JP2011128299A - Image heating device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress reduction of a contact force onto a heater of an overheat protector caused by bending of a holding member without enlarging an image heating device. <P>SOLUTION: A reinforcing spring 15 having an elastically deformable elastic part 15c is provided on a thermostat holder 14. When a bending force is applied to the thermostat holder 14 by receiving a bending moment from a thermostat panel 9 and a thermostat 7, the reinforcing spring 15 applies to the thermostat holder 14, a bending moment in the reverse direction to the bending direction of the thermostat holder 14. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer having a function of forming an image on a recording material such as a sheet, and more particularly to an image heating apparatus provided in these apparatuses.

  The fixing device (image heating device) applies heat from a heater to a recording material to melt and fix the toner image on the recording material. The fixing device includes an overheat protector such as a thermostat or a thermal fuse that cuts off power to the heater when the heater abnormally generates heat when a temperature detection element or the like fails (see, for example, Patent Documents 1 and 2). Hereinafter, an example of a conventional fixing device will be described. FIG. 5 is a cross-sectional view showing a schematic configuration of a conventional fixing device. The fixing device 101 includes a fixing film unit 120 and a pressure roller 106, and fixes the molten toner to the recording material P as follows. That is, the heat of the heater 102 is applied to the recording material P through the endless fixing film 104 that rotates around the heater holder 103 made of heat resistant plastic, and the toner image T on the recording material P is melted. At the same time, a spring (not shown) presses the heater 102 against the pressure roller 106 via the fixing stay 105 made of a substantially U-shaped metal and the heater holder 103, and the recording material P passing between them. Fix the molten toner.

  FIG. 6 is a perspective view illustrating a schematic configuration of the fixing film unit 120. A thermostat 107 as an overheat protector is held by a thermostat holder 108 made of heat-resistant plastic as a holding member. The thermostat 107 is pressed against the heater 102 by a thermostat spring 109 that is a compression spring compressed between the fixing stay 105 and the thermostat holder 108. The thermostat 107 is arranged in series with the power source PS that energizes the heating resistor of the heater 102, and the energization is interrupted when the heater 102 reaches a predetermined temperature or more (refer to Patent Document 3 for the thermostat structure). 7A to 7C are perspective views for explaining a schematic configuration of the thermostat unit 110. FIG. In FIG. 7B, the thermostat 107 is shown in the upper diagram, and the thermostat holder 108 is shown in the lower diagram. In FIG.7 (c), the lower figure shows the side press-contacted to the heater 102 among the thermostat units 110, and the back side is shown in the upper figure. The thermostat spring 109 is inserted into a boss 108 d provided on the thermostat holder 108. The thermostat 107 is held by the thermostat holder 108 as follows. That is, the main body portion 107a is inserted into the main body holding portion 108a, and the electric wire 107b and the electric wire 107c laid so as to avoid the thermostat spring 109 by being folded back at the notch portion 108b are arranged in the electric wire holding portion 108c. It is held by the holder 108.

  Conventionally, there has been a demand for a smaller fixing film in order to reduce the space occupied by the fixing device. As one means for realizing this, as shown in FIG. 8 (a), there is a configuration in which a thermostat spring 109 is disposed on the outer side in the longitudinal direction from the electric wire 107b of the thermostat 107 folded back. 8B is a schematic view of the fixing film unit including the thermostat unit 110 shown in FIG. 7C, and the CC cross-sectional view of FIG. 8C is FIG. It is the schematic of the fixing film unit provided with the thermostat unit 112 shown by a). The thermostat spring 109 present on the same cross section as the electric wire 107b of the thermostat 107 folded in FIG. 8B does not exist in FIG. 8C. Therefore, in the configuration of the thermostat unit 112, the fixing stay 105 and the fixing film 104 can be made small.

Japanese Patent Laid-Open No. 6-314040 JP-A-5-323828 JP 2003-045304 A

  However, the configuration of the thermostat unit 112 has the following problems. FIG. 9 shows the force acting on the thermostat holder 111. The thermostat holder 111 receives the force fs of the thermostat spring 109 at both ends, and receives the drag ft equivalent to the resultant force 2 fs from the thermostat 107 at the center. Therefore, the thermostat holder 111 bends in the direction of the arrow 113 and further creeps if stored for a long time in that state. As a result, the operating length of the thermostat spring 109 increases by the amount of bending, and the force that presses the thermostat 107 against the heater 102 decreases. In this case, there is a possibility that the time until the thermostat 107 cuts off the power supply to the heater 102 is delayed when the heater 102 is abnormally heated.

  It is possible to prevent bending and creep by changing the material of the thermostat holder 111 to ceramic or metal which is more rigid than plastic. However, ceramic is susceptible to brittle fracture, and there is a concern that the metal contacts the terminal portion 107d of the thermostat 107 and short-circuits. Further, if the thermostat holder 111 is to have a rigid shape, a space is eventually required.

  The present invention has been made in view of the circumstances as described above, and the pressure contact force of the overheat protector to the heater is reduced by bending the holding member without increasing the size of the image heating apparatus. It aims at suppressing.

In order to achieve the above object, the present invention provides:
A heater that generates heat when energized;
An overheat protector which is provided in contact with the heater and which cuts off the power to the heater when detecting abnormal heat generation of the heater;
A holding member for holding the overheat protector;
An urging member that urges the holding member to press-contact the overheat protection body held by the holding member to the heater, and urges portions of the holding member on both sides of the overheat protection body, respectively. Two biasing members that
An image heating apparatus for heating a recording material on which a developer image is formed,
An elastic member having an arc-shaped elastic portion that is elastically deformable is provided on the holding member,
When the elastic member receives a bending moment from the two urging members and the overheat protector and a bending force acts on the holding member, a bending moment in a direction opposite to the bending direction of the holding member is applied to the holding member. It is characterized by giving.

  According to the present invention, it is possible to prevent the pressure contact force of the overheat protector from being reduced by the bending of the holding member without increasing the size of the image heating apparatus.

FIG. 3 is a perspective view illustrating a schematic configuration of a thermostat unit according to the first embodiment. 1 is a cross-sectional view illustrating a schematic configuration of a fixing device according to a first exemplary embodiment. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment. FIG. 6 is a perspective view illustrating a schematic configuration of a thermostat unit according to a second embodiment. FIG. 6 is a schematic cross-sectional view of a conventional fixing device. The perspective view which shows schematic structure of the fixing film unit of a prior art example. The perspective view which shows schematic structure of the thermostat unit of a prior art example. The perspective view which shows schematic structure of the thermostat unit of a prior art example. The figure which shows the force which acts on the thermostat holder of a prior art example.

  DETAILED DESCRIPTION Exemplary embodiments for carrying out the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

  The image forming apparatus according to Embodiment 1 of the present invention will be described below. FIG. 3 is a cross-sectional view illustrating a schematic configuration of the image forming apparatus according to the present embodiment. In FIG. 3, reference numeral 51 denotes a printer main body as an image forming apparatus. Reference numeral 52 denotes an image forming unit (image forming unit) which is provided in the printer main body 51 and forms an image by electrophotography. The image forming unit 52 includes a photosensitive drum 53 that forms a toner image, a transfer roller 54 that transfers the toner image formed on the photosensitive drum 53 to a recording material P, and the like. In the image forming unit 52 having such a configuration, when an image forming operation is started, first, light 56 corresponding to an image signal is irradiated onto the photosensitive drum 53 by a laser scanner. Then, by irradiating such light 56, a latent image is formed on the photosensitive drum 53. Next, the latent image formed on the photosensitive drum 53 is developed with toner as a developer stored in the toner cartridge 55, thereby forming a toner image (developer image) on the photosensitive drum 53. Is done. In parallel with the toner image forming operation, the recording material P is fed from the recording material storage cassette. Then, the recording material P is conveyed to a transfer unit constituted by the photosensitive drum 53 and the transfer roller 54 in synchronization with the toner image formed on the photosensitive drum 53 by the conveyance roller and the registration roller. In this transfer portion, the toner image is transferred to the recording material P by applying a bias to the transfer roller 54.

  The recording material P to which such a toner image has been transferred is thereafter conveyed to a fixing device 1 as an image heating unit, and the toner image is fixed to the recording material P by being heated in the fixing device 1.

  FIG. 2 is a cross-sectional view illustrating a schematic configuration of the fixing device 1. The fixing device 1 includes a fixing film unit 20 and a pressure roller 6 as a pressure member, and a spring (not shown) is interposed between a fixing stay 5 made of a substantially U-shaped metal and a heater holder 3. The heater 2 is pressed against the pressure roller 6. Then, the recording material P is nipped and conveyed at a nip portion N formed between the heater 2 and the pressure roller 6 via an endless fixing film 4 rotating around the heater holder 3 made of heat-resistant plastic. Thus, the molten toner is fixed to the recording material P. That is, the recording material P is nipped and conveyed at the nip portion N, and the heat of the heater 2 that generates heat when energized is applied to the recording material P through the fixing film 4 to melt the toner image T on the recording material P. By applying pressure at the nip portion N, the molten toner is fixed to the recording material P. Here, the fixing film 4 corresponds to a flexible sleeve that slides on the heater 2.

Fig.1 (a) is a perspective view which shows schematic structure of the thermostat unit 16 in a present Example. A thermostat 7 as an overheat protector is held by a thermostat holder 14 made of heat-resistant plastic as a holding member. Here, as described in the background art section, the overheat protector is provided in contact with the heater 2 and cuts off the power supply to the heater 2 when abnormal heating of the heater 2 is detected. Further, the fixing film unit 20 (thermostat unit 16 and thermostat holder 14) has a longitudinal direction in the width direction orthogonal to the recording material conveyance direction in the image forming surface of the recording material P that is nipped and conveyed by the nip portion N. It is configured. And the thermostat spring 9 which consists of a compression spring as an urging member is arrange | positioned in the thermostat holder 14 at the outer side of the longitudinal direction rather than the electric wire 7b of the thermostat 7 turned back. Here, the thermostat spring 9 presses the thermostat holder 14 so that the thermostat 7 held by the thermostat holder 14 is pressed against the heater 2. The thermostat spring 9 urges the portions on both sides (both ends) of the thermostat holder 14 with the contact portion 7a between the thermostat 7 and the heater 2 interposed therebetween in the longitudinal direction. In this embodiment, a reinforcing spring 15 made of a linear (bar-shaped) hard steel wire (JIS G3521) is bent on the thermostat holder 14 as an elastic member that can be elastically deformed. Here, the reinforcing spring 15 has an elastic portion 15 c that can be elastically deformed, and ends (one ends 15 a and 15 b) provided on both ends of the elastic portion 15 c are attached to the thermostat holder 14. The reinforcing spring 15 is provided as follows with respect to the thermostat holder 14. The reinforcing spring 15 has both end portions (15a, 15b) of the elastic portion 15c installed on both end sides of the abutting portion 7a of the thermostat 7 and the heater 2 in the longitudinal direction. The handling of the electric wires 7b and 7c of the thermostat 7 is the same as the electric wires 107b and 107c described in the conventional example.

  FIG. 1B is a schematic perspective view showing assembly of the reinforcing spring 15 to the thermostat holder 14. The reinforcing spring 15 is assembled to the thermostat holder 14 as follows. After the one end 15a of the reinforcing spring 15 is inserted into the locking portion (attachment portion) 14e, the elastic portion 15c bent in a natural shape (arc shape, bow shape, bow shape) has a small curvature as indicated by a dotted line. The other end 15b is locked to the locking portion 14g while being bent as described above. At this time, the reinforcing spring 15 is attached to the thermostat holder 14 in such a state that the curved shape of the elastic portion 15 c in the natural state is convex toward the direction in which the thermostat spring 9 biases the thermostat holder 14. . In this way, the reinforcing spring 15 is attached (installed) to the thermostat holder 14. In this way, the reinforcing spring 15 is engaged (attached) to the thermostat holder 14 at both ends (15a, 15b) of the elastic portion 15c.

  FIG.1 (c) shows the force which acts on the thermostat holder 14 in a present Example. The thermostat holder 14 receives the force fs of the thermostat spring 9 at both ends in the longitudinal direction, and receives the drag ft equivalent to the resultant force 2 fs from the thermostat 7 at the center in the longitudinal direction. As a result, the thermostat holder 14 tends to bend in the direction of the arrow 13. That is, the thermostat holder 14 receives a bending moment (in the direction of arrow 13) from the thermostat spring 9 and the thermostat 7. As a result, a bending force acts on the thermostat holder 14.

  On the other hand, in this embodiment, since the thermostat holder 14 is provided with the reinforcing spring 15, the thermostat holder 14 has a force (elastic force) at which the bent reinforcing spring 15 returns to the natural state at both ends. receive. When the reinforcing spring 15 tries to return to the natural state, the bending moment shown by M in FIG. 1C acts on the thermostat holder 14 by bending so that the curvature of the elastic portion 15c increases. That is, the reinforcing spring 15 imparts a bending moment M to the thermostat holder 14 in the direction opposite to the bending direction of the thermostat holder 14 (the direction of the arrow 13).

This can be paraphrased as follows. The thermostat holder 14 is subjected to a force fr that causes the reinforcing springs 15 bent at both ends to return to the natural state and a reaction force equivalent to the resultant force 2fr at the center. That is, the reinforcing spring 15 applies a force to the thermostat holder 14 to prevent the thermostat holder 14 from bending in the direction of the arrow 13.

  As described above, in this embodiment, the reinforcing spring 15 is provided on the thermostat holder 14 in a state where the elastic portion 15c is elastically deformed, so that the elastic force to return the elastic portion 15c to the natural state is applied to the thermostat holder 14. It is configured to work. Thus, the bending moment M in the direction opposite to the bending direction of the thermostat holder 14 (arrow 13 direction) can be applied to the thermostat holder 14. Thereby, compared with a prior art example (refer FIG. 9), it becomes possible to make small the bending which arises in the thermostat holder 14. FIG. Therefore, it is possible to suppress the bending of the thermostat holder 14, and it is possible to suppress the creep that occurs when the thermostat holder 14 is bent for a long time.

  Further, since only the reinforcing spring 15 is attached to the thermostat holder 14 as a linear elastic member, there is no need to expand the space. From the cross-sectional view of FIG. 2, it can be seen that the reinforcing spring 15 can be attached without making the thermostat holder 14 larger than the conventional thermostat holder 111 shown in FIG. For this reason, it is not necessary to enlarge (enlarge) the fixing stay 5 and the fixing film 4, and it is possible to realize space saving of the fixing device. Here, in the present embodiment, the material of the reinforcing spring 15 is a hard steel wire, but is not limited thereto, and may be a linear elastic body such as a piano wire (JIS G3522).

  In this embodiment, the reinforcing spring 15 is attached to the thermostat holder 14 by bending the elastic portion 15c bent into a curved shape in a natural state so that the curvature becomes small. It is not a thing. The reinforcing spring 15 may be attached to the thermostat holder 14 with the elastic portion 15c bent into a curved shape in a natural state. In this case, a bending moment is received from the thermostat spring 9 and the thermostat 7, and a bending force acts on the thermostat holder 14, whereby the spring force (elastic force) of the reinforcing spring 15 acts on the thermostat holder 14. By the action of the spring force of the reinforcing spring 15, a bending moment in the direction opposite to the bending direction of the thermostat holder 14 is applied to the thermostat holder 14. In this embodiment, the fixing film unit in which the fixing film 4 slides on the heater 2 has been described. However, the present invention is not limited to this. In the present invention, the urging members that press the holding member that holds the overheat protector to press the overheat protector held by the holding member against the heater are provided on both sides of the overheat protector in the holding member, respectively. Any image heating apparatus provided so as to be energized can be suitably applied.

  FIG. 4A is a perspective view illustrating a schematic configuration of the thermostat unit 17 according to the second embodiment of the present invention. Note that the same components as those of the first embodiment described above are denoted by the same reference numerals, and description thereof is omitted. The thermostat 7 is held by a thermostat holder 18 made of heat-resistant plastic as a holding member. The thermostat springs 19a and 19b made of compression springs as urging members are arranged on the outer side in the longitudinal direction from the electric wire 7b of the folded thermostat 7. In this embodiment, the two thermostat springs 19a and 19b are connected by a reinforcing spring 19c as an elastic member (elastic portion) bent in the shape of a bow with the same material and the same diameter, and the two thermostat springs 19a and 19b. The reinforcing spring 19c is integrally formed. The reinforcing spring 19 c is bent on the thermostat holder 18. Here, the function of the reinforcing spring 19c is the same as that of the elastic portion 15c of the first embodiment.

FIG. 4B is a schematic perspective view showing the assembly of the thermostat springs 19 a and 19 b connected by the reinforcing spring 19 c to the thermostat holder 18. After inserting one thermostat spring 19a into the boss 18a, the reinforcing spring 19c bent in a bow shape in a natural state is bent into a groove 18f while being bent so as to have a smaller curvature as shown by the dotted line, and the other thermostat spring 19b is inserted. Is inserted into the boss 18b. Since the reinforcing spring 19c tries to return to the natural state when the thermostat unit 17 is in a single state, the thermostat holder 18 is provided with locking portions 18h and 18i for restricting it.

  FIG. 4C shows the force acting on the thermostat holder 18 in this embodiment. Also in this embodiment, the thermostat holder 18 receives the force fs of the thermostat springs 19a and 19b at both ends in the longitudinal direction, and receives the drag ft equivalent to the resultant force 2fs from the thermostat 7 at the center in the longitudinal direction. As a result, the thermostat holder 14 tends to bend in the direction of the arrow 13. On the other hand, since the reinforcing springs 19c are integrally formed with the thermostat springs 19a and 19b, the thermostat holder 18 has a force (elastic force) at which the reinforcing springs 19c bent at both ends tend to return to a natural state. Receive. When the reinforcing spring 19c is returned to its natural state, the thermostat holder 18 is bent so as to have a large curvature, whereby a bending moment indicated by M in FIG. That is, the reinforcing spring 19c gives the thermostat holder 18 a bending moment M in the direction opposite to the bending direction of the thermostat holder 18 (arrow 13 direction).

  This can be paraphrased as follows. The thermostat holder 18 receives the resultant force fs-fr of the force fs of the thermostat springs 19a and 19b and the force fr of the reinforcing spring 19c trying to return to the natural state at both ends in the longitudinal direction. The thermostat holder 18 receives a reaction force 2fr from the reinforcing spring 19c at the center in the longitudinal direction and a drag force ft equivalent to the resultant force 2fs of the thermostat springs 19a and 19b from the thermostat 7. That is, since the forces acting on both ends in the longitudinal direction of the thermostat holder 18 are reduced by fr as compared with the conventional example (see FIG. 9), the bending of the thermostat holder 18 in the direction of arrow 13 can be reduced.

  As described above, also in this embodiment, it is possible to obtain the same effect as that of the first embodiment described above. Furthermore, in this embodiment, the thermostat springs 19a and 19b and the reinforcing spring 19c are integrally formed, so that the number of parts is reduced and the assembly workability can be improved.

  DESCRIPTION OF SYMBOLS 1 Fixing device; 2 Heater; 7 Thermostat; 9 Thermostat spring; 14 Thermostat holder; 15 Reinforcement spring

Claims (7)

A heater that generates heat when energized;
An overheat protector which is provided in contact with the heater and which cuts off the power to the heater when detecting abnormal heat generation of the heater;
A holding member for holding the overheat protector;
An urging member that urges the holding member to press-contact the overheat protection body held by the holding member to the heater, and urges portions of the holding member on both sides of the overheat protection body, respectively. Two biasing members that
An image heating apparatus for heating a recording material on which a developer image is formed,
An elastic member having an arc-shaped elastic portion that is elastically deformable is provided on the holding member,
When the elastic member receives a bending moment from the two urging members and the overheat protector and a bending force acts on the holding member, a bending moment in a direction opposite to the bending direction of the holding member is applied to the holding member. An image heating apparatus characterized by being provided.   The image heating apparatus according to claim 1, wherein the elastic member is provided on the holding member in a state where the elastic member is bent so that a curvature of the elastic portion is smaller than a natural state.   The image heating apparatus according to claim 1, wherein the urging member is provided at both ends of the elastic portion, so that the elastic member and the urging member are integrally configured.   The image heating apparatus according to claim 1, wherein the holding member is made of plastic.   The image heating apparatus according to claim 4, wherein the overheat protector is a thermostat. A flexible sleeve that slides on the heater;
A recording material on which a developer image is formed between the flexible sleeve and the pressure member in a nip portion formed between the heater and the pressure member via the flexible sleeve. The image heating apparatus according to claim 1, wherein the image heating apparatus sandwiches and conveys the image and heats the image. Image forming means for forming a developer image on a recording material;
An image heating apparatus according to any one of claims 1 to 6,
With
An image forming apparatus, wherein a developer image formed on a recording material by the image forming means is heated by the image heating device.

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