JP2001331003A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device making the developer density fluctuation reduced, and realizing the further stabilization of the image density and making scattering and fogging possible to be reduced. SOLUTION: In this image forming device controlling the developer density by the output of a patch pattern read out sensor 3, developing bias for developing a latent image of the patch pattern and the developing bias for developing the latent image other than the patch image are different, and moreover, transfer bias for transferring the developing toner image of the patch image and transfer bias for transfer of developing toner image other than patch image are different.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally forms a latent image on an image carrier, and converts the latent image into a visible image (toner image) using a two-component developer having a toner and a carrier. The present invention relates to an image forming technique, and more particularly, to an image forming apparatus that forms a fixed patch image on a recording material carrier or an intermediate transfer body, detects an image density, and thereby controls a developer density.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, for example, a drum-shaped electrophotographic photosensitive member as an image carrier, that is, the surface of a photosensitive drum is uniformly charged, and the surface is exposed to light corresponding to an image signal, and is statically charged. An electrostatic latent image is formed, and the electrostatic latent image is developed by a developing device having a toner as a developer, thereby forming a visible image (toner image).

After transferring the toner image onto a recording material using a transfer unit, an unfixed toner image is formed on the recording material in an image forming apparatus such as a copier printer using a fixing device. (Hereinafter, referred to as “image forming unit”), and in each image forming unit,
For example, toner images of different colors, such as yellow, magenta, cyan, and black, are formed on respective photosensitive drums, and the respective toner images are sequentially carried on the same recording material that is carried and conveyed on recording material conveying means. It is superimposed and transferred.

Further, there have been proposed various image forming apparatuses for obtaining a color image by collectively fixing the superposed color unfixed toner images on a recording material.

Here, a conventional image forming apparatus is shown in FIG.
This will be described with reference to FIG. FIG. 6 shows an image forming apparatus which includes a plurality of image forming units, forms toner images of different colors in each image forming unit, and sequentially superimposes the toner images on the same recording material to form a color image. It is a partial block diagram of an example of an apparatus.

The image forming apparatus shown in FIG. 6 is a rotatable photosensitive drum 201a which rotates in the direction of an arrow.
Each of 201b, 201c, and 201d is uniformly charged by each primary charger, and then irradiates a color-separated light image to form an electrostatic latent image.

Next, the photosensitive drums 201a, 201b, 2
The electrostatic latent images on 01c and 201d are developed by a developing unit provided in each image forming unit to be a visible toner image.

The photosensitive drums 201a, 201a,
The toner images formed on 201b, 201c, and 201d are over-transferred onto the recording material G by transfer chargers 214a, 214b, 214c, and 214d provided in each image forming unit.

Next, when detecting the density of the developer, the same process as that for forming an image on a recording material is performed up to a certain point, that is, uniform charging of the photosensitive drum and image exposure of the density detection patch pattern. The process is similarly performed up to the development of the patch pattern latent image.

Thereafter, unlike the case of forming an image on a recording material, the photosensitive drums 201a, 201b, 2
The transfer charger 21 directly transfers the patch pattern toner images formed on the transfer belts 01c and 201d to the conveying belt 202 of the recording material.
The patches are transferred by 4a, 214b, 214c, and 214d, and the patch pattern formed on the conveyor belt 202 is read by the patch pattern reading sensor 203, and is calculated by an arithmetic unit (not shown). As a result, if necessary,
The toner is supplied to the developing device, and control is performed to keep the image density constant.

In the case where the developer density is controlled by such a method, if the same developing bias is used for forming a density detection patch image and for forming a normal image,
The image density fluctuation due to the fluctuation of the mixture ratio of the toner and the carrier of the developer is small, and therefore, the fluctuation of the developer density hardly appears as the fluctuation of the image density. The above problem can be prevented by using different developing biases at the time of patch image formation and at the time of normal image formation as disclosed in JP-A-6-274034. Some do so.

[0012]

However, in the above-mentioned conventional example, if the same developing bias is used for forming a patch image for density detection and for forming an ordinary image, the mixing ratio of toner and carrier of the developer is reduced. Fluctuations in image density due to fluctuations are small. Therefore, fluctuations in developer density hardly appear as fluctuations in image density, and fluctuations in developer density become large and unstable, which may cause scattering and fogging.

In order to solve such a problem, it has been proposed to use a different developing bias between the time of forming a patch image and the time of forming a normal image. However, when a patch image is formed on a recording material conveying belt, transfer is not sufficiently performed, and it is not possible to determine a correct patch image density. As a result, there is a problem that the developer density fluctuation becomes large, and scattering or fogging occurs. Had occurred.

Therefore, an object of the present invention is to reduce fluctuations in the developer density, and further stabilize the image density,
An object of the present invention is to provide an image forming apparatus capable of reducing fog.

[0015]

In order to achieve the above object, an image forming apparatus according to the present invention comprises at least one image carrier for carrying a latent image, and a latent image formed on the image carrier. At least one or more developing devices for developing an image using a two-component developer having a toner and a carrier, a recording material carrier for carrying a recording material on which the developed toner image on the image carrier is transferred, and A density detection sensor for detecting the density of a patch image transferred from the image carrier to the recording material carrier, and an image forming apparatus that controls a developer density by an output of the density detection sensor; A developing bias for developing a latent image and a developing bias for developing a latent image other than the patch image are different, and a transfer bias for transferring a developed toner image of the patch image, A transfer bias for transferring the developed toner image other than the patch images are different.

Further, at least one or more image carriers for carrying a latent image, and at least one or more images for developing the latent image formed on the image carrier using a two-component developer having a toner and a carrier. A developing device, an intermediate transfer member to which a developed toner image on the image carrier is transferred, and a density detection sensor for detecting the density of a patch image transferred from the image carrier to the intermediate transfer member. An image forming apparatus that controls the developer concentration based on the output of the concentration detection sensor;
A developing bias for developing a latent image of the patch image and a developing bias for developing a latent image other than the patch image are different, and a transfer bias for transferring a developed toner image of the patch image, The transfer bias for transferring the developed toner image other than the patch image is different.

Further, a transfer bias for transferring the developed toner image of the patch image is a transfer charge output larger than a transfer bias for transferring the developed toner image other than the patch image.

Further, a developing bias for developing the latent image of the patch image has a higher frequency than a developing bias for developing a latent image other than the patch image.

In the developing bias for developing the latent image of the patch image, an alternating electric field is formed intermittently.

As described above, according to the present invention, the developing bias of a patch image formed on a recording material carrier or an intermediate transfer member is different from the developing bias of an image other than a patch image. When an image is formed, the amount of toner can be largely changed with respect to the developer concentration, and when an image other than a patch image is formed, the amount of toner can be not greatly changed with respect to the developer concentration which is a mixing ratio of toner and carrier. Therefore, it is possible to reliably perform the density control and to improve the image quality at the time of image formation.

Further, since the transfer bias of the patch image formed on the recording material carrier or the intermediate transfer member is different from the transfer bias of the image other than the patch image, the developer concentration is stabilized, The occurrence of fogging can be prevented.

[0022]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The materials, shapes, relative arrangements, and the like are not intended to limit the scope of the present invention only to them unless otherwise specified.

In the following drawings, the same members as those described in the above-mentioned drawings are denoted by the same reference numerals.

(First Embodiment) FIG. 1 shows a configuration diagram of an image forming apparatus according to a first embodiment of the present invention. In the present embodiment, the present invention relates to a color laser beam printer (hereinafter simply referred to as “printer”) having a plurality of image forming units.
Call. ), But it should be understood that the invention is not so limited.

According to the present embodiment, the first, second, third, and fourth image forming units Pa,
Although Pb, Pc, and Pd are juxtaposed, the present invention is not limited to this, and the number of image forming units can be arbitrarily selected.

The printer of this embodiment has image forming units Pa, Pb, Pc, and Pd having substantially the same configuration. These image forming units are respectively yellow (Y), magenta (M), and magenta (M). An image forming unit that forms cyan (C) and black (Bk) images.

Each of the image forming units Pa to Pd has a drum-shaped electrophotographic photosensitive member as an image carrier which is a component of the present invention, that is, a photosensitive drum 1a, 1
b, 1c and 1d are supported. Each photosensitive drum 1a-
1d is driven to rotate at a peripheral speed of 100 mm / sec.

Each of the photosensitive drums 1a to 1d, primary chargers 12a, 12b, 12 arranged along the outer peripheral surface thereof.
c and 12d are uniformly charged, and the surfaces thereof are provided with optical systems 16a and 16 including an imaging lens and a laser scanner, respectively.
Each of the photosensitive drums 1a to 1d scans spot laser beams corresponding to image signals b, 16c, and 16d corresponding to color-separated image signals.
The surface is exposed, and an electrostatic latent image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (Bk) is formed on each surface.

The electrostatic latent images of the respective colors formed in this way are used as developing agents as yellow (Y), magenta (M), cyan (C), and cyan as the photosensitive drums 1a to 1d rotate.
Developing devices 13a and 13 as developing devices, each of which is a constituent element of the present invention and accommodates a black (Bk) color toner, respectively.
3b, 13c, and 13d, and reaches a developing region, where the toner is electrostatically attracted and becomes a visible image to form a photosensitive drum 1a.
1d are formed on the respective color toner images.

The printer according to the present embodiment has a cassette 4
The recording material G sent out into the image forming apparatus by the paper feed roller 10 is used as a recording material conveying means at a moving speed equal to the peripheral speed of the photosensitive drum 100 mm / sec. An endless belt circulating at a speed of i.e., a transport belt 2 as a recording material carrier, which is a component of the present invention, passes from the first image forming section Pa to the fourth image forming section Pd, and further to the fixing device 6. It is carried and transported all the way.

The transport belt 2 is a dielectric thin belt (dielectric sheet) driven endlessly by a drive roller 7 in the direction of the arrow, and includes the drive roller 7 and the Andorra rollers 8a and 8b provided near the cassette 4. , And the tension adjusting roller 9.

When the image forming operation is started, the recording material G fed into the image forming apparatus is carried on the transport belt 2 in synchronization with the registration roller pair 11, and the transport belt carrying the recording material G With the movement in the direction of the arrow 2, the image forming units Pa to Pd start forming the respective color toner images on the respective photosensitive drums 1a to 1d at desired timings.

That is, the recording material G is formed by each of the photosensitive drums 1a to 1a.
1d, a blade-shaped transfer charging member as a transfer unit,
That is, the transfer charging blades 14a, 14b, 14c,
14d sequentially pass through the transfer nip that contacts the transfer belt 2 via the transfer belt 2. A transfer bias voltage is applied to the transfer charging blades 14a to 14d from a transfer bias high voltage power supply (not shown), and the toner images of the respective colors on the photosensitive drums 1a to 1d are sequentially transferred onto the same recording material G. Recording material G
On top, a color unfixed toner image is synthesized.

The recording material G carrying the unfixed color image is
After passing through the final fourth image forming portion Pd, the toner image is separated from the conveyor belt 2 and sent to the fixing device 6, and the color unfixed toner image is transferred to the recording material G by heat and pressure in the fixing device 6.
The image is fused and fixed to form a permanent image.

After that, the recording material G is discharged out of the image forming apparatus main body 3 and stored in the external tray 5. Further, each of the photosensitive drums 1a to 1d having completed the transfer of the toner image of each color is
Each of the cleaning devices 15a, 15b, 15c, and 15d having a blade-shaped cleaning unit removes residual toner and the like to prepare for a subsequent image forming operation.

Here, the dielectric sheet material as the conveyor belt 2 includes polyethylene terephthalate, polyacetal, polyamide, polyvinyl alcohol, polyether ketone, polystyrene, polybutylene terephthalate,
Thin films of engineering plastics including polymethylpentene, polypropylene, polyethylene, polyphenylene sulfide, polyurethane, silicone resin, polyamide imide, polycarbonate, polyphenylene oxide, polyether sulfone, polysulfone, aromatic polyester, polyetherimide, aromatic polyimide, etc. Films and belts are generally used.

In the present embodiment, the transport belt 2 includes
An aromatic polyimide was used from the viewpoint of mechanical properties, electrical properties, flame retardancy, and the like, and a seamless type having a volume resistivity of 10 ¹⁷ Ω · m and a thickness of 75 μm was used.

Further, the fourth image forming portion Pd and the fixing device 6
A patch pattern reading sensor (hereinafter simply referred to as a density detection sensor), which is a component of the present invention, for reading a patch pattern for controlling the developer density formed on the conveyance belt 2 is provided above the conveyance belt 2. 3) is disposed.

The sensor 3 reads the patch pattern when a patch pattern is formed on the conveyor belt 2 by a method described later, and performs an arithmetic processing by an arithmetic unit (not shown). The toner is supplied to the developing device as necessary. By doing so, the developer concentration is controlled.

Next, the present invention will be described in more detail by taking the first image forming unit Pa as an example. The other image forming units Pb,
The same applies to Pc and Pd, and a description thereof will be omitted.

In the image forming section Pa, the primary charging device 12a uniformly charges the photosensitive drum 1a and uniformly charges the photosensitive drum 1a to approximately -500V. Next, a portion corresponding to the image portion is exposed by the laser beam, and the surface potential of the portion on the photosensitive drum 1a is reduced to approximately -150 V, thereby forming an electrostatic latent image.

As described above, when the formed electrostatic latent image is moved to the developing position, a developing bias in which an alternating current is superimposed on a direct current is applied to the developing device 13a to be a toner image.

In the normal image formation, the developing device 13
As the developing bias applied to a, an AC waveform in which an alternating electric field is intermittently formed as shown in FIG. 2 was superimposed on a DC component of approximately -300 V. FIG. 2 is a waveform diagram of a developing bias in which an alternating electric field applied to the image forming apparatus shown in FIG. 1 is formed intermittently.

An example of specific numerical values of the waveform shown in FIG. 2 is shown below. Overall frequency 2.66 kHz Rectangular part frequency 8.00 kHz Blank part time 250 μsec peak-to-peak voltage 2 kV

By using this developing bias waveform, it is possible to increase the developing efficiency and to increase the maximum output image density as compared with a continuous developing bias waveform which does not have a blank portion and which is generally used, as will be described later. Becomes
When a two-component developer is used as in the present embodiment,
Even if the concentration of the developer, that is, the mixing ratio between the toner and the carrier (hereinafter, referred to as T / D ratio) changes, the change in the amount of toner to be developed can be suppressed to be small. This will be described with reference to FIG. FIG. 3 is a diagram showing the characteristics of the amount of developing toner with respect to the developing contrast voltage when a waveform for forming an alternating electric field intermittently applied to the image forming apparatus shown in FIG. 1 is used as a developing bias.

FIG. 3 is a plot of development characteristics for each developer having a different T / D ratio when the development contrast voltage is plotted on the horizontal axis and the amount of toner developed on the photosensitive drum is plotted on the vertical axis. is there. As shown in FIG.
Even when the / D ratio was changed to 7%, 8%, and 9%, the amount of toner to be developed hardly changed.

The reason why such development characteristics are exhibited is that not only a toner having a certain specific charge amount is developed, but also
It is considered that the charge amount of the toner and the charge amount per unit mass of the toner (hereinafter referred to as Q / M), which is called tribo, are developed over a relatively wide range.

Therefore, when an attempt is made to transfer a developed toner image having such characteristics, the conventional
Compared with the transfer of a toner image developed with a continuous developing bias waveform without a blank portion, which has been generally used, transfer can be performed with a small transfer charge output value.

For this reason, in the present embodiment, during normal image formation, the transfer charging output is controlled at a constant current, and the output control value is set to approximately 10 μA for each color.

On the other hand, when forming a latent image for a patch image for controlling the developer density, an electrostatic latent image corresponding to the patch image is formed in the same manner as in the normal image formation. However, in developing, a developing bias different from that in the case of performing normal image formation is applied to the developing device 13a to convert a latent image for a patch image into a toner image.

In forming this patch image, the developing device 13
The developing bias applied to a was obtained by superimposing an AC waveform in which a rectangular alternating electric field was formed in a linked manner on a DC component of approximately -300 V.

An example of specific numerical values of this waveform is shown below. Frequency 2.00kHz pp voltage 2kV

When such a continuous developing bias waveform having no blank portion is used, the concentration of the developer, that is, the toner and carrier, is compared with the case where the developing bias waveform having the blank portion is used. The variation in the amount of toner to be developed when the mixing ratio varies varies.

This will be described with reference to FIG. FIG.
Is a developer applied to the image forming apparatus shown in FIG. 1, in which the horizontal axis represents the development contrast voltage and the vertical axis represents the amount of toner developed on the photosensitive drum, and the T / D ratios are different. FIG. 9 is a diagram plotting development characteristics for each case, and is a diagram illustrating characteristics of a development toner amount with respect to a development contrast voltage when a rectangular wave (2 KHz, 2 KVpp) is used as a development bias.

As shown in FIG. 4, it can be seen that when the T / D ratio of the developer is changed to 7%, 8%, and 9%, the amount of toner developed greatly changes. Thus, T
The change in the T / D ratio can be accurately detected by a large change in the amount of toner to be developed with respect to the change in the / D ratio.

However, when trying to transfer the toner developed with the developing bias having such a waveform, as described above,
A transfer current having a larger value is required as compared with the case of transferring toner developed with a developing bias having a waveform having a blank portion. Therefore, in the present embodiment, the transfer charge output control value at the time of forming a patch image is set to 14 μA.
And

As described above, according to the present embodiment, as described above, during the image formation, the developing bias is used in which the amount of toner to be developed does not largely change with respect to the change in the T / D ratio of the developer. By adopting a transfer bias adapted to use the developing bias that greatly changes the amount of toner to be developed with respect to a change in the T / D ratio of the developer at the time of forming a patch image, and employing a transfer bias adapted to the developing characteristics, It has become possible to stabilize the developer density and always keep the output image density stable without causing scattering or fogging.

(Second Embodiment) Next, an image forming apparatus according to a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a configuration diagram of a second embodiment of the image forming apparatus according to the present invention.

The printer of this embodiment has image forming units Pa, Pb, Pc and Pd having substantially the same configuration as the printer shown in the first embodiment, and these image forming units are Are image forming units for forming yellow (Y), magenta (M), cyan (C), and black (Bk) images, respectively.

In each of the image forming units Pa to Pd, a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 101, which is a component of the present invention, is driven to rotate in the direction of the arrow.
a, 101b, 101c, and 101d are supported.

Each of the photosensitive drums 101a to 101d is driven to rotate at a peripheral speed of 100 mm / sec. Each photosensitive drum 10
1a to 101d, primary chargers 112a, 112b, 112c, 112d arranged along respective outer peripheral surfaces are uniformly charged, and the surfaces thereof have optical systems 116a, 116b, including an imaging lens and a laser scanner, respectively. 11
6c and 116d scan spot laser beams corresponding to the color-separated image signals to scan each of the photosensitive drums 101a to 101d.
1d surface is exposed, and yellow (Y),
An electrostatic latent image corresponding to each color of magenta (M), cyan (C), and black (Bk) is formed.

The electrostatic latent images of the respective colors formed in this way are rotated by the rotation of the photosensitive drums 101a to 101d.
Developing devices 113a, 113b, 113c, 113 that respectively store yellow (Y), magenta (M), cyan (C), and black (Bk) toners as developers.
The photosensitive drums 101a to 101d form a color toner image on each of the photosensitive drums 101a to 101d.

Reference numeral 102 denotes an endless belt (intermediate transfer belt) as an intermediate transfer member which is a component of the present invention. The intermediate transfer belt 102 is provided below the image forming units Pa, Pb, Pc, and Pd under the photosensitive drums 101a, 101b, and 101 of the image forming units.
c, 101d, the drive roller 10
7, the secondary transfer facing roller 108 and the driven roller 109
The photosensitive drums 101a, 101b, 101c, and 101d are rotationally driven in the clockwise direction of the arrow at the same peripheral speed as the photosensitive drums 101a, 101b, 101c, and 101d.

114a, 114b, 114c, 114d
Are the first members disposed inside the intermediate transfer belt 102, respectively.
To the fourth four primary transfer rollers. The first primary transfer roller 114a is an image forming unit Pa for yellow.
The intermediate transfer belt 102 is provided on the lower surface of the photosensitive drum 101a.
Contacting the ascending side belt portion of the primary transfer portion 112
a. The second primary transfer roller 114b is a photosensitive drum 101b of the image forming unit Pb for magenta.
A primary transfer portion 121b is formed by abutting the lower surface of the intermediate transfer body belt 102 with the ascending belt portion therebetween.

The third primary transfer roller 114c contacts the lower surface of the photosensitive drum 101c of the cyan image forming unit Pc with the ascending side belt portion of the intermediate transfer belt 102 interposed therebetween to form a primary transfer portion 121c. .

The fourth primary transfer roller 114d contacts the lower surface of the photosensitive drum 101d of the black image forming unit Pd with the ascending belt portion of the intermediate transfer belt 102 interposed therebetween to form a primary transfer portion 121d. .

Each primary transfer roller 114a, 114b, 1
A transfer bias having a polarity opposite to that of the toner is applied from a transfer bias power supply (not shown) to the photosensitive drums 101a, 101b, 101c, and 1c.
The toner images on the 01d side are transferred to the primary transfer units 121a and 121
b, 121c and 121d, the intermediate transfer belt 10
2 is electrostatically transferred to the ascending side belt surface.

In the case of this embodiment, first, a yellow image is transferred from the surface of the photosensitive drum 101a to the ascending belt surface of the intermediate transfer belt 102 in the primary transfer section 121a of the image forming unit Pa for yellow. Next, the magenta image, the cyan image, and the black image are transferred in a similar manner so as to overlap the ascending belt surface of the intermediate transfer belt 102, and a full-color image is synthesized and formed.

The above-described image forming units Pa, Pb, and P for yellow, magenta, cyan, and black, respectively.
In c and Pd, the developing devices 113a, 113b, 113c, and 1 as the developing components, respectively, of the present invention.
13d denotes photosensitive drums 101a, 101b, 101c,
The photosensitive drums 101a, 101b, 101c, 1 after transferring the image from the surface 101d to the surface of the intermediate transfer belt 102
The image forming units Pa, Pb, Pc, and Pd are each provided with a photosensitive drum cleaning device as a dedicated device, which also serves as a cleaning unit (simultaneous development cleaning) for removing transfer residual toner remaining on the 01d surface. Not (cleanerless system).

The surface of the intermediate transfer belt 102 on which the full-color image has been formed as described above is formed by the secondary transfer opposing roller 108 and the secondary transfer roller 117 by the subsequent rotation of the intermediate transfer belt 102. Transfer unit 1
It reaches 18. The secondary transfer roller 117 abuts on the secondary transfer opposing roller 108 with the intermediate transfer member belt 102 interposed therebetween.
A next transfer portion 118 is formed, and a transfer bias having a polarity opposite to that of the toner is applied from a transfer bias power supply (not shown).

Reference numeral 104 denotes a paper feed cassette; and 110, a paper feed roller for feeding out a recording material (transfer material) G from the paper feed cassette 104. From the paper feed roller 110 to the fixing unit 1
The member that conveys the recording material G up to 06 may be a recording material carrier that is a component of the present invention.

Reference numeral 111 denotes a pair of registration rollers, which transfer the recording material G fed from the paper feed cassette 104 to the secondary transfer unit 1.
18 at a predetermined timing.

That is, when the leading end of the full-color image formed on the surface of the intermediate transfer belt 102 reaches the secondary transfer unit 118 due to the rotation of the intermediate transfer belt 102,
The recording material G is fed, and a full-color image on the intermediate transfer belt 102 surface side is collectively transferred to the fed recording material G in the secondary transfer unit 118.

The recording material G that has exited the secondary transfer section 118 is separated from the surface of the intermediate transfer belt 102 and is fixed to the fixing unit 10.
6 is subjected to heat fixing of the image introduced therein, and is discharged to a tray 105 outside the apparatus as an image formed product.

Also, at the time of the secondary transfer, the intermediate transfer belt 10
The transfer residual toner remaining on the two surfaces is removed from the surface of the intermediate transfer belt 102 by the intermediate transfer belt cleaner 119.

Here, the material of the intermediate transfer belt 102 is polyethylene terephthalate, polyacetal, polyamide, polyvinyl alcohol, polyether ketone, polystyrene, polybutylene terephthalate,
Thin films of engineering plastics including polymethylpentene, polypropylene, polyethylene, polyphenylene sulfide, polyurethane, silicone resin, polyamide imide, polycarbonate, polyphenylene oxide, polyether sulfone, polysulfone, aromatic polyester, polyetherimide, aromatic polyimide, etc. Films and belts are generally used.

In this embodiment, the intermediate transfer belt 10
2 is made of aromatic polyimide from the viewpoint of mechanical properties, electrical properties, flame retardancy, etc., and has a volume resistivity of 10 ¹⁴ Ω ·
m, a seamless type having a thickness of 75 μm was used.

Also, above the intermediate transfer belt 102 between the fourth image forming portion Pd and the driving roller 107, a patch pattern for controlling the developer density formed on the intermediate transfer belt 102 is read. A patch pattern reading sensor 103 as a density detection sensor, which is a component of the present invention, is disposed.

When a patch pattern is formed on the intermediate transfer belt 102 by the same method as that described in the first embodiment, the sensor 103 reads this patch pattern, and performs arithmetic processing by an arithmetic unit (not shown). The developer concentration is controlled by supplying toner to the developing device as necessary.

Next, the present invention will be described in more detail by taking the first image forming portion Pa as an example. The other image forming units Pb,
The same applies to Pc and Pd, and a description thereof will be omitted.

In the image forming section Pa, the photosensitive drum 101
is uniformly charged by the primary charger 112a, and the photosensitive drum 101a is uniformly charged to approximately -500V.
Next, the portion corresponding to the image portion is exposed by the laser beam, and the surface potential of the portion on the photosensitive drum 1a becomes approximately -1.
The voltage drops to 50 V, and an electrostatic latent image is formed.

When the formed electrostatic latent image is moved to the developing position as described above, a developing bias in which alternating current is superimposed on direct current is applied to the developing device 113a, and is converted into a toner image.

In the normal image formation, the developing device 11
As the developing bias applied to 3a, a developing bias in which an alternating waveform in which an alternating electric field is intermittently formed as shown in FIG.

An example of specific numerical values of this waveform is shown below. Overall frequency 2.66 kHz Rectangular part frequency 8.00 kHz Blank part time 250 μsec peak-to-peak voltage 2 kV

Using this developing bias waveform, the first
As in the first embodiment, the developing efficiency is increased as compared with a continuous developing bias waveform having no blank portion, and the maximum output image density can be increased.

Further, when a two-component developer is used as in the present embodiment, development is performed even if the concentration of the developer, that is, the mixture ratio of toner and carrier (hereinafter referred to as T / D ratio) changes. Fluctuations in the amount of toner can be kept small. This situation is
Since this is the same as that described in the first embodiment with reference to FIG. 3, detailed description is omitted in this embodiment.

Also in the present embodiment, when an attempt is made to transfer a developed toner image having such characteristics onto an intermediate transfer member, the toner image developed with a continuous developing bias waveform without a blank portion is used. Can be transferred with a smaller transfer charging output value than in the case of transferring For this reason, in the present embodiment, during normal image formation, the transfer charging output is controlled at a constant voltage, and the output control value is set to approximately 20 for each color.
0 V was applied.

On the other hand, when a latent image for a patch image for controlling the developer density is formed, an electrostatic latent image corresponding to the patch image is formed in the same manner as in the normal image formation. However, in developing, a developing bias different from that in the case of performing normal image formation is applied to the developing device 13a to convert a latent image for a patch image into a toner image.

In forming this patch image, the developing device 11
As the developing bias applied to 3a, a developing bias obtained by superimposing an AC waveform in which a rectangular alternating electric field is connected to a DC component of approximately -300 V was used.

An example of specific numerical values of this waveform is shown below. Frequency 2.00kHz pp voltage 2kV

When such a continuous developing bias waveform having no blank portion is used, compared with the case of using the developing bias waveform having the blank portion as in the first embodiment, the development is performed. When the concentration of the agent, that is, the mixing ratio of the toner and the carrier (hereinafter, referred to as T / D ratio) changes, the amount of toner to be developed greatly fluctuates.

As described above, since the amount of toner to be developed greatly changes in response to the change in the T / D ratio, the change in the T / D ratio can be accurately detected as in the first embodiment. It becomes possible.

However, when trying to transfer the toner developed with the developing bias having such a waveform, as described above,
A transfer electric field having a larger value is required as compared with the case where toner developed with a developing bias having a waveform having a blank portion is transferred. Therefore, in the present embodiment, the transfer charge output control value at the time of forming a patch image is set to about 300.
V.

As described above, according to the present embodiment, as described above, at the time of image formation, a developing bias is used in which the amount of toner to be developed does not greatly change with respect to a change in the T / D ratio of the developer. By using a transfer bias that adopts a transfer bias that is adapted to greatly change the amount of toner to be developed with respect to a change in the T / D ratio of the developer when forming a patch image, and adopting a transfer bias that is adapted to this development characteristic, Also in an image forming apparatus using a transfer member, it is possible to stabilize the developer density and to keep the output image density constantly stable without causing scattering or fogging.

[0095]

As described above, in the image forming apparatus according to the present invention, the developing bias for forming the patch image for controlling the developer density and the developing bias for forming the normal image are different from each other. A configuration in which a developing bias for forming a patch image for controlling a developer concentration is a developing bias having a higher frequency than a developing bias for forming an ordinary image or a developing bias in which an alternating electric field is intermittently formed is used. By selecting a transfer bias in accordance with these different developing biases, it is possible to reduce fluctuations in the developer concentration and reduce scattering, fogging and the like.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a waveform diagram of a developing bias applied to the image forming apparatus shown in FIG. 1 in which an alternating electric field is intermittently formed.

FIG. 3 is a diagram showing a characteristic of a developing toner amount with respect to a developing contrast voltage when a waveform for forming an alternating electric field intermittently is used as a developing bias, which is applied to the image forming apparatus shown in FIG.

FIG. 4 is a diagram showing characteristics of a developing toner amount with respect to a developing contrast voltage when a rectangular wave (2 KHz, 2 KVpp) is used as a developing bias, which is applied to the image forming apparatus shown in FIG.

FIG. 5 is a configuration diagram of a second embodiment of the image forming apparatus according to the present invention.

FIG. 6 is a partial configuration diagram of a conventional image forming apparatus.

[Explanation of symbols]

1a, 1b, 1c, 1d Photosensitive drum 2 Conveyor belt 3 Patch pattern reading sensor 13a, 13b, 13c, 13d Developing device 14a, 14b, 14c, 14d Transfer charging member 101a, 101b, 101c, 101d Photosensitive drum 102 Intermediate transfer belt 103 patch pattern reading sensor 113a, 113b, 113c, 113d developing unit 114a, 114b, 114c, 114d transfer charging member 201a, 201b, 201c, 201d photosensitive drum 202 transport belt 203 patch pattern reading sensor 213a, 213b, 213c, 213d developing unit 214a, 214b, 214c, 214d Transfer charging member

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/14 G03G 21/00 372 F term (Reference) 2H027 DA09 DE07 EA06 EC03 EC06 ED09 ED24 EE02 FA28 2H030 AB02 BB23 BB34 BB36 BB42 BB44 BB54 BB63 2H032 AA05 AA15 BA09 BA18 CA02 CA12 CA15 2H073 BA04 BA06 BA09 BA13 BA28 CA03 CA22 2H077 AD06 AD36 AE06 DA04 DA05 DA47 DA49 DA63 DB03 DB08 DB14 DB15 EA01

Claims (5)

[Claims] At least one or more image bearing members carrying a latent image, and at least one or more of a latent image formed on the image bearing member are developed using a two-component developer having a toner and a carrier. A developing device; a recording material carrier for carrying a recording material onto which the developed toner image on the image carrier is transferred; and detecting a density of a patch image transferred from the image carrier to the recording material carrier. An image forming apparatus comprising: a density detection sensor; and controlling a developer density based on an output of the density detection sensor. And a transfer bias for transferring a developed toner image of the patch image and a transfer bias for transferring a developed toner image other than the patch image are different. Image forming apparatus. 2. A method for developing a latent image formed on at least one image carrier using a two-component developer having a toner and a carrier. A developing device; an intermediate transfer member onto which the developed toner image on the image carrier is transferred; and a density detection sensor for detecting the density of a patch image transferred from the image carrier to the intermediate transfer member. An image forming apparatus for controlling a developer density by an output of the density detection sensor, wherein a developing bias for developing a latent image of the patch image and a developing bias for developing a latent image other than the patch image are different. And an image forming apparatus having a different transfer bias for transferring a developed toner image of the patch image and a different transfer bias for transferring a developed toner image other than the patch image. 3. The image forming apparatus according to claim 1, wherein a transfer bias for transferring the developed toner image of the patch image is larger than a transfer bias for transferring a developed toner image other than the patch image. The image forming apparatus as described in the above. 4. A developing bias for developing a latent image of the patch image has a higher frequency than a developing bias for developing a latent image other than the patch image.
The image forming apparatus according to claim 1. 5. The image forming apparatus according to claim 1, wherein an alternating electric field is intermittently formed in a developing bias for developing the latent image of the patch image.