JP2000235317A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device preventing the rear side of transferred material from being solid with toner, and preventing a transfer side of the transferred material from becoming dirty with the black toner from transfer memory. SOLUTION: This device is provided with the image carrier 12 carrying the development image developed from the electrostatic latent image, the transfer device 26 transferring the image developed from the image carrier 12 to material P transported by the image carrier 12, power units 32 and 34 respectively applying bias voltage to the transfer device 26 while switching polarity opposite to each other at the transferring time and the non-transferring time, and a feed paper sensor 42 detecting the passing of the trailing edge of the material P and the leading edge of the subsequent material. In such a manner, the device is allowed to change the time from detecting the passing of the trailing edge of the material P until switching polarity of the bias voltage of the transfer device 26, based on the interval time when the feed paper sensor 42 detects the passing of the trailing edge of the material P and detects the passing of leading edge of the subsequent material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic method for developing an electrostatic latent image on an image carrier using a developer such as a toner and transferring the developed image to a transfer material. The present invention relates to an image forming apparatus such as a printer using a method.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus such as a printer using an electrophotographic system has been widely used. Generally, an image forming apparatus using the electrophotographic method uniformly charges the surface of a drum-shaped image carrier (photosensitive drum, intermediate transfer drum, or the like), and charges the charged surface of the image carrier. Irradiating light forms an electrostatic latent image on the image carrier, electrostatically develops the electrostatic latent image with a charged developer (toner), and covers the developed image. This is a device that can obtain a print image by transferring to a transfer material (paper, film, etc.).

One of the transfer methods for transferring a developed image onto a transfer material is to use a transfer roller that rotates while being in contact with an image carrier and is applied with a bias voltage having a polarity opposite to that of the developed image. 2. Description of the Related Art A method is known in which a transfer material is sandwiched between a body and a transfer roller, and a developed image formed on an image carrier is electrostatically transferred to the transfer material.

[0004]

Normally, a positive bias voltage is applied to the transfer roller when the transfer material is sandwiched between the transfer roller and the image carrier, and the transfer material is interposed between the transfer roller and the image carrier. When the transfer roller is not sandwiched, a reverse bias voltage having a polarity opposite to the positive bias voltage is applied to the transfer roller in order to prevent the adhesion of the normally charged toner.

[0005] However, in a high humidity environment where the charging voltage of the developer decreases, the toner of the opposite polarity may be mixed with the normally charged toner. Since the reverse polarity toner moves in a direction opposite to that of the normally charged toner, the toner adheres to the transfer roller when the reverse bias voltage is applied (at the time of non-transfer) and actively stains the transfer roller.

On the other hand, the timing at which the forward bias voltage applied to the transfer roller during the transfer operation is switched to the reverse bias voltage at the end of the transfer is adjusted so as not to affect the image bearing member inside the rear end of the transfer material (transfer material (Before the rear end of the transfer roller passes the transfer position). In this case, there is a problem that the back surface of the transfer material, that is, the surface on which the developed image is not transferred, particularly the back surface of the rear end portion of the transfer material may be stained with toner.

In order to prevent the back surface of the transfer material from being stained by the toner, the timing of switching from the forward bias voltage to the reverse bias voltage is set outside the rear end of the transfer material (the rear end of the transfer material). After passing through the transfer position), if the switching is performed outside the rear end of the transfer material in this manner, the transfer is performed in a state where the transfer material does not exist between the image carrier and the transfer roller. Since the bias voltage is applied to the image carrier, a portion (so-called transfer memory) where charging is insufficient in the next charging step is formed.

In the transfer memory, when the interval time between the rear end of the transfer material and the front end of the subsequent transfer material is shorter than one cycle of the image carrier, the transfer of the subsequent transfer material is performed. There is a problem that a stain such as a streak of black toner sometimes occurs on the transfer surface.

In view of the above problems, the present invention can reduce the contamination of the back surface of the transfer material to which the developed image is not transferred with toner, and can transfer the developed image of the transfer material by the transfer memory. It is an object of the present invention to provide an image forming apparatus which can reduce the occurrence of black toner stain on the transfer surface of the transfer member.

[0010]

In order to solve the above-mentioned problems, an image forming apparatus according to the present invention comprises an image carrier for carrying a developed image obtained by developing an electrostatic latent image with a developer; A transfer device that transfers a developed image from an image carrier to a transfer target material that has been conveyed therebetween, and a power supply device that switches and applies bias voltages having opposite polarities to each other during transfer and non-transfer to the transfer device, A feed sensor for detecting the passage of the rear end of the transfer material and the passage of the front end of the succeeding transfer material, and detecting the passage of the rear end of the transfer material, The time from when the rear end of the transfer material is detected to when the power supply switches the polarity of the bias voltage applied to the transfer device is changed according to the interval time until the front end of the transfer material is detected. It is characterized by the following.

According to the image forming apparatus having such a configuration,
The power supply device detects the passage of the rear end of the transfer material and detects the passage of the rear end of the transfer material according to an interval time from when the feed sensor detects the passage of the rear end of the transfer material to when the passage of the front end of the subsequent transfer material is detected. Changes the time until the polarity of the bias voltage applied to the transfer device is changed, so that the back surface of the transfer material on which the developed image is not transferred can be reduced from being stained with toner, and the transfer memory can be transferred by the transfer memory. It is possible to reduce the occurrence of black toner stain on the transfer surface on which the developed image of the material is transferred.

[0012]

Embodiments of the present invention will be specifically described below with reference to the drawings. 1 to 5
FIG. 1 is a diagram referred to for describing a first embodiment of an image forming apparatus according to the present invention.

An image forming apparatus 10 according to the present embodiment shown in FIG. 1 includes, for example, a photosensitive drum 12 having an outer diameter of 30 mm.
(Image carrier), a charging roller 16 for uniformly charging the surface of the photosensitive drum 12 when the photosensitive drum 12 rotates in the direction of arrow A, and a surface by exposing the photosensitive drum 12 with a laser beam L. An exposure device (not shown) for forming an electrostatic latent image on the photoconductor, a developing sleeve 21 for developing the electrostatic latent image on the photosensitive drum 12 with a developer to form a developed image (toner image), which will be described later. The sheet P sent from the registration roller 40 while being guided by the sheet guide 22
A transfer roller 26 (transfer device) for transferring the developed image of the photoconductive drum 12 to (a material to be transferred), and a cleaner 3 for removing toner remaining on the surface of the photoconductive drum 12 after the transfer
1 and a static eliminator 3 having a static elimination brush 30a for eliminating static electricity in order to peel the sheet P after transfer from the photosensitive drum 12.
0.

The transfer roller 26 is a transfer roller 2
6 is connected to a transfer power supply 32 that applies a bias voltage to the transfer roller 6. The transfer power supply 32 switches a polarity of a bias voltage applied to the transfer roller 26.
It is connected to the. Further, the polarity switching device 34 is connected to a polarity switching control device 36 that controls timing for switching the polarity of the bias voltage. The polarity switching control device 36 is connected to a registration sensor 42 and a control circuit 38 described later.

As described above, the polarity of the bias voltage applied to the transfer roller 26 is switched by the polarity switching device 34. Therefore, the power supply device according to the present invention employs a transfer power supply in this embodiment. 3
2 and a polarity switching device 34.

The transfer timing of the sheet P conveyed from a sheet tray (not shown) is adjusted on the right side of the transfer roller 26 in FIG. 1 to transfer the sheet P to the transfer roller 26 and the photosensitive drum 12. A registration roller 40 that conveys the paper P to a transfer position sandwiched therebetween, and a registration sensor 42 (feed sensor) that detects whether the leading end and the trailing end of the sheet P have passed are disposed.

When the registration sensor 42 detects that the trailing edge of the sheet P has passed and the detection signal is input to the polarity switching control device 36, the polarity switching control device 36 There is a built-in timer (not shown) that starts counting a predetermined time until the polarity of the bias voltage applied to is switched.

The operation of the image forming apparatus 10 will be described below. The process speed of the image forming apparatus 10 is 4
8 mm / sec, the surface of the photosensitive drum 12 is uniformly charged to -680 V by the charging roller 16, and the charged surface is irradiated with the laser beam L, and the voltage of the irradiation area becomes -80 V. An electrostatic latent image is formed. When the electrostatic latent image reaches the developing area, toner is electrostatically attached by the developing sleeve 21 to develop the electrostatic latent image, and a developed image is formed on the photosensitive drum 12.

A DC bias voltage of -450 V is applied to the developing sleeve 21. When the developed image on the photosensitive drum 12 reaches the transfer position where it comes into contact with the transfer roller 26, the developed image is transferred to the paper P conveyed from the registration roller 40 to the transfer position in synchronization with the arrival time. That is, a positive bias voltage having a polarity opposite to that of the developed image on the photosensitive drum 12 is applied to the transfer roller 26, whereby the developed image on the photosensitive drum 12 is electrostatically transferred to the paper P.

Thereafter, the discharging brush 30a of the discharging device 30
Thus, the paper P after the transfer is neutralized, and the paper P is conveyed to a fixing device (not shown) via the discharge conveyance path 44 without being wound around the photosensitive drum 12. The toner remaining on the photosensitive drum 12 after the transfer is removed by the cleaner 31 and the photosensitive drum 12 proceeds to the next latent image forming step.

The operation of switching the polarity of the bias voltage in the transfer end process of the transfer roller 26 will be described below with reference to the flowchart of FIG. When the paper P passes at the transfer position, the transfer is performed. Near the end of the transfer of the paper P, first, it is determined whether the rear end of the paper P has passed the detection position of the registration sensor 42 (whether the paper P has passed). The determination is made based on the detection signal from the registration sensor 42 (Step S1 in FIG. 2).

If YES in step S1, it is determined whether the image forming apparatus 10 is in the manual feed mode (step S2 in FIG. 2). In the case of YES here, the trailing edge of the paper P is
945ms by the timer after passing through the detection position of
Is counted, that is, when the transfer position N is outside the rear end of the sheet P as in the case of the sheet P in FIG. 5C, the polarity of the bias voltage of the transfer roller 26 is changed by the polarity switching device 34. Switching is performed (step S6 in FIG. 2), and the transfer is completed (see FIG. 4).

In this case, the transfer is terminated after the trailing edge of the sheet P passes the transfer position N, and the trailing edge of the sheet P is shifted to the transfer position N.
The polarity of the bias voltage of the transfer roller 26 is switched after passing, so that the back surface of the rear end portion of the paper P can be prevented from being stained by the stain of the transfer roller 26 to which the opposite polarity toner has adhered.

In the manual feed mode, the interval between paper feeds is often long regardless of the size of the paper P. Therefore, as described above, the transfer surface of the paper P is stained with black toner lines as described above. Occurrence can be reduced. This is because it is known that when the interval time between the trailing edge of the sheet P and the leading edge of the succeeding sheet P is longer than one cycle of the photosensitive drum 12, the transfer surface is not stained by the transfer memory. It is.

If NO in step S2, it is next determined whether the size of the sheet P is smaller than B5 (A5 or less) (step S3 in FIG. 2). Where YE
In the case of S, the trailing edge of the paper P is
After 945 ms after passing through the detection position 2, the polarity of the bias voltage of the transfer roller 26 is switched (step S6 in FIG. 2). Also in this case, it is possible to prevent the rear surface of the rear end portion of the sheet P from being stained by the stain on the transfer roller 26 to which the opposite polarity toner has adhered.

When the size of the sheet P is smaller than A5, the interval between sheet feedings is often long, and the interval between the rear end of the sheet P and the front end of the succeeding sheet P is long.
Since the period is longer than one cycle of 2, it is possible to reduce the occurrence of black toner streaks on the transfer surface of the paper P by the transfer memory.

In the case of NO in step S3, it is next determined whether or not a signal for requesting printing of the succeeding paper P has been input from the control circuit 38 to the polarity switching control device 36 (step S4 in FIG. 2). In the case of NO here, intermittent paper feeding may be considered instead of continuous paper feeding, and the time between paper feedings is often long, so that the trailing edge of the paper P passes through the detection position of the registration sensor 42 again. From 945ms
Thereafter, the polarity of the bias voltage of the transfer roller 26 is switched (Step S6 in FIG. 2). Therefore, in this case, too,
It is possible to prevent the rear surface of the rear end portion of the paper P from being stained by the stain of the transfer roller 26 due to the opposite polarity toner.

When the control circuit 38 does not request the printing of the succeeding paper P, the interval between the paper feeds is often long as described above. Is often longer than one cycle of the photosensitive drum 12, and the transfer memory can reduce the generation of black toner streaks on the transfer surface of the paper P.

On the other hand, if the determination in step S4 is YES, the paper P is continuously fed with a size of B5 or more. In this case, the trailing end of the paper P is
847 ms after passing through the detection position of FIG.
2A, the polarity of the bias voltage of the transfer roller 26 is switched shortly before the rear end of the sheet P passes through the transfer position N (step S5 in FIG. 2).
(See FIG. 3).

In this case, since the transfer positive bias voltage is not applied to the photosensitive drum 12 in a state where the paper P does not exist between the photosensitive drum 12 and the transfer roller 26, the transfer memory It is possible to prevent the stripes of the black toner from being stained on the transfer surface of the paper P.

In the above-described embodiment, the case where the transfer roller 26 transfers the developed image on the photosensitive drum 12 to the sheet P has been described. The developed image on the intermediate transfer drum on which
Accordingly, the present invention can also be applied to the case of secondary transfer to the paper P.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and based on the technical idea of the present invention, various other embodiments are possible. Can be changed.

[0033]

As described above, according to the image forming apparatus of the present invention, the feed sensor detects the passage of the rear end of the transfer material and then detects the passage of the front end of the subsequent transfer material. The time from when the rear end of the transfer material is detected to when the power supply unit switches the polarity of the bias voltage applied to the transfer device is changed according to the interval time until the developed image of the transfer material is changed. It is possible to reduce the contamination of the back surface of the non-transferred surface with the toner, and to reduce the occurrence of black toner contamination on the transfer surface on which the developed image of the transfer-receiving material is transferred by the transfer memory.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation procedure of the image forming apparatus.

FIG. 3 is a time chart showing that the polarity of the transfer roller is switched 847 ms after the detection of the passage of the trailing edge of the sheet by the registration sensor.

FIG. 4 is a time chart showing that the polarity of the transfer roller is switched 945 ms after the detection of the passage of the trailing edge of the sheet by the registration sensor.

FIG. 5 is a conceptual diagram for explaining a positional relationship between a detection position S of a registration sensor, a transfer position N of a transfer roller, and each of a rear end position of a sheet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photoreceptor drum 16 Charging roller 21 Developing sleeve 22 Paper guide 26 Transfer roller 30 Static eliminator 30a Static elimination brush 31 Cleaner 32 Transfer power supply 34 Polarity switching device 36 Polarity switching control device 38 Control circuit 40 Registration roller 42 Registration sensor 44 Discharge transport path

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA32 DA38 DC03 DC10 DE01 EA03 EA18 EC02 EC09 ED17 ED18 ED24 ED26 EE02 EF06 EJ17 FA15 JC13 JC16 ZA01 2H032 AA05 BA16 BA29 BA30 CA02 CA13 CA15 DA02

Claims (2)

[Claims] An image carrier for carrying a developed image obtained by developing an electrostatic latent image with a developer, and a developed image is transferred from the image carrier to a transfer material conveyed between the image carrier. A transfer device, a power supply device that switches and applies a bias voltage having a polarity opposite to each other between the transfer device and the non-transfer device to the transfer device, and a power supply device that passes a rear end of the transfer material and a front end of a subsequent transfer material. A paper feed sensor for detecting the passage of the material to be transferred, based on an interval time from when the paper feed sensor detects the passage of the trailing end of the material to be transferred to when the passage of the leading edge of the subsequent material to be transferred is detected. An image forming apparatus, wherein the time from when the trailing end is detected to when the power supply switches the polarity of the bias voltage applied to the transfer device is changed. 2. The method according to claim 1, wherein the interval between the detection of the passage of the rear end of the transfer material by the paper feed sensor and the detection of the passage of the front end of the subsequent transfer material is equal to or less than a predetermined value. A first time after detecting the passage of the rear end of the material, the power supply device switches the polarity of the bias voltage applied to the transfer device, and detects the passage of the rear end of the material to be transferred by the paper feed sensor. If the interval time between the detection of the passage of the leading end of the subsequent transfer material and the detection of the passage of the rear end of the transfer material is longer than a predetermined value, the second time longer than the first time after the detection of the passage of the rear end of the transfer material The power supply device switches the polarity of the bias voltage applied to the transfer device later, and the first time is a time at which the rear end of the material to be transferred comes to a position before passing the transfer position of the transfer device, In the second time, the rear end of the material to be transferred is The image forming apparatus according to claim 1, wherein the time is a time at which the apparatus arrives at a position after passing through a transfer position of the apparatus.