JPH04310988A - Drum heating device - Google Patents

Abstract

PURPOSE:To adopt simple structure and to uniformly heat a rotary drum in its circumferential direction by arranging a magnet forming a magnetic field passing through the circumference of a drum elementary tube, therein. CONSTITUTION:In a drum heating device heating the rotary drum having the drum elementary tube 100 made of a conductive material, the magnet 20 forming the magnetic field passing through the circumference of the drum elementary tube 100 is arranged. Desirably, the coefficient of the thermal expansion of the magnet 20 and the drum elementary tube 100 is set so that the magnet 20 is brought into contact with the inner periphery of the drum elementary tube 100 at a prescribed temp. or more, and rotated together with the drum elementary tube 100. At this time, when the drum elementary tube 100 is rotated, it crosses the magnetic field, and an eddy current is generated around the whole the drum elementary tube 100. Consequently, the drum elementary tube 100 generates heat by Jule heat accompanying with the eddy current, to be uniformly heated over the full arc without requiring a power source. Thus, electrical wiring is not required, structure is simplified, and reduction in cost is attained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drum heating device for heating a rotating drum such as a photosensitive drum installed in an image forming apparatus such as a copying machine or a printer.

0002

[Prior Art] The characteristics of the photosensitive material coated on the photosensitive drum of an electrophotographic copying machine change depending on the temperature.
In particular, the charging ability and sensitivity are significantly reduced at low temperatures. In order to compensate for changes in characteristics of the photosensitive material due to temperature, the photosensitive drum is equipped with a heating device.

[0003] As this type of drum heating device, an electric heater is generally used. This electric heater was developed in Japanese Patent Application Publication No. 53
As shown in JP-A-47838, JP-A-54-30047, and JP-A-55-53376,
It is usually incorporated inside the photoreceptor drum, and from the viewpoint of uniformly heating the photoreceptor drum over its entire circumference,
In many cases, a seat heater is attached to the entire circumference of the inner surface.

0004

[Problems to be Solved by the Invention] When an electric heater is incorporated inside the photoreceptor drum as described above, it becomes difficult to connect the electric heater to various process devices such as a charging charger, a developing unit, a transfer charger, etc. arranged around the photoreceptor drum. This eliminates interference with the heater, which is convenient for uniformly heating the photoreceptor drum in the circumferential direction. However, on the other hand, the electric heater within the photoreceptor drum must be connected to an external power source, which complicates the wiring structure. In particular, when the electric heater inside the sheet heater that is attached to the inner surface of the photoreceptor drum rotates as the photoreceptor drum rotates, the wiring at the joint that connects the fixed side and the rotating side of the wiring. The disadvantage is that the structure becomes complicated.

The present invention solves the above-mentioned drawbacks of the prior art, and its purpose is to provide a drum heating device that does not require electrical wiring, has a simple structure, and can heat a rotating drum uniformly in the circumferential direction. There is a particular thing.

[0006]

Means for Solving the Problems The drum heating device of the present invention is a drum heating device for heating a rotating drum having a drum tube made of a conductive material. The above object is achieved by arranging a magnet that forms a magnetic field that penetrates the circumferential surface of the magnet.

[0007] Preferably, the coefficients of thermal expansion of both magnets are set so that the magnet comes into contact with the inner peripheral surface of the drum tube at a predetermined temperature or higher and rotates with the drum tube. Preferably, means is provided for moving the magnet toward and away from the drum tube depending on the temperature of the drum tube.

[0008]

[Operation] According to the above configuration, when the drum tube rotates,
The drum tube crosses the magnetic field, which generates eddy currents around the entire circumference of the drum tube. As a result, the drum tube generates heat due to Joule heat associated with the eddy current, and as a result, the drum tube is uniformly heated over its entire circumference without a power source.

[0009]

[Examples] Examples of the present invention will be described below.

FIG. 1 shows an electrophotographic copying machine to which the present invention is applied, in which light I corresponding to an original image is applied to the surface of a photosensitive drum 10 rotated in the direction of arrow A via a mirror 1. is exposed. Prior to exposure, the surface of the photosensitive drum 10 is uniformly charged by the main charger 2, and an electrostatic latent image is formed in the exposed area. Next, the developing unit 3 supplies toner to this electrostatic latent image, thereby forming a toner image. The toner image is conveyed to the position of the transfer charger 4 as the photosensitive drum 10 rotates. A sheet of paper is conveyed to the position of the transfer charger 4 in synchronization with the rotation of the photoreceptor drum 10, and the toner image on the photoreceptor drum 10 is transferred to the sheet of paper. The paper onto which the toner image has been transferred is peeled off from the surface of the photoreceptor drum 10 by a peeling charger 5 and conveyed to a position of a fixing device (not shown). Then, after the fixing process is completed, it is discharged outside the machine.

After the transfer process, some toner that does not contribute to the transfer remains on the surface of the photosensitive drum 10 as residual toner, but the cleaner section 6 scrapes off the residual toner from the surface of the photosensitive drum 10. Thereafter, the static elimination lamp 7 eliminates the residual charge on the photoreceptor drum 10.

Next, details of the photoreceptor drum 10 and the drum heating device incorporated in the photoreceptor drum 10 will be explained with reference to FIG. The photosensitive drum 10 is formed by coating a drum tube 100 made of a conductive material such as aluminum with a photosensitive material. Flanges 11 are attached to both ends of the photosensitive drum 10. A drum support shaft 12 passes through the center of the flange 11. Drum support shaft 12
is fixed horizontally and rotatably supports the photosensitive drum 10 via the flange 11 . Then, the photosensitive drum 10 is rotated in the circumferential direction together with the flange 11 by a driving means (not shown) connected to the main motor.

The drum heating device of the present invention incorporated into the photosensitive drum 10 has a cylindrical magnet 20 disposed inside the photosensitive drum 10 . The magnet 2
0 has approximately the same overall length as the photoreceptor drum 10, and has north poles 20a and south poles 20b arranged alternately in the circumferential direction. The magnet 20 forms a magnetic field B shown by a broken line in the figure over its entire length and circumference on its outer surface side. The magnetic field B penetrates the circumferential surface of the photoreceptor drum 10, more specifically, the drum tube 100. The magnet 20 is attached to the drum support shaft 12 via a connecting member 21.

In addition, the outer circumferential surface of the magnet 20 has a uniform slight gap G in the circumferential direction, so that the outer circumferential surface of the magnet 20 is connected to the photoreceptor drum 1 with a uniform slight gap G in the circumferential direction.
It faces the inner peripheral surface of 0. Gap G is drum tube 1
Difference in thermal expansion coefficient between 00 and magnet 20 (magnet 20
>Drum tube 100). Therefore,
When the temperature inside the machine reaches a predetermined temperature or higher, the outer peripheral surface of the magnet 20 comes into contact with the inner peripheral surface of the drum tube 100, and the magnet 20 rotates together with the photoreceptor drum 10. On the other hand, at a temperature below a predetermined temperature, the gap G is ensured and the two do not rotate together.

In the above configuration, when a copying operation is performed at a temperature below a predetermined temperature, the photosensitive drum 10 rotates in the circumferential direction, and the drum tube 100 crosses the magnetic field B accordingly. As a result, according to the law of electromagnetic induction, the drum material tube 10
An eddy current C shown in FIG. 3 is generated on the surface of 0. Therefore,
The drum tube 100 generates heat due to the eddy current C, and eventually,
The photosensitive drum 10 is heated uniformly over its entire length and circumference without a power source. Therefore, if such a drum heating device is incorporated into the photosensitive drum 10, there will be no reduction in charging ability or sensitivity at low temperatures. Moreover, according to the drum heating device having such a configuration, electrical wiring for connecting the drum heating device to a power source becomes unnecessary. Furthermore, since the drum heating device is disposed inside the photoconductor drum 10, it does not interfere with the main charger 2, developing unit 3, transfer charger 4, etc. disposed on the outer circumferential side of the photoconductor drum 10.

On the other hand, when the temperature is above a predetermined temperature, the magnet 20 rotates together with the drum tube 100, so the drum tube 100 does not cross the magnetic field B in this case. Therefore,
The photosensitive drum 10 is not heated unnecessarily.

FIG. 4 shows another embodiment of the invention. In this embodiment, the magnet 20 has a north pole 20a and a south pole 2.
0b are butted against each other to form a rod shape. The magnet 20 faces the inner surface of the photoreceptor drum over its entire length. The magnet 20 is attached to the drum support shaft 12 via a connecting member 21. magnet 20
The mounting position is set at a position substantially opposite to the developing unit 3 disposed on the outer surface side of the photoreceptor drum 10.

In the case of this embodiment as well, when the photosensitive drum 10 rotates at a temperature below a predetermined temperature, the drum tube 100 crosses the magnetic field B, and as a result, the photosensitive drum 1
0 heating is performed. Further, according to this embodiment, due to the above-mentioned mounting structure, the carrier in the developer stored in the developing unit 3 is not attracted to the magnet 20 and is not consumed. Therefore, the copy image quality is not impaired.

FIG. 5 shows yet another embodiment of the invention. In this embodiment, a magnet 20 similar to the previous embodiment is used.
is attached to the drum support shaft 12 via a plate spring 25 made of a normal material and a plate spring 26 made of a shape memory alloy. The operating temperature of the shape memory alloy forming the leaf spring 26 is, for example, 20°C. When the internal temperature of the photoreceptor drum 10 is below this operating temperature, the normal leaf spring 2
The elastic force of the leaf spring 5 exceeds the elastic force of the leaf spring 26. This results in
The positional relationship between the magnet 20 and the magnetic field B is as shown in FIG. 6(a). On the other hand, when the internal temperature of the photoreceptor drum 10 exceeds the operating temperature of the shape memory alloy forming the leaf spring 26, the elastic force of the plate spring 26 exceeds the elastic force of the normal plate spring 25. Thereby, the positional relationship between the magnet 20 and the magnetic field B becomes the state shown in FIG. 6(b). Therefore, in the former state, the drum tube 100 crosses the magnetic field B, so the photoreceptor drum 10 is heated, and in the latter state, the drum tube 100 does not cross the magnetic field B, so the photoreceptor drum 10 is not heated. Therefore, according to this embodiment, unnecessary heating of the photoreceptor drum 10 is prevented. Further, since the movement of the magnet 20 toward and away from the photosensitive drum 10 is performed using the shape memory alloy, no power source is required for this movement. In addition,
Depending on the temperature of the photoreceptor drum 10, the photoreceptor drum 10
It is also possible to preheat the photosensitive drum 10 by rotating it in advance before the photosensitive drum 10 starts its normal rotation operation.

In the above embodiments, the present invention is applied to heating a photoreceptor drum, but it can be similarly applied to other objects to be heated.

[0021]

[Effects of the Invention] According to the drum heating device of the present invention as described above,
No power supply is required to heat the drum, eliminating the need for electrical wiring. Therefore, the structure becomes simple and costs can be significantly reduced. Furthermore, there is no possibility of wire breakage, etc.
This has the advantage of reducing the frequency of maintenance.

Further, especially according to the drum heating device according to the second or third aspect, the drum tube is not heated unnecessarily.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view of a copying machine to which the present invention is applied.

FIG. 2 is a cross-sectional view schematically showing the drum heating device of the present invention.

FIG. 3 is a perspective view showing the principle of generation of eddy current.

FIG. 4 is a sectional view schematically showing another embodiment of the drum heating device.

FIG. 5 is a sectional view schematically showing still another embodiment of the drum heating device.

6 is a diagram illustrating the operation of the drum heating device shown in FIG. 5. FIG.

[Explanation of symbols]

10 Photoreceptor drum 12 Drum support shaft 20 Magnet 20a N pole 20b S pole 100 Drum tube B Magnetic field C Eddy current

Claims (3)

[Claims] 1. A drum heating device for heating a rotating drum having a drum tube made of a conductive material, wherein a magnet is provided inside the drum tube to form a magnetic field that penetrates the circumferential surface of the drum tube. Drum heating device installed. 2. The drum heating device according to claim 1, wherein the coefficient of thermal expansion of both magnets is set so that the magnet contacts the inner circumferential surface of the drum tube at a predetermined temperature or higher and rotates with the drum tube. . 3. The drum heating device according to claim 1, further comprising means for moving the magnet toward and away from the drum tube in accordance with the temperature of the drum tube.