JPH10161370A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a satisfactory image by eliminating an image defect which is caused by a transfer auxiliary device. SOLUTION: Between a developing device 13 and a transfer charger 14, pretransfer destaticization charger which discharges a photoreceptor drum 12 to reduce force with which a developer image is electrostatically attracted to a photoreceptive drum is provided. In the case image density that is higher than a specific value is set by a density set key on an operation panel, a CPU 62 actuates the prehansfer destaticization charger before the transfer of the developer image, thereby improving efficiency in transferring the developer image.

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 for forming an image by an electrophotographic method, such as a copying machine and a printer.

[0002]

2. Description of the Related Art Electrophotographic copying machines, printers, and the like are widely known as image forming apparatuses. 2. Description of the Related Art In an electrophotographic copying machine or the like, a photosensitive drum is uniformly charged by a charging charger, and then an original on a platen is exposed, and reflected light is imaged on the photosensitive drum to form a photosensitive drum. An electrostatic latent image is formed thereon. Toner particles are supplied to the electrostatic latent image on the photosensitive drum by a developing device to perform electrostatic development, and the formed toner image is transferred onto a transfer paper charged by a transfer charger to form an image. .

In the copying machine of this type, the copying speed has been increasing in recent years. However, with the increase in the diameter of the photosensitive drum and the increase in the peripheral speed of the photosensitive drum, the copying speed has been increased. There is a tendency that the transfer efficiency of the toner image electrostatically adhered to the toner is deteriorated.

That is, when the toner image formed on the photosensitive drum is transferred to transfer paper, if the electrostatic adhesion of the toner to the photosensitive drum is large, the toner image on the photosensitive drum is sufficiently transferred on the transfer paper. However, image defects such as blurring of an image, insufficient image density, deterioration of image density, and occurrence of transfer omission occur. Such image defects tend to increase as the copying speed increases.

Therefore, in order to efficiently transfer the toner image electrostatically attached to the photosensitive drum onto transfer paper, an auxiliary discharging means is often provided after development and before transfer. The pre-transfer auxiliary charge removing unit functions to reduce the electrostatic adhesion between the toner on the photosensitive drum and the photosensitive drum by static elimination after development and before transfer, and to transfer the toner efficiently onto transfer paper.

The pre-transfer assisting means mainly includes a pre-transfer static elimination light source (pre-transfer lamp, hereinafter referred to as PTL) for eliminating charges on the photoconductor by light, and a charge on the photoconductor by discharging from a wire or the like. And a pre-transfer charger (pre-transfer charger, hereinafter referred to as PTC) for eliminating static electricity and improving the transferability of the toner itself.

PTL is a means for eliminating charges on a photoreceptor by static elimination light to reduce the electrostatic adhesion between the photoreceptor and toner, and generally uses a cold cathode tube, an LED, or the like. Further, with the recent increase in the speed of the electrophotographic copying machine, it is necessary to increase the transfer efficiency. For this purpose, it is effective to increase the light amount of the pre-transfer static elimination light source. Therefore, as the PTL, a cold cathode tube having a larger light amount than the LED is often used.

[0008] PTC is a means for discharging a photoreceptor by charging to weaken the electrostatic adhesion between the photoreceptor and toner, and to further charge and transfer the toner more easily. A device that discharges a DC charge of the opposite polarity (same polarity as the toner) or a DC bias of the opposite polarity (same polarity as the toner)
A device for discharging the C charge is used.

[0009]

As described above, in an electrophotographic copying machine, particularly in a copying machine in which the speed of a photosensitive drum is increased in order to increase the copying speed,
In order to increase the transfer efficiency, a cold cathode tube is often used as a pre-transfer static elimination light source to assist the transfer of the toner image,
When a cold cathode ray tube is used as a pre-transfer static elimination light source, the following problems are raised as characteristics of the cold cathode tube.

That is, the fluctuation of the light quantity of the cold-cathode tube is large. This is because, for example, after the cold-cathode tube is continuously turned on, that is, after continuous copying by a copying machine, the lamp is left in an unlit state for a long time, and then turned on, the light amount immediately after the lighting is low, and gradually becomes brighter. To go.

For this reason, when the light amount of the cold cathode tube is set so that the light amount during continuous lighting is such that image defects such as transfer omissions can be prevented, the transfer immediately after lighting for a long time is performed. Insufficient light intensity of the pre-elimination light causes a decrease in transfer efficiency, and eventually causes a transfer omission. For this reason, it is necessary to set the light intensity of the cold-cathode tube immediately after lighting after leaving it for a long time to a sufficient light amount that does not cause transfer omission, but in this case, the light intensity of the cold-cathode tube during continuous lighting is reduced. It becomes excessive and causes a defect on an image such as an image memory. That is, when a cold cathode tube is used, the optimum light amount width at which no image defect occurs immediately after lighting and during continuous lighting is small (transfer loss, light amount margin of image memory is small).

Further, the cold cathode fluorescent lamp is used in a low temperature environment, for example,
In an environment of 5 to 10 ° C. and 20 RH%, the light quantity is also reduced. Therefore, when the cold cathode tube is used in a low-temperature environment, the light quantity is insufficient, and image defects such as missing transfer occur.

On the other hand, the PTC discharges the charge of the photosensitive drum by discharging a charge having a polarity opposite to that of the photosensitive drum. This is to increase the transfer efficiency by charging the toner in the image area more because it also has the same polarity as the toner, but a slight amount of weakly charged toner adhering to the non-image area (white background area) This also charges the so-called toner on the drum. This weakly charged toner is carried to the cleaning unit without being transferred when there is no PTC.
When charged by TC, transfer becomes easy, and fog on paper becomes extremely large. As described above, when PTC is used, there is a problem that the fog level is deteriorated.

Such a defective image due to the PTC, that is, fogging, mainly occurs when the photosensitive drum approaches the end of its life (due to an increase in white background potential) or in a humid environment (due to a decrease in developer charge). .

As described above, in each case of PTL and PTC, an adverse effect occurs. However, when compared to fog of PTC, the poor rise of the PTL has a greater adverse effect. There are many.

When PTC is used alone, the level of adverse effects is smaller than that at the initial copy due to poor rise of PTL. However, since fogging occurs, the PTC is conventionally used only when there is no help for the transfer efficiency without the function of the pre-transfer auxiliary static eliminator.
Is turned on. Here, the case where nothing can be done is the case of copying both sides during the double-sided copy operation, and the transfer efficiency is reduced due to the curl of the paper or the deterioration of the surface properties of the paper due to once passing through the fixing device. Is the case. Therefore, except for the above, the PTC is not turned on, and as a result, the transfer efficiency at the time of one-side full-copy is PTL.
It will be lower than the case of installation.

[0017] The rate at which the transfer efficiency is reduced depends on the characters of the original.
The larger the area ratio of the image is, the larger the area ratio is. Therefore, when copying a solid image or the like on the entire surface, the transfer efficiency is remarkably deteriorated, and white spots due to carrier adhesion and toner clamp become more conspicuous.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to provide an image forming apparatus capable of eliminating an image defect caused by a transfer assisting device and obtaining a good image. is there.

[0019]

According to a first aspect of the present invention, there is provided an image forming apparatus, comprising: a charging unit for charging an image carrier; and exposing the charged image carrier to light. Exposure means for forming an electrostatic latent image on the image carrier; developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image; A transfer unit for transferring a developer image formed on the body to a transfer material; and discharging the image carrier to discharge the image carrier before the transfer of the developer image, thereby removing the developer from the image carrier. A pre-transfer neutralization charger for reducing an electrostatic attraction force of an image; density adjusting means for adjusting the image density of a developer image developed by the developer; and a predetermined value for the image density adjusted by the density adjusting means. If higher, the pre-transfer static elimination charger is activated, If serial lower than a predetermined value is characterized by and a control means for maintaining a pre-transfer discharger stopped.

According to the image forming apparatus having the above-described configuration, when the image density higher than the predetermined value is set by the density adjusting unit, the control unit detects this and activates the pre-transfer charge removing charger. Thereby, the image carrier is discharged before the transfer of the developer image, and the electrostatic attraction of the developer image to the image carrier is reduced, and as a result, transfer efficiency is improved. Therefore, good image formation can be performed even when image formation with high image density is performed.

According to a second aspect of the present invention, there is provided an image forming apparatus, comprising: charging means for charging an image carrier; optically scanning a document placed on a document table; Exposure means for exposing the charged image carrier to form an electrostatic latent image on the image carrier, and developing the electrostatic latent image formed on the image carrier with a developer to form a developer image A transfer means for transferring a developer image formed on the image carrier to a transfer material; and discharging the image carrier by discharging the image carrier before the transfer of the developer image. A pre-transfer static eliminator for reducing the electrostatic attraction of the developer image to the image carrier; and adjusting an image density of a developer image developed by the developer by changing an exposure light amount of the exposure unit. A density adjusting unit, and the image density adjusted by the density adjusting unit is a predetermined value. If higher than the value, actuates the pre-transfer discharger, is lower than the predetermined value is characterized in that and a control means for maintaining a pre-transfer discharger stopped.

According to the present invention, in the image forming apparatus, the control means controls the pre-transfer neutralization charger when the exposure light amount is adjusted so that the reflectance of the 50% halftone image of the document becomes 30% or more. Is operated.

According to a fourth aspect of the present invention, there is provided an image forming apparatus, comprising: a document placing portion on which a document is placed; document detecting means for detecting the presence of a document on the document placing portion; A cover for opening and closing the unit, an opening and closing detection unit for detecting the opening and closing of the cover, a charging unit for charging the image carrier, and an electrostatic latent image corresponding to a document by exposing the charged image carrier. Exposing means for forming on the image carrier, developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image, and forming on the image carrier Transfer means for transferring the developer image onto a transfer material, and discharging the image carrier before the transfer of the developer image to eliminate the charge on the image carrier,
A pre-transfer static eliminator for reducing the electrostatic attraction of the developer image to the image carrier; a document absence detected by the document detection means; and an open state of the lid member detected by the open / close detection means. At this time, the pre-transfer static elimination charger is operated, and when the lid member is open and there is a document on the document mounting table, and when the lid member is closed, the pre-transfer static elimination charger is stopped. And control means for maintaining.

According to the image forming apparatus having the above structure, when the cover is opened and the original is not placed on the original placing table, that is, when a solid image is formed, the control means controls the pre-transfer static elimination charger. Is operated, the transfer efficiency of the developer image is improved. For this reason, problems such as missing transfer and occurrence of white spots are prevented, and good image formation becomes possible.

According to a fifth aspect of the present invention, there is provided an image forming apparatus according to the present invention, wherein a charging means for charging the image carrier, the charged image carrier is exposed, and an electrostatic latent image is formed on the image carrier. Exposure means for forming, developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image, supply means for supplying a transfer material through the image carrier, A transfer unit for transferring the developer image formed on the image carrier to a transfer material supplied by the supply unit; and discharging the image carrier by discharging the image carrier before the transfer of the developer image. A pre-transfer static eliminator for reducing the electrostatic attraction of the developer image to the image carrier; and an automatic transfer device for reversing the transfer material on which the developer image has been transferred by the transfer unit and supplying the material to the image carrier Double-sided means and an image of a developer image developed by the developer A concentration adjusting means for adjusting the degree,
When the image density adjusted by the density adjusting means is higher than a predetermined value, and when the transfer material is inverted by the automatic double-sided means and supplied to the image carrier, the pre-transfer static elimination charger is operated. And control means for causing

According to the image forming apparatus having the above configuration, in addition to the case where the image density higher than the predetermined value is set by the density adjusting means, the transfer material is inverted by the automatic double-sided means and supplied to the image carrier. In this case, in other words, when performing image formation on both surfaces of the transfer material, the pre-transfer static elimination charger is operated to increase the efficiency of transfer of the developer image.

According to an eighth aspect of the present invention, there is provided an image forming apparatus according to the present invention, wherein a charging means for charging an image carrier, and the charged image carrier is exposed to form an electrostatic latent image on the image carrier. Exposure means, developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image, and transferring the developer image formed on the image carrier to a transfer material A transfer unit for transferring, a pre-transfer charge eliminator that discharges the image carrier by discharging the image carrier before the transfer of the developer image, and irradiates the image carrier with light before the transfer of the developer image. A pre-transfer static elimination light source for static elimination of the image carrier, density adjusting means for adjusting the image density of a developer image developed by the developer, and an image density adjusted by the density adjusting means having a predetermined value. If the charge is higher than the above, the pre-transfer In the case of lower than the value it is characterized by comprising a control means for actuating the pre-transfer light scanning lamp.

According to the image forming apparatus having the above structure, when the image density lower than the predetermined value is set by the density adjusting means, the control means performs the charge elimination of the image carrier by the pre-transfer charge elimination light source. Only when the image density is higher than a predetermined value, the pre-transfer static elimination charger is operated. Thereby, the image carrier is discharged before the transfer of the developer image, and the electrostatic attraction of the developer image to the image carrier is reduced, and as a result, transfer efficiency is improved. Therefore, good image formation can be performed even when image formation with high image density is performed.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine will be described below in detail with reference to the drawings. First, the overall configuration of the copying machine will be schematically described. As shown in FIG. 1, the copying machine includes a housing 10 and an image carrier, for example, made of arsenic selenium is provided at a substantially central portion in the housing. The photosensitive drum 12 is rotatably provided. Around the photosensitive drum 12, a charging charger 11 functioning as a charging means, a developing device 13 functioning as a developing means, a transfer charger 14 functioning as a transferring means, a peeling charger 15, a peeling claw 1
6, a cleaning device 17, and a static elimination lamp 18 are arranged in this order to form an image forming unit 20.

A document table 32 made of transparent glass is provided on the upper surface of the housing 10, and an automatic document feeder (hereinafter referred to as ADF) 8 for automatically feeding the document D onto the document table.
0 is provided.

The ADF 80 is also configured as a cover for opening and closing the document table 32 and a document holder. The document tray 82 on which the document D is mounted and the document tray 82 are provided so as to face almost the entire surface of the document table. And a conveyor belt 85 for conveying. Then, the document placed on the document tray 82 is guided onto the document placing table 32 via the transport path 84, and is transported and positioned at a predetermined position by the transport belt 85.
Then, the original read by the scanner described later is
The document is discharged to a document discharge section 88 on the upper surface of the ADF 80 by a transfer belt 85 through a transfer path 86.

A pair of hinges (not shown) that support the ADF 80 on the document table 32 so as to be openable and closable are provided with an AD.
An opening / closing sensor for detecting opening / closing of F80 is provided.
Further, a document sensor for detecting the presence or absence of a document on the document table is provided below the document table 32.
The opening / closing sensor functioning as the opening / closing detecting means and the document sensor functioning as the document detecting means output detection results to a CPU 62 as a control means described later.

A scanner 22 for reading an image of a document D placed on the document table 32 is provided below the document table 32 in the housing 10. This scanner 2
2 includes an exposure lamp 24 whose back is surrounded by a reflector 23, and a first reflection mirror 25 mounted on a first carriage 33 together with the exposure lamp. The scanner 22 is mounted on the second carriage 34 and can move integrally with the second and third reflection mirrors 2.
6, 27, a lens 28, and fixed fourth, fifth and sixth
And the reflection mirrors 29, 30, and 31 of FIG.

First and second carriages 33, 34
Is moved at a predetermined speed along the document table 32, and scans the document D by the irradiation light from the exposure lamp 24. Then, the reflected light from the document D is guided to the photosensitive drum 12 by the first to sixth reflecting mirrors and the lens 28 to expose the surface of the photosensitive drum. Thus, the scanner 2
Reference numeral 2 denotes an exposure unit in the present invention.

As a result, an electrostatic latent image corresponding to the image of the original is formed on the surface of the photosensitive drum 12 uniformly charged by the charging charger 11 as described later. The formed electrostatic latent image is developed by the developing device 13 using toner as a developer to form a toner image.

An automatic exposure sensor 21 for measuring the amount of exposure light is provided between the third reflection mirror 27 and the lens 28. Then, part of the light reflected by the third mirror 27 is incident on the automatic exposure sensor 21 and is
Outputs an output voltage corresponding to the image density to a CPU 92 described later as a document density signal.

At the lower part of the side surface of the housing 10, first and second paper feed cassettes 35 and 36 each containing a large number of papers P as transfer materials are detachably mounted. The first and second sheet cassettes 3 are provided in the housing 10.
The paper P taken out of the photosensitive drum 12
A transfer path 38 for transferring the sheet through a transfer portion located between the transfer path and the transfer charger 14 is formed, and a fixing device 40 is provided at the end of the transfer path. A discharge port 42 is formed on a side wall of the housing 10 facing the fixing device 40, and a discharge tray 43 is mounted on the discharge port 42.

The fixing device 40 includes a heat roller 40a having a built-in heater, and a pressure roller 40 which is in contact with the heat roller.
b, a thermistor 4 for detecting the temperature of the heat roller 40a
0c and the like.

First and second paper cassettes 35 and 36
Are provided with pickup rollers 44 for taking out the paper P from the paper feed cassettes, respectively.
A registration roller 46 for aligning the paper P is provided upstream of the photosensitive drum 12 in the transport path 38. A sensor 48 for detecting the arrival of the sheet P is provided near the registration roller 46.

The paper P taken out one by one from the first or second paper feed cassette 35 or 36 by the pickup roller 44 is sent to the transfer unit after being aligned by the registration roller 46. Then, in the transfer section, the toner image on the photosensitive drum 12 is transferred onto the sheet P by the transfer charger 14.

The sheet P on which the toner image has been transferred is separated from the photosensitive drum 12 by the AC corona discharge from the separation charger 15 and the separation claw 16, and is transferred to the fixing device 40 via the transfer belt 50 forming the transfer path 38. Conveyed.
Then, the sheet P on which the toner image has been fused and fixed by the fixing device 40 is discharged onto a sheet discharge tray 43 by a sheet discharge roller 51. Note that the pickup roller 44, the registration roller 46, and the transport belt 50 function as a supply unit.

The fixing device 4 is located below the conveyance path 38.
An automatic double-sided device 51 is provided which guides the sheet P, which has passed through 0, to the transfer section via the registration roller 46 after reversing the sheet P. Automatic duplexer 51 functioning as automatic duplexer
Is a reversing path 52 for branching off the transport path 38 and reversing the sheet P, a temporary accumulating section 53 for temporarily accumulating the inverted sheet P, and conveying the sheet P from the temporary accumulating section to the registration roller 46. And a re-transport path 54.

A sorting gate 55 for guiding the sheet P to the reversing path 52 is provided between the fixing device 40 and the sheet discharging roller 51, and a plurality of feed rollers 56 are arranged in the reversing path 52 and the re-conveying path 54. Has been established. In addition, the temporary accumulating unit 53
Inside, a pickup roller 57 for taking out the stacked sheets P one by one and sending it to the re-transport path 54 is provided.

When performing double-sided copying, the sheet P that has passed through the fixing device 40 is moved by the sorting gate 55 to the reversing path 5.
2 and is accumulated in the temporary accumulation unit 53 after being inverted. After the accumulated paper P is taken out of the temporary accumulation section 53 by the pickup roller 57, the paper P is re-conveyed.
The toner image is then transferred to the registration roller 46, where the toner image is rearranged, and then the toner image is transferred again to the rear surface of the sheet P at the transfer unit. After that, the paper P is transferred to the conveyance path 38 and the fixing device 4.
The paper is discharged to the paper discharge tray 43 via the paper discharge roller 51 and the paper discharge roller 51.

Next, the configurations of the photosensitive drum 12 and the image forming section 20 will be described in detail. As shown in FIG. 2, the charger 11 for uniformly charging the surface of the photosensitive drum 12 to a predetermined potential has a corona wire 11a and a grid 11b, and a voltage is applied to the corona wire to perform corona discharge. A power source (not shown) to be generated is connected. A high voltage transformer 60 for applying a grid voltage is connected to the grid 11b. These power supply and high-voltage transformer 60 are connected to a CPU as control means.
62.

With respect to the rotation direction of the photosensitive drum 12, an exposure position 12a on the surface of the photosensitive drum 12 exposed by the reflected light from the scanner 22 is located downstream of the charging charger 11, and at this exposure position, An electrostatic latent image is formed on the surface of the photosensitive drum.

An LED 65 for partial erasure is provided between the exposure position 12a and the charger 11. The developing device 13 has a developing roller 13a for supplying toner particles to the electrostatic latent image on the surface of the photosensitive drum 12 to develop the electrostatic latent image. The developing roller 13a is controlled by a high-voltage transformer 76 under the control of the CPU 62. A development bias is applied.

A thermistor 66 for detecting the temperature of the surface of the photosensitive drum 12 is provided between the developing unit 13 and the LED 65, and an actuator 66a of the thermistor 66 is in contact with the drum surface at the end of the photosensitive drum. .
Then, the thermistor 66 outputs a detection signal to the CPU 62.

Also, between the developing device 13 and the LED 65,
A surface potential sensor 67 for detecting the surface potential of the photosensitive drum 12 is provided. A transfer charger 14 for transferring the toner image formed on the photosensitive drum 12 to the paper P,
The separation charger 15 for separating the sheet P from the photosensitive drum is provided downstream of the developing device 13 in the rotation direction A of the photosensitive drum 12. The transfer charger 14 and the peeling charger 15 are integrally formed and connected to the CPU 62 via high-voltage transformers 68 and 70, respectively.

Between the developing device 13 and the transfer charger 14, a pre-transfer neutralization charger (PTC) 104 is provided. The pre-transfer static elimination charger 104 discharges electricity to the surface of the photoconductor drum 12 to eliminate static electricity, thereby reducing the electrostatic adhesion of the toner image to the surface of the photoconductor drum, and charging the toner to facilitate the transfer.

As the pre-transfer charger 104, a platinum clad wire (φ65 μm) extending along the axial direction of the photosensitive drum 12 is used.
62. The pre-transfer charger 104 is capable of changing its discharge output, that is, the charge elimination capability, in accordance with the applied voltage.
Controlled off.

The peeling claw 1 is located downstream of the peeling charger 15.
6, and a cleaning device 17 having a cleaning blade 78 is provided downstream of the peeling claw. The cleaning blade 78 is provided for the photosensitive drum 1.
The toner that is provided in contact with the surface of No. 2 and that remains on the drum surface without being transferred is scraped off from the drum surface.

A charger 77 having a corona wire for applying AC to the photosensitive drum 12 as an auxiliary cleaning mechanism is provided between the peeling claw 16 and the cleaning device 17.
Is provided.

A static elimination lamp 18 is provided between the cleaning device 17 and the charger 11.
The discharging lamp 18 is connected to the CPU 62 via a light source driver 94.
, And the light amount of the neutralization lamp 18 can be changed by changing the voltage applied to the light source driver 94 under the control of the CPU.

The CPU 62 is connected to a memory 93 storing various control data, an opening / closing sensor 110, and a document sensor 112, and to an operation panel 114 described later.

As shown in FIG. 3, the operation panel 1 of the copying machine
14 is provided at the front upper surface of the housing 10. On the operation panel 114, a display unit 115 for displaying various messages, a paper size selection key 116, a document size selection key 117, a ten key 118, a copy start key 12
0, a mode setting key 122 for setting a mode such as double-sided copying or editing is provided. The operation panel 114
Are provided with a copy magnification setting key 124, a density setting key 126 functioning as density adjusting means for setting an image density, and the like.

In the copying machine configured as described above,
The pre-transfer static elimination charger 104 is turned on only in a predetermined case under the control of the CPU 62, and discharges to the surface of the photosensitive drum 12, thereby preventing problems such as missing transfer and occurrence of image glare.

That is, in the present embodiment, the pre-transfer static elimination charger 104 is turned on at the time of both-side copying in the double-side copying operation, and neutralizes the photosensitive drum 12. This is because, in copying on both sides, the transfer paper is often curled, and the transfer efficiency is lowered due to the deterioration of the surface properties of the paper caused by once passing through the fixing device 40.

The pre-transfer neutralization charger 104 is turned on only during two copy operations described in detail below, and is kept off during all other copy operations. First, the user operates the density setting key 1 on the operation panel 114.
In particular, when the image density is set to the “dark” side by operating the button 26, the density setting key is set to a predetermined density level (DMAX).
Alternatively, if it is set to (N + 4), the pre-transfer neutralization charger 104 is turned on. That is, the CPU 62 adjusts the amount of light of the exposure lamp 24 of the scanner 22 according to the density level set by the density setting key 126, thereby adjusting the image density of the developer image. When the density on the “dark” side is set by the density setting key 126, the light amount of the exposure lamp 24 of the scanner 22 decreases, and the reflectance of the original image increases.

According to the present embodiment, when the density setting key 126 sets the density level at which the reflectance of a 50% halftone image becomes 30% or more, the CPU
62 detects this and turns on the pre-transfer static elimination charger 104 to perform pre-transfer static elimination.

That is, most of the originals requiring extremely high exposure as described above are originals having a larger image area ratio at the center of solids than character originals. In this case, it is necessary to increase the transfer efficiency with a large image area ratio of the original, and it is considered that there are many solid copies.
There is a need to make vitiligo less noticeable.

FIG. 4 shows the relationship between the density level by the density setting key and the fogging state. As can be seen from this figure, when the density level is set to the “dark” side, the fog level is extremely deteriorated regardless of whether the pre-transfer charge removal charger 104 is off or on.
Then, the difference in fog level between when the pre-transfer static elimination charger 104 is on and when it is off is almost eliminated, and the fog caused by the pre-transfer static elimination charger can be ignored.

Accordingly, when the density level is set to N + 4 or more, the fogging problem does not occur even if the pre-transfer static elimination charger 104 is turned on, which is effective in improving the transfer efficiency.

On the other hand, in the second copy operation for turning on the pre-transfer charge removing charger 104, the ADF 80 is rotated to the open position, the original placing table 12 is in the open state, and the original is placed on the original placing table. This is a case where the copying operation is performed in a state where the copying operation is not performed. That is, the CPU 62 controls the open / close sensor 11
When the ADF 80 is detected to be open based on the detection signal from 0 and the absence of a document is detected based on the detection signal from the document sensor 112, the pre-transfer neutralization charger 104 is turned on.

Such a copying operation is performed, for example, in a test of a copying machine, in which all solid images are copied to check the adhesion state of carriers and the occurrence of white spots. In this case, it is necessary to increase the transfer efficiency by turning on the pre-transfer neutralization charger 104 and make the white spots less noticeable. Since the entire image is a solid image, fog can be safely ignored.

As a case where a copy operation is performed with the ADF 80 opened, book copy may be considered in addition to the above-described acquisition of all solid images. However, in this case, fogging poses a problem. Therefore, even when the ADF 80 is opened, the CPU 62 determines whether the pre-transfer static elimination charger 1 is in the presence of a document.
04 is kept off, and is turned on only when there is no original.

FIG. 5 shows the pre-transfer neutralization charger 1 described above.
04 shows the control operation flow, and the CPU 62
When the copy start key 120 is turned on, the density setting key 1
The density level is detected from the set position 26, and when the set density level is N + 4, DMAX, the output of the pre-transfer neutralization charger 104 is turned on.

When the set density level is N + 4, DMAX
Otherwise, it is determined whether or not it is a double-sided copy. If it is a double-sided copy, the output of the pre-transfer neutralization charger 104 is turned on at the time of copying both sides.

If it is not a double-sided copy, it is determined whether or not the ADF 80 is in an open state based on a detection signal from the open / close sensor 110.
Further, the presence or absence of a document is detected based on a detection signal from the document sensor 112. Then, when there is no original, the output of the pre-transfer charge removing charger 104 is turned on.

Both when the ADF 80 is closed and when there is a document, the charge removal charger 10 before transfer is used.
4 is kept off. In the test in the above-described embodiment, as a copying machine, Toshiba's analog PPCF154 (65 CPM machine) under development, and the developer was D-1
710, T-2510 for the toner, OPC drum (φ100) manufactured by Yamanashi Electronics for the photosensitive drum, and Hammermill Tidal-DP paper for the evaluation paper.

In the first and second cases described above, the output value of the pre-transfer charge removing charger 104 is +8 μA / 50 mm for the entire surface of the paper regardless of the paper size. Further, in the double-sided copy operation, the output value of the pre-transfer static elimination charger 104 at the time of copying both sides is changed along the sheet moving direction so that fog is not conspicuous, and the pre-transfer static elimination is performed according to the sheet size. Charger is turned on and off.

According to the copying machine configured as described above,
When the density level is set to a level higher than the predetermined value, the pre-transfer static elimination charger is turned on, so when copying an original with a large area ratio of characters and images, or a full solid image, etc. However, the transfer efficiency can be increased, and the occurrence of white spots due to carrier adhesion and toner clamp can be reduced to an inconspicuous level without causing a fogging problem.

In addition, since the ADF is opened and the pre-transfer static elimination charger is turned on even when a solid image is taken without any original, the occurrence of carrier adhesion and white spots due to a decrease in transfer efficiency is caused. Can be reduced. Therefore, it is possible to eliminate a defect of an image caused by the pre-transfer charge removing charger and obtain a good image.

The present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the present invention. For example, the density level at which the pre-transfer charge removal charger is turned on is not limited to the above-described embodiment, and can be variously changed as needed.

Further, in the above-described embodiment, the configuration in which only the pre-transfer charge eliminating device 104 is provided as the pre-transfer charge eliminating device has been described. However, as shown in FIG. It may be configured by using both the 104 and the pre-transfer neutralization lamp 105.

In this case, for example, a cold-cathode tube is used as the pre-transfer neutralizing lamp 105, and the light source driver 108
Is connected to the CPU 62 via the. And CPU
62, when the image density set by the density setting key 126 of the operation panel 114 is equal to or more than a predetermined value, the pre-transfer static elimination charger 104 is turned on to neutralize the photosensitive drum 12, and the set image density Is less than or equal to a predetermined value, the pre-transfer static elimination lamp 105 is operated to eliminate static electricity from the photosensitive drum.

The pre-transfer static elimination lamp 105 has poor initial lighting characteristics and may not provide a sufficient static elimination light amount. However, even in this case, the original to be used for copying is originally an original having a low image density. There is no problem such as transfer omission. Further, since the pre-transfer static elimination lamp 105 is turned on, it is possible to prevent a decrease in transfer efficiency that is likely to occur at the time of double-sided copying. As in the embodiment described above, it is possible to provide an image forming apparatus capable of eliminating a defect of an image due to a pre-transfer charge removing unit and obtaining a good image.

In FIG. 6, the other structure is the same as that of the above-described embodiment, and the same portions are denoted by the same reference characters and detailed description thereof will not be repeated. Further, the present invention is not limited to an analog type copying machine, but is applicable to other image forming apparatuses such as a digital copying machine and a printer.

[0079]

As described above in detail, according to the present invention, the transfer assisting device is controlled in accordance with the set image density and in accordance with the opening / closing of the document table and the presence / absence of the document. Accordingly, it is possible to provide an image forming apparatus capable of eliminating a defect of an image caused by the transfer assist device and obtaining a good image.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a copying machine according to an embodiment of the present invention.

FIG. 2 is an enlarged schematic view showing an image forming unit of the copying machine.

FIG. 3 is a plan view showing an operation panel of the copying machine.

FIG. 4 is a bluff showing a relationship between a density setting level and fog in the copying machine.

FIG. 5 is a flowchart showing a control operation of a pre-transfer charge removing charger in the copying machine.

FIG. 6 is an enlarged schematic view showing an image forming unit of a copying machine according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 ... Photoreceptor drum 11 ... Charging charger 13 ... Developer 14 ... Transfer charger 17 ... Cleaning device 22 ... Scanner 24 ... Exposure lamp 62 ... CPU 104 ... Electric discharge charger before transfer 105 ... Electric discharge lamp before transfer 110 ... Open / close sensor 112 ... Document Sensor 114: Operation panel 126: Density setting key

Claims (9)

[Claims] A charging means for charging the image carrier; an exposure means for exposing the charged image carrier to form an electrostatic latent image on the image carrier; Developing means for developing the formed electrostatic latent image with a developer to form a developer image; transfer means for transferring the developer image formed on the image carrier to a transfer material; A pre-transfer neutralization charger that discharges the image carrier before the transfer to discharge the image carrier, and reduces an electrostatic attraction force of the developer image on the image carrier; and a developer developed by the developer. Density adjusting means for adjusting the image density of an image; and if the image density adjusted by the density adjusting means is higher than a predetermined value, the pre-transfer static elimination charger is operated, and if the image density is lower than the predetermined value. Is a control method to keep the pre-transfer static elimination charger stopped. An image forming apparatus comprising the and. A charging means for charging the image carrier, optically scanning a document placed on a document table, and exposing the charged image carrier by light reflected from the document to form an image bearing member. Exposure means for forming an electrostatic latent image on the body; developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image; Transferring means for transferring the formed developer image to a transfer material; discharging the image carrier to discharge the image carrier before transferring the developer image; and removing the developer image with respect to the image carrier. A pre-transfer static elimination charger for reducing the electroadhesive force; a density adjusting unit for changing an exposure light amount of the exposure unit to adjust an image density of a developer image developed by the developer; If the image density is higher than a predetermined value, Actuating the catcher, an image forming apparatus characterized by and a control means for maintaining a pre-transfer discharger stopped when lower than the predetermined value. 3. The apparatus according to claim 2, wherein said control means activates said pre-transfer charge elimination charger when the exposure light quantity is adjusted to a reflectance of a 50% halftone image of said document of 30% or more. 3. The image forming apparatus according to 2. An original placing portion on which the original is placed; an original detecting means for detecting the presence of the original on the original placing portion; a lid for opening and closing the original placing portion; Opening / closing detecting means for detecting opening / closing of the image carrier, charging means for charging the image carrier, and exposing means for exposing the charged image carrier and forming an electrostatic latent image corresponding to a document on the image carrier Developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image; and transferring the developer image formed on the image carrier to a transfer material. A transfer unit, and a pre-transfer neutralization charger that discharges the image carrier before the transfer of the developer image to eliminate the charge of the image carrier, and reduces an electrostatic attraction force of the developer image to the image carrier; The absence of a document is detected by the document detection means, and
When the open state of the lid member is detected by the open / close detection unit, the pre-transfer static elimination charger is operated, and when the lid member is in the open state and there is a document on the document table,
An image forming apparatus comprising: a control unit configured to maintain the pre-transfer static removal charger in a stopped state when the lid member is closed. A charging means for charging the image carrier; an exposure means for exposing the charged image carrier to form an electrostatic latent image on the image carrier; Developing means for developing the formed electrostatic latent image with a developer to form a developer image; supplying means for supplying a transfer material through the image carrier; and supplying the developer image formed on the image carrier to the developer. A transfer unit for transferring the image onto the transfer material supplied by the supply unit; and discharging the image carrier by discharging the image carrier before the transfer of the developer image, and removing the developer image with respect to the image carrier. A pre-transfer static elimination charger for reducing the electro-adsorption force; automatic double-sided means for inverting a transfer material on which a developer image has been transferred by the transfer means and supplying the image to the image carrier; Density adjusting means for adjusting the image density of the image; Control means for operating the pre-transfer static elimination charger when the image density adjusted by the means is higher than a predetermined value, and when the transfer material is reversed by the automatic double-side means and supplied to the image carrier. An image forming apparatus comprising: 6. A charging means for charging the image carrier, an exposure means for exposing the charged image carrier to form an electrostatic latent image on the image carrier, and a charging means for forming an electrostatic latent image on the image carrier. Developing means for developing the formed electrostatic latent image with a developer to form a developer image; supplying means for supplying a transfer material through the image carrier; and supplying the developer image formed on the image carrier to the developer. A transfer unit for transferring the image onto the transfer material supplied by the supply unit; and discharging the image carrier by discharging the image carrier before the transfer of the developer image, and removing the developer image with respect to the image carrier. A pre-transfer static elimination charger for reducing the electro-adsorption force, an automatic double-sided means for inverting a transfer material on which a developer image has been transferred by the transfer means and supplying the image to the image carrier, and a developer developed by the developer Density adjusting means for adjusting the image density of the image; When the image density adjusted by the means is higher than a predetermined value, and, when the transfer material is inverted by the automatic double-sided means and supplied to the image carrier, control means for activating the pre-transfer static elimination charger, An image forming apparatus comprising: 7. A document placing portion on which a document is placed, document detecting means for detecting the presence or absence of a document on the document placing portion, a lid for opening and closing the document placing portion, and the lid Opening / closing detecting means for detecting the opening / closing of the document, charging means for charging the image carrier, optically scanning the document placed on the document table, and reflecting the charged image carrier by reflected light from the document. Exposure means for exposing to form an electrostatic latent image on the image carrier, developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image, A transfer unit for transferring a developer image formed on the image carrier to a transfer material; and discharging the image carrier to transfer the developer image before the transfer of the developer image, thereby discharging the image carrier, and removing the developer from the image carrier. A pre-transfer static elimination charger that reduces the electrostatic attraction force of the developer image; Density adjusting means for adjusting the image density of a developer image developed by the developer; and activating the pre-transfer charge removing charger when the image density adjusted by the density adjusting means is higher than a predetermined value. And control means for activating the pre-transfer neutralization charger when the absence of a document is detected by the document detection means and the open state of the lid member is detected by the open / close detection means. Characteristic image forming apparatus. 8. A charging means for charging the image carrier, an exposure means for exposing the charged image carrier to form an electrostatic latent image on the image carrier, and a charging means for forming an electrostatic latent image on the image carrier. Developing means for developing the formed electrostatic latent image with a developer to form a developer image; transfer means for transferring the developer image formed on the image carrier to a transfer material; A pre-transfer neutralization charger which discharges the image carrier by discharging the image carrier before transfer; and a pre-transfer which irradiates the image carrier with light before the transfer of the developer image to remove the image carrier. A static elimination light source; density adjusting means for adjusting the image density of a developer image developed by the developer; and the pre-transfer static elimination charger when the image density adjusted by the density adjusting means is higher than a predetermined value. And if it is lower than the predetermined value, the pre-transfer static elimination light An image forming apparatus, comprising: control means for operating a source. 9. A charging unit for charging an image carrier, an exposure unit for exposing the charged image carrier to form an electrostatic latent image on the image carrier, and a charging unit for forming an electrostatic latent image on the image carrier. Developing means for developing the formed electrostatic latent image with a developer to form a developer image; supplying means for supplying a transfer material through the image carrier; and supplying the developer image formed on the image carrier to the developer. Transfer means for transferring to the transfer material supplied by the supply means; a pre-transfer charge removing device for discharging the image carrier to discharge the image carrier before transferring the developer image; and transferring the developer image. A pre-transfer static elimination light source for irradiating the image carrier with light before the image carrier is removed, and an automatic supply for inverting a transfer material on which a developer image has been transferred by the transfer unit and supplying the transfer material to the image carrier. Double-sided means, and the image density of the developer image developed by the developer A density adjusting means for adjusting the transfer material by the automatic double-sided means, and when the image density adjusted by the density adjusting means is higher than a predetermined value when supplying the image to the image carrier, Control means for activating the pre-electrification charger and activating the pre-transfer static elimination light source when the image density adjusted by the density adjusting means is lower than the predetermined value. apparatus.