JPH05181351A - Image forming device - Google Patents

Abstract

PURPOSE:To easily remove an attachment from a charging means at the time of charging an image carrier by the contact type charging means. CONSTITUTION:In an image forming device in which an image carrier 1 is charged by applying a voltage to a charging means 2 making contact with the image carrier 1, a control means 14 for forming, between the image carrier 1 and the charging means 2, a first electric field in a determined direction and a second electric field in the reversed direction to the first electric field by applying a determined voltage to the charging means 2 at the time of non- image formation is provided. Thus, a positively or negatively charged attachment adhered to the charging means is moved on the image carrier side by either of the first and second electric field, and the removal of the attachment from the charging means is facilitated.

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 utilizing an electrostatic transfer process such as an electrostatic copying machine or an electrostatic printer, and more particularly to an image forming apparatus in which an image carrier is charged by a contact type charging means. ..

[0002]

2. Description of the Related Art As a charging means for charging an image carrier of an image forming apparatus such as a copying machine, a corona charger using corona discharge has been widely used. On the other hand, the corona charger has disadvantages that it requires a high-voltage power supply, has a low charging efficiency, generates ozone and the like during discharge, and easily stains the charging wire. A contact type charging means for contacting the means with an image carrier to charge the same has been widely used.

This contact type charging means is, for example, 1 to 2 KV.
It is composed of a conductive charging roller to which a DC voltage of a certain degree is applied. The charging roller is brought into contact with a photosensitive drum which is an image carrier, and the charging roller is driven to rotate along with the rotation of the photosensitive drum. The photosensitive drum can be uniformly charged to a predetermined potential.

By the way, in the image forming apparatus, a process cartridge for integrally attaching and detaching the photosensitive drum and other process equipment to the main body of the apparatus is used, and each equipment in the process cartridge has reached the end of its life or the like. In many cases, instead of replacing the individual devices, the entire process cartridge is replaced to facilitate the maintenance.

Conventionally, the charging roller has been conventionally incorporated into a process cartridge together with a photosensitive drum and the like, and is often thrown away when the process cartridge is replaced. However, the performance is improved by improving the material. The number of prints has been extended to tens of thousands to several hundreds of thousands, and a life approximately equal to that of the main body of the apparatus has been obtained. Therefore, in consideration of cost advantage, there is also an image forming apparatus in which the charging roller is provided on the apparatus main body side outside the process cartridge.

[0006]

However, in the image forming apparatus using the contact type charging means as described above, the toner,
Paper dust, dust, etc. float in the main body of the device, and the suspended matter adheres to the charging roller outside the process cartridge to stain the charging roller and cause uneven charging on the photosensitive drum, and the life of the charging roller. There was an inconvenience that it also lowered.

Further, as the number of prints increases, the charging roller is uncleaned and contaminated by the toner remaining on the photosensitive drum, which causes uneven charging of the photosensitive drum.

The present invention has been made in view of the above problems, and an object thereof is to easily remove deposits attached to the charging means when the image bearing member is charged by contacting the charging means, An object is to provide an image forming apparatus that does not cause uneven charging or the like on the image carrier.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is an image forming apparatus in which a voltage is applied to a charging means that is in contact with an image carrier to charge the image carrier at the time of non-image formation. A control unit that forms a first electric field in a predetermined direction and a second electric field in a direction opposite to the first electric field is provided between the image carrier and the charging unit by applying a predetermined voltage to the charging unit. It is characterized by

Further, according to the present invention, in an image forming apparatus in which a voltage is applied to a charging means contacting an image carrier to charge the image carrier, a predetermined voltage is applied to the charging means during non-image formation. A control means for forming an electric field for moving the toner or the like attached to the charging means and having a constant polarity from the charging means side to the image carrier side is provided.

[0011]

The toner or the like in the developing means floats when the process cartridge is attached or detached or when the jam processing is performed, and the floating matter adheres to the charging means, or the residual toner on the image carrier adheres to the charging means, resulting in uneven charging. And other inconveniences.

Therefore, at the time of non-image formation, a predetermined voltage is applied to the charging means, for example, the charging means is set to a high potential and the image carrier is set to a low potential to form a first electric field from the charging means to the image carrier side. The adhered substances having a positive polarity are moved to the image carrier side by the Coulomb force.
Similarly, the charging unit is set to a low potential and the image carrier is set to a high potential to form a second electric field from the image carrier to the charging unit side. Move to the side of the carrier.

Therefore, the positively and negatively charged deposits adhering to the charging means are moved to the image carrier side, and the charging means is cleaned. Then, the attached matter that has moved to the image carrier is cleaned by the cleaning means on the image carrier side.

In the case of removing only the toner or the like attached to the charging means and having a constant polarity, it is necessary to match the polarity of the toner or the like.
It suffices to form only an electric field that moves the toner and the like from the charging means to the image carrier side.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, a first embodiment of the present invention will be described with reference to FIGS.
Will be described. FIG. 1 shows a cross section of a main part of an electrostatic printer (for example, a laser beam printer), and in FIG. Around the photosensitive drum 1, a charging roller (charging member) 2 as a charging unit, a developing unit 3 as a developing unit, a transfer charging unit 4 as a transfer unit, and a cleaning unit 5 as a cleaning unit are arranged. Of these, the photosensitive drum 1, the developing device 3, and the cleaning device 5 are integrally housed in the cartridge frame 6a, and are detachably arranged in the apparatus main body 12 as the process cartridge 6. The process cartridge 6 is attached to and detached from the apparatus main body 12 by opening and closing the main body door 12a.

A paper feed cassette 7, a paper feed roller 8, and a registration roller 9 are provided on the paper feed side of the photosensitive drum 1, and a fixing device 10, a paper discharge tray 11, etc. are provided on the paper discharge side of the photosensitive drum 1. It is provided.

When the photosensitive drum 1 uniformly charged by the charging roller 2 is exposed to the image light L through a scanner unit (not shown), an electrostatic latent image is formed on the photosensitive drum 1. To be done. The electrostatic latent image is directed toward the developing device 3 as the photosensitive drum 1 rotates, and toner is supplied by the developing device 3 to be visualized as a toner image. Then, this toner image is transferred onto the transfer material P via the transfer charging device 4, and the residual toner of the photosensitive drum 1 after the transfer is cleaned by the cleaning device 5 to prepare for the next image formation. . The toner in the developing device 3 is assumed to be negatively charged by internal agitation or the like.

On the other hand, the transfer material P in the paper feeding cassette 7 is taken out one by one via the paper feeding roller 8 and then sent to the registration roller 9, and the timing is adjusted by the registration roller 9 to adjust the photosensitive drum. 1 and the transfer charger 4. Then, the photosensitive drum 1 is transferred through the transfer charger.
The transfer material P on which the upper toner image is transferred is sent to the fixing device 10, and the toner image is fixed as a permanent image by the fixing device 10, and then is stacked on the paper discharge tray 11.

Here, the charging roller 1 is composed of an elastic member having conductivity, and is brought into contact with the photosensitive drum 1 at a predetermined pressure so as to form a nip portion, and is driven to rotate as the photosensitive drum 1 rotates. It has become. Then, a DC voltage of, for example, -1300 V is applied to the core metal portion 2a of the charging roller 2 from a power source (not shown) via the high voltage substrate 13, whereby the organic light of the photosensitive drum 1 is applied. The conductive layer is uniformly charged to, for example, −700 V, and the image light L
The exposed portion (image portion) of (1) is attenuated to -100 V to form a latent image.

Now, in the image forming apparatus as described above,
Since the charging roller 2 is outside the process cartridge 6,
When the process cartridge 6 is attached / detached to / from the apparatus main body 12 or when a jam is processed, toner or the like floating in the apparatus main body 12 adheres to the charging roller 2 during image formation, which causes uneven charging of the photosensitive drum 1. Further, due to long-time use of the apparatus, the cleaning of the photosensitive drum 1 by the cleaning device 5 becomes insufficient, and the toner remaining on the photosensitive drum 1 without being cleaned adheres to the charging roller 2 and charges the photosensitive drum 1. There is an inconvenience of causing unevenness.

Therefore, in this embodiment, although the photosensitive drum 1 is rotating, when a non-image is formed in which it is not necessary to form a latent image or a toner image on the photosensitive drum 1, more specifically, a plurality of continuous photosensitive drums are continuously formed. When the image is formed on the transfer material P, a predetermined negative or positive voltage is applied to the charging roller 2 at least during one rotation of the charging roller 2 when the paper is present between the transfer material P and the next transfer material P. Then, next, at least while the charging roller 2 makes one rotation, a predetermined positive or negative voltage opposite to the above is applied to the charging roller 2 to positively or negatively charge the charging roller 2. Adhesive substances such as toner, paper powder, and dust are attached to the photosensitive drum 1 side to easily clean the charging roller 2.

That is, when the controller 14 controls the timing of voltage application to the charging roller 2 and the like, the positive and negative predetermined voltages are applied to the transfer roller 2 through the high voltage substrate 13 for a predetermined time during the interval between the transfer materials P. The toner or the like that is positively or negatively charged and adheres to the charging roller 2 is the charging roller 2
The electric field that moves from the side to the photosensitive drum 1 side is formed between the charging roller 2 and the photosensitive drum 1, and the charging roller 2 is electrically cleaned. Hereinafter, this will be described with reference to the timing chart of FIG.

During the paper interval time T0 from time a when the trailing edge of the previous transfer material P passes the position of the transfer charger 4 to time b when the leading edge of the next transfer material P reaches the position of the transfer charger 4. , The charging roller 2 from the high voltage substrate 13 via the controller 14
, A negative DC voltage (for example, -1300 V) is applied for at least the time T1 for one rotation of the charging roller 2, and then at least the time T for the next one rotation of the charging roller 2 is applied.
During 1, the charging roller 2 receives a positive DC voltage (for example, +1
300 V) is applied.

In this way, when the first voltage of -1300V is applied, the negatively charged toner and other adhering substances adhered around the charging roller 2 are caused by the Coulomb force to the photosensitive drum 1 (this photosensitive drum 1 is charged by the charging roller 2). When the voltage of + 1300V is applied next time, the positively charged toners and the like attached to the periphery of the charging roller 2 move toward the photosensitive drum 1 (this is charged to about -700V). In this case, the photosensitive drum 2 is slightly charged to a positive potential).

If the photosensitive drum 1 is negatively charged even after the transfer, it is not necessary to positively charge the charging roller 2, and even if the charging roller 2 is still at OV, the surroundings of the charging roller 2 The positively charged toner of the photosensitive drum 1
Move to the side.

Next, at time a, after the time T2 when the point on the photosensitive drum 1 which contacts the charging roller reaches the position of the transfer charger 4 as the photosensitive drum rotates, the charging roller 2 also rotates once for the transfer charger 4. The positive voltage moved to the photosensitive drum 1 by applying a negative voltage for a time T1 to a constant current value of −150 μA and a positive voltage for the same time T1 of a constant current value of +150 μA, for example. , Negative deposits are prevented from moving to the transfer charger 4 side. Further, as described above, when a positive voltage is applied to the charging roller 2, the photosensitive drum 1 is slightly positively charged, so that the negatively charged toner in the developing device 3 moves to the photosensitive drum 1 side. Since there is a possibility that development work may be performed, the time required for the point on the photosensitive drum 1 to move to the position of the developing device 3 when a positive voltage (+1300 V) is applied to the charging roller 2 in order to prevent this. After T3, a positive voltage (for example, +50 V) is applied to the developing device 3 for a time T1. Then, the attached matter moved to the cleaning device 5 side as the photosensitive drum 1 rotates is cleaned by the cleaning device 5. Therefore, the cleaning of the charging roller 2 is performed within one rotation of the photosensitive drum 1.

As described above, the positive and negative voltages are applied to the charging roller 2 via the controller 14 during the interval between the transfer materials P, and the adhering substances charged to the positive and negative polarities are the charging rollers 2 respectively. Since an electric field that moves from the side to the photosensitive drum 1 side is formed, the charging roller 2 can be cleaned by this, and the charging roller 2 can be used stably for a long period of time without causing uneven charging. It will be possible. Further, since the cleaning device 5 may be finally used for cleaning, a special cleaning device is not required, and it is possible to suppress an increase in size and cost of the device.

Next, a second embodiment of the present invention will be described with reference to FIGS.
Will be described. It should be noted that components having the same functions as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the present embodiment, in view of the fact that toner, paper dust, etc. floating in the apparatus body 12 are easily attached to the charging roller 2 when the process cartridge 6 is attached to or detached from the apparatus body 12 or when jamming, the process cartridge 6 is considered. Immediately after the main body door 12a is closed (before image formation), such as after attachment / detachment or after completion of jam processing, a predetermined positive / negative predetermined DC voltage is applied to the charging roller 2 for a predetermined time to deposit the adhered matter on the charging roller 2. Was transferred to the photosensitive drum 1 side to clean the charging roller 2.

That is, as shown in FIG. 3, the apparatus main body 12
A close sensor 15 for detecting the closing (close) of the main body door 12a is provided on the side, and a controller 14 is operated by a signal from the close sensor 15, and the controller 14 applies a positive voltage to the charging roller 2 for a predetermined time via a high voltage substrate 13. A negative voltage is applied to move the positively and negatively charged deposits adhering to the charging roller 2 to the photosensitive drum 1 side.

As shown in FIG. 4, when the door close sensor 15 detects the closing of the main body door 12a and issues a door close signal c, the charging roller 2 has a time T4 during which the charging roller 2 rotates twice. (At least 1 charging roller
A negative DC voltage (for example, -1300 V) is applied during the rotation time, and subsequently, the charging roller 2 makes the next two rotations T4 (in this case, at least the charging roller 2 makes one rotation). (It is necessary to take time), a positive DC voltage (eg, + 1300V) is applied to the charging roller 2.
Is applied. By doing so, an electric field is formed from the charging roller 2 side toward the photosensitive drum 1 side as in the case of the first embodiment, and the positively and negatively charged adhered substances adhering to the charging roller 2 reach the photosensitive drum 1 side. Moving. Also in this case, if the photosensitive drum 1 is negatively charged even after the transfer, it is not necessary to positively charge the charging roller 2.

Also in this embodiment, the photosensitive drum 1 is also used.
When the positive and negative deposits from the charging roller 2 are moved to the vicinity of the transfer charger 4 by the rotation of, the transfer charger 4 also has a negative voltage so as to have a constant current value of, for example, −150 μA for a time T4. Then, a positive voltage is applied so that the constant current value becomes +150 μA at a constant current value for the same time T4 to prevent the adhered matter from moving to the transfer charger 4. Similarly, when the charging roller 2 is positively charged, a positive voltage (for example, + 50V) is applied to the developing device 3 for a time T4 in order to prevent the toner from moving from the developing device 3 to the photosensitive drum 1 side. Finally, the adhering matter on the photosensitive drum 1 is cleaned by the cleaning device 5. In this embodiment, the photosensitive drum 1 is 1.
It is rotated 5 times.

As described above, also in this embodiment, the same effect as in the first embodiment can be obtained. Particularly in the case of the present embodiment, since the charging roller 2 is cleaned after the process cartridge 6 in which toner or the like is easily attached to the charging roller 2 is mounted or after the jam processing, the cleaning of the charging roller 2 is transferred. The cleaning effect is greater and the number of cleanings can be reduced as compared with the case of the first embodiment, which is performed when the material P is between sheets. Incidentally, in this embodiment as well, the charging roller 2 may of course be cleaned during the interval between sheets, as in the case of the first embodiment.

Further, in this embodiment, the main body door 12
Although the positive and negative voltages are applied to the charging roller 2 and the like via the controller 14 in conjunction with the closing of a, the main power source of the apparatus main body 12 is turned on to start the image forming work. Even in the case, in conjunction with the ON signal of the main power,
Of course, the voltage may be applied to the charging roller 2 and the like via the controller 14. Furthermore, since it is considered that the most amount of toner attached to the charging roller 2 is the toner from the developing device 3 that has been negatively charged, as shown in FIG. The charging roller 2 may be cleaned by applying only a negative voltage (+ 1300V).

In the above first and second embodiments, the case of so-called reversal development in which the photosensitive drum 1 is negatively charged and a toner image is formed on the photosensitive drum 1 by the negatively charged toner has been described. The present invention is not limited to this, and it is needless to say that the present invention can be similarly applied to the case of so-called regular development using positively charged toner. Further, the present invention can be applied to an image forming apparatus having no process cartridge.

The process cartridge is a cartridge in which at least one of a charging unit, a developing unit, a cleaning unit and an electrophotographic photosensitive member are integrated into a cartridge, and the cartridge is used as an image forming apparatus (for example, a copying machine, a laser beam printer, etc.). ) Although it is detachable from the main body, in the case of the present invention, the process cartridge 6 which does not include the charging means therein is targeted.

[0038]

As is apparent from the above description, according to the present invention, a predetermined voltage is applied to the contact type charging means through the control means at the time of non-image formation so that the forward and reverse directions are applied between the image carrier and the charging means. Two
Since the first and second electric fields in the directions are formed, the charging means is easily cleaned by the action of the first and second electric fields. Therefore, this charging means does not cause uneven charging on the image carrier side, and the life of the charging means can be maintained long. Further, as described above, when cleaning the charging means, no special cleaning means is required, so that the apparatus does not become large.

In the case of excluding only the toner or the like attached to the charging means and having a constant polarity, the
Only the electric field in the predetermined direction needs to be formed between the image carrier and the charging means, and the number of times of forming the electric field can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an image forming apparatus according to a first embodiment.

FIG. 2 is a timing chart for cleaning a charging roller of the image forming apparatus.

FIG. 3 is a sectional view of an image forming apparatus according to a second embodiment.

FIG. 4 is a timing chart for cleaning the charging roller of the image forming apparatus.

FIG. 5 is another timing chart for cleaning the charging roller of the image forming apparatus.

[Explanation of symbols]

 1 Photosensitive Drum (Image Carrier) 2 Charging Roller (Charging Means) 6 Process Cartridge 12a Main Body Door 14 Controller (Control Means)

Claims (6)

[Claims] 1. In an image forming apparatus in which a voltage is applied to a charging unit abutting on an image carrier to charge the image carrier, a predetermined voltage is applied to the charging unit at the time of non-image formation, thereby the image carrier. Between the charging means and the charging means in a predetermined direction
An image forming apparatus comprising: a control unit that forms a second electric field in a direction opposite to the first electric field and the second electric field. 2. The image forming apparatus according to claim 1, wherein the non-image forming time is a paper interval of the transfer material when images are continuously formed on a plurality of transfer materials. 3. The image forming apparatus according to claim 1, wherein the non-image formation is performed immediately after the power of the image forming apparatus main body is turned on or immediately after the main body door is closed. 4. The charging means is disposed outside the process cartridge when the process cartridge is detachably disposed inside the main body of the image forming apparatus. Image forming device. 5. The charging means is a charging roller that rotates with the rotation of the image carrier, and the formation time of each of the first and second electric fields formed between the charging roller and the image carrier is at least charged. The image forming apparatus according to claim 1, 2, 3, or 4, wherein the time is equal to or longer than one rotation of the roller. 6. An image forming apparatus in which a voltage is applied to a charging unit that is in contact with an image carrier to charge the image carrier, and a predetermined voltage is applied to the charging unit during non-image formation, so that the charging unit is charged. An image forming apparatus comprising: a control unit that forms an electric field that moves the attached toner or the like charged to a constant polarity from the charging unit side to the image carrier side.