JP2017194500A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that can suppress a variation in nip pressure when the nip pressure is reduced, and an image forming apparatus.SOLUTION: A compression spring 34 provides a nip pressure to a nip part between a fixing roller 11 and a pressure roller 12. A cam 33 displaces the position of an end of the compression spring 34 on a side of a pressing lever 32 at least between a first position to provide a first nip pressure to the nip part and a second position to provide a second nip pressure lower than the first nip pressure to the nip part. A regulation bolt 36 regulates an extension of the compression spring 34 exceeding a specific length while the position of the end of the compression spring 34 on the side of the pressing lever 32 is between the first position and the second position and within a range from a middle position at which the length of the compression spring becomes the specific length to the second position.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing device and an image forming apparatus.

  The fixing device includes a pair of fixing members, that is, a heating member such as a fixing roller or a fixing belt, and a pressure member such as a pressure roller pressed against the heating member using a compression spring. In such a fixing device, when a toner image is fixed on a sheet such as an envelope, the nip pressure may be reduced from the normal nip pressure in order to prevent wrinkles.

  For example, an upper pressure lever that abuts the shaft end of the pressure member and a lower pressure lever that abuts the pressure cam are connected via a compression spring, and the nip pressure is increased by rotating the pressure cam. There is known a fixing device capable of adjusting the angle (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-179435

  Incidentally, in recent years, there has been a demand for downsizing and speeding up of the fixing device. For this purpose, it is advantageous to use a compression spring having a large spring constant. However, when a compression spring having a large spring constant is used, the elastic force changes greatly only by slightly changing the length of the compression spring, so that the nip pressure variation tends to increase when the nip pressure is reduced.

  An object of the present invention is to provide a fixing device and an image forming apparatus capable of suppressing variations in nip pressure when the nip pressure is reduced.

  A fixing device according to one aspect of the present invention includes a pair of fixing members, a compression spring, a nip pressure changing mechanism, and a regulating member. The pair of fixing members form a nip portion. The compression spring applies a nip pressure to the nip portion. The nip pressure changing mechanism includes at least a first position of the compression spring, a first position that applies a first nip pressure to the nip portion, and a second nip pressure that is lower than the first nip pressure at the nip portion. Is displaced between the second position and the second position. The regulating member is configured such that the position of the first end of the compression spring is between the first position and the second position, and the length of the compression spring becomes a specific length from the midway position to the second position. The expansion exceeding the specific length of the compression spring is restricted while being within the range up to.

  An image forming apparatus according to another aspect of the present invention includes an image forming unit and the fixing device. The image forming unit forms a toner image on a sheet. The fixing device fixes the toner image on the sheet.

  According to the present invention, there are provided a fixing device and an image forming apparatus capable of suppressing variations in nip pressure when the nip pressure is reduced.

FIG. 1 is a view showing an appearance of an image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of the fixing unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating the configuration of the fixing unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration of the fixing unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 5 is a diagram showing the configuration of the fixing unit of the image forming apparatus according to the second embodiment of the present invention. FIG. 6 is a diagram showing the configuration of the fixing unit of the image forming apparatus according to the second embodiment of the present invention. FIG. 7 is a diagram illustrating the configuration of the fixing unit of the image forming apparatus according to the second embodiment of the present invention. FIG. 8 is a diagram illustrating a configuration of a fixing unit of an image forming apparatus according to a modification of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

[First Embodiment]
First, the configuration of the image forming apparatus 1 according to the first embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the image forming apparatus 1 includes a sheet cassette 2, an image forming unit 3, a fixing unit 4, a control unit 5, and the like. The fixing unit 4 or a combination of the fixing unit 4 and the control unit 5 is an example of the fixing device of the present invention. The present invention is not limited to a printer, and can be applied to an arbitrary image forming apparatus such as a copier, a facsimile machine, or a multifunction machine.

  The sheet cassette 2 stores sheets such as recording paper.

  The image forming unit 3 includes a photosensitive drum, a charger, an exposure device, a developing device, a transfer device, and the like. The image forming unit 3 forms a toner image on the sheet fed from the sheet cassette 2.

  The fixing unit 4 fixes the toner image on the sheet by heating and pressing the sheet on which the toner image is formed. A specific configuration of the fixing unit 4 will be described later.

  The control unit 5 includes control devices such as a CPU, a ROM, and a RAM. The CPU is a processor that executes various arithmetic processes. The ROM is a non-volatile storage unit in which information such as a control program for causing the CPU to execute various processes is stored in advance. The RAM is a volatile or nonvolatile storage unit used as a temporary storage memory (working area) for various processes executed by the CPU. In addition, the control part 5 may be provided with the electronic circuit which implement | achieves the said various processes.

[Configuration of Fixing Unit According to First Embodiment]
Next, the configuration of the fixing unit 4 according to the first embodiment of the present invention will be described with reference to FIGS.

  The fixing unit 4 includes a fixing roller 11 and a pressure roller 12. The fixing roller 11 and the pressure roller 12 are an example of a pair of fixing members of the present invention.

  The fixing roller 11 is supported so as to be rotatable about a rotation shaft 21. The pressure roller 12 is supported so as to be rotatable about a rotation shaft 22. The fixing roller 11 is heated by a heater (not shown) such as a halogen lamp or an induction heater provided inside or outside the fixing roller 11.

  Both ends in the axial direction of the rotation shaft 22 of the pressure roller 12 are pressed toward the fixing roller 11 by the pressure mechanism 30. As a result, the pressure roller 12 is pressed against the fixing roller 11, and a nip portion is formed between the fixing roller 11 and the pressure roller 12. The pressure roller 12 is rotated by a rotational driving force from a motor (not shown). When the pressure roller 12 rotates, the rotational driving force is transmitted from the pressure roller 12 to the fixing roller 11 through the nip portion, and the fixing roller 11 also rotates. In this state, when the sheet on which the toner image is formed passes through the nip portion, the sheet is heated and pressurized, and the toner image is fixed to the sheet.

  By the way, when a toner image is fixed on a sheet such as an envelope, the nip pressure may be reduced from the normal nip pressure in order to prevent wrinkles. For example, an upper pressure lever that abuts the shaft end of the pressure member and a lower pressure lever that abuts the pressure cam are connected via a compression spring, and the nip pressure is increased by rotating the pressure cam. A fixing device capable of adjusting the angle is known. Incidentally, in recent years, there has been a demand for downsizing and speeding up of the fixing device. For this purpose, it is advantageous to use a compression spring having a large spring constant. However, when a compression spring having a large spring constant is used, the elastic force changes greatly only by slightly changing the length of the compression spring, so that the nip pressure variation tends to increase when the nip pressure is reduced. On the other hand, in this embodiment, it is possible to suppress variations in nip pressure when the nip pressure is reduced by employing a pressurizing mechanism 30 as described below.

  The pressurizing mechanism 30 includes a pressurizing lever 31, a pressing lever 32, a cam 33 (an example of the nip pressure changing mechanism of the present invention), a compression spring 34, a guide 35, a regulating bolt 36, and a nut 37. Prepare.

  The pressure lever 31 is supported so as to be swingable about a rotation axis P <b> 1 provided at the base end of the pressure lever 31. The pressing lever 32 is supported so as to be swingable about a rotation axis P <b> 2 provided at the base end of the pressing lever 32.

  A compression spring 34 is provided between the pressure lever 31 and the pressing lever 32. That is, the pressing lever 32 is connected to the pressure lever 31 via the compression spring 34. The end of the compression spring 34 on the side of the pressure lever 31 (an example of the second end of the present invention) is supported by the tip side of the pressure lever 31. An end of the compression spring 34 on the side of the pressing lever 32 (an example of the first end of the present invention) is supported by a guide 35 provided on the tip side of the pressing lever 32.

  The pressure lever 31 presses the rotating shaft 22 of the pressure roller 12 toward the fixing roller 11 by the elastic force of the compression spring 34. As a result, the pressure roller 12 is pressed against the fixing roller 11. In other words, the compression spring 34 applies a nip pressure to the nip portion between the fixing roller 11 and the pressure roller 12.

  The cam 33 is supported so as to be rotatable about the rotation axis P3. The cam 33 swings the pressing lever 32 in the contact / separation direction (the direction toward and away from the pressure lever 31). The cam 33 is rotated by a rotational driving force from a motor (not shown).

  The cam 33 has a position of an end portion of the compression spring 34 on the side of the pressing lever 32, at least a first position that gives a normal nip pressure (an example of the first nip pressure of the present invention) to the nip portion, and the nip portion. And a second position that gives a nip pressure lower than the normal nip pressure (an example of the second nip pressure of the present invention).

  The first position is a position corresponding to a predetermined first printing condition, and the second position is a position corresponding to a second printing condition different from the first printing condition. For example, when the sheet passing through the nip portion is a sheet S1 such as plain paper (an example of the first printing condition), the cam 33 causes the end of the compression spring 34 on the side of the pressing lever 32 to be the first sheet. Displaced to position. Thereby, the nip pressure of the nip portion becomes a normal nip pressure. On the other hand, when the sheet passing through the nip portion is a sheet S1 like an envelope (an example of the second printing condition), the end of the compression spring 34 on the pressing lever 32 side is moved to the second position by the cam 33. Is displaced. Thereby, the nip pressure of the nip portion becomes a nip pressure lower than the normal nip pressure.

  FIG. 2 shows a state of the fixing unit 4 (hereinafter referred to as a normal state) when the end of the compression spring 34 on the side of the pressing lever 32 is in the first position. FIG. 3 shows a state of the fixing unit 4 when the end of the compression spring 34 on the side of the pressing lever 32 is at a predetermined position (hereinafter referred to as a halfway position) between the first position and the second position ( Hereinafter, it is referred to as an intermediate state). FIG. 4 shows the state of the fixing unit 4 (hereinafter referred to as a reduced pressure state) when the end of the compression spring 34 on the side of the pressing lever 32 is in the second position.

  The restriction bolt 36 includes a head portion 36a (an example of a locking portion of the present invention), a central portion 36b (an example of a hanging portion of the present invention) provided between the pressure lever 31 and the pressing lever 32, and a tip. Part 36c (an example of the hanging part of the present invention). The head 36 a has a larger diameter than the through hole provided in the guide 35. The central portion 36 b has a smaller diameter than the through hole provided in the guide 35 and a larger diameter than the through hole provided in the pressure lever 31. That is, the central portion 36 b is slidably supported by the guide 35. The tip portion 36 c has a smaller diameter than the through hole provided in the pressure lever 31. A nut 37 (an example of the locking portion of the present invention) is fixed to the tip portion 36c. Therefore, the distance between the pressure lever 31 and the guide 35 is limited by the nut 37 and the head 36a. Therefore, the length of the compression spring 34 does not become longer than the length L2 shown in FIGS.

  As shown in FIG. 2, when the fixing unit 4 is in the normal state, the pressing lever 32 is pressed by the cam 33, whereby the position of the end of the compression spring 34 on the pressing lever 32 side is the position shown in FIG. (The first position). At this time, the length of the compression spring 34 is the length L1 shown in FIG. Further, a gap d is formed between the head 36 a of the restriction bolt 36 and the guide 35. In this state, the fixing process is performed on the sheet S1 such as plain paper.

  On the other hand, when a fixing process is performed on the sheet S2 such as an envelope, a motor (not shown) is controlled by the control unit 5 to drive the cam 33, so that the fixing unit 4 has the above-described function as shown in FIG. Depressurized state.

  When the fixing unit 4 shifts from the normal state to the reduced pressure state, the gap d gradually decreases as the cam 33 approaches the rotational position shown in FIG. 4 from the rotational position shown in FIG. Then, when the position of the end of the compression spring 34 on the side of the pressing lever 32 is displaced to the position shown in FIG. 3 (the midway position), the gap d becomes exactly zero. At this time, the length of the compression spring 34 is the length L2 shown in FIG. 3 (where L2> L1). This length L2 is an example of the specific length of the present invention.

  When the cam 33 is displaced from the rotational position shown in FIG. 3 to the rotational position shown in FIG. 4, the position of the end of the compression spring 34 on the pressing lever 32 side is shown in FIG. 4 from the midway position shown in FIG. Displace to the second position. During this time, further extension of the compression spring 34 (ie, extension beyond the length L2) is prevented by the restriction bolt 36. That is, while the position of the end portion of the compression spring 34 on the pressing lever 32 side is within the range from the midway position to the second position, the head 36a of the regulating bolt 36 moves away from the pressing lever 32 (pressurization). The movement in the direction away from the lever 31 is stopped. Thereby, the length of the compression spring 34 is regulated to the length L2 by the regulation bolt 36.

  As shown in FIG. 4, when the fixing unit 4 is in the reduced pressure state, the position of the end of the compression spring 34 on the side of the pressing lever 32 is the second position shown in FIG. At this time, the length of the compression spring 34 becomes the length L2. In this state, the elastic force of the compression spring 34 is greater than the force with which the rotating shaft 22 of the pressure roller 12 presses the end of the compression spring 34 on the pressure lever 31 side via the pressure lever 31. . Therefore, for the rotating shaft 22 of the pressure roller 12, the compression spring 34 is an inelastic body having a length L2. Therefore, in this state, the position of the rotation shaft 22 of the pressure roller 12 is not affected by the elastic force of the compression spring 34 and is a fixed position corresponding to the rotation position of the cam 33. Therefore, the nip pressure between the fixing roller 11 and the pressure roller 12 is constant.

  As described above, in the first embodiment, by restricting the extension of the compression spring 34 by the restriction bolt 36, it is possible to suppress variation in the nip pressure when the nip pressure is reduced.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. However, the second embodiment is different from the first embodiment only in the pressure mechanism 30 of the fixing unit 3. Therefore, description of components other than the pressurizing mechanism 30 is omitted.

  As shown in FIGS. 5 to 8, the pressure mechanism 30 in the second embodiment includes a pressure lever 31, a pressure lever 32, a cam 33, a compression spring 34, a guide 35, a regulation bolt 36, and a load. And an adjustment plate 38. The pressurizing lever 31, the pressing lever 32, the cam 33, the compression spring 34, and the guide 35 are the same as those in the first embodiment, and thus description thereof is omitted.

  FIG. 5 shows the fixing unit 4 in the normal state. FIG. 6 shows the fixing unit 4 in the halfway state. FIG. 4 shows the fixing unit 4 in the reduced pressure state.

  The restriction bolt 36 has a head portion 36a, a central portion 36b, and a tip portion 36c. The head 36 a has a larger diameter than the through hole provided in the guide 35. The central portion 36 b has a smaller diameter than the through hole provided in the guide 35 and a larger diameter than the through hole provided in the pressure lever 31. That is, the central portion 36 b is slidably supported by the guide 35. The tip portion 36 c has a smaller diameter than the through hole provided in the pressure lever 31.

  In the second embodiment, a load adjusting plate 38 is fixed on the central portion 36b (an example of the hanging portion of the present invention) of the regulating bolt 36 so that the position can be adjusted. The end of the compression spring 34 on the pressure lever 31 side is supported by a load adjustment plate 38. The central portion 36b of the regulating bolt 36 is cylindrical, and the load adjusting plate 38 and the central portion 36b of the regulating bolt 36 are fixed by a screw thread provided on each. Therefore, the position of the load adjusting plate 38 in the axial direction of the regulating bolt 36 can be adjusted by rotating the regulating bolt 36 around the axis of the central portion 36b with respect to the load adjusting plate 38.

  As shown in FIG. 5, when the fixing unit 4 is in the normal state, the pressing lever 32 is pressed by the cam 33, whereby the position of the end of the compression spring 34 on the pressing lever 32 side is the position shown in FIG. (The first position). At this time, the length of the compression spring 34 is the length L3 shown in FIG. Further, a gap d is formed between the head 36 a of the restriction bolt 36 and the guide 35. In this state, the fixing process is performed on the sheet S1 such as plain paper. The length L3 varies depending on the position of the load adjustment plate 38. When the length L3 changes, the elastic force of the compression spring 34 changes, so the nip pressure also changes. Therefore, for example, the nip pressure in the normal state can be finely adjusted to the optimum nip pressure by finely adjusting the position of the load adjusting plate 38 by rotating the regulating bolt 36 with a screwdriver.

  On the other hand, when the fixing process is performed on the sheet S2 such as an envelope, the control unit 5 controls a motor (not shown) to drive the cam 33, so that the fixing unit 4 has the above-described function as shown in FIG. Depressurized state.

  When the fixing unit 4 shifts from the normal state to the reduced pressure state, the gap d gradually decreases as the cam 33 approaches the rotational position shown in FIG. 7 from the rotational position shown in FIG. Then, when the position of the end of the compression spring 34 on the side of the pressing lever 32 is displaced to the position shown in FIG. 6 (the midway position), the gap d becomes exactly zero. At this time, the length of the compression spring 34 is the length L4 shown in FIG. 6 (where L4> L3). This length L4 is an example of the specific length of the present invention.

  When the cam 33 is displaced from the rotational position shown in FIG. 6 to the rotational position shown in FIG. 7, the position of the end of the compression spring 34 on the pressing lever 32 side is shown in FIG. 7 from the midway position shown in FIG. Displace to the second position. During this time, further extension of the compression spring 34 (ie, extension beyond the length L 4) is prevented by the restricting bolt 36. That is, while the position of the end portion of the compression spring 34 on the pressing lever 32 side is within the range from the midway position to the second position, the head 36a of the regulating bolt 36 moves away from the pressing lever 32 (pressurization). The movement in the direction away from the lever 31 is stopped. Thereby, the length of the compression spring 34 is regulated to the length L4 by the regulation bolt 36.

  As shown in FIG. 7, when the fixing unit 4 is in the reduced pressure state, the position of the end of the compression spring 34 on the side of the pressing lever 32 is the second position shown in FIG. At this time, the length of the compression spring 34 is the length L4. In this state, the elastic force of the compression spring 34 is such that the rotary shaft 22 of the pressure roller 12 causes the end of the compression spring 34 on the pressure lever 31 side via the pressure lever 31, the center portion 36 b and the load adjustment plate 38. It is larger than the pressing force. Therefore, for the rotating shaft 22 of the pressure roller 12, the compression spring 34 is an inelastic body having a length L2. Therefore, in this state, the position of the rotary shaft 22 of the pressure roller 12 does not depend on the elastic force of the compression spring 34, does not depend on the position of the load adjusting plate 38 in the axial direction of the regulating bolt 36, and the cam It becomes a fixed position corresponding to the rotational position of 33. Therefore, the nip pressure between the fixing roller 11 and the pressure roller 12 is constant.

  As described above, in the second embodiment as well, similarly to the first embodiment, by restricting the extension of the compression spring 34 by the restriction bolt 36, it is possible to suppress the variation in the nip pressure when the nip pressure is reduced. It is.

[Modification]
In the first embodiment and the second embodiment, the central portion 36b of the regulating bolt 36 is slidably supported by the guide 35 so that the regulating bolt 36 can easily slide smoothly. The invention is not limited to this. In another embodiment, the central portion 36 b of the restriction bolt 36 may be slidably supported by the pressing lever 32 without using the guide 35.

  Moreover, in the said 1st Embodiment and the said 2nd Embodiment, although the control bolt 36 is arrange | positioned in the position which penetrates the inside of the compression spring 34, this invention is not limited to this. In other embodiments, the regulating bolt 36 may be disposed outside the compression spring 34. However, if the restriction bolt 36 is disposed at a position penetrating the inside of the compression spring 34 as in the first embodiment and the second embodiment, the restriction bolt 36 can be used as a positioning member for the compression spring 34. Is possible.

  Moreover, in the said 1st Embodiment and the said 2nd Embodiment, although the head 36a of the control bolt 36 has faced the press lever 32 side, this invention is not limited to this. In other embodiments, the head 36a of the regulation bolt 36 may face the pressure lever 31 side.

  In the first embodiment and the second embodiment, the rotation shaft 22 of the pressure roller 12 is pressed toward the fixing roller 11 by the pressure lever 31, but the present invention is not limited to this. In another embodiment, the rotation shaft 21 of the fixing roller 11 may be pressed toward the pressure roller 12 by the pressure lever 31.

  Moreover, in the said 1st Embodiment and the said 2nd Embodiment, although the press lever 32 is pressed by the cam 33, this invention is not limited to this, The press lever 32 is pressed by other arbitrary power transmission mechanisms. May be.

  Moreover, in the said 1st Embodiment and the said 2nd Embodiment, although the rotating shaft P1 of the pressurization lever 31 and the rotating shaft P2 of the press lever 32 are provided in a different position, this invention is not restricted to this, The rotation axis P1 of the pressure lever 31 and the rotation axis P2 of the pressing lever 32 may be coaxial.

  Moreover, in the said 1st Embodiment and the said 2nd Embodiment, although expansion | extension of the compression spring 34 is restrict | limited by the regulation bolt 36, this invention is not restricted to this. For example, as shown in FIG. 8, the extension of the compression spring 34 may be limited by a hanging portion 39 and a locking portion 40 extending from the pressure lever 31.

  Moreover, in the said 2nd Embodiment, although the edge part by the side of the pressurization lever 31 of the compression spring 34 is supported by the load adjustment board 38, this invention is not limited to this, The press lever 32 side of the compression spring 34 is provided. The end portion may be supported by the load adjustment plate 38.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Sheet cassette 3 Image forming part 4 Fixing part 5 Control part 11 Fixing roller 12 Pressing roller 21 Rotating shaft 22 Rotating shaft 30 Pressing mechanism 31 Pressing lever 33 Pressing lever 33 Cam 34 Compression spring 35 Guide 36 Regulation Bolt 36a Head part 36b Center part 36c Tip part 37 Nut 38 Load adjustment plate 39 Hanging part 40 Locking part S1, S2 Seat P1-P3 Rotating shaft

Claims (7)

A pair of fixing members forming a nip portion;
A compression spring for applying a nip pressure to the nip portion;
The position of the first end of the compression spring is at least a first position that applies a first nip pressure to the nip portion, and a second position that applies a second nip pressure lower than the first nip pressure to the nip portion. A nip pressure changing mechanism that is displaced between,
The position of the first end of the compression spring is between the first position and the second position, and the length of the compression spring is within a range from the midway position to the second position where the length is a specific length. For a while, a regulating member that regulates the extension of the compression spring beyond the specific length;
A fixing device. A pressure lever for pressing one of the pair of fixing members;
A pressure lever connected to the pressure lever via the compression spring;
Further comprising
The nip pressure changing mechanism is a cam that swings the pressing lever in a contact / separation direction with respect to the pressing lever;
The restriction member has a hanging portion provided between the pressure lever and the pressure lever, and a position of the first end of the compression spring is in a range from the midway position to the second position. A locking portion for locking movement of at least one of the pressure lever and the pressing lever in the separating direction.
The fixing device according to claim 1. A load adjusting plate supporting either one of the first end of the compression spring and the second end of the compression spring, the position of which is fixed on the hanging portion so as to be adjustable;
The fixing device according to claim 2. The hanging part is cylindrical,
The load adjustment plate and the hanging part are fixed by the screw threads provided on each,
The position of the load adjusting plate in the axial direction of the hanging part is configured to be adjustable by rotating the hanging part around the axis with respect to the load adjusting plate,
The fixing device according to claim 3. The first position is a position corresponding to a predetermined first printing condition, and the second position is a position corresponding to a second printing condition different from the first printing condition;
The fixing device according to claim 1. The second printing condition includes that the sheet passing through the nip portion is an envelope;
The fixing device according to claim 5. An image forming unit for forming a toner image on a sheet;
The fixing device according to claim 1, wherein the toner image is fixed on the sheet.
An image forming apparatus comprising:

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