Patent Application
20230273558
The present invention relates to a fixing apparatus preferably used in an image forming apparatus that utilizes an electrophotographic technique, such as a printer, a copying machine, a facsimile, or a multifunction machine.
Image forming apparatuses are equipped with a fixing apparatus for fixing a toner image on a recording material by applying heat and pressure to the recording material on which the toner image is formed. The fixing apparatus includes a rotating endless fixing belt, a fixing pad arranged non-rotatably on an inner circumference side of the fixing belt, and a pressure roller abutting against an outer circumference surface of the fixing belt. In the fixing apparatus, the fixing belt is pressed by the fixing pad and the pressure roller, by which a fixing nip portion is formed between the fixing belt and the pressure roller, and heat and pressure is applied to the recording material passing through the fixing nip portion, by which the toner image is fixed to the recording material.
If frictional force between the fixing belt and the fixing pad is great, rotation of the fixing belt is obstructed. Thus, an apparatus including a slide member that slides against a fixing belt to reduce the frictional force between the fixing belt and the fixing pad at the fixing nip portion where the pressure is high is proposed (Japanese Patent Application Laid-Open Publication No. 2017-181948). Recently, a slide member having a plurality of projected portions formed on a surface thereof is used to reduce the frictional force between the fixing belt and the slide member.
The fixing pad is provided with a fitting portion having a recessed shape, hereinafter referred to as a groove portion, in which the slide member is fit so that the slide member is retained on the fixing pad. Hitherto, the recording material could not be easily separated from the fixing belt due to the projected portions formed on the slide member, such that fixing failures on the recording material may occur.
In view of the problems mentioned above, the present technique aims at providing a fixing apparatus related to a configuration of fitting a slide member to a groove portion of a fixing pad and retaining the same therein, capable of suppressing occurrence of fixing failures on the recording material caused by the recording material not being separated from a fixing belt due to projected portions formed on the slide member.
According to a first aspect of the present invention, a fixing apparatus includes a belt having an endless shape and configured to apply heat to a recording material, a rotary member configured to abut against an outer circumference surface of the belt in a pressing direction, a pad member configured to form a nip portion by nipping the belt with the rotary member at an inner side of the belt, the rotary member being configured to nip and convey a recording material in a conveyance direction with the belt at the nip portion while applying heat and pressure to a toner image on the recording material to fix the toner image, and a slide member retained by the pad member and configured to slide against an inner circumference surface of the belt at the nip portion. The slide member includes a plurality of projections that protrude toward the rotary member on a side that slides against the belt and slide against the inner circumference surface of the belt. The pad member includes a guide portion that guides the belt after passing through the nip portion. In a state where the nip portion is formed, a distance in the conveyance direction between a first position and a second position is 3.0 mm or less, the first position being a downstream edge of a tip of a projection positioned most downstream in a direction of rotation of the belt among the plurality of projections, the second position being an upstream edge, in the direction of rotation of the belt, of the guide portion that comes into contact with the inner circumference surface of the belt. A distance in the pressing direction between a third position and a fourth position is 0.4 mm or more and 2.0 mm or less, the third position being the tip of the projection positioned most downstream in the direction of rotation of the belt among the plurality of projections, the fourth position being the upstream edge, in the direction of rotation of the belt, of the guide portion that comes into contact with the inner circumference surface of the belt.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A fixing apparatus according to a present embodiment will be described. At first, a general configuration of an image forming apparatus that is preferable for adopting the fixing apparatus according to the present embodiment will be described with reference to
An image forming apparatus 1 is a full-color printer adopting an electrophotographic system that includes four image forming units Pa, Pb, Pc, and Pd disposed to correspond to four colors, which are yellow, magenta, cyan, and black. The present embodiment is a tandem-type image forming apparatus 1 in which the image forming units Pa, Pb, Pc, and Pd are arranged along a direction of rotation of an intermediate transfer belt 204 described below. The image forming apparatus 1 forms a toner image on a recording material according to an image signal from a document reading apparatus 2 connected to an apparatus body 3 of the image forming apparatus 1 or a host apparatus such as a personal computer connected in a communicatable manner to the apparatus body 3. Examples of the recording material include paper, plastic films, cloths and other sheet materials.
As illustrated in
The apparatus body 3 is equipped with a plurality of image forming units Pa, Pb, Pc, and Pd, and image is formed in each image forming unit based on the above-mentioned image signals. That is, the image signals are converted into laser beams that have been subjected to pulse width modulation control (PWM) by the control unit 30. A polygon scanner 31 serving as an exposing unit scans laser beams corresponding to image signals. Then, laser beams are irradiated to photosensitive drums 200a to 200d serving as image bearing members of the respective image forming units Pa to Pd.
The image forming units form toner images of corresponding colors, wherein the image forming unit Pa forms a yellow (Y) toner image, the image forming unit Pb forms a magenta (M) toner image, the image forming unit Pc forms a cyan (C) toner image, and an image forming unit Pd forms a black (Bk) toner image. These image forming units Pa to Pd adopt an approximately identical configuration, such that the following description will describe the image forming unit Pa for forming a yellow (Y) toner image, and the descriptions on the other image forming unit Pb to Pd are omitted. In the image forming unit Pa, a toner image is formed on the surface of the photosensitive drum 200a based on image signals.
A charging roller 201a serving as a primary charger charges a surface of the photosensitive drum 200a to predetermined potential and prepares for the formation of an electrostatic latent image. The electrostatic latent image is formed on the surface of the photosensitive drum 200a charged to predetermined potential by laser beams from the polygon scanner 31. A developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a and forms a toner image. A primary transfer roller 203a performs discharge from a rear side of the intermediate transfer belt 204, applies a primary transfer bias of opposite polarity as toner, and transfers the toner image on the photosensitive drum 200a to the intermediate transfer belt 204. The surface of the photosensitive drum 200a after transfer is cleaned by a cleaner 207a.
Further, the toner image on the intermediate transfer belt 204 is conveyed to the subsequent image forming units, where toner images of respective colors formed in each of the image forming units are sequentially transferred in the order of Y, M, C, and Bk, such that a four-color image is formed on the surface thereof. The toner image having passed through the image forming unit Pd of Bk which is positioned most downstream in a direction of rotation of the intermediate transfer belt 204 is conveyed to a secondary transfer portion T2 composed of a secondary transfer roller pair 205, 206. Thereafter, by having a secondary transfer electric field having opposite polarity as the toner image on the intermediate transfer belt 204 is applied at the secondary transfer portion T2, by which a toner image is secondarily transferred from the intermediate transfer belt 204 to the recording material.
The recording material is stored in a cassette 9, and the recording material fed from the cassette 9 is conveyed to a registration portion 208 composed of a pair of registration rollers, for example, where it stands by at the registration portion 208. Thereafter, the timing at the registration portion 208 is controlled such that the toner image on the intermediate transfer belt 204 corresponds to the paper position, and the recording material is conveyed to the secondary transfer portion T2.
The recording material having the toner image transferred thereto at the secondary transfer portion T2 is conveyed to a fixing apparatus 8, and heat and pressure is applied at the fixing apparatus 8, by which the toner image borne on the recording material is fixed to the recording material. The recording material having passed through the fixing apparatus 8 is discharged onto a sheet discharge tray 7. When forming images on both sides of the recording material, after completing transferring and fixing of a toner image to a first surface, i.e., front surface, the surface of the recording material is reversed via a reverse conveyance portion 10, and transferring and fixing of a toner image to a second surface, i.e., rear surface, of the recording material is performed before the recording material is stacked on the sheet discharge tray 7.
The control unit 30 performs control of the entire image forming apparatus 1, as described above. Further, the control unit 30 is capable of performing various settings based on an input from an operation unit 4 included in the image forming apparatus 1. The control unit 30 includes a Central Processing Unit (CPU), a Read Only Memory (ROM), and a Random Access Memory (RAM). The CPU performs control of various units by reading programs corresponding to the control procedures stored in the ROM. The RAM stores work data and input data, and the CPU refers to the data stored in the RAM based on the programs described above and performs control.
Next, the configuration of the fixing apparatus 8 according to the present embodiment will be described with reference to
The fixing apparatus 8 includes a fixing belt 301 that is endless and rotatable, the pressure roller 305 that abuts against the fixing belt 301 and that serves as an opposing member that forms the fixing nip portion N together with the fixing belt 301, a heating roller 307, and a fixing pad unit 300.
The fixing belt 301 is arranged in a replaceable manner in the fixing pad unit 300. The fixing belt 301 has thermal conductivity and heat-resisting property, and it is formed in a thin cylindrical shape. In the present embodiment, the fixing belt 301 adopts a three-layer structure in which a base layer 301a is disposed on an inner circumference side, an elastic layer 301b is arranged on an outer circumference of the base layer 301a, and a release layer 301c is formed on an outer circumference thereof, as illustrated in
The pressure roller 305 is supported rotatably on a fixing frame (not shown) of the fixing apparatus 8, wherein a gear (not shown) is fixed to one end portion thereof in a width direction, and the pressure roller 305 is driven to rotate by being connected via the gear to a drive source such as a motor (not shown). In a state where the pressure roller 305 is rotated, rotational force of the pressure roller 305 is transmitted to the fixing belt 301 by frictional force generated at the fixing nip portion N. Thereby, the fixing belt 301 is rotated following the rotation of the pressure roller 305. That is, the pressure roller 305 is an example of a rotary member configured to abut against an outer circumference surface of the fixing belt 301 in a pressing direction.
The pressure roller 305 has an elastic layer 305b formed on an outer circumference of a rotation shaft 305c, and a release layer 305a is formed on an outer circumference of the elastic layer 305b, as illustrated in
As illustrated in
The heating roller 307 is arranged on an inner circumference side of the fixing belt 301, and stretches the fixing belt 301 together with the fixing pad unit 300. The heating roller 307 is formed in a cylindrical shape of metal such as aluminum and stainless steel, and a halogen heater 306 serving as a heat source for heating the fixing belt 301 is arranged in the inner side thereof. The heating roller 307 is heated to a predetermined temperature by the halogen heater 306.
In the present embodiment, the heating roller 307 is formed of an aluminum pipe having a thickness of “1 mm”, for example, from the viewpoint of thermal conductivity, and a surface layer thereof is subjected to anodizing treatment. The number of the halogen heater 306 can be one, but from the viewpoint of facilitating temperature distribution control of the heating roller 307 in the rotational axis direction, i.e., width direction, a plurality of halogen heaters 306 are desirably provided. The plurality of halogen heaters 306 have mutually varying light distributions in the width direction, and according to the size of the recording material, a lighting ratio is controlled by the control unit 30 (refer to
The heating roller 307 can have a pivot axis arranged either on one end or near a center of the rotational axis direction, i.e., width direction, and that swings so as to generate a tension difference between one side and the other side of the fixing belt 301 in the width direction to thereby move the fixing belt 301 in the width direction. That is, the fixing belt 301 may be skewed to one side of the end portions in the width direction, which is so-called belt skew, during rotation, due to a diametral accuracy of the heating roller 307 stretching the belt or an alignment accuracy with a fixing pad 303 described later. Therefore, by swinging the heating roller 307, the position of the fixing belt 301 in the rotational axis direction, i.e., skew position, is controlled. Further, the heating roller 307 is urged by a spring supported on a frame (not shown) of the fixing apparatus 8, and it can also serve as a tension roller for applying a predetermined tension to the fixing belt 301.
Next, the fixing pad unit 300 will be described. As illustrated in
In the present embodiment, the fixing belt 301 is pressed toward the pressure roller 305 from the inner circumference side by the fixing pad 303 supported on the fixing stay 302. Thereby, the fixing nip portion N having a wide nip with sufficient conveyance direction length and width direction length is formed between the pressure roller 305 and the fixing belt 301. Further, by having the fixing pad 303 made of resin supported by the fixing stay 302 made of metal having a greater rigidity, deflection of the fixing pad 303 caused by the pressure received during pressing operation is reduced, such that a uniform fixing nip width in the width direction can be obtained.
The fixing pad 303 serving as a retaining member is disposed non-rotatably on an inner circumference side of the fixing belt 301 and includes a groove portion 303f (refer to
As illustrated in
If frictional force between the fixing belt 301 and the fixing pad 303 is great, the rotation of the fixing belt 301 is obstructed. Therefore, according to the present embodiment, as illustrated in
The slide member 304 has a heat-resisting property and strength, and is provided with a slide surface that abuts against the inner circumference surface of the fixing belt 301 being rotated and slides against the fixing belt 301 in a state retained by the fixing pad 303. By interposing the slide member 304 between the fixing pad 303 and the fixing belt 301, frictional force between the fixing pad 303 and the fixing belt 301 is reduced, such that the rotation of the fixing belt 301 is not obstructed by the fixing pad 303. A lubricant for smoothly sliding the fixing belt 301 against the slide member 304 can be applied on the inner circumference surface of the fixing belt 301. For example, a silicone oil can be used as the lubricant.
As described above, according to the present embodiment, frictional force between the fixing pad 303 and the fixing belt 301 is reduced by the slide member 304, and according to the present embodiment, the slide member 304 has a slide surface that slides against the fixing belt 301 formed in a concave-convex shape or an embossed shape, as illustrated in
The slide member 304 is formed of a metal material such as stainless steel (SUS), copper, or aluminum. In the case of the present embodiment, a stainless steel (SUS) having a thickness of “1 mm” is used to form the slide member 304. The slide member 304 is not limited to metal, and it can be formed using engineering plastics such as polyimide resin (PI), polyether ether ketone resin (PEEK), or LCP (liquid crystal polymer resin).
As illustrated in
Further, a low friction layer 304c for reducing frictional force generated between the fixing belt 301 is provided on the surface of the slide member 304 using polytetrafluoroethylene resin (PTFE), or PFA, for example. In the present embodiment, a PTFE with a thickness of “20 μm” is coated on the surface of the base 304a and the projected portions 304b.
As illustrated in
As described above, the fixing pad 303 retains the slide member 304 such that the inner circumference surface of the fixing belt 301 slides against the tip surface of the projected portions 304b. In order to do so, the groove portion 303f having a recessed shape is formed on the fixing pad 303 for fitting and retaining the slide member 304 on the opposite side from the side being supported by the fixing stay 302.
According to the present embodiment, the slide member 304 has a first planar area 3041 and a second planar area 3042 on both end portions in the conveyance direction, i.e., short direction, in which projected portions 304b are not formed. The first planar area 3041 is a flat portion area from a downstream edge of the base 304a to a most downstream projected portion 304b1 that is formed most downstream among the plurality of projected portions 304b in the conveyance direction. The second planar area 3042 is a flat portion area from an upstream edge of the base 304a to a most upstream projected portion 304b2 that is formed most upstream among the plurality of prof ected portions 304b in the conveyance direction. In the present embodiment, in a state where the slide member 304 is retained by the fixing pad 303, the first planar area 3041 and the second planar area 3042 are in contact with the bottom surface 303h of the groove portion 303f of the fixing pad 303, similar to the base 304a.
In the case of a configuration in which the slide member 304 is fit to and retained by the groove portion 303f of the fixing pad 303, the recording material is not easily separated appropriately from the fixing belt 301, and fixing failures of the recording material may be caused. This comparative configuration will be described based on
In the following description, in a state where the slide member 304 slides against the fixing belt 301, a difference between a tip of the most downstream projected portion 304b1 that is arranged most downstream in the conveyance direction, i.e., arrow X direction, among the projected portions 304b and a proximity position 303b1 that is closest to the fixing nip portion N in the downstream-side guide portion 303b regarding the direction of protrusion of the projected portions 304b, i.e., opposite direction as arrow Z, when viewed in the width direction, i.e., arrow Y direction, is denoted as height “H”. Further, a distance between a downstream end of the tip of the most downstream projected portion 304b1 and the proximity position 303b1 regarding the conveyance direction is denoted as distance “L”. A stretched state of the fixing belt 301 by the fixing pad 303 and the slide member 304 downstream of the fixing nip portion N is changed in accordance with the height “H” and the distance “L”.
According to the stretched state of the fixing belt 301 in the case where the height “H” is smaller than a predetermined height and the distance “L” is greater than a predetermined distance, the fixing belt 301 that has passed through the fixing nip portion N cannot be raised sharply, and so it is difficult to ensure a separating function of the recording material from the fixing belt 301. For example, as illustrated in
If the fixing belt 301 forms a trajectory in proximity to the recording material, the force for separating the recording material having passed through the fixing nip portion N from the fixing belt 301 becomes small, such that the desired separating function cannot be obtained. Then, excessive heat is applied to the recording material from the fixing belt 301, such that fixing failures of toner image occurs by excessive heating. Further, the recording material having passed through the fixing nip portion N may be waved or deformed by having heat and pressure applied thereto. If the recording material having passed through the fixing nip portion N and the fixing belt 301 are in proximity, the recording material having passed through the fixing nip portion N will have some areas come into contact with the fixing belt 301 and other areas that do not, and fixing failures such as gloss unevenness occur.
Further, as illustrated in
Therefore, according to the present embodiment, the fixing belt 301 is caused to rotate along a trajectory that is raised sharply after passing through the fixing nip portion N such that the height “H” is equal to or greater than the predetermined height and the distance “L” is equal to or smaller than the predetermined distance to suppress the occurrence of fixing failures as described above. The configuration of such a present embodiment will be described below with reference to
In the present embodiment, the height “H” is “0.4 mm or more and 2 mm or less”, and the distance “L” is “3 mm or less”. That is, in a state slid against the fixing belt 301, the tip of the most downstream projected portion 304b1 in the slide member 304 is protruded by “0.4 mm or more and 2 mm or less” from the proximity position 303b1 closest to the fixing nip portion N in the downstream-side guide portion 303b when viewed in the width direction. Further, the slide member 304 has the most downstream projected portion 304b1 formed on the base 304a such that the distance in the conveyance direction between the downstream edge of the tip of the most downstream projected portion 304b1 and the proximity position 303b1 (distance “L”) is “3 mm or less”. In that case, the downstream-side guide portion 303b is positioned such that the proximity position 303b1 is retreated in the arrow Z direction from the tip of the most downstream projected portion 304b1. That is, in a state where the fixing nip portion N is formed, the distance L is a distance in the conveyance direction between a first position and a second position. The first position is a downstream edge of a tip of the projected portion 304b1 positioned most downstream in a direction of rotation of the fixing belt 301 among the plurality of projected portions 304b. The second position is an upstream edge, in the direction of rotation of the fixing belt 301, of the downstream-side guide portion 303b that comes into contact with the inner circumference surface of the fixing belt 301. Also, the height H is a distance in the pressing direction between a third position and a fourth position. The third position is the tip of the projected portion 304b1 positioned most downstream in the direction of rotation of the fixing belt 301 among the plurality of projected portions 304b. The fourth position is the upstream edge, in the direction of rotation of the fixing belt 301, of the downstream-side guide portion 303b that comes into contact with the inner circumference surface of the fixing belt 301.
Thereby, in the present embodiment, as can be recognized in comparison to the comparative example illustrated in
In the present embodiment, a configuration is adopted in which the height “H” is “0.4 mm or more and 2 mm or less” and the distance “L” is “3 mm or less” across at least the entire sheet passing area of the fixing nip portion N in the width direction. Therefore, even in the case of a recording material of any size, the desired separating function can be obtained, and fixing failures can be suppressed.
If the height of the plurality of projected portions 304b on the slide member 304 is not uniform, unevenness of pressure may be generated in the fixing nip portion N and fixing failures may be caused in the recording material. The height difference of the projected portions 304b that causes fixing failures is, for example, approximately 20 to 50 μm. In order to prevent fixing failures of the recording material caused by the height of the projected portions 304b, for example, a contactless inspection apparatus by laser scanning is used to measure the heights of the plurality of projected portions 304b and perform inspection of the slide member 304. The contactless inspection apparatus measures the heights of the projected portions 304b by a line scanning sensor, called a scan sensor, using laser light, and compares the measured values with a reference value that is provided in a projected portion shape profile prepared in advance. Then, if the difference between the measured values and the reference value is within a predetermined range, such as 15 μm or less, it is determined that the slide member 304 is a good product. The slide member 304 that is not determined as a good product will not be used.
When being formed of a base material such as stainless steel, the slide member 304 may be warped from a center portion in the width direction, i.e., longitudinal direction, due to the accuracy of the base material or the residual stress during processing of the base material. The difference in height between the end portions and the center portion in the width direction caused by warping is approximately “2 mm”, for example, though it may vary among the individual slide members 304. If the slide member 304 is warped, it is difficult to measure the height of the projected portions 304b using the contactless inspection apparatus with high accuracy, such that it is necessary to measure the height of the projected portions 304b after straightening the warping of the slide member 304. In order to straighten the warping of the slide member 304, the slide member 304 is nipped between and fixed, i.e., clamped, by the surface plate and clamp members, as described below. If the thickness of the base 304a is “1.0 mm”, for example, a clamping force by clamp members (not shown) that is required to straighten the warping of the slide member 304 is set to approximately “2 to 4 N”.
In the present embodiment, the first planar area 3041 and the second planar area 3042 are clamped, such that the height of the projected portions 304b is measured in a state where the warping of the slide member 304 is straightened (refer to
In order to clamp the slide member 304 reliably and straighten the warping thereof, the conveyance direction length of the first planar area 3041 and the second planar area 3042 is preferably “1.0 mm” or more. Further, the first planar area 3041 and the second planar area 3042 are preferably formed across the entire area in the width direction, i.e., entire area in the longitudinal direction, of the slide member 304. In the present embodiment, the first planar area 3041 and the second planar area 3042 are formed across an entire area of the slide member 304 in the width direction intersecting the conveyance direction.
In the case of the slide member 304 of the present embodiment, as illustrated in
As described above, from the viewpoint of clamping the slide member 304 infallibly, the conveyance direction length of the first planar area 3041 and the second planar area 3042 (L1, L2) is “0.5 mm” or more, preferably “1.0 mm” or more. However, if the conveyance direction length of the first planar area 3041 and the second planar area 3042 (L1, L2) is longer than necessary, the conveyance direction length of the fixing nip portion N (refer to
In view of the above-mentioned points, the conveyance direction length of the first planar area 3041 and the second planar area 3042 is set to “2.0 mm” or less. In conclusion, the conveyance direction length (L1, L2) of the first planar area 3041 and the second planar area 3042 is “0.5 mm or more and 2.0 mm or less”, preferably “1.0 mm or more and 1.5 mm or less”. The conveyance direction length (L1) of the first planar area 3041 is smaller than the above-mentioned distance “L” (L1<L). The first planar area 3041 and the second planar area 3042 are examples of planar areas at each of both end portions in the short direction in a range of 0.5 mm or more and 2.0 mm or less in the short direction from each of both edges of the slide member 304. Also, the first planar area 3041 and the second planar area 3042 are areas where the plurality of projected portions 304b are not formed and the slide member 304 is not in contact with the fixing belt 301.
The embodiments described above is not limited to the configuration of heating the fixing belt 301, and the present technique is applicable to a configuration in which a pressing belt in the shape of a belt is used instead of the pressure roller 305, wherein the pressing belt is heated by a heater. In that case, a direction in which the pressing belt presses the opposing roller is referred to as the pressing direction.
According to the present technique, a configuration of fitting and retaining a slide member in a groove portion of a retaining member can be realized by a simple configuration while suppressing the occurrence of fixing failures of the recording material caused by the recording material not being separated desirably from the fixing belt due to projected portions formed on the slide member.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2022-028927, filed Feb. 28, 2022 which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-028927 | Feb 2022 | JP | national |
