JP2000227692A - Color image forming device and register mark detection device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize register-mark detection error caused by flutter of a carrying belt and to obtain satisfactory contrast even in the detection of register marks of arbitrary colors on the carrying belt. SOLUTION: In the color image forming device in which toner images of specific colors formed by an image forming part are superimposed and transferred to a recording medium S carried by a carrying belt 60 and are fixed thereon, a register mark detection device 51 detects register marks formed corresponding with the toner image of several colors on the belt 60 in order to detect the displacement of the toner images of several colors on the medium S. The device 51 comprises two light sensors 511a and 511a' for detecting the same part N of the register mark K1 and two light sources 512a and 512a' corresponding to the sensors 511a and 511a' and used for emitting light to the mark K1, and arranges the sensors and the respective light sources so that they are axially symmetrical with respect to an axis H in the direction of the normal line of the face of the belt 60 on which the mark K1 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus having a plurality of image forming units, and for transferring and fixing a predetermined color toner image formed by the image forming units on a recording medium conveyed by a conveying belt. A registration mark for detecting a registration mark formed on the recording medium or on the transport belt corresponding to each of the plurality of color toner images in order to detect a positional shift of the multicolor toner image on the recording medium. The present invention relates to a detection device and a color image forming apparatus including the registration mark detection device.

[0002]

2. Description of the Related Art In a color image forming apparatus such as a color laser printer, a plurality of image forming sections are provided so that toner images of predetermined colors different from each other can be formed for each image forming section. There is a color image forming apparatus in which a predetermined color toner image is transferred onto a recording medium conveyed by a conveying belt and transferred and fixed.

In the field of such a color image forming apparatus, in order to obtain a color image by superposing a plurality of color toner images on a recording medium, it is necessary to superimpose a predetermined color toner image formed in each image forming section. A problem arises in that misalignment between the toner images (images) of the respective colors due to the alignment occurs. In other words, when the position between the toner images (images) of each color is shifted, the image obtained on the recording medium undergoes a change in tint or a color shift, and the image quality is significantly reduced. For this reason, such a color image forming apparatus is provided with, for example, a registration mark formed on a conveyance belt corresponding to each of the multicolor toner images in order to detect a positional shift of the multicolor toner images. And a correction unit that corrects the position of a predetermined color toner image formed in each image forming unit according to the positional deviation amount of each color toner image detected by the detection device. Often have.

The registration mark detecting device for detecting a registration mark formed on the conveyor belt has the following problems. That is, if the belt flaps due to the movement of the surface of the transport belt, a detection error of the registration mark due to the flutter of the transport belt may occur. Further, if a good contrast between the conveyor belt and the registration marks of the respective colors formed thereon is not obtained, the detection accuracy tends to decrease.

Therefore, in such a registration mark detecting device, detection accuracy is ensured by suppressing the occurrence of detection errors due to the fluttering of the conveyor belt and obtaining a good contrast between the conveyor belt and the registration marks of each color. It is important to: In order to secure the detection accuracy by obtaining a good contrast between the conveyor belt and the registration mark of each color, for example, Japanese Patent Application Laid-Open No. Sho 63-3002
In Japanese Patent No. 62, a registration mark of each color formed in the registration mark formation region is detected by making the formation region of the registration mark on the color (for example, orange) transfer belt white achromatic. It is disclosed that the device can be easily identified.

Further, in order to suppress the occurrence of a detection error due to fluttering of the conveyor belt, for example, a light source and a detector for detecting reflected light reflected on a registration mark on the conveyor belt by light irradiation from the light source. A registration mark detection device including an optical sensor, and by arranging the direction of incidence of reflected light on the detection optical sensor and the normal direction of the surface of the conveyor belt to be aligned, the registration due to fluttering of the conveyor belt, etc. It has also been proposed to suppress the occurrence of mark detection errors.

[0007]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open
In the registration mark detection taught by JP-A-300262, a white achromatic area must be formed in a part of a colored conveyor belt, which is disadvantageous in cost compared to using a uniform color conveyor belt. This is inevitable. Also, with the use of the conveyor belt, the registration mark forming area of the white achromatic portion becomes stained with time, which causes a problem that the contrast with the registration mark of each color is reduced and a registration mark detection error occurs. is there.

Further, in a registration mark detecting device in which a detection optical sensor is arranged so that the light incident direction on the detection sensor and the normal direction of the surface of the conveyor belt coincide with each other, the diffused light of the registration mark illumination is used. Therefore, the contrast of the detected registration mark of each color is low, and the detection accuracy tends to decrease. Accordingly, the present invention provides a color image forming apparatus having a plurality of image forming units, wherein a toner image of a predetermined color formed by the image forming unit is transferred onto a recording medium conveyed by a conveyor belt and is fixed thereon. A registration mark detection device for detecting registration marks formed on the recording medium or the transport belt corresponding to the plurality of color toner images, respectively, for detecting the positional shift of the multicolor toner image. A registration mark detection error that can suppress a registration mark detection error due to the fluttering of the conveyance belt, and can obtain a good contrast even when a registration mark is detected on a conveyance belt of an arbitrary color, thereby increasing detection accuracy. It is an object to provide a device.

According to another aspect of the present invention, there is provided a color image forming apparatus having a plurality of image forming portions, wherein a predetermined color toner image formed by the image forming portion is transferred onto a recording medium conveyed by a conveying belt, and is fixed. A registration mark for detecting a registration mark formed on the recording medium or on the transport belt corresponding to each of the plurality of color toner images, in order to detect a positional shift of the multicolor toner image on the recording medium. A color image forming apparatus provided with a detection device, wherein a registration mark detection error due to fluttering of the conveyor belt can be suppressed to a small value, and a good contrast can be obtained even when a registration mark is detected on an arbitrary color conveyor belt. A registration mark detecting device capable of increasing the detection accuracy, thereby obtaining a good color image in which color misregistration is suppressed. And to provide a color image forming apparatus that can.

[0010]

In order to solve the above-mentioned problems, the present invention provides a registration mark detecting device and a color image forming apparatus in the following color image forming apparatus. (1) Registration mark detection device in a color image forming apparatus A color image having a plurality of image forming units, and a toner image of a predetermined color formed by the image forming unit is transferred onto a recording medium conveyed by a conveying belt, transferred and fixed. In the forming apparatus, a registration mark formed on the recording medium or on the transport belt corresponding to each of the multicolor toner images is detected in order to detect a positional shift of the multicolor toner image on the recording medium. A registration mark detection device, two optical sensors for detecting the same predetermined part of the registration mark by reflected light from the part, and corresponding to each of the optical sensors, for irradiating the registration mark with light. Including two light sources,
Each corresponding optical sensor and light source are normal to the recording medium surface or the conveyor belt surface on which the registration mark is formed, and to a normal axis crossing a normal path of a predetermined portion of the registration mark. Are arranged symmetrically with respect to each other (including the case where they are completely axially symmetric and the case where they may be regarded as being axially symmetric). A registration mark detecting device in a color image forming apparatus, wherein each sensor is arranged to detect the predetermined portion from a different direction so that a time lag occurs in the detection of the predetermined portion. (2) Color Image Forming Apparatus A color image forming apparatus having a plurality of image forming sections, wherein a predetermined color toner image formed by the image forming section is transferred onto a recording medium conveyed by a conveying belt, transferred and fixed. A registration mark for detecting a registration mark formed on the recording medium or on the transport belt corresponding to each of the plurality of color toner images, for detecting a positional shift of the multicolor toner image on the recording medium. A color image forming apparatus provided with a detection device, wherein the registration mark detection device includes two optical sensors for detecting the same predetermined portion of the registration mark by reflected light from the portion, and each of the optical sensors. Corresponding, including two light sources for irradiating the registration mark with light, the corresponding light sensor and light source respectively correspond to the recording medium surface or the recording medium on which the registration mark is formed. Axisymmetric with respect to the normal axis of the conveyor belt surface and the normal axis that intersects the normal path of the predetermined portion of the registration mark. And the sensors are arranged in different directions so that when the path of the predetermined portion of the registration mark deviates from the regular path, the detection of the predetermined portion by each sensor causes a time lag. A color image forming apparatus, wherein the color image forming apparatus is arranged so as to detect a color image.

According to the registration mark detecting apparatus and the color image forming apparatus according to the present invention, it is possible to detect the registration marks formed on the recording medium or the transport belt in correspondence with the multicolor toner images. Based on this detection value, the displacement of the multicolor toner image can be obtained. In the registration mark detection device and the color image forming apparatus, the corresponding optical sensor and light source are arranged so that the corresponding light sensor and the light source intersect the normal path of the predetermined portion of the registration mark on the normal axis of the recording medium surface or the conveyance belt surface. They are arranged symmetrically with respect to the linear axis.

With the two sets of photosensors and light sources arranged in this way, registration marks formed on the recording medium or on the transport belt corresponding to the multicolor toner images, respectively, are detected. That is, light is emitted from the two light sources to the resist mark. At this time, since the light sensor and the light source corresponding to each other are arranged axially symmetrically with respect to the normal direction axis, the incident light of the light emitted from each light source to the registration mark and the predetermined portion of the registration mark The reflected light beam reflected toward the corresponding light sensor is axially symmetric with respect to the normal axis. Thus, each optical sensor can detect light that is regularly reflected at a predetermined portion of the registration mark by light irradiation from the corresponding light source. By arranging the optical sensor and the light source corresponding to each other in a regular reflection relationship with respect to the registration mark in this manner, it is possible to increase the SN ratio of the detection signal by each optical sensor, and Detection can be performed while obtaining a high contrast with the resist mark. This makes it possible to accurately detect a registration mark on a recording medium of an arbitrary color or on a transport belt of an arbitrary color.

In the registration mark detecting apparatus and the color image forming apparatus according to the present invention, each pair of the corresponding photosensors and light sources is operated by each sensor when the path of the predetermined portion of the registration mark deviates from the regular path. Each sensor is arranged to detect the predetermined portion from a different direction so that a time lag occurs in the detection of the predetermined portion.

The following can be exemplified as such an arrangement relationship. That is, one optical sensor is arranged on the upstream side in the registration mark traveling direction with respect to a plane substantially perpendicular to the registration mark passage including the normal axis, and the corresponding light source is arranged on the downstream side, The other optical sensor is disposed on the downstream side in the registration mark traveling direction and the corresponding light source is disposed on the upstream side, so that each sensor detects specularly reflected light from a predetermined portion of the registration mark. Two optical sensors are arranged on the upstream side (or downstream side) in the registration mark traveling direction with respect to the first surface including the normal axis and perpendicular to the registration mark passage, and on the downstream side (or upstream side). Light sources corresponding to the sensors are arranged, and each optical sensor includes the normal direction axis but from a direction at the same angle with respect to the conveyor belt surface (or the surface of the recording medium thereon). Specular reflection light of the predetermined portion of the registration mark is detected from a direction making a different angle (different in absolute value) with respect to a second surface perpendicular to the first surface. Two optical sensors are arranged on the upstream side (or downstream side) of the registration mark traveling direction with respect to a plane including the normal direction axis and perpendicular to the registration mark passage, and the downstream side (or the upstream side)
Light sources corresponding to these sensors are arranged, and each optical sensor detects specularly reflected light of the predetermined portion of the registration mark from a direction making a different angle with respect to the conveyor belt surface (or the surface of the recording medium thereon). To do.

Due to such an arrangement relationship, the two optical sensors detect the predetermined portion of the registration mark, and the transport belt does not flutter, so that the predetermined portion of the registration mark travels on a regular path. Sometimes, regular reflection light from the same predetermined portion of the registration mark due to light irradiation from the light source corresponding to the two optical sensors is simultaneously detected.

In other words, when the two optical sensors and the light source detect the registration mark, when the conveyor belt is not fluttering, the two optical sensors respectively reflect light regularly reflected by the registration mark. Are detected, the registration mark positions obtained by the detection coincide with each other. As described above, the registration mark position obtained by the two optical sensors simultaneously detecting the same predetermined portion of the registration mark is a proper (regular) registration mark position.

When the conveyor belt flaps and the predetermined portion of the registration mark passes through a position deviated from its regular path, the position of each sensor and the corresponding light source, the projection of each light source onto the predetermined portion of the registration mark. Depending on the direction, angle, etc. of the optical path, the light source traverses the light projecting line from the light source to the predetermined portion earlier or later than the time when the predetermined portion travels along the normal path, whereby each sensor is moved to the predetermined position. The portion is detected earlier or later in time than when it travels along the regular path, and a time lag occurs in the detection of the predetermined portion of the registration mark between the two sensors. This means that the registration mark position detected by each sensor differs.

For example, the two sets of optical sensors and the light source are both disposed above the conveyor belt, and are upstream of the registration mark advancing direction with respect to a plane including the normal axis and perpendicular to the registration mark passage. One light sensor is arranged on the side and the corresponding light source is arranged on the downstream side, and the other light sensor is arranged on the downstream side in the registration mark traveling direction and the corresponding light source is arranged on the upstream side Each sensor detects regular reflection light from a predetermined portion of the registration mark. In this case, when the transport belt flutters in the direction approaching each optical sensor, the optical sensor on the upstream side in the registration mark advancing direction detects a predetermined portion of the registration mark later than the optical sensor on the downstream side (described later). (See FIG. 5 and its description).

According to the registration mark detecting apparatus and the color image forming apparatus of the present invention, the two optical sensors detect registration mark position information obtained by detecting light regularly reflected at the same predetermined portion of the registration mark. If a calculation formula that can calculate the proper registration mark position is determined in advance in consideration of the arrangement relationship of the two optical sensors when the substitution is made, and the predetermined calculation formula is set in advance, the By substituting the registration mark position information detected by each optical sensor into a predetermined calculation formula and performing arithmetic processing,
The two (2) optical sensors simultaneously detect the light regularly reflected on the same predetermined portion of the registration mark in the proper (regular) registration mark position, that is, in a state where the conveyor belt is not fluttering. The obtained registration mark position can be obtained, and this can be used as registration mark detection information. Thereby, the registration mark detection error due to the fluttering of the transport belt can be suppressed to be small.

An example of the signal form of the position information detected by the two optical sensors is an electric signal. in this case,
Examples of the two optical sensors include a photoelectric conversion element that can convert received light into an electric signal, for example, a photodiode. In the color image forming apparatus according to the present invention, in order to perform arithmetic processing by the predetermined calculation formula, based on position information of registration marks obtained from two optical sensors in the registration mark detection device,
An arithmetic processing unit for calculating an appropriate position of the registration mark can be provided. In this case, the predetermined calculation formula is set in advance in the arithmetic processing unit, and the two optical sensors detect light regularly reflected on the same predetermined portion of the registration mark by the arithmetic processing unit. The proper registration mark position can be obtained by substituting the obtained registration mark position information into the predetermined formula and performing arithmetic processing, and this can be used as registration mark position detection information.

The registration mark position information obtained by the two optical sensors detecting the light that is specularly reflected at the registration mark includes a predetermined detection reference time (for example, before the two optical sensors perform the detection operation). A first time T from when light emission from the two light sources is started to when one of the optical sensors detects light specularly reflected at the registration mark.
X and a second time TY from the predetermined detection reference time to the time when the other optical sensor detects light regularly reflected by the registration mark.

For example, the two sets of optical sensors and the light source are both disposed above the conveyor belt, and the registration mark travel direction is defined by a first surface including the normal axis and perpendicular to the registration mark passage. Arrange one optical sensor on the upstream side and the corresponding light source on the downstream side,
The other optical sensor is arranged on the downstream side in the registration mark traveling direction and the corresponding light source is arranged on the upstream side,
Further, it is assumed that the optical sensor and the light source on the upstream side and the optical sensor and the light source on the downstream side with respect to the first surface are symmetrically arranged so that each sensor can detect regular reflection light from a predetermined portion of the registration mark. .

In this case, when the conveyor belt flutters toward both sensors, registration mark detection by the upstream optical sensor is performed when the registration mark is located downstream from the proper registration mark detection position. The registration mark detection by the downstream optical sensor is performed when the registration mark is located upstream of the proper registration mark detection position. In addition, in a state where the conveyor belt flutters away from both sensors, registration mark detection by the upstream optical sensor is performed when the registration mark is located upstream from the proper registration mark detection position. The detection of the registration mark by the downstream optical sensor is performed when the registration mark is located downstream of the proper registration mark detection position.

In any of these cases, the proper registration mark position can be considered to be in the middle of the registration mark detection position by both optical sensors. Therefore, assuming that the times TX and TY are used as registration mark detection position information by the optical sensor, (TX + TY) / 2 can be exemplified as an equation for calculating an appropriate registration mark position (FIG. 5 and FIG. 6 and its description). Alternatively, (conveying belt advancing speed) × (TX + TY) / 2 can be used. This can be used as registration mark detection information, and a registration mark detection error due to fluttering of the conveyor belt can be substantially canceled.

As described above, the registration mark detection apparatus and the color image forming apparatus according to the present invention can increase the detection accuracy of the registration marks, and the image forming apparatus can provide a good color image without color misregistration. Images can be obtained. As a method for detecting the positional shift of each color toner image, a plurality of registration marks of the same color, which are displaced in a direction orthogonal to the recording medium conveyance direction, on a recording medium conveyance belt or on a recording medium conveyed by the conveyance belt. And sequentially forming such a registration mark row by shifting the position in the recording medium conveyance direction for each color, and forming each registration mark row in the registration mark row in the direction orthogonal to the recording medium conveyance direction. By arranging the registration mark detection devices corresponding to the marks, and sequentially detecting the registration marks of each color arranged in the recording medium conveyance direction by each registration mark detection device, in the recording medium conveyance direction in the image finally obtained. Color shift and recording medium in the recording medium transport direction (sub-scanning direction) in each part in the direction (main scanning direction) orthogonal to There is a method of detecting the respective color shift direction (main scanning direction) perpendicular to the feeding direction.

Therefore, in the color image forming apparatus according to the present invention, a plurality of the plurality of recording media formed on the recording medium or the transport belt are shifted in a direction orthogonal to the transport direction of the recording medium by the transport belt. In order to detect the registration marks, the registration mark detection devices can be arranged in a direction perpendicular to the recording medium conveyance direction so as to correspond to the respective registration marks.

In addition, the registration mark detecting device detects the registration deviation between the registration marks of each color, for example, with reference to the registration mark of any color (for example, black), the amount of registration deviation between the registration marks of each color, and further, the toner of each color. This can be performed by detecting the amount of displacement between images. Based on this information, it is possible to correct the positional deviation of each color toner image. In any case, as the shape of the registration mark, the conveyance direction orthogonal line parallel to the direction orthogonal to the recording medium conveyance direction, and the conveyance direction orthogonal line at a different position in the direction orthogonal to the conveyance direction. And V-shaped resist marks formed by oblique lines having gradually different intervals from each other.

According to the registration mark, the amount of positional deviation between the registration marks in the recording medium transport direction (sub-scanning direction), and furthermore, the difference between the toner images in each color, is determined based on the detected position information of the line section orthogonal to the transport direction by the resist mark detection device. The displacement amount can be obtained. Further, based on the detection position information of the oblique line portion and / or the line portion orthogonal to the transport direction by the resist mark detection device, the amount of positional deviation between the resist marks of each color in the direction orthogonal to the recording medium transport direction (main scanning direction), The amount of displacement between the respective color toner images can be obtained.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing a schematic configuration of an example of a full-color image forming apparatus provided with a registration mark detecting device according to an embodiment of the present invention. FIG. 2 is a laser scanning optical device in the image forming apparatus shown in FIG.
FIG. 3 is an exploded perspective view of a photoconductor, a transfer / transport device, and a registration mark detection device as viewed from above a sheet discharge side.

The full-color image forming apparatus shown in FIG. 1 is an electrophotographic image forming apparatus in which image forming units 100c, 100m, 100y, and 100k of toner images of different colors (cyan, magenta, yellow, and black) are provided. They are arranged in order along a certain direction. Image forming unit 100
c to 100k are drum-shaped photoconductors 1c, 1c,
m, 1y, and 1k. The laser scanning optical device 3 is disposed above the photoconductors 1c to 1k.

Around each photoconductor 1c-1k,
Main charger 2c, 2m, 2y, 2k, developing device 4
c, 4m, 4y, 4k, transfer chargers 6c, 6m, 6
y, 6k, cleaning blades 7c, 7m, 7y, 7
k and the discharge lamps 8c, 8m, 8y, 8k are arranged in this order. The photoconductors 1c to 1k are respectively driven to rotate in the X direction in the drawing. Transfer charger 6c ~
6k face the photoconductors 1c to 1k, respectively, and form transfer sites Pc, Pm, Py, and Pk in the figure.

A transfer / conveyance device 600 is provided below the transfer portions Pc to Pk. The apparatus 600 includes transfer chargers 6c to 6k, a tension roller 62, a driving roller 63, a driven roller 61, and a transport belt 60 wound around these rollers.
It is constituted by. The transport belt 60 is driven in the V direction in the figure as the driving roller 63 rotates in the Y direction in the figure, and sequentially passes through the transfer portions Pc to Pk.

In the transfer device 600, the transfer chargers 6c to 6c
6k, power supplies PW3c, PW3m,
Transfer voltages can be applied from PW3y and PW3k, whereby the respective toner images on the photoconductors 1c to 1k can be overlaid and transferred onto the recording medium S conveyed by the conveyance belt 60. The recording medium S is held on the conveyor belt 60 by an electrostatic or mechanical holding device (not shown), and is conveyed in the direction V in the drawing. Further, a registration mark detection device 5 described later
In the detection of image misregistration by 1, 52, and 53, registration marks of a predetermined shape formed on each of the photoconductors 1c to 1k can be transferred onto the transport belt 60.

A timing roller pair 11 is provided on the right side of the transport device 600 in the figure, and a paper feeding unit (not shown) is provided. On the left side, registration mark detection devices 51 to 53 and a fixing roller pair 14 are sequentially provided, and a discharge roller pair and a paper discharge tray (not shown) are further provided. The registration mark detection device 51
1 to 53 are arranged at intervals in the direction V in the figure, downstream of the image forming unit 100k, above the conveyor belt 60, and in a direction perpendicular to the conveyance direction V, as shown in FIG. I have.

The main chargers 2c to 2k can apply a high voltage from the power supplies PW1c, PW1m, PW1y and PW1k, respectively, thereby charging the photoconductors 1c to 1k. The developing devices 4c to 4k include developing rollers 41c, 41m, 41y, and 41k, and a device case 4 respectively.
2c, 42m, 42y, and 42k, and the device cases 42c to 42k are respectively a cyan developer Dc, a magenta developer Dm, a yellow developer Dy, and a black developer Dk.
To accommodate. The developers Dc to Dk include cyan toner, magenta toner, yellow toner, and black toner, respectively. The developing rollers 41c to 41k are respectively driven to rotate, and the power sources PW2c, PW2m, PW2y, PW2
The developing bias voltage can be applied from k. Thereby, the electrostatic latent images on the photoconductors 1c to 1k can be developed.

As shown in FIG. 2, the laser scanning optical device 3 includes laser emitting units 310a and 310b and a laser deflecting unit 32.
0, laser imaging units 330a, 330b, laser reflecting unit 3
40a and 340b. Laser emitting unit 3
10a, laser imaging section 330a, laser reflection section 340a
Is located upstream of the laser deflecting unit 320 in the transport direction V of the recording medium S by the transport belt 60, and the laser emitting unit 310b, the laser imaging unit 330b, and the laser reflecting unit 340b are located downstream.

The laser beams Lc and Lm are applied to the laser emitting section 3
After being emitted from the laser deflector 10a and entering the laser deflecting unit 320, the light is deflected by the deflecting unit 320 in the main scanning direction parallel to the direction orthogonal to the transport direction V, and is exposed through the laser imaging unit 330a and the laser reflecting unit 340a. An image is formed on the surface of the body 1c, 1m. Thereby, an electrostatic latent image can be formed on the photoconductors 1c and 1m. The laser beams Ly and Lk are emitted from the laser emitting unit 310b, are incident on the laser deflecting unit 320, are deflected in the main scanning direction by the deflecting unit 320, and are respectively transmitted through the laser imaging unit 330b and the laser reflecting unit 340b. An image is formed on the surfaces of the photoconductors 1y and 1k. Thus, an electrostatic latent image can be formed on the photoconductors 1y and 1k.

The laser deflection section 320 includes the deflector 30 and the deflection substrate 30 '. The deflector 30 is a rotary polygon mirror (here, a hexahedral polygon mirror), and is disposed on the substrate 30 'via a polygon motor (not shown).
The deflector 30 is rotated in the direction D in FIG. Thereby, the laser emitting unit 310
a, the laser beams Lc, Lm respectively emitted toward the laser imaging unit 330a, and the laser beams Ly, L respectively emitted from the laser emission unit 310b.
k can be deflected in the main scanning direction toward the laser imaging section 330b.

The laser emitting section 310a is connected to the laser light source 31.
c, 31m, collimator lenses 32c, 32m, a combining mirror 33a, and a cylindrical lens 34a. Here, the laser light sources 31c and 31m are laser diodes, and can emit laser beams Lc and Lm for forming electrostatic latent images corresponding to cyan and magenta images on the photoconductors 1c and 1m, respectively. The collimator lenses 32c and 32m can convert the laser beams Lc and Lm emitted from the laser light sources 31c and 31m into parallel light beams. The combining mirror 33a reflects the laser beam Lc passing through the collimator lens 32c and transmits the laser beam Lm. Thereby, the laser beams Lc and Lm can be incident on the cylindrical lens 34a. The cylindrical lens 34a can narrow the laser beams Lc and Lm from the combining mirror 33a to the polarizing section 320.

The laser imaging section 330a is provided with a scanning lens 35.
a, 35a ', 38c, and 38m. Lens 3
5a, 35a 'and 38c apply the laser beam Lc from the laser deflecting unit 320, and the lenses 35a, 35a' and 38m apply the laser beam Lm from the laser deflecting unit 320 to the photoconductors 1c and 1m via the laser reflecting unit 340a. I can form an image.

The laser reflecting section 340a is provided on the separation mirror 36.
a, folding mirrors 36a ', 36a ", 37a. The mirror 36a can reflect the laser beam Lm from the lens 35a' and guide it to the mirror 36a ',
The laser beam Lc can be transmitted. The mirror 36a 'can reflect the beam Lm from the mirror 36a and guide it to the mirror 36a ", and the mirror 36a" can reflect the beam Lm and guide it to the scanning lens 38m. Mirror 3
7a can reflect the laser beam Lc passing through the mirror 36a from the lens 35a 'and guide it to the scanning lens 38c.

Laser emitting section 310b, laser image forming section 33
0b and the laser reflecting unit 340b
10a, laser imaging section 330a, laser reflection section 340a
, And these components are symmetrically arranged with respect to the laser deflection unit 320. That is, the laser emitting unit 310b includes the laser light sources 31y and 31k, the collimator lens 32y,
32k, synthetic mirror 33b, cylindrical lens 34
b. The laser light sources 31y and 31k are composed of laser diodes, and can emit laser beams Ly and Lk for forming electrostatic latent images corresponding to yellow and black images on the photoconductors 1y and 1k, respectively. The collimator lenses 32y and 32k can convert the laser beams Ly and Lk into parallel light beams. The combining mirror 33b transmits the laser beam Ly and reflects the laser beam Lk. This allows the laser beams Ly and Lk to be incident on the cylindrical lens 34b. The cylindrical lens 34 b can narrow the laser beams Ly and Lk to the polarization section 320.

The laser imaging section 330b is provided with a scanning lens 35.
b, 35b ', 38y, and 38k. Lens 3
5b, 35b 'and 38y apply the laser beam Ly from the laser deflecting unit 320, and the lenses 35b, 35b' and 38k apply the laser beam Lk from the laser deflecting unit 320 to the photoconductors 1y and 1k via the laser reflecting unit 340b. I can form an image.

The laser reflecting section 340b is connected to the separation mirror 36.
b, folding mirrors 36b ', 36b "and 37b. The mirror 36b can reflect the laser beam Ly from the lens 35b' and guide it to the mirror 36b '.
The laser beam Lk can be transmitted. The mirror 36b 'can reflect the beam Ly from the mirror 36b and guide it to the mirror 36b ", and the mirror 36b" can reflect the beam Ly and guide it to the scanning lens 38y. Mirror 3
7b can reflect the laser beam Lk passing through the mirror 36b from the lens 35b 'and guide it to the scanning lens 38k.

As shown in FIG. 1, the cleaning blade 7
Each of c to 7k is a blade-shaped photosensitive member 1c.
Ｋ1k. Thereby, the photoconductors 1c to
The untransferred toner remaining on the recording medium S without being transferred onto the recording medium S can be removed. Lamp 8c for static elimination
8k can irradiate the photoconductors 1c to 1k with light, and thereby the electric charges on the photoconductors 1c to 1k can be removed by light.

In this image forming apparatus, the above-described registration mark detection for detecting the displacement of the multi-color toner images (cyan toner image, magenta toner image, yellow toner image, black toner image) on the recording medium S is performed. Devices 51, 52, 53
It has. FIG. 3 shows a state where the registration mark is transferred onto the transport belt 60 and an arrangement state of the registration mark detection devices 51, 52 and 53 in the image forming apparatus shown in FIG. , 1k
The figure which looked at from the top in the state where it removed is shown.

When detecting the misregistration of the multicolor toner image on the recording medium S, as shown in FIG.
0, three positions corresponding to the registration mark detection devices 51, 52, and 53 in a direction (main scanning direction) orthogonal to the conveyance direction V, and at predetermined intervals in the conveyance direction V (sub-scanning direction). The registration marks C1, C2, C3 corresponding to the cyan toner image, the registration marks M1, M2, M3 corresponding to the magenta toner image, and the registration marks Y1, Y2, Y3 corresponding to the yellow toner image correspond to the black toner image. Registration marks K1, K2, K3
Are formed by transfer.

The registration marks C1 to C3, M1 to M3,
Y1 to Y3 and K1 to K3 are patterns of the same shape and size, respectively, and are provided at different positions in a direction orthogonal to the transport direction V in a direction parallel to the transport direction V and in a direction orthogonal to the transport direction V. This is a V-shaped registration mark composed of oblique lines having gradually different intervals from the line orthogonal to the transport direction.

The registration mark detecting device 51 uses the recording medium S
In order to detect the positional deviation of the multicolor toner images, the registration marks C1, M1, Y1, and K1 formed on the conveyor belt 60 corresponding to the multicolor toner images are detected. Similarly, the registration mark detection device 52 detects the registration marks C2, M2, Y2, and K2, and the registration mark detection device 53 detects the registration marks C3, M3, Y3, and K3.

As described above, the registration mark detecting device 51,
By arranging 52 and 53, forming registration marks, and sequentially detecting registration marks of each color arranged in the recording medium conveyance direction by each registration mark detection device, in the recording medium conveyance direction in an image finally obtained. It is possible to detect a color shift in a recording medium transport direction (sub-scanning direction) and a color shift in a direction (main scanning direction) orthogonal to the recording medium transport direction in each area or portion in a direction (main scanning direction) perpendicular to the recording medium.

Next, registration mark detection devices 51, 52,
The configuration and the like of the detection device 53 will be described.
Have substantially the same configuration, only the detection device 51 will be described here, and description of the detection devices 52 and 53 will be omitted. FIG. 4 shows a registration mark detection device 51.
4 (A) is a plan view of a registration mark K1 detected by the registration mark detection device 51, and FIG. 4 (B) is a diagram showing the registration mark detection device 51 shown in FIG. 4 (A). FIG. 3 shows a side view of the detection state of the sigma.

As described above, the registration mark K1 shown in FIG. 4 is composed of a line V1 composed of an orthogonal line K1y in the transport direction parallel to the direction orthogonal to the transport direction V and an oblique line K1x.
It is a registration mark of a character-shaped line. As shown in FIG. 4, the registration mark detection device 51 includes measurement systems 510, 51.
0 '. The measurement system 510 includes the optical sensor unit 5
11 and a light source unit 512, and a measurement system 510 ′
Is composed of a light sensor section 511 'and a light source section 512'. The optical sensor units 511 and 511 ′ are components that perform substantially the same function, and
1a, 511a 'and condenser lenses 511b, 511b'
Contains. The light source units 512 and 512 ′ are components that perform substantially the same function, and are respectively light sources 512a and 512a ′ and projection lenses 512b and 512b.
12b '. These two optical sensors 511a,
Reference numeral 511a ′ is a photodiode that can convert the received light into an electric signal.

The corresponding optical sensor unit 511 and light source unit 512, and the optical sensor unit 511 'and light source unit 512' correspond to the normal axis of the upper surface of the conveyor belt 60 on which the registration mark K1 is formed, and correspond to the registration mark K1. They are arranged axially symmetric with respect to a normal axis H intersecting the normal passage of the predetermined portion N. More specifically, the measurement systems 510 and 510 'are both disposed above the conveyor belt 60 and extend in the registration mark advancing direction V with respect to the first surface including the normal axis H and perpendicular to the registration mark passage. One optical sensor unit 511 ′ is arranged on the upstream side, the corresponding light source unit 512 ′ is arranged on the downstream side, and the other optical sensor unit 511 is arranged on the downstream side in the registration mark traveling direction V. The corresponding light source unit 512 is disposed on the upstream side, and further, the light sensor unit 511 ′ and the light source unit 512 on the upstream side and the light sensor unit 511 and the light source unit 512 ′ on the downstream side are symmetrical with respect to the first surface. Are located in
The measuring systems 510 and 510 'are offset about the normal axis H so as not to interfere with each other.

Thus, the registration marks K from each of the light sources 512a, 512a 'via the lenses 512b, 512b'.
By irradiating light to each of the sensors 511a and 511,
a 'can detect specularly reflected light from a predetermined portion of the registration mark (a predetermined portion N at the detection timing shown in FIG. 4) via the condenser lenses 511b and 511b'. The other registration mark detection devices 52 and 53 have the same configuration.

The image forming apparatus has an arithmetic processing unit CONT as shown in FIG. The registration mark detection devices 51, 52, and 53 are connected to the arithmetic processing unit CONT, respectively, and can send detection values detected by two optical sensors provided respectively to the arithmetic processing unit CONT. The arithmetic processing unit CONT can calculate a proper (regular) registration mark position based on the registration mark position information obtained from the two optical sensors in the registration mark detection devices 51, 52, and 53. This calculation process will be described later in detail.

The detection value calculated by the arithmetic processing unit CONT is sent to a main control unit (not shown) for controlling the entire image forming apparatus. The main control unit is mainly composed of a computer, and calculates an amount of misregistration of each color registration mark based on the detection value calculated by the arithmetic processing unit CONT, and forms an image forming unit for forming each color toner image. 100
The position of each color toner image (image) at the time of normal image formation formed by c, 100m, 100y, and 100k can be corrected. This correction is performed by a conventionally known method. The detection and correction of the positional deviation are performed at a predetermined time (for example, before normal image formation, after image formation is completed, at a predetermined number of times of image formation, and the like).

According to the image forming apparatus described above, the photoconductors 1c, 1m, 1y, and 1k are driven to rotate at predetermined timings, respectively, and the main chargers 2c, 2m, and 2k are rotated.
It is uniformly charged by y and 2k. As shown in FIG. 2, in the laser scanning optical device 3, the laser light sources 31c and 31c
Laser beams are emitted from m, 31y, and 31k at predetermined timings. Laser light sources 31c, 31m, 31
The laser beams y and 31k modulate the laser beams Lc, Lm, Ly and Lk based on image information of cyan, magenta, yellow and black sent from an image reading device or the like (not shown).

The laser light sources 31c, 31m, 31y, 31
k, Lc, Lm, L
y and Lk are collimator lenses 32c, 32m, 32y,
The light beams are made substantially parallel by 32k. The laser beams Lc and Lk are respectively combined with the combining mirrors 33a and 33b.
And is incident on a portion below the mirror surface of the deflector 30 via the cylindrical lenses 34a and 34b. The laser beams Lm and Ly pass through the combining mirrors 33a and 33b, respectively, and the portions above the mirror surface of the deflector 30 via the cylindrical lenses 34a and 34b, ie, the laser beam L
Light is incident above the incident positions of c and Lk.

The rotation of the deflector 30 deflects the laser beams Lc and Lm in the main scanning direction toward the scanning lenses 35a and 35a '. In addition, laser beams Ly, L
k is deflected in the main scanning direction toward the scanning lenses 35b and 35b '. The laser beam Lc passing through the scanning lenses 35a and 35a 'and the separation mirror 36a and the laser beam Lk passing through the scanning lenses 35b and 35b' and the separation mirror 36b are turned back mirrors 37a and 37b, respectively.
To the photoreceptor 1 via the scanning lenses 38c and 38k.
c, 1k. The laser beam Lm that has passed through the scanning lenses 35a and 35a 'is reflected by the separation mirror 36a and the return mirrors 36a' and 36a ",
The light is irradiated to the photoconductor 1m through 8m. The laser beam Ly passing through the scanning lenses 35b and 35b 'is reflected by the separation mirror 36b and the return mirrors 36b' and 36b ", and is irradiated on the photoreceptor 1y via the scanning lens 38y.

Thus, the photosensitive members 1c, 1m, 1y,
The charged area above 1k is exposed, and an electrostatic latent image is sequentially formed on each surface. Then, first, a cyan visible toner image is formed on the photoreceptor 1c in the formation transfer unit 100c. As shown in FIG. 1, the electrostatic latent image corresponding to the cyan image on the photoconductor 1c by the laser beam Lc from the laser scanning optical device 3 is developed with the rotation of the photoconductor 1c.
Move to

The developing device 4c supplies a cyan developer Dc to the electrostatic latent image formed on the photoreceptor 1c with the rotation of the developing roller 41c, and develops the latent image under application of a developing bias voltage. , A visible toner image Tc. The visible toner image Tc on the photoconductor 1c moves to the transfer portion Pc. Transfer part Pc
Is transferred to the recording medium S. The recording medium S is sent out from a paper supply tray (not shown) by a paper supply roller (not shown), and is sent to the timing roller pair 11. The timing roller pair 11 synchronizes with the toner image Tc on the photoconductor 1c and
Send out. The recording medium S is transported along with the rotation of the transport belt 60 of the transport device 600 and moves to the transfer section Pc.

In the transfer section Pc, the transfer charger 6c applies a voltage from the power supply PW3c to the recording medium S via the transport belt 60. As a result, the toner image Tc on the photoreceptor 1c
Is transferred to the recording medium S. The recording medium S is provided on the photoconductor 1c.
The remaining toner that has not been transferred to the
The cleaning blade 7c removes the residual toner. Thereafter, light is irradiated from the discharging lamp 8c to the photoconductor 1c, and the residual potential on the photoconductor 1c is removed. Then, the photoconductor 1c is prepared for the next image formation. The recording medium S further moves to the transfer portion Pm as the transport belt 60 moves.

In the same manner as described above, the formation and transfer sections 100m, 1m
At 00y and 100k, laser beams Lm, Ly, and Lk are emitted from the laser scanning optical device 3, and the photoconductors 1m and 1m are irradiated.
After an electrostatic latent image corresponding to a magenta image, a yellow image, and a black image is formed on y and 1k and developed, a visible toner image of each color is sequentially formed and transferred to the recording medium S, and a visible toner image of each color is formed. Can be stacked.

After transferring the toner image at the transfer portion Pk, the recording medium S is conveyed to the fixing roller pair 14, where the toner image is fixed on the recording medium S. Thereafter, the sheet is discharged to a sheet discharge tray by a sheet discharge roller pair (not shown). At the time of detecting the registration mark, similar to the above-described normal image formation,
Each image forming unit 100c, 100m, 100y, 100k
Then, the registration marks for each color registration are transferred onto the conveyor belt 60 (see FIG. 3). Conveyor belt 60
Is driven by a driving roller 63 as shown in FIGS. 1 and 2, and the registration marks of each color move at a substantially constant speed in the direction of arrow V in the figure. The registration marks of each color sequentially conveyed on the conveyance belt are detected by a registration mark detecting device 5.
1, 52 and 53 are detected.

Each image forming unit 100c, 100m, 100
For y and 100k, actually, the main scan writing position shift, the sub-scan writing position shift, the main scanning magnification shift, the main scanning partial magnification shift, the main scanning direction bending shift, the sub-scanning direction bending shift, the main scanning direction tilt shift, Sub-scanning magnification deviation, sub-scanning partial magnification deviation, and the like occur in a complex manner, causing a deviation in the toner image (image) position of each color, and almost no registration mark of each color is formed at a predetermined position. In other words, the deviation of the toner image (image) position of each color appears as a deviation of the registration mark of each color from a predetermined position.

The detection of the displacement of the registration mark of each color is performed as follows.
This is performed by detecting the amount of deviation of the registration mark of another color from the registration mark of the reference color. Similarly, the misregistration correction of the toner image (image) of each color is also performed by matching the toner image (image) of the reference color. In this example, black is used as a reference in both the detection of the displacement of the registration mark of each color and the correction of the displacement of the toner image (image) of each color.

Each of the registration mark detecting devices 51, 52, 5
(3) From the detected position information of the V-shaped registration mark orthogonal to the transport direction of the registration mark, the positional deviation amount between the respective color registration marks in the recording medium transport direction (sub-scanning direction), and furthermore, the positional deviation amount between the respective color toner images, Can be. Also, based on the detection position information of the oblique line portion and / or the line portion orthogonal to the conveyance direction by the registration mark detection device, the amount of misalignment between the registration marks of each color in the direction (main scanning direction) orthogonal to the recording medium conveyance direction, and thus the toner of each color The amount of displacement between images can be obtained.

The positional deviation of each color registration mark in the main scanning direction is specifically determined by the registration mark detecting devices 51, 52, 53 arranged at three places in the main scanning direction.
Is measured by measuring the elapsed time between the detection of two lines of the V-shaped registration mark conveyed by the conveyance belt 60 in the sub-scanning direction. When there is no displacement, the registration mark detection output values for each color obtained from the three registration mark detection devices 51 to 53 are all the same, but actually, various positional displacements occur as described above. , Each of the registration mark detection devices 51 to 53,
The registration mark detection output value differs for each color. these,
The position shift amount of each of the above-described various images is calculated based on the detection results of the plurality of registration mark detection devices 51 to 53. The calculation method is known, and the description is omitted here. The registration mark detection will be described in more detail.

Next, registration mark detection devices 51, 52,
The operation of the detection device 53 will be described. However, since the detection devices 51 to 53 shown in FIG. 2 are devices that perform substantially the same operation based on the same principle, only the detection device 51 will be described here, and the detection devices 52 and 53 will be described. Description of 53 will be omitted. Further, registration marks C1 to C3, M1 to M3, Y1 to Y3, K1 to K3 formed on the conveyor belt 60 are formed.
Are the same pattern, so only the detection of the registration mark K1 will be described here, and the description of the detection of other registration marks will be omitted.

As described above, the registration mark detection device 51 detects the position of the conveyance direction orthogonal line K1y and the position of the oblique line K1x with respect to the registration mark K1, and the conveyance direction orthogonal line K1y and the oblique line K1x are detected. Since the detection of K1x by the detection device 51 is performed by the same operation, the detection of the transport direction orthogonal line K1y by the detection device 51 will be described here, and the detection of the oblique line K1x will be omitted.

As shown in FIG. 4, the registration mark detecting device 51, as described above,
11a and light source 512a, optical sensor 511a 'and light source 51
2a ', and are arranged in the relationship described above. In detecting the registration mark K1, light is emitted from the two light sources 512a and 512a 'to the registration mark K1 on the transport belt 60.

At this time, the corresponding optical sensors 511a, 511a,
11a 'and the light sources 512a, 512a'
Are arranged axially symmetrically with respect to each other, the incident light beams E1 and E1 ′ of the light emitted from the two light sources 512a and 512a ′ to the registration mark K1 (the predetermined portion N of the line K1y orthogonal to the transport direction) and the resist The reflected light beams E2 and E2 'reflected at the mark K1 and traveling toward the two optical sensors 511a and 511a' are respectively axially symmetric with respect to the normal axis H. Thereby, two optical sensors 511a,
511a 'can detect light that is regularly reflected at the registration mark K1 by light irradiation from the corresponding light source 512a, 512a'. Thus, the SN ratio of the detection signals from the two optical sensors 511a and 511a 'is increased. Thus, a high contrast between the conveyor belt 60 and the registration mark K1 can be obtained and the mark can be detected. As a result, a good contrast can be obtained even when a registration mark is detected on a transport belt of an arbitrary color.

The two optical sensors 511a, 511a '
In the detection of the predetermined portion N of the registration mark, when the conveyor belt 60 is not fluttering, and thus the predetermined portion N of the registration mark is traveling on a regular path, the light source 5
Specularly reflected light from the same predetermined portion N of the registration mark K1 due to light irradiation from 12a and 512a 'is simultaneously detected.

In other words, the two optical sensors 511a, 511a,
11a 'detects the registration mark K1, and when the conveyor belt 60 is not fluttering (in a position shown by a chain line in FIG. 5), the two optical sensors respectively emit light that is specularly reflected by the registration mark. The positions of the registration marks K1 obtained by the detection coincide with each other, and the detected position is B in the figure.

However, when the conveyor belt 60 flaps,
When the predetermined portion N of the registration mark passes through a path deviated from its normal path toward the measuring systems 510 and 510 'as shown by a solid line in FIG. 5, for example, the optical sensor located upstream in the traveling direction V of the registration mark K1. 511a 'detects the registration mark predetermined portion N later than the optical sensor 511a on the downstream side. The downstream optical sensor 511a detects the registration mark predetermined portion N earlier than the upstream optical sensor 511a '.

When the conveyor belt 60 is fluttering, the registration mark predetermined portion N is moved from its regular path to the measurement system 51.
0, 510 ', the optical sensor 511a' on the upstream side in the traveling direction V of the registration mark K1 is replaced with the optical sensor 511 on the downstream side.
Detecting the predetermined portion N of the registration mark earlier than a
The downstream optical sensor 511a detects the registration mark predetermined portion N later than the upstream optical sensor 511a '.

The color image forming apparatus shown in FIG. 1 is provided with the arithmetic processing unit CONT, as described above, into which the registration mark position information detected by the two optical sensors 511a, 511a 'is input. You. An arithmetic expression TＣＯ (T1 + T2) / 2 is set in the arithmetic processing unit CONT. In the arithmetic processing unit, the optical sensors 511a, 51
1a ', the registration mark position information detected in subroutine 1a' is substituted into the equation, and the calculation is performed. Based on the calculation result, the regular registration mark (line K) when the conveyance belt 60 is not fluttering is obtained.
1y) The detection position.

The above equation will be described.
As shown in FIG. 5B and FIG. 5, when the transport belt 60 is not fluttering (in FIG. 5, a chain line), the two optical sensors 511a and 511a ′ are used to determine whether the registration mark (line K1y) on the transport belt 60 is correct. Is read at position B. FIG. 6A shows detection output values obtained from the optical sensors 511a and 511a 'at this time.

The line K1y on the conveyor belt 60 is indicated by B in the figure.
, When the two optical sensors 511a, 511
a ′ simultaneously detects the same portion N of the line K1y,
The output value of each optical sensor at that time draws a curve having a half-width determined by the width of the line K1y and the transport speed of the transport belt 60, as shown in FIG. At this time, an elapsed time from a predetermined reference time to a registration mark detection position B is set to T [sec]. Here, the predetermined detection reference time is defined as a time when light emission from the two light sources 512a and 512a 'is started before the two optical sensors 511a and 511a' perform a detection operation (the time axis in FIG. 6). At zero).

As shown in FIG. 5, when the transport belt 60 is fluttering (solid line in the figure), each optical sensor 511
a, Registration mark by 511a '(line K1y)
The detection position is different. That is, the optical sensor 511a detects the line K1y when the line K1y reaches the position A in the figure (solid line in the figure), and the optical sensor 511a 'detects the line K1y.
When 1y comes to the position of C in the figure, the line K1y is detected (broken line in the figure). Each optical sensor 511a, 511
FIGS. 6B and 6C show detection output values obtained from a ′.
Shown in

The graph shown in FIG.
It shows the detection output value of 1a. The elapsed time from the detection reference time to the registration mark detection position A is T1 [s
ec]. The graph shown in FIG.
11a 'shows the detected output value. The elapsed time from the detection reference time to the registration mark detection position C is T2
[Sec]. Here, two optical sensors 511a,
Since 511 a ′, light sources 512 a, 512 a ′, and the normal axis H of the surface of the conveyor belt 60 are arranged as described above, the above-mentioned T ≒ (T 1 + T 2) / 2 [s
ec].

As a result, even when the transport belt 60 flaps, the average value of the position information of the registration marks obtained from the two optical sensors 511a and 511a 'is calculated, so that the transport belt 60 does not flutter. Two optical sensors 511a and 511 from the detection reference time in the state
A time T until a ′ simultaneously detects light regularly reflected at the same portion N of the line K1y can be obtained. Based on this time T and the transport speed of the registration mark K1 by the transport belt 60, the transport belt 60 The detection position B of a proper (regular) registration mark (line K1y) in a state where the registration mark does not flutter can be estimated, and this can be used as registration mark detection information. This makes it possible to cancel registration mark detection errors due to the fluttering of the conveyor belt 60. Note that the diagonal line K1x of the registration mark K1 can be similarly detected.

Of course, the other registration marks Y1, M1, C
1, K2, Y2, M2, C2, C3, Y3, M3, K3
Can be similarly detected in position, and similar advantages can be obtained. As described above, in the color image forming apparatus including the registration mark detection devices 51, 52, 53,
The detection accuracy of the registration mark can be increased.

Based on the detected values, the main control unit (not shown) can correct the position of each color image during normal image formation.
The registration mark on the conveyor belt 60 after the detection of the image position shift is removed by a cleaning blade (not shown) arranged in contact with the conveyor belt 60. In the example described above, the registration marks are transferred onto the conveyor belt 60 and the registration marks are detected by the registration mark detection devices 51 to 53.
It may be transferred to the upper side and detected by the registration mark detection devices 51 to 53.

In the example described above, the image forming unit 1
00c to 100k employ an electrophotographic recording method in which a toner image based on image information is once formed on the photoconductors 1c to 1k and indirectly recorded on the recording medium S, but without forming an electrostatic latent image, An image forming unit of a direct recording system that forms an image by, for example, directly flying toner on an appropriate image carrier or a recording medium based on image information may be employed.

[0086]

According to the present invention, there is provided a color image forming apparatus having a plurality of image forming sections, wherein a predetermined color toner image formed by the image forming sections is transferred onto a recording medium conveyed by a conveying belt, and is fixed thereon. A registration mark for detecting a registration mark formed on the recording medium or on the transport belt corresponding to each of the plurality of color toner images in order to detect a positional shift of the multicolor toner image on the recording medium. A detection device, wherein a registration mark detection error due to the fluttering of the transport belt can be suppressed to a small value, and a good contrast can be obtained even when register marks are detected on a transport belt of an arbitrary color, and the detection accuracy can be increased. Can be provided.

According to the present invention, there is provided a color image forming apparatus having a plurality of image forming units, wherein a predetermined color toner image formed by the image forming unit is transferred onto a recording medium conveyed by a conveying belt, and is fixed. A register for detecting a registration mark formed on the recording medium or on the transport belt in correspondence with the multicolor toner image for detecting a positional shift of the multicolor toner image on the recording medium. A color image forming apparatus provided with a mark detection device, wherein a registration mark detection error due to the fluttering of the transport belt can be suppressed to a small value, and a good contrast can be obtained even when register marks are detected on a transport belt of an arbitrary color. And a registration mark detection device that can increase the detection accuracy, so that good color image formation with suppressed color misregistration can be achieved. It is possible to provide a capability of color image forming apparatus.

[Brief description of the drawings]

FIG. 1 is a side view illustrating a schematic configuration of an example of a full-color image forming apparatus including a registration mark detection device according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of a laser scanning optical device, a photoconductor, a transfer / transport device, and a registration mark detection device in the image forming apparatus shown in FIG.

FIG. 3 is a top view of the image forming apparatus shown in FIG. 2 in which a registration mark is transferred onto a conveyance belt and a registration mark detection device is disposed from above with a laser optical device and each photoconductor removed; is there.

4A and 4B are diagrams showing an arrangement state of a registration mark detection device, FIG. 4A is a plan view of a registration mark detection state by the registration mark detection device, and FIG.
5 is a side view of a registration mark detection state by the registration mark detection device shown in FIG.

FIG. 5 is a side view of a registration mark detection state by the registration mark detection device in a state where the conveyance belt flutters in a direction approaching the optical sensor.

FIG. 6A is a graph showing a detection output value of a registration mark by an optical sensor in a state where the conveyance belt is not fluttering, and FIG. 6B is a graph showing a registration mark in a state where the conveyance belt is fluttering. FIG. 7C is a graph showing a detection output value of a registration mark by an optical sensor that detects a mark first, and FIG. 7C illustrates detection of the registration mark by an optical sensor that detects the registration mark later with the conveyance belt fluttering; It is a graph which shows an output value.

[Explanation of symbols]

100c Image forming section for cyan visible toner image 100m Image forming section for magenta visible toner image 100y Image forming section for yellow visible toner image 100k Image forming section for black visible toner image 1c, 1m, 1y, 1k Photoconductor 2c, 2m, 2y 2k main charger 3 laser scanning optical device 310a, 310b laser emitting unit 31c, 31m, 31y, 31k laser light source 32c, 32m, 32y, 32k collimator lens 33a, 33b combining mirror 34a, 34b cylindrical lens 320 laser deflecting unit 30 deflector 30 'Deflection substrate 330a, 330b Laser imaging unit 35a, 35a', 35b, 35b 'Scan lens 340a, 340b Laser reflection unit 36a, 36b Separation mirror 36a', 36a ", 37a Folding mirror 36b ', 36b", 7b Folding mirrors 38c, 38m, 38y, 38k Scanning lenses Lc, Lm, Ly, Lk Laser beams 4c, 4m, 4y, 4k Developing devices 41c, 41m, 41y, 41k Developing rollers 42c, 42m, 42y, 42k Device case 51, 52, 53 Registration mark detecting device 510, 510 'Measuring system 511, 511' Optical sensor unit 512, 512 'Light source unit 511a, 511a' Optical sensor 511b, 511b 'Condenser lens 512a, 512a' Light source 512b, 512b 'Projection lens 6c, 6m, 6y, 6k Transfer Charger 7c, 7m, 7y, 7k Cleaning Blade 8c, 8m, 8y, 8k Static Elimination Lamp 11 Timing Roller Pair 14 Fixing Roller Pair 600 Transfer Transport Device 60 Transport Belt 61, 63 Drive Roller 62 Tension roller C1, C2, C3 Cyan resist mark M1, M2, M3 Magenta resist mark Y1, Y2, Y3 Yellow resist mark K1, K2, K3 Black resist mark K1y Transport direction orthogonal line K1x diagonal line A, B, C resist Mark detection position CONT Arithmetic processing unit E1, E1 'Incident light rays of light applied to registration mark K1 E2, E2' Reflected light reflected by registration mark K1 toward optical sensor N Same part of detected registration mark K1 H Normal axis of the surface of the conveyor belt 60 Direction axis Dc Cyan developer Dm Magenta developer Dy Yellow developer Dk Black developer Pc, Pm, Py, Pk Transfer site PW1c, PW1m, PW1y, PW1k Power source PW2c, PW2m, PW2y, PW2k Power supply PW3c, PW3m, PW3 y, PW3k power supply S recording medium Tc visible toner image

Continuation of the front page (72) Inventor Yasushi Nagasaka 2-3-13 Azuchicho, Chuo-ku, Osaka-shi F-term in Osaka International Building Minolta Co., Ltd. (reference) 2H027 DA21 DA32 DE02 DE07 EB04 EB06 EC03 EC06 EC07 ED04 ED16 EE01 EF09 FA28 HB07 ZA07 2H030 AA01 AB02 BB02 BB16 5C074 AA10 BB03 DD15 EE11 FF15 GG02 GG14

Claims (6)

[Claims] 1. A color image forming apparatus comprising a plurality of image forming units, wherein a predetermined color toner image formed by the image forming units is transferred onto a recording medium conveyed by a conveyor belt and fixed thereon. A registration mark detection device that detects registration marks formed corresponding to the plurality of color toner images on the recording medium or on the transport belt, respectively, for detection of a positional shift of the multicolor toner image. Two optical sensors for detecting the same predetermined portion of the registration mark with reflected light from the portion, and two light sources corresponding to the respective optical sensors and irradiating the registration mark with light, The corresponding optical sensor and light source are each a normal path of a predetermined portion of the registration mark, the axis being a normal axis of the recording medium surface or the conveyance belt surface on which the registration mark is formed. The registration marks are arranged axially symmetrically with respect to the intersecting normal axis. A registration mark detecting device in a color image forming apparatus, wherein sensors are arranged so as to detect the predetermined portion from different directions. 2. A registration mark detecting device in a color image forming apparatus according to claim 1, wherein said two optical sensors are photodiodes capable of converting received light into an electric signal. 3. A color image forming apparatus having a plurality of image forming units, wherein a predetermined color toner image formed by said image forming unit is transferred onto a recording medium conveyed by a conveying belt, and is fixed thereon. A registration mark detection device that detects registration marks formed on the recording medium or on the transport belt corresponding to the plurality of color toner images, respectively, for detecting a positional shift of the multicolor toner image on the recording medium. A color image forming apparatus, wherein the registration mark detection device corresponds to two optical sensors for detecting the same predetermined portion of the registration mark by reflected light from the portion, and the respective optical sensors. And two light sources for irradiating the registration mark with light, and the corresponding light sensors and light sources are respectively provided on the recording medium surface or the conveyance belt surface on which the registration mark is formed. Along with a normal axis, which is arranged axially symmetrically with respect to a normal axis intersecting the normal path of the predetermined portion of the registration mark, each of the predetermined portions of the registration mark is displaced from the normal path. A color image forming apparatus, wherein each sensor is arranged to detect the predetermined portion from a different direction so that a time lag occurs in the detection of the predetermined portion by the sensor. 4. A method for detecting a plurality of registration marks formed on the recording medium or the transport belt by displacing a position in a direction orthogonal to a transport direction of the recording medium by the transport belt. 4. The color image forming apparatus according to claim 3, wherein the registration mark detection devices are arranged in a direction orthogonal to a recording medium conveyance direction in correspondence with the registration marks. 5. The color image forming apparatus according to claim 3, wherein the two optical sensors in the registration mark detecting device are photodiodes that can convert received light into an electric signal. 6. An arithmetic processing unit for calculating a proper registration mark position based on registration mark position information obtained from two optical sensors in the registration mark detecting device. The color image forming apparatus as described in the above.