JP5863314B2 - Color image forming apparatus - Google Patents

Description

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

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

  In such a color image forming apparatus, color misregistration (positional misregistration) occurs when images of the respective colors are superimposed. In particular, this problem is conspicuous in a configuration having a laser scanner (optical scanning device) and a photosensitive drum independently in each color image forming unit. That is, the positional relationship between the laser scanner and the photosensitive drum is different for each color, or the positions of the colors are not synchronized due to various factors such as optical characteristics, speed differences in exposure and transfer, 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, when it takes time to perform the color misregistration correction control, a so-called down time occurs, which gives stress to the user. That is, it is desired to shorten the time required for color misregistration correction control as much as possible.

  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 shorten the time required for color misregistration correction control as much as possible. Other issues can be understood throughout the specification.

In order to solve the above-described problems, the present invention has the following configuration.
An image comprising: a photosensitive member that is driven to rotate; a process unit that is disposed around the photosensitive member and that acts on the photosensitive member; and a light irradiation unit that performs light irradiation to form an electrostatic latent image on the photosensitive member. A forming apparatus that detects an output through the process means when an electrostatic latent image for correction formed by light irradiation by the light irradiation means passes through a position facing the process means. And a reference value that is a value related to a time from when an electrostatic latent image is formed on the photoconductor until it is detected by the detecting unit, corresponding to each of a plurality of rotational phases of the photoconductor Is held by the holding unit with respect to a rotation phase at the time of formation, which is a phase of the photosensitive member when the electrostatic latent image for correction is formed, and a detection result from the detecting unit. Based on the reference value, image formation Image forming apparatus characterized by and a control means for correcting the conditions for forming an electrostatic latent image.

  According to the present invention, the time required for color misregistration correction control can be further shortened.

Configuration diagram of tandem (4 drum system) color image forming apparatus (A) Configuration diagram of a high-voltage power supply device provided with a plurality of high-voltage power supplies, (b) Charging high-voltage power supply circuit diagram, hardware block diagram of the engine control unit, (c) functional block diagram relating to the engine control unit Flow chart showing reference value acquisition processing (A) A diagram showing an example of a state of forming a color misregistration detection mark (for color misregistration correction) formed on the intermediate transfer belt, and (b) an electrostatic latent image for color misregistration detection (for color misregistration correction). The figure which shows a mode that it was formed on the photosensitive drum (on a photoconductor) (A) A diagram showing an example of a surface potential information detection result of the photosensitive drum, (b) a schematic diagram showing a surface potential of the photosensitive drum when no toner is attached to the electrostatic latent image, and (c) an electrostatic latent Schematic diagram showing the surface potential of the photosensitive drum when toner adheres to the image (A) Timing chart of signal output of home position detection signal, laser signal, and electrostatic latent image detection signal, (b) Table holding reference values corresponding to each phase. Flow chart of color misregistration correction control Diagram for explaining how laser irradiation position is corrected Charged high voltage power supply circuit diagram with common ammeter Flow chart showing another reference value acquisition process Another color misregistration correction control flowchart Flow chart of color misregistration correction control Another table holding reference values for each phase Primary transfer high-voltage power supply circuit diagram and development high-voltage power supply circuit diagram

  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.

  FIG. 1 is a configuration diagram of a tandem (4-drum system) color image forming apparatus 10. First, 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 include reflection mirrors and laser diodes (light emitting elements), and sequentially apply 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 (developing sleeves 24a to 24d) output a voltage of, for example, -350 V, supply toner to the electrostatic latent images on the photosensitive drums 22a to 22d, and form a toner image on the photosensitive drum (photosensitive member). Form. 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 a toner image, such as a charging roller, a developing device, and a primary transfer roller, including a scanner unit and a photosensitive drum, is referred to as an image forming unit. In some cases, the image forming unit may be referred to without including the scanner unit 20. 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. A plurality of types of members can correspond to the process means.

  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 at the secondary transfer position of the secondary transfer roller 27 so that the timing coincides with the conveyed toner image. Then, the toner image is transferred from the intermediate transfer belt 30 onto the recording material (on the recording medium 12) by the secondary transfer roller 27.

  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. In the above description, the image forming apparatus having the intermediate transfer belt 30 is 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.

[Configuration diagram of high-voltage power supply unit]
Next, the configuration of the high-voltage power supply device in the image forming apparatus of FIG. 1 will be described with reference to FIG. The high-voltage power supply circuit device shown in FIG. 2A includes charging high-voltage power supply circuits 43a to 43d, development high-voltage power supply circuits 44a to 44d, primary transfer high-voltage power supply circuits 46a to 46d, and secondary transfer high-voltage power supply circuit 48. .

  The charging high-voltage power supply circuits 43a to 43d can form a background potential on the surface of the photosensitive drums 22a to 22d by applying a voltage to the charging rollers 23a to 23d, and can form an electrostatic latent image by laser light irradiation. Put it in a state. Here, each of the charging high-voltage power supply circuits 43a to 43d includes current detection circuits 50a to 50d.

  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.

[Circuit diagram of high-voltage power supply]
A circuit configuration of the charging high-voltage power supply circuit 43 in the high-voltage power supply device of FIG. 2A will be described with reference to FIG. In FIG. 2B, the transformer 62 boosts the voltage of the AC signal generated by the drive circuit 61 to an amplitude several tens of times. A rectifier circuit 51 including diodes 1601 and 1602 and 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 has a driving circuit so that the voltage of the output terminal 53 divided by the detection resistors 67 and 68 is equal to the voltage set value 55 set by the control unit 54 (hereinafter simply referred to as the control unit 54). The output voltage of 61 is controlled. Then, a current flows according to the voltage of the output terminal 53 and via the photosensitive drum 22, the charging roller 23, and the ground.

  Here, the current detection circuit 50 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 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 rising detection timing and the falling detection timing 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.

[Hardware Block Diagram of Engine Control Unit 54]
The controller 54 will be described. The control unit 54 comprehensively controls the operation of the image forming apparatus described with reference to FIG. The CPU 321 uses the RAM 323 as a main memory and work area, and controls the engine mechanism described above according to various control programs stored in the EEPROM 324. Further, the ASIC 322 performs control of each motor, high voltage power supply control of the developing bias, and the like in various print sequences under the instruction of the CPU 321. 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. A part of the function of the control unit 54 may be assigned to other hardware equivalent to the control unit 54.

[Function block diagram]
Next, a functional block diagram related to the engine control unit 54 will be described with reference to the block diagram of FIG. The actuator 326 and the sensor 325 indicate hardware. Each of the patch forming unit 327, the process means control unit 328, and the color misregistration correction control unit 329 indicates a functional block. Each of these will be specifically described below.

  The actuator 326 generically represents actuators such as a drum drive motor and a developer separation motor. The sensor 325 generically represents sensors such as the registration sensor 111 and the current detection circuit 50. The control unit 54 performs various processes based on information acquired from the various sensors 325. The actuator 326 functions as, for example, a drive source that drives a cam for separating developing sleeves 24a to 24d described later from the photosensitive drum.

  Further, the patch forming unit 327 controls the scanner units 20a to 20d to form latent image marks to be described later on the drums 22a to 22d. The process means control unit 328 controls the operation / setting of each process means at the time of electrostatic latent image detection, as will be described with reference to a flowchart of FIG. The color misregistration correction control unit 329 calculates the color misregistration correction amount and reflects the color misregistration correction amount from the timing detected by the detection voltage 561 by a calculation method described later.

  It should be noted that in realizing the functions described here, the form of hardware is not limited, and any of CPU 321, ASIC 322, and other hardware may be operated. The processing may be shared among the hardware by arbitrary distribution.

[Description of color misregistration correction control]
Hereinafter, the color misregistration correction control in this embodiment will be described in detail. First, by the image forming apparatus described above, a color misregistration correction mark by a toner image is formed on the intermediate transfer belt 30 to reduce the color misregistration amount at least. Then, after at least reducing the color misregistration state, the time for the electrostatic latent image 80 to reach the positions of the charging rollers 23a to 23d is measured by detecting a change in the charging current, and based on the measurement result, the color misregistration is performed. Set the reference value for correction control. At this time, the time as a reference value for the electrostatic latent image 80 to reach the positions of the charging rollers 23a to 23d is managed for each of a plurality of phases of the photoconductor.

  In color misregistration correction control that is performed when the temperature inside the apparatus changes during continuous printing, pay attention to the rotational phase of the photosensitive drum according to the situation, and again detect the change in charging current to The time for the electrostatic latent image 80 to reach the positions of the charging rollers 23a to 23d is measured. 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. 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 or the mechanical position adjustment of the reflection mirror included in each of the scanner units 20a to 20d may be used. Details will be described below.

[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 with reference to FIGS. FIG. 3A shows the process for yellow, but it is assumed that the same process is performed for other colors except for step S301.

  First, in step S301, the control unit 54 causes a toner mark for color misregistration correction to be formed on the intermediate transfer belt 30 by the image forming unit. The color misregistration correction toner mark is referred to as a color misregistration correction toner mark because it is a toner image used for color misregistration correction. Here, FIG. 4 shows how toner marks for color misregistration correction are formed.

  In FIG. 4A, reference numerals 400 and 401 denote toner marks (also referred to as patterns) for detecting a color misregistration amount in the paper conveyance direction (sub-scanning direction). Reference numerals 402 and 403 denote toner marks for detecting the amount of color misregistration in the main scanning direction orthogonal to the paper transport direction, and are inclined 45 degrees in this example. 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. In detecting the color misregistration correction toner image, it is possible to apply an optical sensor that receives reflected light when the toner image is irradiated with light and detects a voltage corresponding to the received light amount. it can.

First, with respect to the sub-scanning direction, 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 pattern (400, 401) and the Y pattern is dsM, dsC, dsBk. And For example, the color misregistration amount δesM of the M color when Y is the reference color is expressed by the following formula 1. The same applies to δesC and δesBk, and detailed description thereof is omitted. Here, dsM represents an ideal distance between the Y pattern and the M pattern.
δesM = v × {(tsf2−tsf1) + (tsr2−tsr1)} / 2−dsM Expression 1

Further, regarding the main scanning direction, the misregistration amounts of the left and right colors are δemf and δemr. For example, regarding δemf, the misregistration amount δemfM of the M color when Y is the reference color is expressed by the following Equation 2. expressed. The same applies to δemfC, δemfBk, δemrM, δemrC, and δemrBk, and detailed description thereof is omitted.
δemfM = v × (tmf2−tsf2) −v × (tmf1−tsf1) Equation 2

  Then, the deviation direction can be determined from the sign of the calculation result, the writing position is corrected from δemf, and the main scanning width (main scanning magnification) is corrected from δemr−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.

  As described above, the process of step S301 can basically be based on a state in which the amount of color misregistration is at least small in the control by the subsequent electrostatic latent image for color misregistration correction.

  Returning to the flowchart of FIG. In step S302, the control unit 54 detects a so-called home position Hp of the photosensitive drum 22a as a reference position (reference phase). When the photosensitive drum driving gear is provided on the rotating shaft of the photosensitive drum, the reference position (reference phase) of the driving gear of each photosensitive drum is substantially detected.

  Next, in step S303, the control unit 54 starts a timer. Note that the process of step S303 is executed substantially simultaneously with the process of the previous step S302.

Next, the control unit 54 performs a loop process of i = 1 to 6 in steps S304 to S307. In step S305 in the loop process, the control unit 54 sequentially outputs laser signals. The scanner unit 20a performs light irradiation according to the output electrostatic latent image signal. In step S306, the control unit 54 performs standby processing for a predetermined time. Here, standby is performed only for the time required for the photosensitive drum to rotate 60 °. By the loop processing in steps S304 to S307, the electrostatic latent image 80 is formed with a phase of φ ₁ to φ ₆ with respect to the home position. Note that the rotation angle of the photosensitive drum corresponding to the standby time is determined by how many electrostatic latent images are formed, and is not limited to 60 ° described here.

  Further, until the electrostatic latent image formed on the photosensitive drum passes directly below each process means, the developing sleeve 24a disposed upstream of each charging roller 23a where the electrostatic latent image is detected. The primary transfer roller 26a is separated from the photosensitive drum 22a. Alternatively, the applied voltage is set to off (zero), and the operation to the photosensitive drum is at least reduced as compared with normal toner image formation. Further, the developing bias high-voltage power supply circuit (developing high-voltage power supply circuits 44a to 44d) may be configured not to adhere toner by applying a bias voltage having a reverse polarity to that of the normal one. Further, when adopting the jumping development method in which the photosensitive drum and the developing sleeve are brought into a non-contact state with respect to the developing sleeves 24a to 24d and the voltage application is performed by superimposing the AC bias on the DC bias, the voltage application is simply turned off. good. The correspondence between the separation and the applied voltage off is continued until the flowchart of FIG. 3 is completed. The same applies to FIG. 7 described later.

[Formation of latent image mark]
FIG. 4B is a diagram showing a state in which 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 drawing, a state in which the electrostatic latent image 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 30 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.

  Next, the flowchart of FIG. 3B will be described. FIG. 3B also shows processing for yellow, but it is assumed that similar processing is performed for other colors. The control unit 54 performs a loop process of i = 1 to 6 in steps S311 to S314. In step S312, the control unit 54 sets the edge detection timing Ty (i) (i = 1 to 6) from the reference timing for the six electrostatic latent images formed in the flowchart of FIG. To detect. The control unit 54 performs edge detection when the output of the binarized voltage value 561 changes. In step S313, the detected timer value Ty (i) is temporarily stored in the RAM 323.

[Description of drum surface potential change]
FIG. 5A shows an output value related to the surface potential of the photosensitive member (photosensitive drum 22a) from the current detection circuit 50a when the electrostatic latent image 80 reaches the charging roller 23a as the process means. It is a thing. In FIG. 5A, the vertical axis represents the voltage indicating the detected current change, and the horizontal axis represents time. The waveform of FIG. 5A shows a characteristic that the electrostatic latent image 80 is minimized when the electrostatic latent image 80 reaches the charging roller 23a, and then returns.

  Here, the reason why the detected voltage value decreases will be described. FIG. 5B is a schematic diagram showing the surface potential of the photosensitive drum 22a when the toner is attached to the electrostatic latent image and when the toner is not attached. 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 indicates the potential, and the dark potential of the photosensitive drum 22a is described as VD (for example, −700 V), the bright potential is set as VL (for example, −100 V), and the charging bias potential of the charging roller 23a is described as VC (for example, −1000 V).

  In the region 93 of the electrostatic latent image 80, the potential difference 96 between the charging roller 23a and the photosensitive drum 22a is larger than the potential difference 95 in other regions. For this reason, when the electrostatic latent image 80 reaches the charging roller 23a, the value of the current flowing through the charging roller 23a increases. As the current increases, the voltage value at the output terminal of the operational amplifier 70 decreases. The above is the reason why the detected voltage value decreases. The detected current value reflects the surface potential of the photosensitive drum 22a. In FIG. 5, the difference between the photosensitive drum surface potential and the output voltage of the charging roller 23a has been described as an example. However, the same applies to the change in the amount of current, the photosensitive drum surface potential and the transfer voltage or development. It can also be said between voltages.

  In the above description, the configuration in which the developing sleeve 24a is separated from the photosensitive drum 22a without detecting toner 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. 5C is a schematic diagram showing a potential difference between the photosensitive drum 22a and the charging roller 23a when toner is placed on the electrostatic latent image 80. FIG. The same elements as those in FIG. 5B 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 charging roller 23a and the photosensitive drum 22a is smaller than the potential difference 96 when no toner is placed. Therefore, the difference between the potential difference 95 and the potential difference 97 in the other regions 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.

Returning to the flowchart description of FIG. 3 (b), the control unit 54, in step S315, the Ty1~Ty6 stored in step S313, and stores the EEPROM324 in correspondence with phi ₁ to [phi] _6. 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. Note that φ _{1 to} φ ₆ can be referred to as a rotation phase at the time of formation in the meaning of the rotation phase of the photosensitive drum when the electrostatic latent image 80 is formed.

FIG. 6A is a timing chart showing the relationship among home position detection, laser signal output, and electrostatic latent image detection signal output. In the figure, a state where a home position detection signal is output every rotation of the photosensitive drum is shown. In the figure, Td means the time required for one rotation of the photosensitive drum. Then, in response to the detection of the home position, laser signals are sequentially output corresponding to φ ₁ to φ ₆ . In the drawing, the interval between φ _{1 to} φ ₆ is a value obtained by dividing the period Td of the photosensitive drum into six equal parts. Then, after each of the times T1 to T6, signals indicating the detection of electrostatic latent images formed corresponding to φ _{1 to} φ ₆ are output. Here, the length of T1 to T6 is at least approximately equal to the time until the laser exposure position reaches the charging roller facing position. The values of T1 to T6 change from time to time depending on the color misregistration occurrence state in the sub-scanning direction.

FIG. 6B shows a state where T1 to T6 obtained corresponding to φ ₁ to φ ₆ of each color are held in the table. These 24 values are generated and updated by executing the flowchart of FIG. 3 described above corresponding to each color. In the table shown in FIG. 6B, only _six phase angles φ _{1 to} φ ₆ and measured values corresponding to each phase angle are shown, but finer values are held in the table. You may make it do. For example, the approximation function may be calculated by the control unit 54 based on the correspondence between φ _{1 to} φ ₆ and T _{1 to} T ₆ , and the measurement values for all the phase angles may be predicted and stored in a table. By doing so, it is not necessary to perform the processing of S702 in the flowchart of FIG.

[Flow chart of color misregistration correction control]
Next, FIG. 7A shows a flowchart of color misregistration correction control. This flowchart shows the control unit when a preset predetermined condition is satisfied, for example, when the temperature in the apparatus changes due to continuous printing or other factors, when a certain number of sheets are printed, or after a certain period of time has elapsed. This is executed when it is judged by 54. FIG. 7A shows processing for yellow, but it is assumed that similar processing is performed for other colors.

First, in step S701, the control unit 54 detects and specifies the current rotational phase φ _yn of the photosensitive drum. For example, the current phase of the photosensitive drum is detected from the total rotation amount of the photosensitive drum since the photosensitive drum home position was previously detected.

In step S702, the control unit 54 obtains _{i satisfying} φ _i <φ _yn <φ _{i + 1} based on the rotation phase φ _yn specified in S701. Here, i takes a value in the range of _{1 to 6} , and φ ₁ to φ ₆ correspond to φ ₁ to φ ₆ shown in FIG.

In step S703, the control unit 54 refers to the table in FIG. 6B based on i specified in step S702, and acquires the corresponding Ty value in step S704. The gray marker portion in FIG. 7B shows a state where φ ₃ corresponds to φ _{i + 1} and T _y3 corresponding to φ ₃ is acquired by the control unit 54.

In step S705, the control unit 54 starts a timer in response to the rotational phase of the photosensitive drum having reached φ _{i + 1} , and substantially simultaneously outputs a laser signal in step S706 to cause the scanner unit 20a to emit light. Then, an electrostatic latent image 80 is formed on the photosensitive drum.

  Thereafter, in step S707, the control unit 54 determines whether or not the rising edge of the electrostatic latent image 80 formed corresponding to step S706 has been detected. Td is held, and the process proceeds to step S708.

In step S708, the control unit 54 calculates (Td−Ty _{i + 1} ). When the difference is 0 or more, that is, when the timing until the electrostatic latent image 80 is detected is delayed from the reference, the control unit 54 advances the yellow laser beam emission timing by an amount corresponding to the difference value. . On the other hand, when the difference is less than 0, that is, when the timing until the electrostatic latent image 80 is detected is earlier than the reference, the control unit 54 delays the yellow laser beam emission timing by the difference value. The As a result, the current color misregistration state of yellow can be returned to the reference color misregistration state (reference state).

FIG. 8 is a schematic diagram showing how the laser irradiation position (timing) is corrected and corrected to the correct laser irradiation position in step S709. Tn represents an ideal reference value with respect to the phase φ _{n with} respect to the reference home position Hp. Then, Tn ″ (Td) corresponds to an actual measurement value when the laser irradiation light 21a is shifted to the exposure scanning position of the laser irradiation light 21a ′ with respect to the photosensitive drum 22a due to the temperature rise. To do. Tn ′ = Tn, and Δt in the figure indicates the difference between the reference value Tn and the measured value.

  The flowchart of FIG. 7 is similarly executed for colors other than yellow, and the control unit 54 corrects the laser beam emission timing as an image forming condition for magenta, cyan, and black. In this way, the current color misregistration state can be returned to the reference color misregistration state (reference state) by the flowchart of FIG.

  As described above, according to the above implementation, it is possible to further reduce the time required for color misregistration correction control. In addition, color misregistration in the recording medium conveyance direction (sub-scanning direction) can be corrected in a state where toner is saved and in a short time of less than one turn of the photosensitive drum. That is, it is possible to eliminate the problem in the conventional detection of the toner image for detection by the optical sensor and to make the image forming apparatus have usability. Further, according to the above-described implementation, for example, color misregistration correction control can be performed within the image interval of image formation without stopping the image forming job and performing a new color misregistration correction sequence. As a specific example, when the photosensitive drum diameter is 24 mm and the image forming process speed is 200 mm / s, the time required for one rotation of the photosensitive drum is about 377 ms. The belt moving distance in the apparatus which proceeds during this time is about 74 mm. As described above, according to the above-described embodiment, by performing the sequential correction control at the image forming interval, the downtime is suppressed as much as possible, and stable image quality is maintained without causing a large color shift. be able to.

  In the above-described charging high-voltage power supply circuit, a current detection circuit 43 is provided for each charging roller. However, it is not limited to this form. The electrostatic latent image 80 may be detected using a current detection circuit common to the charging rollers 23a to 23d of the respective colors. You may do it. This will be described in detail below.

[Circuit diagram of a charged high-voltage power supply with a common ammeter]
FIG. 9 shows circuit configurations of the charging high-voltage power supply circuits 143a to 143d and the current detection circuit 150. In addition, the same code | symbol is attached | subjected to the same structure as FIG.2 (b), and the description is abbreviate | omitted. In FIG. 9, the drive circuits 61a to 61d operate based on the set values 55a to 55d input to the comparators 60a to 60d, and output desired voltages to the outputs 53a to 53d. The point that the current flows through the current detection circuit 150 via the photosensitive drums 22a to 22d, the charging rollers 23a to 23d, and the grounding point 57 is the same as that shown in FIG. In the detection voltage 56, a voltage corresponding to a value obtained by superimposing the currents of the output terminals 53a to 53d appears.

  Also in FIG. 9, as in FIG. 2B, 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 varies due to the operation of the charging high-voltage power supply circuit of another color, and this hardly affects the operation of the charging high-voltage power supply circuit of another color. In other words, the plurality of charged high-voltage power supply circuits 143a to 143d are not affected by each other and operate in the same manner as the charged high-voltage power supply circuit 43 in FIG.

<Deformation flowchart of FIGS. 3 and 7>
A flowchart illustrating reference value acquisition processing in color misregistration correction control using the current detection circuit described in FIG. 9 will be described with reference to the flowcharts in FIGS. 10 and 11. In addition, it demonstrates centering on the difference with FIG.3 and FIG.7.

  First, in step S1001, processing similar to that in step S301 in FIG. 3 is performed. Next, in step S1002, the control unit 54 determines the rotational phase relationship (rotational position) between the photosensitive drums 22a to 22d in order to suppress the influence of fluctuations in the rotational speed (circumferential surface speed) of the photosensitive drums 22a to 22d. (Relationship) is adjusted 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. When the photosensitive drum driving gear is provided on the rotating shaft of the photosensitive drum, the phase relationship of the driving gear of each photosensitive drum is substantially adjusted. In step S1003, the so-called home position Hp of the photosensitive drum 22a is detected as in step S302.

  Next, in steps S1005 to S1008 in FIG. 10, the control unit 54 performs a loop process of i = 1 to 24. The control unit 54 waits for a rotation angle of 15 ° of the photosensitive member every time the i-th electrostatic latent image is formed in step S1006. More specifically, the control unit 54 first outputs laser signals in the order of yellow, magenta, cyan, and black at i = 1 to 4, and repeats this six times to perform loop processing of i = 1 to 24. Do. Thereby, in each color, an electrostatic latent image for color misregistration correction can be formed at a period of about 1/6 of the photosensitive drum.

  Next, in steps S1011 to S1014 in the flowchart of FIG. 10B, the control unit 54 detects and stores the edges of 48 electrostatic latent images 80 corresponding to the loop processing of i = 1 to 24. .

Further, in the flowchart of FIG. 10C, the control unit 54 performs a loop process of k = 1 to 6. In step S1022, the control unit 54 calculates the first to sixth detection results for each color based on the average of the difference between the rising edge and the falling edge. Then, Ty _{1 to} Ty ₆ , Tm _{1 to} Tm ₆ , Tc _{1 to} Tc ₆ , Tbk _{1 to} Tbk ₆ are stored as reference values in correspondence with φ ₁ to φ ₆ , which are moving rotations at the time of formation, and held as a table To do. Incidentally, strictly speaking, phi ₁ yellow corresponds to 0 ° (reference phase), magenta, cyan and phi ₁ corresponding to each of the black 15 °, 30 °, corresponding to 45 °. However, the phase angles of magenta, cyan, and black correspond to the yellow φ ₁ (0 °), and the phase angles of φ _{1 to} φ ₆ are represented by the yellow phase angles representing the four colors. You may make it allocate. Of course, the measured values may be associated with φ ₁ to φ ₆ for each color and held in a table. That is, the formation rotation phase angle may be a phase angle when the accidental electrostatic latent image 80 is formed, or may be a phase angle of a representative color. Next, FIGS. 11 and 12 are flowcharts of color misregistration correction control according to the second embodiment. First, the flowchart of FIG. 11A will be described.

  In step S1101, the control unit 54 performs the same process as in step S1002 of FIG. Further, the control unit 54 performs the same processing as steps S701 to S703 in FIG. 7 in steps S1102 to S1104.

In step S1105, the reference values are set to Ty _{i + 1} , Tm _{i + 1} , Tc _{i + 1} , and Tbk _{i + 1} . At substantially the same time as step S1105, in step S1106, the control unit 54 starts a timer and starts the loop processing of steps S1107 to S1110.

  In this loop processing, the control unit 54 outputs the first yellow laser signal, then waits for a rotation angle of 15 ° in step S1109, and sequentially outputs yellow, magenta, cyan, and black forward laser signals. To do. Here, the standby for 15 ° is the electrostatic latent image formed with the reference values set in step S1105 excluding the first yellow, with the standby for the rotation angle of 15 ° of the photosensitive drum in the flowchart of FIG. This is because the value corresponds to.

  On the other hand, in FIG. 11B, each electrostatic latent image formed by the loop processing of steps S1107 to S1110 is detected. The process of FIG. 11B is performed in parallel with the process of FIG. Here, since rising and falling are detected separately, the control unit 54 detects a total of eight edges.

Then, in step S1201 of FIG. 12, the control unit 54 performs the calculations of the following formulas 3 to 6 for the detection results T1 to T8 detected in steps S1107 to S1110 of FIG. 11, and the calculation result is stored in the EEPROM 324 in step S1202. To remember.
dTy = (T (1) + T (2)) / 2 Equation 3
dTm = (T (3) + T (4)) / 2 Formula 4
dTc = (T (5) + T (6)) / 2 Equation 5
dTbk = (T (7) + T (8)) / 2 Equation 6

In step S1203, the control unit 54 calculates a difference between dTy stored in step S1202 and the reference value Ty _{i + 1} set in step S1105 of the flowchart of FIG. Then, when the difference is 0 or more, that is, when the yellow color detection timing is delayed from the reference, the control unit 54 advances the yellow laser beam emission timing by the difference value. On the other hand, when the difference is less than 0, that is, when the yellow color detection timing is earlier than the reference, the control unit 54 delays the yellow laser beam emission timing by the difference value. Thereby, the amount of yellow color misregistration can be suppressed.

  Also in steps S1206 to S1214, the control unit 54 performs the same processing as the yellow color for colors other than the yellow color. By doing in this way, the effect similar to Example 1 can be acquired, using the current detection circuit common with respect to the charging rollers 23a-23d of each color.

  In each of the above-described embodiments, the reference value has been set for each color. However, the present invention is not limited to this. For example, the reference value may be set as a relative difference between the measurement colors with respect to the reference color (for example, yellow). This will be described in detail below.

In step S1002 of the flowchart of FIG. 10 in the second embodiment, the rotational phase relationship (rotational position relationship) between the photosensitive drums 22a to 22d is set to a predetermined state. Accordingly, the relative rotational phase difference of the reference color with respect to the measurement color is constant / substantially constant. For example, when yellow is used as the reference color, the reference value of each measurement color (M, C, Bk) is set as a difference with respect to yellow. Can be set. That is, the table described with reference to FIG. 7B is defined as a difference between Ty _n (n = 1 to 6) of the rotational phase φy _n (n = 1 to 6) of the yellow photosensitive drum for magenta, cyan, and black. it can. FIG. 13 shows a table created by the definition of the third embodiment.

Then, the control unit 54, the detection results obtained from the flow chart of FIG. 11 (b), for example with respect to magenta, and calculates the Δ _{(Ty n} -Tm n) in [phi] y _n, measured color reference color of The difference with respect to the detected value is obtained. In addition, the control unit 54 similarly obtains differences for the other colors. Then, the control unit 54 controls the laser beam emission timing of the measurement color as described in the flowchart of FIG. 12 according to the obtained size. By carrying out in this way, the same effect as in the second embodiment can be obtained.

  In each of the above-described embodiments, the charging rollers 23a to 23d have been described as an example of the process means for performing current detection. However, a primary transfer roller or a developing sleeve may be applied as the process means for performing current detection. . FIG. 14A shows a primary transfer high-voltage power supply circuit, and FIG. 14B shows a development high-voltage power supply circuit. Here, the current detection circuit shown in FIG. 14A or FIG. 14B may be provided independently for each color as described in FIG. 2A or described in FIG. As described above, a plurality of colors may be provided in common.

[Development and transfer high-voltage power supply circuit]
A primary transfer high-voltage power supply circuit is shown in FIG. The difference from FIG. 2B is that the directions of the anodes and cathodes of the diodes 1601 and 1602 are opposite, but the others are the same. Further, a transfer bias (transfer voltage) of, for example, +1000 V is output from the output terminal 53. The primary transfer high-voltage power supply circuit shown in FIG. 14A may be replaced with the above-described charging high-voltage power supply circuit, and the flowcharts shown in FIGS. 3 and 7 and processes related thereto may be executed. Moreover, what is necessary is just to perform the flowchart of FIG.10, FIG11 and FIG.12 and the process relevant to it. As a matter of course, at this time, the primary transfer roller 26a needs to be brought into contact with the photosensitive drum 22a.

  In the primary transfer high-voltage power supply circuit shown in FIG. 14A, the control unit 54 is used not only for detection of the electrostatic latent image but also for setting related to the primary transfer voltage. Specifically, the control unit 54 measures the detection value 56 of the current detection circuit 47 at the AD input port at a timing immediately after the start of printing and before the toner image reaches the primary transfer roller 26a. Then, the control unit 54 sets the voltage setting value 55 (primary transfer condition) so that the detection value 56 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. As described above, as the primary transfer high-voltage power supply circuit, a circuit used in normal image formation can be used.

  A development high-voltage power supply circuit is shown in FIG. For example, a developing bias (developing voltage) of −400 V is applied from the output terminal 53. The difference from FIG. 2B is that a reverse development bias output circuit is added. When an electrostatic latent image is detected, the output of CLK2 is turned off and the output of CLK1 is validated. To work. Further, during normal image formation, the output of CLK1 is set to OFF and the output of CLK2 is set to be valid.

  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. Corresponding to this, for example, in the circuit of FIG. 14B, the output of CLK2 is turned off, the output of CLK1 is made effective, and a reverse polarity voltage (reverse bias) is output. Even if there is no reverse development bias output circuit, for example, when VL is negative voltage and −100V, the output of the development high voltage power supply circuits 44a to 44d is negative voltage and the absolute value is −50V smaller than VL. Set it. Then, the development high-voltage power supply circuit may be replaced with the above-described charging high-voltage power supply circuit, and the flowcharts shown in FIGS. 3 and 7 and processes related thereto may be executed. Moreover, what is necessary is just to perform the flowchart of FIG.10, FIG11 and FIG.12 and the process relevant to it.

[Modification]
In each of the embodiments described above, the reference value acquisition process, which is a criterion for determining the color misregistration state, is performed each time. 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 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.

  Although FIG. 9 illustrates an example in which one current detection circuit 150 is provided in common for the four-color charging high-voltage power supply circuit or the four-color charging rollers 23a to 23d, the present invention is not limited to this. For example, one current detection circuit may be provided for one charging high-voltage power supply circuit or charging roller for one color, and a common current detection circuit may be provided for the remaining three charging high-voltage power supply circuits or charging rollers. good. That is, a common current detection circuit can be provided for two or more high-voltage power supply circuits (power supply means) or charging rollers. This is not limited to the charging high-voltage power supply circuit, and the same applies to the development high-voltage power supply circuit or developing sleeve, the transfer high-voltage power supply circuit, or the transfer roller.

  As described above, according to the above description, the color misregistration correction control can be realized without transferring the detection toner image in the color misregistration correction control from the photosensitive drum to the image carrier (belt), and the usability is maintained as much as possible. Therefore, color misregistration correction control can be performed.

  On the other hand, the method for predicting and calculating the color misregistration amount from the amount of change in the temperature in the apparatus does not require the use of toner, but has a problem in accuracy. According to the above description, this point can also be solved.

  In addition, as compared with the case where a toner pattern for color misregistration correction is formed on the intermediate transfer belt, according to the above description, there is an effect that the waiting time until detection of the electrostatic latent image can be shortened.

  Further, in the method of transferring an electrostatic latent image for color misregistration correction onto the intermediate transfer belt, it is necessary to increase the belt time constant τ, which has a demerit that image defects are likely to occur. On the other hand, according to the above description, the time constant τ of the belt can be reduced and image defects can be reduced.

20a to 20d Scanner unit 22a to 22d Photosensitive drum 24a to 24d Developing sleeve 26a to 26d Primary transfer roller 30 Intermediate transfer belt 46a to 46d Primary transfer high voltage power supply circuit 47a to 47d Current detection circuit 80 Electrostatic latent image

Claims (11)

A rotationally driven photoreceptor;
Process means disposed around the photoreceptor and acting on the photoreceptor;
A light irradiating means for irradiating light to form an electrostatic latent image on the photoreceptor, and an image forming apparatus comprising:
Detection means for detecting an output through the process means when the electrostatic latent image for correction formed by light irradiation by the light irradiation means passes through a position facing the process means;
A holding unit that holds a reference value that is a value related to a time from when an electrostatic latent image is formed on the photoconductor until it is detected by the detecting unit, corresponding to each of a plurality of rotational phases in the photoconductor. When,
Based on a detection result from the detection unit and a reference value held in the holding unit with respect to a rotation phase during formation that is a phase of the photoconductor when the electrostatic latent image for correction is formed, An image forming apparatus comprising: a control unit that corrects conditions for forming an electrostatic latent image during image formation. The controller is configured to display the electrostatic latent image at the time of image formation so that the state in which the electrostatic latent image for correction is detected by the detecting unit approaches a reference state in which at least misregistration is suppressed. The image forming apparatus according to claim 1, wherein conditions for forming are corrected. The control unit forms an electrostatic latent image at the time of image formation so that the state in which the correcting electrostatic latent image is detected by the detecting unit returns to a reference state in which positional deviation is suppressed. The image forming apparatus according to claim 1, wherein a condition for performing the correction is corrected. A toner image detecting means for detecting a toner image for correction;
4. The control unit according to claim 1, wherein the control unit corrects a condition for forming an electrostatic latent image during image formation based on a detection result from the toner image detection unit. 5. The image forming apparatus described. Power supply means for supplying power to the process means;
5. The detection unit according to claim 1, wherein the detection unit detects an output of the power source unit when the electrostatic latent image for correction passes a position facing the process unit. 6. The image forming apparatus described. A plurality of the photoreceptors;
The detecting means can commonly detect the electrostatic latent images for correction formed on the plurality of photoconductors, and the detecting means can detect the electrostatic latent images for correction in the plurality of photoconductors. The image forming apparatus according to claim 1, wherein detection timings for detecting the image are not overlapped. A plurality of the photoreceptors;
A plurality of detection means corresponding to the plurality of photoconductors,
6. The image forming apparatus according to claim 1, wherein the plurality of detection units independently detect the electrostatic latent image for correction formed on the corresponding photosensitive member. apparatus. A plurality of the photoreceptors;
8. The control unit according to claim 1, wherein the control unit corrects a color shift between the plurality of photosensitive members by correcting a condition for forming an electrostatic latent image at the time of image formation. The image forming apparatus according to claim 1.   The control unit corrects the light irradiation timing by the light irradiation unit or corrects the conditions for forming an electrostatic latent image at the time of image formation, or the light irradiation by the light irradiation unit is performed. The image forming apparatus according to claim 1, wherein the speed of the photosensitive member is corrected.   The image forming apparatus according to claim 1, wherein the detection unit detects the electrostatic latent image for correction that has not been developed.   The process means is any one of a charging means for charging the photoconductor, a developing means for developing an electrostatic latent image as a toner image, and a transfer means for transferring the toner image to a transfer target. The image forming apparatus according to claim 1.

Images