JPH10207167A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tandem image forming device with a simple device constitution, capable of detecting information on the speed of a carrying belt, the phase of an image, etc., by reading some patterns formed on the carrying belt and a driving roller. SOLUTION: A sensor 80 provided in a copying machine main body reads equal pitch patterns 45 obtained by notching the carrying belt 4. The equal pitch patterns 45 have noncontinuous parts 46 formed at intervals corresponding to the length of the outer periphery of the driving roller 41. For detecting the phase deviation in each color image, photoreceptor drums 51C-51K are scanned by optical units 6C-6K and resist marks 47 of a prescribed shape are written in the end parts of the photoreceptor drums, developed in toner images and transferred onto the carrying belt, to be detected by the sensor 80. The resist marks are formed on the noncontinuous parts 46, to be easily identified by the sensor 80.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color copying machine and a laser printer, and more particularly to a tandem type image forming apparatus.

[0002]

2. Description of the Related Art In general, a color image forming apparatus forms a toner image of each color of yellow, magenta, cyan, black and the like on a photosensitive drum, and superimposes and transfers these on a recording sheet. A tandem type is known in addition to a transfer drum type in which a recording sheet is wound around a transfer drum to transfer an image.

The tandem type is disclosed in Japanese Patent Laid-Open No. 1-177569.
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, a plurality of image forming units having a photosensitive drum and an image exposing unit are arranged side by side along a transport belt, and the image forming unit performs image formation while transporting a transfer sheet by the transport belt. The toner images are sequentially transferred by passing through the position, and images can be formed at a high speed.However, advanced technology is required to align each color image, and the transfer belt There has been developed a device having a function of detecting speed unevenness and deviation of each color image and correcting the speed unevenness and image deviation based on the detection result.

For example, in Japanese Patent Application Laid-Open No. 1-177569, if the speed of the conveyance belt is uneven due to eccentricity of a driving roller for driving the conveyance belt, the image formed on the photosensitive drum is transferred to a transfer sheet. It describes that when the image is expanded and contracted, this causes a magnification error and a positional shift of each color image. On the other hand, marks of equal pitch are formed on the conveyor belt or its drive roller, and the speed unevenness information of the conveyor belt is measured by detecting the mark with a sensor while rotating the drive roller at a constant speed in advance. In addition, there is disclosed a technique for controlling the driving roller based on the information to eliminate the uneven speed of the transport belt.

In Japanese Patent Application Laid-Open No. 1-142678, for example, a registration mark is written on a photosensitive drum of each color, transferred to a conveyor belt, and detected by a sensor to measure the amount of misregistration of each color image. A technique for performing positioning based on the measured amount is disclosed.

[0006]

By combining the above-described techniques, a sensor for reading a registration mark transferred onto a conveyance belt and a sensor for reading a mark of equal pitch previously formed on the conveyance belt are provided. Then, it is considered that by using the data read by each sensor, it is possible to adjust the speed fluctuation of the transport belt and to perform the position adjustment of each color image.

Similarly, in a tandem-type image forming apparatus, registration is performed using information obtained by reading a registration mark transferred onto a conveyance belt by a sensor, and a uniform pitch formed on a drive roller is formed. It is considered that it is possible to adjust the speed fluctuation of the conveyor belt using the information obtained by reading the mark with a sensor. By the way, it is desired that the configuration of the tandem image forming apparatus be as simple as possible by reducing the number of parts.

The present invention has been made under such considerations, and a tandem-type image forming apparatus includes:
By reading several patterns formed on the conveyor belt and the drive roller, it is possible to detect information on the speed of the conveyor belt, image misalignment, etc., and provide a simple device configuration. The purpose is to do.

[0009]

In order to achieve the above object, the present invention relates to a tandem type image forming apparatus, wherein a sensor provided so that a first pattern formed on a conveyor belt enters a detection field of view. And a pattern forming means for forming a second pattern identifiable from the first pattern by transferring the second pattern from the photosensitive drum on the conveyor belt within the detection field of the sensor.

With such a configuration, the first pattern and the second pattern on the conveyor belt can be read by one sensor, and information can be obtained from each of the first pattern and the second pattern. Can be. For example, information on the speed of the conveyor belt can be obtained from the first pattern, and information on the positional deviation of each color image can be obtained from the second pattern.

According to the present invention, in a tandem-type image forming apparatus, a sensor provided so that a first pattern formed on a driving roller enters a detection field of view, and a conveyance belt in a detection field of the sensor. And a pattern forming means for forming a second pattern identifiable from the first pattern by transferring the second pattern from the photosensitive drum. Even with such a configuration, the first pattern on the drive belt and the second pattern on the transport belt can be read by one sensor, and information is read from each of the first pattern and the second pattern. Obtainable.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A digital full-color copying machine according to an embodiment of the present invention will be described below. (First Embodiment) [Overall Configuration of Copying Machine] FIG. 1 is a front view of a copying machine according to an embodiment of the present invention. This copier is
A so-called tandem-type copying machine, in which a paper feed cassette 2 is set on a right side wall 1a of a housing 1 so as to be freely inserted and removed, and a discharge tray 3 is attached to a left side wall 1b in an outwardly protruding posture, A transport belt 4 is horizontally installed in a lower space from the paper feed cassette 2 to the paper output tray 3, and a plurality (four in FIG. 1) of transport belts 4 are arranged on the transport belt 4 along the belt longitudinal direction. Image forming units 5C, 5M, 5Y, and 5K each including photoconductor drums 51C to 51K are arranged in rows. Then, while the recording sheet is being conveyed by the conveyance belt 4, a color image is formed by superimposing and transferring the toner images of the respective color components onto the recording sheet by the respective image forming units.

Although the configuration of the control unit 100 for controlling the entire apparatus is not shown, a laser diode is provided in addition to a CPU, a timer for generating a reference clock and measuring time, an image memory for storing image data, and the like. 61C-6
A laser diode driver for driving 1K, a motor control circuit for controlling the rotation speed of various motors such as a drive motor 43 and a polygon motor, and the like are provided, and the following copy operation is achieved.

An image reader section 10 is provided on the upper portion of the housing 1, and image data obtained by optically reading a document is sent to a control section 100. The control unit 100 performs necessary image processing on this image data, and outputs Y, M,
The image data is decomposed into C and K color components and temporarily stored in an image memory. Then, by instructing the laser diode driver, the C, M, Y, and K images stored in the image memory are read out in parallel for each main scanning line, and the image forming units 5C to 5C.
The laser diodes 61C to 61K of the optical units 6C to 6K arranged above K are optically modulated and written on the photosensitive drums 51C to 51K of the image forming units 5C to 5K.

The image forming units 5C to 5K are provided around a photosensitive drum 51C to 51K, and a cleaner 52 is provided around the photosensitive drums.
C to 52K, charging chargers 53C to 53K, developing machine 5
This is a unit structure including 4C to 54K and the like, and forms an image by an electrostatic copying method. That is, the developing units 54C to 54K of the respective units correspond to the optical units 6C to 6K.
C, M, Y, K toners corresponding to the light modulation color components of
By supplying the photosensitive drums 51C to 51K as a developer, the electrostatic latent image written on the photosensitive drum is visualized as a toner image.

On the other hand, in synchronization with the image forming operation of the image forming units 5C to 5K, the sheet feeding roller 21 and the timing roller 22
And a sheet feeding mechanism such as a conveyor belt 4 feeds out the recording sheet S from the sheet feeding cassette 2 and the photosensitive drums 51C to 51K.
Paper is sequentially fed to each lower transfer position. At each transfer position, transfer chargers 55C to 55Y are arranged below the conveyor belt 4, and the toner images formed on the photosensitive drums 51C to 51K are sequentially transferred onto the recording sheet S by the transfer chargers. Is done.

Thereafter, the recording sheet S is conveyed by a conveying belt 4 and toner particles on the recording sheet surface are melted and adhered to the sheet surface by a fixing device 7 to be fixed.
Is discharged on top. FIG. 2 is a diagram illustrating a drive mechanism of the photosensitive drum and the transport belt, and the like. As shown in the figure, the transport belt 4 is an endless belt stretched around a drive roller 41 and a support roller 42, and the drive roller 41 is driven to rotate by a drive motor 43. In addition, the transport belt 4
Are pressed against the photosensitive drums 51C to 51K by pressing rollers 44C to 44K (in FIG. 2, the pressing roller on the back side is hidden by the transport belt 4). The drums 51C to 51K rotate. Guide portions 4 a are provided at both ends of the inner peripheral surface of the transport belt 4 so that the transport belt 4 does not come off the rollers 41 and 42.

[Explanation of transport belt speed detection mechanism, drive roller phase detection mechanism, and phase shift detection mechanism of each color image] In this copying machine, an optical encoder as described below is provided, and The peripheral speed of the belt 4 can be measured. A uniform pitch pattern 45 is engraved on the conveyor belt 4 over the entire outer circumference on one side thereof, and is arranged at a predetermined position (the driving roller 41 in the drawing) of the copying machine main body.
Is provided with a sensor 80 that reads the uniform pitch pattern 45.

The sensor 80 is a photoelectric sensor having a light emitting element, a light receiving element, and an imaging lens. The light emitting element irradiates a target object at a measurement position with light, and forms an image of reflected light. The light is condensed on a light receiving element by a lens, and the light amount is measured by the light receiving element. The sensor 80 reads the equi-pitch pattern 45 passing through the measurement position with the movement of the conveyor belt 4, generates a pulse signal corresponding to the moving distance of the peripheral surface of the conveyor belt 4, and sends the pulse signal to the controller 100. In the control unit 100,
By counting the pulse signals, the moving distance and moving speed of the conveyor belt 4 can be detected.

The copying machine is provided with a mechanism for detecting the phase of the drive roller 41 as described below. The above-mentioned uniform pitch pattern 45 is formed continuously over the entire circumference of the conveyor belt 4, but discontinuous portions 46 are formed at intervals corresponding to the length of the outer circumference of the drive roller 41. In the discontinuous portion 46 in the present embodiment, the pattern having the same pitch is blank (see the blank portion 46a in FIG. 5A). The circumferential length of the transport belt 4 is set to an integral multiple of the outer circumferential length of the drive roller 41, and the discontinuous portion 46 always meets a specific position on the circumferential surface of the drive roller 41.

The sensor 80 can detect the discontinuous portion 46 in addition to the above-described read of the uniform pitch pattern 45. When the discontinuous portion 46 is detected, the sensor 80 issues a reference signal to notify the control unit 100. In the control unit 100,
By measuring the moving distance of the conveyor belt 4 from the time when the reference signal is issued, the driving roller 41 at that moment is measured.
Can be detected.

By using the peripheral speed data of the conveyor belt 4 and the phase data of the driving roller 41 measured in this way, the control unit 100 controls the operation of the apparatus at the time of image formation, thereby correcting color misregistration. Can be. For example, JP
Using the technology described in -177569,
In advance, while rotating the drive motor 43 at a constant speed, the data of the periodic peripheral speed fluctuation of the conveyor belt 4 is measured in association with the phase of the drive roller 41, and the fluctuation is corrected at the time of image formation. By controlling the rotational driving of the driving motor 43, the color misregistration can be corrected.

Alternatively, the data of the peripheral speed fluctuation of the conveyor belt 4 is measured in advance in correspondence with the phase of the drive roller 41, and the image data written on the photosensitive drum is corrected at the time of image formation. This makes it possible to correct color misregistration. Next, in the copying machine, the optical units 6C to 6K scan the photosensitive drums 51C to 51K and detect the photosensitive drums 51C to 51K in order to detect a positional shift of each color image.
A resist mark 47 having a predetermined shape is provided at an end of C to 51K.
C to 47K (electrostatic latent image) is written, developed into a toner image by a developing machine, transferred to a conveyor belt, and detected by the sensor 80. It should be noted that the registration mark is detected by the sensor 80 after being detected by the sensor 80.
Will be erased by

Each of the registration marks 47C to 47K has such a shape that the sensor 80 can identify the same pitch pattern 45, and is, for example, a thick line or cross mark. 1
The optical units 6C to 6K are connected to the registration marks 4 so that the sensors 80 can read the registration marks 47C to 47K as well as read the uniform pitch pattern 45.
The position in the main scanning direction where 7C to 47K is written is set to the same position as the equal pitch pattern 45.

Further, as described below, the writing timing of the registration marks 47C to 47K by the optical units 6C to 6K is adjusted so that the sensor 80 can easily identify the registration marks.
7K is formed on the discontinuous portion 46 (blank portion 46a). FIG. 3 is a diagram illustrating the timing of writing the registration mark 47.

The distance along the peripheral surface of the photosensitive drum 51 from the laser light writing position P to the transfer position Q is represented by L
1 (mm), the distance along the surface of the conveyor belt 4 from the transfer position Q to the reading position R of the sensor 80 is L2 (m
m), the length of the outer periphery of the drive roller 41 is L3 (mm),
The moving speed of the conveyor belt 4 is (Xmm / s). Further, it is assumed that the registration mark 47 is written with a laser beam after t seconds from the time when the sensor 80 detects the discontinuous portion 46.

In this case, since the time required for the drive roller 41 to make one rotation is L3 / X, the discontinuous portion 46 that has passed through the sensor 80 at the reference time is replaced by the nth discontinuous portion 46.
In order to transfer the registration mark 47 thereon, the following expression 2 may be satisfied.

[0028]

(Equation 2) Therefore, as shown in the flowchart of FIG.
00 detects the discontinuous portion 46 (Ye in S1).
s), if the registration mark 47 is written after the time t shown in Expression 2 has elapsed (S2) (S3, S
4), the registration mark 47 is transferred so as to overlap the discontinuous portion 46. When the drive roller 41 rotates n times from the reference time, the sensor 80 detects the registration mark 47 transferred onto the discontinuous portion 46.

If a sensor that can identify the colors of C, M, Y, and K is used as the sensor 80, the registration marks 47C to 47C can be used.
Even if 47K is transferred over the same discontinuous portion, this can be identified. Then, based on the measured shift amounts of the registration marks 47C to 47K, each optical unit 6
By adjusting the timing of writing the image on the photosensitive drum by C to 6K, or adjusting the positions of the image forming units 5C to 5K, it is possible to correct the positional deviation of each color image in the sub-scanning direction. .

For example, each of C, M, Y, and K is obtained by using a technique disclosed in Japanese Patent Application Laid-Open No. 1-142678.
The relative position in the sub-scanning direction where the registration mark 47 is transferred is measured, and based on the measured relative position, the writing timing of each color image is adjusted, and the installation positions of the image forming units 5C to 5K are adjusted. It is possible to correct a shift in the sub-scanning direction of each color image transferred to the recording sheet.

In this embodiment, a blank portion 46a as shown in FIG. 5A is formed as the discontinuous portion 46 of the equal pitch pattern 45, and the registration mark 47 is overlapped on the blank portion 46a. However, the shape of the discontinuous portion 46 may be any shape that can be detected by the sensor 80. For example, instead of the blank portion 46a, as shown in FIG. As shown in FIG. 5C, a discontinuous portion 46c formed of a thin line-shaped mark, and a discontinuous portion 46 formed of a high-density line as shown in FIG.
d may be formed.

As the shape of the registration mark 47, in addition to the thick registration mark 47a parallel to the uniform pitch pattern 45 as shown in FIG.
A thick line-shaped resist mark 47b orthogonal to the line of the equal pitch pattern 45 as shown in FIG. Also,
In this embodiment, the registration mark 47 is transferred to the blank portion 46a so that the registration mark 47 can be easily identified. However, the registration mark 47 can be identified without necessarily overlapping the discontinuous portion 46. It is possible.

For example, in the case of a thick resist mark formed in a direction perpendicular to the line of the uniform pitch pattern 45, as in a resist mark 47b shown in FIG.
The sensor 80 detects this mark continuously for a long time at the registration mark 47b. Therefore, even if the registration mark 47b is transferred over the uniform pitch pattern 45 as shown in FIG. 6B, the sensor 80 can reliably detect this.

(Embodiment 2) FIG. 7 is a perspective view of the periphery of a conveying roller of a copying machine according to the present embodiment. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals. The copying machine according to the present embodiment has the same overall configuration as the copying machine according to the first embodiment. However, in the first embodiment, the uniform pitch pattern 45 is formed on the transport belt 4. In the present embodiment, a uniform pitch pattern 145 is formed at the outer peripheral end of the drive roller 141.

The uniform pitch pattern 145 is formed continuously over the entire circumference of the drive roller 141.
A discontinuous portion (blank portion) 146 is formed only at one location. Note that the transport belt 104 is not provided with a member such as the guide portion 4a of the first embodiment, but is provided with a separate guide portion (for example, a guide portion is provided on the pressure contact rollers 44C to 44K). Edge 104a of
The position of the transport belt 104 in the main scanning direction is determined so that is overlapped on the equal pitch pattern 145. And
The sensor 80 is disposed at a position corresponding to the edge of the conveyor belt 104, and along the edge, the uniform pitch pattern 145 is formed.
Read.

In the control section 100, the peripheral speed of the drive roller 41, that is, the moving speed of the transport belt 4 can be detected by the sensor 80 reading the equal pitch pattern 145 and counting the pulse signals generated.
Can detect the phase of the drive roller 41 from the reference signal generated by detecting the discontinuous portion 146. Control unit 100
In the same manner as in the first embodiment, the operation of the apparatus during image formation is controlled by using the measured peripheral speed data of the transport belt 104 and the phase data of the driving roller 41, and thereby color misregistration can be corrected. .

As in the first embodiment, in order to detect the phase shift of each color image, the photosensitive units 51C to 51K are scanned by the optical units 6C to 6K, and the ends of the photosensitive drums 51C to 51K are scanned. In the part, register marks 147C-1
47K (indicated by reference numeral 147 in FIG. 7) is written, is visualized into a toner image by a developing machine, is transferred onto a transport belt, and is detected by a sensor 80.

Here, the reading of the equal pitch pattern 45 by one sensor 80 and the registration mark 147 are performed.
The optical units 6C to 6C are used to detect C to 47K.
The position in the main scanning direction where K writes the registration marks 147C to 147K is set in accordance with the edge of the transport belt 104. In addition, the writing timing of the registration marks 147C to 147K by the optical units 6C to 6K is adjusted so that the sensor 80 can easily identify both patterns, so that the registration marks 147C to 147K overlap the discontinuous portion 146. .

As in the first embodiment, the control section 100 can measure the shift amount of each of the registration marks 147C to 147K and correct the positional shift of each color image in the sub-scanning direction. (Embodiment 3) FIG. 8 is a perspective view around a transport roller of a copying machine according to the present embodiment. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals.

The copying machine of the present embodiment is the same as the copying machine of the second embodiment.
In the present embodiment, the uniform pitch pattern 245 is formed at the center of the drive roller 241, while the uniform pitch pattern 145 is formed at the end of the drive roller 241.
The transport belt 4 is made of a transparent material. The uniform pitch pattern 245 is formed continuously over the entire circumference of the drive roller 241, but only one discontinuous portion 246 is formed.
(Thick marks in the figure).

The sensor 80 is arranged at a position where the uniform pitch pattern 245 of the driving roller 241 is read via the transport belt 4 and receives light reflected by the uniform pitch pattern 245 and transmitted through the transport belt 4. ing.
Further, in order to detect the positional shift of each color image, the photosensitive units 51C to 51K are scanned by the optical units 6C to 6K, and a registration mark is written in the center of the photosensitive drums 51C to 51K, and is written by a developing machine. Visualized into a toner image,
The transferred registration mark 24 is transferred onto the conveyor belt 4.
7 is read by the sensor 80.

The controller 100 measures the peripheral speed of the conveyor belt 4 and the phase of the drive roller 41, and measures the amount of deviation between the registration marks 247C to 247K of each color, as in the second embodiment. , Color shift can be corrected. FIG. 9 is a cross-sectional view of the drive roller 241. The drive roller 241 includes a cylindrical core body 241a made of a highly rigid material (for example, a metal-based material), and a cylindrical cover body 241b made of an elastic material (for example, a rubber-based material) provided on the peripheral surface thereof. It is composed of And the core 24
The central portion of 1a is exposed on the peripheral surface of the drive roller 241, and the uniform pitch pattern 245 is formed on the exposed surface 241c.

On the other hand, portions other than the center of the peripheral surface of the core 241a are covered with a cover 241b. Although the surface of the cover 241b is formed slightly higher than the exposed surface 241c, the cover 241b is driven when the drive roller 241 is driven.
Is pressed against the conveyor belt 4 so that the surface of the cover body 241b has the same height as the exposed surface 241c.

In the present embodiment, by using such a driving roller 241, a good adhesion between the driving roller 241 and the transport belt 4 is obtained during driving, and a slip does not easily occur. Further, since the equi-pitch pattern 245 is formed on a highly rigid material, there is little deformation and the peripheral speed can be detected with high accuracy. Further, since the registration marks 247C to 247K are also formed at the center of the transport belt 4, the pattern is less deformed, and highly accurate detection can be performed.

[Consideration of Image-Forming Position by Sensor Lens] By the way, the driving roller 241 is detected by the sensor 80.
Comparing the case of detecting the pattern 245 on the surface of the conveyor belt and the case of detecting the registration marks 247C to 247K on the conveyor belt 4, the distance from the sensor 80 to the pattern to be measured changes by the thickness of the conveyor belt 4. So
Defocus on the light receiving element becomes a problem.

FIG. 10 is a schematic diagram showing the state of image formation by the image forming lens of the sensor 80. The measurement position A is a mark position (equal pitch pattern 24) on the surface of the drive roller 241.
5), and the measurement position B represents the mark position (the position of the registration mark 247) on the surface of the conveyor belt 4. As shown in the figure, the measurement position A
The image of the mark existing at the image position is formed at the image forming position A, and the image of the mark existing at the measurement position B is formed at the image forming position B.

The distance between the imaging lens 81 and the measurement position A (the distance from the imaging lens 81 to the surface of the conveyor belt 4) is a,
Distance between imaging lens 81 and imaging position A (imaging lens 81
Is the distance from the measurement roller A to the surface of the drive roller 241), and the distance between the measurement position A and the measurement position B (the thickness of the transport belt 4) is Δ
a, the distance between the image forming position A and the image forming position B is Δb, and the focal length of the image forming lens 81 is f, the following expressions 3 and 4 hold.

[0048]

(Equation 3)

[0049]

(Equation 4) Looking at one point of the mark at the measurement position B, the image becomes a point at the image forming position B, but becomes out of focus and circular at the image forming position A. Assuming that the diameter of the circle is W and the diameter of the imaging lens 81 is d, the following equation (5) holds.

[0050]

(Equation 5) From Equations (3), (4) and (5), when b and △ b are eliminated, Equation (6) below is derived.

[0051]

(Equation 6) As shown in FIG. 10, when the position of the light receiving element 82 of the sensor 80 is adjusted to the image forming position B, a point on the measuring position B is imaged as a point image on the light receiving element 82, The image of the point is defocused on the light receiving element 82 in a circular shape having a diameter W. In this case, assuming that the pitch of the equal pitch pattern 245 is P, in order for the sensor 80 to read the equal pitch pattern 245 on the drive roller 241, the sensor 8
It can be said that the pitch P of the equal pitch pattern 245 on 0 is larger than W, that is, it is necessary to satisfy the following equation (7).

[0052]

(Equation 7) (Embodiment 4) The copying machine of the present embodiment is the same as the copying machine of Embodiment 3, except that the sensor 80 is provided with a mechanism for adjusting the focus of the imaging lens. . FIG. 11 is a schematic diagram illustrating a focus adjustment mechanism of the imaging lens of the sensor 80. As in FIG. 10, the measurement position A indicates the position of the surface of the drive roller 241 and the measurement position B indicates the surface position of the transport belt 4. Represents.

The sensor 80 is provided with an actuator 83 for moving the imaging lens 81 between the lens position A and the lens position B.
Is set so that the object at the measurement position A is imaged on the light receiving element 82, and when the imaging lens 81 is at the lens position B, the object at the measurement position B is imaged on the light receiving element 82. Have been.

The actuator 83 is composed of, for example, a voice coil type motor used in an optical disk device or the like. The control unit 100 controls the actuator 8
By controlling the operation 3, the imaging lens 81 is usually positioned at the lens position A, and the imaging lens 81 is moved to the lens position B in accordance with the timing of detecting the registration mark 247. Thus, the focus is adjusted accurately both when reading the uniform pitch pattern 245 and the discontinuous portion 246 and when detecting the registration mark 247.

Note that such focus adjustment is performed by the sensor 8.
Although it is possible to move the entirety 0 by the thickness of the transport belt 4 using an actuator, the thickness of the transport belt is usually as small as 50 to 150 μm, so that it is difficult to accurately move the sensor 80 by that distance. On the other hand, in the method of moving the imaging lens 81 as described above, the movement distance (the distance between the lens position A and the lens position B) can be set relatively large, so that the movement is easy. This is a practical focus adjustment method.

As a practical focus adjustment mechanism of the imaging lens, in addition to the method of moving the imaging lens 81,
A system in which a focus adjustment plate is inserted and removed between the imaging lens 81 and the light receiving element 82 may be used. (Embodiment 5) The copying machine of the present embodiment is the same as the copying machine of Embodiment 3, but in Embodiment 3, a registration mark formed on a photosensitive drum is transferred onto a conveyor belt 4. In the present embodiment, on the other hand, the bow / skew detection mark formed on the photosensitive drum is transferred to the conveyor belt 4 and detected.

FIG. 12 is a perspective view of the vicinity of the transport roller of the copying machine according to the present embodiment. In this copier,
In addition to the sensor 80 installed at the center, similar sensors 91 and 92 are arranged on both sides thereof, and a total of three sensors 80, 91 and 92 are arranged in the main scanning direction. In the present embodiment, the photoconductor drums 51C to 51K are scanned by the optical units 6C to 6K, and the photoconductor drums 51C to 51K are scanned.
A linear bow / skew detection mark extending in the main scanning direction is written in K, and this is visualized as a toner image by a developing machine and transferred onto the transport belt 4.

Here, the control unit 100 controls the bow / skew so that the bow / skew detection mark 347 transferred onto the conveyor belt 4 overlaps the discontinuous portion 246 on the drive roller 241.
Adjust the timing of writing the skew detection mark. The sensor 80 reads the equi-pitch pattern 245 on the drive roller 241 and detects the discontinuous portion 246, and also detects the center of the bow skew detection mark 347. The sensors 91 and 92 detect both ends of the bow / skew detection mark 347.

As in the case of the fourth embodiment, the control unit 100 determines that the sensor 80 has an equal pitch pattern 245 and a discontinuous portion 246.
, The peripheral speed of the conveyor belt 4 and the phase of the drive roller 41 can be measured. Further, the control unit 100 controls the inclination of the bow / skew detection mark 347 based on the timing of each signal generated when each of the sensors 80, 91 and 92 detects the center and both ends of the bow / skew detection mark 347. And the degree of curvature and the like. Then, by adjusting the optical units 6C to 6K and the like based on the measurement result, it is possible to correct the deviation of each color image transferred to the recording sheet.

(Other Matters) In the above-described embodiment, a tandem type copying machine of a driven type in which the photosensitive drum is driven by the transport belt has been described. The present invention can be implemented in a tandem-type copying machine driven by a computer.

[0061]

As described above, according to the present invention, in a tandem type image forming apparatus, a sensor provided so that a first pattern formed on a conveyor belt is within a detection field of view, Pattern forming means for forming a second pattern identifiable from the first pattern by transferring it from the photosensitive drum is provided on the transport belt in the field of view.

With this configuration, the first pattern and the second pattern on the conveyor belt can be read by one sensor, so that a simple device configuration can be achieved. Then, it is possible to obtain information from each of the first pattern and the second pattern (for example, information on the speed of the transport belt from the first pattern and information on the positional deviation of each color image from the second pattern).

Here, if the first pattern is a line pattern of an equal pitch continuously formed along the moving direction of the conveyor belt, and a discontinuous portion is formed at a predetermined position of the line pattern, a sensor is used. By reading the first pattern, information on the speed of the conveyor belt can be obtained, and by detecting a discontinuous portion, information on the position of the conveyor belt can also be obtained.

If the discontinuous portion corresponds to a specific position of the driving roller, information on the phase of the driving roller can be obtained by detecting the discontinuous portion. Further, if the pattern forming means forms the second pattern so that the transfer position of the second pattern onto the transport belt coincides with the discontinuous portion, the detection of the second pattern by the sensor can be performed. It can be done easily.

Further, according to the present invention, in a tandem type image forming apparatus, a sensor provided so that a first pattern formed on a driving roller enters a detection field of view, and a conveyance belt within a detection field of the sensor. And a pattern forming means for forming a second pattern identifiable from the first pattern by transferring the second pattern from the photosensitive drum. With such a configuration, the first pattern on the drive roller and the second pattern on the transport belt can be read by one sensor, so that a simple device configuration can be achieved. Then, from the first pattern, for example, information on the speed of the conveyor belt and phase information on the drive roller can be obtained, and from the second pattern, for example, information on the position of each color image can be obtained.

Here, if an optical sensor having sensitivity to light having a wavelength transmitted through the conveyor belt is used as the sensor, even if the first pattern on the drive roller is covered with the conveyor belt, this is read by the sensor. be able to. Therefore, the first pattern can be provided at the center of the driving roller. If the surface of the drive roller is formed of a rigid material at the portion where the second pattern is formed, and at least a portion other than the portion where the second pattern is formed is formed of an elastic material, Occasionally, good adhesion is obtained between the drive roller and the conveyor belt, and slip is unlikely to occur. In addition, since the second pattern is formed on a rigid material, the second pattern is less deformed and can perform highly accurate detection.

In the sensor, a light receiving section, an image forming lens for forming an image of an object present at the measurement position on the light receiving section, and an image forming lens are operated to operate the surface of the driving roller and the surface of the transport belt. By providing the measurement position switching means for selectively switching the measurement position, both the first pattern and the second pattern can be accurately read.

Further, if the first pattern is a line pattern of equal pitch formed along the moving direction of the peripheral surface of the driving roller and a discontinuous portion is formed at a predetermined position of the line pattern, the first pattern is formed by the sensor. By reading the first pattern, information on the speed of the conveyor belt can be obtained, and by detecting the discontinuous portion, information on the position of the conveyor belt and the phase of the drive roller can also be obtained.

Further, if the pattern forming means forms the second pattern so that the transfer position of the second pattern onto the conveyor belt coincides with the discontinuous portion, the second pattern at the sensor can be obtained. The pattern can be easily detected.

[Brief description of the drawings]

FIG. 1 is a front view of a copying machine according to a first embodiment.

FIG. 2 is a diagram showing a driving mechanism of a photosensitive drum and a conveyor belt in the copying machine;

FIG. 3 is an explanatory diagram of a timing of writing a registration mark in the copying machine.

FIG. 4 is a flowchart showing an operation of writing a registration mark in the copying machine.

FIG. 5 is a modified example of a discontinuous portion of an equal pitch pattern in the copying machine.

FIG. 6 is a modified example of a registration mark in the copying machine.

FIG. 7 is a perspective view of the vicinity of a conveying roller of the copying machine according to the second embodiment.

FIG. 8 is a perspective view around a transport roller of a copying machine according to a third embodiment.

FIG. 9 is a sectional view of a drive roller according to a third embodiment.

FIG. 10 is a schematic diagram showing a state of image formation by an image forming lens of the sensor according to the third embodiment.

FIG. 11 is a schematic diagram showing a focus adjustment mechanism of an imaging lens of a sensor according to a fourth embodiment.

FIG. 12 is a perspective view of the vicinity of a conveyance roller of a copying machine according to a fifth embodiment.

[Explanation of symbols]

 Reference Signs List 4 Conveyor belt 5 Image forming unit 6 Optical unit 41 Drive roller 42 Support roller 44 Press-contact roller 45 Equal pitch pattern 46 Discontinuous portion 46a Blank portion 47 Registration mark 51 Photoconductor drum 61 Laser diode 80 Sensor 81 Imaging lens 82 Light receiving element 83 Actuator 91, 92 Sensor 100 Controller 104 Conveyor belt 141 Driving roller 145 Equal pitch pattern 146 Discontinuous part 147 Registration mark 241 Driving roller 241a Core 241b Cover body 245 Equal pitch pattern 246 Discontinuous part 247 Registration mark 347 Skew detection mark

Continued on the front page (72) Inventor Nozomu Kondo 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Inventor Hideyuki Kurahashi 2-chome, Azuchi-cho, Chuo-ku, Osaka-shi, Osaka No. 13 Osaka International Building Minolta Co., Ltd.

Claims (10)

[Claims] An image forming unit configured to scan a peripheral surface of each of the plurality of photosensitive drums to form an image;
A transport belt for transporting a transfer material, wherein the image formed on each of the photosensitive drums is sequentially transferred onto a transfer material transported by the transport belt, a tandem-type image forming apparatus, A sensor provided such that the first pattern formed in the detection field of view, and a second pattern identifiable from the first pattern on a conveyor belt in the detection field of view of the sensor, An image forming apparatus comprising: a pattern forming unit that forms the image by transferring the image from a photosensitive drum. 2. The first pattern is a line pattern of an equal pitch continuously formed along the moving direction of the transport belt, and a discontinuous portion is formed at a predetermined position of the line pattern. The image forming apparatus according to claim 1, wherein: 3. The pattern forming device according to claim 2, wherein the pattern forming unit forms the second pattern such that a transfer position of the second pattern onto the transport belt coincides with the discontinuous portion. The image forming apparatus as described in the above. 4. An image forming means for forming an image by scanning a plurality of photosensitive drums and a peripheral surface of each of the photosensitive drums,
A transport belt that transports a transfer material while being driven by a drive roller, and a tandem-type image forming apparatus that sequentially transfers images formed on the respective photosensitive drums onto a transfer material transported by the transport belt. A sensor provided so that a first pattern formed on the driving roller enters a detection field of view, and a second pattern that can be distinguished from the first pattern on a transport belt in the detection field of view of the sensor. An image forming apparatus, comprising: a pattern forming unit configured to transfer the pattern from the photosensitive drum. 5. The image forming apparatus according to claim 4, wherein the sensor is an optical sensor having sensitivity to light having a wavelength transmitted through the transport belt. 6. A surface portion of the drive roller, in which a portion where the second pattern is formed is made of a rigid material, and at least a part other than a portion where the second pattern is formed is made of an elastic material. The image forming apparatus according to claim 4, wherein: 7. The sensor, comprising: a light receiving unit; an imaging lens for forming an image of an object present at a measurement position on the light receiving unit; and a surface of the driving roller by operating the imaging lens. The image forming apparatus according to claim 4, further comprising a measurement position switching unit that selectively switches a measurement position on a surface of the transport belt. 8. The first pattern is a line pattern of equal pitch formed along a moving direction of a peripheral surface of the driving roller, and a discontinuous portion is formed at a predetermined position of the line pattern. The image forming apparatus according to claim 4, wherein the image forming apparatus is formed. 9. The sensor comprises: a light receiving unit; and an imaging lens that forms an image of an object present at a measurement position on the light receiving unit, and is configured to satisfy Expression 1. The image forming apparatus according to claim 8, wherein: (Equation 1) 10. The pattern forming device according to claim 8, wherein the pattern forming unit forms the second pattern such that a transfer position of the second pattern onto the transport belt coincides with the discontinuous portion. The image forming apparatus as described in the above.