JPH09179358A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image memory from occurring on an image carrier and to attain an excellent image. SOLUTION: A pretransfer discharge lamp 96 is arranged between a developing unit 13 and a transfer charger 14 by being faced to a photoreceptor drum 12. The lamp 96 is formed so that the light quantity thereof can be adjusted by a CPU 62 through an inverter circuit 97. Then, the electrostatic attaching force of a developer image is reduced with respect to the drum 12 by discharging the drum 12. Besides, an image density sensor 98 detecting the image density of the developer image formed on the drum 12 is arranged between the developing unit 13 and the lamp 96. Then, the light quantity of the lamp 96 is adjusted by the CPU 62 according to the detected image density.

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

[0002]

2. Description of the Related Art Electrophotographic copying machines, printers, and the like are widely known as image forming apparatuses. In an electrophotographic copying machine or the like, an electrostatic latent image is formed by exposing the surface of a charged photosensitive drum to light, and then the electrostatic latent image is developed with toner as a developer to form the surface of the photosensitive drum. An image is obtained by forming a toner image on the top and further transferring the formed toner image onto a transfer sheet.

In this type of copying machine and the like, in recent years, the image forming speed has been increased, but with the increase in the speed, the transfer efficiency of the toner image electrostatically adhered onto the photosensitive drum tends to be deteriorated. . That is, in the image forming process, if the electrostatic adhesion of the toner image formed on the photoconductor drum to the photoconductor drum is large, the toner image is not sufficiently transferred from the photoconductor drum onto the transfer paper, and the image is not sufficiently blurred. In addition, image defects such as insufficient image density and deterioration of image density may occur.

Therefore, in order to efficiently transfer the toner image onto the transfer sheet, after the development and before the transfer, the surface of the photosensitive drum is neutralized by an auxiliary static eliminator so that the electrostatic adhesion force of the toner to the photosensitive drum is increased. It is becoming weaker in many cases.

Such pre-transfer auxiliary static eliminators are broadly divided into those for neutralizing the photoconductor drum by an AC voltage, and those for neutralizing the photoconductor drum by using a light source such as a cold cathode tube or an LED. Things are offered. And
As described above, it is necessary to increase the transfer efficiency as the image forming speed increases. For this purpose, it is effective to increase the efficiency of the pre-transfer auxiliary static eliminator.

[0006]

As described above, in order to improve the transfer efficiency in, for example, a high speed copying machine,
It is necessary to increase the light amount of the pre-transfer auxiliary static eliminator, for example, the pre-transfer static erasing lamp. However, when the pre-transfer charge eliminating lamp irradiates the surface of the photosensitive drum with light while the toner image is formed on the surface of the photosensitive drum, the toner on the surface of the photosensitive drum, for example, the white background portion of the image is The strong light of the pre-transfer charge erasing lamp is directly applied to the area where no is attached. On the contrary, in the solid portion of the image, a large amount of toner adheres to the surface of the photoconductor drum, and it is difficult for the light of the pre-transfer charge eliminating lamp to reach the surface of the photoconductor drum.

Therefore, for example, a white background portion and a solid portion, where toner is present on the surface of the photoconductor drum and where toner is absent, cause a light fatigue step due to the light from the pre-transfer charge eliminating lamp. Then, this step appears as a memory image in the image formed on the transfer sheet, and deteriorates the quality of the formed image.

Further, when the surface potential of the photosensitive drum is high, the environment is changed, the characteristics of the developer are changed due to the life of the developer, or the image density of the solid portion is high. That is, the greater the amount of toner that develops the electrostatic latent image on the photosensitive drum, the greater the step difference in light fatigue described above.

In order to prevent the occurrence of such an image memory, it is conceivable that the light quantity of the pre-transfer charge eliminating lamp is further increased so that the area of the surface of the photosensitive drum on which the toner adheres is also fatigued. If the light quantity of the pre-transfer charge eliminator is increased under normal conditions, that is, even when the image density is not high, the life of the pre-transfer charge eliminator lamp will be shortened, and the character dust will be deteriorated when the image density is normal. Problem arises.

Also, when the AC charger is used as the pre-transfer charge eliminator, the problem of the image memory occurs similarly to the above. In order to prevent the generation of the image memory, the efficiency of the AC charger may be increased to increase the AC applied voltage to the photosensitive drum. However, if the AC applied voltage is constantly increased, the amount of ozone generated Is increased, and there is a problem such as current leakage to the photosensitive drum, which is not desirable.

Therefore, the present invention has been made in consideration of the above-mentioned conventional problems, and an object thereof is to prevent the occurrence of an image memory on an image carrier without causing the problems of the prior art. An object is to provide an image forming apparatus capable of obtaining a good image.

[0012]

In order to achieve the above object, an image forming apparatus of the present invention according to claim 1 comprises an image carrier and an image forming means for forming a developer image on the image carrier. A transfer means for transferring the developer image formed on the image carrier to a transfer material, and a transfer means provided between the image forming means and the transfer means so as to face the image carrier. Reduction means for reducing the electrostatic adhesion force of the developer image, detection means for detecting the image density of the developer image formed on the image carrier, and the reduction means according to the detected image density. And a control means for changing the efficiency of.

According to the image forming apparatus having the above structure, the image density of the developer image formed on the image bearing member is detected by the detecting means, and the controlling means determines the efficiency of the reducing means according to the detected image density. Adjust. Then, the reducing unit reduces the electrostatic adhesion force of the developer image to the image carrier with the adjusted efficiency. As a result, the transfer efficiency of the developer image by the transfer unit is improved and the occurrence of the image memory of the image carrier is prevented.

According to a second aspect of the present invention, in an image forming apparatus of the present invention, an image carrier, an image forming means for forming a developer image on the image carrier, and a developer image formed on the image carrier. And a transfer unit for transferring the image to a transfer material, and a reduction unit that is provided between the image forming unit and the transfer unit so as to face the image carrier and reduces the electrostatic adhesion force of the developer image to the image carrier. Means, and an image density detecting means provided between the image forming means and the reducing means so as to face the image carrier, and detecting an image density of the developer image formed on the image carrier, And a control unit that changes the efficiency of the reduction unit according to the detected image density.

According to the image forming apparatus having the above-mentioned structure, the image density of the developer image is detected on the image carrier by the image density detecting means, and the efficiency of the reducing means is changed according to the detected image density. ing.

According to a third aspect of the present invention, in an image forming apparatus of the present invention, an image carrier, latent image forming means for exposing the image carrier to form an electrostatic latent image on the image carrier, and the image carrier. Developing means for supplying a developer to the electrostatic latent image formed on the body to form a developer image; transfer means for transferring the developer image formed on the image carrier to a transfer material; Means for reducing the electrostatic adhesion force of the developer image to the image carrier, which is provided between the means and the transfer means so as to face the image carrier, and the image carrier by the latent image forming means. And a control means for changing the efficiency of the reduction means according to the detected exposure amount.

According to the image forming apparatus having the above structure, the image density of the developer image formed on the image carrier is detected by detecting the exposure amount of the latent image forming means by the detecting means,
The efficiency of the reducing means is changed according to the detected image density.

According to a fourth aspect of the present invention, there is provided an image forming apparatus, an image carrier, an image forming unit for forming a developer image on the image carrier, and a developer image formed on the image carrier. Is provided between the image forming means and the transfer means for transferring the image to a transfer material, and the image carrier is irradiated with a discharging light so that the electrostatic force of adhesion of the developer image to the image carrier is increased. Pre-transfer charge eliminating light source for reducing, detecting means for detecting the image density of the developer image formed on the image carrier, and control means for changing the efficiency of the auxiliary charge eliminating light source according to the detected image density. It is characterized by having and.

According to the image forming apparatus having the above structure, the pre-transfer charge eliminating light source irradiates the image bearing member with the charge eliminating light before the developer image formed on the image bearing member is transferred by the transfer means. The carrier is discharged to reduce the electrostatic adhesion of the developer image to the image carrier. Then, the efficiency of the pre-transfer charge eliminating light source is changed according to the image density detected by the detecting means.

According to a fifth aspect of the present invention, in an image forming apparatus, an image carrier, image forming means for forming a developer image on the image carrier, and a developer image formed on the image carrier. Is provided between the image forming means and the transfer means for transferring the toner image to a transfer material, and the AC voltage is applied to the image carrier to remove the electric charge, so that the developer image on the image carrier is removed. AC charging means for reducing the electrostatic adhesion force, detecting means for detecting the image density of the developer image formed on the image bearing member, and the above-mentioned A according to the detected image density.
And a control means for changing the efficiency of the C charging means.

According to the image forming apparatus having the above structure, the AC charger applies the AC voltage to the image carrier to transfer the image before the developer image formed on the image carrier is transferred by the transfer means. The body is destaticized to reduce the electrostatic adhesion of the developer image to the image carrier. Then, the efficiency of the AC charger is changed according to the image density detected by the detecting means.

[0022]

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.
A photosensitive drum 12 as an image bearing member is rotatably provided at a substantially central portion of the housing. Around the photosensitive drum 12, a charger 11 and a developing device 1 are provided.
3, the transfer charger 14, the peeling charger 15, the peeling claw 16, the cleaning device 17, and the charge eliminating lamp 18 are arranged in this order to form an image forming unit 20.

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

The ADF 80 is configured to also serve as a document holder for opening and closing the document placing table 32, and is provided so as to face the document tray 82 on which the document D is placed and almost the entire surface of the document placing table, and conveys the document. And a belt 85. 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 document read by the scanner described later is discharged to a document discharge unit 88 on the upper surface of the ADF 80 through the conveyance path 86 by the conveyance belt 85.

A scanner 22 that functions as a reading unit for reading an image of the original document D placed on the original document table 32 is disposed below the original document table 32 in the housing 10. The scanner 22 includes an exposure lamp 24 having a back portion surrounded by a reflector 23, and a first reflection mirror 25 mounted on the first carriage 33 together with the exposure lamp. In addition, the scanner 22 is the second
Mounted on the carriage 34 of the second movable integrally
And the third reflecting mirrors 26 and 27, the lens 28,
Fixed fourth, fifth and sixth reflecting mirrors 29, 30, 3
1 and.

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.

As a result, an electrostatic latent image corresponding to the image of the original is formed on the surface of the photosensitive drum 12 that is 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 reflecting mirror 27 and the lens 28. Specifically, the automatic exposure sensor 21 includes the lens 2
In the same plane as the surface on which 8 is arranged, that is, in the region where the light propagating from the third reflecting mirror 27 to the fourth reflecting mirror 29 passes, and blocks the light traveling to the fourth reflecting mirror 29. It is provided in a unique position.

Then, a part of the light reflected by the third mirror 27 enters the automatic exposure sensor 21, and the automatic exposure sensor 2
A CPU 92, which will be described later, outputs an output voltage according to the image density.
It is output as a document density signal. That is, the automatic exposure sensor 21 functions as a detection unit that detects the image density of the document D.

First and second paper feed cassettes 35 and 36, each containing a large number of papers P as transfer materials, are detachably attached to the lower side surface of the housing 10. Further, in the housing 1, the first and second paper feed cassettes 3
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 the side wall of the housing 1 facing the fixing device 40, and a discharge tray 43 is attached to this discharge port.

First and second paper feed cassettes 35, 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 picked up one by one from the first or second paper feed cassette 35, 36 by the pickup roller 44 is aligned by the registration roller 46 and then sent to the transfer section. 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 is transferred is peeled from the photosensitive drum 12 by the AC corona discharge from the peeling charger 15 and the peeling claw 16, and is transferred to the fixing device 40 via the conveyance belt 50 forming the conveyance path 38. Be transported.
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.

The fixing device 4 is provided below the conveying path 38.
There is provided an automatic double-sided device 51 which reverses the paper P that has passed 0 and guides it again to the transfer portion via the registration roller 40. The automatic double-sided device 51 includes 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 a sheet from the temporary accumulating section to the registration roller 46. Re-transport path 5 for transporting P
4 is provided.

A distribution gate 55 for guiding the sheet P to the reversing path 52 is provided between the fixing device 40 and the discharge roller 51, and a plurality of feed rollers 56 are arranged in the reversing path 52 and the re-conveying path 54. It is set up. 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 paper P that has passed through the fixing device 40 is fed to the reverse path 5 by the sorting gate 55.
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.
Then, the toner image is transferred to the registration roller 46 through the registration roller 46, and is arranged here. After that, the paper P is conveyed to the conveyance path 38 and the fixing device 40.
Then, the sheet is discharged to the sheet discharge tray 43 via the sheet discharge roller 51.

Next, the structures of the photosensitive drum 12 and the image forming section 20 will be described in detail. As shown in FIG. 2, the photoconductor drum 12 has a cylindrical element tube made of, for example, aluminum and a photoreceptor layer formed on the outer peripheral surface of the element tube, for example, arsenic selenium. A heater (not shown) for heating the photosensitive drum is provided on the inner peripheral surface of the tube.

The charging charger 11 for uniformly charging the surface of the photosensitive drum 12 to a predetermined electric charge is a high voltage transformer 6.
It is connected to the CPU 62 as a control means via 0. With respect to the rotation direction of the photoconductor drum 12, an exposure position 12a on the surface of the photoconductor drum 12 that is exposed by the reflected light from the scanner 22 is provided on the downstream side of the charger 11. At this exposure position, the photoconductor drum surface is exposed. An electrostatic latent image is formed. The charging charger 11 and the scanner 22 constitute the latent image forming means in this invention.

An LED 65 for partial erasing is arranged between the exposure position 12a and the charger 11. Further, a developing device 13 as a developing means for supplying toner particles to the electrostatic latent image on the surface of the photosensitive drum 12 to develop the electrostatic latent image, and LE.
A thermistor 66 that detects the temperature of the surface of the photoconductor drum 12 is provided between the photoconductor drum 12 and D65. An actuator 66a of the thermistor 66 is in contact with the drum surface at the end of the photoconductor drum. Then, the thermistor 66 outputs a detection signal to the CPU 62.

The transfer charger 14 functioning as a transfer means for transferring the toner image formed on the photoconductor drum 12 to the paper P and the peeling charger 15 for separating the paper P from the photoconductor drum 12 are the photoconductor drum 12. It is provided on the downstream side of the developing device 13 with respect to the rotation direction A. 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.

The peeling claw 16 located on the downstream side of the peeling charger 15 is driven by a solenoid 71, which is connected to a CPU 62 via a driver 72. The charging charger 11, the developing device 13 and the like also function as image forming means in the present invention.

On the downstream side of the peeling claw 16, a cleaning device 17 for cleaning the toner remaining on the surface of the photosensitive drum 12 without being transferred to the sheet, and a charge eliminating lamp 18 are arranged in order. The cleaning device 17 includes a main cleaning mechanism 74 and an auxiliary cleaning mechanism 76 provided upstream of the main cleaning mechanism in the rotation direction of the photoconductor drum 12.

The main cleaning mechanism 74 has a cleaning blade 78, which is provided in contact with the surface of the photosensitive drum 12 and scrapes off the toner remaining on the drum surface from the drum surface.

The auxiliary cleaning mechanism 76 includes a charger 90 for applying an AC voltage to the surface of the photosensitive drum 12, and an AC power source 92 for supplying an AC voltage to the charger.
The power source is connected to the CPU 62. Further, the charge eliminating lamp 18 is connected to the CPU 62 via the light source driver 94.

Further, according to the present embodiment, the developing device 13
A pre-transfer static eliminator 96 having a cold cathode tube is provided as a pre-transfer static eliminator between the transfer charger 14 and the transfer charger 14 and faces the photoconductor drum 12. The pre-transfer charge eliminating lamp 96 is connected to the CPU 62 via an inverter circuit 97 for causing the charge eliminating lamp to emit light. Then, by controlling the voltage applied to the inverter circuit 97 by the CPU 62, the light amount of the pre-transfer charge eliminating lamp 96 can be adjusted. Inverter circuit 97 and CPU
62 constitutes the control means in the present invention. A memory 93 in which desired control data and the like are stored is connected to the CPU 62.

The pre-transfer charge eliminating lamp 96 also functions as the reducing means in the present invention, and the photoconductor drum 12
By irradiating the surface with light, the charge on the surface of the photosensitive drum is removed, and the electrostatic adhesion between the toner image formed on the surface of the photosensitive drum and the photosensitive drum is weakened. As a result, the transfer efficiency of the toner image at the transfer position is improved.

Further, the developing device 13 and the pre-transfer charge eliminating lamp 96
A reflection type image density sensor 98 for detecting the amount of toner adhering to the surface of the photosensitive drum 12, that is, the image density is provided between and. The image density sensor 98 is
By having a light emitting unit and a light receiving unit (not shown), the surface of the photosensitive drum 12 is irradiated with detection light from the light emitting unit, and the reflected light from the photosensitive drum is received, whereby a detection signal corresponding to the reflected light is sent to the CPU 62. Output. The image density sensor 98 functions as the detecting means and the image density detecting means in the present invention.

Then, the CPU 62 causes the image density sensor 9
The voltage applied to the inverter circuit 97 is adjusted in accordance with the output of No. 8 to adjust the light amount of the pre-transfer charge eliminating lamp 96. That is, FIG. 3 shows the relationship between the presence / absence of toner on the photoconductor drum 12 and the output value of the image density sensor 98. The reflected light is strong and the output of the image density sensor is high. On the contrary, in the portion of the surface of the photoconductor drum 12 where the toner is attached, the reflected light from the photoconductor drum is weak and the output of the image density sensor 98 is also low. Therefore, the output of the image density sensor 98 changes according to the image density, that is, the toner density on the surface of the photosensitive drum.

On the other hand, as can be seen from FIG. 4, when the light amount of the pre-transfer charge eliminating lamp 96 is constant, the level of the image memory produced on the photoconductor drum 12 by irradiating the pre-transfer charge eliminating lamp is the same as that of the photoconductor drum 12. The higher the image density of the toner image formed on the surface is, that is, the higher the amount of toner particles attached to the electrostatic latent image on the photosensitive drum is, the higher the image density is.

FIG. 5 shows the relationship between the light amount of the pre-transfer charge eliminating lamp 96 and the level of the image memory. From this figure, when the image density of the toner image on the surface of the photosensitive drum 12 is high, That is, even if the amount of toner particles attached to the electrostatic latent image on the photosensitive drum is large, it is understood that the image memory can be reduced by increasing the light amount of the pre-transfer charge eliminating lamp.

The measurement of the image memory shown in FIGS. 4 and 5 was carried out under the environmental conditions of room temperature and normal humidity (23 ° C., 50 RH%) using a Toshiba copier (Rheo Dry 6550). The potential was fixed at 700 V and various image densities were measured.

Therefore, according to the present embodiment, when the output of the image density sensor 98 is high, the pre-transfer charge eliminating lamp 9 is used.
The amount of light of 6 is increased to prevent the occurrence of image memory, and at the same time, the electrostatic attraction force of the toner image to the surface of the photosensitive drum 12 is weakened to improve the transfer efficiency, and conversely, the image density sensor 9
When the output of 8 is low, the surface of the photoconductor drum is discharged with the light amount of the pre-transfer charge eliminating lamp 96 being reduced to improve the transfer efficiency.

According to the present embodiment, as shown in FIG. 6, the light quantity of the pre-transfer charge eliminating lamp 96, that is, the voltage applied to the inverter circuit 97 is set in advance in three stages according to the image density. . Then, when the image density of the toner image formed on the photoconductor drum 12 is low, that is, when the output of the image density sensor 98 is high, the voltage applied to the inverter circuit 97 is not changed and a normal voltage, for example, 24V is applied. Is controlled to increase with increasing image density, that is, as the output of the image density sensor 98 decreases, the voltage applied to the inverter circuit 97 is increased stepwise to increase the light amount of the pre-transfer charge eliminating lamp 96. doing.

As described above, according to the copying machine according to the present embodiment, the pre-transfer charge elimination is performed according to the image density of the toner image on the photosensitive drum detected by the image density sensor 98, that is, the toner adhesion amount. Since the light amount of the lamp 96 is changed, when the image density is high, the light amount of the pre-transfer charge eliminating lamp 96 can be increased to prevent the occurrence of an image memory, and when the image density is low. Therefore, the light quantity of the pre-transfer charge eliminating lamp is not unnecessarily increased, and it is possible to prevent problems such as shortening of the life of the pre-transfer charge eliminating lamp and deterioration of image quality.

Therefore, the transfer efficiency can be improved without generating an image memory, and as a result, a good image can be obtained even when the copying speed is increased. In the above-described embodiment, the light amount of the pre-transfer charge eliminating lamp 96 is changed stepwise according to the output of the image density sensor 98. However, the present invention is not limited to this, and the light output of the image density sensor is changed. It may be changed linearly. Further, the pre-transfer charge eliminating lamp is not limited to the cold cathode tube, and the same effect as described above can be obtained by using an LED.

Further, the pre-transfer static eliminator as the reducing means is not limited to the static eliminator lamp, but as shown in FIG.
It may be configured by 0. This AC charger 100
Is connected to an AC power supply 102 for supplying an AC voltage, and the AC power supply is connected to the CPU 62. Then, the CPU 62 controls the AC power source to the AC charger 100.
By controlling the supply voltage to the AC charger 100
The AC applied voltage can be adjusted.

By applying an AC voltage from the AC charger 100 to the surface of the photosensitive drum 12, the charges on the surface of the photosensitive drum and the toner image are canceled, and the toner image formed on the surface of the photosensitive drum and the photosensitive drum are formed. The electrostatic adhesive force with and is reduced. As a result, the transfer efficiency of the toner image at the transfer position can be improved.

Then, similarly to the above-described embodiment, the AC voltage is changed according to the output voltage of the image density sensor, that is, the image density of the toner image formed on the photosensitive drum 12.
By changing the AC applied voltage of the charger 100,
Only when the image density is high, the AC applied voltage is increased to prevent the occurrence of the image memory, and when the image density is low, the AC applied voltage is not unnecessarily increased and the ozone generation amount is increased, the current leaks, etc. The problem of can be prevented.

Therefore, the transfer efficiency can be improved without generating an image memory, and a good image can be obtained even when the copying speed is increased. Also,
In the above-described embodiment, the efficiency of the pre-transfer static eliminator is changed according to the output of the image density sensor 96, but the output of the automatic exposure sensor 21 is used to change the efficiency of the pre-transfer static eliminator. You may do it.

That is, the automatic exposure sensor 21 uses the document D
The output voltage corresponding to the image density of
Output to U62. As shown in FIG. 8, the output value of the automatic exposure sensor 21 decreases as the image density of the document D decreases, and linearly increases as the image density increases. The higher the image density of the original document, the greater the amount of the developer supplied to the photoconductor drum 12 by the developing device 13, and the higher the image density of the toner image formed.

Therefore, the CPU 62 changes the voltage applied to the inverter circuit 97 or the voltage applied to the AC power source 102 stepwise or linearly in accordance with the image density of the document D detected by the automatic exposure sensor 21 before transfer. Light intensity of the static elimination lamp 96 or AC of the AC charger 100
By adjusting the applied voltage, generation of an image memory can be prevented and a good image can be formed at high speed.

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 present invention is not limited to analog copying machines, but may be applied to other image forming apparatuses such as digital copying machines and laser printers. In this case, the efficiency of the pre-transfer charge eliminator can be adjusted according to the image density detected by the image processing circuit.

[0063]

As described above in detail, according to the present invention, the image density of the developer image formed on the image bearing member is detected, and the efficiency of the pre-transfer charge eliminating means is increased according to the detected image density. By changing it, the life of the pre-transfer charge eliminating means is shortened,
Deterioration of the formed image, increase of ozone generation amount, current leakage, and other conventional problems do not occur, and the degree of fatigue on the photoconductor drum is set to a fixed value, and image defects such as image memory do not occur and good results are obtained. An electrophotographic image forming apparatus capable of obtaining an image can be provided.

[Brief description of the drawings]

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

FIG. 2 is a diagram schematically showing an image forming unit and a drive control system of the copying machine.

FIG. 3 is a graph showing the relationship between the image density and the output of the image density sensor in the copying machine.

FIG. 4 is a graph showing the relationship between image density and image memory.

FIG. 5 is a graph showing a relationship between a voltage applied to a pre-transfer charge eliminating lamp and an image memory in the copying machine.

FIG. 6 is a graph showing the relationship between the output of the image density sensor and the applied voltage in the copying machine.

FIG. 7 is a diagram schematically showing a main part of a copying machine according to another embodiment of the present invention.

FIG. 8 is a graph showing the relationship between the image density of a document and the output of the automatic exposure sensor.

[Explanation of symbols]

 12 ... Photosensitive drum 13 ... Developing device 14 ... Transfer charger 20 ... Image forming part 21 ... Automatic exposure sensor 22 ... Scanner 62 ... CPU 96 ... Pre-transfer static elimination lamp 97 ... Inverter circuit 98 ... Image density sensor 100 ... AC charger 102 … AC power supply

Claims (9)

[Claims] 1. An image carrier, image forming means for forming a developer image on the image carrier, transfer means for transferring the developer image formed on the image carrier to a transfer material, and A reduction unit that is provided between the image forming unit and the transfer unit so as to face the image carrier and reduces the electrostatic adhesion force of the developer image to the image carrier, and is formed on the image carrier. An image forming apparatus comprising: a detection unit that detects the image density of the developer image, and a control unit that changes the efficiency of the reduction unit according to the detected image density. 2. An image carrier, image forming means for forming a developer image on the image carrier, transfer means for transferring the developer image formed on the image carrier to a transfer material, and A reduction unit that is provided between the image forming unit and the transfer unit so as to face the image carrier and reduces the electrostatic adhesion force of the developer image to the image carrier, and the image formation unit and the reduction unit. And an image density detecting unit that is provided between the image carrier and detects the image density of the developer image formed on the image carrier, and the reducing unit according to the detected image density. An image forming apparatus comprising: a control unit that changes the efficiency of the image forming apparatus. 3. An image bearing member, latent image forming means for exposing the image bearing member to form an electrostatic latent image on the image bearing member, and developing the electrostatic latent image formed on the image bearing member. Developing means for supplying a developer to form a developer image, transfer means for transferring the developer image formed on the image carrier to a transfer material, and the image carrying means between the developing means and the transfer means. A reduction unit that is provided so as to face the body and reduces the electrostatic adhesion force of the developer image to the image carrier; a detection unit that detects the exposure amount of the image carrier by the latent image forming unit; An image forming apparatus comprising: a control unit that changes the efficiency of the reduction unit according to the detected exposure amount. 4. An image carrier, image forming means for forming a developer image on the image carrier, transfer means for transferring the developer image formed on the image carrier to a transfer material, and A pre-transfer charge erasing light source provided between the image forming unit and the transfer unit to reduce the electrostatic adhesion of the developer image to the image carrier by irradiating the image carrier with the charge erasing light; An image comprising: a detection unit that detects the image density of the developer image formed on the body; and a control unit that changes the efficiency of the auxiliary static elimination light source according to the detected image density. Forming equipment. 5. An image carrier, image forming means for forming a developer image on the image carrier, transfer means for transferring the developer image formed on the image carrier to a transfer material, and AC charging means which is provided between the image forming means and the transfer means and reduces the electrostatic adhesion force of the developer image to the image carrier by applying AC voltage to the image carrier to eliminate the charge. A detection means for detecting the image density of the developer image formed on the image carrier, and a control means for changing the efficiency of the AC charging means in accordance with the detected image density. A characteristic image forming apparatus. 6. A rotatably provided photosensitive drum, image forming means for forming a developer image on the photosensitive drum, and a developer image formed on the photosensitive drum transferred to a transfer material. Is provided between the image forming unit and the transfer unit so as to face the photoconductor drum, and the charge is removed from the photoconductor drum to electrostatically adhere the developer image to the photoconductor drum. Static elimination means for reducing, a detection means for detecting the image density of the developer image formed on the photosensitive drum, and a control means for increasing the efficiency of the static elimination means in accordance with the increase in the detected image density. An image forming apparatus comprising: 7. A photosensitive drum rotatably provided, image forming means for forming a developer image on the photosensitive drum, and the developer image formed on the photosensitive drum is transferred to a transfer material. And a transfer unit that is provided between the image forming unit and the transfer unit so as to face the photoconductor drum, and irradiates the photoconductor drum with static elimination light to electrostatically charge the developer image to the photoconductor drum. The pre-transfer charge eliminating light source for reducing the adhesive force, the detecting means for detecting the image density of the developer image formed on the photosensitive drum, and the pre-transfer charge eliminating light source for the pre-transfer charge eliminating light source according to the increase in the detected image density. An image forming apparatus comprising: a control unit that increases the amount of light. 8. A photosensitive drum rotatably provided, an image forming means for forming a developer image on the photosensitive drum, and a developer image formed on the photosensitive drum is transferred onto a transfer material. And a transfer unit that is provided between the image forming unit and the transfer unit so as to face the photoconductor drum. By applying an AC voltage to the photoconductor drum to remove the charge, the development of the photoconductor drum is performed. AC charging means for reducing the electrostatic adhesion force of the agent image, detecting means for detecting the image density of the developer image formed on the photoconductor drum, and AC for the increase in the detected image density. An image forming apparatus comprising: a control unit that increases an AC voltage of a charging unit. 9. A rotatable photosensitive drum, reading means for reading an image of an original, image forming means for forming a developer image corresponding to the image of the read original on the photosensitive drum, A transfer unit that transfers the developer image formed on the photosensitive drum to a transfer material, and is provided between the image forming unit and the transfer unit so as to face the photosensitive drum, and removes the electric charge from the photosensitive drum. Reducing means for reducing the electrostatic adhesion force of the developer image to the photosensitive drum, detecting means for detecting the image density of the original read by the reading means, and the detecting means for detecting the image density of the document read by the reading means. An image forming apparatus comprising: a control unit that changes the efficiency of the reduction unit.