JP2002006568A - Tandem-type full color image forming device equipped with image density measuring sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tandem-type full color image forming device where the measuring accuracy of an image density detection sensor is improved, by which a vivid full color image is obtained stably and where the sensor is prevented effectively from being stained by toner. SOLUTION: In this tandem-type full color image device, image-forming areas where images having a different color from each other are formed are arranged plurally in tandem, and a transfer belt stretched and laid between a pair of rollers travels between the photoreceptor drum of each image forming area and a transfer roller. The image density detection sensor is arranged on a more downstream side in a transfer paper carrying direction than the image forming area, where a toner image is finally transferred to the surface of transfer paper on the transfer belt and provided to slide in the vertical directions. When detecting toner density, the sensor is made to descend, and when forming the image by carrying the transfer paper by the transfer belt, the sensor is made to ascend and retreat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tandem type full-color image forming apparatus in which a plurality of photosensitive drums for forming images of different colors are arranged on a transfer belt.

[0002]

2. Description of the Related Art In an apparatus for forming a full-color image by an electrophotographic method, for example, a toner image formed on the surface of a photoreceptor drum by a toner of each color such as a black toner, a cyan toner, a magenta toner, and a yellow toner is formed. A full-color transfer image is formed by transferring and superimposing the transfer image on the transfer paper, and the transfer paper having such a transfer image is introduced into a fixing device arranged on the discharge side of the transfer belt, and the transfer image is transferred. An image is formed by fixing on paper. In such a full-color image forming apparatus, a dedicated photosensitive drum is used for each color toner,
A so-called tandem-type full-color image forming apparatus in which these photosensitive drums are juxtaposed on a transfer belt that conveys transfer paper has been put to practical use. This type of full-color image forming apparatus has an advantage that an image can be formed while a transfer sheet is continuously conveyed by a transfer belt.

Further, in a full-color image forming apparatus, since a full-color image is formed by superimposing toner images of each color, it is necessary that each toner image of each color is always formed at an appropriate density. That is, if a toner image of any color is not formed at an appropriate density, the formed full-color image becomes unclear.

In the above-described tandem full-color image forming apparatus, an image density detecting sensor is provided on the traveling path of the transfer belt so that toner images of respective colors are always formed at an appropriate density. That is, the transfer belt is run without transferring the transfer paper, and in this state, a solid patch toner image of any color is formed on the surface of the photoreceptor drum, and the toner image is formed under the same conditions as in normal image formation. Is transferred onto the transfer belt, and the image density of the solid patch toner image transferred onto the transfer belt is detected by the image density detection sensor. The image forming conditions are adjusted based on the result, and the adjustment is performed so that the toner images of any colors are always formed with an appropriate density. For example, when the density is lower than the appropriate density, the developing bias voltage, the transfer voltage, and the like when forming the toner image of the color are adjusted, or the toner charge amount is increased by replenishing or stirring the toner of the color. Is adjusted.

[0005]

In the tandem type full-color image forming apparatus described above, the toner density detected by the image density detecting sensor is lower than the density of the toner image actually transferred to the transfer paper. There was a problem in terms of measurement accuracy. Further, there is another problem that the sensor surface of the image density detection sensor is easily contaminated by the toner scattered in the apparatus, and the sensor must be frequently cleaned.

Accordingly, it is an object of the present invention to provide a tandem type full-color image sensor in which the measurement accuracy of an image density detection sensor is improved, a clear full-color image can be stably obtained, and toner contamination of the sensor is effectively prevented. An object of the present invention is to provide an image forming apparatus.

[0007]

According to the present invention, a plurality of image forming areas for forming images of different colors are juxtaposed, and each image forming area has a photosensitive drum,
A transfer roller is provided below the drum so as to face the drum, and a transfer belt stretched between the pair of rollers is a photosensitive drum and a transfer roller in each image forming area. And transfer paper is conveyed by the transfer belt, and the transfer paper passes between the photosensitive drum and the transfer roller in the image forming area, thereby forming the photosensitive drum formed on each photosensitive drum. In the tandem type full-color image forming apparatus in which the transfer of the toner image to the transfer paper surface is sequentially performed, the transfer paper is transported on the transfer belt more than the image forming area where the transfer of the toner image to the transfer paper surface is performed last. An image density detection sensor is arranged on the downstream side in the direction, and the image density detection sensor is provided so as to be slidable up and down, and lowers the image density sensor, and any one of the image forming areas. A toner image of a solid patch is formed on a photosensitive drum provided in the image forming apparatus, and the transfer belt is run without transporting the transfer paper to transfer the toner image of the solid patch to the surface of the transfer belt; Tandem-type full-color image forming apparatus, wherein when the transfer paper is conveyed by the transfer belt, the image density sensor is retracted upward. Is provided.

The present inventors have studied the problem of the measurement accuracy of the image density detection sensor described above, and have found that such a problem is largely related to the position of the sensor. That is, an image density detection sensor (hereinafter, referred to as an ID sensor) irradiates a certain amount of light and detects the image density based on the reflectance of the reflected light. In addition, it is necessary to provide the toner image close to the surface of the transfer belt on which the solid patch toner image to be measured is formed. For this reason, in a conventionally known tandem-type full-color image forming apparatus, the ID sensor is disposed on a traveling path below a transfer belt that runs while being stretched between a pair of rollers. An image forming area is formed on the upper traveling path, and serves as a transfer sheet transport path.
As a result, when the ID sensor is arranged on the upper traveling road,
This is because the transfer of the transfer paper is hindered by the ID sensor, or the transfer toner image formed on the surface of the transfer paper is disturbed by contact with the ID sensor. However, if the ID sensor is disposed on the lower traveling road, not only does the conveying distance (corresponding to the distance between the image forming area and the ID sensor) of the solid patch toner image to be measured for density become long, but also the transfer belt The solid patch toner image not fixed thereon is conveyed on the traveling path below the transfer belt against the weight. As a result, a part of the toner constituting the solid patch toner image is
The toner is scattered while being conveyed to and from the D sensor, and as a result, a toner density lower than the density of the toner image formed on the surface of the transfer paper by actual image formation is detected.

Accordingly, in the present invention, the ID sensor is arranged on the transfer paper transport path of the transfer belt, so that the sensor is slidable up and down, and when the toner concentration is measured, the sensor is lowered to lower the transfer belt. And during normal image formation, it is necessary to retract this sensor upward. As described above, in order to detect the toner concentration with high accuracy, it is necessary to bring the ID sensor close to the transfer belt. However, if the ID sensor is always arranged close to the transfer belt, the transfer The conveyance of the paper is hindered, and the toner image is disturbed by the contact between the transferred toner image on the transfer paper and the ID sensor. Therefore, only at the time of toner concentration measurement, the ID sensor is lowered to approach the transfer belt, and at the time of transfer of the transfer paper (at the time of image formation), the ID sensor is retracted upward.

Further, according to the present invention, as a result of arranging the ID sensor on the transfer paper conveyance path of the transfer belt, the sensor surface necessarily faces downward. As a result, there is also achieved an advantage that contamination of the sensor surface due to toner scattered or floating in the apparatus is effectively prevented.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific examples shown in the accompanying drawings. FIG. 1 is a view showing a schematic structure of a tandem image forming apparatus of the present invention, and FIGS. 2A and 2B are views showing a mounting structure of an ID sensor provided in the apparatus of FIG. FIG. 3 is a diagram for explaining the orientation of an ID sensor provided in the apparatus of FIG.

In FIG. 1, the tandem-type image forming apparatus includes a transfer belt 1 that runs while being stretched between a pair of rollers. A transfer paper 2 is introduced onto the transfer belt 1 from the right side in the figure. The transfer paper 2 conveyed by the transfer belt 1 is discharged to the left side in the figure. In addition, a fixing device 4 is provided on the conveyance path on the discharge side from the transfer belt 1.

On the traveling path above the transfer belt 1, that is, on the transfer path of the transfer paper 2, in order from the right, a monochrome image forming area B, a cyan image forming area C, a magenta image forming area M, and a yellow image forming area. Y is provided, and the photosensitive drum 6 is arranged in each of the image forming areas. The photosensitive drum in the monochrome image forming area B is 6B, the photosensitive drum in the cyan image forming area C is 6C, the photosensitive drum in the magenta image forming area M is 6M, and the photosensitive drum in the yellow image forming area Y is 6Y. Indicated. Also,
A transfer roller 7 is arranged below the transfer belt 1 so as to face each of the photosensitive drums 6. (Note that the arrangement order of the image forming areas is not particularly limited, and this arrangement can be appropriately changed.)

In each image forming area, around the photosensitive drum 6, a main charger 8, an optical system 9 for image exposure, and a developing device specific to each image forming area are arranged in this order. I have. That is, in the monochrome image forming region B, the monochrome developing device 10B filled with black toner, in the cyan image forming region C, the cyan developing device 10C filled with cyan toner, and in the magenta image forming region M, magenta toner is filled. In the magenta developing device 10M and the yellow image forming area Y, a yellow developing device 10Y filled with yellow toner is provided. Further, a static eliminator (not shown) and a cleaning device 12 are arranged between the area where the transfer roller 7 is provided and the main charger 8.

The image forming cycle in each image forming area is
A description will be given taking the monochrome image forming area B as an example. First,
The photoconductor drum 6B is uniformly charged to a predetermined polarity by the main charger 8 including a corona charger or a contact charging roller. Next, image exposure is performed by light irradiation from an optical system 8 such as an LED, and an electrostatic latent image is formed on the surface of the photosensitive drum 6B. This electrostatic latent image is developed by the monochrome developing device 10B filled with black toner, and a toner image is formed on the surface of the photosensitive drum 6B. The charge polarity of the toner image is the same as the charge polarity of the photosensitive drum 6B charged by the main charger 8 when development is performed by so-called reverse development. , The charge polarity of the photosensitive drum 6B is opposite to the polarity. The toner image formed on the surface of the photosensitive drum 6 </ b> B in this manner is transferred onto the transfer paper 2 conveyed on the transfer belt 1 in a region (transfer region) facing the transfer roller 7. This transfer is performed by applying a bias voltage having a polarity opposite to that of the toner image to the transfer roller 7. After the transfer is completed, the static eliminator and the cleaning device 12 (not shown) remove the charge of the photosensitive drum 6B and clean the toner remaining on the surface of the drum 6B, and the next image forming cycle is performed.

As described above, in the monochrome image forming area B, a monochrome image composed of black toner is formed on the transfer paper 2, and similarly, in the cyan image forming area C, the cyan toner is formed on the transfer paper 2. In the magenta image forming region M, a red image formed of magenta toner is formed, and in the yellow image forming region Y, a yellow image formed of yellow toner is formed. That is, when forming a monochrome image, the above-described image forming cycle is executed only in the monochrome image forming area B, and a monochrome image is formed on the transfer paper 2. When a full-color image is formed, the above-described image forming cycle is executed in each of the image forming areas B, C, M, and Y.
The toner images of the respective colors are superimposed to form a full-color image on the transfer paper 2. The transfer paper 2 on which the above-described image is formed is discharged from the transfer belt 1 and introduced into the fixing device 4, where the image is fixed by heat, pressure or the like and discharged.

A belt cleaning device 15 such as a brush or a blade is provided on the lower traveling path of the transfer belt 1, that is, in a region where the transfer paper 2 is not conveyed. The transfer surface can be kept clean.

According to the present invention, the image forming area (the yellow image forming area Y in FIG. 1) in which the transfer of the toner image to the surface of the transfer paper 2 is last performed on the traveling path above the transfer belt 1. Also, an image density detection sensor (ID sensor) 20 is provided slidably up and down on the downstream side in the transfer paper transport direction.

Using this ID sensor 20, it is detected whether or not the toner image formed in each image forming area has an appropriate density, and based on the result, the image in each image forming area is detected. Adjustment of the forming conditions is performed. In detecting such toner concentration, first, the ID sensor 20 is lowered to bring the ID sensor 20 close to the transfer belt 1. Further, without transferring the transfer paper 2, a solid patch toner image is formed on the surface of the photosensitive drum 5 with a toner of a predetermined color for each image forming area, and the solid patch toner image is formed on the surface of the transfer belt 1. Transcribe. This transfer can be performed in the same manner as the transfer of the toner image onto the transfer paper 2. The image density of the solid patch toner image of each color formed in each image forming area in this way is detected by the ID sensor 20 close to the transfer belt 1, and when the toner density is lower than the appropriate toner density, Adjust image forming conditions in the image forming area, for example, supply new toner to the developing unit,
Due to the rise of development bias voltage and transfer bias voltage,
That is, an image having an appropriate toner density is obtained. When the detection of the image density by the ID sensor 20 is completed, the ID sensor 20 is slid upward and retracted, and the solid patch toner image is removed from the lower cleaning device 15.
And the surface of the transfer belt 1 is kept clean.

In the conventionally known tandem type full-color image forming apparatus, the above-described ID sensor 20 is disposed on the traveling road side below the transfer belt 1, but in the present invention,
Since the ID sensor 20 is disposed on the traveling path above the transfer belt 1, the solid patch toner image formed in any of the image forming areas B, C, M, and Y does not cause toner scattering or the like. Since the density detection is immediately performed by the ID sensor 20, there is almost no measurement error with the toner image formed on the transfer paper 2 by the actual image formation, and the density detection can be performed with high accuracy. Further, a cleaning device 15 for cleaning a solid patch image is provided.
It is preferable to dispose on the traveling path below the transfer belt 1 at a position where the traveling distance from the ID sensor 20 is as short as possible. This is because the longer this distance is, the more the toner scatters from the solid patch image.

The above-mentioned up and down sliding of the ID sensor 20 can be easily performed by using, for example, a rack-pinion mechanism. FIGS. 2A and 2B show an example of an ID sensor mounting structure using such a rack-pinion mechanism. 2 (a) is a side view, and FIG. 2 (b) is a plan view, in which the transfer belt 1 is omitted.

2 (a) and 2 (b), a guide rail 31 is fixed to the apparatus housing or the machine frame 30, and a rack 32 is provided slidably up and down along the guide rail 31. I have. This rack 32
Are engaged with a pinion 36 attached to the rotating shaft of the stepping motor 35,
By the operation of 2, the rack 32 slides up and down along the guide rail 31. Further, the ID sensor 20 described above is connected to the rack 32, and the ID sensor 20 also slides up and down along the guide rail 31 as the rack 32 slides up and down. As described above, the ID sensor 20 is slidably mounted up and down in accordance with the operation of the stepping motor 32. In the above-described toner concentration detection operation, the ID sensor 20 moves downward, and during normal image formation, The upward movement of the Id sensor is performed.

Referring to FIG. 3 showing the above-described ID sensor 20 in an enlarged manner, the sensor surface 2 of the ID sensor 20 will be described.
It is preferable to dispose the ID sensor 20 in such a direction that 0a forms a horizontal plane with θ of 45 ° or less. That is,
By arranging the ID sensor 20 in the above-described orientation, toner adhesion to the sensor surface 20a is most effectively prevented, and the distance between the sensor surface 20a and the transfer belt 1 is reduced as much as possible. Accuracy can be improved.
In order to accurately measure the toner concentration, the sensor surface 2
0a and the surface of the belt 1 are arranged substantially in parallel. For example, the angle of the sensor surface 20a with respect to the surface of the belt 1 is set to about 5 ° or less. Further, the sensor surface 20a and the transfer belt 1 during the toner concentration measurement operation of the ID sensor 20 are
(Denoted by d in FIG. 3) depends on the performance of the sensor, but is usually preferably 2 mm or less.

[0024]

According to the present invention, since the ID sensor is disposed on the traveling path (transfer sheet transport path) above the transfer belt, the accuracy of measuring the toner density is improved, and a stable clear full-color image is obtained. Can be formed. Further, since the sensor surface of the ID sensor faces downward, toner contamination on the sensor surface is effectively prevented, and maintenance such as cleaning of the sensor can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic structure of a tandem image forming apparatus of the present invention.

2A and 2B are diagrams illustrating an example of an attached state of an ID sensor used in the image forming apparatus of FIG. 1; FIG.
(B) is a plan view.

FIG. 3 is a view for explaining the orientation of an ID sensor provided in the apparatus of FIG. 1;

[Explanation of symbols]

 1: transfer belt 2: transfer paper 6: photosensitive drum 15: belt cleaning device 20: image density detection sensor (ID sensor)

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Claims (3)

[Claims] A plurality of image forming areas for forming images of different colors are juxtaposed. Each image forming area includes a photosensitive drum and a lower side of the drum so as to face the drum. A transfer roller is provided, and a transfer belt stretched between a pair of rollers is running between the photosensitive drum and the transfer roller in each image forming area. By transferring the transfer paper and passing the transfer paper between the photoconductor drum and the transfer roller in the image forming area, the transfer of the toner image formed on each photoconductor drum to the surface of the transfer paper is performed in order. In the tandem-type full-color image forming apparatus, an image density detection sensor is provided on the transfer belt at a position downstream of the image forming area where the transfer of the toner image to the transfer paper surface is finally performed in the transfer paper transport direction. The image density detection sensor is provided so as to be slidable up and down, and lowers the image density sensor to form a solid patch toner image on a photosensitive drum provided in any of the image forming areas. By moving the transfer belt without transferring the transfer paper, the toner image of the solid patch is transferred to the surface of the transfer belt, and the density of the solid patch toner image transferred to the transfer belt surface by the sensor is detected. A tandem type full-color image forming apparatus, wherein the image density sensor is retracted upward when the transfer paper is conveyed by the transfer belt. 2. The image forming apparatus according to claim 1, wherein the image density sensor is arranged such that an angle θ between the sensor surface and a horizontal plane is 45 ° or less. 3. The image forming apparatus according to claim 1, wherein a cleaning device for belt cleaning is disposed on a traveling path below the transfer belt.