JP2006308834A - Roller unit and fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device, wherein the exterior perimeter surface is not deformed even when a thin fixing roller is used. <P>SOLUTION: When a coil spring 62 is heated higher than a fixing temperature, an internal perimeter surface 52b of a metal core 52 is pressurized outward by the coil spring 62. However, when the temperature of the coil spring 62 is lower than the fixing temperature, the coil spring 62 is separated from the interior perimeter surface 52b of the core metal 52. Furthermore, although a moving unit 90 pressurizes a pressurizing roller 70 to the fixing roller 50 during image formation on a recording medium by a copying machine 10 (when the fixing roller 50 is at the fixing temperature), when the image formation is completed on the recording medium (when the fixing roller 50 is at the temperature lower than the fixing temperature), the pressurizing roller 70 is moved so that the pressurizing roller 70 is separated from the fixing roller 50. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a roller unit that conveys a recording medium while being sandwiched between other rollers, and a fixing device incorporating the roller unit.

  2. Description of the Related Art As an output device for a computer or workstation, an electrophotographic image forming apparatus that forms an image on a recording medium using a powder developer (toner) is known. In such an image forming apparatus, for example, an image bearing member such as a photosensitive drum is irradiated with light carrying image information (for example, a laser) to form an electrostatic latent image, and a developing roller is used for the electrostatic latent image. Then, toner is supplied to form a developed image, and this developed image is transferred to a recording medium using a transfer roller or the like to form a transferred image (developed image). The recording medium on which the transfer image is formed is conveyed to a fixing device, and the transfer image is fixed on the recording medium in the fixing device.

  The fixing device is usually provided with a fixing roller having a built-in heater and a pressure roller pressed against the outer peripheral surface of the fixing roller. When the transfer image is fixed on the recording medium, the transfer image is transferred to a predetermined position while the recording medium is nipped and conveyed at the nip portion between the fixing roller and the pressure roller (the portion where the fixing roller and the pressure roller are in contact with each other). Heat at the fixing temperature and pressurize at the same time. The transfer image is fixed on the recording medium by this heating and pressurization. The recording medium on which the transferred image is fixed is discharged while being sandwiched between discharge rollers or the like.

  The fixing device will be described with reference to FIG.

  FIG. 5 is a schematic diagram illustrating a schematic configuration of a conventional fixing device.

  The fixing device 100 is for making a toner (image) 102 a permanent visible image on a recording medium 104 such as recording paper. The recording medium 104 conveyed in the direction of arrow A by a conveyance unit (not shown) is guided by the fixing inlet guide 106 and enters a portion (nip portion) 108 where the fixing roller 120 and the pressure roller 130 contact each other.

  The fixing roller 120 is for heating and melting the toner 102. The thermistor 140 is in contact with the outer peripheral surface (front surface) of the fixing roller 120, and the thermistor 140 is configured to measure the temperature of the outer peripheral surface of the fixing roller 120. Further, the fixing roller 120 incorporates a heat source (a heating element) such as a halogen lamp 122. A controller (not shown) controls the halogen lamp 122 based on the outer peripheral surface temperature measured by the thermistor 140, whereby the outer peripheral surface temperature of the fixing roller 120 is maintained at a predetermined fixing temperature.

  As the fixing roller 120, for example, an outer peripheral surface of a cored bar 124 made of, for example, an iron or aluminum pipe is coated with a fluororesin layer 126 having good releasability. The fixing roller 120 is rotated in the direction of arrow B by a drive source (not shown).

  The pressure roller 130 is for pressing the recording medium 104 against the fixing roller 120 with a predetermined pressure. As the pressure roller 130, for example, an outer peripheral surface of a metal core 132, for example, covered with an elastic body layer 134 such as silicone rubber or fluororubber with a predetermined thickness is generally used. While pressing the pressure roller 130 against the fixing roller 120 with a predetermined pressure and rotating it in the direction of arrow C, a load for fixing the toner 102 to the recording medium 104 is applied.

  When the recording medium 104 enters the nip portion 108, the toner 102 on the recording medium 104 is melted at the fixing temperature, and the melted toner 102 is pressed against the recording medium 104 with the load described above. Fixed to 104. The recording medium 104 on which the toner 102 is fixed is separated from the fixing roller 120 and the pressure roller 130 by a separation claw 142 and reaches a paper discharge roller (not shown), and is discharged out of the apparatus by the paper discharge roller.

  The fixing roller 120 described above is required to rise quickly from the viewpoint of energy saving. For this reason, there is an image forming apparatus in which the time (rise time) from when the image forming apparatus main body is completely cooled to when the main switch is turned on and when the first copy is discharged is 30 seconds or less. This rise time is getting shorter year by year.

  Further, in a standby state where the main switch of the image forming apparatus main body is turned on, it is required to reduce the power consumption for keeping the fixing device warm as much as possible. For this reason, in the above standby state, it is necessary to completely turn off the heater of the fixing device. In this way, when the heater of the fixing device is completely turned off in the standby state, in order to bring the fixing roller to a predetermined temperature almost simultaneously with turning on the heater, the thickness of the fixing roller is reduced to reduce its heat capacity. It is necessary to keep. For this reason, a fixing roller made of an aluminum alloy having a good thermal conductivity is often used.

  In order to shorten the rise time described above, the thickness of the fixing roller 120 made of aluminum has recently been reduced to about 0.8 mm. When the thickness of the fixing roller 120 is further reduced, the fixing is performed when the recording medium 104 is sandwiched between the fixing roller 120 and the pressure roller 130 (nip portion 108) and the developed image is fixed with heat and pressure. The roller 120 may be deformed.

  In order to solve the above problems, a technique has been proposed in which a helical coil spring is inserted into the fixing roller 120 to reinforce the fixing roller 120 (see, for example, Patent Document 1).

  This technique will be described with reference to FIG.

  FIG. 6 is a cross-sectional view showing the fixing roller into which the coil spring is inserted. In this figure, the same components as those shown in FIG. 5 are denoted by the same reference numerals.

A coil spring 150 wound spirally is inserted into the inner space of the cored bar 124. The coil spring 150 extends in the longitudinal direction of the cored bar 124, contacts the inner peripheral surface of the cored bar 124, and presses the inner peripheral surface outward. Since the cored bar 124 is very thin, the pressing force received by the outer peripheral surface of the fixing roller 120 also affects the coil spring 150. When the fixing roller 120 starts to rotate and the pressure roller 130 starts to rotate, the pressed fixing roller 120 and the coil spring 150 also start to move in the longitudinal direction thereof. In this case, the movement of the fixing roller 120 is suppressed by a roller stopper (not shown).
JP-A-10-116675

  While an image is being formed on the recording medium by the image forming apparatus, as described above, a controller (not shown) controls the halogen lamp 122 based on the outer peripheral surface temperature measured by the thermistor 140, and the fixing roller The outer peripheral surface temperature of 120 is maintained at a predetermined fixing temperature. Accordingly, the coil spring 150 is also held at the predetermined fixing temperature or a temperature in the vicinity thereof.

  On the other hand, after the image formation on the recording medium 104 is completed, the energization of the halogen lamp 122 is turned off and the fixing roller 120 starts to be cooled. In this case, the core metal 124 may contract faster than the coil spring 150 due to a difference in expansion coefficient between the core metal 124 and the coil spring 150. The problem in this case will be described with reference to FIG.

  FIG. 7 is an enlarged schematic view showing a part of the fixing roller in which the core metal contracts faster than the coil spring.

  When the core metal 124 contracts earlier than the coil spring 150, the coil spring 150 strongly presses the outer peripheral surface of the core metal 124 from the inside. For this reason, when the cored bar 124 is thin, the portion of the outer peripheral surface of the cored bar 124 where the coil spring 150 is in contact with the inner peripheral surface on the opposite side is different from that shown in FIG. It protrudes slightly outside the part. As a result, the outer peripheral surface of the fixing roller 120 may be deformed after the fixing roller 120 is cooled. When the outer peripheral surface of the fixing roller 120 is deformed, a fixing failure occurs.

  In view of the above circumstances, an object of the present invention is to provide a roller unit whose outer peripheral surface is not deformed even if it is a thin cylindrical roller, and a fixing device in which this roller unit is incorporated.

In order to achieve the above object, the roller unit of the present invention comprises:
(1) a hollow cylindrical roller;
(2) When heated above a predetermined temperature, it contacts the inner peripheral surface of the cylindrical roller and presses the inner peripheral surface outward, and when the temperature is lower than the predetermined temperature, the inner peripheral surface of the cylindrical roller And a wire rod extending in the longitudinal direction of the cylindrical roller while being spirally wound in the hollow portion of the cylindrical roller, which is non-contact.

The fixing device of the present invention for achieving the above object is
(3) a fixing roller having a built-in heat source;
(4) When heated to a predetermined fixing temperature or higher, it contacts the inner peripheral surface of the fixing roller and presses the inner peripheral surface outward, and when the temperature is lower than the fixing temperature, the inner peripheral surface of the fixing roller. A wire that extends in the longitudinal direction of the fixing roller while being spirally wound in the hollow portion of the fixing roller,
(5) When the wire is heated to the fixing temperature or higher, it is pressed against the outer peripheral surface of the fixing roller, and when the wire is lower than the fixing temperature, it is not contacted with the outer peripheral surface of the fixing roller. And a pressure roller.

  Here, when the wire is heated above the fixing temperature, the pressure roller is moved so as to press against the outer peripheral surface of the fixing roller, and when the wire is lower than the fixing temperature, the pressure roller There may be provided a moving means for moving the pressure roller so as not to contact the outer peripheral surface of the fixing roller.

  In the roller unit of the present invention, only when the wire is heated to a predetermined temperature or more, it comes into contact with the inner peripheral surface of the cylindrical roller and presses the inner peripheral surface outward to reinforce. Even if the outer peripheral surface is pressed from the outside, the outer peripheral surface is not deformed. When the wire is below a predetermined temperature, it is not in contact with the inner peripheral surface of the cylindrical roller. Therefore, the outer peripheral surface of the thin cylindrical roller is not deformed by the wire.

  In the fixing device of the present invention, when the wire is heated to a temperature equal to or higher than the fixing temperature and presses the inner peripheral surface of the fixing roller outward, the pressure roller is pressed against the outer peripheral surface of the fixing roller. Therefore, even a thin fixing roller can withstand the pressing force from the pressure roller. On the other hand, when the wire is below the fixing temperature, the wire is not in contact with the inner peripheral surface of the fixing roller and the pressure roller is not in contact with the outer peripheral surface of the fixing roller. For this reason, when the pressing force from the pressure roller does not act on the fixing roller, the wire does not press the inner peripheral surface of the fixing roller. Accordingly, the outer peripheral surface of the thin fixing roller is not deformed by the wire.

  Here, when the wire is heated above the fixing temperature, the pressure roller is moved so as to press against the outer peripheral surface of the fixing roller, and when the wire is lower than the fixing temperature, the pressure roller However, when the moving means for moving the pressure roller so as to be in non-contact with the outer peripheral surface of the fixing roller is provided, the pressure roller can be easily moved.

  The present invention is realized in a roller unit and a fixing device in an image forming apparatus.

  A schematic structure of an image forming apparatus incorporating an embodiment of a roller unit of the present invention will be described with reference to FIG.

  FIG. 1 is a schematic diagram showing a digital copying machine as an example of an image forming apparatus in which an embodiment of a roller unit of the present invention is incorporated.

  On the top surface of the copying machine 10, a rectangular parallelepiped original pressing plate 12 that can be opened and closed is disposed. An image reading device 14 that reads an image recorded on the original is disposed below the original pressing plate 12. The upper surface (upper wall) of the image reading device 14 is a document table glass (not shown) on which a document is placed.

  An operation panel (not shown) for inputting the number of copies and the like is arranged on the front side (front side) of the original cover 12. A cassette 16 that stores a plurality of cut sheets is provided at the lower part of the copying machine 10 so as to be freely inserted into and removed from the copying machine 10. In addition, a space is formed in the left portion of the copying machine 10, and a paper discharge tray 18 on which the discharged recording paper is stacked is formed.

  A procedure for forming an image with the copying machine 10 will be described.

  In order to form an image recorded on an original on a recording medium, the original pressure plate 12 is opened, and the original is placed on the upper surface of an original platen glass (not shown) so that the image surface faces downward. The original is pressed and fixed by the original pressing plate 12. Next, by pressing a predetermined operation button or the like, the image recorded on the document is read by the image reading device 14. The read image is converted into a digital signal, and this digital signal is transmitted to the laser scanner 20.

  The signal transmitted to the laser scanner 20 is converted into laser light, and this laser light is irradiated onto the photosensitive drum 22 via the scanner mirror 20a and the folding mirror 20b that rotate at high speed. The photosensitive drum 22 is uniformly charged by a charger 24, and an electrostatic latent image is formed on the photosensitive drum 22 irradiated with laser light. The electrostatic latent image is developed with the developer supplied from the developing roller 26 to form a developed image.

  On the other hand, a recording medium such as recording paper is fed from the cassette 16 in the direction of arrow E (paper feeding direction) by the paper feeding roller 28 and conveyed to the transfer roller 34 by the conveying roller 30 and the registration roller 32. The transfer roller 34 transfers the developed image of the photosensitive drum 22 to the recording medium while sandwiching the recording medium together with the photosensitive drum 22. The recording medium to which the developed image is transferred is guided to the fixing device 40 by the conveyance guide 36. The fixing device 40 is provided with a fixing roller 50 (which is an example of a roller unit in the present invention) and a pressure roller 70. The pressure roller 70 is pressed against the fixing roller 50 by a pressure spring 72 (see FIG. 2). The recording medium is conveyed while being sandwiched between the two rollers 50 and 70, and the developed image is fixed on the recording medium. The recording medium on which the developed image is fixed in this manner is discharged by the discharge roller 80 and stacked on the discharge tray 18.

  The basic configuration of the fixing device 40 is the same as that of the conventional fixing device 100 shown in FIG. The fixing device 40 is different from the fixing device 100 in that the fixing roller 50 and the pressure roller 70 are moved. The structure of the fixing roller will be described with reference to FIGS.

  FIG. 2 is a cross-sectional view showing the inside of the fixing roller that has reached the fixing temperature, cut in the longitudinal direction. FIG. 3 is a cross-sectional view showing the inside of a fixing roller having a temperature lower than the fixing temperature, cut in the longitudinal direction.

  The fixing roller 50 includes a pipe-shaped (hollow cylindrical) cored bar 52 (an example of the cylindrical roller according to the present invention) made of, for example, an aluminum alloy. The outer diameter of the central portion in the longitudinal direction of the cored bar 52 is smaller than the outer diameters at both ends in the longitudinal direction. For this reason, the cored bar 52 has an inverted crown shape. Since the cored bar 52 has an inverted crown shape in this way, the clamping force (the recording medium is pressed against both ends) in the longitudinal direction of the fixing roller 50 in the nip portion formed by the fixing roller 50 and the pressure roller 70. Force) is greater than the central portion in the longitudinal direction. Accordingly, no twist or wrinkle occurs on the recording medium conveyed while being sandwiched between the fixing roller 50 and the pressure roller 70. In addition, the diameter of the longitudinal direction both ends of the metal core 52 is larger by about 0.07 mm to 0.13 mm than the longitudinal center. Further, the cored bar 52 may be formed in a crown shape, and in this case, the outer diameter of the central part in the longitudinal direction of the cored bar 52 is larger than the outer diameter of both end parts in the longitudinal direction. In addition, convex portions 52 a for preventing the coil spring 62 from popping out are formed at both longitudinal ends of the cored bar 52.

  The cored bar 52 is cut so that the thickness thereof is about 0.3 to 0.4 mm over the entire region. Here, the thickness of the cored bar 52 is 0.4 mm, and the outer diameter of the cored bar 52 is 30 mm. A release layer 54 is formed on the outer peripheral surface of the cored bar 52. This release layer 54 is a fluororesin having high releasability, oil-impregnated silicone rubber, or a silicone rubber layer having a fluororesin layer formed on the surface thereof. A halogen lamp 60 (see FIG. 4) extending in alignment with the rotation center axis is disposed in the hollow portion of the core metal 52 (inside the fixing roller 50).

  In the hollow portion of the cored bar 52 (inside the fixing roller 50), for example, a stainless steel coil spring 62 (an example of a wire rod according to the present invention) wound in a spiral shape is disposed. Further, here, when the coil spring 62 is heated to the fixing temperature or higher, the coil spring 62 presses the inner peripheral surface 52b of the cored bar 52 outward as shown in FIG. However, when the coil spring 62 is lower than the fixing temperature, the coil spring 62 moves away from the inner peripheral surface 52b of the cored bar 52 (not in contact with the inner peripheral surface 52b) as shown in FIG.

  As described above, the coefficient of thermal expansion of the coil spring 62 is such that when the coil spring 62 is equal to or higher than the fixing temperature, the inner peripheral surface 52b of the core metal 52 is pressed outward, and when the coil spring 62 is lower than the fixing temperature, the core metal 52 is pressed. It is determined not to contact the inner peripheral surface 52b. Therefore, the thermal expansion coefficient of the coil spring 62 is larger than the thermal expansion coefficient of the core metal 52.

  While the image is formed on the recording medium by the copying machine 10 (when the fixing roller 50 is at the fixing temperature), as described above, the halogen lamp 60 is controlled so that the outer peripheral surface temperature of the fixing roller 50 is a predetermined fixing temperature. Held at temperature. In this case, the coil spring 62 is also held at this fixing temperature. Accordingly, while the image is formed on the recording medium by the copying machine 10, the coil spring 62 presses the inner peripheral surface 52 b of the core metal 52 outward to reinforce the core metal 52. Even if the pressure roller 70 is pressed, the fixing roller 50 is not deformed.

  On the other hand, after the image has been formed on the recording medium, the energization of the halogen lamp 60 is turned off and the fixing roller 50 starts to be cooled. In this case, the coil spring 62 contracts faster than the cored bar 52 and moves away from the inner peripheral surface 52b of the cored bar 52 as shown in FIG. Accordingly, the cored bar 52 is not reinforced by the coil spring 62. However, as described later, after the image is formed on the recording medium (when the fixing roller 50 is lower than the fixing temperature), the pressure roller 70 is configured to be separated from the fixing roller 50. 50 does not deform.

  A mechanism for moving the pressure roller 70 will be described with reference to FIG.

  FIG. 4 is a schematic diagram showing a mechanism for moving the pressure roller. In this figure, the same components as those shown in FIGS. 1 to 3 are denoted by the same reference numerals.

  The pressure roller 70 has substantially the same length as the fixing roller 50 and extends in a direction perpendicular to the paper surface of FIG. The pressure roller 70 is driven to rotate by the fixing roller 50 with a rotation shaft 72 longer than the pressure roller 70 as a central axis. A moving unit 90 (which is an example of a moving means in the present invention) that moves the pressure roller 70 at a predetermined timing is disposed at each of both ends in the longitudinal direction of the rotating shaft 72. The moving unit 90 presses the pressure roller 70 against the fixing roller 50 while the image is being formed on the recording medium by the copying machine 10 (when the fixing roller 50 is at the fixing temperature), but has finished forming the image on the recording medium. After that (when the fixing roller 50 is below the fixing temperature), the pressure roller 70 is moved so that the pressure roller 70 is separated from the fixing roller 50.

  The moving unit 90 includes a moving rod 92 extending in a direction orthogonal to the rotating shaft 72 and a cylinder 94 that moves the longitudinal end portion 92a of the moving rod 92 up and down. The other end 92b of the moving rod 92 in the longitudinal direction is fixed to the shaft 92c. Therefore, the moving bar 92 rotates around the shaft 92c.

  When the fixing roller 50 is at the fixing temperature, the cylinder 94 is turned on, and the moving plate 96 fixed to the lower end of the shaft 94a of the cylinder 94 moves to the position indicated by the solid line. Along with this movement, the moving rod 92 rotates in the direction of arrow D about the shaft 92c, and the pressure roller 70 is pressed against the fixing roller 50. In this case, as described above, the inner peripheral surface of the cored bar 52 is pressed outward by the coil spring 62, so that the outer periphery of the cored bar 52 is pressed even when the pressure roller 70 presses the outer peripheral surface of the fixing roller 50. The surface does not deform.

  On the other hand, when the fixing roller 50 is lower than the fixing temperature, the cylinder 94 is turned off, and the moving plate 96 moves to a position indicated by a two-dot chain line. With this movement, the moving bar 92 rotates about the shaft 92c in the direction opposite to the arrow D direction, and the pressure roller 70 is separated from the fixing roller 50. In this case, since the inner peripheral surface of the cored bar 52 is not pressed outward by the coil spring 62 as described above, the outer peripheral surface of the cored bar 52 even if the pressure roller 70 is separated from the outer peripheral surface of the cored bar 52. Does not deform.

  As described above, when the fixing roller 50 is equal to or higher than the fixing temperature, the pressure roller 70 presses the outer peripheral surface of the fixing roller 50, and the coil spring 62 presses the inner peripheral surface of the fixing roller outward to reinforce. Therefore, the outer peripheral surface of the cored bar 52 is not deformed. On the other hand, when the fixing roller 50 is lower than the fixing temperature, the pressure roller 70 is separated from the outer peripheral surface of the fixing roller 50, but the coil spring 62 is not in contact with the inner peripheral surface of the fixing roller. The outer peripheral surface of 52 is not deformed.

1 is a schematic diagram showing a digital copying machine as an example of an image forming apparatus in which an embodiment of a roller unit of the present invention is incorporated. FIG. 4 is a cross-sectional view showing the inside of a fixing roller that has reached a fixing temperature, cut in the longitudinal direction. FIG. 3 is a cross-sectional view showing the inside of a fixing roller having a temperature lower than the fixing temperature, cut in the longitudinal direction. It is a schematic diagram which shows the mechanism which moves a pressure roller. FIG. 10 is a schematic diagram illustrating a schematic configuration of a conventional fixing device. It is sectional drawing which shows the fixing roller in which the coil spring was inserted. FIG. 4 is an enlarged schematic view illustrating a part of a fixing roller in which a core metal contracts earlier than a coil spring.

Explanation of symbols

10 Copier 40 Fixing Device 50 Fixing Roller 52 Core Bar 62 Coil Spring 70 Pressing Roller 90 Moving Unit 92 Moving Bar 94 Cylinder 96 Moving Plate

Claims (3)

A hollow cylindrical roller;
When heated above a predetermined temperature, it contacts the inner peripheral surface of the cylindrical roller and presses the inner peripheral surface outward, and when the temperature is lower than the predetermined temperature, it does not contact the inner peripheral surface of the cylindrical roller. A roller unit comprising: a wire rod that is spirally wound in a hollow portion of the cylindrical roller and extends in a longitudinal direction of the cylindrical roller. A fixing roller with a built-in heat source,
When heated above a predetermined fixing temperature, it contacts the inner peripheral surface of the fixing roller and presses the inner peripheral surface outward, and when it is lower than the fixing temperature, it does not contact the inner peripheral surface of the fixing roller. A wire extending in the longitudinal direction of the fixing roller while being spirally wound in the hollow portion of the fixing roller,
A pressure roller that is pressed against the outer peripheral surface of the fixing roller when the wire is heated to the fixing temperature or higher, and is not in contact with the outer peripheral surface of the fixing roller when the wire is lower than the fixing temperature; A fixing device comprising: When the wire is heated above the fixing temperature, the pressure roller is moved so as to press against the outer peripheral surface of the fixing roller, and when the wire is below the fixing temperature, the pressure roller moves the fixing roller. The fixing device according to claim 2, further comprising a moving unit that moves the pressure roller so as not to contact the outer peripheral surface of the roller.

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