JP4615768B2 - Charging device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charging device provided in an image forming apparatus using an electrophotographic system such as a copying machine, a facsimile machine, and a printer, and an image forming apparatus provided with the charging device.
[0002]
[Prior art]
In order to form an image by electrophotography, it is necessary to perform so-called charging in which a positive or negative charge is given to the photosensitive member in advance in order to hold the charge carrier toner.
[0003]
Conventionally, in order to perform this charging, a corona charging method using corona discharge using a fine metal wire has been used. However, when this conventional corona charging method is used, there is a problem in that ozone is generated by discharge.
[0004]
Therefore, recently, a contact charging method in which charging is performed in contact with a photosensitive member has been adopted. Charger shapes used in the contact charging method include a rotating roller method and a non-rotating brush method, and charging methods include a charge injection method and a minute gap discharge method, each having advantages and disadvantages.
[0005]
The feature of these contact charging methods is that ozone is generated very little during discharge because of discharge or charge injection at a close distance. However, the biggest drawback of the contact type is that if the toner adhering to the photoreceptor cannot be completely removed when it comes to the charging part in the process of rotation, it will adhere to the charging part and accumulate gradually. This is to weaken the performance or transfer the image again to the photoconductor to cause smearing of the image.
[0006]
Further, according to the contact charging method, since the charger is in contact with the photosensitive member, the components of the roller and brush as the charger gradually deposit on the surface, contaminating the photosensitive member and causing white spots on the image. A so-called bleed phenomenon causing a defect occurred. Furthermore, since the charger and the photoconductor are in contact with each other, there is a problem that the photoconductor is worn away and durability is deteriorated.
[0007]
A non-contact charging method is desirable in order to prevent such problems, and in order to reduce ozone generation as much as possible, it is necessary to reduce the gap between the photoreceptor and the charger.
[0008]
However, in corona discharge using a fine metal wire, the fine metal wire vibrates, as can be seen from careful observation of the state during discharge.
In the non-contact type charging, even if it is a minute gap, in principle, it is charging by movement of corona ions, and the minimum discharge start distance at atmospheric pressure in the air based on Paschen's law is about 70 μm.
[0009]
[Problems to be solved by the invention]
However, it is difficult to secure this distance across the entire width with a vibrating wire, and it may come into contact with the photoconductor in the center, and if touched, it may short-circuit at that portion and damage the photoconductor. Cannot be uniformly charged.
[0010]
On the other hand, it is considered to keep the distance by giving the end part a predetermined thickness by the conventional roller method, but when the sliding is constantly in contact with the photosensitive member, the photosensitive member or the roller sliding part is worn. However, there is a problem that the uniformity of charging is impaired by repeated use.
[0011]
Therefore, the present invention generates less ozone, can uniformly charge the photoconductor, has high durability, and facilitates fine adjustment of the distance between the surface of the photoconductor and the discharge electrode. It is an object of the present invention to provide a charging device and an image forming apparatus.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention is directed to a charging device including a floating electrode that is magnetically levitated with respect to a fixed magnet, and a discharge electrode that faces the surface of the photoreceptor. The charging device is characterized in that a heating element and / or an endothermic body that changes the temperature of at least one of the side magnets are provided on the fixed side magnet side and / or the floating side magnet side. In this configuration, fine adjustment can be easily performed by a heat generation element and / or a heat absorption element by local heat generation near the magnet or a temperature change due to cooling. Furthermore, when used in an image forming apparatus, the temperature inside the machine may change during use. Even in such a case, the magnet temperature is controlled to a constant temperature by operating the heating element and / or the heat absorption element. The optimum state of the charging unit can be kept constant.
[0013]
According to a second aspect of the present invention, in the charging device according to the first aspect, the heating element and / or the endothermic body is provided on a side plate disposed on a side surface of the floating magnet. Yes. In this configuration, the discharge gap can be easily adjusted by a local heat generation near the magnet or a temperature change due to cooling by the heat generator and / or the heat absorber.
[0014]
According to a third aspect of the present invention, in the charging device according to the first aspect, the distance between the surface of the photoreceptor and the discharge electrode is controlled by changing a temperature of at least one of the fixed side magnet and the floating side magnet. It is characterized by that. In this configuration, it is possible to easily adjust the discharge gap with high accuracy by a local heat generation near the magnet or a temperature change due to cooling by the heat generator and / or the heat absorber.
[0015]
According to a fourth aspect of the present invention, in the charging device according to the second aspect, the side plate is provided with temperature detecting means for detecting a temperature, and a signal detected by the temperature detecting means is supplied to the heating element and / or the heat absorbing body. The distance between the photosensitive member surface and the discharge electrode is controlled by feedback. In this configuration, the discharge current can be managed to keep the discharge condition at the optimum condition, but if the temperature coefficient of magnetic force is known in advance by the type of magnetized body, the temperature rise or temperature drop with respect to the set temperature By detecting the minute, it can be easily controlled by feeding back to the heat absorption and heating element.
[0016]
According to a fifth aspect of the present invention, in the charging device according to any one of the second to fourth aspects, the heating element and / or the endothermic element is an electronic refrigeration element. In this configuration, by using an electronic refrigeration element, heating and cooling can be easily controlled by switching the control current direction.
[0017]
A sixth aspect of the present invention is an image forming apparatus including the charging device according to any one of the first to fifth aspects. In this configuration, in addition to the effects of the first to fifth aspects, the magnet temperature is controlled to a constant temperature by operating the heating element and / or the heat absorbing element even when the temperature inside the apparatus is changed during use of the image forming apparatus. Thus, the optimum state of the charging unit can be kept constant.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view 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, and a charging unit that performs a non-contact charging process on the photosensitive drum 11A. A charging device 12 having an exposure unit, an exposure unit 13 serving as an exposure unit for laser light, reflected light from a document, and the like, a developing roller 14 serving as a developing unit for attaching toner to the electrostatic latent image on the photosensitive drum 11A, and a charging device. 12, the power pack 15 for applying a discharge voltage to the sheet 12, the transfer roller 16 serving as a transfer unit for transferring the toner image on the photosensitive drum 11A to the recording paper 17, and the photosensitive drum 11A after the transfer process. For example, the cleaning device 18 is a cleaning unit 18 and a surface potential meter 19 for measuring the surface potential of the photosensitive drum 11A. In FIG. 1, other functional units normally required in the electrophotographic process are omitted because they are not required in this specification.
[0019]
2A is a diagram showing a charging device according to an embodiment of the present invention, FIG. 2B is a diagram showing a modification of the charging device in FIG. 2A, and FIG. It is a top view of the charging device shown to (A).
[0020]
As shown in FIGS. 2A and 3, the charging device 12 is levitated so that the same polarity is opposed to the fixed side magnet 21 and the fixed side magnet 21 and magnetically levitates outside the photosensitive drum 11A. A side magnet 23, a discharge electrode 25 attached to the floating side magnet 23 so as to face the photosensitive drum 11 </ b> A, a side plate 24 as a side plate sandwiching body that regulates the attitude of the floating side magnet 23, and an outer peripheral surface of the side plate 24 And a temperature sensor 51 provided at the lower end of the side plate 24. The side plate 24 is integrally formed by injection molding. As the fixed-side magnet 21, a magnetized substrate in which the outer peripheral side of the photosensitive drum substrate is magnetized to the N pole and the inner peripheral side to the S pole may be used.
[0021]
The discharge electrode 25 attaches a low resistance to the floating magnet 23 and applies a voltage between the discharge drum 25 and the photosensitive drum 11A to charge the photosensitive drum 11A by corona discharge. In this case, if a metal wire is attached to the floating magnet 23 as a low resistance, the discharge efficiency is good.
[0022]
As the heat-absorbing and heating element 26, any of a heating element, a heat-absorbing body, a heat-generating and heat-absorbing function, and the like 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 functions. In FIG. 3, symbol S is a gap for allowing the floating magnet 23 to move up and down. As shown in FIG. 2 (B), the heat absorption and heating element 26 may be provided on the inner peripheral surface of the side plate 24.
[0023]
In the present invention, the charging device 12 is completely non-contacted, and the minute gap is stably maintained without causing a vibration like a charge wire to ensure the uniformity of charging.
[0024]
Its principle configuration is magnetic levitation. That is, the magnetic material of the same polarity moves away by the repulsive force, but when the magnetic material of the same polarity is arranged in the vertical direction, it stays where the force is balanced by gravity. Using this principle and magnetizing a Gaussian amount of magnet that matches the gravity, it can be held at a predetermined gap. That is, the parallel magnetic poles of the magnetic flux density G Tesla having a weight W gram per unit length of a rod-like or plate-like shape, the force of dropping Wg with the acceleration of gravity g against the presence of the opposing magnetic flux density G 'Tesla and the tip The repulsive force of GG ′ / d and the attractive force GG ′ / (d + 1) at the opposite extreme side of the magnet having a different polarity 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 force of the fixed magnet 21 and the floating magnet 23 and the weight of the floating magnet 23.
[0025]
The distance is preferably about 5 mm to 10 mm because a photoconductor having a predetermined thickness passes between the fixed magnet 21 and the floating magnet 23. The distance between the photoconductor drum 11A and the floating magnet 23 is preferably about 50 μm to 0.1 mm in order to prevent charging of the photoconductor surface due to corona discharge and dissipation of generated ozone.
The distance can be adjusted by finely adjusting the stationary magnet 21 with a spacer interposed between the stationary photosensitive drum 11A and the wire charger attached to the lower end of the floating magnet 23.
[0026]
By the way, the floating magnet 23 repelled and levitated with the same polarity is reversed or rotated and attracts and falls if there is no support because the opposite pole is attracted to the fixed magnet 21. If the magnetic field is a parallel magnetic field with respect to different poles of the same magnetic flux density, the moment of rotation increases as the distance between the magnetic poles increases. However, in the magnetic field generated by the nearby fixed side magnet 21, the fixed side magnet 21 and the floating side magnet 23 having a different polarity. The closer the end of the magnet is, the stronger the attractive force is. Therefore, it is preferable that the different polarity of the floating side magnet 23 is as far as possible from the fixed side magnet 21, that is, the distance between NS of the magnets is as large as possible.
[0027]
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 floating side magnet 23 is on this line of magnetic force, and the line of magnetic force completely coincides with the line of gravity of the gravitational field. If the pole is along this line of force, there will be no rotational moment. However, if there are magnetic poles of the same polarity, the magnetic lines of force of the fixed magnet 21 are repelled by the magnetism of the floating magnet 23 and the magnetic lines of curvature are deflected to the outside, so that there is a slight deviation in the shape accuracy and magnetization accuracy of the floating magnet 23. It takes place and considering the productivity, it is not realistic to reduce the theoretical accuracy.
[0028]
Therefore, if the side plates 24 along the magnets are arranged on both sides of the long magnet as a sandwiching body, even if the magnets can be rotated, they are obstructed by the side plates 24 and cannot be reversed or rotated. Further, if there is a deviation in the longitudinal direction (the direction of the rotation axis of the photoconductor drum 11A), there is a possibility that the direction will be shifted in a direction where the force is weak. Accordingly, it is appropriate that the side plate (clamping body) 24 is squarely enclosed. In that case, it is possible to form four wells by sticking four flat plates. However, if the left and right dimensions of the through hole are different due to the amount of adhesive, the magnet will not be parallel to the photoreceptor axis, and Since the distance from the body varies depending on the location, the charging may become uneven in the axial direction.
[0029]
In order to prevent this, it is desirable to integrally mold the side plate 24 having a through hole, and such a shape can be easily manufactured by injection molding.
Also, if the side plate 24 is a conductor, if the electrode under the magnet contacts with the magnet when it fluctuates up and down during voltage application, electricity may short-circuit and cause damage, so the side plate 24 may be damaged. An insulator is desirable.
[0030]
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 corona discharged from the discharge electrode 25 to the surface of the photosensitive member. Since the corona ions are moved and charged, the gap must be kept as accurate as possible in order to charge uniformly. For this reason, in order to control the position of the floating side magnet 23, the position of the floating side magnet 23 is moved by a repulsive force by mechanically moving the fixing base of the fixed side magnet 21 up and down and finely adjusting the position. However, it has been desired to adjust the adjustment gap with higher accuracy by a simpler method.
[0031]
According to this charging device 12, the floating magnet 23 balances the repulsive force of the same polarity with the fixed magnet 21 and the gravity acting on the floating magnet 23, and remains floating at the balance position. Since the side plate 24 is disposed so as to surround the floating side magnet 23, the movement of the floating side magnet 23 is restricted by the side plate 24 except in the vertical direction.
[0032]
The permanent magnets used in the floating side magnet 23 and the fixed side magnet 21 have a magnetic force that is temperature-dependent. The magnetic force decreases as the temperature increases, and the magnetic force increases as the temperature decreases. Therefore, after setting the fixed side magnet 21, when the distance between the floating side magnet 23 and the photosensitive drum 11 </ b> A is not in the optimal discharge state, the magnetic force of the floating side magnet 23 can be adjusted to a predetermined desired gap by increasing / decreasing the magnetic force.
[0033]
The magnetic force of the floating magnet 23 can be increased or decreased by attaching a temperature-controllable heating element or cooling body to the side plate 24 that regulates the floating magnet 23, or by using the side plate 24 itself as a heat generating cooling body.
A panel heater can be used as the heating element, and a Peltier element panel used for electronic refrigeration can be used for both heating and cooling.
[0034]
Further, a temperature sensor 51 as a temperature detector (temperature sensor) is attached to the near field of the magnet to be controlled in order to make the temperature control of the heat generating / cooling body precise, and a detection signal as temperature information is fed back to the heat absorption / heat generating body 26. To do. Although it is possible to manage with the discharge current to keep the discharge condition at the optimum condition, if the temperature coefficient of the magnetic force is known in advance by the type of magnetized body, it detects the temperature rise and temperature drop with respect to the set temperature By doing so, it can be easily controlled by feeding back to the heat absorption and heating element.
[0035]
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 wrap around the charged part in the next process, but the magnetic toner that leaks from the cleaning is attracted to the charged part by the magnet in the charging method using this magnet to contaminate the charged part. . For this reason, there is a risk of occurrence of uneven charging. Therefore, the use of nonmagnetic toner can prevent the occurrence of uneven charging as much as possible.
[0036]
Next, a basic image forming operation in the 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 photosensitive drum 11A, the surface of the photosensitive drum 11A is uniformly charged to a high potential by corona discharge. Immediately thereafter, when image light is irradiated onto the surface of the photosensitive drum 11A by the exposure means 13, the potential of the irradiated portion of the photosensitive drum 11A decreases. It is known that the charging mechanism to the surface of the photosensitive 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 photosensitive drum 11A.
[0037]
Since the image light has a light amount distribution corresponding to the image, when the image light is irradiated, the potential distribution corresponding to the recorded image on the surface of the photosensitive drum 11A by the irradiation of the image light, that is, an electrostatic latent image. Is formed. When the portion of the photosensitive drum 11A on which the electrostatic latent image is thus formed passes through the developing roller 14, toner adheres according to the level of the potential, and a toner image that visualizes the electrostatic latent image becomes a toner image. It is formed. The recording paper 17 is conveyed by a registration roller (not shown) at a predetermined timing to the portion of the photosensitive drum 11A where the toner image is formed, and overlaps the toner image. Then, after the toner image is transferred to 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 outside the apparatus. When the transfer is completed in this manner, the surface of the photosensitive drum 1A is cleaned by the cleaning device 18, and residual charges are removed by a quenching lamp (not shown), so that the next image forming process is performed. Prepared for.
[0038]
According to the above image forming apparatus, since the discharge electrode 25 of the charging device 12 is magnetically levitated and vibration is prevented, the discharge electrode 25 and the surface of the photosensitive drum 11A can be arranged at a minute interval over the entire width. The generation of ozone can be made extremely small, and stable and uniform charging can be performed. Further, since the discharge electrode 25 does not vibrate, the discharge electrode 25 and the surface of the photoconductor drum 11A do not come into contact with each other, a short circuit between the discharge electrode 25 and the photoconductor drum 11A can be prevented, and the photoconductor drum 11A is damaged. Therefore, it is possible to prevent adverse effects such as image deterioration due to damage to the photosensitive drum 11A. Further, since there is no worn portion between the photosensitive drum 11A and the charging device 12 such as contact charging, there is an advantage of having high durability.
[0039]
Further, since the attitude of the floating magnet 23 is regulated by the side plate 24, the floating magnet 23 can be stably levitated and can be prevented from falling. Further, the positional deviation of the floating magnet 23 in the rotation axis direction of the photosensitive drum 11A can be restricted. Thereby, the minute gap between the discharge electrode 25 fixed on the lower surface of the floating magnet 23 and the photosensitive drum 11A can be stably maintained, and the uniformity of charging of the photosensitive drum 11A is ensured. be able to. Therefore, it is possible to prevent image deterioration due to uneven charging of the photosensitive drum 11A.
[0040]
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-like photoconductor 11B, which is a flexible photoconductor, is used instead of the above-described photoconductor drum 11A. This belt-like photoconductor 11B is rotationally driven by a driving roller 41 and a driven roller. Around the belt-like photoreceptor 11B, a charging device 12, an exposure means 13, a surface potential meter 19, a developing roller 14, a transfer roller 16, and the like are provided.
[0041]
FIG. 5 is a view showing a charging device according to another embodiment of the present invention.
As shown in FIG. 5, the charging device 12 used in the image forming apparatus of FIG. 4 is supported on the fixed side magnet support 22 and the fixed side magnet support 22 with, for example, the N pole of the magnetic pole as the upper end. The fixed magnet 21, the floating magnet 23 arranged with the N pole at the lower end to oppose the N pole of the fixed magnet 21, and the photosensitive surface of the belt-shaped photosensitive body 11 </ b> B on the upper surface of the floating magnet 23. The discharge electrode 25 provided in this manner, the side plate 24 similar to the side plate shown in FIG. 3, and the electronic refrigerating element that is a heating / cooling body as the heat absorbing / generating body 26 provided, for example, on the outer surface of the side plate 24 And. The charging device 12 is an example in which the fixed side magnet 21 and the floating side magnet 23 are attached below the belt-like photoconductor 11B on the same surface (outside) of the belt-like photoconductor 11B. This charging device 12 is an example in which both the fixed side magnet 21 and the floating side magnet 23 can be heated and cooled. In this case, the stationary magnet support 22 may also be an electronic refrigeration element. Moreover, this charging device 12 can be unitized by extending the lower end of the side plate 24 and attaching it to the fixed-side magnet support 22, for example.
[0042]
FIG. 6 is a diagram showing a charging device according to another embodiment of the present invention.
As shown in FIG. 6, in this embodiment, the fixed-side magnet 21 is provided with an absorption and heating element. In this manner, the magnetic force of the fixed-side magnet 21 may be adjusted by controlling the temperature of the fixed-side magnet 21 with the heat absorbing and heating element.
[0043]
Example 1
As shown in FIG. 1, image formation having a charging unit (charging device 12), an exposure unit (exposure unit 13), a developing unit (developing roller 14), a transfer unit (transfer roller 16) and the like around the photosensitive drum 11 </ b> A. In the apparatus, a fixed-side magnet formed in a rectangular parallelepiped shape having a lateral width of 3 mm, a height of 8 mm, and a length of 320 mm is disposed at the upper position in the photosensitive drum 11A with a 3 mm width portion having a magnetic flux density of 70 mT (millitesla). The upper part is fixed to the main body side, and the samarium (Sm) ferrite magnet having the same magnetic flux density at 20 ° C. and the same shape as the fixed side magnet outside (upper) of the photoconductor, with the N pole at the bottom. It was installed as a floating side magnet. At that time, the magnet on the floating side is set in the side plate 24 having a rectangular frame shape with a rectangular through hole so as not to be reversed or laterally shifted, and the bottom surface of the side plate 24 is 1 mm above the bottom surface of the magnet on the floating side. The width of the through hole was 3.1 mm long. As shown in FIG. 2, the side plate 24 is provided with a panel heater and a temperature sensor 51 that can control the temperature. A tungsten wire of 20 μmφ thin wire is attached to the lower end of the floating magnet. This fine wire is connected to the high-voltage power source from the floating magnet end by wiring.
[0044]
The weight of the floating side magnet per unit dimension is 1.14 g / cm, repels the same pole of the fixed side magnet and floats at a distance of 6 mm from the fixed side magnet. Is negligible and does not affect the spacing.
[0045]
The position of the fixed-side magnet was roughly adjusted up and down to set the distance between the floating-side magnet and the surface of the photoreceptor to about 0.1 mm, but there was uneven discharge. Therefore, the floating magnet was heated while energizing the heating element attached to the side plate 24. The discharge could be made uniform at a temperature rise of about 15 ° C.
While rotating the photosensitive member in such a layout, a DC voltage of 2 kV was applied between the floating-side magnet and wire and the photosensitive member, and the surface of the photosensitive member was charged with a minute gap discharge to create an image.
[0046]
The image was created well and almost no ozone odor like corona charging on the charge wire was detected. In addition, there was no abnormality even with repetition of 30,000 sheets or more, and it was good. Furthermore, the corona light at the time of discharge was observed in the dark. This is because an attractive force should act between the charging device 12 and the photosensitive drum 11A by applying a voltage to the balance between the magnetic force and the gravity. This is because it is not attractive enough to move.
[0047]
(Example 2)
As shown in FIG. 4, a charging unit (charging device 12), an exposure unit (exposure unit 13), a developing unit (developing roller 14), a transfer unit (transferring) around a belt-shaped photoconductor 11B, which is a flexible photoconductor. As shown in FIG. 5, a fixed-side magnet formed in a rectangular parallelepiped shape having a width of 3 mm, a height of 8 mm, and a length of 320 mm is provided at a position below the belt-like photoconductor 11B in an image forming apparatus having a roller 16). A 3 mm wide part with a density of 70 mT (millitesla) was fixed with the north pole on top. A floating wedge-shaped magnet, which is a wedge-shaped discharge wedge-edge magnet having the same magnetic flux density as that of the fixed magnet, is levitated between the belt-shaped photoreceptor 11B and the fixed magnet with the N pole as the lower part. The charging part was installed.
[0048]
A conductive thin wire is attached and connected to a high voltage power source so that a high voltage can be applied from the lower end in the axial direction of the wedge-shaped magnet on the floating side. At this time, the wedge-shaped magnet on the floating side is set in the side plate 24 having a rectangular frame shape having a rectangular through-hole so as not to be reversed or laterally displaced, and the upper surface of the side plate 24 is higher than the head surface of the wedge-shaped magnet on the floating side. It set so that it might become 1 mm lower part. The side plate 24 serving as a sandwiching body is made of ABS resin by injection molding, the hole width is 1.1 mm, and as shown in FIG. A temperature sensor was installed in the same manner as the charging device.
[0049]
The weight of the floating-side wedge-shaped magnet per unit dimension is 3.0 g / cm, repels the same polarity of the fixed-side magnet and floats at a distance of 10.0 mm from the fixed-side magnet. 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 photosensitive member is set to about 0.1 mm, and the heating element is energized so that the optimum discharge state is obtained at a temperature of 35 ° C. .
[0050]
While rotating the belt-shaped photoconductor 11B in such a layout, a DC voltage of 2 kV and an AC AC voltage of 900 Hz and 2 kV are superimposed and applied between the wedge-shaped magnet on the floating side and the belt-shaped photoconductor 11B. Then, the surface of the photoreceptor was charged with a minute gap discharge to form an image.
The image was created well and almost no ozone odor like corona charging on the charge wire was detected.
In addition, the temperature inside the apparatus increased to 35 ° C. with repeated use, but there was no change in charging, and there was no abnormality even after repeating 30,000 sheets or more.
[0051]
(Example 3)
In Example 2, the charged state was set to be optimal at 25 ° C., and even when the in-machine temperature increased, the discharge part was kept at 25 ° C. to repeatedly form an image. A good image and repeated durability were obtained.
[0052]
(Comparative Example 1)
In the image forming apparatus of Example 1, a charging roller that can rotate as a charging unit is disposed. Since the charging roller is constantly in contact with the photosensitive drum, the charging roller and the photosensitive drum are worn by repeated wear, and after 10,000 times, charging unevenness starts to occur and the image quality deteriorates.
[0053]
(Comparative Example 2)
The charging part using the charging roller of Comparative Example 1 was slightly lifted from the photosensitive drum, and image formation was repeated without contact. The roller end for maintaining the gap has a large diameter and is in contact with the photoconductor. However, after 20,000 times, the end and the photoconductor are worn and the variation in charge amount begins to increase, resulting in deterioration of image quality. .
[0054]
(Comparative Example 3)
In the image forming apparatus of the example, a charging wire type corona discharge housing was attached to the charging portion. A strong ozone odor was generated outside the device every time image formation was activated. When the corona light from the discharge was observed in the dark, it was observed that the corona light was constantly oscillating.
In addition, this invention is not limited to the said Example. That is, various modifications can be made without departing from the scope of the present invention.
[0055]
【The invention's effect】
As described above, according to the first aspect of the present invention, the generation of ozone is small, the photosensitive member can be uniformly charged, has high durability, and further, the surface of the photosensitive member and the discharge electrode A charging device can be obtained in which fine adjustment of the interval is easy.
[0056]
According to the second aspect of the present invention, the discharge gap can be easily adjusted by a temperature change caused by local heat generation or cooling in the vicinity of the magnet by the heat generator and / or the heat absorber.
[0057]
Further, according to the invention of claim 3, the discharge gap can be easily adjusted with high accuracy by the heat generation and / or the heat absorption body and the local heat generation near the magnet or the temperature change caused by the cooling.
[0058]
Further, according to the invention of claim 4, it is possible to easily control by detecting the temperature rise or temperature drop with respect to the set temperature and feeding back to the heat absorbing / generating body.
[0059]
According to the invention of claim 5, heating and cooling can be easily controlled by switching the control current direction by using the electronic refrigeration element.
[0060]
According to the sixth aspect of the invention, in addition to the effects of the first to fifth aspects, the heating element and / or the endothermic element can be operated even when the temperature inside the apparatus is changed during use of the image forming apparatus. It is possible to keep the optimum state of the charging unit constant by controlling the magnet temperature to a constant temperature.
[Brief description of the drawings]
FIG. 1 is a schematic view of an image forming apparatus including a charging device according to an embodiment of the present invention.
2A is a diagram illustrating a charging device according to an embodiment of the present invention, and FIG. 2B is a diagram illustrating a modification of the charging device in 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 present 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 present invention.
[Explanation of symbols]
11A Photosensitive drum
11B Belt-shaped photoreceptor (flexible photoreceptor)
12 Charging device (charging unit)
13 Exposure means (exposure section)
14 Developing roller (developing part)
15 Power Pack
16 Transfer roller (transfer section)
17 Recording paper
21 Fixed magnet
23 Floating magnet
24 Side plate (clamping body)
25 Discharge electrode (discharge part)
26 Heat-absorbing / heating element (heating / cooling body)
51 Temperature sensor

Claims (6)

In the charging device provided with the discharge electrode facing the surface of the photoreceptor on the floating magnet that floats magnetically with respect to the fixed magnet,
A charging device, wherein a heating element and / or an endothermic body that changes a 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. 2. The charging device according to claim 1, wherein the heat generating body and / or the heat absorbing body are provided on a side plate disposed on a side surface side of the floating side magnet. The charging device according to claim 1, wherein a distance between the surface of the photosensitive member and the discharge electrode is controlled by changing a temperature of at least one of the fixed side magnet and the floating side magnet. The side plate is provided with temperature detection means for detecting temperature, and a signal detected by the temperature detection means is fed back to the heating element and / or heat absorption body to control the distance between the surface of the photoreceptor and the discharge electrode. The charging device according to claim 2, wherein: The charging device according to claim 2, wherein the heating element and / or the endothermic body is an electronic refrigeration element. An image forming apparatus comprising the charging device according to claim 1.

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