CN106842871B

CN106842871B - Fixing device

Info

Publication number: CN106842871B
Application number: CN201710139705.5A
Authority: CN
Inventors: 横山秀治; 河岛裕树
Original assignee: Toshiba Corp; Toshiba TEC Corp
Current assignee: Toshiba Corp; Toshiba TEC Corp
Priority date: 2014-11-27
Filing date: 2015-11-09
Publication date: 2020-04-28
Anticipated expiration: 2035-11-09
Also published as: JP6579812B2; CN105652626B; CN106842871A; JP2016110058A; CN105652626A

Abstract

The invention provides a fixing device capable of preventing IGBT element from being damaged. The fixing device of the embodiment includes: a tape comprising a ferromagnetic layer; a ferromagnetic plate disposed within the band and having a Curie point lower than a Curie point of the ferromagnetic layer; an induction heater configured to cause heat to be generated in the ferromagnetic layer and the ferromagnetic plate, the induction heater comprising a coil; a drive line configured to output a high-frequency current to the coil and change the high-frequency current; a temperature sensor configured to measure a temperature of the coil; and a controller configured to control the driving line to reduce the high-frequency current if the temperature of the coil measured by the temperature sensor is higher than a predetermined value.

Description

Fixing device

This application is a divisional application of a patent application having an application date of 2015, 11/9, application number of 201510760493.3, and an invention name of "fixing device", the entire contents of which are incorporated herein by reference.

Technical Field

Embodiments of the present invention relate to a fixing device.

Background

Currently, there are Multi Function printers (hereinafter, referred to as "MFPs") and image forming apparatuses such as printers. The image forming apparatus includes a fixing device. The fixing device heats the conductive layer of the fixing belt by an electromagnetic induction heating method (hereinafter referred to as an "IH method"). The fixing device fixes the toner image on the recording medium by using heat of the fixing belt. For example, the fixing device includes a heat generation assisting unit facing the induction current generating unit across the fixing belt. The induction current generating unit generates a magnetic flux by application of a high-frequency current from the inverter driving circuit. The converter driving circuit includes an IGBT (Insulated Gate Bipolar Transistor) element. The heat generation auxiliary portion concentrates a magnetic flux during electromagnetic induction heating, and increases a heat generation amount of the fixing belt. Here, the heat generation of the fixing belt is adjusted by power control. In order to keep the temperature of the fixing belt (hereinafter referred to as "belt temperature") constant, the induced current generating portion is controlled to a constant output. When the heat generation auxiliary portion is formed of a permalloy, the heat generation auxiliary portion loses magnetism beyond the curie point, and a magnetic path is not formed. If the magnetic circuit of the heat generation auxiliary portion is not formed, the load (resistance) of the induced current generation portion decreases. The fixing device increases the current flowing through the inverter driving circuit by the load reduction of the induction current generating unit, and keeps the output of the induction current generating unit constant. If the current flowing through the inverter driving circuit is increased, the current flowing through the IGBT element is also increased, and therefore, the temperature of the IGBT element may be excessively increased, and the IGBT element may be damaged.

Disclosure of Invention

The problem to be solved by the present invention is to provide a fixing device capable of preventing damage to an IGBT element.

A fixing device according to a first aspect of the present invention includes a fixing belt, an induced current generation portion, a heat generation assisting portion, a measurement portion, and a control portion. The fixing belt includes a conductive layer. The induction current generating portion is opposed to the fixing belt. The induction current generating section has a first coil that electromagnetically induction-heats the conductive layer. The heat generation auxiliary portion is opposed to the induced current generation portion with the fixing belt interposed therebetween. The heat generation auxiliary portion is made of a magnetic material having a Curie point lower than that of the conductive layer. The measuring unit measures the state of the heat generation assisting unit. And a control unit that controls to reduce the output of the induced current generation unit when the heat generation assisting unit is determined to have exceeded the curie point based on the measurement result of the measurement unit.

A fixing device of a second aspect of the present invention includes: a fixing belt provided with a conductive layer; an induction current generating section having a coil that is opposed to the fixing belt and that electromagnetically induction-heats the conductive layer; a heat generation auxiliary portion facing the induced current generation portion with the fixing belt interposed therebetween and made of a magnetic material having a curie point lower than that of the conductive layer; a measurement unit that measures a state of the heat generation assisting unit; and a control unit that controls to reduce the output of the induced current generation unit, which functions as the measurement unit, when it is determined that the heat generation assisting unit has exceeded the curie point based on the measurement result of the measurement unit.

Drawings

Fig. 1 is a side view of an image forming apparatus according to a first embodiment.

Fig. 2 is a side view of a control module including an IH coil unit and a main body control circuit according to the first embodiment.

Fig. 3 is a perspective view of an IH coil unit according to the first embodiment.

Fig. 4 is an explanatory diagram of a magnetic path of the magnetic flux of the main coil to the fixing belt and the heat generation auxiliary plate according to the first embodiment.

Fig. 5 is a block diagram showing a control system mainly for controlling the IH coil unit according to the first embodiment.

Fig. 6 is a side view of a main part of the fixing device according to the first embodiment.

Fig. 7 is a flowchart illustrating an example of the operation of the fixing device according to the first embodiment.

Fig. 8 is a side view of a main part of the fixing device according to the second embodiment.

Fig. 9 is a side view of a main part of a fixing device according to a third embodiment.

Detailed Description

[ first embodiment ]

Next, an image forming apparatus 10 according to a first embodiment will be described with reference to the drawings. In the drawings, the same reference numerals are attached to the same components.

Fig. 1 is a side view of an image forming apparatus 10 according to a first embodiment. Next, the MFP 10 will be described as an example of the image forming apparatus 10.

As shown in fig. 1, the MFP 10 includes a scanner 12, a control panel 13, and a main body 14. The scanner 12, the control panel 13, and the main body 14 each include a control unit. The MFP 10 includes a system control unit 100 as a control unit integrating the respective control units. The system control Unit 100 includes a CPU (Central Processing Unit) 100a, a ROM (Read only Memory) 100b, and a RAM (Random Access Memory) 100c (see fig. 5). The system control unit 100 controls a main body control circuit 101 (see fig. 2) which is a control unit of the main body unit 14.

The main body control circuit 101 includes a CPU, a ROM, and a RAM, which are not shown. The main body 14 includes a supply cassette unit 16, a printer unit 18, a fixing device 34, and the like. The main body control circuit 101 controls the supply cassette unit 16, the printer unit 18, the fixing device 34, and the like.

The scanner 12 reads an original image. The control panel 13 includes input keys 13a and a display unit 13 b. For example, the input key 13a accepts input from the user. For example, the display unit 13b is of a touch panel type. The display unit 13b receives an input from a user and displays the input to the user.

The cassette unit 16 includes a paper feed cassette 16a and a pickup roller 16 b. The paper feed cassette 16a stores sheets (sheets) P as recording media. The pickup roller 16b takes out the sheet P from the paper feed cassette 16 a.

The paper feed cassette 16a supplies unused sheets P. The paper feed tray 17 feeds an unused sheet P by a pickup roller 17 a.

The printer section 18 performs image formation. For example, the printer section 18 performs image formation of a document image read by the scanner 12. The printer section 18 includes an intermediate transfer belt 21. The printer section 18 supports the intermediate transfer belt 21 by a support roller 40, a driven roller 41, and a tension roller 42. The support roller 40 includes a driving unit (not shown). The printer section 18 rotates the intermediate transfer belt 21 in the arrow m direction.

The printer section 18 includes four sets of

image forming stations

22Y, 22M, 22C, and 22K. The respective

image forming stations

22Y, 22M, 22C, and 22K are used for image formation of Y (yellow), M (magenta), C (cyan), and K (black), respectively. The

image forming stations

22Y, 22M, 22C, and 22K are arranged in parallel on the lower side of the intermediate transfer belt 21 in the rotational direction of the intermediate transfer belt 21.

The printer section 18 includes ink cartridges (cartridges) 23Y, 23M, 23C, and 23K above the

image forming stations

22Y, 22M, 22C, and 22K. The

respective cartridges

23Y, 23M, 23C, and 23K store toner for supplying Y (yellow), M (magenta), C (cyan), and K (black), respectively.

Next, the image forming station 22Y of Y (yellow) among the

image forming stations

22Y, 22M, 22C, and 22K will be described as an example. The

image forming stations

22M, 22C, and 22K have the same configuration as the image forming station 22Y, and thus detailed description thereof is omitted.

The image forming station 22Y includes a charging charger 26, an exposure scanning head 27, a developing device 28, and a photoreceptor cleaner 29. The charging charger 26, the exposure scanning head 27, the developing device 28, and the photoreceptor cleaner 29 are disposed around the photoreceptor drum 24 that rotates in the arrow n direction.

The image forming station 22Y includes a primary transfer roller 30. The primary transfer roller 30 is opposed to the photosensitive drum 24 via the intermediate transfer belt 21.

The image forming station 22Y is charged by the charging charger 26 and then exposed by the exposure scanning head 27. The image forming station 22Y forms an electrostatic latent image on the photosensitive drum 24. The developing device 28 develops the electrostatic latent image on the photosensitive drum 24 using a two-component developer formed of a toner and a carrier.

The primary transfer roller 30 primarily transfers the toner image formed on the photoconductive drum 24 onto the intermediate transfer belt 21. The

image forming stations

22Y, 22M, 22C, and 22K form color toner images on the intermediate transfer belt 21 by the primary transfer roller 30. The color toner image is formed by sequentially superimposing toner images of Y (yellow), M (magenta), C (cyan), and K (black). The photoreceptor cleaner 29 removes the toner remaining on the photoreceptor drum 24 after the primary transfer.

The printer section 18 includes a secondary transfer roller 32. The secondary transfer roller 32 is opposed to the support roller 40 via the intermediate transfer belt 21. The secondary transfer roller 32 secondarily transfers the color toner images on the intermediate transfer belt 21 to the sheet P at once. The sheet P is fed from the feed cassette portion 16 or the manual paper feed tray 17 along the conveying path 33.

The printer section 18 includes a belt cleaner 43 facing the driven roller 41 via the intermediate transfer belt 21. The belt cleaner 43 removes the toner remaining on the intermediate transfer belt 21 after the secondary transfer. Further, the image forming portion includes an intermediate transfer belt 21, four sets of image forming stations (22Y, 22M, 22C, and 22K), and a secondary transfer roller 32.

The printer section 18 includes a registration roller 33a, a fixing device 34, and a discharge roller 36 along the conveyance path 33. The printer section 18 includes a branch section 37 and a reverse conveyance section 38 downstream of the fixing device 34. The branch portion 37 sends the sheet P after fixing to the discharge portion 20 or the reversing and conveying portion 38. In the case of duplex printing, the reversing and conveying portion 38 reverses and conveys the sheet P fed from the branch portion 37 in the direction of the registration roller 33 a. The MFP 10 forms a fixed toner image on the sheet P in the printer section 18 and discharges it to the discharge section 20.

The MFP 10 is not limited to the tandem developing system, and the number of the developing devices 28 is not limited. In addition, the MFP 10 can directly transfer the toner from the photosensitive drum 24 to the sheet P.

Next, the fixing device 34 will be described in detail.

Fig. 2 is a side view of a control module including an electromagnetic induction heating coil unit 52 (induction current generating unit) (hereinafter referred to simply as IH coil unit 52) according to the first embodiment and a main body control circuit 101 (control unit). Hereinafter, the electromagnetic induction heating coil unit is referred to as "IH coil unit"

As shown in fig. 2, the fixing device 34 includes a fixing belt 50, a pressure roller 51, an IH coil unit 52, a heat generation auxiliary plate 69 (ferromagnetic plate), a second coil unit 84 (measuring unit), and a main body control circuit 101.

The fixing belt 50 is a cylindrical endless belt. A belt internal mechanism 55 including a nip pad 53 and a heat generation assisting plate 69 is disposed on the inner peripheral side of the fixing belt 50.

The fixing belt 50 is formed by stacking a heat generating layer 50a (conductive layer) and a parting (detachable) layer 50c in this order on a base layer 50b (see fig. 4). The layer structure is not limited as long as the fixing belt 50 includes the heat generating layer 50 a.

The base layer 50b is formed of, for example, polyimide resin (PI). The heat generating layer 50a is formed of a non-magnetic metal such as copper (Cu), for example. For example, the parting layer 50c is formed of a fluororesin such as tetrafluoroethylene-perfluoroalkylvinylether copolymer resin (PFA).

In order to perform rapid warm-up, the fixing belt 50 reduces the heat capacity by making the heat-generating layer 50a thin. The fixing belt 50 having a small heat capacity shortens the time required for warm-up, saving power consumption.

For example, the fixing belt 50 has a copper layer of the heat generating layer 50a with a thickness of 10 μm in order to reduce the heat capacity. The heat generating layer 50a is covered with a protective layer such as nickel, for example. The protective layer of nickel or the like inhibits oxidation of the copper layer. The protective layer such as nickel improves the mechanical strength of the fixing belt 50.

Further, the heat generating layer 50a may be formed by performing copper electroplating while performing electroless nickel electroplating on the base layer 50b formed of polyimide resin. By performing electroless nickel plating, the adhesion strength between the base layer 50b and the heat generating layer 50a is improved. The electroless nickel plating improves the mechanical strength of the fixing belt 50.

In addition, the surface of the base layer 50b may be roughened by sandblasting or chemical etching. By roughening the surface of the base layer 50b, the adhesion strength of the nickel plating of the base layer 50b and the heat generating layer 50a is further improved.

In addition, a metal such as titanium (Ti) may be dispersed in the polyimide resin forming the base layer 50 b. By dispersing the metal in the base layer 50b, the adhesion strength of the nickel plating of the base layer 50b and the heat generating layer 50a is further improved.

For example, the heat generating layer 50a may be formed of nickel, iron (Fe), stainless steel, aluminum (Al), silver (Ag), and the like. The heat generating layer 50a may be formed of two or more kinds of alloys, or may be formed by stacking two or more kinds of metals in a layered manner.

Fig. 3 is a perspective view of the IH coil unit 52 according to the first embodiment.

As shown in fig. 3, the IH coil unit 52 includes a main coil 56 (first coil), a first core 57, and a second core 58.

The main coil 56 generates a magnetic flux by application of a high-frequency current. The main coil 56 is disposed on the outer peripheral side of the fixing belt 50. The main coil 56 is opposed to the fixing belt 50 in the thickness direction. The main coil 56 has a longitudinal direction aligned in the width direction of the fixing belt 50 (hereinafter referred to as the "belt width direction").

The first core 57 and the second core 58 cover the opposite side (hereinafter referred to as "back side") of the main coil 56 from the fixing belt 50. The first core 57 and the second core 58 suppress leakage of the magnetic flux generated by the main coil 56 on the rear surface side. The first core 57 and the second core 58 concentrate the magnetic flux from the main coil 56 on the fixing belt 50.

The first magnetic core 57 includes a plurality of tab portions (tab portions) 57 a. The plurality of fin portions 57a are arranged in a staggered manner with respect to each other so as to be axisymmetrical about a center line 56d along the longitudinal direction of the main coil 56.

The second cores 58 are disposed on both sides of the first core 57 in the longitudinal direction. The second magnetic core 58 has a plurality of two-wing portions 58a spanning the two wings of the main coil 56.

For example, the fin portion 57a and the both fin portions 58a are formed of a magnetic material such as nickel-zinc alloy (Ni — Zn) or manganese-nickel alloy (Mn — Ni).

The first magnetic core 57 restricts the magnetic flux generated by the main coil 56 by a plurality of flap portions 57 a. The magnetic flux generated by the main coil 56 is axially symmetric about the center line 56d and is mutually restricted by each of the vanes of the main coil 56. The first magnetic core 57 concentrates the magnetic flux from the main coil 56 to the fixing belt 50 by the plurality of tab portions 57 a.

The second magnetic core 58 restricts the magnetic flux generated by the main coil 56 by a plurality of two wings 58 a. The magnetic flux generated by the main coil 56 is restricted by both wings of the main coil 56 in both sides of the first magnetic core 57. The second magnetic core 58 concentrates the magnetic flux from the main coil 56 to the fixing belt 50 by a plurality of two wings 58 a. The magnetic flux concentration force of the second magnetic core 58 is larger than that of the first magnetic core 57.

The main coil 56 includes a first blade 56a and a second blade 56 b. The first fin 56a is disposed on one side with respect to the center line 56 d. The second wing 56b is disposed on the other side with respect to the center line 56 d. A window 56c is formed between the first and

second blades

56a and 56b, i.e., on the inner side in the longitudinal direction of the main coil 56.

For example, the main coil 56 uses a twisted wire. The litz wire is formed by bundling a plurality of copper wire materials coated with heat-resistant polyamide-imide, which is an insulating material. The main coil 56 is formed around a conductive coil.

As shown in fig. 2, the main coil 56 generates magnetic flux by application of high-frequency current from the inverter driving circuit 68. For example, the inverter driving circuit 68 includes switching elements such as an IGBT (Insulated Gate Bipolar Transistor) element 68a and a MOSFET (Metal Oxide semiconductor field effect Transistor) element (not shown). IGBT element 68a is connected to the MOSFET element. By alternately turning ON (ON)/OFF (OFF) the IGBT element 68a and the MOSFET element, a high-frequency current flows through the main coil 56. By causing a high-frequency current to flow in the main coil 56, a high-frequency magnetic field is generated around the main coil 56. An eddy current is generated in the heat generating layer 50a of the fixing belt 50 by the magnetic flux of the high-frequency magnetic field. Joule heat is generated by the eddy current and the resistance of the heat generating layer 50 a. The fixing belt 50 is heated by the generation of the joule heat.

For example, the on period of IGBT element 68a is constant. By changing the on period of the MOSFET element, the high-frequency current flowing in the main coil 56 changes. The output of the electromagnetic induction heating changes with a change in the high-frequency current flowing through the main coil 56.

The heat generation assisting plate 69 is disposed on the inner peripheral side of the fixing belt 50. The heat generation assisting plate 69 is formed in an arc shape along the inner peripheral surface of the fixing belt 50 as viewed in the belt width direction. The heat generation auxiliary plate 69 faces the main coil 56 with the fixing belt 50 interposed therebetween. The heat generation auxiliary plate 69 has a magnetic material (ferromagnetic material) lower than the curie point of the heat generation layer 50 a. A magnetic flux is generated between the heat generation assisting plate 69 and the fixing belt 50 by the magnetic flux generated by the main coil 56. By the generation of the magnetic flux, joule heat is generated in the heat generating layer 50a of the fixing belt 50. The heating of the fixing belt 50 of the main coil 56 is assisted by the generation of the joule heat.

The arc-shaped both ends of the heat generation auxiliary plate 69 are supported by a base (not shown). The radially outer side surface of the heat generation assisting plate 69 is distant from the inner peripheral surface of the fixing belt 50. For example, the interval between the radially outer surface of the heat generation assisting plate 69 and the inner circumferential surface of the fixing belt 50 is about 1mm to 2 mm. Further, the radially outer side surface of the heat generation assisting plate 69 may contact the inner circumferential surface of the fixing belt 50.

For example, the length of the heat generation assisting plate 69 in the belt width direction is larger than the length of the paper passing region in the belt width direction (hereinafter referred to as "sheet width"). The sheet width is the width of the sheet having the shortest side width among the sheets used. For example, the sheet width is slightly greater than the short edge width of the A3 paper.

Fig. 4 is an explanatory diagram of a magnetic path of the magnetic flux of the main coil 56 to the fixing belt 50 and the heat generation auxiliary plate 69 according to the first embodiment.

As shown in fig. 4, the magnetic flux generated by the main coil 56 forms a first magnetic path 81 induced by the heat generating layer 50a of the fixing belt 50. The first magnetic circuit 81 is formed to surround the first and

second limbs

56a and 56b of the main coil 56. The first magnetic path 81 passes through the first magnetic core 57, the second magnetic core 58, and the heat generating layer 50 a. In addition, the magnetic flux generated by the main coil 56 forms a second magnetic circuit 82 induced by the heat generation auxiliary plate 69. The second magnetic path 82 is formed at a position adjacent to the first magnetic path 81 in the radial direction of the fixing belt 50 (hereinafter referred to as "belt radial direction"). The second magnetic circuit 82 passes through the heat generation auxiliary plate 69 and the heat generation layer 50 a.

The heat generation assisting plate 69 is formed of a thin metal member made of a permalloy such as iron or a nickel alloy having a curie point of 220 to 230 ℃. The heat generation assisting sheet 69 loses magnetism beyond the curie point. Specifically, the heat generation assisting plate 69 changes from ferromagnetic to paramagnetic when it exceeds the curie point. When the heat generation assisting plate 69 exceeds the curie point, the second magnetic circuit 82 is not formed, and the heating of the fixing belt 50 is not assisted. By forming the heat generation assisting plate 69 from a permalloy, the temperature rise of the fixing belt 50 can be assisted at a low temperature and the excessive temperature rise of the fixing belt 50 can be suppressed at a high temperature, with the curie point as a boundary.

Here, the heat generation of the fixing belt 50 is adjusted by the power control of the IH control circuit 67. To keep the belt temperature constant, the IH coil unit 52 is controlled to a constant output. When the heat generation auxiliary plate 69 is formed of a permalloy, the heat generation auxiliary plate 69 loses its magnetism beyond the curie point, and the second magnetic circuit 82 is not formed. If the second magnetic circuit 82 is not formed, the load (resistance) of the IH coil unit 52 decreases.

The increase in the current flowing through the inverter driving circuit 68 by the IH control circuit 67 corresponds to the decrease in the load of the IH coil unit 52, and keeps the output of the IH coil unit 52 constant. If the current flowing through inverter drive circuit 68 increases, the current flowing through IGBT element 68a also increases, and therefore the temperature of IGBT element 68a may rise excessively, and IGBT element 68a may be damaged. Therefore, in the present embodiment, as will be described later, the change in magnetism of the heat generation assisting plate 69 is estimated by measuring the resistance of the second coil 84 a. Then, the IH control circuit 67 controls the IH coil unit 52 so that the output of the electromagnetic induction heating is reduced when the measured resistance is smaller than the threshold value.

The heat generation auxiliary plate 69 may be formed of a thin sheet metal member having magnetic properties such as iron, nickel, and stainless steel. The heat generation auxiliary plate 69 may be made of a resin containing magnetic powder, for example, if it has magnetic properties. In addition, the heat generation assisting plate 69 may be formed of the following magnetic material (ferrite). The magnetic material (ferrite) passes the magnetic flux of the induced current and promotes the heat generation of the fixing belt 50. The magnetic material (ferrite) does not generate heat by itself even if exposed to the magnetic flux of the induced current. The heat generation assisting plate 69 is not limited to a thin plate member.

As shown in fig. 2, a cover (shield)76 is disposed on the inner peripheral side of the heat generation assisting plate 69. The cover 76 is formed in an arc shape similar to the heat generation assisting plate 69. The cover 76 supports both ends of the arc shape on a base (not shown). Further, the cover 76 may support the heat generation assisting plate 69. For example, the cap 76 is made of a nonmagnetic material such as aluminum or copper. The cover 76 blocks the magnetic flux from the IH coil unit 52. The cover 76 suppresses the influence of the magnetic flux on the measurement voltage of the thermistor, etc.

The nip pad 53 is a pressing portion that presses the inner peripheral surface of the fixing belt 50 toward the pressure roller 51. A nip 54 is formed between the fixing belt 50 and the pressure roller 51. The nip pad 53 has a nip forming surface 53a forming a nip 54 between the fixing belt 50 and the pressure roller 51. The nip forming surface 53a is curved in a convex shape on the inner peripheral side of the fixing belt 50 as viewed in the belt width direction. The nip forming surface 53a is curved along the outer peripheral surface of the pressure roller 51 when viewed in the belt width direction.

For example, the pressure roller 51 includes a heat-resistant silicone sponge, a silicone rubber layer, and the like around the core iron. For example, a parting layer is disposed on the surface of the pressure roller 51. The parting layer is formed of a fluorine-based resin such as PFA resin. The pressure roller 51 presses the fixing belt 50 by a pressing mechanism. The pressure roller 51 is a pressure portion that presses the fixing belt 50 together with the nip pad 53.

One motor 51b is provided as a drive source for the fixing belt 50 and the pressure roller 51. The motor 51b is driven by a motor drive circuit 51c controlled by the main body control circuit 101. The motor 51b is connected to the pressure roller 51 via a first gear train (not shown). The motor 51b is connected to a belt driving member (not shown) via a second gear train and a one-way clutch. The pressure roller 51 rotates in the arrow q direction by the motor 51 b. When the fixing belt 50 and the pressure roller 51 abut against each other, the fixing belt 50 is driven by the pressure roller 51 and rotates in the arrow u direction. The fixing belt 50 is rotated in the arrow u direction by the motor 51b when the fixing belt 50 and the pressure roller 51 are separated. The fixing belt 50 may be provided with a drive source independently of the pressure roller 51.

The central thermistor 61 and the edge thermistor 62 measure the ribbon temperature. The measurement result of the belt temperature is input to the main body control circuit 101. The central thermistor 61 is disposed on the inner side in the belt width direction. The edge thermistor 62 is disposed in the width direction in the heating region of the IH coil unit 52 and does not pass through the paper region. The body control circuit 101 controls the IH coil unit 52 so as to stop the output of the electromagnetic induction heating when the belt temperature measured by the edge thermistor 62 is equal to or higher than a threshold value. When the temperature of the non-sheet passing area of the fixing belt 50 is excessively increased, the output of electromagnetic induction heating is stopped, thereby preventing damage to the fixing belt 50.

The main body control circuit 101 controls the IH control circuit 67 based on the measurement results of the belt temperatures of the center thermistor 61 and the edge thermistor 62. The IH control circuit 67 controls the magnitude of the high-frequency current output from the inverter drive circuit 68 by the control of the main body control circuit 101. The fixing belt 50 maintains various control temperature ranges according to the output of the inverter drive circuit 68. The IH control circuit 67 includes a CPU, a ROM, and a RAM, which are not shown.

The thermostat device 63 functions as a safety device of the fixing device 34. The thermostat device 63 operates when the fixing belt 50 abnormally generates heat and the temperature rises to the blocking threshold. The current flowing to the IH coil unit 52 is shut off by the operation of the thermostat device 63. By interrupting the current flowing through the IH coil unit 52, the MFP 10 stops driving, and abnormal heat generation of the fixing device 34 is suppressed.

Next, the control system 110 of the IH coil unit 52 that generates heat in the fixing belt 50 will be described in detail.

Fig. 5 is a block diagram showing a control system 110 mainly for controlling the IH coil unit 52 according to the first embodiment.

As shown in fig. 5, the control system 110 includes a system control unit 100, a main body control circuit 101, an IH circuit 120, and a motor drive circuit 51 c.

The control system 110 provides power to the IH coil unit 52 using the IH circuit 120. The IH circuit 120 includes a rectifier circuit 121, an IH control circuit 67, an inverter drive circuit 68, and a current measurement circuit 122.

The IH circuit 120 receives an input of current from the ac power supply 111 via the relay 112. The IH circuit 120 rectifies the input current by the rectifier circuit 121 and supplies it to the converter driving circuit 68. When the thermostat 63 is turned off, the relay 112 interrupts the current from the ac power supply 111. Inverter drive circuit 68 includes drive IC 68b of IGBT element 68 a. The IH control circuit 67 controls the drive IC 68b based on the measurement results of the belt temperatures of the center thermistor 61 and the edge thermistor 62. The IH control circuit 67 controls the drive IC 68b, and controls the output of the IGBT element 68 a. The current measurement circuit 122 transmits the measurement result of the output of the IGBT element 68a to the IH control circuit 67. The IH control circuit 67 controls the drive IC 68b so that the output of the IH coil unit 52 is constant, based on the measurement result of the output of the IGBT element 68a of the current measurement circuit 122.

The main body control circuit 101 obtains a measurement value R (see fig. 7) described later from the resistance measurement circuit 84 b. The body control circuit 101 controls the IH coil unit 52 based on the measurement value R. The main body control circuit 101 determines whether or not the measurement value R is smaller than a threshold value Rt. The main body control circuit 101 controls either the continuation of the driving of the fixing device 34 or the reduction of the output of the IH coil unit 52 based on the determination result. Further, the decrease in the output of the IH coil unit 52 includes the stop of the IH coil unit 52.

Fig. 6 is a side view of a main part of the fixing device 34 according to the first embodiment.

As shown in fig. 6, the second coil unit 84 includes a second coil 84a and a resistance measurement circuit 84b (resistance measurement unit). The second coil unit 84 determines whether or not the heat generation assisting plate 69 is in a state of exceeding the curie point. The second coil 84a is formed separately from the main coil 56. The second coil 84a generates a magnetic field by energization through the heat generation auxiliary plate 69. For example, the second coil 84a is formed of a litz wire. The resistance measuring circuit 84b measures the resistance of the second coil 84 a. The measurement result of the resistance of the second coil 84a is input to the main body control circuit 101.

Next, in the heat generation assisting plate 69, in the circumferential direction of the fixing belt 50 (hereinafter referred to as "belt circumferential direction"), a region facing the IH coil unit 52 with the fixing belt 50 interposed therebetween is referred to as a facing region 69 a. The end 69c of the heat generation assisting plate 69 is an end of the heat generation assisting plate 69 in the belt circumferential direction, and is a region adjacent to the facing region 69 a. An end 69c of the heat generation assisting plate 69 does not face the IH coil unit 52 across the fixing belt 50 in the belt radial direction.

The end 52c of the IH coil unit 52 is an end of the first core 57 and the second core 58 in the belt circumferential direction, and includes a region protruding inward in the belt radial direction.

The second coil 84a is disposed in a region S1 (see fig. 2) that faces the heat generation assisting plate 69 and does not face the main coil 56. Specifically, the area S1 is located between the end 52c of the IH coil unit 52 and the fixing belt 50 in the belt diameter direction. The region S1 is a range from the outer side of the main coil 56 to the end 69c of the heat generation assisting plate 69 in the belt circumferential direction. The region S1 faces the end 52c of the IH coil unit 52 in the belt circumferential direction and faces the end 69c of the heat generation assisting plate 69 across the fixing belt 50. One end (inner end) in the tape circumferential direction in the region S1 faces the boundary between the end 52c of the IH coil unit 52 and the main coil 56 in the tape radial direction. The other end (outer end) in the belt width direction in the region S1 sandwiches the leading end (both ends of the arc shape) of the end 69c of the fixing belt 50 facing the heat generation assisting plate 69 in the belt diameter direction.

In the present embodiment, the second coil 84a is disposed on the outer peripheral side of the fixing belt 50. The second coil 84a faces the end 69c of the heat generation assisting plate 69 across the fixing belt 50.

Further, the second coil 84a may be opposed to the opposed region 69a of the heat generation assisting plate 69 across the fixing belt 50 in a range not opposed to the main coil 56.

The second coil 84a is fixed to the fixing belt 50 at a predetermined interval. The second coil 84a is opposed to at least the paper passing area in the width direction. For example, the second coil 84a is opposed to the central portion of the fixing belt 50.

The size of the second coil 84a is smaller than that of the main coil 56. This is because the resistance measuring circuit 84b can measure the resistance of the second coil 84a by the second coil 84a generating a magnetic field through the heat generation assisting plate 69 by the energization.

In addition, the second coil 84a can be easily arranged in the region S1, as compared with the case where the size of the second coil 84a is equal to or larger than the main coil 56.

The magnetic flux generated by the second coil 84a forms a third magnetic circuit 85 induced by the heat generating layer 50a of the fixing belt 50. The third magnetic circuit 85 passes through the heat generating layer 50 a. The magnetic flux generated by the second coil 84a forms a fourth magnetic circuit 86 induced by the heat generation auxiliary plate 69 before the heat generation auxiliary plate 69 exceeds the curie point and loses magnetism. The fourth magnetic path 86 is formed at a position adjacent to the third magnetic path 85 in the belt diameter direction. The fourth magnetic circuit 86 passes through the heat generation auxiliary plate 69 and the heat generation layer 50 a. The resistance of the second coil 84a changes with the change in magnetism of the heat generation auxiliary plate 69. That is, the resistance of the second coil 84a changes depending on whether the fourth magnetic circuit 86 is formed.

By flowing a weak high-frequency current (hereinafter referred to as a "high-frequency weak current") through the second coil 84a, the resistance of the second coil 84a can be measured. For example, a resistance measuring circuit 84b is connected to the upstream side and the downstream side of the second coil 84a, and the resistance is measured from the current values on the upstream side and the downstream side of the second coil 84 a. The high-frequency weak current is a current weaker than the high-frequency current output from the inverter drive circuit 68.

Next, an example of the operation of the fixing device 34 according to the first embodiment will be described with reference to fig. 7.

Fig. 7 is a flowchart illustrating an example of the operation of the fixing device 34 according to the first embodiment.

In Act100, the resistance measurement circuit 84b causes a high-frequency weak current to flow through the second coil 84 a. For example, the high-frequency weak current has a frequency of 60kHz and a current of 10 mA.

In Act101, the resistance measurement circuit 84b measures the resistance of the second coil 84 a. In the present embodiment, the resistance of the second coil 84a measured by the resistance measurement circuit 84b is "measurement value R". The main body control circuit 101 acquires the measurement value R from the resistance measurement circuit 84 b.

The main body control circuit 101 may acquire the measurement value R via another circuit such as a logic circuit.

In Act102, the main body control circuit 101 determines whether or not the measurement value R acquired in Act101 is smaller than a threshold value Rt (e.g., 1[ Ω ]).

By determining whether or not the measurement value R is smaller than the threshold value Rt for the following reason, it is possible to determine the change in magnetism of the heat generation assisting plate 69.

When the measured value R is equal to or greater than the threshold value Rt, the heat generation assisting plate 69 has a ferromagnetic property exceeding the curie point. When the heat generation auxiliary plate 69 has a strong magnetism, the magnetic flux generated by the second coil 84a forms the third magnetic circuit 85 and the fourth magnetic circuit 86.

On the other hand, when the measured value R is smaller than the threshold value Rt, the heat generation assisting plate 69 exceeds the curie point and changes to paramagnetic property. When the heat generation auxiliary plate 69 becomes paramagnetic, the fourth magnetic circuit 86 is lost.

Therefore, by determining whether or not the measurement value R is smaller than the threshold value Rt, the magnetic change of the heat generation assisting plate 69 can be estimated.

When the main body control circuit 101 determines that the measurement value R is smaller than the threshold Rt (yes in Act 102), the process proceeds to Act 104. When determining that the measurement value R is equal to or greater than the threshold Rt (no in Act 102), the main body control circuit 101 advances the process to Act 103.

At Act103, the fixing device 34 continues to be driven. For example, when high-output driving such as continuous paper feeding and warm-up is performed, the fixing device 34 continues the high-output driving.

In Act104, the body control circuit 101 controls the IH coil unit 52 based on the measurement value R. The control of the main body control circuit 101 based on the measurement value R is performed for the following reason.

At Act105, the body control circuit 101 determines whether to stop the IH coil unit 52 based on the measurement value R. For example, the body control circuit 101 determines to stop the IH coil unit 52 when the measured value R is less than 0.5[ Ω ]. When the body control circuit 101 determines that the IH coil unit 52 is stopped (yes in Act 105), the process ends. The body control circuit 101 stops the IH coil unit 52, thereby suppressing an excessive temperature rise of the IGBT element 68 a. Body control circuit 101 prevents IGBT elements 68a from being damaged by suppressing an excessive temperature rise of IGBT elements 68 a.

When determining that the IH coil unit 52 is not to be stopped (no in Act 105), the main body control circuit 101 advances the process to Act 106.

At Act106, the body control circuit 101 lowers the output of the IH coil unit 52. For example, the body control circuit 101 reduces the power supplied to the IH coil unit 52. The body control circuit 101 reduces the output of the IH coil unit 52, thereby suppressing an excessive temperature rise of the IGBT element 68 a. Body control circuit 101 prevents IGBT elements 68a from being damaged by suppressing an excessive temperature rise of IGBT elements 68 a.

At Act103, the fixing device 34 continues to be driven in a state where the output of the IH coil unit 52 is lowered.

The operation of the fixing device 34 during warm-up will be described below.

As shown in fig. 2, the fixing device 34 rotates the fixing belt 50 in the arrow u direction at the time of warm-up. The IH coil unit 52 generates a magnetic flux on the fixing belt 50 side by application of a high-frequency current to the inverter driving circuit 68.

For example, in the warm-up, the fixing belt 50 is rotated in the arrow u direction while the fixing belt 50 is separated from the pressure roller 51. At the time of warm-up, the fixing belt 50 is rotated in a state of being separated from the pressure roller 51, thereby achieving the following effects. As compared with the case where the fixing belt 50 is rotated while being in contact with the pressure roller 51, it is possible to avoid the heat of the fixing belt 50 being taken away by the pressure roller 51. The warm-up time can be shortened by avoiding the heat of the fixing belt 50 being taken away by the pressure roller 51.

In the warm-up, the pressure roller 51 is rotated in the arrow q direction in a state where the pressure roller 51 is brought into contact with the fixing belt 50, whereby the fixing belt 50 can be driven and rotated in the arrow u direction.

As shown in fig. 4, the IH coil unit 52 heats the fixing belt 50 by the first magnetic circuit 81. The heat generation assisting plate 69 assists the heating of the fixing belt 50 by the second magnetic circuit 82. The rapid warm-up of the fixing belt 50 is promoted by assisting the heating of the fixing belt 50.

As shown in fig. 2, the IH control circuit 67 controls the inverter drive circuit 68 based on the result of measurement of the belt temperature of the center thermistor 61 or the edge thermistor 62. The converter drive circuit 68 supplies a high frequency current to the main coil 56.

Next, the operation of the fixing device 34 in the fixing operation will be described.

After the fixing belt 50 reaches the fixing temperature and the warm-up is completed, the pressure roller 51 is brought into contact with the fixing belt 50. In a state where the pressure roller 51 is in contact with the fixing belt 50, the pressure roller 51 is rotated in the arrow q direction, whereby the fixing belt 50 is driven and rotated in the arrow u direction. If there is a print request, the MFP 10 (refer to fig. 1) starts a printing operation. The MFP 10 forms a toner image on the sheet P by the printer section 18, and conveys the sheet P to the fixing device 34.

The MFP 10 passes the sheet P on which the toner image is formed through a nip (nip)54 between the fixing belt 50 and the pressure roller 51, which reach the fixing temperature. The fixing device 34 fixes the toner image on the sheet P. During the fixing, the IH control circuit 67 controls the IH coil unit 52 to keep the fixing belt 50 at a fixing temperature.

The fixing belt 50 is deprived of heat by the sheet P by the fixing operation. For example, in the case of continuously passing paper at a high speed, since the amount of heat taken away by the sheet P is large, the fixing belt 50 having a low heat capacity may not be maintained at the fixing temperature. The heating of the fixing belt 50 by the second magnetic circuit 82 assists in compensating for the shortage of the belt heat generation amount. The heating assistance of the fixing belt 50 of the second magnetic circuit 82 maintains the belt temperature at the fixing temperature even when the paper is continuously passed at high speed.

However, in order to prevent damage to IGBT element 68a, it is considered necessary to provide a thermistor for measuring the temperature of IGBT element 68 a. The thermistor is mounted in a case not in the IGBT element 68a itself but in the inverter drive circuit 68. When the thermistor measures the temperature rise of IGBT element 68a, main body control circuit 101 drives the fan to cool IGBT element 68 a. The thermistor can measure a gradual temperature rise of the IGBT element 68 a. However, it is difficult to measure a rapid temperature rise with a thermistor, and there is a limit to the temperature following ability of the IGBT element 68 a. Further, since the thermistor is mounted in the case, it is difficult to measure the correct temperature of the IGBT element 68a in the thermistor. The measured temperature of IGBT element 68a using the thermistor may deviate from the actual internal temperature of IGBT element 68 a. Further, it is difficult to cool IGBT elements 68a by cooling IGBT elements 68a with a fan, and there is a limit to sufficiently cool IGBT elements 68 a. Therefore, there is a possibility that the IGBT element 68a cannot be prevented from being broken by temperature measurement using the thermistor and cooling using the fan.

In contrast, according to the first embodiment, the resistance measuring circuit 84b measures the resistance of the second coil 84 a. By measuring the resistance of the second coil 84a, a slow temperature rise and a rapid temperature rise of the IGBT element 68a can be indirectly measured. By measuring the resistance of the second coil 84a, the temperature of the IGBT element 68a can be indirectly measured in real time as compared with the case where the thermistor is provided. Further, by measuring the resistance of the second coil 84a, the deviation from the actual internal temperature of the IGBT element 68a described above is not a problem.

Further, the main body control circuit 101 acquires the resistance (measured value R) of the second coil 84a from the resistance measurement circuit 84 b. The body control circuit 101 controls the IH coil unit 52 so that the output of the electromagnetic induction heating is reduced when the measured value R is smaller than the threshold value. When the measured value R is smaller than the threshold value, the output of electromagnetic induction heating is reduced, whereby an excessive temperature rise of IGBT element 68a can be suppressed. Specifically, the main body control circuit 101 determines whether or not the measurement value R is smaller than the threshold value Rt. When the measurement value R is smaller than the threshold value Rt, the body control circuit 101 can reduce the output of the IH coil unit 52. For example, by stopping the IH coil unit 52 or reducing the output of the IH coil unit 52, an excessive temperature rise of the IGBT element 68a can be suppressed. Thus, IGBT element 68a can be prevented from being broken.

Further, since the second coil 84a is formed separately from the main coil 56, the resistance measuring circuit 84b can measure the resistance of the second coil 84a as needed. Therefore, the main body control circuit 101 can acquire the measurement value R as needed.

Further, by disposing the second coil 84a in the region S1 that does not face the main coil 56 and faces the heat generation assisting plate 69, the following effects are obtained. Compared to the case where the second coil 84a is disposed in the region facing the main coil 56, the second coil 84a can be suppressed from being affected by the large magnetic force of the main coil 56, and therefore the resistance of the second coil 84a can be measured with high accuracy.

Further, the second coil 84a faces the end 69c (a portion adjacent to the facing region 69 a) of the heat generation assisting plate 69 across the fixing belt 50, and the following effects are obtained. The second coil unit 84 is capable of measuring the resistance of the second coil 84a at a portion having a temperature change equivalent to the facing region 69a (a portion having a correlation with the temperature change of the facing region 69 a).

Further, since the second coil 84a faces at least the sheet passing region in the width direction, the second coil unit 84 can be separated from the non-sheet passing region to measure the resistance of the second coil 84 a. Therefore, the main body measurement circuit 101 can acquire the measurement value R separately from the non-sheet passing region.

[ second embodiment ]

Next, a second embodiment will be described with reference to fig. 8. Note that the same reference numerals are used to designate the same aspects as those of the first embodiment, and description thereof will be omitted.

Fig. 8 is a side view of a main part of a fixing device 234 according to the second embodiment. Fig. 8 is a side view corresponding to fig. 6.

As shown in fig. 8, the fixing device 234 according to the second embodiment does not include the second coil 84a according to the first embodiment. The fixing device 234 according to the second embodiment is different from the first embodiment in that it includes the measurement portion 284 using the main coil 56. In fig. 8, reference numeral 284b denotes a resistance measurement circuit.

The IH coil unit 52 has a main coil 56 (coil) that electromagnetically induction-heats the heat generating layer 50 a. The IH coil unit 52 functions as a measurement unit 284. The measurement unit 284 generates a magnetic field that passes through the heating auxiliary plate 69 by applying a current to the main coil 56. The measurement unit 284 measures the resistance of the main coil 56.

The magnetic flux generated by the main coil 56 forms a first magnetic circuit 81 and a second magnetic circuit 82. The resistance of the main coil 56 changes with the magnetic change of the heat generation auxiliary plate 69.

By causing a high-frequency weak current to flow through the main coil 56, the resistance of the main coil 56 can be measured.

The resistance measuring circuit 284b measures the resistance of the main coil 56. In the present embodiment, the resistance of the main coil 56 measured by the resistance measurement circuit 284b is referred to as a "measurement value R". The main body control circuit 101 acquires the measurement value R from the resistance measurement circuit 284 b.

The main body control circuit 101 determines whether or not the obtained measurement value R is smaller than a threshold value Rt (e.g., 1[ Ω ]).

When the measured value R is equal to or greater than the threshold value Rt, the heat generation assisting plate 69 does not exceed the curie point and has a strong magnetism. When the heat generation auxiliary plate 69 has a strong magnetism, the magnetic flux generated by the main coil 56 forms a first magnetic circuit 81 and a second magnetic circuit 82.

On the other hand, when the measured value R is smaller than the threshold value Rt, the heat generation assisting plate 69 exceeds the curie point and becomes paramagnetic. When the heat generation auxiliary plate 69 becomes paramagnetic, the second magnetic circuit 82 is lost.

The body control circuit 101 controls the IH coil unit 52 so as to lower the output of electromagnetic induction heating when the obtained measurement value R is smaller than the threshold value Rt.

According to the second embodiment, the same effects as those of the first embodiment are obtained.

In addition, compared with the case where the second coil 84a opposes the end portion 69c of the heat generation assisting plate 69 via the fixing belt 50, the resistance of the main coil 56 can be measured at a point facing the opposing region 69 a. Therefore, the change in the magnetism of the facing region 69a can be determined.

Further, the resistance of the main coil 56 can be measured at a timing (timing) when the IH coil unit 52 is not heated. For example, the resistance of the main coil 56 can be measured during a job other than the continuous sheet passing and the preheating (for example, 10 sheets per sheet passing). Therefore, during the work, the change in the magnetism of the opposing region 69a can be determined.

In addition, compared to the case where the second coil 84a and the main coil 56 are formed separately, the number of components can be reduced, and the structure of the fixing device 234 can be simplified.

Further, the resistance of the main coil 56 may be measured at a timing when the IH coil unit 52 is caused to generate heat. For example, the resistance of the main coil 56 may be measured while continuously passing through the sheet and while preheating. By measuring the resistance of the main coil 56 during continuous paper passage and during preheating, the resistance of the main coil 56 can be measured in real time at a point facing the opposing region 69 a. Therefore, the change in the magnetism of the facing region 69a can be determined in real time during continuous paper passage and during preheating.

[ third embodiment ]

Next, a third embodiment will be described with reference to fig. 9. Note that the same reference numerals are used to designate the same aspects as those of the first embodiment, and description thereof will be omitted.

Fig. 9 is a side view of a main part of a fixing device 334 according to a third embodiment. Fig. 9 is a side view corresponding to fig. 6.

As shown in fig. 9, the fixing device 334 according to the third embodiment does not include the second coil 84a according to the first embodiment. The fixing device 334 according to the third embodiment is different from the first embodiment in that it includes the second coil 384a disposed on the inner circumferential side of the fixing belt 50. The second coil 384a is disposed radially inward of the heat generation assisting plate 69 (radially inward of the fixing belt with respect to the heat generation assisting portion 69). In fig. 9, reference numeral 384 denotes a second coil unit, and reference numeral 384b denotes a resistance measurement circuit.

The magnetic flux generated by the second coil 384a forms the fifth magnetic circuit 87 induced by the heat generation auxiliary plate 69 before the heat generation auxiliary plate 69 loses magnetism beyond the curie point. The fifth magnetic path 87 passes through the heat generation auxiliary plate 69 without protruding outward in the belt radial direction of the heat generation auxiliary plate 69.

When the heat generation auxiliary plate 69 passes the curie point and loses its magnetic properties, the magnetic flux generated by the second coil 384a forms a sixth magnetic circuit 88 induced by the heat generation layer 50a of the fixing belt 50. The sixth magnetic circuit 88 protrudes outward in the belt radial direction of the heat generation auxiliary plate 69 and passes through the heat generation layer 50 a. The resistance of the second coil 384a changes with the change in magnetism of the heat generation auxiliary plate 69.

By flowing a high-frequency weak current through the second coil 384a, the resistance of the second coil 384a can be measured.

The resistance measurement circuit 384b measures the resistance of the second coil 384 a. In the present embodiment, the resistance of the second coil 384a measured by the resistance measurement circuit 384b is referred to as "measurement value R". The main body control circuit 101 acquires the measurement value R from the resistance measurement circuit 384 b.

When the measurement value Rt is equal to or greater than the threshold value Rt, the heat generation assisting plate 69 does not exceed the curie point and has a strong magnetism. When the heat generation assisting plate 69 has a strong magnetism, the magnetic flux generated by the second coil 384a forms the fifth magnetic circuit 87.

On the other hand, when the measurement value R is smaller than the threshold value Rt, the heat generation assisting plate 69 exceeds the curie point and becomes paramagnetic. When the heat generation auxiliary plate 69 becomes paramagnetic, the magnetic flux generated by the second coil 384a forms the sixth magnetic circuit 88. Further, in the case where the heat generation auxiliary plate 69 becomes paramagnetic, the fifth magnetic circuit 87 is lost.

According to the third embodiment, the same effects as those of the first embodiment are obtained.

Further, by disposing the second coil 384a radially inward of the heat generation assisting plate 69 on the inner peripheral side of the fixing belt 50, the following effects are obtained. Compared to the case where the second coil 84a is disposed on the outer circumferential side of the fixing belt 50, the second coil 384a can be integrated with the heat generation assisting plate 69 on the inner circumferential side of the fixing belt 50.

According to the fixing device of at least one embodiment described above, since an excessive temperature rise of the IGBT elements 68a can be suppressed, breakage of the IGBT elements 68a can be prevented.

The heat generating layer 50a may be made of a magnetic material such as nickel.

The measuring unit is not limited to the one provided with the resistance measuring unit. For example, the measuring unit may include a temperature measuring unit that measures the temperature of the heat generation auxiliary plate 69. For example, the temperature measuring unit uses a temperature sensor. By measuring the temperature of the heat generation assisting plate 69, it is possible to directly determine whether or not the heat generation assisting plate 69 exceeds the curie point. That is, the measuring unit may measure the state of the heat generation auxiliary plate 69.

The main body control circuit 101 is not limited to indirectly determining whether or not the heat generation assisting plate 69 exceeds the curie point based on the measurement result of the resistance measurement circuit. For example, the main body control circuit 101 can directly determine whether or not the heat generation assisting plate 69 exceeds the curie point based on the measurement result of the temperature sensor. That is, the main body control circuit 101 may control the output of the IH coil unit to be lowered when it is determined that the heat generation assisting plate 69 exceeds the curie point based on the measurement result of the measuring unit.

The functions of the fixing device in the above-described embodiments may be implemented by a computer. In this case, the functions may be realized by recording a program for realizing the functions on a computer-readable recording medium, reading the program recorded on the recording medium into a computer system, and executing the program. Further, the "computer system" referred to herein includes hardware such as an OS, external devices, and the like. The term "computer-readable recording medium" refers to a removable medium such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and a storage device such as a hard disk incorporated in a computer system. The "computer-readable recording medium" may further include: a medium that dynamically holds a program for a short time, such as a communication line when the program is transmitted via a network such as the internet or a communication line such as a telephone line; and a medium that holds a program for a certain period of time, such as a volatile memory in a computer system constituting the server and the client at this time. The program may be a program for realizing a part of the above-described functions, or may be a program for realizing the above-described functions by combining with a program already recorded in a computer system.

Several embodiments of the present invention have been described, but these embodiments are only provided as examples and are not intended to limit the scope of the present invention. These embodiments can be implemented in other various ways, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and spirit of the invention, and are within the scope of the invention described in the claims and the equivalent thereof.

Description of the symbols

10 fixing device for

image forming apparatus

34, 234, 334

50 fixing belt 50a heating layer (conductive layer)

52IH coil unit (induction current generating part)

56 Main coil (coil, first coil)

69 heating auxiliary plate (heating auxiliary part)

84. 384 second coil Unit (measuring part)

84a, 384a second coil 101 main body control circuit (control part)

284 measures the area of the section S1.

Claims

1. A fixing device, characterized by comprising:

a tape comprising a ferromagnetic layer;

a ferromagnetic plate disposed within the band and having a Curie point lower than a Curie point of the ferromagnetic layer;

an induction heater configured to cause heat to be generated in the ferromagnetic layer and the ferromagnetic plate, the induction heater comprising a coil;

a drive line configured to output a high-frequency current to the coil and change the high-frequency current;

a measurement unit configured to output a signal indicating whether a temperature of the ferromagnetic plate exceeds a predetermined value;

a temperature sensor configured to measure a temperature of the coil; and

a controller configured to control the drive line to reduce the high-frequency current if the temperature of the coil measured by the temperature sensor is higher than a predetermined value, characterized in that the predetermined value refers to the curie point of the ferromagnetic plate;

wherein the measurement unit includes:

a second coil positioned proximate to the ferromagnetic plate; and

a resistance measurement circuit configured to measure a resistance of the second coil, the resistance of the second coil decreasing with increasing temperature of the second coil.

2. A fixing device according to claim 1, wherein said coil is at a position corresponding to a paper passing area of said belt in a width direction of said belt.

3. A fixing device according to claim 1,

the driving circuit comprises a switching element, and the switching element comprises an insulated gate bipolar transistor and a metal oxide semiconductor field effect transistor; and is

The controller reduces the high frequency current by extending an on time of the metal oxide semiconductor field effect transistor.

4. A fixing device, characterized by comprising:

a tape comprising a ferromagnetic layer;

a measurement unit configured to output a signal indicating whether a temperature of the ferromagnetic plate exceeds a predetermined value; and

a controller configured to:

receiving the signal output from the measurement unit;

determining whether the temperature of the ferromagnetic plate exceeds the predetermined value based on the signal; and is

Controlling said drive circuitry to reduce said high frequency current if said temperature of said ferromagnetic plate exceeds said predetermined value, wherein said predetermined value is said curie point of said ferromagnetic plate;

wherein the measurement unit includes:

a second coil positioned proximate to the ferromagnetic plate; and

5. The fixing device according to claim 4, wherein the coil is at a position corresponding to a paper passing area of the belt in a width direction of the belt.

6. A fixing device according to claim 4,

7. A fixing device according to claim 4, wherein said measurement unit is a temperature sensor.

8. The fixing device according to claim 4, wherein the measurement unit includes a resistance measurement line configured to measure a resistance of the coil, the resistance of the coil decreasing as the temperature of the coil increases.

9. A fixing device, characterized by comprising:

a tape comprising a ferromagnetic layer;

a drive line configured to output a high-frequency current to the coil and change the high-frequency current by switching on and off of a switching element;

a controller configured to:

receiving the signal output from the measurement unit;

the measurement unit includes:

a second coil positioned proximate to the ferromagnetic plate; and

10. The fixing device according to claim 9, wherein the coil is at a position corresponding to a paper passing area of the belt in a width direction of the belt.

11. The fixing device according to claim 9,

12. A fixing device according to claim 9, wherein said measuring unit is a temperature sensor.

13. A fixing device according to claim 9, wherein said measurement unit includes a resistance measurement circuit configured to measure a resistance of said coil, said resistance of said coil decreasing with an increase in said temperature of said coil.