JP2003005492A - Electrifying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrifying device capable of restraining the production of ozone, uniformly electrifying a photoreceptor, and having high durability and further realizing the facilitation of the fine adjustment of space between the surface of the photoreceptor and a discharge electrode. SOLUTION: This electrifying device is equipped with the discharge electrode 25 opposed to the surface of the photoreceptor in a floating side magnet 23 magnetically floating from a fixed side magnet 21. It is provided with heat absorbing and generating body 26 for changing the temperature of at least either of the magnets 21 and 23 on the side of the fixed side magnet and/or the side of the floating side magnet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device provided in an electrophotographic image forming apparatus such as a copying machine, a facsimile or a printer, and an image forming apparatus provided with the charging device.

[0002]

2. Description of the Related Art In order to form an image by an electrophotographic method, so-called charging, which is to give positive or negative electric charge to a photosensitive member, must be carried out in advance in order to hold a toner of a charge carrier.

In order to carry out this charging, a corona charging method using a corona discharge using a fine metal wire has been conventionally used. However, when this conventional corona charging method is used, there is a problem that ozone is generated due to discharge.

Therefore, in recent years, a contact charging method has been adopted in which the photosensitive member is brought into contact with and charged. The shape of the charger used in this contact charging method includes a rotating roller method and a non-rotating brush method, and the charging method includes a charge injection method and a minute gap discharge method, each of which has advantages and disadvantages.

The feature of these contact charging methods is that the discharge or charge injection at a close range causes very little ozone generation during discharge. However, the biggest drawback of the contact type is that if the toner that adheres to the photoconductor cannot be completely removed when it comes to the charging part during the process of its rotation, it will accumulate on the charging part and gradually accumulate and become charged. It is to weaken the performance or transfer it to the photoconductor again to stain the image.

Further, according to the contact charging method, since the charger is in contact with the photoconductor, the components of the roller and the brush as the charger are gradually deposited on the surface of the photoconductor, and the photoconductor is contaminated to form an image. The so-called bleeding phenomenon, which causes the white spot defect, was caused. Further, since the charger and the photoconductor are in contact with each other, there is a problem that the photoconductor wears faster and the durability deteriorates.

A non-contact charging system is desirable in order to prevent such a problem, and it is necessary to reduce the gap between the photoconductor and the charger in order to reduce ozone generation as much as possible.

However, in corona discharge using a fine metal wire, the fine metal wire is vibrating, as can be seen by carefully observing the state during discharge. In the non-contact type charging, even a small gap is charged by the movement of corona ions in principle, and the minimum discharge start distance at atmospheric pressure in air based on Paschen's law is about 70.
μm.

[0009]

However, it is difficult to secure this distance over the entire width with a vibrating wire.
The photoconductor may come into contact at the center, and if it comes in contact with the photoconductor, the photoconductor may be damaged due to short-circuiting at that portion, so that the entire photoconductor cannot be uniformly charged.

On the other hand, in the conventional roller system, it has been considered to maintain a distance by giving a predetermined thickness to the end portion or the like, but when sliding continuously in contact with the photoconductor, the photoconductor or the roller slides. There is a problem that the parts become worn and the uniformity of charging is impaired by repeated use.

Therefore, according to the present invention, the amount of ozone generated is small, the photoconductor can be uniformly charged, and further, the photoconductor has high durability. Further, the distance between the photoconductor surface and the discharge electrode can be finely adjusted. It is an object of the present invention to provide an easy charging device and an image forming apparatus.

[0012]

In order to achieve the above object, the invention of claim 1 comprises a charging device comprising a floating magnet which is magnetically levitated with respect to a fixed magnet, and a discharge electrode which opposes the surface of the photosensitive member. In the charging device, a heating element and / or a heat absorbing element for changing the temperature of at least one of the fixed-side magnet and the floating-side magnet are provided on the fixed-side magnet side and / or the floating-side magnet side. Is. With this configuration, it is possible to easily finely adjust the temperature change due to local heat generation or cooling near the magnet by the heat generating element and / or the heat absorbing element. Furthermore, when used in an image forming apparatus, the temperature inside the machine may change during use, but even in that case, the magnet temperature is controlled to a constant temperature by operating the heating element and / or the heat absorbing element. The optimum state of the charging section can be kept constant.

According to a second aspect of the present invention, in the charging device according to the first aspect, the heating element and / or the heat absorbing element is provided on a side plate disposed on a side surface side of the floating magnet. Is characterized by. With this configuration, it is possible to easily adjust the discharge gap by a local heat generation in the vicinity of the magnet or a temperature change due to cooling due to the heat generating element and / or the heat absorbing element.

According to a third aspect of the present invention, in the charging device according to the first aspect, the temperature of at least one of the fixed-side magnet and the floating-side magnet is changed so that the surface of the photoconductor and the discharge electrode are separated from each other. It is characterized by controlling the distance. With this configuration, it is possible to easily and highly accurately adjust the discharge gap by a local heat generation near the magnet or a temperature change due to cooling due to the heat generating element and / or the heat absorbing element.

According to a fourth aspect of the invention, in the charging device according to the second aspect, the side plate is provided with temperature detecting means for detecting a temperature, and the signal detected by the temperature detecting means is supplied to the heating element and / or the heating element. The distance between the surface of the photoconductor and the discharge electrode is controlled by feeding back to the heat absorber. With this configuration, it is possible to control the discharge current in order to maintain the discharge condition at the optimum condition, but if the temperature coefficient of the magnetic force is known in advance by the type of magnetized body, the amount of temperature rise or temperature drop relative to the set temperature It can be controlled easily by detecting the minute and feeding it back to the heat absorbing / heating element.

According to a fifth aspect of the invention, in the charging device according to any of the second to fourth aspects, the heating element and / or the heat absorbing element is an electronic refrigeration element.
With this configuration, by using the electronic refrigeration element, heating and cooling can be easily controlled by switching the control current direction.

According to a sixth aspect of the invention, there is provided an image forming apparatus including the charging device according to any one of the first to fifth aspects.
With this configuration, in addition to the actions of claims 1 to 5, even if the temperature inside the machine changes during use of the image forming apparatus, the magnet temperature is controlled to a constant temperature by operating the heating element and / or the heat absorbing element. Therefore, the optimum state of the charging section can be kept constant.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an image forming apparatus including a charging device according to an embodiment of the present invention. As shown in FIG. 1, an image forming apparatus provided with this non-contact type charging device includes a photosensitive drum 11A on which an electrostatic latent image is formed.
A charging device 12 having a charging unit that performs a charging process in a non-contact manner with the photoconductor drum 11A; an exposure unit 13 that is an exposure unit for exposing a laser beam, reflected light from a document; and an electrostatic latent image on the photoconductor drum 11A. A developing roller 14 that is a developing unit that attaches toner to the toner, a power pack 15 that applies a discharge voltage to the charging device 12, and a transfer unit that transfers the toner image on the photosensitive drum 11A onto the recording paper 17. Transfer roller 16
And a cleaning device 18 which is a cleaning unit for cleaning the photosensitive drum 11A after the transfer processing.
And a surface potential meter 19 for measuring the surface potential of the photosensitive drum 11A. Note that, in FIG. 1, other functional units normally required in the electrophotographic process are omitted because they are not required in this specification.

FIG. 2A is a diagram showing a charging device of an embodiment according to the present invention, FIG. 2B is a diagram showing a modification of the charging device of FIG. 2A, and FIG. FIG. 3 is a plan view of the charging device shown in FIG.

In the charging device 12, as shown in FIGS. 2A and 3, the fixed magnet 21 and the fixed magnet 21 have the same poles facing each other, and the magnetic force is applied to the outside of the photosensitive drum 11A. The floating magnet 23 that floats and the discharge electrode 25 that is attached to the floating magnet 23 so as to face the photoconductor drum 11A.
A side plate 24 as a side plate holding body that regulates the attitude of the floating magnet 23; a heat sink / heat generator 26 provided on the outer peripheral surface of the side plate 24; and a temperature sensor 51 provided at the lower end of the side plate 24. I have it. The side plate 24 is integrally formed by injection molding. As the fixed-side magnet 21, a magnetized base in which the outer peripheral side of the photosensitive drum base is magnetized as the N pole and the inner peripheral side is magnetized as the S pole may be used.

The discharge electrode 25 has a low resistance member attached to the floating magnet 23 and a voltage is applied between the discharge electrode 25 and the photoconductor drum 11A to charge the photoconductor drum 11A by corona discharge.
In this case, if a metal wire is attached to the floating magnet 23 as a low resistance element, the discharge efficiency is particularly good.

As the heat-absorbing body 26, a heat-generating body, a heat-absorbing body,
Any of those having heat generating and heat absorbing functions can be used. For example, a panel heater can be used as the heating element, and a Peltier element, which is an electronic refrigeration element, can be used as the heat absorbing element, or one having heat generation and heat absorbing function. In FIG. 3, reference symbol S is a gap for allowing the floating magnet 23 to move up and down. The heat-absorbing body 26 may be provided on the inner peripheral surface of the side plate 24, as shown in FIG.

In the present invention, the charging device 12 is made completely non-contact, and the minute gap is stably maintained without causing the vibration like the charge wire to ensure the charging uniformity.

The principle configuration is magnetic levitation. That is, the magnetic substance of the same pole moves away by the repulsive force, but when the magnetic substance of the same pole is arranged in the vertical direction, the force remains due to the force balance due to gravity. By utilizing this principle and magnetizing a Gaussian amount of a magnet commensurate with gravity, the magnet can be stopped at a predetermined gap. That is, in the case of a parallel magnetic pole having a magnetic flux density G tesla of a weight W gram per unit length in the shape of a rod or plate, the force of the drop of Wg and the tip of the tip of the Wg at the acceleration g of gravity against the existence of the magnetic flux density G'tesla of the opposing magnet The repulsive force of GG '/ d and the attractive force GG' / (d + 1) of the same extreme part on the opposite side of the magnet having a different pole with a width of length l are balanced at a certain position. The distance between the magnets can be set to a desired value by arbitrarily selecting the magnetic forces of the stationary magnet 21 and the floating magnet 23 and the weight of the floating magnet 23.

The distance between the fixed magnet 21 and the floating magnet 2
Since a photoconductor having a predetermined thickness passes between the photoconductors 3 and 3, it is desirable that the length is about 5 mm to 10 mm. And the photosensitive drum 11A
The distance between the floating magnet 23 and the floating magnet 23 is preferably about 50 μm to 0.1 mm in order to prevent the charging of the surface of the photoconductor due to corona discharge and the dissipation of generated ozone. The distance can be adjusted by finely adjusting the stationary magnet 21 with a spacer interposed between the stationary photoconductor drum 11A and the wire charger attached to the lower end of the floating magnet 23.

By the way, the levitating magnet 23 repulsively levitated with the same pole falls and turns upside down or rotates to attract each other unless the opposite pole on the opposite side attracts the fixed magnet 21. The moment of this rotation becomes larger as the distance between the magnetic poles becomes larger in the case of a parallel magnetic field with respect to different poles of the same magnetic flux density, but in the magnetic field by the fixed side magnets 21 in the vicinity, the fixed side magnet 21 and the floating magnet 23 of different poles. The closer the end of the magnet is, the stronger the attractive force is.
It is better that the distance is as far as possible, that is, the distance between the NSs of the magnets is as large as possible.

Further, it is ideal that the magnetic line of force by the fixed-side magnet 21 is a straight line in the vertical direction and the levitation magnet 23 is on this line of magnetic force, and the line of magnetic force perfectly matches the line of force of the gravitational field. If the 23 NS pole is along this line of force, no rotational moment occurs. However, if magnetic poles of the same polarity exist, the magnetic field lines from the fixed-side magnet 21 will be
The magnetic field lines are repelled by the magnetism of No. 3 and are warped to the outside, and a slight deviation occurs in the shape accuracy of the floating magnet 23 and the accuracy of magnetization. Therefore, it is realistic to reduce the theoretical accuracy in consideration of productivity. Not.

Therefore, if the side plates 24 along the magnet are arranged as a sandwiching body on both sides of the long magnet, even if the magnet is rotatable, it cannot be inverted or rotated by the side plate 24. Further, if there is a deviation in the lengthwise direction (the rotation axis direction of the photoconductor drum 11A), it may shift to a direction in which the force is weak. Therefore, it is desirable to prevent the positional deviation also in the axial direction. Therefore, it is appropriate to make the side plate (holding body) 24 into a square shape. In that case, it is possible to form a flat shape by laminating four flat plates, but if the right and left dimensions of the through hole differ due to the amount of adhesive, the magnet will not be parallel to the photoconductor axis and Since the distance to the body differs depending on the place, the charging may be uneven in the axial direction.

In order to prevent this, it is desirable to integrally form the side plate 24 having a through hole, and such a shape can be easily manufactured by injection molding. Further, when the side plate 24 is a conductor, if the electrode under the magnet comes into contact with the magnet as it fluctuates up and down during voltage application, electricity may be electrically short-circuited, which may cause damage.
Is preferably an electrical insulator.

By the way, the distance (gap) between the surface of the photosensitive drum 11A and the discharge electrode 25, that is, the distance between the surface of the photosensitive drum and the lower end of the floating magnet 23 is determined by the discharge electrode 2
Since it is charged by moving corona ions from 5 to move corona ions to the surface of the photoconductor, the gap must be kept as accurate as possible for uniform charging. Therefore, in order to control the position of the floating magnet 23,
The fixed base of the fixed-side magnet 21 can be mechanically moved up and down to finely adjust the position, and the position of the levitation magnet 23 can be moved by the repulsive force accordingly. However, the adjustment gap can be adjusted more accurately with a simpler method. It was desired to make adjustments.

According to this charging device 12, the floating magnet 2
In 3, the repulsive force between the same poles as the fixed magnet 21 and the gravity acting on the levitation magnet 23 are balanced, and the float 3 stays at the balanced position. Since the side plate 24 is arranged so as to surround the side of the floating magnet 23, the movement of the floating magnet 23 is restricted by the side plate 24 except in the vertical direction.

The magnetic force of the permanent magnets used for the floating magnet 23 and the fixed magnet 21 has temperature dependency, and the magnetic force decreases as the temperature rises, and the magnetic force increases as the temperature falls. . Therefore, after the fixed-side magnet 21 is set, if the distance between the floating magnet 23 and the photosensitive drum 11A is not in the optimum discharge state, the magnetic force of the floating magnet 23 can be increased or decreased to adjust to a predetermined desired gap.

The magnetic force of the levitation magnet 23 can be increased or decreased by attaching a temperature controllable heating element or a cooling element to the side plate 24 which regulates the levitation magnet 23, or by using the side plate 24 itself as a heat generation cooling element. Is. A panel heater can be used as the heating element, and a Peltier element panel used for electronic refrigeration or the like can be used for both heating and cooling.

Further, a temperature sensor 51 as a temperature detector (temperature detecting sensor) is mounted in the near field of a magnet for controlling the temperature of the heat-generating cooling body to be precise, and a detection signal which is temperature information is absorbed by the heat-generating body. Give feedback to 26. It is possible to control the discharge current in order to maintain the discharge condition at the optimum condition, but if the temperature coefficient of the magnetic force is known in advance by the type of magnetized body, the temperature rise or temperature drop relative to the set temperature can be detected. By doing so, it is possible to easily control by feeding back to the heat absorbing and heating element.

It is desirable to use a non-magnetic toner as the toner. Originally, the toner is cleaned after the transfer process in the electrophotographic process, and should not go around to the charging part in the next process, but the magnetic toner leaking the cleaning is attracted to the charging part by the magnet in the charging method using this magnet and stains the charging part. . For this reason, there is a risk of uneven charging. Therefore, it is possible to prevent uneven charging as much as possible by using a non-magnetic toner.

Next, a basic image forming operation in this magnetic levitation charging type image forming apparatus will be described. When a DC voltage is supplied from the power pack 15 to the discharge electrode 25 floating on the photoconductor drum 11A, the photoconductor drum 1
The surface of 1A is uniformly charged to a high potential by corona discharge. Immediately after that, when the image light is applied to the surface of the photoconductor drum 11A by the exposure means 13, the photoconductor drum 11A is exposed.
The electric potential of the irradiated portion of is decreased. It is known that such a charging mechanism for the surface of the photoconductor drum 11A by the charging device 12 is a discharge according to Paschen's law in a minute space between the charging device 12 and the photoconductor drum 11A.

Since the image light has a distribution of the amount of light according to the image, when the image light is irradiated, the potential distribution corresponding to the recorded image, that is, the static electricity distribution, is generated on the surface of the photosensitive drum 11A by the irradiation of the image light. A latent image is formed. When the portion of the photoconductor drum 11A on which the electrostatic latent image is formed passes the developing roller 14 as described above, toner adheres according to the level of the potential, and a toner image that visualizes the electrostatic latent image is formed. It is formed. The recording paper 17 is conveyed by a registration roller (not shown) at a predetermined timing to the portion of the photoconductor drum 11A on which the toner image is formed, and the recording paper 17 overlaps the toner image. Then, after this toner image is transferred onto the recording paper 17 by the transfer roller 16, the recording paper 17 is separated from the photosensitive drum 11A. The separated recording paper 17 is conveyed through a conveyance path, heated and fixed by a fixing unit (not shown), and then discharged to the outside of the machine. When the transfer is completed in this manner, the surface of the photosensitive drum 1A is cleaned by the cleaning device 18, and further, by a quenching lamp (not shown).
The residual charges are removed, and the next image forming process is prepared.

According to the above image forming apparatus, the charging device 1
Since the second discharge electrode 25 is magnetically levitated and the vibration is prevented, the discharge electrode 25 and the surface of the photoconductor drum 11A can be arranged at a minute interval over the entire width, and the generation of ozone can be made extremely small. In addition, stable and uniform charging can be performed. Furthermore, since the discharge electrode 25 does not vibrate, the discharge electrode 25 and the photosensitive drum 1
1A does not come into contact with the surface of the photosensitive drum 1A, and a short circuit between the discharge electrode 25 and the photosensitive drum 11A can be prevented.
It is possible to prevent adverse effects such as image deterioration due to damage to the photosensitive drum 11A without damaging 1A. Further, the photosensitive drum 11A and the charging device 1 such as contact charging.
Since there is no part to be worn between the two, there is an advantage that it has high durability.

Further, the posture of the floating magnet 23 is set to the side plate 24.
Since it is regulated by, the floating magnet 23 can be stably levitated and the falling magnet can be prevented. Further, the positional deviation of the floating magnet 23 in the rotation axis direction of the photoconductor drum 11A can also be restricted. As a result, the discharge electrode 2 fixed to the lower surface of the floating magnet 23
It is possible to stably maintain the minute gap between the photosensitive drum 11A and the photosensitive drum 11A, and to ensure the uniformity of charging of the photosensitive drum 11A. Therefore, it is possible to prevent image deterioration due to uneven charging of the photoconductor drum 11A.

FIG. 4 is a diagram showing a main part of an image forming apparatus according to another embodiment of the present invention. In the image forming apparatus of this embodiment, a belt-shaped photoconductor 11B which is a flexible photoconductor is used in place of the photoconductor drum 11A described above. The belt-shaped photoconductor 11B is rotationally driven by the driving roller 41 and the driven roller 42. Around the belt-shaped photoconductor 11B, a charging device 12, an exposure unit 13, a surface potential meter 19, a developing roller 14, a transfer roller 16 and the like are provided.

FIG. 5 is a diagram showing a charging device of another embodiment according to the present invention. As shown in FIG. 5, the charging device 12 used in the image forming apparatus of FIG.
2, a fixed-side magnet 21 supported on the fixed-side magnet support 22 with the N-pole of the magnetic pole as the upper end, and the N-pole with the N-pole as the lower end to face the N-pole of the fixed-side magnet 21. The floating magnet 23, the discharge electrode 25 provided on the upper surface of the floating magnet 23 so as to face the photoconductor surface of the belt-shaped photoconductor 11B, the side plate 24 similar to the side plate shown in FIG. 3, and the side plate 24. Of the heat-absorbing body 26 provided on the outer surface, for example
And an electronic refrigeration element as a heating / cooling body. The charging device 12 is an example in which the fixed magnet 21 and the floating magnet 23 are attached below the belt-shaped photoreceptor 11B on the same surface (outside) of the belt-shaped photoreceptor 11B.
In this charging device 12, both the fixed magnet 21 and the floating magnet 23 can be heated and cooled. In this case, the fixed-side magnet support 22 may also be an electronic refrigeration element. The charging device 12 can be unitized by, for example, extending the lower end of the side plate 24 and attaching it to the stationary magnet support 22.

FIG. 6 is a view showing a charging device of another embodiment according to the present invention. As shown in FIG. 6, in this embodiment, the fixed-side magnet 21 is provided with an absorbing / heating element. In this way, the magnetic force of the fixed-side magnet 21 may be adjusted by controlling the temperature of the fixed-side magnet 21 by means of the heat absorbing / heating element.

(Embodiment 1) As shown in FIG. 1, a charging portion (charging device 12), an exposure portion (exposure means 13), a developing portion (developing roller 14), a transfer portion (transferring) around a photosensitive drum 11A. In an image forming apparatus having rollers 16), etc.,
At the upper part of the photosensitive drum 11A, a fixed side magnet having a lateral width of 3 mm, a height width of 8 mm, and a length of 320 mm, which is formed in a rectangular parallelepiped shape, has a magnetic flux density of 70 mT (millitesla) of 3 mm.
It is fixed to the main body side with the N pole as the upper part in the width part, and has the same shape as the fixed side magnet outside (above) the photoconductor and at 20 ° C
Then, a samarium (Sm) ferrite-based magnet having the same magnetic flux density was installed as a magnet on the floating side with the N pole facing down. At that time, the magnet on the levitation side is set in the side plate 24 having a rectangular frame shape in a plan view having a rectangular through hole so that the magnet on the levitation side is not inverted or laterally displaced, and the bottom surface of the side plate 24 is located 1 mm above the bottom surface of the magnet on the levitation side. The width of the through hole was set to 3.1 mm. As shown in FIG. 2, a panel heater and a temperature sensor 51 for controlling the temperature are attached to the side plate 24. Further, a tungsten wire of 20 μmφ fine wire is attached to the lower end of the magnet on the floating side. This thin wire is connected from the end of the magnet on the floating side to the high-voltage power supply by wiring.

The magnet on the floating side has a weight per unit size of 1.14 g / cm, and is repulsed from the same pole of the fixed side magnet and floats at a distance of 6 mm from the fixed side magnet. The weight of is almost negligible and does not affect the spacing.

By roughly adjusting the position of the fixed-side magnet up and down, the distance between the floating-side magnet and the photosensitive member surface is about 0.1 mm.
However, the discharge was uneven. Therefore, the magnet on the floating side was warmed while energizing the heating element attached to the side plate 24. The discharge could be made uniform by raising the temperature to about 15 ° C.
While rotating the photosensitive member in such a layout, a DC voltage of 2 kV was applied between the magnet and wire on the floating side and the photosensitive member, and the surface of the photosensitive member was charged by a minute gap discharge to form an image.

The image was well formed, and almost no ozone odor such as corona charging on the charge wire was detected. Further, there was no abnormality even after repeating 30,000 sheets or more, which was good. Furthermore, when the corona light at the time of discharge was observed in the darkness, it was still shining well. Although an attractive force should act between the charging device 12 and the photoconductor drum 11A by applying a voltage against the balance between the magnetic force and the gravity, the weight of the floating magnet 23 causes a large inertial force, and This is because the attraction is not enough to move it.

(Embodiment 2) As shown in FIG. 4, a charging section (charging device 12), an exposure section (exposure means 13), and a developing section (development) are provided around a belt-shaped photoreceptor 11B which is a flexible photoreceptor. In the image forming apparatus having the roller 14), the transfer portion (transfer roller 16), etc.
As shown in, width 3mm, height 8mm, length 320mm
The magnet on the fixed side formed in the rectangular parallelepiped shape has a magnetic flux density of 70 m.
A 3 mm wide portion of T (millitesla) was fixed with the N pole as the upper part. Then, between the belt-shaped photoconductor 11B and the fixed-side magnet, the wedge-shaped magnet on the floating side, which is a knife-edge magnet of wedge-shaped discharge having the same magnetic flux density as that of the fixed-side magnet, is floated with the N pole at the bottom. Therefore, the charging unit was installed.

A conductive thin wire is attached to the lower end of the wedge-shaped magnet in the axial direction in the axial direction so that a high voltage can be applied, and the wire is connected to a high voltage power source. At that time, the wedge-shaped magnet on the floating side is set in a side plate 24 having a rectangular frame shape in a plan view having a rectangular through hole so as not to be inverted or laterally displaced, and the upper surface of the side plate 24 is located above the head surface of the wedge-shaped magnet on the floating side. It was set to be 1 mm lower. The side plate 24 serving as the sandwich is made of ABS resin by injection molding, and the width of the hole is 1.1 mm. Further, as shown in FIG. A temperature sensor was attached like the charging device.

The wedge-shaped magnet on the floating side has a weight per unit size of 3.0 g / cm, and repels the same pole of the fixed side magnet and the distance between the fixed side magnet and the fixed side magnet is 10.0 mm. There is. By adjusting the position of the fixed magnet up and down, the distance between the wedge-shaped magnet on the floating side and the surface of the photoconductor is set to about 0.1 mm,
A heating element was energized at a temperature of 35 ° C. so that an optimum discharge state was obtained.

With such a layout, the belt-shaped photoreceptor 1
While rotating 1B, a DC voltage of 2 kV and 900 Hz between the wedge-shaped magnet on the floating side and the belt-shaped photoreceptor 11B,
An AC alternating voltage of kV was superimposed and applied, and the surface of the photoconductor was charged by a minute gap discharge to form an image. The image was well formed, and almost no ozone odor such as corona charge on the charge wire was detected. Further, the temperature inside the machine rose to 35 ° C. after repeated use, but there was no change in charging, and there was no abnormality even after repeating 30,000 sheets or more, which was good.

(Example 3) In Example 2, the charged state was 25 ° C.
The image was formed repeatedly by keeping the discharge part at 25 ° C. even when the temperature inside the machine rises, and good images and repeated durability were obtained as in Example 2. Was obtained.

(Comparative Example 1) In the image forming apparatus of Example 1, a rotatable charging roller was arranged as a charging section. Since the charging roller is in constant contact with the photoconductor drum, the charging roller and the photoconductor drum were repeatedly worn and the charging unevenness began to occur after 10,000 times, and the image quality was deteriorated.

(Comparative Example 2) The charging section using the charging roller of Comparative Example 1 was slightly lifted from the photosensitive drum and the image formation was repeated without contact. The roller end to maintain the gap has a large diameter and is in contact with the photoconductor.
After 10,000 times, the edges and the photoconductor were worn, and the variation in the charge amount began to increase, and the image quality deteriorated.

Comparative Example 3 In the image forming apparatus of the example, a charge wire type corona discharge housing was attached to the charging portion. A strong ozone odor was generated outside the apparatus each time the image forming operation was performed. Also, when observing the corona light of the discharge in the dark, it was observed that the corona light was constantly vibrating. The present invention is not limited to the above embodiment. That is, various modifications can be made without departing from the gist of the present invention.

[0055]

As described above, according to the first aspect of the invention, the generation of ozone is small, the photoconductor can be uniformly charged, and further, the photoconductor has a high durability, and the photoconductor surface It is possible to obtain a charging device in which fine adjustment of the distance between the discharge electrode and the discharge electrode is easy.

According to the second aspect of the invention, the discharge gap can be easily adjusted by the temperature change due to local heat generation or cooling near the magnet by the heat generating element and / or the heat absorbing element.

According to the third aspect of the invention, the heating element and / or the heat absorbing element can easily adjust the discharge gap with high accuracy by a local temperature change near the magnet or a temperature change caused by cooling.

Further, according to the invention of claim 4, it is possible to easily control by detecting the amount of temperature rise or the amount of temperature drop with respect to the set temperature and feeding it back to the heat absorbing and heating element.

Further, according to the invention of claim 5, by using the electronic refrigeration element, heating and cooling can be easily controlled by switching the control current direction.

According to the invention of claim 6, claim 1
In addition to the effects of 5 to 5, even if the temperature inside the apparatus changes during use of the image forming apparatus, the magnet temperature is controlled to a constant temperature by operating the heat generating element and / or the heat absorbing element to optimize the charging unit. Can be held constant.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus including a charging device according to an exemplary embodiment of the present invention.

FIG. 2A is a diagram showing a charging device according to an embodiment of the present invention, and FIG. 2B is a diagram showing a modified example of the charging device of FIG. 2A.

FIG. 3 is a plan view of the charging device shown in FIG.

FIG. 4 is a diagram showing a main part of an image forming apparatus according to another embodiment of the invention.

FIG. 5 is a diagram showing a charging device according to another embodiment of the present invention.

FIG. 6 is a diagram showing a charging device according to another embodiment of the invention.

[Explanation of symbols]

11A photoconductor drum 11B Belt-shaped photoreceptor (flexible photoreceptor) 12 Charging device (charging part) 13 Exposure means (exposure section) 14 Developing roller (Developing section) 15 power packs 16 Transfer roller (transfer section) 17 Recording paper 21 Fixed magnet 23 Floating magnet 24 Side plate (holding body) 25 Discharge electrode (Discharge part) 26 Heat absorbing / heating body (heating / cooling body) 51 Temperature sensor

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Claims (6)

[Claims] 1. A charging device comprising a floating magnet that is magnetically levitated with respect to a stationary magnet and a discharge electrode facing the surface of the photoconductor, wherein the temperature of at least one of the stationary magnet and the floating magnet is changed. A charging device comprising a heating element and / or a heat absorbing element to be provided on the fixed-side magnet side and / or the floating-side magnet side. 2. The charging device according to claim 1, wherein the heating element and / or the heat absorbing element is provided on a side plate disposed on a side surface side of the floating magnet. 3. The distance between the surface of the photoconductor and the discharge electrode is controlled by changing the temperature of at least one of the fixed magnet and the floating magnet. Charging device. 4. The side plate is provided with a temperature detecting means for detecting a temperature, and by feeding back a signal detected by the temperature detecting means to the heating element and / or the heat absorbing element,
The charging device according to claim 2, wherein a distance between the surface of the photoconductor and the discharge electrode is controlled. 5. The charging device according to claim 2, wherein the heating element and / or the heat absorbing element is an electronic refrigeration element. 6. An image forming apparatus comprising the charging device according to claim 1.