JP4928293B2 - Fixing device - Google Patents

Description

The present invention, electronic photocopiers, relates to a fixing apparatus mounted on an image forming apparatus such as an electrophotographic printer (fixing device).

As a fixing device (fixing device) mounted on an electrophotographic copying machine or printer, a heater having a heating element on a ceramic substrate, a flexible member that moves while contacting the heater, and a flexible member There are some which have a pressure roller which forms a heater and a nip part via. Patent Documents 1 and 2 describe this type of fixing device. The recording material carrying the unfixed toner image is heated while being nipped and conveyed by the nip portion of the fixing device, whereby the image on the recording material is heated and fixed on the recording material. This fixing device has an advantage that the time required for starting energization of the heater and raising the temperature to the fixable temperature is short. Therefore, a printer equipped with this fixing device can shorten the time (FPOT: first printout time) after the printer command is input until the first image is output. This type of fixing device also has an advantage that power consumption during standby for waiting for a print command is small.

  By the way, when a small-size recording material is continuously printed at the same print interval as a large-size recording material with a printer equipped with a fixing device using a flexible member, the area where the recording material of the heater does not pass (non-sheet passing area) Is known to increase excessively (so-called non-sheet passing portion temperature increase). If the non-sheet passing area of the heater is excessively heated, the holder and the pressure roller that hold the heater may be damaged by heat.

  Therefore, a printer equipped with the above fixing device has a control to widen the print interval when continuously printing a small size recording material than when continuously printing a large size recording material, and overheats the non-sheet passing area of the heater. Keeping the temperature down.

  However, the control to increase the print interval is to reduce the number of output sheets per unit time, so-called throughput, and it is desired to suppress the number of output sheets per unit time to the same level or slightly less than the case of a large size recording material.

  Therefore, conventionally, the heater of the fixing device has been improved.

  Patent Documents 3, 4, and 5 propose heaters that can suppress excessive temperature rise in the non-sheet passing region. An example of the heater is shown in FIG.

  The heater 23 is provided with conductive portions 29 and 30 along the longitudinal direction of the substrate 27 on one end side and the other end side in the lateral direction (width direction) orthogonal to the longitudinal direction of the elongated substrate 27, respectively. A heating element 26 having a PTC (positive temperature coefficient of resistance) characteristic is provided between the conductive portions 29 and 30 along the longitudinal direction of the substrate 27. The heating element 26 generates heat by energizing the conductive portions 29 and 30 through the power supply electrodes 29a and 30a.

In the above heater, when a small size recording material is passed through an area (large size paper passing area) through which a large size recording material used in a printer passes, an area (small size) through which the small size recording material passes. A non-paper passing area is generated outside the size paper passing area). In the small-size sheet passing area, the recording material is deprived of heat, so that the heat is relatively lowered. However, in the non-sheet passing area, the recording material is not deprived of heat, and the temperature rises. However, as the heat is generated, the resistance of the heating element increases and the effect of suppressing the heat generation works, so that the temperature increase in the non-sheet passing region can be suppressed.
JP 2000-173752 A Japanese Patent Laid-Open No. 2001-100556 Japanese Patent Laid-Open No. 5-19652 JP 2005-209493 A JP 2005-234540 A

  In the above heater, if the heater cracks in the short direction of the substrate due to thermal stress at abnormal temperature rise or mechanical stress due to impact etc., the conductive part and the heating element may be disconnected in the longitudinal direction of the substrate. is there. In that case, if the conductive part and the heating element remain between the electrode and the disconnection point, an energization path is formed, and thus the heating element generates heat by energizing the conductive part.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device capable of detecting energization to a heating element when a conductive portion and the heating element are disconnected in the longitudinal direction of the substrate.

The configuration for achieving the above object is as follows:
A cylindrical fixing film;
A first conductive portion provided along the longitudinal direction of the substrate, a second conductive portion provided along the longitudinal direction of the substrate, and the first conductive portion along the longitudinal direction of the substrate. A heating element connected between the conductive part and the second conductive part, a first electrode electrically connected to the first conductive part and connected to the power feeding connector, and the second conductive part electrically A second electrode to which a power feeding connector is connected, and the first electrode and the second electrode are provided at the end of the same side in the longitudinal direction of the substrate, A heater in contact with the inner surface;
A pressure roller that forms a fixing nip portion that sandwiches and conveys a recording material carrying an image together with the heater through the fixing film in a direction perpendicular to the longitudinal direction;
A safety element that senses the temperature of the heater and shuts off the power to the heating element when the heater is abnormally heated;
In a fixing device having
The safety element is provided in an end portion of the heating element on the side where the first and second electrodes are provided in the longitudinal direction.

According to the present invention, it is possible to provide a fixing device that can detect energization of a heating element when the conductive portion and the heating element are disconnected in the longitudinal direction of the substrate.

  The present invention will be described with reference to the drawings.

(1) Example of Image Forming Apparatus Figure 8 is a block schematic drawing of an example of an image forming apparatus capable of mounting the constant Chakusochi engagement Ru in the present invention. This image forming apparatus is a laser beam printer using a transfer type electrophotographic process.

  Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier, which is rotated at a predetermined peripheral speed in the direction of an arrow. The photosensitive drum 1 is configured by forming a photosensitive material such as OPC or amorphous silicon on a cylindrical substrate such as aluminum or nickel.

  The outer peripheral surface (surface) of the rotating photosensitive drum 1 is uniformly charged by a charging roller 2 as charging means. Next, the uniformly charged surface of the photosensitive drum 1 is subjected to scanning exposure with a laser beam L modulated in accordance with image information output from a laser beam scanner 3 serving as an image exposure unit. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1. This electrostatic latent image is developed (visualized) as a toner image by the developing device 24 with toner (developer).

  On the other hand, the recording material P as a material to be heated is separated and fed one by one from the feeding cassette 5 by the feeding roller 6 and sent to the registration roller 7. The recording material P is synchronized with the toner image formed on the surface of the photosensitive drum 1 by the registration roller 7 and is introduced into the transfer nip T formed by the photosensitive drum 1 and the transfer roller 9 through the sheet path 8a. The That is, when the leading edge of the toner image on the surface of the photosensitive drum 1 reaches the transfer nip T, the registration roller 7 causes the recording material P so that the leading edge of the recording material P just reaches the transfer nip T. Is controlled.

  The recording material P introduced into the transfer nip T is nipped and conveyed by the transfer nip T. During this time, a transfer bias having a polarity opposite to that of toner is applied to the transfer roller 9 from a transfer bias application power source (not shown). The toner image on the surface of the photosensitive drum 1 is electrostatically transferred onto the recording material P surface by the action of the transfer bias.

  The recording material P that has received the transfer of the toner image at the transfer nip T is separated from the surface of the photosensitive drum 1 and conveyed to the fixing device 11 through the sheet path 8b. The fixing device 11 heats and fixes the toner image on the surface of the recording material P. The recording material P exiting the fixing device 11 is guided to the sheet path 8c side and is discharged from the discharge port 13 onto the discharge tray.

  After the transfer of the toner image, the surface of the photosensitive drum 1 is cleaned by the cleaning device 10 after removal of transfer residual toner, paper dust, and the like, and is repeatedly used for image formation.

(2) Fixing Device FIG. 2 is a vertical cross-sectional model view of an example of the fixing device 11. FIG. 3 is a schematic cross-sectional view of the fixing device 11. FIG. 4 is a view of the fixing device 11 as viewed from the recording material introduction side.

  In the following description, with respect to the fixing device or the members constituting the fixing device, the longitudinal direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The short side direction is a direction parallel to the recording material conveyance direction on the surface of the recording material.

Also relates to a heater as a heating body shown in this embodiment, in order that the conventional heater and configuration Naruue differences can be readily appreciated, the same members and parts as the conventional heaters are denoted by the same reference numerals Yes.

  The fixing device 11 shown in the present embodiment includes a ceramic heater 23 as a heating body, a fixing film 22 as a flexible member, a stay 21 as a guide member, and a pressure roller 24 as a pressure member. Have. The stay 21, the film 22, the heater 23, and the pressure roller 24 are all elongated members in the longitudinal direction.

  The stay 21 is formed in a vertical cross-sectional saddle shape using a predetermined material having heat resistance and rigidity. The stay 21 holds a heater 23. The film 22 is formed endless (cylindrical) by a heat resistant film. The film 22 is fitted on the stay 21. The inner peripheral length of the film 22 and the outer peripheral length of the stay 21 are made larger by about 3 mm for the film 22, for example. Therefore, the film 22 is externally fitted to the stay 21 with a margin in circumference. A lubricant (not shown) is interposed between the inner peripheral surface of the film 22 and the outer peripheral surface of the stay 21. This reduces the sliding resistance of the film 22 that rotates while contacting the outer peripheral surface of the stay 21. As the lubricant, PFPE (perfluoropolyether) grease thickened with fluororesin PTFE is used.

  Each member will be described in more detail.

1) Fixing Film In the film 22, in order to reduce the heat capacity and improve the quick start property, the film thickness is set to 100 μm or less, preferably 50 μm or less to 20 μm or more. As the material of the film 22, a heat resistant single layer film such as PTFE, PFA, FEP or the like, or a composite layer in which PTFE, PFA, FEP, etc. are coated on the outer peripheral surface of a film such as polyimide, polyamideimide, PEEK, PES, PPS Film can be used. In this example, the film 22 was formed by coating PTFE on the outer peripheral surface of a polyimide film having a thickness of about 50 μm. The outer diameter of the film 22 was 18 mm.

2) Stay The stay 21 can be composed of a high heat resistant resin such as polyimide, polyamideimide, PEEK, PPS, liquid crystal polymer, or a composite material of these resins with ceramics, metal, glass, or the like. In this embodiment, a liquid crystal polymer is used, and the liquid crystal polymer is injected into a mold and molded to form a vertical cross-sectional shape. Both ends of the stay 21 in the longitudinal direction are held by a pair of side plates (not shown) of the fixing device 11. A concave groove 21a is provided along the longitudinal direction on the lower surface of the stay 21 on the pressure roller 24 side, and the heater 23 is held by the groove 21a.

3) Pressure roller The pressure roller 24 includes a cored bar 24a, an elastic layer 24b provided around the cored bar 24a, and an outermost release layer 24c provided around the elastic layer 24b. And having. The pressure roller 24 is rotatably held by bearings 32L and 32R at both ends in the longitudinal direction of the cored bar 24a on the side plate pair of the fixing device 11. In this embodiment, the core metal 24a is made of aluminum, the elastic layer 24b is made of silicone rubber, and the release layer 24c is made of a PFA tube having a thickness of about 30 μm. The outer diameter of the pressure roller 24 was 20 mm, and the thickness of the elastic body layer 24b was 3 mm. The pressure roller 24 arranged in parallel with the film 22 below the film 22 has both ends of the cored bar 24a pressed against the stay 21 by a pressing means such as a pressure spring. Thus, the pressure roller 24 has a predetermined width necessary for heating and fixing the unfixed toner image t on the recording material P with the film 22 interposed between the outer peripheral surface (front surface) of the pressure roller 24 and the heater 23. A nip portion N (fixing nip portion) is formed.

4) Heater FIG. 1 shows an example of the heater 23 according to this embodiment. (A) is a rear view of the heater 23, (b) is a front view of the heater 23, (c) is a cross-sectional view of the heater 23 of (b), and an example of an energization control circuit used for the heater 23. FIG.

The heater 23 has a resistance heating element 26 and a conductive portion 29 as a first conductive portion on one surface (surface on the nip portion N side) of a heat-resistant, insulating, and good heat conductive substrate 27 elongated in the longitudinal direction . This is a heating body with a low heat capacity as a whole, including the conductive portion 30 as the second conductive portion, the power supply electrode 29a as the first electrode, the electrode 30a as the second electrode, and the heat-resistant overcoat layer 28. . That is, on one surface of the substrate 27 (hereinafter referred to as the surface), conductive portions 29 and 30 are provided along the longitudinal direction of the substrate 27 on one end side and the other end side in the short direction, respectively, and between the conductive portions 29 and 30. Is provided with a heating element 26 having a PTC (positive temperature coefficient of resistance) characteristic. The power supply electrodes 29 a and 30 a are provided at one end in the longitudinal direction of the substrate 27.

The heating element 26 is obtained by forming a paste prepared by kneading ruthenium oxide, glass powder (inorganic binder), and organic binder into a line band shape on the substrate 27 by screen printing. As a material for the heating element 26, in addition to ruthenium oxide (RuO ₂ ), an electric resistance material such as silver palladium (Ag / Pd) or Ta ₂ N may be used, or a mixture thereof may be used. The resistance value of the heating element 26 was 20Ω at room temperature.

For the substrate 27, for example, a ceramic material such as alumina or aluminum nitride is used. In this embodiment, an alumina substrate having a width of 7 mm in the short side direction, a length of 270 mm in the long side direction, and a thickness of 1 mm is used. A silver screen printing pattern was used for the electrodes 29a and 30a. The overcoat layer 28 is mainly intended to ensure electrical insulation between the heating element 26 and the surface of the heater 23 and slidability between the surface of the heater 23 and the inner peripheral surface of the film 22.
The overcoat layer 28 is provided on the surface of the substrate 27 so as to cover the heating element 26, the conductive portions 29 and 30, and the electrodes 29a and 30a. In this example, a heat-resistant glass layer having a thickness of about 50 μm was used as the overcoat layer 28. In FIG. 5C, the overcoat layer 28 is omitted so that the relationship between the heating element 26 and the electrodes 29a and 30a can be easily understood.

The electrodes 29a and 30a are connected to conductive portions 29 and 30 each having a width of about 2 mm provided so as to be spaced apart from each other by a predetermined distance with respect to the short direction of the substrate 27. That is, the electrode 29 a is electrically connected to the conductive portion 29, and the electrode 30 a is electrically connected to the conductive portion 30. The electrodes 29a and 30b are for energizing the corresponding conductive portions 29 and 30, respectively. The conductive portions 29 and 30 are made of the same material as the electrodes 29a and 30a. The heating element 26 is formed about 220 mm along the longitudinal direction of the substrate 27 between the conductive portions 29 and 30 (between the conductive portions) so as to connect the conductive portions 29 and 30 to each other. The heating element 26 is supplied with power to the conductive portions 29 and 30 through electrodes 29a and 30a connected to a power supply connector (not shown) and generates heat.

  Further, the heater 23 has a temperature detection element (hereinafter referred to as a temperature detection element) 25 on the back surface of the substrate 25 (the surface opposite to the pressure roller 24). The temperature measuring element 25 is provided to detect the temperature of the heater 23. In this embodiment, an external contact type thermistor separated from the heater 23 is used as the temperature measuring element. The external contact type thermistor 25 has, for example, a heat insulating layer (not shown) provided on a support (not shown), an element of the chip thermistor is fixed on the heat insulating layer, and the element faces the back surface of the substrate 27. A structure is adopted in which the support is attached to the back surface of the substrate 27 by applying pressure with a predetermined pressure. In this example, a highly heat-resistant liquid crystal polymer was used as the support, and ceramic paper was laminated as the heat insulating layer. The external contact type thermistor 25 is disposed in the minimum size sheet passing region through which the recording material P of a predetermined size introduced into the nip portion N always passes.

  In the heater 23, the substrate 27 is fixed in the groove 21 a of the stay 21 with the surface of the substrate 27 facing downward. Thereby, the overcoat layer 28 of the heater 23 is brought into contact with the inner peripheral surface of the film 22.

(3) Heat Fixing Operation of Fixing Device When the driving gear G (FIG. 4) provided at the end of the core metal 24a of the pressure roller 24 is rotationally driven by the fixing motor M, the pressure roller 24 is moved in the direction of the arrow. Rotate to. By the rotation of the pressure roller 24, a rotational force acts on the film 22 by the frictional force between the surface of the pressure roller 24 and the surface of the film 22 at the nip portion N. With the rotational force, the film 22 is driven in the direction of the arrow around the outside of the stay 21 in the direction of the arrow at the same circumferential speed as the rotational speed of the pressure roller 24 while the inner surface of the film 22 slides in close contact with the surface of the heating body 23 at the nip N. Rotate.

  The CPU 41 (FIG. 1) as the control means turns on the triac 42 as the energization control means. As a result, the electrodes 29a and 30a of the heater 23 are energized from the AC power supply 43 through the security element 100 described later. When the heater 23 is energized through the electrodes 29a and 30a to the conductive portions 29 and 30, the entire heating element 26 generates heat and the temperature rises. The thermistor 25 detects the temperature of the substrate 27 heated in accordance with the temperature rise. The CPU 41 captures the output (detected temperature) of the thermistor 25 by A / D conversion. Based on the output from the thermistor 25, the electric power supplied to the heater 23 by the triac 42 is controlled by phase control, wave number control, or the like to control the temperature of the heater 23. That is, the CPU 41 controls the triac 42 so as to raise the heater 23 when the temperature detected by the thermistor 25 is lower than a predetermined set temperature (target temperature) and to lower the heater 23 when higher than the set temperature. As a result, the heater 23 is kept at the set temperature. In the present embodiment, the output is changed in 21 steps in increments of 5% from 0 to 100% by phase control. The output 100% indicates the output when the heater 23 is fully energized.

The recording material P is introduced into the nip portion N in a state where the temperature of the heater 23 rises to the set temperature and the rotational peripheral speed of the film 22 is stabilized by the rotation of the pressure roller 24. The recording material P is nipped and conveyed together with the film 22 in the nip portion N in the short direction perpendicular to the longitudinal direction of the substrate 27 of the heater 23, so that the heat of the heater 23 is transferred to the recording material P through the film 22. The applied unfixed toner image t on the recording material P is heat-fixed on the recording material P surface. The recording material P that has exited the nip N is separated from the surface of the film 22 and conveyed.

(4) Arrangement Mode of Safety Element to Heater FIG. 5A shows a heat generation distribution when the heater 23 is normal, and FIG. 5B shows a heat generation distribution when the heater 23 is abnormal.

  The heater 23 (see (a)) in which no heater crack or the like has occurred in the short direction of the substrate 27 is energized to the entire heating element 26 through the conductive portions 29 and 30, so the heating distribution curve of the heater longitudinal is the heating element. The temperature corresponds to the heat generation temperature of 26.

  On the other hand, in the heater 23 (see (b)) in which the heater crack or the like is generated in the short direction of the substrate 27, the conductive portions 29 and 30 and the heating element 26 are caused by the substrate destruction and the print pattern destruction due to the heater crack or the like. There is a possibility of disconnection in the longitudinal direction of the substrate 27. In this case, if the conductive portions 29 and 30 and the heating element 26 remain between the electrodes 29a and 30a and the disconnection portion, the heat generation distribution curve of the heater longitudinal becomes a temperature corresponding to the heating temperature of the heating element 26.

Therefore, in this embodiment, in order to be able to detect (sense) the energization of the heating element 26 when the conductive portions 29 and 30 and the heating element 26 are disconnected in the longitudinal direction of the substrate 27, The temperature detection type safety element 100 is provided at one end of the electrodes 29a and 30a ( the end of the heating element 26 on the side where the electrodes 29a and 30a are provided) . In particular, on the other surface of the substrate 27 (the surface opposite to the nip portion N), the security element 100 is provided at the boundary between the heating element 26 and the longitudinal end of the heating element. As a result, the thermal fuse 100 is placed in the heat generating region of the heat generating element 26 that constitutes the current-carrying path together with the conductive portions 29 and 30 regardless of where the conductive portions 29 and 30 and the heat generating element 26 are disconnected in the longitudinal direction of the substrate 27. It can be positioned reliably. In the present embodiment, the safety element 100 is a thermal fuse that responds to heat and interrupts the energization of the electrode 29a. FIG. 6 is a structural model diagram of an example of the thermal fuse 100.

  Reference numeral 131 denotes an exterior metal case of the thermal fuse 100. Reference numeral 132 denotes a first lead wire. The first lead wire 132 has a cylindrical member 133 made of an insulating ceramic at its distal end, and the case 131 is caulked by inserting the cylindrical member 133 into one end side of the case 131 and the case 131. It is insulated and secured. Reference numeral 134 denotes a second lead wire. The end of the second lead wire 134 is inserted into the other end of the case 131 and the case 131 is caulked to electrically connect with the case 131 to prevent it from coming off. 135, 136, 137, 138, 139, and 140 are respectively arranged in the case 131 sequentially from the first lead wire 132 side to the second lead wire 134 side, the first spring, the movable electrode, the disc, The second spring, disc, and temperature sensitive pellet. The first spring 135 is contracted between the cylindrical member 133 and the movable electrode 136. The second spring 138 is contracted between the disc 137 and the disc 139. The spring force of the second spring 138 is larger than that of the first spring 135. Reference numeral 141 denotes a sealing (sealing) resin portion that is coated and formed on the end surface of the case 131 on the first lead wire mounting side and the first lead wire base portion in order to maintain airtightness in the case 131.

  In the thermal fuse 100, the first spring 135 is pushed between the movable electrode 136 and the cylindrical member 133 by the tension force between the discs 137 and 139 of the second spring 138 in the normal state shown in FIG. Has been shortened. In addition, the movable electrode 136 is pressed against the tip portion of the first lead wire 132, and electrical continuity with the first lead wire 132 is maintained. Further, the temperature-sensitive pellet 140 made of an organic substance, which is a temperature-sensitive member, is received by being in contact with the tip of the second lead wire 134, and is maintained as a spacer member between the disc 139 and the tip of the second lead wire 134. It is. The movable electrode 136 has an outer peripheral edge that is in contact with the inner surface of the case 131, maintains electrical continuity with the case 131, and is movable in the axial direction within the case 131.

  In the normal state of the thermal fuse 100, the energization of the electrode 29a of the heater 23 is performed by passing the second lead wire 134, the temperature sensitive pellet 140, the disc 137, the movable electrode 136, and the first lead wire 132 connected to the power source 33. Done via.

  On the other hand, when the heater 23 runs away due to a failure of the energization control circuit and the temperature rises abnormally, the heat of the heater 23 is transmitted from the substrate 27 to the temperature-sensitive pellet 140 through the case 131. When the temperature of the temperature-sensitive pellet 140 becomes equal to or higher than a predetermined operating temperature, the temperature-sensitive pellet 140 melts or sublimates and becomes liquid or disappears as shown in FIG. Then, the second spring 138 is pushed toward the second lead wire 134 by the spring force of the first spring 135, and the movable electrode 136 is separated from the tip of the first lead wire 132. Thereby, the energization to the electrode 29a of the heater 23 is interrupted. That is, the energization to the electrode 29a can be cut off when the heater 23 is abnormally heated (runaway).

  In the thermal fuse 100, there is no difference in operating time even if the temperature sensitive pellet 140 faces the heating element 26 side of the heater 23 or the temperature sensitive pellet 140 faces the electrode 29a side of the heater 23. The direction of the thermal fuse 100 may be any direction. In this embodiment, the direction of the temperature fuse 100 is set so that the temperature-sensitive pellet 140 faces the heating element 26 side of the heater 23.

(5) Experimental Example In the following, another heater configuration capable of stopping energization at the time of runaway by providing the thermal fuse 100 will be used as a comparative example, and the heater 23 of this embodiment and how to use the heater 23 will be described. The effectiveness of is explained. In the heater of a comparative example, the same code | symbol is attached | subjected to the member and part which has the same function as the heater 23 of a present Example.

  The cost, compactness, and strength of PTC characteristics were evaluated in three stages of ○, Δ, and × from the advantageous one.

  Comparative Example 1: The heater 23 shown in FIG. 7A has conductive portions 29 and 30 along the longitudinal direction of the substrate 27 on one end side and the other end side in the short direction of the substrate 27, respectively. A heating element 26 is provided between the portions 29 and 30. Electrodes 29 a and 30 a are provided at both ends in the longitudinal direction of the substrate 27.

  Comparative Example 2: The heater 23 shown in FIG. 7B has conductive portions 29 and 30 along the longitudinal direction of the substrate 27 on one end side and the other end side in the short direction of the substrate 27, respectively. A heating element 26 is provided between the portions 29 and 30. One of the electrodes 29 a and 30 a provided at one end in the longitudinal direction of the substrate 27 is folded back in the longitudinal direction of the substrate 27.

  Comparative Example 3: The heater 23 shown in FIG. 7C has conductive portions 29 and 30 along the longitudinal direction of the substrate 27 on one end side and the other end side in the short direction of the substrate 27, respectively. A heating element 26 is provided between the portions 29 and 30. At one end in the longitudinal direction of the substrate 27, the electrode 30 a of one conductive portion 30 is provided on the surface of the substrate 27, and the electrode 29 a of the other conductive portion 29 is provided on the back surface of the substrate 27. The electrode 29a of the other conductive portion 29 is connected to the conductive portion 29 on the surface of the substrate 27 through a through hole 27h provided at the other end portion of the substrate 27 in the longitudinal direction.

  Comparative Example 4: The heater 23 shown in FIG. 7D has conductive portions 29 and 30 along the longitudinal direction of the substrate 27 on one end side and the other end side in the short direction of the substrate 27, respectively. In addition, a common conductive portion 31 is provided along the longitudinal direction of the substrate 27 in the center in the short direction of the substrate 27. Between the common conductive part 31 and the conductive part 29 and between the common conductive part 31 and the conductive part 30, heating elements 26-1 and 26-2 are provided, respectively. Then, electrodes 29 a and 30 a are provided at one end of the substrate 27 in the longitudinal direction.

In the heater 23 of Comparative Example 1, since the electrodes 29a and 30a are at both ends in the longitudinal direction of the substrate 27, a plurality of electrode connection connectors (power supply connectors) must be provided. Further, by providing the connectors at both ends of the substrate 27 in the longitudinal direction, it is necessary to secure the cost and space for the connectors, which increases the cost and impairs the compactness.

  The heater 23 of Comparative Example 2 must provide an extra space on the substrate 27 for turning back the electrode 29a. For that purpose, the size on the substrate 27 must be secured, which increases the cost. Compactness is impaired. The reason is as follows. As one of the conditions for providing the print pattern, in order to make the heat generation uniform in the longitudinal direction of the substrate 27, as described in JP 2005-209493 A and JP 2005-234540 A described above. It is necessary to satisfy the relationship between electrode resistance and heating element resistance. Furthermore, when the sheet resistance of the heating element 26 increases, there is a characteristic that the PTC characteristic gradually changes to the NTC characteristic. For this reason, in order to maintain the PTC characteristic strongly, it is necessary to adjust the resistance by the dimensions of the conductive portions 29 and 30 and the heating element 26 while keeping the sheet resistance low to some extent. For this reason, the compactness is impaired and the cost is increased.

  The heater 23 of Comparative Example 3 does not have to provide a space for folding the electrode 29a on the surface of the substrate 27 on the side of the heating element 26, and although the compactness can be ensured, 27 is provided with a through hole 27h. Therefore, the cost increases.

  The heater 23 of Comparative Example 4 must provide an extra space on the substrate 27 for turning back the common conductive portion 31. For that purpose, the size on the substrate 27 must be secured, and the cost increases. However, the compactness is impaired.

  Even if it compares with the above comparative examples 1-4, the printing pattern in the heater 23 of a present Example is effective from any viewpoints of cost, compactness, and the strength of PTC characteristics. The heater 23 of this embodiment is also effective in that the current supply to the electrode 29 a is interrupted by the thermal fuse 100 when the conductive portions 29 and 30 and the heating element 26 are disconnected in the longitudinal direction of the substrate 27.

  In the present embodiment, the temperature detection type thermal fuse 100 is used as the safety element, but the safety element is not limited to the temperature fuse 100, and other temperature detection type safety elements such as a thermo switch and a thermostat may be used.

  In the present embodiment, an example of a heater using a thermistor (temperature detection element) as a safety element will be described. Members / portions common to the heater 23 of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 9 is a diagram illustrating an example of the configuration of the heater 23 according to the present embodiment and an energization control circuit used for the heater 23.

  The heater 23 of this embodiment is provided with a thermistor 25a as a safety element at the same position as the position where the temperature fuse 100 is provided in the heater 23 of the first embodiment. This ensures that the thermistor 25a is placed in the heat generating region of the heat generating element 26 that constitutes the energization path together with the conductive parts 29 and 30, no matter where the conductive parts 29 or 30 and the heat generating element 26 are disconnected in the longitudinal direction of the substrate 27. Can be located. Thereby, when the conductive portions 29 and 30 and the heating element 26 are disconnected in the longitudinal direction of the substrate 27, it is possible to detect the energization of the heating element 26. The CPU 41 captures the output (detected temperature) of the thermistor 25a through A / D conversion. Then, the CPU 41 determines whether or not the detected temperature of the thermistor 25a exceeds a certain threshold value. When the detected temperature exceeds the threshold value, the energization interruption provided in the AC line between the power source 43 and the thermal fuse 100 is interrupted. The relay 44 as a means is turned off. Thereby, like the heater 23 of the first embodiment, when the conductive portions 29 and 30 and the heating element 26 are disconnected in the longitudinal direction of the substrate 27, the energization to the heating element 26 can be stopped. Further, when the heater 23 runs away, the thermal fuse 100 provided at a predetermined position on the back surface of the substrate 27 is activated to stop energization of the electrodes 29a and 30a.

It is a structural model figure of an example of a heater, (a) is a rear view of a heater, (b) is a front view of a heater, (c) is a cc cross section of the heater of (b), and is used for the heater. Diagram showing an example of energization control circuit Vertical section model diagram of an example of a fixing device Cross-sectional model of fixing device View of fixing device from recording material introduction side (A) is a heat distribution diagram when the heater is normal, and (b) is a heat distribution diagram when the heater is abnormal. Diagram showing configuration and operation of an example of thermal fuse Structural model of heater of comparative example A structural model of an example of an image forming apparatus The figure showing an example of the composition of other examples of a heater, and an energization control circuit used for the heater. Diagram showing the configuration of a conventional heater

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Fixing device, 22 ... Fixing film, 23 ... Ceramic heater, 24 ... Pressure roller, 25a ... Thermistor, 26 ... Resistance heating element, 27 ... Substrate, 29.30 ... Conductive part, 29a, 30a ... Power supply electrode, 100 ... Temperature fuse, P ... Recording material

Claims (2)

A cylindrical fixing film;
A first conductive portion provided along the longitudinal direction of the substrate, a second conductive portion provided along the longitudinal direction of the substrate, and the first conductive portion along the longitudinal direction of the substrate. A heating element connected between the conductive part and the second conductive part, a first electrode electrically connected to the first conductive part and connected to the power feeding connector, and the second conductive part electrically A second electrode to which a power feeding connector is connected, and the first electrode and the second electrode are provided at the end of the same side in the longitudinal direction of the substrate, A heater in contact with the inner surface;
A pressure roller that forms a fixing nip portion that sandwiches and conveys a recording material carrying an image together with the heater through the fixing film in a direction perpendicular to the longitudinal direction;
A safety element that senses the temperature of the heater and shuts off the power to the heating element when the heater is abnormally heated;
In a fixing device having
The fixing device, wherein the security element is provided at an end portion of the heating element on the side where the first and second electrodes are provided in the longitudinal direction. The fixing device according to claim 1, wherein the security element is a thermistor, a thermal fuse, a thermo switch, or a thermostat .