JP5636780B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

2. Description of the Related Art Image forming apparatuses such as color printers and color copiers that form a color image by superimposing a plurality of color images on a recording medium such as paper are widely used. In this type of image forming apparatus, in general, positional deviation control (so-called “registration control”) is performed in which the positional deviation amount of each color image superimposed on a recording medium is measured in advance and the positional deviation of each color image is corrected. ing.
For example, Patent Document 1 discloses that each image forming unit sequentially forms yellow, magenta, cyan, and black color marks on a transfer belt before starting image formation such as when power is turned on. Is a technique for calculating the positional deviation amount of each color from the reading result of the sensor and feedback controlling the formation timing of the image of each color.

JP-A-8-248721

Here, generally, for example, if position measurement data relating to a large number of marks formed on a transfer body is used, the correction accuracy of the positional deviation of each color image is improved. However, if a large number of marks are used, the time for measuring the positions of the marks becomes longer, and the amount of toner consumed also increases.
SUMMARY OF THE INVENTION An object of the present invention is to reduce the time required for correcting the misregistration of each color image in an image forming apparatus that forms a color image.

According to the first aspect of the present invention, a plurality of image forming units that form images of the respective colors and the images of the respective colors formed by the plurality of image forming units are sequentially directly transferred, or the images are A transfer member that sequentially conveys recording materials to be transferred, and a plurality of image forming units sequentially form a first misregistration correction index at a first position on the transfer member, and a second on the transfer member. An index forming means for sequentially forming a second misregistration correction index different from the first misregistration correction index at the position, and opposed to the first position on the transfer body, First detection means for detecting a first misregistration correction index, and a second detecting means for detecting the second misregistration correction index, arranged opposite to the second position on the transfer body. Detection unit and the plurality of image forming units along the moving direction of the transfer body Forming the first misregistration correction index and the second misregistration correction index in one length region, and a detection result of the first misregistration correction index by the first detection unit; A first misalignment correction format for performing misalignment correction based on both the detection result of the second misalignment correction index by the second detection means, and a first position shorter than the first length region. A second misalignment correction index is formed in the second length region, and the misalignment correction is performed based on the detection result of the first misalignment correction index by the first detection unit. Correction means for correcting the positional deviation of the images of the respective colors formed by the plurality of image forming units according to any one of the positional deviation correction formats, and the index forming unit is provided in the plurality of image forming units. Of each color image formed The first misregistration correction index for detecting the misregistration amount in both the scanning direction and the sub-scanning direction is formed, and the position of each color image in either the main scanning direction or the sub-scanning direction The second misregistration correction index for detecting the misregistration amount is formed, and the correction means is formed in the plurality of image forming units by executing the first misregistration correction format. Correcting a positional shift in both or any one of the main scanning direction and the sub-scanning direction and an inclination in the sub-scanning direction and a magnification in the main scanning direction in each color image, By performing the positional deviation correction format 2, the positional deviation in the main scanning direction and / or the sub-scanning direction in the image of each color is corrected. The image forming apparatus.

According to the first aspect of the present invention, in the image forming apparatus for forming a color image, it is possible to reduce the time required for correcting the misregistration of each color image, and to suppress a decrease in image productivity .

1 is a diagram illustrating a configuration of an image forming apparatus to which the exemplary embodiment is applied. It is a figure explaining the structure for performing position shift control. It is a figure explaining the structure of the reading function part which reads the 1st image quality adjustment pattern in a 1st position detection sensor part. It is a figure explaining the structure of the reading function part which reads the 2nd image quality adjustment pattern in a 2nd position detection sensor part. It is a block diagram explaining the function of a main control part, a 1st position detection sensor part, and a 2nd position detection sensor part. FIG. 4 is a diagram illustrating an example of a first image quality adjustment pattern formed on an intermediate transfer belt by each image forming unit. It is a timing chart explaining the signal which the 1st position detection sensor part generates. FIG. 6 is a diagram illustrating an example of a second image quality adjustment pattern formed on an intermediate transfer belt by each image forming unit. It is a timing chart explaining the signal which a 2nd position detection sensor part generates. It is a figure explaining the detection method of the amount of position shift using the 1st image quality adjustment pattern. It is a figure which shows the other example of the 2nd image quality adjustment pattern. It is a figure which shows the other example of the 2nd image quality adjustment pattern.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 1 to which the exemplary embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem type digital color printer, and an image forming process unit 20 that forms a color image based on image data, and a main control that controls the operation of the image forming process unit 20. Part 60.

The image forming process unit 20 forms each color toner image of yellow (Y), magenta (M), cyan (C), and black (K), which are arranged in parallel at a predetermined interval. As an example, four image forming units 30Y, 30M, 30C, and 30K (hereinafter also collectively referred to as “image forming unit 30”) are provided. In addition to this, for example, in addition to those that form toner images of each color such as light cyan (LC), light magenta (LM), and corporate color, an image forming unit of five or more colors may be provided.
The image forming unit 30 is formed on the photosensitive drum 31, a photosensitive drum 31 on which an electrostatic latent image is formed while rotating in the direction of arrow A, a charging roll 32 that charges the surface of the photosensitive drum 31, and the photosensitive drum 31. A developing device 33 for developing the electrostatic latent image and a drum cleaner 34 for cleaning the surface of the photosensitive drum 31 after the primary transfer are provided. The developing device 33 disposed in each image forming unit 30 generates an electrostatic latent image on the photosensitive drum 31 with each color toner of Y, M, C, and K supplied from the toner containers 35Y, 35M, 35C, and 35K. develop.

The image forming process unit 20 also includes a laser exposure device 26 as an example of an exposure unit that exposes each photosensitive drum 31 provided in each image forming unit 30 with, for example, laser light, and each photosensitive member of each image forming unit 30. Each color toner image formed on the body drum 31 is multiplex-transferred, and an intermediate transfer belt 41 is provided as an example of a transfer body that conveys the multiplex-transferred color toner images while holding them. Further, a primary transfer roll 42 that sequentially transfers (primary transfer) each color toner image of each image forming unit 30 to the intermediate transfer belt 41 in the primary transfer portion Tr1, and a superimposed toner image transferred onto the intermediate transfer belt 41. A secondary transfer roll 40 that performs batch transfer (secondary transfer) onto a sheet P (P1, P2), which is a recording material (recording sheet), at the secondary transfer unit Tr2, and fixes the secondary transferred image on the sheet P And a fixing device 25 to be operated.
In addition, an example of the first detection unit is located on the upstream side in the moving direction of the intermediate transfer belt 41 as viewed from the secondary transfer portion Tr2 (secondary transfer roll 40) and downstream of the black image forming unit 30K. A first position detection sensor unit 80 and a second position detection sensor unit 90 as an example of second detection means are arranged. The first position detection sensor unit 80 and the second position detection sensor unit 90 are respectively arranged on both end sides in a direction orthogonal to the moving direction of the intermediate transfer belt 41 (see FIG. 2 in the subsequent stage). Then, the first image quality adjustment pattern and the second image quality adjustment pattern (image quality adjustment toner image) for performing the alignment formed in the respective regions on both ends of the intermediate transfer belt 41 are read. The position of each image quality adjustment toner image is detected when the positional deviation control of each color image quality adjustment toner image to be described is performed.

The laser exposure device 26 includes a semiconductor laser 27 as a light source, a scanning optical system (not shown) that scans and exposes a laser beam to the photosensitive drum 31, and a rotary polygon mirror (polygon mirror) 28 formed of, for example, a regular hexagonal body. And a laser driver 29 for controlling the driving of the semiconductor laser 27. The laser driver 29 acquires image data that has undergone image processing, a control signal for correcting exposure timing in the main scanning direction and the sub-scanning direction, a control signal for correcting the laser light amount, and the like from the main control unit 60. The lighting control of the semiconductor laser 27 is performed.
The primary transfer roll 42 is supplied with a primary transfer bias voltage from a primary transfer power source (not shown), and primarily transfers each color toner image onto the intermediate transfer belt 41. The secondary transfer roll 40 is supplied with a secondary transfer bias voltage from a secondary transfer power source (not shown), and secondarily transfers each color toner image onto the paper P.
The fixing device 25 fixes the toner image on the paper P by passing the paper P holding the unfixed toner image between a fixing roll having a heating source therein and a pressure roll.

In the image forming apparatus 1 of the present embodiment, the intermediate transfer belt 41 is used as an example of a transfer body, but a configuration using a drum-shaped intermediate transfer drum as an example of a transfer body may be employed. Further, as an example of a transfer body, a configuration is adopted in which a sheet conveying member that directly conveys the sheet P is used, and each color toner image is directly transferred to the sheet P from each photosensitive drum 31 provided in each image forming unit 30. It's okay.
Further, in the image forming apparatus 1 of the present embodiment, the laser exposure device 26 is used as an example of the exposure unit, but an example of using the LED (Light Emitting Diode) array as an example of the exposure unit, an organic EL (Electro-Luminescence). ) May be used.

<Description of image forming operation>
The image forming apparatus 1 acquires image data from a personal computer (PC), an image reading apparatus (scanner), and the like, performs predetermined image processing on the acquired image data, and decomposes the image for each color. Data (each color image data) is generated. Then, the generated color image data is supplied to the laser exposure device 26 of the image forming process unit 20.
Meanwhile, the photosensitive drum 31 is charged by the charging roll 32. The laser exposure device 26 scans and exposes the photosensitive drum 31 charged by each image forming unit 30 with laser light whose lighting is controlled based on the supplied color image data and various control signals. Thereby, an electrostatic latent image of each color is formed on each photosensitive drum 31. The formed electrostatic latent image is developed by each developing device 33, and each color toner image is formed on each photosensitive drum 31.

Each color toner image formed by each image forming unit 30 is primary-transferred sequentially by a primary transfer roll 42 onto an intermediate transfer belt 41 that circulates in the direction of arrow B in FIG. As a result, a superimposed toner image is formed on the intermediate transfer belt 41 by superimposing the toner images of the respective colors. The superimposed toner image is conveyed toward the secondary transfer portion Tr2 in which the secondary transfer roll 40 and the backup roll 49 are arranged as the intermediate transfer belt 41 moves.
On the other hand, the image forming apparatus 1 is provided with a plurality of sheet holding portions 71A and 71B, for example. Then, for example, based on an instruction input by a user from an operation input panel (not shown), for example, the paper P1 held in the paper holding unit 71A is taken out. The taken paper P1 is conveyed one by one along the conveyance path R1, and is conveyed to the secondary transfer unit Tr2 in accordance with the timing at which the superimposed toner image is conveyed to the secondary transfer unit Tr2 on the intermediate transfer belt 41. The The superimposed toner images are secondarily transferred collectively onto the paper P1 by the action of the transfer electric field formed on the secondary transfer portion Tr2.
Note that the conveyance of the paper P to the secondary transfer unit Tr2 is used during duplex printing on the paper P in addition to the conveyance path R1 through which the papers P1 and P2 held by the paper holding units 71A and 71B are conveyed. This is also performed from the double-sided conveyance path R2 and the conveyance path R3 from the manual sheet holding unit 75 used when manually feeding the sheet P.

Thereafter, the sheet P1 on which each color toner image is electrostatically transferred in the secondary transfer portion Tr2 is peeled off from the intermediate transfer belt 41 and conveyed toward the fixing device 25. In the fixing device 25, each color toner image is fixed on the paper P1. Then, the paper P1 on which the fixed image is formed is carried out to a paper stacking unit 79 provided in the discharge unit of the image forming apparatus 1. On the other hand, the toner (transfer residual toner) adhering to the intermediate transfer belt 41 after the secondary transfer is removed by a belt cleaner 45 disposed in contact with the intermediate transfer belt 41 to prepare for the next image forming cycle.
In this manner, image formation in the image forming apparatus 1 is repeatedly executed for the designated number of sheets.

<Description of misregistration control>
Next, positional shift control (color shift control, so-called “registration control”) on the intermediate transfer belt 41 for each color toner image formed by each image forming unit 30 will be described.
The photosensitive drums 31 arranged in each of the image forming units 30 are normally positioned relative to the intermediate transfer belt 41 due to assembly errors at the time of manufacture or variations in setting in the image forming apparatus 1. Variation has occurred. Further, the scanning optical system disposed in the laser exposure device 26 also has an assembly error during manufacture, and further, a relative position to a mirror or the like constituting the scanning optical system due to a change in environmental temperature, a temperature rise in the apparatus, or the like. There may be a shift in the relationship. Regarding the assembly error at the time of manufacture and the setting variation in the image forming apparatus 1, each image forming apparatus 1 has inherently. Usually, the positional deviation of each color toner image is within an allowable level before shipment from the factory. Adjusted to fit. However, since it is difficult in the manufacturing process to cope with fluctuations in the environmental temperature and temperature rise in the apparatus, the image forming apparatus 1 according to the present embodiment performs the above-described misregistration control for each color toner image. Yes.
That is, in the image forming apparatus 1 of the present embodiment, each color is changed when the temperature inside the apparatus fluctuates beyond a predetermined temperature, or when the image forming operation exceeds a predetermined number of cycles. Control (position shift control, color shift control, registration control) is performed to adjust the position shift of the toner image on the intermediate transfer belt 41 within an allowable level and suppress the occurrence of color shift in the image.

<Description of Configuration for Executing Misregistration Control>
Next, FIG. 2 is a diagram illustrating a configuration for executing the positional deviation control. As shown in FIG. 2, in the image forming apparatus 1 of the present embodiment, a black image is formed on the upstream side in the moving direction of the intermediate transfer belt 41 as viewed from the secondary transfer portion Tr2 (secondary transfer roll 40). A first position detection sensor unit 80 as an example of a first detection unit and a second position detection sensor unit as an example of a second detection unit on the downstream side of the photosensitive drum 31 arranged in the unit 30K. 90. Each of the first position detection sensor unit 80 and the second position detection sensor unit 90 is disposed on both end sides in a direction orthogonal to the moving direction of the intermediate transfer belt 41. For example, the first position detection sensor unit 80 is disposed in the end region on the intermediate transfer belt 41 facing the region where scanning exposure is started on the photosensitive drum 31 by the laser exposure device 26, and scanning exposure ends. A second position detection sensor unit 90 is disposed in an end region on the intermediate transfer belt 41 facing the region.

The main control unit 60 is in a region (first position) on one end side where the first position detection sensor unit 80 on the intermediate transfer belt 41 faces the image forming units 30Y, 30M, 30C, and 30K. The first image quality adjustment pattern T1 is formed, and if necessary, the second image quality adjustment pattern T2 is formed in a region (second position) on the other end side facing the second position detection sensor unit 90. Instruct to form. Then, the first position detection sensor unit 80 reads the first image quality adjustment pattern T1, and the second position detection sensor unit 90 reads the second image quality adjustment pattern T2, and the position of each image quality adjustment pattern. Is sent to the main controller 60.
The main control unit 60 corrects the exposure timing in the main scanning direction and the sub-scanning direction for each image forming unit 30 based on detection signals from the first position detection sensor unit 80 and the second position detection sensor unit 90. Control signal is generated. Then, this control signal is transmitted to the laser driver 29 of the laser exposure device 26.

<Description of Configuration of First Position Detection Sensor Unit>
Next, the configuration of the reading function unit that reads the first image quality adjustment pattern T1 in the first position detection sensor unit 80 will be described.
FIG. 3 is a diagram illustrating a configuration of a reading function unit that reads the first image quality adjustment pattern T1 in the first position detection sensor unit 80. As shown in FIG. 3, the first position detection sensor unit 80 includes a first LED (Light Emitting Device) 81 and a second LED 82 that irradiate the toner image holding surface of the intermediate transfer belt 41. Further, the first position detection sensor unit 80 is based on the first image quality adjustment pattern T1 formed on the intermediate transfer belt 41 and the intermediate transfer belt 81 irradiated by the first LED 81 and the second LED 82. PD (Photo Diode) 83 that receives the reflected light and outputs a current value having an intensity corresponding to the amount of received light.

  The first LED 81, the second LED 82, and the PD 83 are accommodated in a case 84 having a downward opening so as to be arranged in a direction orthogonal to the moving direction of the intermediate transfer belt 41. The light emitted from the first LED 81 passes through a first exit slit 84a provided in the case 84, and illuminates the surface of the intermediate transfer belt 41 at an angle of 70 °, for example. The case 84 is also provided with a second exit slit 84b that guides the irradiation light from the second LED 82 to the surface of the intermediate transfer belt 41. The irradiation light from the second LED 82 is configured to illuminate the intermediate transfer belt 41 at an angle of, for example, 135 °. Further, the case 84 is incident to allow the reflected light from the intermediate transfer belt 41 and the first image quality adjustment pattern T1 (image quality adjustment toner image) formed on the surface of the intermediate transfer belt 41 to pass toward the PD 83. A slit 84c is also provided. The incident slit 84 c is provided in a direction of 110 °, for example, with respect to the surface of the intermediate transfer belt 41. Therefore, the reflected light (regularly reflected light) regularly reflected by the intermediate transfer belt 41 and the first image quality adjustment pattern T1 is incident on the PD 83. On the other hand, reflected light (diffuse reflected light) diffused by the intermediate transfer belt 41 and the first image quality adjustment pattern T1 is incident on the PD 83. For example, in a black toner image, light absorption by the toner is large, so that the amount of light received may be insufficient with only diffused light. For this reason, in the 1st position detection sensor part 80 which concerns on this Embodiment, 1st LED81 and 2nd LED82 which each varied the attachment angle are used as a light source. In addition, a lens 85 for condensing incident light on the light receiving surface of the PD 83 is mounted inside the incident slit 84c. The opening of the entrance slit 84c is set to φ0.8, for example.

  As described above, the first position detection sensor unit 80 includes the regular reflection light from the first image quality adjustment pattern T1 in the light emitted from the first LED 81 and the first of the light emitted from the second LED 82. By making the diffuse reflection light from one image quality adjustment pattern T1 incident on the PD 83, the first image quality adjustment pattern T1 made of each color toner including black toner can be detected with high accuracy. On the other hand, since two light sources are required and the first exit slit 84a and the second exit slit 84b having different angle settings with respect to the surface of the intermediate transfer belt 41 need to be formed, the first The manufacturing cost of the position detection sensor unit 80 is expensive.

<Description of Configuration of Second Position Detection Sensor Unit>
Next, the configuration of the reading function unit that reads the second image quality adjustment pattern T2 in the second position detection sensor unit 90 will be described.
FIG. 4 is a diagram illustrating a configuration of a reading function unit that reads the second image quality adjustment pattern T2 in the second position detection sensor unit 90. As shown in FIG. 4, the second position detection sensor unit 90 includes an LED 91 that irradiates the toner image holding surface of the intermediate transfer belt 41, and the intermediate transfer belt 41 and the intermediate transfer belt 81 that are irradiated by the LED 91. A PD 93 is provided which receives reflected light from the formed second image quality adjustment pattern T2 and outputs a current value having an intensity corresponding to the amount of received light.

  These LEDs 91 and PD 93 are accommodated in a case 94 having a downward opening so as to be arranged in a direction orthogonal to the moving direction of the intermediate transfer belt 41. The light emitted from the LED 91 passes through a first exit slit 94a provided in the case 94, and illuminates the surface of the intermediate transfer belt 41 at an angle of 70 °, for example. In addition, incident light for passing the reflected light from the intermediate transfer belt 41 and the second image quality adjustment pattern T2 (image quality adjustment toner image) formed on the surface of the intermediate transfer belt 41 toward the PD 93 is incident on the case 94. A slit 94c is also provided. The incident slit 94 c is provided in a direction of 110 °, for example, with respect to the surface of the intermediate transfer belt 41. Therefore, the reflected light regularly reflected by the intermediate transfer belt 41 and the second image quality adjustment pattern T2 is incident on the PD 93 out of the light irradiated by the LED 91. A lens 95 for concentrating incident light on the light receiving surface of the PD 93 is mounted inside the incident slit 94c. The opening of the entrance slit 94c is set to φ0.8, for example.

  As described above, the second position detection sensor unit 90 causes the regular reflection light from the second image quality adjustment pattern T2 out of the light emitted from the LED 91 to enter the PD 93, so that the second image quality of each color toner is obtained. The adjustment pattern T2 is detected. For this reason, the detection accuracy related to the second image quality adjustment pattern T2 is lower than the detection accuracy related to the first image quality adjustment pattern T1 by the first position detection sensor unit 80 because the diffused light is not used. On the other hand, the number of light sources is one, and the angle setting with respect to the surface of the intermediate transfer belt 41 is formed symmetrically with respect to the normal line of the intermediate transfer belt 41 (one-dot chain line in the figure) at the exit slit 94a and the entrance slit 94c. For example, the manufacturing cost of the second position detection sensor unit 90 is low.

<Description of functions such as a main control unit that executes misregistration control>
Next, functions of the main control unit 60, the first position detection sensor unit 80, and the second position detection sensor unit 90 that execute the positional deviation control will be described.
FIG. 5 is a block diagram illustrating functions of the main control unit 60, the first position detection sensor unit 80, and the second position detection sensor unit 90. In FIG. 5, only a block related to the above-described misregistration control among a plurality of controls executed by the main control unit 60 is shown.
The main control unit 60 includes a CPU (Central Processing Unit) 61 that executes arithmetic processing when controlling the image forming operation and misregistration control by the image forming apparatus 1, and the image forming operation and misregistration control executed by the CPU 61. A ROM (Read Only Memory) 63 storing a software program for controlling the program, and a RAM (Random Access Memory) 62 for storing various counter values and temporary data generated during the execution of the program. In the present embodiment, the CPU 61 functions as a correction unit.

Further, the main control unit 60 obtains image information in an actual image forming operation based on a command from the CPU 61 and image information for forming the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2. An image output circuit 64 as an example of an image output means to output, and image information (image data of control marks) for forming the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2 are stored in advance. And an image quality adjustment pattern data storage unit 65 as an example of the storage means. From the image output circuit 64, the image information in the actual image forming operation, the first image quality adjustment pattern T 1, and the second image quality adjustment pattern T 2 are sent to the laser exposure device 26 corresponding to each image forming unit 30. Image information for forming the image is output. The image output circuit 64 and the image quality adjustment pattern data storage unit 65 here function as index forming means.
Further, the main control unit 60 includes a first light source driving circuit 66 that controls lighting of the first LED 81 and the second LED 82 provided in the first position detection sensor unit 80, and a second position detection sensor unit 90. And a second light source driving circuit 67 for controlling the lighting of the LED 91 provided in.

  On the other hand, the first position detection sensor unit 80 and the second position detection sensor unit 90 read the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2 shown in FIGS. In addition to the function unit, detection circuits 89 and 99 are provided. Each of the detection circuits 89 and 99 converts the current value corresponding to the amount of received light output from the PD 83 and PD 93 (see FIG. 2) into a voltage value corresponding to the magnitude, and further amplifies the sensor output signal. Generate. Then, the maximum value of the generated sensor output signal is detected to further generate a peak detection signal, which is output to the main control unit 60.

<Description of First Image Quality Adjustment Pattern>
Next, FIG. 6 shows a first image quality adjustment read out from the image quality adjustment pattern data storage unit 65 by the image output circuit 64 of the main control unit 60 and formed on the intermediate transfer belt 41 by each image forming unit 30. It is a figure which shows an example of pattern T1. As shown in FIG. 6, the first image quality adjustment pattern T1 includes control marks M1Y, M1M, M1C, and M1K (hereinafter also collectively referred to as “control marks M1”) for each color. Are arranged so as to be alternately arranged so as to sandwich a reference cyan (C) control mark M1C. Each of the control marks M1 substantially intersects with both the moving direction of the intermediate transfer belt 41 (sub-scanning direction: process direction) and the direction perpendicular to the moving direction (main scanning direction: lateral direction). It is composed of a first side Ma and a second side Mb that form a character "". The first side Ma and the second side Mb have an inclination angle of 45 ° with respect to the process direction and the lateral direction, respectively, and the first side Ma and the second side Mb have an angle of 90 °. Cross at °. With this configuration, the first image quality adjustment pattern T1 detects the amount of positional deviation in both the main scanning direction (lateral direction) and the sub-scanning direction (process direction), as will be described with reference to FIG. It functions as a first misregistration correction index (mark) having the configuration described above.

In the first image quality adjustment pattern T1 of the present embodiment, the C control mark M1C is used as a reference, but the control marks (M1Y, M1M) of other colors (Y, M, K) are used. , M1K) as a reference, the first image quality adjustment pattern T1 may be employed.
In addition, “black” that is a color constituting the black (K) control mark M1K in the present embodiment includes “achromatic colors equivalent to black” such as dark dark gray, matte black, and dark black. .
The same applies to the second image quality adjustment pattern T2 described later.

<Description of Operation of First Position Detection Sensor Unit>
Next, the operation of the first position detection sensor unit 80 that reads the first image quality adjustment pattern T1 will be described.
FIG. 7 is a timing chart for explaining a signal generated by the first position detection sensor unit 80. FIG. 7A shows the reflected light intensity of the specularly reflected light component from the first image quality adjustment pattern T1 received by the PD 83 of the first position detection sensor unit 80, and FIG. 7B shows the first position detection sensor. The reflected light intensity of the diffuse reflected light component from the first image quality adjustment pattern T1 received by the PD 83 of the unit 80, (c) is the specular reflected light component of (a) and the diffuse reflected light component of (b). A pattern detection signal generated by combining, (d) indicates a peak detection signal output when the first position detection sensor unit 80 detects the minimum value (peak) of the pattern detection signal. .
As shown in FIG. 7, each control mark M 1 constituting the first image quality adjustment pattern T 1 formed on the intermediate transfer belt 41 by each image forming unit 30 is accompanied by the circulating movement of the intermediate transfer belt 41. Thus, it passes through the position facing the first position detection sensor unit 80 and crosses the visual field region R1 of the PD 83 (see FIG. 3) arranged in the first position detection sensor unit 80. At this time, first, the first side Ma of the control mark M1 enters the visual field region R1. When the first side Ma of the control mark M1 enters the visual field region R1, reflected light from the control mark M1 (first side Ma) is incident on the PD 83 of the first position detection sensor unit 80. The In this case, the reflected light intensity of the regular reflection light component of the reflected light from the control mark M1 varies according to the profile shown in FIG.

  That is, when the first side Ma of the control mark M1 enters the visual field region R1, the reflected light from the control mark M1 (first side Ma) enters the PD 83 of the first position detection sensor unit 80. Is done. The reflected light intensity of the specularly reflected light component (FIG. 7 (a)) from the control mark M1 in this case is from the time when the visual field region R1 and the control mark M1 (first side Ma) start to overlap. The change starts, the control mark M1 (first side Ma) moves and the area of the control mark M1 (first side Ma) included in the visual field region R1, that is, the visual field region R1 and the first side Ma Decreases as the overlap area increases. Then, when the visual field region R1 is substantially covered by the first side Ma, the reflected light intensity of the specularly reflected light component reaches a peak (minimum value). Thereafter, the reflected light intensity of the specularly reflected light component increases as the control mark M1 (first side Ma) moves and the overlapping area between the visual field region R1 and the first side Ma decreases, It becomes maximum when the overlap with the control mark M1 (first side Ma) ends.

When the control mark M1 further moves and the second side Mb of the control mark M1 enters the visual field region R1 of the PD 83, the specularly reflected light component changes again in the same manner as the first side Ma.
Thus, the specularly reflected light component from each control mark M1 becomes smaller as the overlapping area with the visual field region R1 increases due to light absorption by the control mark M1, and increases as the overlapping area decreases. (Time of reflected light intensity).

On the other hand, the diffuse reflected light component fluctuates according to the profile shown in FIG. That is, since the diffuse reflected light component has a spread, the reflected light intensity of the diffuse reflected light component starts to overlap between the visual field region R1 and the control mark M1 (the first side Ma and the second side Mb). The change starts before the point in time, and increases as the overlapping area of the visual field region R1 and the control mark M1 increases. Then, at the time when the visual field region R1 is almost covered with the control mark M1, the reflected light intensity of the diffuse reflected light component reaches a peak (maximum value). After that, the diffuse reflected light component decreases in reflected light intensity by moving the control mark M1 (the first side Ma and the second side Mb) and reducing the overlapping area with the visual field region R1. It becomes the minimum after the point when the overlap with the control mark M1 ends.
Thus, the diffusely reflected light component from the control mark M1 has a profile that increases as the overlapping area with the visual field region R1 increases and decreases as the overlapping area decreases.
Regarding the K control mark M1K, since the light absorption by the black toner is large, the reflected light intensity of the diffuse reflected light component is extremely small. For this reason, the pattern detection signal related to the K control mark M1K described below forms a profile that is substantially the same as the regular reflection light component.

The increase / decrease in the reflected light intensity related to the regular reflection light component and the diffuse reflection light component from the control mark M1 is repeated for each control mark M1. Then, as shown in FIG. 7C, the first position detection sensor unit 80 uses the regular reflection light component (FIG. 7A) and the diffuse reflection light component (FIG. 7B) from the control mark M1. )) And the pattern detection signal generated by combining the center position of the first side Ma in the thickness direction with the center position of the visual field region R1 of the PD 83 and the thickness of the second side Mb. A minimum profile is formed when the center position in the vertical direction substantially coincides with the center position of the visual field region R1 of the PD 83.
As a result, the detection circuit 89 (see FIG. 5) of the first position detection sensor unit 80 detects the instantaneous minimum value (peak) in the pattern detection signal as shown in FIG. A peak detection signal that rises from a low level (“L”) to a high level (“H”) in synchronization with the moment when the minimum value occurs is generated. As a result, the rising edge portion of the peak detection signal indicates the substantially center position of the first side Ma or the second side Mb of the control mark M1, and the first position detection sensor unit 80 takes this position. The positions of the first side Ma and the second side Mb are detected. Then, the first position detection sensor unit 80 outputs the generated peak detection signal to the main control unit 60.

  In this case, as the control marks M1Y, M1M, M1C, and M1K for each color constituting the first image quality adjustment pattern T1, the image density (image area ratio Cin (Input Coverage)) is, for example, 100%, 75%, A plurality of combinations (in this case, four sets) of control marks M1 composed of 50% and 25% as shown in FIG. 6 are continuously formed along the moving direction (sub-scanning direction) of the intermediate transfer belt 41. However, the first position detection sensor unit 80 may be configured to detect these image densities. Accordingly, the main control unit 60 determines in advance the image density of the control mark M1 for each color and the image density of the control mark M1 for each color based on the detection result for each image area ratio Cin of the control mark M1 for each color by the first position detection sensor unit 80. An error from the predetermined density target value is calculated. Then, the main control unit 60 calculates the correction amount of the laser power in the laser exposure device 26 for each color, and sets the laser power based on the obtained correction amount. As a result, the image density of each color toner image formed by each image forming unit 30 is adjusted to take into account the influence of environmental conditions and the like at that time. As a result, the color reproduction and gradation of a full color image formed by superimposing single color toner images are highly accurate.

<Description of Second Image Quality Adjustment Pattern>
Next, FIG. 8 shows a second image quality adjustment read out from the image quality adjustment pattern data storage unit 65 by the image output circuit 64 of the main control unit 60 and formed on the intermediate transfer belt 41 by each image forming unit 30. It is a figure which shows an example of pattern T2. As shown in FIG. 8, the second image quality adjustment pattern T2 includes control marks M2Y, M2M, M2C, and M2K (hereinafter also collectively referred to as “control marks M2”) for each color. Are arranged so as to be alternately arranged so as to sandwich a reference cyan (C) control mark M2C. Each control mark M2 is formed in a “one” shape formed along a direction (main scanning direction: lateral direction) orthogonal to the moving direction (sub-scanning direction: process direction) of the intermediate transfer belt 41. Has been. Accordingly, the second image quality adjustment pattern T2 is used as a second misalignment correction index (mark) having a configuration for detecting the misalignment amount in the sub-scanning direction (process direction), as will be described later. Function.

<Description of Operation of Second Position Detection Sensor Unit>
Next, the operation of the second position detection sensor unit 90 that reads specularly reflected light from the second image quality adjustment pattern T2 will be described.
FIG. 9 is a timing chart for explaining a signal generated by the second position detection sensor unit 90. FIG. 9A shows a pattern detection signal generated when the second position detection sensor 90 reads specularly reflected light from the second image quality adjustment pattern T2, and FIG. 9B shows a second position detection sensor. Each of the peak detection signals output when the unit 90 detects the minimum value (peak) of the pattern detection signal is shown.
As shown in FIG. 9A, each control mark M 2 constituting the second image quality adjustment pattern T 2 formed on the intermediate transfer belt 41 by each image forming unit 30 is rotated by the intermediate transfer belt 41. Along with the driving, it passes through the position facing the second position detection sensor unit 90 and crosses the visual field region R2 of the PD 93 (see FIG. 4) arranged in the second position detection sensor unit 90. At this time, since the control mark M2 enters the visual field region R2, the detection circuit 99 (see FIG. 5) of the second position detection sensor unit 90 generates based on the output signal from the PD 93. The pattern detection signal to be changed (FIG. 9A) starts changing. When the control mark M2 is further moved, the area of the control mark M2 included in the visual field region R2, that is, the overlapping area of the visual field region R2 and the control mark M2 is increased, so that the pattern detection signal gradually decreases. The pattern detection signal has a minimum value (peak) at a position where the visual field region R2 is substantially covered by the control mark M2.

  The thickness of the control mark M2 is set slightly smaller than the diameter of the visual field region R2 of the PD93. For this reason, after passing the position where the pattern detection signal of the control mark M2 is minimized, the overlapping area between the visual field region R2 and the control mark M2 decreases thereafter, and the pattern detection signal gradually increases. Then, at the position where the control mark M2 is completely removed from the visual field region R2 of the PD 93, the pattern detection signal becomes maximum again.

  Such rising / falling of the pattern detection signal is repeated for each control mark M2. Then, as shown in FIG. 9B, the center position of the control mark M2 in the thickness direction matches the center position of the visual field region R2 of the PD 93, and the center position of the control mark M2 in the thickness direction. At the position that coincides with the center position of the visual field region R2 of the PD 93, an instantaneous minimum value (peak) in the pattern detection signal occurs. As a result, the detection circuit 99 (see FIG. 5) of the second position detection sensor unit 90 detects an instantaneous minimum value (peak) in the pattern detection signal, and synchronizes with the moment when the minimum value is generated, so that the low level is reached. A peak detection signal that rises from (“L”) to a high level (“H”) is generated. Thus, the rising edge portion of the peak detection signal indicates the center position of the control mark M2, and the second position detection sensor unit 90 detects the position of the control mark M2. Then, the second position detection sensor unit 90 outputs the generated peak detection signal to the main control unit 60.

<Description of Detection of Misalignment Amount by First Position Detection Sensor Unit>
Next, detection of the amount of displacement by the first position detection sensor unit 80 will be described.
FIG. 10 is a diagram for explaining a method of detecting the amount of misalignment using the first image quality adjustment pattern T1.
As described above with reference to FIG. 6, the first image quality adjustment pattern T1 has the first side Ma for detecting the amount of deviation in both the main scanning direction (lateral direction) and the sub-scanning direction (process direction). And it has the structure provided with 2nd edge | side Mb. As described with reference to FIG. 7, the first position detection sensor unit 80 includes the first side Ma and the second side of each control mark M1 constituting the first image quality adjustment pattern T1. The position of Mb is detected. Here, in FIG. 10, the control mark M1 indicated by the solid line is the detection target this time, and the control mark M1 ′ indicated by the broken line is formed at the ideal position (hereinafter referred to as “ideal state control mark”). M1 ′ ”).
As shown in FIG. 10, the distance from the reference position preset on the intermediate transfer belt 41 to the detection position A of the first side Ma is DA, and from the reference position to the detection position B of the second side Mb. , DB is a shift amount of the control mark M1 in the main scanning direction (lateral direction) (hereinafter referred to as “main scanning shift amount”) Lerr symmetrically between the first side Ma and the second side Mb. Since it is formed, it corresponds to the difference between DA and DB. That is, in the control mark M1 ′ in the ideal state (broken line in FIG. 10), the first side Ma is detected at the detection position A ′, and the second side Mb is detected at the detection position B ′. When the difference between DA and DB is DW, the main scanning deviation amount Lerr (1) is obtained by the following equation (1).
Lerr (1) = ((DB-DA-DW) × 0.5) × tan θ (1)
Here, θ is an angle formed by the first side Ma and the second side Mb with respect to the sub-scanning direction, and is 45 ° in the present embodiment. Further, DW assumes that the visual field region R1 of the PD 83 of the first position detection sensor unit 80 is installed at the intermediate position in the main scanning direction of the control mark M1 ′ in the ideal state. It is calculated by multiplying the length of the side Mb by cos θ.

Further, the amount of deviation of the control mark M1 in the sub-scanning direction (process direction) (hereinafter referred to as “sub-scanning deviation amount”) Perr is also obtained based on DA and DB. That is, if the intermediate position between the detection position A ′ and the detection position B ′ when the control mark M1 ′ in the ideal state is detected is C ′, and the distance from the reference position to the intermediate position C ′ is DP, Since the first side Ma and the second side Mb are formed symmetrically, the scanning deviation amount Perr (1) is obtained by the following equation (2).
Perr (1) = 0.5 × (DA + DB) −DP (2)
Note that the distance from the reference position to the detection position A ′ of the first side Ma in the ideal control mark M1 ′ is DA ′, and the distance from the reference position to the detection position B ′ of the second side Mb is DB ′. Then, DP = (DA ′ + DB ′) / 2.

Actually, the first position detection sensor unit 80 outputs to the main control unit 60 peak detection signals at the detection position A of the first side Ma and the detection position B of the second side Mb. Accordingly, the main control unit 60 uses the timing at which the peak detection signals at the detection position A and the detection position B are received from the first position detection sensor unit 80, and the main scanning deviation amount Lerr (1) and the sub-scanning deviation amount. Perr (1) is calculated. That is, the main control unit 60 measures the reception timing of the peak detection signal at the detection position A and the detection position B as times TA and TB from the reference position, respectively. Here, when the moving speed (process speed) of the intermediate transfer belt 41 is V, DA = TA × V and DB = TB × V. The time TW required for the intermediate transfer belt 41 to move the distance DW is obtained by dividing the length of the first side Ma or the second side Mb by cos θ by the process speed V. . Furthermore, since θ = 45 °, tan θ = 1.
Therefore, the main control unit 60 uses the reception timings TA and TB of the peak detection signals at the detection position A and the detection position B with the reference position as a reference, to set the main scanning deviation amount Lerr (1) as the following (3). The sub-scanning deviation amount Perr (1) is obtained by the equation (4).
Lerr (1) = (TB−TA−TW) × V × 0.5 (3)
Perr (1) = (0.5 × (TA + TB) −TP) × V (4)
The time TP here is the time required for the intermediate transfer belt 41 to move the distance DP from the reference position to the intermediate position C ′, and is TP = (DA ′ + DB ′) / 2V.

  As described above, in the image forming apparatus 1 according to the present embodiment, the first image quality adjustment pattern T1 is used to detect the shift amount in both the main scanning direction (lateral direction) and the sub-scanning direction (process direction). A control mark M1 including the second side Ma and the second side Mb is formed. Further, such a first image quality adjustment pattern T1 is placed at a predetermined position (for example, an end region on the intermediate transfer belt 41 facing the region where scanning exposure is started on the photosensitive drum 31). Detection is performed by the arranged first position detection sensor unit 80. Further, the main control unit 60 uses the equations (3) and (4) to shift the main scanning deviation with respect to the control mark M1Y, M1M, M1C, M1K for each color with reference to the control mark M1 ′ in the ideal state. An amount Lerr (1) and a sub-scanning deviation amount Perr (1) are obtained. Then, the main control unit 60, for example, for the control marks M1Y, M1M, and M1K, the relative main scanning deviation amount Lerr (1) ′ and the sub-scanning deviation from the reference cyan (C) control mark M1C. The quantity Perr (1) ′ is calculated.

<Description of Detection of Misalignment by Second Position Detection Sensor Unit>
Next, the detection of the amount of positional deviation by the second position detection sensor unit 90 will be described.
As described with reference to FIG. 7, the second image quality adjustment pattern T2 includes the control mark M2 having a configuration for detecting the amount of deviation in the sub-scanning direction (process direction). As described above with reference to FIG. 9, the second position detection sensor unit 90 detects the position of each control mark M2 constituting the second image quality adjustment pattern T2, and each control mark M2 is detected. The peak detection signal at is output to the main control unit 60. The main control unit 60 uses the reception timing of the peak detection signal related to each control mark M2, for example, for the control marks M2Y, M2M, and M2K, relative to the reference cyan (C) control mark M2C. A sub-scanning deviation amount Perr (2) ′ is obtained.
That is, for example, when the time interval of the reception timing of the peak detection signal between each control mark M2Y, M2M, M2K and the control mark M2C is T (= TY, TM, TK: see FIG. 9), The main control unit 60 sets the ideal time interval for each control mark M2 (M2Y, M2M, M2K) as T0, and sets the relative sub-scanning deviation amount Perr (2) ′ for the control mark M2 to (5 ).
Perr (2) ′ = (T−T0) × V (5)

<Description of misregistration control performed using detected misregistration amount>
The main control unit 60 detects the amount of displacement in both the main scanning direction and the sub-scanning direction detected by the first position detection sensor unit 80, and further detects the sub-scanning detected by the second position detection sensor unit 90 as necessary. By using the positional deviation amount in the direction, a control signal for correcting the exposure timing in the main scanning direction and the sub-scanning direction is generated so as to correct these deviation amounts, and is sent to the laser driver 29 of the laser exposure device 26. Send to.
In the image forming apparatus 1 according to the present embodiment, for example, when a main power source (not shown) of the image forming apparatus 1 is turned on or when a front cover (front door) of the image forming apparatus 1 is opened. In addition, when a long time has passed since the previous image forming operation performed by the image forming apparatus 1 and the temperature environment in the image forming apparatus 1 is assumed to be fluctuating, the position of each color image is shifted. Since there is a possibility that (color misregistration) has occurred, highly accurate misregistration control (hereinafter referred to as “first misregistration control mode”: first misregistration correction format) is executed. That is, in such a situation, the first position detection sensor unit 80 detects the amount of displacement using both the first position detection sensor unit 80 and the second position detection sensor unit 90. The positional deviation control based on the positional deviation amount detected by both the second position detection sensor unit 90 and the second positional detection sensor unit 90 is performed. At that time, the circumferential direction (sub-scanning direction) range (hereinafter referred to as “detection range”) of the photosensitive drum 31 that forms the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2 is defined as follows. For example, a wide detection range (first length region) is set such that the range is equal to or more than four rotations of the photosensitive drum 31. The circumferential detection range of the photosensitive drum 31 corresponds to a length region along the moving direction of the intermediate transfer belt 41 on the intermediate transfer belt 41.
Such a highly accurate first misregistration control mode is a personal computer connected to the operation panel (not shown) of the image forming apparatus 1 or the image forming apparatus 1 via a communication means such as a LAN (Local Area Network). The same process is executed when the user requests execution of misregistration control, such as when an instruction is received from (PC).

  In the image forming apparatus 1, for example, the photosensitive drum 31 has an eccentricity, and a gear that transmits driving to the photosensitive drum 31 has a pitch unevenness. The position of the photoconductor drum 31 in FIG. 1 (hereinafter, “relative position of the photoconductor drum 31”) fluctuates with the rotation cycle of the photoconductor drum 31. Factors that cause fluctuations in the position of the photosensitive drum 31 are basically suppressed by increasing the assembly accuracy and component accuracy in the manufacturing process, but remain slightly. It is. As a result, the fluctuation amount of the relative position of the photosensitive drum 31 due to these factors is added to the positional deviation amount detected by the first position detection sensor unit 80 and the second position detection sensor unit 90. The detection accuracy of the detected positional deviation amount decreases accordingly. On the other hand, the change in the relative position of the photosensitive drum 31 based on such factors has a characteristic of forming a unique profile (increasing / decreasing characteristic) that continuously increases / decreases with the rotation cycle of the photosensitive drum 31. For this reason, the amount of change in the relative position of the photosensitive drum 31 is canceled (cancelled) by taking the average of one or more rotations of the photosensitive drum 31.

  Accordingly, in the first misregistration control mode, the detection range for the first image quality adjustment pattern T1 by the first position detection sensor unit 80, and further the second image quality adjustment by the second position detection sensor unit 90. The detection range for the pattern T2 is a range in which the photosensitive drum 31 is rotated a plurality of times with one rotation as one unit. As a result, the factors that cause fluctuations in the relative position of the photosensitive drum 31 are canceled out by averaging, and the detection values of the positional deviation amounts by the first position detection sensor unit 80 and the second position detection sensor unit 90 are It is calculated as being caused only by the amount of displacement caused by temperature fluctuations such as environmental temperature fluctuations and temperature rises in the machine. As described above, as the rotation amount of the photosensitive drum 31 is increased as the detection range, the error in the detected value of the displacement amount caused by the positional fluctuation amount of the photosensitive drum 31 is averaged and canceled, and the accuracy is improved. For this reason, when performing highly accurate positional deviation control as described above, the detection range is set wide, for example, to a range of four or more rotations of the photosensitive drum 31.

  Here, the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2 formed in the first misregistration control mode in order to cancel out the fluctuation amount of the relative position of the photosensitive drum 31 described above are: The integer number of control marks M1 and M2 are arranged in a range corresponding to the length of one cycle of the photosensitive drum 31 on the intermediate transfer belt 41. For example, one set of control marks M1Y, M1M, M1C, and M1K for each color shown in FIG. 6 for each range corresponding to the length of a half cycle of the photosensitive drum 31 on the intermediate transfer belt 41. A plurality of sets are arranged so that one set or a plurality of sets of M2Y, M2M, M2C, and M2K for each color shown in FIG. 8 are arranged. Thereby, in the first misregistration control mode, an error component caused by a factor that continuously increases or decreases in the rotation cycle of the photosensitive drum 31 is canceled, and the misregistration amount detection accuracy is improved. The same applies to the second misregistration control mode described below.

  On the other hand, in the image forming apparatus 1 according to the present embodiment, when the image forming apparatus 1 is in the image forming operation, the internal temperature fluctuates beyond a predetermined temperature, or the image forming operation is determined in advance. Executed when the number of cycles exceeds the predetermined number, when the duration of the image forming operation exceeds a predetermined time, or when the standby time of the image forming operation exceeds a predetermined time. In the positional deviation control, the positional deviation amount is detected using only the first position detection sensor unit 80, and the positional deviation control based on the positional deviation amount detected by the first position detection sensor unit 80 (hereinafter referred to as “second”). Position misalignment control mode ": second misalignment correction format). At that time, the range (second length region) in the circumferential direction (sub-scanning direction) of the photosensitive drum 31 that forms the first image quality adjustment pattern T1 is set in the first misregistration control mode. The width is set to be narrower, for example, a range shorter than the detection range (first length region), for example, about two rotations of the photosensitive drum 31.

  As described above, the image forming apparatus 1 has a factor that causes a change in the relative position of the photosensitive drum 31. Therefore, also in the positional deviation control executed during such an image forming operation, it is more accurate to set a wider detection range for forming the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2. Deviation control is executed. However, in the misregistration control during the image forming operation, if the detection range is set wide and detected by the first position detection sensor unit 80 and the second position detection sensor unit 90, the misregistration control is applied. The time becomes longer, and the productivity related to image formation decreases. In addition, since both the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2 are formed, the amount of toner consumption increases. On the other hand, since the image forming operation is being performed, the internal temperature largely fluctuates over a long time since the previous image forming operation such as when the main power supply (not shown) of the image forming apparatus 1 is turned on. This situation rarely occurs.

For this reason, in the second misregistration control mode performed when the temperature inside the apparatus fluctuates beyond a predetermined temperature during the image forming operation, only the first image quality adjustment pattern T1 is formed and the first position is set. This is detected using only the detection sensor unit 80. Furthermore, the detection range of the range in the circumferential direction (sub-scanning direction) of the photosensitive drum 31 that forms the first image quality adjustment pattern T1 is narrower than when the first misregistration control mode is executed. For example, it is set in a range of about two rotations of the photosensitive drum 31. Then, the main scanning deviation amount Lerr (1) ′ and the sub scanning deviation amount Perr (1) ′ are calculated based on the positional deviation amounts in the main scanning direction and the sub scanning direction detected by the first position detection sensor unit 80. To do. Thereby, simple misregistration control is performed in which only the misregistration amount in both the main scanning direction and the sub-scanning direction is corrected.
As described above, in the second misregistration control mode, correction is performed so that the misregistration amount in both the main scanning direction and / or the sub-scanning direction is within an allowable range, and a decrease in productivity related to image formation and toner are performed. The increase in consumption is suppressed.

  In contrast, in the first misregistration control mode performed when the main power source of the image forming apparatus 1 is turned on, the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2 are formed. These are detected using both the first position detection sensor unit 80 and the second position detection sensor unit 90. Furthermore, the range in the circumferential direction (sub-scanning direction) of the photosensitive drum 31 that forms the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2 is, for example, four rotations or more of the photosensitive drum 31. By setting a wide range such as a range, the accuracy of canceling error components caused by factors that continuously increase or decrease in the rotation cycle of the photosensitive drum 31 is increased. Then, the main scanning deviation amount Lerr (1) ′ and the sub scanning deviation amount Perr (1) ′ are calculated based on the positional deviation amounts in the main scanning direction and the sub scanning direction detected by the first position detection sensor unit 80. Then, the sub-scanning deviation amount Perr (2) ′ is calculated based on the positional deviation amount in the sub-scanning direction detected by the second position detection sensor unit 90. Thus, using these, not only correction of deviation in both the main scanning direction (lateral direction) and sub-scanning direction (process direction) but also correction of inclination deviation (so-called “skew”) in the sub-scanning direction can be performed. The first positional deviation control mode having a high value is executed.

Here, the second position detection sensor unit 90 of the present embodiment is along a direction (main scanning direction) orthogonal to the moving direction (sub-scanning direction) of the intermediate transfer belt 41 as shown in FIG. The main control unit 60 reads each control mark M2 formed in the shape of the letter “1” and uses the control mark M2C related to each control mark M2Y, M2M, M2K as a reference based on the detection result. The relative sub-scanning deviation amount Perr (2) ′ is calculated (see the above equation (5)). Therefore, in the present embodiment, when executing the above-described highly accurate first positional deviation control mode, correction of the positional deviation amount in the main scanning direction and the sub-scanning direction and correction of the inclination deviation in the sub-scanning direction are performed. It will be.
As shown in FIG. 4, the second position detection sensor unit 90 is configured such that the reflected light that is regularly reflected by the intermediate transfer belt 41 and the second image quality adjustment pattern T2 is incident on the PD 93. . Thereby, depending on the color of the toner image, the detection accuracy related to the second image quality adjustment pattern T2 is lower than that of the first position detection sensor unit 80, and in particular, an obliquely entering the visual field region R2 of the PD 93 with an angle. The detection accuracy for lines is reduced. On the other hand, since the number of the light sources is one, the second position detection sensor unit 90 can be obtained at a low cost. Therefore, the second position detection sensor unit 90 of the present embodiment is set so as to read the second image quality adjustment pattern T2 including the control mark M2 that enters substantially parallel to the visual field region R2 of the PD 93. Thus, only the sub-scanning deviation amount Perr (2) ′ is detected.

  As the second position detection sensor unit 90, the reflected light that is regularly reflected and diffused from the second image quality adjustment pattern T2 as in the first position detection sensor unit 80 shown in FIG. 3 is used. It is also possible to use a configuration that detects both of the above. In this case, as shown in FIG. 11 (a diagram showing another example of the second image quality adjustment pattern T2), an angle of 45 ° obliquely with respect to the moving direction (sub-scanning direction) of the intermediate transfer belt 41 A second image quality adjustment pattern T2 made up of control marks M2 formed to be inclined in the direction may be used. Accordingly, the main scanning deviation amount Lerr (2) ′ is calculated by the main control unit 60 from the detection result of the second position detection sensor unit 90. As a result, in this case, when executing the above-described highly accurate first positional deviation control mode, correction of the positional deviation amount in the main scanning direction and the sub-scanning direction and correction of the magnification deviation in the main scanning direction are performed. And will do.

  Further, as shown in FIG. 12 (a diagram showing another example of the second image quality adjustment pattern T2), the direction (main scanning direction) is orthogonal to the moving direction (sub-scanning direction) of the intermediate transfer belt 41. 45 degrees oblique to the control mark M21 (control marks M21Y, M21M, M21C, M21K) formed in a “one” shape and the moving direction (sub-scanning direction) of the intermediate transfer belt 41. The second image quality adjustment pattern T2 including both of the control marks M22 (control marks M22Y, M22M, M22C, M22K) formed so as to be inclined in the angle direction may be used. As a result, the main scanning deviation amount Lerr (2) ′ and the sub-scanning deviation amount Perr (2) ′ are calculated by the main control unit 60 from the detection result of the second position detection sensor unit 90. As a result, in this case, when executing the above-described highly accurate first positional deviation control mode, correction of the positional deviation amount in the main scanning direction and the sub-scanning direction, inclination deviation in the sub-scanning direction, and main scanning are performed. Correction of magnification deviation in the direction is performed.

  By the way, regarding the first image quality adjustment pattern T1 detected by the first position detection sensor unit 80, the case where the first position deviation control mode is executed differs from the case where the second position deviation control mode is executed. An image quality adjustment pattern of a form may be used. For example, when executing the second misregistration control mode, the size of the first image quality adjustment pattern T1 is set to be smaller than that when the first misregistration control mode is executed in order to further reduce the toner consumption. May be set to be small. Furthermore, the line width may be set to be narrower than the first image quality adjustment pattern T1 when the first misregistration control mode is executed. Further, for example, in the second misregistration control mode, setting is made so that the image density of each color toner image is not adjusted, and the image density of the control mark M1 for each color constituting the second image quality adjustment pattern T2 ( For example, the image area ratio Cin) may be set to be 50%. In other words, the amount of toner consumption is smaller than that of the first image quality adjustment pattern T1 used when the first misregistration control mode is executed, and the misregistration amount in the main scanning direction and the sub scanning direction can be detected. Any image quality adjustment pattern may be used as the first image quality adjustment pattern T1 used when the second misregistration control mode is executed.

  As described above, in the image forming apparatus 1 of the present embodiment, for example, when the time environment has passed since the previous image forming operation in the image forming apparatus 1 and the temperature environment is assumed to change. In this case, both the first position detection sensor unit 80 and the second position detection sensor unit 90 are used to form the first image quality adjustment pattern T1 and the second image quality adjustment pattern T2. The first misregistration control mode in which the range in the circumferential direction (sub-scanning direction) is set wide is executed. Accordingly, not only the correction of the positional deviation amount in the main scanning direction and the sub-scanning direction but also the detection value of the positional deviation amount by both the first position detection sensor unit 80 and the second position detection sensor unit 90 is used. Any one of the magnification deviation in the scanning direction and the inclination deviation in the sub-scanning direction is corrected. Further, when the temperature inside the apparatus fluctuates beyond a predetermined temperature during the image forming operation, the photoconductor that forms the first image quality adjustment pattern T1 using only the first position detection sensor unit 80. A second misregistration control mode in which the range in the circumferential direction (sub-scanning direction) of the drum 31 is set narrow is executed. Thereby, simple misregistration control is performed in which only the misregistration amount in both the main scanning direction and the sub scanning direction or only one of them is corrected. As described above, by controlling the misregistration in different modes according to the operation status of the image forming apparatus 1, the misregistration of each color toner image is adjusted, and the decrease in productivity and increase in toner consumption related to image formation are suppressed. To achieve both.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 26 ... Laser exposure apparatus, 30 (30Y, 30M, 30C, 30K) ... Image forming unit, 41 ... Intermediate transfer belt, 60 ... Main control part, 80 ... First position detection sensor part, 90 ... Second position detection sensor unit

Claims (1)

A plurality of image forming units for forming images of each color;
The image of each color formed in each of the plurality of image forming units is directly transferred in order, or a transfer body that conveys a recording material to which the image is transferred in order,
The plurality of image forming units sequentially form a first misregistration correction index at a first position on the transfer body, and the first misregistration correction index at a second position on the transfer body. Are indicator forming means for sequentially forming different second misalignment correction indicators,
A first detection unit disposed opposite to the first position on the transfer body to detect the first misalignment correction index;
A second detection unit disposed opposite to the second position on the transfer body and detecting the second misalignment correction index;
The plurality of image forming units form the first misregistration correction index and the second misregistration correction index in a first length region along the moving direction of the transfer body, and the first misregistration correction index. First misalignment correction is performed based on both the detection result of the first misregistration correction index by the detection means and the detection result of the second misregistration correction index by the second detection means. The first misregistration correction index and the second length region shorter than the first length region are used to form the first misregistration correction index, and the first detection unit detects the first misregistration. Correction means for correcting the positional deviation of the images of the respective colors formed by the plurality of image forming units by any one of the second positional deviation correction formats for performing the positional deviation correction based on the detection result of the correction index. And
The index forming means is a first misalignment correction index for detecting misalignment amounts in both the main scanning direction and the sub scanning direction of the images of the respective colors formed by the plurality of image forming units. Forming the second misregistration correction index for detecting the misregistration amount in either the main scanning direction or the sub-scanning direction of the image of each color,
The correction means executes the first misalignment correction format and / or the main scanning direction and / or the sub-scanning direction in each color image formed by the plurality of image forming units. The main-scan in the image of each color is corrected by correcting the misalignment and the inclination in the sub-scanning direction and the magnification in the main-scanning direction and executing the second misalignment correction format. An image forming apparatus that corrects misregistration in either or both of the direction and the sub-scanning direction.

Images