JPH08292650A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device constituted so that irregularities are prevented from occurring in an image by lowering the potential of a transfer material detection member triboelectrified in the midst of a paper passing time every interval of papers. CONSTITUTION: The image forming device is provided with a photoreceptive drum(image carrier) 1, a transfer roller(transfer means) 5 transferring a developer image formed on the surface of the drum 1 on a transfer material P at a transfer part and a fixing device(fixing means) 7 fixing the developer image on the material P. Besides, the paper detection sensor(transfer material detection member) 10 is arranged on a carrying guide(transfer material carrying path) 6 leading to the fixing device 7 from the roller 5. Then, the sensor 10 is not grounded when it is brought into contact with the material P and it is grounded when it is not brought into contact with the material P. By such constitution, since electric charge accumulated in the sensor 10 is discharged by grounding the sensor 10 at a paper non-passing time such as the interval between the papers of a continuous paper passing time, the potential of the sensor 10 is lowered and the irregularities are prevented from occurring in the image when the next material P arrives.

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 an electrophotographic copying machine, a printer and a fax machine.

[0002]

2. Description of the Related Art There are electrophotographic copying machines, fax machines, laser beam printers and the like as image forming apparatuses to which electrophotography is applied. FIG. 7 shows a schematic cross section of a laser beam printer as an example.

In FIG. 7, reference numeral 101 denotes a photosensitive drum which is an image carrier, and the photosensitive drum 101 is composed of a photosensitive layer and a substrate, and is rotationally driven in the direction of the arrow shown in the figure.

The photosensitive drum 101, which is uniformly charged by the primary charging roller 102, has an electrostatic latent image formed on its surface by the irradiation of the laser beam 103 modulated according to the image signal. Then, the photosensitive drum 101
The upper electrostatic latent image is visualized as a toner image by a developing process by the developing device 104, and the toner image on the photosensitive drum 101 is transferred onto a transfer material by a transfer roller 105 to which a bias having a polarity opposite to the charging polarity of the toner is applied. Transcribed on P.

The transfer material P which has received the transfer of the toner image is
The toner image is guided along the guide 107 to the fixing device 106, where the toner image is fixed by heat and pressure in the fixing device 106, and then discharged as a hard copy to the outside of the apparatus. The untransferred developing toner remaining on the photosensitive drum 101 is cleaned by the cleaning device 108, the photosensitive drum 101 is sent to the first step of the primary charging process, and thereafter, it is repeatedly used in the same manner.

By the way, in such an image forming apparatus, a paper detection sensor 110 is provided in the guide 107 for guiding the transfer material P from the transfer portion to the fixing portion, and the retention of the transfer material P is detected to prevent the occurrence of a jam in the user. A notification structure is adopted. Alternatively, by devising the arrangement position of the sensor in the paper passing width direction, it is possible to determine whether the transfer material is a small size paper or a large size paper and feed back the determination result to various control units. . As such, as the transfer material advances, the lever tilts in the moving direction of the transfer material, the lever continues to tilt while the transfer material is at the sensor position, and the lever moves when the trailing edge of the transfer material passes the sensor position. Is generally configured to return to the original.

[0007]

By the way, since the toner image on the transfer material is only restricted by the electrostatic force on the back surface of the transfer material between the transfer portion and the fixing portion, the state is very unstable. . Therefore, the unfixed toner image on the transfer material may be disturbed by the electrical characteristics of the sensor arm with which the transfer material contacts between the transfer portion and the fixing portion. For example, when the sensor arm is a mold having a high insulating property, the sensor arm is strongly charged by rubbing against the transfer material in a low humidity environment, and the unfixed toner image on the transfer material is disturbed.

Even when the sensor arm is made of a metal having high conductivity, if the sensor arm is in a non-grounded state, if the continuous paper feeding is performed, the charge amount of the sensor arm exceeds the charge attenuation. However, the same problem as in the case where the sensor arm is formed by molding occurs.

Conversely, if the sensor arm is made of a highly conductive metal and is grounded, the charge on the back surface of the transfer material escapes from the sensor arm, and the toner image transfer material is transferred onto the contact portion of the sensor arm. Since the restraint force to the upper part is weakened, the toner in that portion is attracted and moved by the electric charge in the other portion, which also disturbs the image. Further, even if the image is not disturbed at that time, if the fixing process is attempted as it is, a part of the toner image is transferred to and adheres to the fixing roller due to the weak binding force, and a so-called fixing offset phenomenon occurs. Since the electric charge easily escapes in the OHP paper having the surface subjected to the conductive treatment, the occurrence of the fixing offset phenomenon is remarkable when the OHP paper is used as the transfer material.

The present invention has been made in view of the above problems. An object of the present invention is to prevent image disturbance by lowering the potential of a transfer material detecting member that is frictionally charged during sheet feeding for each sheet interval. It is to provide an image forming apparatus capable of

[0011]

To achieve the above object, the invention according to claim 1 transfers an image carrier and a developer image formed on the surface of the image carrier to a transfer material at a transfer site. In an image forming apparatus having a transfer means and a fixing means for fixing the developer image on the transfer material, a conductive transfer material detecting member is arranged on a transfer material conveying path from the transfer means to the fixing means, and It is characterized in that the transfer material detecting member is not grounded when the transfer material is in contact with the transfer material and is grounded when the transfer material is not in contact with the transfer material.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the transfer material detecting member is grounded via a resistor when the transfer material contacts.

[0013]

According to the first aspect of the invention, since the transfer material detecting member is brought into a non-grounded state when it comes into contact with the transfer material, escape of potential from the transfer material can be prevented. When the sheet is not continuously fed, such as between sheets, the transfer material detection member is set to the grounded state, and the charge accumulated in the transfer material detection member is released. It is possible to prevent the image from being disturbed when the image comes.

According to the second aspect of the present invention, a large current is prevented from flowing through the ground line, so that no electrical noise is generated when switching the non-ground / ground of the transfer material detecting member. Problems such as malfunction of the CPU and circuit and electromagnetic interference are solved.

[0015]

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

<First Embodiment> FIG. 1 is a schematic sectional view of a laser beam printer according to a first embodiment of the present invention, and FIGS. 2 and 3 are enlarged sectional views for explaining the operation of a paper detection sensor. .

In FIG. 1, reference numeral 1 denotes a photosensitive drum which is an image carrier, and the photosensitive drum 1 is composed of an OPC photosensitive member having a diameter of 24 mm. Around the photosensitive drum 1, a charging roller 2, a developing device 4, a transfer roller 5 and the like are arranged.

The photosensitive drum 1 rotates in the direction of the arrow in FIG. 1, and the surface thereof is -700 by the charging roller 2.
When the photosensitive drum 1 is irradiated with the laser beam 3 uniformly charged with V and modulated according to an image signal, an electrostatic latent image is formed on the photosensitive drum 1. Then, the electrostatic latent image is visualized as a toner image by the negative toner in the developing device 4.

On the other hand, when the transfer material P is supplied to the transfer portion between the photosensitive drum 1 and the transfer roller 5, a positive transfer bias is applied to the transfer roller 5 by a power source (not shown),
The toner image on the photosensitive drum 1 is transferred onto the transfer material P.
The transfer roller 5 has an EPDM on the core metal 5a having a diameter of 6 mm.
The outer diameter of the sponge rubber 5b is 1
It is set to 4 mm.

Then, the transfer material P which has received the transfer of the toner image
Passes over the transport guide 6 and is guided to the fixing device 7, where the toner image is fixed by heat and pressure in the fixing device 7, and then discharged to the outside of the machine.

By the way, in the present embodiment, as the transfer guide 6, an Alster steel plate pressed is used, and as shown in detail in FIG. 2 and FIG.
Ribs are erected on a to reduce the contact resistance with the transfer material P, and the entire surface of the conveying surface 6a is coated with an epoxy-based insulating paint. The transport guide 6 has a sheet metal surface 6b.
Is grounded.

A paper detection sensor 10 is attached to the transport guide 6, and the paper sensor 10 is composed of a sensor member 11 and a sensor holder 12. The sensor member 11 is rotatably supported by a sensor holder 12 by a shaft 14, and the sensor member 1
1 is divided into an arm portion 11a and a light shielding portion 11b.
As shown in FIG. 3, when the transfer material P is not on the transport guide 6, the arm portion 11a is in an upright state, and at this time, the light shielding portion 11b includes the photo interrupter 13 (see FIG. 1) installed on the electrical component substrate 8. ) The light from the LED is blocked.

As shown in FIG. 3, when the transfer material P is on the transport guide 6, the arm portion 11a of the sensor member 11 is tilted in the transport direction, and the light shielding portion 11b is inevitably lifted. Therefore, the LEDs of the photo interrupter 13 cannot be shielded from light, and the photo interrupter 13 is blocked.
An electric current will flow through. ON / OFF of this current
Is detected by the CPU and the presence or absence of the transfer material P is determined.

By the way, in this embodiment, the sensor member 1
Reference numeral 1 is made of a highly conductive metal (for example, aluminum, copper, iron, etc.), the sensor holder 12 uses an insulating mold, and examples of the material of the mold include ABS and PC. .

As shown in FIG. 2, when the sensor member 11 is standing, the arm portion 1 of the sensor member 11 is raised.
1a contacts a sensor contact portion A provided on the transport guide 6. The transport guide 6 has a transport surface (painted surface) as described above.
6a and sheet metal surface 6b, but sensor contact portion A
Is a sheet metal, and therefore, in the state shown in FIG. 2, the sensor member 11 is grounded via the transport guide 6.

Then, when the transfer material P comes on the conveyance guide 6 and the sensor member 11 falls down as shown in FIG. 3, the arm portion 11a of the sensor member 11 separates from the sensor contact portion A, and the sensor holder Since 12 is made of an insulating mold, the sensor member 11 is in a non-grounded state (float). In this state, the contact portion of the sensor member 11 with the transfer material P is gradually charged by sliding as the transfer material P moves. However, since the sensor member 11 is made of metal, its charge amount is smaller than that of the insulator, and the image is not disturbed when one sheet of the transfer material P is passed.

When the transfer material P passes and the sensor member 11 which has fallen up again stands up as shown in FIG. 2, the arm portion 11a of the sensor member 11 again touches the contact portion A, and the sensor member 11 is grounded. The Rukoto. At this time, the charges accumulated in the sensor member 11 escape to the ground, and the charging potential of the sensor member 11 immediately decreases.

Since the above process can be sufficiently performed between the sheets even if the sheet is continuously fed, when the transfer material P arrives again, the charge amount of the sensor member 11 becomes almost zero. Therefore, by repeating the above process, the charge of the sensor member 11 can be removed every time one sheet of the transfer material P is passed, and the disturbance of the toner image due to the charging of the paper detection sensor 10 can be prevented.

Further, since the sensor member 11 is in a non-grounded state (float) during the passage of the paper, the charge on the back surface of the transfer material P does not escape, and scattering and offset do not occur.

Regarding the way of grounding when paper is not passing, see FIG.
Alternatively, the method shown in FIG. 5 may be used, or any other method may be used. In the system shown in FIG. 4, the sensor member 11 is a conveyance guide 6 embedded in the sensor holder 12.
5 is grounded through the sheet metal surface 6b, and in the system shown in FIG.
The light shielding portion 11b of the sensor member 11 comes into contact with the earth contact 15 on the same substrate as the photo interrupter. FIG. 5 shows an example in which the sensor member 11 does not necessarily have to be grounded via the sheet metal surface 6b of the transport guide 6.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. 6 is an enlarged sectional view of the paper detection sensor section of the image forming apparatus according to the second embodiment.

In the case of adopting the configuration of the first embodiment, electrical noise is generated when the sensor member 11 is switched between non-grounded / grounded, and the CPU or circuit malfunctions or electromagnetic interference occurs. I was afraid. This is because when the sensor member charged to a certain potential approaches the earth contact, a discharge occurs between the two before they completely contact each other, or a large current flows through the earth line. In this embodiment, in order to prevent this, the sensor member is grounded via a resistor.

Specifically, as shown in FIG. 6, the resistance value of the contact portion A of the earth line with the sensor member 11 is 1 ×.
A plate-shaped resistor 16 made of a medium resistance material of about 10 ⁷ to 1 × 10 ¹² Ω is arranged to prevent the sensor member 11 from being directly grounded. Various materials such as mold and rubber are conceivable as the medium resistance material forming the resistor 16, but in the present embodiment, PBT mixed with a surfactant is used, and the material is attached to the contact portion A to be a sensor member. The resistance from 11 to ground is 1 × 10 ⁸ Ω.

Here, according to the measurement by the present inventor, the electric capacity of the sensor member 11 in the apparatus used in this embodiment is about 1 pF.
Even if the resistance 16 of 1 × 10 ⁸ Ω is used, the time required for the potential to be reduced by 95% is about 3 × 10.
^-4 sec. Therefore, in the image forming apparatus according to the present exemplary embodiment, since the sheet interval is 1.0 sec or more, the accumulated charge can be sufficiently removed between the sheet intervals.

Although a medium resistance plate is used as the resistance 16 in this embodiment, the contact portion A may be coated with a thin layer of insulating paint to form the resistance.

<Third Embodiment> In this embodiment, the surface of the sensor member 11 is coated with an insulating coating so that the sensor member 11 has a predetermined resistance. Specifically, the epoxy-based insulating paint is applied to the entire surface of the sensor member 11
It was coated with a thickness of about 30 μm so that the resistance value between the sensor member 11 and the ground was about 1 × 10 ⁸ Ω.

Thus, as in this embodiment, the sensor member 1
When the surface of 1 is coated with an epoxy-based paint, the epoxy-based paint is negatively charged by rubbing against the transfer material, so the transfer material is charged to the same polarity as the charge on the back surface of the transfer material, and the The effect on the image is also less. In addition, PFA and P in the paint
It is also possible to disperse a fluororesin such as TFE to improve the slidability of the sliding contact portion of the sensor member 11 with the transfer material.

[0038]

As is apparent from the above description, according to the present invention, an image carrier and a transfer means for transferring a developer image formed on the surface of the image carrier to a transfer material at a transfer site.
In an image forming apparatus having a fixing means for fixing a developer image on a transfer material, a conductive transfer material detecting member is arranged on a transfer material conveying path from the transferring means to the fixing means, and the transfer material detecting member is provided. Is configured so that it is not grounded when the transfer material is in contact with it, and is grounded when the transfer material is not in contact.Therefore, it is possible to prevent image distortion by lowering the potential of the transfer material detection member that has been triboelectrically charged during paper passing for each paper interval. The effect of being able to be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a laser beam printer according to a first embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view for explaining the operation of the paper detection sensor.

FIG. 3 is an enlarged cross-sectional view for explaining the operation of the paper detection sensor.

FIG. 4 is a cross-sectional view showing another embodiment of how to ground the paper detection sensor when the paper is not passed.

FIG. 5 is a cross-sectional view showing another embodiment of how the paper detection sensor is grounded when no paper is passed.

FIG. 6 is an enlarged cross-sectional view of the paper detection sensor unit of the image forming apparatus according to the second embodiment of the present invention.

FIG. 7 is a schematic sectional view of a conventional laser beam printer.

[Explanation of symbols]

 1 Photosensitive Drum (Image Carrier) 5 Transfer Roller (Transfer Means) 6 Conveyance Guide (Transfer Material Conveyance Path) 7 Fixing Device (Fixing Means) 10 Paper Detection Sensor (Transfer Material Detection Member) 11 Sensor Member 12 Sensor Holder 16 Resistance P Transfer material

Claims (2)

[Claims] 1. An image carrier, a transfer means for transferring the developer image formed on the surface of the image carrier to a transfer material at a transfer site, and a fixing means for fixing the developer image on the transfer material. In the image forming apparatus, a conductive transfer material detecting member is arranged on the transfer material conveying path from the transfer means to the fixing means, and the transfer material detecting member is not grounded when the transfer material is in contact with the transfer material and is not grounded when the transfer material is not in contact. An image forming apparatus configured to be grounded. 2. The image forming apparatus according to claim 1, wherein the transfer material detecting member is grounded via a resistor when the transfer material contacts.