JP2018112678A - Image formation device and method for correction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a precise correction of a printing concentration.SOLUTION: The present invention includes: a data input section in which a plurality of concentration values are input detected continuously by a sensor in association with the rotation of a rotary body; a processing target data control section which determines a predetermined number of toner concentration values as processing target data from the plurality of toner concentration values on a rotation cycle-by-rotation cycle basis of the rotary body; and a correction processing section which performs predetermined correction processing for correcting a printing concentration, using the processing target data determined by the processing target data control section on a rotation cycle-by-rotation cycle basis of the rotary body.SELECTED DRAWING: Figure 22

Description

  The present invention relates to an image forming apparatus and a correction method.

  Conventionally, in an image forming apparatus such as a laser printer, a toner image is formed by using a cylindrical rotating body such as a photosensitive drum or a developing roller, and this toner image is transferred to a recording paper, so that the print data can be printed. A technique for printing a printed image is known.

  In such an image forming apparatus, when the rotating body is eccentric or the cross section of the rotating body is not a perfect circle, the pressure at which the toner image is transferred is not uniform, and printing unevenness occurs. In view of this, conventionally, a technique has been devised in which the printing unevenness can be eliminated by correcting the printing density based on the density value of the toner image detected by the sensor (for example, see Patent Document 1 below). .

  Further, in the image forming apparatus, when the rotating body is eccentric or the cross section of the rotating body is not a perfect circle, temporal unevenness occurs in the rotation cycle of the rotating body. For this reason, in the conventional image forming apparatus, the number of data acquired from the sensor is different for each rotation period of the rotating body, and the correction data for correcting the print density fluctuates. For this reason, there has conventionally been a problem that the print density cannot be corrected with high accuracy.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems of the prior art, and to perform printing density correction with high accuracy.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a data input unit to which a plurality of toner density values continuously detected by a sensor as the rotating body rotates, A processing target data control unit that determines a predetermined number of toner density values from among the plurality of toner density values as processing target data for each rotation cycle, and the processing target data control unit for each rotation cycle of the rotating body. And a correction processing unit that performs a predetermined correction process for correcting the print density using the processing target data determined by the above.

  According to the present invention, printing density can be corrected with high accuracy.

1 is a schematic configuration diagram illustrating an image forming apparatus 1 according to a first embodiment of the present invention. FIG. 3 is an enlarged configuration diagram illustrating an image forming unit in an enlarged manner. FIG. 3 is an enlarged configuration diagram illustrating a Y photoconductor and a charging device in an enlarged manner. FIG. 2 is an enlarged perspective view showing an enlarged Y photoconductor. It is a graph which shows the time-dependent change of the output voltage from the photoconductor rotation sensor for Y. FIG. 2 is a configuration diagram illustrating a developing device for Y together with a part of a photoreceptor for Y. FIG. 2 is a block diagram illustrating a main part of an electric circuit of the image forming apparatus. It is an enlarged block diagram which shows the reflection type photosensor for Y mounted in the optical sensor unit. It is an enlarged block diagram which shows the reflection type photosensor for K mounted in the optical sensor unit. FIG. 6 is a schematic plan view showing patch pattern images of respective colors transferred to an intermediate transfer belt of an image forming unit. It is a graph which shows the approximate linear type | formula of the relationship between the toner adhesion amount and development bias constructed | assembled by process control processing. FIG. 4 is a schematic plan view illustrating solid density unevenness detection toner images of respective colors transferred to an intermediate transfer belt of an image forming unit. 6 is a graph showing a relationship among a periodic fluctuation of a toner adhesion amount of a solid density unevenness detection toner image, a sleeve rotation sensor output, and a photosensitive member rotation sensor output. It is a graph for demonstrating an average waveform. It is a graph for demonstrating the principle of the algorithm used when developing development pattern data is constructed. It is a timing chart which shows the timing of each output at the time of image formation. It is a graph which shows the time-dependent change of the toner adhesion variation | change_quantity in the average waveform of the cut-out waveform cut out by the sleeve rotation period, and the reproduction waveform which converted this for reproduction. It is a graph which shows the time-dependent change of the toner adhesion fluctuation amount in the average waveform referred when constructing the latent image fluctuation pattern data for changing the writing light quantity, and the reproduction waveform converted for reproduction. It is a graph which shows the relationship between the absolute value of a latent image potential, a writing light quantity, or development potential. 3 is a flowchart showing a control processing flow executed by control means (a control unit and a writing control unit) of the image forming apparatus. 1 is a diagram illustrating a partial configuration of an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the function structure of the correction | amendment part which concerns on 1st Embodiment of this invention. It is a conceptual diagram which shows the process target data determined by the process target data control part which concerns on 1st Embodiment of this invention. It is a conceptual diagram which shows the process target data determined by the process target data control part which concerns on 1st Embodiment of this invention. It is a figure which shows the specific example of the process target data determined by the process target data control part which concerns on 1st Embodiment of this invention. It is a timing chart of the various signals which the process target data control part which concerns on 1st Embodiment of this invention uses. It is a figure which shows the specific example of the determination process of the process target data by the process target data control part which concerns on 1st Embodiment of this invention. It is a figure which shows the specific example of the determination process of the process target data by the process target data control part which concerns on 1st Embodiment of this invention. It is a figure which shows the function structure of the correction | amendment part which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the procedure of the process by the correction | amendment part which concerns on 2nd Embodiment of this invention. It is a figure which shows the modification of the correction | amendment part which concerns on 2nd Embodiment of this invention.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

(FIGS. 1 to 20: Premise Configuration of Image Forming Apparatus)
First, a prerequisite configuration of the image forming apparatus 1 according to the first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic configuration diagram showing an image forming apparatus 1 according to the first embodiment of the present invention. 1, the image forming apparatus 1 includes an image forming unit 100 that forms an image on a recording sheet, a paper feeding device 200 that supplies the recording sheet 5 to the image forming unit 100, a scanner 300 that reads an image of a document, and the like. ing. The image forming apparatus 1 also includes an automatic document feeder (ADF) 400 attached to the upper part of the scanner 300. The image forming unit 100 is provided with a manual feed tray 6 for manually setting the recording sheets 5 and a stack tray 7 for stacking the recording sheets 5 on which the images have been formed.

  FIG. 2 is an enlarged configuration diagram illustrating the image forming unit 100 in an enlarged manner. The image forming unit 100 is provided with a transfer unit including an endless intermediate transfer belt 10 as a transfer body. The intermediate transfer belt 10 of the transfer unit is endlessly moved in the clockwise direction in the drawing by being rotationally driven by any one of the support rollers while being stretched around the three support rollers 14, 15, and 16. Of the support rollers 14, 15, 16, yellow (Y), cyan (C), magenta (M) are provided on the front surface of the belt portion that moves between the first support roller 14 and the second support roller 15. ), Four image forming units of black (K) face each other. Further, on the front surface of the belt portion that moves between the second support roller 15 and the third support roller 16, the image density of the toner image formed on the intermediate transfer belt 10 (toner adhesion amount per unit area). ) Are opposed to each other.

  In FIG. 1, a laser writing device 21 is provided above the image forming units 18Y, 18C, 18M, and 18K. The laser writing device 21 emits writing light based on image information of a document read by the scanner 300 or image information sent from an external personal computer. Specifically, the laser writing device 21 emits writing light by driving the semiconductor laser by the laser control unit based on the image information. Then, the laser writing device 21 exposes and scans the drum-shaped photoconductors 20Y, 20C, 20M, and 20K as latent image carriers provided in the image forming units 18Y, 18C, 18M, and 18K by the writing light. As a result, an electrostatic latent image is formed on the photosensitive member. Note that the light source of the writing light is not limited to a laser diode, and may be an LED, for example.

  FIG. 3 is an enlarged configuration diagram illustrating the Y photoconductor 20Y and the charging device 70Y in an enlarged manner. The charging device 70Y includes a charging roller 71Y that rotates in contact with the photoreceptor 20Y, a charging cleaning roller 75Y that rotates in contact with the charging roller 71Y, and a rotation attitude detection sensor described later.

  FIG. 4 is an enlarged perspective view showing the Y photoconductor 20Y in an enlarged manner. The photoconductor 20Y has a cylindrical main body 20aY, large-diameter flanges 20bY disposed on both ends of the main body 20aY in the rotation axis direction, a rotary shaft 20cY that is rotatably supported by a bearing, and the like. doing.

  One of the rotation shaft portions 20cY protruding from the end surfaces of the two flange portions 20bY passes through the photoconductor rotation sensor 76Y, and a portion protruding from the photoconductor rotation sensor 76Y is received by the bearing. The photoreceptor rotation sensor 76Y includes a light shielding member 77Y that is fixed to the rotation shaft portion 20cY and rotates integrally with the rotation shaft portion 20cY, a transmissive photosensor 78Y, and the like. The light shielding member 77Y has a shape protruding in the normal direction at a predetermined location on the peripheral surface of the rotation shaft portion 20cY, and the light emission of the transmission type photosensor 78Y when the photoconductor 20Y assumes a predetermined rotation posture. It is interposed between the element and the light receiving element. As a result, the light receiving element does not receive light, and the output voltage value from the transmissive photosensor 78Y is greatly reduced. In other words, the transmissive photosensor 78Y detects that the photoreceptor 20Y is in a predetermined rotational posture, and greatly reduces the output voltage value.

  FIG. 5 is a graph showing the change with time of the output voltage from the Y photoconductor rotation sensor 76Y. The output voltage from the photoconductor rotation sensor 76Y is specifically the output voltage from the transmissive photosensor 78Y. As shown in FIG. 5, when the photoconductor 20Y is rotating, a voltage of 6 [V] is output from the photoconductor rotation sensor 76Y for most of the time. However, every time the photoconductor 20Y makes a round, the output voltage from the photoconductor rotation sensor 76Y greatly decreases to near 0 [V] for a moment. This is because the light shielding member 77Y is interposed between the light emitting element and the light receiving element of the transmissive photosensor 78Y every time the photoconductor 20Y makes a round, so that the light receiving element does not receive light. The timing at which the output voltage greatly decreases in this way is the timing at which the photoconductor 20Y assumes a predetermined rotational posture. Hereinafter, this timing is referred to as a reference posture timing.

  In FIG. 3, the charging cleaning roller 75Y of the charging device 70Y includes a conductive mandrel, an elastic layer coated on the peripheral surface thereof, and the like. The elastic layer is made of a sponge-like member obtained by finely foaming melamine resin, and rotates while being in contact with the charging roller (71Y). The elastic layer suppresses the occurrence of abnormal images by removing dust such as residual toner adhering to the charging roller 71Y from the main body as it rotates.

  In FIG. 2, the four image forming units 18Y, 18C, 18M, and 18K have substantially the same configuration except that the colors of the toners used are different. For example, the Y image forming unit 18Y that forms a Y toner image includes a photoreceptor 20Y, a charging device 70Y, a developing device 80Y, and the like.

  The surface of the photoreceptor 20Y is uniformly charged to a negative polarity by the charging device 70Y. Of the surface of the photoreceptor 20Y that is uniformly charged in this manner, the portion irradiated with the laser beam by the laser writing device 21 attenuates the potential and becomes an electrostatic latent image.

  FIG. 6 is a configuration diagram showing the Y developing device 80Y together with a part of the Y photoconductor 20Y. The developing device 80Y is a two-component developing system that performs development using a two-component developer containing a magnetic carrier and a non-magnetic toner, but a one-component developing system that uses a one-component developer that does not contain a magnetic carrier. May be adopted. The developing device 80Y includes a stirring unit and a developing unit provided in the developing case. In the stirring unit, a two-component developer (hereinafter simply referred to as a developer) is stirred and conveyed by three screw members and supplied to the developing unit.

  The developing portion is provided with a developing sleeve 81Y that is rotationally driven while a part of its peripheral surface is opposed to the photoreceptor 20Y through a predetermined developing gap G through the opening of the developing device main body case. . The developing sleeve 81Y, which is a developer carrying member, is included so that the magnet roller does not rotate with itself.

  The supply screw 84Y of the stirring unit, the recovery screw 85Y, and the developing sleeve 81Y of the developing unit are arranged in parallel so as to extend in the horizontal direction. On the other hand, the agitating screw 86Y of the agitating unit is disposed so as to have an inclined posture in which the ascending gradient is formed from the near side to the far side in the direction orthogonal to the paper surface of FIG.

  The supply screw 84Y of the stirring unit supplies the developer to the developing sleeve 81Y of the developing unit while conveying the developer from the back side to the near side in the direction orthogonal to the paper surface of the drawing as it rotates. The developer that has been transported to the front end in the above direction in the developing device without being supplied to the developing sleeve 81Y is dropped onto a recovery screw 85Y disposed immediately below the supply screw 84Y.

  The developer supplied to the developing sleeve 81Y by the supply screw 84Y of the stirring unit is pumped up to the surface of the developing sleeve 81Y by the action of the magnetic force generated by the magnet roller included in the sleeve. The developer pumped up on the surface of the developing sleeve 81Y becomes a spiked state by the magnetic force generated by the magnet roller to form a magnetic brush. Then, as the developing sleeve 81Y rotates, the developer passes through a regulating gap formed between the tip of the regulating blade 87Y and the developing sleeve 81Y, and the layer thickness is regulated. Then, the developer faces the photoreceptor 20Y. To the developing area.

  In the developing region, an electrostatic force directed toward the electrostatic latent image is applied to the toner in the developer facing the electrostatic latent image on the photoreceptor 20Y by the developing bias applied to the developing sleeve 81Y. The developing potential that works. Further, among the toners in the developer, a background potential that imparts an electrostatic force toward the sleeve surface acts on the toner facing the background portion on the photoreceptor 20Y. As a result, the toner is transferred to the electrostatic latent image on the photoconductor 20 to develop the electrostatic latent image. In this way, a Y toner image is formed on the photoreceptor 20Y. The Y toner image enters a primary transfer nip for Y, which will be described later, with the rotation of the photoreceptor 20Y.

  The developer that has passed through the developing region with the rotation of the developing sleeve 81Y is transported to the region where the magnetic force of the magnet roller is weakened, and is separated from the surface of the developing sleeve 81Y and returned onto the collecting screw 85Y of the stirring unit. The collecting screw 85Y conveys the developer collected from the developing sleeve 81Y from the back side to the near side in the direction orthogonal to the paper surface of the drawing with its rotation. Then, the developer conveyed to the front end in the same direction in the developing device is delivered to the stirring screw 86Y.

  The developer transferred from the collecting screw 85Y to the stirring screw 86Y is conveyed from the near side to the far side in the direction along with the rotation of the collecting screw 85Y. In the process, the toner concentration is detected by a toner concentration sensor (82Y in FIG. 7 described later) including a magnetic permeability sensor, and an appropriate amount of toner is replenished according to the detection result. This replenishment is performed by driving a toner replenishing device according to a detection result by the toner density sensor by a control unit described later. The developer replenished with an appropriate amount of toner is transported to the far end in the above direction and delivered to the supply screw 84.

  The development region length L, which is the length of the development region in the sleeve rotation direction, varies depending on the diameter of the development sleeve 81Y, the development gap G, the regulation gap, and the like. As the development area length L increases, the chance of toner contact with the electrostatic latent image on the photoconductor 20Y in the development area increases, so that development efficiency increases. For this reason, it is possible to cope with high-speed printing by increasing the development area length L. However, if the development area length L is too large, there is a high possibility of causing problems such as toner scattering, toner fixation, and photoreceptor rotation lock. For this reason, it is desirable to set the development area length L to an appropriate value according to the characteristics of the apparatus specification.

  The image formation of the Y toner image in the image forming unit 18Y for Y has been described. In the image forming units 18C, M, and K for C, M, and K, the photoreceptors 20C, 20M, and A C toner image, an M toner image, and a K toner image are formed on the surface of 20K.

  In FIG. 2, primary transfer rollers 62Y, 62C, 62M, and 62K for Y, C, M, and K are disposed inside the loop of the intermediate transfer belt 10, and photosensitive for Y, C, M, and K are disposed. The intermediate transfer belt 10 is sandwiched between the bodies 20Y, 20C, 20M, and 20K. As a result, a primary transfer nip for Y, C, M, and K where the front surface of the intermediate transfer belt 10 and the Y, C, M, and K photoconductors 20Y, 20C, 20M, and 20K abut is formed. Has been. A primary transfer electric field is generated between the primary transfer rollers 62Y, 62C, 62M, and 62K for Y, C, M, and K to which the primary transfer bias is applied and the photoconductors 20Y, 20C, 20M, and 20K, respectively. Is formed.

  The front surface of the intermediate transfer belt 10 sequentially passes through the primary transfer nips for Y, C, M, and K as the belt moves endlessly. In this process, Y toner images, C toner images, M toner images, and K toner images on the photoconductors 20Y, 20C, 20M, and 20K are sequentially superimposed and sequentially transferred onto the front surface of the intermediate transfer belt 10. . As a result, a four-color superimposed toner image is formed on the front surface of the intermediate transfer belt 10.

  Below the intermediate transfer belt 10, there is disposed an endless transport belt 24 stretched by a first stretch roller 22 and a second stretch roller 23. As the tension roller rotates, it moves endlessly in the counterclockwise direction in the figure. The transport belt 24 has its front surface in contact with a portion of the intermediate transfer belt 10 that is wound around the third support roller 16 to form a secondary transfer nip. In the vicinity of the secondary transfer nip, a secondary transfer electric field is formed between the grounded second stretching roller 23 and the third support roller 16 to which the secondary transfer bias is applied.

  In FIG. 1, the image forming unit 100 sequentially conveys the recording sheet 5 fed from the paper feeding device 200 or the manual feed tray 6 to the secondary transfer nip, a fixing device 25 described later, and a discharge roller pair 56. The conveyance path 48 is provided. Further, a feeding path 49 for conveying the recording sheet 5 fed from the sheet feeding device 200 to the image forming unit 100 to the entrance of the conveying path 48 is also provided. A registration roller pair 47 is disposed at the entrance of the conveyance path 48.

  When the print job is started, the recording sheet 5 fed out from the paper feeding device 200 or the manual feed tray 6 is conveyed toward the conveyance path 48 and abuts against the registration roller pair 47. The registration roller pair 47 starts to rotate at an appropriate timing to feed the recording sheet 5 toward the secondary transfer nip. In the secondary transfer nip, the four-color superimposed toner image on the intermediate transfer belt 10 is in close contact with the recording sheet 5. Then, the four-color superimposed toner image is secondarily transferred onto the surface of the recording sheet 5 by the action of the secondary transfer electric field and nip pressure to form a full-color toner image.

  The recording sheet 5 that has passed through the secondary transfer nip is conveyed toward the fixing device 25 by the conveying belt 24. The full color toner image is fixed on the surface of the fixing device 25 by being pressurized and heated. Thereafter, the recording sheet 5 is discharged from the fixing device 25 and then stacked on the stack tray 7 via the discharge roller pair 56.

  FIG. 7 is a block diagram illustrating a main part of an electric circuit of the image forming apparatus 1. In FIG. 7, a control unit 110 as a control unit includes a CPU, a RAM, a ROM, a nonvolatile memory, and the like. The control unit 110 is electrically connected to toner density sensors 82Y, 82C, 82M, and 82K of developing devices 80Y, 80C, 80M, and 80K for Y, C, M, and K. Accordingly, the control unit 110 grasps the toner concentrations of the Y developer, the C developer, the M developer, and the K developer stored in the Y, C, M, and K developing devices 80Y, 80C, 80M, and 80K. can do.

  Y, C, M, and K unit detachment sensors 17Y, 17C, 17M, and 17K are also electrically connected to the control unit 110. Unit attachment / detachment sensors 17Y, 17C, 17M, and 17K as attachment / detachment detection means detect that the image forming units 18Y, 18C, 18M, and 18K have been removed from the image forming unit 100, and are attached to the image forming unit 100. Can be detected. Accordingly, the control unit 110 can grasp that the image forming units 18Y, 18C, 18M, and 18K have been attached to and detached from the image forming unit 100.

  Further, Y, C, M, and K developing power supplies 11Y, 11C, 11M, and 11K are also electrically connected to the control unit 110. The control unit 110 can individually adjust the values of the developing bias output from the developing power supplies 11Y, 11C, 11M, and 11K by individually outputting control signals to the developing power supplies 11Y, 11C, 11M, and 11K. it can. That is, the control unit 110 can individually adjust the values of the developing bias applied to the developing sleeves 81Y, 81C, 81M, and 81K for Y, C, M, and K.

  In addition, Y, C, M, and K charging power sources 12Y, 12C, 12M, and 12K are also electrically connected to the control unit 110. The control unit 110 individually outputs control signals to the charging power sources 12Y, 12C, 12M, and 12K, thereby individually setting the DC voltage value at the charging bias output from the charging power sources 12Y, 12C, 12M, and 12K. Can be controlled. In other words, the control unit 110 can individually adjust the DC voltage values of the charging bias applied to the Y, C, M, and K charging rollers 71Y, 71C, 71M, and 71K.

  The control unit 110 also includes photoreceptor rotation sensors 76Y and 76C for individually detecting that the photoreceptors 20Y, 20C, 20M, and 20K for Y, C, M, and K are in a predetermined rotation posture. , 76M, 76K are also electrically connected. Based on the outputs from the photoconductor rotation sensors 76Y, 76C, 76M, and 76K, the control unit 110 assumes predetermined rotation postures for the Y, C, M, and K photoconductors 20Y, 20C, 20M, and 20K. Can be grasped individually.

  Further, sleeve rotation sensors 83Y, 83C, 83M, and 83K of the developing devices 80Y, 80C, 80M, and 80K are also electrically connected to the control unit 110. The sleeve rotation sensors 83Y, 83C, 83M, and 83K serving as the rotation posture detection means have a predetermined rotation posture with respect to the developing sleeves 81Y, 81C, 81M, and 81K, with the same configuration as the photoconductor rotation sensors 76Y, 76C, 76M, and 76K. It is detected. That is, the control unit 110 can individually grasp the timing at which the developing sleeves 81Y, 81C, 81M, and 81K have reached a predetermined rotation posture based on the outputs from the sleeve rotation sensors 83Y, 83C, 83M, and 83K. .

  The control unit 110 is also electrically connected with a writing control unit 125, an environment sensor 124, an optical sensor unit 150, a process motor 120, a transfer motor 121, a registration motor 122, a paper feed motor 123, and the like. The environmental sensor 124 detects the temperature and humidity in the machine. The process motor 120 is a motor that is a drive source of the image forming units 18Y, 18C, 18M, and 18K. The transfer motor 121 is a motor that is a drive source of the intermediate transfer belt 10. The registration motor 122 is a motor that is a drive source of the registration roller pair 47. The paper feed motor 123 is a motor that is a drive source of the pickup roller 202 for feeding the recording sheet 5 from the paper feed cassette 201 of the paper feed device 200. The writing control unit 125 controls driving of the laser writing device 21 based on the image information. The role of the optical sensor unit 150 will be described later.

  The image forming apparatus 1 periodically performs a process called a process control process at a predetermined timing in order to stabilize the image density over a long period of time regardless of environmental fluctuations. In the process control process, the image forming apparatus 1 forms a Y patch pattern image including a plurality of patch-like Y toner images on the Y photoconductor 20 </ b> Y, and transfers the image to the intermediate transfer belt 10. Each of the plurality of patch-like Y toner images is a toner adhesion amount detection toner image for detecting the Y toner adhesion amount. The controller 110 similarly forms C, M, and K patch pattern images on the photoconductors 20C, 20M, and 20K and transfers them to the intermediate transfer belt 10 so as not to overlap them. Then, the image forming apparatus 1 detects the toner adhesion amount of each toner image in the patch pattern image by the optical sensor unit 150. Next, the image forming apparatus 1 individually adjusts image forming conditions such as a developing bias reference value that is a reference value of the developing bias Vb for each of the image forming units 18Y, 18C, 18M, and 18K based on the detection results. .

  The optical sensor unit 150 includes four reflective photosensors arranged at a predetermined interval in the belt width direction of the intermediate transfer belt 10. Each reflection type photosensor outputs a signal corresponding to the light reflectance of the intermediate transfer belt 10 and the patch-like toner image on the intermediate transfer belt 10. Of the four reflective photosensors, three output both regular reflection light and diffuse reflection light on the belt surface so as to output in accordance with the Y toner adhesion amount, C toner adhesion amount, and M toner adhesion amount. And output according to each light quantity.

  FIG. 8 is an enlarged configuration diagram showing a Y reflective photosensor 151Y mounted on the optical sensor unit 150. As shown in FIG. The reflection photosensor 151Y for Y includes an LED 152Y as a light source, a regular reflection type light receiving element 153Y that receives regular reflection light, and a diffuse reflection type light reception element 154Y that receives diffuse reflection light. The regular reflection type light receiving element 153Y outputs a voltage corresponding to the amount of regular reflection light obtained on the surface of the Y-patch toner image. The diffuse reflection type light receiving element 154Y outputs a voltage corresponding to the amount of diffuse reflection light obtained on the surface of the Y patch toner image. The controller 110 can calculate the Y toner adhesion amount of the Y patch toner image based on these voltages. The reflective photosensor 151Y for Y has been described, but the reflective photosensors 151C and 151M for C and M have the same configuration as that for Y.

  FIG. 9 is an enlarged configuration diagram illustrating the K reflection type photosensor 151 </ b> K mounted on the optical sensor unit 150. The K reflection type photosensor 151K includes an LED 152K as a light source and a regular reflection type light receiving element 153K that receives regular reflection light. The regular reflection type light receiving element 153K outputs a voltage corresponding to the amount of regular reflection light obtained on the surface of the K-patch toner image. The controller 110 can calculate the K toner adhesion amount of the K patch toner image based on the voltage.

  As the LEDs (152Y, C, M, K), GaAs infrared light emitting diodes having a peak wavelength of emitted light of 950 nm are used. Further, as the regular reflection light receiving elements (153Y, C, M, K) and the diffuse reflection light receiving elements (154Y, C, M), Si phototransistors having a peak light receiving sensitivity of 800 nm are used. However, the peak wavelength and the peak light receiving sensitivity are not limited to the values described above.

  A gap of about 5 mm is provided between the four reflective photosensors and the front surface of the intermediate transfer belt 10.

  The control unit 110 performs process control processing at a predetermined timing, such as when the main power is turned on, when waiting after a predetermined time has elapsed, or when waiting after outputting a predetermined number of prints. Then, when the process control process is started, the control unit 110 first acquires environmental information such as the number of sheets to be passed, the printing rate, the temperature, and the humidity, and then develops each development characteristic in the image forming units 18Y, 18C, 18M, and 18K. To figure out. Specifically, the control unit 110 calculates the development γ and the development start voltage for each color. More specifically, each of the photoreceptors 20Y, 20C, 20M, and 20K is uniformly charged while rotating. As for this charging, a charging bias output from the charging power sources 12Y, 12C, 12M, and 12K is different from that during normal printing. Specifically, the absolute value of the DC voltage of the charging bias DC voltage and AC voltage composed of the superimposed bias is gradually increased rather than a uniform value. The controller 110 scans the photoconductors 20Y, 20C, 20M, and 20K charged under such conditions with a laser beam by the laser writing device 21 to produce a patch-like Y toner image and a patch-like C toner image. A plurality of electrostatic latent images for patch-like M toner images and patch-like K toner images are formed. These are developed by developing devices 80Y, 80C, 80M, and 80K, thereby forming Y, C, M, and K patch pattern images on the photoreceptors 20Y, 20C, 20M, and 20K. During development, the control unit 110 gradually increases the absolute values of the developing bias applied to the developing sleeves 81Y, 81C, 81M, and 81K of the respective colors. At this time, the control unit 110 stores the difference between the electrostatic latent image potential in each patch-like toner image and the development bias in the RAM as the development potential.

  FIG. 10 is a schematic plan view showing patch pattern images of the respective colors transferred to the intermediate transfer belt 10 of the image forming unit 100. As shown in FIG. 10, the Y, C, M, and K patch pattern images are arranged in the belt width direction so as not to overlap on the intermediate transfer belt 10. Specifically, the Y patch pattern image YPP is transferred to one end of the intermediate transfer belt 10 in the width direction. The C patch pattern image CPP is transferred to a position slightly shifted to the center side from the Y patch pattern image in the belt width direction. Further, the M patch pattern image MPP is transferred to the other end of the intermediate transfer belt 10 in the width direction. The K patch pattern image KPP is transferred to a position slightly shifted to the center side of the K patch pattern image in the belt width direction.

  The optical sensor unit 150 includes a Y reflective photosensor 151Y that detects light reflection characteristics of the belt at different positions in the belt width direction. The optical sensor unit 150 also includes a reflective photosensor 151C for C, a reflective photosensor 151K for K, and a reflective photosensor 151M for M.

  The reflection photosensor 151Y for Y is disposed at a position for detecting the amount of Y toner attached to the Y patch-like toner image of the Y patch pattern image YPP formed at one end in the width direction of the intermediate transfer belt 10. . The C-th reflective photosensor 151C is arranged at a position for detecting the C toner adhesion amount of the C patch-like toner image of the C patch pattern image CPP located near the Y patch pattern image YPP in the belt width direction. It is installed. The M reflection type photosensor 151M is disposed at a position for detecting the M toner adhesion amount of the M patch-like toner image of the M patch pattern image MPP formed at the other end in the width direction of the intermediate transfer belt 10. Yes. Further, the K reflection type photosensor 150c is disposed at a position for detecting the K toner adhesion amount of the K patch-like toner image of the K patch pattern image KPP located near the M patch pattern image MPP in the belt width direction. Has been.

  The control unit 110 calculates the light reflectance of each color patch-like toner image based on the output signals sequentially sent from the four reflective photosensors of the optical sensor unit 150, and the toner adhesion amount based on the calculation result. Is stored in the RAM. The patch pattern image of each color that has passed through the position facing the optical sensor unit 150 as the intermediate transfer belt 10 travels is cleaned from the front surface of the belt by a cleaning device.

  FIG. 11 is a graph showing an approximate linear expression of the relationship between the toner adhesion amount and the developing bias constructed by the process control process. Next, the control unit 110 uses a linear approximation formula (Y) based on the toner adhesion amount stored in the RAM, and the latent image potential data and the development bias Vb data in each patch toner image stored separately in the RAM. = A * Vp + b) is calculated. Specifically, as shown in FIG. 11, this linear approximate expression is an approximate linear expression showing the relationship between the two-dimensional coordinates in which the y-axis is the toner adhesion amount and the x-axis is the development potential. Then, the control unit 110 obtains the development potential Vp that realizes the target toner adhesion amount based on the approximate linear equation, and the development bias reference value and the charging bias reference value that are the development bias Vb that realizes the development potential Vp, (And LD power). These results are stored in non-volatile memory. The control unit 110 calculates and stores the development bias reference value and the charging bias reference value (and LD power) for each color of Y, C, M, and K, and ends the process control process. Thereafter, in the print job, the control unit 110 sets development bias Vb having values based on the development bias reference values stored in the nonvolatile memory for development power supplies 11Y, 11C, and 11K for Y, C, M, and K, respectively. Output from 11M and 11K. Further, the control unit 110 outputs the charging bias Vd having a value based on the charging bias reference value stored in the nonvolatile memory from the charging power sources 12Y, 12C, 12M, and 12K, and outputs the LD power to the laser writing device. 21.

  The control unit 110 performs such a process control process to determine a development bias reference value and a charging bias reference value (and optical writing intensity (LDP described later)) that realize a target toner adhesion amount. For each of Y, C, M, and K colors, the image density of the entire image can be stabilized over a long period of time. However, periodic image density unevenness in the page due to the development gap fluctuation (hereinafter referred to as gap fluctuation) between the photoconductors 20Y, 20C, 20M, and 20K and the development sleeves 81Y, 81C, 81M, and 81K. Will cause.

  This image density unevenness is a superimposition of what occurs at the rotation cycle of the photoconductors 20Y, 20C, 20M and 20K and that which occurs at the rotation cycle of the developing sleeves 81Y, 81C, 81M and 81K. Specifically, if the rotation axes of the photoconductors 20Y, 20C, 20M, and 20K are decentered, a gap fluctuation that becomes a sine curve-like fluctuation curve occurs around the photoconductor. As a result, the electric field strength that forms a sine-curve variation curve around the photosensitive member also in the developing electric field formed between the photosensitive members 20Y, 20C, 20M, and 20K and the developing sleeves 81Y, 81C, 81M, and 81K. Variations occur. The fluctuation in the electric field intensity causes image density unevenness that becomes a sine curve-like fluctuation curve around the photoreceptor. In addition, the outer shape of the surface of the photoreceptor is not a little distorted. Image density unevenness is also generated due to periodic gap fluctuations with the characteristics of the same pattern per circumference of the photoconductor according to this distortion. Further, periodic image density unevenness due to the fluctuation of the sleeve rotation cycle due to the eccentricity of the developing sleeves 81Y, 81C, 81M, 81K and the external distortion also occurs. In particular, image density unevenness due to eccentricity and external distortion of the developing sleeves 81Y, 81C, 81M, and 81K having a smaller diameter than the photoconductors 20Y, 20C, 20M, and 20K occurs at a relatively short period, and thus becomes conspicuous.

  Therefore, the control unit 110 performs the following output change process for each of the colors Y, C, M, and K during a print job. That is, the control unit 110 outputs a development bias output pattern for causing fluctuations in the development electric field intensity that can cancel out image density unevenness that occurs in the photosensitive member rotation period for each of Y, C, M, and K colors. Data is stored in a non-volatile memory. In addition, the control unit 110 also stores development fluctuation pattern data for causing development electric field intensity fluctuations that can cancel out the image density unevenness generated in the developing sleeve rotation cycle in the nonvolatile memory. Hereinafter, the former development fluctuation pattern data is referred to as development fluctuation pattern data for the photoconductor cycle. The latter development fluctuation pattern data is referred to as development fluctuation pattern data for the sleeve cycle.

  The development fluctuation pattern data for the four photosensitive member cycles corresponding to Y, M, C, and K individually are patterns corresponding to one rotation cycle of the photosensitive member, and the photosensitive member 20Y, 20C, 20M, and 20K. A pattern based on the reference posture timing is shown. The development variation pattern data is obtained by outputting the development bias from the development power supply (11Y, 11C, 11M, 11K) based on the development bias reference value for Y, C, M, K determined in the process control process. It is for changing. For example, in the case of data table type data, a data group indicating a development bias output difference for each predetermined time interval is stored within a period of one cycle from the reference posture timing. The first data of the data group indicates the development bias output difference at the reference posture timing, and the second, third, fourth,... Data indicate the development bias output difference at predetermined time intervals thereafter. Yes. The output pattern composed of data groups of 0, −5, −7, −9. [V], −9 [V]... If only the image density unevenness that occurs in the photosensitive member rotation cycle is to be suppressed, a developing bias having a value obtained by superimposing these values on the developing bias reference value may be output from the developing power source. However, since the image forming apparatus 1 also suppresses image density unevenness that occurs in the developing sleeve rotation cycle, the development bias output difference for suppressing the image density unevenness in the photosensitive member rotation cycle and the image density unevenness in the developing sleeve rotation cycle are suppressed. Therefore, the development bias output difference is superimposed.

  The development variation pattern data for four sleeve periods corresponding to Y, C, M, and K individually is a pattern corresponding to one rotation period of the development sleeve, and a reference for the development sleeves 81Y, 81C, 81M, and 81K. A pattern based on posture timing is shown. The development variation pattern data is obtained from the development power supply (11Y, 11C, 11M, 11K) with reference to the development bias reference values for Y, C, M, K determined in the process control process as the reference value determination process. This is for changing the output of the developing bias. In the case of data table type data, the first data of the data group indicates the development bias output difference at the reference posture timing, and the second, third, fourth,. The development bias output difference for each interval is shown. The time interval is the same as the time interval reflected by the data group of the development variation pattern data for the photoconductor cycle.

  At the time of image forming processing, the control unit 110 reads data from development variation pattern data for the photosensitive member cycle corresponding to each of Y, C, M, and K at predetermined time intervals. At the same time, the control unit 110 reads data from the development fluctuation pattern data for the sleeve period corresponding to Y, C, M, and K, respectively, at the same time interval. Regarding the data reading from the development fluctuation pattern data for the photosensitive member cycle, the timing at which the reference posture timing signal is sent from the photosensitive member rotation sensors (76Y, 76C, 76M, 76K) is set as the reference posture timing. For reading data from the development fluctuation pattern data for the sleeve cycle, the timing at which the reference posture timing signal is sent from the sleeve rotation sensor (83Y, 83C, 83M, 83K) is used as the reference posture timing.

  In the process of reading such data for each of Y, C, M, and K, the controller 110 reads from the data read from the development fluctuation pattern data for the photoreceptor period and the development fluctuation pattern data for the sleeve period. The superimposed value is obtained by adding the read data. For example, when the data read from the development fluctuation pattern data for the photoconductor cycle is −5 [V] and the data read from the development fluctuation pattern data for the sleeve cycle is 2 [V] Is obtained by adding −5 [V] and 2 [V] to obtain a superimposed value of −3 [V]. Then, for example, when the development bias reference value is −550 [V], the control unit 110 outputs −553 [V] obtained by adding the superimposed value from the development power supply. The control unit 110 performs such processing for each of Y, C, M, and K at predetermined time intervals.

  As a result, the control unit 110 performs electric field strength fluctuation by superimposing the following two electric field strength fluctuations on the developing electric field between the photoconductors 20Y, 20C, 20M, and 20K and the developing sleeves 81Y, 81C, 81M, and 81K. Electric field strength fluctuations that can be offset are generated. That is, fluctuations in electric field strength caused by gap fluctuations generated in the photosensitive member rotation period due to eccentricity and external distortion of the photoconductors 20Y, 20C, 20M, and 20K, and sleeves due to eccentricity and external distortion of the developing sleeves 81Y, 81C, 81M, and 81K. It is the electric field strength fluctuation that occurs in the rotation period. In this way, the control unit 110 applies a substantially constant developing electric field to the photosensitive member and the developing sleeve regardless of the rotational postures of the photosensitive members 20Y, 20C, 20M, and 20K and the developing sleeves 81Y, 81C, 81M, and 81K. Form between. As a result, it is possible to suppress both image density unevenness occurring in the photosensitive member rotation cycle and image density unevenness occurring in the sleeve rotation cycle.

  For the development variation pattern data for the four photosensitive member cycles corresponding to Y, C, M, and K, and the development variation pattern data for the four sleeve cycles, the construction process is performed at a predetermined timing. Build by. The predetermined timing includes a timing prior to the first print job after factory shipment (hereinafter referred to as initial activation timing) and a timing at which replacement of the image forming units 18Y, 18C, 18M, and 18K is detected (hereinafter referred to as replacement detection timing). ). At the initial start timing, development variation pattern data for the photoreceptor period is constructed for all the colors Y, C, M, and K, respectively. Also, development fluctuation pattern data for the sleeve cycle is constructed. On the other hand, at the replacement detection timing, the development fluctuation pattern data for the photosensitive member cycle and the development fluctuation pattern data for the sleeve cycle are constructed only for the image forming unit in which the replacement is detected. As shown in FIG. 7, unit detachment sensors 17Y, 17C, 17M, and 17K for individually detecting the replacement of the image forming units 18Y, 18C, 18M, and 18K are provided so as to enable such construction. Is provided.

  In the construction process at the initial activation timing, first, a Y solid density unevenness detection toner image composed of a Y solid toner image is formed on the photoconductor 20Y. Further, a C solid density unevenness detection toner image, an M solid density unevenness detection toner image, and a K solid density unevenness detection toner image, each of which is composed of a C solid toner image, an M solid toner image, and a K solid toner image, are represented by a photoconductor 20C and a photoconductor 20M. , An image is formed on the photoconductor 20K. Then, these solid density unevenness detection toner images are primarily transferred to the intermediate transfer belt 10 as shown in FIG. FIG. 12 is a schematic plan view showing solid density unevenness detection toner images of the respective colors transferred to the intermediate transfer belt 10 of the image forming unit 100. In FIG. 12, the Y solid density unevenness detection toner image YIT is used to detect image density unevenness that occurs in the rotation cycle of the photoconductor 20Y. Therefore, the Y solid density nonuniformity detection toner image YIT is longer than the circumference of the photoconductor 20Y in the belt movement direction. It is formed with a large length. Similarly, the C solid density non-uniformity detection toner image CIT, the M solid density non-uniformity detection toner image MIT, and the K solid density non-uniformity detection toner image KIT also have a length in the belt moving direction around the photoconductors 20C, 20M, and 20K. It is larger than the length.

  FIG. 12 shows an example in which four solid density unevenness detection toner images (YIT, CIT, MIT, KIT) are arranged in a straight line in the belt width direction for convenience. However, in practice, the formation position of each density unevenness detection toner image on the belt may be shifted by the same value as the circumferential length of the photosensitive member at the maximum in the belt moving direction. For example, for each color, the front end position of the solid density unevenness detection toner image and the reference position in the circumferential direction of the photosensitive member (the photosensitive member surface position that enters the developing region at the reference posture timing) are matched. This is because image formation of a solid density unevenness detection toner image is started. That is, the solid density unevenness detection toner images of the respective colors are formed so that the front ends thereof coincide with the reference position in the circumferential direction of the photoreceptor.

  As the density unevenness detection toner image, a halftone toner image may be formed instead of the solid toner image. For example, a halftone toner image having a dot area ratio of 70 [%] may be formed.

  Further, the control unit 110 is configured to perform the construction process as a set with the process control process. Specifically, the control unit 110 performs a process control process immediately before executing the construction process, and determines a development bias reference value for each color. Then, in the construction process performed immediately after the process control process, the control unit 110 develops the solid density unevenness detection toner image for each color under the condition of the development bias reference value determined in the process control process. Therefore, theoretically, the solid density unevenness detection toner image is formed so as to have the target toner adhesion amount, but in reality, subtle density unevenness appears due to the development gap fluctuation.

  After image formation of the solid density unevenness detection toner image is started (after the start of writing of the electrostatic latent image), the detection position of the front end of the solid density detection toner image by the reflective photosensor of the optical sensor unit 150 is detected. The time lag until it enters is a different value for each color. However, for the same color, the value is constant over time (hereinafter, this value is referred to as write-detection time lag).

  The control unit 110 stores a write-detection time lag for each color in a nonvolatile memory in advance. Then, the control unit 110 starts sampling the output from the reflective photosensor from the time when the writing-detection time lag has elapsed after starting the formation of the solid density unevenness detection toner image for each color. This sampling is repeated at predetermined time intervals over one rotation of the photosensitive member. The time interval is the same value as the time interval for reading individual data in the output pattern data used in the output change process. The control unit 110 constructs a density unevenness graph indicating the relationship between the toner adhesion amount (image density) and time (or the photoreceptor surface position) for each color based on the sampling data. Extract density unevenness pattern. The first is a solid density unevenness pattern generated at the photosensitive member rotation period. The second is a solid density unevenness pattern generated in the developing sleeve rotation cycle.

  The controller 110 calculates a toner adhesion amount average value (image density average value) by extracting the solid density unevenness pattern generated in the photosensitive member rotation period based on the sampling data described above for each color. The average toner adhesion amount is a value that substantially reflects the average value of the change in the development gap during one rotation of the photoreceptor. Therefore, the control unit 110 constructs photoconductor cycle output pattern data for canceling the solid density unevenness pattern of the photoconductor rotation cycle based on the average value of the toner adhesion amount. Specifically, the control unit 110 calculates bias output differences individually corresponding to a plurality of toner adhesion amount data included in the solid density pattern. The bias output difference is based on the toner adhesion amount average value. The control unit 110 calculates the bias output difference corresponding to the toner adhesion amount data having the same value as the toner adhesion amount average value as zero.

  Further, the control unit 110 calculates a bias output difference corresponding to toner adhesion amount data larger than the toner adhesion amount average value as a positive polarity value corresponding to the difference between the toner adhesion amount and the toner adhesion amount average value. To do. Since this is a positive polarity bias output difference, it is data for changing the negative polarity development bias to a value lower than the development bias reference value (a value having a small absolute value).

  Further, the control unit 110 calculates a bias output difference corresponding to toner adhesion amount data smaller than the toner adhesion amount average value as a negative polarity value corresponding to the difference between the toner adhesion amount and the toner adhesion amount average value. To do. Since this is a negative polarity bias output difference, it is data for changing the negative polarity development bias to a value higher than the development bias reference value (a value having a large absolute value).

  In this way, the control unit 110 obtains a bias output difference corresponding to each toner adhesion amount data, and constructs data obtained by arranging them in order as photoconductor periodic output pattern data as output pattern data.

  Further, when the solid density unevenness pattern generated in the developing sleeve rotation cycle is extracted for each color based on the sampling data described above, the control unit 110 calculates the toner adhesion amount average value (image density average value). . The average toner adhesion amount is a value that substantially reflects the average value of the change in the development gap in one rotation period of the development sleeve. Therefore, the control unit 110 constructs sleeve cycle output pattern data for canceling out the density unevenness pattern of the developing sleeve rotation cycle with reference to the average toner adhesion amount. The specific method is the same as the method of constructing photoconductor cycle output pattern data for canceling out the density unevenness pattern of the photoconductor rotation cycle.

  FIG. 13 is a graph showing the relationship between the periodic fluctuation of the toner adhesion amount of the solid density unevenness detection toner image, the sleeve rotation sensor output, and the photosensitive member rotation sensor output. The vertical axis of the graph indicates the toner adhesion amount [10 −3 mg-cm 2], which is obtained by converting the output voltage from the reflective photosensor 151 of the optical sensor unit 150 to the toner adhesion amount based on a predetermined conversion formula. It is the converted numerical value. It can be seen that periodic density unevenness occurs in the solid transfer unevenness detection toner image in the moving direction of the intermediate transfer belt.

  When constructing development fluctuation data for the sleeve cycle, first, in order to remove a cycle fluctuation component that is different from the sleeve cycle, data on the temporal variation of the toner adhesion amount is cut out every sleeve rotation cycle and averaged. Do. Specifically, since the length of the solid density unevenness detection toner image is a value of 10 times or more of the developing sleeve circumference, the data on the variation in the toner adhesion over time is equal to or more than 10 cycles of the developing sleeve. Is acquired over. The fluctuation waveform based on the data is cut out every one cycle of the sleeve with the sleeve reference posture timing as the head. As a result, when ten cutout waveforms are obtained, the cutout waveforms are overlapped and averaged to analyze the average waveform while synchronizing the sleeve reference posture timing as shown in FIG. FIG. 14 is a graph for explaining the average waveform. An average waveform obtained by averaging ten cut-out waveforms is indicated by a thick line in FIG. The individual cut-out waveforms are ramped including a period fluctuation component different from the sleeve rotation cycle, but the ramping of the average waveform is reduced. In the image forming apparatus 1, averaging processing is performed with ten clipped waveforms, but other methods may be employed as long as a fluctuation component of the sleeve rotation period can be extracted.

  FIG. 15 is a graph for explaining the principle of an algorithm used when constructing development variation pattern data. In the image forming apparatus 1, the development variation data for the photoconductor cycle is also averaged by the cut-out waveform cut out in the photoconductor cycle, similarly to the sleeve cycle, and is constructed based on the result. . The development fluctuation data based on the average waveform can be realized by converting the toner adhesion amount into the development bias fluctuation amount using the following algorithm. That is, for example, as shown in FIG. 15, the algorithm is capable of generating a development bias fluctuation that gives a fluctuation control waveform having an opposite phase to the toner adhesion amount detection waveform.

  FIG. 16 is a timing chart showing the timing of each output during image formation. As described above, the development power source (11Y, 11C, 11M, 11K) of the development bias Vb in the output change process using the photosensitive member periodic output pattern data and the sleeve periodic output pattern data constructed in the construction process for each color. Change the output from. Specifically, as shown in FIG. 16, development is performed according to a superimposed waveform in which the development bias fluctuation waveform based on the development fluctuation pattern data for the photoreceptor period and the development bias fluctuation waveform based on the development fluctuation pattern data for the sleeve period are superimposed. The bias is changed periodically. As a result, it is possible to suppress the occurrence of solid image density unevenness that occurs in the photosensitive member rotation cycle and solid image density unevenness that occurs in the developing sleeve rotation cycle.

  Next, a characteristic configuration of the image forming apparatus 1 will be described. Even if the output of the charging bias is periodically changed based on the charging fluctuation pattern data, a periodic density fluctuation may be caused in the halftone portion. Hereinafter, the concentration variation is referred to as residual cycle variation. Further, in addition to periodically changing the development bias and the charging bias, the remaining period fluctuation can be suppressed by periodically changing the latent image writing intensity by the laser writing device 21, that is, the write light amount.

  Therefore, in the image forming apparatus 1, when forming an image based on a command from the user, the control unit performs control to periodically change the writing light amount of the latent image in addition to the developing bias and the charging bias. 110 and the writing control unit 125 are configured. Thereby, residual period fluctuation | variation can be suppressed compared with the past.

  Next, the image forming apparatus 1 of each example in which a more characteristic configuration is added to the image forming apparatus 1 according to the embodiment will be described. The configuration of the image forming apparatus 1 according to each example is the same as that of the embodiment unless otherwise specified below.

  FIG. 17 is a graph showing the change over time of the toner adhesion fluctuation amount in the average waveform of the cut-out waveform cut out at the sleeve rotation period and the reproduced waveform converted for reproduction. In FIG. 17, the average waveform is obtained by averaging ten cutout waveforms cut out from the density unevenness pattern data at the sleeve rotation cycle in order to construct development fluctuation pattern data for the sleeve cycle. This average waveform can be reproduced almost completely by superimposing a plurality of sine waves that fluctuate at a cycle 20 times the sleeve rotation cycle. However, the image density variation accompanying the development bias variation becomes less followable as the bias variation frequency increases.

  The reason will be described. The development of the electrostatic latent image on the photoconductor is performed when the electrostatic latent image is within the development area length L shown in FIG. Even if the output value of the development bias is slightly changed within the time from when the electrostatic latent image enters the development area until it exits the development area, the image density of the electrostatic latent image is subtly followed by the change. It is very difficult to change. This is because the average bias value within the time greatly affects the image density of the electrostatic latent image, and the instantaneous bias change does not significantly affect the image density. If the development area length L is made too small in order to avoid this phenomenon, the required developing ability cannot be obtained. Therefore, there is an upper limit to the frequency of the periodically varying component of the image density that can be suppressed by fluctuations in the developing bias. is there.

  For this reason, in the image forming apparatus 1, the frequency that is three times the sleeve rotation period is set as the upper limit of the frequency of the periodic fluctuation component to be extracted. That is, the average waveform is reproduced by superimposing a plurality of sine waves that fluctuate at a cycle three times the sleeve rotation cycle. The reproduced waveform shown in FIG. 16 is obtained by such reproduction. Based on the reproduced waveform, the control unit 110 constructs development fluctuation pattern data for the photoreceptor period and development fluctuation pattern data for the sleeve period.

  The specific procedure of the construction method is as follows. First, the control unit 110 performs frequency analysis on the average waveform. The frequency analysis may be performed by Fourier transform (FFT) or by quadrature detection. The image forming apparatus 1 is configured to perform quadrature detection.

The average waveform shown in FIG. 14 is expressed by superposition of sine waves that periodically change at a frequency that is an integral multiple of the sleeve rotation period, as shown in the following equation. In the following equation, x is an upper limit value of the fluctuation frequency of the sine wave.
f (t) = A ₁ × sin (ωt + θ ₁ ) + A ₂ × sin (2 × ωt + θ ₂ ) + A ₃ × sin (3 × ωt + θ ₃ ) +... + A _x × sin (xx × ωt + θ _x )

This equation can be changed to the following equation.
f (t) = ΣA _i × sin (i × ωt + θ _i )
: However, i = 1 to x is a natural number

The parameters indicated by each symbol are as follows.
F (t): average waveform [10 ⁻³ mg / cm ² ] of the cutout waveform of the toner adhesion fluctuation amount
A _i : amplitude of sine wave [10 ⁻³ mg / cm ² ]
.Omega .: Angular velocity of the sleeve or photoconductor [rad / s]
・ Θ _i : Phase of sine wave [rad]
T: Time [s]

The image forming apparatus 1 calculates Ai and θi by orthogonal detection, and calculates density unevenness components for each frequency. Then, the image forming apparatus 1 constructs a reproduction waveform for constructing the development fluctuation pattern data for the sleeve cycle and a reproduction waveform for constructing the development fluctuation pattern data for the photosensitive member cycle based on the following equations. .
f _1/2 (t) = ΣA _i × sin (i × ωt + θ _i )
: However, i = 1 to 3
i = 1 is a rotation period of the sleeve or the photosensitive member.

  Although the construction of the development fluctuation pattern data has been described, the charging fluctuation pattern data is constructed in the same manner.

  FIG. 18 is a graph showing an average waveform that is referred to when constructing latent image fluctuation pattern data for changing the amount of writing light, and a change with time of the toner adhesion fluctuation amount in a reproduction waveform obtained by converting the average waveform for reproduction. is there. In the image forming apparatus 1, during the print job, the amount of writing on the photoconductor is changed based on the latent image fluctuation pattern data, thereby suppressing the residual period fluctuation of the image density. The latent image variation pattern data is constructed based on the density variation pattern of the solid density variation detection toner image formed to construct the development variation pattern data. As described above, the development fluctuation pattern data and the charging fluctuation pattern data are constructed based on a reproduced waveform obtained by extracting up to a period fluctuation component having a frequency three times the sleeve rotation period. For this reason, a high-frequency periodic fluctuation component remains as image density unevenness. This is the residual period fluctuation of the image density of the image forming apparatus 1. This residual cycle fluctuation pattern can be grasped based on the density unevenness pattern of the solid density unevenness detection toner image formed to construct the development fluctuation pattern data.

Image density fluctuations due to fluctuations in the amount of writing light can be generated in units of dots, so that it can be used as an effective means for canceling periodic fluctuation components that occur at high frequency periods. is there. Therefore, the control unit 110 constructs a reproduction waveform for constructing the latent image variation pattern data for the sleeve period and a reproduction waveform for constructing the latent image variation pattern data for the photosensitive member period based on the following equations. To do.
f ₃ (t) = ΣA _i × sin (i × ωt + θ _i )
: However, i = 4-20 natural number

  The reproduced waveform constructed in this way is shown in FIG. Based on the reproduced waveform, latent image fluctuation pattern data for the sleeve period and latent image fluctuation pattern data for the photosensitive member period are constructed. These data are data reflecting the amount of writing light (optical writing intensity LDP (laser diode power) [%]). It is only necessary to multiply the write light amount by an appropriate gain so as to reduce the high frequency component in the target image density. In the present invention, the exposure intensity: LD power is periodically changed so as to cancel out the high frequency component indicated by the thick line in FIG.

  When forming an image based on a user command, the latent image fluctuation pattern data for the photoreceptor period, the latent image fluctuation pattern data for the sleeve period, the photoreceptor reference posture timing, and the sleeve reference posture timing are used. Thus, the following superimposition variation pattern data is constructed. That is, it is superimposition variation pattern data for generating a superimposition variation waveform in which a latent image variation waveform (write light amount variation waveform) of the photosensitive member rotation cycle and a latent image variation waveform of the sleeve rotation cycle are superimposed. The superimposed variation pattern data is sequentially transmitted from the control unit 110 to the write control unit 125. The writing control unit 125 periodically varies the writing light amount based on the superimposed variation pattern data. Such processing is performed individually for each of the colors Y, C, M, and K.

  FIG. 19 is a graph showing the relationship between the absolute value of the latent image potential and the write light quantity or the development potential. In such a configuration, it is possible to effectively suppress the high frequency residual period fluctuation that remains even if the development bias and the charging bias are cyclically changed. In addition, the following effects can also be achieved. That is, as shown in FIG. 19, due to the light attenuation characteristics of the photoconductor, the electric field fluctuation is reduced in the high image density region, and therefore there is a limit to the width that can be corrected. This is because the latent image potential is unlikely to fluctuate, and the correction range of the toner adhesion amount is narrowed. In general, the amplitude of the periodic fluctuation of the image density generated in the sleeve rotation cycle or the photoconductor rotation cycle is larger as the low-frequency component is smaller, and is smaller as the frequency component is higher. In the image forming apparatus 1, a low-frequency periodic fluctuation component capable of ensuring a large amplitude is reduced by a development bias or a charging bias periodic fluctuation. On the other hand, a high frequency periodic fluctuation component having a relatively small amplitude is corrected by the amount of writing light. As a result, even in a high image density region, it is possible to ensure the desired fluctuation range of the latent image potential without saturating the writing light amount at the upper limit.

  FIG. 20 is a flowchart illustrating a processing flow of control performed by the control unit (the control unit 110 and the writing control unit 125) of the image forming apparatus 1. The control means first forms a solid density unevenness detection toner image (step S1). At this time, the developing bias, the charging bias, and the writing light amount are set to constant values. Next, the control means detects the density unevenness pattern of the solid density unevenness detection toner image (step S2), and then constructs development fluctuation pattern data based on the density unevenness pattern and the like (step S3). After that, the control means forms a halftone density unevenness detection toner image while periodically changing the development bias based on the development fluctuation pattern data (step S4), and then the density unevenness of the halftone density unevenness detection toner image. A pattern is detected (step S5). Further, the control means constructs the charge fluctuation pattern data based on the density unevenness pattern or the like (step S6), and then latentizes based on the density unevenness pattern of the solid density unevenness detection toner image detected in S2. Image variation pattern data is constructed (step S7). Finally, the control means updates each of the development fluctuation pattern data, the charge fluctuation pattern data, and the latent image fluctuation pattern data stored until immediately before the start of the control to new data obtained by this control (step). S8). The control means individually executes such a series of processing flows for each of Y, C, M, and K. Regarding implementation, processing for only one color may be performed in order, or processing for two or more colors may be performed in parallel.

(FIGS. 21 to 28: Further configurations of the image forming apparatus 1)
Next, with reference to FIGS. 21 to 28, a description will be given of a further configuration relating to correction of print density, which is included in the image forming apparatus 1 according to the first embodiment of the present invention.

(ADC 115 and correction unit 500)
FIG. 21 is a diagram showing a partial configuration of the image forming apparatus 1 according to the first embodiment of the present invention. As shown in FIG. 21, the image forming apparatus 1 according to the present embodiment further includes an ADC (analog-digital converter) 115 and a correction unit 500 in the control unit 110. The ADC 115 converts the analog signal output from the toner density sensor 82 into a digital signal. The correction unit 500 corrects the print density based on the output values from the sensors (toner density sensor 82, photoconductor rotation sensor 76, and sleeve rotation sensor 83) of the image forming unit 18. As a result, the correction unit 500 can eliminate printing unevenness due to fluctuations in the sampling period caused by defects in the rotating body (for example, the photoconductor 20 and the developing sleeve 81). Hereinafter, this point will be specifically described.

(Functional configuration of the correction unit 500)
FIG. 22 is a diagram illustrating a functional configuration of the correction unit 500 according to the first embodiment of the present invention. As illustrated in FIG. 22, the correction unit 500 includes a data input unit 510, a correction processing unit 520, a data storage unit 530, a CPU IF unit 540, an interrupt control / error processing unit 550, and a processing target data control unit 560.

  The data input unit 510 includes an ADC IF unit 511, a sensor IF unit 512, a buffer 513, a buffer 514, a buffer 515, and a buffer 516. The ADC IF unit 511 receives the toner density value output from the ADC 115. The ADC IF unit 511 converts the toner density value input as serial data into parallel data. The sensor IF unit 512 receives an attitude timing signal (hereinafter referred to as “HP (Home Position) signal”) output from the photosensitive member rotation sensor 76 and the sleeve rotation sensor 83. This HP signal can be used to specify the rotation cycle of the rotator (photosensitive member 20 and data input unit 510). For example, a period from when one HP signal is received until the next HP signal is received can be specified as one rotation period (HP period) of the rotating body.

  Based on the HP signal received by the sensor IF unit 512, the buffers 513 to 516 convert the toner density value received by the ADC IF unit 511 into an even number of turns (0, 2, 4,...) For each rotating body. And odd-numbered turns (1, 3, 5,...) Are stored separately.

  Specifically, the buffer 513 stores the toner density value detected in the even number circumference of the photoconductor 20 among the toner density values received by the ADC IF unit 511. Further, the buffer 514 stores toner density values detected in odd-numbered circumferences of the photoconductor 20 among the toner density values received by the ADC IF unit 511.

  The buffer 515 stores the toner density value detected in the even circumference of the developing sleeve 81 among the toner density values received by the ADC IF unit 511. The buffer 516 stores the toner density value detected in the odd number circumference of the developing sleeve 81 among the toner density values received by the ADC IF unit 511.

  The correction processing unit 520 includes an averaging processing unit 521, an adhesion amount conversion processing unit 522, and an orthogonal detection unit 523. The averaging processing unit 521 performs the above-described averaging process. The adhesion amount conversion processing unit 522 performs the adhesion amount conversion process described above. The quadrature detection unit 523 performs the above-described quadrature detection. The correction processing unit 520 performs a series of correction processing (averaging processing, adhesion amount conversion processing, and quadrature detection) for each rotating body, distinguishing between even and odd cycles (that is, for each of the buffers 513 to 516). Do.

  For example, the correction processing unit 520 includes first to fourth processing units that can perform parallel processing. The first processing unit performs a series of correction processing on the processing target data for the even number of revolutions of the photoconductor 20 stored in the buffer 513. The second processing unit performs a series of correction processing on the processing target data for odd-numbered circumferences of the photoconductor 20 stored in the buffer 514. The third processing unit performs a series of correction processes on the processing target data for the even number of turns of the developing sleeve 81 stored in the buffer 515. The fourth processing unit performs a series of correction processing on the processing target data for odd-numbered circumferences of the developing sleeve 81 stored in the buffer 516.

  The data storage unit 530 stores processing result data by the correction processing unit 520 (that is, processing result data of each of the first to fourth processing units). When storing the processing result data, the data storage unit 530 outputs an end interrupt to the interrupt control / error processing unit 550.

  The CPU IF unit 540 performs an interface with the CPU. For example, when an end interrupt from the interrupt control / error processing unit 550 is detected by the CPU, the CPU reads the processing result data stored in the data storage unit 530 via the CPU IF unit 540.

  The processing target data control unit 560 performs a series of corrections by the correction processing unit 520 among the toner density values received by the ADC IF unit 511 for each HP cycle (for each rotation cycle) of the rotating body (the photoconductor 20 and the developing sleeve 81). A predetermined number of process target data to be corrected is determined. The details of the process for determining the process target data by the process target data control unit 560 will be described with reference to FIG.

(Processing target data determined by the processing target data control unit 560)
23 and 24 are conceptual diagrams showing the processing target data determined by the processing target data control unit 560 according to the first embodiment of the present invention. FIG. 23 shows the processing target data determined by the processing target data control unit 560 when the HP cycle is shorter than the theoretical value. On the other hand, FIG. 24 illustrates the processing target data determined by the processing target data control unit 560 when the HP cycle is longer than the theoretical value.

  Here, in the correction unit 500, a predetermined number of processing target data for one cycle is determined in advance according to the theoretical value of the HP cycle (cycle from HP position detection to next HP position detection (real time)). It has been. However, when the periodic variation of the rotating body occurs, the HP cycle may be shorter or longer than the theoretical value. In this case, the processing target data control unit 560 determines processing target data for one cycle as follows.

  As shown in FIG. 23, when the HP cycle is shorter than the theoretical value, the HP of the second round (HP2 in the figure) is detected before the number of data acquisitions of the first round reaches a predetermined number. In this case, the processing target data control unit 560 stores data until the number of data acquisitions in the first round reaches a predetermined number (shaded portion in the figure) in the buffer as processing target data in the first round. The processing target data for the second round is also stored in the buffer.

  On the other hand, as shown in FIG. 24, when the HP cycle is longer than the theoretical value, the HP for the second round (HP2 in the figure) is not detected even after the number of data acquisitions for the first round reaches a predetermined number. Become. In this case, the processing target data control unit 560 discards the data until the second round HP (HP2 in the figure) is detected (the hatched portion in the figure) instead of the processing target data.

  In this way, the processing target data control unit 560 processes a predetermined number of data for each HP cycle, both when the HP cycle is shorter than the theoretical value and when the HP cycle is longer than the theoretical value. Determine as target data.

  FIG. 25 is a diagram illustrating a specific example of the processing target data determined by the processing target data control unit 560 according to the first embodiment of the present invention. Here, three consecutive HP cycles will be described as an example. Here, the predetermined number of data to be processed according to the theoretical value of the HP cycle is “624”.

  As shown in FIG. 25A, when all three HP periods coincide with the theoretical values, 624 pieces of data are acquired in each HP period. In this case, the processing target data control unit 560 determines, for each HP cycle, 624 data acquired in the HP cycle as processing target data.

  Further, as shown in FIG. 25B, when the HP cycle of the first round is longer than the theoretical value, 624 or more data are acquired in the HP cycle. In this case, the processing target data control unit 560 sets up to 624 pieces of data as processing target data for the HP cycle, and discards the subsequent data (the hatched portion in the figure) without setting it as processing target data. In this case, the number of data necessary for the correction process of the three HP cycles is the number of data discarded in the 624 × 3 + 1 round.

  Further, as shown in FIG. 25C, when the HP cycle of the first round is shorter than the theoretical value, less than 624 data are acquired in the HP cycle. In this case, the processing target data control unit 560 adds the less than 624 data acquired in the HP cycle and the data acquired in the second HP cycle (the hatched portion in the figure). 624 pieces of data are set as data to be processed in the HP cycle. In this case, the number of data necessary for the correction process of the three HP cycles is the number of data deficient in the 624 × 3-1 round.

  In FIG. 25, the method for determining the processing target data for the photosensitive member 20 has been described. However, the method for determining the processing target data for the developing sleeve 81 is the same (however, the HP cycle (for the photosensitive member 20 and the developing sleeve 81) That is, the predetermined number of processing target data) is different).

(Timing chart of various signals used by the correction unit 500)
FIG. 26 is a timing chart of various signals used by the processing target data control unit 560 according to the first embodiment of the present invention.

  The HP signal shown in FIG. 26 (first stage) is a signal supplied from the photoconductor rotation sensor 76 and is a signal that can specify the HP cycle of the photoconductor 20.

  The start signal shown in FIG. 26 (fourth and fifth stages) is a pulse generated by detecting the assertion of the HP signal. In the example shown in FIG. 26, every time an assertion of the HP signal is detected, an even start signal (fourth stage) indicating the start of an even number of cycles and an odd start signal (fifth stage) indicating the start of an odd number of cycles are generated. Are generated alternately.

  The HP enable signal shown in FIG. 26 (second and third stages) is a signal which is set to H during the enable period, and is a period until a predetermined number of data is acquired. In the example shown in FIG. 26, an even HP enable signal (second stage) for even-numbered turns and an oddHP enable signal (third stage) for odd-numbered turns are shown. The enable period of the evenHP enable signal starts with the generation of the even start signal pulse. On the other hand, the enable period of the oddHP enable signal starts with the generation of the pulse of the odd start signal.

  The enable period of each HP enable signal is a period until a predetermined number of data is acquired according to the theoretical value of the HP cycle. Therefore, when a deviation from the theoretical value occurs in the actual HP period, the enable period of each HP enable signal is different from the period of the HP signal.

  In FIG. 26, various signals used for the correction process for the photosensitive member 20 have been described. Similarly, for the correction process for the developing sleeve 81, the HP signal, the enable signal, and the signal corresponding to the HP cycle of the developing sleeve 81 are also described. A start signal is used (however, the HP cycle (that is, the predetermined number of data to be processed) differs between the photoconductor 20 and the developing sleeve 81).

(Specific example of processing target data determination processing by the processing target data control unit 560)
27 and 28 are diagrams illustrating specific examples of processing target data determination processing by the processing target data control unit 560 according to the first embodiment of the present invention. Here, the predetermined number of data to be processed according to the theoretical value of the HP cycle is “624”. Here, the toner density data acquired by the ADC 115 is referred to as “ADC acquisition data”.

  FIG. 27 illustrates a case where the HP cycle of the first round is shorter than the theoretical value. In the example of FIG. 27, first, the enable period of the evenHP enable signal is started together with the generation of an even start signal pulse indicating the start of the HP cycle of the first round. In this case, the process target data control unit 560 determines the subsequent ADC acquisition data as the process target data 0, 1, 2, 3,.

  Subsequently, the enable period of the oddHP enable signal is started together with the generation of the pulse of the odd start signal indicating the start of the HP cycle of the second round. In this case, the processing target data control unit 560 determines the subsequent ADC acquisition data as the processing target data 0, 1, 2, 3,.

  In the example shown in FIG. 27, when the processing target data 620 (621-th processing data) of the first cycle HP cycle is determined, the second cycle HP cycle is started. In this case, the processing target data control unit 560 obtains 621 ADC acquisition data acquired in the first cycle HP cycle and three ADC acquisition data acquired in the next second HP cycle (see FIG. 624 ADC acquisition data obtained by adding the middle I1) are determined as processing target data for the first cycle of the HP cycle. That is, the processing target data 0, 1, 2 of the second cycle HP cycle is also used as the processing target data 621, 622, 623 of the first cycle HP cycle. As a result, a predetermined number of 624 pieces of data are determined as the processing target data of the HP cycle of the first round.

  FIG. 28 illustrates a case where the HP cycle of the first round is longer than the theoretical value. In the example of FIG. 28, first, the enable period of the evenHP enable signal is started together with the generation of an even start signal pulse indicating the start of the HP cycle of the first round. In this case, the correction unit 500 determines the subsequent ADC acquisition data as the processing target data 0, 1, 2, 3,.

  Subsequently, the enable period of the oddHP enable signal is started together with the generation of the pulse of the odd start signal indicating the start of the HP cycle of the second round. In this case, the correction unit 500 determines the subsequent ADC acquisition data as the processing target data 0, 1, 2, 3,.

  In the example shown in FIG. 27, when the processing target data 623 (624th processing data) of the HP cycle of the first cycle is determined, the HP cycle of the second cycle has not yet started. In this case, the correction unit 500 discards more than 624 pieces of ADC acquisition data (I2 in the figure) among the ADC acquisition data acquired until the second cycle HP cycle is started. As a result, a predetermined number of 624 pieces of data are determined as the processing target data of the HP cycle of the first round.

  27 and 28, the processing target data determination method for the photosensitive member 20 has been described. However, the processing target data determination method for the developing sleeve 81 is the same (however, the photosensitive member 20 and the developing sleeve 81 are the same). HP cycle (that is, a predetermined number of data to be processed) is different).

  As described above, the image forming apparatus 1 according to the first embodiment of the present invention determines a predetermined number of toner density values as processing target data for each rotation cycle of the rotating body (the photoconductor 20 and the developing sleeve 81). Then, predetermined correction processing (averaging processing, adhesion amount conversion processing, and quadrature detection) is performed using the processing target data. For this reason, according to the image forming apparatus 1, even when temporal unevenness occurs in the rotation cycle of the rotating body, it is possible to prevent fluctuations in correction data for correcting the print density. . Therefore, according to the image forming apparatus 1, the print density can be corrected with high accuracy.

[Second Embodiment]
FIG. 29 is a diagram illustrating a functional configuration of a correction unit 500 ′ according to the second embodiment of the present invention. Here, changes from the first embodiment will be described. 29 is different from the correction unit 500 of the first embodiment (FIG. 22) in that it further includes a second data storage unit 570. The correction unit 500 ′ of the second embodiment is configured to supply a mode selection signal input from the CPU (see FIG. 21) via the CPU IF unit 540 to the data input unit 510 and the correction processing unit 520. ing. Then, the correction unit 500 ′ uses the mode selection signal to perform a first correction process (when in the HP detection mode) accompanied by a fluctuation factor of the rotating body and a second correction process (when the fluctuation factor of the rotating body is not involved) It is configured so that it is possible to selectively switch between the case of not being in the HP detection mode and the case of performing process control. Hereinafter, each case will be described.

(When selection is made not to perform quadrature detection)
When selection is made not to perform quadrature detection by the mode selection signal, the correction unit 500 ′ performs averaging processing and adhesion amount as the second correction processing that does not involve a variation factor of the rotating body without performing quadrature detection. Implement one or both of the conversion processes. Then, the correction unit 500 ′ stores at least one of the ADC acquisition data, the averaged data, and the adhesion amount conversion value in the second data storage unit 570 as the processing result data. That is, in this case, the processing result data stored in the second data storage unit 570 is read out by the CPU. In this case, since quadrature detection is not performed, it is not necessary to consider the rotation unevenness of the rotating body, and therefore data acquisition synchronized with the origin of the HP signal is not necessary. Therefore, the correction unit 500 ′ does not need to perform the correction process (one or both of the averaging process and the adhesion amount conversion process) for each rotating body, and does not need to be performed for each HP cycle. Therefore, the correction unit 500 ′ may acquire the processing result data from the processing system of the processing target data stored in any one of the buffers 513 to 516. For example, in the example shown in FIG. 29, the processing result data is obtained from the processing system of the processing target data (data on the even number of circumferences of the photoconductor 20) stored in the buffer 513.

(When selection to perform quadrature detection is made)
When the selection to perform the quadrature detection is made by the mode selection signal, the correction unit 500 ′ performs the first correction process with the variation factor of the rotator as described in the first embodiment for each rotator, and A predetermined number of data to be processed is determined for each HP cycle based on the HP signal. Then, the correction unit 500 ′ uses a predetermined number of processing target data determined separately for even and odd cycles for each rotating body, and performs a series of correction processing (averaging processing, adhesion amount conversion processing, And quadrature detection). Then, the correction unit 500 ′ stores processing result data of a series of correction processes in the data storage unit 530. That is, in this case, the processing result data stored in the data storage unit 530 is read by the CPU.

(Processing procedure by the correction unit 500 ′)
FIG. 30 is a flowchart illustrating a processing procedure performed by the correction unit 500 ′ according to the second embodiment of the present invention.

  First, the ADC IF unit 511 acquires the toner density value output from the ADC 115 (step S3001). Next, based on the mode selection signal input from the CPU (see FIG. 21) via the CPU IF unit 540, the data input unit 510 determines whether the HP detection mode is set (step S3002).

  If it is determined in step S3002 that the current mode is not the HP detection mode (step S3002: No), the data input unit 510 stores the toner density value acquired in step S3001 in the buffer 513 as processing target data as it is (step S3002: NO). Step S3003). Then, the averaging processing unit 521 performs an averaging process using the processing target data stored in the buffer 513 (step S3004). Further, the adhesion amount conversion processing unit 522 performs an adhesion amount conversion process using the processing target data stored in the buffer 513 (step S3005). Then, the correction processing unit 520 stores the processing result data of steps S3004 and S3005 in the second data storage unit 570 (step S3006), and the correction unit 500 ′ advances the process to step S3013.

  On the other hand, if it is determined in step S3002 that the current mode is the HP detection mode (step S3002: Yes), the processing data control unit 560 determines for each rotating body and every HP cycle from the toner density values acquired in step S3001. Then, processing target data is determined (step S3007). Then, the data input unit 510 stores the processing target data determined in step S3004 in the buffers 513 to 516 for each rotating body and for each HP cycle (for each even number and odd number) (step S3008).

  Subsequently, the averaging processing unit 521 uses the processing target data stored in the buffers 513 to 516 to perform an averaging process for each rotating body and for each HP cycle (even-numbered and odd-numbered cycles) (step S3009). . Further, the adhesion amount conversion processing unit 522 performs the adhesion amount conversion process for each rotating body and for each HP cycle (for each even number and odd number) using the processing target data stored in the buffers 513 to 516 (step S3010). ). Further, the quadrature detection unit 523 performs quadrature detection for each rotating body and for each HP cycle (for each even number and odd number) using the processing target data stored in the buffers 513 to 516 (step S3011). Then, the correction processing unit 520 stores the processing result data of steps S3009 to S3011 in the data storage unit 530 (step S3012), and the correction unit 500 ′ advances the process to step S3013.

  In step S3013, the interrupt control / error processing unit 550 outputs an end interrupt to the CPU. Then, the correction unit 500 ′ ends the series of processes shown in FIG.

  According to the correction unit 500 ′ of the second embodiment, it is possible to realize the first correction process with the variation factor of the rotating body and the second correction process without the variation factor of the rotation body with the same circuit. Therefore, the circuit scale concerning these correction processes can be suppressed.

(Modification)
FIG. 31 is a diagram showing a modification of the correction unit 500 ′ according to the second embodiment of the present invention. A correction unit 500 ″ shown in FIG. 31 is a modification of the correction unit 500 ′ of the second embodiment, and supplies a mode selection signal input from an external terminal to the data input unit 510 and the correction processing unit 520. It is configured.

  According to this modification, once the mode selection signal is supplied from the external terminal to the correction unit 500 ″, the correction process executed by the correction unit 500 ″ is changed to the first correction process or the second correction process. Can be fixed. In other words, according to this modification, it is not necessary to supply the mode selection signal to the correction unit 500 '' unless the correction process executed by the correction unit 500 '' is changed. Such a load can be suppressed.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to these embodiments, and various modifications or changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 18 Image forming unit 20 Photoconductor 81 Developing sleeve 82 Toner density sensor 76 Photoconductor rotation sensor 83 Sleeve rotation sensor 110 Controller 115 ADC
500, 500 ′, 500 ″ correction unit 510 data input unit 511 ADC IF unit 512 sensor IF unit 513 to 516 buffer 520 correction processing unit 521 averaging processing unit 522 adhesion amount conversion processing unit 523 orthogonal detection unit 530 data storage unit 540 CPU IF unit 550 Interrupt control / error processing unit 560 Processing target data control unit 570 Second data storage unit

JP 2007-140402 A

Claims (8)

A data input unit for inputting a plurality of toner density values continuously detected by the sensor as the rotating body rotates;
A processing target data control unit that determines a predetermined number of toner density values as processing target data from the plurality of toner density values for each rotation period of the rotating body;
A correction processing unit that performs a predetermined correction process for correcting the print density using the processing target data determined by the processing target data control unit for each rotation period of the rotating body. Image forming apparatus. The processing target data control unit
The predetermined number of toner density values are determined as the processing target data for each of an even number of rotations of the rotating body and an odd number of rotations of the rotating body,
The correction processing unit
The predetermined correction process using the processing target data of the even number of turns of the rotating body and the predetermined correction process using the processing target data of the odd number of turns of the rotating body are performed in parallel. The image forming apparatus according to claim 1. The processing target data control unit
When the number of the plurality of toner density values detected by the sensor does not reach the predetermined number in one rotation period, the toner density value detected by the sensor in the next rotation period is included. The image forming apparatus according to claim 1, wherein the predetermined number of toner density values are determined as the processing target data. The processing target data control unit
When the number of the plurality of toner density values detected by the sensor exceeds the predetermined number in one rotation period, the predetermined number of toner density values excluding the amount exceeding the predetermined number are processed in the processing. The image forming apparatus according to claim 1, wherein the image forming apparatus determines the target data. The processing target data control unit
For each of a plurality of rotating bodies provided in the image forming apparatus, the predetermined number of toner density values are determined as the processing target data,
The correction processing unit
The image forming apparatus according to claim 1, wherein the plurality of predetermined correction processes for each of the rotating bodies are performed in parallel. The correction processing unit
It is possible to selectively switch between the first predetermined correction process involving the fluctuation factor of the rotating body and the second predetermined correction process not involving the fluctuation factor of the rotating body. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An external terminal to which a mode selection signal for switching selection of the first predetermined correction process or the second predetermined correction process is input;
The correction processing unit
When one mode selection signal is input, until the next mode selection signal is input, the first predetermined correction process or the second predetermined process selected by the one mode selection signal The image forming apparatus according to claim 6, wherein the correction processing is repeatedly performed. A data input step in which a plurality of toner density values continuously detected by the sensor as the rotating body rotates are input;
A processing target data determining step for determining a predetermined number of toner density values as processing target data from the plurality of toner density values for each rotation period of the rotating body;
A correction processing step of performing a predetermined correction process for correcting the print density using the processing target data determined in the processing target data determination step for each rotation period of the rotating body. Correction method.

Images