JP2007333878A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of surely preventing the excessive temperature rise at both end parts of a heating member and a fixing member in the width direction even if it is impossible to accurately vary the adjustment range of a magnetic flux acting on the heating member, and to provide an image forming apparatus. <P>SOLUTION: The fixing device includes: a magnetic flux generation means for generating the magnetic flux; the heating member 23 heated by the magnetic flux; a magnetic flux adjustment member 29 for reducing the magnetic flux acting on the heating member 23 related to the prescribed adjustment range in the width direction; and varying means 50 and 51 for varying the adjustment range by driving the magnetic flux adjustment member 29 so that the heating range of the heating member 23 may be varied in accordance with the size of the recording medium in the width direction. The drive control of the magnetic flux adjustment member 29 is performed by the varying means 50 and 51 so that the heating range may be fixed after the adjustment range is gradually reduced from a state of becoming the largest L1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a fixing device installed therein, and in particular, a fixing device using an electromagnetic induction heating method. And an image forming apparatus.

  Conventionally, in an image forming apparatus such as a copying machine or a printer, a fixing device using an electromagnetic induction heating method has been known for the purpose of saving energy by reducing the rise time of the device (see, for example, Patent Document 1). .)

  In Patent Document 1, etc., an electromagnetic induction heating type fixing device mainly includes a support roller (heating roller), a fixing auxiliary roller (fixing roller), and a fixing belt (heat-resistant belt) stretched between the supporting roller and the fixing auxiliary roller. ), Magnetic flux generating means facing the support roller via the fixing belt, and a pressure roller facing the fixing auxiliary roller via the fixing belt. The magnetic flux generation means includes a coil portion extending in the width direction (a direction perpendicular to the recording medium conveyance direction), a core portion (excitation coil core) facing the coil portion, and the like.

The fixing belt is heated at a position facing the magnetic flux generating means. The heated fixing belt heats and fixes the toner image on the recording medium conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, when a high-frequency alternating current is passed through the coil portion, a magnetic field is formed around the coil portion, and an eddy current is generated on the surface of the support roller. When an eddy current is generated in the support roller, Joule heat is generated by the electrical resistance of the support roller itself. The fixing belt wound around the support roller is heated by the Joule heat.
It is known that a fixing device using such an electromagnetic induction heating method can raise the surface temperature (fixing temperature) of a fixing belt to a desired temperature with a small start-up time with low energy consumption.

On the other hand, Patent Document 2 and Patent Document 3 disclose a fixing device using an electromagnetic induction heating method, and a fixing roller for the purpose of suppressing a temperature rise in a non-sheet passing region in the fixing roller (heating medium). Discloses a technique of providing magnetic flux shielding means for shielding a part of magnetic flux generated from magnetic flux generating means (induction coil) provided in the apparatus.
Specifically, the magnetic flux shielding means changes its position in accordance with the paper passing area in the fixing roller, thereby changing the range for shielding the magnetic flux. This technique aims to block the magnetic flux reaching the fixing roller in the non-sheet passing area and suppress the temperature rise in the non-sheet passing area.

  Further, Patent Document 4 discloses a fixing device using an electromagnetic induction heating method, in which an internal core in which a magnetic flux adjusting member (shielding member) is installed while suppressing an excessive temperature rise in a non-sheet passing region in a fixing belt. The technique which provides a protrusion part in the both ends of is disclosed. Also in Patent Document 4, etc., the magnetic flux adjusting member is driven according to the size in the width direction of the recording medium, and the heating range in the heating roller (supporting roller) in which the inner core and the magnetic flux adjusting member are provided is varied. At this time, the magnetic flux adjusting member is driven and controlled so that the heating range of the heating roller can be finely adjusted based on the detection result of the temperature sensor.

JP 2002-123106 A Japanese Patent Laid-Open No. 10-74009 JP 2002-83676 A JP 2005-258383 A

  The conventional technology described above cannot reliably suppress the temperature rise at both ends in the width direction of the heating member (or the fixing member) that occurs when a recording medium having a short width direction size is continuously fixed. .

Details are as follows.
A general image forming apparatus is configured to form an image on several types of recording media having different sizes in the width direction. Here, the recording media having different sizes in the width direction include recording media of irregular sizes in addition to recording media of various regular sizes in the A and B rows of JIS dimensions. Even in the case of recording media of the same size (for example, A4 size), the transport direction is the short direction (the direction perpendicular to the longitudinal direction) when the longitudinal direction is the transport direction. In some cases, recording media having different sizes in the width direction are handled.

  When fixing such a recording medium having different width direction sizes with the fixing device, the temperature distribution in the width direction of the fixing belt varies depending on the width direction size of the recording medium, resulting in temperature unevenness. was there. For example, when fixing by passing a recording medium having a small size in the width direction, a lot of heat is taken away at the position of the fixing belt corresponding to the size in the width direction of the recording medium (the paper passing area). The fixing temperature is lower than at other positions (non-sheet passing area). Such a phenomenon becomes particularly prominent when a recording medium having a small size in the width direction is continuously fed.

  Therefore, when trying to control the fixing temperature in the entire width direction of the fixing belt with reference to the fixing temperature in the center portion in the width direction of the fixing belt, the fixing temperature in the center portion in the width direction of the fixing belt can be controlled to a desired temperature. The fixing temperature at both ends in the direction will increase. As described above, when a large recording medium in the width direction is fixed in a state where the fixing temperature at both ends in the width direction of the fixing belt is increased, a hot offset occurs on the recording medium corresponding to the temperature increase position. Further, when the fixing temperature at both ends in the width direction exceeds the heat resistance temperature of the fixing belt, it is also conceivable that the fixing belt is thermally damaged.

  On the other hand, if it is attempted to control the fixing temperature in the entire width direction of the fixing belt based on the fixing temperature at both ends in the width direction of the fixing belt, the fixing temperature at both ends in the width direction of the fixing belt can be controlled to a desired temperature. However, the fixing temperature at the center in the width direction is lowered. As described above, when the recording medium is fixed in a state where the fixing temperature at the center portion in the width direction of the fixing belt is lowered, fixing failure or cold offset occurs on the recording medium corresponding to the temperature lowered position.

  In order to solve such a problem, in Patent Document 2 and Patent Document 3 described above, the magnetic flux in the non-sheet passing region is changed by changing the position of the magnetic flux shielding member (magnetic flux shielding means) according to the size of the recording medium. Since it is shielded, the effect of suppressing the temperature rise in the non-sheet passing area can be expected to some extent even when a recording medium having a small size in the width direction is continuously fed.

However, in the above-described technique, when the size of the recording medium is frequently changed, there is a possibility that the magnetic flux shielding member may not be moved to the correct position according to the size change. That is, in the conventional technique, since the position of the magnetic flux shielding member that has moved cannot be accurately grasped, an error may occur in the position control of the magnetic flux shielding member while the magnetic flux shielding member is repeatedly moved. There was sex.
As described above, when an error occurs in the position control of the magnetic flux shielding member, the magnetic flux in the region where the magnetic flux is desired to be shielded cannot be shielded, and the temperature rise in the non-sheet passing region may occur.

On the other hand, in Patent Document 4 and the like, since the magnetic flux adjusting member is driven and controlled so that the heating range in the heating roller can be finely adjusted based on the detection result of the temperature sensor, the temperature rise in the non-sheet passing region is increased. The effect which becomes difficult to occur can be expected.
However, the above-described technique may cause an error in the position control of the magnetic flux shielding member and increase the temperature in the non-sheet passing area when the detection accuracy of the temperature sensor is lowered due to a failure or the like. there were. Further, since the magnetic flux adjusting member is driven and controlled so that the heating range of the heating roller is determined after the adjustment range of the magnetic flux acting on the heating roller is gradually increased from a state where it becomes the minimum, the magnetic flux adjustment driven from the home position. If the member drive time (internal core rotation time) is insufficient, the magnetic flux in the region where the magnetic flux is desired to be shielded cannot be shielded, and the temperature in the non-sheet passing region may increase.

  The present invention has been made to solve the above-described problems. Even when the adjustment range of the magnetic flux acting on the heating member cannot be accurately changed, the width of the heating member and the fixing member at both ends in the width direction is not limited. An object of the present invention is to provide a fixing device and an image forming apparatus capable of reliably suppressing excessive temperature rise.

  According to a first aspect of the present invention, there is provided a fixing device for fixing a toner image onto a recording medium, a magnetic flux generating means for generating a magnetic flux, a heating member heated by the magnetic flux, and the heating A magnetic flux adjusting member that reduces the magnetic flux acting on the member within a predetermined adjustment range in the width direction, and driving the magnetic flux adjustment member so that the heating range of the heating member varies according to the size in the width direction of the recording medium. Variable means for varying the adjustment range, and the variable means drives and controls the magnetic flux adjustment member so that the heating range is determined after the adjustment range is gradually reduced from the maximum state. is there.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the state in which the adjustment range is maximized is the state in which the entire width direction of the heating member is in the non-heating range. Is.

  According to a third aspect of the present invention, there is provided a fixing device according to the first or second aspect, further comprising a detecting unit that detects a position of the magnetic flux adjusting member driven by the variable unit, Based on the driving time for one cycle until the detection means detects the home position of the magnetic flux adjusting member again after detecting the home position of the magnetic flux adjusting member, the magnetic flux adjusting member is moved to the home in order to determine the heating range. A predetermined time for driving from the position is calculated, and the variable means drives the magnetic flux adjusting member for the predetermined time after the detecting means detects the home position of the magnetic flux adjusting member.

  According to a fourth aspect of the present invention, there is provided the fixing device according to any one of the first to third aspects, wherein the detecting means detects the position of the magnetic flux adjusting member driven by the variable means. A drive time for one cycle until the home position of the magnetic flux adjustment member is detected again after the detection means detects the home position of the magnetic flux adjustment member, and the drive time for the one cycle is equal to or greater than a predetermined value. It detects a device failure when it fluctuates.

According to a fifth aspect of the present invention, there is provided the fixing device according to the fourth aspect, wherein the magnetic flux adjusting member is configured to change the adjustment range stepwise, and the magnetic flux adjusting member The number of times that the adjustment range can be varied stepwise is N, the latest driving time for the one cycle detected by the detecting means is T1, and the driving time for the past one cycle detected by the detecting means is When T2
T1-T2 ≧ T2 / N
A failure of the apparatus is detected when the following relationship is established.

  According to a sixth aspect of the present invention, there is provided the fixing device according to any one of the first to fifth aspects, wherein the detecting means detects the position of the magnetic flux adjusting member driven by the variable means. And detecting the failure of the apparatus when the heating member is heated by the variable means being determined and the displacement of the magnetic flux adjusting member is detected by the detecting means. It is.

  According to a seventh aspect of the present invention, in the fixing device according to any one of the first to sixth aspects, the magnetic flux generating means extends in the width direction so as to face the heating member. A magnetic flux shielding member disposed between the coil portion and the inner core, the coil portion and an inner core facing the coil portion via the heating member. It is a thing.

  According to an eighth aspect of the present invention, in the fixing device according to the seventh aspect, the magnetic flux shielding member can gradually increase or decrease the range covering the outer periphery of the inner core facing the coil portion. It is formed as follows.

  According to a ninth aspect of the present invention, there is provided the fixing device according to the eighth aspect, wherein the magnetic flux shielding member is arranged so that the variable means gradually decreases the range covering the outer periphery of the inner core. It is a means for driving.

  According to a tenth aspect of the present invention, in the fixing device according to any one of the seventh to ninth aspects, the magnetic flux generating means faces the coil portion on a side not facing the heating member. In addition, a core portion having a center core is provided, and the magnetic flux shielding member covers an outer periphery of the inner core facing the center core.

  According to an eleventh aspect of the present invention, in the fixing device according to any one of the first to tenth aspects, the heating member heats the fixing member that melts the toner image.

  The fixing device according to a twelfth aspect of the present invention is the fixing device according to the eleventh aspect, wherein the fixing member is a fixing belt, and the heating member stretches the fixing belt together with a fixing auxiliary roller. The magnetic flux generating means is arranged to face the fixing belt.

  The fixing device according to a thirteenth aspect of the present invention is the fixing device according to the twelfth aspect of the present invention, wherein the auxiliary fixing roller is arranged with respect to a pressure roller that presses a conveyed recording medium via the fixing belt. It is arrange | positioned so that it may contact | abut.

  A fixing device according to a fourteenth aspect of the present invention is the fixing device according to any one of the first to tenth aspects, wherein the heating member is a fixing member that melts a toner image.

  According to a fifteenth aspect of the present invention, in the fixing device according to the fourteenth aspect of the present invention, the fixing member is a fixing belt, and the magnetic flux generation means is arranged to face the fixing belt. It was established.

  According to a sixteenth aspect of the present invention, in the fixing device according to the fifteenth aspect, the fixing belt is stretched between a support roller and a fixing auxiliary roller, and the fixing auxiliary roller is conveyed. It is disposed so as to abut against a pressure roller for pressing the recording medium via the fixing belt.

  A fixing device according to a seventeenth aspect of the present invention is the fixing device according to the fourteenth aspect, wherein the fixing member is a fixing roller that contacts a pressure roller that presses a recording medium to be conveyed. The magnetic flux generating means is disposed so as to face the fixing roller.

  An image forming apparatus according to an eighteenth aspect includes the fixing device according to any one of the first to seventeenth aspects.

  In the present invention, the magnetic flux adjusting member is driven and controlled so that the heating range of the heating member is determined after the adjustment range of the magnetic flux acting on the heating member is gradually reduced from the maximum state. As a result, even if the adjustment range of the magnetic flux acting on the heating member cannot be accurately changed, at least both ends of the heating member and the fixing member in the width direction are surely reduced in at least the region where the magnetic flux is to be adjusted. Thus, it is possible to provide a fixing device and an image forming apparatus in which excessive temperature rise is reliably suppressed.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is a main body of a laser printer as an image forming apparatus, 3 is an exposure unit that irradiates a photosensitive drum 18 with exposure light L based on image information, and 4 is detachably installed on the apparatus main body 1. A process cartridge as an image forming unit; 7, a transfer unit for transferring a toner image formed on the photosensitive drum 18 to a recording medium P; 10, a paper discharge tray on which an output image is placed; A paper feeding unit in which a recording medium P such as paper is stored, 13 is a registration roller that conveys the recording medium P to the transfer unit 7, 15 is a manual paper feeding unit, and 20 is a fixing unit that fixes an unfixed image on the recording medium P. Device.

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, exposure light L such as laser light based on image information is emitted from the exposure unit 3 (writing unit) toward the photosensitive drum 18 of the process cartridge 4. The photosensitive drum 18 rotates counterclockwise in the figure, and a toner image corresponding to image information is formed on the photosensitive drum 18 through a predetermined image forming process (charging process, exposure process, development process). Is done.
Thereafter, the toner image formed on the photosensitive drum 18 is transferred onto the recording medium P conveyed by the registration roller 13 in the transfer unit 7.

On the other hand, the recording medium P conveyed to the transfer unit 7 operates as follows.
First, one of the plurality of paper feeding units 11, 12, and 15 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 11 is selected). To do.) Each of the plurality of paper feeding units 11 and 12 stores a recording medium P having a different size and a recording medium P having the same size and different transport directions.

  Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 11 is transported toward the position of the transport path K. Thereafter, the recording medium P passes through the conveyance path K and reaches the position of the registration roller 13. Then, the recording medium P that has reached the position of the registration roller 13 is conveyed toward the transfer unit 7 at the same timing in order to align with the toner image formed on the photosensitive drum 18.

After the transfer process, the recording medium P passes through the position of the transfer unit 7 and then reaches the fixing device 20 through the conveyance path. The recording medium P that has reached the fixing device 20 is fed between the fixing belt and the pressure roller, and the toner image is fixed by the heat received from the fixing belt and the pressure received from the pressure roller. The recording medium P on which the toner image has been fixed is sent from between the fixing belt and the pressure roller, and then is discharged from the image forming apparatus main body 1 as an output image and placed on the paper discharge tray 10.
Thus, a series of image forming processes is completed.

Next, the configuration / operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIG.
As shown in FIG. 2, the fixing device 20 includes a fixing auxiliary roller 21, a fixing belt 22, a support roller 23 (heating roller), an induction heating unit 24, a pressure roller 30, a thermopile 37, a thermistor 38, an oil application roller 34, It comprises a guide plate 35, a separation plate 36, and the like.

Here, the fixing auxiliary roller 21 has an elastic layer such as silicone rubber formed on the surface thereof, and is driven to rotate counterclockwise in FIG. 2 by a driving unit (not shown).
The support roller 23 as a heating member is a cylindrical body made of a nonmagnetic material such as SUS304, and rotates counterclockwise in the figure. Inside the support roller 23, an internal core 28 made of a ferromagnetic material such as ferrite and a magnetic flux shielding member 29 (magnetic flux adjusting member) covering a part of the outer periphery of the internal core 28 are rotatably installed. . The inner core 28 faces the coil portion 25 through the fixing belt 22 and the support roller 23. The rotational drive of the inner core 28 and the magnetic flux shielding member 29 is performed separately from the rotational drive of the support roller 23. The configuration and operation of the support roller 23 provided with the inner core 28 and the magnetic flux shielding member 29 will be described in detail later.

The fixing belt 22 as a fixing member is stretched and supported by a support roller 23 and a fixing auxiliary roller 21. The fixing belt 22 is a multi-layered endless belt in which a heating layer, an elastic layer, and a release layer are formed on a base material.
The base material of the fixing belt 22 is made of a heat-resistant resin material. For example, polyimide, polyamideimide, PEEK (polyetheretherketone), PES (polyethersulfone), PPS (polyphenylene sulfide), fluororesin, or the like can be used. . As the heating layer, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, an alloy composed of a plurality of these metals, or the like can be used. As the elastic layer, silicone rubber, fluorosilicone rubber, or the like can be used. As the release layer, fluorine resins such as tetrafluoroethylene resin (PTFE) and tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (FEP), or a mixture of these resins can be used.

  In the first embodiment, the base material of the fixing belt 22 and the heating layer are mixed layers. Specifically, three heating layers made of silver are formed at intervals in a base material made of polyimide. Then, an elastic layer and a release layer are sequentially formed on the hybrid layer.

The induction heating unit 24 as a magnetic flux generation unit includes a coil unit 25, a core unit 26, a coil guide 27, and the like.
Here, the coil portion 25 is wound around a litz wire in which fine wires are bundled so as to cover the outer peripheral surface of the fixing belt 22 wound around the support roller 23 and is in the width direction (in the direction perpendicular to the paper surface of FIG. 2). It is extended. The coil guide 27 is made of a highly heat-resistant resin material or the like, and holds the coil part 25 and functions as a frame of the induction heating part 24. The core part 26 is made of a ferromagnetic material such as ferrite having a relative permeability of about 2500, and is provided with a center core part 26a and a side core 26b. The core part 26 is installed so as to face the coil part 25 extending in the width direction. The center core 26a is at a substantially central position in the circumferential direction of the coil portion 25, and is a position where the density of magnetic flux formed around the coil portion 25 is the highest. The coil unit 25 is connected to a high frequency power supply unit (not shown), and an alternating current of 10 k to 1 MHz is applied from the high frequency power supply unit.

  The pressure roller 30 is formed by forming an elastic layer such as fluorine rubber or silicone rubber on a cylindrical member made of aluminum, copper, stainless steel or the like. The elastic layer of the pressure roller 30 has a thickness of 1 to 5 mm and an Asker hardness of 20 to 50 degrees. The pressure roller 30 is in contact with the fixing auxiliary roller 21 via the fixing belt 22. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing belt 22 and the pressure roller 30.

A guide plate 35 for guiding the conveyance of the recording medium P is disposed on the entrance side of the contact portion between the fixing belt 22 and the pressure roller 30.
A separation plate 36 that guides conveyance of the recording medium P and promotes separation of the recording medium P from the fixing belt 22 is disposed on the exit side of the contact portion between the fixing belt 22 and the pressure roller 30.

  An oil application roller 34 is in contact with a part of the outer peripheral surface of the fixing belt 22. The oil application roller 34 supplies oil such as silicone oil onto the fixing belt 22. Thereby, the toner releasability on the fixing belt 22 is further ensured. The oil application roller 34 is in contact with a cleaning roller 33 that removes dirt on the surface.

A non-contact type thermopile 37 is installed at a position facing the outer peripheral surface of the fixing belt 22 and in the center in the width direction. Further, a contact type thermistor 38 is provided at a position in contact with the outer peripheral surface of the fixing belt 22 and at an end in the width direction.
The surface temperature (fixing temperature) on the fixing belt 22 is detected by the thermopile 37 and the thermistor 38, and the output in the induction heating unit 24 having an inverter circuit is adjusted. Thus, the fixing temperature on the fixing belt 22 is kept constant.

The fixing device 20 configured in this way operates as follows during the fixing process.
By the rotation driving of the auxiliary fixing roller 21, the fixing belt 22 rotates in the direction of the arrow in FIG. 2, the support roller 23 also rotates counterclockwise, and the pressure roller 30 also rotates in the direction of the arrow. The fixing belt 22 is heated at a position facing the induction heating unit 24. Specifically, the magnetic field lines are alternately switched between the core part 26 and the inner core 28 by passing a high-frequency alternating current through the coil part 25. At this time, an eddy current is generated on the surface of the support roller 23 and the heating layer of the fixing belt 22, and Joule heat is generated by the electrical resistance of the support roller 23 and the heating layer. Thus, the fixing belt 22 is heated by the heat received from the heat-generating support roller 23 and the heat generated by its own heating layer. That is, the support roller 23 functions as a heating member, and the fixing belt 22 functions as a heating member as well as a member to be heated.

Thereafter, the surface of the fixing belt 22 heated by the induction heating unit 24 passes through the position of the thermistor 38 and then reaches the contact portion with the pressure roller 30. Then, the toner image T on the conveyed recording medium P is heated and melted.
Specifically, the recording medium P carrying the toner image T through the image forming process described above is fed between the fixing belt 22 and the pressure roller 30 while being guided by the guide plate 35 (indicated by the arrow Y). It is movement in the transport direction.) The toner image T is fixed to the recording medium P by the heat received from the fixing belt 22 and the pressure received from the pressure roller 30, and the recording medium P is sent from between the fixing belt 22 and the pressure roller 30.

The surface of the fixing belt 22 that has passed through the position of the pressure roller 30 sequentially passes through the positions of the oil application roller 34 and the thermopile 37, and then reaches the position facing the induction heating unit 24 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

The configuration and operation of the support roller 23 will be described in detail with reference to FIG.
FIG. 3 is a view of the support roller 23 installed in the fixing device 20 of FIG. 2 as viewed in the width direction, and shows the inside of the support roller 23. The upper side in FIG. 3 is the position of the center core 26a.

  As shown in FIG. 3, the support roller 23 as a heating member has a cylindrical portion 23a made of a nonmagnetic material such as SUS304 (a main portion of the heating member heated by electromagnetic induction), at both ends of the cylindrical portion 23a. It is composed of a press-fitted resin flange 23b (with a bearing inserted), and the like. The support roller 23 is rotatably supported by the shaft portion 28a of the inner core 28 via a bearing of the flange 23b. The shaft portion 28 a is rotatably supported by the side plate 52 of the fixing device 20 via the bearing 53. The support roller 23 rotates in a predetermined direction following the travel of the fixing belt 22 due to the frictional resistance with the fixing belt 22 in contact therewith. A retaining ring 46 is provided at both end surfaces of the support roller 23 and on the shaft portion 28a to restrict the movement of the support roller 23 (cylindrical portion 23a) in the thrust direction.

  On the other hand, an inner core 28 and a magnetic flux shielding member 29 are rotatably installed in the cylindrical body of the support roller 23. The inner core 28 is driven to rotate at a predetermined timing together with the magnetic flux shielding member 29 by the driving force of the motor 50 as a variable means, independently of the rotation of the support roller 23. Specifically, the motor 50 such as a DC motor is fixed to the apparatus main body 1. Then, the driving force of the motor 50 is transmitted to the shaft portion 28a via the worm gear of the motor 50, the driving gear train 51, and the gear 45 (fixed to the D-cut portion of the shaft portion 28a), so that the internal The core 28 is rotationally driven. In addition, by installing a worm gear on the motor shaft of the motor 50, rotation of the motor 50 when an external force is applied from the driven side can be suppressed.

  Here, the cylindrical inner core 28 made of a ferromagnetic material such as ferrite and the magnetic flux shielding member 29 made of a diamagnetic material such as copper are integrally installed. The magnetic flux shielding member 29 is formed so as to increase or decrease the range in which the outer peripheral surface of the inner core 28 is shielded from the end surface side in a stepwise manner (four steps in the first embodiment). Thereby, by rotating the inner core 28 together with the magnetic flux shielding member 29, the shielding range (adjustment range) in the width direction of the inner core 28 facing the coil portion 25 of the induction heating unit 24 can be varied.

  Specifically, referring to FIG. 4, magnetic flux shielding member 29 is provided between center core 26 a of induction heating unit 24 (the position where the magnetic flux density is highest in the configuration of the first embodiment) and internal core 28. Is present, the normal magnetic flux (indicated by the broken line B in FIG. 4) formed when there is no magnetic flux shielding member 29 is weakened. Thereby, in the position of the support roller 23 which has arrange | positioned the magnetic flux shielding member 29, a heating efficiency falls with the fall of the magnetic flux which acts.

  Here, the range in the width direction (adjustment range) for reducing the magnetic flux can be varied by changing the posture of the magnetic flux shielding member 29 facing the coil portion 25. Specifically, by rotating and driving (drive control) the magnetic flux shielding member 29 together with the inner core 28, the adjustment range (shielding range) for reducing the magnetic flux can be varied in the range of 0 to L1 in FIG. Thus, the magnetic flux shielding member 29 functions as a magnetic flux adjusting member that reduces the magnetic flux acting on the support roller 23 (or the fixing belt 22) in the adjustment range in the width direction.

  The rotational drive (drive control) of the inner core 28 and the magnetic flux shielding member 29 is performed by variable means 50 and 51 (drive means) connected to the shaft portion 28a of the inner core 28. The motor 50 is a drive system different from a drive motor (not shown) that drives the auxiliary fixing roller 21, the fixing belt 22, the support roller 23, and the like.

Specifically, the inner core 28 and the magnetic flux shielding member 29 are rotated by a predetermined angle in the circumferential direction so that the maximum range of the magnetic flux shielding member 29 is opposed to the center core 26a. At this time, the adjustment range in which the magnetic flux is reduced is maximized, and the entire width direction (the region of the width L1) becomes the non-heating range.
On the other hand, when the inner core 28 and the magnetic flux shielding member 29 are further rotated by a predetermined angle in the circumferential direction, a part of the magnetic flux shielding member 29 faces the center core 26a. At this time, a range outside the adjustment range in which the magnetic flux is reduced by the magnetic flux shielding member 29 is a main heating range of the fixing belt 22. This heating range corresponds to the width direction size (sheet passing area) of the recording medium P.

  Here, with reference to FIG. 3 and FIG. 5, a detected plate 41 is fixed to the D cut portion of the shaft portion 28 a of the inner core 28 by screws 47. The detected plate 41 rotates together with the magnetic flux shielding member 29 as the inner core 28 rotates. As shown in FIG. 5, the detected plate 41 is formed in a semicircular plate shape, and can correspond to the position where the magnetic flux shielding member 29 is installed. That is, the orientation of the magnetic flux shielding member 29 in the rotational direction can also be grasped by the orientation of the detected plate 41 in the rotational direction. 5 is a diagram of the detected plate 41 and the support roller 23 as viewed from the direction A in FIG. 3, and the right side of the support roller 23 in the drawing is the position of the induction heating unit 24 (center core 26a). .

On the other hand, a transmission type photosensor 42 (home position detection sensor) as a detection means is installed in the vicinity of the detected plate 41. The transmissive photosensor 42 detects the presence or absence of the plate 41 to be detected between a light emitting element made of a laser diode or the like and a light receiving element made of a photodiode or the like (the position of the reference numeral 42a in FIG. 5). Specifically, when the inner core 28 is rotated counterclockwise in FIG. 5 and the transmission type photosensor 42 detects the detected plate 41 from the non-detected plate 41, the magnetic flux shielding member 29 The posture is as shown in FIG.
In the first embodiment, the state shown in FIG. 5 is set as a home position (reference position), and after the magnetic flux shielding member 29 is moved to the home position, the support roller 23 is heated in accordance with the size in the width direction of the recording medium P. The adjustment range (shielding range) of the magnetic flux shielding member 29 is varied so that the range is variable.

  Here, in the first embodiment, the magnetic flux adjustment range is gradually decreased from the state in which the above-described magnetic flux adjustment range is maximized (in the first embodiment, the entire width direction is the non-heating range). The magnetic flux shielding member 29 is driven and controlled so that the heating range of the support roller 23 is determined. That is, when changing the heating range in accordance with the width direction size of the recording medium P, the magnetic flux shielding member always changes the entire width direction from the adjustment range (shielding range) to the desired adjustment range (shielding range). 29 is driven to rotate. Accordingly, even when changing to any heating range, a rotational drive in one direction from the large adjustment range (small heating range) to the small adjustment range (large heating range) is always performed (the magnetic flux shielding member in the direction of the arrow in FIG. 5). 29 is driven).

  Specifically, referring to FIG. 5 and FIGS. 6A to 6D, the heating range is variable according to the width direction size of the recording medium P (in the first embodiment, the heating range is variable in four stages). .), First, the magnetic flux shielding member 29 is moved to the home position (the state shown in FIG. 5). Thereafter, the magnetic flux shielding member 29 is always driven to rotate in the direction of the arrow in FIG. 5 and FIG. 6 (counterclockwise direction). That is, the magnetic flux shielding member 29 passes through a position (the position shown in FIG. 6A) that has been rotated 1/10 from the home position (the position shown in FIG. 5), and is further turned 1/4. Passing through the position (the position shown in FIG. 6 (B)) and further passing through the position (a position shown in FIG. 6 (C)) that has been rotated by a quarter turn, a further quarter turn. Passing through the position (the position shown in FIG. 6D), it returns to the home position again, and one rotation (one cycle) is completed.

Here, the position in FIG. 6A is a position rotated by 1/10 from the home position, and is a position when the entire width direction of the support roller 23 is set as a non-heated range (a non-heated range). It is. Here, the position rotated by 1/10 from the home position is set to a position where the adjustment range is maximized in consideration of detection error by the photosensor 42.
The position in FIG. 6B is a position rotated by (1/4 + 1/10) from the home position, and a range corresponding to A5 size, postcard size, etc. (the range L2 in FIG. 3) is a heating range. It is a position when. When the heating range is set at this position, it is always changed from the state where the entire width direction is set as the non-heating range. Therefore, even if the adjustment range cannot be accurately changed, the area where the magnetic flux is to be reduced (non-sheet passing area) ) Can be reliably reduced.

The position in FIG. 6C is a position rotated by (1/2 + 1/10) from the home position, and is a position when a range (210 mm) corresponding to A4 (vertical) size is set as a heating range. When the heating range is set at this position, the heating range is always changed from the shorter heating range (the state shown in FIG. 6B), so even if the adjustment range cannot be accurately changed, the magnetic flux is reduced. It is possible to reliably reduce the magnetic flux in the region (non-sheet passing region) to be made.
The position in FIG. 6D is a position rotated (3/4 + 1/10) from the home position, and a range (297 mm) corresponding to A3 (vertical) size or A4 size (horizontal) is set as a heating range. Is the position of time. When the heating range is set at this position, the heating range is always changed from the shorter heating range (the state shown in FIG. 6C), so that the magnetic flux is reduced even when the adjustment range cannot be accurately changed. It is possible to reliably reduce the magnetic flux in the region (non-sheet passing region) to be made.
As described above, according to the first embodiment, the rotation of the magnetic flux shielding member 29 is not sufficiently performed due to the gear tooth breakage of the drive gear train 51, the overload of the motor 50, or the like. 22) Even if the adjustment range of the magnetic flux acting on 22) cannot be accurately changed, the magnetic flux in at least the region where the magnetic flux is to be adjusted is reliably reduced. Excessive temperature rise is reliably suppressed.

Hereinafter, based on the flowchart of FIG. 7, the characteristic control in the first embodiment will be described in detail with reference to FIG. 6 as appropriate.
When a print command is issued in the apparatus main body 1, the heating range of the support roller 23 (or the fixing belt 22) (FIG. 6B to FIG. ) Is selected (step S1).

First, driving of the motor 50 is started (step S2), and the home position is detected for the first time while the inner core 28 and the magnetic flux shielding member 29 are rotationally driven in a predetermined direction (step S3). Specifically, the photo sensor 42 detects the time X1 when the detected plate 41 is not present and changes to a certain state (detection of the state of FIG. 5).
Similarly, the second home position is detected (time X2 is detected) (step S4).

  Then, a difference T1 (= X2−X1) between the time X2 obtained in step S4 and the time X1 obtained in step S3 is calculated (step S5). T1 calculated here is a driving time for one rotation of the inner core 28 and the magnetic flux shielding member 29 (a driving time for one cycle). Then, the driving time T1 for one rotation calculated in step S5 is compared with the driving time T2 for one rotation calculated and stored in the past, so that the driving time T1 for one rotation is not less than a predetermined value. When it fluctuates, a failure of the fixing device is detected.

Specifically, it is determined whether a relationship of T1-T2 <T2 / N is established (step S6). Here, N in the above equation is the number of times that the adjustment range (heating range) can be varied stepwise by the magnetic flux shielding member 29 as the magnetic flux adjustment member, and is set to 4 times in the first embodiment. .
If it is determined in step S6 that the relationship of T1-T2 <T2 / N is not established, the fluctuation of the driving time for one rotation is large, and the fixing device malfunctions (mainly variable means 50, 51). The operation of the fixing device is stopped (step S7).

On the other hand, if it is determined in step S6 that the relationship of T1-T2 <T2 / N is established, it is assumed that the fluctuation of the driving time for one rotation is small and there is no failure of the fixing device. Prepare to start printing. Specifically, the home position is detected again, and the magnetic flux shielding member 29 is rotationally driven from the home position (in the state of FIG. 5) to position the magnetic flux shielding member 29 (step S8). For example, when the recording medium P to be passed is A3 (vertical) size, the magnetic flux shielding member 29 changes from the home position (the state shown in FIG. 5) to the states shown in FIGS. Then, the driving is stopped in the state of FIG.
Here, the time (rotation angle) for driving the magnetic flux shielding member 29 from the home position is obtained based on the drive time T1 for one rotation calculated in step S5. Therefore, compared to the case where the time for driving the magnetic flux shielding member 29 from the home position is a fixed value, the influence of errors such as load fluctuation of the motor 50, deterioration with time, rotation fluctuation due to voltage fluctuation, etc. can be reduced. Position accuracy can be improved.

  At this time, even if the driving time difference (T1-T2) is generated, if the time difference is smaller than T2 / N (= T2 / 4), the error with respect to the target heating range can be reduced. At that time, since the heating range is determined by changing from the heating range shorter than the target heating range, the magnetic flux in at least the non-sheet passing region is surely reduced, and excessive temperature rise at both ends in the width direction is suppressed. Can do. Note that the accuracy of failure detection can be increased by setting T2 / N in the above equation to a smaller value.

Then, after the magnetic flux shielding member is positioned (fixed heating range) in step S8, printing is started (step S9).
At this time, a failure of the apparatus is detected when the displacement of the magnetic flux shielding member 29 is detected by the photosensor 42 (detection means) during the printing operation. Specifically, it is determined whether an on / off signal is detected from the photosensor 42 (home position detection sensor) (step S10). As a result, if it is determined that there is an on / off signal, it is determined that there is a failure in the fixing device (mainly a failure in the variable means 50 and 51), and the operation of the fixing device is stopped (step S11). .

On the other hand, if it is determined in step S10 that there is no ON / OFF signal, the printing operation is continued assuming that there is no failure in the fixing device, and the printing is terminated (step S12).
At this time, the latest driving time T1 calculated in step S5 is overwritten and stored as data of the past driving time T2 (step S13). Thus, this flow is finished.

  As described above, in the first embodiment, the magnetic flux shielding member 29 (magnetic flux) is set so that the heating range is determined after the adjustment range of the magnetic flux acting on the support roller 23 and the fixing belt 22 is gradually reduced from the maximum state. The adjustment member is driven and controlled. Thereby, even if the adjustment range of the magnetic flux acting on the support roller 23 and the fixing belt 22 cannot be accurately changed, at least the magnetic flux in the region where the magnetic flux is to be adjusted is reliably reduced. It is possible to reliably suppress an excessive temperature rise at both ends in the width direction of the belt 22.

  In the first embodiment, the fixing belt 22 having a heating layer and the support roller 23 are used as heating members. On the other hand, only one of the fixing belt 22 and the support roller 23 can be used as a heating member. In such a case, the same effect as in the first embodiment can be obtained.

  In the first embodiment, the present invention is applied to the monochrome image forming apparatus 1. However, the present invention can also be applied to a color image forming apparatus. Even in this case, the same effect as in the first embodiment can be obtained.

  In the first embodiment, the transmission type photosensor 42 is used as the detection unit. However, a reflection type photosensor may be used as the detection unit. In other words, when the transmission type photosensor 42 is used, the light emitted from the light emitting element is identified as having no detected plate 41 when the light receiving element receives the light, whereas the reflection type photosensor is used. In this case, when the light receiving element receives the reflected light of the light emitted from the light emitting element, it is identified that the detected plate 41 is present. Also in this case, the same effect as in the first embodiment can be obtained.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 8 is a cross-sectional view showing the fixing device 20 according to the second embodiment. The fixing device according to the second embodiment uses the fixing roller 31 as a heating member and a fixing member, and the above embodiment uses a fixing belt as a fixing member using a support roller and a fixing belt as the heating member. It differs from one.

As shown in FIG. 8, the fixing device 20 according to the second embodiment includes a fixing roller 31 (fixing member), a pressure roller 30, an induction heating unit 24, and the like.
The fixing roller 31 includes a heating layer 31a, an elastic layer made of silicone rubber or the like, a release layer made of fluorine compound, or the like. The inside of the fixing roller 31 has a hollow structure, and the inner core 28 and the magnetic flux shielding member 29 are rotatably installed. In addition, although not shown, a plate to be detected is installed on the shaft portion that supports the inner core 28 and the magnetic flux shielding member 29, as in the first embodiment. Further, a photo sensor (detecting means) for detecting the position of the detected plate is installed at a position facing the detected plate.

The induction heating unit 24 includes a coil unit 25, a core unit 26, a coil guide 27, and the like, as in the first embodiment. Then, when an alternating current of 10 k to 1 MHz is supplied to the coil portion 25, magnetic lines of force are formed between the core portion 26 and the inner core 28, and the fixing roller 31 is heated by electromagnetic induction. In this way, the heated fixing roller 31 heats and melts the toner image on the recording medium P conveyed from the arrow Y direction, and fixes the toner image on the recording medium P.
Also in the second embodiment, the magnetic flux shielding member 29 (magnetic flux adjusting member) is set so that the heating range is determined after the adjustment range of the magnetic flux acting on the fixing roller 31 (heating member) is gradually reduced from the maximum state. Drive control.

  As described above, in the second embodiment, as in the first embodiment, even if the adjustment range of the magnetic flux acting on the fixing roller 31 (heating member) cannot be accurately varied, at least the magnetic flux Since the magnetic flux in the region where the adjustment is desired is reliably reduced, it is possible to reliably prevent excessive temperature rise at both ends in the width direction of the fixing roller 31.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing a fixing device installed in the image forming apparatus of FIG. 1. FIG. 3 is a view showing a support roller installed in the fixing device of FIG. 2. FIG. 3 is an enlarged view showing the vicinity of an induction heating unit in the fixing device of FIG. 2. It is a side view which shows the to-be-detected plate installed in the support roller of FIG. It is a schematic diagram which shows operation | movement of a magnetic flux adjustment member. 6 is a flowchart illustrating control performed by the fixing device. It is sectional drawing which shows the fixing device in Embodiment 2 of this invention.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20 fixing device, 21 fixing auxiliary roller,
22 fixing belt (fixing member),
23 support roller (heating member),
24 induction heating part (magnetic flux generating means), 25 coil part,
26 core part, 26a center core, 26b side core,
28 inner core, 28a shank,
29 magnetic flux shielding member (magnetic flux adjusting member), 30 pressure roller,
31 fixing roller (heating member, fixing member),
41 Detected plate,
42 Photosensor (detection means), 42a Light emitting element / light receiving element,
50 motor (variable means), 51 drive gear train (variable means).

Claims (18)

A fixing device for fixing a toner image on a recording medium,
Magnetic flux generating means for generating magnetic flux;
A heating member heated by the magnetic flux;
A magnetic flux adjusting member that reduces the magnetic flux acting on the heating member for a predetermined adjustment range in the width direction;
Variable means for driving the magnetic flux adjusting member to vary the adjustment range so that the heating range of the heating member is variable according to the size in the width direction of the recording medium;
The fixing device drives and controls the magnetic flux adjusting member so that the heating range is determined after the adjustment range is gradually reduced from a maximum state.   The fixing device according to claim 1, wherein the state in which the adjustment range is maximized is a state in which the entire width direction of the heating member is a non-heating range. Detecting means for detecting the position of the magnetic flux adjusting member driven by the variable means;
Based on the driving time for one cycle until the detecting means detects the home position of the magnetic flux adjusting member again after detecting the home position of the magnetic flux adjusting member, the magnetic flux adjusting member is used to determine the heating range. Calculate the predetermined time to drive from the home position,
3. The fixing device according to claim 1, wherein the variable unit drives the magnetic flux adjustment member for the predetermined time after the detection unit detects a home position of the magnetic flux adjustment member. Detecting means for detecting the position of the magnetic flux adjusting member driven by the variable means;
After the detecting means detects the home position of the magnetic flux adjusting member, the driving time for one cycle until the home position of the magnetic flux adjusting member is detected again is obtained, and the driving time for the one cycle fluctuates by a predetermined value or more. The fixing device according to claim 1, wherein a failure of the device is sometimes detected. The magnetic flux adjustment member is configured to change the adjustment range in stages,
The number of times that the adjustment range can be changed stepwise by the magnetic flux adjusting member is N, and the latest driving time for the one cycle detected by the detecting means is T1, and the past 1 detected by the detecting means is used. When the driving time for a period is T2,
T1-T2 ≧ T2 / N
The fixing device according to claim 4, wherein a failure of the device is detected when the relationship is established. Detecting means for detecting the position of the magnetic flux adjusting member driven by the variable means;
A failure of the apparatus is detected when the heating range is determined by the variable means and the heating member is heated, and when the displacement of the magnetic flux adjusting member is detected by the detecting means. The fixing device according to any one of claims 1 to 5. The magnetic flux generating means includes a coil portion extending in the width direction so as to face the heating member, and an inner core facing the coil portion via the heating member,
The fixing device according to claim 1, wherein the magnetic flux adjusting member is a magnetic flux shielding member disposed between the coil portion and the inner core.   The fixing device according to claim 7, wherein the magnetic flux shielding member is formed so that a range covering an outer periphery of the inner core facing the coil portion can be increased or decreased stepwise.   The fixing device according to claim 8, wherein the variable unit is a unit that drives the magnetic flux shielding member so as to gradually decrease a range covering an outer periphery of the inner core. The magnetic flux generating means includes a core portion that faces the coil portion on the side not facing the heating member and has a center core.
The fixing device according to claim 7, wherein the magnetic flux shielding member covers an outer periphery of the inner core facing the center core.   The fixing device according to claim 1, wherein the heating member heats a fixing member that melts a toner image. The fixing member is a fixing belt,
The heating member is a support roller that stretches the fixing belt together with a fixing auxiliary roller,
The fixing device according to claim 11, wherein the magnetic flux generation unit is disposed to face the fixing belt.   The fixing device according to claim 12, wherein the fixing auxiliary roller is disposed so as to come into contact with a pressure roller that presses a conveyed recording medium via the fixing belt.   The fixing device according to claim 1, wherein the heating member is a fixing member that melts a toner image. The fixing member is a fixing belt,
The fixing device according to claim 14, wherein the magnetic flux generation unit is disposed to face the fixing belt. The fixing belt is stretched between a support roller and a fixing auxiliary roller,
The fixing device according to claim 15, wherein the fixing auxiliary roller is disposed so as to come into contact with a pressure roller that presses a conveyed recording medium via the fixing belt. The fixing member is a fixing roller that contacts a pressure roller that presses a recording medium to be conveyed,
The fixing device according to claim 14, wherein the magnetic flux generation unit is disposed to face the fixing roller. An image forming apparatus comprising the fixing device according to claim 1.

Images