JPH09297476A - Image forming device and method for controlling transfer device incorporated therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which provides a proper transfer bias in a transfer device of a constant-current bias system. SOLUTION: In the image forming device 2, the transfer bias supplied to a transfer roller 16 by a transfer bias generation circuit 108 is a constant-current transfer bias from a constant-current transformer 108a, under environmental conditions in which temperature is lower than 25 deg.C and humidity is lower than 75%. Under environmental conditions in which temperature is higher than 25 deg.C and humidity is higher than 75%, on the other hand, the transfer bias supplied to the transfer roller 16 is switched to a fixed transfer bias voltage of approximately 1kV which is outputted from a constant-voltage transformer 108b connected to the constant-current transformer in series. This prevents a change in transfer-image density with the environmental conditions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus including a contact type transfer device, which can provide a stable image regardless of the characteristics of the transfer medium represented by the material, thickness and size. The present invention relates to an apparatus and a control method of a transfer apparatus incorporated in the image forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic process, a photoconductive photoconductor is charged to a predetermined potential, and then light corresponding to an image is irradiated to selectively attenuate the potential. An electrostatic latent image is formed by the above process, and the toner image obtained by developing the electrostatic latent image with a toner as a developer is transferred to a transfer target material to form a copy image of an object to be copied or an image to be printed. Form. Around the photoconductor, a charging device for applying a predetermined surface potential to the photoconductor, a developing device for developing an electrostatic image on the photoconductor surface with toner to form a toner image, and a toner image on the photoconductor as a recording material A transfer device for transferring, a cleaning device for cleaning the toner on the surface of the photoconductor and returning the charge distribution to an initial state, and the like are arranged in order along the direction in which the photoconductor is rotated. Also,
An exposure device that forms an electrostatic image by exposing an image on a photoconductor between a developing device and a charging device at a predetermined position inside the device,
Further, a fixing device and the like for fixing the toner image developed by the transfer device onto the sheet are arranged.

A photoreceptor is provided on a rotatable cylindrical or endless belt-shaped conductor such as aluminum.
For example, selenium (Se) or OPC (Organic-Ph
An optical semiconductor in which a photoconductive substance such as an otoConductor (an organic photoreceptor) is formed to a predetermined thickness. The photoconductor functions as a conductor only in the area where the light is irradiated by irradiating the light corresponding to the image from the exposure device in a state of being charged to a predetermined potential, and generates a charge distribution. Retain the corresponding latent image.

[0004] The charging device has a charging wire for corona discharge, and is connected to a charging device via a power supply device connected to the charging wire.
By applying a voltage of ８8 kilovolts, a surface potential of, for example, −600 volts is applied to the photoconductor surface.

The exposure device converts from image data stored in advance in the image memory or an image of an original at a position upstream of a developing position in which the photosensitive member is rotated to face the developing device and in which the photosensitive member is rotated. Light for generating a potential distribution on the surface of the photoconductor is irradiated on the basis of the image data thus obtained, and an electrostatic image is formed on the surface of the photoconductor.

The developing device is opposed to the photoconductor at a developing position on the surface of the photoconductor, and forms a developer on the photoconductor, the developer including the toner and a carrier for frictionally charging the toner to a predetermined polarity and forming a magnetic brush. The electrostatic image is supplied to the electrostatic image, and only the toner is attached to the electrostatic image to form a toner image. As the developing device, one-component development using only toner or two-component development including toner and carrier (magnetic material) is widely used.

The transfer device includes a corona discharge device similar to a charging device or a metal roller formed so as to be capable of supplying a predetermined transfer bias voltage to the photoconductor, and is supplied to the electrostatic image on the photoconductor by the developing device. The toner, that is, the toner image formed on the photoreceptor is transferred to the recording material supplied as the photoreceptor rotates.

The fixing device is a pair of rollers each having a heater incorporated therein. The fixing device electrostatically adheres to the recording material by heating the paper and the toner while applying a predetermined pressure between the rollers. The toner present is melted and fixed on the recording material.

The cleaning device has a discharge lamp for irradiating the entire surface of the photoconductor with light and a cleaner for scraping off the untransferred toner remaining on the surface of the photoconductor, and erases the residual charge on the photoconductor and the next image. Stabilizes the surface condition of the photoconductor for the forming operation.

In the above-mentioned image forming apparatus, the light corresponding to the image data is emitted from the exposure device while the photoconductor is charged by the charging device at a predetermined surface potential, so that the electrostatic charge corresponding to the image data is generated. An image is formed on the photosensitive drum.

The electrostatic image formed on the photoreceptor is developed with toner from the developing device and converted into a toner image. This toner image is applied to the recording material electrostatically adsorbed on the photoconductor by a transfer device applying a transfer bias voltage having the same polarity as the surface potential provided to the photoconductor from the back surface of the recording material. , Transcribed.

As a transfer device, a transfer charger system is generally used, in which a high voltage is applied to a charging wire for corona discharge to electrostatically attract toner from a photoconductor by corona discharge, as in the charging device. Is widely used. However, when the polarity of the charged potential (surface potential) of the photoconductor is negative and the polarity of the toner is positive, a negative transfer bias voltage is applied to the transfer charger.
There is a problem that ozone is generated.

Therefore, in recent years, a contact transfer device has been proposed in which a transfer roller or a conductive brush formed in a roller shape is brought into contact with the photosensitive member from the back surface of the recording material at a predetermined pressure. It is known that the contact transfer device can reduce the amount of ozone generated by negative corona discharge and can improve transfer efficiency as compared with transfer by corona discharge. When the transfer efficiency is improved, the sizes of the transfer device and the image forming device can be reduced.

[0014]

In the contact transfer apparatus as described above, there are a constant voltage bias method for setting a voltage to a predetermined value and a constant current bias method for setting a transfer bias current to a predetermined value. It has been known.

However, in the constant voltage bias method,
For example, there is a problem that the appropriate transfer bias voltage changes due to the change in the thickness of the recording material such as copy paper and OHP sheet. Further, since the proper transfer bias voltage changes as the environmental conditions change, it is necessary to constantly observe and adjust the thickness of the recording medium and the environmental conditions in order to always obtain a proper transfer state. Here, observing the thickness of the recording medium and the environmental conditions at all times increases the cost of the apparatus because many sensors are required to observe the thickness and the environmental conditions. Therefore, in many image forming apparatuses using the constant voltage bias method,
There is a problem that a proper transfer state cannot always be obtained in some thicknesses of recording materials and environmental conditions.

On the other hand, in the constant current bias method in which the transfer bias current is set to a predetermined value, compared to the constant voltage bias method, the transfer efficiency does not fluctuate depending on the environmental conditions, but the specific condition, For example, it is difficult to obtain a proper transfer efficiency when the resistance value of the paper is reduced in an environment such as high temperature and high humidity. An object of the present invention is to provide an image forming apparatus capable of providing a proper transfer bias in a transfer apparatus using a constant current bias method.

[0017]

The present invention has been made on the basis of the above-mentioned problems. It is a developing means for developing an image formed on an image carrier, and the developing means forms the image on the image carrier. And a transfer unit for transferring the developer image to the transfer medium by either of a constant current transfer bias and a constant voltage transfer bias according to a change in resistance value of the transfer medium. It is provided.

Further, according to the present invention, the developing means for developing the image formed on the image carrier and the developer image formed on the image carrier by the developing means are subjected to a constant current transfer bias according to environmental conditions. And a transfer means for transferring to a transfer medium by either of a constant voltage transfer bias and an image forming apparatus.

Further, according to the present invention, the developing means for developing the image formed on the image bearing member and the developer image formed on the image bearing member by the developing means are exposed to the temperature and humidity fluctuations. An image forming apparatus comprising: a transfer unit that switches from a constant current transfer bias to a constant voltage transfer bias and transfers the transfer target medium when the resistance value of the transfer medium falls below a predetermined value. is there. Still further, the present invention includes a developing means for developing an image formed on an image carrier, a transfer bias voltage supplying means capable of outputting a constant voltage and a transfer bias current supplying means capable of outputting a constant current, and And the humidity is higher than a predetermined condition and the humidity is higher than the predetermined condition, the transfer voltage due to the constant current from the transfer bias current supply means and the resistance value of the transfer medium that fluctuates according to the fluctuation of the temperature and the humidity is lower than the predetermined value. In this case, there is provided an image forming apparatus comprising: a transfer unit that transfers the developer image formed on the image carrier to the transfer medium by the constant voltage transfer bias voltage from the transfer bias voltage supply unit. To do.

Further, according to the present invention, a developing means for developing an image formed on an image carrier, a transfer bias current supplying means capable of outputting a constant current, and a constant connecting in series with the transfer bias current supplying means. A transfer bias voltage supply means capable of outputting a voltage, and the temperature and humidity fluctuate according to the constant current from the transfer bias current supply means and the temperature and humidity fluctuations under environmental conditions of higher temperature and higher humidity than predetermined conditions. When the transfer voltage due to the resistance value of the transfer medium is lower than a predetermined value, the developer image formed on the image carrier is transferred to the transfer medium by the constant voltage transfer bias voltage from the transfer bias voltage supply means. The present invention provides an image forming apparatus including a transfer unit.

Still further, according to the present invention, a developing means for developing the image formed on the image carrier, and a transfer means for transferring the developer image formed on the image carrier by the developing means to a transfer medium. And an image forming apparatus comprising: a transfer bias supply unit for supplying either a constant current transfer bias or a constant voltage transfer bias to the transfer unit according to temperature and humidity fluctuations. It is a thing.

Furthermore, the present invention further comprises a developing means for developing the image formed on the image carrier, and a transfer means for transferring the developer image formed on the image carrier by the developing means to a transfer medium. And a transfer bias voltage supply unit capable of outputting a constant voltage and a transfer bias current supply unit capable of outputting a constant current, the transfer bias current supply unit under environmental conditions where temperature and humidity are higher and higher than predetermined conditions. When the transfer voltage due to the resistance value of the medium to be transferred which fluctuates according to the fluctuation of the constant current and the temperature and the humidity from the predetermined value is lower than a predetermined value, the transfer means transfers the constant voltage transfer bias from the transfer bias voltage supply unit. An image forming apparatus comprising: a transfer bias supply unit for supplying a voltage.

Further, according to the present invention, a developing means for developing the image formed on the image carrier, and a transfer means for transferring the developer image formed on the image carrier by the developing means to a transfer medium. And a transfer bias current supply unit capable of outputting a constant current and a transfer bias voltage supply unit connected in series with the transfer bias current supply unit and capable of outputting a constant voltage, the temperature and humidity being higher than a predetermined condition. And when the transfer voltage due to the constant current from the transfer bias current supply unit and the resistance value of the transfer target medium that has changed in accordance with changes in temperature and humidity under a humid environment condition is lower than a predetermined value, An image forming apparatus comprising: a transfer bias supply unit that supplies a constant voltage transfer bias voltage from the transfer bias voltage supply unit.

Furthermore, the present invention is set in accordance with the resistance value of the transfer target when transferring the developer image, in which the developer is supplied to the image formed on the image bearing member, to the transfer target. First
And the second transfer bias set according to the environmental conditions are applied at the same time, and the effective output of the first transfer bias is decreased by decreasing the resistance value of the transfer target by the environmental conditions. The present invention provides a control method for a transfer device, which is characterized in that compensation is performed by a second transfer bias.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the laser exposure type copying apparatus 2 generally includes a photosensitive drum 10 on which an electrostatic latent image corresponding to an image to be recorded is formed by a laser beam supplied from a laser exposure apparatus described later. It has in the center.

Around the photoconductor drum 10, a charging device 12 for charging the surface of the photoconductor drum 10 to a predetermined potential along the rotation direction of the photoconductor drum 10 indicated by an arrow a.
A developing device 14 that develops an electrostatic latent image by supplying toner as a developer to a latent image formed on the photosensitive drum 10 by a laser exposure device described below, and on the photosensitive drum 10 developed by the developing device 14 Transfer device 16 for transferring the toner image on paper as a recording medium, and photosensitive drum 10
Cleaning device 18 for scraping off untransferred toner remaining on the surface of the photoreceptor drum 1
The static eliminators 20 for removing the residual charges on the surface of the zero are arranged in order.

The charging device 12 includes a corona wire 12a and a grid screen 12b, is connected to a charging voltage generating circuit 102 and a grid bias voltage generating circuit 104 which will be described later with reference to FIG. Charged to the electric potential of.

The developing device 14 holds the two-component developer in which the non-magnetic toner and the carrier to which the magnetism is applied in a predetermined ratio are held on the outer periphery, and will be described later with reference to FIG. The toner negatively charged by the developing bias voltage from the developing bias generating circuit 106 is applied to the photosensitive drum 10.
And a developing roller 14a that adheres to the electrostatic latent image formed in the image forming apparatus. The two-component developer D and the developing roller 1
4a is accommodated in the housing 14b.

Developing roller 14a and housing 14b
The developing bias voltage generating circuit 106 causes the carrier C and the toner T, that is, the developer D stored in
A predetermined developing bias voltage is applied.

Hereinafter, when developing the electrostatic latent image formed on the surface of the photosensitive drum 10, a carrier formed on the sleeve along the magnetic lines of force generated from the main magnetic pole of the magnet medium of the developing roller 14a. In the developing area where the toner adhered by the image force to the ears (ears) of the photoconductor drum 10 and the developing roller 14a face each other,
The electrostatic latent image is moved toward the latent image by an electric field formed by the potential of the electrostatic latent image of 0 and the developing bias voltage, and the electrostatic latent image is developed.

The transfer device 16 is formed in the shape of a roller that rotates in contact with the outer peripheral surface of the photosensitive drum 10. The transfer bias generation circuit 108 described later with reference to FIG. The toner image on the surface of the photoconductor drum 10 supplied with the toner and developed is electrostatically attracted to the recording sheet and transferred. The transfer roller 16 is formed by forming an ion conductive elastic body having a predetermined resistance value into a roller shape as described later with reference to FIG. The transfer roller 16 is pressed against the surface of the photosensitive drum 10 with a predetermined pressure by a spring or the like (not shown).

The cleaning device 18 includes the photosensitive drum 1
It has a blade 18a that is pressed against the surface of the photosensitive drum 10 to scrape off the transferred toner on the surface of the photosensitive drum 10, and scrapes off and accumulates the untransferred toner on the surface of the photosensitive drum 10.

The static eliminator 20 is turned on so as to provide a predetermined amount of light through a lamp regulator (lighting circuit) (not shown), and erases the residual potential remaining on the surface of the photosensitive drum 10.

An image reading unit 30 for reading an image of a document D, which is an object to be copied, as light and dark information of light is arranged above the photosensitive drum 10, that is, above the main body of the apparatus. The image reading unit 30 includes a document table 31 for holding the document D, an illumination lamp 32 for illuminating the document D placed on the document table 31, and a reflector 33 for condensing illumination light emitted from the illumination lamp 32 onto the document D. A first mirror 34 for guiding the reflected light from the document D in a direction parallel to the document table, a second mirror 35 for bending the light reflected by the first mirror 34 by 90 °, and a second mirror 35 for bending the light. A third mirror 36 and the like for bending the applied light further by 90 ° and guiding it again in a direction parallel to the original table are provided. The illumination lamp 32 and the first
By moving the third to third mirrors 34, 35 and 36 along the original table 31, the original table 31 is moved.
Is transmitted to the CCD sensor 38 at the subsequent stage as light / dark information of light. As is well known, the second mirror 35 and the third mirror 36 are driven by a driving mechanism (not shown) at a half of the moving speed of the first mirror 34.
Driven by the first mirror 34 at the speed of

Within the plane including the optical axis of the light reflected by the third mirror 36, an image forming lens 37 for converging the reflected light from the document D and the reflected light converged by the image forming lens 37 are photoelectrically converted. A CCD sensor 38 for conversion is arranged.

At a position near the photoconductor drum 10 where light corresponding to the original image can be irradiated on the surface of the photoconductor drum 10, the photoconductor drum 10 to which a predetermined surface potential is applied by the charging device 12 is provided. Laser exposure device 4 for irradiating the surface of the substrate with a laser beam whose light intensity is changed based on an image
0 is arranged.

At a position corresponding to the upstream side in the direction in which the photosensitive drum 10 is rotated and the toner image developed by the developing device 14 is conveyed by the rotation of the photosensitive drum 10, a predetermined size is set. Of the recording paper (transferred material) and a paper cassette 52 having a size display mechanism (not shown) for displaying the size of the recording paper stored therein are inserted. Two slots 50a and 50b are formed. 1st, 2nd
In the slots 50a and 50b, the size of the recording paper accommodated in the cassette 52 # is set based on a size display (not shown) set corresponding to the size of the paper accommodated in the cassette 52 #. Size detection sensors 51a and 51b for notifying the CPU 102 of the size are provided.

Above the first slot 50a,
By-pass passage 53 that enables the feeding of recording materials other than the standard type
It is formed integrally with the first slot 50a. In the manual passage 53, a paper guide 53a for preventing the paper guided in the passage from being inclined with respect to the direction in which the paper is transported is arranged. The paper guide 53a is the size of the paper.
(Width), and a paper sensor 53b that detects the size (width) of the paper inserted into the manual passage 53 by detecting the position of the paper guide 53a. Are formed so that they can be input.

Photoreceptor drum 10 and each slot 50a, 5
0b, the cassettes 52 # are arranged corresponding to the respective slots 50a, 50b and inserted into the slots.
Paper feed roller 5 that pulls out one sheet of paper from each of ‥‥
4a, 54b, papers drawn by the paper feed rollers 54a, 54b, are conveyed to the photoconductor drum 10, and are conveyed by the conveyance rollers 56a, 56b and the conveyance rollers 56a, 56b. By stopping the sheet, the inclination of the sheet with respect to the conveying direction is corrected, and the speed at which the surface of the photosensitive drum 10 is moved by aligning the leading edge of the toner image on the photosensitive drum 10 with the leading edge of the sheet. An aligning roller 58 that delivers the paper at the same speed is arranged. The sheet supplied from the manual passage 53 is guided toward the transport roller 56a.

In the vicinity of the aligning roller 58, in order to stop the sheet through the aligning roller 58,
An aligning switch 58a for detecting the leading edge of the sheet being conveyed is provided.

A toner image formed on the photosensitive drum 10 is transferred to a position corresponding to the downstream side of the photosensitive drum 10 in the rotational direction, and the sheet is conveyed in a state where the toner is electrostatically attached. The belt 60, the fixing device 62 that heats the toner transferred onto the paper and presses it onto the paper, and the paper ejection roller that ejects the paper on which the toner image is fixed to the paper ejection tray outside the copying apparatus 2. 64
Is arranged.

The fixing device 62 is provided near the paper discharge roller 64.
A paper discharge switch 64a for detecting whether or not a paper exists between the paper and the paper discharge roller 64 is arranged. When the rear end of the paper is detected by the paper discharge switch, the paper currently being conveyed. It is detected that the image formation for is completed.

FIG. 2 is a block diagram showing a schematic control block centered on the image forming section of the image forming apparatus shown in FIG. As shown in FIG. 2, each mechanical unit of the laser exposure type copying apparatus 2 has a CPU 100 which is a main controller.
Controlled by.

The corona discharge member 12a of the charging device 12 is
When a high voltage is applied, a predetermined charge is given to the surface of the photoconductor drum 10. This high voltage is
It is the output of the high voltage generation circuit 102 corresponding to the charging voltage control signal input from 0 to the high voltage generation circuit 102. Further, the grid electrode 12b of the charging device 12 stabilizes the electric charge provided from the corona discharge member 12a on the surface of the photoconductor drum 10 by being supplied with the bias voltage. This bias voltage is the output of the bias voltage generation circuit 104 corresponding to the bias voltage signal instructed by the CPU 100 to the bias voltage generation circuit 104. In this way, the surface of the photosensitive drum 10 is charged to the desired potential.

The developing roller 14 of the developing device 14 carries a two-component developer contained in the housing 14b, that is, a toner and a carrier mixed in a predetermined ratio. A predetermined developing bias voltage is applied to the developing roller 14a from the developing bias voltage generating circuit 106 under the control of the CPU 100. This developing bias voltage prevents toner from adhering to the image portion on the surface of the photoconductor drum 10 and toner from adhering to the non-image portion, that is, the area where the image information is not exposed by the exposure device 40, thereby causing white background fog. To be done.

The transfer roller 16 is supplied with a transfer bias current of a predetermined magnitude, and transfers the developer image, that is, the toner image formed on the photosensitive drum 10 onto the paper.
This transfer bias current is transferred to the transfer bias generation circuit 108.
Output from The transfer bias current is output only when the recording sheet is passing between the photoconductor drum 10 and the transfer roller 16.

The transfer bias generation circuit 108 includes a constant current transformer 108a and a constant voltage transformer 108b connected in series with the constant current transformer 108a. The transfer bias generator 108 outputs the transfer bias current output from the constant current transformer 108a in accordance with environmental conditions. Change the size. When the environmental conditions are high temperature / high humidity (30 ° C./85%), the output voltage of the constant current transformer 108a decreases as shown in FIG. A constant voltage transfer bias voltage is supplied by the voltage transformer 108b.

Next, the transfer device applied to the embodiment shown in FIGS. 1 and 2 will be described in detail. FIG.
FIG. 3 is a sectional view of a transfer roller (transfer device) 16.

The transfer roller 16 has, for example, a conductive elastic body 16b in which a foamable elastomer such as urethane rubber is cylindrically bonded or integrally formed on the outer peripheral surface of a shaft 16a made of stainless steel or the like. The shaft 16a has a diameter of 8 millimeters (hereinafter, mm
The stainless steel rod of (shown as) is used.

As the conductive elastic body 16b, for example,
15 megohms (hereinafter, MΩ
Ion conductive urethane set to the resistance value of () is used.

Next, the printing operation of the laser exposure type copying apparatus shown in FIGS. 1 and 2 will be described in detail. The photoconductor drum 10 is rotated by a motor drive pulse input from a motor control circuit 110 to a main motor (not shown) in response to a motor drive signal output from the CPU 100. It is rotated at a moving speed of 125 mm / sec (hereinafter referred to as mm / s). At the same time, the surface of the photosensitive drum 10 is uniformly charged to a predetermined surface potential by the supply of the charge by the charging device 12.

Specifically, the corona wire 1 of the charging device 12
The radiation amount of the corona discharge supplied to the surface of the photosensitive drum 10 by the corona discharge from the grid screen 1 a
It is appropriately adjusted by the grid bias voltage applied to 2b. As an example, the grid screen 12b
The grid voltage generating circuit 104 applies a grid bias voltage of approximately −650 V to the corona wire 12 a due to the high voltage from the charging voltage generating circuit 102.
The initial surface potential supplied to the photoconductor drum 10 via is set to about -650V.

Subsequently, the laser exposure device 40 responds to the image data to be copied or printed on the surface of the photosensitive drum 10, that is, the image information corresponding to the image of the original or the image signal supplied from the host device (not shown). A laser beam whose intensity is modulated according to the printed signal is emitted.

When a laser beam is emitted from the laser exposure device 40, a print signal is printed on the outer peripheral surface of the photosensitive drum 10.
An electrostatic latent image corresponding to (image data) is formed. The electrostatic latent image thus formed is, by the developing bias generating circuit 106, a developing roller 14a of the developing device 14 to which a developing bias voltage of, for example, -400V is applied.
Is developed by the toner T supplied from the printer. In this developing step, the chain-shaped carrier C formed on the outer peripheral surface of the developing roller 14a along the magnetic force lines generated from the main magnetic pole of a magnet (not shown) fixed inside the developing roller 14a. In the developing area where the photosensitive drum 10 and the developing roller 14a are opposed to each other, the toner adhered by the image force at the rising edge is caused by the electric field formed by the potential of the electrostatic latent image on the photosensitive drum 10 and the developing bias voltage. By moving the toner, the electrostatic latent image formed on the surface of the photosensitive drum 10 is developed. As the developer to be charged into the developing device 14, preferably, a magnetic carrier having an average particle diameter of 65 microns (hereinafter, referred to as μm) is coated with a toner having an average particle diameter of 9 μm by 6% by weight.
(wt%) is used.

The toner image developed by the developing device 14 is
At the transfer position where the photosensitive drum 10 and the transfer roller 16 face each other, the transfer bias current from the transfer roller 16 to which a constant current transfer bias current is applied via the transfer bias generation circuit 108 is guided in advance. Transferred to the paper in order. At this time, the magnitude of the transfer bias current applied from the transfer bias generation circuit 108 to the transfer roller 16 is, for example, a sheet size of A3 and a thickness of 80.
In the case of plain paper of g / m ² , it is set to about 20 microamperes (hereinafter referred to as μA) by the constant current transformer 108a regardless of environmental conditions. The magnitude of the transfer bias current applied to the transfer roller 16 is optimally changed in the range of 10 μA to 26 μA according to the size of the paper.

The toner image transferred onto the sheet is separated from the surface of the photosensitive drum 10 while being electrostatically adhered to the sheet, and is conveyed to the fixing device 62 by the conveying belt 60, and is then conveyed by the fixing device 62. , Fixed on paper.

The sheets on which the toner images have been fixed are sequentially discharged to the sheet discharge tray 66 via the sheet discharge rollers 64 and stacked. The photosensitive drum 10 on which the toner image has been transferred to the paper is
The rotation of the main motor (not shown) is continued, the untransferred toner is removed by the cleaning device 18, the charge is removed by the charge removing device 20, and the toner is subsequently used for the next image formation.

In this way, a series of image formation is repeated. By the way, as shown in FIG. 4, the magnitude of the transfer bias current from the transfer roller 16 is controlled in the same manner even when the environmental conditions surrounding the copying apparatus 2, that is, the temperature and the humidity are changed. In a high temperature and high humidity environment, there may occur a transfer failure, that is, a phenomenon in which the image density of the toner image transferred onto the paper falls below the allowable range.

More specifically, as shown in FIG. 4, when a constant current is output from the constant current transformer 108a, the constant current transformer 108a and the paper are reduced in resistance to a constant current transformer under a high temperature and high humidity environment. The terminal voltage of 108a, that is, the voltage applied to the transfer roller 16 is greatly reduced. In this case, a constant transfer bias current can be maintained, but an appropriate transfer bias voltage cannot be provided as the transfer bias voltage applied to the transfer roller 16.

Here, as shown in FIG. 2, a constant voltage transformer 108b is connected in series to the constant current transformer 108a, and as shown in FIG. 4, the constant voltage transformer 108b is connected.
From the transfer roller 16 to, for example, 1 kilovolt (hereinafter,
When a transfer bias voltage (denoted as kV) is applied, a constant current bias method is applied to the transfer roller 16 in a region where the voltage applied to the transfer roller 16 is reduced, that is, in an environment of a temperature higher than 25 ° C. and a humidity higher than 75%. A fixed transfer bias voltage of 1 kV is applied from the constant voltage transformer 108b. That is, as shown in FIG. 2, a constant voltage transformer 108b is connected in series to a constant current transformer 108a,
By outputting a fixed transfer bias voltage of 1 kV from the constant voltage transformer 108b, even when the resistance value of the paper is reduced due to a change in environmental conditions when the toner image on the photoconductor drum 10 is transferred to the paper, Constant current transformer 108
The decrease in the effective output of the constant current transfer bias from a can be compensated by the constant voltage transfer bias from the constant voltage transformer 108b.

As a result, as shown by the broken line in FIG.
It is possible to prevent the transfer bias voltage applied to the transfer roller 16 from decreasing in a high temperature and high humidity environment, and to stably transfer a toner image regardless of changes in environmental conditions.

[0062]

As described above, according to the transfer device of the present invention, the image density of the transferred image is lowered even when the resistance value of the paper is lowered due to the change of environmental conditions. Is prevented.

Further, the transfer device is a roller-type contact transfer device formed of an ion conductive elastic body, and is driven by a constant current transfer bias system in a certain environmental condition range, which is not desirable. The generation of significant ozone is suppressed.

Further, the transfer bias applied to the transfer device is a constant voltage transfer bias acting under an environmental condition in which the resistance value of the ion conductive elastic body decreases and a constant current transfer bias acting in a predetermined range under the environmental condition. And are applied at the same time, and when the resistance value of the ion conductive elastic body is reduced, it is possible to output the constant voltage transfer bias without requiring special control, It is possible to transfer a stable toner image regardless of changes in environmental conditions.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an image forming apparatus in which a transfer device according to an embodiment of the present invention is incorporated.

FIG. 2 is a block diagram centering on an image forming unit of the image forming apparatus shown in FIG.

FIG. 3 is a schematic view of a transfer roller used in the transfer device of the image forming apparatus shown in FIGS. 1 and 2.

4 is a graph showing a relationship between a transfer bias current output from the transfer bias generating circuit shown in FIG. 2, a constant voltage transfer bias, and a change in environmental conditions.

[Explanation of symbols]

 2 ... Laser exposure type copying machine (image forming apparatus), 10 ... Photosensitive drum (image carrier), 12 ... Charging device (charging means), 14 ... Developing device, 16 ... Transfer device (transfer means), 16a ... Shaft , 16b ... Conductive elastic body, 18 ... Cleaning device, 20 ... Eliminating device, 31 ... Original table, 32 ... Illumination lamp, 33 ... Reflector, 34 ... First mirror, 35 ... Second mirror, 36 ... Third mirror , 37 ... Imaging lens, 38 ... CCD sensor, 40 ... Laser exposure device, 52a ... Cassette, 52b ... Cassette, 58 ... Aligning roller, 58a ... Aligning switch, 60 ... Conveying belt, 62 ... Fixing device, 100 ... CPU, 100a ... Memory, 102 ... Charging voltage generation circuit, 104 ... Bias voltage generation circuit, 106 ... Development bias voltage Generating circuit, 108 ... Transfer bias generating circuit (driving means), 108a ... Constant current transformer, 108b ... Constant voltage transformer, 120 ... Sensor output input circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuteru Ono Toshiba Intelligent Technology Co., Ltd. 70 Yanagicho, Sachi-ku, Kawasaki-shi, Kanagawa

Claims (9)

[Claims] 1. A developing device for developing an image formed on an image bearing member, and a developer image formed on the image bearing member by the developing device, a constant current according to a change in resistance value of a transfer medium. An image forming apparatus comprising: a transfer unit that transfers to the transfer medium by either a transfer bias or a constant voltage transfer bias. 2. A developing unit for developing an image formed on an image carrier, and a developer image formed on the image carrier by the developing unit, a constant current transfer bias and a constant voltage transfer according to environmental conditions. An image forming apparatus comprising: a transfer unit that transfers to a transfer target medium according to any one of biases. 3. A developing means for developing an image formed on an image carrier, and a developer image formed on the image carrier by the developing means, the resistance of a transfer medium according to temperature and humidity fluctuations. An image forming apparatus comprising: a transfer unit that switches from a constant current transfer bias to a constant voltage transfer bias and transfers the transfer target medium when the value falls below a predetermined value. 4. A temperature and humidity device including a developing unit for developing an image formed on an image carrier, a transfer bias voltage supplying unit capable of outputting a constant voltage and a transfer bias current supplying unit capable of outputting a constant current. When the transfer voltage due to the constant current from the transfer bias current supply means and the resistance value of the transfer medium that has changed in accordance with the change in temperature and humidity is lower than the predetermined value under the environmental conditions of higher temperature and higher humidity than the predetermined condition. An image forming apparatus comprising: a transfer unit configured to transfer the developer image formed on the image carrier to a transfer medium by a constant voltage transfer bias voltage from the transfer bias voltage supply unit. 5. A developing means for developing an image formed on an image carrier, a transfer bias current supply means capable of outputting a constant current, and a constant voltage connected in series with the transfer bias current supply means. The transfer bias voltage supply means, and the resistance of the transfer medium that has changed in accordance with the constant current from the transfer bias current supply means and the change in temperature and humidity under environmental conditions where the temperature and humidity are higher and higher than predetermined conditions. A transfer means for transferring the developer image formed on the image carrier to the transfer medium by the constant voltage transfer bias voltage from the transfer bias voltage supply means when the transfer voltage according to the value is lower than a predetermined value. An image forming apparatus having. 6. A developing means for developing an image formed on an image carrier, a transfer means for transferring the developer image formed on the image carrier by the developing means to a transfer medium, and a transferring means. And a transfer bias supply unit for supplying either a constant current transfer bias or a constant voltage transfer bias in accordance with changes in temperature and humidity. 7. A developing means for developing an image formed on an image carrier, a transfer means for transferring the developer image formed on the image carrier by the developing means onto a transfer medium, and a constant voltage. A transfer bias voltage supply unit capable of outputting and a transfer bias current supply unit capable of outputting a constant current, and a constant current from the transfer bias current supply unit under an environmental condition where temperature and humidity are higher and higher than predetermined conditions. When the transfer voltage due to the resistance value of the transfer medium that has changed according to the change in temperature and humidity is lower than a predetermined value, the transfer unit supplies a constant voltage transfer bias voltage from the transfer bias voltage supply unit to the transfer unit. An image forming apparatus comprising: a bias supply unit. 8. A developing unit for developing an image formed on an image carrier, a transfer unit for transferring the developer image formed on the image carrier by the developing unit to a transfer medium, and a constant current. An environmental condition in which the transfer bias current supply unit capable of outputting and a transfer bias voltage supply unit connected in series with the transfer bias current supply unit capable of outputting a constant voltage and having a temperature and humidity higher and higher than predetermined conditions are used. In the case where the transfer voltage due to the constant current from the transfer bias current supply unit and the resistance value of the transfer medium that has changed in accordance with changes in temperature and humidity is lower than a predetermined value,
An image forming apparatus comprising: a transfer bias supply unit that supplies a constant voltage transfer bias voltage from the transfer bias voltage supply unit. 9. A first transfer bias set according to a resistance value of a transfer target when transferring a developer image, in which a developer is supplied to an image formed on an image bearing member, to the transfer target. And a second transfer bias that is set according to the environmental conditions are applied at the same time, and the resistance value of the transfer target is reduced by the environmental conditions.
A method for controlling a transfer device, wherein the second transfer bias compensates for a decrease in the effective output of the transfer bias.