JPS6234180A - Fixing device of electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To attain an optimum fixing even in the case of a thick transfer sheet for a offset master and the like by providing a path switching member and selecting roller fixing and/or radiant heat fixing. CONSTITUTION:A roller fixing device 16, a radiant heat fixing device 17 and the sheet path switching member 18 are disposed at the downstream side of a photosensitive unit 5. The radiant heat fixing device 17 is constructed with a heat-resistant conveyance drum 22 such as a wire net and a heat source 23. A normal transfer sheet is roller-fixed, guided on the switching member 18 and discharged outside the machine. On the other hand, the switching member 18 takes the position of a chain line 18A in the case of the thick sheet for a offset master and the like. After fixed, the sheet reaches the radiant heat fixing device 17, clamped 24 by a claw, fixed by the heat source 23 and discharged to a tray 33. Accordingly the thick sheet can be satisfactorily fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a fixing device for an electrophotographic copying machine, and more particularly, to a fixing device having a heated roller fixing device and a radiant heat fixing device.

(Prior art) Devices for thermally fixing powder images obtained by electrophotography on copy sheets such as photoreceptor sheets, transfer paper, and offset master sheets include roller fixing devices that pass copy sheets between a pair of rollers; Radiant heat fixing devices that irradiate a powder image with heat rays are well known. On the other hand, a radiant heat fixing device has excellent fixing properties for surface images.

The printing durability of offset masters largely depends on the quality of the image fixation.The paper used for offset master sheets is thicker than the commonly used copy sheets. Therefore, in order to fix the offset master sheet, it is necessary to sufficiently fix the line image and the plane image by increasing the amount of heat for thermal fixing.

The fixing speed is fast for fixing on general copy sheets.
A roller fixing device is advantageous because it is safe and effective, but when fixing an offset master sheet, considering its low fixing properties and the fixation of surface images, it is more durable to use both a roller fixing device and a radiant heat fixing device. You can obtain an offset master with high printability.

(Objective) An object of the present invention is to provide a heat fixing device that exhibits excellent fixing properties, particularly for offset master sheets.

(Structure) The present invention is equipped with a roller fixing device and a radiant heat fixing device, and a copy sheet on which a toner image is formed can be transferred to only the roller fixing device or to both the roller fixing device and the radiant heat fixing device. It is designed so that it can be selectively guided by a passage switching member.

The present invention will be explained below with reference to one illustrated embodiment.

FIG. 1 is a sectional view of an electrophotographic copying machine equipped with a fixing device according to the present invention, in which an original placed on a reciprocating original platen glass 1 is illuminated by a light source 2 while a lighting window 3 is illuminated. While moving in the direction, an electrostatic latent image is formed by the optical system unit 4 on a photoconductor unit 5 including a photoconductor belt, and this electrostatic latent image is developed with toner by a developing device 6 including a magnetic brush. It will be done.

A copy sheet 7 is stored at the bottom of the copying machine. One copy sheet sent out by a paper feed roller 8 is transferred to a transfer section having a transfer charger 12 by a pair of sheet conveyance rollers 9 and 10 and a pair of registration rollers 11. 13, and the toner image on the photoreceptor unit 5 is transferred thereto. The copy sheet S onto which the toner image has been transferred is sent to the fixing device 15 via the guide plate 14.

The developing device 15 includes a roller fixing device [16], a radiant heat fixing device 17, and a sheet path switching member 18.

The roller fixing device 16 consists of a heating roller 20 containing a heat source 19 and a roller 21 that is in pressure contact with the heating roller 20.
Further, the radiant heat fixing device 17 includes a heat-resistant conveying drum 22 made of wire mesh or the like and a heat source 23.

The conveyance drum 22 is provided with a clamp claw 24 that grips the leading edge of the offset master sheet. This clamp claw 24 has a similar structure to a clamp claw normally provided in an offset printing machine, and is provided with an opening/closing operation by an arm 26 whose base end is fixed to a clamp claw shaft 25 and a fixed cam 27. It will be done.

That is, the roller 28 provided at the free end of the arm 26.

As shown in the figure, when the clamp claw 24 is in pressure contact with the large diameter portion 27a of the cam 27, the clamp claw 24 is kept open, the conveyance drum 22 rotates in the direction of the arrow, and the clamp claw 24
When the roller 28 is positioned to receive the leading edge of the offset master sheet sent out from the roller fixing device 16, the roller 28 moves from the large diameter portion 27a of the cam 27 to the small diameter portion 2.
It drops to 7b and closes.

The sheet path switching member 18 has its base pivotally connected to a stationary part of the fixing device by a shaft 29, and is configured to be able to swing between a first position shown by a solid line and a second position shown by a chain line 18A. has been done. This sheet path switching member 18 is switched to the first position when one normal copy sheet 7 is fed, and to the second position when an offset master sheet different from the copy sheet 7 is fed. The offset master sheet is inserted into the copying machine through its own paper feed port 30, and is then sent to the optical system unit 5 by the conveyance roller 10 in the same way as the copy sheet 7.

A sheet detection switch 31 is arranged in the paper feed port 30, and when this switch 31 detects the leading edge of the inserted sheet, the sheet path switching member 18 is switched to the second position based on this detection operation. At the same time, in conjunction with the operation of the sheet path switching member 18, the heat source 23 is energized to prepare for radiant heat fixing, and the offset master sheet having the toner image transferred thereto is transferred to the roller fixing device [16].
, after passing through a pair of conveying rollers 32, the tip thereof is held by a clamp claw 24 and conveyed, and after being subjected to a fixing action by a heat source 23, it is discharged onto a paper discharge tray 33.

The energization of the heat 'g23 and the switching operation of the sheet path switching member 18 may be performed based on the operation of a detection switch 34 disposed between the roller fixing device 16 and the conveying roller 32.

The detection switch 34 is effective only when activated after the first detection switch 31 is activated, and its operation is invalid when it detects a copy sheet 7 that does not activate the first detection switch 31.

It is also possible to control the conveyance drum 22 so that it is normally stopped, rotated based on a signal from the detection switch 34, rotated once, and then stopped.

When performing normal copying, the copy sheet 7 is used for copying by operating a print button (not shown), and the copy sheet to which the toner image has been transferred is fixed by the roller fixing device 16. After receiving the sheet, the sheet is guided by the transport roller pair 33 and the upper surface of the sheet path switching member 18 and sent out of the machine.

The radiant heat fixing device is advantageous not only for offset master sheets but also for thick copy sheets and copies with many side images, so when making many such copies,
Of course, instead of inserting copy sheets one by one from the paper feed port 25, it is possible to feed the copy sheets automatically and use the radiant heat fixing device, as in the case of the copy sheet 7.

(Effects) According to the present invention, optimal fixing can be performed depending on the type of copy sheet containing an offset master.

A simple explanatory diagram of the V side is a sectional view showing an example of an electrophotographic copying machine having the fixing device of the present invention.

16...Roller fixing device, 17...Radiant heat fixing device, 18...Sheet path switching member.

Claims (1)

[Claims] A roller fixing device and a radiant heat fixing device for fixing the toner image on the sheet, and a radiant heat fixing device disposed between the two fixing devices, and selectively transferring the copy sheet that has passed through the roller developing device into and outside the radiant heat fixing device. A fixing device for an electrophotographic copying machine having a sheet path switching member for guiding the sheet.