JP2005326702A - Belt fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt fixing device which can suppress an increase in driving torque of a fixing belt and can prevent the breakage of a driving mechanism including a motor. <P>SOLUTION: The belt fixing device 10 comprises: a fixing belt 12 the inner surface of which is coated with a lubricant; a nip forming member 16 fixed in the fixing belt 12; a pressure roller 20 pressed to the nip forming member 16 via the fixing belt 12 and driven to rotate; and a lubricant replenishing means 19, 24 for performing predetermined operation to replenish a lubricant to the contact part of the nip forming member 16 where the fixing belt 12 slides under friction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a belt fixing device used in an electrophotographic image forming apparatus.

  Conventionally, for example, in Patent Documents 1 and 2 below, an elastic roller is pressed against a pressure pad via an endless fixing belt, and the elastic belt is driven to rotate so that the fixing belt rubs on the pressure pad. In a belt fixing device that is driven to rotate while sliding, a technique has been proposed in which a lubricant is applied to the inner surface of the fixing belt to reduce the frictional resistance with the pressure pad and suppress the driving torque.

JP 2001-341143 A JP 2001-228731 A

  However, it is structurally difficult to seal the lubricant inside the fixing belt, and the lubricant gradually leaks from the inside of the fixing belt during use. As a result, the lubricant in the frictional sliding portion between the pressure pad and the fixing belt will eventually be exhausted. For this reason, the frictional resistance between the pressure pad and the fixing belt increases, and the driving torque of the elastic roller that drives the fixing belt increases. As a result, even if a lubricant is used, an increase in driving torque cannot be prevented, so that it is necessary to use a large motor or a large driving mechanism after all.

  SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide a belt fixing device that can suppress an increase in driving torque of a fixing belt and prevent an increase in size and damage of a driving mechanism including a motor.

  In order to achieve the above object, a belt fixing device according to the present invention includes an endless belt having an inner surface coated with a lubricant, a nip forming member fixedly disposed in the endless belt, and the endless belt. Lubricant replenishment that performs a predetermined operation to replenish lubricant to a contact portion between the elastic roller that is rotationally driven in pressure contact with the nip forming member and the nip forming member on which the endless belt frictionally slides Means.

  The belt fixing device of the present invention may further include a torque detection unit that detects a driving torque of the endless belt, and the lubricant supply unit may be operated based on a detection result of the torque detection unit.

  In the belt fixing device of the present invention, the torque detecting means may detect torque based on the rotational speed of the endless belt or the rotational speed of a driven roller that rotates in accordance with the rotation of the endless belt. Good.

  In the belt fixing device of the present invention, the torque detection unit may detect torque based on a loop amount of the paper introduced into a nip portion between the endless belt and the elastic roller.

  In the belt fixing device of the present invention, the torque detection unit may detect torque based on a current of a motor that drives the elastic roller.

  In the belt fixing device of the present invention, the predetermined operation may be to temporarily reduce the pressure load of the elastic roller.

  In the belt fixing device of the present invention, the predetermined operation may be to temporarily reversely drive the elastic roller.

  Furthermore, in the belt fixing device of the present invention, the predetermined operation may be to notify the replacement timing of the lubricant supply member disposed in contact with the inner surface of the endless belt.

  According to the belt fixing device of the present invention, the lubricant replenishing means temporarily reduces the pressure contact load of the elastic roller, temporarily rotates the elastic roller in reverse, notifies the replacement timing of the lubricant supply member, etc. By performing this operation, the lubricant is replenished between the endless belt that is being depleted of the lubricant and the nip forming member. As a result, the lubrication state between the endless belt and the nip forming member is recovered and an increase in the driving torque of the endless belt can be suppressed, so that the drive mechanism including the motor can be prevented from being enlarged or damaged.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is an overall configuration diagram of a belt fixing device 10 according to an embodiment of the present invention. The belt fixing device 10 includes an endless film-like fixing belt (endless belt) 12. For example, the fixing belt 12 has a cylindrical outer diameter of 50 mm, a width in the longitudinal direction (the depth direction in FIG. 1, the same applies hereinafter) of about 240 mm, and a thickness of 70 μm made of polyimide (PI). A base material, an elastic layer having a thickness of 200 μm made of silicon rubber, and a release layer having a thickness of 30 μm made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) are sequentially laminated from the inside.

  The fixing belt 12 is wound around a heating roller 14 that is rotatably arranged, and a nip forming member 16 that is fixedly arranged in the fixing belt 12 so as to be parallel and non-rotatable away from the heating roller 14. The heating roller 14 is made of, for example, a metal cylinder having an outer diameter of 35 mm, and incorporates a heater 15 made of, for example, a halogen lamp.

  The nip forming member 16 is configured by providing an elastic layer made of, for example, silicon rubber on a main body made of, for example, a heat-resistant resin, and extends in the longitudinal direction with a length equal to or greater than the width of the fixing belt 12. The surface of the elastic layer of the nip forming member 16 that is in contact with the inner surface of the fixing belt 12 is covered with a low friction layer made of a material having a low coefficient of friction (for example, PFA, PTFE (polytetrafluoroethylene), etc.).

  The nip forming member 16 is reinforced by a reinforcing member 18 made of, for example, a metal cylindrical bar, and is thereby prevented from being bent in a direction perpendicular to the longitudinal direction. A space for heat insulation is secured between the main body of the nip forming member 16 and the reinforcing member 18.

  A lubricant supply member 19 is disposed in contact with the inner surface of the fixing belt 12. The lubricant supply member 19 is preferably made of a porous or fibrous material. For example, ceramic, heat-resistant felt, paper, or the like is suitably used. The lubricant supply member 19 is impregnated with a lubricant such as grease or oil, for example, so that the lubricant is applied to the inner surface of the rotating fixing belt 12.

A pressure roller (elastic roller) 20 is pressed against the nip forming member 16 via the fixing belt 12, and a contact portion between the fixing belt 12 and the pressure roller 20 becomes a fixing nip (nip portion) 22. Yes. For example, the pressure roller 20 has a cylindrical shape with an outer diameter of about 30 mm, and a core layer with an outer diameter of 22 mm is covered with an elastic layer with a thickness of 4 mm to form a release layer with a thickness of 40 μm on the surface of the elastic layer. Has been.
Note that a heater may be provided in the pressure roller 20 so that the paper passes through the fixing nip 22 while the toner image surface of the paper is in contact with the pressure roller 20.

  The pressure roller 20 is connected to the motor 24 via a gear train (not shown) and is driven to rotate. These gear trains and the motor 24 constitute a drive mechanism. In normal operation, when the pressure roller 20 is driven to rotate in the direction of arrow A by the motor 24, the fixing belt 12 rotates in the direction of arrow B while sliding on the nip forming member 16 along with this. ing. The motor 24 is connected to a motor current detection unit (torque detection means) 26 made of, for example, an ammeter, and the driving torque of the fixing belt 12 can be detected by detecting the current flowing through the motor 24. ing.

  The fixing nip forming surface of the nip forming member 16 is formed as a curved surface along the outer peripheral surface of the pressure roller 20. As a result, the pressure distribution in the fixing nip 22 becomes substantially uniform from the entrance to the exit in the sheet passing direction (from bottom to top in FIG. 1), and as a result, a high-quality fixed image can be obtained with a relatively low nip pressure. It is supposed to be. However, the nip pressure in the fixing nip 22 may be high on the inlet side or may be high on the outlet side.

  An end portion of the pressure roller 20 is rotatably supported by a support member 28. The support member 28 is fixed to the frame 30 and is rotatable about a shaft 32. A bent portion 28 a is formed at the upper portion of the support member 28, and the shaft 34 extends through the bent portion 28. A spring 36 is externally provided around the shaft 34 between the bent portion 28 a and the flange portion 34 a at one end of the shaft 34. The other end portion of the shaft 34 is connected to a lever portion 38a of an arcuate gear 38 rotatably supported by a shaft 37 fixed to the frame 30. The arcuate gear 38 meshes with a drive gear 42 that is rotationally driven by a motor 40. As a result, when the drive gear 42 is rotated by the motor 40, the support member 28 is rotated via the arc-shaped gear 38, the shaft 34 and the spring 36, and as a result, the pressure roller 20 is pressed against the nip forming member 16. The pressure contact load can be changed by separating.

Next, the operation of the belt fixing device 10 having the above configuration will be described.
In the belt fixing device 10, the pressure roller 20 is rotationally driven in the direction of arrow A by the motor 24, and the fixing belt 12 rotates in the direction of arrow B accordingly. During this rotation, a lubricant is applied to the inner surface of the fixing belt 12 by the lubricant supply member 19. While rotating in this way, heat is transferred from the heating roller 14 heated by the heater 15, whereby the fixing belt 12 is heated to a predetermined fixing temperature (for example, 180 ° C.) over the entire circumference.

  After the fixing belt 12 is heated to a predetermined fixing temperature, a sheet carrying an unfixed toner image on the surface thereof is introduced into the fixing nip 22 from below in the state with the image surface facing the fixing belt 12 side. The toner image is heated and melted while passing through the toner 22 and fixed on the paper.

  The lubricant gradually leaks from the inside of the fixing belt 12 while the belt fixing device 10 operates over a long period of time. Further, even if it does not leak, the lubricant easily moves to a lower pressure side and accumulates on the nip forming member 16 on the inlet side and the outlet side of the contact portion between the fixing belt 12 and the nip forming member 16 with use. Therefore, the lubricant is exhausted between the fixing belt 12 and the nip forming member 16. As a result, the frictional resistance with respect to the nip forming member 16 increases, and the driving torque of the fixing belt 12 increases.

  As the driving torque of the fixing belt 12 increases, the current of the motor 24 that drives the pressure roller 20 increases. When this increase in current is detected by the motor current detection unit 26, the control unit of the image forming apparatus in which the belt fixing device 10 is incorporated notifies the user that it is time to replace the lubricant supply member 19. The notification method includes, for example, displaying on the display unit of the operation panel and notifying by voice.

  Accordingly, when the user replaces the lubricant supply member 19 impregnated with the lubricant, the lubricant is applied to the inner surface of the fixing belt 12 and replenished to the contact portion between the nip forming member 16. As a result, the depletion of the lubricant is eliminated, the lubricating state is recovered, and the driving torque of the fixing belt 12 is reduced.

  As described above, according to the belt fixing device 10 of the present embodiment, an increase in the driving torque of the fixing belt 12 can be suppressed, so that the drive mechanism including the motor 24 can be prevented from being enlarged or damaged.

  In the above description, the lubricant is supplied between the fixing belt 12 and the nip forming member 16 by exchanging the lubricant supply member 19, but before the lubricant supply member 19 is replaced, the following operation is performed. A lubricant may be supplied to the contact portion between the fixing belt 12 and the nip forming member 16. When an increase in the current of the motor 24 is detected, the pressure roller 20 is temporarily reversely driven by the motor 24 to reversely rotate the fixing belt 12. As a result, the lubricant accumulated on the outlet side of the contact portion between the fixing belt 12 and the nip forming member 16 is introduced into the contact portion, and the exhausted state of the lubricant is eliminated. Alternatively, the pressing load of the pressure roller 20 may be temporarily reduced by driving the motor 40 when an increase in the current of the motor 24 is detected. Also by this, the lubricant accumulated on the inlet side and the outlet side of the contact portion between the fixing belt 12 and the nip forming member 16 flows into the contact portion, and the lubricant depletion state is eliminated. The reverse rotation of the fixing belt 12 and the change of the pressure contact load of the pressure roller 20 are performed when paper is not passed.

  In the belt fixing device 10, the motor current detection unit 26 is used as the torque detection unit of the fixing belt 12. However, the present invention is not limited to this, and the following torque detection unit may be used.

For example, a large number of reflecting portions are arranged at equal intervals around the entire periphery of the edge of the fixing belt 12, and light is irradiated to the arranged portions. Then, the light reflected by the reflecting plate is received by the light receiving sensor 44, and the received light signal is input to the belt rotation speed detection unit 46 to detect the rotation speed of the fixing belt 12. When the lubricant is depleted at the contact portion between the fixing belt 12 and the nip forming member 16, the driving torque of the fixing belt 12 increases accordingly, and as a result, the rotation speed of the fixing belt 12 is reduced. Thus, by detecting the rotational speed of the fixing belt 12, an increase in driving torque can be detected.
Note that a decrease in the rotation speed of the fixing belt 12 causes a decrease in the rotation speed of the heating roller 14 that is a driven roller. Therefore, the rotation speed of the heating roller 14 may be detected by a similar method.

  Further, when the driving torque of the fixing belt 12 increases due to the exhaustion of the lubricant, the pressure roller 20 slips with respect to the fixing belt 12, so that the sheet conveyance speed in the fixing nip 22 decreases. When the sheet is introduced into the fixing nip 22 where the conveyance speed is thus lowered at a predetermined conveyance speed, the sheet swells in a loop from a sheet conveyance path 48 indicated by a one-dot chain line in the drawing. The loop amount of the paper may be detected by the sensor 50, and various lubricant supply operations as described above may be performed based on the detection result.

  Here, a comparative experiment for confirming the effect of the belt fixing device 10 was performed. The result is shown in the graph of FIG. This graph represents the relationship between endurance time and drive torque. In the experiment, an experiment was performed using the belt fixing device 10 when the lubricant supply member 19 was provided and when the lubricant was first applied to the inner surface of the fixing belt 12 without providing the lubricant supply member 19. Went. Even when the lubricant supply member 19 is not provided, in the conventional case where the fixing belt 12 is continuously rotated without the lubricant supply operation, when the lubricant is supplied by temporarily reversing the fixing belt 12, the pressure is increased. Three cases were investigated in which the lubricant was replenished by temporarily separating the rollers 20 to reduce the pressure contact load.

  The pressure contact load of the pressure roller 20 was set to 300 N, and grease made from Dow Corning, in which perfluoropolyether was thickened with a fluororesin, was used as the lubricant. For durability, the fixing belt 12 was continuously rotated by adjusting the temperature to a predetermined fixing temperature without passing paper, and the change in driving torque was measured in this state.

  In the case of reverse operation, the drive torque was measured before and after 10 seconds of reverse operation at each time point of 100 hours, 200 hours, and 300 hours. In the case where there was a pressure separation, the driving torque was measured before and after the driving was stopped at each time point of 100 hours, 200 hours, and 300 hours, the pressure contact load was temporarily released and set to 300 N again. When there is a lubricant supply member, a 2 mm thick non-woven fabric made of aramid fibers is used as the lubricant supply member 19 and contacts the inner surface of the fixing belt 12 with the same width as the fixing belt 12 in the longitudinal direction and 10 mm width with respect to the rotational direction. Then, an initial impregnation with 2 g of a lubricant was used, and replaced with a new one at 300 hours.

  As is apparent from the graph of FIG. 4, it was confirmed that the driving torque suppression effect was the greatest when the lubricant supply member was present, and that the driving torque suppression effect was obtained even when there was reverse rotation and pressure contact separation.

1 is an overall configuration diagram of a belt fixing device. The graph which shows the result of a comparative experiment.

Explanation of symbols

10 ... belt fixing device 12 ... fixing belt (endless belt)
14 ... Heating roller 16 ... Nip forming member 19 ... Lubricant supply member 20 ... Pressure roller (elastic roller)
22. Fixing nip (nip part)
24 ... motor 26 ... motor current detector (torque detector)
28 ... support member 34 ... shaft 36 ... spring 38 ... arc-shaped gear 40 ... motor 42 ... drive gear 44 ... light receiving sensor (torque detection means)
46... Belt rotation speed detection unit (torque detection means)
50. Sensor (torque detection means)

Claims (8)

  An endless belt having an inner surface coated with a lubricant, a nip forming member fixedly disposed in the endless belt, and a rotationally driven elastic roller pressed against the nip forming member via the endless belt A belt fixing device comprising: a lubricant replenishing unit that performs a predetermined operation to replenish a lubricant to a contact portion with the nip forming member on which the endless belt frictionally slides.   2. The belt fixing device according to claim 1, further comprising torque detecting means for detecting a driving torque of the endless belt, wherein the lubricant replenishing means is operated based on a detection result of the torque detecting means.   3. The belt according to claim 2, wherein the torque detection unit detects torque based on a rotation speed of the endless belt or a rotation speed of a driven roller that rotates in accordance with the rotation of the endless belt. Fixing device.   The belt fixing device according to claim 2, wherein the torque detection unit detects torque based on a loop amount of a sheet introduced into a nip portion between the endless belt and the elastic roller.   The belt fixing device according to claim 2, wherein the torque detecting unit detects torque based on a current of a motor that drives the elastic roller.   The belt fixing device according to claim 1, wherein the predetermined operation is to temporarily reduce a pressure contact load of the elastic roller.   The belt fixing device according to claim 1, wherein the predetermined operation is to temporarily reversely drive the elastic roller.   The belt fixing device according to claim 1, wherein the predetermined operation is to notify a replacement timing of a lubricant supply member disposed in contact with an inner surface of the endless belt.

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