JPH10247007A - Power source device and power supplying method for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent potential by electrification from being changed even by increasing a transfer current at the power source device of an image forming device where a high voltage power source supplying an electrifying device and a transferring device with high voltage is made common. SOLUTION: A variable high voltage resistance 11 is serially inserted into between the electrifying device 2 and the high voltage power source 10, and a grid voltage controlling means 12 increasing and decreasing supplied voltage to the grid electrode 2a of the electrifying device 2 is provided, and a transfer mode changeover means 17 and a controller 16 are provided. Then, when the changeover means 17 instructs the increase of a transfer current to the controller 16, the controller 16 increases the output of the high voltage power source 10, and decreases grid voltage by using the grid voltage controlling means 12. Or, the resistance value of the variable high voltage resistance 11 is increased, so that the grid voltage is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for an image forming apparatus and a method for supplying electric power, and more particularly to an apparatus of a type in which a high voltage power supply is commonly used for a charging device and a transfer device.

[0002]

2. Description of the Related Art FIG. 5 shows a main part of an image forming apparatus using a conventional electrophotographic process. As shown in FIG. 1, the image forming apparatus includes a charging device 2 around a cylindrical photoconductor 1.
The developing device 3, the transfer device 4, and the cleaning device 5 are arranged.

The photoreceptor 1 rotates clockwise in the drawing, and the surface thereof is uniformly charged by a charging device 2. The charged photoconductor 1 receives light from an optical device (not shown) in the direction of arrow a, and forms an electrostatic latent image of a document image on the surface of the photoconductor 1.

When the photosensitive member 1 rotates, the electrostatic latent image is
Is reached, the toner supplied from the developing device is attracted to the electrostatic latent image and becomes a toner image to be visualized. Next, when the toner image reaches the transfer device 4, transfer paper is supplied from the direction of arrow b. Since the transfer paper is charged to the opposite polarity by the transfer device 4, the toner image on the photoconductor is transferred to the transfer paper.
Thereafter, the copy paper onto which the toner image has been transferred is sent to a fixing device (not shown), where the toner is heated and melted and fixed, thereby completing the copying of the original image.

Most of the toner on the photoreceptor 1 is
The toner is transferred to the transfer paper by the transfer device 4, but a small amount of toner remains on the photoconductor 1. Therefore, the residual toner is scraped off by the cleaning device 5. The residual charge on the photosensitive member is removed by a discharging lamp (not shown), the photosensitive member 1 is returned to the initial state, charged again by the charging device, and the process proceeds to the next copy cycle.

[0006] In the above-described process, substantially the same high voltage is applied to the charging device 2 for charging the photoconductor with static electricity and the transfer device 4 for transferring the photoconductor to the transfer paper.

In recent years, in the above-mentioned image forming apparatus, the miniaturization of the image forming apparatus to save space and cost reduction have been advanced, and the usable range of the image forming apparatus has been expanded by making the image forming apparatus small and inexpensive. Was. As one method of such cost reduction, in order to reduce power supply cost, a charging device using a high voltage and a power supply to a transfer device are integrated.

The charging device always charges the surface of the photosensitive drum with a constant voltage. However, in the case of a transfer device, it is not always necessary that the high-voltage output is always constant. In a machine that automatically copies both sides of the transfer paper, it is preferable to increase the transfer current when copying the back side of the transfer paper once copied than when copying the front side of the transfer paper.

This is related to the volume resistance of the transfer paper,
This is because, when copying on the back surface, a larger transfer current is required because the volume resistance is increased.

[0010]

However, in a so-called one-transformer power supply in which a high-voltage power supply is shared between a charging device and a transfer device, only the transfer current cannot be changed alone. If the high voltage output is increased to increase the transfer current, the charging current also changes, and the latent image potential changes, causing an abnormal image. Accordingly, it is an object of the present invention to provide a power supply device of an image forming apparatus and a power supply method capable of preventing a change in charging potential even when a transfer current is increased.

[0011]

In order to achieve the above object, a power supply for an image forming apparatus according to the present invention has a high voltage power supply for supplying a high voltage to a charging device and a transfer device. In the power supply device, a variable high-voltage resistor is inserted in series between the charging device and the high-voltage power supply, the charging device has a grid electrode, and grid voltage control means capable of raising and lowering a supply voltage to the grid electrode. And a transfer mode switching means.

The image forming apparatus has a lamp voltage control means for raising and lowering a voltage applied to an exposure lamp, a resistance control means for the variable high-voltage resistor and a grid voltage control in accordance with an instruction from a transfer mode switching means. The control means for controlling the means may be provided, or the control means may also control the lamp voltage control means.

A power supply method for an image forming apparatus according to the present invention comprises:
In the power supply method for an image forming apparatus using the power supply device for any one of the image forming apparatuses, when the transfer mode switching unit instructs an increase in the transfer current, the output of the high-voltage power supply is increased and the grid voltage is increased. It is characterized by reducing.

Alternatively, in the power supply method for an image forming apparatus using the power supply device for any one of the image forming apparatuses described above,
When the transfer mode switching means instructs to increase the transfer current, the resistance value of the variable high-voltage resistor may be increased and the grid voltage may be increased in order to increase the transfer current.

In any of the above methods, when the transfer mode switching means instructs an increase in the transfer current, the output of the high-voltage power supply is increased to increase the transfer current, and the exposure lamp voltage is increased. It is also possible.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of the image forming apparatus of the present invention. The basic configurations of the photoconductor 1, the charging device 2, the developing device 3, the transfer device 4, the cleaning device 5, and the like are the same as those described in the conventional example.

Although the charging device 2 and the transfer device 4 are supplied with electricity from the same high-voltage power supply 10, it is the same as the conventional device, though not described in the conventional example. However, in the present invention, a variable high-voltage resistor 11 is inserted in series between the high-voltage power supply 10 and the charging device 2. The charging device 2 has a grid electrode 2a, and a grid voltage control means 12 for raising and lowering a supply voltage to the grid electrode 2a is provided.

The output current of the high-voltage power supply 10 can be adjusted by the power supply control means 13. Further, the variable high-voltage resistor 11 is formed of, for example, an electronic volume and has a resistance control means 14 so that the resistance value can be increased or decreased.

The image forming apparatus has an exposure lamp 6, and a lamp voltage control means 15 for controlling a voltage applied to the exposure lamp 6.

In the above configuration, the power control means 13,
The resistance control means 14 and the lamp voltage control means 15 are intensively controlled by a control means 16 such as a computer CPU. Further, there is a transfer mode switching unit 17, and this instruction is input to the control unit 16. As the transfer mode switching means 17, for example, a paper detection switch of a transfer paper tray that stores the transfer paper on which the front side copy has been completed when performing double-sided copy can be used.

Next, a first embodiment of the power supply method of the present invention will be described. First, it is assumed that the image forming apparatus is provided with a paper feed tray (not shown) for performing automatic double-sided copying, and the automatic double-sided copy mode is selected on an operation panel (not shown). After performing copying on the front side of the transfer sheet, the image forming apparatus temporarily stores the transfer sheet in the above-described sheet feed tray, and subsequently feeds the sheet from the sheet feed tray to copy the back side.

When the toner image is transferred to the front surface, the toner image reaches the fixing device, where the toner image is heated, and the toner is melted and fixed. By the heating, the water content of the transfer paper decreases,
Since the resistance of the transfer paper increases, it is necessary to increase the transfer current when copying the back side rather than when copying the front side.

Therefore, when the transfer mode switching means 17 provided on the paper feed tray or the like detects that the back side copy is to be performed, the control means 16 controls the high voltage power supply 10 via the power supply control means 13. Command output up. As a result, the transfer current supplied from the high voltage power supply increases.

However, when the transfer current is increased, the value of the current supplied to the charging device 2 is also increased because of one transformer, and the charged potential of the photosensitive member becomes higher than a target value.

FIG. 2 shows the high-voltage power supply current Im and the transfer current I
FIG. 4 is a diagram showing a mutual relationship among t, charging current Ic, and charging potential Vo. The high-voltage power supply current Im and the transfer current It have a linear relationship, the transfer current It and the charging current Ic have a linear relationship, and the charging current Ic and the charging potential Vo have a linear relationship.

For example, in the case of a front side copy, the high voltage current Im has a value M shown by a dotted line, and the transfer current It has a value T.
It is assumed that the charging current Ic becomes C, the charging potential becomes Vo, and a proper copy is obtained. Next, in order to copy the back surface, the high-voltage power supply current is increased to M 'so that the transfer current It becomes T'. Then, the charging current Ic also becomes C
′, And the charging potential rises to Vo ′.

Therefore, in the present invention, the control means 16 instructs the grid voltage control means 12 to lower the voltage of the grid electrode 2a provided in the charging device 2 as the high-voltage power supply current increases. When the grid voltage decreases by an appropriate value, the relationship between the charging current Ic and the charging potential Vo changes from a straight line to a straight line, and it becomes possible to keep the charging potential unchanged even when the charging current increases. . next,
A second embodiment of the power supply method according to the present invention will be described.

When copying is performed on the back surface, the transfer current It is increased as described above. In this embodiment, however, a high-voltage variable resistor 11 provided between the charging device 2 and the high-voltage power supply 10 is used. The transfer current It is increased by controlling the resistance value to increase.

FIG. 3 is a diagram showing the relationship between the resistance value R of the variable high-voltage resistor 11, the charging current Ic, and the transfer current It when the total current of the high-voltage power supply 10 is fixed. The relationship between the resistance value R and the charging current Ic is represented by a straight line, and the charging current Ic
And the transfer current It have a relationship indicated by a straight line, and have an inversely proportional relationship. That is, when the total current is constant because of one transformer, the transfer current It increases, but the charging current Ic decreases. Since the charging current decreases, the charging potential of the photoconductor 1 becomes lower than a target value. Therefore, in this case, in the present invention, the grid electrode 2
The control means 16 controls the grid voltage control means 12 so that the voltage of a becomes high.

A description will be given of a third embodiment of the power supply method according to the present invention. If the transfer current It is increased by increasing the total current Im of the high-voltage power supply 10 when performing the back side copying, the charging current Ic also increases.
The background potential also increases, resulting in darker images. Therefore, in the present invention, the exposure lamp voltage control means 15
, The voltage applied to the exposure lamp 6 is increased to increase the amount of light, thereby preventing the image from becoming dark.

FIG. 4 is a diagram showing the relationship between the background potential and the charging current Ic. When the voltage of the exposure lamp 6 is constant,
The relationship between the two is as shown by a straight line. When the voltage of the exposure lamp is increased, the gradient of the straight line decreases, and the straight line moves clockwise.

When the charging current Ic increases from C to C ', the background potential increases from V to V'. Therefore, the voltage applied to the exposure lamp 6 is increased by the lamp voltage control means 15 and shifted from a straight line. Then, even if the charging current Ic increases from C to C ′, the background potential can be maintained at V.

[0033]

As described above, according to the present invention, in an image forming apparatus in which a charging device and a transfer device are supplied with power from a common power supply, a high-voltage power supply current is increased in order to increase a transfer current. At this time, since the grid voltage of the charging device is controlled to be low, the charging potential of the photoconductor can be kept constant.

When the resistance value of the variable resistor provided in series between the charging device and the high-voltage power supply is increased in order to increase the transfer current, the grid voltage is controlled so as to be higher. The photoconductor charging potential can be kept constant.

When the high-voltage power supply current is increased to increase the transfer current, the charging current is also increased, and the background potential of the photosensitive member is also increased, so that the image becomes dark. At this time, the exposure lamp voltage is increased. , The surface potential of the photoconductor can be kept constant.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a power supply device of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating a relationship among a high-voltage power supply current, a transfer current, a charging current, and a charging potential.

FIG. 3 is a diagram illustrating a relationship between a resistance value of a variable high-voltage resistor, a transfer current, and a charging current when a high-voltage power supply current is fixed.

FIG. 4 is a diagram showing a relationship between a transfer current and a background potential.

FIG. 5 is a diagram illustrating a schematic configuration of a main part of a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 2a Grid electrode 4 Transfer device 6 Exposure lamp 10 High voltage power supply 11 Variable high voltage resistance 12 Grid voltage control means 13 Power supply control means 14 Resistance control means 15 Lamp voltage control means 16 Control means 17 Transfer mode switching means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhiko Yuki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Kentaro Matsumoto 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Inside Ricoh Company (72) Inventor Kenji Karashima 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company

Claims (7)

[Claims] 1. A power supply device for an image forming apparatus in which a high-voltage power supply for supplying a high voltage to a charging device and a transfer device is common, wherein a variable high-voltage resistor is inserted in series between the charging device and the high-voltage power supply. A charging device having a grid electrode, a grid voltage control means capable of raising and lowering a supply voltage to the grid electrode, and a transfer mode switching means; 2. A power supply apparatus for an image forming apparatus according to claim 1, wherein said image forming apparatus has a lamp voltage control means for raising and lowering a voltage applied to an exposure lamp. 3. The image forming apparatus according to claim 1, further comprising control means for controlling the resistance control means of the variable high-voltage resistor and the grid voltage control means in accordance with an instruction from the transfer mode switching means. Power supply. 4. A power supply device for an image forming apparatus according to claim 3, wherein said control means also controls said lamp voltage control means. 5. A power supply method for an image forming apparatus using the power supply device for an image forming apparatus according to claim 1, wherein when the transfer mode switching unit instructs an increase in transfer current, A power supply method for an image forming apparatus, comprising: increasing an output of the high-voltage power supply and decreasing a grid voltage. 6. A power supply method for an image forming apparatus using the power supply device for an image forming apparatus according to claim 1, wherein when the transfer mode switching unit instructs an increase in the transfer current, A method for supplying power to an image forming apparatus, comprising increasing a resistance value of the variable high-voltage resistor and increasing a grid voltage in order to increase a transfer current. 7. The power supply method for an image forming apparatus according to claim 5, wherein the output of the high-voltage power supply is increased to increase the transfer current when the transfer mode switching means instructs an increase in the transfer current. And increasing the exposure lamp voltage.