JP2003287933A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus by which a cleaning electric field is secured as larger than a development electric field even when a photosensitive drum is degraded and dark potential is lowered. <P>SOLUTION: When photosensitive drum is replaced (ST1), a development bias is set as -300 V (ST2), the dark potential and bright potential of the photosensitive drum are detected (ST3). At an early stage of replacement of the photosensitive drum, the dark potential is about -800 V, the bright potential is about -500 V and a development bias voltage is left as -300 V. When the detected dark potential becomes -700 V and the bright voltage becomes -40 V at an intermediate stage of the replacement (ST5), the development bias voltage is set as -250 V (ST6), and furthermore, when the detected dark potential becomes -500 V and the bright potential becomes -20 V in the case that the replacement reaches the last stage (ST4), the development bias voltage is set as -180 V (ST7). Thus, a ratio value of cleaning electric field and the development electric field is held as larger than 1 and constant even when the photosensitive drum is degraded. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a multifunction machine having a multi-function such as a copying function and a fax function.

[0002]

2. Description of the Related Art Among printers used in image forming apparatuses, there are electrophotographic cleaner-less printers having a photoconductor. In this type of cleanerless image forming apparatus, as shown in FIG. 6, the developing bias potential and the bright potential (L
By utilizing the difference [developing electric field] from the potential of the surface of the photoconductor in the exposure area by ED light, toner is attached to the surface of the photoconductor drum, and the dark potential (photoelectric drum after charging the photoconductor drum by the charging roller) is applied. The residual toner on the drum surface is recovered by utilizing the difference [cleaning electric field] between the potential on the surface of the body drum) and the developing bias potential. Thus, in order to collect the residual toner, the cleaning electric field needs to be higher than the developing electric field.

[0003]

Generally, as shown in FIG. 5, the photoconductor drum has a characteristic that the dark potential on the surface of the photoconductor sequentially decreases according to the total image forming time. Therefore, in some cases, the cleaning electric field becomes smaller than the developing electric field (eg, see the latter part of FIG. 6), and there is a problem that cleaning is not performed well.

The present invention has been made in view of the above problems, and it is possible to secure a cleaning electric field larger than the developing electric field even if the photoconductor drum deteriorates and the dark potential decreases. It is an object of the present invention to provide an image forming apparatus that can be used.

[0005]

The image forming apparatus of the present invention has a surface potential detecting means for detecting the potential of the surface of the photosensitive member, and the dark potential and the bright potential are detected by the surface potential detecting means to develop the image. During processing, the difference between the dark potential and the developing bias potential and the difference between the developing bias potential and the bright potential change according to the change in the dark potential and the bright potential, and the difference between the dark potential and the developing bias potential becomes the developing bias potential. A developing bias voltage that holds a relationship larger than the difference in bright potential is applied to the developing roller.

In the image forming apparatus of the present invention, for example, the developing bias and the potential are set to -300 at the initial stage of replacement of the photosensitive drum.
As V, the detected dark potential is −800 V and the detected bright potential is −50 V, the image forming time elapses, and the dark potential decreases. For example, the detected dark potential is −500 V and the detected bright potential is −20 V. If so, the developing bias voltage is set to −180 V so that the cleaning electric field is always higher than the developing electric field.

In this image forming apparatus, the difference between the dark potential and the bright potential is changed in accordance with the change in the dark potential and the potential difference between the dark potential and the developing bias is larger, but the relationship is maintained.
It is advisable to change the developing bias potential so that the difference between the two maintains a constant ratio value.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to embodiments. 1 and 2 are block diagrams showing a schematic configuration of the entire image forming apparatus according to the embodiment of the present invention.

This image forming apparatus is configured as a so-called multi-function machine having a facsimile function and a copy function, and includes MPU1 and NCU (Network Control Circuit: Network Control Circuit).
l Unit) 2, MODEM 3, ROM 4, RAM 5, image memory 6, CODEC (encoder / decoder: Coder and De)
coder) 7, an operation unit 8, a scanner 9, a printer I / F (interface) 10 to which a personal computer PC is connected, and a printer 10a.

The MPU 1 has a function of controlling each circuit section which constitutes this device. NCU2 is a telephone network (P
It has a function of controlling the connection with the STN), a function of transmitting a dial signal corresponding to the telephone number (including the FAX number) of the destination, and a function of detecting an incoming call. M
ODEM3 is based on ITU (International Telecommunication Union) -T recommendation T.264. 30 based on the facsimile transmission control procedure according to V.30. 17, V.I. 27 ter, V.I. The transmission data is modulated and the reception data is demodulated according to 29 or the like. Alternatively,
In addition to these, V. Modulation of transmission data and demodulation of reception data according to 34 are performed.

The ROM 4 stores a program for controlling this device. The RAM 5 temporarily stores data and the like. The image memory 6 temporarily stores the received image data and the image data read by the scanner 9. COD
The EC7 sends the read image data to the M7.
Encoding by H, MR, MMR system, etc.
Then, the received image data is decoded. Operation part 8
Is for the user to instruct FAX transmission / reception, printing, and the like. The scanner 9 reads image data of an original when transmitting or copying by FAX and generates binary or multi-valued image data.

A printer 10a in this apparatus includes a printer controller (control unit) 1 for controlling each unit of the printer.
2 is provided.

Inside the printer, a photosensitive drum 13 having a photoconductive film on the outer peripheral surface is arranged as a photosensitive member, and the photosensitive drum 13 is rotated by a motor (not shown). Around the photosensitive drum 13, a charging brush 14 is arranged as a brush roller type charging device.
A predetermined charging bias voltage is applied to 4 by a charging bias applying circuit 15. The charging brush 14 to which the charging bias voltage is applied uniformly charges the outer peripheral surface of the photosensitive drum 13 while rotating.

The LED print head 16 as an exposure unit arranged around the photosensitive drum 13 has a large number of LEDs.
Are arranged in parallel, and the outer peripheral surface of the photosensitive drum 13 is irradiated with light based on the input image information, and an electrostatic latent image corresponding to the image information is formed on the outer peripheral surface.

Further, the developing device arranged around the photosensitive drum 13 is composed of a supply roller 17, a developing roller 18, a surface potential sensor 19, a developing bias applying circuit 20 and the like. The supply roller 17 supplies the toner from the toner case 28 containing the toner to the developing roller 18 while charging the toner. The supply roller 17 and the photosensitive drum 13 are charged.
A predetermined bias voltage is applied by the developing bias applying circuit 20 to the developing roller 18 arranged in contact with.

The surface potential sensor 19 is a photosensitive drum 13.
The dark and bright potentials of are detected.

Further, a transfer roller 21 as a transfer device arranged around the photoconductor drum 13 is arranged so as to contact the outer peripheral surface of the photoconductor drum 13 with the sheet conveying path P interposed therebetween, and is rotated by a main motor. It This transfer roller 2
A predetermined bias voltage is applied to 1 by the transfer bias applying circuit 22. The current of the transfer roller 21 is detected by the current detector 28, and the detected current value is held in the printer controller 12. Printer controller 1
2 refers to the transfer bias determination table at the time of printing to obtain the transfer voltage corresponding to the current value, and the transfer bias applying circuit 22 applies the bias voltage to the transfer roller 21.

The fixing device arranged on the paper delivery side of the paper transport path is composed of a heating roller 23 having a heater such as a halogen lamp, a heater driving circuit 24, a press roller 25 and the like. The heater of the heating roller 23 is heated to a predetermined temperature by the heater driving circuit 24. The heating roller 23 and the press roller 25 fix the toner image on the paper by heating and pressing the paper after the transfer by the transfer roller 21. Further, a temperature sensor 29 for detecting the fixing temperature is provided near the pressure roller 23.

In this apparatus, a memory removing brush 26 is arranged around the photosensitive drum 13. The memory removal brush 26 is for removing a toner image (memory image) remaining on the outer peripheral surface of the photoconductor drum 13 along the contour of the image even after transfer. A predetermined bias voltage is applied by the circuit 27.

In the image forming apparatus constructed as described above, the printing operation is well known, but the outline is that the photosensitive drum 13 is uniformly charged by the charging brush 14.
An electrostatic latent image corresponding to image information is formed on the photosensitive drum 13 by the LED print head 16, and toner is adsorbed by the electrostatic latent image on the photosensitive drum 13 by the developing roller 18, so that the electrostatic latent image on the photosensitive drum 13 is absorbed. A toner image is formed on. Then, the transfer roller 21 transfers the toner image on the photosensitive drum 13 onto the sheet. After the transfer, the heating roller 23 and the press roller 25 heat and pressurize the paper to fix the toner image on the paper.

Next, the developing bias voltage setting routine in the facsimile apparatus of this embodiment will be described. The developing bias voltage setting routine is executed at an appropriate timing of image formation, every time a predetermined number of sheets are printed, or every time a predetermined time elapses. The processing content will be described with reference to the flowchart shown in FIG.

When entering this processing routine, first, at step ST1, it is judged if the photosensitive drum 13 has been replaced. If it has been exchanged, then step S
Move to T2. On the other hand, if the photosensitive drum 13 has not been replaced this time, the process proceeds to step ST3. In step ST2, after the replacement of the photosensitive drum 13, the initial developing bias potential of -300 V is set [see FIG. 3]. Then, the process proceeds to step ST3.

In step ST3, the surface potential sensor 19 detects the dark potential and the bright potential of the photosensitive drum 13. Immediately after the developing bias potential is set to −300 V (when the photosensitive drum 13 is replaced), as shown in FIG.
It is assumed that the dark potential is −800V and the bright potential is −50V.
It can be said that the dark potential is close to −800 V and the bright potential −50 V at the very beginning of the exchange even if some time has passed after the photoconductor drum 13 was exchanged. Then, the process proceeds to step ST4.

In step ST4, the dark potential is -5.
It is determined whether the voltage is 00V or the bright potential is -20V. As shown in FIG. 3, this is to determine whether or not image formation is in the second half after the replacement of the photosensitive drum 13. If the dark potential has not dropped to −500V and the bright potential has not shifted to −20V,
If it is the initial stage after the replacement of the photosensitive drum 13, the determination is NO, and the process proceeds to step ST5. On the other hand, if the dark potential is -500V or the bright potential is -20V, the process proceeds to step ST7.

In step ST5, the dark potential is -7.
It is determined whether or not it becomes 00V or the bright potential becomes -40V. Here, as shown in FIG. 3, it is determined whether or not image formation has started from the initial stage of replacement of the photosensitive drum 13 to the middle stage of replacement. Dark potential is -700
If it is V or the bright potential is -40V, the process proceeds to step ST6. On the other hand, the dark potential is still -700V
If the bright potential is not -40V, the process returns to step ST3. And, if the dark potential becomes -700V,
Until the bright potential becomes -40V, steps ST3, ST
4. The processing of ST5 is repeated.

In step ST6, the developing bias voltage is set to -260V (see FIG. 3). Then return. When the time of image formation has progressed and the photoconductor drum 13 has been replaced late, the dark potential becomes −500V or the light potential becomes −20V.
At T7, the developing bias voltage is set to −180V (see FIG. 3). Then return.

As described above, the developing bias voltage is changed from -300V to -260V even when the initial, middle, and late exchanges are performed.
→ By changing the setting to -180V, the cleaning electric field and the developing electric field are 500V / 250V and 440V / 2.
Since the ratio of 20V, 320V / 160V, 2: 1 is maintained, it is possible to always secure a larger amount than the cleaning electric field and the developing electric field.

In the above description, when it is judged from the detection values of the dark potential and the bright potential that the middle and late stages of exchange have been reached,
Although the developing bias voltage is changed, the setting of the developing bias voltage may be changed at a finer timing.

[0029]

According to the present invention, the surface potential detecting means is provided, and the surface potential detecting means detects the dark potential and the bright potential. The difference between the bias potential and the bright potential changes in accordance with the change in the dark potential and the bright potential, and the difference between the dark potential and the developing bias potential is larger than the difference between the developing bias potential and the bright potential. Since such a developing bias potential that is applied to the developing roller is applied to the developing roller, even if the photoconductor drum deteriorates and the dark potential decreases, the cleaning electric field is reduced and the developing electric field is reduced.
The cleaning electric field can always be made larger than the developing electric field, and therefore, it is possible to reliably prevent the toner from remaining on the surface of the photoconductor drum, and to suppress the occurrence of ghost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration (a part) of a facsimile apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration (remaining part) of the facsimile apparatus according to the first embodiment together with FIG.

FIG. 3 is a diagram illustrating changes in dark potential, bright potential, cleaning electric field, and developing electric field in an initial stage, a middle period, and a latter period after replacement of a photosensitive drum of the facsimile apparatus according to the first embodiment.

FIG. 4 is a flowchart showing a processing routine for setting a developing bias voltage in the facsimile apparatus of the embodiment.

FIG. 5 is a characteristic diagram showing a change in dark potential of the surface of the photoconductor drum over time of image formation.

FIG. 6 is a diagram illustrating changes in the dark potential, the bright potential, the cleaning electric field, and the developing electric field in the early, middle, and late stages after the replacement of the photosensitive drum in the conventional image forming apparatus.

[Explanation of symbols]

1 MPU 10a printer 12 Printer controller 13 Photosensitive drum 14 charging brush 15 Charging bias application circuit 16 LED print head 17 Supply roller 18 Developing roller 19 Surface potential sensor 20 Development bias application circuit

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Claims (2)

[Claims] 1. A surface potential detecting means for detecting the potential of the surface of a photoconductor, which detects a dark potential and a bright potential, and a difference between the dark potential and the developing bias potential during development processing. The difference between the developing bias potential and the bright potential changes in accordance with the change in the dark potential and the bright potential, and the difference between the dark potential and the developing bias potential is larger than the difference between the developing bias potential and the bright potential. An image forming apparatus characterized in that a developing bias voltage is applied to a developing roller. 2. A developing bias in which the difference between the dark potential and the developing bias potential and the difference between the developing bias potential and the bright potential change while maintaining a predetermined ratio value according to the change in the dark potential and the bright potential. The image forming apparatus according to claim 1, wherein a voltage is applied to the developing roller.