Patent Grant
7620356
1. Field of the Invention
The present invention relates to a fixing apparatus for fixing a toner image.
2. Description of the Related Art
The conventional image forming apparatus such as printer and copier performs fixation of a toner image on a sheet by forming a toner image using an electrophotographic recording method, and by transferring the toner image onto the sheet, then by applying heat and pressure to the sheet to fix the toner image on the sheet.
That type of fixing apparatus for fixing the toner image onto the sheet includes the one, which has a metal roller having a heater therein, and has an elastic fixing belt in pressure contact with the metal roller.
In the color laser printer 100, after a toner image is formed by the image forming portion 102, the toner image is transferred onto the sheet P. Then, the sheet P is sent to the fixing apparatus 105. After that, the sheet P is heated and pressed in the fixing apparatus 105 to fix the toner image onto the sheet.
As illustrated in
The fixing belt unit 53 has a fixing belt 531 which is an endless belt, and a pressure pad portion 540 which is brought into pressure contact with the fixing roller 510 through the fixing belt 531 in a direction indicated by the arrow PF to form a fixing nip.
Here, the fixing belt 531 is passed around an inlet roller 532, a separation roller 533, and a steering roller 534. The separation roller 533 is made of metal such as stainless steel, and is brought into pressure contact with the fixing roller 510 through the fixing belt 531 in a direction indicated by the arrow SF. One end of the steering roller 534 is movable in directions indicated by the double-headed arrow B. The deviation of the fixing belt 531 can be corrected by moving the one end of the steering roller 534.
The pressure pad portion 540 is disposed between the inlet roller 532 and the separation roller 533, and has a base 541 made of metal such as stainless steel, a pressure pad 542, and a slide sheet 543 disposed between the pressure pad 542 and the fixing belt 531. The slide sheet 543 is made of PI film, while the pressure pad 542 is made of silicon rubber.
An oil felt 536 impregnated with silicone oil is disposed between the inlet roller 532 and the pressure pad 540. The oil felt 536 applies oil onto an inner surface of the fixing belt 531 so that the friction force between the fixing belt 531 and the slide sheet 543 decreases.
Here, for that type of conventional fixing apparatus 105, unless the fixing roller 510 and the fixing belt 531 in a waiting operation are kept at a specified temperature, the next image formation output takes a time until the fixing roller 510 and the fixing belt 531 reach the specified temperature. Therefore, even in the waiting operation, the fixing roller 510 and the fixing belt 531 are required to be kept heated.
By the way, the uses of forming color image have been increasing in recent years. Accordingly, in addition to the ability of outputting an image of the normal quality, the image forming apparatus is required further to have the ability of outputting a high gloss image of a quality comparable to a silver halide photography. To this point, a coat paper is used in some cases as a sheet to improve the color-forming property of the toner image and the quality of the image. That type of coat paper is prepared by coating a coat layer comprising synthetic resin on the surface of the sheet at a thickness of several tens of micrometers.
When the fixing apparatus 105 fixes a toner image on a coat paper after the toner image is transferred onto the coat paper, if an excess heat is applied to the coat paper, the water in the coat paper evaporates and the thus evaporated water may partially destroys the coat layer applied on the surface of the sheet. If the coat layer is destroyed, the image loses the smoothness. In particular, the fixing apparatus using the fixing belt has a wide nip, which applies the large amount of heat to the coat paper, so that such a fixing apparatus likely poses the above problem.
In this regard, according to the related art, when the apparatus is in a waiting operation, contrary to the image forming operation mode illustrated in
In the state illustrated in
The temperature of the fixing belt 531 is set to a temperature lower than the temperature of the fixing roller 510 to some extent, thereby reducing the heat applied to the backside of the coat paper to suppress the evaporation of water in the coat paper, thus preventing the occurrence of the above phenomenon.
Referring back to
The sensor lever 583 has a contact portion 583b which projects by a spring (not shown) from an opening (not shown) above a sheet guide 570 when there is no sheet on a sheet guide 570, and a shutter portion 583a to shield the photo-interrupter 584.
When there is no sheet in the fixing nip, the sensor lever 583 moves so as the contact portion 583b to project above the sheet guide 570, as illustrated in
Even when the shutter portion 583a shields the photo-interrupter 584, the controller (not shown) neglects the signal of the sheet presence or absence detecting sensor 580 as far as the conveying of the sheet P is correctly conducted.
Once jamming of sheet occurred in the printer main body, the controller (not shown) forcefully retreats the fixing belt unit 53 with respect to the fixing roller 510, as illustrated in
If, however, the sensor lever 583 is used to detect the presence or absence of jammed sheet at the fixing nip as described above, the pressing of the sensor lever 583 induces deformation of the leading edge of the sheet P, which worsens the shape of sheet entering the fixing nip, or which results in unstable behavior of sheet. Once the sheet entering shape becomes worse, or the sheet behavior becomes unstable, there is a possibility to cause the poor fixation (defective image) on fixing the toner image in the fixing nip.
A measure to prevent the leading edge deformation of sheet P is that the sheet presence or absence detecting sensor is formed as a photo-coupler integrating an infrared luminous element with an infrared light-receiving element to detect the presence or absence of the sheet by irradiating the infrared light to the backside of the sheet, (refer to, for example, Japanese Patent Application Laid-Open No. H06-175524).
With the conventional fixing apparatus and image forming apparatus detecting the presence or absence of a sheet using that type of photo-coupler, there is a need of forming a hole in the sheet guide to irradiate the infrared light to the backside of the sheet. With that hole, however, toner and paper dust may pass through the hole to adhere to the photo-coupler, which raises a problem of failing in the detection of the presence or absence of the sheet.
To this point, for example, it is considered to project the sensor lever of the sheet presence or absence detecting sensor to above the sheet guide only when the detection of the presence or absence of a sheet is required, while a solenoid usually retreats the sensor lever from the sheet guide(refer to, Japanese Patent Application Laid-Open No. H06-175524).
Although the above construction can prevent the deformation of leading edge of the sheet P, the construction presents other problems of a cost increase caused by the addition of a drive source such as a solenoid, an additional space for installing the solenoid, and an additional drive controller for the solenoid.
Furthermore, when the sensor lever is used to detect the presence or absence of the sheet, it is necessary to provide the sheet guide with an opening through which the sensor lever can be projected to above and retreated from the sheet guide. When, however, the sensor lever is retreated from the sheet guide, the leading edge of a sheet may be caught by the opening. Once the leading edge of the sheet is caught by the opening, the shape of the sheet entering fixing nip may be deteriorated so that there is a possibility that a poor fixing occurs.
The present invention has been derived to overcome the disadvantages of the aforementioned conventional image forming apparatuses. Further, an aspect of the present invention is to provide a fixing apparatus, an image forming apparatus and sheet conveying apparatus, which can simplify structure the apparatus.
According to an aspect of the present invention, a fixing apparatus is provided having a fixing rotary member and a pressure rotary member, wherein the pressure rotary member is configured to be separable from and in pressure contact with the fixing rotary member, and wherein the fixing rotary member and the pressure rotary member are configured to fix a toner image onto a sheet. The fixing apparatus includes a pressure unit which includes the pressure rotary member and which is configured to be movable between a fixing position in which the pressure rotary member is in pressure contact with the fixing rotary member and a waiting position in which the pressure rotary member is separated from the fixing rotary member; a guide member which forms a conveying path to guide a sheet on which the toner image is fixed by the fixing rotary member and the pressure rotary member; a sheet detecting member which is configured to be movable by being pressed by the sheet in the conveying path, wherein the sheet detecting member is movable between a detecting position in which the sheet detecting member is projected into the sheet conveying path so that the sheet detecting member can be pressed by the sheet in the conveying path, and a retreat position in which the sheet detecting member is retreated from the sheet conveying path; and a detecting sensor configured to detect a presence or absence of the sheet in the sheet conveying path based on a position of the sheet detecting member. The sheet detecting member is moved to the detecting position in association with a movement of the pressure unit to the waiting position, and is moved to the retreat position in association with a movement of the pressure unit to the fixing position.
According to the present invention, the sheet detecting member is moved to the detecting position or the retreat position in association with the movement of rotary member, thereby the sheet detecting member can be moved to the detecting position without an additional drive source only when a sheet is jammed. With the aforementioned measures, the apparatus is simply structured.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Exemplary embodiments of the present invention will now herein be described below in detail referring to the drawings.
The printer main body 101 has an image forming portion 102 to form an image on a sheet P, a sheet conveying portion 103 to convey the sheet P to the image forming portion 102, and a fixing apparatus 7. The image forming portion 102 has process stations Pa, Pb, Pc, and Pd for forming toner images with four colors: yellow (Y), magenta (M), cyan (C), and black (Bk). The process stations Pa to Pd have photosensitive drums 1 (1a, 1b, 1c, and 1d) as image-bearing members bearing four color-toner images of yellow, magenta, cyan, and black, respectively, and rotating in the clockwise direction.
Further, as illustrated in
Once the image forming operation begins in the color laser printer 100, laser light emitted from the scanner 111 based on the reading information from the image reading portion 110 irradiates the photosensitive drum 1 of which the surface is uniformly charged by the charge roller 12.
The irradiation creates the respective latent images on the photosensitive drums for yellow (Y), magenta (M), cyan (C), and black (Bk) toners. Then, the developing units 2 develop the latent images to sequentially form the toner images of yellow, magenta, cyan, and black on the respective photosensitive drums.
In parallel to the toner image formation, the sheets P contained in a sheet cassette 11 are picked up by a sheet feeding roller 51, and then separated one by one by a separation roller pair 52. The separated sheet is fed to a registration roller pair 54, which corrects the skew feed of the sheet. After that, the sheet is placed on a transfer belt 31 in synchronism with the image forming operation by a registration roller pair 54, and then is conveyed to a transfer portion in which the transfer belt 31 is in pressure contact with the photosensitive drum 1.
Onto the sheet P thus conveyed to the transfer portion, the toner images in individual colors on the photosensitive drums 1 are sequentially transferred and superposed by the action of transfer rollers 3 (3a, 3b, 3c, and 3d) which are located in respective transfer portions as illustrated in
Then, the sheet P is heated and pressed in the fixing apparatus 7. As a result, respective color toners on the sheet are fused and mixed with one another and are fixed on the sheet, and thus a full-color print image as a permanent image is fixed on the sheet.
The sheet P on which the toner image is thus fixed is conveyed to a discharged sheet processing apparatus 6 to be subjected to a specified sheet processing. After that, the sheet P is discharged onto discharged sheet trays 62 and 63 by a conveying roller 61. The discharged sheet trays 62 and 63 move downward to accept large number of discharged sheets being piled.
As illustrated in
The fixing roller 71 has an elastic layer 712 made of silicon rubber formed on the surface layer of a core metal 711 made of aluminum, and a releasing layer 713 made of PFT tube provided on the surface layer of the elastic layer 712 to improve the releasability of the toner. In addition, a heater 721 as a heat source is positioned in the fixing roller near the center of the fixing roller.
The fixing belt 731, which is a pressure rotary member separable from the fixing roller 71 and brought into pressure contact with the fixing roller 71 of the fixing belt unit 73 is passed around an inlet roller 732, a separation roller 733, and a steering roller 734. The separation roller 733 is made of metal such as stainless steel (SUS), and is in pressure contact with the fixing roller 71 via the fixing belt 731. One end of the steering roller 734 is movable in directions indicated by the double-headed arrow T to correct the deviation of the fixing belt 731.
The pressure pad portion 740 is positioned between the inlet roller 732 and the separation roller 733, and has a base 741 made of metal such as stainless steel (SUS), a pressure pad 742, and a slide sheet 743, which is disposed between the pressure pad 742 and the fixing belt 731. The slide sheet 743 is made of PI film, and the pressure pad 742 is made of silicon rubber.
An oil felt 735 impregnated with silicone oil is disposed between the inlet roller 732 and the pressure pad portion 740. The oil felt 735 applies oil on the inner surface of the fixing belt 731 to decrease the friction force between the fixing belt 731 and the slide sheet 743.
Furthermore, when a coat paper is used, it is necessary to prevent the problem of evaporation of water contained inside the coat paper, as described above. To this end, with respect to the image forming operation illustrated in
In the state of
The temperature of the fixing belt 731 is set to a temperature lower than the temperature of the fixing roller 71 to some degree. As a result, the heat applied to the backside of the coat paper can be reduced so that the evaporation of water in the coat paper can be reduced, thereby preventing the above phenomenon from occurring.
The pressure mechanism of the fixing belt unit 73 to bring the fixing belt unit 73 into contact with the fixing roller 71 and separate the fixing belt unit 73 from the fixing roller 71 is described below referring to
A pressure mechanism 75 brings the fixing belt unit 73 into contact with the fixing roller 71 and separates the fixing belt unit 73 from the fixing roller 71. The pressure mechanism 75 is provided at each end of the fixing belt unit 73.
The pressure mechanism 75 holds the inlet roller 732 and the separation roller 733 through bearings 732a and 733a rotatably, and has a roller pressure holder 751 rotatable about a rotary shaft 754. Also the pressure mechanism 75 holds (a base 741 of) a pressure pad portion 740, and has a pad pressure holder 752 rotatable about the rotary shaft 754.
Furthermore, the pressure mechanism 75 has a pressure holder 753 rotatable about the rotary shaft 754. The pressure holder 753 is disposed below the roller pressure holder 751 and the pad pressure holder 752, and supports the roller pressure holder 751 and the pad pressure holder 752 from below.
A roller pressure spring 757 is disposed between the pressure holder 753 and the roller pressure holder 751. A first guide shaft 755 fixed to the pressure holder 753 extends through the roller pressure spring 757 and a hole (not shown) provided in the roller pressure holder 751, and then the upper end of the first guide shaft 755 projects above form the roller pressure holder 751. Furthermore, the upper end of the first guide shaft 755 is provided with a stopper portion 755a.
A pad pressure spring 758 is disposed between the pressure holder 753 and the pad pressure holder 752. A second guide shaft 756 fixed to the pressure holder 753 extends through the pad pressure spring 758 and a hole (not shown) provided in the pad pressure holder 752, and then the upper end of the second guide shaft 756 is projected above from the pad pressure holder 752. Furthermore, the upper end of the second guide shaft 756 is provided with a stopper portion 756a.
Further, the pressure holder 753 has a receiving portion 759 which contacts with a pressure cam 761 which is fixed to a shaft 760 rotated by a drive device (not shown) provided in the printer main body 101. The rotation of the pressure cam 761 rotates the pressure holder 753 about the rotary shaft 754 in the vertical direction. In association with the rotation of the pressure holder 753, the roller pressure holder 751 and the pad pressure holder 752 also rotates in the vertical direction as described later.
A pad pressure stay 762 connects the pad pressure holders 752 provided at both ends of the pad pressure stay 762. On the pad pressure stay 762 at almost center in width direction perpendicular to the sheet conveying direction, there are provided the thermistor 736 and a sensor oscillation lever 763, which oscillates a sheet presence or absence detecting sensor 780 as described later.
The sheet guide 770 is a guide member provided on the upstream side of the inlet roller 732 in the sheet conveying direction. The sheet guide 770 guides the leading edge of the sheet into the fixing nip formed by pressing the fixing belt unit 73 against the fixing roller 71. The sheet guide 770 forms a conveying path 301 (see
The sheet presence or absence detecting sensor 780 has a sensor table 781 which is a body portion rotatable about a rotary shaft 781b, a sensor lever 783 as a sheet detecting member provided rotatably about a shaft 782 on the sensor table 781, and a photo-interrupter 784.
Further, the sensor lever 783 has a contact portion 783b projecting from the sheet guide 770 by a spring 785, and a shutter portion 783a to shield the photo-interrupter 784. The sheet guide 770 is provided with an opening (not shown) through which the contact portion 783b of the sensor lever 783 is projected from the sheet guide 770.
During the normal image forming operation, in the sheet presence or absence detecting sensor 780, the shutter portion 783a is moved to a position for shielding the photo-interrupter 784, as illustrated in
The output of the sheet presence or absence detecting sensor 780 enters a controller 130 provided in the printer main body 101, as illustrated in
Once an image forming signal enters the pressure mechanism 75 having the above construction, a drive system (not shown) rotates the rotary shaft 760, and thereby the pressure cam 761 rotates as illustrated in
When the pressure holder 753 thus rotates upward, the roller pressure holder 751 is pressed by the roller pressure spring 757 to rotate upward about the rotary shaft 754, and the fixing belt 731 is pressed against the fixing roller 71 by a pressure force SF via the separation roller 733. Similarly, the pad pressure holder 752 is urged by the pad pressure spring 758 to rotate upward about the rotary shaft 754, and the fixing belt 731 is pressed against the fixing roller 71 by a pressure force PF via the fixing pad portion 740.
At this moment, the sensor oscillation lever 763 provided on the pad pressure stay 762 is separated from a pressing portion 781a positioned at a lower end of the sensor table 781. In this state, the sensor lever 783 contacts with a stopper portion 770a of the sheet guide 770, thus the sensor lever 783 is held at a retreat position.
When the fixing roller 71 rotates in the direction indicated by the arrow G in this state, the fixing belt 731 also rotates in the direction indicated by the arrow G following the rotation of the fixing roller 71. After that, when the sheet conveyed in the direction indicated by the arrow H enters a fixing nip (a pressure contact portion) M between the fixing roller 71 and the fixing belt 731, the toner on the sheet is fused by the heat of the fixing roller 71 and the fixing belt 731. By the pressure of the pressure pad portion 740, the toner is pressed against the sheet and fixed on the sheet.
According to the embodiment, the retreat position of the sensor lever 783 is selected to a position in which the contact portion 783b of the sensor lever 783 is substantially coplanar with the sheet guide surface 770b without projecting above from a sheet guide surface 770b of the sheet guide 770.
By selecting the retreat position of the sensor lever 783 to that position, the sheet can enter the fixing nip M without being caught by the sensor lever 783. In addition, the sheet can enter the fixing nip M without being caught by an opening (not shown), which is formed in the sheet guide 770 to allow the contact portion 783b of the sensor lever 783 to project from the sheet guide 770 through the opening.
By retreating the sensor lever 783 during the image forming operation to the retreat position in which the sensor lever 783 is substantially coplanar with the sheet guide surface 770b, the unstable behavior of the sheet and the deformation of the sheet caused by the leading edge of the sheet contacting with the sensor lever 783 can be avoided. As a result, the shape of the sheet entering the fixing nip M is stabilized, and good fixation can be performed.
During the above operation, the shutter portion 783a shields the photo-interrupter 784, and thereby the sheet presence or absence detecting sensor 780 is turned ON. In the embodiment, however, even if the sheet presence or absence detecting sensor 780 is turned ON to send a signal, the controller 130 ignores the signal when no jamming has occurred in the printer main body 101.
On the other hand, in a state that no sheet is conveyed or in a state that the apparatus is in a standby state for waiting output of the image, the pressure cam 761 rotates, as illustrated in
Once the pressure holder 753 thus rotates downward, the roller pressure holder 751 is locked by the stopper portion 755a on the upper end of the first guide shaft 755 to rotate downward about the rotary shaft 754, and then the separation roller 733 and the fixing belt 731 are separated from the fixing roller 71. Similarly, the pad pressure holder 752 is locked by the stopper portion 756a on the upper end of the second guide shaft 756 to rotate downward about the rotary shaft 754, and then the fixing pad portion 740 and the fixing belt 731 are separated from the fixing roller 71.
As a result, with the pressure mechanism 75, the fixing belt unit 73 (the fixing belt 731) can be moved between a fixing position in which the fixing belt 731 is in pressure contact with the fixing roller 71 and a waiting position in which the fixing belt 731 is separated from the fixing roller 71.
Furthermore, when the pressure holder 753 is rotated downward as described above, the sensor oscillation lever 763 provided on the pad pressure stay 762 constituting the interlocking member is rotated upward to press upward the pressing portion 781a on the sensor table 781 from below. When the sensor table 781 is pressed upward from below, the sensor table 781 is rotated about the rotary shaft 781b in the direction indicated by the arrow X against the urging force of the urging unit (not shown), thereby releasing the lock of the sensor lever 783 from the stopper portion 770a of the sheet guide 770.
As a result, by the spring 785, the sensor lever 783 moves to a position in which the contact portion 783b is projected above from the sheet guide surface 770b. The position of the sensor lever 783 illustrated in
With the fixing apparatus 7 having the above structure, when a jamming of a sheet occurs in the printer main body 101, the controller 130 controls the pressure mechanism 75 to move the fixing belt unit 73 and the sensor lever 783 to the position illustrated in
If a jamming of a sheet occurs between the fixing roller 71 and the fixing belt unit 73, the condition becomes as illustrated in
Next, an example detection operation of a residual sheet will be described referring to the flowchart of
In the normal condition, when the print key (not shown) provided on the printer main body 101 is turned ON, (YES of S50), the pressure mechanism 75 is actuated. The fixing belt 731 is brought into pressure contact with the fixing roller 71 (S52) as illustrated in
When, however, the jamming detecting sensor (not shown) is turned ON (YES of S56) by detecting that a jamming of a sheet occurs during a sheet conveyance after the print operation begins, the jamming detecting sensor outputs a detection signal to the controller 130. Based on the detection signal, the controller 130 immediately stops the fixing roller 71 (S58), and further drives the pressure mechanism 75 to separate the fixing belt 731 from the fixing roller 71 (S60). Thereby, the fixing apparatus 7 is changed from the state as illustrated in
When the jammed sheet is removed, the state of
If the operator failed to recognize a jammed sheet in the fixing apparatus 7, and if the jammed sheet is not removed from the fixing apparatus 7 as illustrated in
Now referring back to
On the other hand, even if the residual sheet is removed and the sheet presence or absence detecting sensor 780 is turned OFF (NO of S62), when the jamming detecting sensor stays in the turned-ON state (YES of S56), the controller 130 detects the occurrence position of the jamming other than the fixing apparatus 7. Then, the controller 130 displays the jamming processing indication at the jamming occurrence position on the operation portion (not shown) (S66). After that, when the operator has removed the residual sheet in accordance with the residual sheet processing indication, the apparatus is allowed to receive the image forming signal again so that an image formation is enabled.
As described above, by moving the sensor lever 783 between the detection position and the retreat position in association with the movement of the fixing belt unit 73, the sensor lever 783 can be moved to the detection position only in case of sheet jamming. That is, according to the embodiment, an interlocking mechanism is provided to link the movement of the fixing belt unit 73 with the movement of the sensor lever 783, thereby moving the sensor lever 783 between the detection position and the retreat position by the interlocking mechanism. As a result, the deformation of the leading edge of a sheet is prevented with a simple structure without adding any drive source, and the occurrence of a poor fixation can be prevented.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2006-071871, filed Mar. 15, 2006, which is incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-071871 | Mar 2006 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5365322 | Hamada et al. | Nov 1994 | A |
| 6647216 | Tanaka | Nov 2003 | B2 |
| 7280775 | Kubochi et al. | Oct 2007 | B2 |
| Number | Date | Country |
|---|---|---|
| 06-175524 | Jun 1994 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20070217839 A1 | Sep 2007 | US |
