JPH05107954A - Image forming device - Google Patents

Abstract

PURPOSE:To stably separate a transfer sheet and to prevent toner from being attracted to a destaticizing means by bringing the destaticizing means into contact with a photosensitive drum and applying a voltage to a transfer roller for prescribed length of time. CONSTITUTION:Since the destaticizing means C is in contact with the photosensitive drum 31, the destaticizing means C is in secure contact with the sheet after transfer, and the destaticization of the sheet is securely performed. The destaticizing means C is composed of a flexible member, therefore it does not scratch the photosensitive drum 31 even when being in contact with the photosensitive drum 31. Additionally, a voltage is applied to the transfer roller 71 by an application control means 73 also during the prescribed times before and after the passing of the transfer sheet through a transfer position; therefore, toner is attracted to the transfer roller 71 before reaching the destaticizing means C even when a toner image on the photosensitive drum 31 and the transfer sheet are slightly displaced out of alignment in the transfer area and even when the toner is attracted to the part which is further downstream than the front end of the transfer sheet on the surface of the photosensitive drum 31 or the part which is further upstream than the rear end of the sheet.

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 or a laser beam printer, and more particularly to an image forming apparatus using a transfer roller.

[0002]

2. Description of the Related Art Conventionally, in a copying machine or the like, an electric charge having a first polarity is applied to a photosensitive drum, and an optical image as image information is projected on the photosensitive drum to form an electrostatic latent image. On the transfer sheet, which is formed between the photosensitive drum and the transfer roller, a visible image is formed by toner having a second polarity (first polarity when reverse development is performed) different from the first polarity. There is a so-called transfer roller system in which a visible image is transferred to the. A voltage having a polarity different from that of the toner (including ground) is usually applied to the transfer roller, and the transfer roller applies a so-called back surface charge to the surface of the transfer sheet that is not in contact with the photosensitive drum.

In this transfer roller system, since it is not necessary to give an excessive back surface charge to the transfer paper as in the case of transfer by corona discharge, the toner on the photosensitive drum is transferred before or after the transfer. Attracted to the paper,
There is an advantage that it is possible to suppress the generation of an image scattered around characters. Further, since the transfer sheet is introduced between the photosensitive drum and the transfer roller and comes into contact with the photosensitive drum side with a predetermined pressing force, the transfer sheet is reliably conveyed, and the shift between the photosensitive drum and the transfer sheet occurs. There is an advantage that the transfer deviation due to is not generated.

However, when an image having a relatively low printing rate (a large amount of white paper is formed) is formed mainly when reversal development is performed, after the transfer paper passes between the photosensitive drum and the transfer roller, the transfer paper There is a problem that the transfer sheet is attracted to the photosensitive drum side by the electrostatic attraction force of the back surface charge and the surface charge of the photosensitive drum, and the separation of the transfer sheet from the photosensitive drum becomes unstable.

Therefore, in order to stably separate the transfer sheet, there is provided an image forming apparatus in which a charge eliminating needle for removing charge from the transfer sheet is provided at a position near the downstream side of the transfer roller in the transfer sheet conveying direction ( See, for example, JP-A 1-2696969).

[0006]

However, since the static elimination needle is made of a conductive rigid body such as SUS, it must be separated from the photoconductor drum by a predetermined distance so as not to damage the photoconductor drum. Therefore, the charge removal needle of the transfer sheet cannot be surely contacted with the back surface of the transfer sheet, so that the charge removal of the transfer sheet becomes insufficient and the transfer sheet may be wound around the photosensitive drum. Therefore, there remains a problem that the separation of the transfer paper is unstable.

An object of the present invention is to solve the above technical problems and to provide an image forming apparatus capable of stably separating transfer sheets.

[0008]

As an image forming apparatus of the present invention for achieving the above object, a developing device for visualizing an electrostatic latent image formed on a photoconductor and a transfer of this visual image In an image forming apparatus provided with a transfer roller for transferring onto a sheet and a charge removing unit disposed on the downstream side of the transfer roller in the transfer sheet conveying direction for removing the charge from the transfer sheet, the charge removing unit is configured by a flexible member. Voltage application to the transfer roller is started a predetermined time before the leading edge of the transfer paper reaches the transfer position by contacting the photoconductor, and voltage is applied to the transfer roller a predetermined time after the rear end of the transfer paper passes the transfer position. The present invention is characterized in that an application control means for canceling is provided.

[0009]

According to the image forming apparatus having the above-described structure, since the charge eliminating means is brought into contact with the photoconductor, the charge eliminating means surely contacts the sheet after transfer, and surely removes electricity from the sheet. be able to. Since the charge eliminating means is made of a flexible member, it does not damage the photoconductor even if it comes into contact with the photoconductor as described above.

Further, since the voltage is applied to the transfer roller by the application control means for a predetermined time before and after the transfer sheet passes through the transfer position, the following operation is achieved. That is, when the toner image on the surface of the photoconductor and the transfer sheet are aligned in the transfer area, a slight deviation may occur. Even if the toner is adsorbed on a portion on the downstream side in the rotational direction of the portion where the leading edge of the paper comes into contact, or a portion on the upstream side in the rotational direction than the portion where the rear end of the transfer paper comes into contact, the toner Is attracted to the transfer roller side before reaching the charge eliminating means in contact with the photoconductor and is not attracted to the charge eliminating means.

[0011]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 2 is a schematic configuration diagram of a copying machine as an image forming apparatus showing an embodiment of the present invention. FIG. 1 is a schematic configuration diagram of the transfer device. Referring to FIG. 2, this copying machine A
Is an optical system 2 for illuminating and scanning a document placed on the contact glass 11 in the apparatus main body 1, and guiding the reflected light from the document P to the photoconductor drum 31 as a photoconductor, the photoconductor drum 31. The electrostatic latent image formed on the developing device 33 is visualized by the developing device 33, and then transferred to the transfer paper by the transfer roller 71, and the fixing unit 41 that fixes the toner image transferred to the transfer paper in the middle. And a paper transport unit 4 for discharging the above-mentioned paper from the paper feed cassette 42 or the paper feed tray 43 into the apparatus main body 1 and then discharging it from the paper discharge unit 44 through the image forming unit 3.

As the image forming unit 3, the photosensitive drum 31 is used.
A charger 32, a developing device 33, a transfer device B, a charge eliminating means C and a cleaner 34 are provided around the photosensitive drum 3 around the photosensitive drum 3.
1 are arranged in this order along the rotation direction of 1. Referring to FIGS. 1 and 2, the transfer device B includes a casing 7
0, and a transfer roller 7 which is axially supported at the upper end position of the casing 70 and introduces a transfer sheet between the photosensitive drum 31 and the photosensitive drum 31.
1 and the transfer roller 7 disposed inside the casing 70.
Cleaning device 7 for scraping off the toner adhered to 1
2 and an application controller 73 for controlling voltage application, which is interposed between the power source D for applying a voltage to the transfer roller 71 and the transfer roller 71.

The cleaning device 72 includes a casing 72.
a, a fur brush 72b arranged in the casing 72a and in contact with the peripheral surface of the transfer roller 71, and a blade 72c mounted in the casing 72a for contacting the fur brush 72b and scraping off the adhered toner into the casing 72a. It has and. Referring to the timing chart of FIG. 3, the application control unit 73 can start the voltage application to the transfer roller 71 a predetermined time before the timing a when the leading edge Qa of the transfer sheet Q reaches the transfer position (see FIG. 4). Then, a voltage is applied at a timing d after a predetermined time has passed since the registration roller 45 was turned on at a timing c. Further, the application control unit 73 controls the trailing edge Q of the transfer sheet Q.
In order that the voltage application can be released at a timing f after a predetermined time from the timing b when the b reaches the transfer position (see FIG. 5), the voltage is applied at the timing f after a predetermined time from the turning off of the registration roller 45 shown at the timing e. Release the voltage.

Next, the operation of the image forming unit 3 will be described.
The charging charger 32 imparts a uniform negative charge to the surface of the photosensitive drum 31. The optical system 3 irradiates the charged photosensitive drum 31 with light according to the original image. As a result, the photosensitive drum 31
The upper part is divided into a part where light irradiation is applied and the potential is lowered, and a part where light irradiation is not performed and the potential is high. Then, the developing device 33 is attached to the portion where the potential is lowered by the light irradiation.
The so-called reversal development is performed to develop the electrostatic latent image by using the negative polarity toner supplied from. The visible image thus formed on the photoconductor drum 31 is taken out from the paper feed cassette 42, and introduced into the transfer position (between the photoconductor drum 31 and the transfer roller 71) at the same timing by the registration roller 45. The image is transferred onto a transfer sheet (not shown). After the transfer process ends, the cleaner 34 removes residual toner from the photoconductor drum 31.

As the charge eliminating means C, a brush-like material made of a flexible material, such as conductive rayon or stainless fiber, which does not damage the photosensitive drum 31 even if it comes into contact with the photosensitive drum 31. Stuff used.
The charge eliminating means C is in contact with the entire width of the photosensitive drum 31 in the longitudinal direction while being supported by the support C1. When performing the reversal development as described above, it is desirable that the charge eliminating means C is grounded or has the same polarity as that of the photosensitive drum 31 in order to stabilize the separation.

According to this embodiment, the charge eliminating means C is brought into contact with the photoconductor drum 31, so that the charge eliminating means C is surely brought into contact with the transfer sheet after the transfer so that the charge of the transfer sheet is surely eliminated. It can be carried out. Therefore, the transfer paper does not wind around the photoconductor drum 31 due to insufficient charge removal, and the transfer paper can be reliably separated from the photoconductor drum 31. Moreover, since the static elimination means is made of a flexible brush, the photosensitive drum 31 is not damaged even if it comes into contact with the photosensitive drum 31 as described above.

Further, since the voltage is applied to the transfer roller 71 by the application control means 73 for a predetermined time before and after the transfer paper Q passes through the transfer position, the toner image on the photoconductor drum 31 and the transfer paper, for example. In the case where a slight misalignment occurs in the alignment with Q in the transfer area, a portion 31a (on the downstream side in the rotation direction of the surface of the photosensitive drum 31 that is in contact with the leading edge Qa of the transfer sheet Q). (See Figure 4)
Alternatively, even if the toner is adsorbed to the portion 31b (see FIG. 5) that is on the upstream side in the rotation direction with respect to the portion to which the rear end Qb of the transfer sheet Q comes into contact, the toner does not reach the static eliminator C. Then, it is attracted to the transfer roller 71 side. Therefore, even if the charge eliminating unit C is in contact with the photoconductor drum 31 as described above, the toner is not adsorbed to the charge eliminating unit C side, and the charge eliminating unit C can be prevented from being contaminated.

The present invention is not limited to the above embodiment, but can be applied to the case of regular development. In addition, various design changes can be made within the scope of the present invention without changing the gist of the present invention, such as a belt-shaped photoreceptor.

[0019]

【The invention's effect】 . As described above, according to the image forming apparatus of the present invention, since the charge eliminating means is brought into contact with the photoconductor, the charge of the transfer paper can be surely eliminated, and the transfer paper is stably separated from the photoconductor drum. You can do it. Moreover, since the charge eliminating means is made of a flexible member, it does not damage the photoconductor even if it comes into contact with the photoconductor as described above.

Further, since the voltage is applied to the transfer roller by the application control means for a predetermined time before and after the transfer paper passes through the transfer position, the position of the toner image on the photoconductor and the transfer paper in the transfer area is maintained. When a slight misalignment occurs in the alignment, the photosensitive member surface is more downstream than the contacting portion of the transfer paper leading edge in the rotation direction and the contacting portion of the transfer paper rear end. Even if the toner is adsorbed on the portion on the upstream side in the rotation direction, the toner is
Before reaching the charge eliminating means, it is attracted to the transfer roller side.
Therefore, as described above, even if the charge eliminating unit is in contact with the photoconductor, the toner is not adsorbed on the charge eliminating unit side, and the charge eliminating unit can be prevented from being contaminated.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a transfer device of a copying machine according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the copying machine.

FIG. 3 is a diagram showing a timing chart.

FIG. 4 is a schematic diagram of a main part showing a state in which a front end of a transfer sheet reaches a transfer position.

FIG. 5 is a schematic view of a main part showing a state where the rear end of the transfer sheet has reached the transfer position.

[Explanation of symbols]

 31 Photosensitive Drum 33 Developing Device 71 Transfer Roller 73 Application Control Means C Electrification Means Q Transfer Paper Qa Front Edge Qb Rear Edge

Claims (1)

[Claims] 1. A developing device that visualizes an electrostatic latent image formed on a photoconductor, a transfer roller that transfers the visualized image to a transfer sheet, and a transfer roller downstream of the transfer roller in the transfer sheet conveying direction. In the image forming apparatus provided with a charge removing unit for removing charge from the transfer sheet, the charge removing unit is configured by a flexible member and is brought into contact with the photoconductor, and a predetermined time before the leading edge of the transfer sheet reaches the transfer position. An image forming apparatus comprising: an application control unit that starts voltage application to the transfer roller and releases the voltage application to the transfer roller after a predetermined time has passed since the trailing edge of the transfer sheet passed the transfer position.