JP2011095692A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent malfunction of an excessive temperature increase prevention device by overshooting and allow rapid restart of operation even when a sudden stop occurs during continuous paper feeding, in a fixing device for high-speed machine image forming, or an image forming apparatus using it. <P>SOLUTION: This fixing device includes a fixing rotator heated by a heating element, an abnormal temperature detecting means for detecting a case where the heating element reaches an abnormal temperature, and an excessive temperature increase preventing means for forcibly blocking current-carrying to the heating element when the temperature of the heating element increases abnormally. The fixing device includes a position changing means for moving any of the abnormal temperature detecting means and the heating element and changing the distance between the abnormal temperature detecting means and the heating element, and a position driving controller for detecting the current-carrying state to the heating element and controlling the position changing means. The abnormal temperature detecting means is held at the position in heating and temperature control having a narrow distance to the heating element during the current-carrying to the heating element for heating and temperature control, and is separated from the heating element when the current-carrying to the heating element is stopped. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device including an excessive temperature rise prevention device and an image forming apparatus using the same.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a heating body (heating member) such as a heating roller or a fixing roller heated by a heater or an electromagnetic induction heating device is installed in the fixing device. In recent years, there has been a demand for speeding up of color copiers, and a belt fixing system that is smaller and can cope with a higher linear speed than conventional roller fixing is widely used (see FIGS. 36 and 37). In belt fixing as shown in FIGS. 36 and 37, a fixing heating roller 254 having a heater (heating body) 253 inside supplies heat to the fixing belt 251.

  The heater 253 (heating means) of the fixing heating roller 254 is a halogen heater, and both ends thereof are fixed to side plates (not shown) of the fixing device. Then, with the main switch 301 of the image forming apparatus main body turned on, power is supplied from the commercial power source 400 to the heater 253 via the main control device (apparatus main body control device) 302 and the heater control circuit 303 of the image forming apparatus main body. Is done. Then, the fixing heating roller 254 is heated by the radiant heat from the heater 253 whose output is controlled by the heater control circuit 303, and further, the toner image Ta on the transfer sheet P is heated from the surface of the fixing belt 251 heated by the heating roller 254. Is added. In the illustrated example, the pressure roller 256 also includes a heater 257 and is controlled by the heater control circuit 303 in the same manner as the heater 253.

  The output control of the heater 253 is performed based on the detection result of the belt surface temperature by the temperature sensor 303A (thermopile) as temperature detecting means that faces the surface of the fixing belt 251 in a non-contact manner. Specifically, the AC voltage is applied to the heater 253 for the energization time determined based on the detection result of the temperature sensor 303A as the temperature detection means. By such output control of the heater 253, the temperature of the fixing belt 251 (fixing temperature) is adjusted and controlled to a desired temperature (target control temperature). The output control of the heater 257 is similarly performed based on the temperature detection result of the temperature sensor 303B.

  Various materials are used for the base material of the fixing belt 251. Recently, polyimide resin is often used because of heat resistance and high durability. The fixing heating roller 254 is biased upward by a tension spring 255 and applies tension to the fixing belt 251. A pressure roller (pressing member) 256 including a halogen heater 257 is disposed opposite the fixing roller 252 to form a fixing nip portion. In the image forming apparatus, there are known problems that the heating body of the fixing device is excessively heated after the printing operation is finished, and the fixing device is damaged or an abnormal image is generated.

  Specifically, in general, the fixing device takes heat from the surface of the fixing belt during the printing operation, particularly during continuous paper passing, so that the heating continues to maintain the temperature of the fixing belt, and the core temperature of the heating roller is extremely high. To be high. This is more conspicuous as the CPM is higher and the basis weight of the transfer paper is larger. Thus, when the printing operation is finished in such a state that the temperature of the heating core roller is high, the movement of the heat taken away by the transfer paper suddenly disappears, and thus the surface temperature of the heating roller abnormally increases. . Such a phenomenon is called overshoot after continuous paper feeding (see FIG. 38). In the illustrated fixing device, in order to prevent such an overshoot, a thermostat 258 is fixed near the upper portion of the fixing belt 251 (support structure omitted). The thermostat 258 detects the temperature of the fixing belt (fixing rotator) 251 and forcibly cuts off the energization to the halogen heater 253 and the halogen heater 257 when the temperature reaches an abnormal temperature.

  Several techniques have already been proposed for the purpose of preventing such overshoot. For example, in order to prevent the overshoot itself, Japanese Patent Laid-Open No. 2004-228561 suppresses the occurrence of overshoot by stopping the heating operation of the heating body to the recording medium before the end of the print job for the recording medium of the last page. Technology is disclosed. Also, the final printed paper has a heater output narrowed (for example, see Patent Document 1), a fixing device having a fan (for example, Patent Document 2), a cooling roller for cooling a heating roller, and a fan A thing (for example, refer to patent documents 4) etc. which have a fan (for example, refer to patent documents 4) etc. which have a fan which cools a pressure member are known.

  In the above-mentioned patent document 4, when the temperature of the heating body suddenly rises in the vicinity of the heating body, an overheat prevention device comprising a thermostat that forcibly cuts off energization to the heating body is attached, and overshoot occurs. In this case, it has been proposed to forcibly cut off the energization of the heating body to suppress an abnormal increase in the heating temperature of the heating body.

  The disclosed technologies of Patent Documents 1 to 4 listed above are effective when the apparatus is operating normally. However, a cooling device is necessary, and the size of the device increases. Also, no consideration is given to the case where normal control does not operate, for example, when the main power supply is turned off during operation.

  As a known proposal other than the above, there is also Patent Document 5, and the disclosed technique assumes overshoot when the power is turned off, but prevents a problem when the power is turned on again, and cannot prevent overshoot itself.

  Various devices for cooling the excessive temperature rise prevention device are known. For example, in Patent Document 6, the overheat prevention device is cooled during the normal heating operation, and the cooling operation is stopped when the abnormal temperature detection means detects an abnormally high temperature. However, in this configuration, the cooling fan that cools the excessive temperature rise prevention device operates and cools during normal operation, that is, when the recording medium is transported and during the printing operation. When is stopped, it will not operate. Therefore, even if the printing operation is stopped and the energization to the heating body is stopped, the heat of the heating body by the recording medium is not absorbed, so the temperature of the heating body rises, along with the temperature rise of the heating body, In some cases, the temperature of the overheat prevention device rises and the overheat prevention device is activated, and the overheat prevention device is activated and the state where the energization to the heating element is interrupted is maintained. . Also, unexpected power-off and the like are not taken into consideration, and in such a case, the thermostat may malfunction.

  By the way, in the conventional color 40 CPM machine (printing speed: 40 sheets per minute), the overshoot temperature was about 230 ° C. However, with the recent increase in speed, the 75 sheet machine has an overshoot temperature of 270 ° C. It may be quite hot as above. This is caused by a difference in power supplied to the heating roller during continuous paper feeding. At 40 CPM, the temperature during sheet feeding can be maintained at a stable value of about 500 W. In order to prevent the temperature drop at the start of paper feeding, about 1.5 times that at the time of stability is required, and the heater rating (number of watts) is 750 W or more. On the other hand, when it is 75 CPM, 900 W or more is required when the paper is stable, and the heater rating (W number) is 1350 W or more. In addition to the fixing heater, several hundreds of watts of electric power is required for driving various motors. As described above, the maximum power consumption of conventional copying machines is about 1500 W, but due to the recent market demand for higher production, high-speed copying machines with a maximum power consumption of 2000 W or more have increased. The above-described overshoot problem becomes significant in such a high-speed copying machine having a maximum power consumption of 2000 W or more.

  On the other hand, from the viewpoint of energy saving in recent years, shortening of the warm-up time of the fixing unit has been demanded, and the heating roller has been made thinner and the use of a high-speed rising heater has been advanced. However, the increase in the temperature increase rate due to the thinning of the heating roller significantly narrows the degree of freedom in designing a general overheat prevention device composed of a thermostat or the like.

  That is, if the temperature rise rate of the thermostat bimetal part temperature is slower than the temperature rise rate of the heating roller, a desired protective operation cannot be expected. Therefore, it is necessary to use a thermostat having a low operating temperature in order to surely prevent overheating problems of the fixing unit due to runaway at startup. However, when a thermostat having a low operating temperature is used in this way, if the fixing device normally operates and the temperature around the fixing unit rises, there is a high possibility of a malfunction that causes the thermostat to operate unintentionally. This malfunction often occurs especially at the time of overshoot immediately after the sheet passing when the temperature of the heating member becomes the highest. Among them, the overshoot becomes the largest when a so-called jam occurs during continuous paper feeding or in an immediate stop state due to power-off or the like.

  During this overshoot, the heater is not energized, so there is no danger of smoke and fire, but the energization is not possible due to the operation of the thermostat despite the absence of energization of the heater (FIG. 39). (See), and until it comes back up (until you change the thermostat for an irreversible thermostat), there will be “downtime” when the user cannot use the machine.

  By the way, in the past, high-speed copiers using large-capacity fixing heaters had a large heat capacity of the fixing unit and required a very long rise time. Was. However, energy saving is also required for high-speed machines, and even high-speed copying machines with a maximum power consumption of 2000 W or more are increasing in startup time of 60 seconds or less.

  As an example of a fixing unit of such a copying machine, a heating roller has a diameter: aluminum φ30, a thickness: 0.6 mm, a heater has a rating of 1800 W, and as a thermostat, a thermostat operation rated temperature: 160 ° C., a thermostat Gap: 0.7 A combination of mm is actually used. However, it is difficult to say that the performance of the excessive temperature rise prevention device is sufficient, and in some cases, “downtime” occurs. There are concerns that these problems will become more prominent when the capacity of the heater further increases in the future, or when the heating roller is reduced in capacity to further shorten the rise time. Specifically, the outer diameter of the heating roller is φ22 to φ45, the thickness of the heating roller (aluminum) is 0.3 mm to 1.5 mm, and the thickness of the heating roller (iron) is 0.3 mm to 0.7 mm. It has been confirmed that the problem becomes significant. Accordingly, there is a demand for improved performance of the overtemperature prevention device corresponding to recent high-speed copying machines.

  The present invention has been made in consideration of the above circumstances, and in a fixing device for high-speed image formation or an image forming apparatus using the same, even if it suddenly stops during continuous paper feeding, it is excessively increased due to overshoot. The purpose is to prevent malfunction of the temperature prevention device and to enable quick operation restart.

  In order to solve the above-described problems, the fixing device of the present invention includes a fixing rotating body that is heated by a heating element and heat-fixes an unfixed toner image on a recording medium, and a heating element that is installed in the vicinity of the heating element to an abnormal temperature. A fixing device for an image forming apparatus, comprising: an abnormal temperature detecting means for detecting when the temperature has reached; and an excessive temperature rise preventing means for forcibly shutting off power to the heat generating element when the heat generating element reaches an abnormal temperature , The abnormal temperature detecting means and the heating element are moved, the position changing means for changing the distance between the abnormal temperature detecting means and the heating element, the energization state of the heating element is detected, and the position changing means is controlled. When the heating element is energized and controlled for heating temperature control, the distance between the abnormal temperature detection means and the heating element is kept at the heating temperature control position. When power to the heating element is stopped, Characterized in that for separating the the heating element normal temperature detecting means.

  With the above configuration, even when the fixing unit suddenly stops due to JAM or the like during sheet passing and the heating element temperature rises due to overshoot, the energization to the heating element stops, Since the excessive temperature rise prevention device does not operate by separating the heating element, it becomes possible to operate immediately after the JAM processing, and machine downtime such as replacement of the excessive temperature rise prevention device can be prevented. .

  In the fixing device of the present invention, in the fixing device, the position changing means includes a swing arm having one end pivotally supported so as to be swingable and having the abnormal temperature detecting means attached to the free end, and the swing arm. An over-temperature rise prevention device position drive cam that is brought into contact with the free end and a motor that rotationally drives the over-temperature rise prevention device position drive cam controlled by the position drive control device.

  In the fixing device of the present invention, in the fixing device, the position changing means includes a swing arm having one end pivotally supported so as to be swingable and having the abnormal temperature detecting means attached to the free end, and the swing arm. A solenoid as a driving source for biasing the vicinity of the free end of the motor is included. As a result, even if the power is suddenly turned off while the paper is being passed and the temperature of the heating element rises due to overshoot, the overheat prevention device will not operate. Prevention of machine downtime such as device replacement can be achieved with a simple configuration.

  In the fixing device of the present invention, in the above fixing device, the heating element is an AC heater and is connected to a commercial power source via a switch, and the solenoid drive coil is connected to a DC power source directly connected to the commercial power source. I did it. As a result, even if the power is suddenly turned off while the paper is being passed and the temperature of the heating element rises due to overshoot, the overheat prevention device will not operate. Prevention of machine downtime such as device replacement can be achieved with a simple configuration.

  In the fixing device of the present invention, in the above fixing device, the heating element is a heater, and the heater and solenoid drive coil are connected in parallel to a single DC power source connected to a commercial power source via a switch. I did it.

  Further, the fixing device of the present invention includes a thermostat functioning as an abnormal temperature detecting means for detecting the temperature of the fixing rotating body as an excessive temperature rise preventing means for forcibly shutting off the power supply to the heating element. I used it. Space saving can be achieved and control can be simplified.

  An image forming apparatus according to the present invention includes the fixing device. By providing each fixing device of the present invention, an effect corresponding to each fixing device can be obtained.

  In the image forming apparatus of the present invention, in the image forming apparatus, the position drive control device that controls the position changing unit is operated by a separate power source independent of the main power source for image forming operation, and the position is controlled by the separate power source. The change means is driven. As a result, even when the main power supply is turned off during continuous paper feeding, the temperature rise of the overheat prevention device is delayed by keeping the position of the overheat prevention device away from the heating element, and overheating is prevented by overshoot. It is possible to prevent malfunction of the apparatus.

  In the image forming apparatus of the present invention, the separate power source is a battery in the image forming apparatus. As a result, in addition to the case where the main power supply is turned off during continuous paper feeding, even when a power failure occurs, the temperature rise of the overheat prevention device can be reduced by separating the overheat prevention device from the heating element. It is possible to prevent the malfunction of the excessive temperature rise prevention device due to overshoot.

  In the image forming apparatus of the present invention, in the image forming apparatus, the separate power source is a rechargeable battery that is charged by the main power source. As a result, even if the main power is turned off during continuous paper feeding or a power failure occurs in the same manner as described above, the temperature rise of the overheat prevention device can be reduced by moving the overheat prevention device away from the heating element. This makes it possible to prevent the excessive temperature rise prevention device from malfunctioning due to overshooting, and to obtain the effect of eliminating the need for maintenance and inspection of another power source.

  According to the present invention, even when the fixing unit suddenly stops due to JAM or the like during sheet passing and the temperature of the heating body rises due to overshoot, the excessive temperature rise prevention device does not operate. Operation becomes possible, and machine downtime such as replacement of an excessive temperature rise prevention device can be prevented.

  In particular, when the position changing means and the position drive control device are connected to a commercial power source without a switch, or when the position change means and the position drive control device are driven by separate power sources, suddenly during paper feeding It can cope with the case where the power is turned off. A device using a solenoid as a drive source can cope with power OFF without using a separate power source.

1 is a longitudinal sectional view showing an overall schematic configuration example of a laser copying machine according to an embodiment of the present invention. FIG. 3 is a diagram illustrating an enlarged configuration example of a main part of the fixing device according to the embodiment of the present invention. FIG. 3 is a diagram illustrating an enlarged configuration example of a main part of the fixing device according to the embodiment of the present invention. 1 is a diagram illustrating a schematic example of a main part including a control unit of an image forming apparatus according to an embodiment of the present invention. It is a graph which shows the example of the heating roller temperature at the time of occurrence of overshoot in this embodiment, and thermostat temperature. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 2nd Embodiment. It is a graph which shows the example of the heating roller temperature at the time of the overshoot occurrence in 2nd Embodiment, and a thermostat temperature. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 3rd Embodiment. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 4th Embodiment. It is a figure which shows the principal part schematic example also including a control part of the image forming apparatus of 5th Embodiment. It is a figure which shows the principal part schematic example also including the control part of the image forming apparatus of 6th Embodiment. FIG. 3 is a diagram illustrating an enlarged configuration example of a main part in which the present invention is applied to a different fixing device. FIG. 3 is a diagram illustrating an enlarged configuration example of a main part in which the present invention is applied to a different fixing device. FIG. 3 is a diagram illustrating an enlarged configuration example of a main part in which the present invention is applied to a different fixing device. FIG. 10 is a diagram illustrating an enlarged configuration example of a main part of a fixing device of an image forming apparatus according to a seventh embodiment. FIG. 10 is a diagram illustrating an enlarged configuration example of a main part of a fixing device of an image forming apparatus according to a seventh embodiment. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 7th Embodiment. It is a graph which shows the example of the heating roller temperature at the time of the overshoot occurrence in 7th Embodiment, and a thermostat temperature. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 8th Embodiment. It is a graph which shows the example of the heating roller temperature at the time of the overshoot generation | occurrence | production in 8th Embodiment, and a thermostat temperature. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 9th Embodiment. It is a graph which shows the example of the heating roller temperature at the time of the overshoot generation in 9th Embodiment, and a thermostat temperature. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 10th Embodiment. It is a figure which shows the principal part schematic example also including a control part of the image forming apparatus of 11th Embodiment. It is a figure which shows the principal part schematic example also including a control part of the image forming apparatus of 12th Embodiment. FIG. 20 is a diagram illustrating an enlarged configuration example of a main part of a fixing device of an image forming apparatus according to a thirteenth embodiment. FIG. 20 is a diagram illustrating an enlarged configuration example of a main part of a fixing device of an image forming apparatus according to a thirteenth embodiment. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 13th Embodiment. It is a graph which shows the example of the heating roller temperature at the time of the overshoot generation | occurrence | production in 13th Embodiment, and a thermostat temperature. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 14th Embodiment. It is a graph which shows the example of the heating roller temperature at the time of the overshoot occurrence in 14th Embodiment, and a thermostat temperature. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 15th Embodiment. It is a figure which shows the schematic example of the principal part also including the control part of the image forming apparatus of 16th Embodiment. It is a figure which shows the principal part schematic example also including a control part of the image forming apparatus of 17th Embodiment. It is a figure which shows the principal part schematic example also including a control part of the image forming apparatus of 18th Embodiment. FIG. 10 is an enlarged configuration diagram illustrating a main part of a conventional fixing device. It is a figure which shows the schematic example of the principal part also including the control part of the conventional image forming apparatus. It is a graph which shows the example of the heating roller temperature change at the time of overshoot occurrence. It is a graph (conventional example) which shows the heating roller temperature and thermostat temperature at the time of overshoot occurrence.

  [First Embodiment] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view showing an overall schematic configuration example of a laser copying machine which is a first embodiment of an image forming apparatus provided with a fixing device according to the present invention. FIG. 2 shows a configuration example of a main part of the fixing device which is a feature of the present embodiment. In FIG. 1, the fixing device is shown in a simplified manner (refer to FIG. 2 for details).

  In FIG. 1, reference numeral 10 denotes an image forming apparatus main body. In the image forming apparatus main body 10, a drum-shaped image carrier (hereinafter referred to as a photoreceptor) 12 is provided. Around the photosensitive member 12, a charging device 13, a developing device 14, a transfer / conveying device 15, a cleaning device 16, a static eliminating device 17, and the like are arranged. A laser writing device 18 is provided above each of these components. The laser writing device 18 includes a light source 20 such as a laser diode, a scanning rotary polygon mirror 21, a polygon motor 22, a scanning optical system 23 such as an fθ lens, and the like. On the left side of the cleaning device 16 in the drawing, a fixing device 250 (detailed configuration is shown in FIG. 2), which will be described in detail later, is arranged.

  In the image forming unit exemplified here, the surface of the photoconductor is charged to a predetermined polarity by the charging device 13 when the drum-like photoconductor 12 as an example of the image carrier rotates in the clockwise direction. The charged surface is irradiated with a light-modulated laser beam L emitted from a laser writing device 18 which is an example of an image forming unit, whereby an electrostatic latent image is formed on the surface of the photoreceptor.

  The electrostatic latent image is visualized as a toner image by the developing device 14, and the toner image is transferred onto the recording material fed by the paper feeding unit by the action of the transfer / conveyance device 15. Transfer residual toner adhering to the surface of the photoconductor after the toner image is transferred is removed by a cleaning brush or a cleaning blade (not explicitly shown) provided in the cleaning device 16.

  In the paper feeding unit 43 located at the lower part of the main body 10, the recording material P made of, for example, sheet-like transfer paper or resin sheet accommodated in the cassette 44 or the like is sent out by the rotation of the feeding roller 45, and the sent recording material P is sent out. Is transferred to the transfer unit between the photosensitive member 12 and the transfer / conveyance device 15 at a predetermined timing after waiting at the position of the registration roller pair 48 by the rotation of the conveyance roller pair 74, 37. Here, as described above The toner image on the photoreceptor 12 is transferred onto the recording material and carried as an unfixed image Ta. The recording material P to which the toner image has been transferred is continuously conveyed to the fixing device 250 and fed into the nip portion between the fixing belt 251 and the pressure roller 256 that are in a pressure contact state (see FIG. 2). Then, the toner image Ta is fixed on the surface of the transfer sheet S by being heated by the fixing belt 251 and the pressing force of the fixing belt 251 (fixing roller 252) and the pressure roller 256. The recording material P that has passed through the fixing device 250 is discharged onto a tray (not shown) outside the apparatus.

  Reference numeral 35 denotes a double-sided unit. When recording is performed on the back side of a sheet using this copying machine, after recording on one side, it is put into the double-sided unit 35 through a reversing path 39, and then reversed to be again an image carrier. The image formed on the image carrier 12 is transferred to the back surface in the same manner, and then discharged onto a tray (not shown).

  A document reading device 30 is provided in the upper part of the apparatus main body 10. The document reading device 30 is provided with a light source 31, a plurality of mirrors 32, an imaging lens 33, an image sensor 34 such as a CCD. Reference numeral 40 is a contact glass, and reference numeral 41 is a well-known automatic document feeder that automatically conveys a sheet document to a document reading position to read document information, and automatically discharges the scanned document from the document reading position. It is a feeder (ADF).

  The document reading device 30 includes a light source (lamp) 31 that scans and irradiates a document on the document stacking table 40. Reflected light from the document obtained by irradiation of the lamp 31 is reflected by a plurality of mirrors 32 and is incident on an imaging lens 33. This light passes through the imaging lens 33 and is incident on a light receiver configured as a CCD 34 as image light. The CCD 34 converts incident image light into a digital signal and outputs the digital signal, and the output is subjected to necessary processing in the image processing unit in the image recording processing unit to be converted into a signal for recording and forming an image.

  A control unit (system controller) (not shown) mounted in the apparatus main body includes a CPU, a ROM, a RAM, and the like as is well known, and is based on image information sent from a personal computer (not shown). Device (static discharge lamp) 17, charging device (charging roller) 13, optical writing unit 18, developing device 14, developing bias applying means, feeding unit, transfer bias applying means, transfer roller, etc. The image forming operation is performed.

  The control unit includes a rotation unit including a motor, each drive system of a conveyance mechanism, various sensors including a toner density sensor and a reflection density sensor (referred to as a P sensor), a data storage unit including a RAM and a ROM, An operation display unit composed of a touch panel or the like is connected and controlled. Based on the detection result of the reference density toner image (reflection density sensor output), process control for adjusting the bias voltage of the developing sleeve to an appropriate value is also performed.

  Next, the fixing device 250, which is a characteristic part of the present embodiment device, will be described in detail. A schematic configuration example of the fixing belt type fixing device 250 is shown in FIG. 2 and FIG. 3 (positions are different when the thermostat 258 is biased). This fixing device 250 has a fixing roller 252 (φ52, t = 52) of silicon foam rubber positioned inside (inside the circumference) a fixing belt 251 (belt length of about 70 mm) as a fixing rotating body whose surface is covered with a PFA tube. 10 mm) and an aluminum fixing heating roller 254 (φ35, t = 0.6 mm), which is a heated body including a halogen heater 253 (1200 W) as a heating element. The fixing (heating) roller 254 also serves as a tension roller, and is biased outward (upward in the drawing) by a tension spring 255 to apply tension to the fixing belt 251. A pressure roller (pressure member) 256 as a pressure rotator is arranged on the opposite side of the fixing belt peripheral circuit with respect to the fixing roller 252 with the fixing belt 251 interposed therebetween. A fixing nip portion is formed. The pressure roller 256 also includes a halogen heater 257 (1200 W) and serves as a heating source during the fixing operation. Reference numeral 254C denotes a temperature sensor (thermopile) as temperature detecting means that faces the surface of the fixing belt 251 in a non-contact manner, and controls the output of the heater 253 based on the detection result of the belt surface temperature. Is adjusted to a desired temperature (target control temperature).

  In the vicinity of the fixing heating roller 254 (above here), an excessive temperature rise prevention device having an excessive temperature rise prevention means for detecting an abnormal temperature rise of the fixing heating roller 254 and shutting off the power supply to the heater 253. As shown, a thermostat 258 is movably disposed. Although the wiring is not shown, the thermostat 258 is interposed in the power supply path to the heater 253. That is, here, the thermostat 258 has an abnormal temperature detection function for detecting the temperature of the fixing belt (fixing rotating body) 251 and forcibly energizes the halogen heater 253 (heating element) when the heating element temperature reaches the abnormal temperature. Shut off. The shut-off operation of the thermostat 258 is thermally irreversible.

  The thermostat 258 can be moved by a position changing means 260 as a means for driving the position of the excessive temperature rise prevention device to change the distance from the heating element. The position changing means 260 includes a swing arm 261, an excessive temperature rise prevention device position drive cam 262, and a cam drive motor (hereinafter simply referred to as a motor) 263. More specifically, one end is pivotally supported by a support shaft 264, and the thermostat 258 is attached to the other end side (free end side), and the free end side is biased in a direction away from the fixing heating roller 254. Oscillating arm 261 biased by 265, and overheat prevention device position drive cam (here, eccentric disc cam) in which the cam surface is in contact with the oscillating arm 261 in the vicinity of the free end (the other end side). 262, a motor 263 (not shown) that rotationally drives the excessive temperature rise prevention device position drive cam 262, and a control unit (not shown) that drives and controls the motor 263. By changing the distance of the thermostat 258 from the fixing heating roller 254, the thermostat 258 can be moved away from the position (referred to as position A). That. The image forming apparatus according to the embodiment has been described above. However, the other portions, such as the toner scattering prevention device 70 connected to the developing device 14 and the like, which are indicated only by the reference numerals in FIG. 1, are not directly related to the present invention. Therefore, explanation was omitted.

  FIG. 4 shows a schematic example of the main part related to the image forming apparatus including the configuration for control. In this embodiment, the image forming apparatus is supplied with electric power from the commercial power source 400 via the main switch 301, and each part of the fixing device and the like is controlled (including power supply operation, here referred to as control).

  The control unit 300 includes an image forming apparatus control apparatus (hereinafter referred to as a main control apparatus) 302, a heater control circuit 303, a current sensor 304, and a drive cam control circuit 305 as an excessive temperature rise prevention apparatus position control circuit. Yes. The excessive temperature rise prevention device position drive cam 262 constituting the over temperature rise prevention device is controlled by a drive cam control circuit 305. On / off of the halogen heater 253 is controlled by the heater control circuit 303 based on the detection result of the belt surface temperature by a temperature sensor (thermopile) 254C as temperature detection means that faces the surface of the fixing belt 251 in a non-contact manner. The suspension of energization of the heating element for heating temperature control is treated as an energization operation in terms of control. All power supplied to these units is cut off by turning off the main switch 301. As described above, the drive cam control circuit 305 and the excessive temperature rise prevention device position drive motor 263 are operated by appropriately transforming and supplying the commercial power supply 400 (the power optimization circuit is not shown).

  Next, details of the position control operation by the position changing unit 260 will be described. When the heater 253 is turned off, for example, when the apparatus is on standby, the thermostat 258 moves away from the heating roller: the position A (FIG. 2) and stays at the position A (FIG. 2). Absent.

  On the other hand, when the heater 253 is lit, the thermostat 258 moves to a position close to the heating roller: position B (FIG. 3), and the thermostat 258 is directly warmed by the heat of the heating roller. Therefore, in the unlikely event of an abnormal temperature rise, the temperature quickly rises to the operating temperature of the thermostat 258, and the power to the heater 253 can be cut off appropriately without delay.

The process linear velocity of the image forming apparatus of the present embodiment described above is 352 mm / sec, and the productivity is 75 cpm on A4 paper.
Control temperature during standby is heating roller: 170 ° C
Pressure roller: 150 ° C
The set temperature when passing paper is the heating roller: 165 ° C
Pressure roller: 120 ° C
It is.
The rated operating temperature of the thermostat 258 is 180 ° C.
The thermostat 258 temperature at the time of occurrence of overshoot after passing the paper is shown in FIG.

  As described above, in the first embodiment, when the heater 253 that is the heating body is not energized and the temperature of the heating roller 254 does not rise, the thermostat 258 that is an overtemperature prevention device By increasing the distance of the heating element, the fixing unit suddenly stops due to JAM or the like during paper passing, and even if the heating element temperature rises due to overshoot, the excessive temperature rise prevention device will not operate. It is possible to reduce the downtime by preventing the machine downtime due to the replacement of the prevention device, etc., and it becomes possible to restart the operation immediately after the JAM repair process.

  [Second Embodiment] Next, different embodiments will be exemplified. A schematic example of an image forming apparatus according to a second embodiment of the present invention is shown in FIG. The schematic configuration of the entire apparatus and the configurations of the fixing device 250 and the position changing unit 260 are the same as those in the first embodiment, and a description thereof is omitted. Also, the position control operation of the position changing means 260 is the same as in the first embodiment, and the description will not be repeated.

  In this embodiment, the components of the control unit 300 are the same as those in the first embodiment, but only the method of supplying power to each unit is different. In other words, the fixing device and the image forming apparatus are controlled by being supplied with power via the main switch 301 by the commercial power source 400. These powers are cut off by turning off the main switch 301. On the other hand, the drive cam control circuit 305 and the excessive temperature rise prevention device position drive motor 263 are directly supplied with power by the commercial power source 400 (the power optimization circuit is not shown). For these, even if the main switch 301 is turned off. However, the electric power is not cut off and can operate. In other words, in this embodiment, the excessive temperature rise prevention device position drive cam 262 is controlled by the over temperature rise prevention device position drive cam control circuit 305 using a commercial power source branched to a system separate from the image forming apparatus. Yes.

  Accordingly, during normal operation, the drive cam control circuit 305 detects energization to the heater 253, and when the energization to the heater 253 is stopped by turning off the main switch 301, the thermostat 258 remains moved to the position A (FIG. 2). reference). Thus, as in the first embodiment, since the heat of the heating roller 254 is not easily transmitted, the temperature of the thermostat 258 does not rise more than necessary, and even when the temperature of the heating body rises due to overshooting, the excessive temperature rise is prevented. Downtime can be shortened without operating the device. FIG. 7 shows the temperature of the thermostat 258 when overshoot occurs after the paper is passed in the second embodiment apparatus (equivalent result in FIG. 5).

  [Third Embodiment] FIG. 8 shows a schematic example of an image forming apparatus according to a third embodiment of the present invention. The schematic configuration of the entire apparatus, the configuration of the fixing device 250 and the position changing unit 260, and the position control operation of the position changing unit 260 are the same as those in the first embodiment, and will be omitted.

  In the present embodiment, the method of supplying power to the above-described components of the control unit 300 is different, and the drive cam control circuit 305, the excessive temperature rise prevention device position drive motor 263, and the excessive temperature rise prevention device position drive. The cam 262 is controlled using a power source independent of the image forming apparatus. The fixing device and the image forming apparatus are controlled by being supplied with electric power via the main switch 301 by the commercial power source 400 as in the previous embodiments. However, the drive cam control circuit 305 and the excessive temperature rise prevention device position drive motor 263 are operated by being supplied with electric power from a battery power source 500 completely independent of the commercial power source 400.

  By turning off the main switch 301, the fixing device and the image forming apparatus are powered off. However, the driving cam control circuit 305 and the excessive temperature rise prevention device position driving motor 263 are separately powered by the battery power source 500. Even if the main switch 301 is supplied, the electric power is not cut off and can operate. Therefore, the drive cam control circuit 305 detects energization to the heater 253, and when the energization to the heater 253 is stopped by turning off the main switch 301, the thermostat 258 moves to the position A, and the thermostat 258 becomes more than necessary. The temperature does not rise (see FIG. 2), and downtime can be shortened. When the temperature of the thermostat 258 at the time of occurrence of overshoot was measured after passing the paper with the third embodiment apparatus, the same result as that shown in FIG. 5 was obtained.

  In FIG. 8, the power supply battery 500 is always connected. Alternatively, an appropriate switching circuit is inserted into the drive cam control circuit 305 and the power supply line of the overheat prevention device position drive motor 263. However, it is possible to adopt a known configuration that normally operates with electric power from the commercial power supply 400 via a switching circuit, and performs backup operation with the power supply battery 500 switched by the switching circuit when the commercial power supply 400 is off. An effect is obtained.

  [Fourth Embodiment] FIG. 9 shows a schematic example of relevant parts of an image forming apparatus including a configuration for controlling the image forming apparatus according to a fourth embodiment of the present invention. 8 is provided with a rechargeable battery 501 instead of the power supply battery 500 and a charging circuit 502 that uses power from the commercial power supply 400 for charging the rechargeable battery 501 via the main controller 302. In this embodiment, the drive cam control circuit 305 and the excessive temperature rise prevention device position drive motor 263 are supplied with power by the rechargeable battery 501. The fixing device and the image forming apparatus are controlled by being supplied with electric power via a main switch 301 by a commercial power source 400. When the main switch 301 is turned off, the supplied electric power is cut off.

  Since the position control operation of the position changing means 260 is performed using the power of the rechargeable battery 501, the position control operation (cooling operation) can be performed even when the main switch 301 is turned off or a power failure occurs, and a thermostat due to overshoot. 258 malfunction can be prevented. When the thermostat 258 temperature at the time of overshooting was measured after passing the paper with the fourth embodiment device, the result was the same as that shown in FIG. It turns out that an effect is acquired. In particular, charging of the rechargeable battery 501 is supplied with power from the commercial power supply 400 and controlled by the main controller 302, and is supplemented and maintained in a fully charged state as necessary, so that maintenance such as battery replacement is unnecessary. There are advantages.

  [Fifth Embodiment] In each of the embodiments described so far, an excessive temperature rise prevention device position drive cam 262 and a motor (cam drive motor) 263 are used as the drive mechanism of the swing arm 261 of the position changing means 260. However, a drive source for moving the thermostat 258 may be other than the motor and the drive cam. An example in which a solenoid is used as a drive source will be described. FIG. 10 shows a schematic example of a fixing device of an image forming apparatus according to a fifth embodiment of the present invention and related main parts for control. A fixing belt type fixing device 250 is the same as that described so far, and the description thereof is omitted.

  Similarly to the previous embodiments, the fifth embodiment apparatus is also located near the upper side of the fixing heating roller 254, and supplies power to the heater 253 and an abnormal temperature detecting means for detecting an abnormal temperature increase of the fixing heating roller 254. A position change means 260 is provided which includes a thermostat 258 that also serves as an excessive temperature rise prevention means for shutting off the heat and a swing arm 261 that supports the thermostat movably.

  One end of the swing arm 261 is pivotally supported by a support shaft 264, the thermostat 258 is attached to the free end of the other end, and a heating prevention device position drive solenoid (hereinafter simply referred to as a solenoid) is attached to the free end end. ) The movable body distal end portion of 270 is locked. This solenoid 270 is driven by a DC power source, and when energized, pulls the free end of the swing arm 261 together with the thermostat 258 and moves it to a heating temperature control position where the distance from the fixing heating roller 254 and thus the heater 253 as a heating element is reduced. Hold. Further, a biasing spring 265 is attached to the swing arm 261 at the center, and the free end side is biased away from the fixing heating roller 254. Accordingly, when the solenoid 270 is not energized, the thermostat 258 at the free end of the swing arm 261 is moved and held at a position separated from the heater 253.

  The control unit 300A is controlled by a main control device (image forming device control device) 302, a heater control circuit 303A for controlling on / off of the halogen heater 253 and an excessive temperature rise prevention device position, and a heater control circuit 303. A DC power supply circuit 306 that drives the halogen heater 253 and the solenoid 270 is configured. Here, the DC power supply circuit 306 functions as a position drive control device that controls the position changing means.

  The image forming apparatus is supplied with power via a main switch 301 by a commercial power source 400, and each part such as a fixing device is controlled. Solenoid 270 and heater 253 are driven by DC power supply circuit 306. The DC power supply circuit 306 obtains a DC2 4 V power source by transforming / rectifying and smoothing the commercial power source 400 (here, 100 V) via the main switch 301, and is on / off controlled by the control output of the main controller 302. The DC power output is commonly connected to the solenoid 270 and the heater 253 using a DC 24V power supply (the solenoid 270 and the heater 253 are connected in parallel). With this connection, power is supplied to the solenoid 270 only when the heater 253 is energized.

  When power is supplied to the solenoid 270, the thermostat 258 approaches the heating roller 254. That is, when the heater 253 shown in FIG. 10 is turned on, the thermostat 258 stays at a position close to the heating roller 254: position B, and the thermostat 258 is directly warmed by the heat of the heating roller 254. Therefore, in the unlikely event of an abnormal temperature rise, the temperature quickly rises to the operating temperature of the thermostat 258, and the power to the heater 253 can be cut off appropriately without delay.

  On the other hand, when the power supply of the solenoid 270 is cut off due to the heater 253 being turned off when a jam occurs, the thermostat 258 is separated from the heating roller 254 by the biasing spring 265 (not shown). Thus, when the heater 253 is extinguished (the power is shut off), the thermostat 258 moves to a position away from the heating roller 254: position A, and the heat of the heating roller 254 is difficult to be transmitted, so that the thermostat 258 may rise more than necessary. Absent.

  Thus, the thermostat 258 moves its position by the solenoid 270 and the urging spring 265 constituting the position changing means 260 according to whether the heater 253 is turned on / off, and the distance from the heating element is changed. It is possible to prevent an excessive temperature rise. Thereby, in each of the present embodiments, just as in each of the embodiments described above, even if the apparatus suddenly stops and the heating body temperature rises due to overshoot, the excessive temperature rise prevention device does not operate. It is possible to reduce the downtime by preventing the machine downtime due to the replacement of the excessive temperature rise prevention device or the like, and it is possible to immediately restart after the JAM repair process.

  [Sixth Embodiment] Another embodiment in which a solenoid 270 is used as a drive source for moving the thermostat 258 will be described with reference to a schematic example of the image forming apparatus shown in FIG. In this embodiment, the heater 253 is driven by a commercial power supply 400 of AC100V, but the solenoid 270 is driven by a DC power supply, and this DC power supply is connected in parallel to the same AC100V power supply as the heater 253 using the AC100V power supply. Then, a voltage converted into DC24V output from a DC power supply unit composed of a voltage conversion transformer 307, a diode 308, and a smoothing capacitor 309 sequentially connected in series is used. With this connection, power is supplied to the solenoid 270 only when the heater 253 is energized.

  In each of the embodiments described above, in a heat fixing apparatus including a fixing belt, fixing is performed by a pressing force between a pressing member that forms a nip portion by sandwiching a fixing belt as a toner heating medium and a driving roller. An example has been described, but the present invention is not limited to each embodiment. The position change control unit that moves the above-described abnormal temperature detection unit to change the distance from the heating element and the position drive control unit that detects the energization state of the heating element and controls the position change unit have versatility. Yes, applicable fixing devices are not limited. For example, the fixing rotator may simply be a roller.

  Further, the pressure member pressed against the fixing member is not limited to the above-described pressure roller that is a pressure rotating body, and may be a belt without tension or a pressure belt that is wound around a plurality of rollers. Alternatively, it may be a pressure pad that does not rotate or run, and the same effects as those of the above-described embodiments can be obtained.

  For example, as shown in the schematic configuration diagram of FIG. 12, the present invention can be applied to a fixing device 250A using a belt that is not tensioned as a pressure member. The fixing device 250A in FIG. 12 is the fixing belt 251 already described as a heating member that is stretched by the fixing heating roller 254 and the fixing roller 252 that are heated to include the halogen heater 253 and heats the recording material P that is conveyed. (Fixing rotor). Reference numeral 255 denotes a tension spring. Then, the endless belt 662 that faces the fixing roller 252 and is in contact with the fixing belt 251, and the endless belt 662 is pressed against the fixing roller 252, and a contact portion (nip portion) is provided between the fixing roller 252 and the endless belt 662. A pressing member 663 is formed. Further, a sliding member 664 that improves the sliding property between the endless belt 662 and the pressing member 663 is provided between the endless belt 662 and the pressing member 663.

  The pressing member 663 has a concave surface shape, and is positioned adjacent to the first pressure member 631 on the upstream side and the downstream side of the first pressure member 638 that mainly forms the contact portion and the contact portion N. The second pressure member 639 having a U-shaped cross section is integrally formed. The endless belt 662 is circulated and supported by a pressing member 663 disposed therein, a belt travel guide 665, and edge guides (not shown) disposed at both ends of the endless belt 662.

  Then, between the inner peripheral surface of the endless belt 662 and the pressing member 663, the sheet passes through the contact portion N from the upstream side of the contact portion N and reaches the belt traveling guide 665 located on the downstream side of the contact portion N. One end of the sliding member 664 is fixed to a fixing member 666 that is movable in the direction of arrow D in the drawing along the traveling direction of the endless belt 662. The pressing member 663 and the belt travel guide 665 are held by a metal holder 667. Note that the movement of the fixing member 666 is controlled by control means not described here.

  In the same manner as already described above, the fixing device 250A has a thermostat 258 that swings in support of it and moves the position of the thermostat 258 to change the distance from the heating element. The position changing means 260 is disposed (FIG. 12 shows a state corresponding to FIG. 3 in which the thermostat 258 is closest to the fixing heating roller 254). Other parts shown in the drawing are denoted by the same reference numerals as those in the above-described embodiment. A duplicate description of each part common to the above-described embodiments is omitted. The control of the position changing means 260 can be combined with an appropriate one of the control circuits already shown. In the fixing device 250A of FIG. 12, the solenoid already described may be adopted as a drive source, and in that case, the control drive corresponding to the energized state of the heater is performed using the corresponding control circuit exemplified. Just do it.

  Further, as shown in FIG. 13, the present invention is applied to a fixing device 250 </ b> B having a pressure pad that extends in the axial direction of the fixing roller 252 and is pressed toward the fixing roller 252. It is also possible. The fixing device 250B has a heating unit including the fixing belt 251 described above and a position changing unit 260. The thermostat 258 is disposed above the fixing heating roller 254 in the same manner as described above. Further, a position changing means 260 is arranged for swinging and moving the position of the thermostat 258 to change the distance from the heating element (FIG. 13 shows that the thermostat 258 is attached to the fixing heating roller 254. At the time of closest approach). In the figure, the same reference numerals are given to the respective parts corresponding to those of the above-described embodiment, and redundant description is omitted.

  A pressure member 756 configured by a pressure pad 758 made of a heat-resistant elastic member is disposed so as to face the fixing roller 252. Hereinafter, a known pressure member 756 will be described. As shown in FIG. 13, the pressure member 756 is provided on the surface of the pressure member main body 757 having a rectangular cross section extending in the axial direction of the fixing roller (heating roll) 252 and on the surface of the pressure member main body 757 facing the fixing roller 252. And a pressure pad 758 made of a heat-resistant elastic member.

  In FIG. 13, the pressure member main body 757 has a plate-like shape with a rectangular cross section perpendicular to the longitudinal direction, and the thickness thereof is the thickest at the center and is continuously reduced toward both ends. The upper surface to which the pressure pad 758 is bonded is flat, but the lower surface on the opposite side is formed in a curved surface projecting downward along the longitudinal direction, and has the largest cross-sectional secondary moment at the center in the axial direction. The cross-section secondary moment is reduced as it goes to both ends in the direction. A positioning projection is provided on the lower surface of the central portion in the longitudinal direction of the pressure member main body 757.

  In FIG. 13, the pressure member 756 having the pressure member main body 757 and the pressure pad 758 is supported by a pressing member 759. The pressing member 759 is made of a material having high rigidity so as not to bend, and has a pressing member support portion 761 at the upper end portion thereof. The pressure member support portion 761 is formed with a pressure member accommodating recess 762 for accommodating the pressure member 756. A support hole is formed in the center in the longitudinal direction of the bottom surface of the pressurizing member housing recess 762, and is configured to support the protrusions in a swingable manner.

  A belt guide 764 having an arc surface is connected to the lower end of the pressing member 759 via a connecting member 763. The pressing member 759 is provided with a belt end guide member which does not appear in the drawing at both ends of the pressing member support portion 761. The pressing member 759 is supported by a compression spring that presses the lower surface of the belt end guide member upward at both ends of the pressing member support portion 761, and is pressed toward the fixing roller 252. An endless fixing belt 259 is rotatably supported around the pressing member 759 and the belt guide 764. The movement of both ends of the fixing belt 259 is restricted by the belt end guide member.

  With the above configuration, the pressing member 759 is loaded at both ends by the compression springs, and the load is applied to the pressure member main body 757 at the central portion in the axial direction. A pressure pad 758 is pressed against the fixing roller 252 and the fixing belt 251 to form a fixing nip N in the pressure contact area. The fixing operation in this embodiment is well known and will not be described here. Also, the control of the position changing means 260 has already been described in the other embodiments, and will be omitted. Also in the fixing device 250B, the solenoid already described as a drive source can be adopted, and in this case, the control drive corresponding to the energized state of the heater is performed using the corresponding control circuit exemplified.

  Furthermore, as shown in the schematic configuration diagram of FIG. 14, a pressure belt stretched around a pressure roller is also used on the pressure portion side, and the belt is covered between the fixing belt and the pressure belt. The present invention can be similarly applied to a known fixing device of a type in which a fixing object is sandwiched and pressed.

  In the fixing device 250C of FIG. 14, the fixing belt 251 is disposed horizontally. That is, the fixing belt (rotating member for fixing) 251 is a fixing heating roller 254 (including a halogen heater 253 as a heating element) that also serves as an inlet-side belt support member on the recording material P loading side. And an exit side roller (outlet side support roller) 254B that also serves as an exit side belt support member on the side from which the recording material P is discharged. Reference numeral 255A denotes a tension roller.

  An endless pressure belt 259 is opposed to the fixing belt 251 by a fixing roller (pressure roller) 252A that is a pressure member and an exit side support roller 252B. The fixing roller 252A is in pressure contact with the fixing heating roller 254 via the pressure belt 259 and the fixing belt 251, and the outlet side roller 252B is in pressure contact with the outlet side support roller 254B via the pressure belt 259 and the fixing belt 251. is doing.

  In the same manner as already described above, the thermostat 258 is supported and swings above the fixing heating roller 254 of the fixing device 250C to move the position of the thermostat 258 to change the distance from the heating element. The position changing means 260 is disposed (FIG. 14 shows when the thermostat 258 is closest to the fixing heating roller 254). In the figure, the same reference numerals are given to the respective parts corresponding to those of the above-described embodiment, and redundant description is omitted. Further, since the control of the position changing means 260 has already been described, the description thereof will be omitted. Also in the fixing device 250C, the solenoid already described as a drive source can be adopted, and in that case, the control drive corresponding to the energized state of the heater is performed using the corresponding control circuit exemplified.

  Each roller 254, 254B, 252A, 252B rotates in the direction of the arrow, and accordingly, the fixing belt 251 and the pressure belt 259 are driven to run in synchronization with the directions indicated by arrows E, F in FIG. The recording material P carrying the unfixed toner image T is conveyed toward the fixing device 250C, and is fed between the fixing belt 251 and the pressure belt 259 while being guided by the recording material guide. At this time, the toner image T comes into contact with the surface of the fixing belt 251. In this way, the recording material P carrying the toner image T is placed on the pressure contact portion (nip portion) N between the heated and driven fixing belt 251 and the fixing roller 252A, and the toner image T is placed on the surface of the fixing belt. Pass in the direction of contact. At this time, pressure is applied to the toner image T on the recording material, heat is applied to the toner of the toner image from the fixing belt 251, the toner is melted by heat, and the toner adheres to the surface of the fixing belt 251. And fixed.

  [Seventh Embodiment] Hereinafter, different embodiments will be described in detail with reference to the drawings. Note that the schematic configuration of the entire apparatus is the same as that of the first embodiment, and a description thereof will be omitted. FIG. 15 shows a configuration example of a main part of a fixing device that is a feature of the present embodiment.

  The fixing device 250, which is a characteristic part of the present embodiment device, will be described in detail. FIG. 15 and FIG. 16 (positions are different when the fixing heating roller 254 is biased) are shown in FIG. 15 and FIG. This fixing device 250 has a fixing roller 252 (φ52, t = 52) of silicon foam rubber positioned inside (inside the circumference) a fixing belt 251 (belt length of about 70 mm) as a fixing rotating body whose surface is covered with a PFA tube. 10 mm) and an aluminum fixing heating roller 254 (φ35, t = 0.6 mm), which is a heated body including a halogen heater 253 (1200 W) as a heating element. The fixing (heating) roller 254 also serves as a tension roller, and is biased outward (upward in the drawing) by a tension spring 255 to apply tension to the fixing belt 251. A pressure roller (pressure member) 256 as a pressure rotator is arranged on the opposite side of the fixing belt peripheral circuit with respect to the fixing roller 252 with the fixing belt 251 interposed therebetween. A fixing nip portion is formed. The pressure roller 256 also includes a halogen heater 257 (1200 W) and serves as a heating source during the fixing operation. Although not shown, as in the case of the first embodiment, a temperature sensor (thermopile) 254C is provided as a temperature detection unit that faces the surface of the fixing belt 251 in a non-contact manner. Based on the output control of the heater 253, the temperature of the fixing belt 251 (fixing temperature) may be adjusted to a desired temperature (target control temperature).

  In the vicinity of the fixing heating roller 254 (above here), an excessive temperature rise prevention device having an excessive temperature rise prevention means for detecting an abnormal temperature rise of the fixing heating roller 254 and shutting off the power supply to the heater 253. As shown, a thermostat 258 is provided. Although the wiring is not shown, the thermostat 258 is interposed in the power supply path to the heater 253. That is, here, the thermostat 258 has an abnormal temperature detection function for detecting the temperature of the fixing belt (fixing rotating body) 251 and forcibly energizes the halogen heater 253 (heating element) when the heating element temperature reaches the abnormal temperature. Shut off. The shut-off operation of the thermostat 258 is thermally irreversible.

  The fixing heating roller 254 can be moved by a position changing means 260 as a means for driving the position of the heated object, and can change the distance from the thermostat 258 which is an excessive temperature rise prevention device. The position changing means 260 includes a swing arm 261, a heated object position driving cam 267, and a cam driving motor (hereinafter simply referred to as a motor) 268. More specifically, one end is pivotally supported by a support shaft 264 and the other end (free end side) is connected to a fixing heating roller 254 (here, downward) a tension spring 255 is attached. The swinging arm 261 is biased by a biasing spring 265 in a direction away from the thermostat 258 on the free end side, and the cam surface is in contact with the swinging arm 261 near the free end (the other end side). Heating body position driving cam (here, eccentric disc cam) 267, motor 268 (not shown) for rotationally driving the heated body position driving cam 267, and a control unit not shown here for driving and controlling the motor 268 The distance between the fixing heating roller 254 and the thermostat 258 is changed by the cooperative action, thereby further separating the fixing heating roller 254 from the thermostat 258. It can be moved away to the position (referred to as position A).

  FIG. 17 shows a schematic example of the main part related to the image forming apparatus including the configuration for control. In this embodiment, the image forming apparatus is supplied with electric power from the commercial power source 400 via the main switch 301, and each part of the fixing device and the like is controlled (including power supply operation, here referred to as control).

  The control unit 300 includes an image forming apparatus control device (hereinafter referred to as a main control device) 302, a heater control circuit 303, a current sensor 304, and a drive cam control circuit 307 as a heated object position control circuit. The heated object position drive cam 267 is controlled by a drive cam control circuit 307. On / off of the halogen heater 253 is controlled by the heater control circuit 303 based on the detection result of the belt surface temperature by a temperature sensor (thermopile) 254C as temperature detection means that faces the surface of the fixing belt 251 in a non-contact manner. The suspension of energization of the heating element for heating temperature control is treated as an energization operation in terms of control. All power supplied to these units is cut off by turning off the main switch 301. Thus, the drive cam control circuit 307 and the heated object position drive motor 268 are operated by appropriately transforming and supplying the commercial power supply 400 (the power supply optimization circuit is not shown).

  Next, details of the position control operation by the position changing unit 260 will be described. When the heater 253 is turned off, such as when the apparatus is on standby, the fixing heating roller 254 moves to a position away from the thermostat 258: position A (FIG. 15). In other words, the heater 253, which is a heating element included in the fixing heating roller 254, moves to the position A that is a position away from the thermostat 258 and stays there. That is, since the heat of the fixing heating roller 254 is not easily transmitted, the temperature of the thermostat 258 does not rise more than necessary.

  On the other hand, when the heater 253 is turned on, the fixing heating roller 254 moves to a position close to the thermostat 258: position B and remains (FIG. 16). In other words, the heater 253, which is a heating element included in the fixing heating roller 254, moves to and stays at the position B that is close to the thermostat 258. That is, the thermostat 258 is directly warmed by the heat of the fixing heating roller 254. Therefore, in the unlikely event of an abnormal temperature rise, the temperature quickly rises to the operating temperature of the thermostat 258, and the power to the heater 253 can be cut off appropriately without delay.

The process linear velocity of the image forming apparatus of the present embodiment described above is 352 mm / sec, and the productivity is 75 cpm on A4 paper.
Control temperature during standby is heating roller: 170 ° C
Pressure roller: 150 ° C
The set temperature when passing paper is the heating roller: 165 ° C
Pressure roller: 120 ° C
It is.
The rated operating temperature of the thermostat 258 is 180 ° C.
FIG. 18 shows the thermostat 258 temperature when overshoot occurs after the paper is passed.

  As described above, in the seventh embodiment, when the heater 253 that is the heating body is not energized and the temperature of the fixing heating roller 254 does not rise, the thermostat 258 that is an overtemperature prevention device. By increasing the distance between the heating member contained in the fixing heating roller 254 and the fixing unit, the fixing unit suddenly stops due to JAM or the like during paper passing, and even if the heating member temperature rises due to overshoot, Since it does not operate, it is possible to reduce the downtime by preventing the machine downtime due to the replacement of the excessive temperature rise prevention device, etc., and it becomes possible to immediately restart the operation after the JAM repair process.

  [Eighth Embodiment] Next, different embodiments are illustrated. FIG. 19 shows a schematic example of an image forming apparatus according to the eighth embodiment of the present invention. The schematic configuration of the entire apparatus and the configurations of the fixing device 250 and the position changing unit 260 are the same as those in the seventh embodiment, and a description thereof will be omitted. Also, the position control operation of the position changing means 260 is the same as in the seventh embodiment, and the description will not be repeated.

  In this embodiment, the components of the control unit 300 are the same as those in the seventh embodiment, but only the method of supplying power to each unit is different. In other words, the fixing device and the image forming apparatus are controlled by being supplied with power via the main switch 301 by the commercial power source 400. These powers are cut off by turning off the main switch 301. On the other hand, the drive cam control circuit 307 and the heated object position drive motor 268 are directly supplied with electric power from the commercial power source 600, and operate without being cut off even if the main switch 301 is turned off. be able to. In other words, in the present embodiment, the heated object position driving cam 267 is controlled by the heated object position driving cam control circuit 307 using a commercial power supply different from that of the image forming apparatus. Further, as in the second embodiment, the heated object position driving cam 267 is controlled by the heated object position driving cam control circuit 307 using a commercial power source branched to a system separate from the image forming apparatus. (The power optimization circuit is not shown).

  Accordingly, during normal operation, the drive cam control circuit 307 detects energization to the heater 253, and when the energization to the heater 253 is stopped by turning off the main switch 301, the fixing heating roller 254 remains moved to the position A ( FIG. 15). Thus, similarly to the seventh embodiment, since the heat of the heating roller 254 is not easily transmitted, the temperature of the thermostat 258 does not rise more than necessary, and even when the heating body temperature rises due to overshooting, an excessive temperature rise is prevented. Downtime can be shortened without operating the device. FIG. 20 shows the temperature of the thermostat 258 when overshoot occurs after passing paper in the eighth embodiment (the same result as FIG. 18).

  [Ninth Embodiment] FIG. 21 shows a schematic example of an image forming apparatus according to a ninth embodiment of the present invention. The schematic configuration of the entire apparatus, the configuration of the fixing device 250 and the position changing unit 260, and the position control operation of the position changing unit 260 are the same as those in the seventh embodiment, and will be omitted.

  In this embodiment, the method of supplying power to each component described above of the control unit 300 is different, and the drive cam control circuit 307, the heated object position drive motor 268, and the heated object position drive cam 267 are: Control is performed using a power source 500 independent of the image forming apparatus. The fixing device and the image forming apparatus are controlled by being supplied with electric power via the main switch 301 by the commercial power source 400 as in the previous embodiments. However, the drive cam control circuit 307 and the heated object position drive motor 268 are operated by being supplied with electric power from a battery power source 500 completely independent of the commercial power source 400.

  By turning off the main switch 301, the fixing device and the image forming apparatus are powered off, but the driving cam control circuit 307 and the heated object position driving motor 268 are separately supplied with power by the battery power source 500. Even if the main switch 301 is turned off, the electric power is not cut off and can operate. Therefore, the drive cam control circuit 307 detects energization to the heater 253, and when the energization to the heater 253 is stopped by turning off the main switch 301, the fixing heating roller 254 moves to the position A and needs a thermostat 258. As a result, the temperature does not rise (see FIG. 15) and the downtime can be shortened. When the thermostat 258 temperature at the time of occurrence of overshoot was measured after passing paper with the ninth embodiment device, the result shown in FIG. 22 was obtained.

  In FIG. 21, the power supply battery 500 is always connected, but an appropriate switching circuit is inserted into the power supply line of the drive cam control circuit 307 and the heated body position drive motor 268 to normally supply commercial power. It is possible to use a known configuration that operates with power from the switching circuit 400 and operates with the power source battery 500 switched by the switching circuit when the commercial power supply 400 is off. In this case, the same effect can be obtained.

  [Tenth Embodiment] FIG. 23 shows a schematic example of relevant parts of an image forming apparatus including a configuration for controlling the image forming apparatus according to a tenth embodiment of the present invention. In place of the power battery 500 in FIG. 21, a rechargeable battery 501 and a charging circuit 502 that uses power from the commercial power supply 400 for charging the rechargeable battery 501 via the main controller 302 are provided. In the present embodiment, the driving cam control circuit 307 and the heated object position driving motor 268 are supplied with power by the rechargeable battery 501. The fixing device and the image forming apparatus are controlled by being supplied with electric power via a main switch 301 by a commercial power source 400. When the main switch 301 is turned off, the supplied electric power is cut off.

  Since the position control operation of the position changing means 260 is performed using the power of the rechargeable battery 501, the position control operation (cooling operation) can be performed even when the main switch 301 is turned off or a power failure occurs, and a thermostat due to overshoot. 258 malfunction can be prevented. When the thermostat 258 temperature at the time of overshooting was measured after passing the paper with the tenth embodiment, the result was the same as that shown in FIG. It turns out that an effect is acquired. In particular, charging of the rechargeable battery 501 is supplied with power from the commercial power supply 400 and controlled by the main controller 302, and is supplemented and maintained in a fully charged state as necessary, so that maintenance such as battery replacement is unnecessary. There are advantages.

  [Eleventh Embodiment] In each of the embodiments described so far, the heated object position drive cam 267 and the motor (cam drive motor) 268 are used as the drive mechanism of the swing arm 261 of the position changing means 260. A drive source for moving the thermostat 258 may be other than the motor and the drive cam. An example in which a solenoid is used as a drive source will be described. FIG. 24 shows a schematic example of a fixing device of an image forming apparatus according to an eleventh embodiment of the present invention and related main parts for control. A fixing belt type fixing device 250 is the same as that described so far, and the description thereof is omitted.

  Similarly to each of the previous embodiments, the eleventh embodiment is also located near the upper portion of the fixing heating roller 254, and supplies power to the abnormal temperature detecting means for detecting abnormal temperature increase of the fixing heating roller 254 and the heater 253. A position change means 260 including a thermostat 258 that also serves as an excessive temperature rise prevention means for shutting off the heat and a swing arm 261 that movably supports the fixing heating roller 254.

  One end of the swing arm 261 is pivotally supported by a support shaft 264, and a tension spring 255 is provided on the free end side of the other end connected to the fixing heating roller 254 (downward here) and attached freely. A movable body distal end portion of a heated body position drive solenoid (hereinafter simply referred to as a solenoid) 269 is locked to the end distal end portion. This solenoid 269 is driven by a DC power source, draws the free end of the swing arm 261 when energized, and has a heating temperature adjustment position in which the distance between the heater 253 that is a heating element contained in the fixing heating roller 254 and the thermostat 258 is narrowed. Move to and hold. Further, a biasing spring 265 is attached to the swing arm 261 at the center, and the free end side is biased in a direction away from the thermostat 258. Therefore, if the solenoid 269 is not energized, the fixing heating roller 254 at the free end of the swing arm 261 is moved and held at a position separated from the thermostat 258.

  The control unit 300A includes a main control device (image forming device control device) 302, a heater control circuit 303 for controlling on / off of the halogen heater 253 and the position of the overheat prevention device and the object to be heated, and a heater control circuit. The DC power supply circuit 306 is driven by the halogen heater 253 and the solenoid 269 under the control of 303. Here, the DC power supply circuit 306 functions as a position drive control device that controls the position changing means.

  The image forming apparatus is supplied with power via a main switch 301 by a commercial power source 400, and each part such as a fixing device is controlled. Solenoid 269 and heater 253 are driven by DC power supply circuit 306. The DC power supply circuit 306 obtains a DC2 4 V power source by transforming / rectifying and smoothing the commercial power source 400 (here, 100 V) via the main switch 301, and is on / off controlled by the control output of the main controller 302. The DC power supply output is commonly connected to the solenoid 269 and the heater 253 using a DC 24V power supply (the solenoid 269 and the heater 253 are connected in parallel). With this connection, power is supplied to the solenoid 269 only when the heater 253 is energized.

  When power is supplied to the solenoid 269, the heating roller 254 approaches the thermostat 258. That is, when the heater 253 shown in FIG. 24 is turned on, the heating roller 254 moves to a position close to the thermostat 258: position B and remains. That is, the thermostat 258 is directly warmed by the heat of the heating roller 254. Therefore, in the unlikely event of an abnormal temperature rise, the temperature quickly rises to the operating temperature of the thermostat 258, and the power to the heater 253 can be cut off appropriately without delay.

  On the other hand, when the power of the solenoid 269 is shut off due to the heater 253 being turned off when a jam occurs, the heating roller 254 is separated from the thermostat 258 by the biasing spring 265 (not shown). Thus, when the heater 253 is extinguished (power is cut off), the heating roller 254 moves to a position away from the thermostat 258: position A and remains. Therefore, since the heat of the heating roller 254 is not easily transmitted to the thermostat 258, the temperature of the thermostat 258 does not rise more than necessary.

  In this way, the heating roller 254 moves its position by the solenoid 269 constituting the position changing means 260 and the urging spring 265 according to the turning on / off of the heater 253, and the distance from the excessive temperature rise prevention device is increased. It has been changed to prevent excessive temperature rise. Thereby, in each of the present embodiments, just as in each of the embodiments described above, even if the apparatus suddenly stops and the heating body temperature rises due to overshoot, the excessive temperature rise prevention device does not operate. It is possible to reduce the downtime by preventing the machine downtime due to the replacement of the excessive temperature rise prevention device or the like, and it is possible to immediately restart after the JAM repair process.

  [Twelfth Embodiment] Another embodiment in which a solenoid 269 is used as a drive source for moving the thermostat 258 will be described with reference to a schematic example of an image forming apparatus shown in FIG. In this embodiment, the heater 253 is driven by a commercial power supply 400 of AC100V, but the solenoid 269 is driven by a DC power supply, and this DC power supply is connected in parallel to the same AC100V power supply as the heater 253 using the AC100V power supply. A voltage converted into DC24V output from a DC power supply unit composed of a voltage conversion transformer 307, a diode 308, and a smoothing capacitor 309, which are sequentially connected in series, is used. With this connection, power is supplied to the solenoid 269 only when the heater 253 is energized.

  In each of the embodiments described above, in a heat fixing apparatus including a fixing belt, fixing is performed by a pressing force between a pressing member that forms a nip portion by sandwiching a fixing belt as a toner heating medium and a driving roller. An example has been described, but the present invention is not limited to each embodiment. The position change means for moving the heated object described above and changing the distance from the overheat prevention device, and the position drive control device for detecting the energization state to the heating element and controlling the position change means are general-purpose. The fixing device that can be applied is not limited. For example, the fixing rotator may simply be a roller.

  In addition, the pressure member pressed against the fixing member is not limited to the pressure roller described above which is a pressure rotator, and may be a belt without tension or a pressure pad which does not rotate or run. The same effects as those of the above-described embodiments can be obtained.

  For example, as in the example shown in the schematic configuration diagram of FIG. 12 described above, the present invention can also be applied to the fixing device 250A using a belt that is not tensioned as a pressure member. The fixing device 250 </ b> A is stretched by a fixing heating roller 254 and a fixing roller 252, which are heated objects including a halogen heater 253, and has already been described as a fixing belt 251 (a fixing member) as a heating member for heating the recording material P to be conveyed. A rotating body). Reference numeral 255 denotes a tension spring. Then, the endless belt 662 that faces the fixing roller 252 and is in contact with the fixing belt 251, and the endless belt 662 is pressed against the fixing roller 252, and a contact portion (nip portion) is provided between the fixing roller 252 and the endless belt 662. A pressing member 663 is formed. Further, a sliding member 664 that improves the sliding property between the endless belt 662 and the pressing member 663 is provided between the endless belt 662 and the pressing member 663.

  The pressing member 663 has a concave surface shape, and is positioned adjacent to the first pressure member 631 on the upstream side and the downstream side of the first pressure member 638 that mainly forms the contact portion and the contact portion N. The second pressure member 639 having a U-shaped cross section is integrally formed. The endless belt 662 is circulated and supported by a pressing member 663 disposed therein, a belt travel guide 665, and edge guides (not shown) disposed at both ends of the endless belt 662.

  Then, between the inner peripheral surface of the endless belt 662 and the pressing member 663, the sheet passes through the contact portion N from the upstream side of the contact portion N and reaches the belt traveling guide 665 located on the downstream side of the contact portion N. One end of the sliding member 664 is fixed to a fixing member 666 that is movable in the direction of arrow D in the drawing along the traveling direction of the endless belt 662. The pressing member 663 and the belt travel guide 665 are held by a metal holder 667. Note that the movement of the fixing member 666 is controlled by control means not described here.

  Although not shown, a thermostat 258 is disposed above the fixing heating roller 254 of the fixing device 250A, and supports a tension spring 255 below and swings to move the position of the fixing heating roller 254, thereby preventing an excessive temperature rise. Position changing means 260 for changing the distance between the two is disposed. The control of the position changing means 260 can be combined with an appropriate one of the control circuits already shown. Note that the solenoid already described may be employed as the drive source, and in that case, control drive corresponding to the energized state of the heater may be performed using the corresponding control circuit exemplified.

  Similarly to the above-described example shown in FIG. 13, the fixing device 250 </ b> B having a pressure pad that extends in the axial direction of the fixing roller 252 and is pressed toward the fixing roller 252 between the fixing roller 252 and the fixing roller 252. It is also possible to apply the present invention. The fixing device 250B includes a heating unit including the fixing belt 251 described above and a position changing unit 260. A thermostat 258 is disposed above the fixing heating roller 254, and a tension spring 255 is disposed below. Position changing means 260 is arranged for swinging and moving the position of the fixing heating roller 254 to change the distance from the excessive temperature rise prevention device.

  A pressure member 756 configured by a pressure pad 758 made of a heat-resistant elastic member is disposed so as to face the fixing roller 252. The known pressure member 756 is the same as that described with reference to FIG.

  [Thirteenth Embodiment] In an image forming apparatus including a fixing device, the temperature in the apparatus varies greatly depending on the location. That is, the temperature near the center in the axial direction of the fixing unit is high, and the temperature near the end in the axial direction is relatively low. Further, the outside of the fixing unit in the axial direction has a lower temperature because the influence of outside air is larger. Therefore, in the present embodiment, when the temperature of the heated object rises due to overshoot or the like, the image forming apparatus includes a configuration for moving the excessive temperature rise prevention device to the outside in the axial direction, which is not easily affected by the heat of the heating element. Will be described with reference to the drawings. Note that the schematic configuration of the entire apparatus is the same as that of the first embodiment, and a description thereof will be omitted. FIG. 26 and FIG. 27 show a configuration example of the main part of the fixing device which is a feature of the present embodiment. 26 and 27A are cross-sectional views of the fixing device, and FIG. 26B is a side view of the fixing device.

  The fixing device 250, which is a characteristic part of the present embodiment device, will be described in detail. FIG. 26 and FIG. 27 (the position of the thermostat 258 is different between when the light is extinguished and when it is overheated) are shown in FIG. 26 and FIG. 27. The fixing device 250 includes, for example, a fixing roller 252 (φ52, φ52) made of silicon foam rubber, which is positioned inside (inside) a fixing belt 251 (belt length of about 70 mm) as a fixing rotating body whose surface is covered with a PFA tube. t = 10 mm) and an aluminum fixing heating roller 254 (φ35, t = 0.6 mm), which is a heated body including a halogen heater 253 (1200 W) as a heating element. The fixing (heating) roller 254 also serves as a tension roller, and is biased outward (upward in the drawing) by a tension spring 255 to apply tension to the fixing belt 251. A pressure roller (pressure member) 256 as a pressure rotator is arranged on the opposite side of the fixing belt peripheral circuit with respect to the fixing roller 252 with the fixing belt 251 interposed therebetween. A fixing nip portion is formed. The pressure roller 256 also includes a halogen heater 257 (1200 W) and serves as a heating source during the fixing operation. Although not shown, as in the case of the first embodiment, a temperature sensor (thermopile) 254C is provided as a temperature detection unit that faces the surface of the fixing belt 251 in a non-contact manner. Based on the output control of the heater 253, the temperature of the fixing belt 251 (fixing temperature) may be adjusted to a desired temperature (target control temperature).

  In the vicinity of the fixing heating roller 254 (above here), an excessive temperature rise prevention device having an excessive temperature rise prevention means for detecting an abnormal temperature rise of the fixing heating roller 254 and shutting off the power supply to the heater 253. As shown, a thermostat 258 is provided. Although the wiring is not shown, the thermostat 258 is interposed in the power supply path to the heater 253. That is, here, the thermostat 258 has an abnormal temperature detection function for detecting the temperature of the fixing belt (fixing rotating body) 251 and forcibly energizes the halogen heater 253 (heating element) when the heating element temperature reaches the abnormal temperature. Shut off. The shut-off operation of the thermostat 258 is thermally irreversible.

  The thermostat 258 can move its position by a position changing means 260 as a means for driving the excessive temperature rise prevention device position to change the distance from the heating element. The position changing means 260 includes a swing arm 261, an excessive temperature rise prevention device drive gear 280, and a drive motor (hereinafter simply referred to as a motor) 263. That is, the position of the thermostat 258 can be changed by the excessive temperature rise prevention device drive gear 280 and the motor 263. For example, when the heater is extinguished, the excessive temperature rise prevention device drive gear 280 and the motor 263 change the position of the thermostat 258 to a position (referred to as position A) separated from the fixing heating roller 254 axis having a low ambient temperature. You can keep away. This makes it difficult for heat from the fixing heating roller 254 to be transmitted, and the temperature of the thermostat 258 can be prevented from rising more than necessary.

  FIG. 28 shows a schematic example of the main part related to the image forming apparatus including the configuration for control. In this embodiment, the image forming apparatus is supplied with electric power from the commercial power source 400 via the main switch 301, and each part of the fixing device and the like is controlled (including power supply operation, here referred to as control).

  The control unit 300 includes an image forming apparatus control device (hereinafter referred to as a main control device) 302, a heater control circuit 303, a current sensor 304, and a drive motor control circuit 310 as an overheat prevention device position control circuit. Yes. The excessive temperature rise prevention device drive gear 280 is controlled by the drive motor control circuit 310. On / off of the halogen heater 253 is controlled by the heater control circuit 303 based on, for example, a detection result of the belt surface temperature by a temperature sensor (thermopile) 254C as temperature detection means that faces the surface of the fixing belt 251 in a non-contact manner. . The suspension of energization of the heating element for heating temperature control is treated as an energization operation in terms of control. All power supplied to these units is cut off by turning off the main switch 301. As described above, the excessive temperature rise prevention device drive gear 280 and the over temperature rise prevention device position drive motor 263 are operated by appropriately transforming and supplying the commercial power source 400 (the power supply optimization circuit is not shown).

  Next, details of the position control operation by the position changing unit 260 will be described. When the heater 253 is turned off, such as when the apparatus is on standby, the thermostat 258 moves to a position away from the fixing heating roller 254 axis: position A (FIG. 26). In other words, the thermostat 258 moves and stays at the position A that is a position away from the heater 253 that is a heating element included in the fixing heating roller 254. That is, since the heat of the fixing heating roller 254 is not easily transmitted, the temperature of the thermostat 258 does not rise more than necessary.

  On the other hand, when the heater 253 is lit, the thermostat 258 moves to a position near the fixing heating roller 254 axis: position B and remains (FIG. 27). In other words, the thermostat 258 moves and stays at the position B, which is a position close to the heater 253 that is a heating element included in the fixing heating roller 254. That is, the thermostat 258 is directly warmed by the heat of the fixing heating roller 254. Therefore, in the unlikely event of an abnormal temperature rise, the temperature quickly rises to the operating temperature of the thermostat 258, and the power to the heater 253 can be cut off appropriately without delay.

The process linear velocity of the image forming apparatus of the present embodiment described above is 352 mm / sec, and the productivity is 75 cpm on A4 paper.
Control temperature during standby is heating roller: 170 ° C
Pressure roller: 150 ° C
The set temperature when passing paper is the heating roller: 165 ° C
Pressure roller: 120 ° C
It is.
The rated operating temperature of the thermostat 258 is 180 ° C.
FIG. 29 shows the thermostat 258 temperature when an overshoot occurs after the paper is passed.

  As described above, in the apparatus according to the thirteenth embodiment, when the heater 253 that is the heating body is not energized and the temperature of the fixing heating roller 254 does not rise, the thermostat 258 that is an overtemperature prevention device. Is moved to a position that is less susceptible to the influence of the fixing heating roller 254 containing the heating body, so that the fixing unit suddenly stops due to JAM or the like during paper passing, and even if the heating body temperature rises due to overshoot, Since the temperature prevention device does not operate, it is possible to reduce the downtime by preventing the machine downtime due to the replacement of the excessive temperature rise prevention device and the like, and it becomes possible to reactivate immediately after the JAM repair process.

  [Fourteenth Embodiment] Next, different embodiments are illustrated. FIG. 30 shows a schematic example of an image forming apparatus according to the fourteenth embodiment of the present invention. The schematic configuration of the entire apparatus and the configurations of the fixing device 250 and the position changing unit 260 are the same as those in the thirteenth embodiment, and a description thereof will be omitted. Also, the position control operation of the position changing means 260 is the same as in the thirteenth embodiment, and the description will not be repeated.

  In this embodiment, the components of the control unit 300 are the same as those in the thirteenth embodiment, but only the method of supplying power to each unit is different. In other words, the fixing device and the image forming apparatus are controlled by being supplied with power via the main switch 301 by the commercial power source 400. These powers are cut off by turning off the main switch 301. On the other hand, the drive motor control circuit 310 and the excessive temperature rise prevention device position drive motor 263 are directly supplied with electric power by the commercial power supply 600 (the power supply optimization circuit is not shown). For these, even if the main switch 301 is turned off. However, the electric power is not cut off and can operate. In other words, in the present embodiment, the excessive temperature rise prevention device position drive motor 263 is controlled by the over temperature rise prevention device position drive motor control circuit 310 using a commercial power supply different from that of the image forming apparatus. Further, as in the second embodiment, a commercial power source in which the excessive temperature rise prevention device position drive motor 263 is branched to a separate system from the image forming apparatus by the excessive temperature rise prevention device position drive motor control circuit 310 is used. You may make it control (a power supply optimization circuit is abbreviate | omitting illustration).

  Accordingly, during normal operation, the drive motor control circuit 310 detects energization to the heater 253, and when the energization to the heater 253 is stopped by turning off the main switch 301, the thermostat 258 remains moved to the position A (FIG. 26). reference). Thus, similarly to the thirteenth embodiment, since the heat of the heating roller 254 is not easily transmitted, the temperature of the thermostat 258 does not rise more than necessary, and even when the temperature of the heating body rises due to overshooting, overheating is prevented. Downtime can be shortened without operating the device. FIG. 31 shows the temperature of the thermostat 258 when overshoot occurs after the sheet is passed in the fourteenth embodiment (results equivalent to FIG. 29).

  [Fifteenth Embodiment] FIG. 32 shows a schematic example of an image forming apparatus according to a fifteenth embodiment of the present invention. The schematic configuration of the entire apparatus, the configuration of the fixing device 250 and the position changing unit 260, and the position control operation of the position changing unit 260 are the same as those in the thirteenth embodiment, and will be omitted.

  In the present embodiment, the method of supplying power to the above-described components of the control unit 300 is different, and the drive motor control circuit 310, the excessive temperature rise prevention device position drive motor 263, and the excessive temperature rise prevention device position drive gear. 280 is controlled using a power source independent of the image forming apparatus. The fixing device and the image forming apparatus are controlled by being supplied with electric power via the main switch 301 by the commercial power source 400 as in the previous embodiments. However, the drive motor control circuit 310, the excessive temperature rise prevention device position drive motor 263, and the excessive temperature rise prevention device position drive gear 280 are operated by being supplied with electric power from a battery power source 500 completely independent of the commercial power source 400.

  By turning off the main switch 301, the fixing device and the image forming apparatus are cut off from power, but the drive motor control circuit 310, the excessive temperature rise prevention device position drive motor 263, and the excessive temperature rise prevention device position drive gear 280 Even if power is separately supplied from the battery power source 500 and the main switch 301 is turned off, the power is not cut off and the battery can be operated. Therefore, the drive motor control circuit 310 detects the energization to the heater 253, and when the energization to the heater 253 is stopped by turning off the main switch 301, the thermostat 258 moves to the position A, and the thermostat 258 becomes more than necessary. The temperature does not increase (see FIG. 26), and downtime can be shortened. With the fifteenth embodiment, the temperature of the thermostat 258 when overshoot occurred after paper passing gave a result equivalent to that previously shown in FIG.

  In FIG. 32, the power battery 500 is always connected. For example, an appropriate switching circuit is usually inserted into the power supply lines of the drive motor control circuit 310 and the overheat prevention device position drive motor 263, The power source battery 500 may be configured to operate with power from the commercial power source 400 via the switching circuit, and when the commercial power source 400 is turned off, and the power source battery 500 may be backed up. It is done.

  [Sixteenth Embodiment] FIG. 33 shows a schematic example of relevant parts of an image forming apparatus including a configuration for controlling the image forming apparatus according to a sixteenth embodiment of the present invention. 32 is provided with a rechargeable battery 501 instead of the power supply battery 500 and a charging circuit 502 that uses power from the commercial power supply 400 for charging the rechargeable battery 501 via the main controller 302. In the present embodiment, the drive motor control circuit 310 and the excessive temperature rise prevention device position drive motor 263 are supplied with power by the rechargeable battery 501. The fixing device and the image forming apparatus are controlled by being supplied with electric power via a main switch 301 by a commercial power source 400, and the supply power is cut off when the main switch 301 is turned off.

  Since the position control operation of the position changing means 260 is performed using the power of the rechargeable battery 501, the position control operation (cooling operation) can be performed even when the main switch 301 is turned off or a power failure occurs, and a thermostat due to overshoot. 258 malfunction can be prevented. In the sixteenth embodiment, the temperature of the thermostat 258 at the time of overshoot after paper passing was measured. As a result, the overheat prevention device did not operate and the downtime was shortened. It turns out that an effect is acquired. In particular, charging of the rechargeable battery 501 is supplied with power from the commercial power supply 400 and controlled by the main controller 302, and is supplemented and maintained in a fully charged state as necessary, so that maintenance such as battery replacement is unnecessary. There are advantages.

  [Seventeenth Embodiment] In each of the embodiments described so far, the excessive temperature rise prevention device position drive gear 280 and the motor 263 are used as the drive mechanism of the position changing means 260 for changing the position of the thermostat 258. A drive source for moving 258 may be other than the motor and gear. Hereinafter, an example in which a solenoid is used as a drive source will be described. FIG. 34 shows a schematic example of a fixing device and related main parts for control of the image forming apparatus of the seventeenth embodiment of the present invention. A fixing belt type fixing device 250 is the same as that described so far, and the description thereof is omitted.

  Similarly to each of the previous embodiments, the seventeenth embodiment is also located near the upper portion of the fixing heating roller 254 and supplies power to the heater 253 for detecting an abnormal temperature of the fixing heating roller 254. A position change means 260 is provided which includes a thermostat 258 that also serves as an excessive temperature rise prevention means for shutting off the heat and a swing arm 261 that supports the thermostat movably.

  The thermostat 258 is attached to the lower side of the swing arm 261, a heating prevention device position drive solenoid (hereinafter simply referred to as a solenoid) 270 is locked to one end, and a spring 281 is connected to the other end. The solenoid 270 is driven by a DC power source, and when energized, the swing arm 261 is pulled together with the thermostat 258 and moved to a heating temperature adjustment position where the distance from the fixing heating roller 254 is reduced and held. A biasing spring 281 is attached to the end of the swing arm 261 opposite to the solenoid 270 locking side, and the thermostat 258 is biased in a direction away from the fixing heating roller 254 axis. Accordingly, when the solenoid 270 is not energized, the thermostat 258 is moved and held at a position separated from the heater 253.

  The control unit 300A is controlled by a main control device (image forming device control device) 302, a heater control circuit 303 for controlling on / off of the halogen heater 253 and an excessive temperature rise prevention device position, and a heater control circuit 303. A DC power supply circuit 306 that drives the halogen heater 253 and the solenoid 270 is configured. Here, the DC power supply circuit 306 functions as a position drive control device that controls the position changing means.

  The image forming apparatus is supplied with power via a main switch 301 by a commercial power source 400, and each part such as a fixing device is controlled. Solenoid 270 and heater 253 are driven by DC power supply circuit 306. The DC power supply circuit 306 obtains a DC24V power supply by transforming / rectifying and smoothing the commercial power supply 400 (here, 100V) via the main switch 301, and is on / off controlled by the control output of the main controller 302. The DC power output is commonly connected to the solenoid 270 and the heater 253 using a DC 24V power supply (the solenoid 270 and the heater 253 are connected in parallel). With this connection, power is supplied to the solenoid 270 only when the heater 253 is energized.

  When power is supplied to the solenoid 270, the thermostat 258 approaches the heating roller 254. That is, when the heater 253 shown in FIG. 34 is lit, the thermostat 258 stays at a position close to the heating roller 254: position B, and the thermostat 258 is directly warmed by the heat of the heating roller 254. Therefore, in the unlikely event of an abnormal temperature rise, the temperature quickly rises to the operating temperature of the thermostat 258, and the power to the heater 253 can be cut off appropriately without delay.

  On the other hand, when the power supply of the solenoid 270 is shut off by turning off the heater 253 when a jam occurs or the like, the thermostat 258 is separated from the fixing heating roller 254 by the biasing spring 281 (not shown). Thus, when the heater 253 is turned off (the power is shut off), the thermostat 258 moves to a position away from the heating roller 254: position A, and the heat of the fixing heating roller 254 is difficult to be transmitted, so that the thermostat 258 rises more than necessary. There is no.

  Thus, the thermostat 258 moves its position by the solenoid 270 constituting the position changing means 260 and the biasing spring 281 in accordance with the turning on / off of the heater 253, and the distance from the heating element is changed. It is possible to prevent an excessive temperature rise. Thereby, in each of the present embodiments, just as in each of the embodiments described above, even if the apparatus suddenly stops and the heating body temperature rises due to overshoot, the excessive temperature rise prevention device does not operate. It is possible to reduce the downtime by preventing the machine downtime due to the replacement of the excessive temperature rise prevention device or the like, and it is possible to immediately restart after the JAM repair process.

  [Eighteenth Embodiment] Another embodiment in which a solenoid 270 is used as a drive source for moving a thermostat 258 will be described with reference to a schematic example of an image forming apparatus shown in FIG. In this embodiment, the heater 253 is driven by a commercial power supply 400 of AC100V, but the solenoid 270 is driven by a DC power supply, and this DC power supply is connected in parallel to the same AC100V power supply as the heater 253 using the AC100V power supply. A voltage converted into DC24V output from a DC power supply unit composed of a voltage conversion transformer 307, a diode 308, and a smoothing capacitor 309, which are sequentially connected in series, is used. With this connection, power is supplied to the solenoid 270 only when the heater 253 is energized.

  In each of the embodiments described above, in a heat fixing apparatus including a fixing belt, fixing is performed by a pressing force between a pressing member that forms a nip portion by sandwiching a fixing belt as a toner heating medium and a driving roller. An example has been described, but the present invention is not limited to each embodiment. The position change control unit that moves the above-described abnormal temperature detection unit to change the distance from the heating element and the position drive control unit that detects the energization state of the heating element and controls the position change unit have versatility. Yes, applicable fixing devices are not limited. For example, the fixing rotator may simply be a roller.

  Further, the pressure member pressed against the fixing member is not limited to the above-described pressure roller that is a pressure rotating body, and may be a belt without tension or a pressure belt that is wound around a plurality of rollers. Alternatively, it may be a pressure pad that does not rotate or run, and the same effects as those of the above-described embodiments can be obtained.

  For example, as in the example shown in the schematic configuration diagrams of FIGS. 12, 13, and 14 described above, the fixing roller 252 between the fixing device 250 </ b> A using a belt without pressure and the fixing roller 252. A fixing device 250B having a pressure pad that extends in the axial direction and is pressed toward the fixing roller 252; and a pressure belt stretched around the pressure side roller on the pressure portion side, The above-described embodiment can also be applied to a fixing device of a type in which an object to be fixed is sandwiched and pressed between two belts, a fixing belt and a pressure belt. The description of FIGS. 12 to 14 is the same as described above, and will be omitted.

  In addition, the present invention is not limited to the above-described embodiments, and it is apparent that the embodiments can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the embodiments. It is. In each embodiment, the present invention is applied to a fixing device that uses a halogen heater to heat a heating element by radiant heat. However, the present invention is naturally applied to a fixing device that heats a heating element by electromagnetic induction heating. In this case, the same effect as in the present embodiment can be obtained.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus main body 12 Image carrier 13 Charging device 14 Developing device 15 Transfer / conveyance device 16 Cleaning device 17 Static elimination device 18 Laser writing device 30 Document reading device 41 Automatic document feeding device (ADF)
43 Paper Feed Unit 250 Fixing Device 250A, 250C, 250B Fixing Device 251 Fixing Belt 252 Fixing Roller 253 Halogen Heater 254 Fixing Heating Roller 255 Biasing Spring (Tension Spring)
256 Pressure roller (Pressure member)
257 Halogen heater 258 thermostat (abnormal temperature detection means and excessive temperature rise prevention means)
260 Position change means (over temperature rise prevention device position drive means)
261 Swing arm 262 Over temperature rise prevention device position drive cam 263 Cam drive motor (over temperature rise prevention device position drive motor)
267 Heated object position drive cam 268 Cam drive motor (heated object position drive motor)
280 Overheating prevention device position drive gear 281 Spring 301 Main switch 302 Main control device (image forming device control device)
303 Heater control circuit 304 Current sensor 305 Drive cam control circuit (over temperature rise prevention device position control circuit)
307 Drive cam control circuit (heated object position control circuit)
310 Drive motor control circuit (over temperature rise prevention device position control circuit)
400 Commercial power supply 500 Battery power supply 501 Rechargeable battery 502 Charging circuit P Recording material T Toner image

JP 2004-102104 A JP 2000-75707 A JP 2006-227374 A JP 2006-119430 A Japanese Patent Laid-Open No. 2005-37539 JP 2006-172781 A

Claims (12)

A fixing rotator for heating and fixing an unfixed toner image on a recording medium heated by a heating element;
An abnormal temperature detection means that is installed in the vicinity of the heating element and detects when the heating element reaches an abnormal temperature;
In a fixing device for an image forming apparatus, comprising: an excessive temperature rise prevention unit that forcibly cuts off power to the heating element when the heating element reaches an abnormal temperature;
Position changing means for moving either the abnormal temperature detection means or the heating element and changing the distance between the abnormal temperature detection means and the heating element;
A position drive control device that detects the energization state of the heating element and controls the position changing means;
When the heating element is energized and controlled for heating temperature control, it is held at the heating temperature control position in which the distance between the abnormal temperature detection means and the heating element is reduced,
The fixing device, wherein when the energization to the heating element is stopped, the abnormal temperature detecting means and the heating element are separated from each other.   The fixing device according to claim 1, wherein the position changing unit moves the abnormal temperature detecting unit to change a distance between the abnormal temperature detecting unit and the heating element.   The position changing means includes a swinging arm pivotally supported at one end and mounted with the abnormal temperature detecting means on the free end side, and an excessive temperature rise prevention in contact with the swinging arm in the vicinity of the free end. The fixing device according to claim 1, further comprising: a device position driving cam; and a motor that is controlled by the position driving control device to rotationally drive the overheat prevention device position driving cam. .   The position changing means includes a swing arm having one end pivotally supported to be swingable and having the abnormal temperature detecting means attached to a free end side, and a solenoid as a drive source for biasing the vicinity of the free end of the swing arm. The fixing device according to claim 1, further comprising a fixing device.   The heating element is an AC heater and is connected to a commercial power source through a switch, and the drive coil of the solenoid is connected to a DC power source directly connected to the commercial power source. The fixing device described.   The heating element is a heater, and the heater and the drive coil of the solenoid are connected in parallel to a single DC power supply connected to a commercial power supply via a switch. Fixing device.   The fixing device according to claim 1, wherein the position changing unit moves a heat generating body that includes the heating element, and changes a distance between the abnormal temperature detecting unit and the heating element.   The thermostat functioning also as the abnormal temperature detecting means for detecting the temperature of the fixing rotating body is used as the excessive temperature rise preventing means for forcibly cutting off the power supply to the heating element. The fixing device according to claim 1.   An image forming apparatus comprising the fixing device according to claim 1.   10. The position drive control device that controls the position changing unit is operated by a separate power source independent of a main power source for image forming operation, and drives the position changing unit by the separate power source. The image forming apparatus described in 1.   The image forming apparatus according to claim 10, wherein the separate power source is a battery.   The image forming apparatus according to claim 10, wherein the separate power source is a rechargeable battery that is charged by the main power source.

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