JP2015035005A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in conventional detection of a toner image for the detection by an optical sensor, and to bring usability to an image forming apparatus.SOLUTION: An image forming apparatus includes process means closely arranged around each photoreceptor and acting on the photoreceptor. An electrostatic latent image for detection is formed on the photoreceptor by light-irradiating means; passing of the electrostatic latent image at a position opposing to the process means is detected; and correction of color shift is controlled on the basis of the detection result.

Description

  The present invention relates to a color image forming apparatus using an electrophotographic method, and more particularly to an image forming apparatus capable of forming an electrostatic latent image.

  In an electrophotographic color image forming apparatus, a so-called in-line method in which an image forming unit for each color is independently provided for high-speed printing is known. In this in-line type color image forming apparatus, an image is sequentially transferred from an image forming portion of each color to an intermediate transfer belt, and further, an image is transferred collectively from the intermediate transfer belt to a recording medium.

  In such a color image forming apparatus, color misregistration (positional misregistration) occurs when images are overlapped due to mechanical factors in the image forming unit of each color. In particular, in a configuration having a laser scanner (optical scanning device) and a photosensitive drum independently in each color image forming unit, the positional relationship between the laser scanner and the photosensitive drum differs for each color, and the laser on the photosensitive drum is different. The scanning position cannot be synchronized and color misregistration occurs.

  In order to correct these color misregistrations, color misregistration correction control is performed in the color image forming apparatus as described above. In Patent Document 1, a detection toner image of each color is transferred from a photosensitive drum onto an image carrier (such as an intermediate transfer belt), and the relative position of the detection toner image in the scanning direction and the conveyance direction is measured using an optical sensor. Thus, color misregistration correction control is performed.

JP-A-7-234612

  However, the detection of the detection toner image by the optical sensor in the conventionally known color misregistration correction control has the following problems. That is, since the toner image for detection (100% density) in the color misregistration correction control is used from the photosensitive drum to the image carrier (belt), it takes time for cleaning and the like, and the usability of the image forming apparatus is reduced. I will let you.

  An object of the present invention is to solve at least one of such problems and other problems. For example, an object of the present invention is to eliminate the problem of conventional detection of a toner image for detection by an optical sensor and to provide usability of an image forming apparatus. Other issues can be understood throughout the specification.

  In order to solve the above-described problems, the present invention has the following configuration.

(1) A photoconductor that is driven to rotate, a process unit that is disposed in the vicinity of the photoconductor and acts on the photoconductor, and light irradiation that forms an electrostatic latent image on the photoconductor by performing light irradiation. A color image forming apparatus for forming a toner image on a belt by operating the image forming unit, the light irradiating unit corresponding to each color. Forming means for controlling and forming an electrostatic latent image for color misregistration on each color photoconductor, power source means for the process means corresponding to each color, and color misregistration correction formed on the photoconductor for each color Detecting the output of the power supply means for each color when the electrostatic latent image for use passes through the position facing the process means, and returning the color misregistration state to the reference state based on the detection result by the detection means. The color misregistration correction control is performed on Characterized in that it comprises a control means.

  According to the present invention, it is possible to eliminate the problem in the conventional detection of the toner image for detection by the optical sensor and to provide the usability of the image forming apparatus.

1 is a configuration diagram of an inline type (4-drum system) color image forming apparatus. FIG. It is a block diagram of a high voltage power supply device. 2 is a block diagram of a hardware configuration of a printer system. FIG. It is a circuit diagram of a high voltage power supply. It is a flowchart which shows a reference value acquisition process. FIG. 6 is a diagram illustrating an example of a state of forming a color misregistration detection mark (for color misregistration correction) formed on an intermediate transfer belt. FIG. 6 is a diagram illustrating a state where an electrostatic latent image for color misregistration detection (color misregistration correction) is formed on a photosensitive drum. It is a figure which shows an example of the surface potential information detection result of a photosensitive drum. (A) Schematic diagram showing the surface potential of the photosensitive drum when no toner is attached on the electrostatic latent image, (b) Surface potential of the photosensitive drum when the toner is attached on the electrostatic latent image It is a schematic diagram which shows. It is a figure which shows the flowchart of color misregistration correction control. It is a block diagram of another in-line type (4-drum type) color image forming apparatus. It is a flowchart which shows another reference value acquisition process. It is a figure which shows the flowchart of another color misregistration correction control. It is a figure which shows an example of the dispersion | distribution mode of the photosensitive drum phase at the time of data sampling. It is a figure for demonstrating paper size and a non-image area width. (A) Circuit diagram of another high-voltage power source, (b) Circuit diagram of another high-voltage power source provided with another current detection circuit, (c) A diagram showing an example of the surface potential information detection result of the photosensitive drum. It is a block diagram of another high voltage power supply device. It is a circuit diagram of another high voltage power supply device. It is a flowchart which shows another reference value acquisition process. FIG. 6 is a diagram illustrating a state where an electrostatic latent image for color misregistration detection (color misregistration correction) for each color is formed on a photosensitive drum. It is a figure which shows the flowchart of another color misregistration correction control. It is a block diagram of another high voltage power supply device. It is a flowchart which shows another reference value acquisition process. It is a flowchart which shows another reference value acquisition process. 6 is a timing chart relating to formation of an electrostatic latent image for color misregistration detection (color misregistration correction). It is a figure which shows the flowchart of another color misregistration correction control. It is a figure which shows the flowchart of another color misregistration correction control. It is a flowchart which shows another reference value acquisition process. It is a figure which shows the flowchart of another color misregistration correction control.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the constituent elements described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them.

[Configuration diagram of in-line (4-drum) color image forming apparatus]
FIG. 1 is a configuration diagram of a color image forming apparatus 10 of an inline type (4-drum system). The recording medium 12 fed out by the pickup roller 13 is temporarily stopped from being transported at a position where the front end slightly passes through the pair of transport rollers 14 and 15 after the front end position is detected by the registration sensor 111.

  On the other hand, the scanner units 20a to 20d sequentially irradiate laser beams 21a to 21d to the photosensitive drums 22a to 22d serving as rotationally driven photosensitive members. At this time, the photosensitive drums 22a to 22d are previously charged by the charging rollers 23a to 23d. Each charging roller outputs a voltage of −1200 V, for example, and the surface of the photosensitive drum is charged at −700 V, for example. When an electrostatic latent image is formed by irradiation of the laser beams 21a to 21d at this charging potential, the potential of the portion where the electrostatic latent image is formed becomes, for example, -100V. The developing units 25a to 25d and the developing sleeves 24a to 24d output a voltage of −350 V, for example, and put toner on the electrostatic latent images on the photosensitive drums 22a to 22d to form toner images on the photosensitive drums. The primary transfer rollers 26a to 26d output a positive voltage of +1000 V, for example, and transfer the toner images on the photosensitive drums 22a to 22d to the intermediate transfer belt 30 (endless belt). A group of members that directly form toner images of the charging roller, the developing device, and the primary transfer roller, including the scanner unit and the photosensitive drum, is referred to as an image forming unit. In some cases, the scanner unit 20 may not be included and may be referred to as an image forming unit. Each member (charging roller, developing device, and primary transfer roller) that is disposed in the vicinity of the periphery of the photosensitive drum and acts on the photosensitive drum is referred to as a process unit. In this way, the process means can correspond to a plurality of types of members.

  The intermediate transfer belt 30 is driven by rollers 31, 32, and 33 to convey the toner image to the position of the secondary transfer roller 27. At this time, conveyance of the recording medium 12 is resumed so that the timing coincides with the toner image conveyed at the position of the secondary transfer roller 27, and the secondary transfer roller 27 moves from the intermediate transfer belt 30 onto the recording material (on the recording medium 12). The toner image is transferred to the surface.

  Thereafter, the toner image on the recording medium 12 is heated and fixed by the fixing roller pairs 16 and 17, and then the recording medium 12 is output to the outside of the apparatus. Here, the toner that has not been transferred from the intermediate transfer belt 30 to the recording medium 12 by the secondary transfer roller 27 is collected in the waste toner container 36 by the cleaning blade 35. The operation of the color misregistration detection sensor 40 that performs toner image detection will be described later. Here, the alphabetic character a of each symbol indicates yellow, b indicates magenta, c indicates cyan, and d indicates black.

  In FIG. 1, the system for performing light irradiation by the scanner unit has been described. However, the present invention is not limited to this, and in the sense that color misregistration (position misregistration) occurs, for example, an image forming apparatus including an LED array as a light irradiation unit can be applied to each of the following embodiments. . In the following description, as an example, a case where a scanner unit is provided as a light irradiation unit will be described.

[Configuration diagram of high-voltage power supply unit]
Next, the configuration of the high-voltage power supply device in the image forming apparatus shown in FIG. 1 will be described with reference to FIGS. The high-voltage power supply circuit device shown in FIG. 2A includes a charging high-voltage power supply circuit 43, development high-voltage power supply circuits 44a to 44d, primary transfer high-voltage power supply circuits 46a to 46d, and a secondary transfer high-voltage power supply circuit 48. The charging high-voltage power supply circuit 43 forms a background potential on the surface of the photosensitive drums 22a to 22d by applying a voltage to the charging rollers 23a to 23d, so that an electrostatic latent image can be formed by laser light irradiation. To do. The development high-voltage power supply circuits 44a to 44d apply a voltage to the development sleeves 24a to 24d to place toner on the electrostatic latent images on the photosensitive drums 22a to 22d, thereby forming toner images. The primary transfer high-voltage power supply circuits 46 a to 46 d transfer the toner images on the photosensitive drums 22 a to 22 d to the intermediate transfer belt 30 by applying a voltage to the primary transfer rollers 26 a to 26 d. The secondary transfer high voltage power supply circuit 48 applies a voltage to the secondary transfer roller 27 to transfer the toner image on the intermediate transfer belt 30 to the recording medium 12.

  The primary transfer high-voltage power supply circuits 46a to 46d include current detection circuits 47a to 47d. This is because the toner image transfer performance of the primary transfer rollers 26a to 26d changes in accordance with the amount of current flowing through the primary transfer rollers 26a to 26d. The bias voltage (high voltage) for applying a voltage to the primary transfer rollers 26a to 26d is adjusted according to the detection results of the current detection circuits 47a to 47d, and the transfer performance is kept constant even when the temperature and humidity in the apparatus change. It is configured as follows. During primary transfer, constant voltage control is performed with a bias voltage set so that the amount of current flowing through the primary transfer rollers 26a to 26d becomes a target value.

  2B is different from FIG. 2A in that charging high-voltage power supply circuits 43a to 43d are individually provided for the charging rollers 23a to 23d. The charging high-voltage power supply circuits 43a to 43d are provided with current detection circuits 50a to 50d, respectively. Since the other configuration is the same as that of FIG. 2A, detailed description thereof is omitted here.

[Hardware block diagram of printer system]
Next, a general hardware configuration of the printer system will be described with reference to FIG. First, the video controller 200 will be described. A CPU 204 controls the entire video controller. A nonvolatile storage unit 205 stores various control codes executed by the CPU 204, and corresponds to a ROM, an EEPROM, a hard disk, or the like. A temporary storage RAM 206 functions as a main memory, work area, and the like for the CPU 204.

  Reference numeral 207 denotes a host interface unit (indicated as a host I / F in the figure) which is an input / output unit for printing data and control data with the external device 100 such as a host computer. The print data received by the host interface unit 207 is stored in the RAM 206 as compressed data. A data decompression unit 208 decompresses the compressed data. Arbitrary compressed data stored in the RAM 206 is expanded into image data in line units. The decompressed image data is stored in the RAM 206.

  Reference numeral 209 denotes a DMA (Direct Memory Access) control unit. The DMA control unit 209 transfers the image data in the RAM 206 to the engine interface unit 211 (described as engine I / F in the figure) in accordance with an instruction from the CPU 204. Reference numeral 210 denotes a panel interface unit (described as a panel I / F in the drawing) that receives various settings and instructions from the operator from a panel unit provided in the printer main body 1 of the color image forming apparatus 10 main body. Reference numeral 211 denotes an engine interface unit (denoted as engine I / F in the figure) which is a signal input / output unit with the printer engine 300, which sends data signals from an output buffer register (not shown) and Perform communication control. A system bus 212 has an address bus and a data bus. Each of the above-described components is connected to the system bus 212 and can access each other.

  Next, the printer engine 300 will be described. The printer engine 300 is roughly divided into an engine control unit 54 (hereinafter simply referred to as the control unit 54) and an engine mechanism unit. The engine mechanism is a part that operates according to various instructions from the controller 54. First, details of the engine mechanism will be described, and then the controller 54 will be described in detail.

  The laser / scanner system 331 includes a laser light emitting element, a laser driver circuit, a scanner motor, a polygon mirror, a scanner driver, and the like. This is a part where a latent image is formed on the photosensitive drum 22 by exposing and scanning the photosensitive drum 22 with laser light in accordance with image data sent from the video controller 200. The laser / scanner system 331 and the image forming system 332 described below correspond to a portion called an image forming unit described in FIG. The image forming system 332 is a central part of the image forming apparatus, and is a part that forms a toner image based on the latent image formed on the photosensitive drum 22 on the sheet (on the recording medium 12). Each process means (a plurality of types of process means) acting on the photosensitive drum 22 described above is also included. The process cartridge 11, the intermediate transfer belt 30, process elements such as a fixing device, and a high-voltage power supply circuit that generates various biases (high voltage) for image formation. In addition, a motor for driving each member such as a motor for driving the photosensitive drum 22 is also included.

  The process cartridge 11 includes a static eliminator, a charger 23 (charging roller 23), a developing device 25, a photosensitive drum 22, and the like. Further, the process cartridge 11 is provided with a nonvolatile memory tag, and the CPU 321 or the ASIC 322 reads / writes various information from / to the memory tag.

  The sheet feeding / conveying system 333 is a part that controls sheet feeding and conveyance of the sheet (recording medium 12), and includes various conveying system motors, a sheet feeding tray, a sheet discharging tray, various conveying rollers (such as a sheet discharging roller), and the like. Is done.

  The sensor system 334 is a sensor group for collecting information necessary for the CPU 321 and the ASIC 322 to be described later to control the laser / scanner system 331, the image forming system 332, and the paper feed / conveyance system 333. This sensor group includes at least various sensors already known, such as a temperature sensor for a fixing device and a density sensor for detecting the density of an image. Further, a color misregistration detection sensor 40 for detecting the toner image described above is also included. Although the sensor system 334 in the drawing is described separately as the laser / scanner system 331, the image forming system 332, and the paper feed / conveyance system 333, it may be considered to be included in any mechanism.

  Next, the control unit 54 will be described. A CPU 321 uses the RAM 323 as a main memory and work area, and controls the engine mechanism unit described above according to various control programs stored in the EEPROM 324. More specifically, the CPU 321 drives the laser / scanner system 331 based on a print control command and image data input from the video controller 200 via the engine I / F 211 and the engine I / F 325. A volatile memory with a backup battery may be substituted for the nonvolatile memory. The CPU 321 controls various print sequences by controlling the image forming system 332 and the paper feed / conveyance system 333. Further, the CPU 321 drives the sensor system 334 to acquire information necessary for controlling the image forming system 332 and the paper feed / conveyance system 333.

  On the other hand, the ASIC 322 performs high-voltage power supply control such as control of each motor and development bias for executing the various print sequences described above under the instruction of the CPU 321. Reference numeral 326 denotes a system bus having an address bus and a data bus. Each component of the control unit 54 is connected to the system bus 326 and is accessible to each other. Note that part or all of the functions of the CPU 321 may be performed by the ASIC 322, and conversely, part or all of the functions of the ASIC 322 may be performed by the CPU 321 instead.

[Circuit diagram of high-voltage power supply]
Next, the circuit configuration of the primary transfer high-voltage power supply circuit 46a in the high-voltage power supply device of FIG. 2 will be described with reference to FIG. Since the primary transfer high-voltage power supply circuits 46b to 46d for the other colors have the same circuit configuration, the description thereof is omitted.

  In FIG. 4, the transformer 62 boosts the voltage of the AC signal generated by the drive circuit 61 to an amplitude several tens of times. The rectifier circuit 51 including the diodes 64 and 65 and the capacitors 63 and 66 rectifies and smoothes the boosted AC signal. The rectified and smoothed voltage signal is output to the output terminal 53 as a DC voltage. The comparator 60 controls the output voltage of the drive circuit 61 so that the voltage of the output terminal 53 divided by the detection resistors 67 and 68 is equal to the voltage setting value 55 set by the control unit 54. Then, according to the voltage of the output terminal 53, a current flows through the primary transfer roller 26a, the photosensitive drum 22a, and the ground.

  Here, the current detection circuit 47 a is inserted between the secondary circuit 500 of the transformer 62 and the ground point 57. Further, since the input terminal of the operational amplifier 70 has high impedance and almost no current flows, almost all direct current flowing from the ground point 57 to the output terminal 53 through the secondary circuit 500 of the transformer 62 flows to the resistor 71. Has been. Further, since the inverting input terminal of the operational amplifier 70 is connected to the output terminal via the resistor 71 (negatively fed back), it is virtually grounded to the reference voltage 73 connected to the non-inverting input terminal. Therefore, a detection voltage 56 proportional to the amount of current flowing through the output terminal 53 appears at the output terminal of the operational amplifier 70. In other words, when the current flowing through the output terminal 53 changes, the current flowing through the resistor 71 changes in such a manner that the detection voltage 56 at the output terminal of the operational amplifier 70, not the inverting input terminal of the operational amplifier 70, changes. . The capacitor 72 is for stabilizing the inverting input terminal of the operational amplifier 70.

  The current characteristics of the primary transfer rollers 26a to 26d vary depending on factors such as the degree of deterioration of various members and the environment such as the in-machine temperature. Therefore, the control unit 54 measures the detection value 56 (detection voltage 56) of the current detection circuit 47a at the A / D input port at the timing immediately after the start of printing and before the toner image reaches the primary transfer roller 26a. Then, the voltage setting value 55 is set so that the detection value 56 (detection voltage) becomes a predetermined value. Thereby, the transfer performance of the toner image can be kept constant even when the ambient temperature, humidity, or the like changes.

[Description of color misregistration correction control]
Thereafter, by the image forming apparatus described above, a color misregistration detection mark is first formed on the intermediate transfer belt 30 to reduce the color misregistration amount at least. Then, after eliminating (at least reducing) the color misregistration state, the time for the electrostatic latent image 80 to reach the position of the primary transfer roller 26a is measured by detecting the change in the primary transfer current. Is set as a reference value for color misregistration correction control.

  In the color misregistration correction control that is performed when the apparatus internal temperature changes due to continuous printing or the like, the time for which the change in the primary transfer current is detected again and the electrostatic latent image 80 reaches the position of the primary transfer roller 26a. Measure. The change in the arrival time measured here reflects the color shift amount as it is. Accordingly, the timing at which the scanner unit 20a irradiates the laser beam 21a is adjusted so as to cancel this during printing, and color misregistration is corrected. Details will be described below. Note that the control of the image forming conditions related to correction for color misregistration is not limited to the control of the light irradiation timing. For example, the speed control of the photosensitive drum described in the second embodiment described later, or the mechanical position adjustment of the reflection mirror included in each of the scanner units 20a to 20d may be used.

[Reference Value Acquisition Process Flowchart]
The flowchart of FIG. 5 is a flowchart showing a reference value acquisition process in the color misregistration correction control. First, the flowchart of FIG. 5 is executed after color misregistration correction control (hereinafter referred to as normal color misregistration correction control) is performed by detecting the toner mark (FIG. 6) of the color misregistration detection sensor 40. Further, when the components such as the photosensitive drum 22 and the developing sleeve 24 are replaced and the normal color misregistration correction control is executed, the flowchart of FIG. 5 is executed corresponding to only the normal color misregistration correction control at a specific timing. Also good. Further, the flowchart of FIG. 5 is performed independently for each color. The color misregistration detection sensor 40 includes a light emitting element such as an LED, and the light emitting element emits light to the color misregistration detection toner image formed on the belt. It is configured to detect the position (detection timing) of the image. This is a technique already known from many documents, and detailed description thereof will be omitted here.

  The description of FIG. 5 will be given. In step S501, the control unit 54 causes the image forming unit to form a toner mark for color misregistration detection on the intermediate transfer belt 30. Since the toner mark for color misregistration detection is a toner image used for color misregistration correction, it can also be called a color misregistration correction toner image. Here, FIG. 6 shows how toner marks for color misregistration detection are formed. By the processing in step S501, it is possible to basically use a state in which the color misregistration amount is at least small in the subsequent control using the electrostatic latent image for color misregistration correction.

  In FIG. 6, reference numerals 400 and 401 denote patterns for detecting the amount of color misregistration in the paper transport direction (sub-scanning direction). Reference numerals 402 and 403 denote patterns for detecting the amount of color misregistration in the main scanning direction orthogonal to the paper transport direction, and in this example, the pattern is inclined 45 degrees. Further, tsf1 to 4, tmf1 to 4, tsr1 to 4, and tmr1 to 4 indicate detection timings of the respective patterns, and an arrow indicates a moving direction of the intermediate transfer belt 30.

The moving speed of the intermediate transfer belt 30 is vmm / s, Y is a reference color, and the theoretical distance between each color of the paper transport direction patterns (400, 401) and the Y pattern is dsMmm, dsCmm, dsBkm. With Y as a reference color, the color misregistration amount δes of each color in the transport direction is expressed by the following [Expression 1] to [Expression 3].
δesM = v × {(tsf2−tsf1) + (tsr2−tsr1)} / 2−dsM.
δesC = v × {(tsf3−tsf1) + (tsr3−tsr1)} / 2−dsC.
δesBk = v × {(tsf4−tsf1) + (tsr4−tsr1)} / 2−dsBk Equation 3
With respect to the main scanning direction, the positional deviation amounts δemf and δemr for each of the left and right colors are
dmfY = v × (tmf1−tsf1) Equation 4
dmfM = v × (tmf2−tsf2) Equation 5
dmfC = v × (tmf3-tsf3) Equation 6
dmfBk = v × (tmf4-tsf4) Equation 7
When,
dmrY = v × (tmr1−tsr1) Equation 8
dmrM = v × (tmr2−tsr2) Equation 9
dmrC = v × (tmr3-tsr3) Equation 10
dmrBk = v × (tmr4-tsr4) Equation 11
From
δemfM = dmfM−dmfY Equation 12
δemfC = dmfC−dmfY Equation 13
δemfBk = dmfBk−dmfY Equation 14
When,
δemrM = dmrM−dmrY Equation 15
δemrC = dmrC−dmrY Equation 16
δemrBk = dmrBk−dmrY Equation 17
Thus, the direction of deviation can be determined from the sign of the calculation result, and the writing position can be determined from δemf as δem.
The main scanning width (main scanning magnification) is corrected from r-δemf. When there is an error in the main scanning width (main scanning magnification), the writing position is calculated not only by δemf but also by taking into account the amount of change in the image frequency (image clock) that has changed with the main scanning width correction.

  Then, the control unit 54 changes the emission timing of the laser beam by the scanner unit 20a as an image forming condition so as to eliminate the calculated color misregistration amount. For example, if the amount of color misregistration in the sub-scanning direction is an amount of −4 lines, the control unit 54 instructs the video controller 200 to advance the laser light emission timing by +4 lines.

  In the description with reference to FIG. 6, the description has been made so that the color misregistration detection toner mark is formed on the intermediate transfer belt 30, but the color misregistration detection toner mark is formed where the optical sensor (color misregistration detection sensor) is formed. It is not limited to the form whether it detects by 40). For example, a toner mark for color misregistration detection may be formed on the photosensitive drum 22 and the detection result of a color misregistration detection sensor (optical sensor) arranged so as to be able to detect it may be used. Alternatively, a toner mark for color misregistration detection may be formed on paper (on a recording material), and a detection result of a color misregistration detection sensor (optical sensor) arranged so that it can be detected may be used. It is assumed that the toner marks for color misregistration detection are formed on various transferred materials or toner image carriers.

  Returning to the flowchart of FIG. In step S <b> 502, the control unit 54 sets the rotational phase relationship (rotational position relationship) between the photosensitive drums 22 a to 22 d in order to suppress the influence when the rotational speed (peripheral surface speed) of the photosensitive drums 22 a to 22 d varies. Adjust to a predetermined state. Specifically, under the control of the control unit 54, the phases of the photosensitive drums of other colors are adjusted with respect to the phase of the photosensitive drum of the reference color. Further, when a photosensitive drum driving gear is provided on the shaft of the photosensitive drum, the phase relationship of the driving gear of each photosensitive drum is substantially adjusted. As a result, the rotation speed of the photosensitive drum when the toner image developed on each photosensitive drum is transferred to the intermediate transfer belt 30 tends to be substantially the same or has a similar speed fluctuation tendency. Specifically, the control unit 54 issues a speed control instruction to a motor that drives a photosensitive drum (not shown) so that the rotational phase relationship between the photosensitive drums 22a to 22d matches a predetermined state. If the photosensitive drum rotation speed fluctuation is negligible, the process of step S502 may be omitted.

  In step S503, the control unit 54 causes the scanner units 20a to 20d to emit laser light at a predetermined rotational phase in each rotating photosensitive drum, and the electrostatic latent image for color misregistration correction on the photosensitive drum. (First color misalignment correcting electrostatic latent image) is formed.

  FIG. 7 is a diagram showing a state where an electrostatic latent image (which can also be referred to as an electrostatic latent image for positional deviation correction) is formed on the photosensitive drum using the yellow photosensitive drum 22a. In the figure, an electrostatic latent image in which 80 is formed is shown. The electrostatic latent image 80 is drawn as wide as possible in the image area width in the scanning direction, and has a width of about 5 lines in the transport direction. In addition, the width in the main scanning direction is desirably formed with a width of more than half of the maximum width in order to obtain a good detection result. In addition, it is more preferable that the width of the electrostatic latent image 80 is increased to a region that further exceeds the paper region outside the image region (printed image region on the paper) and that can form an electrostatic latent image. It is. At this time, for example, by setting the developing sleeve 24a to be separated (separated) from the photosensitive drum 22a, the electrostatic latent image 80 is conveyed to the position of the primary transfer roller 26a without adhering toner. Further, under the instruction of the control unit 54, the voltage output from the development bias high voltage power supply circuits (development high voltage power supply circuits) 44a to 44d is set to zero, or a bias voltage having a polarity opposite to that of the normal voltage is applied. You may make it not adhere. In this way, the developing sleeve 24a disposed upstream of the primary transfer roller 26a in the rotational direction of the photosensitive drum is separated or more effective on the photosensitive drum than when a normal toner image is formed by the image forming unit. It is necessary to operate so that it is at least small.

  Further, the control unit 54 starts a timer prepared corresponding to each of the YMCKs simultaneously or substantially simultaneously with the process of step S503 (step S504). Also, sampling of the detection value of the current detection circuit 47a is started. At this time, the sampling frequency is, for example, 10 kHz.

  In step S505, the control unit 54 measures the time (timer value) at which the detection value of the primary transfer current is minimized by detecting the electrostatic latent image 80, based on the data acquired by sampling in step S504. To do. By this measurement, passage of the electrostatic latent image 80 formed on the photosensitive drum to a position facing the primary transfer roller can be detected. FIG. 8 shows an example of the detection result.

  FIG. 8 shows an output value related to the surface potential of the photosensitive member (photosensitive drum 22a) from the current detection circuit 47a when the electrostatic latent image 80 reaches the primary transfer roller 26a as the process means. Is. As will be described in detail later with reference to FIG. 9, the information shown in FIG. 8 corresponds to the surface potential of the photosensitive drum 22a and can be referred to as surface potential information of the photosensitive drum 22a. In FIG. 8, the vertical axis indicates the detected current, the horizontal axis indicates time, and one scale on the horizontal axis indicates the time for which the laser scanner scans one line. The current waveforms 90 and 91 are detected at different timings. Each of the current waveforms 90 and 91 shows a characteristic in which the electrostatic latent image 80 reaches a primary transfer roller 26a and becomes a minimum at time 92 and then returns.

  Here, the reason why the detected current value decreases will be described. FIG. 9 is a schematic diagram showing the surface potential of the photosensitive drum 22a with and without toner adhesion on the electrostatic latent image. The horizontal axis indicates the surface position of the photosensitive drum 22a in the transport direction, and the region 93 indicates the position where the electrostatic latent image 80 is formed. The vertical axis represents the potential, and the dark potential of the photosensitive drum 22a is described as VD (for example, −700 V), the bright potential is set to VL (for example, −100 V), and the transfer bias potential of the primary transfer roller 26a is described as VT (for example, +1000 V). .

  In the region 93 of the electrostatic latent image 80, the potential difference 96 between the primary transfer roller 26a and the photosensitive drum 22a is smaller than the potential difference 95 in other regions. For this reason, when the electrostatic latent image 80 reaches the primary transfer roller 26a, the current value flowing through the primary transfer roller 26a decreases. This is the reason why the minimum value in FIG. 8 described above is detected. The detected current value reflects the surface potential of the photosensitive drum 22a. In FIG. 9, the difference between the photosensitive drum surface potential and the output voltage of the primary transfer roller 26a has been described as an example. However, the same is true for the change in the amount of current. Or, it can be said between the development voltage.

  Returning to the flowchart of FIG. Finally, in step S506, the control unit 54 stores the time (timer value) measured in step S505 in the EEPROM 324 as a reference value. The stored information here indicates a reference state that is a target when color misregistration correction control is performed. In the color misregistration correction control, the control unit 54 performs control so as to eliminate the deviation from the reference state, in other words, to return to the reference state.

  Here, the timer value obtained in step S506 is based on the electrostatic latent image formation timing (reference) by the scanner units 20a to 20d in step S503. The electrostatic latent image formation timing is based on the electrostatic latent image formation timing, for example, one second before the electrostatic latent image formation, but not the electrostatic latent image formation timing itself. It means that timing is acceptable. The EEPROM 324 may be a RAM with a backup battery, for example. The stored time information only needs to be able to specify the time. For example, information on the number of seconds itself or a clock count value may be used.

[Detailed Description of Step S505]
Here, the reason why it is preferable to measure the time when the detection waveforms (current waveforms) 90 and 91 are minimized will be described. This is because the timing at which the electrostatic latent image 80 reaches the primary transfer roller 26a can be accurately measured even when the absolute values of the measured currents are different as in the detection waveforms (current waveforms) 90 and 91. This is because it can be done. The reason why the detection pattern (electrostatic latent image for color misregistration correction) is shaped like the electrostatic latent image 80 in FIG. 7 is that the change in the current value is greatly increased by making the pattern wide in the main scanning direction. It is to do. Further, by setting the width for several lines in the conveyance direction (sub-scanning direction) of the photosensitive drum 22, a point that becomes a minimum appears sharply while maintaining a large change in the current value. Accordingly, the optimum shape of the electrostatic latent image 80 varies depending on the configuration of the apparatus, and is not limited to the shape having a width of 5 lines in the transport direction used in this embodiment.

  Further, although the detection result shown in FIG. 8 is suitable, for example, by setting 20 lines more than 5 lines in the transport direction of the electrostatic latent image 80, an area that is flat in the detection result is created, and its midpoint May be detected. That is, it is only necessary to detect a position that matches the specific condition (characteristic position) detected in the flowchart of FIG. 5 from the detection result when the flowchart of FIG. If it is such an aspect, not only the minimum position mentioned above but the characteristic position of various detection results can be applied to the judgment object of step S505 of FIG. 5, FIG. The same applies to FIGS. 12 and 13 described later.

  In the above description, the configuration in which the developing sleeve 24a is separated from the photosensitive drum 22a and the toner is not placed on the electrostatic latent image 80 when color misregistration is detected according to the flowchart of FIG. However, it is not limited to this. Color misregistration can be detected even when toner is placed.

  FIG. 9B is a schematic diagram showing a potential difference between the photosensitive drum 22a and the primary transfer roller 26a when toner is placed on the electrostatic latent image 80. FIG. The same elements as those in FIG. 9A are denoted by the same reference numerals, and the description thereof is omitted. When toner is placed on the electrostatic latent image 80, in the region 93 of the electrostatic latent image 80, the potential difference 97 between the primary transfer roller 26a and the photosensitive drum 22a is larger than the potential difference 96 when no toner is placed. Further, the difference from the potential difference 95 in the other region becomes small. However, changes can be fully detected. Here, it is necessary to clean the toner on the photosensitive drum 22 and the intermediate transfer belt 30 after detecting the color misregistration. However, if the density is not high, simple cleaning is sufficient and there is no substantial problem. Cleaning can be performed in a shorter time compared to the case where the toner image for detection in color misregistration correction at 100% density is transferred to at least the intermediate transfer belt 30 or the like and cleaned.

[Flow chart of color misregistration correction control]
Next, color misregistration correction control in the present embodiment will be described using the flowchart of FIG. In addition, the flowchart of FIG. 10 shall be performed independently about each color. Further, as described above, the flowchart of FIG. 10 shows the case where the temperature inside the apparatus changes due to continuous printing, the case where the color misregistration correction control instruction of FIG. It is executed under predetermined conditions, such as when the internal environment has changed significantly. This also applies to FIGS. 13, 21, 25, and 27 described later.

  First, in steps S502 to S505, processing similar to that in the flowchart of FIG. 5 is performed. When the axis of the photosensitive drum 22a is biased, the time until the electrostatic latent image 80 described above reaches the primary transfer roller 26a also changes. In order to detect this change, an electrostatic latent image 80 is formed at the same position as in step S503 in FIG. 5 also in step S503 in FIG. Here, the same position (phase) may be exactly the same, or as long as the accuracy of color misregistration detection can be improved as compared with the case where the electrostatic latent image 80 is formed at an arbitrary position. The position may be approximately the same position or approximately the same position. Here, the electrostatic latent image for color misregistration correction formed on the photosensitive drum in each of step S503 in FIG. 5 and step S503 in FIG. 2 and an electrostatic latent image for color misregistration correction.

  Then, the control unit 54 compares the timer value when the current minimum is detected in step S1001 with the reference value stored in step S506 of the flowchart of FIG. When the timer value is larger than the reference value in step S1002, the control unit 54 corrects the laser beam emission timing as an image forming condition so that the laser beam emission timing is advanced at the time of printing. How much the controller 54 sets the laser beam emission timing earlier may be adjusted according to how much the measured time is larger than the reference value. On the other hand, when the timer value detected in step S1003 is smaller than the reference value, the control unit 54 delays the timing of emitting the laser beam during printing. How much the control unit 54 performs the setting for delaying the laser beam emission timing may be adjusted according to how much the measured time is smaller than the reference value. The current color misregistration state can be returned to the reference color misregistration state (reference state) by the image forming condition correction processing in steps S1002 and S1003.

  In addition, although it demonstrated that the control part 54 compared with the reference value preserve | saved at step S506 in step S1001 of the flowchart of FIG. 10 with the timer value at the time of detecting current minimum, it is not limited to it. From the viewpoint of maintaining the color misregistration state at a certain timing, Steps S502 to S506 may be executed in an arbitrary color misregistration occurrence state, and the stored reference value may be used as a comparison target in Step S1001. The same applies to FIGS. 12 and 13 described later.

[Description of effects]
As described above, the flowchart of FIG. 10 is executed by the control unit 54, so that the detection toner image (100% density) in the color misregistration correction control is not transferred from the photosensitive drum to the image carrier (belt). Color misregistration correction control can be realized. That is, color misregistration correction control can be performed while maintaining usability of the image forming apparatus as much as possible.

  On the other hand, it has also been conventionally known that a color shift amount change tendency with respect to a change amount in the apparatus temperature is measured in advance, the color shift amount is predicted based on the measured apparatus temperature, and color shift correction control is performed. It has been. This color misregistration correction control method has an advantage that it is not necessary to form a detection toner image on the image carrier. However, in the color misregistration correction control method that predicts and calculates the color misregistration amount, although toner consumption can be suppressed, the actual color misregistration amount does not necessarily match the prediction calculation result. There was a difficulty in terms of. On the other hand, according to the flowchart of FIG. 10, it is possible to ensure a certain accuracy of color misregistration correction control while making it possible to suppress toner consumption.

  Further, as color misregistration correction control using an electrostatic latent image, for example, a mode in which an electrostatic latent image for color misregistration correction is transferred onto an intermediate transfer belt and a potential sensor for detecting the electrostatic latent image is provided can be considered. However, in this case, a standby time occurs until the electrostatic latent image transferred onto the intermediate transfer belt is detected by the potential sensor. On the other hand, according to the above embodiment, the standby time can be further shortened and usability is not lowered.

Further, in the method of transferring an electrostatic latent image for color misregistration correction onto an intermediate transfer belt, the potential of the electrostatic latent image for color misregistration correction on the intermediate transfer belt must be held until detection. For this reason, it is necessary to increase the time constant τ by making the belt material have a high resistance (e13 Ωcm or more) so that the charge on the belt does not escape instantaneously (for example, 0.1 seconds). However, an intermediate transfer belt having a large time constant τ has a demerit that image defects such as ghosts and discharge marks due to belt charge-up are likely to occur. On the other hand, according to the above embodiment, the time constant τ of the intermediate transfer belt can be reduced, and image defects due to charge-up can be reduced.

  FIG. 11 is a configuration diagram of an image forming apparatus in a form different from that of the first embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The difference from the image forming apparatus described with reference to FIG. 1 is that the developing sleeves 24a to 24d are always separated from the photosensitive drums 22a to 22d and do not act on the photosensitive drum in the configuration of FIG. During printing, the developing high-voltage power supply circuits 44a to 44d apply an alternating bias voltage to the developing sleeves 24a to 24d, thereby causing the toner to reciprocate between the photosensitive drums 22a to 22d and the developing sleeves 24a to 24d. Toner is attached to the electrostatic latent image. In this configuration, the toner does not adhere to the electrostatic latent image 80 on the photosensitive drum 22 simply by stopping the development high-voltage power supply circuits 44a to 44d.

  In the configuration of FIG. 11, the photosensitive drums 22a to 22d are driven by independent driving sources 28a to 28d, and the rotational speeds can be set respectively. Therefore, by changing the rotation speed of the photosensitive drums 22a to 22d, the time from the irradiation of the laser beams 21a to 21d until the electrostatic latent image 80 reaches the primary transfer rollers 26a to 26d is adjusted to be constant. The detected color misregistration amount in the transport direction is canceled out. For example, when the rotational speed of the photosensitive drum is increased, the interval in the sub-scanning direction of the electrostatic latent image on the photosensitive drum is increased. However, if the rotation speed (movement speed) of the intermediate transfer belt 30 is not changed, the interval between the transfer positions of the toner images in the sub-scanning direction is conversely narrowed. Therefore, the expansion and contraction of the image formed on the intermediate transfer belt 30 in the sub-scanning direction is not substantially a problem.

  On the other hand, in the present embodiment, it is assumed that the phase of each of the photosensitive drums 22a to 22d is not detected. However, when the axis of the photosensitive drum 22a has a non-negligible bias, the measurement result of the time required for the electrostatic latent image 80 to reach the primary transfer roller 26a also changes. Therefore, in this embodiment, the measurement is performed a plurality of times, and the color shift is corrected based on the average. Needless to say, the processes of the flowcharts shown below are also applicable when the image forming apparatus described with reference to FIG. 1 is used.

  The flowchart in FIG. 12 is a flowchart illustrating the reference value acquisition process in the second embodiment. Note that the flowchart of FIG. 12 is performed independently for each color.

  First, the processing of steps S1201 to S1205 is the same as the processing of steps S501 to S505 in FIG. 5, and detailed description thereof is omitted here.

  In step S1206, the control unit 54 repeats the processes in steps S1203 to S1205 until the timer value measurement for detecting the minimum is repeated n times in order to cancel the influence of the bias of the photosensitive drums 22a to 22d. Control to execute. Note that n is an integer value of 2 or more. In addition, when the electrostatic latent image for n color misregistration correction is less than one revolution of the photosensitive drum, for example, the half of the photosensitive drum, the color misregistration correction static image at the predetermined rotation phase in step S1203. The formation of an electrostatic latent image is particularly effective.

  In step S1206, when the control unit 54 determines that n measurements have been completed, in step S1207, the control unit 54 calculates an average value of timer values (time) obtained by the n measurements. In step S1208, the control unit 54 stores the average value data (representative time) in the EEPROM 324 as a representative value (reference value). The stored information here indicates a reference state that is a target when color misregistration correction control is performed. In the color misregistration correction control, the control unit 54 performs control so as to eliminate the deviation from the reference state, in other words, to return to the reference state. As for the average calculation method, various calculation methods such as simple average and weighted average are assumed. In addition, the method is not limited to the method of calculating the average value in the sense of canceling the photosensitive drum rotation period component such as the eccentricity of the photosensitive drum. For example, a simple sum or a weighted sum may be used as long as it is a calculation for canceling the rotation period component of the photosensitive drum. Note that the cancellation here does not mean complete cancellation, but is used in the sense of at least reducing the influence of the component of the rotation cycle of the photosensitive drum. Of course, as long as it can be completely canceled, it is possible to do so. Thus, in step S1208, since the reference value is calculated based on a plurality of acquired data, the accuracy can be improved as compared to calculating the reference value based on at least a single data.

[Flow chart of color misregistration correction control]
Next, the flowchart of FIG. 13 will be described. The same steps as those in FIG. Note that the flowchart of FIG. 13 is performed independently for each color.

  First, the processing in steps S1202 to S1205 in FIG. 13 is the same as the corresponding processing in FIG. 12 as described above. In order to suppress the influence when the rotating shafts of the photosensitive drums 22a to 22d are biased, the control unit 54 repeatedly executes the processing of steps S1203 to S1205 until the timer value measurement for detecting the minimum is repeated n times.

  Then, when the control unit 54 determines that n measurements have been completed in step S1301, the control unit 54 calculates the average of the timer values measured n times in step S1302. In step S1303, the control unit 54 reads the reference value stored and saved in step S1208 of FIG. 12 from the storage unit (EEPROM 324). Then, the control unit 54 compares the calculated average value with the read representative value (reference value). Note that the meaning of canceling the photosensitive drum cycle component is not limited to the average value, as described in steps S1207 and S1208.

  If the average value is larger than the reference value, the control unit 54 increases the rotational speed of the photosensitive drum as the image forming condition, that is, accelerates the motor by the time during printing in step S1304. On the other hand, if the average value is smaller than the reference value, in step S1305, the control unit 54 reduces the rotation speed of the photosensitive drum as an image forming condition by the time during printing, that is, by decelerating the motor. Correct the deviation. In this manner, the current color misregistration state can be returned to the reference color misregistration state (reference state) by the processing in steps S1304 and S1305. In steps S1304 and S1305 in FIG. 13, the processing in steps S1002 and S1003 described in the flowchart in FIG. 10 may be performed as correction of the image forming conditions.

[Photosensitive drum phase dispersion]
When the electrostatic latent image scanning process in step S1203 in FIGS. 12 and 13 is executed in a non-image area between pages, the number of determinations n in step S1206 in FIG. 12 and step S1301 in FIG. It is determined by the dimensions of each member. Specifically, it is determined from the paper size, the drum circumferential length of the photosensitive drum, and the width of the non-image area in the image movement direction (photosensitive drum rotation direction).

  For example, when the paper size is A4 (297 mm), the image moving direction width of the non-image area is 64.0 mm, and the drum circumference is 75.4 mm, what is the phase of the photosensitive drum at the center of each non-image area? The graph of FIG. FIG. 14B shows an example in which the paper size, the non-image area width, and the drum circumference are different values. What is described in FIG. 14 is the same for each color.

  These graphs of FIG. 14 are diagrams showing to which photosensitive drum phase an electrostatic latent image is formed when step S1203 of FIGS. 12 and 13 is executed at the center of each non-image area. is there. 14A and 14B, if the electrostatic latent image in step S1203 of FIGS. 12 and 13 is formed in each non-image area a plurality of times, the phase condition of the photosensitive drum is averaged / dispersed. Has been shown to be.

  Here, FIG. 15 is a diagram for explaining what the paper size and the non-image area width indicate. FIG. 15 shows the correspondence between the primary transfer position when the toner image is transferred onto the intermediate transfer belt and the phase of the photosensitive drum when exposure corresponding to the toner image is performed. The non-image area is an area on the photosensitive drum, such as an area on the photosensitive drum other than an area where an electrostatic latent image can be formed in image formation (effective image area), or an inter-page area (inter-paper area). Can be defined. It can also be defined as a period (time) in which the scanner unit 20 does not perform laser irradiation for image formation on each page.

  In FIG. 15, the phases of the start position 1502 (1506), the center 1504 (1508) and the end position 1503 (1507) of the non-image area 1505 (1509) are the same as the phase of the photosensitive drum corresponding to the position 1501 and the paper. It depends on the size. Note that, as described above, the phase of each photosensitive drum is the phase of the photosensitive drum when the toner image is exposed assuming that the toner image is primarily transferred.

  In FIG. 15, the phase of 1501 is shown as zero, but any other value is acceptable. That is, even if the phase of 1501 is not zero, the appearance timing is only shifted with respect to how many (how many) non-image areas the phase change shown in FIG. 14 appears. That is, there is not much difference in the sense that the photosensitive drum phase is dispersed when forming the electrostatic latent image in step S1203 of FIGS.

  As described above, by executing the flowcharts of FIGS. 12 and 13 by the control unit 54, in addition to the same effects as those of the first embodiment, more accurate color misregistration correction control using the average value can be realized. Further, it is possible to perform color misregistration correction control independent of the phase of the photosensitive drum when forming an electrostatic latent image for color misregistration correction, and to have more flexibility in the start timing of color misregistration correction control. .

  In the above embodiment, it has been described that the current value flowing through the primary transfer roller 26a, the photosensitive drum 22a, and the ground according to the output voltage of the output terminal 53 is detected as the output value related to the surface potential of the photosensitive drum 22a. However, it is not limited to this. In addition to the primary transfer rollers 26a to 26d, charging rollers 23a to 23d, developing sleeves 24a to 24d, and the like are provided around the photosensitive drums 22a to 22d. The first or second embodiment can be applied to the charging rollers 23a to 23d and the developing sleeves (developing rollers) 24a to 24d. That is, the photosensitive drum when the electrostatic latent image 80 formed on the photosensitive drums 22a to 22d reaches the charging rollers 23a to 23d and the developing sleep (developing rollers) 24a to 24d as process means as described above. You may detect the output value which concerns on the surface potential of 22a-22d.

  Hereinafter, as an example, a case where a current value flowing through the charging roller 23 and the photosensitive drum 22 is detected as an output value related to the surface potential of the photosensitive drum 22 will be described. In this case, charging high-voltage power supply circuits 43a to 43d (FIG. 2B) connected to each charging roller are provided, and each charging high-voltage power supply circuit is provided with a circuit similar to the high-voltage power supply circuit shown in FIG. The terminal 53 may be connected to the corresponding charging roller 23.

  The charging high-voltage power supply circuit 43a in this case is shown in FIG. One difference from FIG. 4 is that the output terminal 53 is connected to the charging roller 23a. Another difference is that the diodes 1601 and 1602 whose cathode and anode directions are opposite to the diodes 64 and 65 constitute a high-voltage power supply circuit. This is because in the image forming apparatus of this embodiment, the primary transfer bias voltage is a positive voltage, whereas the charging bias voltage is a negative voltage. The charging high-voltage power supply circuits 43b to 43d for the other colors are the same as the circuit configuration shown in FIG. 16A, and thus detailed description thereof is omitted as in the case of the primary transfer high-voltage power supply circuit.

  The flowcharts of FIGS. 5, 10, 12, and 13 may be executed by operating the charging high-voltage power supply circuits 43 a to 43 d (not shown) instead of the primary transfer high-voltage power supply circuits 46 a to 46 d. At this time, the current target value set in advance for the detection voltage 56 is appropriately set in consideration of the characteristics of the charging roller 23 and the relationship with other members.

  Further, the current detection circuits 50 a to 50 d of the charging high voltage power supply circuits 43 a to 43 d are operated, and the latent image mark (electrostatic latent image 80) formed on each photosensitive drum is a nip portion between the photosensitive drum and the intermediate transfer belt 30. The primary transfer rollers 26a to 26d are preferably separated from the belt when passing through the belt. Further, the high voltage output of the primary transfer rollers 26a to 26d may be turned off (zero) without being separated. This is more positive in the portion of the dark potential VD (for example, −700 V) on the photosensitive drum by the positive charge supplied from the primary transfer roller than the portion of the bright potential VL (for example −100 V). Because. That is, the width of the contrast between the dark potential VD and the light potential VL is reduced by the above-described plus. Conversely, if this is avoided, the contrast width between the dark potential VD and the light potential VL can be maintained, and the change range of the detected current can be kept wide.

  FIG. 16B shows another charging high-voltage power supply circuit 43a. The difference from FIG. 16A is that the detection voltage 56 indicating the detected current amount is input to the negative input terminal (inverted input terminal) of the comparator 74. The threshold value Vref75 is input to the positive input terminal of the comparator 74. When the input voltage at the inverting input terminal falls below the threshold value, the output becomes Hi (positive) and the binarized voltage value 561 (Hi). Voltage) is input to the controller 54. The threshold value Vref75 is set to a value between the minimum value of the detection voltage 561 when the electrostatic latent image for color misregistration correction passes the position facing the process means and the value of the detection voltage 561 before passing. Then, the rise and fall of the detection voltage 561 are detected by detecting the electrostatic latent image once. For example, the control unit 54 sets the midpoint between the rise and fall of the detection voltage 561 as the detection position. Further, the control unit 54 may detect only one of the rising edge and the falling edge of the detection voltage 561.

  In the first and second embodiments, it has been described that when detecting that the output of the high-voltage power supply circuit satisfies a predetermined condition, the detection voltage 56 takes a minimum value lower than a certain value as the predetermined condition. . However, this predetermined condition only needs to indicate the passage of the electrostatic latent image 80 formed on the photosensitive drum at the position facing the process means. For example, as described with reference to FIG. 16B, the predetermined condition may be that the detection voltage 561 falls below a threshold value. This has already been described in the detailed description of step S505 of the first embodiment using FIG. Accordingly, various conditions are assumed as conditions for detecting the electrostatic latent image 80 in the flowcharts already described and the flowcharts described later.

  In addition to charging and transfer, there is also development. For the development, the development high-voltage power supply circuits 44a to 44d (including the current detection circuit) are operated, and the flowcharts of FIGS. 5, 10, 12, and 13 are performed. May be executed. The target current value at this time is the same as in the case of the charging high-voltage power supply circuits 43a to 43d, and may be appropriately set in consideration of the characteristics of the developing sleeve 24, the relationship with other members, and the like.

  When operating the development high-voltage power supply circuits 44a to 44d, it is necessary to make the output voltage higher than VL so that the toner does not adhere to the photosensitive drum. For example, when VL is a negative voltage of −100 V, the outputs of the development high-voltage power supply circuits 44 a to 44 d may be set to a negative voltage of −50 V, whose absolute value is smaller than VL. Alternatively, a circuit similar to the high-voltage power supply circuit described with reference to FIG. 4 is added to the development high-voltage power supply circuits 44a to 44d so that when VL is -100V with a negative voltage, a reverse polarity voltage (reverse bias) is output. May be.

  As described above, according to the third embodiment, an electrostatic latent image for color misregistration correction can be detected using the charging roller 23 and the developing sleeve 24. According to this, in addition to the effects similar to those of the first and second embodiments, the following effects can be obtained. That is, when the primary transfer roller 26 is used, a belt is interposed between the primary transfer roller 26 and the photosensitive drum 22, whereas when the charging roller 23 or the developing sleeve is used, such a case. Detection relating to the surface potential of the photosensitive drum can be performed in a situation where there is no significant intervention.

  In the above-described high voltage power supply circuits of the first to third embodiments, the current detection circuit 47 is individually provided for each of the process means. However, it is not limited to this form. FIGS. 17A and 17B show another example of the high-voltage power supply device. The configuration shown in FIG. 17A has a primary transfer high-voltage power supply circuit 146a to 146d independent of the primary transfer rollers 26a to 26d for each color and a current common to the primary transfer rollers 26a to 26d for each color. A detection circuit 147. Further, in FIG. 17B, a primary transfer high-voltage power supply circuit 46 is further shared by a plurality of primary transfer rollers 26a to 26d with respect to FIG. 17A. Note that in both FIGS. 17 (a) and 17 (b), the same reference numerals are given to components common to those in FIG. 2, and detailed description thereof is omitted here.

[Circuit diagram of high-voltage power supply]
The circuit configurations of the primary transfer high-voltage power supply circuits 146a to 146d and the current detection circuit 147 shown in FIG. 17A will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the same structure as FIG. 4, and the description is abbreviate | omitted. In FIG. 18, the control unit 54 controls the drive circuits 61a to 61d based on the set values 55a to 55d set for the comparators 60a to 60d, and outputs desired voltages to the outputs 53a to 53d. Also, the current output from the primary transfer high-voltage power supply circuits 146a to 146d flows through the current detection circuit 147 via the primary transfer rollers 26a to 26d, the photosensitive drums 22a to 22d, and the grounding point 57 as shown in FIG. It is the same. In the detection voltage 56, a voltage proportional to the value obtained by superimposing the currents of the output terminals 53a to 53d appears.

  Also in FIG. 18, as in FIG. 4, the inverting input terminal of the operational amplifier 70 is virtually grounded to the reference voltage 73 and has a constant voltage. Therefore, the voltage of the inverting input terminal 70 fluctuates due to the operation of the primary transfer high-voltage power supply circuit for another color, and this hardly affects the operation of the primary transfer high-voltage power supply circuit for another color. In other words, the plurality of primary transfer high-voltage power supply circuits 146a to 146d are not affected by each other and operate in the same manner as the primary transfer high-voltage power supply circuit 46 in FIG.

  On the other hand, the details of the primary transfer high-voltage power supply circuit 46 and the current detection circuit 47 shown in FIG. 17B are the same as those of the primary transfer high-voltage power supply circuit 46a and the current detection circuit 47a described in FIG. This is the same as described in FIG.

  FIG. 17A and FIG. 17B only differ depending on whether the number of current generation sources is one or more, and the current detection operates in the same mechanism. Therefore, in the following current detection, the high voltage power supply device of FIG. 17A will be taken as an example for explanation.

[Description of color misregistration correction control]
Next, with the configuration described with reference to FIGS. 17 and 18, the electrostatic latent images 80a to 80d are detected by a common current detection circuit for a plurality of primary transfer high-voltage power supplies (process means), and color misregistration correction control is performed. Processing to be performed will be described.

[Reference Value Acquisition Process Flowchart]
FIG. 19 is a flowchart of reference value acquisition processing in color misregistration correction control. The processing in the first steps S501 and S502 is as described in FIG.

  Next, in steps S1901 to S1904, a loop process of n = 1 to 4 is performed to form an electrostatic latent image for color misregistration correction. If the electrostatic latent image formed here is the first electrostatic latent image for color misregistration correction control, the electrostatic latent image formed in the flowchart of FIG. It can be distinguished as an image. FIG. 20 is a diagram illustrating a state in which the electrostatic latent images 80a to 80d for color misregistration correction are formed on the photosensitive drums 22a to 22d immediately after the loop processing is completed.

  Here, first, in step S1902 in the loop processing of n = 1, the control unit 54 causes the yellow scanner unit 20a to emit laser light, and forms an electrostatic latent image 80a for color misregistration correction on the photosensitive drum 22a. To do. At this time, the control unit 54 operates the developing sleeve 24a so as to be separated (separated) from the photosensitive drum 22a. Further, as described in step S503, the voltage output from the high-voltage power supply circuit (developing high-voltage power supply circuit) 44a may be zero, or a bias voltage having a polarity opposite to that of the normal voltage may be applied. Also in step S1902, the developing sleeve 24a disposed on the upstream side of the primary transfer roller 26a is separated, or the action on the photosensitive drum is at least less than that during normal toner image formation by the image forming unit. It is operating. This correspondence is continued until the flowchart is completed.

  Thereafter, in step S1903, the control unit 54 performs a standby process for a predetermined time. This is to prevent the detection results of the electrostatic latent images formed in the respective colors from overlapping, and even if the maximum color shift assumed in the image forming apparatus occurs, the electrostatic latent images do not overlap each other. The standby time is set. Further, it is desirable that the standby processing time is less than the time for which the photosensitive drum rotates once.

  In the same manner, the control unit 54 generates the electrostatic latent image 80b in the loop processing of n = 2, the electrostatic latent image 80c in the loop processing of n = 3, and the electrostatic latent image 80d in the loop processing of n = 4. Each is formed on the photosensitive drum in the same manner as when n = 1. In this embodiment, electrostatic latent images 80a to 80d are formed on the photosensitive drums 22a to 22d in the order of n = 1 for yellow, n = 2 for magenta, n = 3 for cyan, and n = 4 for black. It is not limited to this order, and it is possible to implement even if the order is different.

  Returning to the flowchart of FIG. In the next step S1905, the control unit 54 starts sampling of the detection value of the current detection circuit 47. The sampling frequency at this time is about 10 kHz, for example.

  Next, in step S1906, the control unit 54 determines whether or not the detected value of the primary transfer current has become a minimum by detecting the electrostatic latent image 80, based on the data acquired by sampling. Here, the detected value indicating the minimum value means that the electrostatic latent image 80a formed first has reached the position of the primary transfer roller 26a. In other words, the detection in step S1906 can detect the passage of the electrostatic latent image 80 formed on the photosensitive drum to a position facing the primary transfer roller as the process means. Here, the detection current of the current detection circuit 47 is a value obtained by superimposing the current flowing through the primary transfer rollers 26 a to 26 d via the resistor 71. If a minimum current value is detected in step S1906, a timer is started in step S1907.

  Thereafter, the control unit 54 performs a loop process of n = 1 to 3 in steps S1908 to S1911. In this loop processing, the control unit 54 measures a temporal difference between the timing when the detected value of the reference color is minimized and the timing when the detected value of the measurement color (Y, M, C) is minimized. In step S1909, the time (timer value) at which the detected value is minimized by the electrostatic latent images 80b to 80d of the second color (n = 1) to the fourth color (n = 3) is measured. In step S1910, the nth It is stored in the EEPROM 324 as a reference value. The stored information here indicates a reference state that is a target when color misregistration correction control is performed. In the color misregistration correction control, the control unit 54 performs control so as to eliminate the deviation from the reference state, in other words, to return to the reference state. The reference value stored here indicates the difference between the arrival timing of the yellow electrostatic latent image and the arrival timing of magenta when n = 1. Further, n = 2 indicates the difference between the arrival timing of the yellow electrostatic latent image and the arrival timing of cyan, and n = 3 indicates the difference between the arrival timing of the yellow electrostatic latent image and the arrival timing of black.

[Flow chart of color misregistration correction control]
FIG. 21 is a flowchart showing the color misregistration correction control in this embodiment. First, steps S502 to S1907 are the same as those in the flowchart of FIG.

  Next, in steps S2101 to S2106, the control unit 54 performs a loop process of n = 1-3. In step S2102, the control unit 54 first sets n = 1, and measures the time (timer value) from when the detection result of the reference color becomes minimum until the detection value becomes minimum, as in step S1909 of FIG. . In step S2103, the control unit 54 compares the time measured in step S2102 with the reference value corresponding to the n value stored in step S1910 in FIG.

  If the measured time is greater than the stored reference value, the control unit 54 corrects the magenta laser beam emission timing at the time of printing to be advanced in step S2104. How much the controller 54 sets the laser beam emission timing earlier may be adjusted according to how much the measured time is larger than the reference value. On the other hand, if the detected timer value is smaller than the reference value, the control unit 54 corrects the magenta laser beam emission timing during printing to be delayed in step S2105. How much the control unit 54 performs the setting for delaying the laser beam emission timing may be adjusted according to how much the measured time is smaller than the reference value. As described above, the current color misregistration state can be returned to the reference color misregistration state (reference state) by the processing in steps S2104 and S2105. In the same manner, n = 2 and the processes of steps S2101 to S2106 are performed for cyan, and n = 3 and the processes of steps S2101 to S2106 are performed for black.

  In the above description, the primary transfer rollers 26a to 26d have been described as an example of process means for performing current detection. However, a charging roller or a developing sleeve can also be applied as process means for performing current detection.

  In the case of a charging roller, a common current detection circuit is provided for one or a plurality of charging high-voltage power supply circuits, and the flowcharts of FIGS. 19 and 21 may be executed by the current detection circuit. This corresponds to the charging high-voltage power supply circuit described in the fifth embodiment described later, and the operation of each developing sleeve and each transfer roller when using the current detection circuit of the charging high-voltage power supply circuit is also described in detail in the fifth embodiment. I will explain.

  In the case of the developing sleeve, a current detection circuit is provided in common with one or a plurality of development high-voltage power supply circuits, and the flowcharts of FIGS. 19 and 21 may be executed by the current detection circuit. Note that how to control the output voltage from one or a plurality of development high-voltage power supply circuits is as described in the third embodiment.

  As described above, in the present embodiment, the control unit 54 performs the standby process of S1903 so that the detection timings of the electrostatic latent images do not overlap with each other. A common current detection circuit 147 can be used for the circuits 46a to 46d. Thereby, the structure which concerns on a current detection circuit can be simplified.

  In this embodiment, the positional deviation of the yellow color as a reference cannot be measured and corrected, but the relative color shift amount of other colors (measured color / detected color) when the yellow color is used as a reference is corrected. As a result, the absolute positional deviation of each color can hardly be determined. Therefore, sufficient print quality can be obtained as in the above embodiment. In this embodiment, although the yellow color is used as a reference color, it is needless to say that the above embodiment can be implemented using another color as a reference color.

  On the other hand, using the common current detection circuit 147 described in the fourth embodiment, processing similar to the flowcharts in FIGS. 5 and 10 and the flowcharts in FIGS. 12 and 13 described in the first to third embodiments is executed. You can also. In this case, the process of step S1906 in FIG. 19 is omitted, and the loop process of steps S1908 to S1911 is executed for n = 1 to 4. Then, after that, in the flowchart of FIG. 21, the process of S1906 may be omitted, and the processes of steps S2101 to S2106 may be executed for n = 1 to 4. The above-described processing may be executed similarly when a charging high-voltage power supply circuit or a development high-voltage power supply circuit is used instead of the primary transfer high-voltage power supply circuit.

  In the embodiment described above, a common current detection circuit is used for a plurality of process means, and the electrostatic latent images for correction 80a to 80d are formed at specific positions (phases) of the photosensitive drums 22a to 22d. I have explained that. Further, when a common current detection circuit is used in a plurality of color process means, as described in the second embodiment, the electrostatic latent image for color misregistration correction is not related to the position (phase) of the photosensitive drum. It is also possible to perform color misregistration correction. Hereinafter, the form will be described.

[Configuration diagram of high-voltage power supply unit]
FIG. 22 shows the configuration of the high-voltage power supply device according to the fifth embodiment. The same components as those in FIGS. 2 and 17 are denoted by the same reference numerals. The difference is that the charging high-voltage power supply circuit 43 is provided with a common current detection circuit 50 for the charging rollers 23a to 23d as a plurality of process means. That is, in this embodiment, a process for detecting a current value flowing through the charging roller 23 and the photosensitive drum 22 will be described. The details of the circuit configuration of the charging high-voltage power supply circuit 43 and the current detection circuit 50 are as described in FIG. 16 (43a, 50a), and a detailed description thereof is omitted here.

  FIG. 22 shows only the case where the charging high-voltage power supply circuit is common to the charging rollers 23a to 23d, but the form is not limited thereto. Similarly to the primary transfer high-voltage power supply circuits 146a to 146d described with reference to FIG. 17A, a case where individual charging high-voltage power supply circuits are provided for the respective charging rollers 23a to 23d may be applied. This is because the current source is different depending on whether the current source is a single source or a plurality of sources, and the current detection operates in the same manner.

[Reference Value Acquisition Process Flowchart]
First, a flowchart illustrating reference value acquisition processing in color misregistration correction control according to the present embodiment will be described using FIGS. 23A and 23B together with FIG. First, the process of step S501 executed first in the flowchart of FIG. 23A is as described in FIG. Then, before the processing of step S1907 in FIG. 23, preparations for forming an electrostatic latent image for color misregistration correction on the photosensitive drum are performed at timings T1 to T3 in FIG. Note that the state before the timing T1 in FIG. 24 shows a state immediately after the color misregistration correction control in step S501. The term “immediately after here” refers to a state in which the color misregistration correction control in step S501 is reflected as it is.

  First, the control unit 54 outputs a drive signal for driving a cam for separating the developing sleeves 24a to 24d at timing T1. At timing T2, the developing sleeves 24a to 24d operate so as to be separated from the state in which they are in contact with the photosensitive drums 22a to 22d. Further, the control unit 54 controls the primary transfer high voltage from the on state to the off state at the timing T3. More specifically, the controller 54 sets the set value 55 to zero in the circuit of FIG. In the circuit of FIG. 18, the control unit 54 sets the set values 55a to 55d to zero. As described in the above embodiment, the developing sleeve 24 is not separated at the timing T1, but the voltage output from the developing high-voltage power supply circuits 44a to 44d is set to zero, or the voltage having the opposite polarity to the normal voltage is used. May be applied. The primary transfer rollers 26a to 26d may be separated from each other instead of turning off the primary transfer high pressure.

  Returning to the description of FIG. 23A, the control unit 54 starts the timer in step S1907 after the timing T3, and starts sampling in step S1905. These processes are as described in the previous embodiment.

  Next, the control unit 54 performs a loop process of n = 1 to 12 in steps S2301 to 2304. In step S2302 in the loop processing, the control unit 54 sequentially outputs a total of 12 signals of the laser signals 90a to 90d, 91a to 91d, and 92a to 92d. The scanner units 20a to 20d perform light irradiation according to the electrostatic latent image signal output here. The developing sleeves 24a to 24d and the primary transfer rollers 26a to 26 arranged on the upstream side of the respective charging rollers 23a to 23d where the electrostatic latent images are detected are separated from each other or are photosensitive drums than when a normal toner image is formed. This is the same as the above-described embodiments in that it operates so that the effect on is reduced at least. The same is true in that this correspondence is continued until the flowchart of FIG. Further, the standby time of the standby process in step S2303 is set for the same technical reason as in S1903 in FIG.

  The timing of T1 to T6 in FIG. 24 corresponds to the loop processing of n = 1 to 12, and the state where the electrostatic latent images for color misregistration correction are sequentially formed is shown. In FIG. 24, an electrostatic latent image for color misregistration correction is formed for each photosensitive drum of each color in a period of timing T4 to T6 at intervals of about one third of the photosensitive drum. In the drawing, the electrostatic latent images are formed in the order of laser signals 90a, 90b, 90c, 90d, 91a, 91b, 91c, 91d, 92a, 92b, 92c, and 92d. As described with reference to the current detection circuit 147 in FIG. 18, the detected current value is a value obtained by superimposing the current flowing through the charging rollers 23 a to 23 d. In addition, the current detection signals 95a to 95d, 96a to 96d, and 97a to 97d shown in the figure do not all overlap, and an electrostatic latent image is formed so as to be like this. Here, the current detection signal corresponds to the detection voltage 56 or the detection voltage 561 described above.

Next, FIG. 23B will be described. FIG. 23B shows a process for detecting each electrostatic latent image for color misregistration correction formed by the process of the flowchart of FIG. 23A. As shown at timing T5 in FIG. 24, detection of an electrostatic latent image for color misregistration correction is started before the formation of the electrostatic latent image for color misregistration correction is completed. Therefore, a part of the processing shown in FIG. 23B is executed by the control unit 54 in parallel with the processing of FIG. 23A.

  First, the control unit 54 performs a loop process of i = 1 to 12 in steps S2311 to S2314. In step S2312, the control unit 54 measures the arrival times ts (i) (i = 1 to 12) from the reference timing of the 12 electrostatic latent images formed by the process of FIG. 23A. Through the detection process in step S2312, the passage of each electrostatic latent image formed on the photosensitive drum to the position facing the charging roller can be detected. In step S2313, the actual measurement result is temporarily stored in the RAM 323. In the process of step S2313, a plurality of detection results are stored, and the plurality of detection results become an actual measurement result (first actual measurement result) in which at least the rotational cycle component of the photosensitive drum is reduced.

  A state in which there is a change in current detection between timings T5 and T7 in FIG. 24 is shown. 95a to 95d are results of detecting a change in current due to the electrostatic latent images formed by the laser signals 90a to 90d. Similarly, 96a to 96d are detection results of the laser signals 91a to 91d, and 97a to 97d are detection results of the laser signals 92a to 92d. The detection timing does not overlap, so that a common current detection circuit can be applied to a plurality of detection target process means (charging rollers).

Thereafter, the control unit 54 performs a loop process of k = 1 to 3 in steps S2315 to S2318. In step S2316, the control unit 54 performs the following logical operation on each k value. The calculation method is not particularly limited, and the CPU 321 may perform the calculation based on the program code or may use a hardware circuit or a table.
δesYM (k) = ts (4 × (k−1) + 1 + 1) −ts (4 × (k−1) +1) (18)
δesYC (k) = ts (4 × (k−1) + 1 + 2) −ts (4 × (k−1) +1) Equation 19
δesYBk (k) = ts (4 × (k−1) + 1 + 3) −ts (4 × (k−1) +1) Equation 20

  More specifically, in step S2316, the control unit 54 first sets k = 1 and uses the first yellow as a reference from the measured values of ts (1) to ts (4) based on the above equations 18 to 20. Then, sub-scanning color misregistration amounts δesYM (1), δesYC (1), and δesYBk (1) for each color are calculated. As shown in FIG. 24, ts (1) to ts (4) are actual measurement results corresponding to yellow, magenta, cyan, and black, respectively. Then, the control unit 54 stores δesYM (1), δesYC (1), and δesYBk (1) calculated in step S2317 in the RAM 323. The information stored in step S2317 is also an actual measurement result (first actual measurement result) in which the rotational period component of the photosensitive drum is at least reduced. Further, the control unit 54 performs the same processing using the detection results of ts (5) to ts (8) in the loop of k = 2, and also performs the processing of ts (9) to ts (12) in the loop of k = 3. Similar processing is performed using the detection result.

  Finally, in step S2319, the control unit 54 is data indicating the amount of color misregistration in the sub-scanning direction of each color based on yellow, which is calculated by the loop processing in steps S2315 to S2318, and rotates the photosensitive drum. Data in which the components of the period are canceled is calculated by equations 21-23. Note that the data indicating the color misregistration amount may not be the color misregistration amount itself as long as it is data correlated with the color misregistration state.

  In step S2320, the control unit 54 uses the calculated δes′YM, δes′YC (1), and δes′YBk as data indicating the color misregistration amount obtained by canceling the rotational period component of the photosensitive drum as reference values in the EEPROM 324. Remember. As described above, the information stored in step S2320 is an actual measurement result (first actual measurement result) in which the rotational period component of the photosensitive drum is at least reduced. The stored information here indicates a target reference state when color misregistration correction control is performed. In the color misregistration correction control, the control unit 54 performs control so as to eliminate the deviation from the reference state, in other words, to return to the reference state. In addition, the information stored in step S2313 or step S2317, which is the basis of the information stored in step S2320, can also be regarded as a reference state for color misregistration correction.

[Flow chart of color misregistration correction control]
Next, color misregistration correction control in this embodiment will be described with reference to the flowcharts of FIGS. 25A and 25B. FIG. 25A shows a process for forming an electrostatic latent image, and FIG. 25B shows a process for detecting an electrostatic latent image and correcting the emission timing of a laser beam as an image forming condition. Note that the processing in each step in FIG. 25A is the same as steps S1907 to S2304 in FIG. In addition, the processing in steps S2311 to S2318 in FIG. 25B is also the same as that in steps S2311 to S2318 in FIG. Below, it demonstrates centering around the difference with FIG.

  In step S2501, the control unit 54 calculates (dδes′YM), (dδes′YC), and (dδes′YBk) based on the actual measurement result stored in step S2317 in FIG. 25B. The initial “d” is appended to mean the value actually detected. The details of the specific calculation are substantially as described in the above formulas 21 to 23. Then, the control unit 54 temporarily stores the calculation result (second actual measurement result) in the RAM 323 in step S2502.

  In step S2503, the difference between dδes′YM calculated in step S2502 and δes′YM stored in step S2320 of FIG. When the difference is 0 or more, that is, when the detection timing of magenta when yellow is used as a reference is delayed from the reference, the control unit 54 sets the magenta laser beam emission timing as in S1002 of FIG. Accelerate according to the difference value. On the other hand, when the difference is less than 0, that is, when the magenta detection timing when yellow is used as a reference is earlier than the reference, the control unit 54 delays the magenta laser beam emission timing by the difference value. . Thereby, the amount of color misregistration between yellow and magenta can be suppressed.

Also in steps S2506 to 2511, the control unit 54 corrects the laser beam emission timing as the image forming condition for cyan and black, as in the case of magenta. Thus, also in the flowchart of FIG. 25B, the current color misregistration state can be returned to the reference color misregistration state (reference state).

  In the description of this embodiment, first, an electrostatic latent image 80 is formed with a plurality of photosensitive drum phases, and a reference value obtained by previously canceling the photosensitive drum rotation period component is stored in step S2319. It was. Then, in FIG. 25, an electrostatic latent image 80 is formed again at a plurality of photosensitive drum phases, and a measurement result obtained by canceling the photosensitive drum rotation period component obtained from the detection result is acquired and calculated in advance. The comparison was made with the stored reference value. However, for example, other calculation methods that do not perform comparison with a reference value obtained in advance as an average value are also assumed. For example, the data acquired in step S2301 in FIG. 23A and step S2301 in FIG. 25A are stored, respectively, and the control unit 54 finally uses the stored data to rotate the photosensitive drum rotation cycle. Data corresponding to the amount of color misregistration whose components are canceled may be calculated.

The calculation of the relative color misregistration amount of yellow and magenta will be specifically described as an example. Here, first, the data acquired in steps S2311 to S2314 in FIG. 23B is ts (i) (i = 1 to 12), and the data acquired in steps S2311 to S2314 in FIG. 25B is ts ′ (i) (i = 1-12). First, the difference between the reference color yellow and the measurement color magenta is calculated by the control unit 54 using the following equation 24.
{(Ts ′ (2) + ts ′ (6) + ts ′ (10)) − (ts ′ (1) + ts ′ (5) + ts ′ (9))} − {(ts (2) + ts (6) + ts ( 10))-(ts (1) + ts (5) + ts (9))} Equation 24
(Ts ′ (2) + ts ′ (6) + ts ′ (10)) in Expression 24 corresponds to the second measurement result of magenta in which the rotation period component of the photosensitive drum is canceled, and (ts ′ (1) + ts ′ ( 5) + ts ′ (9)) corresponds to that of yellow. Further, (ts (2) + ts (6) + ts (10)) corresponds to the first magenta measurement result obtained by canceling the rotation period component of the photosensitive drum, and (ts (1) + ts (5) + ts (9) ) Corresponds to that of yellow. Further, the difference between other colors may be calculated in the same manner by the control unit 54.

  Then, in the calculation result obtained by Expression 24 of the control unit 54, for example, when the difference after aging is smaller than the initial difference between magenta and yellow, the control unit 54 emits the laser beam of the magenta measurement color. Delay the timing (light irradiation timing). This is the same correspondence as the processing of S steps S2505, S2508, and S2511 in FIG. 25B. When the calculation result is positive, the control unit 54 performs control opposite to that in the negative case. Similar image forming condition control (light irradiation timing control) is performed for the other colors.

  As described above, for example, the color misregistration amount after canceling the rotation period component of the photosensitive drum can be obtained by another calculation method that does not perform comparison with a reference value obtained in advance as an average value. This can be applied not only to the flowcharts of FIGS. 23 and 25 but also to the flowcharts of FIGS. 12 and 13, for example.

  In the above description, the charging rollers 23a to 23d have been described as an example of process means for detecting current. However, a primary transfer roller or a developing sleeve can be applied as process means for detecting current.

  In the case of the primary transfer roller, a common current detection circuit is provided for one or a plurality of primary transfer high-voltage power supply circuits, and the flow charts of FIGS. 23A and 23B and FIGS. Just do it. This corresponds to the primary transfer high-voltage power supply circuit described in FIG. However, since the process means for detecting the current is the primary transfer roller, the primary transfer high-voltage power supply circuit is kept on even after the timing T3 in FIG.

  In the case of a developing sleeve, a current detection circuit is provided in common with one or a plurality of development high-voltage power supply circuits, and the flowcharts of FIGS. 23A and B and FIGS. 25A and 25B are executed by the current detection circuit. good. Note that how to control the output voltage from one or a plurality of development high-voltage power supply circuits is as described in the third embodiment.

  As described above, in the present embodiment, the control unit 54 performs the standby process of S1903 so that the detection timings of the electrostatic latent images do not overlap with each other. A common current detection circuit 147 can be used for the circuits 46a to 46d. Thereby, the structure which concerns on a current detection circuit can be simplified.

  On the other hand, using the common current detection circuit 50 described in the present embodiment, color misregistration is performed in the same manner as the flowcharts illustrated in FIGS. 5 and 10 and the flowcharts illustrated in FIGS. Correction control can also be executed. This will be described with reference to the flowcharts of FIGS.

  In this case, first, the control unit 54 executes the timing chart of FIG. 24 described above. At this time, the flowcharts of FIG. 23A and FIG. 26 are executed in parallel. If the flowchart of FIG. 26 is demonstrated, the process of step S2311 thru | or S2314 is the same as that of FIG. 23B.

  In steps S2601 to S2604, the control unit 54 performs a loop process of k = 1 to 4. In the loop process of k = 1, in step S2602, the control unit 54 calculates the average value of the first, 1 + 4th, and 1 + 4 + 4th measurement values from the 12 measurement values stored in step S2313 of FIG. In step S2603, it is stored as the first reference value. Note that when the influence of the photosensitive drum eccentricity of each data is different, for example, the control unit 54 may calculate the average value by weighting. And the control part 54 calculates an average value similarly about n = 2-4. The stored information in this loop processing indicates a reference state that is a target when color misregistration correction control is performed. In the color misregistration correction control, the control unit 54 performs control so as to eliminate the deviation from the reference state, in other words, return to the reference state.

  Thereafter, when a predetermined condition is satisfied, the timing chart of FIG. 24 is executed again under the predetermined condition, and then the flowcharts of FIG. 25B and FIG. 27 are executed in parallel. In the flowchart of FIG. 27, the processing of steps S2311 to S2314 is the same as that of FIG. 25B.

  In steps S2701 to S2706, the control unit 54 performs a loop process of k = 1 to 4. In the loop process of k = 1, in step S2702, the control unit 54 calculates the average value of the first, 1 + 4th, and 1 + 4 + 4th measurement values again from the 12 measurement values stored in step S2313 of FIG. To do. In step S2703, the control unit 54 compares the average value calculated in step S2702 for k = 1 with the first reference value stored in step S2603.

  If the average value calculated in step S2702 for k = 1 is larger than the first reference value stored in step S2603, the first color (yellow) is determined in step S2704. Advance the laser beam emission timing. On the other hand, if smaller than the reference value, the emission of the first color is delayed in step S2705. Thereafter, the same loop processing is performed for n = 2 to 4. As a result, the current color misregistration state can be returned to the reference color misregistration state (reference state).

  In the description of the fifth embodiment, the image forming apparatus provided with the charging high-voltage power supply circuit has been described. However, instead of the charging high-voltage power supply circuit, a primary transfer high-voltage power supply circuit or a development high-voltage power supply circuit is used. It is also assumed that the flowchart of FIG. 27 is executed.

In this way, the processing of the flowcharts of FIGS. 23 and 25 described in the fifth embodiment can be executed based on the self-reference of each color. In addition, regarding the calculation of the color misregistration amount at this time, for example, an arithmetic form in which comparison with a reference value obtained in advance as an average value is not performed is assumed. For example, for yellow, magenta, cyan, and black, the control unit 54 obtains the color misregistration amount by an arithmetic method that does not perform comparison with the reference value according to the following formulas 25 to 28.
(Ts ′ (1) + ts ′ (5) + ts ′ (9)) − (ts (1) + ts (5) + ts (9)) Expression 25
(Ts ′ (2) + ts ′ (6) + ts ′ (10)) − (ts (2) + ts (6) + ts (10)) Expression 26
(Ts ′ (3) + ts ′ (7) + ts ′ (11)) − (ts (3) + ts (7) + ts (11)) Expression 27
(Ts ′ (4) + ts ′ (8) + ts ′ (12)) − (ts (4) + ts (8) + ts (12)) Expression 28

  For example, when Expression 26 is described, when the calculation result of Expression 26 by the control unit 54 is negative, the control unit 54 delays the laser beam emission timing (light irradiation timing) of magenta that is the measurement color. For example, when it is determined that it is smaller than the reference value in step S1001 of FIG. 10, when it is determined that it is smaller than the reference value in step S1303 of FIG. 12, when it is determined that it is smaller than the reference value in step S2103 of FIG. This corresponds to the case where it is determined in step S2703 in FIG. 27 that the value is smaller than the reference value. When the calculation result is positive, the control unit 54 performs control opposite to that in the negative case. Similar image forming condition control (light irradiation timing control) is performed for the other colors.

  As described above, even when a common current detection circuit is used for a plurality of process means, an electrostatic latent image for color misregistration correction is formed without depending on the position (phase) of the photosensitive drum. Can do. In this embodiment, although an electrostatic latent image for color misregistration correction is formed three times on each photosensitive drum, the accuracy increases as the number of times increases, and is limited to three. It is not something.

  In each of the above-described embodiments, the reference value acquisition process, which is a criterion for determining the color misregistration state in FIGS. 5, 12, 19, 23A, and 23B, is performed as shown in FIGS. It has been described that this is performed before the color misregistration correction control process. However, when the temperature rises from the in-machine temperature to the normal in-machine temperature, the reference value acquisition process does not necessarily have to be performed as long as it returns to a substantially fixed mechanical state.

  A predetermined reference value (reference state) known at the design stage or the manufacturing stage may be used instead. The predetermined reference value is replaced with the value stored in step S506 in FIG. 5, step S1208 in FIG. 12, step S1910 in FIG. 19, step S2313 or S2317 or 2320 in FIG. 23, and step S2603 in FIG. . The predetermined reference state, which is a target when correcting the color misregistration state, is stored in, for example, the EEPROM 324 of FIG. 3 and is referred to by the control unit 54 as appropriate. Then, each flowchart described above is executed by the reference. Thus, the implementation of each of the above embodiments is not limited to the form in which the reference state in the color misregistration correction control is detected and stored each time.

Note that a reference value in place of the value stored in step S506 and step S1208 is preliminarily set to EE.
When stored in the PROM 324, a predetermined rotational phase is stored in association with the stored reference value. Then, the control unit 54 refers to the stored information on the predetermined rotation phase, and forms an electrostatic latent image for color misregistration correction in step S503 and step S1203 at the referred predetermined rotation phase. However, when the electrostatic latent image for n color misregistration correction formed in steps S1203 to S1205 is, for example, one or more rotations of the photosensitive drum, a predetermined rotation phase is set to a predetermined reference value. There is no need to store them in association with each other.

[Modification]
In the above description, the image forming apparatus having the intermediate transfer belt 30 has been described. However, the image forming apparatus can be diverted to other types of image forming apparatuses. For example, an image forming system that includes a recording material conveyance belt and directly transfers a toner image developed on each photosensitive drum 22 onto a transfer material (recording material) conveyed by the recording material conveyance belt (endless belt). Can be diverted to equipment. At this time, the toner color misregistration detection mark described with reference to FIG. 6 is formed on the recording material conveyance belt (endless belt).

  The primary transfer roller 26a has been described as an example of the primary transfer unit. However, for example, a contact-type primary transfer unit using a transfer blade may be applied. In addition, a primary transfer unit that forms a primary transfer nip portion by surface pressing as disclosed in Japanese Patent Application Laid-Open No. 2007-156455 may be applied.

  In the above description, the current information is detected by the current detection circuit 47a as the surface potential information reflecting the surface potential of the photosensitive drum. This is because the controller 54 performs constant voltage control during primary transfer during image formation. On the other hand, as another primary transfer method, it is also known to apply a transfer voltage to the primary transfer means by a constant current application method. That is, it may be assumed that constant current control is adopted as a primary transfer method during image formation. In this case, voltage fluctuation is detected as surface potential information reflecting the surface potential of the photosensitive drum. Similar to the case of FIG. 8, the same processing as in the flowchart described above may be performed for the time until the characteristic shape of the voltage change is detected. The same applies to the charging high-voltage power supply circuits 43a to 43d and the development high-voltage power supply circuits 44a to 44d described in the third embodiment and the high-voltage power supply devices described in the fourth and fifth embodiments.

  In the fourth and fifth embodiments, the case where the high-voltage power supply circuit in which the current detection circuit is shared by a plurality of process means is used is described, but the present invention is not limited to this. For example, the present invention can also be implemented using the high-voltage power supply circuit described with reference to FIGS. 2A and 2B and the development high-voltage power supply circuits 44a to 44d illustrated in FIGS. 16A and 16B of the third embodiment.

  In each of the above-described embodiments, the color image forming apparatus has been described as an example. However, the above-described electrostatic latent image for color misregistration correction can be used as an electrostatic latent image for detection in other applications. . For example, in a black and white printer, it can be used when the toner image forming position on the recording material is appropriately controlled. In this case, after the detection electrostatic latent image is formed on the photosensitive drum, the passage of the detection electrostatic latent image is detected in the development nip portion, the transfer nip portion, and the charging nip portion. Are stored in the EEPROM 324 in advance. Then, the control unit 54 compares the result measured in step S505 in FIG. 10 or the result calculated in step S1302 in FIG. 13 with the ideal time stored in advance. This ideal time corresponds to the reference value in the flowcharts of FIGS. Then, depending on the size, processing similar to steps S1001 to S1003 in FIG. 10 and steps S1303 to S1305 in FIG. 13 may be performed. Accordingly, the light irradiation position on the photosensitive drum can be corrected to an appropriate position, and the toner image forming position on the recording material can be corrected to a good state. Thereby, for example, a printed matter with a well-designed layout can be obtained in a case where a form is printed on preprinted paper.

20a to 20d Scanner units 22a to 22d Photosensitive drums 24a to 24d Developing sleeves 26a to 26d Primary transfer roller 30 Intermediate transfer belts 46a to 46d Primary transfer high-voltage power supply circuits 47a to 47d Current detection circuit 80 Electrostatic latent image

The present invention relates to images forming apparatus using an electrophotographic system, more particularly to an image forming apparatus capable of forming an electrostatic latent image.

(1) In the image forming apparatus capable of forming a toner image of the electrostatic latent image or correction for correction, a first detecting means for detecting the electrostatic latent image for the correction, the toner image for the correction From the second detection means for detecting, the first correction for correcting the position where the electrostatic latent image is formed at the time of image formation based on the detection result from the first detection means, and from the second detection means Control means for performing a second correction for correcting a position where an electrostatic latent image is formed at the time of image formation based on the detection result of the image forming apparatus, and the control means according to the state of the image forming apparatus, performing a first correction, or images forming apparatus you and performing the second correction.

In the color misregistration correction control that is performed when the apparatus internal temperature changes due to continuous printing or the like, the time for which the change in the primary transfer current is detected again and the electrostatic latent image 80 reaches the position of the primary transfer roller 26a. Measure. The change in the arrival time measured here reflects the color shift amount as it is. Accordingly, the timing at which the scanner unit 20a irradiates the laser beam 21a is adjusted so as to cancel this during printing, and color misregistration is corrected. Details will be described below. Note that the control of the image forming conditions relating to the correction of color misregistration is not limited to the control of the light irradiation timing. For example, the speed control of the photosensitive drum described in the second embodiment described later, or the mechanical position adjustment of the reflection mirror included in each of the scanner units 20a to 20d may be used.

In the above embodiment, it has been described that the current value flowing through the primary transfer roller 26a, the photosensitive drum 22a, and the ground according to the output voltage of the output terminal 53 is detected as the output value related to the surface potential of the photosensitive drum 22a. However, it is not limited to this. In addition to the primary transfer rollers 26a to 26d, charging rollers 23a to 23d, developing sleeves 24a to 24d, and the like are provided around the photosensitive drums 22a to 22d. The first or second embodiment can be applied to the charging rollers 23a to 23d and the developing sleeves (developing rollers) 24a to 24d. That is, the electrostatic latent image 80 formed on as above described photosensitive drum 22a~22d is photosensitive upon reaching the charging roller 23a~23d and the developing sleeves (developing rollers) 24 a to 24 d as a process means You may detect the output value which concerns on the surface potential of drum 22a-22d.

The charging high-voltage power supply circuit 43a in this case is shown in FIG. The difference from FIG. 4, there is a point at which one output terminal 53 is connected to the charging roller 23a. Another difference is that the diodes 1601 and 1602 whose cathode and anode directions are opposite to the diodes 64 and 65 constitute a high-voltage power supply circuit. This is because in the image forming apparatus of this embodiment, the primary transfer bias voltage is a positive voltage, whereas the charging bias voltage is a negative voltage. The charging high-voltage power supply circuits 43b to 43d for the other colors are the same as the circuit configuration shown in FIG. 16A, and thus detailed description thereof is omitted as in the case of the primary transfer high-voltage power supply circuit.

Claims (16)

A rotatingly driven photosensitive member; a charging unit that charges the photosensitive member; a light irradiating unit that irradiates light to form an electrostatic latent image on the photosensitive member; and a toner placed on the electrostatic latent image A color image forming apparatus provided with an image forming unit corresponding to each color, including a developing unit that forms a toner image on a photoconductor and a transfer unit that transfers a toner image attached on the photoconductor onto a belt. There,
Forming means for controlling the light irradiation means corresponding to each color to form an electrostatic latent image for color misregistration correction on the photoreceptor of each color;
The charging means, the developing means, or the power supply means of the transfer means arranged for each color photoconductor;
The output of the power supply means for each color when the electrostatic latent image for color misregistration correction formed on the photoconductor of each color passes through a position facing the charging means, the developing means, or the transfer means. Detecting means for detecting;
A color image forming apparatus comprising: control means for performing color misregistration correction control so as to return the color misregistration state to a reference state based on a detection result by the detection means. A rotationally driven photoconductor, a process unit disposed in the vicinity of the photoconductor and acting on the photoconductor, a light irradiation unit that irradiates light and forms an electrostatic latent image on the photoconductor, A color image forming apparatus for forming a toner image on a belt by operating the image forming unit.
Forming means for controlling the light irradiation means corresponding to each color to form an electrostatic latent image for color misregistration correction on the photoreceptor of each color;
Power supply means of the process means corresponding to each color;
Detecting means for detecting the output of the power supply means for each color when an electrostatic latent image for color misregistration correction formed on the photoreceptor of each color passes through a position facing the process means;
A color image forming apparatus comprising: control means for performing color misregistration correction control so as to return the color misregistration state to a reference state based on a detection result by the detecting means. The image forming unit forms a color misregistration correction toner image on a transfer target,
A toner image detection means for detecting the color misregistration correction toner image formed on the transfer body;
The control unit causes the light irradiating unit to emit light and reflect the color on the photoconductor in a state in which the color misregistration correction control based on the detection result of the color misregistration correction toner image by the toner image detecting unit is reflected. The color image forming apparatus according to claim 1, wherein an electrostatic latent image for deviation correction is formed.   The control means causes the light irradiating means to emit light at the same or substantially the same rotational position as the photosensitive member when the color misregistration correcting electrostatic latent image is formed. The color image forming apparatus according to claim 1, wherein the electrostatic latent image for color misregistration correction is formed on the color image forming apparatus. The forming unit forms an electrostatic latent image for color misregistration correction on each color photoconductor at a plurality of positions on the photoconductor,
The control unit is configured to correct the color misregistration so that the color misregistration state is returned to the reference state based on the detection result of the electrostatic latent image for color misregistration correction formed at the plurality of positions on the photoconductors of the respective colors by the detection unit. The color image forming apparatus according to claim 1, wherein control is performed. 6. The reference state is based on a detection result of an electrostatic latent image for color misregistration correction formed at a plurality of positions of the photoconductor, or is predetermined. A color image forming apparatus described in 1. The forming means forms a first electrostatic latent image for color misregistration correction on each photoconductor at a plurality of positions on the photoconductor,
The control unit causes the storage unit to store the detection result of the first latent image for color misregistration correction formed on each photoconductor by the detection unit,
The forming unit forms a second electrostatic latent image for color misregistration correction on each photoconductor at a plurality of positions on the photoconductor under predetermined conditions.
The control means includes a detection result of the first electrostatic latent image for color misregistration correction stored in the storage means by the detecting means, and the detection means for the second electrostatic latent image for color misregistration correction. 5. The color image forming apparatus according to claim 1, wherein the color misregistration correction control is performed based on a detection result obtained by the method. The forming unit forms the electrostatic latent image for color misregistration correction at a plurality of positions of the photoconductor;
The detection means detects the time until the plurality of color misregistration correction electrostatic latent images pass through a position facing the process means, respectively.
5. The color image forming apparatus according to claim 2, wherein the control unit performs the color misregistration correction control based on a detection result of each time and a reference value.   9. The color image forming apparatus according to claim 8, wherein the detection results of the respective times by the detection means are actual measurement results in which at least a component of the rotation period of the photoconductor is suppressed. The forming means forms the electrostatic latent image for color misregistration correction on each color photoconductor at a plurality of positions on the photoconductor,
The control unit acquires a first measurement result obtained by reducing at least a component of the rotation period of the photoconductor based on the detection results of the plurality of electrostatic latent images for color misregistration correction by the detection unit,
The forming means again forms the electrostatic latent image for color misregistration correction on each color photoconductor at a plurality of positions of the photoconductor under a predetermined condition, and the control means is formed again. Based on the detection result of the electrostatic latent image for color misregistration correction, a second actual measurement result obtained by reducing at least a component of the rotation period of the photoconductor is obtained, and the control means includes the first actual measurement result, 5. The color image forming apparatus according to claim 2, wherein the color misregistration correction control is performed based on a second actual measurement result. The process means is composed of a plurality of types of process means,
The control means causes other process means arranged upstream of any process means to be detected by the detection means in the direction of movement of the electrostatic latent image to electrostatically control the color misregistration correction. When the latent image passes through a position facing the other process means, it is separated from the toner image forming position, or the action on the photoconductor is set to be at least smaller than that during normal toner image formation. The color image forming apparatus according to claim 2, wherein the color image forming apparatus is a color image forming apparatus.   The color image forming apparatus according to claim 11, wherein the process unit to be detected is a transfer unit, and the other process unit is a developing unit. When the process means to be detected is a charging means,
The control means sets the developing means as the other process means to be separated from the toner image forming position, or at least is set to have a smaller action on the photoconductor than during normal toner image formation,
Separating the transfer means as the other process means from a toner image forming position;
Alternatively, the color image forming apparatus according to claim 11, wherein at least the action on the photosensitive member is set to be smaller than that during normal toner image formation.   The detection means is common to a plurality of the photoconductors, and the detection timing of the electrostatic latent image for color misregistration correction by the detection means does not overlap in the plurality of photoconductors. Item 14. The color image forming apparatus according to any one of Items 1 to 13.   15. The color image forming apparatus according to claim 1, wherein the detection unit detects that an output output from the power source unit satisfies a predetermined condition.   The color according to claim 1, wherein a width of the electrostatic latent image for color misregistration correction in the main scanning direction is at least half of an image area width in the main scanning direction. Image forming apparatus.

Images