JPH10133438A - Electrophotographic image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always detect an accurate image density irrespective of soiling by forming a test image in a position out of the soiled part on an image carrier having the occurrence of the soil caused by rollers different in carrying speed. SOLUTION: A region on a recording medium which is not a region where a pair of separating rollers 9 and a pair of carrying rollers 10, which are different in the carrying speed of the recording medium and adjacent to each other are in contact with each other, comes into contact with a transfer drum 5. A patch T is formed in the region on the drum 5 and the density of the patch T is read by an optical sensor 20 consisting of light emitting and receiving elements. At this time, a pair of the separating rollers 9 and a pair of the carrying rollers 10 are arranged in the center in the width direction of the carried recording medium. Therefore, a belt of soil 29 is generated in the center of the surface of the drum 5 as well. In such a case, the patch T is formed in the position out of the center of the surface of the drum 5. Moreover, the position where the patch T is formed exists within the region where a smallest size recording medium on which recording can be made by an image forming device is wound on the transfer drum 5, outside the belt 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus capable of accurately controlling density when forming an image by an electrophotographic method.

[0002]

2. Description of the Related Art Conventionally, as a configuration of an apparatus for forming a multicolor image by an electrophotographic method, a photosensitive drum, which is an electrophotographic photosensitive member, is charged with a developer of a different color (hereinafter referred to as "toner").
Are arranged on a rotation selecting mechanism, and a developing device containing a predetermined color toner is opposed to the photosensitive drum to perform development, and the developed image is transferred to a recording medium. Further, there has been proposed a method of obtaining a multicolor image by performing the development transfer operation for each color.

In such an electrophotographic color image forming apparatus, if the image density fluctuates due to a change in the environment in which the apparatus is used, the number of prints, and other conditions, the original correct color tone cannot be obtained. Therefore, conventionally, a test toner image (patch) for each color toner for density detection is experimentally formed on a photosensitive drum or a transfer drum, which is an electrophotographic photosensitive member, and the densities are determined by an optical density of a photo interrupter. A stable image is obtained by performing image density control that detects the image with a sensor and feeds back the detected value to an exposure amount, a developing bias, and the like.

[0004]

However, in the above-described image forming apparatus, as the number of recorded images increases, a band-shaped stain 51 may be generated on the transfer drum 50 as shown in FIG. Therefore, if the patch is formed at the position of the stain 51, the patch is affected by the stain band, and it becomes difficult to measure the density accurately.

Although the mechanism of the occurrence of the stain is not clearly understood, it is considered at present that the cause is caused by a transport roller for supplying a recording medium.

For example, as shown in FIG. 7, when a recording medium is fed to a transfer drum 50, separation is generally performed by a retard method in order to prevent double feeding. In this retard separation method, a plurality of recording sheets fed by a separation roller pair 52 including a feed roller 52a rotating in a direction for feeding the recording medium and a retard roller 52b rotating in a direction to pull back the recording medium. One of the media is separated, and the separated recording medium is transported to the transfer drum 50 by a transport roller pair 53 located further downstream.

In the above-described separation and conveyance process, the recording medium may be conveyed while being nipped by both the separation roller pair 52 and the conveyance roller pair 53. At this time, the separation roller pair 52 is conveyed by the conveyance roller pair 53. The separation roller pair 52 and the conveyance roller pair are configured to rotate with the flow of the medium.
A transport speed difference occurs between the transport speed and the transport speed.

As a result, the surface of the recording medium is rubbed by the pair of rollers, and the shavings (paper dust) of the surface of the recording medium and the shavings of the rollers generated by the rubbing are removed by the pair of separation rollers 52 on the recording medium. When the recording medium is wound around the transfer drum 50 and adheres to the position corresponding to the conveying roller pair 53, the paper dust and roller shavings adhere to the surface of the transfer drum 50 or are transferred by the paper dust and the like. It is considered that the surface of the drum 50 is damaged and a band 51 of dirt is generated.

The present invention has been made to solve the above problems, and
An object of the present invention is to provide an electrophotographic image forming apparatus capable of performing accurate image density control even when a stain band occurs on an image carrier.

[0010]

A typical configuration according to the present invention for achieving the above object is to form a test image for density measurement on an image carrier and detect the density to control image density. In an electrophotographic image forming apparatus, image forming means for transferring and recording a toner image on a recording medium, conveying means including a plurality of rollers for conveying the recording medium to the image forming means, and an image carrier A density measuring unit for forming a test image and measuring an image density, wherein the density measuring unit is configured such that, among the plurality of rollers of the transporting unit, an adjacent roller having a difference in the transport speed of the recording medium is in contact. A test image is formed on the image carrier, wherein an area on the recording medium other than the designated area contacts the image carrier.

In the above configuration, since a test image is formed on the image carrier at a position where the contamination caused by the roller having the difference in the conveying speed is removed, an accurate image density is always detected regardless of the contamination. Is what you can do.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an electrophotographic image forming apparatus according to one embodiment of the present invention will be described.

[First Embodiment] A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an explanatory diagram showing the positional relationship between the image carrier and the image density detecting means, FIG. 2 is a schematic explanatory diagram showing the overall configuration of the electrophotographic image forming apparatus, and FIG. FIG.
FIG. 4 is an explanatory view of the configuration of the separation / conveyance means.

Here, the overall configuration of the electrophotographic image forming apparatus will be described first, and the positional relationship between the image carrier and the image density detecting means will be described.

{Overall Configuration of Image Forming Apparatus} First, the overall configuration of the image forming apparatus according to the present embodiment will be described. As shown in FIG. A roller charger 2 and four developing devices supported by a rotatable support 3 are provided on the left side of the photosensitive drum 1. The four developing devices are composed of a yellow developing device 4y containing each color toner, a magenta developing device 4m, a cyan developing device 4c, and a black developing device 4b. The development of the toner image of each color is performed.

On the right side of the photosensitive drum 1, a transfer drum 5, which is an image carrier having a function of holding a recording medium and transferring a toner image formed on the photosensitive drum 1 to a recording medium P, is arranged. ing.

Further, a laser diode 6a constituting an exposing means, a polygon mirror 6c rotated by a high-speed motor 6b, a lens 6d, and a folding mirror 6e are arranged in an upper portion in the apparatus main body. Then, for example, when a signal according to a yellow image is input to the laser diode 6a, light information corresponding to yellow is irradiated on the photosensitive drum 1 rotating in the direction of the arrow through an optical path 6f, and a latent image is formed. You. This latent image is developed into a visible image by toner development by the yellow developing device 4y.

On the other hand, the recording medium P loaded and stored in the sheet cassette 7 is conveyed to the transfer drum 5 by the conveying means. That is, the sheet is picked up by a half-moon-shaped pickup roller 8, separated one by one by a separation roller pair 9 composed of a feed roller 9a and a retard roller 9b, and conveyed to a registration roller pair 12 along a guide 11 by a conveyance roller pair 10. . Then, the transfer roller 5 is conveyed to the transfer drum 5 by the registration roller pair 12 in synchronization with the image on the photosensitive drum 1, the leading end thereof is held by the gripper 13, and the transfer is carried while supporting the suction roller 14 and the recording medium P. By applying a voltage to the drum 5, the recording medium P is electrostatically attracted onto the transfer drum 5, and the toner image formed on the photosensitive drum 1 is transferred to the photosensitive drum 1.
Is transferred onto the recording medium P on the transfer drum 5 which rotates in the direction of the arrow in synchronization with the transfer.

After the transfer of the yellow toner image as described above, the developing device is rotated to transfer the respective color toners of magenta, cyan, and black to the recording medium P, thereby forming a color image. Then, the recording medium P on which the color image has been transferred is separated from the transfer drum 5 by the separation claw 15 and further conveyed to the fixing means 16 where the toner image is melted and fixed by applying heat and pressure, and discharged outside the apparatus. It is discharged to the department.

On the other hand, the toner remaining on the photosensitive drum 1 is cleaned by a cleaning means 17 such as a fur brush or a blade. Further, the toner on the transfer drum 5 is also cleaned by a transfer drum cleaning means 18 such as a fur brush or a web, and a residual charge is removed by a charge removing roller 19.

The image forming apparatus has a density measuring means 20 for detecting the density of the toner image formed at a predetermined position on the transfer drum 5. The density measuring means 20 experimentally forms a test image (patch) for density detection formed of each color toner at a predetermined position on the transfer drum 5 and detects the toner density. The image density is controlled by feeding back to a bias or the like. As shown in FIG.
Light is radiated at 20a, and the reflected light is received by the light receiving element 20b to detect the patch density.

{Relationship Between Conveying Means and Concentration Measuring Means} Next, the arrangement relation between the density measuring means 20 and the conveying means will be described. As shown in FIG. 4, the conveying means according to the present embodiment drives the motor 21 when a conveying signal is input, transmits the driving force to the gears 22a and 22b and the spring clutch means 23, and picks up by the operation of the solenoid 25. The pickup roller 8 is intermittently rotated in the direction of the arrow via the roller shaft 24a.

The driving force is applied to the spring clutch means 23.
Gear 22c, drive shaft 24b, gear 22d,
The power is transmitted to the feed roller 9a via the gear 22h and the one-way clutch 26 to rotate the roller 9a in the direction of the solid arrow. Further, the driving force of the motor 21 is a gear 22a, a gear 22a.
i, a constant torque is transmitted to the retard roller 9b via the gear 22e and the torque limiter 27, and a rotational force is transmitted to the roller 9b in the direction of the dashed arrow.

The gears 22e to 22f, 22g,
The driving force is transmitted to the transport roller pair 10 via the shaft 28 to rotate the roller pair 10 in the direction of the arrow.

The retard roller 9b is a torque limiter.
Rotational force smaller than that of the feed roller 9a is transmitted via the feed roller 9a, and when one recording medium is nipped by the separation roller pair 9 and conveyed, the retard roller 9b is driven to rotate by the conveyance of the recording medium. I do. On the other hand, when a plurality of recording media are conveyed between the pair of separation rollers 9, the friction coefficient between the recording media and the retard roller 9b is larger than the friction coefficient between the recording media, so that one of the recording media that contacts the feed roller 9a. Is conveyed, and the other recording medium is returned by the retard roller 9b. As a result, the recording medium is separated and conveyed.

The recording medium separated and conveyed by the separation roller pair 9 is nipped by the conveyance roller pair 10 and conveyed to the registration roller pair 11. At this time, the recording medium is separated by the separation roller pair 9 and the conveyance roller pair. There is a case where both sides of 10 are nipped. In this case, the separation roller pair 9 rotates along with the recording medium conveyed by the conveyance roller pair 10.

In the above conveying step, a difference in conveying speed occurs between the conveying roller pair 10 and the separating roller pair 9 when the separating roller pair 9 is rotating, so that the surface of the recording medium is strongly rubbed. Sometimes. Due to this rubbing, paper dust and the like adhere to the recording medium, and as shown in FIG. In particular, when the surface of the transfer drum 5 is coated with a resin such as polyvinylidene fluoride, polyethylene terephthalate, polycarbonate, or polyurethane, a dirt band 29 easily occurs.

Therefore, in this embodiment, as shown in FIG. 1, adjacent separation roller pairs 9 having a difference in the conveyance speed of the recording medium.
A patch T is formed in a region on the recording medium where the region on the recording medium other than the region where the pair of transfer rollers 10 contact the transfer drum 5, and the density of the patch T is determined from the light emitting element 20a and the light receiving element 20b. It is configured to read by an optical sensor.

That is, in this embodiment, the separation roller pair 9 and the conveyance roller pair 10 are arranged at the center in the width direction of the recording medium to be conveyed. Accordingly, a stain band 29 is also generated at the center of the surface of the transfer drum 5. Therefore, the configuration is such that the patch T is formed at a position avoiding the center of the surface of the transfer drum 5. Further, the portion where the recording medium does not wind around the surface of the transfer drum 5 may also be damaged by the rubbing with the photosensitive drum 1 and the reflectance may be changed. The minimum recording medium that can be recorded by the image forming apparatus is formed in an area wound around the transfer drum 5.

As a result, it is possible to always detect an accurate patch density and perform accurate image density control.

[Second Embodiment] In the first embodiment described above, the separation roller pair 9 and the conveyance roller pair 10 are provided at the center in the width direction of the recording medium to be conveyed. A dirt band 29 occurred in the center.

However, as shown in FIG. 5, when the separation roller pair 9 is disposed substantially at the center of the recording medium in the width direction, two pairs of conveyance rollers 10 may be disposed on both sides in the width direction of the recording medium. In this case, as shown in FIG.
A band 29 such as a stain is formed on the surface of the recording medium at substantially the center and both sides in the width direction of the recording medium corresponding to the position of the roller pair.

Therefore, when the separation roller pair 9 and the conveyance roller pair 10 are arranged as shown in FIG. 5, a patch T for density measurement is formed at a position corresponding to the interval 30 between the respective dirt bands 29. To be configured. Accordingly, the concentration measuring means 20
Are also arranged at positions corresponding to the positions where the patches T are formed.

Although it is possible to form a patch also at the portion 31 in FIG. 5, there is a possibility that the smallest recording medium recordable by the image forming apparatus is outside the area wound around the transfer drum 5. For this reason, it is preferable that the patch T is formed in 30 portions in the above-mentioned region.

Third Embodiment Next, a third embodiment will be described with reference to FIG. It is desirable that the patch in the image density control is formed substantially at the center of the surface of the transfer drum 5 in order to minimize the influence of the distance movement due to the eccentricity of the transfer drum 5. Therefore, as shown in FIG.
Is formed at the center of the transfer drum 5, and the density detecting means 20 is also arranged at a position corresponding to this. Then, to prevent the band 29 such as dirt from being generated at this patch position,
The separation roller pair 9 and the conveyance roller pair 10 are respectively two pairs of roller pairs, and are disposed so as to be located on both sides in the width direction of the recording medium.

Thus, even if the number of recorded images advances, the band
29 are only formed on both sides of the patch T, and do not affect the patch, so that accurate image density control can always be performed.

[Other Embodiments] In the above-described embodiment, the relationship between the positional relationship between the separation roller pair 9 and the transport roller pair 10 and the patch formation position has been described. However, the position of the pickup roller 8 is more preferable.

In the above-described embodiment, the transfer drum 5 is exemplified as the image carrier on which the stain band 29 is generated. However, even if the transfer drum 5 is not as dirty, the photosensitive drum 1 is similarly stained. May occur. Therefore, the present invention is not limited to a color image forming apparatus, and can be similarly applied to an image forming apparatus (particularly, a monochrome image recording apparatus) that forms a patch for density measurement on the photosensitive drum 1 as an image carrier. . Further, similar effects can be obtained by applying the present invention to an image forming apparatus that forms a patch on an intermediate transfer member.

[0039]

According to the present invention, as described above, a test image is formed at a position off the dirt on the image carrier where dirt is generated due to a roller having a difference in transport speed. Irrespective of this, an accurate image density can always be detected.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a positional relationship between an image carrier and an image density detecting unit.

FIG. 2 is a schematic explanatory view showing the overall configuration of the electrophotographic image forming apparatus.

FIG. 3 is an explanatory diagram of an image density detection configuration.

FIG. 4 is an explanatory diagram of a configuration of a separating and conveying means.

FIG. 5 is an explanatory diagram of a second embodiment.

FIG. 6 is an explanatory diagram of a third embodiment.

FIG. 7 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 T ... Patch 1 ... Photoconductor drum 2 ... Charger 3 ... Supporter 4b ... Black developing device 4c ... Cyan developing device 4m ... Magenta developing device 4y ... Yellow developing device 5 ... Transfer drum 6a ... Laser diode 6b ... Motor 6c ... Polygon Mirror 6d… Lens 6e… Mirror 6f… Light path 7… Sheet cassette 8… Pickup roller 9… Separation roller pair 10… Transport roller pair 11… Guide 12… Registration roller pair 13… Gripper 14… Suction roller 15… Separation claw 16… Fixing Means 17 Cleaning means 18 Transfer drum cleaning means 19 Charge eliminating roller 20 Density measuring means 20a Light emitting element 20b Light receiving element 21 Motor 22a to 22h Gear 23 Spring clutch means 23a Gears 24a, 24b Shaft 25 … Solenoid 26… one-way clutch 27… torque limiter 28… axis 29… band 30… pack Hatch forming part 31… Patch forming part

Claims (4)

[Claims] An electrophotographic image forming apparatus for forming a test image for density measurement on an image carrier, detecting the density and controlling the image density, and an image for transferring and recording a toner image on a recording medium. Forming means, conveying means comprising a plurality of rollers for conveying a recording medium to the image forming means, and density measuring means for forming a test image on the image carrier and measuring image density. The density measurement unit is configured to contact the image carrier with an area on a recording medium other than an area where an adjacent roller having a difference in the conveyance speed of the recording medium among the plurality of rollers of the conveyance unit is in contact with the image carrier; An electrophotographic image forming apparatus configured to form a test image on a body. 2. An electrophotographic image forming apparatus according to claim 1, wherein said image forming means is configured to form a color image. 3. An electrophotographic image forming apparatus according to claim 1, wherein said image carrier for forming said test image is a photosensitive drum for forming a latent image. 4. The electrophotographic image forming apparatus according to claim 1, wherein the image carrier for forming the test image is a transfer drum for transferring a toner image to a recording medium.