JP2006106565A - Image forming apparatus, uneven density image discrimination method, and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image output device which can discriminate whether the uneven density in the image is caused by uneven screw pitches or not and can suppress the uneven density due to the uneven screw pitches, and also provide an uneven density discrimination method and an image forming method. <P>SOLUTION: This is an image forming apparatus which forms an electrostatic latent image on an image carrier based on the image forming signals by moving the image carrier in the sub-scanning direction and develops this latent image with the developer to form an image while rotating a screw to convey the developer. It has detector pairs 101aY, 101bY; 101aM, 101bM; 101aC, 101bC; 101aK, 101bK arranged in the main scanning direction with a gap different from the screw pitch to detect the density of the formed image, and an uneven density discriminator 104 to discriminate the uneven density caused by the screw based on the density changes detected by each detector pair. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms an image on recording paper by an electrophotographic method, a density unevenness determination apparatus that is used for the image forming means, and an image forming method.

  Conventionally, in electrophotographic image formation, first, an electrostatic latent image is formed by moving the uniformly charged image carrier while exposing the surface with laser light, and then developing the formed electrostatic latent image. A toner image is formed, and the toner image is further transferred to a recording sheet, or the toner image is transferred to a recording sheet via an intermediate transfer member, and the transferred toner image is fixed by a fixing unit. Here, the moving direction of the image carrier is referred to as the sub-scanning direction, and the direction orthogonal to the sub-scanning direction is referred to as the main scanning direction.

  However, there is a case where density unevenness occurs in an image formed due to a time-dependent change such as a device defect or a developer, or an environmental change such as temperature or humidity. Density unevenness not only deteriorates the image and causes an image defect, but also makes it impossible to accurately measure the density of a predetermined patch based on the measurement result, which may hinder density adjustment. It was. For example, there is an image forming apparatus that measures density unevenness and adjusts density based on the measurement result (see, for example, Patent Document 1). In this image forming apparatus, a photosensitive drum and a developing sleeve as an image carrier. The density unevenness appearing in the sub-scanning direction is detected at the rotation cycle of the cylindrical parts such as the gears and the rotation cycle of the gears for driving them. In addition, the size and position of not only the photosensitive drum and the developing sleeve but also the image forming-related parts such as the exposure unit and the discharge lamp are stored in advance, and density unevenness and potential unevenness are detected by a detection unit that scans two-dimensionally. Therefore, not only the density unevenness that occurs in the sub-scanning direction due to the rotation period, but also the image formation-related component that detects the density unevenness that occurs in the main scanning direction by, for example, an exposure lamp or a discharge lamp, and utters the density unevenness. For example, there is an image forming apparatus that issues a warning (see, for example, Patent Document 2).

  Further, the density unevenness may occur in an oblique direction with respect to the sub-scanning (or main scanning direction) in addition to the sub-scanning and main scanning direction detected by the image forming apparatus. The density unevenness is density unevenness generated by a spiral screw that is provided in the developing unit and is provided in parallel with the developing sleeve to feed and collect the developer with respect to the developing sleeve.

  Here, generation of screw pitch unevenness which is density unevenness due to the screw will be described. Since the screws arranged side by side are spiral, the position where the outer periphery of the developing sleeve and the outer periphery of the screw are closest to each other and the distance is minimum is periodically present in the main scanning direction, which is the axial direction of the screw pitch. To do. Then, the position where this distance is minimum is moved in the main scanning direction by the rotation of the screw, and the developing sleeve is also rotated, so the position where this distance is minimum is moved in an oblique direction with respect to the developing sleeve, Draw a spiral trajectory on the development sleeve. On the other hand, the development performance at the position where the distance is minimized may be deteriorated as compared with others due to, for example, deterioration of the developer over time or environmental conditions, and in this case, the developed electrostatic latent image Causes unevenness in the diagonal direction with respect to the sub-scanning at the pitch of the screw in the main scanning direction.

JP 2004-45903 A Japanese Patent Laid-Open No. 5-224443

  However, in the image forming apparatuses described in Patent Documents 1 and 2, there is no description about the screw pitch unevenness as described above, and it cannot be determined whether or not density unevenness is generated by the screw. Therefore, the screw pitch unevenness cannot be corrected.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to determine whether or not density unevenness occurring in an image is screw pitch unevenness. An object of the present invention is to provide an image output device, a density unevenness determination method, and an image forming method that can be suppressed.

  In order to solve the above-mentioned problems, an invention according to claim 1 is characterized in that an electrostatic latent image based on an image forming signal is formed on the image carrier while moving the image carrier in the sub-scanning direction, and a screw is rotated. An image forming apparatus that forms an image by developing the electrostatic latent image with the developer while transporting the developer, and is disposed at an interval different from a pitch of the screw in the image carrier main scanning direction. And a pair of detection means for detecting the density of the image to be formed, and a discrimination means for discriminating density unevenness due to the screw based on density changes detected by the pair of detection means, respectively. .

  According to a second aspect of the present invention, an electrostatic latent image based on an image forming signal is formed on the image carrier while moving the image carrier in the sub-scanning direction, and the developer is conveyed by rotating a screw. An image forming apparatus that forms an image by developing the electrostatic latent image with the developer, and is formed in the image carrier main scanning direction at an interval different from the pitch of the screw. A pair of detection means for detecting the density of the image, a discrimination means for discriminating density unevenness due to the screw, based on density changes detected by the pair of detection means, and a discrimination means for discriminating density unevenness due to the screw Development condition changing means for changing the development conditions in the case of development, and developing under the changed development conditions to form an image to suppress density unevenness due to the screw It is characterized in Rukoto.

  The invention described in claim 3 is characterized in that the development condition changing means increases the rotational speed of the screw.

  The invention according to claim 4 is characterized in that the rotational speed of the screw is increased to 1.2 times or more and 2 times or less.

  The invention according to claim 5 is characterized in that the discriminating means discriminates density unevenness due to the screw when there is a time difference between the density changes.

  According to a sixth aspect of the present invention, the discriminating means discriminates density unevenness due to the screw when there is a time difference between the respective density changes and the respective density changes change in the same cycle. It is a feature.

  According to a seventh aspect of the present invention, an electrostatic latent image based on an image forming signal is formed on the image carrier while moving the image carrier in the sub-scanning direction, and the developer is conveyed by rotating a screw. On the other hand, a density unevenness determination method in an image forming apparatus that forms an image by developing the electrostatic latent image with the developer, wherein the image carrier main scanning direction has an interval different from the pitch of the screw. The method includes a step of detecting a density of an image to be formed, and a step of determining density unevenness due to the screw based on respective density changes detected at intervals different from the pitch of the screw.

  The invention according to claim 8 forms an electrostatic latent image based on an image forming signal on the image carrier while moving the image carrier in the sub-scanning direction, and rotates the screw to convey the developer. On the other hand, an image forming method for forming an image by developing the electrostatic latent image with the developer, wherein the formed image is formed at an interval different from the screw pitch in the image carrier main scanning direction. A step of detecting density, a step of determining density unevenness due to the screw based on respective density changes detected at intervals different from the pitch of the screw, and a case where density unevenness due to the screw is determined, The method includes the step of changing the development condition, and developing the image under the changed development condition to form an image to suppress density unevenness due to the screw.

  According to the density unevenness image forming apparatus according to claim 1, the screw pitch unevenness is discriminated based on the density change detected by the pair of detection means arranged at intervals different from the pitch of the screw conveying the developer. Can do.

  According to the image forming apparatus of the second aspect, the screw pitch unevenness is discriminated based on the density change detected by the pair of detection means arranged at intervals different from the pitch of the screw that conveys the developer, and the development is performed. The occurrence of screw pitch unevenness can be suppressed by changing the above condition.

  According to the image forming apparatus of the third aspect, it is possible to suppress the occurrence of screw pitch unevenness by increasing the screw rotation speed, and further, no density change is caused.

  According to the image forming apparatus of the fourth aspect, it is possible to suppress the occurrence of screw pitch unevenness, and no malfunction occurs.

  According to the density unevenness image forming apparatus of the fifth aspect, density unevenness generated obliquely with respect to the sub-scanning direction of screw pitch unevenness can be determined by the time difference of density change.

  According to the density unevenness image forming apparatus of the sixth aspect, an accidental density change that is not periodic is not mistakenly identified as screw pitch unevenness.

  According to the density unevenness determination method according to claim 7, the screw pitch unevenness can be determined based on a density change detected by a pair of detection means arranged at intervals different from the pitch of the screw conveying the developer. it can.

  According to the density unevenness correction method of claim 8, the screw pitch unevenness is determined based on the density change detected by the pair of detection means arranged at intervals different from the pitch of the screw conveying the developer, It is possible to suppress the occurrence of screw pitch unevenness by changing the development conditions.

  Hereinafter, a copying machine will be described as an example of an image reading apparatus provided with the density unevenness determination apparatus of the present invention with reference to the drawings.

(overall structure)
FIG. 1 is a sectional configuration diagram showing an embodiment of a copying machine as an image forming apparatus according to the present invention. The copying machine shown in FIG. 1 is a so-called tandem type full-color copying machine, and each of image forming units 10Y, 10M, 10C, which forms images of image colors SC, yellow, magenta, cyan, and black. 10K, an intermediate transfer body unit 7, a paper feeding means 21, and a fixing means 24.

  The image reading unit SC is located above the copying machine and includes an automatic document feeder 201 and a document image scanning exposure device 202, and an image of the document d conveyed by the automatic document feeder 201 is stored in the document image scanning exposure device 202. It is read by a line image sensor CCD, which is an image pickup device, by an optical system and photoelectrically converted into an analog signal.

  The image forming units 10Y, 10M, 10C, and 10K are vertically arranged in a vertical direction, and rollers 71, 72, 73, and 74 are wound around the left side of the photoreceptors 1Y, 1M, 1C, and 1K so as to be rotatable. A stretched semiconductive endless belt-like intermediate transfer member 70 is disposed.

  The intermediate transfer member 70 is conveyed in the direction of the arrow by a driving device (not shown) connected to the intermediate transfer member driving roller 71 by an intermediate transfer member driving roller 71.

  The image forming unit 10Y that forms a yellow image includes a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, density detecting units 101aY and 101bY, a primary transfer roller 5Y, and a cleaning unit 6Y arranged around the photoreceptor 1Y. Have

  An image forming unit 10M that forms a magenta image includes a charging unit 2M, an exposing unit 3M, a developing unit 4M, density detecting units 101aM and 101bM, a primary transfer roller 5M, and a cleaning unit 6M arranged around the photoreceptor 1M. Have

  The image forming unit 10C that forms a cyan image includes a charging unit 2C, an exposing unit 3C, a developing unit 4C, density detecting units 101aC and 101bC, a primary transfer roller 5C, and a cleaning unit 6C arranged around the photoreceptor 1C. Have

  An image forming unit 10K that forms a black image includes a charging unit 2K, an exposure unit 3K, a developing unit 4K, density detecting units 101aK and 101bK, a primary transfer roller 5K, and a cleaning unit 6K arranged around the photoreceptor 1K. Have.

  The charging means 2Y, 2M, 2C, and 2K are, for example, scorotron charging means, and uniformly charge the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K to predetermined polarities and potentials, respectively. This charging is performed after the surface of the photoreceptors 1Y, 1M, 1C, and 1K is removed by uniformly irradiating light with a static elimination lamp (not shown).

  The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, etc. in an image processing unit (not shown), and then exposure means 3Y, 3M, 3C, The image data is sent to 3K as binary or multivalued image data for each color, and electrostatic latent images of the image data are formed on the corresponding drum-shaped photoconductors 1Y, 1M, 1C, and 1K. Also, it receives image data from an external terminal that is communicably connected (not shown), sends the image data to the exposure means 3Y, 3M, 3C, and 3K, and corresponding drum-shaped photoconductors 1Y, 1M, 1C, and 1K. Then, an electrostatic latent image of image data is formed.

  That is, the exposure means 3Y, 3M, 3C, and 3K modulate a laser diode (not shown) based on the gradation value indicated by the image data, and scan the corresponding photoconductors 1Y, 1M, 1C, and 1K with a laser beam to statically. It forms an electrostatic latent image. The photoreceptors 1Y, 1M, 1C, and 1K rotate in the arrow a direction at a peripheral speed vp, and scan the laser beam in a direction perpendicular to the rotation direction. This laser beam scanning direction is referred to as a main scanning direction (image carrier main scanning direction), and the rotation directions of the photosensitive members 1Y, 1M, 1C, and 1K are referred to as sub-scanning directions. The gradation value is a numerical value indicating each pixel of the multi-valued image data step by step in increments of 0 to 1, for example, white being 0 and solid being 255.

  The developing means 4Y, 4M, 4C, and 4K contain a carrier and a developer including yellow, magenta, cyan, and black toners, respectively, and electrostatic latent images of the respective colors are formed on the photoreceptors 1Y, 1M, 1C, and 1K. The corresponding developing devices 4Y, 4M, 4C, and 4K are driven each time they are formed to form respective toner images. The density detection means 101aY and bY, 101aM and bM, 101aC and bC, and 101aK and bK are a pair of detection means for detecting the density of each toner image formed on the photoreceptors 1Y, 1M, 1C, and 1K. The detection result is used to determine whether the density unevenness is screw pitch unevenness (details will be described later).

  Here, the primary transfer rollers 5Y, 5M, 5C, and 5K are controlled so as to selectively operate in accordance with the type of image, and the intermediate transfer body 70 is applied to the corresponding photoreceptors 1Y, 1M, 1C, and 1K, respectively. The images of the respective colors formed on the photoreceptors 1Y, 1M, 1C, and 1K by the image forming units 10Y, 10M, 10C, and 10K are pressed by the intermediate transfer rollers 5Y, 5M, 5C, and 5K. The color image is sequentially transferred onto the body 70 to form a synthesized color image.

  The cleaning units 6Y, 6M, 6C, and 6K remove residual toner on the surface of the photosensitive drum 21 after the toner is transferred to the recording paper.

  On the other hand, the sheet P as a recording medium accommodated in the sheet feeding cassette 20 is fed all the time by the means 21 and passes through a plurality of intermediate rollers 22A, 22B, 22C, 22D and registration rollers 23, and the secondary transfer roller 5A. The color images on the intermediate transfer body 70 are collectively transferred onto the paper P by the secondary transfer roller 5A.

  Here, the secondary transfer roller 5A comes into pressure contact with the roller 72 via the intermediate transfer body 70 and the paper P only when the paper P passes through the secondary transfer roller 5A.

  The sheet P on which the image has been transferred is fixed by the fixing unit 24, is sandwiched between the discharge rollers 25, and is placed on the discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred onto the paper P by the secondary transfer roller 5A, the residual toner is removed by the cleaning means 6A from the intermediate transfer body 70 that has separated the curvature of the paper P.

  The density detectors 101aY and bY, 101aM and bM, 101aC and bC, and 101aK and bK are arranged to face the photoreceptors 1Y, 1M, 1C, and 1K to detect the density of the toner image. However, the density of the toner image may be detected by being arranged opposite to the intermediate transfer body 70, and the toner image (fixed or unfixed) may be arranged opposite to the surface of the paper P on which the toner image is transferred. Any one of the above may be detected. When arranged opposite to the intermediate transfer member 70 and the paper P, the density of each color can be detected by a pair of density detection means.

  As described above, the copier according to the present invention forms a color image on the paper P based on the image data.

(Image creation mechanism)
Further, the outline of the toner image forming mechanism in the image forming units 10Y, 10M, 10C, and 10K will be described with reference to FIGS. 2 is a cross-sectional view showing a schematic configuration of the image forming unit 10Y, FIG. 3 is an explanatory diagram for explaining a potential state on the surface of the photoreceptor 1Y, and FIG. 4 shows a shape of the conveying screw 42aY (42bY). It is a perspective view. In the following description, the yellow color is used as an example. The magenta, cyan and black colors are the same as the yellow color. The yellow color in the description is magenta, cyan or black, and the symbol Y is M, C. Alternatively, each may be replaced with K, and each description is omitted.

  First, as shown in FIG. 2, the surface of the photoreceptor 1Y that rotates in the direction of arrow a at the peripheral speed vp is charged by the charging means 2Y so as to have a negative surface potential Vh. When exposure is performed by scanning the laser beam based on the image by the exposure unit 3Y, the potential of the image portion is greatly attenuated to Vi as shown in FIG. 3, and an electrostatic latent image is formed.

  The electrostatic latent image formed on the photoreceptor 1Y is a developing sleeve that is a developer carrying member of a rotating body that rotates the toner at the peripheral speed vs in the direction of arrow c while the toner is opposed to the photoreceptor 1Y by the developing means 4Y. Development is performed through 41Y to form a yellow toner image. The developing sleeve 41Y is developed by applying a negative developing bias voltage Vb obtained by superimposing an AC component AC bias voltage Vac on a DC component DC bias voltage Vdc by a bias voltage applying means (not shown). Basically, the toner adheres under the condition of | Vi | ≦ | Vb |.

  Further, as shown in FIG. 4, the developer is rotated in the direction of the arrow N in FIG. 2 at a rotational speed N [rpm], and the conveying screw 42bY is moved in the back direction. By being rotated in the direction of arrow e in FIG. 2, it is conveyed to the developing position by the developing sleeve 41Y while being conveyed toward the front. At this time, the toner is agitated with the carrier and charged negatively by frictional charging due to mutual friction. The charged toner adheres to the image portion attenuated to the low potential Vi, and a toner image is formed.

(Screw pitch unevenness)
Here, density unevenness will be described. The density unevenness includes density unevenness that occurs in the sub-scanning in the rotation cycle of each part and density unevenness that occurs in the main scanning direction due to defective parts, etc. In addition, there is screw pitch unevenness that is density unevenness due to the conveying screw 42aY. . The screw pitch unevenness is different from the density unevenness that occurs in the sub-scan in the rotation cycle of each part and the density unevenness that occurs in the main scanning direction due to defective parts, etc., and the pitch of the low-density part is the screw pitch p of the conveying screw 42aY. FIG. 5 shows a schematic diagram of screw pitch unevenness that occurs in an oblique direction with respect to the scanning direction (or main scanning direction).

  FIG. 6 is a top view showing an outline of the image forming unit 10Y for explaining the mechanism of occurrence of screw pitch unevenness. In FIG. 6, the screw shapes of the conveying screws 42aY and 42bY are partially shown by curves, but when the conveying screws 42aY and 42bY rotate as described above, the respective screws are indicated by broken lines from the positions indicated by solid lines. The developer is moved to the position, and the developer is conveyed and circulated as indicated by an arrow. As the toner is transported, the toner and the carrier are agitated, and the toner is replenished from the replenishing port. If the developer transport speed, that is, the rotational speed N of the transport screws 42aY and 42bY is low, the toner becomes insufficient and the density is lowered. If the rotational speed is too high, for example, heat is generated by a bearing (not shown) of the transport screws 42aY and 42bY. Since the toner melts and then cools and adheres to cause operation failure, the rotation speed is set to a speed higher than the developer conveyance speed at which, for example, an image having a predetermined printing rate can be continuously formed.

  On the other hand, since the screw has a spiral shape, there is a position where the outer periphery of the developing sleeve 41Y and the outer periphery of the conveying screw 42aY are closest to each other, and the distance is the smallest, which is the helical pitch of the conveying screw 42aY. Exists periodically. The position where the distance is minimum is moved from the position indicated by the solid line in the main scanning direction to the position indicated by the broken line by the rotation of the conveying screw 42aY, and the developing sleeve 41Y is also rotated (in the direction of arrow c in FIG. 2). Therefore, the position where this distance is minimum moves in an oblique direction with respect to the developing sleeve 41Y, and a spiral locus is drawn on the developing sleeve 41Y as shown in FIG. On the other hand, the development performance at the position where the distance is minimized may be deteriorated as compared with others due to, for example, deterioration of the developer over time or environmental conditions, and in this case, the developed electrostatic latent image Generates a low density portion at a pitch p in the main scanning direction on the photosensitive member 1Y as shown in FIG. 6 in a sub-scanning or oblique direction with respect to the main scanning direction. Then, screw pitch unevenness as shown in FIG. 5 occurs in the image that is transferred to the intermediate transfer body 70 and further transferred onto the paper P. (In FIG. 6, two low density portions in the oblique direction with respect to the sub-scanning direction on the photoreceptor 1Y are shown. Actually, however, the outer periphery of the developing sleeve 41Y and the outer periphery of the conveying screw 42aY in the main scanning direction are shown. All the positions where the closest distance is the smallest are the low density portions.)

  In addition, the density detection units 101aY and 101bY may have a distance different from the screw pitch p of the conveying screw 42aY in the main scanning direction, that is, a distance excluding p, 2p, 3p,... The distance is 1.5p (the reason will be described later).

(Control configuration)
Next, a control configuration of the image forming apparatus according to the present embodiment will be described with reference to a functional block diagram shown in FIG.

  The hardware group 100 is configured to include a drive unit for driving each unit in addition to each unit described with reference to FIG.

  A control unit 102 controls each unit of the image forming apparatus. For this purpose, a CPU (not shown), various programs, and various parameter values related to image formation including various data necessary for executing the programs and parameter values related to development conditions are stored. And a system memory (not shown) that constitutes a work area when executing the program. In addition, each part of the hardware group 100 is controlled so as to form an image based on the image data. In this case, each part of the hardware group 100 is controlled according to various data and various parameter values stored in the system memory. Control. Here, the parameter values related to the development conditions include, for example, the peripheral speeds vp of the photoreceptors 1Y, 1M, 1C, and 1K, the peripheral speeds vs of the developing sleeves 41Y, 41M, 41C, and 41K, the developing sleeves 41Y, 41M, A negative developing bias voltage Vb obtained by superimposing an AC component AC bias voltage Vac on a DC component DC bias voltage Vdc applied to 41C and 41K, and the rotational speed N of each of the conveying screws 42aY, 42aM, 42aC, and 42aK.

  The density detectors 101aY and bY, 101aM and bM, 101aC and bC, and 101aK and bK detect the density of each toner image formed on each photoconductor. For example, a reflection type sensor is used, and the density is detected from the correlation between the output value and the density.

  Density unevenness discrimination means 104 (discrimination means) determines the density of each toner image formed on each photoconductor as a pair of density detection means 101aY and bY, 101aM and bM, 101aC and bC, and 101aK and bK. Whether or not the density unevenness is screw pitch unevenness is determined based on the change in density detected by (see below for details).

  The development condition changing unit 103 rewrites the parameter value related to the current condition of the control unit 102 according to the density unevenness determination result (details will be described later).

  According to the configuration as described above, the parameter value related to the current condition is rewritten, and image formation is performed by controlling each part of the hardware group 100 according to the rewritten parameter value based on the image data. Images can be obtained. In particular, in this embodiment, although details will be described later, it is determined whether or not the density unevenness is screw pitch unevenness, and in the case of screw pitch unevenness, the parameter value corresponding to the screw pitch unevenness is rewritten to control image formation. Therefore, it is possible to suppress the occurrence of screw pitch unevenness.

(Density unevenness discrimination method and image forming method)
Further, the procedure of the image forming method performed by the image forming apparatus will be described with reference to the flowchart shown in FIG. FIG. 8 is a flowchart showing the procedure of the image forming method according to the present invention. The density unevenness determination method will be clarified in the process of explaining the procedure of the image forming method.

  First, in the case of creating a density unevenness detection image (hereinafter referred to as a detection image) (step S101, Y. Hereinafter, step S101 is abbreviated as S101. The other steps are also the same. The hardware group 100 is controlled to create a detection image (S102). Here, the detection image creation may be, for example, when a predetermined number of images are formed, when a predetermined time has elapsed, or when the power is turned on. Further, the detection image may be a patch having a uniform density formed at a position that can be detected by both of the pair of density detection means, and an A4 size is appropriate. Further, the concentration may be a low concentration in order to suppress toner consumption.

  Next, density unevenness is determined (S103). An example of discrimination of density unevenness for the yellow color will be described with reference to FIG. FIG. 9 is a diagram illustrating an example of the density detection results of the density detection units 101aY and 101bY.

  First, the density of the detection image is detected by the density detectors 101aY and 101bY. Then, the density change ΔD in the detection image is detected from the density detection result of the density detection means 101aY or 101bY. If ΔD is equal to or greater than a predetermined density value, it is detected as density unevenness.

  Next, the density unevenness determination unit 104 determines whether the density unevenness is screw pitch unevenness. As described above, the screw pitch unevenness can be determined as the screw pitch unevenness by detecting that the density change is oblique because the density change occurs in the oblique direction with respect to the sub-scanning at the screw pitch p of the conveying screw 42aY. . If the unevenness of the screw pitch as shown in FIG. 5 is detected as the distance between the density detecting means 101aY and the density detecting means 101bY being the same distance as the screw pitch p, p, 2p, 3p,. The outputs of 101aY and density detection means 101bY are the same. However, in the present embodiment, the distance between the density detector 101aY and the density detector 101bY is a distance (for example, 1.5p) different from the screw pitch p. Therefore, as shown in FIG. 9, for example, the times ta and tb from the start of the density detection of the detection image to the detection of the low density part are detected differently. On the other hand, in the case of density unevenness appearing in the rotation period of each part in the sub-scanning direction, ta and tb are the same even if the distance between the density detection means 101aY and the density detection means 101bY is different from the screw pitch p. Become. Therefore, when ta and tb are different, that is, when there is a time difference in density change, it can be detected that the density unevenness is oblique, and can be determined as screw pitch unevenness.

  Further, the detection of the uneven density unevenness is performed by detecting the time difference Δt of the density change time detected by the density detecting means 101aY and the density detecting means 101bY shown in FIG. If there is a time difference Δt, it may be determined that the screw pitch is uneven. Furthermore, in addition to the above-described conditions, when the density change in the density detection means 101aY and 101bY is periodic, that is, for example, when the period T is detected, it may be identified as screw pitch unevenness, and the period T is detected. By doing so, an accidental density change that is not periodic is not mistakenly identified as screw pitch unevenness.

  When density unevenness is detected (S104, Y) and determined to be screw pitch unevenness (S105Y), the development condition changing means 103 includes parameter values stored in the system memory of the control means 102. One of the parameter values of the current condition relating to the screw pitch unevenness is rewritten to a value in a direction in which the current condition is improved. For example, the rotation speed of the conveying screws 42aY and 42bY is increased, the DC bias voltage Vdc or the AC bias voltage is increased for the developing bias voltage Vb, and is increased for the peripheral speed vs of the developing sleeve 41Y. In this way, the development performance is improved and the occurrence of screw pitch unevenness is suppressed. However, if the developing bias voltage Vb and the peripheral speed vs of the developing sleeve 41Y are changed, the density may change. However, even if the number of rotations of the conveying screws 42aY and 42bY is increased, the density is not changed. It is desirable to change the rotation speed of the conveying screws 42aY and 42bY.

  On the other hand, when the density unevenness is detected (S104, Y) and it is determined that the screw pitch unevenness is not found (S105N), the development condition changing unit 103 includes the parameter values stored in the system memory of the control unit 102. The parameter values of the development conditions that are not related to the screw pitch unevenness are rewritten, but the rotation speed parameters of the conveying screws 42aY and 42bY are excluded. This is because the rotational speeds of the conveying screws 42aY and 42bY are effective in suppressing the occurrence of screw pitch unevenness.

  In the above description, the yellow color is described, but the density unevenness is similarly determined for other colors and the density unevenness correction is performed.

  Here, when the rotational speed of the conveying screws 42aY and 42bY is 1.2 times or more when the screw pitch unevenness occurs, the screw pitch unevenness is eliminated. However, as described above, if it is too fast, it may cause a malfunction.

  When screw pitch unevenness occurs as described above, the parameter value is rewritten, and the control unit performs image formation based on the rewritten parameter value, so that the occurrence of screw pitch unevenness can be suppressed. . Further, when density correction is performed based on the density detection result, density correction can be performed more accurately by suppressing the occurrence of screw pitch unevenness.

1 is a cross-sectional view showing a schematic mechanical configuration of a copying machine as an image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view illustrating a schematic configuration of an image forming unit of the copier illustrated in FIG. 1. It is a figure for demonstrating the state of the electric potential on the surface of a photoreceptor. It is a perspective view which shows the shape of a conveyance screw. It is a schematic diagram of screw pitch unevenness. It is a top view which shows the outline of the image formation part for demonstrating the generation | occurrence | production mechanism of screw pitch nonuniformity. 3 is a functional block diagram showing a control configuration of the copying machine according to the present embodiment. FIG. 3 is a flowchart illustrating a procedure of an image forming method according to the present invention. It is a figure which shows an example of a density | concentration detection result.

Explanation of symbols

SC image reading unit 10Y, M, C, K image forming unit 1Y, M, C, K photoconductor 4Y, M, C, K developing means 41Y, M, C, K developing sleeve 42aY, M, C, K conveying screw 100 hardware group 101aY, M, C, K density detection means 101bY, M, C, K density detection means 102 control means 103 development condition change means 104 density unevenness discrimination means

Claims (8)

An electrostatic latent image based on an image forming signal is formed on the image carrier while moving the image carrier in the sub-scanning direction, and the developer is transported by rotating a screw while developing the electrostatic latent image. An image forming apparatus that forms an image by developing with an agent,
A pair of detection means arranged in the image carrier main scanning direction at intervals different from the pitch of the screws, and detecting the density of the formed image;
An image forming apparatus comprising: a determination unit configured to determine density unevenness due to the screw based on density changes detected by the pair of detection units. An electrostatic latent image based on an image forming signal is formed on the image carrier while moving the image carrier in the sub-scanning direction, and the developer is transported by rotating a screw while developing the electrostatic latent image. An image forming apparatus that forms an image by developing with an agent,
A pair of detection means arranged in the image carrier main scanning direction at intervals different from the pitch of the screws, and detecting the density of the formed image;
Discrimination means for discriminating density unevenness due to the screw based on density changes detected by the pair of detection means;
Development condition changing means for changing the development condition when the discrimination means determines that the density unevenness is caused by the screw;
An image forming apparatus characterized in that development is performed under the changed development conditions to form an image, and density unevenness due to the screw is suppressed.   The image forming apparatus according to claim 2, wherein the developing condition changing unit increases the number of rotations of the screw.   The image forming apparatus according to claim 3, wherein the number of rotations of the screw is increased to 1.2 to 2 times.   5. The image forming apparatus according to claim 1, wherein the determination unit determines that the unevenness of density is caused by the screw when there is a time difference between the respective density changes. 6.   5. The determination unit according to claim 1, wherein when there is a time difference between the respective density changes and the respective density changes change in the same cycle, the determination unit determines that the density unevenness is caused by the screw. Image forming apparatus. An electrostatic latent image based on an image forming signal is formed on the image carrier while moving the image carrier in the sub-scanning direction, and the developer is transported by rotating a screw while developing the electrostatic latent image. A method for determining density unevenness in an image forming apparatus that forms an image by developing with an agent,
Detecting the density of the formed image at an interval different from the pitch of the screw in the image carrier main scanning direction;
And determining a density unevenness caused by the screw based on respective density changes detected at intervals different from the pitch of the screw. An electrostatic latent image based on an image forming signal is formed on the image carrier while moving the image carrier in the sub-scanning direction, and the developer is transported by rotating a screw while developing the electrostatic latent image. An image forming method for forming an image by developing with an agent,
Detecting the density of the formed image at an interval different from the pitch of the screw in the image carrier main scanning direction;
Determining density unevenness due to the screw based on respective density changes detected at intervals different from the pitch of the screw;
When it is determined that the density unevenness is caused by the screw, the development condition is changed, and development is performed under the changed development condition to form an image to suppress the occurrence of density unevenness due to the screw. An image forming method.

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