JPH10142980A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence transfer defect due to unstable transfer caused by that the impact when a sheet leading end abuts on a fixing device is transmitted to the sheet trailing end existing in a transfer area. SOLUTION: The sheet is allowed to pass through the transfer area, and guided along a before fixation guide 26 to a press contact part of a heat roller 25-1 and a press contact roller 25-2 constituting the fixing device 25. A pair of supporting bodies 30 supporting the heat roller 25-1 or the like consisting the fixing device 25 in rotationally, are movably supported with the roller 32 on a supporting rail 31 provided on a main body side, and connected to a rack 33 provided on a bottom surface of the supporting body 30 so that a driving gear 34 with which the rotation of a driving motor 35 is transmitted, is engaged. Therefore, by letting the supporting body 30 moved in the transporting direction of the sheet by a specific range in exact timing for matching with the time of the sheet P leading end butting to the before fixation guide 26 of the fixing device 25, the impact at the time of the sheet leading end abutting on the fixing device 25 is mitigated. In such a manner, the impact is not transmitted even if the trailing end part of the sheet exists on the transfer area, hence the excellent transfer can be performed without causing any transfer defect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus or the like, for example, an image carried on an appropriately conveyed sheet, for example, a sheet conveyed in contact with a sheet to fix a toner image. The present invention relates to a fixing device that performs fixing while fixing.

[0002]

2. Description of the Related Art In an image forming apparatus, for example, an image forming apparatus using an electrophotographic system, a toner image is formed on a photosensitive member as a recording medium, and the toner image is transferred onto a sheet such as plain paper. In order to hold the toner image transferred thereon as a permanent image, the toner image is passed through, for example, a heat fixing device to fuse the toner and fuse it to a sheet, and then discharge the sheet to the outside of the apparatus main body.

According to such an image forming apparatus, in order to form a desired image on a sheet, the sheet is fed to an image forming position, in particular, a transfer position, and then separated from a photoreceptor to determine an undetermined image on the sheet. To fix the toner image
Guide member for feeding into the fixing device (conveying means, etc.)
Is provided between the transfer position and the fixing device.

For example, as shown in FIG. 5, a transfer device 61 for transfer is opposed to a photoreceptor 60 formed in a drum shape, and a separation charger 62 for separating a sheet in close contact with the photoreceptor 60.
Is attached. The sheet P is sent to a gap between the transfer device 61 and the photoconductor 60, is separated by the operation of the separation charger 62 after the transfer, and is sent to the fixing device 64 via the conveyance unit 63.

In this case, if the leading end of the sheet P contacts the fixing device 64 in a state where the trailing end of the sheet P is present in the transfer area between the photoreceptor 60 and the transfer device 61, the impact at that time will be reduced. As shown in (1), the image is transmitted to the rear end portion of the sheet P where the transfer area exists, causing a problem in the image being transferred, resulting in poor transfer, transfer blur, and the like. In this case, when the conveying speed of the sheet P is low, such an impact is small and is not transmitted to the transfer portion but is absorbed in the middle thereof, so that a problem such as poor transfer does not occur.

However, if the image forming speed of the image forming apparatus, that is, the processing speed is increased, the conveying speed of the sheet P is naturally increased, and the leading end of the sheet P is fixed to the fixing device 6.
4, the impact on the sheet P existing in the transfer portion cannot be satisfactorily performed.

For this reason, conventionally, by setting the conveying distance of the sheet by the conveying means 63 longer than the length in the conveying direction of the maximum size sheet that can be processed by the image forming apparatus,
In a state where the leading end of the sheet P is in contact with the fixing device 64, the trailing end of the sheet P is out of the transfer area. With this configuration, the transfer failure does not occur due to the vibration of the sheet P due to the impact as shown in FIG.

On the other hand, if the length of the conveying means 63 for conveying the sheet P to the fixing device 64 is set long, transfer failure due to the impact of the leading edge of the sheet against the fixing device 64 can be prevented. The whole becomes larger in the sheet conveying direction. In this case, although there is no problem in a large-sized image forming apparatus having a sufficient space, in a small-sized image forming apparatus having no sufficient space, the conveying unit 63 cannot be set long as described above. When the trailing edge of the sheet P is in the transfer area, the leading edge of the sheet P may come into contact with the fixing device 64.

Therefore, one means for alleviating the impact when the leading end of the sheet P of the fixing device 64 abuts as described above is as follows.
This is proposed in Japanese Patent Application Laid-Open No. 5-35134. In the apparatus disclosed in the publication, for example, as shown in FIG. 6, the conveying means 63 is divided into two parts, one conveying means (guide) 63-1 is arranged corresponding to the position of the transfer area, and the fixing device 64 is moved. It is arranged so as to be lowered by one step, and another conveying means (guide etc.) 63-2 is arranged correspondingly. In this way, after the sheet P descends by its own weight to the conveyance unit 63-2 which has been lowered by one level, the sheet P is guided to the fixing device 64, and the step of the conveyance unit 63-1 and 63-2 At the position, the sheet P is bent by gravity. Therefore, the impact when the leading edge of the sheet P contacts the fixing device 64 is absorbed by the above-described curved portion of the sheet P so that the impact does not affect the trailing edge of the sheet existing in the transfer area.

[0010]

As described above, according to the conventional apparatus described in Japanese Patent Application Laid-Open No. Hei 5-35134, when the sheet P is guided to the fixing device after the transfer, the sheet P is curved. Therefore, the impact when the leading edge of the sheet P contacts the fixing device can be effectively absorbed.

However, it is necessary to form the transporting means 63 in an upper and lower step structure, which complicates the structure. Further, since the fixing device 64 needs to be provided one step lower, a useless space is generated, and at the same time, the entire image forming apparatus is enlarged in the space.

Further, when the transferred sheet P is guided to the fixing device, it is guided to the fixing device 64 via the lower conveying device 63-2 after leaving the upper conveying device 63-1. Then, an impact occurs when the leading end of the sheet P contacts the conveying means 63-2. It is conceivable that the impact is absorbed by the curved portion, but if the impact is not absorbed, the transfer at the rear end portion of the sheet P existing in the transfer area becomes unstable. In particular, when the sheet P has a strong stiffness, for example, in the case of a thick sheet P, the impact when the sheet P comes into contact with the lower conveying means 63-2 becomes large, and the transfer to the sheet P existing in the transfer area cannot be performed well. Becomes noticeable.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a fixing device capable of effectively absorbing the impact of a sheet sent to a fixing device after transfer.

It is another object of the present invention to reduce the impact of a sheet on a fixing device even if the sheet conveying speed is increased, and to improve the transfer failure even if a sheet being transferred exists in a transfer area. This enables stable transfer to be performed without the occurrence of the like.

Accordingly, the present invention provides a sheet conveying speed,
It is an object of the present invention to provide a fixing device capable of reducing the size of an image forming apparatus without changing the transport direction or the like on the way.

[0016]

According to the present invention, there is provided a fixing device for transferring an unfixed image onto a sheet in a transfer area, and then transporting the sheet and simultaneously fixing the unfixed image. In a fixing device for fixing a fixed image, a support for supporting a heat roller and a pressure roller constituting the fixing device is provided so as to be movable in a sheet conveying direction, and a leading end of the sheet is fixed to the fixing device. A movement control means is provided for moving the support in the sheet conveying direction in accordance with the timing of contact.

According to the fixing device having such a configuration, the support supporting the heat roller or the like is moved in the sheet conveying direction in accordance with the timing when the leading end of the sheet after the transfer contacts the fixing device, for example, the heat roller or the like. , The impact caused by the contact of the sheet P is almost eliminated as compared with the state where the sheet P is arranged in the fixed state. Therefore, even if the trailing edge of the sheet exists in the transfer area, transfer failure does not occur.

Therefore, in the fixing device having the above-described structure, the speed at which the support is moved by the movement control means is set to a speed lower than the sheet conveying speed.
By moving this for a certain period of time, the support moves a certain distance. Therefore, when the support is moving, the leading end of the sheet is guided to the pressure contact portion between the heat roller and the pressure roller constituting the fixing device, so that the fixing can be performed reliably. In addition, the moving distance at that time is small, the sheet conveying distance is not greatly extended, and it is not necessary to enlarge the entire image forming apparatus.

In the above-described fixing device, the support further supports a pre-fixing guide for guiding the pre-fixing guide to a pressure contact portion between the heat roller and the pressure contact roller. If the movement of the support is controlled, the sheet can be reliably guided to the press-contact portion. In particular, the pre-fixing guide is provided so as not to cause wrinkling of the sheet sandwiched between the rollers to be pressed, and since the positional relationship between the pressing portion and the pre-fixing guide does not change, the occurrence of wrinkling is reduced. In the stopped state, the leading end of the sheet P can be reliably guided to the press contact portion.

On the other hand, in a fixing device having another configuration for achieving the object of the present invention, in particular, in the above-described fixing device, it is impossible to prevent an impact on the next sheet P while the support is moved, so that the A fixing device for solving the problem is a fixing device for transferring an unfixed image onto a sheet in a transfer area, and then fixing the carried unfixed image while conveying the sheet. A support for supporting the heat roller and the pressure contact roller is provided so as to be movable in the conveying direction of the sheet, and the support is attached to the sheet at the timing when the leading end of the sheet comes into contact with the fixing device. A movement control unit for moving the sheet in the conveyance direction, wherein the movement control unit further returns the sheet to the original position after the rear end of the sheet being fixed passes through the transfer area. It characterized in that for return movement of the support in the direction opposite to the conveying direction of the sheet.

Therefore, after the rear end of the sheet has passed through the transfer area, the support supporting the heat roller and the like is returned to the original position, so that the fixing device can be put on standby for the next sheet. Further, at the time of return, the rear end of the sheet has passed through the transfer area, and there is no factor that causes transfer failure of the rear end portion of the sheet due to the movement of the support in the direction in which the sheet is fed back.

In the above-described fixing device, in the state where the sheet is being fixed, the returning movement speed of the support is set to be lower than the moving speed when the support is moved in accordance with the leading edge of the sheet. By doing so, it is possible to stabilize the fixing of the sheet during fixing and to prevent disturbance of the unfixed image carried on the sheet. That is, when the support is returned to the original position in a state where the sheet is pressed, the unfixed image can be prevented from being disturbed by an impact when the conveyed sheet moves in the reverse direction. Then, in a state where the sheet is not fixed, if the support is returned and moved at a speed higher than the conveying speed of the sheet, the original sheet is returned to the fixing device before the next sheet reaches the fixing device. It is possible to return to the position. In this case, since the unfixed image on the sheet has been fixed,
There is no problem at all.

Further, in the fixing device having the above-described configuration, if it is determined whether or not to move the support in the sheet conveying direction in accordance with the size and thickness of the sheet, the support can be moved indiscriminately. There is no need to control movement. That is, when the sheet to be processed is short, for example, when the leading end of the sheet reaches the fixing device, if the trailing end of the sheet completely passes through the transfer area, the movement control may not be performed. Also,
When the sheet is thin, there is almost no impact when the leading end of the sheet is negotiated with the fixing device, so that even in this case, the movement control can be omitted.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view showing the overall structure of a fixing device according to the present invention. The fixing device of the present invention is provided such that the entire unit is movable,
The sheet P is moved in the sheet conveying direction in accordance with the timing at which the leading edge of the transferred sheet P contacts.
FIG. 2 is a flowchart for explaining operation control in the movement control means for moving the fixing device of the present invention. FIG. 3 is a cross-sectional view illustrating a digital copying machine as an image forming apparatus including the fixing device of the present invention.

Referring first to FIG. 3, a digital copier according to the present invention will be described. The main body of the digital copying machine has an original mounting table 1 at an upper portion, and an optical system 2 below the original mounting table 1. The optical system 2 is a scanner for optically reading an image of a document by scanning a document (not shown) placed on the document table 1 while irradiating the document with light. It comprises a plurality of reflecting mirrors 4 for guiding reflected light from a document to a CCD 6 which is an image reading element, and a lens unit 5 arranged in the optical path of the reflected light and forming an image on the CCD 6.

An automatic document feeder (ADF) for automatically feeding the originals set on a mounting tray (not shown) to the original mounting table 1 one by one is placed on the original mounting table 1. 7) is provided. This ADF7 is
In order to read not only an image of a sheet-shaped original but also an image of a book-shaped original, one side is pivotally supported with respect to the original mounting table 1 and is provided so as to be openable and closable.

The read data of the document read by the optical system 2, that is, the scanner, is temporarily stored in a storage unit (not shown), is subjected to image processing into information for reproduction, and is disposed below the scanner. Image forming unit, ie, printer unit 8
Reproduced in. The printer unit 8 includes a photoconductor 9 formed in a drum shape that is rotated in the direction of an arrow at substantially the center,
Around the periphery thereof, a charger (charging device) 10 for charging the surface of the photoconductor 9 to a predetermined potential, an eraser (not shown) for unnecessary areas between images and sides, and an electrostatic latent formed on the surface of the photoconductor 9 A developing device 11 for developing an image; a transfer charger (transfer device) 12 for transferring a toner image formed on the surface of the photoconductor 9 to a sheet; a separation charger 13 for separating the transferred sheet from the photoconductor 9; The cleaning device 14 for removing unnecessary toner remaining on the surface, a static eliminator (not shown), and the like are arranged in the above-described order.

The printer section 8 is provided with a photosensitive member 9 uniformly charged to form an electrostatic latent image on the surface of the photosensitive member 9.
A writing unit 15 for irradiating the surface with optical information according to the image data is provided. The writing unit 15
Image data obtained by performing image processing on the read data read by the above-described scanner 2 is received, and, for example, ON-OFF drive control of the semiconductor laser is performed in accordance with the image data. To photoconductor 9
Irradiate, write on top. Thus, an electrostatic latent image is formed on the surface of the photoconductor 9 according to the image data.

On the other hand, on the paper entry side (right side in the figure) with respect to the photosensitive member 9, a timing roller 16 for controlling the conveyance of the sheet P at a predetermined timing, feeding and separating rollers 17, 1 are provided.
8, a pickup roller 19 and a manual paper feed tray 20 are provided. Further, cassette (tray) sheet feeding devices 21 and 22 for appropriately feeding the sheet P are provided below the photoconductor 9, similarly to the sheet feeding from the manual sheet feeding tray 20. Sheets fed from these sheet feeding portions are sent to the timing roller 16 via a plurality of conveyance rollers 23 provided on a conveyance path leading to the timing roller 16.

When the sheet P is fed from a cassette sheet feeding device or a manual sheet feeding tray, the sheet P is sent via a timing roller 16 to a transfer area between the photoconductor 9 and the transfer device 12. After the toner image formed on the photoreceptor 9 is electrostatically transferred by the operation of the transfer device 12, the sheet P is separated from the closely contacted photoreceptor 9 by the operation of the separation charger 13. A transport device 24 for guiding the sheet P to the next fixing device 25 according to the present invention is provided corresponding to the separation position.

As shown in the figure, the transport device 24 stretches an endless transport belt between rollers, and rotates one of the rollers to hold the sheet P separated from the photosensitive member 9 on the transport belt. It is sent to the fixing device 25. Therefore, the transport device 24 is provided with a suction unit (not shown) for holding the sheet P on the transport belt so that the sheet P is attracted onto the belt.

Between the transport device 24 and the fixing device 25,
A pre-fixing guide 26 for guiding the sheet P to rollers constituting the fixing device 25 is provided. The fixing device 25 includes, for example, a heat roller 2 that is controlled to be heated to a predetermined temperature in order to fix a toner image carried on the sheet P.
5-1 and a pressure roller 25-2 for bringing the sheet P into close contact with the heat roller. Before the sheet P is guided to the pressure contact portion between the heat roller 25-1 and the pressure roller 25-2, the sheet P is first guided to the peripheral surface of the heat roller 25-1 by the pre-fixing guide 26 in order to prevent wrinkles. It is guided. Then, the heat roller 25-1 is guided to the press contact portion in accordance with the rotation of the heat roller 25-1.

On the sheet discharge side of the fixing device 25,
Discharge roller 2 for discharging sheet P out of the digital copying machine
7 are provided. A sheet post-processing device 28 for aligning the pages of the discharged sheet P is provided so as to face the discharge roller 27. The sheet post-processing device 28 includes a two-stage discharge tray, and various transport rollers so as to enable switchback transport in which sheet feeding is reversed through the tray. That is, the image is selectively discharged to the upper or lower discharge tray with the image surface formed on the sheet P up or down.

The sheet post-processing device 28 discharges the sheet P to a discharge tray, and turns over the sheet.
Or, in a posture as it is, the digital copying machine is provided with a transport path and a transport means leading to an intermediate tray 29 disposed between the photoreceptor 9 and the cassette paper feeder 21 so that the feeding direction of the sheet P is appropriately adjusted. Switching control is performed.

In the digital copying machine constructed as described above, when the image forming operation is started, the sheet P is transferred from the manual sheet feed tray 20 or the cassette sheet feeder 21 or the sheet feeder to the position of the timing roller 16 in advance. Sent from 22. Then, a toner image corresponding to the image is formed on the photoreceptor 9, and the sheet P, which has been waiting at the position of the timing roller 16, is synchronized with the timing at which the leading end of the toner image is sent to the transfer position of the transfer device 12. Is sent to the transfer position.

After the toner image on the photoconductor 9 is transferred by the operation of the transfer unit 12, the sheet P is separated from the photoconductor 9 via the separation charger 13.
It is sent to 5. In this case, when the leading edge of the sheet P reaches the fixing device 25, the rear portion of the sheet P is positioned in the transfer area where the transfer device 12 is located.
And the fixing device 25 are set. Therefore, the entire fixing device 25 including the heat roller 25-1 and the like is moved in the sheet P conveyance direction at the timing when the leading end of the sheet P reaches the fixing device 25. By this movement, the impact at the time when the leading end of the sheet P comes into contact with the fixing device 25, particularly the pre-fixing roller 26, is greatly reduced, and the impact at that time does not reach the transfer area, so that good transfer can be performed.

(One Embodiment) Next, the detailed structure of the fixing device 25 according to the present invention will be described with reference to FIG. In particular, a moving mechanism for moving the fixing device 25 according to the present invention and its control will be described below.

First, the structure of the moving mechanism of the fixing device 25 will be described. The fixing device 25 includes a heat roller 25-1.
A pair of supports 30 are provided on both sides to rotatably support the pressing roller 25-2. The support 30
Has a U-shaped cross section, and its upper side is supported via a rotatable roller 32 on both rails 31 fixed to a housing of the digital copying machine. . The rollers 32 are rotatably provided on the support 30. In addition, a rack 33 for moving the support 30 is provided below the support 30, that is, on the bottom surface.

A drive gear 34 for moving the fixing device, which meshes with the wraps 33, is connected to the wrap 33. The drive gear 34 is fixed to a rotary shaft 36 to which the rotational force of a drive motor 35 is transmitted. . Accordingly, the rotation of the drive motor 35 causes the support 30 to move along the rail 31. The rotating shaft 33 is rotatably supported by the above-described housing of the copying machine main body, and the driving motor 35 is fixed to the housing and is capable of rotating forward and backward.

Accordingly, the support 30 supporting the fixing device 25, that is, the heat roller 25-1 and the like, includes the support rail 31, the roller 32, the driving motor 35, the rack 33, the driving gear 34, the rotating shaft 36 and the like. Movably provided by a moving mechanism composed of

The support 30 is provided with a heat roller 2.
5-1 is rotatably supported, and the pressing roller 25-2 is supported.
At the same time as the heat roller 25-1 is rotatably supported.
It is movably provided so as to be pressed against the side. For this reason, the pressing roller 25-2 has both ends of the rotating shaft 37 penetrated through the elongated hole 30-1 formed in the support 30 in an upright shape in the vertical direction, and rotates the both ends of the penetrating rotating shaft 37. It is provided so as to be supported by a moving support lever 38. One end of the support lever 38 is rotatably provided on the support 30, and the other end is urged upward by a spring 39. Therefore, the pressing roller 25-2 is rotatably supported on the support lever 38, and is actuated by the spring 39 along the elongated hole 30-1 by the action of the spring 39.
Is pressed against the side.

On the other hand, the heat roller 25-1 is rotatably supported by the support 30 via a bearing or the like, and a driven gear 40 for driving is fixed to one end. The driven gear 40 is provided so as to mesh with one side of a timing belt 41 provided endlessly. The timing belt 41 is provided with a drive gear 42 and a driven gear 43 for stretching and running the timing belt 41 on both sides thereof. The drive gear 42 is connected to a drive motor 44 for rotating the fixing device 25, particularly the heat roller 25-1, and is rotated in accordance with the drive of the drive motor 44. Thereby, the heat roller 25-1 can be rotated in the direction of the arrow via the timing belt 41. At this time, the rotation speed of the drive motor 44 is set so that the rotation speed of the heat roller 25-1, particularly, the peripheral speed substantially matches the conveyance speed of the sheet P.

The drive motor 44 is mounted on the above-described housing of the copying machine, and is controlled to rotate in one direction. The drive gear 42 and the driven gear 43 are rotatably supported by the housing.

Further, a pre-fixing guide 26 for guiding the sheet P to the fixing device 25 is used to transfer the sheet P to the heat roller 2.
Both ends are attached to a pair of support members 30 in a state of being inclined upward for guiding to the peripheral surface of 5-1. In particular, the pre-fixing guide 26 is formed such that the leading end portion of the sheet P in the transport direction is curved so that the central portion protrudes as shown in the drawing. This is because when the leading end of the sheet P guided to the peripheral surface of the heat roller 25-1 is fed to the pressure contact portion with the pressure roller 25-2 and is conveyed, the sheet is squeezed by the curved portion of the pre-fixing guide 26. So that
It plays a role in suppressing the occurrence of wrinkling of the sheet P.

The movable fixing device 25 having the above-described structure.
Will be described below with reference to the control flow of FIG. Means for controlling the movement of the fixing device of the present invention,
That is, in the control of FIG. 2, the fixing device 2 is detected by detecting the conveyed sheet P, detecting the thickness of the sheet P, and the like.
In particular, the movement of the support 5 is controlled.

Therefore, the detection mechanism of the sheet P will be described with reference to FIG. Before the timing roller 16, a pre-transfer sheet detection sensor (means) S <b> 1 is provided so that the state of the sheet P at the position of the timing roller 16 can be detected. Further, a pre-fixing sheet detection sensor (means) S2 for detecting the presence or absence of a sheet before being conveyed to the fixing device 25 is disposed in the conveying device 24 that conveys the transferred sheet P.

The pre-fixing sheet detecting sensor S2 is disposed, for example, about 150 mm before the pressure contact portion between the rollers of the fixing device 25 and about 150 mm downstream from the transfer area end position of the transfer unit 12.

A thickness detection sensor T for detecting the thickness of the conveyed sheet P is disposed downstream of the timing roller 16, particularly in front of the photosensitive member 9. As the thickness detection sensor T of the sheet P, a conventionally known sensor is used.

Further, the fixing device 2 is set so that the distance L from the pressure contact portion between the heat roller 25-1 and the pressure contact roller 25-2 to the transfer area end position is, for example, about 300 mm.
5 are set. The following control will be described assuming that the transport speed of the sheet P is controlled at a transport speed of 400 mm / sec.

Therefore, in the control flow of FIG. 2, the sheet P is placed in the manual paper feed tray 2 in accordance with the image forming operation.
0 or paper is fed (n1) from the cassette paper feeder 21 or 22. When the leading edge of the sheet P is sent to the timing roller 16, it is detected by the sensor S <b> 1, and after a certain time from the detection point, the upstream conveying roller or the like is stopped, and the leading edge of the sheet P is moved to the timing roller 1.
6 (n2).

Thereafter, the timing roller 16 is synchronized with the position of the tip of the toner image formed on the photosensitive member 9 by
The conveyance of the sheet P is started, and the sheet P is sent to a transfer area where the transfer device 12 faces the photoconductor 9. The thickness of the fed sheet P is detected by the thickness detection sensor T, and the transfer operation is performed. The detection of the thickness of the sheet P is used as one of the conditions for determining whether to perform the movement control of the fixing device 25 according to the present invention. Another condition for controlling the movement of the fixing device 25 is the size of the conveyed sheet P, particularly the length in the sheet conveying direction. Therefore, in step n3, the type of the sheet, particularly the thickness and length are recognized (determined).

Then, when the leading end of the sheet P passes through the transfer area of the transfer unit 12 and is separated by the separation charger 13, the sheet P is transported to the fixing device 25 by the transport unit 24. On the way, the sensor S2 detects the leading edge of the sheet P. After the sheet P is detected (n4) by the sensor S2, the leading end of the sheet P contacts the fixing device 25, for example, first contacts the pre-fixing guide 26, and the impact at that time is located in the transfer area. In step n5, it is determined whether or not transfer failure occurs at the trailing edge of the sheet P. If the transfer failure does not occur, the movement control of the fixing device 25 is not performed, and the process proceeds to the discharge process (n12) for performing the process of fixing the normal sheet P.

That is, as a criterion in step n5, for example, the length of the sheet P in the transport direction is 3
If it is less than 00 mm, the leading edge of the sheet P is
When the sheet P comes into contact with the pre-fixing guide 26 of No. 5, the rear end of the sheet P is out of the transfer area of the transfer device 12 and is conveyed by the conveyance device 24. For example, when the sheet P has a fixed size of A4 or less, the length is slightly less than 300 mm even in the longitudinal direction (vertical feed direction of the sheet), and the cause of the transfer failure is eliminated. Therefore, sheet P is A
If it is less than 4, it is determined in step n5 that the movement control of the fixing device 25 is not performed.

Here, the length of the conveyed sheet P is recognized in step n3 described above. This can be recognized in advance when a sheet P of a standard size is fed. That is, in the cassette sheet feeding device 21 or 22,
The standard size of the accommodated sheet P is detected in advance as is conventionally known. Therefore, for the sheet P fed from the cassette sheet feeding device 21 or 22,
The length is recognized in advance, and it is determined in step n5 whether the fixing device 25 is immediately moved.
This determination time is not limited to the time when the sensor S2 detects the leading edge of the sheet.

The sheet P fed from the manual sheet feed tray 20 is not always a sheet of a standard size. Therefore, in FIG. 3, the length of the sheet P in the transport direction can be recognized from the time from when the leading edge of the fed sheet passes to when the trailing edge passes. For this reason, a detection sensor is disposed downstream of the feed roller 17 of the manual paper feed tray 20, and the time counting is performed from the time when the detection of the leading edge of the sheet is performed until the trailing edge of the sheet is passed. I do. The length of the sheet P in the sheet conveyance direction can be obtained by dividing the counted time from the sheet P conveyance speed of 400 mm / sec. In this case, since the sheet P is temporarily stopped at the position of the timing roller 16, if the trailing end of the sheet P is not detected by the sensor at that time, the time counting is temporarily stopped and the conveyance of the sheet P is started. The counting may be started again from the point in time.

On the other hand, when it is recognized that the fed sheet P is a standard size B4 or A3,
Its longitudinal direction greatly exceeds 300 mm. for that reason,
If the sheet P of that size is fed in step n1 and the size is confirmed in step n3, in step n5, the movement control of the fixing device 25 described below is performed.

When it is determined in step n5 that the fixing device 25 needs to be moved, a timer for counting a predetermined time t is started (n6), and whether or not the timer has counted the predetermined time t is determined. At step n7. In short, the timer is set to the time from the position where the leading end of the sheet P is detected by the sensor S2 to the time when the sheet P comes into contact with the pre-fixing guide 26 of the fixing device 25 in particular. Therefore, the sensor S
2, since the distance to the pre-fixing guide 26 is set to about 150 mm, the distance is set to the transport speed 40 of the sheet P.
The value obtained by dividing the value by 0 mm / sec is counted by the timer as t.
Is set as Therefore, the timer setting time t
Is set to, for example, 375 msec. This time is completely the same depending on the size of the sheet P.

When the timer measures the set time t, the fixing device 25 is moved along the sheet P conveying direction.
Therefore, the drive gear 34 in the figure is rotated in the counterclockwise direction via the drive motor 35 in FIG. 1, thereby moving the entire fixing device 30 including the support 30 in the sheet P conveyance direction. The moving speed at this time is set to の of the sheet conveying speed, for example, 200 mm / sec. The driving time is set to about 200 msec. As a result, the fixing device 25 moves a position away from the initial position by a certain distance in the sheet conveying direction, that is, moves about 40 mm. Therefore, the impact when the leading edge of the sheet P contacts the fixing device 25 is reduced.

That is, when the sheet P contacts the fixing device 25 (contacts the pre-fixing guide 26), the transport speed of the sheet P is substantially 200 mm / sec, and the transport speed of the sheet P is halved. It has the same effect as when dropped. Therefore, it is possible to prevent the transfer failure of the sheet P existing in the transfer area due to the impact.

FIG. 4B shows a state in which the fixing device 25 is moved for, for example, 200 msec in step n8. That is, the fixing device 2 is moved from the initial position indicated by the broken line to the position indicated by the solid line. That is, in a state where the rear end of the sheet P has the transfer area, the fixing device 25 moves to the position shown by the solid line. At the movement completion position at that time, the heat roller 25-1 of the fixing device 25 is rotationally driven in accordance with the operation of the timing belt 41 to perform the fixing operation, and the leading end of the sheet P is
The fixing operation is performed by guiding to the pressure contact portion between the pressure roller -1 and the pressure roller 25-2 via the pre-fixing guide 26.

Here, in a state where the fixing device 25 continues to move while the leading end of the sheet P is pinched and conveyed by the pressing portion, the sheet P is pulled and the rear end of the sheet P is pulled out from the transfer area. Act like so. However, the movement of the fixing device 25 is very small, so that the movement of the fixing device 25 is completed at the time when the leading end of the sheet P is clamped by the pressing portion in order to match the timing at which the leading end of the sheet P contacts the pre-fixing guide 26. can do.

When the movement control of the fixing device 25 described above is completed, the fixing device 25 is returned to the original initial position in order to deal with the next sheet P to be conveyed. The return timing is set after the trailing edge of the sheet P is out of the transfer area. Therefore, the timing at which the trailing edge of the sheet P passes through the transfer area is set (n9) according to the size of the sheet P fed in step n1. For example, if the sheet P is A3 size, the length of the sheet P is about 420 mm.
The time that the trailing edge of the sheet P passes through the transfer area from the time when is operated is 675 msec later. This time
The arrangement position of the sensor S2 is about 150 mm from the rear of the transfer area, and the difference 270 mm is set to a conveyance speed 400 m
It is obtained by dividing by m / sec. Therefore, in consideration of an error or the like, after 700 msec (n10), the fixing device 25
Is returned to the initial position (n11).

The returning movement speed and time for returning the fixing device 25 to the initial position are naturally set to be lower than the moving speed for moving the leading edge of the sheet P to avoid impact.
This determines the time to return. For example, FIG.
In order to return the fixing device 25 to the initial position from the position (b) to the position shown in FIG. 4C, the driving motor 35 is rotated in the reverse direction, and the fixing device 25 is rotated at a speed of 60 mm / sec. It is driven for 667 msec and stopped. That is,
In FIG. 4C, when the rear end of the sheet P completely passes through the transfer area, the return movement control of the fixing device 25 from the position indicated by the solid line to the position indicated by the broken line is performed.

The reason for making the return moving speed lower than the moving speed is also to reduce the impact when the sheet P moves in the opposite direction because the sheet P is conveyed through the conveying device 24. . That is, it is possible to prevent the unfixed toner image carried on the sheet P from being disturbed by vibration or the like when the sheet P is temporarily moved in the reverse direction.

If the size of the conveyed sheet P is B4 at the above-described arrangement position of the sensor S2 and the conveying speed of the sheet, if the size of the conveyed sheet P is B4, 560 msec after the detection of the leading edge of the sheet by the sensor S2, and the legal size In this case, the setting may be made after 540 msec, and in the case of the W letter size, after 730 msec.

The return timing of the fixing device 25 to the initial position is set such that the rear end of the sheet completely passes through the transfer area and is conveyed by the conveying device 24 as described above. The present invention is not limited to this, and the sheet P may be returned before the leading edge of the next sheet P is conveyed to the fixing device 25. Therefore, the rear end of the sheet P is completely fixed to the heat roller 25-1 of the fixing device 25 and the pressing roller 25-2.
If there is a sheet conveyance interval such that the leading edge of the next sheet P does not reach the position of the fixing device 25 at the time when the rear end of the sheet P completely passes through the pressure contact portion, A return operation may be performed. In this case, there is no problem even if the speed for returning to the fixing device 25 is set faster than the moving speed.

As described above, since the movement of the fixing device 25 is controlled before the sheet P comes into contact with the fixing device 25, the impact when the sheet P comes into contact with the fixing device 25 is greatly reduced, and the sheet Transfer failure and the like can be prevented.

The moving distance of the fixing device 25 is as follows.
In the above example, the length is about 40 mm, and if it is in the range up to 50 mm, the length of the sheet conveyance system is not so long. Therefore, there is not much useless space, and the entire image forming apparatus is not enlarged.

Further, the pre-fixing guide 26 to which the sheet P first comes in contact is fixed to the same support 3 as the heat roller 25-1 and the like.
0, and moves simultaneously with the movement of the fixing device. Therefore, the positional relationship between the pre-fixing guide 26 and the press-contact portions of the heat roller 25-1 and the press-contact roller 25-2 does not change at all, and the sheet P is securely pressed. I can guide you to In addition, the role of the pre-fixing guide 26 can be exhibited without any change.

It should be noted that the above-described various numerical values are examples for facilitating understanding of the description of the embodiment, and it is a matter of course that the present invention is not limited thereto.

In the description of the embodiment, the movement control of the fixing device 25 is performed according to the length of the sheet to be processed. However, the control may be performed for all the sheets. Of course. In this case, when the sheet P of the minimum size that can be processed is being conveyed, the rear end of the sheet exists in the transfer area of the transfer unit 12 while the leading end of the sheet is in contact with the pre-fixing guide 26 of the fixing device 25. Is the case. By doing so, the conveyance path of the sheet P to the fixing device 25 is of course very short, and the entire image forming apparatus can be further downsized.

The condition for controlling the movement of the fixing device 25 is not limited to the size of the sheet, but the movement of the fixing device 25 may be controlled according to the thickness of the sheet P. is there. That is, in step n3 in FIG. 2, the thickness of the sheet P is detected. Therefore, if the detected thickness is a predetermined thickness or more in step n5, the processing can be performed as a condition for moving the fixing device 25.

For example, when the sheet P is thin, there is almost no impact when the leading end of the sheet P comes into contact with the fixing device 25. Therefore, the movement control of the fixing device 25 is not performed in step n5, and The processing of n12 is executed. Then, when the thickness of the sheet P at which a considerable impact occurs due to the contact of the leading end of the sheet P is detected, whether or not the movement control as described above including the condition of the sheet length is performed in step n5. To make a decision. Accordingly, whether or not to move the fixing device 25 including the thickness of the sheet P is determined by the movement control means, so that transfer failure and the like are effectively prevented, and at the same time, the fixing device 25 is moved needlessly. Can be avoided.

[0074]

According to the fixing device of the present invention, by moving the fixing device, it is possible to prevent an impact at the time when the leading end of the sheet comes into contact with the fixing device.

According to the present invention, the sheet conveying speed is not reduced and the sheet conveying path is not changed at all. By applying the fixing device of the present invention to a device whose speed is increased, the effect can be sufficiently exhibited.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a fixing device for fixing an unfixed image carried on a sheet according to the present invention.

FIG. 2 is a control flowchart relating to movement control of a fixing device according to the present invention.

FIG. 3 is a cross-sectional view illustrating an overall structure of an image forming apparatus including a fixing device of the present invention, particularly, a digital copying machine.

FIG. 4 is a diagram for describing an operation in movement control of the fixing device of the present invention.

FIG. 5 is a cross-sectional view illustrating an example of a conventional fixing device.

FIG. 6 is a cross-sectional view illustrating another example of a conventional fixing device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 9 photoconductor 12 transfer device 13 separation charger 16 timing roller 20 manual feed tray 21 cassette feeder 22 cassette feeder 24 transport device 25 fixing device 25-1 heat roller 25-2 pressure contact roller 26 guide before fixing 30 support Body 31 Support rail 33 Rack 34 Drive gear 35 Drive motor 36 Rotation axis P sheet

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norihide Nakano 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Souichi Takada 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka In the company

Claims (6)

[Claims] 1. A fixing device for transferring an unfixed image onto a sheet in a transfer area and then fixing the carried unfixed image while conveying the sheet. A support for supporting the roller and the pressing roller is provided so as to be movable in the sheet conveyance direction, and the support is moved in the sheet conveyance direction in accordance with the timing at which the leading end of the sheet comes into contact with the fixing device. A fixing device comprising a movement control means for moving the fixing device. 2. The fixing device according to claim 1, wherein the movement control means moves the support at a constant speed at a speed lower than the sheet conveying speed. 3. The supporting member further supports a pre-fixing guide for guiding to a pressure contact portion between the heat roller and the pressure contact roller, and the movement control means controls a timing at which a sheet front end contacts the pre-fixing guide. The fixing device according to claim 1, wherein the control unit controls the movement of the support according to the condition. 4. A fixing device for transferring an unfixed image onto a sheet in a transfer area, and then fixing the carried unfixed image while conveying the sheet, wherein the heat constituting the fixing device is provided. A support for supporting the roller and the pressing roller is provided so as to be movable in the sheet conveyance direction, and the support is moved in the sheet conveyance direction in accordance with the timing at which the leading end of the sheet comes into contact with the fixing device. Moving control means for moving the support body in the direction opposite to the sheet conveying direction in order to return to the original position after the rear end of the sheet during the fixing process has passed through the transfer area. A fixing device characterized by performing a return movement. 5. The apparatus according to claim 1, wherein, in a state where the fixing of the sheet is performed, the moving speed of returning the support is further lower than a moving speed of moving the support in accordance with the leading edge of the sheet. 5. The fixing device according to claim 4, wherein, in a state where the sheet is not fixed, the support is set at a higher speed than the sheet conveying speed. 6. The apparatus according to claim 1, wherein said movement control means determines whether or not to move the support in the sheet conveying direction according to the size and thickness of the sheet. The fixing device as described in the above.