JP2006172781A - Heating device and image forming device mounting it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always grasp temperature of a body to be heated accurately, to maintain an excessive temperature rise preventing device at a low temperature at the time of a normal heating operation, and to make it work properly at the time when the temperature of the body to be heated rises to an abnormal temperature. <P>SOLUTION: The heating device 30 provided as a heating means of a fixation part 20 is equipped with a halogen lamp 31 as a heating body, a temperature detection means 32, the excessive temperature rise preventing device 33, a cooling means 34 and a control means 35. At the time of a normal heating operation for a thermal roller 21 which is the body to be heated, the control means 35 controls the cooling means 34 and refrigerates the excessive temperature rise preventing device 33 and maintains it at a low temperature. When the temperature detection means 32 detects that surface temperature of the thermal roller 21 reaches a predetermined temperature, the control means 35 switches off driving of the cooling means 34 and stops cooling of the excessive temperature rise preventing device 33 by the cooling means 34. Thus, the temperature of excessive temperature rise preventing device 33 rapidly rises and the excessive temperature rise preventing device 33 forcibly breaks power distribution to the halogen lamp 31. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heating device provided with an excessive temperature rise prevention means. The present invention also relates to an image forming apparatus in which the heating device is mounted as a heating unit for a fixing unit.

  In an electrophotographic image forming apparatus typified by a copying machine or a printer, a thermal fixing method is widely used as a method for fixing an unfixed toner image transferred onto a sheet by a transfer unit. In this heat fixing method, two rotating members composed of a roller and a belt are pressed against each other to form a nip, and a heating member is arranged in one or both of the rotating members to arrange the rotating member. The toner is fixed to the paper by heating and inserting the paper carrying the unfixed toner image in the nip.

  As the fixing section of the heat fixing system, a roller that directly contacts a toner image of a sheet is used as a heat roller, and a heating body such as a halogen lamp is provided on the heat roller. The built-in one is common. In order to obtain stable fixing properties, the surface temperature of the heat roller is monitored by temperature detection means comprising a temperature sensor such as a thermistor, and the surface temperature of the heat roller is controlled by controlling the amount of heat generated by a heating element such as a halogen lamp. Maintain at the proper temperature.

In such a heating device that can be used as a heating unit of the fixing unit, there is a concern that a problem may occur that the heated object unintentionally reaches a high temperature. When the heated body reaches an abnormally high temperature, the heated body may be damaged or the components around the heated body may be adversely affected. Further, in the fixing unit as described above, the paper inserted through the nip may be burned out. In order to solve such a problem, when the temperature of the object to be heated rises to an abnormal temperature, heating with an excessive temperature rise prevention means constituted by a thermostat or the like forcibly cuts off the power to the heating element. An apparatus is proposed, an example of which can be seen in US Pat.
JP 2004-133444 A (page 6-16, FIG. 11)

  In recent years, the image forming apparatus is required to shorten the warm-up time of the fixing unit from the viewpoint of energy saving. As a result, the application of means such as thinning of the heat roller and the use of a high-speed rising heater is being promoted. However, when the thickness of the heat roller is reduced, the heat capacity of the roller is reduced, and so-called overshoot and undershoot that cannot maintain the surface temperature of the heat roller at an appropriate temperature become severe. If the change in the surface temperature of the heat roller becomes severe in this way, the excessive temperature rise prevention means constituted by a thermostat or the like will be adversely affected, and there is a risk that the energization of the heating body will be forcibly interrupted unintentionally. is there. Therefore, a heating device that keeps the excessive temperature rise prevention means at a low temperature during normal heating operation of the fixing unit and forcibly cuts off the power supply to the heating body such as a halogen lamp when the surface temperature of the heat roller rises to an abnormal temperature. Is required.

  In the fixing device (heating device) described in Patent Document 1, a thermostat (overheating prevention means) is cooled by a fan during a normal heating operation of the fixing unit, and an abnormality occurs in the operation of the fan. Thus, there has been proposed a method of forcibly shutting off the energization to the heating means (heating body) by operating the thermostat by stopping the rotation of the fan. However, while the fan is rotating, the fan always cools the thermostat, and the thermostat itself monitors the surface temperature of the fixing roller, which is the object to be heated. It may not be possible to grasp. Accordingly, the heating means is cut off before the fixing roller reaches the surface temperature at which fixing can be performed, or even if the surface temperature of the fixing roller reaches a temperature at which heating by the heating means should be stopped, the heating is continued to be high. There is a risk that the timing of operating the thermostat will be wrong.

  Further, in the fixing device described in Patent Document 1, the thermostat is cooled away from the surface of the fixing roller by the negative pressure generated by driving the fan during the normal heating operation of the fixing unit, and there is an abnormality in the operation of the fan. A method has also been proposed in which the thermostat approaches the fixing roller and becomes hot due to the fan rotation being stopped due to, for example, the occurrence of this, and the energization to the heating means is forcibly cut off. However, according to this method, when the rotation of the fan stops and the thermostat approaches the fixing roller, there is a possibility that the temperature is shifted from a predetermined place and the accurate temperature cannot be grasped.

  The present invention has been made in view of the above points, and in a heating apparatus provided with an excessive temperature rise prevention means for forcibly cutting off energization to a heating body when an abnormality occurs, the temperature of the object to be heated is set. Heating that allows the temperature rise prevention means to be kept at a low temperature during normal heating operation, and allows the temperature rise prevention means to function properly when the temperature of the object to be heated rises to an abnormal temperature, while always accurately grasping An object is to provide an apparatus. It is another object of the present invention to provide an image forming apparatus equipped with such a heating device.

  In order to solve the above-described problems, the present invention controls a heating body, temperature detection means for detecting the temperature of a heated body heated by the heating body, and information received from the temperature detection means. In the heating apparatus, comprising: a control means for controlling and an excessive temperature rise prevention means for forcibly shutting off the energization to the heating body when the temperature of the heated body reaches an abnormal temperature. The control means controls the cooling means to cool the excessive temperature rise prevention means during a normal heating operation by the heating body, and the heated body has reached a predetermined temperature. When the temperature detecting means detects this, cooling of the excessive temperature rise preventing means is stopped.

  In the present invention, the heating device is mounted on the image forming apparatus as a heating unit of the fixing unit.

  According to the configuration of the present invention, when the temperature of the heated body reaches an abnormal temperature, in the heating device including the excessive temperature rise preventing means for forcibly cutting off the energization to the heated body, the over temperature rise preventing means is A cooling means for cooling, and the control means controls the cooling means to cool the excessive temperature rise prevention means during a normal heating operation by the heating body, and the temperature detection means indicates that the heated body has reached a predetermined temperature. Since the cooling of the overheating prevention means is stopped when detected, the overheating prevention means can be cooled while monitoring the temperature of the heated object by the temperature detection means. That is, the temperature detection of the object to be heated is not affected by cooling, and the temperature of the object to be heated can be accurately grasped by the temperature detection means, so that the timing for operating the overheat prevention means is not mistaken. Therefore, it is possible to keep the excessive temperature rise prevention means at a low temperature during a normal heating operation, and allow the excessive temperature rise prevention means to function suitably when the temperature of the object to be heated rises to an abnormal temperature.

  In the present invention, since the heating device is mounted on the image forming apparatus as a heating unit of the fixing unit, the normal heating operation is performed while always accurately grasping the temperature of the heated object such as a heat roller. A high-performance image forming apparatus provided with a fixing unit that sometimes maintains an excessive temperature rise prevention means at a low temperature, and allows the excessive temperature rise prevention means to function properly when the temperature of the heated object rises to an abnormal temperature. Obtainable.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. It is assumed that the heating device according to this embodiment is used as a heating unit that heats the heat roller in the fixing unit of the image forming apparatus.

  First, an image output operation of an image forming apparatus equipped with a heating device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic vertical sectional front view showing an image forming apparatus. Note that solid line arrows in the figure indicate the sheet conveyance path and conveyance direction, and alternate long and short dash line arrows indicate the laser beam L.

  As shown in FIG. 1, a paper feeding unit 2 is disposed at the lower part of the image forming apparatus 1. Inside the sheet feeding unit 2, sheets P such as cut paper before printing are stacked and accommodated, and the sheets P are separated and sent out one by one.

  A paper transport unit 3 is provided inside the image forming apparatus 1 and on the left side of the paper feed unit 2. The paper P sent out from the paper supply unit 2 is conveyed vertically upward along the side surface of the image forming apparatus 1 by the paper conveyance unit 3 and reaches a transfer unit 8 described later.

  On the other hand, a document feeding unit 4 is provided on the upper surface of the image forming apparatus 1, and a document image reading unit 5 is provided below the document feeding unit 4. When a user copies a document, a document on which an image such as a character, a figure, or a pattern is drawn is stacked on the document feeding unit 4. The document feeding unit 4 separates the documents one by one and sends the document, and the document image reading unit 5 reads the image data. The information of the image data is sent to the laser irradiation unit 6 disposed above the paper feeding unit 2 and in the center of the image forming apparatus 1. The laser beam L controlled based on the image data is irradiated by the laser irradiation unit 6 toward the image forming unit 7 described later.

  An image forming unit 7 and a transfer unit 8 are provided above the paper transport unit 3 and to the left of the laser irradiation unit 6. In the image forming unit 7, an electrostatic latent image of the document image is created by the laser light L irradiated by the laser irradiation unit 6. A toner image is formed from the electrostatic latent image, and the toner image is transferred by the transfer unit 8 to the pre-printing paper P sent in synchronization by the paper transport unit 3.

  A fixing unit 20 is provided above the transfer unit 8. The paper P carrying the unfixed toner image in the transfer unit 8 is sent to the fixing unit 20, and the toner image is heated and melted by the heat roller heated by the heating device 30 and fixed.

  A branching section 9 is provided above the fixing section 20. The paper P discharged from the fixing unit 20 is discharged from the branching unit 9 to a paper discharge tray 10 provided in the cylinder of the image forming apparatus 1 when double-sided printing is not performed.

  The discharge port portion from which the paper P is discharged from the branch portion 9 toward the paper discharge tray 10 functions as the switchback portion 11. When performing duplex printing, the switchback unit 11 switches the transport direction of the paper P discharged from the fixing unit 20. Then, the sheet P is sent downward through the fixing unit 20 and the left side of the transfer unit 8, and is sent again to the transfer unit 8 through the sheet transport unit 3.

  Next, a detailed configuration of the fixing unit 20 provided with the heating device 30 will be described with reference to FIGS. 2 and 3. FIG. 2 is an enlarged schematic vertical sectional view of the fixing unit, and FIG. 3 is a perspective view of the fixing unit. In FIG. 2, white arrows indicate the direction of air movement.

  As shown in FIG. 2, the fixing unit 20 includes a heat roller 21 and a pressure roller 22. The heat roller 21 and the pressure roller 22 are brought into pressure contact with each other with a predetermined pressure, and form a fixing nip having a predetermined width in the sheet conveyance direction. The sheet P carrying unfixed toner passes through the fixing nip.

  The heat roller 21 is driven to rotate by driving means (not shown). The pressure roller 22 rotates according to the rotation of the heat roller 21 by being in contact with the heat roller 21. In a normal fixing operation, the heat roller 21 is rotated clockwise and the pressure roller 22 is counterclockwise so as to fix the unfixed toner on the surface of the sheet P while conveying the sheet P from below to above in FIG. Rotate.

  The heat roller 21 has a diameter of 40 mm and includes an elastic member layer on the surface of a core material such as an aluminum tube. The elastic member layer is made of silicon rubber and has a thickness of 2 mm. A release layer is provided in close contact with the surface of the elastic member layer to improve smoothness and toner release properties. For the release layer, a fluorine-based resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) is used, and the layer is provided by applying a paint or covering the tube. A PFA tube has a thickness of 60 μm, and a fluororesin paint has a thickness of 25 μm.

  The pressure roller 22 is provided with sponge silicon rubber constituting an elastic member layer on the outside of a cored bar made of stainless steel.

  As shown in FIGS. 2 and 3, a heating device 30 is provided in the vicinity of the heat roller 21. The heating device 30 includes a halogen lamp 31 that is a heating body, a temperature detection unit 32, an excessive temperature rise prevention unit 33, a cooling unit 34, and a control unit 35.

  The halogen lamp 31 that is a heating body is disposed inside the heat roller 21 that is a heated body, and heats the heat roller 21 from the inside. The halogen lamp 31 has a rod shape extending in the axial direction of the heat roller 21, and two halogen lamps 31 are provided. The heat generated from the halogen lamp 31 is transmitted through the core material and the elastic member layer of the heat roller 21 and reaches the surface, and the heat of the surface of the heat roller 21 melts the unfixed toner carried on the paper P.

  As shown in FIG. 3, the temperature detection means 32 is disposed outside the heat roller 21 and at a substantially central portion in the axial direction of the heat roller 21. The temperature detection means 32 is configured by a thermistor that is a temperature sensor, and the temperature detection unit is in contact with the surface of the heat roller 21. Thereby, the temperature detection means 32 detects the surface temperature of the heat roller 21 which is a heated object.

  Similar to the temperature detection unit 32, the excessive temperature rise prevention unit 33 is disposed outside the heat roller 21 and at a substantially central portion in the axial direction of the heat roller 21. The excessive temperature rise prevention means 33 is constituted by a thermostat, and its temperature detection part is arranged at a predetermined distance from the surface of the heat roller 21. The excessive temperature rise prevention means 33 is electrically connected in series between the halogen lamp 31 and its power source (not shown). Bimetal is used for the temperature detection part of the excessive temperature rise prevention means 33. When the surface temperature of the heat roller 21 reaches an abnormal temperature, the bimetal is deformed and the switch is turned OFF, and the energization to the halogen lamp 31 is forcibly cut off. Is done.

  The cooling unit 34 is configured by a fan that generates an airflow, and is disposed below the fixing unit 20. The lower frame 23 of the fixing unit 20 is provided with a duct 24 that guides air upward from below the fixing unit 20 toward the excessive temperature rise prevention means 33. The cooling means 34 feeds air into the duct 24 and cools the excessive temperature rise prevention means 33.

  The control unit 35 receives information from the temperature detection unit 32 and controls the halogen lamp 31 and the cooling unit 34.

  Next, the heating operation by the heating device 30 in the fixing unit 20 will be described with reference to FIG. 4 in addition to FIGS. 2 and 3. FIG. 4 is a graph showing temperature changes between the heat roller and the excessive temperature rise prevention means. The horizontal axis in FIG. 4 indicates the time from the start of heating of the heat roller 21, and the vertical axis indicates the temperature. In the figure, the solid line H indicates the surface temperature of the heat roller 21, the solid line A indicates the temperature of the excessive temperature rise prevention means 33 of the heating device 30 of the present invention, and the solid line B indicates the temperature of the excessive temperature rise prevention means of the conventional heating device. Show. The broken line X indicates the temperature at which the overheating prevention means 33 is energized and cuts off the halogen lamp 31.

  As shown in FIG. 4, the surface temperature H of the heat roller 21 gradually increases with the start of heating, and the surface temperature H of the heat roller 21 reaches 200 ° C. in about 15 seconds. Here, the control means 35 receives the information from the temperature detection means 32 and controls the amount of heat generated by the halogen lamp 31 so that the surface temperature H of the heat roller 21 does not rise too much. Thereafter, the control unit 35 repeats ON / OFF of the halogen lamp 31, and the surface temperature H of the heat roller 21 is maintained at an appropriate temperature of about 220 ° C.

  On the other hand, in the excessive temperature rise prevention means 33, the temperature rise is moderately because it is arranged at a predetermined distance from the surface of the heat roller 21. The temperature A of the excessive temperature rise prevention means 33 is stabilized as the surface temperature H of the heat roller 21 is stabilized after about 25 seconds from the start of heating of the heat roller 21. During such a normal heating operation, the control means 35 cools the excessive temperature rise prevention means 33 by the cooling means 34, and the temperature A of the excess temperature rise prevention means 33 is maintained at about 130 ° C.

  According to FIG. 4, the temperature B of the overheating prevention means of the conventional heating device is generally higher than the temperature A of the overheating prevention means 33 of the heating device 30 of the present invention. Then, when the stable state is reached, the temperature B of the excessive temperature rise prevention means of the conventional heating apparatus becomes very close to the energization cutoff temperature X to the halogen lamp 31 of the excessive temperature rise prevention means. As a result, in the conventional heating device, there is a high possibility that the excessive temperature rise prevention means will exceed the energization cut-off temperature X to the halogen lamp 31, and the energization to the halogen lamp 31 is forcibly cut off unintentionally. There is a risk. However, in the heating device 30 of the present invention, the temperature of the excessive temperature rise prevention means 33 is maintained at a low temperature with respect to the energization cutoff temperature X to the halogen lamp 31 by the action of the cooling means 34.

  Next, a method for controlling the heating device 30 will be described with reference to FIG. FIG. 5 is a flowchart showing a method for controlling the heating device.

  When the image forming apparatus 1 is turned on, first, in step S101, the control unit 35 of the heating device 30 starts energizing the halogen lamp 31 that is a heating body, and heating of the heat roller 21 is started. At the same time, in step S102, the control means 35 drives the fan as the cooling means 34 and starts cooling the excessive temperature rise prevention means 33. Although not shown in FIG. 5, the surface temperature of the heat roller 21 is constantly monitored by the temperature detection means 32.

  When the surface temperature of the heat roller 21 reaches an appropriate temperature, the control unit 35 performs temperature control so that the surface temperature of the heat roller 21 maintains the appropriate temperature in step S103. This is done by the control means 35 receiving information from the temperature detection means 32 for detecting the surface temperature of the heat roller 21 and turning on / off the halogen lamp 31 to control the heat generation amount. During such a normal heating operation, the control means 35 cools the excessive temperature rise prevention means 33 by the cooling means 34, and the excess temperature rise prevention means 33 is maintained at a low temperature.

  During the heating operation as described above, in step S104, the control unit 35 checks whether or not the surface temperature of the heat roller 21 has reached a predetermined temperature. The “predetermined temperature” referred to here is a temperature that serves as a criterion for preventing the surface temperature of the heat roller 21 from excessively rising. Therefore, when the surface temperature of the heat roller 21 has not reached the predetermined temperature, the process returns to step S103 again, and the normal heating operation is repeated.

  In step S104, when the temperature detection unit 32 detects that the surface temperature of the heat roller 21 has reached the predetermined temperature, the process proceeds to step S105, where the control unit 35 turns off the driving of the cooling unit 34 and the cooling unit 34 is turned off. The cooling of the excessive temperature rise prevention means 33 due to is stopped. As a result, the temperature of the excessive temperature rise prevention means 33 rapidly increases, and in step S106, the excessive temperature rise prevention means 33 detects that the surface temperature of the heat roller 21 has reached an abnormal temperature, and the halogen lamp 31 is detected. Forcibly cuts off power to the. Then, printing is forcibly terminated.

  In this way, when the temperature of the heat roller 21 that is a heated body reaches an abnormal temperature, the heating device is provided with the excessive temperature rise prevention means 33 that forcibly cuts off the power supply to the halogen lamp 31 that is the heated body. 30 includes a cooling means 34 for cooling the excessive temperature rise prevention means 33, and the control means 35 controls the cooling means 34 to cool the excessive temperature rise prevention means 33 during a normal heating operation by the halogen lamp 31, When the temperature detection means 32 detects that the heat roller 21 has reached a predetermined temperature, the over temperature rise prevention means 33 is stopped from cooling, so that the temperature detection means 32 monitors the temperature of the heat roller 21 while The prevention means 33 can be cooled. That is, the temperature detection of the heat roller 21 is not affected by the cooling, and the temperature detection means 32 can accurately grasp the temperature of the heat roller 21, so that the timing for operating the excessive temperature rise prevention means 33 is incorrect. Absent. Accordingly, it is possible to keep the excessive temperature rise prevention means 33 at a low temperature during a normal heating operation, and allow the excessive temperature rise prevention means 33 to function suitably when the temperature of the heat roller 21 rises to an abnormal temperature.

  In the present invention, since the heating device 30 is mounted on the image forming apparatus 1 as a heating unit for the fixing unit 20, the temperature of the heat roller 21 is always accurately grasped, and an excessive temperature rise prevention unit is normally used during a heating operation. Obtaining a high-performance image forming apparatus 1 having a fixing unit 20 capable of suitably functioning the excessive temperature rise prevention means 33 when the temperature of the heat roller 21 rises to an abnormal temperature while maintaining the temperature 33 at a low temperature. Can do.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  INDUSTRIAL APPLICABILITY The present invention can be used in a heating apparatus provided with an excessive temperature rise prevention unit that forcibly cuts off power to the heating body when the temperature of the heated body reaches an abnormal temperature.

1 is a schematic vertical sectional front view of an image forming apparatus equipped with a heating device according to an embodiment of the present invention. It is a model vertical cross-section enlarged view of a fixing part. It is a perspective view of a fixing unit. It is a graph which shows the temperature change of a heat roller and an excessive temperature rise prevention means. It is a flowchart which shows the control method of a heating apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Fixing part 21 Heat roller (to-be-heated body)
30 Heating device 31 Halogen lamp (heating body)
32 Temperature detection means 33 Over temperature rise prevention means 34 Cooling means 35 Control means

Claims (2)

A heating body, temperature detecting means for detecting the temperature of the heated body heated by the heating body, control means for receiving the information from the temperature detecting means and controlling the heating body, and the temperature of the heated body In a heating apparatus provided with an excessive temperature rise prevention means for forcibly cutting off the energization to the heating body when an abnormal temperature is reached,
A cooling means for cooling the overheating prevention means; and the control means controls the cooling means to cool the overheating prevention means during a normal heating operation by the heating body, so that the heated object When the temperature detecting means detects that the temperature has reached a predetermined temperature, the cooling of the excessive temperature rise preventing means is stopped.   An image forming apparatus comprising the heating device according to claim 1 mounted as a heating unit of a fixing unit.

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