JPH103194A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably detect positional deviation measuring mark with high accuracy. SOLUTION: In this image forming device for developing electrostatic latent images on plural photoreceptors 1B, 1Y, 1M and 1C and successively transferring the developed images to a transfer papers 2 on a transfer paper carrying belt 3 superposedly on each other, deviation measuring marks are formed in the previously set positions of the transfer paper carrying belt 3 by the photoreceptors 1B, 1Y, 1M and 1C, a pair of rollers 16a and 16b for exerting tensile force on the belt 3 to secure flatness at the fixed part of the transfer paper carrying belt 3 are provided and the gap between both rollers 16a and 16b is set at a detecting region, to detect the marks in the mentioned region.

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 having a plurality of photoreceptors and capable of forming multicolor images, and more particularly, to a transfer paper for detecting a displacement of an image transfer position. The present invention relates to an image forming apparatus provided with a means for providing a mark on a conveyor belt.

[0002]

2. Description of the Related Art An image forming apparatus having a plurality of photoconductors is
For example, it is widely used in electrophotographic devices, laser beam printers, printing devices, and the like. In such an image forming apparatus, when sequentially transferring images formed by the image forming units of a plurality of photoconductors to transfer paper, if the image transfer position is shifted from a predetermined position for each image forming unit, Good color quality cannot be obtained because the color is different from the original or the image has a color shift. Therefore, in order to eliminate the color misregistration, adjustments such as changing the timing of writing on the photoconductor are performed. At this time, in order to measure the deviation between the colors, a mark for measuring the deviation is formed on the transfer belt or the conveyance belt, and a mark detecting device for detecting or measuring the mark is provided. I try to adjust the timing.

A mark detecting device irradiates light to a position on the transfer or conveyor belt where a mark is formed, and detects a reflected light that changes as the mark passes through the mark. As disclosed in Japanese Patent Publication No. 300259, a transparent portion is provided on a transfer or conveyance belt, a mark is formed on the transparent portion, and a transmissive type detecting a change in the amount of light passing through the transparent portion through the mark portion is detected. There are things. The transmission type is more resistant to noise than the reflection type, and has an advantage that it can be configured at low cost. In the transmission type, the light receiving unit is brought close to the transfer belt, and the gap between the slit for detecting the mark and the image of the mark formed on the belt is reduced.
There is also an advantage that the mark can be detected with higher accuracy.

[0004]

However, in the transmission type, when the light receiving portion or the slit is brought close to the belt, the influence of the above-mentioned change in the gap becomes large,
A stable mark cannot be detected. Further, when the light receiving portion contacts the belt, the image of the mark formed on the surface of the transfer or transfer belt is disturbed due to frictional charging of the belt, and the mark is accurately and reliably detected. You will not be able to do it.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances of the prior art, and an object of the present invention is to provide an image forming apparatus capable of detecting a displacement detecting mark with high accuracy and stability. It is in.

[0006]

In order to achieve the above object, a first means is to form a plurality of photosensitive members on a transfer paper conveyed by a transfer paper conveyance belt stretched between a driving roller and a driven roller. Image formation in which an image is formed by transferring the formed visual image, and a preset mark is transferred onto the transfer paper transport belt, and the mark is detected by a detecting unit to detect a positional shift of the image. In the apparatus, a pair of rollers for separately applying a tension to the transfer paper transport belt to secure the flatness is provided, and the detecting means detects the mark in a region sandwiched between these rollers.

The second means is characterized in that the detecting means in the first means comprises a light transmission type optical sensor in which a light emitting section and a light receiving section are arranged with a conveyance belt interposed therebetween.

The third means is characterized in that the light receiving section in the second means is supported by the same member as the roller.

According to a fourth aspect, in the first or the third aspect, the roller is made of a conductive material and is grounded.

[0010]

Embodiments of the present invention will be described below with reference to the drawings, taking a color printer as an example. This color printer is black (BK), yellow (Y),
The image forming system includes magenta (M) and cyan (C) image forming systems, and is configured to transfer a toner image of each color in a superimposed manner on one sheet of transfer paper. The scanner unit, image processing unit, and paper supply unit and fixing unit that supply transfer paper, which are a document reading unit, are configured in the same manner as a known color printer, and thus detailed description and illustration thereof are omitted. Only the writing unit and the transfer unit that constitute the printer unit are illustrated and described.

FIG. 1 is a schematic configuration diagram showing a writing unit and a transfer unit of a color printer, and FIG. 2 is a schematic configuration diagram showing a cross section of a part of the mark detection device in FIG.

An image information signal of an original image picked up by the scanner unit is simultaneously corrected and converted for each color by an image processing unit in accordance with the characteristics of a writing unit, and BK, Y, M, and C generated by the image processing unit. Each image signal of the component is applied to a laser driver (not shown) provided in the writing unit. The laser driver of the writing unit drives a semiconductor laser (not shown) for each color component, and outputs a laser beam modulated with an image signal of the corresponding color component. In the writing section, each laser beam is guided to a drum-shaped photoconductor 1B, 1Y, 1M, 1C via an optical system. These photoconductors 1B, 1Y, 1M, and 1C are disposed at intervals above a transfer paper transport belt 3 that places and transports the transfer paper 2 supplied from a paper feeder via a transport path. . Each of the photoconductors 1B, 1Y, 1M, and 1C transfers the formed image to the transfer paper 2 and forms a mark for measuring the displacement on the transfer paper transport belt 3. Each photoconductor 1B, 1Y, 1M,
Although not shown, known image forming elements such as a charging charger and a developing unit are arranged around 1C.

The transfer paper transport belt 3 is a transparent endless belt stretched between a driving roller 4 and a driven roller 5, and transfers the transfer paper 2 to a first station 6 of the photosensitive member 1B and a second station 6 of the photosensitive member 1Y. The transfer paper is sent to the station 7, the third station 8 of the photoconductor 1M, and the fourth station 9 of the photoconductor 1C, and the transfer paper is separated by the transfer paper separation unit 10. Further, the transfer devices 11B, 11Y, and 11C are opposed to the photoconductors 1B, 1Y, 1M, and 1C with the transfer paper transport belt 3 interposed therebetween.
11M and 11C are provided. Transfer paper transport belt 3
Below the belt, the belt static eliminator 12 and the mark detector 1
3 are provided.

The marks detected by the mark detecting device 13 are detected by the photoconductors 1B, 1Y, 1M, and 1C at the stations 6 to 8 at preset timings.
Thus, an image of each color is formed on the transfer paper transport belt 3. This timing is set so as to be between sheets,
It is intended not to affect the transfer of the transfer paper 2 and the transfer of the image. Note that the mark formation position may be any position in the width direction of the transfer paper transport belt 3, and is appropriately set according to the arrangement of other components.

The mark detecting device 13 includes a detecting portion and a tension roller portion, and the detecting portion is opposed to the transfer paper conveying belt 3 as described above. That is, as shown in detail in FIG. 2, the detecting unit includes the light emitting unit 14 disposed on the lower surface side of the transfer paper transport belt 3 and the light emitting unit 1.
And a light receiving unit 15 disposed so as to face the transfer paper transport belt 3 with the transfer paper transport belt 3 interposed therebetween.
Through the light receiving element.

As shown in FIG. 2, the tension roller section 16 includes a pair of tension applying rollers 16a and 16b, and the light receiving section 15 is disposed between the tension applying rollers 16a and 16b. Thus, a mark on the transfer paper transport belt 3 to which a tension is applied in a planar shape is detected.

The light emitting section 14 may use a lamp or the like instead of a light emitting element such as a light emitting diode. The light receiving unit 15 includes a slit 17 that receives light passing through the transfer paper transport belt 3 and a light receiving element 18 that detects light transmitted through the slit 17 and outputs an electric signal. As the light receiving element 18, for example, a photodiode is used.

With this configuration, the transfer paper transport belt 3 rotates counterclockwise, and the first to fourth stations 6 to 6 rotate.
The 9 photoconductors 1B, 1Y, 1M, and 1C are driven to rotate clockwise, and a toner image is formed on the photoconductor 8 through processes such as charge removal, charging, exposure, and development. This toner image is transferred to the transfer devices 11B and 11B at the respective stations.
The image is transferred onto the transfer paper 2 by Y, 11M, and 11C. The transfer paper 2 is sent from a paper feeding device (not shown) to a transfer paper transport belt 3 via a transport path, and is transported while being attracted to the surface of the transfer paper transport belt 3. Each station 6-9
When the transfer of all color images is completed in
Is separated from the transfer paper transport belt 3 by a transfer paper separation unit 10 and discharged through a fixing device (not shown). On the other hand, after the transfer step, residual toner and the like adhere to the surfaces of the photoconductors 1B, 1Y, 1M, and 1C, which are removed and cleaned by a cleaning device (not shown).

In the first to fourth stations 6 to 9, images are formed using B, Y, M, and C toners of different colors as described above. In parallel with the image formation, A mark of each color is formed on the transfer paper transport belt 3 at a preset timing, the position of the mark is detected, the detection timing is measured, and the state of the color misregistration is monitored based on the timing. That is, in order to detect a shift in the image forming position in each of the stations 6 to 9, a mark for a shift measurement is formed on the transfer paper transport belt 3 in each of the photoconductors 1B, 1Y, 1M, and 1C in each of the stations 6 to 9. These marks are received by the light receiving unit 15 with the light emitted from the light emitting unit 14 of the mark detecting device 13 and detected as a change in the amount of light due to the passage of the mark formed on the transfer paper transport belt 3. In this embodiment, black B formed first is used as a reference toner, and yellow Y, magenta M and cyan C which are formed next are comparison marks. The shift between these marks detected by the mark detecting device 13 is signal processed by a control circuit (not shown) as a timing shift, and the photosensitive drums 1B to 1C
, The transfer timing in the transfer devices 11B to 11C, the rotation speed of the transfer paper transport belt 3, and the like, or a combination thereof is corrected. In addition, formation of this mark, reading,
It is not always performed, but is performed at every preset timing, every preset number of image formations, or at every preset time, and is automatically corrected. As a result, control is performed such that the image shift always falls within a preset allowable range.

At this time, the light emitting section 14 of the mark detecting device 13
And the light receiving section 15 are located between the tension rollers 16a and 16b, and the transfer paper transport belt 3 is stretched in a plane at the mark detection position, and no mark reading error or reading disturbance occurs due to waving of the belt or the like. Like that.

FIG. 3 is a view showing another embodiment of the mark detecting device. In this embodiment, the light receiving portion 15 and the stretching roller 16 of the mark detecting device are integrally supported by the support frame 21. It is an example. Further, in this case, each stretching roller 16 is made of a conductive material, and the static electricity and the like are grounded.
To drop to ground. By doing so, the rollers 16a and 16 for applying tension to the transfer paper transport belt 3 are installed in the same structure as the support frame 21 together with the light receiving unit 15 of the mark detection device 13, so that the accuracy of the mounting position is improved. Is improved, the gap between the transfer paper transport belt 3 and the slit 16 of the light receiving unit 15 and the gap between the sensor 17 are easily managed, and stable and highly accurate mark detection is possible.

Further, static electricity and the like charged on the transfer belt
Since the rollers 16a and 16b made of a conductive material and the ground plate 22 can be dropped out of the apparatus,
The mark image on the transfer paper transport belt 3 is not disturbed by static electricity or the like, and the accuracy of mark detection can be improved.

In this embodiment, an example is described in which a light transmission type optical sensor (light emitting element and light receiving element) is used, but tension is applied by a pair of rollers 16a and 16b, and both rollers 16a and 16b are used. As long as the flatness between them is ensured, sufficient accuracy can be ensured even if a light-reflective optical sensor that detects light with the light-emitting element and the light-receiving element positioned on one side of the transfer paper transport belt 3 is used. It goes without saying that you can do it.

[0024]

As is clear from the above description, a pair of rollers for separately applying a tension to the conveyor belt to secure the flatness is provided, and the detecting means applies the mark in an area sandwiched by these rollers. According to the first aspect of the present invention for detecting, and the second aspect of the invention in which the detecting means is constituted by a light transmission type optical sensor, mark detection can be performed in a state where flatness is secured. It is possible to prevent the mark reading signal from being disturbed due to the waving of the belt or the like, and it is possible to improve the detection accuracy.

According to the third aspect of the present invention, the light receiving portion and the roller are supported by the same member, and the light receiving portion and the roller are supported by the same member, and the relative positions of the two can be changed. Therefore, the gap between the transfer belt and the mark detection device can be easily managed, and stable detection can be performed, and the detection accuracy can be further improved.

According to the fourth aspect of the present invention, the roller is made of a conductive material and grounded, and the static electricity or the like charged on the transfer belt falls outside the apparatus through the roller, and the mark on the transfer belt is caused by the static electricity or the like. Since the image is not disturbed, stable detection becomes possible, and the detection accuracy can be further improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a writing unit and a transfer unit in an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a diagram showing a schematic cross section of a schematic configuration of the mark detection device according to the embodiment of FIG. 1;

FIG. 3 is a diagram showing another embodiment of the mark detection device.

[Explanation of symbols]

 1B, 1Y, 1M, 1C Photoconductor 2 Transfer paper 3 Transfer belt 13 Mark detection device 14 Light emitting unit 15 Light receiving unit 16 Tension roller unit 16a, 16b Roller 21 Support frame 22 Ground plate

Claims (4)

[Claims] An image is formed by transferring visible images formed on a plurality of photoconductors onto transfer paper conveyed by a transfer paper conveyance belt stretched between a driving roller and a driven roller. In an image forming apparatus for transferring a preset mark on a paper transport belt and detecting a displacement of an image by detecting the mark by a detecting unit, tension is applied to the transfer paper transport belt to secure flatness. An image forming apparatus, wherein the detecting means detects the mark in an area sandwiched between the rollers. 2. An image forming apparatus according to claim 1, wherein said detecting means comprises a light transmission type optical sensor having a light emitting section and a light receiving section arranged with a transfer paper conveying belt therebetween. 3. The image forming apparatus according to claim 2, wherein the light receiving unit and the roller are supported by the same member. 4. The image forming apparatus according to claim 1, wherein the roller is made of a conductive material and is grounded.