JP3559224B2 - Tandem type full color image forming apparatus - Google Patents

Description

[0001]
TECHNICAL 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]
[Prior art]
In an apparatus for forming a full-color image by electrophotography, for example, a toner image formed on the surface of a photoconductor drum by toner of each color such as black toner, cyan toner, magenta toner, and yellow toner is transferred onto a predetermined transfer paper. Forming a full-color transfer image by superimposing the transfer image, introducing the transfer paper having such a transfer image into a fixing device arranged on the discharge side of the transfer belt, and fixing the transfer image to the transfer paper. An image is formed. In such a full-color image forming apparatus, a so-called tandem type full-color image forming apparatus in which a dedicated photosensitive drum is used for each color toner and these photosensitive drums are juxtaposed on a transfer belt that conveys transfer paper is practically used. It has been offered to.
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.
[0003]
[Problems to be solved by the invention]
In the above-described tandem-type full-color image forming apparatus, a dedicated photosensitive drum is provided for each color, and these photosensitive drums are arranged side by side on a transfer belt. When a paper jam (JAM) occurs, there is a problem that it is difficult to specify the position.
For example, in a conventionally known full-color tandem image forming apparatus, a paper feed switch is generally provided on a transport path before transfer paper is introduced onto a transfer belt, and further, a transport path of A discharge switch is provided above, and JAM detection is performed by the operation of these switches. That is, the feed switch detects the transfer paper being introduced onto the transfer belt, the discharge switch detects the discharge of the transfer paper from the fixing device, and a certain time elapses after the feed switch detects the transfer paper. Also in this case, JAM is detected because transfer paper is not detected by the discharge switch. However, in the tandem-type full-color image forming apparatus, since the transfer path of the transfer paper by the transfer belt is long, as described above, the JAM detection only by the paper feed switch before the transfer belt and the discharge switch after the fixing device is discharged, This means that the portion where JAM has occurred cannot be specified sufficiently.
[0004]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a tandem type full-color image forming apparatus capable of reliably detecting occurrence of a paper jam (JAM) on a transfer belt.
Another object of the present invention is to provide a tandem-type full-color image forming apparatus capable of reliably detecting occurrence of JAM on a transfer belt without using a switch mechanism and without using a dedicated member for JAM detection. Is to do.
[0005]
According to the present invention, a plurality of image forming areas for forming images of different colors are juxtaposed,
In each image forming area, a photosensitive drum and a transfer roller disposed below the drum so as to face the drum are provided.
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 by the transfer belt and passing the transfer paper between the photosensitive drum and the transfer roller in the image forming area, the toner image formed on each photosensitive drum is transferred to the transfer paper surface. Are sequentially performed in a tandem-type full-color image forming apparatus,
On the transfer belt, an image density detection sensor is disposed downstream of the image forming area where the transfer of the toner image onto the transfer paper surface is performed last in the transfer paper transport direction. Forming a solid patch toner image on the photosensitive drum provided on the transfer belt, transferring the solid patch toner image to the surface of the transfer belt without transferring the transfer paper, and transferring the solid patch toner image to the transfer belt surface. Density detection of the toner image is performed by the image density detection sensor ,
During transfer paper transfer, the image density sensor operates to detect transfer paper transfer , and
When the density of the solid patch toner image is detected, the image density sensor is moved closer to the transfer belt, and when the transfer of the transfer paper is detected, the image density sensor is retracted and conveyed so as to increase the interval between the transfer belt and the transfer paper. Tandem-type full-color image forming apparatus characterized in that the transfer sheet is moved to a margin of the transfer sheet according to the size of the transfer sheet .
[0006]
An important feature of the present invention is that the JAM on the transfer belt is detected by detecting the transfer paper on the transfer belt using an image density detection sensor disposed on the transfer belt.
That is, the image density detection sensor irradiates fixed light and detects the image density based on the reflectance of the reflected light, and is used for adjusting the image forming conditions in the image area of each color. Therefore, since this sensor can be used for the detection of transfer paper, it is possible to detect the occurrence of JAM by arranging this sensor on the transfer paper transport path of the transfer belt. As can be understood from this, the present invention is extremely advantageous in terms of cost because it is not necessary to use a dedicated sensor for detecting the occurrence of JAM on the transfer belt.
[0007]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, the present invention will be described based on 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.
[0008]
The tandem-type image forming apparatus includes a transfer belt 1 stretched between a pair of rollers. A transfer paper 2 is introduced onto the transfer belt 1 from the right side in FIG. The transfer paper 2 is discharged to the left side in the figure. A paper feed switch 3 is provided on a conveyance path on the introduction side of the transfer paper 2 to the transfer belt 1, and a fixing device 4 is provided on a conveyance path on the discharge side from the transfer belt 1. A discharge switch 5 is provided on the discharge side of the device 4.
The paper feed switch 3 and the discharge switch 5 detect the transfer paper 2 by turning when the transfer paper 2 passes.
[0009]
On the transfer belt 1, a monochrome image forming area B, a cyan (blue) image forming area C, a magenta (red) image forming area M, and a yellow (yellow) image forming area Y are provided in this order from the right. A 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.
Further, a transfer roller 7 is disposed 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.)
[0010]
In each image forming area, a main charger 8, an optical system 9 for image exposure, and a developing device specific to each image forming area are arranged around the photosensitive drum 6 in this order. 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.
[0011]
An image forming cycle in each image forming area will be described using the monochrome image forming area B as an example.
First, the photosensitive 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 reversal 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 6B 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.
[0012]
As described above, the monochrome image formed of the black toner is formed on the transfer paper 2 in the monochrome image forming area B, and the blue image formed of the cyan toner is similarly formed on the transfer paper 2 in the cyan image forming area C. In the image and magenta image forming area M, a red image formed of magenta toner is formed, and in the yellow image forming area 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, and the toner images of the respective colors are superimposed to form the full-color image on the transfer paper 2. Is formed.
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 then discharged.
[0013]
In addition, a cleaning device 15 is provided at a lower portion of the transfer belt 1 so that the transport surface of the transfer belt 1 can be kept clean.
[0014]
According to the present invention, on the transfer belt 1, 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 performed last is downstream of the transfer paper transport direction. An image density detection sensor (ID sensor) 20 is arranged in the portion.
[0015]
Using the 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 forming conditions in each image forming area are determined. Adjustments are made.
That is, without transferring the transfer paper 2, a solid patch toner image is formed on the surface of the photosensitive drum 5 with 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 manner is detected by the ID sensor 20. If the image density is lower than the appropriate toner density, the image forming conditions in the image forming area are determined. Is adjusted so that an image having an appropriate toner density can be obtained by, for example, replenishing a new toner to the developing device or increasing a developing bias voltage or a transfer bias voltage. (Because a full-color image is formed by superimposing toner images of each color, if the density of any of the toners is out of an appropriate range, a clear color image cannot be obtained. Required.)
When the image density detection by the ID sensor 20 is completed, the solid patch toner image is removed by the cleaning device 15 below, and the surface of the transfer belt 1 is kept clean.
[0016]
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, the ID sensor 20 is used for detecting the transfer paper 2. Therefore, as shown in FIG. 1, it is necessary to arrange the transfer belt 1 on a traveling path above the transfer belt 1 (that is, on a transfer path of the transfer paper 2).
[0017]
That is, since the ID sensor 20 is a so-called reflection densitometer and detects the toner density based on the light reflectance, the ID sensor 20 can detect the transfer paper 2 using the ID sensor.
In the present invention, the detection of the transfer paper 2 by the ID sensor 20 can be performed only when the JAM occurs, or when the image formation is performed (when the transfer paper 2 is being conveyed). Detection can also be performed.
[0018]
For example, as described above, when the transfer switch 2 is not detected by the discharge switch 5 when a certain period of time has elapsed after the transfer paper 2 is detected by the feed switch 3, the feed switch 3 and the discharge switch 5 The occurrence of JAM in the transport path between is detected. Therefore, in this case, by operating the ID sensor 20 to detect the transfer paper 2, the occurrence position of the JAM can be more accurately specified.
When the transfer sensor 2 is detected by constantly operating the ID sensor 20 during image formation, the transfer sensor 2 is detected by the ID sensor 20 when a certain period of time has elapsed after the transfer paper 2 was detected by the paper feed switch 3. By not being detected, occurrence of JAM is detected. Thus, when the ID sensor 20 is constantly operated to detect the transfer sheet 2, the discharge switch 5 can be omitted.
[0019]
As described above, according to the present invention, the operations of measuring the image density and detecting the transfer paper 2 are performed by the ID sensor 20, and the interval between the ID sensor 20 and the transfer belt 1 is changed for each of the operations. To change . That is, since the image density measurement is performed by measuring the light reflectance from above the transfer belt 1, the ID sensor 20 is attached to the transfer belt 1 as much as possible in order to measure the image density with high accuracy. Should be close. On the other hand, the detection of the transfer paper 2 only needs to detect the presence or absence of the paper, and therefore does not need to be particularly close to the transfer belt 1. Therefore, in order to prevent the transfer of the transfer paper 2 by the ID sensor 20, when the detection of the transfer paper 2 is performed by the ID sensor 20, the ID sensor 20 is retracted upward, and the distance between the transfer belt 1 is increased.
[0020]
Further, since it is difficult for the ID sensor 20 to distinguish between toner and paper, when detecting the transfer paper 2, the ID sensor 20 is moved in the width direction of the transfer belt 1 in accordance with the size of the transfer paper 2. It is moved to position the ID sensor 20 in the margin of the transfer paper 2. Thereby, malfunction of the ID sensor 20 can be prevented, and the transfer sheet 2 can be detected (JAM detection) reliably.
[0021]
The above-described position adjustment of the ID sensor 20, that is, the vertical movement of the ID sensor 20 and the movement of the transfer belt 1 in the width direction are performed by, for example, using a rack-pinion mechanism or the like so that the ID sensor 20 is movable. This can be easily performed.
[0022]
【The invention's effect】
According to the present invention, transfer paper is detected using an image density detection sensor (ID sensor) used in a known tandem-type full-color image forming apparatus without using a dedicated transfer paper detection member. As a result, the position of a paper jam (JAM) can be specified in a narrow range, and in particular, occurrence of JAM on the transfer belt can be reliably detected.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic structure of a tandem image forming apparatus of the present invention.
[Explanation of symbols]
1: transfer belt 2: transfer paper 3: paper feed switch 5: discharge switch 6: photosensitive drum 20: image density detection sensor

Claims (1)

A plurality of image forming areas for forming images of different colors are juxtaposed,
In each image forming area, a photosensitive drum and a transfer roller disposed below the drum so as to face the drum are provided.
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 by the transfer belt and passing the transfer paper between the photosensitive drum and the transfer roller in the image forming area, the toner image formed on each photosensitive drum is transferred to the transfer paper surface. Are sequentially performed in a tandem-type full-color image forming apparatus,
On the transfer belt, an image density detection sensor is disposed downstream of the image forming area where the transfer of the toner image onto the transfer paper surface is performed last in the transfer paper transport direction. Forming a solid patch toner image on the photosensitive drum provided on the transfer belt, transferring the solid patch toner image to the surface of the transfer belt without transferring the transfer paper, and transferring the solid patch toner image to the transfer belt surface. Density detection of the toner image is performed by the image density detection sensor ,
During transfer paper transfer, the image density sensor operates to detect transfer paper transfer , and
When the density of the solid patch toner image is detected, the image density sensor is moved closer to the transfer belt, and when the transfer of the transfer paper is detected, the image density sensor is retracted and conveyed so as to increase the interval between the transfer belt and the transfer paper. Tandem-type full-color image forming apparatus wherein the transfer paper is moved to a margin according to the size of the transfer paper .

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