JP2012128317A - Image-forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a structure capable of reducing unevenness of image density without regard to an image ratio of an output image.SOLUTION: A video counter 80 estimates density of an output image for each pixel based on image data retrieved by a CCD 8c. A CPU 8a calculates an image ratio corresponding to a location of the output image in a vertical scanning direction, based on the estimated density. Then, the timing to supply a developer by a supply device 44 is controlled based on the calculated image ratio.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine having a plurality of these functions, and more specifically, an electrophotographic system using a two-component developer containing toner and carrier. The present invention relates to an image forming apparatus such as an electrostatic recording system.

  Conventionally, an image in which a toner image is formed on a recording material by an image forming principle or process means such as an electrophotographic method or an electrostatic recording method, and the toner image on the recording material is fixed by a fixing means and an image formed product is output. Forming devices are known. Such an image forming apparatus incorporates a developing device for forming a toner image. As this developing device, a two-component developing system using a two-component developer composed of a non-magnetic toner and a magnetic carrier is known. In this structure, the toner supplied from the developer replenishing device (which may include a carrier) and the carrier filled in the developer accommodating portion of the developing device are agitated and conveyed, and the toner charged by friction is photosensitive. An electrostatic latent image formed on an image carrier such as a drum is revealed. Image forming apparatuses using such a two-component developer are widely used because the toner does not need to contain a magnetic material, and the color tone is good.

  In such an image forming apparatus, it is necessary to replenish the toner consumed by the image formation. For this purpose, toner consumption is calculated by image data processing means such as a video counter based on image data input from an image reading device such as a scanner or an external terminal such as a personal computer. Specifically, based on the image data, the video count number obtained by integrating the output levels for each pixel of the digital image signal is uniquely converted into the toner supply amount. Then, the toner replenishment amount is converted into the toner replenishment time, and the driving time and the number of rotations of the developer replenishment conveying member such as a screw of the replenishing device are determined, and the toner is predictedly replenished {Video Count ATR (Auto Toner replenishment)}.

  A structure in which such a video count ATR method is combined with a patch detection ATR method is also known. In this patch detection ATR method, a plurality of patch images having different gradations are formed on a photosensitive drum or an intermediate transfer member, and the density of the patch image is detected to determine whether the toner is excessive or insufficient, and a necessary amount of toner Is to replenish.

  When the video count ATR method and the patch detection ATR method are combined, first, the density level is counted for each pixel from the image signal by the video count method, and the integrated value is calculated. Further, a patch image is formed in a non-image area during normal image formation, and the density signal of the patch image is read and compared with an appropriate value of the patch image. When the patch image is darker than the appropriate value, the amount of toner is high, so the supply is reduced. When the patch image is lighter than the appropriate value, the toner is low and the supply is increased. The integrated value of the density level is corrected. Then, when the integrated value of the density level is accumulated to a predetermined value, the developer replenishment conveying member is operated for a predetermined time to replenish an appropriate amount of toner.

  However, in recent years, the image forming apparatus and the developing apparatus are particularly downsized or the speed of the image forming apparatus is increasing, and the developer capacity tends to decrease or the developer transport speed increases. In this case, an appropriate timing with respect to fluctuations in toner density when toner is consumed in the developing region of the developing sleeve, which is a developer carrying member that carries the developer and develops the electrostatic latent image on the photosensitive drum. Therefore, it is necessary to supply an appropriate amount of toner. If the timing and amount are not appropriate, unevenness occurs in the developer T / D ratio (toner weight ratio with respect to the total amount of developer, toner density ratio) in the developing device, thereby stabilizing the image density. May be impaired.

  In view of such circumstances, there is a structure in which the ripple of the developer concentration in the developer transport path is reduced by making the drive speed of the stirring member of the developing device variable according to the value of the video counter (see Patent Document 1). . There is also a structure in which the amount of developer replenishment, the time for replenishment, and the like are set according to the area ratio for writing the latent image of the image (see Patent Document 2).

JP 2003-57950 A JP-A-8-227213

  However, in the case of the structure described in Patent Document 1 described above, the developer supplied to the developing sleeve because the height of the developer surface changes by changing the driving speed of the developer stirring member during image formation. There is a possibility of unevenness in the amount of the agent in the thrust direction of the developing sleeve. In particular, as the developing device becomes smaller, the unevenness in the surface of the agent may increase. When unevenness of the height of the agent surface occurs, unevenness of density may occur in the image.

  Further, in the case of the structure described in Patent Document 2 described above, it is considered effective when approximately uniform image latent image writing is performed on a recording medium. However, if the output image has an image pattern in which the area where the image ratio is high is biased to a predetermined position in the image forming area of the recording medium, it is difficult to match the toner consumption timing with the replenishment timing. There is a possibility of causing unevenness. That is, in the case of the structure described in Patent Document 2, the developer replenishment timing is not set in consideration of the deviation of the image ratio. For this reason, for example, the developer is not replenished at a timing when the image ratio is high and the toner consumption is large. Therefore, particularly when the recording medium is large, if the latent image writing position with a high image ratio is far from the latent image writing position, the toner replenishment timing does not match and density unevenness occurs.

  For example, if there are high-density image patterns at the leading and trailing edges of A3 paper, if the amount of toner necessary for image formation is replenished at the timing of the leading edge of the image, the amount of toner consumed, the amount of replenishment for that timing, The timing is not right. That is, the amount of toner replenished with respect to the amount of toner consumed increases at the timing of the leading edge of the image, and the amount of toner replenished with respect to the amount of toner consumed at the timing of the trailing edge of the image. Less. For this reason, toner density unevenness may occur, and image density unevenness may occur. In particular, in the case of a small developing device or a high-speed image forming apparatus, this density unevenness may occur remarkably.

  In particular, in a full-color image forming apparatus, the maximum density and halftone density of each color component image are specified to improve the image quality, and are always fixed without being affected by individual differences of the image forming apparatus and environmental fluctuations. Image density control for controlling the density image to be obtained is important. For this reason, in a conventional full-color image forming apparatus, the image density is controlled by periodically detecting the density in order to control the image density, and controlling conditions such as exposure of the electrostatic latent image and development bias. ing.

  However, in such density control, if density detection is performed to control the maximum density or halftone density in a state where the T / D ratio of the developer is greatly different from the appropriate value, image density fluctuation Will become bigger. This is because the image forming conditions are determined based on developers having different T / D ratios while ATR is being performed to return the T / D ratio of the developer to an appropriate value.

  Therefore, in order to further stabilize the image density fluctuation, it is most preferable to perform the image density control at a timing when the T / D ratio is an appropriate value. In order to confirm whether or not the T / D ratio is an appropriate value, a configuration in which a patch image which is a reference density pattern is formed and the density is detected can be considered. However, with this configuration, the downtime of the image forming apparatus is large, and the amount of toner consumed increases. In a full-color image forming apparatus, Y (yellow), M (magenta), C (cyan), and Bk (black) colors must be confirmed, which further increases the problem.

  As described above, if the timing of toner consumption and toner replenishment at the time of development does not match, such a state where the T / D ratio of the developer is greatly different from the appropriate value occurs, and the density fluctuation is likely to occur.

  In view of the above-described circumstances, the present invention has been invented to realize a structure capable of reducing image density unevenness regardless of the image ratio of an output image.

  The present invention relates to an image carrier that carries a toner image, an electrostatic latent image forming unit that forms an electrostatic latent image on the image carrier, and a development that includes toner and a carrier at a development position facing the image carrier. A developer carrying member for carrying and transporting the agent, developing the electrostatic latent image, a replenishing device for supplying toner to the developing device, and the replenishment based on a density distribution in a predetermined direction of the output image. And an image forming apparatus having a control unit for controlling replenishment timing of the apparatus.

  According to the present invention, since the replenishment timing of the replenishing device is controlled based on the density distribution in the predetermined direction of the output image, the image density unevenness can be reduced regardless of the image ratio of the output image.

1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic configuration cross-sectional view showing a part of FIG. FIG. 2 is a schematic cross-sectional view showing a replenishing device and a developing device taken out. FIG. 2 is a schematic configuration plan view showing a part of the developing device along with a photosensitive drum. FIG. 3 is a block diagram for explaining developer supply control according to the first embodiment. The schematic diagram which divided | segmented the output image into the some pixel in order to demonstrate the data processing by a video counter. 5 is a flowchart showing developer replenishment control according to the first embodiment. (A) is the figure which divided | segmented the output image into several, (B) is the figure which formed the image of the whole halftone on the recording material. FIG. 6 is a diagram for explaining developer replenishment timing in the first embodiment. The figure which shows an example of the image pattern of an output image. The figure for demonstrating the supply timing of the developer in the image pattern of FIG. The figure for demonstrating the effect which concerns on 1st Embodiment. FIG. 10 is a diagram for explaining developer replenishment timing in the second embodiment of the present invention. Similarly, the same figure as FIG. The figure for demonstrating the effect which concerns on 2nd Embodiment. 10 is a flowchart showing developer replenishment control according to a third embodiment of the present invention.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. First, the image forming apparatus of the present embodiment will be described with reference to FIGS.

[Image forming apparatus]
The image forming apparatus 100 uses a four-color full-color image of yellow (Y), magenta (M), cyan (C), and black (K) as a recording material (recording paper, plastic sheet, cloth, etc.) using an electrophotographic method. ) Can be formed. Such an image forming apparatus 100 is of a tandem type having four image forming stations for forming yellow, magenta, cyan, and black images, respectively. In the present embodiment, the configuration of each image forming station is substantially the same except that the development colors are different, and therefore will be described generally.

  The image forming station P includes a drum-shaped photosensitive member (photosensitive drum) 1 as an image carrier. Around the outer periphery of the photoreceptor 1, there are a charging device 2 as a charging means, an exposure device as an exposure means (laser exposure optical system in this embodiment) 3, a developing device 4 as a developing means, a transfer device 5 as a transfer means, A cleaning device 7 is provided as a cleaning means. The transfer device 5 has an intermediate transfer belt 51 as an intermediate transfer member. The intermediate transfer belt 51 is wound around a plurality of rollers and rotates (circulates) in the direction of the arrow in FIG. A primary transfer roller 52 as a primary transfer member is disposed at a position facing each photoconductor 1 via the intermediate transfer belt 51. A secondary transfer roller 53 as a secondary transfer member is provided at a position facing one of the rollers around which the intermediate transfer belt 51 is wound.

  At the time of image formation, first, the surface of the rotating photoreceptor 1 is uniformly charged by the charging device 2. Next, an electrostatic latent image is formed on the photosensitive member 1 by scanning and exposing the surface of the charged photosensitive member 1 according to an image information signal by the exposure device 3. The charging device 2 and the exposure device 3 constitute an electrostatic latent image forming unit. Further, the image information signal is image information from a document reading device such as a scanner connected to the image forming apparatus 100 main body (apparatus main body) or a host device such as a personal computer connected to the apparatus main body so as to be communicable. Based.

  The electrostatic latent image formed on the photoreceptor 1 is visualized as a toner image with toner using the developing device 4. The toner image formed on the photosensitive member 1 is subjected to the action of the primary transfer bias applied to the primary transfer roller 52 in the primary transfer portion (primary transfer nip) N1 where the intermediate transfer belt 51 and the photosensitive member 1 abut. Transfer (primary transfer) is performed on the intermediate transfer belt 51. For example, when a four-color full-color image is formed, a toner image is transferred from each photoconductor 1 to the intermediate transfer belt 51 sequentially from the yellow image forming station, and the four-color toner images are superimposed on the intermediate transfer belt 51. A multiple toner image is formed.

  On the other hand, a recording material accommodated in a cassette 9 as a recording material accommodating portion is conveyed by a recording material conveying member such as a pickup roller, a conveying roller, and a registration roller. Then, the recording material is conveyed in synchronization with the toner image on the intermediate transfer belt 51 to the secondary transfer portion (nip portion) N2 where the intermediate transfer belt 51 and the secondary transfer roller 53 abut. The multiple toner images on the intermediate transfer belt 51 are transferred onto the recording material S by the action of the secondary transfer bias applied to the secondary transfer roller 53 in the secondary transfer portion N2.

  Thereafter, the recording material S separated from the intermediate transfer belt 51 is conveyed to the fixing device 6. The toner image transferred onto the recording material S is melted and mixed by being heated and pressurized by the fixing device 6 and is fixed onto the recording material S. Thereafter, the recording material S is discharged out of the apparatus. Deposits such as toner remaining on the photoreceptor 1 after the primary transfer step are collected by the cleaning device 7. Thereby, the photoreceptor 1 is prepared for the next image forming process. Further, deposits such as toner remaining on the intermediate transfer belt 51 after the secondary transfer step are removed by the intermediate transfer body cleaner 56.

  The developing device 4 includes developer (mainly toner but mainly carrier) that is consumed by the developer supply device from the developer container 10 under automatic toner supply control (ATR). ) Is replenished. The developer storage container 10 stores the developer of each color. In the illustrated example, the connecting portion between the developer container 10 and the developing device 4 is omitted.

  Note that the image forming apparatus 100 can form a single-color or multi-color image using an image forming station for a desired single color or several colors among four colors, such as a black single-color image. .

[Developer]
Next, the developing device 4 will be further described with reference to FIGS. The developing device 4 includes a developing container 40 that stores a two-component developer composed of a nonmagnetic toner and a magnetic carrier. A cylindrical developing sleeve 41 as a developer carrying member for carrying and transporting the developer is disposed in the main scanning direction at a portion of the developing container 40 facing the photosensitive member 1. The developing sleeve 41 is made of a nonmagnetic material, and rotates in the direction of the arrow in FIG. 3 during the developing operation (moves in the sub-scanning direction). Note that the rotation axis of the developing sleeve 41 and the rotation axis of the photosensitive member 1 are substantially parallel. In the developing sleeve 41, a magnet roll (magnet) as a magnetic field generating means is fixedly arranged. A regulating blade 42 as a developer amount regulating member for forming a thin layer of developer on the developing sleeve 41 is disposed at a position close to the surface of the developing sleeve 41.

  Further, the inside of the developing container 40 is partitioned into a developing chamber (developer transport path) 43a and a stirring chamber (developer transport path) 43b by a partition wall 43c. A first developer conveying member 43d is disposed in the developing chamber 43a, and a second developer conveying member 43e is disposed in the stirring chamber 43b. At both ends in the longitudinal direction of the partition wall 43c (left side and right side in FIG. 4), delivery portions (developer transport paths) 43f and 43g that allow the developer to pass between the developing chamber 43a and the stirring chamber 43b are provided. ing.

  The first and second developer transport members 43d and 43e are both screw-like members (hereinafter referred to as “first screw” and “second screw”, respectively). In other words, in the present embodiment, the first and second screws 43d and 43e are arranged around the shafts (rotating shafts) 43d-1 and 43e-1 of the magnetic body, respectively, and spiral blades 43d- serving as a conveying unit. 2 and 43e-2. Further, in addition to the blades 43e-2, the second screw 43e has a stirring rib 43e-3 that protrudes in the radial direction from the shaft 43e-1 and has a predetermined width in the developer transport direction. The rib 43e-3 stirs the developer as the shaft 43e-1 rotates.

  The first screw 43d conveys the developer in the developing chamber 43a while stirring. The second screw 43e conveys the developer replenished by the developer replenishing device 44 and the developer already in the stirring chamber 43b while stirring under the automatic toner replenishment control (ATR). Thus, the toner concentration in the developer is made uniform.

  The first and second screws 43d and 43e are disposed substantially in parallel along the rotation axis direction (developing width direction) of the developing sleeve 41. The first screw 43d and the second screw 43e transport the developer in opposite directions along the rotation axis direction of the developing sleeve 41. Thus, the developer is circulated in the developing container 40 by the first and second screws 43d and 43e via the transfer portions 43f and 43g. In other words, the developer in the developing chamber 43a in which the toner is consumed in the developing process due to the conveying force of the first and second screws 43d and 43e and the toner density is reduced is transferred to one of the transfer portions 43f (on the left side in FIG. 4). ) To move into the stirring chamber 43b. Further, the developer in the stirring chamber 43b, which has been replenished with toner and moved, moves to the developing chamber 43a via the other transfer portion 43g (on the right side in FIG. 4).

  The developing chamber 43a of the developing device 4 is opened at a position corresponding to the developing area facing the photoreceptor 1, and the developing sleeve 41 can be rotated so as to be partially exposed to the opening of the developing container 40. Is arranged. The developer is supplied from the developing chamber 43a to the developing sleeve 41. A predetermined amount of the developer supplied to the developing sleeve 41 is carried on the developing sleeve 41 by a magnetic field generated by the magnet roll, and forms a reservoir of the developer. When the developing sleeve 41 rotates, the two-component developer on the developing sleeve 41 passes through the agent reservoir, the layer thickness is regulated by the regulating blade 42, and the developer is conveyed to the developing area facing the photosensitive drum 1. The In the developing area, the developer on the developing sleeve 41 rises to form a magnetic spike.

  In this embodiment, an electrostatic image on the photosensitive drum 1 is developed as a toner image by bringing the magnetic spike into contact with the photosensitive member 1 and supplying the developer toner to the photosensitive drum 1. Further, in order to improve the development efficiency, that is, the application rate of the toner to the latent image, the development sleeve 41 usually has a development bias voltage obtained by superimposing a DC voltage and an AC voltage from a development bias power source as a voltage application unit. Applied. The developer on the developing sleeve 41 after supplying the toner to the photosensitive drum 1 returns to the developing chamber 43a and returns to the developer circulation as the developing sleeve 41 further rotates.

  Further, a developer supply device 44 is connected to the developing device 4. In the replenishing device 44, a toner replenishing screw 44 b is disposed in a toner hopper 44 a connected to the developer container 10. The toner hopper 44a is connected to the upper part of the agitating chamber 43b of the developing container 40 and upstream in the toner conveying direction by the second screw 43e. The developer replenished from the developer container 10 is conveyed by the rotation of the toner replenishing screw 44b, and is supplied from the toner hopper 44a to the stirring chamber 43b by a predetermined amount corresponding to the rotation. Then, the developer for the next developing step is prepared by replenishing the developer consumed by the developing step.

  In the present embodiment, the developing device 4 is a developing cartridge that can be attached to and detached from the apparatus main body. Further, the photosensitive member 1, the charging device 2, and the cleaning device 7 are integrated to form a drum cartridge that can be attached to and detached from the apparatus main body. The developing cartridge and the drum cartridge are installed in the apparatus main body so as to be separated from each other, and each can be taken out separately.

  Further, the developing device 4 is provided with a spacer member for setting and fixing a predetermined distance between the developing sleeve 41 and the photosensitive member 1, and the spacer member is attached to the surface of the photosensitive member with a predetermined contact pressure. Hit it. For this purpose, the developing cartridge installation portion of the apparatus main body is provided with a pressure lever that pressurizes the developing cartridge in the direction of the drum cartridge, and a predetermined contact pressure is applied by rotating the lever. In order to remove the developing cartridge, the pressure lever is rotated to release the pressure applied between the developing cartridge and the drum cartridge. Then, each cartridge is replaced by being pulled out along a guide member provided in the apparatus main body.

  In addition, 44h shown in FIG. 4 is a magnetic permeability sensor which detects a magnetic permeability. The magnetic permeability sensor 44h has an inductance head that detects an apparent magnetic permeability according to a mixing ratio of the magnetic carrier and the nonmagnetic toner and converts it into an electric signal. Then, the toner concentration in the developer in the developer container 40 is detected by an output signal from the inductance head. In the case of this embodiment, in addition to the developer replenishment control described below, the developer replenishment control is performed by comparing the toner density thus detected with the reference value, and the developer replenishment control is performed with higher accuracy. To be able to. The magnetic permeability sensor 44h can be omitted.

[Developer supply control]
Next, the developer replenishment control of this embodiment will be described. For this purpose, first, a video counter 80, which is an image data processing means, and a test image detection means (hereinafter referred to as a patch detection sensor) 57 used when performing developer density and gradation control will be described with reference to FIGS. explain. As shown in FIG. 5, when a document is read by a CCD (Charge Coupled Device) 8c which is an image reading device, a signal is amplified by an AMP 8i and sent to an A / D converter 8d. Then, a PWM signal is generated by the comparator 8h from the input image signal that has passed through the γ conversion 8e and the D / A conversion 8f and the triangular wave generated by the triangular wave generating circuit 8g, and this signal is sent to the exposure control circuit 8j. In the exposure control circuit 8j, an electrostatic latent image is formed on the charged surface of the photoreceptor 1 via a scanner. At the same time, the input image signal (image data) subjected to A / D conversion is integrated by the video counter 80 for each pixel. Then, the CPU 8a as the control means converts the image ratio and the driving of the screws 43d and 43e of the developing device 4 from the integrated value using a table prepared in advance.

  Further, as shown in FIG. 2, the patch detection sensor 57 is disposed downstream of the primary transfer unit N1 and upstream of the secondary transfer unit N2 at a position facing the intermediate transfer belt 51. The photosensitive member 1 and the developing device 4 are adjacent to the photosensitive member 1 in the rotational direction downstream of the photosensitive member 1 and upstream of the opposing portion of the photosensitive member 1 and transfer device 5 in the rotational direction. May be arranged. Such a patch detection sensor 57 includes an LED light emitting unit and a light receiving unit. Then, a numerical value directly received from the light emitting unit and a numerical value of reflected light obtained through a transparent plate with respect to a patch image obtained by developing a halftone of about 20 mm square on the intermediate transfer belt 51 or the photosensitive drum 1 at a certain timing. The toner density is detected by performing a predetermined calculation.

  At this time, it is detected that the toner density is low when the reflected light is bright, and the toner density is high when the reflected light is dark. When it is detected that the toner density is low, the video count value is corrected so as to increase the toner supply until a certain density is reached. On the other hand, when it is detected that the toner density is high, correction is performed so as to reduce toner replenishment with respect to the bidet count value until a certain density is reached. In this way, the toner concentration in the developer is kept constant.

  Next, the developer replenishment control using the video counter 80 will be described with reference to FIGS. First, when an image is read by the scanner, the density of each pixel of the output image based on the image data is integrated by the video counter 80. Specifically, two integrated values are calculated. One of the integrated values (first integrated value) is a density integrated value of the total pixels of the output image. As shown in FIG. 6, the other integrated value (second integrated value) is the pixel density in the main scanning direction which is the vertical direction at the position in the sub-scanning direction (predetermined direction) from the leading edge of the document. The integrated value (ΣDn). That is, ΣDn is the y-axis direction at each of the first to i-th positions in the x-axis direction from the front end of the document, where the x-coordinate is the pixel position in the sub-scanning direction and the y-coordinate is the pixel position in the main scanning direction. It is a value obtained by integrating the densities of the 1st to jth pixels. The two integrated values integrated by the video counter 80 are applied to the CPU (control unit) 8a and stored in the RAM 8b.

  Based on the first integrated value, the CPU 8a uses the toner replenishing screw 44b required to supply the total amount of toner consumed in image formation of the output image and the total amount of toner to be replenished from the replenishing device 44. Obtain the rotation drive time. Further, the CPU 8a calculates an image ratio (density integrated value distribution, density distribution) corresponding to the position in the sub-scanning direction of the output image from the second integrated value, and the replenishing device 44 based on the calculated image ratio. To control the timing of toner supply. That is, a replenishment timing sequence weighted according to the image ratio is created, and the toner replenishment screw 44b is controlled based on the sequence.

  The rotation drive time (number of rotations) of the toner supply screw 44b and the toner supply amount are in a proportional relationship. Therefore, it is only necessary to control the drive circuit of the motor that drives the toner supply screw 44b to drive the toner supply screw 44b for a time corresponding to the toner supply amount predicted from the integrated value. At this time, toner supply is controlled in units of one rotation of the toner supply screw 44b. That is, the replenishment operation is executed for the first time by integrating the integrated image density value by the amount of toner transport for one rotation of the toner replenishment screw 44b. For this purpose, rotation detecting means 44c for detecting the number of rotations of the toner replenishing screw 44b is provided, and a signal detected by the rotation detecting means 44c is sent to the CPU 8a. For example, the rotation detection unit 44c has a structure in which a flag is provided on the rotation shaft of the toner supply screw 44b and the passage of the flag is detected by a photo sensor.

  When the image signal is captured and the density integrated value is stored in the RAM 8b, the CPU 8a determines how many times the toner replenishing screw 44b is rotated in order to supply the total amount of toner obtained from the total density integrated value (first integrated value). calculate. At this time, the density value that cannot be divided by the number of rotations of the screw (toner supply screw 44b) is carried over to the next image forming operation and added to the total density integrated value.

  Next, determination of the replenishment timing will be described. First, the length of the output image in the sub-scanning direction is divided into a plurality of regions corresponding to the number of screw rotations (the number of supply blocks is calculated). For example, it is assumed that the screw is rotated n times in order to supply a toner amount necessary for forming a solid image on a recording material having a predetermined size. In this case, the image forming area of the recording material, that is, the output image is divided into n equal parts in the sub-scanning direction. The output image referred to here is an image of the entire image forming area of the recording material, and includes any portion where no image is formed in the image forming area. Therefore, the number of divisions of the output image is determined by the size of the recording material and the replenishment performance by the replenishing device 44 (specifically, the amount of developer supplied per one rotation of the screw).

  When the output image is divided into a plurality of areas, density integrated values for each area are calculated (image ratio is calculated), and the replenishment timing is determined so that the developer is replenished in the areas where the density integrated values are large. At this time, if the integrated density value is substantially uniform over the entire surface of the recording material, a replenishment timing is assigned to each area on the average with respect to the position in the sub-scanning direction. If the density integrated value in one image formation is less than the replenishment amount for one rotation of the toner supply screw 44b, the position in the sub-scanning direction and the total density integrated value in a plurality of image formations are calculated. To replenish the average position.

  The flow of the developer replenishment control described above is summarized as shown in FIG. That is, when image formation is started (S1), image data is read by a scanner or the like (S2). From the image data, the integrated density value (first integrated value) of all pixels is obtained by the video counter 80, and the total replenishment amount of toner is calculated from the integrated density value, and the number of replenishment blocks is calculated (S3). As described above, the number of supply blocks is calculated according to the number of rotations of the screw when a full solid image is formed on the recording material. Next, the integrated value (image ratio) of the density at the position (each region) in the sub-scanning direction of the output image is calculated from the second integrated value integrated in the video counter 80 (S4). Then, the supply timing is determined based on the calculated image ratio (S5), and the supply operation is started (S6). This replenishment operation is performed in consideration of the timing at which the toner replenished to the stirring chamber 43b is conveyed to the developing chamber 43a and used for image formation.

  Specifically, the replenishment operation is started so that the developer is replenished at a timing when the developer carried on the developing sleeve 41 returns to the developing chamber 43a after developing the electrostatic latent image on the photoreceptor 1. In other words, at a timing after the toner amount with respect to the replenishment amount is consumed, the timing is such that the consumed developer and the replenished developer almost merge. In this embodiment, it can be said that the control method is a feed-forward method in that the amount of toner consumed in the developing process is supplied to the developing container in advance. The correction by the patch detection sensor 57 may be always performed, may be performed as appropriate, or correction control by the patch detection sensor 57 may be omitted.

[Concrete example]
Next, a specific example to which the present embodiment is applied will be described. The density value integrated in the video counter 80 is counted with the density value of each pixel being 0-255. When an image is formed on the entire surface of an A4 size recording sheet at a density of 255 level (full surface), the toner consumed is about 0.4 g. Here, when forming a solid image, the image is formed on the paper output after the fixing process so that the density is 1.4 to 1.5 when measured with a reflection densitometer X-rite. Set process conditions.

  Further, it is assumed that about 0.08 g can be supplied per rotation of the toner supply screw 44b. From this, it is possible to supply the toner supply screw 44b for 5 rotations during the formation of one A4 size image. That is, when the density corresponding to the image ratio of 20% is integrated with respect to the A4 size recording sheet, the toner supply screw 44b is rotated once and the supply is started. At this time, the output image in the case of A4 size paper is divided into five areas in the sub-scanning direction as shown in FIG.

  Under such a premise, when image formation is performed with an entire halftone image pattern shown in FIG. 8B using A4 paper, the following control is performed. When this halftone image is read by the scanner, it is assumed that the density is 40% with respect to the whole solid image. At this time, as shown in FIG. 9, there is a replenishable time for 5 rotations of the toner replenishment screw 44b with respect to the length of the A4 size in the sub-scanning direction, but replenishment for 2 rotations is sufficient.

  In FIG. 9, the horizontal axis represents time t, and the vertical axis represents density or toner amount. The uppermost diagram is the development time (corresponding to the length in the sub-scanning direction) of the entire A4 sheet, and is shown as a reference for the lower diagram. The second row shows an image density profile (density integrated value in the sub-scanning direction), and shows that an image is formed on the entire surface at a density (halftone) of 40% with respect to the entire solid image (max). The third row shows the case of replenishing a predetermined amount of toner at the respective replenishment timings of Comparative Example 1, the fourth row of Comparative Example 2, and the bottom row of this embodiment.

  First, in the case of the comparative example 1, the toner supply screw 44b is continuously rotated twice at the first timing (development start time) to supply the necessary amount of toner. In this case, the amount of toner consumed and the timing thereof do not coincide with the amount of toner replenishment and the timing thereof, so that density unevenness may occur. That is, since toner is replenished at the start of development, toner consumption has already started when the replenished toner reaches the developing sleeve 41, and density unevenness can occur in a portion where toner replenishment is not in time. There is sex. Further, since the replenishment toner intensively reaches the developing sleeve at a certain timing, the replenishment toner is insufficient at other timings, and there is a possibility that density unevenness is generated. On the other hand, in the case of Comparative Example 2, the toner replenishing screw 44b is rotated so as to advance the time ΔT until the toner reaches the developing sleeve 41 from the replenishment position from the replenishing device 44. In this case, since the replenishing toner reaches the developing sleeve 41 at the development start timing, it is considered that density unevenness is less likely to occur than in the first comparative example. However, since the point where toner supply is concentrated first is not different from Comparative Example 1, density unevenness may still occur.

  On the other hand, in the case of the present embodiment, the toner supply screw 44b is rotated at a timing that is equal to the total replenishable time with the time being shifted as in Comparative Example 2. That is, replenishment for one rotation of the replenishing screw is performed at 2/5 and 4/5, respectively, when the A4 size development time is shifted by ΔT. In this case, since the toner replenishment timing is dispersed, as in Comparative Examples 1 and 2, it is possible to prevent the amount of toner consumed and the timing from deviating from the amount of toner replenishment and the timing, thereby reducing density unevenness. it can. Note that the rotation timing of the toner replenishing screw 44b may be, for example, 1/5 or 3/5 when it is shifted by ΔT with respect to the A4 size development time.

  If the density integrated value of one original is less than 20%, which corresponds to the replenishment amount corresponding to one rotation of the replenishing screw, the N number of image forming densities and image forming times are integrated to obtain N number. Replenishment for one rotation of the replenishing screw is performed at an intermediate timing between the sheets. Further, the surplus concentration integrated value is also predicted in the same manner and replenished at an intermediate timing.

  Next, a case where image formation is performed with the image pattern shown in FIG. 10 using A3 paper will be described. Assume that the image pattern at this time is 30% as a whole when the image ratio of the A3 full-color image is 100%. As described above, the A4 paper has an image ratio of 20%, which is equivalent to one screw rotation. Therefore, in the A3 paper, which is twice as large as the A4 paper, one screw rotation corresponds to an image ratio of 10%. Therefore, the replenishment amount with an image ratio of 30% is equivalent to three rotations of the screw.

  Here, since the replenishment timing is that the number of screw rotations that can be replenished with respect to one A3 sheet is 10, the output image is divided into 10 in the sub-scanning direction, and the density integrated value (image ratio) for each area is calculated Determine the replenishment timing. In the case of the image pattern shown in FIG. 10, it can be seen from the image density profile shown in FIG. 11 that there are three regions with a large density integrated value. FIG. 11 is the same diagram as FIG. 9 described above. Therefore, it is only necessary to assign a replenishment timing to these three regions and rotate the replenishment screw at a timing that is advanced by a time lag ΔT seconds from the developer replenishment position to the developing sleeve 41.

  According to the present embodiment as described above, the timing for supplying toner by the replenishing device 44 is controlled based on the image ratio corresponding to the position of the output image in the sub-scanning direction. Density unevenness can be reduced.

[Example 1]
Next, an experiment will be described in which the transition of the image density fluctuation was examined in Comparative Example 1 and the present embodiment (Example 1) in the above-described configuration. In the experiment, a halftone image having an image ratio of 40% with respect to the A4 paper size as shown in FIG. 8 is compared with a mosaic image having an image ratio of 30% with respect to the A3 paper size as shown in FIG. The image forming operation was performed at the replenishment timing in each of Example 1 and Example 1. Then, the density of each formed image was measured. The number of images formed was 15000. The result is shown in FIG. FIG. 12 shows the transition of the image density with respect to the number of formed images. As is apparent from FIG. 12, according to Example 1, it was found that the width of the image density fluctuation can be reduced in the image forming operation over a long period of time, particularly when an image having a high image ratio is formed. As a result, according to the present embodiment, it was found that high-quality and high-quality image formation can be performed even when an image forming operation for a long time is performed.

  In the present embodiment, the feedforward method has been described as an example, but the present invention can also be applied to the following feedback method. In other words, the feedback method is a method in which toner is replenished by the amount of consumed toner after it is actually consumed. In this case, when the area where toner is consumed at the development position reaches the replenishment position, the consumed toner is replenished. When the present invention is applied, the difference from the feed forward method is that the replenishment timing is controlled based on the image information in the sub-scanning direction of the output image that has already been developed. In the present embodiment, the image ratio is calculated by integrating the density for each pixel. However, if there is data that can be used to determine the image ratio without obtaining such an integrated value, the image ratio is used. The developer replenishment timing can also be controlled. For example, if a region having a high image ratio can be grasped by coordinates or the like, the developer is supplied at a timing corresponding to the region having a high image ratio.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, not only the image ratio with respect to the position in the sub-scanning direction of the output image but also the image ratio with respect to the position in the main scanning direction is taken into account to determine the developer replenishment timing. That is, the CPU 8a (see FIG. 5) calculates an image ratio corresponding to the position of the output image in the sub-scanning direction and the main scanning direction, and advances the developer replenishment timing relative to the image ratio as it goes downstream in the main scanning direction. I am doing so. That is, the developer replenishment timing downstream in the main scanning direction is made earlier than the developer replenishment timing upstream in the main scanning direction. For example, when the output image is divided into five in the sub-scanning direction as shown in FIG. 8A, the first and second regions in the sub-scanning direction will be described. In this case, the value of the image ratio downstream of the second area in the main scanning direction is added to the image ratio of the first area, and the value of the image ratio of the first area upstream of the main scanning direction is the image of the second area. It is added to the ratio. For this reason, the developer replenishment amount with respect to the image ratio downstream in the main scanning direction is reflected in a region where the replenishment timing is one step earlier, and the developer replenishment amount with respect to the image ratio upstream in the main scanning direction is in a region where the replenishment timing is one step later. Reflected. As a result, the developer replenishment timing downstream in the main scanning direction is earlier than the developer replenishment timing upstream in the main scanning direction.

  In this embodiment, for this purpose, when the length of the output image in the sub-scanning direction is divided into a plurality of regions corresponding to the number of rotations of the screw (calculation of the number of supply blocks), as shown in FIG. As shown, the output image is divided into regions inclined with respect to the main scanning direction. That is, the developer replenishment with respect to the image ratio downstream in the main scanning direction is reflected in the replenishment timing at an earlier stage than the developer replenishment with respect to the image ratio upstream in the main scanning direction. Then, the integrated density value (image ratio) of each region is calculated, and the replenishment timing is determined.

  In this embodiment, in both feedforward and feedback, the inclination α of the divided region with respect to the sub-scanning direction is determined by the rotational speed of the photosensitive member 1 and the developer transport speed in the developing chamber 43a (of the screw 43d). It was derived from the relationship with the rotation speed. In short, the output image is divided at an inclination α determined by the ratio of the developer transport speed (main scanning direction speed) in the developing chamber 43a (in the developing device) and the photosensitive member rotation speed (sub scanning direction speed).

  That is, when the rotational speed of the screw 43d / the rotational speed of the photoconductor 1 = α, this α becomes the inclination θ of the divided region, and the inclination α with respect to the rotation direction of the photoconductor 1 (the moving direction of the image carrier surface). The replenishment timing is determined by looking at the density distribution in the direction (predetermined direction).

  The transport speed of the developer in the developing device can be obtained as follows. That is, in the form shown in FIG. 4, a high-speed video camera replenishes different colors of toner into the developer from above the developing container, and shoots a moving image of how the toner is conveyed in the developing chamber 43a. And it can obtain | require by specifying the position where the color component of replenishment toner is the darkest by image analysis. For example, a developer filled with a cyan developer is prepared, and about 0.5 g of yellow toner is placed on the developer at the position of the delivery portion 43g in FIG. Thereafter, the developer is taken from above by a high-speed video camera. Then, a transport speed [mm / sec] at which the darkest point of yellow toner is transported is calculated from the captured moving image.

  In order to supply the consumed developer without excess or deficiency, it is ideal that the angle θ of the divided region is set to arctan α. However, if the angle θ is within the range of arctan α ± 16 °, the color variation ΔE due to the division angle θ deviating from arctan α can be suppressed to 3 or less. This will be described below.

  As described above, when θ is in the range of ± 16 °, the color variation ΔE can be suppressed because the shift amount with respect to the area of the divided region determined by α can be 20% or less. is there. When θ shifts in the + direction, the broken line in FIG. 13A rotates clockwise, and when it shifts in the − direction, it rotates counterclockwise, and the divided area shifts from the area determined by arctan α. As a result, the consumption amount allocated to each area and the replenishment toner amount deviate, resulting in a large variation in color. When the range of θ is divided by ± 20 ° ± 25 °, the consumption of the preceding and subsequent divided regions is reflected on the ideal division by 28% and 39%, respectively. In this case, when an image or the like in which two solid bands with a width of 40 mm in the sub-scanning direction are evenly formed is formed, the image density in each region is measured using a spectral densitometer X-rite, and the color variation is obtained. ΔE> 4.5 to 5.5 (measured concentration difference Δ0.1 to 0.2 guideline). Also, density unevenness was confirmed visually.

  On the other hand, by setting ± 16 ° (the area deviation is 19%), the fluctuation of the image density is ΔE of about 2.8 to 3.0, and the fluctuation can be suppressed to a level where it is difficult to visually confirm the density unevenness. . Further, when the deviation amount is set to θ ± 17 to 20, the deviation amount of the area becomes as large as 23 to 29%, and the color variation that can be recognized as ΔE = 3.2 to 3.6 is confirmed. Furthermore, when the ideal center value of the division angle θ is used, ΔE = 2.4, and a more stable color can be obtained.

  From the above, it is possible to suppress the color variation by setting the range θ = arctan α ± 16 °.

  In the feed forward method, ΔT1 in FIG. 14 is a time until the toner reaches the developing sleeve 41 from the replenishment position from the replenishing device 44. In the feedback method, ΔT1 is the time until the development end agent developed by the developing sleeve 41 reaches the replenishment position 44.

  This is because, as shown in FIG. 14, it takes time ΔT2 for the developer existing upstream of the developing chamber 43a to move downstream. That is, the timing at which the developer is transported to the developing sleeve 41 downstream of the developing chamber 43a is delayed by ΔT2 with respect to the timing at which the developer is transported to the developing sleeve 41 upstream of the developing chamber 43a. The developer transport direction in the developing chamber 43a corresponds to the main scanning direction. Therefore, as shown in FIG. 13B, when the output image is divided in parallel with the main scanning direction, the replenishment timing with respect to the toner consumption timing even in the same area of the divided areas of the output image. Will shift. For this reason, in this embodiment, the developer replenishment timing is advanced earlier toward the downstream in the main scanning direction, and the deviation between the toner consumption timing and the replenishment timing in the main scanning direction is eliminated.

  More specific description will be given. First, with respect to the main scanning direction, a time delay of ΔT2 occurs between the development end agent taken in upstream of the developing chamber 43a and the development end agent taken in downstream. For this reason, as shown in FIG. 13B, the development end agent consumed nearer to the downstream side (downstream in the main scanning direction) of the image developing chamber 43a reaches the toner supply position earlier than the upstream side. The mixing with the development end agent in the next area in the sub-scanning direction is repeatedly performed, and the development end agents in the plurality of sub-scanning direction areas are mixed and reach the replenishment position.

  For example, as shown in FIG. 13B, when the output image is divided in parallel with the main scanning direction, the development end upstream in the main scanning direction of the area that reaches the supply position first (the uppermost area in the figure) The agent is mixed with the development end agent downstream in the main scanning direction of the second-arrival area (second area from the top in the figure). That is, the development end agent in the second region is mixed while the development end agent upstream of the first region in the main scanning direction is being conveyed. Similarly, the development end agent downstream in the main scanning direction of the area that finally reaches the replenishment position (the bottom area in the figure) is the second area that reaches the second from the last (the second area from the bottom in the figure). It is mixed with the development terminator upstream of the main scanning direction. For this reason, when the developer replenishment control is performed by dividing the output image as shown in FIG. 13B, the optimal replenishment timing may deviate from the toner consumption timing during image formation. .

  Therefore, as shown in FIG. 13A, in order to match the replenishment timing, the output image is divided into regions inclined by a predetermined angle with respect to the sub-scanning direction, and the concentration is integrated in each region to set the replenishment timing. decide. As a result, the area where the developer is consumed on the side closer to the replenishment position (downstream in the main scanning direction) can be reflected in the replenishment at an early timing, and the developer consumption timing and the replenishment timing can be brought closer to each other. Can be further reduced. Other structures and operations are the same as those in the first embodiment.

[Example 2]
Next, an experiment will be described in which the transition of the image density fluctuation was examined in the above-described configuration (Example 2). In the experiment, a band image having an image ratio of 25% with respect to the A4 paper size was passed through the rear edge of the A3 paper, and 30000 sheets of image forming operations were performed. Then, the density of each formed image was measured. The result is shown in FIG. FIG. 15 shows transition of image density with respect to the number of formed images. Further, Comparative Example 1 and Example 1 are the results when image formation is similarly performed with the configurations shown in Comparative Example 1 and Example 1 described in the example of the first embodiment. . As can be seen from FIG. 15, according to the second embodiment, the width of the image density fluctuation can be further reduced in the image forming operation over a long period of time, particularly when the image having a high image ratio is formed, as compared with the first embodiment. I understood. As a result, according to the present embodiment, it was found that high-quality and high-quality image formation can be performed even when an image forming operation for a long time is performed.

[Third Embodiment]
A third embodiment of the present invention will be described with reference to FIG. In each of the above-described embodiments, a configuration in which more accurate replenishment control is performed by calculating an image ratio with respect to a position in the sub-scanning direction from the front end of the document has been described. However, it takes time until the first copy in order to start image formation after scanning the document and predicting the supply amount and supply timing. In view of this, in the present embodiment, image scanning and density integration are performed almost simultaneously, thereby reducing the processing time of the image data and reducing the time until the first image forming operation of the image forming apparatus.

  Specifically, as shown in FIG. 16, when image formation is started (S21), scanning of image data is started (S22), and at the same time, the first sub-scanning direction pixel i = 1 (see FIG. 6). The pixels in the main scanning direction are integrated (S23). Then, the integrated values are sequentially added in the sub-scanning direction (S24). If there is a density integrated value of the previous job, it is first added to the density integrated value (S25). After adding the density integrated value in the sub-scanning direction, it is determined whether or not the density integrated value corresponding to the supply for one rotation of the supply screw has been reached (S26). If not reached, the pixel moves to the next pixel in the sub-scanning direction (S27), and the main scanning direction density integrated value ΣDn is added (S24). If it has reached, the replenishment operation is performed by rotating the replenishment screw once (S28). At this time, when the sub-scanning direction pixel i = Nth (the last of the image data) is reached (S29), the scanning is terminated (S30). On the other hand, if the image data is not the last, the integrated value for one replenishment rotation is subtracted from the integrated density value (S31), and the process returns to S25.

  According to this embodiment, since image processing is started simultaneously with the start of scanning of image data, the image processing time and the supply control time can be absorbed in the image scanning time, and the time required for the first copy can be shortened. Specifically, when image formation is performed with the configuration of the first embodiment, the time required from the start of image data scan to the start of image forming operation is 4.00 [sec] for the A3 paper size, and the image processing time is 1. It took 5 [sec], and the replenishment amount and timing control processing time required 0.5 [sec]. On the other hand, according to the configuration of the present embodiment, the time required for the first copy can be reduced by about 2.0 [sec]. In this embodiment as well, a time lag is provided at the replenishment timing in consideration of the time during which the toner is conveyed from the toner replenishment position to the development position.

  As described above, by using the configuration of the present embodiment, when an image with a large image ratio is formed by performing replenishment according to image density, stable replenishment is provided and a stable high-quality image without density unevenness is provided. can do. In addition, an image forming apparatus with little downtime can be provided. Other structures and operations are the same as those in the first embodiment or the second embodiment described above.

DESCRIPTION OF SYMBOLS 1 ... Image carrier (photoconductor), 4 ... Developing device, 8a ... Control means (CPU), 44 ... Supply device, 80 ... Image data processing means (video counter), 100 ... Image forming devices

Claims (3)

An image carrier for carrying a toner image;
An electrostatic latent image forming means for forming an electrostatic latent image on the image carrier;
A developing device for developing the electrostatic latent image, comprising a developer carrier that carries and conveys a developer containing toner and a carrier at a development position facing the image carrier;
A replenishing device for replenishing toner to the developing device;
An image forming apparatus comprising: a control unit that controls a replenishment timing of the replenishing device based on a density distribution in a predetermined direction of the output image. The controller supplies the replenishment device so that the amount of toner supplied to the position facing the developer carrier is higher in a region where the image density in a predetermined direction of the output image is higher than in a region where the output image is low. The image forming apparatus according to claim 1, wherein timing is controlled. When (developer transport speed in the developing device) / (rotational speed of the image carrier) = α, the predetermined direction is a direction having an inclination α with respect to the moving direction of the surface of the image carrier. The image forming apparatus according to claim 1, wherein:

Images