image for detecting displacement that has a higher contrast than an image formed by one of the forming means, and the first image detected based on the image for detecting displacement. Based on the information acquisition means for acquiring information indicating the relative displacement amount between the latent images formed by the first and second latent image forming means, and the information indicating the displacement amount, the first and second The positions of the latent images formed by the latent image forming means overlap each other. Ri to suit, characterized in that it comprises a control means for controlling the latent image formed by the first and second latent image forming means.

  In one aspect of the present invention, the image forming unit forms a first unit image by the first latent image forming unit and forms the second latent image as a process of forming the image for detecting misregistration. A process of forming a second unit image by an image forming unit and forming a unit image for detecting misregistration formed by the first and second unit images is performed on the second unit image with respect to the first unit image. Repeatedly shifting the relative position of the unit image.

  In the aspect of the invention, the first and second unit images are images having a common pattern in which a plurality of lines are arranged at a predetermined interval.

  Further, in one aspect of the present invention, the information acquisition unit detects each of the unit images for detecting misalignment, and calculates the amount of the relative position shift and the detected unit image for misalignment detection. Information indicating the amount of positional deviation is obtained from the correspondence.

  In one aspect of the present invention, the image forming unit is configured to detect the misalignment so that a portion where the first and second images overlap is developed and a portion where the first and second images do not overlap is not substantially developed. A latent image of the image is developed to form a developed image of the image for detecting the displacement.

  In the aspect of the invention, the first and second latent image forming units are exposure units that expose the image carrier to form an electrostatic latent image on the image carrier, and the image The forming unit develops the latent image of the image for detecting misregistration using a developer holding body that holds and conveys the developer containing toner, and forms a toner image of the image for detecting misregistration. When a toner image of the image for detecting misregistration is formed, the absolute value of the potential of the portion exposed by one of the first and second latent image forming units is applied to the developer holding member. The absolute value of the potential of the portion exposed by both the first and second latent image forming means is larger than the absolute value of the DC component of the developing bias. small.

  A control device for an image forming apparatus according to the present invention controls an image forming apparatus provided with first and second latent image forming means for forming a latent image on the same image carrier, so that the first latent image is formed. A first image is formed by the forming unit and a second image is formed by the second latent image forming unit on the image carrier so that the first and second images overlap at least partially. An image forming means for forming a misregistration detection image on the image carrier having a larger contrast than an image formed by one of the first and second latent image forming means, and the misregistration detection Information acquisition means for acquiring information indicating a relative positional deviation amount between the latent images formed by the first and second latent image forming means, which is detected based on the first image, and the positional deviation amount. Based on the information shown, the first and second latent image forming hands As the position of the latent image formed overlap each other by, characterized in that it comprises a control means for controlling the latent image formed by the first and second latent image forming means.

  The control program for an image forming apparatus according to the present invention controls an image forming apparatus provided with first and second latent image forming means for forming a latent image on the same image carrier, and controls the first image forming apparatus. The first image is formed by the latent image forming unit, the second image is formed by the second latent image forming unit, and the first and second images are overlapped at least partially on the image carrier. And forming a misregistration detection image having a higher contrast than the image formed by one of the first and second latent image forming means on the image carrier, and the misregistration detection. A procedure for acquiring information indicating a relative positional deviation amount between the latent images formed by the first and second latent image forming units, which is detected based on the image for use, and the positional deviation amount Based on the information, the first and second latent images As the position of the latent image formed by the forming means overlap each other, characterized in that to execute a procedure of controlling the latent image formed by the first and second latent image forming means.

  According to the first aspect of the present invention, it is possible to reduce problems on the image due to a relative positional shift between the latent images formed by the first and second latent image forming units.

  According to the second aspect of the present invention, the change in the pattern of the overlapping portion between the first and second unit images caused by shifting the relative position of the second unit image with respect to the first unit image. By utilizing this, it is possible to detect information indicating the amount of positional deviation.

  According to the third aspect of the present invention, the change in the pattern of the overlapping portion between the first and second unit images caused by shifting the relative position of the second unit image with respect to the first unit image. It becomes possible to clarify.

  According to the fourth aspect of the present invention, it is possible for the image forming apparatus to obtain information indicating the positional deviation amount from the correspondence between the relative positional deviation amount and the unit image for detecting the positional deviation. .

  According to the fifth aspect of the present invention, it is possible to clearly recognize a portion where the first and second images overlap each other.

  According to the invention described in claim 6, it is possible to clearly recognize a portion where the first and second images overlap each other.

  According to the seventh aspect of the present invention, it is possible to reduce problems on the image due to a relative positional shift between the latent images formed by the first and second latent image forming units.

  According to the eighth aspect of the present invention, it is possible to reduce problems on the image due to a relative positional shift between the latent images formed by the first and second latent image forming units.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Image forming apparatus]
FIG. 1 is a schematic side view showing an example of the configuration of the image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 is an apparatus that prints an image on a recording medium such as paper, and is, for example, a copying machine, a printer, or a facsimile.

  In FIG. 1, an image forming apparatus 100 includes an image carrier 1 that holds an image, and first and second latent image forming units 3-1 and 3-2 that form a latent image on the image carrier 1. It has.

  In a specific embodiment, the image forming apparatus 100 performs image formation using an electrophotographic method, and the image carrier 1 is a rotatable drum or belt on which an electrostatic latent image is formed. In the form of a photoconductor. In the following description, “image carrier 1” is appropriately referred to as “photoreceptor 1”.

  The first latent image forming device 3-1 and the second latent image forming device 3-2 expose the surface of the photosensitive member 1 charged by the charger 2 to expose the electrostatic latent image on the photosensitive member 1. Is an exposure device. In the following description, the “first latent image forming device 3-1” is appropriately referred to as “exposure device 3-1,” and the “second latent image forming device 3-2” is appropriately referred to as “exposure device 3-2.” Called.

  In one embodiment, each of the exposure units 3-1 and 3-2 is a solid scanning head that extends in a direction (main scanning direction) orthogonal to the moving direction (sub-scanning direction) of the photoreceptor 1, and is in the sub-scanning direction. Are arranged in parallel. For example, the exposure units 3-1 and 3-2 are light emitting element arrays in which a plurality of light emitting elements are arranged in the main scanning direction. For example, the exposure units 3-1 and 3-2 are LED print heads in which a plurality of LEDs (light emitting diodes) are arranged.

  However, the exposure units 3-1 and 3-2 may be other types such as a laser scanning device, for example.

  On the downstream side of the exposure units 3-1 and 3-2 in the sub-scanning direction, a developing unit 4 that develops an electrostatic latent image on the photoconductor 1 to form a toner image on the photoconductor 1 is disposed. . Specifically, the developing device 4 includes a developer holding body (for example, a developing roll) 4a that holds and conveys a developer containing toner. The developer holder 4a is disposed opposite the photoconductor 1, and a developing bias is applied to the developer holder 4a. Then, the toner on the developer holding member 4a is transferred to the surface of the photosensitive member 1 due to the potential difference between the developer holding member 4a and the surface of the photosensitive member 1, and the latent image on the photosensitive member 1 is developed with the toner.

  On the downstream side of the developing unit 4 in the sub-scanning direction, a transfer unit 5 that transfers a toner image on the photoconductor 1 to a transfer target (a recording medium P supplied from a paper tray 9 in the example of FIG. 1); A cleaner 6 for removing residues such as toner remaining on the surface of the photoconductor 1 after transfer, a static eliminator 7 for removing residual charges on the photoconductor 1 after transfer, and a toner image transferred onto the recording medium P. Is fixed to the recording medium P.

  Further, the image forming apparatus 100 includes a control device 20 that controls the operation of the image forming apparatus 100. In one aspect, the control device 20 is realized by cooperation of hardware resources and software. For example, the control device 20 includes a CPU (Central Processing Unit), a main memory, and a recording medium such as a ROM (Read Only Memory), and the function of the control device 20 is a control recorded on a recording medium such as a ROM. This is realized by reading the program into the main memory and executing it by the CPU. The control program can be provided by being recorded on a computer-readable recording medium, or can be provided by communication as a data signal. However, the function of the control device 20 may be realized only by hardware.

  Next, an image forming operation of the image forming apparatus 100 according to the present embodiment will be described. The image forming operation is controlled by the control device 20.

  The photoreceptor 1 is rotationally driven in the direction of arrow R by a motor (not shown). The charger 2 uniformly charges the surface of the photoreceptor 1 to a predetermined potential. Each of the exposure units 3-1 and 3-2 irradiates light on the uniformly charged surface of the photosensitive member 1 based on the image data to neutralize the surface of the photosensitive member 1, and static images of the image based on the image data are obtained. An electrostatic latent image is formed on the photoreceptor 1.

  Here, as the image data, image data input to the image forming apparatus 100 from an external apparatus (for example, a computer), and an image reading apparatus (not shown) of the image forming apparatus 100 optically converts an original image. There are image data read and generated, image data stored in advance in the image forming apparatus 100, and the like.

  The developing device 4 develops the electrostatic latent image on the photoreceptor 1 with toner to form a toner image on the photoreceptor 1.

  The transfer unit 5 transfers the toner image on the photoconductor 1 onto the recording medium P conveyed from the paper tray 9 to the transfer position in accordance with the rotation of the photoconductor 1.

  After the transfer, the surface of the photoconductor 1 is conveyed by the rotation of the photoconductor 1, the residue on the photoconductor 1 is removed by the cleaner 6, the residual charge on the photoconductor 1 is removed by the static eliminator 7, and then again. Charged by the charger 2.

  On the other hand, the recording medium P to which the toner image has been transferred is conveyed to the fixing device 8, and the toner image is fixed on the recording medium P by the fixing device 8.

  During normal image formation, for example, when printing an image in response to a print request from a client device, or when reading and printing an original image in response to a copy request, the control device 20 performs first and second latent images. The latent image formation by the first and second latent image forming devices is controlled so that the latent images formed by the image forming devices overlap each other. Specifically, the control device 20 controls the first and second latent image forming units so that latent images of substantially the same image are formed at substantially the same position on the image carrier. Controls latent image formation by the first and second latent image formers. In a specific aspect, the control device 20 controls exposure by the exposure units 3-1 and 3-2 so that the latent images formed by the exposure units 3-1 and 3-2 overlap each other. In other words, the control device 20 uses the exposure units 3-1 and 3-2 so that the portion to be exposed on the photoreceptor 1 is exposed by both the exposure units 3-1 and 3-2. Control exposure.

[Control device]
In the configuration in which latent images are formed on the same image carrier using the first and second latent image forming units as described above, between the latent images formed by the first and second latent image forming units. If there is a relative displacement, a problem on the image occurs. For example, when the exposure device is a light emitting element array such as an LED array, the exposure position of each exposure device is shifted from the target position due to assembly variation of each light emitting device array or mounting variation to the image forming apparatus 100. This causes a problem in the image such that the gradation characteristics cannot be obtained and characters and fine lines disappear.

  Therefore, in the present embodiment, as described below, from the viewpoint of reducing problems on the image due to the relative displacement between the latent images formed by the first and second latent image forming units, Control for correcting the deviation is performed.

  FIG. 2 is a block diagram illustrating an example of a functional configuration of the control device 20. Hereinafter, the functional configuration of the control device 20 will be described with reference to FIG.

  In FIG. 2, the control device 20 includes an image forming unit 21, an information acquisition unit 22, and a control unit 23.

  The image forming unit 21 forms the first image on the image holding member by the first latent image forming device and the second image by the second latent image forming device. An image for detecting misregistration formed by the image is formed on the image carrier. Specifically, the image forming unit 21 forms a first image on the photoreceptor 1 by the exposure device 3-1, and a second image by the exposure device 3-2. An image for detecting misregistration formed by the image is formed on the photoreceptor 1.

  The above-described image for detecting misalignment (hereinafter, abbreviated as “image for detecting misalignment” as appropriate) is used to detect a relative misalignment between latent images formed by the exposure units 3-1 and 3-2. It is an image.

  The first image, the second image, and the misregistration detection image will be described in detail later.

  The information acquisition unit 22 detects a relative displacement amount between the latent images formed by the first and second latent image forming units, which is detected based on the displacement detection image formed by the image forming unit 21. Get information indicating Specifically, the information acquisition unit 22 is information that indicates a relative positional shift amount between the latent images formed by the exposure units 3-1 and 3-2 that is detected based on the positional shift detection image. (Hereinafter referred to as “positional deviation amount information”).

  In one aspect, the information acquisition unit 22 detects the misregistration detection image formed by the image forming unit 21, and obtains misregistration amount information based on the detection result.

  In one aspect of this aspect, the information acquisition unit 22 detects the toner image of the misregistration detection image formed by the image forming unit 21. For example, the information acquisition unit 22 uses a density sensor 31 that measures the reflection density on the surface of the photoconductor 1 to measure a density pattern on the surface of the photoconductor 1, thereby detecting misalignment formed on the photoconductor 1. A toner image of the image is detected. Further, for example, the information acquisition unit 22 measures the density pattern on the surface of the transfer body by using the density sensor 32 that measures the reflection density on the surface of the transfer body (the recording medium P in the example of FIG. 1). Alternatively, the toner image of the misregistration detection image transferred to the toner image may be detected. The density sensors 31 and 32 are not particularly limited. For example, a density sensor for controlling the density of a toner image may be used as the density sensor 31 or 32. The information acquisition unit 22 may detect a latent image of the misregistration detection image formed by the image forming unit 21. For example, the information acquisition unit 22 measures the potential pattern on the surface of the photoconductor 1 by using a potential sensor 33 that measures the potential on the surface of the photoconductor 1, thereby detecting a displacement detection image formed on the photoconductor 1. The latent image may be detected. The potential sensor 33 is not particularly limited. For example, a potential sensor for controlling the potential of the photosensitive member 1 may be used as the potential sensor 33. The above-described measurement of concentration and potential is performed, for example, at two locations on both sides in the main scanning direction, but may be performed at one location or three or more locations.

  As the relative positional deviation between the latent images formed by the exposure units 3-1 and 3-2, for example, as shown in FIG. 3, the positional deviation in the sub-scanning direction, the positional deviation in the main scanning direction, and the angle Examples include deviation. Therefore, examples of the positional deviation amount information include information indicating the positional deviation amount in the sub-scanning direction, information indicating the positional deviation amount in the main scanning direction, and information indicating the positional deviation amount related to the angular deviation.

  The misregistration amount information only needs to indicate the relative misregistration amount between the latent images formed by the exposure units 3-1 and 3-2. As the misregistration amount information, for example, the following (a1) The information of (a3) is mentioned.

(A1) Information including a relative positional shift amount between the latent images formed by the exposure units 3-1 and 3-2. That is, information including the relative positional deviation amount between the exposure positions of the exposure units 3-1 and 3-2.
(A2) Information including the amount of displacement of the latent image formed by the exposure device 3-1 with respect to the target position and the amount of displacement of the latent image formed by the exposure device 3-2 with respect to the target position. That is, information including the amount of positional deviation of the exposure position of the exposure unit 3-1 with respect to the target position and the amount of positional deviation of the exposure position of the exposure unit 3-2 with respect to the target position.
(A3) Information including the absolute position of the latent image formed by the exposure unit 3-1 and the absolute position of the latent image formed by the exposure unit 3-2. That is, information including the absolute exposure position of the exposure unit 3-1 and the absolute exposure position of the exposure unit 3-2.

  Note that how to detect the positional deviation amount information from the positional deviation detection image will be described in detail later.

  Further, the processing for forming the above-described misregistration detection image and acquiring the misregistration amount information may be performed at an appropriate timing such as every time the power is turned on, at the time of shipment from the factory, or when the exposure device is replaced.

  Based on the information indicating the amount of positional deviation acquired by the information acquisition unit 22, the control unit 23 controls the first and second latent images formed by the first and second latent image forming units so that the positions of the latent images overlap each other. The latent image formation by the second latent image forming device is controlled. Specifically, during normal image formation, the control unit 23 causes the first and second latent image forming units to generate substantially identical latent images on the image carrier based on the positional deviation amount information. The latent image forming positions of the respective latent image forming units are adjusted so that they are formed at substantially the same position. In a specific mode, the control unit 23 exposes the exposure units 3-1, 3 and 3 so that the latent images formed by the exposure units 3-1, 3-2 overlap each other based on the positional deviation amount information. 2 controls exposure. Specifically, the control unit 23 controls the exposure timing of the exposure units 3-1 and 3-2 (that is, the image writing timing).

  In one aspect, the control unit 23 corrects the exposure position of one exposure unit to match the exposure position of the other exposure unit based on the relative positional deviation amount between the exposure units.

  In another aspect, the control unit 23 corrects the exposure position of each exposure unit to match the target position based on the amount of misalignment of the exposure position of each exposure unit with respect to the target position.

  Since many techniques have already been proposed for correcting the exposure position, a detailed description thereof is omitted here.

  By the way, when the exposure device is a light emitting element array in which a plurality of light emitting elements are arranged, the arrangement position of each light emitting element and the exposure position on the photoreceptor vary due to, for example, assembly variation of the light emitting element array.

  Therefore, in one aspect of the present embodiment, when both or one of the exposure units 3-1 and 3-2 is a light emitting element array in which a plurality of light emitting elements are arranged, the control unit 23 further includes an exposure unit. The exposure device information acquisition unit 24 acquires information (hereinafter referred to as “exposure device information”) indicating the deviation of the exposure position array from the straight line by each light emitting element.

  And the control part 23 is based on the exposure tool information acquired by the exposure tool information acquisition part 24, and the positional offset amount information acquired by the information acquisition part 22, 1st and 2nd exposure machine 3-1, The exposure by the first and second exposure units 3-1 and 3-2 is controlled so that the latent images formed by 3-2 overlap each other. Specifically, the control unit 23 corrects the deviation from the alignment line of the exposure position by each light emitting element of the exposure device based on the exposure device information, and the exposure position between the exposure devices based on the positional deviation amount information. Correct the relative deviation of. For example, the control unit 23 controls the light emission timing of each light emitting element of the exposure device based on the exposure device information so that the arrangement of exposure positions by the light emitting elements of the exposure device is linear along the main scanning direction. .

  The exposure device information is, for example, information indicating the exposure position or the amount of deviation of the exposure position with respect to one or both of the sub-scanning direction and the main scanning direction of all or a predetermined plurality of light-emitting elements in the light-emitting element array. is there. However, the exposure device information may be information of another mode as long as it can correct the deviation of the exposure position array from the straight line by each light emitting element of the exposure device.

  In one embodiment, the image forming unit 21 corrects the deviation from the alignment of the exposure position array by the light emitting elements of the exposure unit based on the exposure unit information acquired by the exposure unit information acquisition unit 24. Then, a misregistration detection image is formed.

  For correcting the deviation of the exposure position array from the straight line by each light emitting element of the exposure device, for example, the techniques described in Patent Documents 2 and 3 can be used, and detailed description thereof is omitted here.

  For example, the exposure unit information acquisition unit 24 may receive input of exposure unit information from an external device such as a computer, or may receive input of exposure unit information from an operator via a user interface. The exposure device information detected by the image forming apparatus 100 may be acquired.

  Further, the exposure unit information acquisition unit 24 may acquire the exposure unit information at an appropriate timing, such as at the time of factory shipment, replacement of the exposure unit, or each time the power is turned on.

  FIG. 4 is a flowchart illustrating an example of an operation procedure of the control device 20. Hereinafter, the operation of the control device 20 will be described with reference to FIG.

  For example, at the time of factory shipment, the control device 20 acquires the exposure device information of each of the exposure devices 3-1 and 3-2 and stores it in an internal nonvolatile storage device (S 1).

  Next, for example, when the power of the image forming apparatus 100 is turned on by the user, the control device 20 shifts the exposure position arrangement from the straight line based on the stored exposure device information of each exposure device. Is corrected, and a latent image of the first image is formed on the photosensitive member 1 by the exposure device 3-1, and a latent image of the second image is formed on the photosensitive member 1 by the exposure device 3-2. Then, the latent image is developed using the developing device 4 to form a toner image of the image for detecting displacement on the photosensitive member 1 (S2).

  Next, the control device 20 detects the misregistration detection image using the density sensor 31 (S3).

  Next, the control device 20 obtains positional deviation amount information indicating the relative positional deviation amount between the latent images formed by the exposure units 3-1 and 3-2 based on the detection result of step S <b> 3. Is stored in the non-volatile storage device (S4).

  When a normal image is formed, for example, when receiving a print request from an external client device or the like, the control device 20 uses the stored exposure device information of each exposure device and the stored positional deviation amount information. Based on this, exposure by the exposure units 3-1 and 3-2 is controlled so that the positions of the latent images formed by the exposure units 3-1 and 3-2 overlap each other, and an image according to the print request is displayed on the recording medium P. (S5).

[Formation of misalignment detection image and detection of misalignment amount information]
The image forming apparatus 100 originally forms one image using both the first and second latent image forming units, and uses only one of the first and second latent image forming units. When an image is formed, the contrast of the image becomes small. Specifically, compared to the case where the same part is exposed by two exposure units, when the exposure is performed by a single exposure unit, the exposure amount is insufficient, the potential contrast of the latent image is reduced, and the density of the toner image is reduced. The contrast is reduced.

  Specifically, assuming that the absolute value VH of the charged potential of the photosensitive member 1 charged by the charger 2 is common, the absolute value VL ′ of the exposure portion potential by a single exposure unit is determined by two exposure units. The absolute value VL of the exposure part potential is larger, and the potential contrast (VH−VL ′) of the latent image by the single exposure unit is smaller than the potential contrast (VH−VL) of the latent image by the two exposure units. . For this reason, it is difficult to measure the potential of the latent image with a single exposure device, compared to the measurement of the potential of the latent image with two exposure devices.

  If the absolute value VB of the DC component of the developing bias applied to the developer holding body 4a of the developing device 4 is common, the developing contrast (VB−VL ′) when a single exposure device is used is also obtained. This is smaller than the development contrast (VB−VL) when two exposure units are used. For this reason, when a single exposure device is used, the density of the toner image in the printed portion (exposed portion) of the image may be reduced, or the printed portion of the image may not be developed. That is, the density contrast of the toner image (the density difference between the print portion and the background portion) is reduced. For this reason, it is difficult to measure the density of a toner image formed by a single exposure device, compared to the measurement of the density of a toner image formed by two exposure devices.

  As described above, when the misregistration detection image is simply formed, the contrast of the misregistration detection image becomes small and accurate misregistration amount information may not be obtained.

  Therefore, in the present embodiment, from the viewpoint of obtaining accurate positional deviation amount information, the image forming unit 21 uses the first latent image forming device to generate the first image and the second latent image forming device to execute the first image. The second image is formed on the image carrier so that the first and second images overlap at least partially, and the image is formed by one of the first and second latent image forming units. In addition, a misregistration detection image having a high contrast is formed on the image carrier. Specifically, the image forming unit 21 at least partially overlaps the first image by the exposure device 3-1, the second image by the exposure device 3-2, and the first and second images. As described above, a misregistration detection image having a higher contrast than the image formed by one of the exposure devices 3-1 and 3-2 is formed on the photoconductor 1.

  In one aspect, from the viewpoint of facilitating detection of the overlapping pattern between the first and second images, the image forming unit 21 develops a portion where the first and second images overlap each other and does not overlap. Is developed so that the developed image of the misregistration detection image is formed. Specifically, the image forming unit 21 uses the developing device 4 to develop the latent image of the misregistration detection image to form a toner image of the misregistration detection image. At this time, the absolute value VL1 of the potential of the portion exposed by the exposure device 3-1 and the absolute value VL2 of the potential of the portion exposed by the exposure device 3-2 are applied to the developer holder 4a of the developing device 4. The absolute value VL of the potential of the portion exposed by both the exposure devices 3-1 and 3-2 is larger than the absolute value VB of the DC component of the developing bias. small.

  Specifically, the following first and second modes are exemplified as modes for forming a positional shift detection image and detecting positional shift amount information from the positional shift detection image. Note that in the following description, the description regarding the level of the potential means the level of the absolute value of the potential.

(First aspect)
The image forming unit 21 forms the first unit image with the first latent image forming unit and also forms the second unit image with the second latent image forming unit, and the first and second unit images. The process of forming the unit image for detecting misregistration formed by the above is repeated while shifting the relative position of the second unit image with respect to the first unit image.

  In one embodiment, the first and second unit images are images having a common pattern in which a plurality of lines are arranged at a predetermined interval. However, the first and second unit images may be images of other patterns such as a solid image or a dot image. Further, the first and second unit images may be images having the same pattern or different patterns.

  Further, in one aspect, the information acquisition unit 22 detects each of the unit images for detecting misalignment, and from the correspondence relationship between the relative position shift amount and the detected unit image for misalignment detection, Information indicating the amount of displacement is obtained.

  5 and 6 are diagrams illustrating an example of a misregistration detection image for detecting the misregistration amount in the sub-scanning direction in the first mode. An example of the misregistration detection image is shown separately in two drawings because of space limitations. Hereinafter, with reference to FIGS. 5 and 6, a specific example of detection of the amount of positional deviation in the sub-scanning direction in the first mode will be described.

  As shown in FIGS. 5 and 6, the image forming unit 21 forms a first unit image with the exposure device 3-1 and forms a second unit image with the exposure device 3-2. The process of forming a unit image for detecting misregistration formed by the second unit image is repeatedly performed while shifting the relative position of the second unit image with respect to the first unit image.

  5 and 6 show a latent image pattern, a latent image potential, and a toner image pattern when there is no relative positional shift between the latent images of the exposure units 3-1 and 3-2. . In the latent image patterns of FIGS. 5 and 6, the diagonally downward hatching indicates a portion exposed by the exposure unit 3-1, and the diagonally upward hatching indicates a portion exposed by the exposure unit 3-2. Indicates a portion exposed by both the exposure units 3-1 and 3-2. Further, in the latent image patterns of FIGS. 5 and 6, the fine grid lines are virtual lines representing dot grids.

  As shown in the latent image patterns of FIGS. 5 and 6, in this example, the first unit image and the second unit image are both ladder pattern images. Specifically, the first unit image and the second unit image are images in which three lines of 1 dot width extending in the main scanning direction are arranged at intervals of 10 dots. Further, in this example, the image forming unit 21 shifts the relative position of the second unit image with respect to the first unit image by one dot in the sub-scanning direction in the process of forming the unit image for detecting the positional deviation. Repeat repeatedly. Specifically, the image forming unit 21 sequentially forms five unit images A1 to A5 for detecting misregistration on the photoreceptor 1 along the sub-scanning direction. 5 and 6, for the third image A3 from the top, the position of the second unit image is the same as the position of the first unit image. With respect to the second image A2 and the first image A1 from the top, the position of the second unit image is shifted by 1 dot and 2 dots, respectively, downstream from the position of the first unit image in the sub-scanning direction. . For the fourth image A4 and the fifth image A5 from the top, the position of the second unit image is shifted by 1 dot and 2 dots upstream from the position of the first unit image in the sub-scanning direction, respectively. ing.

  As shown in the latent image potentials of FIGS. 5 and 6, in this example, the potential of the portion exposed only by the exposure device 3-1 and the potential of the portion exposed only by the exposure device 3-2 are Is higher than the DC component VB of the developing bias, and the potential of the portion exposed by both the exposure devices 3-1 and 3-2 is lower than the DC component VB of the developing bias.

  Therefore, as shown in the toner image patterns of FIGS. 5 and 6, in this example, only the portion where the write images of the exposure units 3-1 and 3-2 overlap is developed.

  In the case where the toner image of the positional deviation detection image is actually formed and the ladder pattern appears at the position corresponding to the image A3, the exposure position between the exposure units 3-1 and 3-2 in the sub-scanning direction is displayed. It can be seen that there is no relative displacement. When a ladder pattern appears at a position corresponding to the image A2 or A1, the exposure position of the exposure unit 3-2 is shifted by 1 dot or 2 dots upstream in the sub-scanning direction with respect to the exposure position of the exposure unit 3-1. I understand that. When a ladder pattern appears at a position corresponding to the image A4 or A5, the exposure position of the exposure unit 3-2 is 1 dot or 2 dots downstream in the sub-scanning direction with respect to the exposure position of the exposure unit 3-1. You can see that it is shifted.

  Therefore, the information acquisition unit 22 uses the density sensor 31 to detect the density of the position corresponding to the unit images A1 to A5 for detecting misalignment, and the first unit image in each unit image for detecting misalignment is detected. The positional shift amount information is obtained from the correspondence between the relative positional shift amount of the second unit image and the density of the position corresponding to each detected positional shift unit image. For example, when the density at the position corresponding to the image A1 is high and the density at the positions corresponding to the other images A2 to A4 is substantially zero, the information acquisition unit 22 determines that the exposure position of the exposure unit 3-2 is the exposure unit. It is determined that 2 dots are shifted to the upstream side in the sub-scanning direction with respect to the exposure position 3-1.

  In one aspect, the detection of the positional deviation amount in the sub-scanning direction is performed at two locations on both sides in the main scanning direction. In this case, as shown in FIG. 7, unit images A <b> 1 to A <b> 5 for detecting misregistration are formed at two positions on both sides in the main scanning direction on the photoreceptor 1. However, the detection of the positional deviation amount in the sub-scanning direction may be performed at one place or three or more places in the main scanning direction.

  FIG. 8 is a diagram illustrating an example of a misregistration detection image for detecting the misregistration amount in the main scanning direction in the first mode. Hereinafter, with reference to FIG. 8, a specific example of the detection of the amount of positional deviation in the main scanning direction in the first mode will be described. The detection of the amount of positional deviation in the main scanning direction is similar to the detection of the amount of positional deviation in the sub-scanning direction, and thus the description overlapping with the description of detecting the amount of positional deviation in the sub-scanning direction is omitted.

  FIG. 8 shows a latent image pattern and a toner image pattern when there is no relative displacement between the latent images of the exposure devices 3-1 and 3-2.

  As shown in the latent image pattern of FIG. 8, in this example, the first unit image and the second unit image are both ladder pattern images. Specifically, the first unit image and the second unit image are images in which three lines of 1 dot width extending in the sub-scanning direction are arranged at intervals of 10 dots. Further, in this example, the image forming unit 21 shifts the relative position of the second unit image with respect to the first unit image by one dot in the main scanning direction in the process of forming a unit image for detecting misregistration. Repeat repeatedly. Specifically, the image forming unit 21 sequentially forms five unit images B1 to B5 for detecting misregistration on the photoconductor 1 along the sub-scanning direction. In FIG. 8, for the third image B3 from the top, the position of the second unit image is the same as the position of the first unit image. For the second image B2 and the first image B1 from the top, the position of the second unit image is shifted by 1 dot and 2 dots to the left in the main scanning direction from the position of the first unit image, respectively. For the fourth image B4 and the fifth image B5 from the top, the position of the second unit image is shifted by 1 dot and 2 dots to the right in the main scanning direction from the position of the first unit image, respectively. Yes.

  Further, as in the case of detecting the amount of positional deviation in the sub-scanning direction, as shown in the toner image pattern of FIG. 8, only the portion where the written images of the exposure units 3-1 and 3-2 overlap is developed. Is done.

  When the toner image of the image for detecting misregistration is actually formed and the ladder pattern appears at the position corresponding to the image B3, the relative exposure position between the exposure units 3-1 and 3-2 in the main scanning direction. It can be seen that there is no significant misalignment. When a ladder pattern appears at a position corresponding to the image B2 or B1, the exposure position of the exposure unit 3-2 is shifted by one or two dots to the right in the main scanning direction with respect to the exposure position of the exposure unit 3-1. I understand that. When a ladder pattern appears at a position corresponding to the image B4 or B5, the exposure position of the exposure unit 3-2 is shifted by 1 dot or 2 dots to the left in the main scanning direction with respect to the exposure position of the exposure unit 3-1. I understand that

  Therefore, the information acquisition unit 22 uses the density sensor 31 to detect the density of the position corresponding to the unit images B1 to B5 for detecting misregistration, and to the first unit image in each unit image for detecting misregistration. The positional shift amount information is obtained from the correspondence between the relative positional shift amount of the second unit image and the density of the position corresponding to each detected positional shift unit image. For example, when the density of the position corresponding to the image B1 is high and the density of the positions corresponding to the other images B2 to B5 is substantially zero, the information acquisition unit 22 determines that the exposure position of the exposure unit 3-2 is the exposure unit. It is determined that 2 dots are shifted to the right in the main scanning direction with respect to the exposure position of 3-1.

  In one aspect, the amount of positional deviation in the main scanning direction is detected at two locations on both sides in the main scanning direction. In this case, as shown in FIG. 9, unit images B <b> 1 to B <b> 5 for detecting misregistration are formed at two positions on both sides in the main scanning direction on the photoreceptor 1. However, the detection of the positional deviation amount in the main scanning direction may be performed at one place or three or more places in the main scanning direction.

(Second aspect)
As shown in FIG. 10, the image forming unit 21 forms a solid image with the exposure device 3-1, and forms a mark image M2 with the exposure device 3-2. The solid image and the mark image M2 are superimposed. Form the image. The mark image M2 is substantially V-shaped, and has two sides M21 and M22 that intersect at an angle of 45 degrees with respect to both the sub-scanning direction and the main scanning direction. FIG. 10 shows a latent image pattern and a toner image pattern. In the latent image pattern of FIG. 10, oblique hatching to the right indicates a portion exposed by the exposure device 3-1, and cross hatching indicates a portion exposed by both the exposure devices 3-1 and 3-2. In FIG. 10, a range between two broken lines indicates a density measurement range of the density sensor 31. The density sensor 31 is not particularly limited, but for example, those described in Patent Documents 7 and 8 can be used.

  FIG. 11 is a timing chart showing changes in the density detection signal of the density sensor 31 when the exposure position of the exposure device 3-2 is not shifted from the target position. That is, FIG. 11 is a timing chart showing an ideal change of the density detection signal. In FIG. 11, a mark image M2 is also displayed in association with the waveform of the density detection signal.

11, the time _{t 20} is the write start time of the mark image M2 by the exposure unit 3-2. Time t ₂₁ is when the sides M21 of the mark image M2 is detected by the concentration sensor 31 is the time at which the peak of the density detection signal is obtained. Time _{t 22} is the center of the mark image M2 is the time passing the density sensor 31. Time t ₂₃ is when the sides M22 of the mark image M2 is detected by the concentration sensor 31 is the time at which the peak of the density detection signal is obtained. Time _{t 22 is} represented as _{t 22 = (t 21 + t} 23) / 2.

  FIG. 12 is a timing chart showing an example of a change in the density detection signal actually measured by the density sensor 31. In FIG. 12, a mark image M2 is also displayed in association with the waveform of the density detection signal. In FIG. 12, the mark image M2 represented by the alternate long and short dash line corresponds to the case where there is no positional deviation.

In FIG. 12, time t ₂₀ ′ is the writing start time of the mark image M2 by the exposure device 3-2. Time t ₂₁ ′ is the time when the peak of the density detection signal is obtained when the side M21 of the mark image M2 is detected by the density sensor 31. Time t ₂₃ ′ is the time when the peak of the density detection signal is obtained when the side M22 of the mark image M2 is detected by the density sensor 31.

The absolute exposure position P _s2 of the exposure device 3-2 with respect to the sub-scanning direction with respect to the position of the density sensor 31 is obtained by the following equation. In the following formula, PS is the moving speed (process speed) of the surface of the photoreceptor 1.
P _s2 = {(t ₂₁ ′ + t ₂₃ ′) / 2−t ₂₀ ′} × PS

The positional deviation amount D _{s2 with} respect to the target position of the exposure position of the exposure device 3-2 in the sub-scanning direction is obtained by the following equation.
D _s2 = {(t ₂₁ ′ + t ₂₃ ′) / 2−t ₂₂ } × PS

The positional deviation amount D _{m2 with} respect to the target position of the exposure position of the exposure device 3-2 in the main scanning direction is obtained by the following equation.
D _m2 = [{(t ₂₃ ′ −t ₂₁ ′) − (t ₂₃ −t ₂₁ )} / 2] × PS

  Next, as shown in FIG. 13, the image forming unit 21 forms a solid image by the exposure device 3-2 and also forms a mark image M1 by the exposure device 3-1, and the solid image and the mark image M1 are formed. A superimposed image is formed. The mark image M1 is substantially V-shaped and has two sides M11 and M12 that intersect at an angle of 45 degrees with respect to both the sub-scanning direction and the main scanning direction. FIG. 13 shows a latent image pattern and a toner image pattern. In the latent image pattern of FIG. 13, oblique hatching rising to the right indicates a portion exposed by the exposure device 3-2, and cross hatching indicates a portion exposed by both the exposure devices 3-1 and 3-2. In FIG. 13, a range between two broken lines indicates a density measurement range of the density sensor 31.

  FIG. 14 is a timing chart showing changes in the density detection signal of the density sensor 31 when the exposure position of the exposure device 3-1 is not shifted from the target position. That is, FIG. 14 is a timing chart showing an ideal change of the density detection signal. In FIG. 14, a mark image M1 is also displayed in association with the waveform of the density detection signal.

14, the time _{t 10} is a write start time of the mark image M1 by the exposure unit 3-1. Time t ₁₁ is when the sides M11 of the mark image M1 is detected by the concentration sensor 31 is the time at which the peak of the density detection signal is obtained. Time _{t 12} is the center of the mark image M1 is the time that passes the density sensor 31. Time t ₁₃ is when the sides M12 of the mark image M1 is detected by the concentration sensor 31 is the time at which the peak of the density detection signal is obtained. Time _{t 12 is} represented as _{t 12 = (t 11 + t} 13) / 2.

  FIG. 15 is a timing chart showing an example of a change in the density detection signal actually measured by the density sensor 31. In FIG. 15, a mark image M1 is also displayed in association with the waveform of the density detection signal. In FIG. 15, the mark image M <b> 1 represented by an alternate long and short dash line corresponds to the case where there is no positional deviation.

In FIG. 15, time t ₁₀ ′ is the writing start time of the mark image M1 by the exposure device 3-1. The time t ₁₁ ′ is the time when the peak of the density detection signal is obtained when the side M11 of the mark image M1 is detected by the density sensor 31. The time t ₁₃ ′ is the time when the peak of the density detection signal is obtained when the side M12 of the mark image M1 is detected by the density sensor 31.

The absolute exposure position P _s1 of the exposure device 3-1 with respect to the sub-scanning direction with respect to the position of the density sensor 31 is obtained by the following equation. In the following formula, PS is the moving speed (process speed) of the surface of the photoreceptor 1.
P _s1 = {(t ₁₁ ′ + t ₁₃ ′) / 2−t ₁₀ ′} × PS

The positional deviation amount D _{s1 with} respect to the target position of the exposure position of the exposure device 3-1 regarding the sub-scanning direction is obtained by the following equation.
D _s1 = {(t ₁₁ ′ + t ₁₃ ′) / 2−t ₁₂ } × PS

The positional deviation amount D _{m1 with} respect to the target position of the exposure position of the exposure device 3-1 regarding the main scanning direction is obtained by the following equation.
D _m1 = [{(t ₁₃ ′ −t ₁₁ ′) − (t ₁₃ −t ₁₁ )} / 2] × PS

Then, the relative displacement amount D _s of the exposure position between the exposure units 3-1 and 3-2 in the sub-scanning direction is obtained by the following equation.
D _s = D _s1 −D _s2

Further, in the main scanning direction, relative positional deviation amount D _m of the exposure position between the exposure unit 3-1 is obtained by the following equation.
D _m = D _m1 −D _m2

  In one aspect, the position shift amount is detected at two locations on both sides in the main scanning direction. In this case, as shown in FIG. 16, mark images M <b> 1 and M <b> 2 are formed at two places on both sides in the main scanning direction on the photoreceptor 1. However, the detection of the displacement amount may be performed at one place or three places or more in the main scanning direction.

Further, in one aspect, the information acquisition unit 22 uses the above-described formulas based on the density detection signal of the density sensor 31 as the positional deviation amount information as a set of P _s1 and P _s2 , D _s1 and D _s2 . A set, a set of D _m1 and D _m2 , a positional deviation amount D _s , a positional deviation amount D _{m and the} like are calculated.

[effect]
According to the present embodiment described above, the following effects (1) to (7) can be obtained.

  (1) In the present embodiment, the first and second latent image forming units form a misregistration detection image on the image carrier, and are detected based on the misregistration detection image. Information indicating a relative positional shift amount between the latent images formed by the second latent image forming unit is acquired, and formed by the first and second latent image forming units based on the information indicating the positional shift amount. The latent image formation by the first and second latent image forming units is controlled so that the positions of the latent images to be overlapped with each other. For this reason, according to the present embodiment, it is possible to reduce problems on the image due to the relative displacement between the latent images formed by the first and second latent image forming units. For example, it is possible to correct the relative misalignment of the exposure position between the exposure devices due to the mounting variation of each exposure device such as an LED print head, and a desired gradation characteristic cannot be obtained, or characters and fine lines disappear. It is possible to reduce such image defects.

  (2) In the present embodiment, the first latent image forming device forms the first image, the second latent image forming device forms the second image, and the first and second images are at least partially. A registration error detection image having a higher contrast than the image formed by one of the first and second latent image forming units is formed on the image holding member so as to overlap. For this reason, according to the present embodiment, it is possible to detect positional deviation amount information with high accuracy based on a positional deviation detection image having a large contrast. In addition, the same misalignment detection image as that in the normal image formation is formed under the same image formation conditions as in the normal image formation, that is, without changing the image formation conditions from the normal image formation. It is possible. For this reason, it is possible to avoid or reduce the disadvantages caused by changing the image forming conditions when forming the misregistration detection image. For example, it is possible to avoid or reduce the complexity of the configuration and the increase in cost by providing a development bias and process speed different from those during normal image formation.

  (3) In one aspect of the present embodiment, the image forming unit forms the first unit image by the first latent image forming device and forms the second latent image as the process of forming the misregistration detection image. A process of forming a second unit image by the image forming unit and forming a unit image for detecting misregistration formed by the first and second unit images is performed on the second unit image with respect to the first unit image. Repeatedly shifting the relative position. In the aspect, as the relative position of the second unit image with respect to the first unit image is shifted, the pattern of the overlapping portion between the first and second unit images in the unit image for detecting displacement is determined. Change. For this reason, according to the aspect, it is possible to obtain the positional deviation amount information using the change in the pattern of the overlapping portion. Thereby, for example, it is possible to improve the detection accuracy of the positional deviation amount information and simplify the configuration for detecting the positional deviation amount information.

  (4) In one aspect of the present embodiment, the first and second unit images are images having a common pattern in which a plurality of lines are arranged at predetermined intervals. In this aspect, the overlapping pattern between the first and second unit images is a solid pattern when the positions of both unit images are shifted from each other, and the pattern of both unit images is coincident with each other. Becomes a ladder pattern. In other words, in this aspect, as the relative position of the second unit image with respect to the first unit image is shifted, the pattern of the overlapping portion between the first and second unit images clearly changes. For this reason, according to the aspect, it is possible to easily detect the positional deviation amount information. For example, since the density change of the toner image pattern in the overlapping portion is clear, it is possible to detect positional deviation amount information using a simple or low-cost density sensor with low spatial resolution or density resolution. For example, a density sensor for controlling the density of the toner image can be used in combination with detection of positional deviation amount information.

  (5) In one aspect of the present embodiment, the information acquisition unit detects the above-described unit images for detecting misalignment, and detects the relative position shift amount and the detected unit image for misalignment detection. The positional deviation amount information is obtained from the corresponding relationship. For this reason, according to this aspect, the image forming apparatus can obtain the positional deviation amount information from the correspondence between the relative positional deviation amount and the unit image for detecting the positional deviation.

  (6) In one aspect of the present embodiment, the image forming unit develops an image for detecting misalignment so that a portion where the first and second images overlap is developed and a portion where the first and second images do not overlap is not substantially developed. The latent image is developed to form a developed image of the misregistration detection image. For this reason, according to the said aspect, it becomes possible to recognize clearly the part which 1st and 2nd images overlapped. Thereby, for example, it is possible to improve the detection accuracy of the displacement amount or to simplify the configuration for detecting the displacement amount. Specifically, for example, when the above aspect is applied to the above aspect (4), when the positions of the first and second unit images are deviated from each other, the unit image for misregistration detection is not developed, When the positions of the first and second unit images coincide with each other, the unit image for detecting misalignment is developed. This facilitates discrimination between the misalignment state and the aligned state.

  (7) In one aspect of this embodiment, the image forming unit develops the latent image of the misregistration detection image using a developer holder that holds and conveys the developer containing toner, When the toner image of the displacement detection image is formed and the toner image of the positional displacement detection image is formed, the absolute value of the potential of the portion exposed by one of the first and second latent image forming units is The absolute value of the potential of the portion exposed by both the first and second latent image forming units is larger than the absolute value of the DC component of the developing bias applied to the developer holder, Less than absolute value. In this aspect, the portion where the first and second images do not overlap is not developed, and the portion where the first and second images overlap is developed. For this reason, according to the said aspect, it becomes possible to recognize clearly the part which 1st and 2nd images overlapped. Thereby, for example, it is possible to improve the detection accuracy of the displacement amount or to simplify the configuration for detecting the displacement amount. Specifically, for example, when the above aspect is applied to the above aspect (4), when the positions of the first and second unit images are deviated from each other, the unit image for misregistration detection is not developed, When the positions of the first and second unit images coincide with each other, the unit image for detecting misalignment is developed. This facilitates discrimination between the misalignment state and the aligned state.

  In addition, this invention is not limited to the said embodiment, It can change variously within the range which does not deviate from the summary of this invention.

  For example, the image forming apparatus only needs to form a latent image on the same image carrier using at least two latent image formers, and the same image carrier using three or more latent image formers. A latent image may be formed on the surface.

  In the above-described embodiment, the image forming apparatus acquires the positional shift amount information from the positional shift detection image using a density sensor or the like. However, the positional shift amount information may be acquired in another manner. Good. For example, the image forming apparatus outputs a recording medium on which a misregistration detection image is printed, and a detection device or a user other than the image forming apparatus reads the misregistration detection image on the recording medium. The positional deviation amount information may be obtained from the read image. In this case, the image forming apparatus may acquire the positional deviation amount information obtained by the detection apparatus or the user from the detection apparatus or may acquire from the user or the like via the user interface. Further, for example, when the image forming apparatus has an image reading apparatus, a user or the like sets the recording medium in the image reading apparatus, and the image forming apparatus uses the image reading apparatus to detect a positional deviation on the recording medium. The positional deviation amount information may be obtained from the read image.

1 is a schematic side view illustrating an example of a configuration of an image forming apparatus according to an embodiment. It is a block diagram which shows an example of a function structure of a control apparatus. It is a figure which illustrates the relative position shift between the latent images formed by two exposure devices. It is a flowchart which shows an example of the operation | movement procedure of a control apparatus. It is a figure which shows an example of the image for a position shift detection for detecting the position shift amount of a subscanning direction in a 1st aspect. It is a figure which shows an example of the image for a position shift detection for detecting the position shift amount of a subscanning direction in a 1st aspect. FIG. 6 is a diagram illustrating an example in which unit images for detecting misregistration are formed at two positions on both sides in the main scanning direction on a photoconductor. It is a figure which shows an example of the image for a position shift detection for detecting the position shift amount of a 1st aspect in the main scanning direction. FIG. 6 is a diagram illustrating an example in which unit images for detecting misregistration are formed at two positions on both sides in the main scanning direction on a photoconductor. It is a figure which shows an example of the image for a position shift detection in a 2nd aspect. It is a timing chart which shows the change of the density detection signal of a density sensor when the exposure position of the 2nd exposure machine has not shifted from the target position. It is a timing chart which shows an example of the change of the density detection signal actually measured by the density sensor. It is a figure which shows an example of the image for a position shift detection in a 2nd aspect. It is a timing chart which shows the change of the density detection signal of a density sensor when the exposure position of the 1st exposure device has not shifted from the target position. It is a timing chart which shows an example of the change of the density detection signal actually measured by the density sensor. It is a figure which shows an example in case a mark image is formed in two places of the both sides of the main scanning direction on a photoreceptor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Image holding body (photosensitive body), 3-1 and 3-2 Latent image forming device (exposure device), 4 developing device, 4a developer holding body, 20 control apparatus, 21 image forming part, 22 information acquisition part, 23 Control unit, 100 image forming apparatus.

Claims (8)

First and second latent image forming means for forming a latent image on the same image carrier;
The first image is formed by the first latent image forming unit, the second image is formed by the second latent image forming unit, and the first and second images are overlapped at least partially. Image forming means for forming on the image carrier a misregistration detection image formed on the holder and having a contrast higher than that of the image formed by one of the first and second latent image forming means; ,
Information acquisition means for acquiring information indicating a relative amount of positional deviation between the latent images formed by the first and second latent image forming means, which is detected based on the image for detecting positional deviation;
Latent image formation by the first and second latent image forming means so that the positions of the latent images formed by the first and second latent image forming means overlap with each other based on the information indicating the amount of displacement. Control means for controlling
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The image forming unit forms the first unit image by the first latent image forming unit and the second latent image forming unit by the second latent image forming unit as a process of forming the image for detecting the displacement. A process of forming a unit image and forming a unit image for detecting misregistration formed by the first and second unit images is a relative position of the second unit image with respect to the first unit image. Repeatedly while shifting
An image forming apparatus. The image forming apparatus according to claim 2,
The first and second unit images are images having a common pattern in which a plurality of lines are arranged at a predetermined interval.
An image forming apparatus. The image forming apparatus according to claim 2, wherein
The information acquisition means detects each unit image for detecting a position shift, and calculates the amount of the position shift based on a correspondence between the amount of relative position shift and the detected unit image for position shift detection. Ask for information to show,
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 4, wherein
The image forming means develops a latent image of the image for detecting misalignment so that a portion where the first and second images overlap is developed and a portion where the first and second images do not overlap is not substantially developed. Forming a developed image of the image for detecting displacement;
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 4, wherein
The first and second latent image forming units are exposure units that expose the image carrier to form an electrostatic latent image on the image carrier,
The image forming unit develops a latent image of the misregistration detection image using a developer holder that holds and conveys a developer containing toner, and forms a toner image of the misregistration detection image. Form the
When the toner image of the image for detecting misregistration is formed, the absolute value of the potential of the portion exposed by one of the first and second latent image forming units is applied to the developer holder. The absolute value of the DC component of the developing bias is greater than the absolute value of the DC component of the developing bias, and the absolute value of the potential of the portion exposed by both the first and second latent image forming units is smaller than the absolute value of the DC component of the developing bias.
An image forming apparatus. An image forming apparatus including first and second latent image forming units that form a latent image on the same image carrier is controlled, so that the first image is formed by the first latent image forming unit and the second image is formed by the second latent image forming unit. The second image is formed on the image carrier by the latent image forming means so that the first and second images overlap at least partly to form the first and second latent images. An image forming means for forming on the image carrier a misregistration detection image having a larger contrast than an image formed by one of the means;
Information acquisition means for acquiring information indicating a relative amount of positional deviation between the latent images formed by the first and second latent image forming means, which is detected based on the image for detecting positional deviation;
Latent image formation by the first and second latent image forming means so that the positions of the latent images formed by the first and second latent image forming means overlap with each other based on the information indicating the amount of displacement. Control means for controlling
A control apparatus for an image forming apparatus, comprising: On the computer,
An image forming apparatus including first and second latent image forming units that form a latent image on the same image carrier is controlled, so that the first image is formed by the first latent image forming unit and the second image is formed by the second latent image forming unit. The second image is formed on the image carrier by the latent image forming means so that the first and second images overlap at least partly to form the first and second latent images. A procedure for forming on the image carrier a misregistration detection image having a greater contrast than an image formed by one of the means;
A procedure for acquiring information indicating a relative positional shift amount between the latent images formed by the first and second latent image forming units, which is detected based on the positional shift detection image;
Latent image formation by the first and second latent image forming means so that the positions of the latent images formed by the first and second latent image forming means overlap with each other based on the information indicating the amount of displacement. The procedure to control,
And a control program for the image forming apparatus.

Images