JP2010181859A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent erroneous operation of an excessive temperature rise preventive means (a thermostat) due to overshooting. <P>SOLUTION: The thermostat 8 is installed for detecting an abnormal temperature rise of a fixing heating roller 1 to interrupt power supply to a heater 5. A heat insulating board 10, movable by a heat insulating board drive gear 11 and a heat insulating board drive motor 12, is positioned between the thermostat 8 and the fixing heating roller 1 (in a position A) to interrupt heat of the fixing heating roller 1, when the heater 5 is not energized, and consequently, the thermostat 8 is prevented from being heated unnecessarily. When the heater 5 is energized, the heat insulating board 10 moves to a position B and the thermostat 8 is heated directly by heat of the fixing heating roller 1. When temperature rises abnormally, the thermostat 8 quickly increases its temperature, and consequently, power supply to the heater 5 is controlled to be cut off. The heat insulating board drive gear 11 and the heat insulating board drive motor 12 moving the heat insulating board 10 are controlled independently of an image forming apparatus by a heat insulating board drive controlling means 13. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to an image forming apparatus having a thermal fixing device.

  In recent years, there has been a demand for speeding up of color copiers and the like, and belt fixing systems that are smaller and can cope with higher linear speeds are widely used compared to conventional roller fixing. In the belt fixing system as shown in FIG. 23, a fixing heating roller 1 having a heater 5 inside supplies heat to the fixing belt 2. Various materials are used for the base material of the fixing belt 2. Recently, polyimide resin is often used because of heat resistance and high durability.

  During continuous paper passing, the transfer paper 9 takes heat from the surface of the fixing belt 2, so that the temperature of the fixing belt 2 is maintained, so that the core metal temperature of the fixing heating roller 1 becomes very high. This is more conspicuous as the CPM (Characters per Minute) is higher and the basis weight of the transfer paper 9 is larger.

  As described above, when the printing operation is finished in a state where the core metal temperature of the fixing heating roller 1 is high, the amount of heat taken away by the transfer paper 9 suddenly disappears, and the surface temperature of the fixing heating roller 1 is abnormally increased. To do. This is called overshoot after continuous paper feeding (see FIG. 24).

  In the conventional color 40 CPM machine, the temperature at the time of overshooting is about 230 ° C., but in recent 75 CPM machines, the temperature may be over 270 ° C. in the 75 CPM machine. This occurs due to a difference in power supplied to the fixing heating roller 1 during continuous paper feeding.

  With a 40 CPM machine, the temperature during sheet feeding can be kept stable at about 500 W. In order to prevent the temperature drop at the start of paper feeding, about 1.5 times the stable time is required, and the heater W number is 750 W or more. On the other hand, in the case of a 75 CPM machine, 900 W or more is required when the paper is stable, and the number of heaters W is 1350 W or more.

  Conventionally, the maximum power consumption of copying machines has been about 1500 W, but due to the recent market demand for higher production, the number of high-speed copying machines with a maximum power consumption of 2000 W or more has increased. In addition to the heater used for fixing, several hundreds of watts are required for driving various motors, so the problem of overshoot becomes significant in such a high-speed copying machine with a maximum power consumption of 2000 W or more.

  On the other hand, from the viewpoint of energy saving in recent years, it is required to shorten the warm-up time of the fixing unit, and the fixing heating roller is thinned and a fast rising heater is being adopted. However, the increase in the heating rate due to the thinning of the fixing heating roller significantly narrows the establishment range of the overheating prevention means constituted by a thermostat or the like.

  In other words, it is necessary to use a thermostat having a low operating temperature in order to reliably prevent overheating of the device due to runaway at startup. This is because the temperature increase rate of the temperature at the bimetal portion of the thermostat is slower than the temperature increase rate of the fixing heating roller.

  When this low operating temperature thermostat is used, when the fixing device normally operates and the ambient temperature rises, there is a high possibility that the thermostat will unintentionally operate. This often occurs at the time of overshoot immediately after the sheet passing when the temperature of the heating member becomes the highest. Among these, the overshoot becomes the largest in an immediate stop state due to a jam during continuous paper feeding or power off.

  When this overshoot occurs, the heater is not energized and there is no danger of smoke or fire, etc. An “down time (device stop time)” that cannot be performed occurs. This is because the thermostat operates even though the heater is not energized (see FIG. 25).

  Conventionally, in a high-speed copying machine using a large-capacity fixing heater, the heat capacity of the fixing device is large and the rise time is very slow, so that an excessive rise prevention means has been sufficiently established. However, energy saving is also required for high-speed machines, and even high-speed copiers with a maximum power consumption of 2000 W or more are increasing in startup time of 60 seconds or less.

  As an example of such a copying machine, a fixing heating roller (diameter: aluminum φ30, wall thickness: 0.6 mm), a heater (1800 W), a thermostat operation rated temperature (160 ° C.), and a thermostat gap (0.7 mm) are established. I am letting. In the future, when the capacity of the heater is further increased, or when the fixing heating roller is reduced in capacity so as to shorten the rise time, these problems become more remarkable.

  Specifically, the outer diameter of the fixing heating roller is φ22 to φ45, the thickness of the fixing heating roller (aluminum) is 0.3 mm to 1.5 mm, and the thickness of the fixing heating roller (iron) is as low as 0.3 mm to 0.7 mm. In the heat capacity belt fixing device, this problem becomes remarkable.

  In order to prevent this problem, several techniques have been proposed. First, as a means for preventing the overshoot itself, one that stops energizing the heater before the fixing operation of the last page of the print is completed (Patent Document 1), one that has a fixing device and a fan that cools the heating member (patent) Documents 2 and 3), a heat absorbing roll for cooling the heating roller, and an air blower (Patent Document 4) are shown.

  Japanese Patent Application Laid-Open No. 2004-151561 discloses a technique for preventing a malfunction at the time of re-powering on the assumption of an overshoot when the power is off. Further, as a cooling device for the overheating prevention device, Patent Document 6 discloses that the overheating prevention device is cooled during a normal heating operation, and the cooling operation is stopped when the temperature detecting means detects an abnormally high temperature. Has been.

  However, Patent Documents 1 to 4 are all effective when the apparatus is operating normally, but consider cases where normal control does not operate, such as when the main power is turned off during operation. Not.

  Further, Patent Document 5 assumes an overshoot when power is turned on again, but does not prevent the overshoot itself. Further, since Patent Document 6 is cooled during normal operation, there is a problem that unexpected operation of the power supply or the like is not taken into consideration and the thermostat may malfunction.

  The present invention solves the above-mentioned problems of the prior art, and prevents malfunction of an excessive rise prevention means (for example, a thermostat) due to overshoot even when the main power supply is turned off during continuous paper feeding. An object is to provide an image forming apparatus.

  In order to achieve the above object, the invention described in claim 1 of the present invention is installed in the vicinity of a heating body and a non-heating body heated by the heating body, and the non-heating body temperature reaches an abnormal temperature. Sometimes, in an image forming apparatus having a fixing device provided with an over-rise prevention means for forcibly shutting off the energization of the heating body, it is inserted between the over-rise prevention means and the non-heating body, It has a heat shield that slows the temperature rise, a position drive means that moves the position of the heat shield, and a means that detects the energization status of the heating body. It is characterized by being inserted between the ascent prevention means and the non-heating body.

  The invention described in claim 2 is installed in the vicinity of the heating body and the non-heating body heated by the heating body, and forcibly energizes the heating body when the non-heating body temperature reaches an abnormal temperature. In an image forming apparatus having a fixing device including an overheat prevention unit that automatically shuts off, a heat shield that is disposed between the overheat prevention unit and the non-heating body and slows the temperature rise of the overheat prevention unit, It has a position driving means for moving the position of the overheating prevention means and a means for detecting the energization state of the heating body. When the heating body is not energized, the overheating prevention means is shielded from the non-heating body. It is characterized by moving so that the body is located.

  With this configuration, by inserting the heat shield between the overheating prevention means and the non-heating body, it is possible to slow the temperature rise of the overheating prevention means and prevent malfunction of the overheating prevention means due to overshoot. it can.

  According to a third to fifth aspect of the present invention, the power source of the position driving unit in the image forming apparatus according to any one of the first and second aspects is a power source different from the main power source of the image forming apparatus, or the image forming apparatus. A battery connected to the apparatus or a rechargeable battery charged by a main power source of the image forming apparatus.

  With this configuration, even when the main power is turned off during continuous paper feeding or when a power failure occurs, the heat shield can be inserted between the overheating prevention means and the non-heating body, and the temperature of the overheating prevention device By slowing the rise, it is possible to prevent malfunction of the excessive rise prevention means due to overshoot.

  According to the sixth and seventh aspects of the present invention, the position driving means in the image forming apparatus of the first, third, and fifth aspects detects that the heating body is not energized and that the temperature is higher than a predetermined temperature of the non-heating body. Only when the heat shield is moved, the cooling operation is performed by inserting the heat shield and inserting between the overheating prevention means and the non-heating body, or the position driving means in the image forming apparatus according to claim 2 energizes the heating body. Cooling operation in which the overheat prevention means is moved so that the heat shield plate is positioned between the overheat prevention means and the non-heating body only when it is not detected and a predetermined temperature or more of the non-heating body is detected. It is characterized by performing.

  With this configuration, during the on / off control of the heating body in normal temperature control, the heat shield plate and the excessive rise prevention plate do not move, and noise associated with the movement of the heat shield plate and the excessive rise prevention plate is prevented. Can do.

  In the invention described in claim 8, the position driving means in the image forming apparatus according to claims 6 and 7 detects a temperature equal to or higher than the second predetermined temperature of the non-heating body higher than the first predetermined temperature at which the cooling operation is performed. Sometimes, the cooling operation is stopped.

  With this configuration, the temperature of the heating body is detected, and when the heating body is over a predetermined temperature at which the runaway of the heating body is considered, by stopping the cooling operation, even if an abnormal temperature rise of the heating body occurs due to a failure of the current sensor, It is possible to reliably operate the thermostat and prevent abnormal heating.

  Further, the invention described in claims 9 and 10 is installed in the vicinity of the heating body heated by the DC heater or the AC heater and the non-heating body heated by the heating body, and the non-heating body temperature has reached an abnormal temperature. Sometimes, in an image forming apparatus having a fixing device provided with an overheating prevention means for forcibly shutting off the energization of the heating body, the image forming apparatus is disposed between the overheating prevention means and the non-heating body, A heat shield that slows the temperature rise, and a position driving means that moves the position of the overheating prevention means. The position driving means is connected to the non-heating body when the heating body is energized. It is a solenoid connected in series with a heating body that is moved to a position without a heat shield between them.

  With this configuration, even if the power supply is suddenly turned off during paper feeding and the temperature of the heating element rises due to overshoot, the overheating prevention means does not operate. Occurrence of stop time due to replacement of the ascent prevention means can be prevented, and this can be achieved with a simple configuration.

  According to the present invention, the position drive means can operate even when the main power supply is turned off or a power failure occurs, and the malfunction prevention means due to overshoot can be prevented, and during normal temperature control, The noise associated with the movement of the heat shield plate is prevented, and even if an abnormal temperature rise occurs due to a failure of the current sensor or the like, the thermostat can be reliably operated to prevent the abnormal heating.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to Example 1 of Embodiment 1 of the present invention. The figure which shows the heat shield in the position B of the fixing device in the first embodiment. The figure which shows the heat shield in the position A of the fixing device in the first embodiment. The figure which shows the thermostat in the position B of another fixing apparatus in the present Example 1. The figure which shows the thermostat in the position A of another fixing apparatus in the present Example 1. 1 is a diagram illustrating a schematic configuration of another image forming apparatus according to the first exemplary embodiment. Diagram showing the relationship between the fixing heating roller temperature and the thermostat temperature when an overshoot occurs immediately after the transfer paper passes continuously FIG. 6 is a diagram illustrating another configuration example 1 of the fixing device according to the first exemplary embodiment. FIG. 10 is a diagram illustrating another configuration example 2 of the fixing device according to the first exemplary embodiment. FIG. 10 is a diagram illustrating another configuration example 3 of the fixing device according to the first exemplary embodiment. 1 is a diagram illustrating a schematic configuration of an image forming apparatus in Example 2 of Embodiment 1. Diagram showing the relationship between the fixing heating roller temperature and the thermostat temperature when an overshoot occurs immediately after the transfer paper passes continuously 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to Example 3 of Embodiment 1. Diagram showing the relationship between the fixing heating roller temperature and the thermostat temperature when an overshoot occurs immediately after the transfer paper passes continuously FIG. 3 is a diagram illustrating a schematic configuration of an image forming apparatus according to Example 4 of the first embodiment. FIG. 5 is a diagram illustrating a schematic configuration of an image forming apparatus according to a second embodiment of the invention. The flowchart which shows the operation | movement of the heat shield by the heat shield drive control means of this Embodiment 2. The figure which shows the relationship between the fixing heating roller temperature of the overshoot prevention rotation implementation after completion | finish of continuous paper passing, and thermostat temperature The flowchart which shows another operation | movement of the heat shield by the heat shield drive control means of this Embodiment 2. A diagram showing the temperature of the fixing heating roller and the thermostat at which the heater control runs out of control after the completion of paper feeding and the heater is continuously lit. FIG. 5 is a diagram illustrating a schematic configuration of an image forming apparatus according to a third embodiment of the present invention. FIG. 5 is a diagram illustrating a schematic configuration of another image forming apparatus according to the third embodiment. A diagram showing the configuration of a conventional fixing device Diagram showing overshoot of fixing heating roller after continuous paper feeding Diagram showing thermostat malfunction due to overshoot after continuous paper feeding

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus in Example 1 of Embodiment 1 of the present invention. FIG. 2 is a view showing a heat shield plate at position B (non-cooling operation) in the fixing device included in the image forming apparatus, and FIG. 3 is a view showing a heat shield plate at position A (cooling operation). 2 and 3 show the state of the heat shield plate 10 during operation (movement from position B to position A or from position A to position B). Here, components having the same functions corresponding to the components described in FIG. 23 showing the conventional example are given the same reference numerals, and the same applies to the following drawings.

  As shown in FIGS. 1 to 3, a fixing roller 3 (φ52, wall thickness: 10 mm) of foamed silicon rubber and an inner portion of a fixing belt 2 (φ70) whose surface is covered with PFA (perfluoroalkoxyalkane) Includes a halogen heater 5 (1200 W) as a heating body, and an aluminum fixing heating roller 1 (φ35, wall thickness: 0.6 mm) which is a non-heating body heated by this. The fixing heating roller 1 also serves as a tension roller, and tension is applied to the fixing belt 2 by a tension spring 4.

  Above the fixing heating roller 1, a thermostat 8 serving as an excessive rise prevention means for detecting an abnormal temperature rise of the fixing heating roller 1 and shutting off the power supply to the heater 5 is disposed. As the heat shield plate position control means, the position of the heat shield plate 10 can be changed by the heat shield plate drive gear 11 and the heat shield plate drive motor 12. The heat shield plate 10 is located between the thermostat 8 and the fixing heating roller 1 (position A) when the heater 5 is not energized and shuts off the heat of the fixing heating roller 1. The temperature will not rise more than necessary.

  Further, when the heater 5 is turned on, the heat shield plate 10 moves to the position B, and the thermostat 8 is directly warmed by the heat of the fixing heating roller 1. Therefore, when the temperature rises abnormally, the temperature can be quickly raised to the operating temperature of the thermostat 8 and the power supply to the heater 5 can be cut off.

  The heat shield drive gear 11 and the heat shield drive motor 12 that move the heat shield 10 are controlled by the heat shield drive control means 13 independently of the image forming apparatus.

The process linear velocity of the specific image forming apparatus in the first embodiment is 352 mm / sec, and the productivity is 75 CPM on A4 landscape paper. In addition, the control temperature of each part during standby is the fixing heating roller: 170 ° C
Pressure roller: 150 ° C
The set temperature at the time of paper feeding is a fixing heating roller: 165 ° C
Pressure roller: 120 ° C
It is. The rated operating temperature of the thermostat 8 is 180 ° C.

  Further, as shown in FIG. 1, the image forming apparatus and the fixing apparatus operate with power supplied from a commercial power source A18 which is a main power source. The heat shield plate drive control means 13 detects the energization of the heater 5 with the current sensor 14, and when this energization stops, the heat shield plate 10 moves between the fixing heating roller 1 and the thermostat 8 (position A). . Furthermore, after moving to the position A, the heat shield plate 10 moves to the position B when a certain time (for example, 400 sec) elapses as a time until the thermostat 8 does not malfunction due to overshoot.

  4 and 5 are diagrams showing another fixing device of the first embodiment. 4 and 5, instead of the heat shield plate 10 moving between the position A and the position B shown in FIGS. 2 and 3, the upper side is covered in the vicinity of the fixing heating roller 1. The heat shield plate 10a is fixedly arranged. In order to move the thermostat 8 between the position A and the position B, an over-rise prevention plate 8a and an over-rise prevention plate driving gear 11a are provided.

  The position of the thermostat 8 can be changed by an over-rise prevention plate drive gear 11a and an over-rise prevention plate drive motor (not shown). When the heater 5 is turned off when the heater 5 is not energized, the thermostat 8 is moved to the position A where the heat shield plate 10a is sandwiched between the fixing heating roller 1 by the excessive rise prevention plate 8a, and the heat of the fixing heating roller 1 is blocked. The temperature of the thermostat 8 does not increase more than necessary.

  When the heater 5 is turned on, the thermostat 8 moves to the position B, and the thermostat 8 is directly warmed by the heat of the fixing heating roller 1. Therefore, when the temperature rises abnormally, the temperature can be quickly raised to the operating temperature of the thermostat 8 and the power supply to the heater 5 can be cut off.

  As shown in FIG. 6, the over-rise prevention plate drive gear 11a for moving the over-rise prevention plate 8a to which the thermostat 8 is attached is driven by the over-rise prevention plate drive motor 12a, and the heat shield plate drive control means 13 controls the image. It is controlled independently of the forming device.

  The image forming apparatus and the fixing apparatus operate by being supplied with power from a commercial power source A18 which is a main power source. The heat shield plate drive control means 13 detects the energization of the heater 5 with the current sensor 14, and when this energization is stopped, the heat shield plate 10 a is placed between the thermostat 8 of the overheating prevention plate 8 a and the fixing heating roller 1. Move to position A where is located. Furthermore, the excessive rise prevention plate 8a moves to the position B after a certain time (for example, 400 sec) elapses after the movement to the position A until a temperature at which the thermostat 8 does not malfunction due to overshoot.

  FIG. 7 is a graph showing the relationship between the fixing heating roller temperature and the thermostat temperature when an overshoot occurs immediately after the transfer paper is continuously passed.

  In addition to the configuration of the fixing device shown in FIGS. 2 to 5 described above, the configuration shown in FIGS. 8 to 10 may be used. As shown in FIG. 8, Example 1 may be used in which the fixing range of the transfer paper 9 is widened by using a pressure belt 6b in addition to the pressure roller 6. The fixing heating roller 1 ′ shown in FIG. Alternatively, the fixing may be performed by using the free pressure belt 6b pressed by the pressure pad 6a, and may be fixed to the pressure roller 6 shown in FIG. 10 by the fixing pad 3a. The third example of the configuration in which the fixing is performed by pressing the belt 2 may be used. The present invention can also be applied to combinations of rollers and belts for fixing and pressing other than the configuration examples shown in FIGS.

  FIG. 11 is a diagram showing a schematic configuration of the image forming apparatus in Example 2 of the first embodiment. As shown in FIG. 11, the image forming apparatus and the fixing apparatus are operated by being supplied with electric power from a commercial power source A18. In this image forming apparatus, the power supply is cut off by turning off the main switch 17.

  On the other hand, the heat shield drive control means 13 and the heat shield drive motor 12 are supplied with power by the commercial power source B19. Even if the main switch 17 is turned off, the power supply is not cut off and the heat shield 10 is moved. It is possible to prevent malfunction of the thermostat 8 due to overshoot.

  The heat shield plate drive control means 13 detects energization to the heater 5 and moves the heat shield plate 10 between the fixing heating roller 1 and the thermostat 8 (position A) when the energization is stopped. Further, after moving to the position A, the heat shield plate 10 moves to the position B after a certain time (400 sec) has elapsed.

  In the second embodiment, the fixing device shown in FIG. 6 operates similarly by moving the excessive rise prevention plate 8a. The same applies to Examples 3 and 4 described later.

  FIG. 12 is a graph showing the relationship between the fixing heating roller temperature and the thermostat temperature when an overshoot occurs immediately after the transfer paper is continuously passed.

  FIG. 13 is a diagram showing a schematic configuration of an image forming apparatus in Example 3 of Embodiment 1. As shown in FIG. 13, the image forming apparatus and the fixing apparatus are operated by being supplied with electric power from a commercial power source A18. In this image forming apparatus, the power supply is cut off by turning off the main switch 17.

  On the other hand, the heat shield plate drive control means 13 and the heat shield plate drive motor 12 are supplied with power by the battery 20 and can move the heat shield plate 10 even when the main switch 17 is turned off or a power failure occurs. A malfunction of the thermostat 8 can be prevented.

  The heat shield plate drive control means 13 detects energization to the heater 5 and moves the heat shield plate 10 between the fixing heating roller 1 and the thermostat 8 (position A) when the energization is stopped. Further, after moving to the position A, the heat shield plate 10 moves to the position B after a certain time (400 sec) has elapsed.

  FIG. 14 is a graph showing the relationship between the fixing heating roller temperature and the thermostat temperature when an overshoot occurs immediately after the transfer paper is continuously passed.

  FIG. 15 is a diagram showing a schematic configuration of an image forming apparatus in Example 4 of the first embodiment. As shown in FIG. 15, the image forming apparatus and the fixing apparatus are operated by being supplied with electric power from a commercial power source A18. In this image forming apparatus, the power supply is cut off by turning off the main switch 17.

  On the other hand, since the heat shield plate drive control means 13 and the heat shield plate drive motor 12 are supplied with power by the rechargeable battery 21, the moving operation of the heat shield plate 10 is possible even when the main switch 17 is turned off or a power failure occurs. A malfunction of the thermostat 8 due to overshoot can be prevented.

  Further, charging of the rechargeable battery 21 is controlled by the image forming apparatus control means 16 and is performed by the charging means 22 supplied with power from the commercial power source A18, so that maintenance such as battery replacement is unnecessary.

  FIG. 16 is a diagram showing a schematic configuration of an image forming apparatus in Embodiment 2 of the present invention. In the configuration of FIG. 15 showing Example 4 of Embodiment 1 described above, a temperature sensor 23 for detecting the temperature of the fixing heating roller 1 is provided in the vicinity of the fixing heating roller 1. In the following, the second embodiment will be described only with respect to differences from the first embodiment, and the same points will be omitted.

  In the case of the specific example shown in Example 1 of Embodiment 1, the heat shield plate drive control means 13 detects energization to the heater 5 by the current sensor 14 and the temperature of the fixing heating roller 1 by the temperature sensor 23. When the energization of the heater 5 is stopped and the temperature of the fixing heating roller 1 is detected to be 200 ° C. or higher, the heat shield plate 10 moves between the fixing heating roller 1 and the thermostat 8 (position A). Further, after moving to the position A, the heat shield plate 10 moves to the position B after a certain time (400 sec) has elapsed.

  FIG. 17 is a flowchart showing the operation of the heat shield plate by the heat shield drive control means of the second embodiment. As shown in FIG. 17, the heat shield drive control means 13 confirms whether or not the heater 5 is energized by the current sensor 14 (S1). In the process S1, when the heater 5 is not energized (Yes in S1), the heat shield drive control means 13 confirms the temperature of the fixing heating roller 1 by the temperature sensor 23 (S2). In the process S2, when the temperature of the fixing heating roller 1 is 200 ° C. or higher (Yes in S2), the heat shield plate 10 is moved between the fixing heat roller 1 and the thermostat 8 by the heat shield plate driving motor 12 and the heat shield plate driving gear 11. To position A (S3). After moving to the position A of the heat shield 10, it is confirmed whether or not 400 sec has passed (S 4). In process S4, when 400 seconds have passed after the movement (Yes in S4), the heat shield plate 10 is moved to the position B (S5).

  In process S1, when the heater 5 is energized (No in S1), in process S2, when the temperature of the fixing heating roller 1 is less than 200 ° C. (No in S2), the heat shield plate 10 is moved to the position B. Control goes to step S5.

  In the normal temperature control of the fixing heating roller 1, the heater 5 repeats on / off control, and the heat shield plate 10 moves depending on whether or not the heater 5 is energized. Drive noise of 12 etc. is generated. For this reason, by configuring as in the second embodiment, the heat shield plate drive control means 13 does not move the heat shield plate 10 when the temperature of the fixing heating roller 1 is less than 200 ° C. No noise is generated at times.

  FIG. 18 is a diagram showing the relationship between the fixing heating roller temperature and the thermostat temperature after normal printing (continuous paper passing) has been completed normally in the image forming apparatus.

  As a countermeasure against overshoot at the end of printing, the fixing heating roller 1 is rotated (overshoot prevention rotation) even after the completion of paper passing. As this overshoot prevention rotation, the rotation is performed for about 200 seconds after the final paper that has been continuously passed is discharged, and after this rotation, the fixing heating roller 1 is stopped. Due to this rotation operation, the overshoot is small, and the temperature of the fixing heating roller 1 is about Max 190 ° C. as shown in FIG. 18. In the case of the second embodiment, the process shown in the process S2 of the flowchart in FIG. As described above, the cooling operation for moving the heat shield plate 10 between the fixing heating roller 1 and the thermostat 8 (position A) is not performed.

  FIG. 19 is a flowchart showing another operation of the heat shield plate by the heat shield drive control means of the second embodiment. In the same way as described with reference to FIG. 16 in the flowchart of FIG. 17 described above, also in FIG. 19, the heat shield plate drive control means 13 confirms whether or not the heater 5 is energized by the current sensor 14 (S11). . In the process S11, when the heater 5 is not energized (Yes in S11), the heat shield drive control means 13 confirms the temperature of the fixing heating roller 1 by the temperature sensor 23 (S12). In the process S12, when the temperature of the fixing heating roller 1 is 200 ° C. or higher (Yes in S12), the heat shield plate 10 is moved between the fixing heating roller 1 and the thermostat 8 by the heat shield plate driving motor 12 and the heat shield plate driving gear 11. To position A (S13).

  Here, after the heat shield 10 is moved to the position A, the temperature of the fixing heating roller 1 is confirmed by the temperature sensor 23 (S14). In process S14, when the temperature of the fixing heating roller 1 is less than 300 ° C. (Yes in S14), it is confirmed whether or not 400 seconds have elapsed after moving to the position A of the heat shield plate 10 (S15). In process S15, when 400 seconds have passed after the movement (Yes in S15), the heat shield plate 10 is moved to the position B (S16).

  Further, when the heater 5 is energized in process S11 (No in S11), and in process S12, the temperature of the fixing heating roller 1 is less than 200 ° C. (No in S12), the temperature of the fixing heating roller 1 is 300 ° C. or higher. (No in S14), the process proceeds to S16 in which the heat shield plate 10 is moved to the position B.

  FIG. 20 is a diagram illustrating the fixing heating roller temperature and the thermostat temperature when the heater control runs out of control and the heater 5 of the fixing heating roller 1 is continuously lit after completion of the sheet passing.

  When the fixing heating roller temperature becomes 200 ° C. or higher, the heat shield plate 10 moves to a position A between the thermostat 8 and the fixing heating roller 1. Further, when the temperature of the fixing heating roller 1 continues to rise and when 300 ° C. or higher is detected, the heat shield plate 10 is moved to the position B and the cooling operation is stopped.

  For this reason, when the current sensor 14 is out of order, it is determined that the heater 5 of the fixing heating roller 1 has runaway due to the fact that the heater 5 is actually energized, even though the heater 5 is energized. Even if it exists, as shown in FIG. 20, the fixing heating roller temperature is 450 ° C. or less, and the thermostat 8 operates, so that it is possible to reliably prevent the problem of heating due to abnormal temperature rise.

  FIG. 21 is a diagram showing a schematic configuration of an image forming apparatus according to Embodiment 3 of the present invention. As shown in FIG. 21, the thermostat 8 is configured such that the position thereof is changed by an excessive rise prevention plate driving solenoid 8c and a spring 8b.

  When power is supplied from the DC power supply 24 to the excessive rise prevention plate drive solenoid 8c by the heater control means 15, the thermostat 8 moves to the position B where it is directly heated by the fixing heating roller 1 against the spring 8b. When the power supplied to the excessive rise prevention plate drive solenoid 8c is cut off, the thermostat 8 is moved to the position A where the heat shield plate 10a is located between the fixing heating roller 1 and the thermostat 8 by the spring 8b. .

  The excessive rise prevention plate drive solenoid 8c is driven by a DC power source, and this DC power source is connected in series with a DC heater 5a using a DC 24V power source. With this connection, the over-rise prevention plate drive solenoid 8c is supplied with power only when the heater 5a is energized and moves to the position B.

  FIG. 22 is a diagram showing a schematic configuration of another image forming apparatus according to the third embodiment. In FIG. 22, the thermostat 8 is configured such that its position is changed by the rise prevention plate driving solenoid 8c and the spring 8b in the same manner as the configuration of FIG. 21 described above. When power is supplied to the overheat prevention plate driving solenoid 8c, the thermostat 8 moves to the position B where it is directly heated by the fixing heating roller 1, and the power supply to the overheat prevention plate driving solenoid 8c is cut off. In this case, the thermostat 8 is moved to the position A where the heat shield plate 10 a is located between the fixing heating roller 1 and the thermostat 8 by the spring 8 b.

  As shown in FIG. 22, the over-rise prevention plate drive solenoid 8c is driven by a DC power source. This DC power source is a voltage conversion transformer 24a and a diode connected in series with an AC heater 5 using an AC 100V power source. 24b, which is converted to DC24V by the smoothing capacitor 24c is used. With this connection, power is supplied to the over-rise prevention plate drive solenoid 8c only when the heater 5 is energized, and can move to the position B.

  With this configuration, the thermostat 8 does not operate even when the power is suddenly turned off during the passage of the paper and the heating body temperature rises due to overshoot, so that the thermostat 8 can operate quickly after the power is restored. The apparatus such as 8 replacement can prevent the stop time from occurring with a simple configuration.

  In the image forming apparatus according to the present invention, even if the main power supply is turned off or a power failure occurs, the position driving unit of the heat shield and the over-rise prevention unit operates to prevent malfunction of the over-rise prevention unit due to overshoot. It is useful as a heat fixing device used for a copying machine, a facsimile, a printer, and the like.

1, 1 'Fixing heating roller 2 Fixing belt 3 Fixing roller 3a Fixing pad 4 Tension springs 5, 5a, 7 Heater 6 Pressing roller 6a Pressing pad 6b Pressing belt 8 Thermostat 8a Over-rise prevention plate 8b Spring 8c Over-rise prevention Plate drive solenoid 9 Transfer paper 10, 10a Heat shield plate 11 Heat shield plate drive gear 11a Over-rise prevention plate drive gear 12 Heat-shield plate drive motor 12a Over-rise prevention plate drive motor 13 Heat shield plate drive control means 14 Current sensor 15 Heater Control means 16 Image forming apparatus control means 17 Main switch 18 Commercial power source A
19 Commercial power supply B
20 Battery 21 Rechargeable Battery 22 Charging Means 23 Temperature Sensor 24 DC Power Supply 24a Transformer 24b Diode 24c Smoothing Capacitor

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

Claims (10)

An overheating prevention means that is installed in the vicinity of a heating body and a non-heating body that is heated by the heating body, and that forcibly cuts off power to the heating body when the non-heating body temperature reaches an abnormal temperature; In an image forming apparatus having a fixing device comprising:
A heat shield inserted between the overheat prevention means and the non-heated body and slowing the temperature rise of the overheat prevention means; a position driving means for moving the position of the heat shield; and energization of the heating body An image forming apparatus comprising: means for detecting a situation; and when the heating body is not energized, the heat shield is inserted between the overheating prevention means and the non-heating body. An overheating prevention means that is installed in the vicinity of a heating body and a non-heating body that is heated by the heating body, and that forcibly cuts off power to the heating body when the non-heating body temperature reaches an abnormal temperature; In an image forming apparatus having a fixing device comprising:
A heat shield that is disposed between the overheating prevention means and the non-heating body and slows the temperature rise of the overheating prevention means; a position driving means that moves the position of the overheating prevention means; and And a means for detecting an energization state, and when the heating body is not energized, the overheat prevention means moves so that the heat shield is positioned between the non-heating body. Image forming apparatus.   3. The image forming apparatus according to claim 1, wherein a power source of the position driving unit is a power source different from a main power source of the image forming apparatus.   3. The image forming apparatus according to claim 1, wherein a power source of the position driving unit is a battery connected to the image forming apparatus.   3. The image forming apparatus according to claim 1, wherein a power source of the position driving unit is a rechargeable battery charged by a main power source of the image forming apparatus.   A cooling operation in which the position driving means moves the heat shield only when the heating body is not energized and detects a temperature above the non-heating body, and is inserted between the overheating prevention means and the non-heating body. The image forming apparatus according to claim 1, wherein:   Only when the position driving means detects that the heating body is not energized and the temperature of the non-heating body is equal to or higher than the predetermined temperature, the over-rise prevention means is provided between the over-heating prevention means and the non-heating body. The image forming apparatus according to claim 2, wherein a cooling operation is performed so that the plate is positioned.   The said cooling operation is stopped when the said position drive means detects more than the 2nd predetermined temperature of the non-heating body higher than the 1st predetermined temperature which performs cooling operation, The said cooling operation is stopped. Image forming apparatus. Installed in the vicinity of a heating body heated by a DC heater and a non-heating body heated by the heating body, and forcibly cuts off the power supply to the heating body when the temperature of the non-heating body reaches an abnormal temperature. In an image forming apparatus having a fixing device provided with an excessive rise prevention means,
A heat shield disposed between the over-rise prevention means and the non-heated body and slowing the temperature rise of the over-rise prevention means; and a position driving means for moving the position of the over-rise prevention means, A solenoid connected in series with the heating body, wherein the position driving means moves the over-rise prevention means to a position without the heat shield between the non-heating body and the energization of the heating body. An image forming apparatus. Installed in the vicinity of a heating body heated by an AC heater and a non-heating body heated by the heating body, and forcibly cuts off the power supply to the heating body when the temperature of the non-heating body reaches an abnormal temperature. In an image forming apparatus having a fixing device provided with an excessive rise prevention means,
A heat shield disposed between the over-rise prevention means and the non-heated body and slowing the temperature rise of the over-rise prevention means; and a position driving means for moving the position of the over-rise prevention means, A solenoid connected in series with the heating body, wherein the position driving means moves the over-rise prevention means to a position without the heat shield between the non-heating body and the energization of the heating body. An image forming apparatus.

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