JPH09134078A - Electrophotographic recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a printing grade without generating fog by applying a voltage only to a conductive part selected according to the width of a paper sheet. SOLUTION: When an operator controls a control panel to set the size of the paper sheet, the output part of a transfer high-voltage power source is selected according to the size of the paper and a transfer voltage is applied to the corresponding conductive parts 49A to 49C from the selected output part. At the time of printing an A4-size paper for instance, the transfer voltage is applied to all the conductive parts 49A to 49C. At the time of printing an A6-size paper, the transfer voltage is applied only to the conductive part 49B. Thus, in a transfer roller 48, the transfer voltage is applied only to a range corresponding to the width of the paper, so that the transfer voltage never leaks to a low impedance part. Since a high voltage is not directly applied to the transfer roller 48, the life of the transfer roller 48 can be prolonged.

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.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic recording apparatus such as an electrophotographic printer, a charged photosensitive drum is irradiated with a light source to form an electrostatic latent image on the surface of the photosensitive drum. Develop the electrostatic latent image into a toner image,
The toner image is transferred onto a sheet and fixed.

FIG. 2 is a block diagram of a printer control circuit in a conventional electrophotographic printer, and FIG. 3 is a time chart of the conventional electrophotographic printer. In the figure, 11 is a microprocessor, ROM, RAM input / output port,
The print control unit 11 includes a timer and the like. The print control unit 11 is provided in the printer unit of the electrophotographic printer and has a control signal SG from a host controller (not shown).
1. The entire printer section is sequence-controlled by the video signal SG2 and the like to perform the printing operation.

When the print control section 11 receives a print instruction by the control signal SG1, first, the fixer temperature sensor 20 detects whether or not the fixer 22 having the heater 22a is in a usable temperature range. If the temperature is not within the temperature range, the heater 22a is turned on to heat the fixing device 22 until the temperature is within the usable temperature range. Next, driver 1
The developing / transferring process motor (PM) 13 is driven via 2 and at the same time, the charge signal SG3 is supplied to the charging high-voltage power supply 2
5, the high voltage power supply 25a for developing bias and the high voltage power supply 25b for toner supply bias are respectively sent and turned on. Then, the charging roller 27 is charged and the toner supply roller 2
A developing bias voltage is applied to 7b, and toner (not shown) is conveyed toward the developing roller 27a.

Further, the sheets set in a sheet cassette (not shown) are detected by the sheet remaining amount sensor 18 and the sheet size sensor 19, and sheet feeding matching the type of sheet is started. Here, the paper feed motor (PM) 15
Can be driven in both directions via the driver 14, and by driving in the opposite direction first, the paper
The paper is taken out from the paper cassette and is fed by the set amount until it is detected by the paper inlet sensor 16. Then, by driving in the forward direction, the paper is conveyed into the printing mechanism of the electrophotographic printer.

At the time when the paper reaches the printable position, the print control section 11 sends a timing signal SG4 (line timing signal, line timing signal,
It includes raster timing signals and the like. ) To receive the video signal SG2. The video signal SG2 edited by the upper controller for each page and received by the print control unit 11 is the actual print data signal DATA.
Is sent to the LED head 21.

Then, when the print control section 11 receives the video signal SG2 for one line, the LED head 2
Latch signal LOAD is sent to 1, and the actual print data signal DA
TA is held in the LED head 21. In addition, the print control unit 11 sends the next video signal SG from the host controller.
Before receiving 2, the print drive signal ST is sent to the LED head 21.
Send B. As a result, the LED head 21 prints according to the held actual print data signal DATA. In addition,
CLK is the actual print data signal DATA for the LED head 21.
Is a clock signal for sending to. Further, the transmission / reception of the video signal SG2 is performed for each print line.

The LED head 21 irradiates a photosensitive drum (not shown) charged to a negative potential to form dots of increased potential on the surface of the photosensitive drum to form an electrostatic latent image. Then, the toner charged to a negative potential is attracted to each dot by an electric attraction force, and a toner image is formed. Then, the toner image is sent to the transfer portion formed in the gap between the photosensitive drum and the transfer roller 28. On the other hand, the print control unit 11
The transfer signal SG5 is sent to the high voltage power supply 26 for transfer having a positive potential to turn it on. As a result, the transfer roller 28 transfers the toner image onto the sheet passing through the transfer section.

Then, the sheet having the transferred toner image is brought into contact with the fixing device 22 and conveyed, and the toner image is fixed on the sheet by the heat of the fixing device 22. The sheet having the fixed toner is further conveyed, passes through the sheet discharge port sensor 17 from inside the printing mechanism of the electrophotographic printer, and is discharged to the outside of the electrophotographic printer. Further, the print control unit 11 responds to the detection of the paper by the paper size sensor 19 and the paper inlet sensor 16 and outputs the transfer signal SG5 to the high voltage power supply 26 for transfer and the charge signal SG3 to the toner supply bias. It sends to each high voltage power supply 25b. Therefore, the transfer high-voltage power supply 26 applies the transfer voltage to the transfer roller 28 only while the sheet is passing through the transfer roller 28. Then, when the printing is completed and the paper passes through the paper discharge port sensor 17, the high voltage power supply 25b for toner supply bias terminates the application of the voltage to the developing device (not shown), and at the same time, the developing / transferring process motor 1
Stop 3

Thereafter, the above operation is repeated. Next, the transfer process will be described. FIG. 4 is an explanatory diagram of a transfer process in a conventional electrophotographic recording device. As shown in the figure, the electrostatic latent image formed on the surface of the photosensitive drum 29 is the developing device 3
0 is developed to form a toner image (not shown). Then, the toner image is transferred to the transfer high-voltage power supply 2 at the transfer portion.
It is transferred onto the sheet 47 by the transfer roller 28 charged by 6. Then, the toner image on the paper 47 is
It is fixed on the sheet 47 by the fixing device 22 (FIG. 2). Incidentally, 31 is a toner.

Next, the developing process will be described. FIG. 5 is a structural diagram showing a developing process of a conventional electrophotographic printer,
FIG. 6 is a diagram showing a process voltage of a conventional electrophotographic printer. In FIG. 6, the horizontal axis indicates the developing roller 27a.
And the vertical axis represents the surface potential of the photosensitive drum 29 and the developing-side potential.

As shown in the drawing, when the photosensitive drum 29 is rotated by driving the developing / transferring process motor 13 (FIG. 2), the charging high-voltage power supply 25 applies a negative voltage to the charging roller 27. And the photosensitive drum 29
The surface of is charged to a constant voltage (about -700 [V]),
A primary charging part is formed. Next, when the LED head 21 irradiates light on a portion of the photosensitive drum 29 where printing is to be performed on the primary charging portion, the light-irradiated portion, that is, the exposed portion has a low potential (about -450 to -550 [. V]) and an electrostatic latent image is formed.

On the other hand, in the developing device 30, the developing bias high-voltage power supply 25a supplies a developing bias voltage of -300 [V] to the developing roller 27a, and the toner supply bias high-voltage power supply 25b supplies the toner supply roller 2.
A voltage of -450 [V] is applied to 7b. When these voltages are applied, the toner 31 in the developing device 30
Has a property of being negatively charged, it is supplied from the toner supply roller 27b toward the developing roller 27a and is attached to the surface of the developing roller 27a. The toner 31 has a potential of about −100 to −150 [V] by being charged. Therefore, the potential of the toner 31 on the developing roller 27a is -4.
It becomes 00-450 [V]. Also, as mentioned above,
The potential of the exposed portion on the photosensitive drum 29 is approximately -450 to -5.
Since it becomes 50 [V], the potential of the non-exposed portion where the electrostatic latent image is not formed remains -700 [V].

By the way, in the developing section where the developing roller 27a and the photosensitive drum 29 are in contact, the potential of the photosensitive drum 29 is higher than the potential of the toner 31, that is, −200 [V] or more to the minus side of the potential of the toner. In other words, the toner 31 on the developing roller 27a is not attracted to the photosensitive drum 29, and when it is not high, the toner 31 on the developing roller 27a is attracted to the photosensitive drum 29.

Therefore, the exposed portion has a potential of about -4.
50 to -550 [V] and the toner potential is about -400.
Since -450 [V], it is -200 [V] between both.
There is no above potential difference. Therefore, the toner 31 on the developing roller 27 a is attracted to the photosensitive drum 29 and forms a toner image on the photosensitive drum 29. Further, since the surface potential of the non-exposed portion is −700 [V] and the toner potential is approximately −400 to −450 [V], there is −2 between them.
There is a potential difference of 00 [V] or more. Therefore, the toner 31 on the developing roller 27a is not attracted to the photosensitive drum 29, and a toner image is not formed on the photosensitive drum 29.

[0016]

However, in the above-mentioned conventional electrophotographic recording apparatus, if the width of the paper 47 on which printing is performed changes, the printing quality will deteriorate. That is, from the photosensitive drum 29 to the paper 4 in the transfer process.
The transfer efficiency of the toner image to the toner image 7 depends on the transfer conditions, such as the size and thickness of the paper 47, the humidity of the atmosphere, the temperature, and so on.
It is necessary to change the transfer voltage applied to the device according to the transfer conditions. For example, the envelope is narrower and thicker than the A4 size cut sheet, and therefore, when printing is performed on the envelope, the transfer voltage is made higher than that when printing is performed on the A4 size cut form. There is a need.

Further, since the transfer voltage is applied to the entire transfer roller 28, when the paper 47 having a narrow width is used, the impedance becomes high in the part where the paper 47 is present in the transfer part, and in the part where the paper 47 is absent. Will be lower. Therefore, the transfer voltage leaks to a portion having a low impedance without the paper 47. as a result,
A high voltage is directly applied to the transfer roller 28, which shortens the life of the transfer roller 28 and causes a transfer failure.

Since the amount of charge of each toner 31 in the developing process is not constant, the predetermined toner 31 may be charged to a higher voltage than other toners 31 or may be positively charged by polarization. There is. As a result, the toner 31 is also attracted to the non-exposed portion, and fine dots are formed on a white background portion to cause fogging.

The fog occurs regardless of the amount of the toner 31 used. However, if the amount of friction between the developing roller 27a and the photosensitive drum 29 increases due to wear or the like, the toner 31 does not.
Since the amount of electrification is increased, fogging is further generated. Further, when the width of the paper 47 is within the range in which printing can be performed by the electrophotographic printer, the toner 31 that causes the fog can be placed on the paper 47 and discharged to the outside of the electrophotographic printer. But paper 4
When the width of 7 is outside the range of the width that can be printed by the electrophotographic printer, the toner 31 adheres to the transfer roller 28 or passes through a cleaning roller (not shown) and adheres to the charging roller 27. Or they will pile up.

As a result, when a wide sheet 47 is used, toner 31 adhering to the transfer roller 28 adheres to the back surface of the sheet 47, or toner 31 sticking to the charging roller 27 causes charging failure. Then, fogging will occur further. The present invention solves the problems of the conventional electrophotographic recording apparatus described above, without causing fogging,
An object of the present invention is to provide an electrophotographic recording device capable of improving print quality.

[0021]

To this end, in the electrophotographic recording apparatus of the present invention, an insulating material is disposed at a set position in the axial direction, and the roller is divided into a plurality of conductive parts by the insulating material. And a voltage applying means for independently applying a voltage to each conductive portion, and a width of paper,
And a conductive portion selection unit that selects a conductive portion to which a voltage is applied.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a vertical sectional view of a transfer roller according to the first embodiment of the present invention, and FIG.
FIG. 8 is a perspective view of the transfer roller according to the first embodiment of the present invention, and FIG. 8 is a sectional view taken along line AA of FIG. 7.

As shown in the figure, the transfer roller 48 comprises a roller 48a made of silicone rubber or the like and a shaft 48b made of a conductor such as metal. The shaft 48b has a tubular conductive portion 4 made of metal or the like.
9A to 49C, and cylindrical insulating portions 50A and 50B formed of an insulating material, and the conductive portions 49A to 49C.
The insulating portions 50A and 50B are alternately stacked in layers.

The insulating portions 50A and 50B are both tubular portions 50a and flange portions 5 extending radially outward from the tubular portions 50a to the surface of the shaft 48b.
0b, and the flange portion 50b divides the conductive portions 49A to 49C in the axial direction corresponding to the width of a sheet (not shown). One end of the shaft 48b constitutes a contact for connecting the transfer roller 48 to a transfer high-voltage power supply 26 as a voltage applying means, and the output parts 26a to 26c of the transfer high-voltage power supply 26 have respective conductive parts 49A.
A transfer voltage is applied to ~ 49C.

Next, the printer control circuit of the electrophotographic printer will be described. FIG. 9 is a block diagram of a printer unit control circuit according to the first embodiment of the present invention. As shown in the figure, the control unit 51 that controls the entire electrophotographic printer and functions as a conductive unit selection unit.
When receiving print data from a host device (not shown) such as a personal computer via the input interface 52, converts the print data into an actual print data signal and sends the actual print data signal to the LED head 21 at a predetermined timing. . The LED head 21 exposes a photosensitive drum (not shown) according to the actual print data signal, and at this time, the control unit 5
1 outputs a control signal to the motor driver 55,
Hopping motor (M) 56 and drum motor (M) 5
7 is driven.

Further, the control section 51 supplies a sheet (not shown) into the printing mechanism inside the electrophotographic printer in accordance with the conversion of the print data into the actual print data. The control unit 51 receives a detection signal output from a medium sensor 53 that detects the presence / absence of a sheet in a sheet cassette (not shown), the width of the sheet, the sheet feeding from the sheet cassette, the sheet discharging from the discharge port, and the like. When there is a sheet in the sheet cassette, the hopping motor 56 and the drum motor 57 are driven via the motor driver 55 to convey the sheet in the printing direction.

When the operator operates the operation panel 54 to set the sheet size, the output units 26a to 26c (FIG. 8) of the transfer high-voltage power supply 26 are selected according to the sheet size and selected. The corresponding conductive portions 49A to 49 from the output portions 26a to 26c
A transfer voltage is applied to C. For example, when printing on A4 size paper, all the output parts 26a to 26c of the high voltage power supply 26 for transfer are selected so that the transfer voltage can be applied to all the conductive parts 49A to 49C. .

When printing on A6 size paper, the output unit 26b of the transfer high-voltage power supply 26 is selected so that the transfer voltage can be applied to the conductive unit 49B. Further, the control unit 51 outputs a control signal to the heat roller controller 58 to control the temperature of the fixing device 22 and also outputs a control signal to the charging / developing power supply 59 to charge a charging roller (not shown). Is charged, a developing bias voltage is applied to the toner, and the toner is conveyed toward the developing roller. Reference numeral 61 is a power supply circuit.

As described above, since the transfer voltage can be applied only to the range corresponding to the width of the paper in the transfer roller 48, the transfer voltage does not leak to a portion having a low impedance. As a result, a high voltage is not directly applied to the transfer roller 48 and the transfer roller 4
8 can be extended in life. Further, the toner image can be transferred well, and the printing quality can be improved.

Further, since the life of the transfer roller 48 is extended, it is not necessary to use the transfer roller 48 as a maintenance replacement part. Therefore, the cost of the electrophotographic printer can be reduced. Next, a second embodiment of the present invention will be described. 10 is a perspective view of the developing roller according to the second embodiment of the present invention, FIG. 11 is a first exploded view of the developing roller according to the second embodiment of the present invention, and FIG.
Is the second of the developing roller in the second embodiment of the present invention.
FIG. 13 is a third exploded view of the developing roller according to the second embodiment of the present invention. FIG. 14 is a fourth exploded view of the developing roller according to the second embodiment of the present invention. Is a conceptual diagram showing a voltage applying method to the developing roller in the second embodiment of the present invention, and FIG. 16 is a voltage applying state diagram to the developing roller in the second embodiment of the present invention.

In the figure, 67 is a developing roller and 68 is a roller.
A shaft and a rubber 69 are arranged on the outer periphery of the shaft 68.
Roller. The rubber roller 69 has a maximum paper width L_MAXof
Have a length. The shaft 68 is made of a metal
First conductive portion 68A, second conductive portion 68B and third conductive portion
It is divided into a part 68C. Then, the first conductive portion 68
A is 2 ・ L_MAXSolid small diameter shuff with a length of / 3
G 68a and L_MAXSolid large diameter with a length of / 3
The second conductive portion 68B is formed of a shaft 68b.
_MAXA hollow medium diameter shaft 68c having a length of / 3, and
And L_MAXHollow large-diameter shaft 68d having a length of / 3
And the third conductive portion 68C is L_MAX/ 3 length
It is composed of a hollow large diameter shaft 68e.

Then, the second conductive portion 68B is attached to the small diameter shaft 68a of the first conductive portion 68A, and the third conductive portion 68C is attached to the medium diameter shaft 68c of the second conductive portion 68B.
After press-fitting, the developing roller 67 can be formed by press-fitting the whole into the rubber roller 69. In addition, between the first conductive portion 68A and the second conductive portion 68B,
An insulating material (not shown) is applied between the second conductive portion 68B and the third conductive portion 68C, and the first conductive portion 68A, the second conductive portion 68B, and the third conductive portion 68C are applied.
Are insulated from each other.

The output portion of a charging / developing power source (not shown) as a voltage applying means, the first conductive portion 68A, the second conductive portion 68B and the third conductive portion 68C are connected to the developing roller 6
The small diameter shaft 68a, the medium diameter shaft 68c, and the large diameter shaft 68e, which are exposed at one end of 7, are respectively connected by pressing contact terminal portions 70a to 70c.

Next, a printer section control circuit of the electrophotographic printer having the above-mentioned structure will be described. FIG. 17 is a block diagram of a printer unit control circuit according to the second embodiment of the present invention. In the figure, 11 is a microprocessor, R
A print control unit including an OM, a RAM input / output port, a timer, and the like. The print control unit 11 is provided inside the print unit of the electrophotographic printer, and has a control signal SG1 from a host controller (not shown) and a video signal. The entire printer section is sequence-controlled by the signal SG2 and the like to perform a printing operation.

When the print control section 11 receives a print instruction via the control signal SG1, the print control section 11 first determines by the fixer temperature sensor 20 whether the fixer 22 having the heater 22a is in a usable temperature range. If the temperature is detected and the temperature is not within the above range, the heater 22a is turned on to heat the fixing device 22 until the temperature is within a usable range. Next, driver 1
The developing / transferring process motor (PM) 13 is driven via 2 and at the same time, the charge signal SG3 is supplied to the charging high-voltage power supply 2
5, the high voltage power supply 25a for developing bias and the high voltage power supply 25b for toner supply bias are respectively sent and turned on. Then, the charging roller 27 is charged, a developing bias voltage is applied to the toner (not shown), and the toner is conveyed toward the developing roller 67.

Further, the sheets set in a sheet cassette (not shown) are detected by the sheet remaining amount sensor 18 and the sheet size sensor 19, and sheet feeding matching the type of sheet is started. Here, the paper feed motor (PM) 15
Can be driven in both directions via the driver 14, and by driving in the opposite direction first, the paper
The paper is taken out from the paper cassette and is fed by the set amount until it is detected by the paper inlet sensor 16. Then, by driving in the forward direction, the paper is conveyed into the printing mechanism of the electrophotographic printer.

The print control section 11 sends a timing signal SG4 (including a line timing signal, a raster timing signal, etc.) to the host controller when the paper reaches the printable position, and the video signal SG.
Receive 2. Then, the video signal SG2 edited by the upper controller for each page and received by the print controller 11 is sent to the LED head 21 as an actual print data signal DATA.

Then, when the print control section 11 receives the video signal SG2 for one line, the LED head 2
Latch signal LOAD is sent to 1, and the actual print data signal DA
TA is held in the LED head 21. In addition, the print control unit 11 sends the next video signal SG from the host controller.
Before receiving 2, the print drive signal ST is sent to the LED head 21.
Send B. As a result, the LED head 21 prints according to the held actual print data signal DATA. In addition,
CLK is the actual print data signal DATA for the LED head 21.
Is a clock signal for sending to. Further, the transmission / reception of the video signal SG2 is performed for each print line.

The LED head 21 irradiates a photosensitive drum (not shown) that has been charged to a negative electric potential, and forms dots with an increased electric potential on the surface of the photosensitive drum.
An electrostatic latent image is formed. Then, on the electrostatic latent image, the toner charged to a negative potential is attracted to each dot by an electric attraction force, and a toner image is formed. Then, the toner image is sent to the transfer portion formed in the gap between the photosensitive drum and the transfer roller 28. On the other hand, the print control unit 11 sends the transfer signal SG5 to the high voltage power supply 26 for transfer having a positive potential to turn it on. As a result, the transfer roller 2
Reference numeral 8 transfers the toner image onto the sheet passing through the transfer section.

The sheet having the transferred toner image is brought into contact with the fixing device 22 and conveyed, and the toner image is fixed on the sheet by the heat of the fixing device 22. The sheet having the fixed toner is further conveyed, passes through the sheet discharge port sensor 17 from inside the printing mechanism of the electrophotographic printer, and is discharged to the outside of the electrophotographic printer. Further, the print control unit 11 responds to the detection of the paper by the paper size sensor 19 and the paper inlet sensor 16 and outputs the transfer signal SG5 to the high voltage power supply 26 for transfer and the charge signal SG3 to the toner supply bias. It sends to each high voltage power supply 25b. Therefore, the transfer high-voltage power supply 26 applies the transfer voltage to the transfer roller 28 only while the sheet is passing through the transfer roller 28. Then, when the printing is completed and the paper passes through the paper discharge port sensor 17, the high voltage power supply 25b for toner supply bias terminates the application of the voltage to the developing device (not shown), and at the same time, the developing / transferring process motor 1
Stop 3

Thereafter, the above operation is repeated. Next, the developing process will be described. FIG. 18 is a diagram showing a developing process of the electrophotographic printer according to the second embodiment of the present invention. In the drawing, the horizontal axis represents the position of the developing roller 67, and the vertical axis represents the surface potential of the photosensitive drum and the developing-side potential.

First, the developing / transferring process motor 13
When the photosensitive drum (not shown) is rotated by driving (Fig. 17), the charging high-voltage power supply 25 applies a negative voltage to the charging roller 27, and the surface of the photosensitive drum is kept at a constant voltage (about -700). [V]) is charged to form a primary charging portion. Next, when the LED head 21 irradiates light on a portion of the photosensitive drum where printing is to be performed on the primary charging portion, the potential of the light-irradiated portion, that is, the exposed portion is low (about -450 to -550 [V ]) And an electrostatic latent image is formed.

On the other hand, in the developing device, the developing bias high voltage power source 25a supplies the developing roller 67 with a developing bias voltage of -300 [V], and the toner supply bias high voltage power source 25b supplies the toner supplying roller 27b with -450 [V]. V] is applied. When these developing bias voltages are applied, the toner in the developing device originally has a property of being negatively charged. Therefore, the toner is supplied from the toner supply roller 27b toward the developing roller 67, and the toner is supplied to the surface of the developing roller 67. Attached. The toner is charged to about −
It has a potential of 100 to −150 [V]. Therefore,
The potential of the toner on the developing roller 67 is -400 to -450.
[V]. Further, as described above, the potential of the exposed portion on the photosensitive drum is about −450 to −550 [V],
The potential of the non-exposed area where the electrostatic latent image is not formed is -700.
It remains [V].

By the way, in the developing portion where the developing roller 67 and the photosensitive drum contact, the potential of the photosensitive drum is -200 from the potential of the toner, that is, the toner potential.
If it is higher than [V] to the minus side, the developing roller 67
The upper toner is not attracted to the photosensitive drum, and when the toner is not high, the toner on the developing roller 67 is attracted to the photosensitive drum.

Therefore, the exposed portion has a potential of about -4.
50 to -550 [V] and the toner potential is about -400.
Since -450 [V], it is -200 [V] between both.
There is no above potential difference. Therefore, the toner on the developing roller 67 is attracted to the photosensitive drum and forms a toner image on the photosensitive drum. Further, the non-exposed portion has a surface potential of −700 [V] and a toner potential of about −400 to −.
Since it is 450 [V], there is a potential difference of -200 [V] or more between them. Therefore, the toner on the developing roller 67 is not attracted to the photosensitive drum, and the toner image is not formed on the photosensitive drum.

By the way, in the electrophotographic printer having the above-mentioned structure, the small-diameter shaft 6 is provided so that the printing quality does not deteriorate even if the width of the paper on which the printing is performed changes.
8a, the medium-diameter shaft 68c, and the large-diameter shaft 68e, and the first conductive portion 68A (FIG. 11), the second conductive portion 68B (FIG. 12), and the third conductive portion 68C (FIG. 1).
The developing bias voltage is selectively applied to 3).

When the width of the paper to be printed is wide, the conductive section selecting means of the print control section 11 uses the switch 7
The first and second conductive portions 68A, 68B and 68 of the developing roller 67 are turned on by turning on Nos. 1 and 72.
A developing bias voltage is applied to all of C. As a result, the surface potential of the developing roller 67 is − in the range of the maximum paper width.
The voltage becomes 400 to -450 [V], and development is possible at any position.

Next, when the width of the paper to be printed is narrow, the print controller 11 sends a paper before the printing by a signal from the host device or a paper setting signal from an operation panel (not shown). Know that the width of the. Then, the print control unit 11 turns on the switch 71 to turn on the switch 7
2 is turned off, and the second conductive portion 6 of the developing roller 67 is turned on.
The developing bias voltage is applied only to 8B. The length of the large-diameter shaft 68d of the second conductive portion 68B is set to be slightly larger than the width of A6 size paper.

As a result, the toner potential on the surface of the developing roller 67 becomes a voltage capable of developing by the width of A6 size paper, as shown in FIG. The toner potential on the surface of the developing roller 67 where the paper does not pass is about -50.
The electric potential of the photoconductor drum becomes −100 [V], and becomes higher than the toner potential by −200 [V] or more to the minus side. Therefore, the toner on the developing roller 67 is not attracted to the photosensitive drum, so that fogging can be prevented.

As a result, even if printing is performed on a wide paper after printing on a narrow paper, the back surface of the paper does not become dirty, and fogging occurs on both ends of the paper. The printing quality can be improved without any occurrence. Further, since the voltage margin for fogging can be increased, the reliability of the electrophotographic printer can be improved.

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

[0052]

As described above in detail, according to the present invention, in the electrophotographic recording apparatus, the insulating material is arranged at the set position in the axial direction, and the insulating material forms a plurality of conductive parts. It has a sectioned roller, a voltage applying means for independently applying a voltage to each conductive portion, and a conductive portion selecting means for selecting a conductive portion to which a voltage is applied according to the width of the paper.

In this case, when the conductive portion selecting means selects the conductive portion to which the voltage is applied according to the width of the sheet, the voltage is applied only to the selected conductive portion. Therefore, when the roller is used as the transfer roller, the transfer voltage can be applied only to the range corresponding to the width of the sheet, so that the transfer voltage does not leak to the low impedance part. As a result, the high voltage is not directly applied to the transfer roller, and the life of the transfer roller can be extended. Further, the transfer can be performed well, and the printing quality can be improved.

Further, since the life of the transfer roller is extended, it is not necessary to use the transfer roller as a maintenance replacement part. Therefore, the cost of the electrophotographic printer can be reduced. Further, when the roller is used as the developing roller, the toner on the developing roller is not attracted to the photosensitive drum, so that fogging can be prevented.

As a result, even if printing is performed on a wide paper after printing on a narrow paper, the back surface of the paper does not become dirty and fogging occurs at both ends of the paper. The printing quality can be improved without any occurrence. Further, since the voltage margin for fogging can be increased, the reliability of the electrophotographic printer can be improved.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view of a transfer roller according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a printer section control circuit in a conventional electrophotographic printer.

FIG. 3 is a time chart of a conventional electrophotographic printer.

FIG. 4 is an explanatory diagram of a transfer process in a conventional electrophotographic recording device.

FIG. 5 is a structural diagram showing a developing process of a conventional electrophotographic printer.

FIG. 6 is a diagram showing a process voltage of a conventional electrophotographic printer.

FIG. 7 is a perspective view of the transfer roller according to the first embodiment of the present invention.

FIG. 8 is a sectional view taken along line AA of FIG. 7;

FIG. 9 is a block diagram of a printer unit control circuit according to the first embodiment of the present invention.

FIG. 10 is a perspective view of a developing roller according to a second embodiment of the present invention.

FIG. 11 is a first exploded view of the developing roller according to the second embodiment of the present invention.

FIG. 12 is a second exploded view of the developing roller according to the second embodiment of the present invention.

FIG. 13 is a third exploded view of the developing roller according to the second embodiment of the invention.

FIG. 14 is a fourth exploded view of the developing roller according to the second embodiment of the invention.

FIG. 15 is a conceptual diagram showing a method of applying a voltage to a developing roller according to the second embodiment of the present invention.

FIG. 16 is a voltage application state diagram to a developing roller according to the second embodiment of the present invention.

FIG. 17 is a block diagram of a printer unit control circuit according to the second embodiment of the present invention.

FIG. 18 is a diagram showing a developing process of the electrophotographic printer according to the second embodiment of the present invention.

[Explanation of symbols]

 11 Printing Control Section 26 High Voltage Power Supply for Transfer 48 Transfer Roller 48a Roller 49A to 49C Conductive Section 50A, 50B Insulating Section 51 Control Section 59 Charging / Developing Power Supply 67 Developing Roller

Claims (3)

[Claims] 1. A roller in which an insulating material is disposed at a set position in the axial direction and is divided into a plurality of conductive portions by the insulating material, and (b) a voltage is independently applied to each of the conductive portions. An electrophotographic recording apparatus comprising: a voltage applying unit that applies a voltage; and (c) a conductive unit selecting unit that selects a conductive unit to which a voltage is applied according to the width of the paper. 2. The electrophotographic recording apparatus according to claim 1, wherein the roller is a transfer roller, and the voltage is a transfer voltage. 3. The electrophotographic recording apparatus according to claim 1, wherein the roller is a developing roller, and the voltage is a developing bias voltage.