JP2001201959A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To moderate a shock given to a photoreceptor by applying intermediate voltage divided into plural stages to a transfer roller for transferring a toner image from the photoreceptor to paper in the midst of applying ordinary voltage after applying cleaning voltage. SOLUTION: By applying the voltage of a specified value from a controller to the transfer roller 26 for transferring the toner image formed on the photoreceptor drum 22 of the image forming device to the paper, the toner image is transferred to the paper. After a fixed recording paper is prepared, a cleaning sequence is set and a mode in which the intermediate voltage is divided to plural stages and applied by the controller 30 between the voltage of -900 V as the cleaning voltage and the value of the transfer voltage of about 3k V is set. Then, the voltage is applied to the roller 26 from a voltage applying circuit 32 based on the information of a sensor 35 and a condition set in a memory 33 while it is successively increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for applying a potential to a contact transfer member for transferring a toner image formed on a photoreceptor of an image forming apparatus to a sheet, and more particularly, to a method for applying a potential after a cleaning sequence is performed. The present invention relates to an apparatus provided with a means for changing a voltage applied when a transfer potential is applied.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, at a portion where a toner image is transferred onto a sheet, an image is written on a photosensitive drum of the image forming section by an image writing device to form an electrostatic latent image. Forming an image, supplying toner from a developing device to visualize the electrostatic latent image as a toner image, transferring the toner image to a sheet, and fixing the sheet carrying the toner image through a fixing device. Make a copy. In the image transfer section from the photoconductor, in addition to using a discharge member such as a corotron, a contact transfer member such as a transfer roller is used. In a contact transfer member such as the transfer roller, a corotron is used. Since no corona discharge is performed as in the case of, no ozone is generated,
There is an advantage that it is not necessary to provide an ozone treatment unit in the exhaust system of the image forming apparatus. In an apparatus using a contact transfer member such as the transfer roller, recording is sequentially performed while continuously transporting the paper in a state where a small gap is provided between the papers in the paper transport path. Since the transfer member is in direct contact with the photoconductor between the sheets, there is a problem that toner, paper powder, and the like adhering to the photoconductor adhere to the contact transfer member and become dirty. Therefore, when printing a large number of sheets, a program is set in the control device to execute a cleaning sequence in a state where a fixed number of sheets have been printed. When the cleaning sequence is performed, operations such as applying a potential having a polarity opposite to the transfer potential to the transfer roller are performed.

[0003]

However, for example, the transfer voltage applied to the contact transfer member is +3 kV at the maximum, and the voltage for performing the cleaning sequence is-.
900V. Therefore, when a transfer voltage is applied after the cleaning sequence is completed, a very large potential difference is generated in the switching portion of the applied voltage, and the large potential difference applied to the surface of the photosensitive member causes the potential on the surface of the photosensitive member to be increased. There is a concern that the image quality will be disturbed and the image quality of the recorded image will be degraded. When such a voltage that changes greatly in a short time is repeatedly applied, the deterioration of the photoconductor is promoted, and the life of the image forming apparatus is greatly affected.

The present invention solves the problem of the difference in voltage applied to the contact transfer member as described above. When switching to a transfer voltage after a cleaning sequence, an intermediate voltage is applied stepwise. By doing so, the object of the present invention is to prevent a large potential difference from affecting the photoconductor.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an image forming apparatus comprising a photosensitive member and a contact transfer member, wherein a transfer bias is applied after a cleaning sequence of the contact transfer member. The invention of claim 1 of the present invention is characterized in that the voltage is changed stepwise and applied to the contact transfer member before the transfer bias is applied after the cleaning sequence. The invention according to claim 2 is characterized in that the photoconductor is a photoconductor drum, and the applied voltage is changed stepwise while the photoconductor drum makes one or two rotations. The invention according to claim 3 is characterized in that the voltage applied to the contact transfer member is changed in two stages.

With the above-described structure, the surface potential of the photoconductor is prevented from suddenly changing, the disturbance of the potential of the photoconductor is reduced, and the quality of an image formed on recording paper is improved. Can be. Further, by providing a control means for switching the applied voltage during one or two rotations of the photosensitive drum, the influence of the switching of the applied voltage on the photosensitive drum can be reduced.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the apparatus of the present invention will be described with reference to the illustrated example. The example illustrated in FIG. 1 illustrates a configuration of a combination member of a photoconductor drum 22 and a developing device 10 provided in an image forming apparatus. The photoconductor drum 22 is disposed in a photoconductor unit 20, The developing roller 14 of the developing device 10 is arranged corresponding to the developing section of the drum 22. In the developing device 10 arranged in combination with the photoreceptor unit 20, the toner container 11
The toner contained in the developing roller 14 is sent out toward the supply roller 13 while being stirred by the agitator 12, and charged with the toner between the developing roller 14 and the developing roller 14 rotating together in the direction of the arrow X so as to be rubbed with the supply roller 13. While applying the action, the toner is adhered to the surface of the developing roller 14 as a thin layer. The toner adhered to the surface of the developing roller 14 is formed as a thin layer having a certain thickness by the blade member 15, is exposed at a position corresponding to the photosensitive drum 22, and rotates in the direction of the arrow X '. It is attached to the electrostatic latent image at a portion that contacts the photosensitive drum 22.

A photosensitive unit 20 arranged in combination with the developing device 10 includes a photosensitive drum 22 serving as a photosensitive member which is arranged on a frame 21 and is rotated at a constant speed by a drive mechanism (not shown); A transfer roller 26 as a contact transfer member for transferring the toner image formed on the sheet 22 to a sheet is disposed. The contact transfer member is not limited to a transfer roller, but may be a brush or a blade. The transfer roller 26 and the memory removing member 2 are arranged around the photosensitive drum 22 according to the rotation direction of the photosensitive drum 22.
3. The charging roller 24 and the writing device 25 are arranged. The writing device 25 irradiates light onto the surface of the photosensitive drum 22 that has been uniformly charged by the charging roller 24 to form an electrostatic latent image. A toner image is formed by supplying toner from the printer 14, and a transfer voltage of a predetermined potential is applied to the paper passing through the image transfer unit from the back surface by a transfer roller 26 to transfer the toner image.

After the toner image is transferred onto the paper by the image transfer unit, a roller-shaped memory removing member formed of a brush or a sponge removes toner (toner memory) remaining on the surface of the photosensitive drum 22. The contact of 23 has the effect of weakening the adhesive force by disturbing it. In the subsequent stage, a brush-like rotatable charging roller 24 imparts a further disturbing action and uniformly charges the surface of the photosensitive drum to cope with writing of the next image. In the apparatus shown in this embodiment, the adherence such as toner remaining on the surface of the photosensitive drum after the toner image is transferred onto the paper is not removed by the cleaning device, but the adhesive force is applied by the memory removing member 23 and the charging roller 24. With developing roller 1
The device 4 is configured as a device of a system of being collected by the developing device 10 and mixed with newly supplied toner and reused, and is configured as a so-called cleaner-less device.

In the transfer roller 26, the applied voltage for transferring the toner image formed on the photosensitive drum 22 to the paper greatly affects the temperature condition inside the image forming apparatus as shown in the graph of FIG. It is known to receive. For example, when the temperature inside the machine is 20 ° C., the applied voltage is about 2 kV. When the temperature inside the machine is 40 ° C., the voltage is about 1 kV. When the temperature inside the machine is 10 ° C. or less, an applied voltage of about 3.5 kV is set. Is needed. By the way, in the graph of FIG. 2, under the condition of 20 ° C. or less, the control is performed according to the curve indicated by the symbol B.
In the above environment, the control is performed in accordance with the control condition as indicated by the curve C. However, by combining the two types of control conditions into one curve A and setting the control condition in accordance with the curve A, over a wide temperature range. Thus, the setting of the applied voltage according to one control condition can be performed.

In addition to the condition of the voltage applied to the transfer roller 26, when an image is formed on a recording sheet in the image forming apparatus, a small gap is set between sheets fed continuously. Then, in the gap between the fed sheets, the transfer roller 26 directly contacts the photosensitive drum 22, so that the toner adhering to the photosensitive drum 22 is transferred to the transfer roller 26 to generate stain. Further, paper dust or other dust floating in the apparatus adheres to the transfer roller 26, and the adhered substance stains the back surface of another paper or is applied from the back surface of the paper. Inconsistencies such as non-uniform transfer of the toner image from the photosensitive drum to the paper due to uneven voltage may occur. Accordingly, in the image forming apparatus, a cleaning sequence of the transfer roller is set at the start of the operation of forming the recording paper or every time the recording paper reaches a certain number, and the toner adhering to the transfer roller 26 is set. An operation of transferring paper dust, paper dust, and the like toward the photosensitive drum 22 is performed.

The cleaning sequence for the transfer roller is performed under the conditions shown in the graph of FIG. 3. In FIG. 3, the horizontal axis represents time and the vertical axis represents applied voltage. In this case, the applied voltage (V0) is set to -900 V, and the transfer voltage (V) is set according to the temperature condition in FIG.
As shown in FIG. 3, a cleaning sequence is set, a voltage of -900 V is applied to the transfer roller,
The transfer roller is cleaned by continuing the applied voltage for a predetermined time (T0). When the cleaning state is completed, the transfer voltage is returned to the normal transfer voltage (V), and a predetermined transfer voltage is applied so that the photosensitive drum transfers the toner image toward the sheet. And a transfer voltage V, an intermediate voltage between V1 and V2 is set, and the voltage applied to the transfer roller 26 is changed stepwise.

The example shown in FIG. 3 shows a case where the voltage V1 is set to 0 V and the voltage V2 is set as a pre-transfer voltage. Can be set to be the same as the voltage applied only for the time t. When returning to the state where the normal transfer voltage is applied after the completion of the cleaning, the time is set as the time for increasing the voltage stepwise from the cleaning voltage to the time when the transfer voltage is applied. At time (T1 + T2), the photosensitive drum 22
It is good to set it as the time for ~ 2 rotations.

As for the step of changing the voltage, as shown in FIG. 4, when the main switch of the image forming apparatus is turned on, the transfer from the initial detection of the resistance value to the transfer roller to the transfer of the transfer voltage is performed. It is also performed when applying a voltage to the roller. In this figure, after the main switch of the image forming apparatus is turned on, the warm-up operation of the fixing device and the like and the initialization operation in the scanning device of the image reading device are performed according to a program set in the main control device. Simultaneously with each of the above operations, a constant voltage is applied to the transfer roller, and the resistance value is measured, so that the surface potential of the photosensitive drum and the resistance value of the transfer roller are measured. Then, a transfer voltage for transferring the toner image from the photosensitive drum to the paper is set according to the detected value.

In the example shown in FIG. 4, when the initial condition (resistance value, etc.) of the transfer roller is detected, the voltage during standby is changed from 0 V during the predetermined time T3 to the voltage-during cleaning.
The operation of applying 900 V and the transfer voltage +3, 5 kV is performed in accordance with the steps set in the control device. Then, the information required during the elapse of the time T3 is obtained, the voltage is returned to 0 V, and thereafter, the transfer voltage V
Until is applied, as in the example shown in FIG.
An operation of changing the voltage stepwise is performed. The setting of the voltage increasing step after the time T3 for detecting the resistance value of the transfer roller means detecting the state of the photosensitive drum or the transfer roller during continuous recording. The steps are set in the same manner. In the step of increasing the voltage stepwise, in any of the cleaning mode and the resistance detection mode, an intermediate voltage between the applied voltage at the time of cleaning -900 V and the transfer voltage +3.5 kV is applied to the transfer roller. By using a method in which the voltage is applied to the photosensitive drum 22 from the transfer roller 26 by changing the voltage in two or three steps, a large shock is not applied to the photosensitive drum 22 at one time. Can be controlled as follows.

As shown in FIGS. 3 and 4, in order to perform control for applying an intermediate voltage, as shown in FIG.
A voltage of a set value is applied to the axis of the transfer roller 26. The transfer voltage control device 30
A voltage application circuit 32 controlled by the control circuit 31 to apply a voltage to the transfer roller; a memory 33 for setting conditions of temperature and applied voltage for the control circuit 31;
A control table 34 for setting control conditions is connected. Further, a sensor 35 for measuring the temperature inside the apparatus of the image forming apparatus is arranged at a predetermined position of the apparatus, and information on the temperature detected by the sensor 35 is input to the control circuit 31 and transferred according to the temperature inside the apparatus. The voltage condition can be changed at any time.

In the transfer voltage control device 30, a cleaning sequence is activated when it is detected that a predetermined number of recording papers have been prepared according to the conditions set in the main control device of the image forming apparatus. And
At the time of the cleaning sequence, the feeding of the paper is stopped, and another voltage applying mechanism for the photosensitive drum 22 is provided.
For example, a cleaning voltage of -900 V is applied to the transfer roller while the operation of applying the voltage to the charging roller 24 is stopped. The application of the cleaning voltage is shown in FIG.
After the lapse of the time T0, the normal transfer voltage is applied to the transfer roller 26 while setting the normal applied voltage to the charging roller 24 and the developing roller 14, but the transfer voltage is transferred. During the application to the roller,
The time during which the intermediate voltage is applied is set to T time. As described above, when applying the intermediate voltage, the state of 0 V may be set to the T time.

The means for changing the voltage applied to the transfer roller 26 can be provided, for example, in an apparatus combined with an image forming apparatus as shown in FIG. The image forming apparatus 1 shown in FIG. 5 is configured as an electrophotographic copying machine in combination with an image reading apparatus, configured as a printer in combination with a personal computer interface, or combined with an image reading apparatus and a facsimile transmission / reception mechanism. It can be configured as a facsimile machine or a multifunction machine combining a plurality of functions.

In the image forming apparatus 1 shown in FIG. 5, the paper is fed one by one by a paper feed roller 3 disposed in a paper feed section of a paper feed tray 2, and transport rollers 4 and 6 pass through a paper transport path 5. When the paper passes between the photosensitive drum 22 and the transfer roller 26, the toner image formed on the photosensitive drum 22 is transferred. Then, the sheet on which the toner image is transferred is fixed between the heat roller 7a and the pressure roller 7b of the fixing device 7, and is discharged to a discharge tray by the discharge roller device 8. In the image forming apparatus 1, the writing information supplied to the writing member 25 may be image information from an image reading apparatus (not shown) provided in combination with the image forming apparatus 1, or a digital signal received by facsimile. Used, the LED element of the writing member 25 emits a dot-like light to write image information on the photoconductor.

In the image forming apparatus, a belt-shaped photoconductor may be used as the photoconductor in addition to the photoconductor drum. In the case where the belt-shaped photoconductor is used, a cleaning voltage is applied. The time and the application time of the intermediate voltage are set as different times from those of the photosensitive drum. The conditions of the voltage applied to the transfer roller also need to be changed depending on the structure of the image forming apparatus and the structure of the fixing device which has a great influence on the temperature change in the apparatus. It is set according to the basic structure of the device.

[0021]

According to the apparatus of the present invention, as described above, the surface potential of the photoconductor is prevented from suddenly changing due to the voltage applied to the transfer roller, and disturbance of the potential of the photoconductor is reduced. In addition, the quality of the image formed on the recording paper can be improved. Further, by providing a control means for switching the applied voltage during one or two rotations of the photosensitive drum, the influence of the switching of the voltage on the photosensitive drum can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a photoconductor unit combined with a developing device.

FIG. 2 is a graph showing temperature characteristics of a voltage applied to a transfer roller.

FIG. 3 is a graph showing a state in which a voltage applied to a transfer roller is changed.

FIG. 4 is a graph showing another example in which the voltage applied to the transfer roller is changed.

FIG. 5 is an explanatory diagram of an image forming apparatus using the photoconductor unit.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 image forming apparatus, 2 paper feed tray, 3 paper feed roller, 4.6 transport roller device, 5 paper transport path, 7 fixing device, 8 discharge roller device, 1
Reference Signs List 0 developing device, 11 toner storage unit, 12 agitator, 13 supply roller, 14 developing roller, 15 blade member, 20 photoconductor unit, 21 frame, 22 photoconductor drum, 2
3 memory removing member, 24 charging roller, 25
Writing member, 26 transfer roller, 30 transfer voltage control device, 31 control circuit, 32 voltage application circuit, 33 memory, 34 control table, 3
5 sensors.

Claims (3)

[Claims] 1. An image forming apparatus comprising: a photosensitive member; and a contact transfer member, wherein a transfer bias is applied after a cleaning sequence of the contact transfer member. An image forming apparatus, wherein the voltage is changed and applied to the contact transfer member. 2. The image forming apparatus according to claim 1, wherein the photoconductor is a photoconductor drum, and the applied voltage is changed stepwise while the photoconductor drum makes one or two rotations. Image forming apparatus. 3. The image forming apparatus according to claim 1, wherein the voltage applied to the contact transfer member is changed in two stages.