JPH01122851A - Fixing device - Google Patents

Abstract

PURPOSE:To enable reliable detection of the passage of a sheet to be printed even when the sheet to be printed is thermally deformed, by a method wherein a protrusion part is formed on a guide surface on the other side of a sheet guide pair and facing a detecting lever position. CONSTITUTION:A protrusion part 18a to correct the passage of a curved sheet 6 to be printed to the detecting lever 16 side is formed to a central part positioned facing the tip of a detecting lever 16 of a sheet to be printed passage detector 15. A slit 18b through which a peel claw 14 and the tip part of the detecting lever 16 pass is formed in the central part of the protrusion part 18a. If so formed sheet guides 18 make a pair, even if the sheet 6 to be printed is about to pass in a manner to avoid the detecting lever 16, the protrusion part 18a corrects the curve of the sheet 6 to be printed to force it to work the detecting lever 16. Thus, the sheet to be printed passage detector 15 enables reliable detection of the passage of the sheet 6 to be printed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fixing device used in an electrophotographic device, etc.
In particular, the present invention relates to the detection of passage of a printing sheet passing through the fixing device.

[Conventional technology]

As shown in FIG. 7, the electrophotographic apparatus uniformly charges a photosensitive drum 1 with a charger 2, exposes it with an exposure device 3, and
A developing device 4 develops the toner to form a toner image. The toner image is transferred onto a printing sheet 6 by a transfer device 5, fixed on the printing sheet 6 by a fixing device 7, and the printing sheet 6 containing the fixing agent is discharged outside the machine.

As shown in FIGS. 8 and 9, the fixing device 7 includes a heating roll 8 that has a heating element inside and whose surface is coated with a heat-resistant mold release material, and a heating roll 8 that cooperates with the heating roll 8 to provide a heating element. A pressure roller 9 is provided to press the printing sheet 6, and the toner image is thermally fixed on the printing sheet 6 passing between the pair of rollers while being pressed. The printing sheet 6 that has passed between the heating roll 8 and the pressure roll 9 passes between the sheet guides 10 and 11,
It is discharged to the outside of the fixing device by a pair of discharge rolls 12 and 13. The peeling claw 14 peels off the printing sheet 6 wound around the heating roll 8.

The detection lever 16 of the sheet passing detector 15 passes through the sheet guide 10 and projects between the sheet guides 10.11, and prevents the sheet 6 from passing between the sheet guides 10.11. Detect. The control system is for printing sheet 6
is not detected by the printing sheet passage detector 15, it is determined that a jam has occurred, the execution of the electrophotographic process is stopped, and a message to that effect is displayed.

Note that such a fixing device 7 is assembled on a fixing device base 17.

By the way, the heating roll 8 in such a fixing device 7
Since the temperature of the printing sheet 6 reaches a high temperature of 100° C. or higher, the printing sheet 6 that passes between the heating roll 8 and the pressure roll 9 is thermally deformed, and the detection lever 16 of the printing sheet passage detector 15 is not correctly detected. There is a problem that it becomes unable to function and malfunctions.

This phenomenon will be explained in detail with reference to FIGS. 10 and 11. Note that both drawings are views of the heating roll 8 and the pressure roll 9 as viewed from the discharge side.

FIG. 10 shows a case where highly hygroscopic paper is used as the printing sheet 6 at a high temperature.

(a) shows the state before the printing sheet 6 is deformed, and (
b) shows the state after deformation. In this example, when the printing sheet 6 passes between the heating roll 8 and the pressure roll 9, the heating roll 8 side is strongly heated, so moisture evaporation on the heating roll 8 side is significant, and the heating roll 8 side is intensely heated. Shrink. For this reason, the printing sheet 6 is curved convexly toward the pressure roll 9 side.

FIGS. 11(a) and 11(b) show a case where paper or an OHP sheet with low hygroscopicity is used as the printing sheet 6. In FIG. In this example, the printing sheet 6 on the heating roll 8 side is strongly elongated due to thermal expansion, and therefore is curved convexly toward the heating roll 8 side.

The detection lever 16 of the printing sheet passage detector 15 passes through the sheet guide 10 on the pressure roll 9 side and passes through the sheet guide 1.
Since it protrudes between 0.11 and 0.11 degrees, there is no particular problem when the printing sheet 6 is deformed convexly toward the pressure roll 9.
If the printing sheet 6 is curved convexly toward the heating roll 8 side, the printing sheet 6 may pass around the tip of the detection lever 15 and cannot be detected.

In such a case, there is a problem in that the control system determines that a jam has occurred and stops execution of the process.

Note that this type of fixing device is disclosed in Japanese Patent Publication No. 61-42267.

[Problem that the invention seeks to solve]

As described above, the conventional fixing device detects the passage of the printing sheet when the heating roll side stretches and curves due to thermal expansion caused by the heating roll, such as dry paper or OHP sheet. There was a problem that the device could not detect the passage of the covered sheet.

Therefore, an object of the present invention is to enable reliable detection of the passage of a printing sheet even when the printing sheet is thermally deformed.

[Means for solving problems]

In order to achieve this object, the present invention provides a heating roll provided with a heating element therein, a pressure roll that presses an image receiving sheet in cooperation with the heating roll, and a method for passing between these rolls. a pair of sheet guides for guiding the top and bottom of the sheet to which a toner image has been thermally fixed; and a detection lever protruding from one side of the pair of sheet guides between the pair of sheet guides. The fixing device is characterized in that a protrusion is provided on the guide surface on the other side of the pair of sheet guides, facing the position of the detection lever.

[Effect]

Even if the printed sheet leaves between the heating roll and the pressure roll and is curved due to thermal expansion, it will not bend between the pair of sheet guides.
At the position of the detection lever of the printing sheet passage detector, the protruding portion corrects it, passes through the position of the detection lever, and acts on it, ensuring that it is detected by the printing sheet passage detector. .

〔Example〕

The fixing device according to the present invention will be specifically explained with reference to FIGS. 1 to 6.

Note that the same reference numerals are given to the same components as those of the conventional fixing device described above, and detailed description thereof will be omitted.

The sheet guide 18 is a sheet guide of the present invention provided in place of the sheet guide 11 of the conventional device, and has a curved central portion facing the tip of the detection lever 16 of the printing sheet passage detector 15. A protrusion 18a is formed to correct the path of the printed sheet 6 toward the detection lever 16 side. This protrusion 18a is formed by extruding the plate material of the sheet guide 18, and a slit 18b is provided in the center of the protrusion 18a for passing the tip of the peeling claw 14 and the detection lever 16. .

With a pair of sheet guides using the sheet guide 18 as described above, even if the printing sheet 6 curves due to thermal expansion and tries to avoid the detection lever 16 and pass through, the protrusion will prevent the sheet from forming, as shown in FIG. 18a corrects the curvature of the printing sheet 6 and causes the detection lever 16 to act accordingly. Therefore, the printing sheet passage detector 15 can reliably detect the passage of the printing sheet 6.

〔Effect of the invention〕

As described above, according to the present invention, the protrusion provided on the sheet guide corrects the curvature of the printing sheet and causes this to reliably act on the detection lever of the printing sheet passage detector. The passage of any sheet having any thermal deformation characteristics can be reliably detected.

[Brief explanation of the drawing]

1 to 6 show a fixing device according to the present invention,
Figure 1 is a vertical side view, Figure 2 is a perspective view of the main part, Figure 3 is a bottom view of the sheet guide, and Figure 4 is IV-mV of Figure 3.
5 is a view taken along the Q arrow in FIG. 3, FIG. 6 is an explanatory diagram of the operation, FIGS. 7 to 11 show a conventional fixing device, and FIG. 7 is an electrophotographic apparatus. FIG. 8 is a vertical side view of the fixing device, FIG. 9 is a perspective view of its main parts, and FIG. 10 is a vertical side view of the fixing device.
Figures (a) and (b) and Figures 11 (a) and (b) are explanatory diagrams of the operation. 6... Imprint sheet, 8... Heating roll, 9...
Pressure roll, 10.18... Sheet guide, 18a.
...Protrusion, 15...Printed sheet passage detector, 16
...Detection lever. Fist l Ro No. 3 Figure 4 No. 5 Koku 13α No. 6 Roa, 5 9 No. 3 No. 9 Mouth 10

Claims (1)

[Claims] 1. A heating roll provided with a heating element therein, and a pressure roll that cooperates with the heating roll to press the printing sheet;
A pair of sheet guides guides the printing sheet on which the toner image is thermally fixed by passing between these rolls, and a pair of sheet guides protruding from one side of the pair of sheet guides between the pair of sheet guides. A fixing device equipped with a sheet passage detector having a detection lever, characterized in that a protrusion is provided on a guide surface on the other side of the pair of sheet guides so as to face the position of the detection lever. Fusing device. 2. The fixing device according to claim 1, wherein the protruding portion is constituted by a plurality of ribs.