JP2937698B2 - Image forming device - Google Patents

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 using a contact type transfer means.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus utilizing an electrophotographic system such as an electrophotographic printer, a charging device generally uniformly and uniformly charges the surface of a photosensitive drum, and the charged photosensitive drum is charged. The exposure device forms an electrostatic latent image on the body drum. Subsequently, the developing device
The electrostatic latent image is developed into a toner image by a dry developer, that is, toner, and the toner image is transferred to a transfer material by a transfer unit. Then, the fixing device fixes the toner image transferred to the transfer material.

Further, a cleaning device is provided to remove toner remaining on the photosensitive drum after transfer. Incidentally, a contact-type transfer unit can be used as the transfer unit. In this case, for example, a roller transfer method is used.
In this roller transfer method, a conductive roller is pressed against a photosensitive drum and a transfer material is passed between the two. At this time, a transfer voltage is applied between the two to form an electric field, and the toner image is transferred to the transfer material. I am trying to do it.

However, in the roller transfer method having the above configuration, when the resistance value of the conductive roller changes due to a change in the environment or the resistance value and the capacity of the transfer material change, the transfer voltage required for the transfer is accordingly changed. , The transfer efficiency is reduced, and the toner image cannot be transferred to the transfer material in a favorable state. Therefore, a transfer method has been provided in which the transfer voltage is controlled in accordance with the change in the resistance value of the conductive roller (see Japanese Patent Application Laid-Open No. 2-123385).

In this case, since the resistance value of the conductive roller is different in a low temperature and low humidity environment, a normal temperature and normal humidity environment, and a high temperature and high humidity environment, there is no transfer material between the photosensitive drum and the conductive roller. The constant current control is performed, the voltage obtained at that time is held, and the held voltage is used as a transfer voltage for each environment. Further, a transfer method has been provided in which a transfer voltage is controlled in accordance with a change in the resistance value of a transfer material (see JP-A-1-265282).

[0006]

However, in the conventional image forming apparatus, the transfer voltage is controlled in accordance with the change in the resistance value of only one of the conductive roller and the transfer material. Does not mean that the transfer voltage is controlled in accordance with the change in the resistance value. Therefore, the image quality is degraded with a change in the environment.

The present invention solves the problems of the above-mentioned conventional image forming apparatus, so that even if the resistance value of the conductive roller changes due to a change in the environment or the resistance value or the capacity of the transfer material changes. It is another object of the present invention to provide an image forming apparatus capable of transferring a toner image to a transfer material in a good condition without lowering transfer efficiency and improving image quality.

[0008]

For this purpose, in an image forming apparatus according to the present invention, a photosensitive drum, a transfer conductive roller pressed against the photosensitive drum, and a conductive drum for transfer are provided. A transfer voltage control circuit that applies a transfer voltage between the rollers and transfers the toner image on the photosensitive drum to the transfer material.

The transfer roller is provided upstream of the transfer material in the transport direction, is made of the same material as the transfer conductive roller, and is shorter than the transfer conductive roller in accordance with the size of the transfer material. A conductive roller for voltage detection, a metal roller pressed against the conductive roller for voltage detection, and a constant current source for supplying a constant current between the conductive roller for voltage detection and the metal roller.

The transfer voltage control circuit applies a transfer voltage having the same value as the voltage when the constant current source supplies a constant current, between the photosensitive drum and the transfer conductive roller.

[0011]

According to the present invention, as described above, in the image forming apparatus, the photosensitive drum and the conductive roller for transfer are pressed against the photosensitive drum, and the transfer voltage control circuit is connected to the photosensitive drum and the conductive roller for transfer. A transfer voltage is applied between the transfer rollers to transfer the toner image on the photosensitive drum to the transfer material.

A voltage detecting conductive roller is disposed on the upstream side in the transport direction of the transfer material, and a metal roller is pressed against the voltage detecting conductive roller. The voltage detecting conductive roller is made of the same material as the transfer conductive roller, and is shorter than the transfer conductive roller in accordance with the size of the transfer material. Further, a constant current source is disposed between the voltage detecting conductive roller and the metal roller, and a constant current flows between them. At this time, the voltage applied between the voltage detecting conductivity and the metal roller is detected. The voltage detection signal is sent to the transfer voltage control circuit, and the transfer voltage control circuit applies a transfer voltage having the same value as the voltage when the constant current source supplies a constant current to the photosensitive drum and the transfer conductor. Applied between rollers.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram of an image forming apparatus showing an embodiment of the present invention. In the figure, 11 is an arrow A
The photoreceptor drum 12 is rotated in the direction, a corona charger 12 as a charging device for uniformly and uniformly charging the surface of the photoreceptor drum 11, and 13 irradiates the charged photoreceptor drum 11 with light. LED array as an exposure device for exposing the photosensitive drum 11 to form an electrostatic latent image on the photosensitive drum 11;
Is a developing device for developing the electrostatic latent image on the photoconductor drum 11 to form a toner image, 15 is a transfer material conveyed in the direction of arrow B, and 16 is a transfer unit pressed against the photoconductor drum 11 Conductive transfer roller, silicone rubber,
It is made of an elastic material such as urethane.

When the transfer material 15 passes between the photosensitive drum 11 and the transfer conductive roller 16, a transfer voltage control circuit 23 applies a transfer voltage between the two to form an electric field.
The toner image on the photosensitive drum 11 is transferred to the transfer material 15.
Reference numeral 17 denotes a voltage detecting conductive roller made of the same material as the transfer conductive roller 16. The voltage detecting conductive roller 17 is disposed on the upstream side in the transport direction of the transfer material 15, and a metal roller 18 is pressed against the voltage detecting conductive roller 17. Reference numeral 21 denotes a constant current source for supplying a constant current set between the voltage detecting conductive roller 17 and the metal roller 18. The voltage detecting conductive roller 17 and the metal roller 18 are both shorter than the transfer conductive roller 16 and are set to be equal to or smaller than the minimum width of the transfer material 15 used in the image forming apparatus.

The voltage when the constant current source 21 supplies a constant current between the conductive roller 17 for voltage detection and the metal roller 18 is detected by a voltmeter 22, and a detection signal of the voltage is transmitted to a transfer voltage control circuit 23. Sent to 25 is the transfer material 1
Reference numeral 26 denotes a fixing device for fixing the toner image transferred to 5, and reference numeral 26 denotes a cleaning device. Next, the operation of the image forming apparatus having the above configuration will be described.

The photosensitive drum 1 rotating in the direction of arrow A
1 is uniformly and uniformly charged by the corona charger 12. In this case, the surface of the photosensitive drum 11 is charged to a negative polarity. Subsequently, the LED array 13 irradiates and exposes the photosensitive drum 11 to light to form an electrostatic latent image on the photosensitive drum 11. Then, the developing device 14 develops the electrostatic latent image on the photosensitive drum 11 to form a toner image. In this case, the toner is charged to a negative polarity, and is developed by a reversal developing method.

Next, when the transfer material 15 passes between the transfer conductive roller 16 and the photosensitive drum 11, a transfer voltage control circuit 23 applies a transfer voltage between the two to form an electric field.
The toner image on the photosensitive drum 11 is transferred to the transfer material 15.
The transfer material 15 is conveyed in the direction of arrow B. Before passing between the transfer conductive roller 16 and the photosensitive drum 11, the transfer material 15 passes between the voltage detection conductive roller 17 and the metal roller 18. pass. At this time, the constant current source 21
Flows a constant current between the voltage detecting conductive roller 17 and the metal roller 18, and the voltmeter 22 detects the voltage when the constant current flows.

In this case, the voltage detecting conductive roller 1
7 and the metal roller 18 are one of the conductive rollers 16 for transfer.
/ 5 length. Therefore, even when the transfer material 15 having a small width is used, the amount of charge per unit area of the transfer material 15 when passing between the voltage detecting conductive roller 17 and the metal roller 18 can be made constant. And
The voltage detection signal is sent to a transfer voltage control circuit 23, which controls the transfer voltage between the photosensitive drum 11 and the transfer conductive roller 16 so that the voltage detected by the voltmeter 22 is equal to the voltage detected by the voltmeter 22. Equal. In this manner, the toner image on the photosensitive drum 11 is transferred onto the transfer material 15 conveyed in a timely manner.

Thereafter, the toner image transferred to the transfer material 15 is fixed by a fixing device 25 to form an image. When the toner image is transferred from the photosensitive drum 11 to the transfer material 15, the toner remaining on the photosensitive drum 11 is removed by the cleaning device 26. Next, control of the transfer voltage in the transfer voltage control circuit 23 will be described.

In the image forming apparatus, when the resistance value of the transfer conductive roller 16 changes due to a change in the environment, or the resistance value and the capacity of the transfer material 15 change, the transfer efficiency is reduced and the image forming apparatus is in a good condition. Therefore, the toner image cannot be transferred to the transfer material 15. Therefore, constant current control is performed in a state where the transfer material 15 is interposed between the photosensitive drum 11 and the transfer conductive roller 16, and the amount of charge per unit area of the transfer material 15 is made constant, so that the transfer efficiency is improved. Can be improved. However, in this case, when the transfer material 15 passes between the photosensitive drum 11 and the transfer conductive roller 16, the area of the portion where the photosensitive drum 11 and the transfer conductive roller 16 are in direct contact is the dimension of the transfer material 15. And the constant current control cannot be performed. Therefore,
The charge amount per unit area of the transfer material 15 cannot be made constant.

On the other hand, when a constant voltage control is performed between the photosensitive drum 11 and the transfer conductive roller 16 in order to correspond to the transfer material 15 having a different size, on the contrary, the transfer conductivity is changed due to a change in environment. When the resistance value of the roller 16 changes or the resistance value or the capacity of the transfer material 15 changes, the charge amount per unit area of the transfer material 15 cannot be made constant.

Accordingly, in the present invention, a voltage detecting conductive roller 17 and a metal roller 18 are provided in addition to the transfer conductive roller 16, and the transfer is performed between the voltage detecting conductive roller 17 and the metal roller 18. The constant current control is performed with the material 15 interposed, the voltage applied between the two at that time is detected, and the voltage is applied as a transfer voltage between the photosensitive drum 11 and the transfer conductive roller 16. ing.

In this case, since the transfer conductive roller 16 and the voltage detection conductive roller 17 are made of the same material, the photosensitive drum 11 and the transfer conductive roller 16 are formed so that transfer efficiency can be improved. When a toner image is transferred by setting a transfer voltage between them, a current flowing between the two, and the same voltage as the transfer voltage is applied between the conductive roller 17 for voltage detection and the metal roller 18 to transfer the transfer material 15. The ratio of the current flowing when passing the sheet does not significantly change even if the resistance value of the transfer conductive roller 16 changes or the resistance value or the capacity of the transfer material 15 changes. Therefore, the transfer voltage can be controlled by the transfer voltage control circuit 23 using this fact.

FIG. 2 is a diagram showing the relationship between voltage and current at room temperature. The figure shows the relationship between voltage and current when a PPC sheet of A4 size is used as the transfer material 15 (FIG. 1) and the PPC sheet is transported at room temperature. The solid line represents the transfer voltage between the photosensitive drum 11 and the transfer conductive roller 16 when the PPC paper is passed between the photosensitive drum 11 and the transfer conductive roller 16 to transfer the toner image. Shows the relationship between the currents flowing through them. The broken line indicates the relationship between the voltage and the current when the PPC sheet is passed between the voltage detecting conductive roller 17 having a length of １ ／ of the transfer conductive roller 16 and the metal roller 18.

Here, in order to improve the transfer efficiency when transferring the toner image onto the PPC paper at room temperature, it is necessary to use 750
It is known that the transfer voltage [V] needs to be applied between the photosensitive drum 11 and the conductive roller 16 for transfer. Then, a transfer voltage of 750 [V] is applied to the photosensitive drum 1.
The current flowing between the transfer roller 1 and the transfer conductive roller 16 when applied between them is 2.4 μA. On the other hand, when a voltage of 750 [V], which is the same as the transfer voltage, is applied between the voltage detecting conductive roller 17 and the metal roller 18 to pass through the PPC sheet, the voltage detecting conductive roller 17 and the metal roller 18 The current flowing between them is 1.9 [μA].

In this case, as described above, since the transfer conductive roller 16 and the voltage detection conductive roller 17 are made of the same material, the flow between the photosensitive drum 11 and the transfer conductive roller 16 is carried out. The ratio of the current of 4 [μA] to the current of 1.9 [μA] flowing between the voltage detecting conductive roller 17 and the metal roller 18 depends on the change in the environment. Transfer material 15
Does not change significantly even if the resistance value or the capacitance of the semiconductor device changes.

Therefore, the voltage detecting conductive roller 17
When the PPC paper passes between and the metal roller 18,
A current of 1.9 μA is set to flow, and the voltage at that time is applied as a transfer voltage between the photosensitive drum 11 and the transfer conductive roller 16 by the transfer voltage control circuit 23. Thus, when the size of the PPC paper is A4 size, a current of approximately 2.4 [μA] is applied to the photosensitive drum 1.
1 and the conductive roller 16 for transfer.
Therefore, transfer efficiency can be improved.

In this case, even if the dimensions of the PPC paper change, the voltage detecting conductive roller 17 and the metal roller
Are not in direct contact with each other, so that a current of 1.9 [μA] can be set to flow when the PPC paper passes between them. Therefore, even if the size of the PPC paper changes, a current of approximately 2.4 [μA] can flow between the photosensitive drum 11 and the transfer conductive roller 16.

Next, the relationship between the voltage and the current when the environment changes will be described. FIG. 3 is a diagram showing the relationship between voltage and current under a high temperature and high humidity environment, and FIG. 4 is a diagram showing the relationship between voltage and current under a low temperature and low humidity environment. FIG. 3 shows the relationship between voltage and current when PPC paper is transported in a high-temperature, high-humidity environment.
When a PC sheet is passed between the photosensitive drum 11 (FIG. 1) and the transfer conductive roller 16 to transfer the toner image,
The relationship between the transfer voltage between the photosensitive drum 11 and the conductive roller 16 for transfer and the current flowing between the two are shown. The broken line indicates the relationship between the voltage and the current when the PPC sheet is passed between the voltage detecting conductive roller 17 and the metal roller 18 having a width of ５ of the transfer conductive roller 16.

Here, the current flowing between the conductive roller 17 for voltage detection and the metal roller 18 under a high temperature and high humidity environment is 1.
When the voltage is set to 9 [μA], the voltage applied between the voltage detecting conductive roller 17 and the metal roller 18 becomes 600 [V]. Therefore, the transfer voltage control circuit 23
When a voltage of 0 [V] is applied between the photosensitive drum 11 and the conductive roller 16 for transfer as a transfer voltage, the current flowing between the photosensitive drum 11 and the conductive roller 16 for transfer is changed to 2.
6 [μA].

FIG. 4 shows the relationship between voltage and current when PPC paper is transported in a low-temperature and low-humidity environment.
The transfer voltage between the photosensitive drum 11 and the transfer conductive roller 16 when the toner image is transferred by passing the PPC paper between the photosensitive drum 11 (FIG. 1) and the transfer conductive roller 16 The relationship between the currents flowing between them is shown. The broken line indicates the relationship between the voltage and the current when the PPC sheet is passed between the voltage detecting conductive roller 17 having a length of １ ／ of the transfer conductive roller 16 and the metal roller 18.

Here, the current flowing between the voltage detecting conductive roller 17 and the metal roller 18 under a low temperature and low humidity environment is 1.
When the voltage is set to 9 [μA], the voltage between the voltage detecting conductive roller 17 and the metal roller 18 becomes 900 [V]. Therefore, when a voltage of 900 [V] is applied as a transfer voltage between the photosensitive drum 11 and the conductive roller 16 for transfer by the transfer voltage control circuit 23, the voltage between the photosensitive drum 11 and the conductive roller 16 for transfer is changed. The flowing current is 2.3 [μA]
Can be

As described above, the current flowing between the photosensitive drum 11 and the conductive roller 16 for transfer under the high-temperature and high-humidity environment and the low-temperature and low-humidity environment is 2.
Although it is slightly different from 4 [μA], it is sufficiently within the range of the current that does not lower the transfer efficiency. Therefore, the transfer efficiency does not decrease even if the environment changes, and the toner image can be transferred to the transfer material 15 in a good condition.

The present invention is not limited to the above embodiments, but can be variously modified based on the gist of the present invention, and these are not excluded from the scope of the present invention.

[0035]

As described above in detail, according to the present invention, in the image forming apparatus, the photosensitive drum and the conductive roller for transfer are pressed against the photosensitive drum, and the transfer voltage control circuit is connected to the photosensitive drum. A transfer voltage is applied between the drum and the transfer conductive roller to transfer the toner image on the photosensitive drum to the transfer material.

A voltage detecting conductive roller is disposed on the upstream side in the transport direction of the transfer material, and a metal roller is pressed against the voltage detecting conductive roller. The voltage detecting conductive roller is made of the same material as the transfer conductive roller, and is shorter than the transfer conductive roller according to the size of the transfer material. Therefore, even when a narrow transfer material is used, the amount of charge per unit area of the transfer material when passing between the conductive roller for voltage detection and the metal roller can be made constant.

A constant current source is disposed between the voltage detecting conductive roller and the metal roller, and a constant current flows between the two. At this time, a voltage applied between the voltage detecting conductive roller and the metal roller is detected. The voltage detection signal is sent to the transfer voltage control circuit, and the transfer voltage control circuit applies a transfer voltage having the same value as the voltage when the constant current source supplies a constant current to the photosensitive drum and the transfer conductor. Applied between rollers.

In this case, since the transfer conductive roller and the voltage detection conductive roller are made of the same material, the current flowing between the photosensitive drum and the transfer conductive roller, the voltage detection conductive roller and the metal The ratio of the current flowing between the rollers does not change significantly even if the resistance value of the transfer conductive roller changes or the resistance value or the capacity of the transfer material changes.

Therefore, even if the resistance value of the transfer conductive roller changes due to a change in the environment or the resistance value or the capacity of the transfer material changes, the amount of charge per unit area of the transfer material is kept constant. Therefore, the transfer efficiency is not reduced, and the toner image can be transferred to the transfer material in a good condition.

[Brief description of the drawings]

FIG. 1 is a schematic view of an image forming apparatus showing an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between voltage and current at room temperature.

FIG. 3 is a diagram showing the relationship between voltage and current under a high temperature and high humidity environment.

FIG. 4 is a diagram showing the relationship between voltage and current under a low-temperature and low-humidity environment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 photoconductor drum 15 transfer material 16 conductive roller for transfer 17 conductive roller for voltage detection 18 metal roller 21 constant current source 23 transfer voltage control circuit

Claims (1)

(57) [Claims] 1. A transfer voltage is applied between (a) a photosensitive drum, (b) a transfer conductive roller pressed against the photosensitive drum, and (c) a transfer voltage between the photosensitive drum and the transfer conductive roller. A transfer voltage control circuit for applying and transferring the toner image on the photosensitive drum to the transfer material; and (d) disposed on the upstream side in the transport direction of the transfer material and comprising the same material as the transfer conductive roller; A voltage detection conductive roller shorter than the transfer conductive roller in accordance with the size of the transfer material; (e) a metal roller pressed against the voltage detection conductive roller; With a constant current source for flowing a constant current between the conductive roller for voltage detection and the metal roller,
(G) The transfer voltage control circuit applies a transfer voltage having the same value as a voltage when the constant current source supplies a constant current between the photosensitive drum and the transfer conductive roller. Forming equipment.