JPH0412383A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent temperature rise at the two terminal parts of a fixing means, to reduce the heat capacity of the fixing means, and to attain miniaturization and light weight even when a sheet of small size is fixed successively by cooling a part not coming in contact with a material to be fixed in the fixing means. CONSTITUTION:A cooling fan 19 and a duct 21 that is the passage of the air sucked by the cooling fan are provided at the upper side of a fixing roller 3. The tip of the duct 21 is branched in two directions, and the aperture part of each tip is arranged so as to confront with both terminal parts of the fixing roller 3. The cooling fan 19 and the duct 21 comprise a cooling means, and the air in the neighborhood of the part not coming in contact with the sheet P of small size i.e. both terminal parts of the fixing roller 3 is sucked, and is exhausted to the outside, which cools both terminal parts of the fixing roller 3. Therefore, since it is possible to prevent the temperature rise occurring at the surface of the fixing roller not coming in contact with the sheet, the heat capacity of the fixing roller 3 is not necessary to be increased. Thereby, the light weight and the miniaturization of a device can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an image forming apparatus having a fixing device.

(Prior Art) A conventional image forming apparatus has a photoreceptor drum for carrying an electrostatic latent image within the apparatus main body, and after the surface of the photoreceptor drum is uniformly charged by a charging device, the electrostatic latent image is A latent image is formed. The electrostatic latent image formed on the surface of the photosensitive drum is developed by a developing device to form a toner image. This toner image is conveyed to a transfer device and transferred onto paper.

Next, after the paper is peeled off from the photoreceptor drum by a peeling device, the toner image is fixed onto the paper in a fixing device.

This fixing device has a fixing roller that rotates in a fixed direction, a halogen lamp that heats the fixing roller, and a pressure roller that rotates while being in pressure contact with the fixing roller. As it passes, the toner image is fixed onto the paper.

(Problem to be Solved by the Invention) By the way, in such a contact heating type fixing device, it is assumed that the maximum size of paper, that is, the paper of a size that contacts the entire surface of the fixing roller, is to be continuously fixed. The temperature distribution on the surface of the fixing roller is made uniform within a predetermined set temperature range.

Therefore, when continuously fixing paper of a size smaller than the maximum size, the temperature of the surface of the fixing roller that does not come into contact with the paper may rise above the set temperature.

Therefore, by increasing the heat capacity of the fixing roller,
This is to prevent the temperature of the surface of the fixing roller that does not come into contact with the paper from rising.

However, increasing the heat capacity of the fixing roller increases the time required for warming up and increases the weight of the fixing device.

The present invention has been made in view of the above problems, and provides a lightweight and compact image forming apparatus that prevents temperature rise on the surface of the fixing roller even when sheets of paper smaller than the maximum size are continuously fixed. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) Means provided by the present invention for achieving the above object includes a contact heating fixing means that has a heat source inside and heats the object by contacting it; The fixing device includes a cooling device for cooling a portion of the fixing device that is not in contact with the object to be fixed.

(Function) According to the present invention, the object to be fixed is heated by contacting with a heating means having a heat source inside, and the object to be fixed is fixed. In addition, the heating means includes a cooling means for cooling a portion of the heating means that does not come into contact with the fixing object, that is, a portion that does not apply heat to the fixing object, so that it can be used even when a small size fixing body is used. To reliably prevent temperature rise in areas where the fixing body does not come into contact even when

(Example) Hereinafter, an example according to the present invention will be described in detail with reference to the drawings.

First, the configuration will be explained with reference to FIG.

FIG. 1 is a sectional view showing a fixing device 1 and its surroundings in an image forming apparatus according to the present invention. A halogen lamp 5 is disposed inside a fixing roller 3 that rotates clockwise. The fixing roller 3 is heated by this halogen lamp 5,
The heated portion, which is the surface of the fixing roller 3, is set uniformly within a predetermined temperature range. That is, the halogen lamp 5 uniformly heats the heated portion of the fixing roller 3 serving as a fixing means in the roller axial direction.

A pressure roller 7 that rotates in the opposite direction, that is, counterclockwise, is arranged below the fixing roller 3. This pressure roller 7 is brought into contact with the fixing roller 3 with a predetermined pressing force due to the elastic force of a spring 9. A guide plate 11 is disposed upstream of the portion where the fixing roller 3 and the pressure roller 7 come into pressure contact. A transfer device (not shown) is disposed further upstream of the conveyance path passing through the guide plate 11, and the toner image on the photosensitive drum (not shown) is transferred onto a sheet of paper.

The paper onto which the toner image has been transferred is conveyed via the guide plate 11 to a fixing area where the fixing roller 3 and the pressure roller 7 are brought into pressure contact. When the paper P, which is the fixing body, is conveyed to the fixing area, the toner image is transferred to the paper P as it passes through the fixing area.
It will be fixed to.

A paper ejection guide 13 and a paper ejection roller 15 are provided on the downstream side of the fixing area.
is provided, and the sheet P on which fixing has been completed is discharged to a paper discharge tray (not shown) via a paper discharge guide 13 and a paper discharge roller 15.

A temperature detector 17 such as a thermistor is provided approximately at the center of the fixing roller 3 in the direction of its rotational axis and is in contact with the surface of the fixing roller 3 to detect the temperature of the surface of the fixing roller 3 .

Further, the fixing device 1 has a temperature control circuit (not shown), and maintains the temperature of the surface of the fixing roller 3 at a predetermined set temperature by controlling the halogen lamp 5 according to the detection information from the temperature detector 17. .

Above the fixing roller 3 is a cooling fan 19 and a duct 2 which is a passage for the air sucked by the cooling fan 19.
1 is provided. The tip of the duct 21 is branched into two directions, and the openings at each tip are arranged to face both ends of the fixing roller 3.

The cooling fan 19 and the duct 21 constitute a cooling means, which sucks air from the heated portion of the surface of the fixing roller 3 that is not in contact with the small paper P, that is, near both ends of the fixing roller 3. By discharging it to the outside,
Both ends of the fixing roller 3 are cooled. In addition, a shutter 23 is provided at each opening at the tip of the duct 21;
A rotating mechanism such as a rotating shaft is provided for rotating the
By rotating the shutter 23 via this rotation mechanism, the opening degree θ of each opening can be adjusted. A detector for detecting the size of the fed paper P is provided near a paper feed cassette (not shown) for feeding the paper P, and the detection information of this detector, that is, the size of the fed paper P, is The opening degree θ of the shutter 23 is adjusted depending on the size of the paper P, the size of the opening of the duct 21, the capacity of the cooling fan 19, the temperature of the surface of the fixing roller 3, etc. For example, when the size of the fed paper P is the smallest, the shutter 23 is rotated to the position po, and the opening degree θ is set to the maximum. Further, as the size of the paper P increases, the opening degree θ is set smaller, and when the size of the paper P is maximum, that is, when the paper P is in contact with the entire surface of the fixing roller 3. , the shutter 23 is in position Pc
, the opening degree θ is set to 0, and the openings at each tip are closed.

In the embodiment described above, the suction type cooling fan 19 was used to exhaust the air near both ends of the fixing roller 3 to the outside. It may be configured to cool both ends of the fixing roller 3 by spraying it to both ends.

Next, the configuration of the circuit section will be explained with reference to FIG.

The CPU 27 is connected to a control panel 29 and manually inputs information related to various operations. Further, the detector 33 detects the size of the paper P fed from the paper feed cassette 31 and outputs the detection information to the CPU 27.

A motor M is a motor for driving the cooling fan 19, and is connected to each collector of the transistors TRI and TR2. A DC power supply is applied to the emitter of the transistor TRI, and the emitter of the transistor TR2 is connected to ground. Transistor TRI is a transistor for controlling the rotational speed of motor M,
The transistor TR2 is a transistor for turning the motor M on and off. The bases of the transistors TRI and TR2 are connected to the CPU 27, and the CPU 27 controls the rotational speed and on/off state of the motor M via the transistors TRI and TR2.

The drive circuit 35 includes transistors TR3 and TR4 and shutter control sections 37 and 39. The base of the transistor TR3 is connected to the CPU 27, and
The collector is connected to a shutter control section 37. Further, the base of the transistor TR4 is connected to the CPU 27, and the collector is connected to the shutter control section 39.

The emitters of transistors TR3 and TR4 are connected to ground. The shutter control unit 37 drives the shutter 23 provided at one opening of the duct 21 to obtain an opening degree θ.
control. Similarly, the shutter control section 39
The opening degree θ is controlled by driving the shutter 23 provided at the other opening.

One opening of the duct 21 is arranged to face one end of the fixing roller 3, and the other opening is arranged to face the other end of the fixing roller 3. The air sent in is blown to both ends of the fixing roller 3 through each opening of the duct 21.

Next, the action will be explained.

First, the action during warming up will be explained.

When a power switch or the like provided on the control panel 29 is operated, the CPU 27 performs warming-up control. That is, the CPU 27 uses the transistor T
Turn off R2 to stop the rotation of motor M, and
The pair of shutters 23 are rotated to the position Pc via the drive circuit 35 to close each opening. Thereby, the temperature of the surface of the fixing roller 3 due to the operation of the halogen lamp 5 can be quickly raised, and the time required for warming up can be shortened.

Next, when the CPU 27 determines that the size of the paper P fed from the paper feed cassette 31 is the maximum size based on the information related to the operation from the control panel 29 or the detection information from the detector 33, the drive circuit 35, the pair of shutters 23 are rotated toward the position Pc side, and the duct 21
Close each opening.

Therefore, when the paper P is in contact with the entire surface of the fixing roller 3, cooling of the surface of the fixing roller 3 is stopped, and a good fixing process is performed without heat loss.

Next, when the CPU 27 determines that the size of the paper P fed from the paper feed cassette 31 is less than the maximum size based on the information related to the operation from the control panel 29 or the detection information from the detector 33, the TR1
and TR2 to control the rotational speed of the motor M according to the size of the paper P. Moreover, the CPU 27 is a drive circuit 35.
to control the rotation angle of the shutter 23, that is, the duct 2
The opening degree θ of the opening 1 is controlled according to the size of the paper P. As a result, air from the outside is blown onto both ends of the fixing roller 3, that is, the surface of the fixing roller 3 with which the paper P does not come into contact, thereby cooling the fixing roller 3.

[Effects of the Invention] As described above, according to the present invention, the part of the fixing means that does not come into contact with the object to be fixed is cooled, so that when continuously fixing small size paper Also, it is possible to prevent temperature rise at both ends of the fixing means. Therefore, the heat capacity of the fixing means can be reduced, and a lightweight and compact image forming apparatus can be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the present invention, and FIG. 2 is a block diagram of a control section. 3... Fixing roller 5... Halogen lamp 7... Pressure roller 19... Cooling fan 21... Duct 23... Shutter M... Motor P... Paper

Claims (1)

[Scope of Claims] A contact heating fixing means having an internal heat source and heating the fixing object in contact with the fixing object; and a cooling means cooling a part of the fixing means that is not in contact with the fixing object. An image forming apparatus characterized by: