JP2005201918A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing apparatus and an image forming apparatus of high performance capable of surely releasing the press contact of a heating member and a pressure member and suppressing the permanent deformation of both members, and also, capable of performing a changeover from the press contact released state of the heating member and the pressure member to the press contact state with a comparatively inexpensive and simple constitution at a high speed. <P>SOLUTION: An operation of making the heating member and the pressure member in the press contact state/press contact released state is performed by rotating a cam 31 in a prescribed direction. The circumferential surface of the cam 31 is provided with a 1st position R1 for making the members in the press contact state and a 2nd position R2 for making the members in the press contact released state. Further, the circumferential surface of the cam 31 is provided with a smooth part R12 which is formed so that a distance from a rotating center on the circumferential surface from the 1st position R1 to the 2nd position R2 may gradually increase when the cam 31 is rotated in the prescribed direction, and a step part R21 which is formed so that the distance from the rotating center on the circumferential surface from the 2nd position R2 to the 1st position R1 may sharply reduce when the cam is rotated in the prescribed direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a fixing device installed therein.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a fixing device using a heat roller system is often used (for example, see Patent Document 1).

Specifically, the fixing device is mainly composed of a fixing roller as a heating member and a pressure roller as a pressure member in pressure contact with the fixing roller.
On the other hand, an image (toner image) is transferred onto the surface of a recording medium that moves along the conveyance path of the image forming apparatus. Then, the recording medium carrying the unfixed image further moves along the transport path and reaches the fixing device. The recording medium that has reached the fixing device is fed between the fixing roller and the pressure roller (a nip), and the image is fixed by heat received from the fixing roller and pressure received from both rollers. The recording medium on which the image is fixed is delivered from between the fixing roller and the pressure roller and then discharged from the image forming apparatus.

  In such a fixing device, it is known that when the fixing roller and the pressure roller are pressed against each other for a long period of time, the elastic layer of the fixing roller and the pressure roller is permanently deformed to cause problems such as fixing failure. (For example, refer to Patent Document 1).

  In order to solve such a problem, Patent Document 1 and the like disclose a technique in which a pressure release mechanism (contact / separation adjusting means) for releasing the pressure contact state of the fixing roller and the pressure roller is installed in the fixing device. . That is, when there is no print job for a certain time or longer, the pressure release mechanism is operated to release the pressure contact state between the fixing roller and the pressure roller.

JP 11-125985 A

  As described above, in the fixing device using the heat roller system, permanent deformation due to long-term pressure contact between the fixing roller and the pressure roller is a problem. That is, when the fixing device is not operated for a long period of time, the contact portions of the fixing roller and the pressure roller always receive a load, and both the rollers are crushed in the radial direction or bent in an arc shape in the axial direction. In such a case, a gap is formed at the contact portion (nip) of both rollers, and fixing failure occurs in the image on the recording medium. Furthermore, abnormal images such as image blur due to conveyance failure by both rollers, abnormal noise due to driving of the deformed roller, and the like may occur.

  In particular, in recent fixing devices, a fixing roller composed of a thin cylindrical body is used for the purpose of reducing power consumption, and a desired nip can be obtained even with a low pressing force corresponding to a thin cylindrical fixing roller having a low strength. A pressure roller made of foamable silicone rubber that can be formed is used. A pressure roller using such a foamable silicone rubber as an elastic layer is relatively easy to be permanently deformed against long-term pressure contact, and thus the above-mentioned problems cannot be ignored.

  On the other hand, in the technique of the above-mentioned Patent Document 1, a pressure release mechanism that releases the pressure contact state of the fixing roller and the pressure roller is installed in the fixing device, and the pressure release is performed when there is no print job for a certain time or more. The mechanism is operated to release the pressure contact state between the fixing roller and the pressure roller. Therefore, the time during which the fixing roller and the pressure roller are in contact with each other is reduced, and a certain effect of preventing the both rollers from being permanently deformed can be expected.

  However, in the above-described control, the contact state between the fixing roller and the pressure roller is maintained when the user turns off the power switch of the image forming apparatus before the fixed time elapses until the pressure release mechanism operates. It will be done. In this case, since the contact state of the fixing roller and the pressure roller is maintained until the power switch of the image forming apparatus is turned on again, there is a high possibility that both rollers are deformed.

  Japanese Patent Application Laid-Open No. 2004-228561 describes that the contact state between the fixing roller and the pressure roller is released when the power switch is turned off, but there is no description about a specific method. Here, even when the power switch is turned off before the lapse of a certain time as described above, the auxiliary power source for operating the pressure release mechanism is used to release the contact state between the fixing roller and the pressure roller. It is also possible to install it separately from the power supply related to the above. However, in that case, the cost and installation space for installing the auxiliary power supply are required.

In order to solve the above-described problem, a measure for operating the pressure release mechanism in conjunction with the presence / absence of input of a job signal related to image formation may be considered.
That is, when the job signal is input, the pressure contact between the fixing roller and the pressure roller is performed, and when the job signal is not input, the pressure contact between the fixing roller and the pressure roller is released. By such control, even when the power switch of the image forming apparatus is turned off by the user immediately after the job related to image formation is completed, the pressure contact between the fixing roller and the pressure roller is surely released. Can do.

  However, in such a case, if the speed at which the pressure contact between the fixing roller and the pressure roller is released to the pressure contact state is not fast enough, the productivity of image formation in the image forming apparatus will be affected. . That is, if the recording medium is sent to the fixing device while the pressure contact state between the fixing roller and the pressure roller is insufficient, a fixing defect occurs in the image on the recording medium. Therefore, in order to ensure a certain productivity of image formation and suppress fixing failure, the drive source for driving the pressure release mechanism becomes high output and expensive. Specifically, if it is a pressure release mechanism that contacts and separates the fixing roller and pressure roller by rotating the cam in a predetermined direction, it is necessary to install a drive motor that can drive the cam at high speed There is.

Such a problem cannot be ignored particularly in a small-sized image forming apparatus having a short conveyance path from the paper feeding unit to the fixing device and a high-speed image forming apparatus having a high conveyance speed of the recording medium.
Further, even in the pressure release mechanism controlled as in the above-mentioned Patent Document 1, the pressure release state is switched from the pressure release state to the pressure contact state. It is necessary to install a high output drive source for driving the mechanism.

  The present invention has been made in order to solve the above-described problems. When the user turns off the power switch of the image forming apparatus immediately after the job related to image formation is completed, the image by the user is provided. Regardless of the mode of operation of the forming apparatus, the press contact between the heating member and the pressure member is reliably released to prevent permanent deformation of both members, and from the press release state to the press contact state with a relatively inexpensive and simple configuration. An object of the present invention is to provide a high-performance fixing device and an image forming apparatus that can speed up switching.

  In the fixing device according to the first aspect of the present invention, a recording medium carrying an image is fed between a heating member and a pressure member pressed against the heating member, and the image is placed on the recording medium. A fixing device for fixing, comprising: a contact / separation adjusting means for rotating and pressing a cam in a predetermined direction between the heating member and the pressure member; and a peripheral surface of the cam is the heating member And a second position for releasing the pressure contact between the heating member and the pressure member, and the cam is rotated in the predetermined direction. A smooth portion formed such that the distance from the rotation center on the circumferential surface from the first position to the second position gradually increases or decreases, and from the second position when rotated in the predetermined direction. Is the center of rotation on the circumferential surface leading to the first position? A step portion distance is formed so as to deplete or proliferation of, those having a.

  The fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the contact / separation adjusting means is configured such that the heating member is provided when a job signal related to image formation is input to the main body of the image forming apparatus. And the pressure member, and when the job signal relating to image formation is not input to the image forming apparatus main body, the pressure contact between the heating member and the pressure member is released.

  A fixing device according to a third aspect of the present invention is the fixing device according to the first or second aspect, wherein the cam includes a plurality of the stepped portions on a circumferential surface thereof.

  According to a fourth aspect of the present invention, in the fixing device according to the third aspect of the present invention, the plurality of step portions are arranged on the circumferential surface of the cam at equal intervals.

  An image forming apparatus according to a fifth aspect of the present invention includes the fixing device according to any one of the first to fourth aspects.

  According to the present invention, a step portion is provided in the cam of the contact / separation adjusting means, and the contact operation of the heating member and the pressure member of the fixing device is performed in conjunction with the presence / absence of input of a job signal to the image forming apparatus main body. . This ensures that the pressure member between the heating member and the pressure member is released regardless of how the image forming apparatus is operated by the user, such as when the power switch of the image forming apparatus is turned off immediately after the job is completed. As a result, it is possible to provide a high-performance fixing device and image forming apparatus capable of suppressing permanent deformation of both members and speeding up the switching from the pressure release state to the pressure contact state with a relatively inexpensive and simple configuration.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, reference numeral 1 denotes an apparatus main body of a copying machine as an image forming apparatus, 2 an original reading unit that optically reads image information of an original D, and 3 an exposure light L based on image information read by the original reading unit 2. Is exposed to the photosensitive drum 5, 4 is an image forming unit that forms an image (toner image) on the photosensitive drum 5, and 7 is an image formed on the photosensitive drum 5 that is transferred to the recording medium P. The transfer unit 10 is a document transport unit (ADF) that transports a set document D to the document reading unit 2, 12 to 14 is a paper feed unit that stores a recording medium P such as transfer paper, and 20 is a recording medium P. A fixing device for fixing the unfixed image above, 21 is a fixing roller as a heating member installed in the fixing device 20, and 24 is a pressure roller as a pressure member installed in the fixing device 20.

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, the document D is conveyed from the document table in the direction of the arrow in the drawing by the conveyance roller of the document conveyance unit 10 and passes over the document reading unit 2. At this time, the document reading unit 2 optically reads the image information of the document D passing above.
Then, the optical image information read by the document reading unit 2 is converted into an electric signal and then transmitted to the exposure unit 3 (writing unit). Then, exposure light L such as laser light based on the image information of the electrical signal is emitted from the exposure unit 3 toward the photosensitive drum 5 of the image forming unit 4.

On the other hand, in the image forming unit 4, the photosensitive drum 5 is rotated in the clockwise direction in the drawing, and image information is transferred onto the photosensitive drum 5 through a predetermined image forming process (charging process, exposure process, development process). An image (toner image) corresponding to is formed.
Thereafter, the image formed on the photosensitive drum 5 is transferred by the transfer unit 7 onto the recording medium P conveyed by the registration roller.

On the other hand, the recording medium P conveyed to the transfer unit 7 operates as follows.
First, one of the plurality of paper feeding units 12, 13, and 14 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 12 is selected). To do.)
Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 12 is transported toward the position of the transport path K.

  Thereafter, the recording medium P passes through the conveyance path K and reaches the position of the registration roller. Then, the recording medium P that has reached the position of the registration roller is conveyed toward the transfer unit 7 at the same timing in order to align with the image formed on the photosensitive drum 5.

After the transfer process, the recording medium P passes through the position of the transfer unit 7 and then reaches the fixing device 20 through the conveyance path. The recording medium P that has reached the fixing device 20 is fed between the fixing roller 21 and the pressure roller 24, and the image is fixed by the heat received from the fixing roller 21 and the pressure received from both rollers 21, 24. The The recording medium P on which the image is fixed is delivered from between the fixing roller 21 and the pressure roller 24 and then discharged from the image forming apparatus main body 1.
Thus, a series of image forming processes is completed.

Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS.
As shown in FIG. 2, the fixing device 20 mainly includes a fixing roller 21, a pressure roller 24, a thermistor 37, a separation claw 38, and contact / separation adjusting means 27 to 31.

  Here, the fixing roller 21 as a heating member includes a thin cylindrical body that rotates in the direction of the arrow in FIG. 2 and a heater 22 fixed inside the cylindrical body. The surface of the cylindrical body of the fixing roller 21 is processed with a fluororesin so as to ensure releasability (peelability) from the toner T. The heater 22 of the fixing roller 21 is a rod-shaped heater having a heating wire inside, and both ends thereof are fixed to the side plate of the fixing device 20. Then, the cylindrical body is heated by the heater 22 whose output is controlled by the control unit 40 of the apparatus body 1, and heat is applied to the toner T on the recording medium P from the surface of the cylindrical body. The output control of the heater 22 is performed based on the detection result of the roller surface temperature by the thermistor 37 that contacts the surface of the fixing roller 21.

  As shown in FIG. 2, a separation claw 38 that is swingably supported is disposed on the outer peripheral side of the fixing roller 21. The separation claw 38 has a tip abutting against the outer peripheral surface of the fixing roller 21, and the recording medium P sent from between the fixing roller 21 and the pressure roller 24 moves along the rotation of the fixing roller 21. The trouble which winds around 21 is suppressed.

  Further, guide plates 35 for guiding the conveyance of the recording medium P are disposed on the entrance side and the exit side of the contact portion between the fixing roller 21 and the pressure roller 24, respectively. The guide plate 35 is fixed to the side plate of the fixing device 20.

  The pressure roller 24 as a pressure member mainly includes a cored bar and a plurality of elastic layers formed on the outer peripheral surface of the cored bar via an adhesive layer. The elastic body layer of the pressure roller 24 has a layer thickness of 1 to 10 mm, and a material such as fluorine rubber, silicone rubber, or foamable silicone rubber is used. A thin release layer having a layer thickness of 300 μm or less (preferably 40 μm or less) is provided on the surface layer of the elastic layer. As the material of the release layer, a single layer film of heat-resistant resin such as polyimide, polyetherimide, PES (polyether sulfide), PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), or a film having a thickness of 20 μm The composite layer film etc. which gave the release coat layer which added the electrically conductive material to fluororesins, such as PTFE (tetrafluoroethylene resin) and PFA, in the surface layer side of 10-30 micrometers can be used. The pressure roller 24 configured in this manner is excellent in elasticity, heat resistance, releasability, and durability.

  Here, the shaft 24 a at both ends of the pressure roller 24 is inserted into a long hole provided in the side plate of the fixing device 20. Referring to FIG. 2, pressure levers 27 are engaged with shaft portions 24a at both ends of pressure roller 24, respectively. One end side of the pressure lever 27 is supported by the support shaft 30, and a tension spring 29 is installed on the other end side. With such a configuration, the pressure roller 24 is pushed up by the pressure lever 27 that rotates about the support shaft 30 by the urging force of the tension spring 29 and presses the fixing roller 21.

  Further, a shaft portion is provided at the lower end of the pressure lever 27 so as to stand upright in the direction perpendicular to the paper surface of FIG. 2, and a bearing 28 is inserted into the shaft portion. The bearing 28 of the pressure lever 27 is configured to be engageable with a cam 31 that rotates in the direction of arrow Y <b> 1 by a drive unit 41.

Referring to FIG. 3, the drive unit 41 that rotationally drives the cam 31 includes a stepping motor 42 and a plurality of gears 44 to 49.
Specifically, after the control unit 40 of the apparatus main body 1 determines whether or not a job signal is input, an operation signal is transmitted from the control unit 40 to the stepping motor 42. When the stepping motor 42 is driven, the driving force is transmitted to an idle gear 45a that meshes with a gear 44 connected to the motor shaft. Further, the drive is transmitted to the worm wheel 46a meshing with the worm gear 45b integrated with the idle gear 45a, and the idle gear 46b integrated with the worm wheel 46a is passed through the two-stage idle gears 47a, 47b and the idle gear 48. Finally, the drive is transmitted to the gear 49 integrated with the cam 31. Thus, the cam 31 is rotationally driven by a predetermined angle in the arrow Y1 direction in FIG. 3 at a predetermined timing.

  Then, as shown in FIG. 4, the cam 31 is driven to rotate in the direction of the arrow Y1, and the top dead center of the cam 31 (the position on the circumferential surface where the distance from the rotation center is the longest) (Position R2) is engaged with the bearing 28, whereby the pressure lever 27 is pushed down in the direction of the arrow Y2 and the pressure roller 24 is moved in the direction of the arrow Y3, so that the fixing roller 21 and the pressure roller 24 are The pressure contact is released.

  Further, the cam 31 is rotationally driven in the direction of the arrow Y1, and the bottom dead center of the cam 31 (a position on the circumferential surface where the distance from the rotation center is the shortest, which is a first position R1 described later). By facing the bearing 28, the pressing of the pressure lever 27 by the cam 31 is released, and the pressure lever 27 and the pressure roller 24 are moved to the positions shown in FIG. The pressure roller 24 is pressed. 2, since the cam 31 and the bearing 28 are not in contact with each other, the pressing force of the fixing roller 21 and the pressure roller 24 is determined by the urging force of the tension spring 29.

Here, as shown in FIG. 5, the cam 31 of the contact / separation adjusting means has a smooth portion R12 in which the distance from the rotation center changes smoothly and a step in which the distance from the rotation center changes abruptly on the circumferential surface. Part R21.
Specifically, a first position R1 for pressing the fixing roller 21 and the pressure roller 24 against the peripheral surface of the cam 31 (the surface that engages with the bearing 28), and the fixing roller 21 and the pressure roller 24. And a second position R2 for releasing the pressure contact. Further, as shown in FIG. 5, when the cam 31 is rotated in the direction of the arrow, the smooth portion R12 has a circumferential surface from the first position R1 to the second position R2 so that the distance from the rotation center gradually increases. Is formed. Further, when the cam 31 is rotated in the arrow direction, a stepped portion R21 is formed on the peripheral surface from the second position R2 to the first position R1 so that the distance from the rotation center is drastically reduced.

When the cam 31 configured as described above is rotationally driven as described above, the contact / separation adjusting means of the fixing device 20 performs the following characteristic operation.
That is, when the fixing roller 21 and the pressure roller 24 shift from the pressure contact state (the state shown in FIG. 2) to the pressure contact released state (the state shown in FIG. 4), depending on the shape of the smooth portion R12 of the cam 31. The transition will proceed slowly. On the other hand, when the fixing roller 21 and the pressure roller 24 shift from the pressure release state to the pressure contact state, the shift is instantaneously advanced by a slight rotation of the cam 31 due to the shape of the step portion R21 of the cam 31.

  Thereby, the fixing roller 21 and the pressure roller 24 can be changed from the pressure release state to the pressure contact state without increasing the rotation speed of the stepping motor 42. Therefore, the cost of the stepping motor 42 is reduced, and the degree of freedom for setting the transport path K of the apparatus main body 1 and setting the copy speed is increased.

The fixing device 20 configured as described above operates under the following control.
First, when the power switch (not shown) of the apparatus main body 1 is not turned on, the state where the cam 31 is engaged with the bearing 28 of the pressure lever 27 is maintained. That is, the pressure contact between the fixing roller 21 and the pressure roller 24 is released (the state shown in FIG. 4). This pressure-release state is maintained even when the power switch of the apparatus main body 1 is turned on.

  When the power switch of the apparatus main body 1 is turned on and the operation unit 55 is operated by the user (for example, when the copy start button is pressed), a job signal related to image formation is sent from the operation unit 55 to the control unit 40. When transmitted, an operation signal is transmitted from the control unit 40 to the drive unit 41. Thereby, the contact / separation adjusting means by the pressure lever 27, the cam 31, the drive unit 41 and the like described above operates, and the pressure contact between the fixing roller 21 and the pressure roller 24 is instantaneously performed. Further, rotation driving of the fixing roller 21 and the pressure roller 24 in the direction of the arrow in FIG. 2 is started.

  At the same time, based on the input of the job signal, the recording medium P is fed from the paper feeding units 12 to 14, and an unfixed image is carried on the recording medium P by the image forming unit 4. The recording medium P carrying the unfixed image T is conveyed in the direction of the arrow Y10 in FIG. 2 and fed into the nip portion between the fixing roller 21 and the pressure roller 24 that are in a pressure contact state. Then, the image T is fixed on the surface of the recording medium P by the heating by the fixing roller 21 and the pressing force of the fixing roller 21 and the pressure roller 24.

Thereafter, the recording medium P sent out from the nip portion by the rotating fixing roller 21 and the pressure roller 24 is conveyed in the direction of the arrow Y11. At this time, the sent recording medium P is detected by a photosensor (not shown) installed on the outlet side of the nip portion. When it is determined that the input of a job signal following the previous job is detected when the trailing edge of the recording medium P is detected, the pressure contact state of the fixing roller 21 and the pressure roller 24 is maintained. Then, the above-described fixing process and control are performed again on the recording medium P related to the next job.
On the other hand, when it is determined that the job signal following the previous job is not input when the trailing edge of the recording medium P is detected, the pressure contact state of the fixing roller 21 and the pressure roller 24 is released. . Then, the pressure release state is maintained until a job signal is input again via the operation unit 55.

  As described above, in the first embodiment, the step portion R21 is provided on the cam 31 of the contact / separation adjusting means. As a result, the responsiveness of the contact / separation operation from the pressure release state to the pressure contact state of the fixing roller 21 and the pressure roller 24 is enhanced, power saving and cost reduction of the drive unit 41 are achieved, and the conveyance path The degree of freedom of design such as the length is increased.

  Further, when the job is not executed, the fixing roller 21 and the pressure roller 24 are brought into the pressure contact released state, and when the job is actually executed, the fixing roller 21 and the pressure roller 24 are brought into the pressure contact state. Thus, even when the power switch is turned off by the user immediately after the recording medium P is ejected from the apparatus main body 1 or when the user is turned off while waiting for a job without executing the job, The pressure contact between the fixing roller 21 and the pressure roller 24 is reliably released. That is, permanent deformation of the fixing roller 21 and the pressure roller 24 is suppressed with a relatively simple configuration, and problems such as fixing failure are prevented.

In the first embodiment, the contact / separation adjusting means is configured so that the fixing roller 21 and the pressure roller 24 are in a pressure contact state when the cam 31 is not engaged with the pressure lever 27. The smooth portion R12 of the cam 31 is formed such that the distance from the rotation center on the circumferential surface from the first position R1 to the second position R2 increases gradually. Further, the step portion R21 of the cam 31 is formed so that the distance from the rotation center on the peripheral surface from the second position R2 to the first position R1 is drastically reduced.
On the other hand, the contact / separation adjusting means can be configured such that when the cam 31 is not engaged with the pressure lever 27, the fixing roller 21 and the pressure roller 24 are in the pressure release state. In this case, the smooth portion R12 is formed so that the distance from the rotation center on the circumferential surface from the first position R1 to the second position R2 gradually decreases, and the step portion R21 is changed from the second position R2 to the first position R1. The effect similar to that of the first embodiment can be obtained by forming so that the distance from the center of rotation on the peripheral surface leading to is increased dramatically.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 6 is a configuration diagram showing the cam 31 installed in the contact / separation adjusting means of the fixing device according to the second embodiment, and corresponds to FIG. 5 of the first embodiment. The second embodiment is different from the first embodiment in that a plurality of stepped portions R21 are provided on the peripheral surface of the cam 31.

As shown in FIG. 6, two smooth portions R <b> 12 and two step portions R <b> 21 are provided at equal intervals on the circumferential surface of the cam 31.
Specifically, the continuous first position R1 is provided in two places on the peripheral surface of the cam 31, and the second position R2 is also provided in two places. Further, when the cam 31 is rotated in the direction of the arrow, a smooth portion R12 is formed on the peripheral surface from the first position R1 to the second position R2 so that the distance from the rotation center gradually increases. Further, when the cam 31 is rotated in the direction of the arrow, a stepped portion R21 is formed on the circumferential surface from the second position R2 to the first position R1 so that the distance from the rotation center is drastically reduced.

As the cam 31 configured as described above is driven to rotate as described above, the contact / separation adjusting means of the fixing device 20 releases the pressure contact between the fixing roller 21 and the pressure roller 24 as in the first embodiment. It is possible to instantaneously shift from the state to the pressure contact state.
Further, by providing the two stepped portions R21 on the peripheral surface of the cam 31, the contact / separation operation can be performed twice while the cam 31 rotates once.

  Thereby, even if the rotation speed of the cam 31 is further reduced, the contact / separation operation of the fixing roller 21 and the pressure roller 24 as in the first embodiment can be performed. Therefore, the cost of the stepping motor 42 is further reduced, and the degree of freedom in setting the transport path K of the apparatus main body 1 and setting the copy speed is further increased. In addition, since the two step portions R21 are equally arranged on the circumferential surface of the cam 31, the contact / separation operation performed twice during one rotation of the cam 31 (from the press release state to the press contact state). This is the operation to reach the pressure release state.)), And the control of the drive unit 41 becomes relatively simple.

As described above, in the fixing device 20 configured as in the second embodiment as well, as in the first embodiment, the contact between the fixing roller 21 and the pressure roller 24 from the pressure release state to the pressure contact state. The responsiveness of the separation operation is enhanced, power saving and cost reduction of the drive unit 41 are achieved, and the degree of freedom of design such as the conveyance path length is increased.
Further, with the reliable release of the pressure contact between the fixing roller 21 and the pressure roller 24, the permanent deformation of the fixing roller 21 and the pressure roller 24 is suppressed with a relatively simple configuration, and there is a problem such as a fixing failure. Is prevented.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIG.
FIG. 7 is a configuration diagram showing the cam 31 installed in the contact / separation adjusting means of the fixing device according to the third embodiment, and corresponds to FIG. 6 of the second embodiment. The third embodiment is different from the second embodiment in which two step portions R21 are provided on the circumferential surface of the cam 31.

As shown in FIG. 7, three smooth portions R <b> 12 and three step portions R <b> 21 are provided at equal intervals on the peripheral surface of the cam 31.
Specifically, a continuous first position R1 is provided in three places on the peripheral surface of the cam 31, and a second position R2 is also provided in three places. Further, when the cam 31 is rotated in the direction of the arrow, a smooth portion R12 is formed on the peripheral surface from the first position R1 to the second position R2 so that the distance from the rotation center gradually increases. Further, when the cam 31 is rotated in the direction of the arrow, a stepped portion R21 is formed on the circumferential surface from the second position R2 to the first position R1 so that the distance from the rotation center is drastically reduced.

When the cam 31 configured as described above is rotationally driven as described above, the contact / separation adjusting unit of the fixing device 20 releases the pressure contact between the fixing roller 21 and the pressure roller 24 as in the above embodiments. It is possible to instantaneously shift from the state to the pressure contact state.
Further, since the three stepped portions R21 are provided on the peripheral surface of the cam 31, the contact / separation operation can be performed three times during one rotation of the cam 31.

  Thereby, even if the rotation speed of the cam 31 is further reduced, the contact / separation operation of the fixing roller 21 and the pressure roller 24 as in the second embodiment can be performed. Therefore, the cost of the stepping motor 42 is further reduced, and the degree of freedom in setting the transport path K of the apparatus main body 1 and setting the copy speed is further increased. In addition, since the three step portions R21 are equally arranged on the circumferential surface of the cam 31, the contact / separation operation performed three times during one rotation of the cam 31 (from the press release state to the press contact state). This is the operation to reach the pressure release state.)), And the control of the drive unit 41 becomes relatively simple.

As described above, also in the fixing device 20 configured as in the third embodiment, the contact between the fixing roller 21 and the pressure roller 24 from the pressure release state to the pressure contact state is the same as in each of the above embodiments. The responsiveness of the separation operation is enhanced, power saving and cost reduction of the drive unit 41 are achieved, and the degree of freedom of design such as the conveyance path length is increased.
Further, with the reliable release of the pressure contact between the fixing roller 21 and the pressure roller 24, the permanent deformation of the fixing roller 21 and the pressure roller 24 is suppressed with a relatively simple configuration, and there is a problem such as a fixing failure. Is prevented.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the above-described embodiments can be modified as appropriate in addition to those suggested in the above-described embodiments. Is clear. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like that are suitable for implementing the present invention can be used.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a configuration diagram illustrating a fixing device installed in the image forming apparatus of FIG. 1. FIG. 3 is a configuration diagram illustrating a driving unit of contact / separation adjusting means in the fixing device of FIG. 2. FIG. 3 is a schematic diagram illustrating a state in which the contact between the fixing roller and the pressure roller is released in the fixing device of FIG. 2. FIG. 3 is a plan view showing a cam of a contact / separation adjusting unit in the fixing device of FIG. It is a top view which shows the cam of the contact-separation adjustment means installed in the fixing device in Embodiment 2 of this invention. It is a top view which shows the cam of the contact-separation adjustment means installed in the fixing device in Embodiment 3 of this invention.

Explanation of symbols

1 image forming apparatus body (apparatus body),
2 Document reading section, 3 Exposure section, 4 Image forming section, 7 Transfer section,
10 Document transport section, 12-14 Paper feed section,
20 fixing device, 21 fixing roller (heating member), 22 heater,
24 pressure roller (pressure member), 27 pressure lever, 28 bearing,
29 tension springs, 30 spindles, 31 cams,
40 control unit, 41 drive unit, P recording medium, K transport path,
R1 first position (pressure contact position), R2 second position (release position),
R12 smooth part, R21 step part.

Claims (5)

A fixing device for feeding a recording medium carrying an image between a heating member and a pressure member pressed against the heating member and fixing the image on the recording medium,
A contact / separation adjusting means for rotating the cam in a predetermined direction to press and release the heating member and the pressure member;
The peripheral surface of the cam includes a first position for pressing the heating member and the pressure member, and a second position for releasing the pressure contact between the heating member and the pressure member.
The cam includes a smoothing portion formed such that when rotated in the predetermined direction, the distance from the rotation center on the peripheral surface from the first position to the second position gradually increases or decreases; and in the predetermined direction And a step portion formed so that the distance from the center of rotation on the peripheral surface from the second position to the first position when it is rotated is drastically reduced or increased. The contact / separation adjusting unit performs pressure contact between the heating member and the pressure member when a job signal related to image formation is input to the image forming apparatus main body, and a job signal related to image formation is transmitted to the image forming apparatus main body. The fixing device according to claim 1, wherein the pressure contact between the heating member and the pressure member is released when no input is made. The fixing device according to claim 1, wherein the cam includes a plurality of the stepped portions on a circumferential surface thereof. The fixing device according to claim 3, wherein the plurality of stepped portions are arranged at equal intervals on a circumferential surface of the cam. An image forming apparatus comprising the fixing device according to claim 1.

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