JPH1026879A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To steadily obtain a proper-density image by forming a patch image in which developer concentration is satisfactorily reflected and correctly controlling the developer density when detecting the density of the patch image formed on an image carrier and controlling the two-component developer, in a developing unit having a plurality of developer carriers. SOLUTION: The sleeve 42, one of the two developing sleeves of the developing unit 4, is put in a developing position in relation to a photoreceptive drum 1 and rotated, and the patch latent image on the photoreceptive drum 1 is developed with the two-component developer by the application of a development bias in which an AC voltage is periodically superimposed to a DC voltage and by the use of the sleeve 42. The other developing sleeve 41 is kept in a refraction position, which is apart from the developing position, in order to prevent it from disturbing the patch latent image and also made nonrotatable, and only an AC voltage is applied to it. The density of the formed patch image is detected by a detection sensor, and it is controlled so as to reach the developer concentration in the developing unit 4, that is, the developer concentration at which the image is developed by both the developing sleeves 41 and 42.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer.

[0002]

2. Description of the Related Art FIG. 9 is a sectional view showing a schematic structure of a conventional color image forming apparatus. The present image forming apparatus has a digital color image reader unit at the top and a digital color image printer unit at the bottom.

In the reader section, the original 30 is placed on an original platen glass 31 and exposed and scanned by an exposure lamp 32 so that a reflected light image from the original 30 is condensed on a full color sensor 34 by a lens 33 and color separation is performed. Obtain an image signal. The color separation image signal is processed by a video processing unit (not shown) via an amplifier (not shown) and sent to a printer unit.

In the printer section, a photosensitive drum 1 serving as an image carrier is rotatably supported in the direction of an arrow. Around the photosensitive drum 1, a pre-exposure lamp 11, a corona charger 2, a laser exposure optical system 3, a potential sensor 12, four developing units 4Y, 4C, 4M, and 4K of different colors, a drum light amount detecting unit (image density detecting unit) 13, a transfer device 5, and a cleaning unit 6 are arranged.

In the laser exposure optical system 3, an image signal from the reader unit is converted into an optical signal by a laser output unit (not shown), and the converted laser light (optical image) E is reflected by the polygon mirror 3a. Then, the surface of the photosensitive drum 1 is linearly scanned (raster scanned) through the lens 3b and the mirror 3c.

The printer unit includes a photosensitive drum 1 during image formation.
Is rotated in the direction of arrow R1, and after the charge is eliminated by the pre-exposure lamp 11, the photosensitive drum 1 is uniformly charged by the charger 2,
An optical image E is emitted for each separation color to form an electrostatic latent image on the surface of the photosensitive drum 1.

Next, a predetermined developing device is operated for each latent image of each separation color to develop the image, and an image is formed on the photosensitive drum 1 using a resin-based toner, that is, a toner image. In this example, the developing units 4Y, 4C, 4M, and 4K contain a two-component developer in which a toner and a magnetic carrier are mixed, and yellow, cyan, magenta, and black toners are used as the toners. . These developing devices 4Y to 4K are
The operation of the eccentric cams 24Y, 24C, 24M, and 24K causes the photosensitive drum 1 to be selectively approached in accordance with the latent image.

On the other hand, the recording material cassette 7a, 7b or 7
c, the recording material is conveyed to the image transfer unit facing the photosensitive drum 1 via the conveyance system and the transfer device 5, and the toner image formed on the photosensitive drum 1 is transferred onto the recording material in the image transfer unit. You.

In the present embodiment, the transfer device 5 includes a transfer drum 5a.
And a transfer charger 5b and an adsorption charger 5c around the transfer charger 5b.
And an attraction roller 5g, an inner charger 5d, an outer charger 5e, and the like opposed thereto. The transfer drum 5a is supported so as to be driven to rotate, and a recording material carrying sheet 5f is integrally extended in a cylindrical shape in a peripheral opening area. As the recording material supporting sheet 5f, a dielectric sheet such as a polycarbonate film is used. The recording material is an adsorption charger 5
Due to the action of c and the suction roller 5g, the sheet is electrostatically adsorbed on the surface of the recording material carrying sheet 5f, and is repeatedly rotated through the image transfer section according to the rotation of the transfer drum 5a.

The toner image on the photosensitive drum 1 is moved to an image transfer section as the photosensitive drum 1 rotates, and is transferred to the transfer drum 5.
The toner image is transferred onto the recording material passing through the image transfer portion by the transfer of the transfer member a by the operation of the transfer charger 5b. In this manner, a desired number of color toner images, in this example, four color toner images are superimposedly transferred onto the recording material on the transfer drum 5a, and a full-color image is formed.

In the case of one-sided full-color image formation, when the transfer of the four-color toner image onto the recording material is completed, the separation claw 8 is formed.
a, the recording material is separated from the transfer drum 5a by the action of the separation push-up roller 8b and the separation charger 5h, and the separated recording material is sent to the heat roller fixing device 9 to be fixed, thereby completing the image formation, and the one-sided full-color image Is discharged onto the tray 10. After the transfer, the photosensitive drum 1 is cleaned by a cleaning device 6 to remove the residual toner on the surface, and then subjected to the image forming process again.

When a full-color image is to be formed on both sides of the recording material, the conveyance path switching guide 19 is driven immediately after the recording material has left the fixing device 9, and the recording material is passed through the conveyance vertical path 20 to the reverse path. 21a. Thereafter, by the reverse rotation of the reversing roller 21b, the recording material is retreated in a direction opposite to the direction in which the recording material is fed, with the rear end when fed in as the head,
It is stored in the intermediate tray 22. Thereafter, the recording material is sent from the intermediate tray 22 to the transfer drum 5a, and a full-color image is formed on the other surface of the recording material again by the above-described image forming process, thereby obtaining a recording material of a double-sided full-color image.

Incidentally, the powder scattered from the photosensitive drum 1, the developing devices 4Y to 4K, the cleaning device 6, etc. adhere to the recording material carrying sheet 5f of the transfer drum 5a, or the recording material jams (paper jam). At this time, the toner adheres and oil adheres to the recording material adhered at the time of forming a double-sided image, thereby causing contamination. On the other hand, the cleaning of the recording material carrying sheet 5f is performed by the action of the fur brush 14 and the backup brush 15 facing each other across the recording material carrying sheet 5f, and the action of the oil removing roller 16 and the backup brush 17. Such cleaning is performed before or after image formation, and as needed when a jam occurs.

In this embodiment, the gap between the recording material carrying sheet 5f and the photosensitive drum 1 is reduced by operating the eccentric cam 25 at a desired timing and operating the cam follower 5i integrated with the transfer drum 5a. The configuration can be set arbitrarily. For example, during standby or when the power is off, the distance between the transfer drum 5a and the photosensitive drum 1 is increased,
Can be independently rotated.

FIG. 10 shows a developing device having improved developability.
As shown in FIG.
1 and 42, the magnet roller 41 disposed inside
A developing device 4 that develops a latent image on the photosensitive drum 1 with a developer carried on the developing sleeves 41 and 42 by the pumping poles a and 42a is known.

To control the concentration of the developer in the developing device 4 by the patch image, a latent image of the patch image is formed on the photosensitive drum 1, the developing sleeves 41 and 42 are rotated in the directions of arrows G and H, and a bias power supply is provided. By applying the same developing bias from 50, the latent image is developed with the developer on the developing sleeves 41 and 42 to form a patch image, and the density of the formed patch image is determined by the detection sensor 13 in FIG. Based on the detection by

[0017]

As described above, one developing unit 4 is provided with a plurality of developing sleeves 41 and 42, and the latent image on the photosensitive drum 1 is transferred to the plurality of developing sleeves 41 and 42.
The method of developing with the above developer can improve the development efficiency of the latent image, so that even if the developer concentration in the developing device 4 is somewhat low, it is possible to obtain an image of an appropriate density.

On the other hand, however, since the developer density is not well reflected on the density of the patch image, even if the developer density is controlled by detecting the density of the patch image, accurate control of the developer density cannot be performed. Therefore, there is a problem that an image having an appropriate density cannot be stably obtained.

An object of the present invention is to provide an image forming apparatus having a developing device having a plurality of developer carrying members and controlling the developer concentration of the developing device by detecting the density of a patch image formed on the image carrying member. In the forming apparatus, by forming a patch image having a density that well reflects the developer density, it is possible to accurately control the density of the developer and stably obtain an image having an appropriate density. It is to provide a forming device.

[0020]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier, a two-component developing unit having a plurality of developer carriers for developing a latent image formed on the image carrier under application of a developing bias, and a developer carrying device. A magnet disposed in the body, and image density detecting means for detecting the density of the patch image formed on the image carrier, and detecting the density of the two-component developer in the developing means based on the detected density of the patch image. In the image forming apparatus to be controlled, the latent image of the patch image is developed using any one of the plurality of developer carriers, and development is performed based on the detected density of the patch image. An image forming apparatus is characterized in that the concentration of a developer in the means is controlled.

According to the present invention, preferably, the developing bias applied to the developer carrier for developing the latent image of the patch image is a DC voltage to which a rectangular wave voltage is periodically applied. At the time of developing the latent image of the patch image, the developer carrier for developing the latent image of the patch image is positioned at a developing position facing the image carrier by applying a pressing operation by a pressing cam, and the other developing devices The developer carrier is not subjected to the pressurizing operation by the pressurizing cam, remains out of the developing position facing the image carrier, and does not rotate. Further, an AC voltage to which no DC is applied is applied.

Further, the magnet in the developer carrier is rotatable, and prior to the development of the latent image of the patch image, the magnet in the developer carrier other than the developer carrier for developing the latent image of the patch image is rotated. Then, the developer pumping pole is moved away from the developer surface in the developing device, and the developer carrier is rotated in this state, thereby eliminating the developer on the surface of the developer carrier facing the image carrier. Can be. A plurality of developing means may be provided around the image carrier.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a sectional view showing a developing unit in an embodiment of the image forming apparatus of the present invention. According to the present invention, when the developing device 4 of the image forming apparatus includes a plurality of developing sleeves 41 and 42 and forms a patch image on the photosensitive drum 1, a latent image of the patch image is formed by one of the developing sleeves 41 and 42. Development is one major feature. The configuration of the image forming apparatus of the present invention is basically the same as that of the conventional image forming apparatus shown in FIG.

As shown in FIG. 1, the developing device 4 (4M to 4M)
K) has two developing sleeves 41 and 42 at the opening facing the photosensitive drum 1, and these developing sleeves 41 and 42
Inside, magnet rollers 41a and 41b are arranged, respectively. Below the developing sleeves 41 and 42, a partition 4 is provided.
Stirring screws 45, 43, 44 isolated at 6, 47
Is installed. Different developing bias power supplies 51 and 52 are connected to the developing sleeves 41 and 42, respectively.
Pressing cams 48 and 49 are in contact with the lower surface of the developing device 4 at positions substantially corresponding to the developing sleeves 41 and 42, respectively.

During image formation, the photosensitive drum 1 rotates in the direction of arrow R1, and a latent image forming means (not shown) forms an electrostatic latent image on the photosensitive drum 1. As the latent image reaches the developing device 4 with the rotation of the photosensitive drum 1, the pressure cams 48 and 49 are rotated to advance the developing device 4 to the photosensitive drum 1, and the developing sleeves 41 and 42 are moved to the photosensitive drum 1. The position is determined at the developing position relative to 1. Further, the developing sleeve 4
1 and 42 are rotated in the directions of arrows A and B, and bias power supplies 51 and 52 apply a developing bias in which an AC voltage and a DC voltage are superposed between the developing sleeves 41 and 42 and the photosensitive drum 1. Thereby, the developing sleeve 41,
From the developer carried on the toner 42, toner flies to and adheres to the latent image, and the latent image is developed and visualized as a toner image.

According to the present invention, at the time of the above-described normal image forming operation, a patch image for controlling the developer density is formed on the photosensitive drum 1 as appropriate, and the density of the patch image is detected as shown in FIG. The toner is supplied from a replenishing tank (not shown) into the developing device 4 based on the detected patch image density detected by the sensor 13, and the density of the developer in the developing device 4 is controlled. According to the present invention, in order to create a patch image at a density that highly reflects the developer density in the developing device 4 at that time, the latent image of the patch image is divided into the first and second developing sleeves 41 and 4 as described above.
The developing is performed using only one of the two, for example, the developing sleeve 42.

As shown in FIG. 1, the first developing sleeve 41 is provided with a pressure cam 48 so as to prevent the developer carried thereon from disturbing the patch latent image on the photosensitive drum 1. Is not advanced with respect to the photosensitive drum 1 on the side of the developing sleeve 41, and the developing sleeve 41 is
From the developing position. Further, as the patch latent image reaches the developing device 4, the rotation of the developing sleeve 41 is stopped, and only the AC bias from the power source 51 is applied to the developing sleeve 41.

On the other hand, the developing sleeve 42 rotates the pressing cam 49 so as to be positioned at the developing position facing the photosensitive drum 1, and simultaneously rotates the developing sleeve 42 in the direction of arrow B. The developing sleeve 4
2 to develop the patch latent image with the developer on the developing sleeve 42.

Another feature of the present invention is that a bias as shown in FIG. 2 is used as a developing bias at the time of developing the patch latent image. This bias is a bias in which a rectangular wave voltage is periodically superimposed on a DC voltage, and this cycle is repeated assuming that the whole of the section E in which the rectangular wave voltage is superimposed and the section F of only the DC voltage is one cycle. In the example of FIG. 2, the superimposition section E of the rectangular wave voltage has a frequency of 8 kHz, one pulse (may be one pulse or more) (note that one pulse is ± 2 peaks), and a time of 8 kHz (time corresponding to 8 kHz, 1 second / (8 × 10 ³ Hz) = 125 μs (hereinafter, the same usage).
In kHz, the total cycle time (period) is 2.66k
Hz.

According to the developing bias to which the rectangular wave voltage is periodically applied, the developing efficiency is increased, and the developing contrast potential is set to about 100 V more than the developing bias using only the normal rectangular wave voltage (frequency: 2 kHz, 2 kVpp). Can be set low.

Using a developing bias to which a rectangular wave voltage is periodically applied as shown in FIG.
FIG. 3 shows the characteristics of the output image density with respect to the input image signal when the development is performed by using the developer density of 4%, 5%, and 6% as parameters. FIG. 4 shows the characteristics of the detection output of the output image by the detection sensor 13 with respect to the input image signal.
Shown in Similarly, the patch latent image is transferred to both developing sleeves 4.
FIG. 5 shows the characteristics of the output image density with respect to the input image signal when the image is developed by using Nos. 1 and 42, and FIG.
Shown in

When a developing bias in which a rectangular wave voltage is periodically superimposed is used, the development of the patch latent image using one developing sleeve 41 is performed by a normal developing operation using both developing sleeves 41 and 42. The change in the density of the output image with respect to the change in the developer density is larger than that at 1 wt.
%, The change in the detected density of the output image is about 250 mV / wt%, which indicates that the sensitivity is high.

As described above, according to the patch image developing method of the present invention, the density of the patch image can be made to reflect the high developer density. Therefore, the developer in the developing device 4 is detected based on the density detection of the patch image. , That is, by controlling the developer concentration when developing using both developing sleeves 41 and 42, the concentration can be accurately controlled. Therefore, the developing sleeve 4
By developing using Nos. 1 and 42, an image having an appropriate density can be stably obtained.

Embodiment 2 In this embodiment, as shown in FIG. 7, the magnet roller 41a and the developing sleeve 42 in the developing sleeve 41 of the developing device 4 are used.
Is characterized in that the inner magnet roller 42a is rotatable in the directions of arrows C and D in the same direction as the rotation directions A and B of the developing sleeves 41 and 42, respectively. Other configurations of the developing device in the present embodiment are basically the same as those of the developing device in Embodiment 1 in FIG. 1, and the same reference numerals in FIG. 7 as those in FIG. 1 indicate the same members.

As in the first embodiment, when the patch latent image on the photosensitive drum 1 is developed by using one of the second developing sleeves 42, for example, the patch latent image by the developer on the first developing sleeve 41 on the non-developing side is used. To prevent image disturbance, the second developing sleeve 42 develops the patch latent image on the photosensitive drum 1 while the rotation of the developing sleeve 41 is stopped and only the AC bias is applied to the developing sleeve 41 from the power supply 51. In this embodiment, however, the developer on the developing sleeve 41 is cut in advance in order to further improve the effect of preventing the patch latent image from being disturbed.

That is, as shown in FIG. 8, by rotating the magnet roller 41a of the first developing sleeve 41 in the direction of arrow C, the developer pumping pole P of the magnet roller 41a is moved from Q1 to Q2. Then, the pumping pole P is moved away from the developer surface in the developing device 4 to eliminate the pumping of the developer to the surface of the developing sleeve 41 by the pumping pole P. In this state, the developing sleeve 41 is rotated in the direction of arrow A so that the surface of the developing sleeve 41 is cut off so that there is no developer, and the surface of the developing sleeve 41 faces the surface of the photosensitive drum 1. Thereafter, as described above, the development of the patch latent image on the photosensitive drum 1 is performed by the second developing sleeve 42 in a state where the rotation of the developing sleeve 41 is stopped and only the AC bias is applied to the developing sleeve 41 from the power supply 51. Let

In the development by the second developing sleeve 42, as in the first embodiment, the developing sleeve 42 is positioned at the developing position with respect to the photosensitive drum 1, and at the same time, the developing sleeve 42 is rotated in the direction of arrow B. A developing bias in which the rectangular wave voltage of FIG. 2 is periodically superimposed is applied to the developing sleeve 42 from the power source 52, and the developer on the developing sleeve 42 is caused to fly to the patch latent image.

According to the present embodiment, the second developing sleeve 42
Prior to the development of the patch latent image using
Since the developer on the developing sleeve 41 is cut off, the prevention of the disturbance of the patch latent image by the developing sleeve 41 can be further improved. Then, as in the first embodiment, an image is formed by reflecting the density of the patch image with a high developer density, and the developer density is controlled based on the density detection of the patch image. Developing sleeve 4
An image having an appropriate density can be stably obtained by development using Nos. 1 and 42.

[0040]

As described above, according to the present invention,
When a patch latent image is developed by a developing device having a plurality of developer carriers, the patch latent image is developed using one of the developer carriers, so that the two-component developer concentration of the developing device is improved. A patch image having the density reflected in the image can be formed. Therefore, by detecting the density of the patch image, it is possible to accurately control the developer density in the developing device. Can be obtained stably.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a developing device in an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a waveform diagram showing a developing bias applied to one developing sleeve used in developing a latent image of a patch image for controlling a developer density in the present invention.

FIG. 3 is a diagram illustrating characteristics of an output image density with respect to an input image signal when a latent image of a patch image is developed using one developing sleeve using the developing bias of FIG. 2;

FIG. 4 is a diagram illustrating characteristics of detection output of an output image by a detection sensor with respect to an input image signal in FIG. 3;

FIG. 5 is a diagram illustrating characteristics of an output image density with respect to an input image signal when a latent image of a patch image is developed using both developing sleeves using the developing bias of FIG. 2;

6 is a diagram illustrating characteristics of detection output of an output image by a detection sensor with respect to an input image signal in FIG. 5;

FIG. 7 is a sectional view showing a developing device according to another embodiment of the present invention.

FIG. 8 is an explanatory view showing that a magnet roller in a developing sleeve is rotated to move a developer pumping pole in order to cut off a developer on a developing sleeve on one non-developing side of the developing device in FIG. 7; It is.

FIG. 9 is a cross-sectional view illustrating a conventional image forming apparatus.

FIG. 10 is a cross-sectional view illustrating a developing device installed in a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 4 Developing device 13 Image density detection sensor 41 1st developing sleeve 42 2nd developing sleeve 41a, 41b Magnet roller 43, 44, 45 Stirring screw 48, 49 Pressing cam 51, 52 Bias power supply

Continuing on the front page (72) Inventor Kazuhiro Hasegawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (7)

[Claims] 1. An image carrier, a two-component developing means having a plurality of developer carriers for developing a latent image formed on the image carrier under application of a developing bias, and disposed in the developer carrier. And an image density detecting means for detecting the density of the patch image formed on the image carrier, and controlling the density of the two-component developer in the developing means based on the detected density of the patch image. In the forming apparatus, the latent image of the patch image is developed using any one of the plurality of developer carriers, and based on the detected density of the patch image, An image forming apparatus for controlling the concentration of a developer. 2. The image forming apparatus according to claim 1, wherein the developing bias applied to the developer carrier for developing the latent image of the patch image is a bias obtained by periodically applying a rectangular wave voltage to a DC voltage. 3. A developing device for developing a latent image of a patch image at the time of developing a latent image of the patch image is positioned at a developing position facing the image carrier by applying a pressing operation by a pressing cam. The image forming apparatus according to claim 1, wherein the other developer carrier is not subjected to the pressing operation by the pressure cam, and is kept out of the developing position facing the image carrier. 4. When developing a latent image of a patch image, a developer carrier other than the developer carrier for developing the latent image of the patch image is
The image forming apparatus according to claim 1, wherein the image forming apparatus does not perform a rotation operation. 5. A method for developing a latent image of a patch image, comprising the steps of:
The image forming apparatus according to claim 1, wherein an AC voltage to which no DC is applied is applied. 6. A magnet in the developer carrier that is rotatable, and rotates a magnet in the developer carrier other than the developer carrier that develops the latent image of the patch image prior to the development of the latent image of the patch image. Then, the developer pumping pole is moved away from the developer surface in the developing device, and the developer carrier is rotated in that state, thereby eliminating the developer on the surface of the developer carrier facing the image carrier. Item 6. The image forming apparatus according to any one of Items 1 to 5. 7. The image forming apparatus according to claim 1, wherein a plurality of developing means are provided around the image carrier.