Fixing device, image forming apparatus, film thickness adjustment method, and film thickness adjustment program

Abstract

To form a film of lubricant with an appropriate film thickness on an inner peripheral surface of a fixing belt.SOLUTION: A fixing device 50 comprises: a pressure roller 55; an endless fixing belt 57; a pad member 60 that is provided inside the fixing belt 57 and facing the pressure roller 55, and forms a nip part N where the fixing belt 57 and the pressure roller 55 are in contact with each other; a grease application part 70 that supplies lubricant to an inner peripheral surface of the fixing belt 57; and a regulation part 80 that adjusts the film thickness of a film of the lubricant formed on the inner peripheral surface of the fixing belt 57.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a fixing device, an image forming apparatus, a film thickness adjustment method, and a film thickness adjustment program, and more particularly to a fixing device that fixes toner to a recording medium, an image forming apparatus including the fixing device, a film thickness adjustment method executed by the fixing device, and a film thickness adjustment program that causes a computer to execute the film thickness adjustment method.

Background Art

[0002] Image forming apparatuses such as copiers, printers, and facsimile machines are provided with a fixing device that fixes toner to paper by pressing and heating the paper on which a toner image formed of toner is formed.

[0003] For example, in Japanese Patent Application Laid-Open No. 2017-227709, an endless fixing belt that is rotatably stretched, a heating unit that heats the fixing belt, a fixing member that is disposed outside the fixing belt and presses against the fixing belt, a pressing member that is disposed inside the fixing belt and presses the fixing member via the fixing belt, and a lubricant supply unit that supplies a lubricant between the pressing member and the fixing belt by supplying the lubricant to the inner peripheral surface of the fixing belt are provided. The lubricant supply unit includes a holding unit that is disposed inside the fixing belt, holds the lubricant, and has a longitudinally shaped lubricant discharge port that extends along the width direction of the fixing belt. According to the fixing device described in Japanese Patent Application Laid-Open No. 2017-227709, the amount of lubricant applied can be made constant.

[0004] However, there is already a lubricating layer attached to the inner surface of the fixing belt, and the thickness of the lubricating layer combined with the supplied amount is not necessarily constant. Furthermore, since the lubricant in the fixing belt contains impurities and its viscosity has changed, even if the amount of lubricant supplied is made constant, the film thickness of the lubricant film cannot always be optimized.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2017-227709 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] One object of the present invention is to provide a fixing device capable of forming a lubricant film having an appropriate film thickness on the inner peripheral surface of a fixing belt.

[0007] Another object of the present invention is to provide an image forming apparatus capable of forming a lubricant film having an appropriate film thickness on the inner peripheral surface of a fixing belt.

[0008] Still another object of the present invention is to provide a film thickness adjusting method capable of forming a lubricant film having an appropriate film thickness on the inner peripheral surface of a fixing belt.

[0009] Still another object of the present invention is to provide a film thickness adjusting program capable of forming a lubricant film having an appropriate film thickness on the inner peripheral surface of a fixing belt. MEANS FOR SOLVING THE PROBLEMS

[0010] According to an aspect of the present invention, a fixing device includes a pressure roller, an endless fixing belt, a pressing member provided inside the fixing belt and facing the pressure roller to form a nip portion where the fixing belt and the pressure roller contact each other, and a lubricant adjusting means for supplying a lubricant to the inner peripheral surface of the fixing belt and adjusting the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt.

[0011] According to another aspect of the present invention, an image forming apparatus includes the above-described fixing device.

[0012] According to still another aspect of the present invention, a film thickness adjustment method is a film thickness control method for controlling a fixing device. The fixing device includes a pressure roller, an endless fixing belt, a pressing member provided inside the fixing belt and facing the pressure roller to form a nip portion where the fixing belt and the pressure roller come into contact with each other, a lubricant adjusting means for supplying a lubricant to the inner peripheral surface of the fixing belt and adjusting the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt, and a control means for controlling the lubricant adjusting means. The fixing device is caused to execute a film thickness detection step of detecting the film thickness, and an adjustment control step of controlling the lubricant adjusting means based on the film thickness detected in the film thickness detection step.

[0013] According to still another aspect of the present invention, a film thickness adjustment program is a film thickness control program executed by a computer for controlling a fixing device. The fixing device includes a pressure roller, an endless fixing belt, a pressing member provided inside the fixing belt and facing the pressure roller to form a nip portion where the fixing belt and the pressure roller come into contact with each other, a lubricant adjusting means for supplying a lubricant to the inner peripheral surface of the fixing belt and adjusting the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt, and a control means for controlling the lubricant adjusting means. The computer is caused to execute a film thickness detection step of detecting the film thickness, and an adjustment control step of controlling the lubricant adjusting means based on the film thickness detected in the film thickness detection step.

Brief Description of the Drawings

[0014]

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Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0016] FIG. 1 is a first perspective view showing the appearance of a printer in one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of the internal configuration of the printer. Hereinafter, for the sake of explanation, the left-right direction in FIG. 2 is referred to as the left-right direction, and the front-back direction is referred to as the depth direction. The direction from left to right in the left-right direction is referred to as the right side direction, and the direction from right to left is referred to as the left side direction. The direction from the front to the back in the depth direction is referred to as the front direction, and the direction from the back to the front is referred to as the back direction.

[0017] Referring to FIGS. 1 and 2, the printer 100 is an example of an image forming apparatus, and includes an image forming unit 140 for forming an image on a sheet based on image data, and a paper feeding unit 150 for supplying paper to the image forming unit 140. The sheet is a recording medium including paper such as paper and an OHP (OverHead Projector) sheet. Here, the case where paper is used as an example of the sheet will be described.

[0018] The image forming unit 140 includes image forming units 20Y, 20M, 20C, and 20K for yellow, magenta, cyan, and black, respectively. Here, "Y", "M", "C", and "K" represent yellow, magenta, cyan, and black, respectively. Printing data for yellow, magenta, cyan, and black are input to the image forming units 20Y, 20M, 20C, and 20K, respectively. Since the image forming units 20Y, 20M, 20C, and 20K only differ in the color of the toner they handle, the image forming unit 20Y for forming a yellow image will be described here.

[0019] The image forming unit 20Y includes an exposure device 21Y into which yellow printing data is input, a photosensitive drum 23Y serving as an image carrier, a charging roller 22Y for uniformly charging the surface of the photosensitive drum 23Y, a developing device 24Y, a primary transfer roller 25Y for transferring the toner image formed on the photosensitive drum 23Y onto the intermediate transfer belt 30 serving as an image carrier by the action of an electric field force, a drum cleaning blade 27Y for removing residual toner on the photosensitive drum 23Y, a toner bottle 41Y, and a toner hopper 42Y.

[0020] The toner bottle 41Y stores yellow toner. The toner bottle 41Y rotates with a toner bottle motor as a drive source and discharges the toner to the outside. The toner discharged from the toner bottle 41Y is supplied to the toner hopper 42Y. The toner hopper 42Y supplies toner to the developing device 24Y when the remaining amount of toner stored in the developing device 24Y becomes equal to or less than a predetermined lower limit value.

[0021] Around the photosensitive drum 23Y, the charging roller 22Y, the exposure device 21Y, the developing device 24Y, the primary transfer roller 25Y, and the drum cleaning blade 27Y are arranged in order along the rotation direction of the photosensitive drum 23Y.

[0022] After the photosensitive drum 23Y is charged by the charging roller 22Y, it is irradiated with laser light emitted by the exposure device 21Y. The exposure device 21Y exposes the image corresponding portion on the surface of the photosensitive drum 23Y to form an electrostatic latent image. Thereby, an electrostatic latent image is formed on the photosensitive drum 23Y. Subsequently, the developing device 24Y develops the electrostatic latent image formed on the photosensitive drum 23Y with charged toner. Specifically, toner is placed on the electrostatic latent image formed on the photosensitive drum 23Y by the action of an electric field force, whereby a toner image is formed on the photosensitive drum 23Y. The toner image formed on the photosensitive drum 23Y is transferred onto the intermediate transfer belt 30 serving as an image carrier by the primary transfer roller 25Y by the action of an electric field force. The toner remaining on the photosensitive drum 23Y without being transferred is removed from the photosensitive drum 23Y by the drum cleaning blade 27Y.

[0023] On the other hand, the intermediate transfer belt 30 is suspended by a driving roller 33 and a driven roller 34 so as not to be slack. When the driving roller 33 rotates counterclockwise in FIG. 2, the intermediate transfer belt 30 rotates counterclockwise in the figure at a predetermined speed. As the intermediate transfer belt 30 rotates, the driven roller 34 rotates counterclockwise.

[0024] Thereby, the image forming units 20Y, 20M, 20C, and 20K transfer toner images onto the intermediate transfer belt 30 in order. The timing at which each of the image forming units 20Y, 20M, 20C, and 20K transfers a toner image onto the intermediate transfer belt 30 is adjusted by detecting a reference mark attached to the intermediate transfer belt 30. Thereby, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 30.

[0025] The toner image formed on the intermediate transfer belt 30 is transferred onto the paper by the action of an electric field force by the secondary transfer roller 26 which is a transfer member. The paper conveyed by the timing roller 31 is conveyed to a nip portion where the intermediate transfer belt 30 and the secondary transfer roller 26 are in contact. The paper onto which the toner image has been transferred is conveyed to the fixing device 50 and heated and pressurized. Thereby, the toner is melted and fixed to the paper. Thereafter, the paper is discharged to the paper discharge tray 39.

[0026] A belt cleaning blade 28 is provided upstream of the image forming unit 20Y of the intermediate transfer belt 30. The belt cleaning blade 28 removes the toner remaining on the intermediate transfer belt 30 without being transferred onto the paper.

[0027] When forming a full-color image, the image forming unit 140 drives all of the image forming units 20Y, 20M, 20C, and 20K. When forming a monochrome image, it drives any one of the image forming units 20Y, 20M, 20C, and 20K. Also, it is possible to form an image by combining two or more of the image forming units 20Y, 20M, 20C, and 20K. Here, an example will be described in which the printer 100 adopts a tandem method equipped with the image forming units 20Y, 20M, 20C, and 20K that form the four colors of toner on paper, but a four-cycle method in which the four colors of toner are sequentially transferred onto the paper using one photosensitive drum may also be adopted.

[0028] The paper feeding unit 150 includes a paper feed cassette 35. A plurality of sheets of paper are set in the paper feed cassette 35. The paper stored in the paper feed cassette 35 is sequentially supplied one by one to the conveyance path 45 by the pickup roller 36 attached to the paper feed cassette 35, and is sent to the timing roller 31 by the paper feed roller 37. Also, when one or more sheets of paper are set in the manual feed cassette 35A, the one or more sheets of paper set in the manual feed cassette 35A are sequentially supplied one by one to the conveyance path 45 by the pickup roller 36A attached to the manual feed cassette 35A, and are sent to the timing roller 31 by the paper feed roller 37.

[0029] FIG. 3 is a plan view of the fixing device. FIG. 4 is a side view of the fixing device. FIG. 4 is a view seen from the left side direction, and the pressure roller 59 is shown by a dotted line. Also, the fixing belt 57 is shown in a state where the back side is visible through, and is hatched. FIG. 5 is a side view of the pad member. FIG. 6 is a cross-sectional view taken along line A-A of FIG. 5. FIG. 7 is a cross-sectional view taken along line B-B of FIG. 5.

[0030] Referring to FIGS. 3 to 7, the fixing device 50 includes a heating unit 51, a pad member 60, a grease application unit 70, a regulating unit 80, a fixing belt 57, and a pressure roller 55. The pressure roller 59 is composed of a core metal, an intermediate layer, and a surface layer. In this embodiment, the outer diameter of the pressure roller 59 is 30 mm. The core metal is made of aluminum or iron, and the thickness of the core metal is 2 to 3 mm. The intermediate layer is an elastic layer and is formed of a material having heat resistance and elasticity such as silicone rubber or silicone sponge. The intermediate layer preferably has a thickness of about 2 to 5 mm. The surface layer is formed of a material having releasability such as a fluorine tube, and the thickness of the surface layer release layer is preferably about 20 to 80 μm.

[0031] The fixing belt 57 is composed of a base layer and an elastic layer. The base layer is composed of a polyimide film with an inner diameter of 40 mm, a width of 340 mm, and a thickness of 70 μm. The elastic layer is preferably about 100 to 150 μm thick using silicone rubber. Also, the surface layer is composed of a releasable PFA, PTFE, etc., and is a coating with a thickness of about 30 μm. The surface layer is formed by coating the elastic layer with a fluororesin.

[0032] The heating unit 51 includes a heating roller 53 and a heat source 54. The heating roller 53 is a hollow cylindrical member, and the rotating shaft is pivotally supported by the main body case. The heating roller 53 incorporates the heat source 54 inside. The inner diameter of the heating roller 53 is set to a size where the heat source 54 does not come into contact. The heating roller 53 is made of stainless steel. Since the heating roller 53 is made of stainless steel, strength is ensured and processing is easy. In this case, the thickness of the heating roller 53 can be around 0.1 mm to 0.2 mm. Note that the heating roller 53 may be made of aluminum. In this case, in order to ensure strength against bending and local deformation, the thickness of the heating roller 53 is preferably 0.25 mm or more. Also, the heating roller 53 may be made of an iron-based metal such as STKM (carbon steel pipe for machine structures).

[0033] The heat source 54 is, for example, a halogen heater. In the present embodiment, two halogen heaters with different emission lengths are used as the heat source 54. Note that the heat source 54 is not limited to a halogen heater, and a resistance heating element or IH (Induction Heating) may be used.

[0034] When the heat source 54 generates heat, the heating roller 53 is heated and the temperature of the heating roller 53 rises. A thermistor (not shown) is disposed at a position separated from the heating roller 53 by a predetermined distance. The temperature of the heating roller 53 is detected by the thermistor. According to the temperature detected by this thermistor, the heat source 54 is controlled to be turned on / off, and the heating roller 53 is controlled to reach a predetermined temperature. By thinning the heating roller 53, the heat capacity of the heating roller 53 becomes smaller. For this reason, since the temperature rising speed of the heating roller 53 becomes faster, the warm-up time until the heating roller 53 reaches a predetermined temperature can be shortened. In addition, the power consumption of the heat source 54 can be reduced.

[0035] The grease application part 70 and the pad member 60 are supported by a common support part 62. The support part 62 is fixed to the main body frame at both ends thereof. The grease application part 70 stores grease, which is a lubricant, and applies the grease to the fixing belt 57 at the portion in contact with the fixing belt 57. The pad member 60 is formed of a resin member having heat resistance.

[0036] The heating roller 53, the regulating part 80, the pad member 60, and the grease application part 70 are arranged in this order inside the fixing belt 57. The fixing belt 57 is suspended by the heating roller 53, the regulating part 80, the pad member 60, and the grease application part 70 so as not to sag. For this reason, the circumferential orbit of the fixing belt 57 is defined by the heating roller 53, the regulating part 80, the pad member 60, and the grease application part 70.

[0037] The pad member 60 is provided to face the pressure roller 55, and the pad member 60 has a pressing portion 63 that forms a nip portion N with the pressure roller 59. The pressure roller 55 is biased toward the pressing portion 63 with a predetermined pressing force. The nip portion N is a portion where the fixing belt 57 contacts the pressure roller 55 between the pressing portion 63 and the pressure roller 55. Here, the rotation axis of the pressure roller 55 is parallel to the depth direction.

[0038] As shown in FIG. 5, the pad member 60 has end guides 65 on the outer sides of both ends of the pressing portion 63, respectively. As shown in FIGS. 5 to 7, the pad member 60 has a pair of guide portions 61 that extend from portions at a predetermined distance from both ends of the pressing portion 63 and from the end guides 65 upstream in the traveling direction of the fixing belt 57. The guide portion 61 has a convex arc-shaped contact surface on the side that contacts the fixing belt 57. Note that the guide portion 61 does not necessarily need to extend upstream in the traveling direction of the fixing belt 57 from the portions at a predetermined distance from both ends of the pressing portion 63 of the pad member 60, and may extend upstream in the traveling direction of the fixing belt 57 from at least a part of the end guides 65.

[0039] As shown in FIG. 4, the length L4 of the pad member 60 in the depth direction is longer than the length L3 of the fixing belt 57 in the depth direction. Therefore, the pad member 60 can define a part of the circumferential orbit of the fixing belt 57. Also, the distance L1 between the pair of guide portions 61 is shorter than the length L3 of the fixing belt 57 in the depth direction. Therefore, as shown in FIG. 6, the fixing belt 57 can be brought into contact with the pair of guide portions 61, so that the circumferential orbit of the fixing belt 57 can be defined by the pair of guide portions 61.

[0040] Also, the distance L1 between the pair of guide portions 61 is longer than the maximum length of the image formed on the sheet Pa passing through the nip portion N. Therefore, it is possible to heat and press all of the image formed on the sheet Pa. Further, if there are portions where a member with which the fixing belt 57 contacts and portions where the fixing belt 57 does not contact are mixed between the pair of guide portions 61, portions with different temperatures in the depth direction of the fixing belt 57 are generated. Since a space where the fixing belt 57 does not contact is formed between the pair of guide portions 61, the temperature distribution of the fixing belt 57 between the pair of guide portions 61 can be made uniform, and the occurrence of image noise such as gloss unevenness can be suppressed.

[0041] As shown in FIG. 4, the length L2 in the depth direction of the pressure roller 55 is the same as the length L2 in the depth direction of the pressing portion 63 and is shorter than the length L3 in the depth direction of the fixing belt 57. Therefore, the pressure roller 55 can be brought into contact with the fixing belt 57, and the pressure roller 55 can be prevented from contacting the pad member 60. As a result, damage due to the frictional force generated when the pressure roller 55 contacts the pad member 60 can be prevented.

[0042] As shown in FIGS. 6 and 7, the pressure roller 55 rotates by a drive motor 55B. Along with the rotation of the pressure roller 55, the fixing belt 57 rotates due to the frictional force received from the pressure roller 55 at the portion where the fixing belt 57 contacts the pressure roller 55. The pressure roller 55 orbits around the heating roller 53, the regulating portion 80, the pad member 60, and the grease application portion 70. The heating roller 53 rotates due to the frictional force received from the fixing belt 57 at the portion where the heating roller 53 contacts the fixing belt 57 along with the rotation of the fixing belt 57. Note that the heating roller 53 may not be rotated and the fixing belt 57 may be slid on the surface of the heating roller 53. The fixing belt 57 is heated to a predetermined temperature by the heat transmitted from the heating roller 53 while in contact with the heating roller 53.

[0043] While the fixing belt 57 passes through the grease application section 70, grease is applied to the inner surface of the fixing belt 57 by the grease application section 70. Thereby, the frictional resistance received from the pad member 60 while the fixing belt 57 passes through the pad member 60 can be made smaller compared to the case where no grease is applied.

[0044] As shown in FIGS. 5 and 7, the pad member 60 further has a guiding portion 67 that extends from the pressing portion 63 upstream in the traveling direction of the fixing belt 57 between a pair of guiding portions 61. The guiding portion 67 is located inside the fixing belt 57 rather than the portions where the fixing belt 57 contacts each of the pair of guiding portions 61. For this reason, a space that does not contact the fixing belt 57 is formed between the pair of guiding portions 61 of the pad member 60. The guiding portion 67 has a guiding surface that connects to the pressing portion 63. This guiding surface is an inclined surface whose distance from the fixing belt 57 becomes shorter as it approaches the pressing portion 63. For this reason, the grease applied to the inner peripheral surface of the fixing belt 57 easily penetrates between the fixing belt 57 and the pressing portion 63.

[0045] The pressing portion 63 of the pad member 60 has a shape approximating the curvature of the pressure roller 55. For this reason, while reducing the amount of elastic deformation of the pressure roller 55, the area of the nip portion N can be made as large as possible. Since the area of the nip portion N can be increased, the time for pressing and heating the paper can be lengthened. Also, since the outer diameter of the pressure roller 55 can be made below a predetermined value, the fixing device 50 can be miniaturized. Also, since the amount of elastic deformation of the pressure roller 55 can be reduced, the pressing force for pressing the pressure roller 55 can be reduced. For this reason, since the strength of the pressure roller 55 can be made below a predetermined value, the wall thickness of the pressure roller 55 can be reduced to reduce the heat capacity. Furthermore, since the heat capacity of the pressure roller 55 can be reduced, the power consumption is reduced.

[0046] A sliding sheet 69 is fixed to the pressing portion 63 of the pad member 60. The sliding sheet 69 is made of a glass cloth having heat resistance coated with a fluororesin, and has heat resistance, abrasion resistance, and slidability. The fixing belt 57 contacts the sliding sheet. Therefore, the slidability of the surface of the pressing portion 63 is increased, and the degree of wear of the fixing belt 57 due to friction can be minimized.

[0047] Referring to FIG. 7, a sheet Pa carrying a toner image To on its surface is conveyed upward from below the fixing device 50, and the sheet Pa passes through the nip portion N. While the sheet Pa passes through the nip portion N, the sheet Pa is heated and pressed by the pressure roller 59 and the heating portion 51, and the toner image To is fixed on the sheet Pa.

[0048] The grease application portion 70 is disposed between the pad member 60 and the heating portion 51, and is arranged in the order of the pad member 60, the grease application portion 70, and the heating portion 51 in the traveling direction of the fixing belt 57. The grease application portion 70 includes an application roller 71 and a storage portion 72. The application roller 71 has a cylindrical shape. The application roller 71 is supported by the support portion 62 in a rotatable state about the axis of rotational symmetry. The application roller 71 is supported by the support portion 62 in a direction in which its rotation axis intersects the traveling direction of the fixing belt 57.

[0049] The storage portion 72 has a box shape extending in the depth direction and has an open upper surface. The storage portion 72 stores grease. The application roller 71 is disposed above the storage portion 72, and the storage portion 72 is supported by the support portion 62 in a state where the lower end of the application roller 71 is positioned below the upper surface of the grease stored in the storage portion 72. Therefore, a part of the application roller 71 is immersed in the grease stored in the storage portion 72. Grease adheres to the portion of the application roller 71 immersed in the grease stored in the storage portion 72.

[0050] The application roller 71 is biased upward by an elastic body such as a spring. Therefore, a part of the side surface of the application roller 71 contacts the inner peripheral surface of the fixing belt 57, and the portion contacting the fixing belt 57 biases the fixing belt 57 upward.

[0051] The application roller 71 has a part immersed in the grease stored in the storage part 72 and another part pressing against the inner peripheral surface of the fixing belt 57. The application roller 71 rotates as the fixing belt 57 rotates. When the application roller 71 rotates, the grease adhering to the part immersed in the grease stored in the storage part 72 of the application roller 71 adheres to the inner peripheral surface of the fixing belt 57. Thereby, grease is applied to the inner peripheral surface of the fixing belt 57. The amount by which the application roller 71 is immersed in the storage part 72 is determined so that the film thickness of the grease formed on the inner peripheral surface of the fixing belt 57 by the application of the application roller 71 to the fixing belt 57 becomes larger than a predetermined set value.

[0052] The regulating part 80 is arranged between the pad member 60 and the heating part 51, and in the advancing direction of the fixing belt 57, the heating part 51, the regulating part 80, and the pad member 60 are arranged in this order. The regulating part 80 regulates the film thickness of the grease applied to the inner peripheral surface of the fixing belt 57 by the grease application part 70.

[0053] FIG. 8 is a side view of the regulating part. FIG. 8 is a view of the regulating part 80 as seen from the left side direction, and a cross-section of the fixing belt 57 is shown. Referring to FIG. 8, the regulating part 80 includes a regulating roller 81, two pressing rollers 82, and two elastic members 83. The regulating roller 81 and the two pressing rollers 82 are cylindrical. The two pressing rollers 82 are connected to both ends of the regulating roller 81. The rotation symmetry axis of the regulating roller 81 and the rotation symmetry axes of the two pressing rollers 82 coincide. The regulating roller 81 and the two pressing rollers 82 may be integrally formed. The regulating roller 81 and the two pressing rollers 82 are supported by the main body frame of the printer 100 in a rotatable state about the rotation symmetry axis. The regulating roller 81 and the two pressing rollers 82 are supported by the main body frame of the printer 100 in a direction in which their rotation axes intersect the advancing direction of the fixing belt 57. Each of the two pressing rollers 82 is biased in the direction toward the fixing belt 57 by an elastic member 83 such as a spring.

[0054] The outer diameters R2 of the two pressing rollers 82 are the same. The outer diameter R1 of the regulating roller 81 is smaller than the outer diameter R2 of the two pressing rollers 82. Therefore, since the two pressing rollers 82 are urged against the fixing belt 57 by the elastic member 83, the two pressing rollers 82 come into contact with the fixing belt 57, and the regulating roller 81 does not come into contact with the fixing belt 57. A gap 82A is formed between the regulating roller 81 and the fixing belt 57. The height of the gap 82A is half of the difference between the outer diameter R2 of the two pressing rollers 82 and the outer diameter R1 of the regulating roller 81. Therefore, the film thickness of the grease formed on the inner peripheral surface of the fixing belt 57 is regulated by the height of the gap 82A.

[0055] Therefore, the film thickness of the grease formed on the inner peripheral surface of the fixing belt 57 immediately before entering the nip portion N of the fixing belt 57 becomes the same thickness as the height of the gap 82A. Therefore, the frictional force generated between the fixing belt 57 and the sliding sheet 69 can be maintained within a predetermined range.

[0056] In the printer 100 according to the present embodiment, the specified value of the film thickness of the grease formed on the inner peripheral surface of the fixing belt 57 is defined as the film thickness h within the range where the oil film parameter Ω in the following formula (1) is 2.7 or more and 6 or less.

[0057]

Equation

[0058] The oil film parameter Ω is a measure representing the degree of direct contact between friction surfaces. The oil film parameter Ω is expressed as the ratio of the film thickness of the lubricant oil film to the combined roughness of two opposing members. The two opposing members are the fixing belt 57 and the sliding sheet 69. The oil film parameter Ω is calculated as a value within the nip portion N. Therefore, by setting the oil film parameter Ω as the ratio of the film thickness of the lubricant film to the combined roughness of the surface roughnesses of the two opposing members, the oil film parameter Ω can be made a value indicating the degree of direct contact. Also, since the combined roughness decreases as the surfaces of the two opposing members wear, the oil film parameter Ω is defined with respect to the combined roughness in the initial state before the surfaces of the two members wear. Since the lubricant flows into the nip portion N in a state heated to the optimum temperature, the position defining the film thickness of the lubricant film is preferably upstream of the nip portion N.

[0059] Figure 9 is a diagram showing an example of the relationship between the film thickness of the lubricant film and the friction coefficient. The oil film parameter Ω is shown on the horizontal axis, and the friction coefficient is defined on the vertical axis. Referring to Figure 9, the dotted line indicates the lower limit value 0.0213 of the friction coefficient when the drive motor 55B breaks down. The upper limit value of the oil film parameter Ω is defined as 6, which is obtained by multiplying the value 8, which is below the lower limit value of the friction coefficient when the drive motor 55B breaks down, by a safety factor of 1.5. Also, the lower limit value of the oil film parameter Ω is defined as 2.7, which is obtained by multiplying the oil film parameter Ω at which the friction coefficient is minimized, which is 2.2, by a safety factor of 1.2.

[0060] <First Modification Example> Figure 10 is a side view of the restricting portion in the first modification example. Figure 10 is a view of the restricting portion 80A in the modification example as seen from the left side direction, and shows a cross section of the fixing belt 57. Referring to Figure 10, the difference between the restricting portion 80A and the restricting portion 80 shown in Figure 8 is that a plurality of intermediate rollers 84 are added. Since the other configurations are the same as those of the restricting portion 80 shown in Figure 8, the description will not be repeated here.

[0061] In the regulating unit 80A, a plurality of intermediate rollers 84 are arranged at a predetermined interval between the two pressing rollers 82. Here, the number of the plurality of intermediate rollers 84 is six, but the number of the intermediate rollers 84 is not limited. Preferably, the plurality of intermediate rollers 84 are arranged at equal intervals. The intermediate roller 84 has a cylindrical shape, and the axis of rotational symmetry thereof coincides with the rotational axes of the regulating roller 81 and the two pressing rollers 82. The outer diameter of the pressing roller 82 is the same as the outer diameter R2 of the two pressing rollers 82. The plurality of intermediate rollers 84 contact the fixing belt 57 in the same manner as the two pressing rollers 82. When the interval between the two pressing rollers 82 becomes equal to or greater than a predetermined length, the fixing belt 57 may be curved, and the height of the gap 82A may not be constant. Since the plurality of intermediate rollers 84 contact the fixing belt 57, the curvature of the fixing belt 57 is suppressed, and the height of the gap 82A in the depth direction can be made uniform. As a result, the film thickness of the grease formed on the inner peripheral surface of the fixing belt 57 can be made as constant as possible.

[0062] <Second Embodiment> In the first embodiment, in the fixing device 50, the pad member 60, the grease application unit 70, the heating roller 53, and the regulating unit 80 are arranged in this order on the inner periphery of the endless fixing belt 57. In the fixing device 50A in the second embodiment, the pad member 60, the heating roller 53, and the grease application unit 70 are arranged in this order on the inner periphery of the endless fixing belt 57. Hereinafter, the differences between the fixing device 50A in the second embodiment and the fixing device 50 in the first embodiment will be mainly described.

[0063] FIG. 11 is a cross-sectional view of the fixing device in the second embodiment. The cross-section shown in FIG. 11 corresponds to the cross-section taken along line B-B in FIG. 5. Referring to FIG. 11, the differences from the fixing device 50 in the first embodiment shown in FIG. 7 are that the grease application unit 70 is changed to the grease application unit 70A, the unit 80 is deleted, and the pad member 60 is changed to the pad member 60A.

[0064] FIG. 12 is a cross-sectional view of the grease application section in the second embodiment. FIG. 12 is a cross-section of the grease application section 70A in the second embodiment cut along a plane perpendicular to the advancing direction of the fixing belt 57. Referring to FIG. 12, the grease application section 70A includes a main body portion 74, two grease reservoirs 75, and two elastic members 76. The main body portion 74 has convex portions 74A protruding downward from both ends in the depth direction. The plurality of grease reservoirs 75 are spaces formed in the main body portion 74. A plurality of grease reservoirs 75 are formed between the two convex portions 74A in the depth direction of the main body portion 74. An example in which two grease reservoirs 75 are formed in the main body portion 74 is shown. The two grease reservoirs 75 have openings that open downward. Each of the two grease reservoirs 75 stores grease.

[0065] The main body portion 74 is biased in the direction toward the fixing belt 57 by elastic members 76 such as springs at both ends in the depth direction.

[0066] Since the main body portion 74 is biased toward the fixing belt 57 by the elastic members 76, the two convex portions 74A come into contact with the fixing belt 57, and the portion between the two convex portions 74A of the main body portion 74 does not come into contact with the fixing belt 57. As a result, a gap 74B is formed between the portion between the two convex portions 74A of the main body portion 74 and the fixing belt 57. The grease stored in the grease reservoir 75 is supplied from the opening to the gap 74B. Gravity may be used, or a mechanism for pressurizing the space of the grease reservoir 75 may be provided.

[0067] The height of the gap 74B is the same as or smaller than the height of the two convex portions 74A. The film thickness of the grease formed on the inner peripheral surface of the fixing belt 57 is regulated by the height of the gap 74B. The height of the convex portion 74A is determined so that the film thickness of the grease formed on the inner peripheral surface of the fixing belt 57 becomes larger than a predetermined value. Therefore, a grease film having a film thickness larger than the specified value of the grease is formed on the inner peripheral surface of the fixing belt 57 immediately before entering the nip portion N of the fixing belt 57.

[0068] FIG. 13 is a side view of a part of the guiding portion of the pad member. FIG. 13 is a view seen from the left side direction. Referring to FIG. 13, the guiding portion 67 of the pad member 60A in the second embodiment has a plurality of grooves 68 formed on its surface. The grooves 68 are inclined with respect to the advancing direction of the fixing belt 57. The depth of the grooves 68 is the same as or greater than the film thickness of the grease film formed on the fixing belt 57. Therefore, the grease formed on the inner peripheral surface of the fixing belt 57 is restricted at the portion where the grooves 68 of the guiding portion 67 are not formed. Therefore, the guiding portion 67 functions as a restricting portion 80. The grease formed on the inner peripheral surface of the fixing belt 57 passes through the guiding portion 67 of the guiding portion 67, and its film thickness is adjusted.

[0069] <Third Embodiment> In the fixing device 50B in the third embodiment, the film thickness of the grease film formed on the inner peripheral surface of the endless fixing belt 57 is measured on the inner periphery of the fixing belt 57, and the film thickness is adjusted based on the measured film thickness. Hereinafter, the differences between the fixing device 50B in the third embodiment and the fixing device 50 in the first embodiment will be mainly described.

[0070] FIG. 14 is a cross-sectional view of the fixing device in the third embodiment. The cross-section shown in FIG. 14 corresponds to the cross-section taken along line B-B in FIG. 5. Referring to FIG. 14, the differences from the fixing device 50 in the first embodiment shown in FIG. 7 are that the grease application portion 70 is changed to the grease application portion 70B, the restricting portion 80 is deleted, and the film thickness detection portion 90 and the control portion 110 are added. Since the other configurations are the same as those shown in FIG. 7, the description will not be repeated here.

[0071] The grease application unit 70B includes an application motor 73 in addition to the application roller 71 and the storage unit 72. The application roller 71 has a cylindrical shape. The application roller 71 is supported by the support portion 62 in a rotatable state about the axis of rotational symmetry. The application roller 71 is supported by the support portion 62 in a direction in which its rotation axis intersects the traveling direction of the fixing belt 57. The rotation axis of the application roller 71 is connected directly or via a gear to the rotation axis of the application motor 73. The application motor 73 is a DC motor or a stepping motor. The application motor 73 is controlled by the control unit 110. When the application motor 73 is driven by the control unit 110, the application roller 71 rotates. The rotation direction of the application roller 71 is such that the surface of the application roller 71 that contacts the fixing belt 57 is in the same direction as the traveling direction of the fixing belt 57.

[0072] The application roller 71 is disposed above the storage unit 72, and the storage unit 72 is supported by the support portion 62 in a state where the lower end of the application roller 71 is positioned below the upper surface of the grease stored in the storage unit 72. For this reason, a part of the application roller 71 is in a state of being immersed in the grease stored in the storage unit 72. Grease adheres to the portion of the application roller 71 that is immersed in the grease stored in the storage unit 72.

[0073] The application roller 71 is biased upward by an elastic body such as a spring. For this reason, a part of the side surface of the application roller 71 contacts the inner peripheral surface of the fixing belt 57, and the portion that contacts the fixing belt 57 biases the fixing belt 57 upward.

[0074] A part of the application roller 71 is immersed in the grease stored in the storage unit 72, and another part presses the inner peripheral surface of the fixing belt 57. The application roller 71 rotates as the application motor 73 rotates.

[0075] The rotation speed of the application roller 71 is controlled by the control unit 110. When the peripheral speed of the application roller 71 when it rotates is equal to or higher than the speed of the fixing belt 57, grease is applied from the application roller 71 to the fixing belt 57. Also, the greater the difference between the peripheral speed of the application roller 71 and the speed of the fixing belt 57 when the application roller 71 rotates, the greater the supply amount of grease applied from the application roller 71 to the fixing belt 57. Conversely, when the peripheral speed of the application roller 71 when it rotates is lower than the speed of the fixing belt 57, the application roller 71 recovers a part from the grease film formed on the fixing belt 57. Also, the greater the difference between the peripheral speed of the application roller 71 and the speed of the fixing belt 57 when the application roller 71 rotates, the greater the recovery amount of grease recovered from the fixing belt 57 by the application roller 71. Therefore, by adjusting the rotation speed of the application roller 71 by the control unit 110, the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57 is adjusted.

[0076] Figure 15 is a perspective view of the film thickness detection unit. Referring to Figure 15, the film thickness detection unit 90 includes a base 91, a first detection plate 92 and a second detection plate 93 that extend in one direction from different positions of the base 91. The first detection plate 92 and the second detection plate 93 are flat plates with different widths. The width of the first detection plate 92 is larger than the width of the second detection plate 93. Also, the thickness of the first detection plate 92 may be thicker than the thickness of the second detection plate 93. The relative position of the base 91 with respect to the fixing belt 57 is determined such that the direction in which the first detection plate 92 and the second detection plate 93 extend intersects the fixing belt 57. A first load cell is connected to a portion of the first detection plate 92 connected to the base 91. The first load cell detects the force received by the first detection plate 92 from the outside and outputs a detection value corresponding to the detected force to the control unit 110. The control unit 110 calculates the amount of deflection of the first detection plate 92 based on the detection value input from the first load cell.

[0077] A second load cell is connected to a portion of the base 91 of the second detection plate 93 that is connected. The second load cell detects the force received by the second detection plate 93 from the outside and outputs a detection value corresponding to the detected force to the control unit 110. The control unit 110 calculates the amount of deflection of the second detection plate 93 based on the detection value input from the second load cell.

[0078] FIG. 16 is a diagram showing an example of the relative position between the first detection plate and the fixing belt. Referring to FIG. 16, a portion at a predetermined distance from the tip of the first detection plate 92 comes into contact with the fixing belt 57 and is in a deflected state. The amount of deflection of the first detection plate 92 is proportional to the distance between the fixing belt 57 and the base 91.

[0079] FIG. 17 is a diagram showing an example of the relative position between the second detection plate and the fixing belt. Referring to FIG. 17, a portion at a predetermined distance from the tip of the second detection plate 93 comes into contact with the surface of the grease film GR formed on the inner peripheral surface of the fixing belt 57 and is in a deflected state. The amount of deflection of the second detection plate 93 is proportional to the distance between the surface of the grease film GR and the base 91.

[0080] The control unit 110 detects the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57 from the detection value input from the first load cell and the detection value input from the second load cell.

[0081] FIG. 18 is a block diagram showing an example of the hardware configuration of the control unit. Referring to FIG. 18, the control unit 110 includes a central processing unit (CPU) 111, a ROM (Read Only Memory) 113, a RAM (Random Access Memory) 115, and a storage device 117.

[0082] The CPU 111 controls the entire printer 100. The ROM 113 stores the program executed by the CPU 111 or the data necessary to execute the program. The RAM 115 is used as a work area when the CPU 111 executes the program. Also, the RAM 114 temporarily stores the image data continuously sent from the document reading unit 130.

[0083] The storage device 117 includes a solid state drive (SSD) or a hard disk drive (HDD) as a mass storage device. Also, a CD-ROM (Compact Disk Read Only Memory) 119 is attached to the storage device 117. The storage device 117 is controlled by the CPU 111. The CPU 111 can access the data stored in the SSD, HDD, or CD-ROM 119. In the present embodiment, an example in which the CPU 111 executes a program stored in the ROM 113 will be described. However, the CPU 111 may control the storage device 117 to read a program from the SSD, HDD, or CD-ROM 119, load the read program into the RAM 115, and execute it.

[0084] Note that the recording medium for storing the program to be executed by the CPU 111 is not limited to the CD-ROM 119, and may be a medium such as a flexible disk, a cassette tape, an optical disk (MO (Magnetic Optical Disc) / MD (Mini Disc) / DVD (Digital Versatile Disc)), an IC card, an optical card, a mask ROM, a semiconductor memory such as an EPROM (Erasable Programmable ROM), etc. Further, the program to be executed by the CPU 111 may be a program downloaded from a computer connected to a network and stored in the storage device 117. Or, the program to be executed by the CPU 111 may be a program stored in the storage device 117 when a computer connected to a network writes the program to the storage device 117. The program referred to here includes not only a program directly executable by the CPU 111, but also a source program, a compressed program, an encrypted program, etc.

[0085] FIG. 19 is a block diagram showing an example of the functions of the CPU included in the printer. The functions shown in FIG. 19 are functions realized in the CPU 111 by the CPU 111 included in the printer 100 executing a film thickness control program stored in the ROM 113 or the storage device 117.

[0086] Referring to FIG. 19, the CPU 111 included in the printer 100 includes a film thickness detection unit 121 and a film thickness adjustment unit 123. The film thickness detection unit 121 controls the film thickness detection unit 90 and detects the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57. The film thickness detection unit 90 receives the detection value output from the first load cell and the detection value output from the second load cell from the film thickness detection unit 90. The film thickness detection unit 90 calculates the deflection amount of the first detection plate 92 and the deflection amount of the second detection plate 93 from the two values, and determines the film thickness of the grease film from the difference in the deflection amounts. The film thickness detection unit 90 outputs the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57 to the film thickness adjustment unit 123.

[0087] The film thickness adjustment unit 123 controls the grease application unit 70B and adjusts the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57. The film thickness adjustment unit 123 compares the film thickness input from the film thickness detection unit 121 with a reference film thickness and determines an adjustment amount. The adjustment amount is the difference between the film thickness input from the film thickness detection unit 121 and the reference film thickness. The adjustment amount is a value obtained by subtracting the film thickness input from the film thickness detection unit 121 from the reference film thickness.

[0088] The film thickness adjustment unit 123 includes a relative speed determination unit 131 and a rotational speed determination unit 133. The relative speed determination unit 131 determines the relative speed from the adjustment amount. The relative speed determination unit 131 outputs the relative speed to the rotational speed determination unit 133. The relative speed is the peripheral speed of the coating roller 71 with respect to the speed of the fixing belt 57. The relative speed is a value obtained by subtracting the peripheral speed of the coating roller 71 from the speed of the fixing belt 57. When the adjustment amount is positive, it is determined as a positive relative speed. A table defining the relationship between the adjustment amount and the relative speed is stored in the storage device 117 in advance. The relative speed determination unit 131 determines the relative speed by referring to the table stored in the storage device 117. A positive relative speed is associated with a positive adjustment amount. For a positive adjustment amount, the larger the adjustment amount, the larger the determined relative speed. A negative relative speed is associated with a negative adjustment amount. For a negative adjustment amount, the smaller the adjustment amount, the smaller the determined relative speed.

[0089] The rotational speed determination unit 133 determines the rotational speed of the coating roller 71 that becomes the peripheral speed corresponding to the relative speed. The film thickness adjustment unit 123 controls the film thickness detection unit 90 to rotate the coating roller 71 at the determined rotational speed by the coating motor 73.

[0090] FIG. 20 is a flowchart showing an example of the flow of the film thickness control process. The film thickness control process is a process executed by the CPU 111 provided in the printer 100 by the CPU 111 executing a film thickness control program stored in the ROM 113 or the storage device 117. Referring to FIG. 20, the CPU 111 provided in the printer 100 detects the film thickness (step S01) and proceeds to step S02. Based on the detection value detected by the film thickness detection unit 90, the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57 is detected.

[0091] In step S02, an adjustment amount is determined, and the process proceeds to step S03. The adjustment amount is determined from the film thickness detected in step S01 and the reference film thickness. The adjustment amount is determined as the value obtained by subtracting the film thickness detected in step S01 from the reference film thickness. A positive adjustment amount indicates that grease is to be supplied, and a negative adjustment amount indicates that grease is to be recovered.

[0092] In step S03, a relative speed is determined, and the process proceeds to step S04. The relative speed corresponding to the adjustment amount determined in step S02 is determined. The table stored in the storage device 117 is referred to, and the relative speed associated with the adjustment amount determined in step S02 is determined. The relative speed is the peripheral speed of the coating roller 71 with respect to the speed of the fixing belt 57.

[0093] In step S04, a rotational speed is determined, and the process proceeds to step S05. Since the traveling speed of the fixing belt 57 is constant, the peripheral speed of the coating roller 71 corresponding to the relative speed is determined. Then, the rotational speed of the coating roller 71 corresponding to the peripheral speed of the coating roller 71 is determined.

[0094] In step S05, the rotational speed is commanded to the grease application unit 70, and the process proceeds to step S06. The rotational speed command includes the rotational speed determined in step S04. Thereby, the application motor 73 of the grease application unit 70 is driven, and the coating roller 71 rotates at the rotational speed.

[0095] In step S06, it is determined whether or not image formation has ended. If image formation has not ended, the process returns to step S01, but if not, the process ends.

[0096] <Second Modification Example> FIG. 21 is a cross-sectional view of the fixing device in the second modification. The cross-section shown in FIG. 21 corresponds to the cross-section taken along line B-B in FIG. 5. Referring to FIG. 21, the fixing device 50C in the second modification is different from the fixing device 50B in the second embodiment shown in FIG. 14 in that the grease application part 70 and the control part 110 are respectively changed to the grease application part 70A and the control part 110A, and the restricting part 80 and the pressing control part 85 are added. Since the other configurations are the same as those shown in FIG. 14, the description will not be repeated here.

[0097] Along the inner circumference of the fixing belt 57, the pad member 60, the heating roller 53, the grease application part 70A, the restricting part 80, and the film thickness detection part 90 are arranged in this order. The grease application part 70A is the same as the grease application part 70A in the second embodiment described with reference to FIG. 12. The restricting part 80 is the same as the restricting part 80 in the first embodiment shown in FIG. 6. The film thickness detection part 90 is the same as the film thickness detection part 90 in the third embodiment shown in FIG. 14. The control part 110A has the same hardware configuration as the hardware configuration shown in FIG. 18.

[0098] The pressing control part 85 is controlled by the control part 110A and adjusts the force for pressing the restricting part 80 against the fixing belt 57. The pressing control part 85 includes, for example, an actuator fixed to the main body frame of the printer 100. The actuator moves the rotation axis of the restricting part 80 parallel to the direction toward the fixing belt 57. When the moving amount changes, the tensile tension of the fixing belt 57 changes, so the force with which the restricting part 80 presses the fixing belt 57 changes.

[0099] FIG. 22 is a block diagram showing an example of the functions of the CPU included in the printer in the second modification. The functions shown in FIG. 22 are functions realized in the CPU 111 when the CPU 111 included in the printer 100 in the second modification executes the film thickness control program stored in the ROM 113 or the storage device 117.

[0100] Referring to FIG. 22, the CPU 111 included in the printer 100 in the second modification includes a film thickness detection unit 121 and a film thickness adjustment unit 123A. The film thickness detection unit 121 controls the film thickness detection unit 90 and detects the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57. The film thickness detection unit 90 is the same as the film thickness detection unit 90 shown in FIG. 19. The film thickness detection unit 90 outputs the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57 to the film thickness adjustment unit 123A.

[0101] The film thickness adjustment unit 123A controls the pressing control unit 85 and adjusts the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57. The film thickness adjustment unit 123A includes a reduction amount determination unit 135 and a pressing force determination unit 137. The reduction amount determination unit 135 compares the film thickness input from the film thickness detection unit 121 with a reference film thickness and determines a reduction amount. The reduction amount is the difference between the film thickness input from the film thickness detection unit 121 and the reference film thickness. The reduction amount is a value obtained by subtracting the reference film thickness from the film thickness input from the film thickness detection unit 121. The reduction amount determination unit 135 outputs the reduction amount to the pressing force determination unit 137.

[0102] The pressing force determination unit 137 determines a pressing force based on the reduction amount. A table defining the relationship between the reduction amount and the pressing force is stored in the storage device 117 in advance. The pressing force determination unit 137 determines the pressing force by referring to the table stored in the storage device 117. The film thickness adjustment unit 123A controls the pressing control unit 85 to press the fixing belt 57 with the pressing force determined by the regulation unit 80.

[0103] FIG. 23 is a flowchart showing an example of the flow of the film thickness control process in the second modification. The difference between the film thickness control process in the second modification shown in FIG. 23 and the film thickness control process shown in FIG. 20 is that steps S02 to S05 are changed to steps S02A, S03A, and S05A. Since the other processes are the same as those shown in FIG. 20, the description will not be repeated here.

[0104] In step S02A, the reduction amount is determined, and the process proceeds to step S03A. The reduction amount is determined from the film thickness detected in step S01 and the reference film thickness. The reduction amount is determined as the value obtained by subtracting the reference film thickness from the film thickness detected in step S01.

[0105] In step S03A, the pressing force is determined, and the process proceeds to step S05A. The pressing force corresponding to the reduction amount determined in step S02 is determined. The table stored in the storage device 117 is referred to, and the pressing force associated with the reduction amount determined in step S02A is determined.

[0106] In step S05A, a pressing command is output to the pressing control unit 85, and the process proceeds to step S06. The pressing command includes the pressing force determined in step S03A. Thereby, the pressing control unit 85 presses the fixing belt 57 against the regulating unit 80 with the pressing force.

[0107] <Fourth Embodiment> The fixing device 50 in the first embodiment has a heating roller 53. The fixing device 50D in the fourth embodiment does not have a heating roller 53.

[0108] FIG. 24 is a cross-sectional view of the fixing device in the third modification. The cross-section shown in FIG. 24 corresponds to the cross-section taken along line B-B of FIG. 5. Referring to FIG. 24, the differences between the fixing device 50D in the fourth embodiment and the fixing device 50 in the first embodiment shown in FIG. 7 are that the heating roller 53 is changed to a tension roller 53A and the heat source 54 is disposed in the pad member 60. Since the other configurations are the same as those shown in FIG. 7, the description will not be repeated here.

[0109] Since the heat source 54 is disposed on the pad member 60, the pressing portion 63 and the sliding sheet 69 are heated by the heat source 54. While the fixing belt 57 passes through the nip portion N, the fixing belt 57 contacts the pressing portion 63 and the sliding sheet 69. Therefore, heat is transferred from the pressing portion 63 and the sliding sheet 69 to the fixing belt 57 while the fixing belt 57 passes through the nip portion N.

[0110] The tension roller 53A has a cylindrical shape. The tension roller 53A is disposed inside the fixing belt 57 at a position facing the pad member 60. The rotation axis of the tension roller 53A is biased in a direction away from the pad member 60 by an elastic member such as a spring. For this reason, the tension roller 53A applies a predetermined tension to the fixing belt 57 so that the fixing belt 57 does not slacken. Thereby, a predetermined pressing force is applied between each of the grease application portion 70 and the restricting portion 80 and the fixing belt 57.

[0111] <Other Modifications> (1) The fixing devices 50, 50A to 50D in the first to fourth embodiments can be combined. Any one of the grease application portions 70, 70A, 70B can be used, and any one of the restricting portions 80, 80A can be used.

[0112] (2) Although the restricting portions 80, 80A are cylindrical, they do not necessarily have to be cylindrical and may be plate-shaped. Even in this case, the film thickness of the grease film can be restricted.

[0113] (3) Further, the heating roller 53 may be disposed outside the fixing belt 57. In this case, the fixing belt 57 rotates around the pad member 60. Further, the heating roller 53 does not necessarily have to be cylindrical, and an induction heating device or a ceramic heater that functions as a heat source can be used.

[0114] (4) In the present embodiment, the pressure roller 55 is pressed against the pad member 60, but the pad member 60 may be pressed against the pressure roller 55.

[0115] (5) In this embodiment, the case where the pressure roller 55 is driven and the fixing belt 57 rotates passively has been described as an example. However, the pressure roller 55 may rotate passively. In this case, instead of the drive motor 59B, a motor for rotating the pressure roller 55 is arranged.

[0116] (6) In this embodiment, an example where the pressure roller 55 is pressed against the fixing belt 57 has been shown. However, while the fixing device 50 is not driven, the pressure roller 55 may be separated from the fixing belt 57. Preferably, the pressure roller 55 is pressed against the pad member 60 at least while the paper passes through the nip portion N. Thereby, the period during which the pressure roller 55 elastically deforms can be limited while the recording medium passes through.

[0117] (7) In this embodiment, the printer 100 has been described as an example of an image forming apparatus. However, the image forming apparatus may be a copying machine, a laser beam printer, a facsimile apparatus, a multifunction peripheral (MFP) combining these, or the like.

[0118] (8) In this embodiment, as an example of the image forming apparatus, the printer 100 that forms a tandem type color image has been described. However, the present invention is not limited to this, and an image forming apparatus that forms a monochrome image may be used. The configurations and arrangements of the image forming units 20Y, 20M, 20C, 20K, the exposure devices 21Y, 21M, 21C, 21K, the charging rollers 22Y, 22M, 22C, 22K, the photosensitive drums 23Y, 23M, 23C, 23K, the developing devices 24Y, 24M, 24C, 24K, the primary transfer rollers 25Y, 25M, 25C, 25K, the secondary transfer roller 26, and the fixing device 50 are not limited to those in this embodiment, and other configurations and arrangements may be used.

[0119] As described above, the fixing device 50 in the present embodiment includes a pressure roller 55, a fixing belt 57, and a pad member 60 that forms a nip portion N where the fixing belt 57 and the pressure roller 55 are in contact with each other. While supplying grease, which is a lubricant, to the inner peripheral surface of the fixing belt 57, the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57 is adjusted. Therefore, a grease film with an appropriate film thickness can be formed on the inner peripheral surface of the fixing belt 57. Further, the fixing device 50 adjusts the film thickness so that the oil film parameter Ω represented by the formula (1) satisfies 2.7 ≦ Ω ≦ 6 using the film thickness of the grease film in the nip portion N. Therefore, the film thickness of the grease can be adjusted to a range in which the frictional force between the fixing belt 57 and the pad member 60 is within a predetermined range.

[0120] Further, the fixing device 50 in the first embodiment includes a regulating unit 80 that reduces the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57 to be equal to or less than a predetermined upper limit value, and a grease application unit 70 that supplies an amount of grease to the inner peripheral surface of the fixing belt 57 such that the film thickness of the grease film becomes equal to or greater than the upper limit value. After an amount of grease such that the film thickness of the grease film becomes equal to or greater than the upper limit value is supplied, the film thickness of the grease film decreases to be equal to or less than the predetermined upper limit value. Therefore, the film thickness can be easily adjusted.

[0121] Further, the regulating unit 80 of the fixing device 50 in the first embodiment and the guiding unit 67 of the fixing device 50A in the second embodiment are arranged on the upstream side in the traveling direction of the fixing belt 57 with respect to the nip portion N, and the inner peripheral surface of the fixing belt 57 does not come into contact with other members between the nip portion N and the regulating unit 80 or the guiding unit 67. Therefore, the film thickness of the grease film formed on the inner peripheral surface of the fixing belt 57 at the nip portion can be made an appropriate film thickness.

[0122] The regulating unit 80 of the fixing device 50 in the first embodiment is pressed against the fixing belt 57 with a predetermined pressure. Therefore, the film thickness of the grease film can be adjusted in a state where the slack of the fixing belt 57 is reduced.

[0123] In the fixing device 50 in the second embodiment, the guiding portion 67 is provided at the upstream end in the advancing direction of the fixing belt 57 of the pad member 60, and one or more grooves 68 are formed on the contact surface that contacts the fixing belt 57. Therefore, since the film thickness of the grease is regulated at the upstream end of the pad member 60, the film thickness at the nip portion of the grease film formed on the inner peripheral surface of the fixing belt 57 can be made an appropriate film thickness.

[0124] The fixing device 50B in the third embodiment includes a film thickness detection unit 90 and a grease application unit 70B. The CPU 111 controls the grease application unit 70B based on the film thickness detected by the film thickness detection unit 90. Therefore, the film thickness of the grease film can be accurately adjusted.

[0125] The grease application unit 70B includes a storage unit 72 that stores grease, and an application roller 71 that is rotatable independently of the fixing belt 57 and is disposed at a position that contacts the inner peripheral surface of the fixing belt 57 and the grease stored in the storage unit 72 while rotating. The CPU 111 determines the rotational speed of the application roller 71 based on the film thickness detected by the film thickness detection unit 90. The CPU 111 determines the relative speed of the application roller 71 with respect to the fixing belt 57 at the portion where the application roller 71 contacts the fixing belt 57 with respect to the film thickness, and rotates the application roller 71 at a rotational speed corresponding to the relative speed. Therefore, the amount of grease supplied to the grease film formed on the fixing belt 57 can be adjusted, and the amount of grease recovered from the grease film can be adjusted.

[0126] The fixing device 50C in the second modification includes a regulating portion 80 and a film thickness detection unit 90 on the inner peripheral surface of the fixing belt 57, and the CPU 111 determines the reduction amount for reducing the film thickness of the grease film by the regulating portion 80 based on the film thickness detected by the film thickness detection unit 90. Therefore, the film thickness of the grease film can be adjusted to an appropriate value.

[0127] <Summary of the Embodiment> (Item 1) A pressure roller, An endless fixing belt, A pressing member that is provided inside the fixing belt and faces the pressing roller, and forms a nip portion where the fixing belt and the pressing roller come into contact with each other. A fixing device including a lubricant adjusting means for supplying a lubricant to the inner peripheral surface of the fixing belt and adjusting the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt.

[0128] According to this aspect, a lubricant is supplied to the inner peripheral surface of the fixing belt, and the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt is adjusted. Therefore, a fixing device capable of forming a lubricant film with an appropriate film thickness on the inner peripheral surface of the fixing belt can be provided.

[0129] (Item 2) The lubricant adjusting means adjusts the film thickness of the lubricant film so that the oil film parameter Ω represented by the formula (1) satisfies 2.7 ≦ Ω ≦ 6 by using the film thickness of the lubricant film in the nip portion. The fixing device according to Item 1.

[0130] According to this aspect, the film thickness of the lubricant can be adjusted to a range in which the frictional force between the fixing belt and the pressing member is within a predetermined range.

[0131] (Item 3) The lubricant adjusting means includes a regulating means for reducing the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt to be equal to or less than a predetermined upper limit value, A supply means that is disposed upstream of the regulating means in the running direction of the fixing belt and supplies an amount of the lubricant to the inner peripheral surface of the fixing belt such that the film thickness of the lubricant film becomes equal to or greater than the upper limit value. The fixing device according to Item 1 or 2.

[0132] According to this aspect, after an amount of lubricant that causes the film thickness of the lubricant film to be equal to or greater than the upper limit value is supplied, the film thickness of the lubricant film decreases to be equal to or less than the predetermined upper limit value. Therefore, the film thickness can be easily adjusted.

[0133] (Item 4) The regulating means is disposed upstream of the nip portion in the running direction of the fixing belt, The fixing device according to claim 3, wherein the inner peripheral surface of the fixing belt does not contact other members between the nip portion and the regulating means.

[0134] According to this aspect, on the upstream side in the traveling direction of the fixing belt from the nip portion, the film thickness is regulated and the inner peripheral surface of the fixing belt does not contact other members, so that the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt at the nip portion can be made an appropriate film thickness.

[0135] (Item 5) The fixing device according to claim 3 or 4, wherein the lubricant adjusting means further includes pressing means for pressing the regulating means against the fixing belt with a predetermined pressure.

[0136] According to this aspect, since the regulating means is pressed against the fixing belt with a predetermined pressure, the film thickness of the lubricant film can be adjusted in a state where the slack of the fixing belt is reduced.

[0137] (Item 6) The fixing device according to any one of Items 3 to 5, wherein the regulating means is provided at an upstream end portion of the pressing member in the traveling direction of the fixing belt, and one or more grooves are formed on a contact surface that contacts the fixing belt.

[0138] According to this aspect, since the film thickness of the lubricant film is regulated at the upstream end portion of the pressing member in the traveling direction of the fixing belt, the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt at the nip portion can be made an appropriate film thickness.

[0139] (Item 7) The fixing device according to Item 1 or 2, further comprising film thickness detection means for detecting the film thickness of the lubricant film, and adjustment control means for controlling the lubricant adjusting means based on the film thickness of the lubricant film detected by the film thickness detection means.

[0140] According to this aspect, since the film thickness of the lubricant film is adjusted based on the detected film thickness, the film thickness of the lubricant film can be accurately adjusted.

[0141] (Item 8) The lubricant adjustment means includes a storage portion for storing the lubricant, a rotation supply means that is arranged at a position where a part thereof contacts the inner peripheral surface of the fixing belt and another part thereof contacts the lubricant stored in the storage portion and is rotatable independently of the fixing belt, The fixing device according to item 7, wherein the rotational speed of the rotation supply means is determined based on the film thickness of the lubricant film detected by the film thickness detection means.

[0142] According to this aspect, the rotation supply means rotates at a rotational speed corresponding to the film thickness of the grease film formed on the inner peripheral surface of the fixing belt. For this reason, the amount of lubricant supplied to the lubricant film formed on the fixing belt can be adjusted, and the amount of lubricant recovered from the lubricant film can be adjusted.

[0143] (Item 9) The lubricant adjustment means includes a supply means for supplying the lubricant to the inner peripheral surface of the fixing belt, a restricting means for reducing the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt, The fixing device according to item 7, wherein a reduction amount for reducing the film thickness of the lubricant film by the restricting means is determined based on the film thickness of the lubricant film detected by the film thickness detection means.

[0144] According to this aspect, based on the detected film thickness of the lubricant film, a reduction amount for reducing the film thickness of the lubricant film is determined. For this reason, the film thickness of the lubricant film can be adjusted to an appropriate value.

[0145] (Item 10) An image forming apparatus including the fixing device according to any one of items 1 to 9.

[0146] (Item 11) A film thickness control method for controlling a fixing device, wherein the fixing device includes a pressure roller, an endless fixing belt, a pressing member provided inside the fixing belt and facing the pressure roller to form a nip portion where the fixing belt and the pressure roller are in contact with each other, Lubricant adjusting means for supplying a lubricant to the inner peripheral surface of the fixing belt and adjusting the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt; Control means for controlling the lubricant adjusting means; A film thickness detection step of detecting the film thickness of the lubricant film; An adjustment control step of controlling the lubricant adjusting means based on the film thickness of the lubricant film detected in the film thickness detection step; A film thickness adjustment method for causing the fixing device to execute.

[0147] According to this aspect, it is possible to provide a film thickness adjustment method capable of forming a lubricant film with an appropriate film thickness on the inner peripheral surface of the fixing belt.

[0148] (Item 12) A film thickness control program executed by a computer for controlling a fixing device, The fixing device includes A pressure roller; An endless fixing belt; A pressing member provided inside the fixing belt and facing the pressure roller, forming a nip portion where the fixing belt and the pressure roller are in contact; Lubricant adjusting means for supplying a lubricant to the inner peripheral surface of the fixing belt and adjusting the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt; Control means for controlling the lubricant adjusting means; A film thickness detection step of detecting the film thickness of the lubricant film; An adjustment control step of controlling the lubricant adjusting means based on the film thickness of the lubricant film detected in the film thickness detection step; A film thickness adjustment program for causing the computer to execute.

[0149] According to this aspect, it is possible to provide a film thickness adjustment program capable of forming a lubricant film with an appropriate film thickness on the inner peripheral surface of the fixing belt.

[0150] The embodiments disclosed herein should be considered illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

Explanation of Signs

[0151] 100 Printer, 110 Control unit, 110A Control unit, 111 CPU, 113 ROM, 114 RAM, 115 RAM, 117 Storage device, 119 CD-ROM, 121 Film thickness detection unit, 123, 123A Film thickness adjustment unit, 130 Original document reading unit, 131 Relative speed determination unit, 133 Rotation speed determination unit, 135 Reduction amount determination unit, 137 Pressing force determination unit, 140 Image forming unit, 150 Paper feeding unit, 20Y, 20M, 20C, 20K Image forming unit, 26 Secondary transfer roller, 30 Intermediate transfer belt, 31 Timing roller, 33 Driving roller, 34 Driven roller, 35 Paper feeding cassette, 36 Take-out roller, 37 Paper feeding roller, 39 Paper discharge tray, 50, 50A, 50C, 50D Fixing device, 51 Heating unit, 53 Heating roller, 53A Tension roller, 54 Heat source, 55 Pressing roller, 55B Driving motor, 57 Fixing belt, 59 Pressing roller, 59B Driving motor, 60, 60A Pad member, 61 Guide unit, 62 Support unit, 63 Pressing unit, 65 Both-end guide unit, 67 Induction unit, 68 Groove, 69 Sliding sheet, 70, 70A, 70B Grease application unit, 71 Application roller, 72 Storage unit, 73 Application motor, 74 Main body unit, 74A Protrusion, 74B Gap, 75 Grease reservoir, 76 Elastic member, 80 Regulation unit, 80A Regulation unit, 81 Regulation roller, 82 Pressing roller, 82A Gap, 83 Elastic member, 84 Intermediate roller, 85 Pressing control unit, 90 Film thickness detection unit, 91 Base, 92 First detection plate, 93 Second detection plate, N Nip portion, Pa Paper, R1 Outer diameter, R2 Outer diameter, To Toner image, h Film thickness, Ω Oil film parameter.

Claims

1. A pressure roller, an endless fixing belt, a pressing member provided inside the fixing belt and facing the pressure roller to form a nip portion where the fixing belt and the pressure roller come into contact, a lubricant adjusting means for supplying a lubricant to the inner peripheral surface of the fixing belt and adjusting the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt. A fixing device comprising:

2. The lubricant adjusting means adjusts the film thickness of the lubricant film such that the oil film parameter Ω represented by the following formula satisfies 2.7 ≤ Ω ≤ 6 using the film thickness of the lubricant film in the nip portion. The fixing device according to claim 1. 【Number 1】

3. The lubricant adjusting means includes a restricting means for reducing the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt to be equal to or less than a predetermined upper limit value, and a supply means disposed upstream in the running direction of the fixing belt from the restricting means for supplying an amount of the lubricant such that the film thickness of the lubricant film becomes equal to or greater than the upper limit value to the inner peripheral surface of the fixing belt. The fixing device according to claim 1.

4. The restricting means is disposed upstream in the running direction of the fixing belt from the nip portion, and the inner peripheral surface of the fixing belt does not contact other members between the nip portion and the restricting means. The fixing device according to claim 3.

5. The lubricant adjusting means further includes a pressing means for pressing the restricting means against the fixing belt with a predetermined pressure. The fixing device according to claim 3.

6. The restricting means is provided at an upstream end in the running direction of the fixing belt of the pressing member, and one or more grooves are formed on a contact surface that contacts the fixing belt. The fixing device according to claim 3.

7. a film thickness detecting means for detecting the film thickness of the lubricant film, and an adjustment control means for controlling the lubricant adjusting means based on the film thickness of the lubricant film detected by the film thickness detecting means. The fixing device according to claim 1.

8. The lubricant adjusting means includes a storage portion for storing the lubricant, and a rotary supply means disposed at a position where a part thereof contacts the inner peripheral surface of the fixing belt and another part contacts the lubricant stored in the storage portion, and is rotatable independently of the fixing belt. The fixing device according to claim 7, wherein the rotational speed of the rotary supply means is determined based on the film thickness of the lubricant film detected by the film thickness detecting means.

9. ​ The lubricant adjustment means includes supply means for supplying the lubricant to the inner peripheral surface of the fixing belt, and restricting means for reducing the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt. The fixing device according to claim 7, wherein a reduction amount for reducing the film thickness of the lubricant film by the restricting means is determined based on the film thickness of the lubricant film detected by the film thickness detection means.

10. An image forming apparatus comprising the fixing device according to any one of claims 1 to 9.

11. A film thickness control method for controlling a fixing device, wherein the fixing device includes a pressure roller, an endless fixing belt, a pressing member provided inside the fixing belt and facing the pressure roller to form a nip portion where the fixing belt and the pressure roller contact each other, lubricant adjustment means for supplying a lubricant to the inner peripheral surface of the fixing belt and adjusting the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt, and control means for controlling the lubricant adjustment means. The film thickness detection step of detecting the film thickness of the lubricant film, and an adjustment control step of controlling the lubricant adjustment means based on the film thickness of the lubricant film detected in the film thickness detection step, and causing the fixing device to execute the film thickness adjustment method.

12. A film thickness control program executed by a computer for controlling a fixing device, wherein the fixing device includes a pressure roller, an endless fixing belt, a pressing member provided inside the fixing belt and facing the pressure roller to form a nip portion where the fixing belt and the pressure roller contact each other, lubricant adjustment means for supplying a lubricant to the inner peripheral surface of the fixing belt and adjusting the film thickness of the lubricant film formed on the inner peripheral surface of the fixing belt, and control means for controlling the lubricant adjustment means. The film thickness detection step of detecting the film thickness of the lubricant film, and an adjustment control step of controlling the lubricant adjustment means based on the film thickness of the lubricant film detected in the film thickness detection step, and causing the computer to execute the film thickness adjustment program.

Images