JPH05173430A - Multiple feeding detection device for image forming device - Google Patents

Abstract

PURPOSE:To surely detect multiple feeding of material to be transferred by separating end edge of paper which is not attracted to a transfer drum to the outer periphery side. CONSTITUTION:This device is utilized in the image forming device provided with the rotatable transfer drum 21 by which a front edge of the paper is grasped by its outer periphery, and is provided with a separating device 40 and an end edge detection sensor 47. The separating device 40 has one part of the transfer drum 21 protruded to the outer periphery side, and the end edge of the paper is separated from the transfer drum 21 to the outer periphery side. The end edge of the paper separated at a separating device 40 is detected by the end edge detection sensor 47.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a multi-feed detection device of an image forming apparatus including a rotatable transfer drum that holds a front edge of a material to be transferred on the outer periphery.

[0002]

2. Description of the Related Art Generally, in a color copying machine, a transfer drum is provided opposite to a photosensitive drum. A material to be transferred such as paper is wound around the outer peripheral surface of the transfer drum, and the toner image formed on the photosensitive drum is transferred to the paper on the transfer drum. In the case of a full-color copying machine, four color toner images of yellow, magenta, cyan and black are sequentially formed on the photosensitive drum, and the toner images are sequentially transferred onto the paper wound around the transfer drum. The transferred full-color toner image is fused and fixed on the sheet by the image fixing device.

[0003]

By the way, in the copying machine, a double feed prevention mechanism is provided in order to prevent two or more sheets from being supplied from the paper feed cassette at the same time. However, there may be a case where two or more sheets are supplied at once due to a sheet separation error. In the above-mentioned conventional configuration, when double feeding is performed, a plurality of sheets are held on the transfer drum,
The toner image is transferred only to the uppermost sheet. At this time, the thickness of the paper becomes more than twice the normal thickness, so the paper may not be sufficiently heated in the fixing device. In this case, the toner transferred onto the paper may be offset on the fixing roller, and the fixing roller may be soiled. If the fixing roller becomes dirty, unnecessary toner will adhere to the paper in the subsequent copying, and the paper will become dirty.

An object of the present invention is to reliably detect the double feeding of the transferred material on the transfer drum.

[0005]

A multi-feed detection device according to the present invention is used in an image forming apparatus having a rotatable transfer drum that holds a front edge of a material to be transferred at an outer periphery, Means and trailing edge detection means. The separating means projects a part of the transfer drum to the outer peripheral side to separate the trailing edge of the transfer target material from the transfer drum to the outer peripheral side. The trailing edge detecting means detects the trailing edge of the transfer material separated by the separating means.

[0006]

In the double feed detecting device according to the present invention, when a plurality of transfer materials are held by the transfer drum, the transfer material in contact with the transfer drum is electrostatically adsorbed by the transfer drum. The paper in the area is not electrostatically attracted, and is easily separated from the paper directly attracted to the transfer drum. Therefore, if a part of the transfer drum is projected to the outer peripheral side by the separating means,
The trailing edge of the transferred material is easily separated from the transfer drum to the outer peripheral side. The trailing edge of the material to be transferred separated from the transfer drum is detected by the trailing edge detecting means, and thus the double feeding of the material to be transferred can be detected.

In this way, it is possible to easily detect the double feeding of the material to be transferred at the transfer drum portion. Therefore, for example, when the double feeding is detected, the fixing device lengthens the fixing time or raises the fixing temperature. Therefore, low temperature offset can be prevented.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a full-color copying machine to which an embodiment of the present invention is applied. In the figure, a document table 2 on which a document is placed is arranged on an upper portion of a copying machine body 1, and a document retainer 3 is provided on the upper surface of the document table 3 so as to be openable and closable. An operation panel 100 is provided on the side of the document retainer 3. A paper discharge tray 4 and a paper feed cassette 5 are arranged on the left side of the copying machine body 1 in the figure. further,
A tray 6 for bypass paper feeding is arranged on the right side of the drawing.

A photoconductor drum 7 is provided inside the copying machine main body 1.
Are arranged. Around the photosensitive drum 7, in addition to the charging device 17, the transfer device 18, and the cleaning device 19, the developing devices 10, 11, 1 arranged side by side in the vertical direction.
A developing device 8 having 2 and 13 is provided. These developing devices 10 to 13 are fixed to the moving frame 9.
The moving frame 9 is vertically movable by a moving mechanism 16 including a stepping motor, a ball screw, a nut and the like.

Below the photosensitive drum 7, a transfer device 18 is provided.
The transfer drums 21 constituting the above are arranged close to each other.
The laser unit 22 is provided above the photoconductor drum 7.
Are arranged. The laser beam from the laser unit 22 is applied to the upper end surface of the photosensitive drum 7. On the other hand, below the document table 2, a reader 23 having a CCD element is arranged. The reader 23 is driven in the left-right direction in the drawing, and is capable of scanning a document placed on the document table 2. The image information read by the reader 23 is sent to the laser unit 22 as an electric signal.

In the paper feed path between the lower part of the transfer drum 21 and the paper feed cassette 5 and the bypass paper feed tray 6, paper feed conveying devices 24 and 25 are arranged, respectively. Each of the paper feeding and conveying devices 24 and 25 is composed of a paper feeding guide and a plurality of paper feeding rollers. A paper discharge path is provided between the transfer drum 21 and the paper discharge tray 4, and a paper discharge conveying device 26 and an image fixing device 27 are arranged in this paper discharge path in order from the transfer drum 21 side. A peeling claw 29 a that constitutes a paper peeling device 29 for peeling the paper on the transfer drum 21 from the transfer drum 21 is provided between the transfer drum 21 and the paper discharge conveyance device 26.

As shown in FIG. 2, inside the transfer drum 21, a transfer charger 21a and a charging charger 21b constituting a transfer device 18 are arranged, and a pair of separation chargers constituting a sheet peeling device 29. 29b
Are arranged. Also, in the lower part of the transfer drum 21,
A timing sensor 38 for detecting the rotation timing of the transfer drum 21 is arranged.

The transfer device 18 is provided with a grip sensor 39, which is an optical sensor of a light emitting / receiving type, for detecting whether or not a material to be transferred such as paper is gripped on the outer periphery of the transfer drum 21. The grip sensor 39 is composed of a light receiver 39a provided in a fixed frame portion inside the transfer drum 21 and a light emitter 39b provided in a frame on the copying machine main body 1 side. The grip sensor 39 detects that the paper is not gripped by the light receiver 39a receiving the light from the light emitter 39b.

A separating device 40 for pressing the transfer sheet 31 (FIG. 3) from the inside is arranged in the fixed side frame portion inside the transfer drum 21. Separator 40
Is composed of a solenoid 41, an arm 42 that moves forward and backward by the solenoid 41, and a pressing roller 43 that is rotatably supported at the tip of the arm 42. Separator 40
Causes the transfer sheet 31 to project to the outer peripheral side by the forward / backward movement of the solenoid 41. The separating device 40 is provided to separate the rear end of the sheet, which is overlapped and grasped on the sheet adsorbed by the transfer drum 21, from the transfer drum 21 when the multi-fed sheet is grasped by the transfer drum 21, for example. It has been done.

A separation device 40 is provided around the transfer drum 21.
Fur brush type cleaner 37
Are arranged. The cleaner 37 is for removing the toner adhering to the transfer drum 21, and can be brought into contact with or separated from the transfer drum 21. Above the cleaner 37, the trailing edge detection sensor 4 for detecting the trailing edge of the sheet separated from the sheet on the transfer drum 21.
7 is provided. The trailing edge detection sensor 47 includes a swinging actuator, and the swinging of the actuator is detected by a photo interrupter.

FIG. 3 shows a schematic structure of the transfer drum 21. As shown in the figure, the transfer drum 21 is mainly composed of a drum frame body 30 and a transparent transfer sheet body 31 made of a dielectric material. The drum frame 30 includes the transfer drum 21.
Ring-shaped drum end portions 32, 33 forming both end portions of
And a support portion 34 that connects the pair of drum end portions 32 and 33. A notch 35 for passing light from the grip sensor 39 is formed in the central portion of the support portion 34 in the axial direction. Further, the transfer sheet body 31 is provided with a spring mechanism 31a (see FIG. 2) at its rear end. The transfer sheet body 31 can be projected outward by the spring mechanism 31a. A plurality of clippers 40 for gripping a sheet or the like are arranged in parallel at the front edge of the support portion 34. A step portion 36 is formed on one end side of the support portion 34 in the circumferential direction.

This copying machine has a control unit 50 shown in FIG. The control unit 50 has a microcomputer including a CPU, RAM, ROM and the like. Control unit 50
Includes an image forming unit 28, a transfer device 18, a separation device 40,
The cleaner 37 and other input / output units are connected. Further, a grip sensor 39, a trailing edge detection sensor 47, a paper discharge conveyance device 26, an image fixing device 27, and a paper peeling device 29 are connected to the control unit 50.

The control unit 50 performs various controls of the copying machine main body 1 and, at the time of gripping a sheet or the like on the transfer drum 21, depending on whether or not the sheet has been double-fed, the sheet discharging and conveying device 2 is provided.
6 and the image-fixing device 27 are controlled in terms of conveyance speed and the like. As shown in FIG. 5, when gripping a sheet, the control unit 50 first closes the clipper 40 at the timing of sheet transport to grip the sheet in step S11. Step S1
At 2, it is determined whether or not the grip sensor 39 is turned on.
When the grip sensor 39 is not turned on, it is determined that the paper is gripped, and the process proceeds to step S13. In step S13, the transfer device 18 is instructed to perform the transfer operation.

Next, in step S14, the separating device 40 is instructed to perform the separating operation. In this separating operation, the arm 42 of the solenoid 4 projects. Then, the pressing roller 4
3 presses the transfer sheet body 31 from the inside to the outside. As a result, a part of the curvature of the transfer sheet body 31 becomes large as shown by the one-dot chain line in FIG. At the portion where the curvature is large, the paper easily separates from the surface of the transfer drum 21. Therefore, when the double feed occurs, the paper on the upper layer of the paper that is in direct contact with the surface of the transfer drum 21 is separated from the paper on the lower layer especially at the rear end portion. The separated trailing edge of the sheet contacts the actuator of the trailing edge detection sensor 47, and the trailing edge detection sensor 47 is turned on.

In step S15, it is determined whether the trailing edge detection sensor 47 is turned on. When double feed is occurring, the trailing edge detection sensor 47 is turned on as described above.
In this case, the process proceeds to step S17. Step S1
In No. 7, the sheet conveying speed in the paper discharge conveying device 26 and the fixing device 27 is slowed down, and the fixing speed is set lower than usual.
As a result, sufficient fixing is performed and low temperature offset at the time of fixing is prevented. If it is determined that the trailing edge detection sensor 47 is not turned on, the process proceeds to step S16. In step S16, the conveyance speed of the paper discharge conveying device 26 and the fixing device 27 is set to the normal speed, and the fixing is performed at the same speed as the normal speed.

When the operation in step S16 or step S17 is completed, the process proceeds to step S18. In step S18, transfer of the second and subsequent colors is instructed. Step S1
At 9, it is determined whether or not all transfer is completed. The process of step S18 is repeated until all the transfers are completed, and when all the transfers are completed, the process proceeds to step S20. In step S20, peeling by the paper peeling device 29 and discharging of the paper by the paper discharging and conveying device 26 are performed.
When these processes are completed, the process proceeds to the next process. If the grip sensor 39 is turned on in step S12 and it is determined that the paper is not gripped, the process proceeds to step S21. In step S21, the jam is displayed and the machine is stopped.

In this case, the transfer sheet main body 31 is projected in the outer peripheral direction, the rear end of the double-fed sheets that are not electrostatically attracted to the transfer sheet main body 31 is detected to detect the double-feed, and the conveyance speed is controlled. .. Therefore, low temperature offset in the image fixing device can be prevented. [Other Embodiments] (a) In the above embodiments, a full-color copying machine using a transfer drum was described as an example, but the present invention can also be applied to other image forming apparatuses such as full-color facsimile machines. (B) In the above embodiment, the solenoid and the roller are used as the separating device, but the structure of the separating device is not limited to this.

[0023]

In the double feed detection device of the image forming apparatus according to the present invention, the trailing edge of the paper which is not attracted to the transfer drum in the double feed is separated to the outer peripheral side by the separating means, and the separated paper is separated. Since the trailing edge can be detected by the trailing edge detecting means, double feeding in the apparatus can be reliably detected, and low-temperature offset and the like due to double feeding can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a full-color copying machine that employs an embodiment of the present invention.

FIG. 2 is an enlarged vertical cross-sectional view showing a structure around a transfer device.

FIG. 3 is a perspective view showing a structure of a transfer drum.

FIG. 4 is a block diagram showing the configuration of a control system.

FIG. 5 is a flowchart showing a paper gripping operation.

[Explanation of symbols]

 1 Full-color copying machine main body 18 Transfer device 21 Transfer drum 40 Separation device 47 Rear end detection sensor

Claims (1)

[Claims] 1. A double-feed detection device for an image forming apparatus, comprising a rotatable transfer drum that holds a front edge of a transfer material at the outer periphery, wherein a part of the transfer drum is projected to the outer peripheral side, An image forming apparatus including: a separating unit that separates a trailing edge of the transfer material from the transfer drum to an outer peripheral side; and a trailing edge detecting unit that detects a trailing edge of the transfer material separated by the separating unit. Double feed detection device.