JPH07234590A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a small low-cost image forming device by reducing the number of various electrifiers installed, and sharply simplifying the structure. CONSTITUTION:This image forming device is provided with at least a power control means 1, a CPU 2 controlling the power control means 1, a sheet tip detecting means 3 for detecting the tip of the sheet entering a transfer body, a sheet rear end detecting means 4 for detecting the rear end of the sheet, a common electrifier 5 having at least two functions of multiple electrifiers around the transfer body in common, and a peeling electrifier 6 for peeling the sheet from the transfer body. The power control means 1 feeds the required voltage to the common electrifier 5 based on the detection signals of the sheet tip detecting means 3 and the sheet rear end detecting means 4.

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,
In particular, the present invention relates to an image forming apparatus that reduces the number of chargers required in the image forming process and simplifies the configuration for applying a high voltage power source for supplying power to the chargers.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or printer, a corona discharger for forming an electrostatic latent image on a photosensitive member, a toner image obtained by toner development are transferred onto a transfer material. A large number of charging devices such as a transfer corotron for removing the transfer material, a corona discharger for adsorbing the transfer material onto the transfer body, and a corona discharger for removing the transfer material or discharging the transfer body are required.

FIG. 6 is a schematic view for explaining the main structure of a copying machine as an image forming apparatus of this type. Reference numeral 7 is a photosensitive drum, which is a photosensitive member, 71 is a photosensitive drum cleaning device, and 72 is a photosensitive member. A charging device for giving a uniform charge to the surface of the body drum, 73 is a pre-transfer charger, 8 is a developing unit, 81, 82, 83, 84 are yellow, magenta, cyan, and black developing devices, respectively, and 9 is A transfer drum, which is a transfer body, 10 is a laser light source, a polygon mirror,
A laser writing unit composed of a reflecting mirror and the like, 11 a sheet conveying path as a transfer material, 12 a sheet, 13 a registration roller, 14 a transfer drum cleaning device, 15 a fixing device, and 16 a transfer device power supply unit.

Numeral 50 is a transfer charger, 51 is an adsorption charger, 52 is an adsorption facing member, 53 is a charge eliminating charger, and 60 is a peeling charger. In the figure, the photosensitive drum 7 is uniformly charged by the charging device 72, and the image signal of the first color (yellow) modulates the laser light of the laser writing unit 10 and writes it on the photosensitive drum 7 with this laser light. Be done. The written electrostatic latent image is developed with the first color toner (yellow toner) of the developing unit 8 to form a toner image.

On the other hand, the sheet 12 reaches the registration roller 13 through the sheet conveying path 11, is tacked to the transfer drum 9 at a predetermined timing, and is electrostatically attracted by the attraction voltage applied to the attraction charger 51 and the attraction counter member. At 52, it is brought into close contact with the transfer drum 9 and conveyed to the position of the transfer charger 50.
The toner image of the first color formed on the photoconductor drum 7 is transferred to the paper 12 by the electrostatic force of the transfer voltage applied to the transfer charger 50 in the transfer charger 50.

After the transfer of the toner image of the first color is completed, the photosensitive drum cleaning device 71 removes the residual toner from the photosensitive drum 7, and the charging device 72 uniformly charges the residual toner, and the second color (magenta) is discharged. Electrostatic latent image of is written.
The written electrostatic latent image is developed with the second color toner (magenta toner) of the developing unit 8 to form a toner image. This magenta toner is transferred onto the paper 12 by the rotation of the transfer drum 9.

Thereafter, in the same manner, a multicolor toner image (cyan) and a fourth color toner image (black) are transferred onto the paper 12 to form a multicolor toner image on which multicolor toners are superposed. To be done. When this transfer operation is completed, the sheet 11 applies a peeling voltage to the peeling charger 60 and
It is peeled off from the transfer drum 9 by the peeling claw 100 and passed to the fixing device 15. The sheet that has passed through the fixing device 15 is discharged to a discharge tray (not shown).

In the copying machine having the above structure, a required voltage is applied from the power supply unit 16 to each charger around the transfer drum. The power supply unit 16 supplies power to the chargers and other devices around the transfer drum, and supplies power required for the chargers and other devices around the photoconductor drum 7.

[0009]

In the above-mentioned conventional technique, the power supply unit 16 has a function of supplying a high voltage to each of the transfer charger 50, the adsorption charger 51, the static eliminator 53, and the peeling charger 6. There is a need to. For example, when the polarity of the toner formed on the photoconductor drum 7 is “−”, a “−” voltage is applied to the attraction charger 51 for attracting the sheet onto the transfer drum 9, and a “−” voltage is applied to the transfer charger 50. Supplies a "+" voltage to the peeling charger 6, and an AC + "-" voltage to the static eliminator 53 from inside and outside the transfer drum 9. Thus, it is necessary to supply five types of high-voltage power supplies to various chargers around the transfer drum.
Therefore, the power supply unit 16 is inevitably complicated in structure, which is a cause of hindering downsizing and cost reduction of the image forming apparatus.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a compact and low-priced image forming apparatus by reducing the number of various chargers installed and greatly simplifying the configuration. To do. It should be noted that in the prior art, two types of voltages are switched and applied to one charger, as disclosed in Japanese Utility Model Laid-Open No. 2-136270 and Japanese Patent Laid-Open No. 3-16757.
There is one disclosed in Japanese Patent Publication No. 9.

However, in the former case, the transfer material guide member (nylon wire or the like) provided in the transfer charger is destaticized, and in the latter case, dust such as toner on the transfer body is reversely transferred to the photosensitive body. However, it does not consider the simplification of the power supply unit. Further, the transfer voltage supplying transformer for the transfer member and the charging voltage supplying transformer for the photosensitive member are made common, and the transfer member has a configuration having various kinds of charging as described above, Unlike the present invention, the common use of the charger is not considered.

[0012]

In order to achieve the above object, as shown in FIG. 1, the invention according to claim 1 is a power supply control means 1 and a CPU 2 for controlling this power supply control means.
At least two of a sheet leading edge detecting means 3 for detecting the leading edge of the sheet that has entered the transfer body, a sheet trailing edge detecting means 4 for detecting the trailing edge of the sheet, and a plurality of chargers around the transfer body. At least a common charger 5 having a common function and a peeling charger 6 for peeling the sheet from the transfer body are provided, and the power supply control means 1 includes the sheet leading edge detecting means 3 and the sheet trailing edge detecting means 4. It is characterized in that a required voltage is applied to the common charger 5 based on a detection signal.

According to a second aspect of the invention, a photosensitive member carrying an electrostatic latent image, a developing device for developing the electrostatic latent image with a toner to form a toner image, and a sheet for adsorbing and carrying the paper. In the image forming apparatus having at least a transfer member for transferring the toner image formed on the photoconductor to the paper carried on the transfer member, the leading end position of the paper entering the transfer charger is set. A sheet leading edge detecting unit for detecting, a sheet trailing edge detecting unit for detecting a trailing edge position of the sheet detached from the transfer charger, and a transfer charger based on a detection signal of the sheet leading edge detecting unit. , The transfer charger based on an adsorption / transfer voltage for adsorbing the paper to the transfer body and transferring the toner image formed on the photoconductor to the paper, and a detection signal of the paper trailing edge detection means. To the transfer body Characterized in that a voltage control means for applying a charge removing voltage electricity.

Further, according to a third aspect of the present invention, a photosensitive member carrying an electrostatic latent image, a developing device for developing the electrostatic latent image with a toner to form a toner image, and a sheet adsorbing and carrying the paper. An image including at least a transfer body, a transfer charger for transferring the toner image formed on the photoconductor to a sheet carried on the transfer body, and a peeling charger for peeling the sheet from the transfer body. In the forming apparatus, a sheet leading edge detecting unit for detecting a leading edge position of the sheet entering the transfer charger, a sheet trailing edge detecting unit for detecting a trailing edge position of the sheet leaving the transfer charger, An adsorption / transfer voltage for adhering the sheet to the transfer body and transferring the toner image formed on the photoconductor to the sheet by the transfer charger based on the detection signal of the sheet leading edge detection means; The peeling charger Voltage control means for applying a peeling voltage for peeling the paper after the transfer from the transfer body and a discharging voltage for discharging the transfer body to the transfer charger based on the detection output of the paper trailing edge detecting means. It is characterized by being provided.

Furthermore, the invention according to claim 3 is a photosensitive member carrying an electrostatic latent image, a developing device for developing the electrostatic latent image with a toner to form a toner image, and adsorbing a sheet. At least a transfer member for carrying and a transfer charger for transferring the toner image formed on the photosensitive member onto the paper carried by the transfer member are provided, and each of the multicolor electrostatic latent images is sequentially corresponded. In an image forming apparatus that forms a multicolor image by developing with multicolor toner and sequentially transferring to the same paper, a paper leading edge detecting means for detecting a leading edge position of the paper entering the transfer charger. A sheet trailing edge detecting means for detecting a trailing edge position of the sheet detached from the transfer charger, and the transfer charger adsorbs the sheet on the transfer body based on a detection signal of the sheet leading edge detecting means. And sequentially formed on the photoconductor Transfer to the transfer charger based on an attraction / transfer voltage for sequentially transferring the formed multicolor toner image to the paper and a detection signal of the paper trailing edge detection means after formation of a predetermined multicolor toner image. It is characterized in that a voltage control means for applying a discharging voltage for discharging the body is provided.

According to a fourth aspect of the invention, a photosensitive member carrying an electrostatic latent image, a developing device for developing the electrostatic latent image with a toner to form a toner image, and a sheet for adsorbing and carrying the paper. And a transfer charger for transferring the toner image formed on the photoconductor to the paper carried on the transfer body, and a peeling charger for peeling the paper from the transfer body. In the image forming apparatus that forms a multicolor image by sequentially developing the multicolor electrostatic latent images with corresponding multicolor toners and sequentially transferring them to the same sheet, the multicolor electrostatic latent images enter the transfer charger. A sheet leading edge detecting means for detecting a leading edge position of the sheet, and a sheet trailing edge detecting means for detecting a trailing edge position of the sheet detached from the transfer charger;
Based on the detection signal of the sheet leading edge detecting means, the transfer charger is configured to attract the sheet to the transfer body and to attract the multicolor toner images sequentially formed on the photoconductor to the sheet in sequence. The transfer voltage, the peeling voltage for peeling the sheet after the transfer of the predetermined multicolor toner image to the peeling charger from the transfer body, and the paper trailing edge detection means after the formation of the predetermined multicolor toner image It is characterized in that the transfer charger is provided with voltage control means for applying a discharging voltage for discharging the transfer body based on the detection output.

In the above, according to the present invention, a suction charging device for a sheet on a transfer body is separately provided so that the transfer charging device has both the transfer function of the toner image and the charge removing function of the transfer body. You can also Further, the magnitude of the direct current component, which is the transfer voltage applied to the transfer charger, can be changed stepwise for the first color, the second color, and the third color. In that case, the transfer device power supply unit may be configured to operate such that its output voltage changes under the control of the control device (CPU), based on the detection signal of the paper edge detection means.

The above-mentioned transfer body is not limited to the drum shape (transfer drum) but may be a known belt shape.

[0019]

In the structure of claim 1, the power supply control means 1 has a function of supplying a required voltage to at least various chargers installed around the transfer body. And CPU
Reference numeral 2 controls the image forming apparatus and the power supply control means. The sheet leading edge detecting unit 3 detects the leading edge of the sheet that has entered the transfer body, and supplies the detection signal to the CPU 2, and the sheet trailing edge detecting unit 4 detects the trailing edge of the sheet and sends the detection signal to the CPU 2. give.

The common charger 5 has a function in which at least two functions of a plurality of chargers required around the transfer body are made common, and the peeling charger 6 peels the sheet on which the toner image is transferred from the transfer body. It has the function of passing it to the fixing means in the latter stage. And
The power supply control means 1 applies a required voltage to the common charger 5 based on the detection signals of the paper leading edge detecting means 3 and the paper trailing edge detecting means 4.

Further, in the structure described in claim 2, the photosensitive member carries an electrostatic latent image, and the electrostatic latent image conveys the toner image developed with the toner from the developing unit to the transfer charger. With. The transfer body adsorbs and carries a sheet of a transfer material and conveys it, and the transfer device, which is a transfer charger, transfers the toner image formed on the photoconductor to the transfer material carried by the transfer body.

Then, the sheet leading edge detecting means detects the leading edge position of the sheet entering the transfer member, and the transfer material trailing edge detecting means detects the trailing edge position of the sheet leaving the transfer charger. An adsorption / transfer voltage for adhering the sheet to the transfer body and transferring the toner image formed on the photoconductor to the sheet by the transfer charger based on the detection signal of the sheet leading edge detection means; It is characterized in that a voltage control means for applying a discharging voltage for discharging the transfer body to the transfer charger based on a detection output of the paper trailing edge detecting means is provided.

Further, in the invention described in claim 3, a photosensitive member carrying an electrostatic latent image, a developing device for developing the electrostatic latent image with a toner to form a toner image, and a sheet for adsorbing and carrying the paper. An image including at least a transfer body, a transfer charger for transferring the toner image formed on the photoconductor to a sheet carried on the transfer body, and a peeling charger for peeling the sheet from the transfer body. In the forming apparatus, a sheet leading edge detecting unit for detecting a leading edge position of the sheet entering the transfer body, a sheet trailing edge detecting unit for detecting a trailing edge position of the sheet leaving the transfer charger, and An adsorption / transfer voltage for adsorbing the sheet to the transfer body and transferring the toner image formed on the photoconductor to the sheet by the transfer charger based on a detection signal of the sheet leading edge detection means; Before peeling charger Provided is a peeling voltage for peeling the transferred sheet from the transfer body, and voltage control means for applying a discharging voltage for discharging the transfer body to the transfer charger based on a detection output of the sheet trailing edge detecting means. It is characterized by that.

Further, the invention according to claim 4 is a photosensitive member carrying an electrostatic latent image, a developing device for developing the electrostatic latent image with a toner to form a toner image, and adsorbing a sheet. At least a transfer member for carrying and a transfer charger for transferring the toner image formed on the photosensitive member onto the paper carried by the transfer member are provided, and each of the multicolor electrostatic latent images is sequentially corresponded. In an image forming apparatus that forms a multicolor image by developing with multicolor toner and sequentially transferring to the same paper, paper leading edge detecting means for detecting the leading edge position of the paper entering the transfer body, A sheet trailing edge detecting means for detecting a trailing edge position of the sheet detached from the transfer charger, and the transfer charger adsorbs the sheet to the transfer body based on a detection signal of the sheet leading edge detecting means. Are formed on the photoreceptor in sequence with The transfer charger is configured to transfer the transfer member to the transfer charger based on the attraction / transfer voltage for sequentially transferring the multicolor toner image to the paper and the detection output of the paper trailing edge detection unit after the predetermined multicolor toner image is formed. It is characterized in that a voltage control means for applying a discharging voltage for discharging is provided.

According to a fifth aspect of the invention, a photosensitive member carrying an electrostatic latent image, a developing device for developing the electrostatic latent image with a toner to form a toner image, and a sheet for adsorbing and carrying the paper. And a transfer charger for transferring the toner image formed on the photoconductor to the paper carried on the transfer body, and a peeling charger for peeling the paper from the transfer body. In an image forming apparatus for forming a multicolor image by sequentially developing multicolor electrostatic latent images with corresponding multicolor toners and sequentially transferring the same on a single sheet, the multicolor electrostatic latent images are inserted into the transfer body. Based on the detection signal of the sheet leading edge detecting means for detecting the leading edge position of the sheet, the sheet trailing edge detecting means for detecting the trailing edge position of the sheet detached from the transfer charger, and the detection signal of the sheet leading edge detecting means. Place the paper in front of the transfer charger. An adsorption / transfer voltage for adsorbing to the transfer body and sequentially transferring the multicolor toner images sequentially formed on the photoconductor onto the paper, and a paper after transfer of the predetermined multicolor toner image to the peeling charger. A peeling voltage for peeling from the transfer body and a discharging voltage for discharging the transfer body are applied to the transfer charger based on the detection output of the paper trailing edge detection unit after forming a predetermined multicolor toner image. It is characterized in that a voltage control means is provided.

In the above, according to the present invention, a sheet adsorbing and charging device for the transfer member may be separately provided so that the transfer charging device has both the transfer function of the toner image and the discharging function of the transfer member. it can. Further, the paper leading edge detecting means and the paper trailing edge detecting means may be installed separately or may be common detecting means. However, at least for detecting the paper leading edge, the paper leading edge detecting means is required. Is installed upstream of the transfer charger.

Further, the magnitude of the DC component, which is the transfer voltage applied to the transfer charger, is determined by the first color, the second color, and the third color.
It is also possible to change the color stepwise. In that case, under the control of the control device (CPU), the transfer device power supply unit operates so as to change its output voltage based on the output signal of the paper leading edge detecting means or the paper trailing edge detecting means. And it is sufficient.

The above-mentioned transfer body is not limited to the drum shape (transfer drum) but may be a known belt shape.

[0029]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a schematic diagram for explaining the configuration of the first embodiment of the image forming apparatus according to the present invention, in which the present invention is applied to a so-called gripless type multicolor image (full color) copying machine.

In the figure, similarly to FIG. 6, 3 is a paper leading edge detector which is a paper leading edge detecting means, and 4 is a paper trailing edge detector which is a paper trailing edge detecting means. And the sheet trailing edge detecting means 4 are commonly used. Further, 7 is a photoconductor drum which is a photoconductor, 71 is a photoconductor drum cleaning device, 72 is a charging device which gives a uniform charge to the surface of the photoconductor drum, 8 is a developing unit, 81, 8
2, 83, 84 are yellow, magenta, cyan, and black developing devices, 9 is a transfer drum as a transfer member, 10 is a laser writing unit including a laser light source, a polygon mirror, a reflecting mirror, and the like, and 11 is a transfer material. A sheet conveying path, 12 is a sheet, 13 is a registration roller, 14 is a transfer drum cleaning device, 15 is a fixing device, and 16 is a transfer device power supply unit. 5 is a transfer charger as a common charger, and 6 is a peel charger.

In this embodiment, the registration roller 13 is arranged so that the paper 12 is tacked to the transfer drum 9 at a position close to the common charger 5. The photoconductor drum 7 is uniformly charged to the "-" polarity by the charging device 72, and the image signal of the first color (yellow) modulates the laser beam of the laser writing unit 10, and the laser beam is applied to the photoconductor drum 7. Written. The written electrostatic latent image is the first image of the developing unit 8.
The toner image is developed with the toner of the color (yellow toner) and is rotated to the position of the common charger 5.

Paper 1 supplied through paper transport path 11
The registration roller 13 enters between the photosensitive drum 7 and the transfer drum 9 at a predetermined timing by the registration roller 13. The transfer drum 9 and the photoconductor drum 7 rotate at the same peripheral speed, and the “+” high voltage applied from the transfer device power supply unit 6 causes the paper 12 to be attracted to the transfer drum 9 and, at the same time, on the photoconductor drum 7. The toner image is transferred to the sheet 12.

After the transfer of the toner image of the first color is completed, the photosensitive drum cleaning device 71 removes the residual toner from the photosensitive drum 7, and the charging device 72 uniformly charges the residual toner, and the second color (magenta) is discharged. Electrostatic latent image of is written.
The written electrostatic latent image is developed with the second color toner (magenta toner) of the developing unit 8 to form a toner image. The sheet of paper passes through the peeling prevention charger 6 by the rotation of the transfer drum 9, reaches the position of the registration roller 13 again, and enters between the photosensitive drum 7 and the transfer drum 9 at a predetermined timing.

The magenta toner of the second color is transferred onto the paper 12 by the rotation of the transfer drum 9. Thereafter, similarly, the third color toner image (cyan) and the fourth color toner image (black) are transferred to the paper 12 to form a multicolor toner image on which the multicolor toners are superimposed.

When this transfer operation is completed, the peeling voltage is applied to the peeling prevention charger 6 in response to the paper trailing edge detection signal from the paper trailing edge detector 4, whereby the paper 11 is transferred onto the paper drum 9.
And is delivered to the fixing device 15. Fixing device 15
The sheet that has passed through is discharged to a discharge tray (not shown).
Further, in accordance with the sheet trailing edge detection signal of the sheet trailing edge detector 4, the transfer device power supply unit 16 supplies AC to the common charger 5.
The charge removal voltage is applied to remove charge from the transfer drum.

The first color, the second color, the third color, the fourth color
In the color transfer operation example, the transfer voltage applied to the common charger 5 is controlled so as to be sequentially increased. In this way, according to the present embodiment, the common charger 5 is configured to simultaneously adsorb the sheet onto the transfer drum 9 and transfer the toner image from the photoconductor drum 7, so that the charger around the transfer drum is used. It is possible to provide a low-cost image forming apparatus by reducing the number of installations, reducing the number of parts, and simplifying the configuration of the power supply unit.

FIG. 3 is a schematic diagram for explaining the configuration of the second embodiment of the image forming apparatus according to the present invention, in which the present invention is applied to a so-called grip type copying machine. In this embodiment, the present invention is applied to an image forming apparatus having a configuration in which a space for arranging a sheet conveying mechanism including registration rollers in the vicinity of a common charger cannot be provided. In the figure,
The same reference numerals as those in FIG. 2 indicate components having the same functions.
Reference numeral 7 is a gripper, and 73 is a pre-transfer charger.

In this embodiment, the gripper 17 grips the leading edge of the sheet that has entered the transfer drum 9, and the common charger 5
To the position. During this conveyance, the paper is not in close contact with the curvature of the surface of the transfer drum 9. Then, when a transfer voltage is applied to the common transfer device 5 to perform transfer by the common transfer device 5, the sheet is attracted to the transfer drum by the electrostatic force of the transfer voltage. That is, the transfer of the toner image onto the paper 12 and the suction of the paper are performed at the same time.

Further, in accordance with the sheet trailing edge detection signal of the sheet trailing edge detector 4, the AC charging voltage is applied from the transfer device power supply unit 6 to the common charger 5 to charge the transfer drum. The transfer voltage applied to the common charger 5 in the transfer operation example of the first color, the second color, the third color, and the fourth color is controlled to be successively increased.

In this way, according to the present embodiment, the common charger 5 attracts the paper to the transfer drum 9 and transfers the toner image from the photosensitive drum 7 at the same time. Similarly to the above, it is possible to reduce the number of chargers installed around the transfer drum, reduce the number of parts and simplify the configuration of the power supply unit, and thus it is possible to provide an inexpensive image forming apparatus.

4A and 4B are explanatory views of the operation around the transfer drum in each embodiment of the multicolor copying machine. FIG. 4A is a rotation order of the transfer drum, FIG. 4B is a toner image to be transferred, and FIG. )
Represents the transfer voltage, and (e) represents the static elimination voltage. In the figure,
The transfer voltage of (c) is turned on / off by the common charger in response to one rotation, two rotations, three rotations, and four rotations of the transfer drum shown in (a), and the yellow (Y) toner shown in (b) is transferred. The image, the magenta (M) toner image, the cyan (C) toner image, and the black (K) toner image are sequentially transferred onto the paper.

After the transfer of all the toner images is completed, the charge eliminating voltage (AC) is applied to the common charger as shown in (d) to eliminate the charge on the transfer drum and prepare for the next copy. The supply of the above-mentioned / adsorption transfer voltage and the supply of the discharging voltage to the common charger are performed by switching the power supply of the transfer device power supply unit at the switching point of (d). FIG. 5 is a flow chart for explaining the control sequence around the transfer drum in each of the above embodiments.

In the figure, first, when the paper leading edge detector detects the leading edge of the paper (S-1), a DC voltage is applied to the common charger. As a result, the sheet is attracted and the toner image is transferred (S-2). Regarding the completion of this transfer operation,
The paper trailing edge detector detects the trailing edge of the paper (S-3), and the rotation number N of the photosensitive drum does not reach 4 (N in S-4).
o) The process returns to (S-1) through the process of forming a toner image of the next color (S-5).

When the number of rotations N of the photosensitive drum reaches 4 (Yes in S-4), a peeling voltage is applied to the peeling charger (S-6), and the trailing edge of the sheet passes through the common charger. The AC charge eliminating voltage is applied to the common charger (S-7). Then, if there is a next copy (Yes in S-8), the process returns to S-1, and if the copy is completed (No in S-8), the image forming operation is ended.

In the description of the above embodiment, the detection signals of the paper leading edge detector and the paper trailing edge detector are adjusted for the time corresponding to the mechanical operation time such as the rotation of the transfer drum and the next operation is performed. Start at the start timing.
Further, although the paper leading edge detector and the paper trailing edge detector have been described as using the common detector in the above-mentioned embodiments, each detector may be installed at a desired position instead. .

Further, the leading edge and the trailing edge of the sheet can be known from the rotational position of the transfer drum by the sheet size which is input in advance or the size detection, and the configuration by this method is also similar to the above. As the charger in the above embodiment, a corona charger, a brush charging roll, a magnetic blade / bias roll, and other known means can be used.

The present invention, as in the above embodiment,
Not only a full-color copying machine, but also a single-color copying machine or other image forming apparatus and a drum-shaped member as a transfer member, a belt-shaped transfer member or an intermediate transfer member is used. It can also be applied to things.

[0048]

As described above, according to the present invention,
It is possible to provide a small-sized and low-priced image forming apparatus by reducing the number of installed chargers and greatly simplifying the configuration.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a basic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a schematic diagram illustrating the configuration of a first embodiment of the image forming apparatus according to the present invention.

FIG. 3 is a schematic diagram illustrating the configuration of a second embodiment of the image forming apparatus according to the present invention.

FIG. 4 is an explanatory diagram of an operation around a transfer drum in each embodiment of the multicolor copying machine.

FIG. 5 is a flow chart illustrating a control sequence around a transfer drum in each embodiment.

FIG. 6 is a schematic diagram illustrating a main configuration of a copying machine as an image forming apparatus.

[Explanation of symbols]

1 ... Power supply control means, 2 ... CPU, 3 ...
.Paper leading edge detecting means, 4 ... Paper trailing edge detecting means, 5
・ ・ ・ Common charger, 6 ・ ・ ・ Peeling charger, 7 ・ ・ ・
-Photosensitive drum, 71 --- Photosensitive drum cleaning device, 72 --- Charging device that applies a uniform charge to the surface of the photosensitive drum, --- Developing unit, 81,8
2,83,84 ... Yellow, magenta, cyan,
Black developing devices, 9 ... Transfer drums, 10 ...
... Laser writing unit including laser light source, polygon mirror, reflecting mirror, etc., 11 ... Paper transport path, 12
.... Paper, 13 ...- Registration roller, 14 ...
..Transfer drum cleaning device, 15 ... Fixing device, 16 ... Transfer device power supply unit

Claims (5)

[Claims] 1. A power supply control means, a CPU for controlling the power supply control means, a paper leading edge detection means for detecting a leading edge of a sheet that has entered a transfer body, and a paper rear side for detecting a trailing edge of the sheet. An end detecting means and a common charger having at least two functions of a plurality of chargers around the transfer body in common,
At least a peeling charger for peeling the paper from the transfer body is provided, and the power supply control means applies a required voltage to the common charger based on the detection signals of the paper leading edge detecting means and the paper trailing edge detecting means. An image forming apparatus having the above structure. 2. A photosensitive member carrying an electrostatic latent image, and a developing device for developing the electrostatic latent image with a toner to form a toner image.
An image forming apparatus having at least a transfer body that adsorbs and carries a sheet and a transfer charger that transfers the toner image formed on the photoconductor onto the sheet carried by the transfer body Based on the detection output of the sheet leading edge detecting means for detecting the leading edge position of the sheet, the sheet trailing edge detecting means for detecting the trailing edge position of the sheet detached from the transfer charger, Based on the attraction / transfer voltage for attracting the paper to the transfer body and transferring the toner image formed on the photoconductor to the paper, and the detection output of the paper trailing edge detection means. An image forming apparatus is provided with a voltage control means for applying a discharging voltage for discharging the transfer body to the transfer charger. 3. A photosensitive member carrying an electrostatic latent image, and a developing device for developing the electrostatic latent image with a toner to form a toner image.
A transfer body that adsorbs and carries a sheet, a transfer charger that transfers the toner image formed on the photoconductor onto the sheet carried by the transfer body, and a peeling charge that separates the sheet from the transfer body. An image forming apparatus having at least a sheet feeding unit, a sheet leading edge detecting unit for detecting a leading edge position of a sheet entering the transfer body, and a sheet trailing unit for detecting a trailing edge position of the sheet leaving the transfer charger. An end detection unit and an adsorption unit for adhering the sheet to the transfer body and transferring the toner image formed on the photoconductor to the sheet, to the transfer charger based on the detection output of the sheet front end detection unit. / Transfer voltage, a peeling voltage for peeling the transferred sheet from the transfer member to the peeling charger, and a discharge output for discharging the sheet to the transfer unit based on the detection output of the paper trailing edge detection unit. An image forming apparatus characterized in that a voltage control means for applying a voltage. 4. A photosensitive member carrying an electrostatic latent image, and a developing device for developing the electrostatic latent image with a toner to form a toner image.
Each of the multi-color electrostatic latent images has at least a transfer body that adsorbs and carries a sheet, and a transfer charger that transfers the toner image formed on the photoconductor onto the sheet carried by the transfer body. In order to detect the leading edge position of the paper entering the transfer charger, in an image forming apparatus that forms a multicolor image by sequentially developing with a multicolor toner and sequentially transferring the same onto the same paper. A sheet leading edge detecting means; a sheet trailing edge detecting means for detecting a trailing edge position of the sheet detached from the transfer charger; and a sheet charging means for loading the sheet on the transfer charger based on a detection output of the sheet leading edge detecting means. Adsorption / transfer voltage for adsorbing to the transfer member and sequentially transferring the multicolor toner images sequentially formed on the photoconductor to the paper, and the paper trailing edge detecting means after formation of a predetermined multicolor toner image Based on the detection output of An image forming apparatus characterized in that a voltage control means for applying a charge removing voltage neutralizes the sheet to the transfer charger. 5. A photosensitive member carrying an electrostatic latent image, a developing device for developing the electrostatic latent image with a toner to form a toner image,
A transfer body that adsorbs and carries a sheet, a transfer charger that transfers the toner image formed on the photoconductor onto the sheet carried by the transfer body, and a peeling charge that separates the sheet from the transfer body. And an image forming apparatus for forming a multicolor image by sequentially developing each of the multicolor electrostatic latent images with a corresponding multicolor toner and sequentially transferring the same onto a single sheet. Paper leading edge detecting means for detecting the leading edge position of the sheet entering the transfer charger, sheet trailing edge detecting means for detecting the trailing edge position of the sheet leaving the transfer charger, and the sheet leading edge detection An adsorption / transfer voltage for adsorbing the paper to the transfer body and sequentially transferring the multicolor toner images sequentially formed on the photoconductor to the paper on the transfer charger based on the detection output of the means; The peeling charger The transfer charger based on the peeling voltage for peeling the paper after the transfer of the predetermined multicolor toner image from the transfer body and the detection output of the paper rear end detection means after the formation of the predetermined multicolor toner image. An image forming apparatus comprising: a voltage control unit that applies a discharging voltage for discharging the transfer member.