JPH07104585A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain the excellent destaticizing effect on recording medium and to prevent from causing the picture defect such as the polka dot by controlling the position of the charge removing needle changing in the direction coming near to and the direction going away from the transporting path of the recording medium. CONSTITUTION:When the upper cap open-close detecting switch or the cartridge load- unload detecting switch SW1 is closed, the closing signal S1 is inputted to the main controlling circuit CPU and the motor controlling circuit 18d is controlled. At this time, the charge removing rod 16 is set and held at the height position that the rear side of the transfer material P is allowed to pass through the transferring part position and separated from the photoreceptor drum 3, is transported through the place about 1-2cm higher above the tip of the upper needle part 16a. In other words, at this time, the charge removing needle 15 is set and held at the height position that the tip of the needle part 16a is brought in the optimum accessing state for attaining the excellent destaticizing effect on the rear side of the transfer material P passing through the transferring part position and separating from the drum 3 to be transported. Thus, the printing is performed in the state of attaining the excellent destaticizing effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an appropriate image formation for an electrophotographic process, an electrostatic recording process, a magnetic recording process or the like on an image carrier such as an electrophotographic photosensitive member, an electrostatic recording dielectric, a magnetic recording magnetic body or the like. A transferable image such as a toner image corresponding to target image information is formed and carried by a process, and the transferable image is recorded by a transfer means such as a transfer roller or a corona discharger to which a transfer bias is applied. The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer that uses a transfer method for transferring to a medium side.

[0002]

2. Description of the Related Art In a transfer type image forming apparatus, a toner image as a transferable image is transferred from an image carrier to a recording medium by applying a transfer bias having a polarity opposite to that of the toner image to the transfer means. The toner image is attracted and moved from the image carrier side to the recording medium side by the action of the electric field thus formed. At this time, the recording medium is charged.

The recording medium to which the toner image has been transferred at the transfer portion is separated from the image carrier and conveyed to an image fixing device to undergo an image fixing process. In this case, when the recording medium is conveyed from the transfer section toward the image fixing device in the above charged state, the recording medium comes into contact with a conveyance guide or the like during the conveyance and electric charges on the recording medium leak. The unfixed toner image on the recording medium is disturbed, and an image defect called a dot pattern is likely to occur.

This image defect is particularly caused when the recording medium is in a high resistance state due to drying in a low humidity environment (for example, 15% RH or less), or in the double-sided or multiple print mode.
This is remarkable at the time of printing on the second surface or the second time when the recording medium is in a high resistance state by being dried by heat after the printing on the first surface or the first time is completed and the recording medium has passed through the thermal fixing device once.

Therefore, in order to prevent the occurrence of the image defect as described above, a charge eliminating means such as a charge eliminating needle is provided immediately after the transfer process so as to eliminate the electric charge excessively accumulated on the recording medium.

The charge elimination of the recording medium by the charge elimination needle is performed by increasing the height of the charge elimination needle to the limit of the conveyance path of the recording medium.
That is, it is effective to set the charge elimination needle so that its tip end is as close as possible to the conveyance path of the recording medium.

[0007]

However, on the other hand, there are the following problems.

(1) The user opens the opening / closing member (opening / closing lid, opening / closing door, etc.) of the image forming apparatus main body for jam processing and the like, and further extracts the process cartridge to open the inside of the main body of the apparatus to the inside of the main body of the apparatus. It is easy to inadvertently touch the fingertip with the sharp tip of the static elimination needle protruding in the recording medium conveyance path when the hands are put in to remove static electricity from the jammed paper.

(2) When the double-sided printing or the multiple print mode is executed, the first surface or the curl of the leading end of the recording medium caused by the fixing separation at the time of the first printing is used as the discharging needle when the second surface or the second printing is executed. It is easy to hit and jam easily.

(3) Depending on the thickness of the recording medium used,
Since the conveyance path of the recording medium exiting the transfer portion changes far and near with respect to the tip of the static elimination needle, the static elimination effect varies.

As a method of coping with the above problem,
Set the height of the static elimination needle to the recording medium conveyance path to a low eye ,. Round the tip of the static elimination needle to prevent the recording medium from getting caught ,. There are methods such as making the holder of the static elimination needle to cover the tip of the static elimination needle more easily to prevent the recording medium from being caught, but in both cases, the static elimination effect is weakened, and images such as polka dots in low humidity environments etc. The effect of preventing defects is reduced.

In the present invention, the charge of the recording medium is similarly removed by the charge removing needle. However, there is no problem as described above.
Moreover, in each case, a sufficient charge removal effect of the recording medium can be obtained.

[0013]

The present invention is an image forming apparatus having the following configuration.

(1) In a transfer type image forming apparatus in which a transferable image formed and carried on an image bearing member is transferred to a recording medium by a transfer means, it is arranged near the transfer portion to remove electricity from the recording medium. An image forming apparatus, wherein the needle is positionally controlled to move toward and away from a conveyance path of a recording medium.

(2) The position of the static elimination needle is displaced in association with the opening / closing operation of the opening / closing member of the image forming apparatus main body or the attaching / detaching operation of the process cartridge with respect to the image forming apparatus main body. The image forming apparatus described.

(3) The image forming apparatus according to (1), wherein the static elimination needle is displaced in accordance with the state of the front and rear ends of the recording member being conveyed.

[0017]

That is, in the image forming apparatus of the transfer system in which the transferable image formed and carried on the image carrier is transferred to the recording medium by the transfer means, the charge removal needle is provided near the transfer portion to remove the charge from the recording medium. By controlling the position displacement in the direction approaching and moving away from the conveyance path of the recording medium,
When the device is opened and the process cartridge is attached and detached, the inside of the device is inspected and maintained, and the jammed paper is removed and processed, the static elimination needle is displaced to the retracted position, so careless It is possible to prevent the fingers from touching the finger, and even if the recording medium is curled or the conveyance path varies depending on the thickness, the static elimination needle can be appropriately displaced to the neutralization needle of the recording medium. It is possible to prevent jamming and prevent jamming, and even in this case, it is possible to obtain a sufficient charge removing effect on the recording medium and prevent image defects such as polka dots.

[0018]

【Example】

Example 1 (FIGS. 1 to 3) (A) Overall Configuration of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an example. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 1 is a general reference numeral of the printer, and reference numeral 1a is an opening / closing upper lid as an opening / closing member of the printer, which can be opened to open the inside of the printer as shown by a chain double-dashed line. You can perform attachment / detachment operations, inspection / maintenance inside the printer, removal of jammed paper, etc.

Reference numeral 3 is an electrophotographic photosensitive drum as an image bearing member. In this example, an OPC photosensitive layer is formed on the outer peripheral surface of a conductive drum substrate such as aluminum. In this example, it is rotationally driven at a process speed (peripheral speed) of 50 mm / sec. The printer has a maximum throughput of 8 sheets of A4 size paper.

The photosensitive drum 3 is charged by the primary charging means 4 during its rotation process. Primary charging means 4 of this example
Is a charging roller that is driven and rotated by pressing and contacting the photosensitive drum 3 with a predetermined pressing force. A charging bias is applied to the charging roller 4 from a high voltage power source (not shown), and the peripheral surface of the photosensitive drum 3 is It is uniformly negatively charged.

The rotary photosensitive drum 3 which has been negatively charged.
The surface is subjected to scanning exposure by the laser light L which is image-modulated in accordance with target image information and output from the laser scanner 5, and the potential of the scanning-exposed portion is attenuated, so that the surface of the rotating photoconductor drum 3 is aimed. An electrostatic latent image corresponding to the image information is formed.

The electrostatic latent image is developed as a toner image by the negative toner 7 of the reversal developing device 6. Reference numeral 8 is a developing sleeve.

Then, the toner image is fed from the paper feeding portion to the transfer portion (pressing nip portion) between the photosensitive drum 3 and the transfer roller 9 as the contact transfer means in synchronism with the rotation of the photosensitive drum 3. The images are sequentially transferred to the transferred recording material P as a recording medium.

The transfer roller 9 is pressed against the photosensitive drum 3 with a predetermined pressing force, and rotates in the forward direction of the rotation of the photosensitive drum 3 at substantially the same peripheral speed as the photosensitive drum 3. A transfer bias is applied from the high voltage power supply 9A (FIG. 2).

Reference numeral 12 denotes a paper cassette of a paper feeding unit, and the paper feed pickup roller 13 and the separation claw cooperate with each other to feed one transfer material P from the cassette, and a pair of registration rollers 14
Are synchronized with each other and delivered to the transcription site.

Numeral 16 is a static elimination needle arranged near the transfer material outlet side of the transfer site. Reference numeral 17 is a holder for accommodating the static elimination needle. The static elimination needle will be described later.

The transfer material P that has passed through the transfer portion is sequentially separated from the rotary photosensitive drum 3, passes through the upper side of the charge eliminating needle 16 closely, and is guided by the conveyance guide 15 to be conveyed to the image fixing device 10. . When the transfer material P approaches the upper side of the charge eliminating needle 16 and approaches, the charge eliminating needle 16 removes excess charges.

The transfer material P conveyed to the image fixing device 10 undergoes a fixing process of the transferred toner image. Fixing rollers 10a and 10b are a fixing roller and a pressure roller. When the transfer material P passes through a nip portion between the rollers 10a and 10b, the toner image is heated and fixed on the surface of the transfer material P.

The fixing roller 10a of the fixing device 10 used in this embodiment has a structure in which a fluororesin layer is provided on the outer surface of a hollow aluminum cored bar and has an outer diameter of φ20. Further, a halogen heater (not shown) is arranged therein. Pressure roller 1
For 0b, a φ20 SUS core having a thickness of 6 mm and an elastic layer of low temperature vulcanizing silicone rubber (LTV) formed thereon was used.

After the toner image is transferred onto the transfer material P, the surface of the photosensitive drum 3 is cleaned by a cleaner 11 to remove adhered residual contaminants such as untransferred toner, and is repeatedly used for image formation.

The process cartridge 2 in the printer of this embodiment includes four process devices including a photosensitive drum 3 as an image carrier, a primary charging roller 4, a developing device 6 and a cleaner 11.

(B) Static elimination needle 16 (a) and (b) of FIG. 2 are enlarged views of the static elimination needle 16 portion, respectively, for explaining the positional displacement control of the static elimination needle. FIG. 3 is a front view of the static elimination needle 16. The static elimination needle 16 is a conductive plate having several saw-toothed needle portions 16a on its upper side. In this example, the material is stainless steel and the thickness is 0.
The needle length is 1 mm, the needle length is 3 mm, and the pitch of the needle portion at the tip is 2 mm.

The static elimination needle 16 is grounded, and the static elimination needle holder 1
It's paid in 7. 18 is a static elimination needle position moving device,
With this device, the height position of the static elimination needle 16 can be changed.

The static elimination needle position moving device 18 of the present embodiment includes a forward / reverse rotation motor 18a such as a pulse motor, a pinion gear 18b provided on the shaft portion thereof, and a vertical rack tooth portion (drive receiving portion) provided on the static elimination needle 16 side. Section 18c and the like, and the pinion gear 18b and the rack tooth portion 18c are meshed with each other. The motor control circuit 18d controls the rotation angle of the motor 18a in a predetermined forward / reverse direction to allow the pinion gear 18b and the rack tooth portion 1 to rotate.
The static elimination needle 16 is moved up and down by 8c and moved up and down.

In this embodiment, the upper and lower lids 1a of the printer 1 are opened and closed.
The motor control circuit 18d is operated in conjunction with the opening / closing operation or the process cartridge 2 attachment / detachment operation to vertically displace the height position of the static elimination needle 16.

That is, when the process cartridge 2 is mounted in the printer 1 and the upper lid 1a is closed as shown in FIG. 1, the upper lid open / closed detection switch or the cartridge attachment / detachment detection switch SW1 (( When a)) is closed, the closing signal S1 is input to the main control circuit CPU, and the motor control circuit 18d is controlled based on the input signal S1.
6, the tip of the needle portion 16a on the upper side is about 1
A position 2 mm apart is set and held at a height position (first height position) through which the back surface of the transfer material P, which is separated from the photosensitive drum 3 and conveyed through the transfer portion, passes. FIG. 2A shows this state.

That is, the static elimination needle 16 at this time is optimal because the tip of the needle portion 16a can obtain a sufficient static elimination effect on the back surface of the transfer material P which is separated from the photosensitive drum 3 and conveyed through the transfer portion. By setting and holding at a height position that is close to the state, the printing is executed in a state where the static elimination effect is large, and in a low-humidity environment, or the transfer material P is heat-dried on the first surface or after the first printing is completed. Even in the case of the above, the occurrence of image defects such as the above-mentioned polka dot pattern is prevented.

Jam processing, process cartridge 2
When the upper lid 1a of the printer 1 is opened for replacement of the printer, inspection / maintenance in the printer, or when the process cartridge 2 is removed from the printer body, the upper lid open / close detection switch or the cartridge attachment / detachment is performed. When the detection switch SW1 is opened, the motor control circuit 18d is controlled based on the signal S2, and at this time, the static elimination needle 16 is lowered by about 2 mm from the first height position state of FIG. 2 (a). As a result of being moved, as shown in FIG. 3, the tip of the needle portion 16a on the upper side is switched and held at a height position (second height position) where the tip of the needle portion 16a is completely accommodated in the static elimination needle holder 17.

Therefore, in this state, even if a hand is put in the printer body for removing jammed paper or the like, the static elimination needle 16 is retracted into the holder 17 and the tip of the needle portion 16a is not exposed. It prevents the finger from touching the static elimination needle carelessly.

When the process cartridge 2 is mounted and the upper lid 1a is returned to the closed state, the static elimination needle 16 moves from the second height position of FIG. 2B to the first position of FIG.
The robot is moved up to the height position of, and returned to and held.

Some image forming apparatuses do not have a lid for opening and closing the main body, so that the static elimination needle may be exposed when the process cartridge is pulled out. In this case, the height of the static elimination needle is increased in conjunction with the attachment and detachment of the process cartridge. The height position is changed to the first and second height positions as described above.

It is needless to say that the static elimination needle position moving device 18 can adopt a structure other than that of this embodiment, and the mechanical mechanism such as a link or a lever can be used to open / close the opening / closing lid of the main body of the device or the process cartridge. The static elimination needle can be similarly displaced in position in association with the attachment / detachment operation.

<Embodiment 2> (FIG. 4) In an image forming apparatus capable of executing double-sided or multiplex printing, the transfer material P that has been printed on the first surface or the first time is recirculated and conveyed to the transfer portion again, and When the toner image is transferred on the surface or the second time, the transfer material P exits the transfer portion and is separated from the photosensitive drum 3 and conveyed, and then the transfer material P passes through the image fixing device 10 when the first surface or the first printing is performed. As a result, the tip may curl downward as shown in FIG. Then, the curl portion Pa is the static elimination needle 1.
The transfer material P may be jammed by being caught in the tip portion 16a of the sheet 6.

Therefore, in the present embodiment, in the double-sided or multiple print mode, the static elimination needle 16 is moved to the first position as shown in FIG.
The transfer material P is neutralized by setting and holding it at the height position, and the main control circuit CPU controls the motor control circuit 18d at a proper predetermined timing at the time of printing on the second surface or the second time to neutralize. By moving the needle 16 downward by about 2 mm, as shown in FIG. 4A, a transfer is performed in which the toner image is transferred to the second surface or the second time, exits the transfer portion, and is separated from the photosensitive drum 3 and conveyed. It is possible to prevent the tip curl portion Pa of the material P from being caught by the needle portion 16a of the static elimination needle 16,
The tip curl portion Pa of the transfer material is the needle portion 16 of the static elimination needle 16.
At the point of time when it has finished passing over a, the main control circuit CPU controls the motor control circuit 18d to move the static elimination needle 16 upward as shown in FIG. 4 (b) to return / hold it at the first height position. Are controlled.

As a result, it is possible to prevent the occurrence of a jam due to the transfer material P having the tip curl portion Pa being caught on the tip portion of the charge eliminating needle 16, and the tip curl portion Pa of the transfer material is attached to the tip portion of the charge eliminating needle 16. Charge elimination needle 16 after passing
Is set and held at the first height position where the tip portion 16a thereof is in an optimum approaching state in which a sufficient static elimination effect can be obtained with respect to the back surface of the transfer material P, and therefore, the first surface or the first printing is performed. The charge on the transfer material P is sufficiently removed on the second printing or the second surface which is dried and has high resistance by execution.
The occurrence of image defects such as a polka dot pattern is also prevented.

Even when the trailing edge of the transfer material is also curled, it is preferable to control the downward movement of the static elimination needle when the trailing edge curl passes the position of the static elimination needle 16.

<Embodiment 3> (FIG. 5) The transfer path of the transfer material P as a recording medium, which is separated from the photosensitive drum 3 and is transferred through the transfer portion, is above the charge eliminating needle 16 and has a thickness of the transfer material P. Different depending on (paper type).

That is, in the case of a transfer material having a small thickness, since the strain is weak and it is easily adsorbed to the surface of the photosensitive drum 3, the charge eliminating needle 16 of the transfer material which is separated from the photosensitive drum 3 and conveyed through the transfer portion is conveyed. 5 is a conveyance path for a transfer material having a normal thickness when P1 is a conveyance path for a transfer material having a normal thickness in FIG. Static elimination needle 16 at the height of 1
There is a case where an image defect such as a polka dot pattern occurs due to an increase in the effect of removing electricity from the tip of the.

On the other hand, in the case of thick paper or the like, since the paper is strongly strained and separated immediately from the surface of the photosensitive drum 3, the transfer path of the transfer material which is separated from the photosensitive drum 3 and transferred through the transfer portion is as shown by P3. , A transfer path P for a transfer material having a normal thickness
The position is below 1 and the tip of the static elimination needle 16 at the first height position in which the normal transfer material is optimally approached is apt to be caught and a jam is likely to occur.

Therefore, in the present embodiment, the thickness of the transfer material P introduced into the apparatus is detected by measuring the axial displacement of the registration roller pair 14 according to the transfer material thickness by the sensor 20,
The static elimination needle 16 is displaced in position according to the detected thickness.

That is, the transfer material introduced and used is thin paper (60
g / m ² paper or less) is detected S3, the main control circuit CPU controls the motor control circuit 18d to move the static elimination needle 16 up about 1 mm higher than the first height position. The tip of the static elimination needle 16 is positioned in an optimum approaching state to the back surface of the thin paper passing through the path P2 above the normal transfer material conveyance path P1. By this, the static elimination effect of the thin paper passing through the path P2 is achieved. Sufficient to prevent the occurrence of image defects such as polka dots.

The transfer material used was thick paper (90 g
/ M ² paper or more) is detected S3, the main control circuit CPU controls the motor control circuit 18d to move the charge elimination needle 16 downward about 1 mm lower than the first height position. It is possible to prevent the thick paper from passing through the path P3 lower than the normal transfer material conveyance path P1 from being caught by the static elimination needle 16, and to position the tip of the static elimination needle 16 in an optimum approach state with respect to the back surface of the thick paper. It is a thing.

When it is detected that the paper is 60 to 90 g / m ^{2 and the} sheet is detected S3, the charge eliminating needle 16 is used as the transfer material having the normal thickness and the charge removing needle 16 is the first one.
Is set and held at the height position of.

It is also possible to appropriately change the height of the discharging needle at the tip of the paper. For detecting the thickness of the transfer material, other means such as a reflection type or a transmission type photosensor may be used, or the thickness information of the transfer material used may be input from a manual switch or a host computer.

The static elimination needle position displacement control means of Examples 1 to 3 as described above may be combined and provided.

[0057]

As described above, according to the present invention, in a transfer type image forming apparatus for transferring a transferable image formed and carried on an image carrier to a recording medium by a transfer means, the transfer type image forming apparatus is disposed in the vicinity of a transfer portion. By controlling the position displacement of the charge removal needle that removes the charge of the recording medium in the direction toward and away from the conveyance path of the recording medium, the device is opened to attach / detach the process cartridge or the inside of the device is operated. It is possible to prevent accidental touching of the static elimination needle with your fingers when inspecting and maintaining the paper, removing jammed paper, and handling it. Even if a difference occurs in the recording medium, the recording medium is prevented from being caught by the static elimination needle to prevent the occurrence of a jam, and even in this case, a sufficient recording medium static elimination effect can be obtained and an image defect such as a polka dot pattern can be generated. It is possible to prevent.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

2A and 2B are explanatory diagrams of position displacement control of a static elimination needle.

FIG. 3 is a front view of the static elimination needle.

4A and 4B are explanatory diagrams of position displacement control of a charge elimination needle of the apparatus according to the second embodiment.

FIG. 5 is an explanatory diagram of position displacement control of a charge eliminating needle of the device of the third embodiment.

[Explanation of symbols]

 3 image carrier (electrophotographic photosensitive drum) 9 transfer means (transfer roller) P recording medium (transfer material) 16 static elimination needle 18 static elimination needle position moving device

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Yuko Ogama Inventor Yuko Ogama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tatsuichi Tsukida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. A charge eliminating needle disposed in the vicinity of a transfer portion for eliminating charge from a recording medium in an image forming apparatus of a transfer system for transferring a transferable image formed and carried on an image bearing member to a recording medium by a transfer means. However, the image forming apparatus is characterized in that the positional displacement of the recording medium is controlled in a direction approaching the recording medium conveyance path and a direction moving away from the recording medium conveyance path. 2. The position of the static elimination needle is displaced in association with an opening / closing operation of an opening / closing member of the image forming apparatus main body or an attaching / detaching operation of the process cartridge with respect to the image forming apparatus main body. Image forming device. 3. The image forming apparatus according to claim 1, wherein the static elimination needle is displaced in position according to the state of the front and rear ends of the recording member being conveyed. 4. The position of the static elimination needle is displaced according to the thickness of the recording medium being conveyed.
The image forming apparatus according to item 1.