JP2987259B2 - Electrophotographic recording 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 electrophotographic recording apparatus for recording an image on a recording medium by an electrophotographic process.

[0002]

2. Description of the Related Art An electrophotographic recording apparatus has many rotating parts, such as a photosensitive drum, a developing roller, a paper feed roller, and a registration roller. In order to rotationally drive these rotating parts, providing respective motors,
This leads to an increase in the size and cost of the apparatus, which is not preferable.

Conventionally, attention has been paid to the fact that the developing operation and the paper passing to the transfer position are performed synchronously, and the developing roller and the registration roller are synchronously rotated by the same motor, so that the number of motors is reduced. To reduce the size and cost of the apparatus.

The developing device has, for example, a configuration shown in FIG. In the figure, 1 is a photosensitive drum, and 2 is a developing device. The developing device 2 includes a hopper 21, a developing roller 22, a blade 23, a developing power source 24, and a switch 25.

In the developing device 2 having the above structure, the hopper 2
The toner (not shown) stored in the developing roller 23 is
And the hopper 2 is rotated by the rotation of the developing roller 23.
1 and is brought into contact with the surface of the photosensitive drum 1. When the toner is carried by the developing roller 23 and transported, the layer thickness is made constant by the blade 23 and the toner is frictionally charged to a negative polarity. The surface of the photosensitive drum 1
After being charged to, for example, about −550 V by a charging device (not shown), by selectively exposing according to an image to be recorded by an exposure device (not shown), the potential of the recording portion is about −50 to −100 V, and the non-recording portion is Is formed at about -550 V. Also, the developing roller 22 includes
For example, a developing bias of -200 V is applied from the developing power supply 24. For this reason, in a portion where the potential of the photosensitive drum 1 is −550 V, the photosensitive drum 1 side has a high potential, so that the toner remains carried on the developing roller 22. Further, in a portion where the potential is −50 to −100 V, the toner adheres to the photosensitive drum 1 because the developing roller 22 side has a high potential.

[0006] When the developing roller 22 and the registration roller (not shown) are driven to rotate by the same motor as described above, the rotation of the developing roller 22 is intermittent. This is because the registration roller adjusts the timing of paper passing to the transfer position, and must be rotated only during the period of paper passing to the transfer position.

When the operation of the developing roller 22 is stopped,
Is also stopped, so that the toner is not charged. In this state, charge leakage occurs in the toner, and the charge amount decreases. During the recording operation, the period during which the paper feed to the transfer position is stopped is only between pages, and since it is a very short period, there is no significant decrease in the charge amount and there is no problem. However, when the operation is started, if the charge amount of the toner is significantly reduced during the stop period, the developing roller 22 does not rotate until immediately before the start of the developing operation, and thus contacts the photosensitive drum 1 at the beginning of the developing operation. The state is such that the charge amount of the toner is reduced. In particular, the toner carried in the region (the region indicated by A in FIG. 3) of the developing roller 22 from the contact position with the blade 23 to the contact position with the photosensitive drum 1 comes into contact with the photosensitive drum 1. Since it is not subjected to friction at least once, the charge amount is extremely low.

[0008] Such a toner having a low charge amount easily adheres to the photosensitive drum 1 and causes image fogging. FIG.
FIG. 5 is a diagram showing the relationship between the number of times the toner contacts the blade 23, the amount of toner charge, and fog on the photoconductor. As can be seen from this figure, the toner charge amount is
It is low when the number of contacts with is small. In addition, when the toner charge amount is low, the rate of fogging on the photoconductor increases.

[0009]

As described above, the conventional electrophotographic recording apparatus has a problem in that, at the beginning of the developing operation, an image is fogged by the toner whose charge amount has been reduced, thereby deteriorating the image quality. .

The present invention has been made in view of such circumstances, and an object of the present invention is to perform rotation driving of a developing roller and a registration roller by the same driving source, thereby increasing the size and cost of the apparatus. An object of the present invention is to provide an electrophotographic recording apparatus capable of suppressing a rise and providing a sufficient charge to toner even at an early stage of a developing operation, thereby preventing occurrence of image fog.

[0011]

According to the present invention, there is provided an apparatus for opening a recording operation.
Prior to executing the recording operation in response to the start instruction, a driving source such as a development registration roller is controlled to rotate the development roller and the registration roller by a predetermined amount.

[0012]

[Action] By taking such measures, the recording operation is performed.
At the time when the start instruction is made, the serial in accordance with the instructions
Prior to performing the recording operation, the driving roller rotates the developing roller by a predetermined amount by a driving source, and the developer carried on the developing roller contacts the charging member to be charged. Therefore, when the recording operation is performed, the developer is in a charged state.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically illustrating a main configuration of an electrophotographic recording apparatus according to the present embodiment. The same parts as those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted. A charging device 3, an exposure device 4, a developing device 2, a transfer device 5, and a cleaning device 6 are provided around the photosensitive drum 1 along its peripheral surface.

The charging device 3 comprises, for example, a well-known scorotron charger and uniformly charges the surface of the photosensitive drum 1 to a predetermined potential. The exposure device 4 includes, for example, a well-known laser scanner or the like.
Is partially exposed. The transfer device 5 includes a transfer roller 51, a transfer power supply 52, a reverse voltage power supply 53, and a switch 5.
Four. The transfer roller 51 is disposed in parallel with and in contact with the photosensitive drum 1, and holds and conveys the recording paper P together with the photosensitive drum 1 when the recording paper P is inserted. The transfer power supply 52 generates a predetermined voltage (transfer voltage) having a polarity opposite to the charge of the toner, that is, a positive polarity, to be applied to the transfer roller 51. The reverse voltage power supply 53 is connected to the transfer roller 5.
1 to generate a predetermined voltage having a polarity opposite to that of the transfer voltage, that is, a negative polarity. The switch 54 performs ON / OFF of voltage application to the transfer roller 51 and selection of a voltage to be applied (either the voltage generated by the transfer power supply 52 or the reverse voltage power supply 53).

Reference numeral 7 denotes a recording paper cassette in which recording paper P is stored. Recording paper P stored in recording paper cassette 7
Is sent out by the paper feed roller 8 to the transport path formed by the guide G.

Reference numeral 9 denotes a registration roller. The registration roller 9 corrects the skew of the recording paper P transported on the transport path by the paper feed roller 8 and transports the recording paper P to a position between the photosensitive drum 1 and the transfer roller 51 (transfer position). In the vicinity of the registration roller 9, a registration sensor 10 composed of, for example, a microswitch is provided.

Reference numeral 11 denotes a main motor, which is a photosensitive drum 1
And the paper feed roller 8 is rotationally driven. However, the rotation of the main motor is transmitted to the paper feed roller 8 via a paper feed clutch 12, and the rotation of the paper feed roller 8 while rotating the photosensitive drum 1 by the contact and separation of the paper feed clutch 12. It is possible to stop it. Reference numeral 13 denotes a development registration motor that synchronously rotates the development roller 22 and the registration roller 9.

Reference numeral 14 denotes a control section for controlling the electrophotographic recording apparatus in general. The control unit 14 includes, for example, a microcomputer as a main control circuit, and includes a pre-toner charging processing unit 14a in addition to a control unit that performs well-known general control in the electrophotographic recording apparatus. I have. The pre-toner charging unit 14a performs a process to be described later for charging the toner when the operation is started.

Next, the operation of the electrophotographic recording apparatus configured as described above will be described according to the processing procedure of the control unit 14.
First, the control unit 14 receives the operation start signal from another unit (the electrophotographic recording apparatus is applied to, for example, a facsimile machine, but in this case, a part that controls the entire facsimile machine). The rotation of the motor 11 is started. However, at this time, the paper feed clutch 12 is in the disconnected state, and the rotation of the main motor 11 is not transmitted to the paper feed roller 8. Therefore, as shown in FIG. 2, only the photosensitive drum 1 starts rotating (at time T1 in FIG. 2). At the same time, the control unit 14 activates the charging device 3 to start charging the photosensitive drum 1, and turns on the switch 54 of the transfer device 5 to the reverse voltage power supply 53 side, so that the transfer roller 51
The application of a negative voltage to is started.

Subsequently, the control unit 14 determines when a time TA required for a certain point of the photosensitive drum 1 to reach from a charging position by the charging device 3 to a contact position (developing position) of the developing roller 22 has elapsed from the time T1. At (T2 in FIG. 2), the switch 25 of the developing device 2 is turned ON, and the application of the developing bias to the developing roller 22 is started. That is, when the charging device 3 starts charging the photosensitive drum 1 and the position at the charging position reaches the developing position, the application of the developing bias to the developing roller 22 is started. Thus, the potential of the photosensitive drum 1 becomes a predetermined charging potential (for example, −55).
0 V), and the potential of the developing roller 22 is about the developing bias voltage (for example, -200 V), so that the toner sufficiently charged to the negative polarity does not adhere to the photosensitive drum 1.

However, when the developing roller 22 stops, the toner whose charge amount has decreased (particularly, the toner carried on the area A of the developing roller 22) easily adheres to the photosensitive drum 1. At this time, the photosensitive drum 1 and the transfer roller 5
1, the toner (fogging toner) adhered to the photosensitive drum 1 adheres to the transfer roller 51 and the transfer roller 51 becomes dirty. Therefore, at the same time T2, the control unit 14 switches the switch 54 of the transfer device 5 to the transfer power supply 52 side, and switches the voltage applied to the transfer roller 51 to the positive transfer voltage. As a result, the fog toner is transferred to the transfer roller 5 by the transfer voltage at the transfer position.
1 and remains attached to the photosensitive drum 1 side,
Does not adhere to the transfer roller 51. And fog toner
It is removed by the cleaning device 6.

At time T2, the control unit 14 starts the rotation of the developing resist motor 13 and
Then, the rotation of the registration roller 9 is started. Then, the control unit 14 determines that the time TB required for the developing roller 22 to rotate by the predetermined amount has passed from the time point T2 (T3 in FIG. 2).
Until the time point), the developing registration motor 13 is rotated to rotate the developing roller 22 and the registration roller 9. Therefore, the developing roller 22 is rotated by a predetermined amount during the period of time TB. The rotation amount of the developing roller 22 during this TB period is:
From the relationship between the number of times the toner contacts the blade 23 and the amount of toner charge as shown in FIG. 4, the amount is set such that most of the toner carried on the developing roller 22 is sufficiently charged. Specifically, to bring all of the toner around the entire circumference of the developing roller 22 into contact with the blade 23 once, the developing roller 22
Needs to be rotated at least once, which is a minimum of one rotation. Then, an optimum rotation speed is set according to the required toner charge amount.

Thus, a state in which a sufficiently charged toner is carried on the developing roller 22 is formed. At this time, the registration roller 9 is also rotating.
As shown in FIG. 2, the paper feed clutch 12 has not been connected yet, and the recording paper P has not been supplied to the registration rollers 9. Therefore, the registration roller 9 is only idle, and the paper is not passed to the transfer position. Control unit 1
Reference numeral 4 switches the switch 54 of the transfer device 5 to the reverse voltage power supply 53 side at time T3, and switches the voltage applied to the transfer roller 51 to the negative polarity. The above processing is the pre-toner charging processing, which is performed by the pre-toner charging processing unit 14a.

Thereafter, the control unit 14 executes an actual recording operation according to a well-known procedure. Specifically, first, the paper feed clutch 1
2 is brought into the coupled state (at time T4 in FIG. 2). As a result, the paper feed roller 8 starts to rotate, and the recording paper P stored in the recording paper cassette 7 is sent out to the transport path formed by the guide G. The leading end of the recording paper P sent to the transport path in this way reaches the registration roller 9 soon. At this time, since the development registration roller 13 is stopped and the registration roller 9 is not rotating, the recording paper P
Stops when the tip abuts against the registration roller 9. When the leading edge of the recording paper P reaches the registration roller 9, the registration sensor 10 is turned on (at time T5 in FIG. 2).

The control unit 14 monitors the output of the registration sensor 10, and when the registration sensor 10 is turned on at the time T5, the control unit 14 puts the paper feed clutch 12 into a disconnected state. Then, the image data is supplied to the exposure device 4 to perform an exposure process.

Subsequently, the control unit 14 controls the developing resist motor 13 at a point in time when a predetermined time TC has elapsed (at a point T7 in FIG. 2) from a point in time when the exposure processing started (point T6 in FIG. 2).
Of the developing roller 22 and the registration roller 9 are started. As a result, the toner is supplied to the surface of the photosensitive drum 1, so that the developing operation is performed and the paper passing to the transfer position is started. At this time, since the toner carried on the developing roller 22 and supplied to the photosensitive drum 1 is sufficiently charged by the above-described toner pre-charging process, normal development is performed without fogging. The time TC is set so that the passage timing of the transfer position of the toner image formed on the photosensitive drum 1 and the paper passing timing to the transfer position match.

Further, the control unit 14 determines whether a predetermined time TD has elapsed from the time T6 when the exposure processing started (FIG. 2).
At the time T8 in the middle), the switch 54 of the transfer device 5 is switched to the transfer power supply 52 side, the voltage applied to the transfer roller 51 is switched to the positive transfer voltage, and the toner image formed on the photosensitive drum 1 is transferred to the transfer position. Is set to a state in which the image can be transferred to the recording paper P passed through the printer. Note that the time TD corresponds to the photosensitive drum 1
A certain point on the surface is the time required for the exposure device 4 to reach the transfer position from the exposure position.

The control unit 14 controls the developing resist motor 13 at a point in time when a predetermined time TE has elapsed (at point T10 in FIG. 2) from the point in time when the exposure processing for one page has been completed (point T9 in FIG. 2). The rotation of the developing roller 22 and the registration roller 9 is stopped. Further, the control unit 14
Is the time TD from the time T9 when the exposure process for one page is completed.
Is passed (time T11 in FIG. 2), the transfer device 5
Is switched to the reverse voltage power supply 53 side, and the voltage applied to the transfer roller 51 is returned to the negative polarity.

The above is the recording operation for one page. Thereafter, if there is a need to record another page, the control unit 14 repeats the same procedure to execute the recording operation of that page. When the operation is stopped, the control unit 14 stops the rotation of the main motor 11 to stop the rotation of the photosensitive drum 1 and the developing device 2
And the switch 54 of the transfer device 5 are turned off to stop the application of the developing bias to the developing roller 22 and the application of the voltage to the transfer roller 51, respectively.

As described above, according to the present embodiment, even if the charge amount of the toner in the developing device 2 is reduced in the operation stop state, it is necessary to start the actual recording operation at the start of the recording operation. Prior to this, the developing roller 22 is rotated by a predetermined amount to charge the toner. Therefore, the developing roller 22 and the registration roller 9 are synchronously driven by the development registration motor 13, and the developing roller 22 is not rotated until immediately before the developing operation is performed during the actual recording operation. Since the toner is sufficiently charged by the toner pre-charging process, image fogging does not occur due to a shortage of the toner charge amount at the beginning of the recording operation. Thus, after preventing the image quality from deteriorating, the rotation of the developing roller 22 and the registration roller 9 is driven by the same drive source (the development registration motor 13), so that it is possible to suppress an increase in the size of the apparatus and an increase in cost. .

The present invention is not limited to the above embodiment. For example, in the above embodiment, the transfer device 5 includes the transfer roller 51, and the polarity of the voltage applied to the transfer roller 51 is reversed during the pre-toner charging process. Need not perform such processing.

The operation timing of each section is not limited to the one described in the above embodiment. If the developing roller 22 is rotated by a predetermined amount before the actual recording operation is performed, other timings are arbitrary. good. In addition, various modifications can be made without departing from the spirit of the present invention.

[0033]

According to the present invention, the start instruction of the recording operation is provided.
Prior to executing the recording operation accordingly, the driving source such as the developing registration roller is controlled to rotate the developing roller and the registration roller by a predetermined amount. To reduce the size and cost of the equipment,
An electrophotographic recording apparatus can be provided with a sufficient charge to the toner even in the early stage of the developing operation, thereby preventing the occurrence of image fog.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a main configuration of an electrophotographic recording apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the operation timing of each unit in FIG.

FIG. 3 is a diagram illustrating a conventional technique.

FIG. 4 is a diagram illustrating a conventional technique.

[Description of Signs] 1 ... photosensitive drum, 2 ... developing device, 22 ... developing roller, 2
DESCRIPTION OF SYMBOLS 3 ... Blade, 3 ... Charging device, 4 ... Exposure device, 5 ... Transfer device, 6 ... Cleaning device, 9 ... Registration roller, 1
3 ... Development registration roller, 14 ... Control unit, 14a ... Toner pre-charging processing means.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 21/00 370-540 G03G 21/14 G03G 15/00 303 G03G 13/08 G03G 15/08-15/08 507 G03G 15/00 550 G03G 21/16-21/18

Claims (1)

(57) [Claims] An image is recorded on a recording medium by an electrophotographic process, and a developing means rotates a developing roller to bring a developer carried on the developing roller into contact with a charging member. In the electrophotographic recording apparatus, wherein a developer is frictionally charged, and the developing roller is rotated synchronously with the registration roller by the same driving source as that for rotating the registration roller, the recording operation is started. An electrophotographic recording apparatus comprising: a control unit that controls the drive source to rotate the developing roller and the registration roller by a predetermined amount before performing a recording operation in accordance with an instruction .