JPH07334017A - Control method of transfer device - Google Patents

Abstract

PURPOSE:To prevent the staining of the back surface of a paper sheet by preventing the fatigue of a photoreceptor drum. CONSTITUTION:The charged photoreceptor drum is exposed to form an electrostatic latent image, toner is stuck thereto to develop it and then, the toner image is transferred to the sheet to form an image. While the image is formed, a constant voltage is applied to a transfer roller 28 to control it with the constant voltage. At this time, even if the width of the sheet is varied, a transfer voltage is never changed so that transfer efficiency can be increased. Moreover, at the point of set time just before the tailing edge of the sheet passes through a transfer part, a changeover from the control with the constant voltage to the control with a constant current is attained. When the tailing edge of the sheet passes through the transfer part, the transfer voltage applied to the transfer roller 28 can be decreased and even if the transfer roller 28 comes into direct contact with the photoreceptor drum, it never be fatigued.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for a transfer device in an electrophotographic printer.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic printer, a charged photosensitive drum is exposed to form an electrostatic latent image, toner is attached to the electrostatic latent image and development is performed to form a toner image. The toner image is transferred to a recording medium to form an image. To that end, electrophotographic printers
The process consists of charging, exposure, development, transfer, fixing, charge removal and cleaning.

FIG. 2 is a schematic view of a conventional electrophotographic printer. In the figure, 11 is a photosensitive drum, 31 is a charging roller for uniformly and uniformly charging the surface of the photosensitive drum 11 to a negative polarity, and 19 is a charging roller 31 in the rotating direction of the photosensitive drum 11. It is arranged on the downstream side,
L for exposing the photoconductor drum 11 to form an electrostatic latent image
It is an ED head. When the LED head 19 irradiates the surface of the photosensitive drum 11 with light, the resistance of the photosensitive layer of the photosensitive drum 11 decreases and the negative charges escape. Therefore, an invisible electrostatic latent image corresponding to the printed image is formed by the portion irradiated with light and the portion not irradiated with light.

Further, 27 is disposed downstream of the LED head 19 in the rotation direction of the photosensitive drum 11,
A developing roller 28 that develops the electrostatic latent image into a toner image by attaching toner charged with a negative polarity to the electrostatic latent image, and 28 is a developing roller 27 in the rotation direction of the photosensitive drum 11. The transfer roller is provided on the downstream side and forms a transfer portion between the transfer roller and the photosensitive drum 11, and transfers the toner image onto the sheet conveyed in the direction of arrow A. When a voltage having a positive polarity is applied to the transfer roller 28 and a positive charge having a polarity opposite to that of the toner is applied from the back side of the paper, the toner is attracted by the positive charge and moves to the paper side.

Reference numeral 32 is disposed downstream of the transfer roller 28 in the rotation direction of the photosensitive drum 11.
The cleaning roller removes the toner remaining on the surface of the photoconductor drum 11. A registration roller 34 is arranged upstream of the transfer section in the sheet conveying direction, and a writing sensor 36 is arranged between the registration roller 34 and the transfer roller 28. Further, a fixing device 22 is arranged on the downstream side of the transfer section in the sheet conveying direction. The fixing device 22 comprises a heat roller 22a and a backup roller 22b. Therefore, heat and pressure can be applied to the toner image transferred to the paper to fix the toner image on the paper.

Next, the operation of the electrophotographic printer having the above structure will be described with reference to FIG. Figure 3
FIG. 3A is a time chart of a transfer unit at the end of printing and an output waveform diagram of a transfer voltage. Detection signal WR of the writing sensor 36
Is a signal indicating that the sheet has been conveyed to the transfer section, and is at a high level (ON) when the sheet is present at the transfer section, and is at a low level (OFF) when the sheet passes through the transfer section. Further, the transfer output signal TR1-N is a signal for controlling the output of the high voltage power source (not shown) to the transfer portion, and is at a low level (ON) when being output, and at a high level (when not being output). Off).

The constant voltage / constant current signal TRSEL2
-P is a signal instructing whether the control of the transfer voltage v _TR should be a constant voltage or a constant current. When the level is high, the constant current control is instructed, and when the level is low, the constant voltage control is instructed. . As shown in FIG. 2, in consideration of the fact that the writing sensor 36 is arranged on the upstream side of the transfer portion in the sheet conveying direction, the slack of the sheet may occur, etc. After the detection signal WR of 36 has become the low level, the transfer output signal TR1- is calculated after a few [ms] has elapsed from the time when the trailing edge of the sheet passed the transfer portion.
N and the constant voltage / current signal TRSEL2-P are set to high level.

Therefore, the transfer voltage v _TR is the transfer output signal TR1-N and the constant voltage / constant current signal TRSEL2-P.
Is set to "0" when becomes high level.

[0009]

However, in the above-mentioned conventional transfer device, the transfer roller 2 is operated until a few [ms] has elapsed from the time when the trailing edge of the sheet passed the transfer portion.
8 and the photoconductor drum 11 are in direct contact with each other,
Since the high transfer voltage v _TR is applied to the transfer roller 28, the photoconductor drum 11 is fatigued.

Moreover, since the transfer voltage v _TR having a positive polarity is applied to the transfer roller 28, the transfer roller 28
The surface of the photoconductor drum 11 in contact with is charged to an extremely positive polarity. Therefore, the surface of the photoconductor drum 11 cannot be sufficiently charged to the negative polarity by the charging roller 31, and the toner of the developing roller 27 adheres to the non-image portion of the photoconductor drum 11.

In this case, the toner attached to the photosensitive drum 11 is further attached to the transfer roller 28 which is in direct contact with the transfer portion, and the toner attached to the transfer roller 28 is the back surface of the paper sheet conveyed next. It adheres to and causes dirt on the back. The present invention solves the problems of the conventional control method of the transfer device, prevents the photoconductor drum from being fatigued, and provides a control method of the transfer device that does not cause back stain on the paper. The purpose is to provide.

[0012]

Therefore, in the control method of the transfer device of the present invention, the charged photosensitive drum is exposed to form an electrostatic latent image, and toner is attached to the electrostatic latent image. After that, development is performed, and then the toner image is transferred to a sheet to form an image. Then, while forming an image, a constant voltage is applied to the transfer roller to perform constant voltage control, and at a set time immediately before the trailing edge of the paper passes through the transfer portion, constant voltage control is performed to constant current control. Switch to.

[0013]

According to the present invention, as described above, in the control method of the transfer device, the charged photosensitive drum is exposed to form an electrostatic latent image, and the toner is attached to the electrostatic latent image. After development, the toner image is transferred onto a sheet to form an image. Then, while forming an image, a constant voltage is applied to the transfer roller to perform constant voltage control. In this case, since the transfer voltage does not change even if the width of the paper changes, the transfer efficiency can be improved.

The constant voltage control is switched to the constant current control at a set time point immediately before the trailing edge of the sheet passes through the transfer section. In this case, by switching to the constant current control, it is possible to reduce the transfer voltage applied to the transfer roller when the trailing edge of the paper passes the transfer portion.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is a block diagram of an electrophotographic printer according to an embodiment of the present invention, FIG. 4 is a first time chart of an electrophotographic printer according to an embodiment of the present invention, and FIG. 5 is a second time chart of an electrophotographic printer according to an embodiment of the present invention. Is a time chart of. Since the structure of the electrophotographic printer is the same as the conventional one, the description thereof will be omitted with reference to FIG.

In FIG. 1, reference numeral 1 denotes a print control unit arranged in the printing unit of the electrophotographic printer.
Is composed of a microprocessor 53, an input / output port 54, a counter 52, not shown ROM, RAM, etc., or a logic circuit having equivalent functions, and is a clock signal CLK, a video signal 11, transmitted from a not shown upper controller. Upon receiving the timing signal 12 and the like, the printing unit is sequence-controlled.

When the command signal is received from the host device via the interface circuit (not shown), the host controller refers to the character font data, the pattern data, etc. stored in the ROM (not shown) in the host controller, and for each page. The print data including characters, figures, etc. is edited into dot data, and the dot data is transferred to the print control unit 1 as the video signal 11.

When the print control unit 1 receives an instruction to start printing by a control signal (not shown) transmitted from the host controller, first, the fixing device 22 having the heater 22a built therein falls within the usable temperature range. It is detected by the fixing device temperature sensor 29. If the temperature is not within the temperature range, the heater 22a is energized by the signal 21 to heat the fixing device 22 to a usable temperature.

Next, the developing / transferring process motor (PM) 3 is started and rotated through the driver 2. At this time, a negative polarity voltage is applied to the charging roller 31 to set the surface potential of the photosensitive drum 11 to a negative polarity, and
High voltage power supply circuit 2 for charging by the charge trigger signal 41
5 is turned on, and a reverse bias voltage, that is, a positive polarity voltage is applied to the developing roller 27.

By the way, the type of the sheet set in the sheet cassette (not shown) is detected by the sheet remaining amount sensor 8 and the sheet size sensor 9, and the sheet feeding suitable for the sheet is started. Here, the paper feed motor (PM) 5 is configured to be bidirectionally rotated via the driver 4, and is first rotated in the opposite direction until the paper inlet sensor 6 detects the set paper. Carry only the set amount. Subsequently, the paper feed motor 5 is rotated in the forward direction to convey the paper to the transfer portion between the photoconductor drum 36 and the transfer roller 28.

When the writing sensor 36 detects that the leading edge of the paper has reached the printable position, the print controller 1 sends a timing signal 12 (including a line timing signal and a raster timing signal) to the host controller. Is transmitted and the video signal 11 is received. The video signal 11 edited by the upper controller for each page and received by the print controller 1 is transferred to the LED head 19 as an actual print data signal 18.

Then, when the video signal 11 for one line is received, the print controller 1 sends a latch signal 17 to the LED head 19. When the latch signal 17 is sent, a latch (not shown) of the LED head 19 holds an actual print data signal 18 for one line stored in a shift register (not shown). Next, before the next video signal 11 is transmitted from the host controller, the print control unit 1 outputs L
The print drive signal 13 is sent to the ED head 19, and the LED head 19 sends the actual print data signal 18 held in the latch.
About. In this case, the transmission / reception of the video signal 11 is performed line by line.

Then, the actual print data signal 18 transferred to the LED head 19 forms an electrostatic latent image composed of dots having an increased potential on the photosensitive drum 11 charged to a negative polarity. Further, in the developing roller 27, the toner for image formation charged to a negative polarity is attracted to each dot by an electric attraction force, the electrostatic latent image becomes a toner image, and the toner image is transferred to the transfer portion. Sent to.

On the other hand, the transfer signal 24 turns on the transfer high-voltage power supply circuit 26, a voltage of positive polarity is applied to the transfer roller 28, and the toner image is transferred onto the sheet passing through the transfer section. Here, the transfer signal 24 is the transfer output signal TR1-N and the constant voltage / constant current signal TRSEL2-P.
become. The transfer output signal TR1-N is a signal for controlling the output of a high-voltage power supply (not shown) to the transfer unit, and is at a low level (ON) when being output, and at a high level (OFF) when not being output. )become.

The constant voltage / constant current signal TRSEL2
-P is a signal instructing whether the control of the transfer voltage v _TR should be a constant voltage or a constant current. When the level is high, the constant current control is instructed. When the level is low, the constant voltage control is instructed. To do. Next, the sheet having the transferred toner image is conveyed while contacting the fixing device 22 having the heater 22a therein, and the toner image is fixed on the sheet by the heat of the fixing device 22. Further, the sheet on which the toner image is fixed is further conveyed, passes through the sheet discharge port sensor 7 from the printing mechanism, and is discharged to the outside of the electrophotographic printer.

The print control unit 1 responds to the detection of the paper by the paper size sensor 9, the paper inlet sensor 6, the writing sensor 36, etc., and only when the paper is passing through the transfer unit, a high voltage power source for transfer is used. The circuit 26 is activated to apply the transfer voltage v _TR to the transfer roller 28. In this case, the writing sensor 3
After the detection signal WR of 6 has become low level, the first set time before the trailing edge of the sheet passes through the transfer portion, for example, 640 in the case of a printer having a printing speed of 4 [p / m].
When [ms] has passed, constant voltage / constant current signal TRSEL
2-P is set to a high level, and then the transfer output signal TR is set after the second set time, for example, 400 [ms] has elapsed.
1-N is set to high level.

Therefore, in the print controller 1, the counter 52 outputs an overflow flag F to the microprocessor 53 when the set time is counted, and the microprocessor 53 outputs the constant voltage / constant current signal T.
RSEL2-P, transfer output signal TR1-N, etc. are generated. Therefore, the output of the transfer high-voltage power supply circuit 26 can be switched from the constant voltage control to the constant current control immediately before the trailing edge of the sheet passes through the transfer section.

The counter 52 is shown in FIG.
As shown in FIG. 5, the clock signal CLK is counted, and whenever the count value reaches 15, the overflow flag F is set and the microprocessor 53 is interrupted. In this case, the time until the counter 52 counts the clock signal CLK 15 times, that is, the time until the overflow flag F is set is 40 [ms], which is the basis of the time setting in the transfer high-voltage power supply circuit 26. ing.

By the way, when the printing speed is changed, the conveyance speed of the paper is also changed accordingly, and after the detection signal WR of the writing sensor 36 becomes low level, the trailing edge of the paper passes through the transfer portion. Time also changes. Therefore, the set time is changed according to the printing speed. Next, the transfer high-voltage power supply circuit 26 will be described.

FIG. 6 is a schematic diagram of a high voltage power supply circuit for transfer in the embodiment of the present invention. As shown in the figure, the transfer high-voltage power supply circuit 26 includes a high-voltage power supply 61, a rectifier circuit 62, a voltage detection unit 63, and a current detection unit 64. Then, the input / output port 54 of the print control unit 1 receives the constant voltage / constant current signal TRSE.
It has a changeover switch SW that is switched by L2-P, and the voltage detection unit 63 and the current detection unit 64 are selectively connected to the high-voltage power supply 61 by the changeover switch SW.

Therefore, constant voltage control is performed when the voltage detection unit 63 and the high voltage power supply 61 are connected by the changeover switch SW, and constant current control is performed when the current detection unit 64 and the high voltage power supply 61 are connected. Be seen. By the way, when the electrophotographic printer is started, the transfer high-voltage power supply circuit 26
First, connect the current detector 64 and the high-voltage power supply 61,
The constant current control is performed to raise a predetermined transfer voltage v _TR . However, if the transfer voltage v _TR is applied to the transfer roller 28 while the constant current control is continued, when the width of the sheet changes, the transfer roller 28 and the photosensitive drum 1 are not changed.
1 (see FIG. 2) and the transfer voltage v _TR fluctuates. Therefore, the transfer efficiency at the transfer portion changes as the transfer voltage v _TR changes, and the image quality deteriorates.

Therefore, when the predetermined transfer voltage v _TR is raised, the control is switched to the constant voltage control to stabilize the transfer voltage v _TR . And in this embodiment,
If the output of the transfer high-voltage power supply circuit 26 is switched from the constant voltage control to the constant current control immediately before the trailing edge of the sheet passes through the transfer section, the trailing edge of the sheet will pass through the transfer section in the constant current control state. Become. In this case, the transfer voltage v _TR decreases as shown in FIG.

Therefore, even if the transfer roller 28 and the photoconductor drum 11 come into direct contact with each other, the photoconductor drum 11 will not be fatigued. The output of the transfer high-voltage power supply circuit 26 is switched from the constant voltage control to the constant current control at the time when the transfer portion is in the margin portion outside the print compensation range on the paper. Further, the surface of the photoconductor drum 11 in the portion in contact with the transfer roller 28 is not charged to an extremely positive polarity, so that the surface of the photoconductor drum 11 is sufficiently charged to a negative polarity by the charging roller 31. be able to. Therefore, the toner on the developing roller 27 does not adhere to the non-image portion of the photosensitive drum 11.

As a result, it is possible to prevent the back stain from occurring on the paper. In this embodiment, the current flowing between the transfer roller 28 and the photoconductor drum 11 in the constant current control is set to 4.2 [μA]. Then, when printing is completed and the paper passes through the paper discharge port sensor 7 (FIG. 1), the application of the voltage to the developing roller 27 by the charging high-voltage power supply circuit 25 is terminated, and at the same time, the developing / transferring process motor 3 is driven. Stop operation.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified within the scope of the present invention, and they are not excluded from the scope of the present invention.

[0036]

As described above in detail, according to the present invention, in the control method of the transfer device, the charged photosensitive drum is exposed to form an electrostatic latent image, and the electrostatic latent image is formed. After the toner is adhered to and developed, the toner image is transferred to a sheet to form an image.

While the image is being formed, a constant voltage is applied to the transfer roller for constant voltage control. In this case, since the transfer voltage does not change even if the width of the paper changes, the transfer efficiency can be improved. Further, the constant voltage control is switched to the constant current control at a set time point immediately before the trailing edge of the sheet passes through the transfer section. In this case, by switching to the constant current control, it is possible to reduce the transfer voltage applied to the transfer roller when the trailing edge of the paper passes the transfer portion.

Therefore, even if the transfer roller and the photoconductor drum come into direct contact with each other, the photoconductor drum is not fatigued. Further, since the surface of the photoconductor drum that is in contact with the transfer roller is not charged with extremely positive polarity, the surface of the photoconductor drum can be sufficiently charged with negative polarity by the charging roller. Therefore, the toner on the developing roller does not adhere to the non-image portion of the photosensitive drum.

As a result, it is possible to prevent the back stains on the sheet.

[Brief description of drawings]

FIG. 1 is a block diagram of an electrophotographic printer according to an embodiment of the present invention.

FIG. 2 is a schematic view of a conventional electrophotographic printer.

FIG. 3 is a time chart of a transfer unit at the end of printing and an output waveform diagram of a transfer voltage.

FIG. 4 is a first time chart of the electrophotographic printer according to the embodiment of the present invention.

FIG. 5 is a second time chart of the electrophotographic printer according to the embodiment of the present invention.

FIG. 6 is a schematic diagram of a transfer high-voltage power supply circuit according to an embodiment of the present invention.

[Explanation of symbols]

11 Photoconductor drum 28 Transfer roller TRSEL2-P Constant voltage / constant current signal v _TR Transfer voltage

Claims (1)

[Claims] 1. A charged photosensitive drum is exposed to form an electrostatic latent image, toner is attached to the electrostatic latent image for development, and then the toner image is transferred to a sheet to form an image. In a method of controlling a transfer device of an electrophotographic printer to be formed, (a)
While forming an image, a constant voltage is applied to the transfer roller to perform constant voltage control. (B) At a set time point immediately before the trailing edge of the paper passes through the transfer portion, the constant voltage control causes a constant current. A method for controlling a transfer device, characterized by switching to control.