Patent Grant
9811033
This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2015-240046 filed on Dec. 9, 2015, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a fixing device mounted in an image forming apparatus employing an electro-photographic method, such as a copier, a printer, a facsimile, and a multifunction peripheral (MFP) equipped with functions of these apparatuses, and in particular, the present disclosure relates to a fixing device capable of releasing nip pressure between a heating member and a pressure member, and an image forming apparatus including such a fixing device.
Conventionally, an image forming apparatus includes a fixing device for fixing a toner image transferred from an image carrier onto a recording material such as a sheet. Known examples of fixing methods employed in fixing devices include a roller fixing method using a heating roller and a pressure roller that rotate in contact with each other, and a belt fixing method using an endless fixing belt as a heating member. For example, in a fixing device employing the roller fixing method, a toner image carried on a sheet is fixed on the sheet by heating and pressing the toner image at a nip portion between a fixing roller and a pressure roller pressed against each other.
In such a fixing device, a sheet jam is sometimes caused where a sheet under conveyance is stuck in a nip portion between the heating roller and the pressure roller. Thus, it is necessary to provide a configuration for releasing nip pressure between a heating member and a pressure member to clear a sheet jam.
For example, there is known a fixing device that includes a pressure mechanism giving nip pressure to a nip portion between a pressure member and a heating member, and a pressure releasing mechanism varying the nip pressure given to the nip portion, the pressure releasing mechanism being an eccentric cam contacting a roller of a spring compression member included in the pressure mechanism, and having a variable distance from its rotation center to its outer peripheral surface.
There is also known a fixing device that includes pressed state switching means switching between a first state where a fixing roller (a heating member) and a pressure member are relatively pressed against each other and a second state where the pressed state is released, the pressed state switching means being an eccentric cam.
According to one aspect of the present disclosure, a fixing device includes a heating member, a pressure member contacting the heating member to form a nip portion, a pressure mechanism giving nip pressure to the nip portion, and a pressure adjustment mechanism varying the nip pressure given to the nip portion. In the fixing device, a recording medium carrying a toner image passes through the nip portion to have the toner image heated and pressed to be fixed on the recording medium. The pressure mechanism includes a pressing member and a biasing member. The pressing member holds one of the pressure member and the heating member, and the pressing member is supported to be swingable in directions toward and away from the other of the pressure member and the heating member. The biasing member has an end thereof in contact with the pressing member to bias the pressing member in a direction toward or away from the other of the pressure member and the heating member. The pressure adjustment mechanism includes an eccentric cam in which a distance from a rotation center of the eccentric cam to an outer peripheral surface of the eccentric cam varies in a circumferential direction, the pressure adjustment mechanism using one of a small-diameter part and a large-diameter part formed in the outer peripheral surface of the eccentric cam to allow the pressure mechanism to give the nip pressure to the nip portion, the pressure adjustment mechanism using the other of the small-diameter part and the large-diameter part to allow the pressure mechanism to release the nip pressure. When the large-diameter part of the eccentric cam is used to allow the pressure mechanism to give the nip pressure to the nip portion or release the nip pressure, the eccentric cam constantly receives reaction force urging the eccentric cam to rotate in a direction toward the small-diameter part.
Further features and specific advantages of the present disclosure will become apparent from the following descriptions of preferred embodiments.
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.
Inside a main body of the image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are arranged in order from a left side in
These image forming portions Pa, Pb, Pc, and Pd include photosensitive drums 1a, 1b, 1c, and 1d, respectively, that carry visible images (toner images) of corresponding colors, and further, an intermediate transfer belt 8 configured to rotate in a counterclockwise direction in
A sheet P, onto which a toner image is to be transferred, is stored in a sheet cassette 16 in a lower part of the main body of the image forming apparatus 100, and the sheet P is conveyed via a sheet feeding roller 12a and a registration roller pair 12b to a secondary transfer roller 9.
Next, the image forming portions Pa to Pd will be described. Provided around and below the photosensitive drums 1a to 1d, which are disposed to be rotatable, are the following components: charging devices 2a, 2b, 2c, and 2d that charge the photosensitive drums 1a, 1b, 1c, and 1d, respectively; an exposure unit 5 that exposes the photosensitive drums 1a to 1d to light based on image data; developing devices 3a, 3b, 3c, and 3d that develop, using toner, electrostatic latent images formed on the photosensitive drums 1a, 1b, 1c, and 1d, respectively; and cleaning devices 7a, 7b, 7c, and 7d that recover and remove developer (toner) remaining on the photosensitive drums 1a, 1b, 1c, and 1d, respectively, after the toner images on the photosensitive drums 1a to 1d are transferred.
In a copying operation, an image reading portion 23 reads image data of a document and converts the image data into an image signal. The charging devices 2a, 2b, 2c, and 2d uniformly charge surfaces of the photosensitive drums 1a, 1b, 1c, and 1d, respectively. Then, based on the image data, the exposure unit 5 irradiates the photosensitive drums 1a to 1d with light to form electrostatic latent images on the photosensitive drums 1a to 1d according to the image data. The developing devices 3a to 3d include developing rollers (developer carriers) each facing a corresponding one of the photosensitive drums 1a to 1d, and the developing devices 3a to 3d are each filled with a predetermined amount of two-component developer containing toner of a corresponding one of the respective colors, namely, magenta, cyan, yellow, and black.
Primary transfer rollers 6a, 6b, 6c, and 6d give a predetermined transfer voltage across the primary transfer rollers 6a, 6b, 6c, and 6d and the photosensitive drums 1a, 1b, 1c, and 1d, respectively. Thereby, the magenta, cyan, yellow, and black toner images formed on the photosensitive drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. Thereafter, residual toner remaining on the surface of each of the photosensitive drums 1a, 1b, 1c, and 1d is removed by the cleaning devices 7a, 7b, 7c, and 7d, respectively.
The intermediate transfer belt 8 is wound around and between a driven roller 10 and a driving roller 11. The intermediate transfer belt 8 starts to rotate in the counterclockwise direction in conjunction with rotation of the driving roller 11 caused by a belt driving motor. Then, the sheet P is conveyed from the registration roller pair 12b at a predetermined timing to a nip portion (a secondary transfer nip portion) between the intermediate transfer belt 8 and the secondary transfer roller 9 contacting the intermediate transfer belt 8. At the nip portion, a full-color image is secondarily transferred onto the sheet P. The sheet P onto which the toner image has been transferred is conveyed through a sheet conveyance path 14 to the fixing device 13.
At the fixing device 13, the sheet P is heated and pressed while passing through a nip portion (a fixing nip portion) between a fixing roller 131 and a pressure roller 132 (for both, see
The fixing roller 131 includes a stainless steel cylinder as a base 131a and an elastic layer 131d made of a silicone rubber sponge, for example. The elastic layer 131d helps improve elasticity and releasing performance of a nip portion N formed by pressing the fixing roller 131 against the pressure roller 132. Between the base 131a and the elastic layer 131d, there is formed a heat insulating layer 131b and an induction heat generation layer 131c in order from the base 131a side.
The pressure roller 132 includes an aluminum core as a base 132a, an elastic layer 132b formed of a silicone rubber on the base 132a, and a release layer 132c formed of a fluorine resin as a tube covering a surface of the elastic layer 132b. The elastic layer 132b gives elasticity to the nip portion N. The release layer 132c helps improve releasing performance in fixing an unfixed toner image by fusing at the nip portion N.
The pressure roller 132 is driven to rotate by a drive source such as a motor (unillustrated), and is further pressed by a later-described pressure mechanism 50 against the fixing roller 131 in a direction toward a center of the fixing roller 131. Thereby, the pressure roller 132 is pressed against the fixing roller 131, and when the pressure roller 132 rotates, the fixing roller 131 also rotates following the rotation of the pressure roller 132 such that surfaces of the fixing roller 131 and the pressure roller 132 facing at the nip portion N move in a same direction.
The temperature sensors 134 are disposed on a surface of the fixing roller 131, one disposed in a sheet-passing region in a middle part of the surface in an axial direction (a direction of the width of the fixing roller 131), another and the other disposed facing each other at end portions of the surface in the axial direction, the end portions being non-sheet-passing regions when a small-size sheet passes or an A4-size sheet passes with a short side thereof ahead, and the temperature sensors 134 detect temperatures of the regions. Based on the temperatures detected by the temperature sensors 134, power supply to the induction heating portion 133 is controlled to maintain temperature of the surface of the fixing roller 131 at a predetermined temperature.
The induction heating portion 133 includes an excitation coil 133a, a bobbin 133b, and a core 133c, and heats the fixing roller 131 by electromagnetic induction. The induction heating portion 133 extends in an axial direction of the fixing roller 131, and is disposed facing the fixing roller 131 to surround part of the outer periphery of the fixing roller 131.
The excitation coil 133a, which is made of a copper wire, is wound on the bobbin 133b to be arranged in a spiral shape across a part of the outer periphery of the fixing roller 131 such that the excitation coil 133a circles around a middle part of the core 133c in an axial direction. The excitation coil 133a is connected to an unillustrated power supply, and generates a magnetic flux using a high-frequency current supplied from the power supply. The magnetic flux from the induction heating portion 133 is guided in a direction parallel to the sheet on which
Based on temperatures detected by the temperature sensors 134, power of the power supply is controlled such that the fixing roller 131 is heated to a predetermined temperature by the induction heating portion 133. When the fixing roller 131 is heated to the predetermined temperature, the sheet P nipped at the nip portion N is heated and is also pressed by the pressure roller 132. Thereby, the toner in a powder state on the paper sheet P is fused to be fixed.
The pressure mechanism 50 presses the fixing roller 131 against the pressure roller 132 to generate nip pressure at the nip portion N (see
The roller pressing member 51 is made of a sheet of metal in a predetermined shape. The pressure roller 132 is rotatably supported on a substantially middle part of the roller pressing member 51. In a lower part of the roller pressing member 51, there is formed a bearing hole 54, in which a support shaft (not shown) provided on the housing of the fixing device 13 is fitted, and the roller pressing member 51 is held by the housing of the fixing device 13 to be swingable about the support shaft as a fulcrum. One end of the pressing spring 53 is in contact with an upper part of the roller pressing member 51.
The spring compression member 52 is made of a sheet of metal in a predetermined shape. At a right side part of the spring compression member 52, there is formed a contact portion 52a, which has a shape of a flat plate. The spring compression member 52 is held on the housing of the fixing device 13 to be swingable about the same fulcrum (the support shaft) as the roller pressing member 51. The other end of the pressing spring 53 is in contact with an upper part of the spring compression member 52. A cylindrical roller 61 is rotatably attached to the spring compression member 52.
Two ends of the pressing spring 53 are respectively in contact with the roller pressing member 51 to compress the spring compression member 52 from its natural length. With this configuration, the roller pressing member 51 and the spring compression member 52 are biased by the pressing spring 53 in directions away from each other, and as a result, the fixing roller 131 is pressed against the pressure roller 132 to give a predetermined pressure to the nip portion N.
The pressure releasing mechanism 60 varies biasing force that the pressing spring 53 generates, and the pressure releasing mechanism 60 includes the pair of eccentric cams 62 disposed one on the side of each end of the fixing roller 131 and a connection shaft 63. Note that
At one end of the connection shaft 63, a drive coupling 65 is disposed to be connected with a gear train 72 of a later-described drive portion 70. The pair of eccentric cams 62 are fixed to the connection shaft 63 to be aligned with each other in phase. Thereby, rotation drive force from the drive portion 70 is transmitted simultaneously to the eccentric cam 62 on the right and to the eccentric cam 62 on the left, such that the biasing force generated by the pressing spring 53 is varied simultaneously on both sides of the fixing roller 131.
Each eccentric cam 62 is rotatable together with the connection shaft 63, and contacts a roller 61 attached to the spring compression member 52. As illustrated in
The distance (a radius) R from the rotation center O to the outer peripheral surface 62b of the eccentric cam 62 is not constant in the vicinity of the pressing position P1, but the radius R varies, continuously increasing in a region (of the angle θ) from the releasing position P2 to the pressing position P1. As a result, the eccentric cam 62 constantly receives from the roller 61 reaction force (resistance force) in a rotation direction (a direction toward the releasing position P2).
The drive portion 70 is disposed at the side of one end of the fixing roller 131, and includes a motor 71 and the gear train 72. The motor 71 is a forwardly and reversely rotatable DC motor, for example. When the motor 71 is driven to rotate by a motor drive circuit (not shown), the eccentric cam 62 is caused to rotate forwardly or reversely via the gear train 72, the drive coupling 65, and the connection shaft 63.
Next, a description will be given of operations of the pressure mechanism 50 and the pressure releasing mechanism 60 in the fixing device 13 of the present embodiment. In a normal printing state, as illustrated in
In a case where a sheet is jammed in the nip portion N, the motor 71 is driven to rotate in a predetermined direction by a predetermined amount to rotate the eccentric cam 62 by 225° from the state illustrated in
After the sheet jam is cleared, the eccentric cam 62 is rotated in a reverse direction by 225° such that the pressing position P1 of the eccentric cam 62 returns into contact with the roller 61 as illustrated in
In the present embodiment, the radius R of the eccentric cam 62 varies continuously increasing from the releasing position P2 to the pressing position P1, and thus, when the eccentric cam 62 is in contact with the roller 61 at the pressing position P1, the eccentric cam 62 constantly receives, from the roller 61, the reaction force urging the eccentric cam 62 in a direction from the pressing position P1 toward the releasing position P2. This helps prevent an abrupt increase of the reaction force in the rotation direction of the eccentric cam 62 from occurring in switching a contact position at which the eccentric cam is in contact with the roller 61 from the pressing position P1 to the releasing position P2. This allows smooth rotation of the eccentric cam 62 and helps reduce noise caused due to backlash (play) in meshing parts of the drive coupling 65 and the gear train 72.
In the present embodiment, the eccentric cam 62 is rotated by 225°, as the rotation angle θ, to switch the contact position of the eccentric cam 62 between the pressing position P1 and the releasing position P2, but the rotation angle θ may be appropriately set as necessary. Here, by setting the rotation angle θ to 180° or larger, it is possible to reduce an amount of variation (a rate of variation per unit angle) in radius R in switching the contact position between the pressing position P1 and the releasing position P2, and to further moderate load variation in releasing the nip pressure.
In the present embodiment, the radius R of the eccentric cam 62 continuously increases in the region from the releasing position P2 to the pressing position P1, but instead, the radius R may continuously increase from the releasing position P2 to a position past the pressing position P1. In this case, it is possible to make the reaction force in the rotation direction act on the eccentric cam 62 more securely when the pressing position P1 of the eccentric cam 62 is in contact with the roller 61.
As is clear from
In contrast, in the case of using the eccentric cam 62 with the radius R constant in the vicinity of the pressing position P1 (indicated by a broken line in
From these results, it was confirmed that the use of the eccentric cam 62 with the radius R continuously increasing from the releasing position P2 to the pressing position P1 effectively reduced noise generated in the course of releasing the nip pressure between the fixing roller 131 and the pressure roller 132.
It should be understood that the present disclosure is not limited to the above embodiments, and various modifications are possible within the scope of the present disclosure. For example, in the above-described embodiments, an example has been dealt with to which the present disclosure is applied to a roller-fixing type fixing device 13, but this is not meant as a limitation. The present disclosure is applicable to a belt-fixing fixing device using an endless fixing belt as a heating member, a fixing device employing a method where a heating member is built by using a fixedly supported heating body and a heat-resistant film slidable in tight contact with the heating body, and the heating body and a pressure roller are pressed against each other with the heat-resistant film interposed therebetween. Further, as for the heat source, the induction heating portion 133 may be replaced with a heater, and the pressure mechanism 50 and the pressure releasing mechanism 60 may be provided on the pressure roller 132.
In the above-described embodiments, the eccentric cam 62 is in contact with the spring compression member 52 on a side opposite to the pressing spring 53, but the eccentric cam 62 may be in contact with the spring compression member 52 on a reverse side (on the pressing spring 53 side). In that case, the eccentric cam 62 compresses the pressing spring 53 to release the nip pressure between the fixing roller 131 and the pressure roller 132 when the large-diameter part (the position of P1 in
And, with the radius R continuously increasing in the range from the small-diameter part to the large-diameter part as in the above-described embodiments, the eccentric cam 62 constantly receives reaction force that urges the eccentric cam 62 to rotate in the direction toward the small-diameter part when the large-diameter part of the eccentric cam 62 is in contact with the spring compression member 52. This makes it possible to effectively reduce noise generated in the course of giving nip pressure between the fixing roller 131 and the pressure roller 132.
The present disclosure is applicable to a fixing device for use in an image forming apparatus employing the electro-photographic method, such as a copier, a printer, a facsimile machine, or a multifunction peripheral having functions of these. By the use of the present disclosure, it is possible to provide a fixing device capable of reducing noise generated in the course of releasing a state where a heating member and a pressure member are pressed against each other, and an image forming apparatus including the same.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-240046 | Dec 2015 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20110222881 | Yamada | Sep 2011 | A1 |
| 20150117920 | Moteki | Apr 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 2012-128222 | Jul 2012 | JP |
| 2013-57791 | Mar 2013 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20170168439 A1 | Jun 2017 | US |
