JP2008033033A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of obtaining stable productivity corresponding to various kinds of image formation and various kinds of paper by preventing the winding of transfer material round a fixing roller and a pressure roller, and an image forming apparatus equipped therewith. <P>SOLUTION: The fixing device 18 is equipped with: the fixing roller 30; the pressure roller 31 forming a fixing nip part by press-contacting with the fixing roller 30; a heating means 32 heating the fixing roller 30; a pressure means 33 making the pressure roller 31 press-contact with the fixing roller 30; a temperature measuring means 34 measuring the temperature of the fixing roller 30; a paper thickness detecting means 35 detecting the thickness of transfer paper P; and a control means 36 controlling the actuation of the heating means 32 and the pressure means 33 in accordance with a result of measurement by the temperature measuring means 34 and a result of detection by the paper thickness detecting means 35. In the fixing device 18, the control means 36 controls the actuation of the heating means 32 and the pressure means 33 in accordance with the result of detection by the paper thickness detecting means 35 and makes the actuation of the heating means 32 and the pressure means 33 differ between the leading edge part and the center and succeeding parts of the transfer paper P. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying apparatus, a printer, a facsimile machine, and a multifunction machine, and more particularly to an image forming apparatus provided with a fixing device that can handle various paper types and sizes from thin paper to thick paper.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus such as a copying apparatus, a printer, and a facsimile, a fixing apparatus having a fixing roller, a pressure roller that is pressed against the fixing roller, and a heating unit that heats the fixing roller is known. A transfer material on which an unfixed toner image is formed is sandwiched and conveyed by a fixing roller having a body (for example, rubber) layer and maintained at a predetermined temperature, and a pressure roller having an elastic layer pressed against the fixing roller. Many heat fixing methods are used while heating. However, in this fixing device, when a solid image is formed on the transfer material, an oil application mechanism for applying oil as a separation material to the fixing roller is necessary to ensure separation, and paper handling and copying are performed. There was a problem in terms of cost.

  The fixing roller has a fluorine resin coating or PFA tube coating with good releasability because the toner welded to the transfer material comes into contact with the surface of the fixing roller. Because of its high viscosity, it easily adheres to the surface of the fixing roller, and the transfer material may be wound around the fixing roller. Therefore, a method of preventing the transfer material from wrapping around the fixing roller by forcibly separating the contact with the separation roller by the fixing roller is adopted. Or the contact mark of the peeling claw sticks to the surface of the fixing roller and the scar appears on the fixed image.

  In addition, when the fixing roller is configured to increase the distortion of the fixing roller to prevent the transfer material from being wound around the fixing roller, and the oil application mechanism is omitted to improve the paper handling and reduce the copy cost, the fixing roller When the convexity of the fixing nip is increased so as to increase the distortion of the sheet to ensure high printing rate, the transfer material is wound around the pressure roller when the white paper transfer material is passed. is there.

  In order to solve the above-mentioned problem, a technique for providing a preheating means for heating before fixing to suppress the toner viscosity and preventing the transfer material from being wrapped around the fixing roller is disclosed in, for example, “Patent Document 1” by using a discharge guide member. For example, “Patent Document 2” and “Patent Document 3” are techniques for preventing the transfer material from being wound around the pressure roller at the time. In “Patent Document 4”, for example, “Patent Document 5” discloses a technique that has a pressure adjusting mechanism and sequentially increases the pressure from the leading edge to the trailing edge when the paper passes through the fixing nip portion.

JP 2005-258209 A JP-A-2005-37435 JP-A-2005-25025 Japanese Patent Application Laid-Open No. 2002-214956 JP 2003-270999 A

  In each of the above-described techniques, when a new heating unit is provided in the fixing device, the size of the image forming apparatus is increased, and the configuration and arrangement position of the discharge portion guide member are limited by the fixing device. When the transfer material is wound around the fixing roller and the pressure roller, it is difficult to remove the transfer material due to the high temperature, and the fixing roller and the pressure roller may be damaged. In addition, the worst problem is that the transfer material, which cannot be detected when the transfer material is damaged during removal, is heated and ignited.

  The technique disclosed in “Patent Document 5” is excellent in the function of removing the curvature of the rear end of the transfer material because the pressurizing force is gradually increased from the front end to the rear end, but does not perform the temperature control. The curvature of the transfer material tip is not positively removed, and the transfer material may be wound by the curvature of the tip. In addition, since the temperature and pressure control is not performed on the thickness of the transfer material, the fixing property on the rear end side of the thick paper that is difficult to be bent may be reduced, and the toner is transferred to the fixing roller by melt adhesion. There is also a problem that the winding of the material is not considered.

  The present invention solves the above-described problems, prevents the transfer material from being wound around the fixing roller and the pressure roller, and can obtain stable productivity corresponding to various image formations and paper types. And an image forming apparatus including the same.

  The invention according to claim 1 includes a fixing roller made of an elastic body, a pressure roller made of an elastic body that presses against the fixing roller to form a fixing nip, a heating unit that heats the fixing roller, and the heating unit. A pressure unit that presses the pressure roller against the fixing roller; a temperature measuring unit that measures the temperature of the fixing roller; a paper thickness detecting unit that detects a paper thickness of the transfer paper; a measurement result of the temperature measuring unit; In the fixing device including a control unit that controls operations of the heating unit and the pressurizing unit according to a detection result of the paper thickness detection unit, the control unit is configured to control the heating according to the detection result of the paper thickness detection unit. And the operation of the pressurizing unit is controlled, and the operation of the heating unit and the pressurizing unit is made different between the leading end portion and the central portion of the transfer paper.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the control unit calculates a basis weight of the transfer paper from the detection result of the paper thickness detection unit and the size and quantity of the transfer paper. The operation of the heating unit and the pressurizing unit is controlled according to the basis weight.

According to a third aspect of the present invention, in the fixing device according to the second aspect, the control unit further controls the operation of the heating unit and the pressure unit when the basis weight is 100 g / m ² or more. It is the same in the front end portion and the central portion and thereafter.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the transfer sheet is further transferred to the downstream side of the fixing nip portion in the transfer sheet conveying direction with the fixing roller and the pressure roller. A separation member that separates from the fixing nip, and the tip portion is at least a distance from the fixing nip portion to the separation member.

  According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects, the pressure unit can switch the pressure contact force of the pressure roller to the fixing roller in a plurality of stages. It is characterized by that.

  According to a sixth aspect of the present invention, in the fixing device according to the fifth aspect, the pressing unit further includes a cam for switching the pressure contact force of the pressure roller with respect to the fixing roller in a plurality of stages.

  A seventh aspect of the invention is an image forming apparatus including the fixing device according to any one of the first to sixth aspects.

  According to the present invention, the operation of the heating unit and the pressurizing unit is controlled according to the detection result of the paper thickness detection unit, and the operation of the heating unit and the pressurizing unit is performed at the leading end portion and the central portion or later according to the transfer paper. Therefore, it is possible to prevent the transfer paper from being wound around the fixing roller and the pressure roller, and to continuously obtain a good image with good fixability.

  FIG. 1 shows an image forming apparatus employing one embodiment of the present invention. In the figure, an image forming apparatus 1 which is an electrophotographic copying apparatus has four image forming portions 2Y (yellow), 2M (magenta), 2C (cyan), and 2B (black) at the center, and is full color. Image formation is possible. Each image forming unit includes a photosensitive drum 3, a charging device 4, a cleaning device 5, a developing device 6, a primary transfer roller 7, and the like.

  Above each image forming portion, a transfer belt 8 supported by four rollers and capable of running in the direction of the arrow in the figure is disposed, and is arranged in pressure contact with the transfer belt 8 on the right side of the transfer belt 8. A secondary transfer roller 9 is provided. Under each image forming unit, an exposure device 10 that forms an electrostatic latent image on the surface of each photosensitive drum 3 is disposed.

A paper feeding device 11 is disposed below and to the right of the exposure device 10. The paper feeding device 11 feeds a paper cassette 12 for storing a plurality of transfer papers P, a pair of paper feed rollers 13 for separating and feeding the transfer papers P in the paper feed cassette 12, and a special thick paper P1 such as a postcard. A manual feed tray 14, a pair of paper feed rollers 15 for separating and feeding the special thick paper P1, a pair of transport rollers 16 for transporting the transfer paper P, and the transfer belt P or the special thick paper P1 at a predetermined timing. A registration roller pair 17 and the like are fed between the secondary transfer roller 9 and the secondary transfer roller 9. Here, the special thick paper P1 refers to a transfer paper having a basis weight of 150 g / m ² or more (continuous amount of 135 kg or more).

  Each photosensitive drum 3 is uniformly charged by each charging device 4, and then an electrostatic latent image is formed on each surface by laser light from the exposure device 10. Each formed electrostatic latent image is visualized by the charged toner supplied from each developing device 6, and each visible image is sequentially superimposed on the transfer belt 8 by each primary transfer roller 7 to perform primary transfer. Is done. After the primary transfer, residual toner that is not transferred and remains on the surface of each photosensitive drum 3 is removed by each cleaning device 5. When the transfer paper P supplied from the paper feed cassette 12 is fed between the transfer belt 8 and the secondary transfer roller 9 by the registration roller pair 17 at a predetermined timing, the secondary transfer roller 9 is transferred to the transfer paper P. On the other hand, the toner image on the transfer belt 8 is transferred onto the transfer paper P by applying a charge having a polarity opposite to the charged polarity of the toner.

  On the downstream side of the transfer sheet conveyance direction of the secondary transfer roller 9, the fixing device 18, which is a feature of the present invention, a paper discharge tray 19 on which the transfer sheet P on which an image is formed is placed, and the transfer sheet P after fixing A pair of discharge rollers 20 for discharging the paper onto the paper discharge tray 19, a reverse conveyance path 21 for temporarily storing the transfer paper P when images are formed on both sides of the transfer paper P, and a reversal disposed in the reverse conveyance path 21. A pair of rollers 22, 23, a double-sided conveyance path 24 through which the reversed transfer paper P is conveyed, a pair of conveyance rollers 25, 26, 27 disposed in the double-sided conveyance path 24, and a switching claw 28 for switching the conveyance direction of the transfer paper P 29, etc. are arranged. The transfer sheet P on which the toner image is fixed by being heated and pressed in the fixing device 18 is conveyed toward the discharge roller pair 20 by the switching claws 28 and 29 occupying the solid line positions in the figure, and the discharge roller pair 20. Is discharged onto the paper discharge tray 19.

  FIG. 2 is a schematic diagram of the fixing device 18. In the present embodiment, the fixing device 18 includes a fixing roller 30, a pressure roller 31, a heater 32 as a heating unit, a pressure unit 33, a temperature measurement unit 34, a paper thickness detection unit 35, a control unit 36, and the like. .

  The fixing roller 30 has a foamed elastic member such as silicon sponge inside, and has a surface coated with a resin layer having heat release properties such as PFA (Perfluoroalkyloxy) and PTFE (Polytetrafluorethylene). ing. A heater 32 made of a halogen heater or an infrared (nichrome wire) heater is provided inside or outside the fixing roller 30, and the surface of the fixing roller 30 is kept at a high temperature. The temperature measuring unit 34 has a known configuration that measures the surface temperature of the fixing roller 30 by a contact method or a non-contact method. The fixing roller 30 is rotationally driven in the direction of the arrow in FIG.

  The pressure roller 31 has a heat-resistant rubber (silicone rubber) layer on its surface, and a pressure means 33 is connected to the pressure roller 31. The pressure roller 31 is driven to rotate when the fixing roller 30 rotates. The pressure unit 33 is configured to be capable of adjusting the pressure applied to the pressure roller 31 so as to adjust the width of the fixing nip formed when the pressure roller 31 is pressed against the fixing roller 30. The fixing roller 30 is made of a foamed elastic member and the pressure roller 31 is made of a rubber material, so that the fixing roller 30 side is recessed. In FIG. 2, reference numerals 37 and 38 denote separation members for preventing the fixing transfer paper P from being wound around the fixing roller 30 and the pressure roller 31. The separation members 37 and 38 try to wrap around the rollers 30 and 31 because the leading edge of the transfer paper P is greatly curved due to the influence other than the influence of the thickness of the transfer paper P or the amount of toner transferred to the transfer paper P. If this happens, separate it.

  The paper thickness detection means 35 is arranged on the transfer path of the transfer paper P, and inputs from the weight of the paper feed cassette 12 and the transfer paper size input means and transfer paper number input means provided on the operation panel 39, Alternatively, the thickness of the transfer paper P is calculated from the load variation on the transfer paper transport path. The control means 36 comprising a known microcomputer having a CPU, ROM, RAM, etc. includes information from the temperature measurement means 34, information from the paper thickness detection means 35, information from the operation panel 39, and an image information storage unit. Based on the image amount information stored in 40, the operation of the heater 32 and the operation of the pressurizing means 33 are controlled. The heater 32 controls the amount of heat supplied, and the pressurizing means 33 controls the applied pressure.

Hereinafter, the operation of the above-described fixing device 18 will be described with reference to the flowchart shown in FIG.
When information such as the transfer paper size and the number of transfer papers set by the operator on the operation panel 39 is sent to the control means 36, and weight information or load information from the paper thickness detection means 35 is sent to the control means 36, the control means 36 calculates the basis weight of the transfer paper P used from each information (ST1). The control means 36 stores in advance a control table shown in FIG. 4 for controlling the operation of the heater 32 and the pressure means 33 in five stages according to the basis weight of the transfer paper P that is normally used.

The control means 36 determines whether the basis weight of the transfer paper P is 100 g / m ² or more or less than 100 g / m ² (ST2), and when it is determined that the basis weight is 100 g / m ² or more, it is shown in FIG. Based on the control table (ST3), the supply heat amount corresponding to the surface temperature of the fixing roller 30 heated by the heater 32 and the pressure by the pressing means 33 are set according to the basis weight (ST4). Here, in the case of thick paper having a basis weight of 100 g / m ² or more, since the waist of the transfer paper P is stronger than the toner adhesion to the transfer roller 30 and the heat shrinkability of the transfer paper P, FIG. , (B), the transfer paper P is difficult to wind around the rollers 30 and 31, and the heat absorbed by the transfer paper P is large, so that a large amount of heat and pressure are required in the fixing process. In addition, since a high set value is required for both the pressure and the pressing force, after the rotation of the fixing roller 30 is started (ST5), the fixing process is completed without changing the setting of the temperature and the pressing force during the fixing process ( ST13).

On the other hand, if it is determined in ST2 that the basis weight is less than 100 g / m ² , the amount of heat supplied corresponding to the surface temperature of the fixing roller 30 heated by the heater 32 based on the control table shown in FIG. 4 (ST6). The pressure by the pressurizing means 33 is set according to the basis weight (ST7). In the case of thin paper having a basis weight of less than 100 g / m ² , the leading edge is likely to be bent due to the weakness of the paper and the shape of the fixing nip portion being recessed toward the fixing roller 30. As shown in b), the smaller the basis weight, the more the paper is discharged toward the pressure roller 31 side, and the pressure roller 31 is more easily wound.

In this embodiment, depending on the basis weight of the transfer paper P, less than the basis weight 60 g / ^{m 2,} a basis weight 60~80g / ^{m 2,} supplied heat quantity in three stages having a basis weight of 80-100 g / ^{m 2} and pressure The pressure is controlled, and each basis weight is set to the minimum heat amount and pressurizing force that can secure the fixing property. By reducing the amount of heat and the applied pressure in this manner, the applied pressure is reduced, so that the amount of depression of the fixing roller 30 in the fixing nip portion is reduced, and the amount of heat is reduced, and the shrinkage of the transfer paper P is reduced. Since the transfer paper P becomes difficult to learn the shape of the fixing nip portion, the transfer paper P is discharged toward the intermediate position of the rollers 30 and 31 as indicated by the solid line in FIG. P winding is prevented.

  After setting the heat supply amount and the applied pressure, the fixing roller 30 is driven to rotate and the fixing process is started (ST8). When the leading edge of the transfer paper P passes through the fixing nip (ST9), the temperature measuring means 34 fixes the fixing roller 30. Is measured (ST10). The control means 36 calculates the difference between the control condition after the center of the transfer paper P stored in the control table and the control condition based on the measured temperature (ST11), and resets the supply heat amount and the applied pressure (ST12). . The supply heat amount and the applied pressure which are reset here are set to numerical values at which stable fixing properties can be obtained. Thereafter, the fixing process is performed by the supplied heat amount and the applied pressure, and when the transfer paper P passes through the fixing nip portion, the fixing process is completed (ST13).

  In the fixing process for the thin paper described above, the transfer paper P is difficult to be wound around the rollers 30 and 31 if the discharge direction of the front end portion is in the middle position of the rollers 30 and 31, and the front end portion is the separation member 37, If the sheet P is transported to a position that passes through 38, the subsequent transfer paper P is separated from the surface of each roller 30, 31 by each separating member 37, 38. What is necessary is just to carry out to the position beyond each separation member 37,38 after the front-end | tip of the transfer paper P passes through a transfer nip part.

  According to the above-described configuration, the operations of the heater 32 and the pressurizing unit 33 are controlled in accordance with the detection result of the paper thickness detecting unit 35, and when the transfer paper P is thin, the heater is formed at the leading end portion and the central portion. 32 and the pressure means 33 can be operated differently, so that the transfer paper P can be prevented from being wound around the rollers 30 and 31, and a good image can be continuously obtained with good fixability.

  FIG. 6 is a specific example of the pressurizing means 33 of the present invention. A heater 32 is provided inside the fixing roller 30, and a temperature measuring unit 34 is disposed in the vicinity of the surface of the fixing roller 30. The fixing roller 30 is heated by the heater 32, the surface temperature of the fixing roller 30 is measured by the temperature measuring unit 34, and the operation of the heater 32 is controlled by the control unit 36 so that the surface temperature of the fixing roller 30 becomes the set temperature. Is done.

  Both ends of the pressure roller 31 are rotatably supported by bearings 41, and are provided so as to be able to contact and separate from the fixing roller 30. One end of a pressure lever 43 is rotatably supported on the side plate 42 of the fixing device 18 by a support shaft 44, and a portion near one end of the pressure lever 43 comes into contact with the bearing 41 so that the pressure roller 31 is fixed to the fixing roller. 30 is in pressure contact. The other end of the tension spring 46 is attached to the other end of the pressure lever 43 with one end fixed to one end of the movable plate 45.

  The movable plate 45 has a long hole at the center and a standing bent portion 45a at the other end, and is supported by a pin 47 implanted in the side plate 42 so as to be movable in the left-right direction in FIG. As shown in FIG. 7, a rotary shaft 48 having a D-shaped cross section is fitted to the other end of the movable plate 45 so as to be rotatable and movable in the left-right direction in FIG. A cam 49 having a mold fitting hole is fixed. As shown in FIG. 7, the cam 49 has a first flat surface portion 49a, a second flat surface portion 49b, and a third flat surface portion 49c, and each flat surface portion 49a, 49b, 49c is a standing bent portion 45a. It is formed so as to be able to adhere to the inner surface side.

  A gear 50 to which a rotational force from a driving means such as a pulse motor (not shown) is transmitted is fixed to one end of the rotating shaft 48, and a disc 51 having a notch 51a is fixed to the other end. Detection means 52 for detecting the notch 51 a is disposed in the vicinity of the disc 51, and a detection signal from the detection means 52 is sent to the control means 36. As shown in FIG. 7A, the detection means 52 detects the notch 51a when the cam 49 occupies a position where the first flat portion 49a is in close contact with the inner surface of the standing bent portion 45a, and controls the control means 36. To output a signal. As shown in FIG. 7A, the control means 36 has a first position where the first flat portion 49a is in close contact with the inner surface of the standing bent portion 45a, and the second flat portion 49b as shown in FIG. 7B. The cam 49 indicates either the second position where the first flat portion 49a is in close contact with the inner surface of the standing bent portion 45a, or the third position where the third flat portion 49c is in close contact with the inner surface of the standing bent portion 45a as shown in FIG. Therefore, the operation of a pulse motor (not shown) is controlled.

  With the above-described configuration, the pressure contact force of the pressure roller 31 to the fixing roller 30 becomes the largest when the cam 49 occupies the first position, and the force applied to the fixing roller 30 when the cam 49 occupies the third position. The pressure contact force of the pressure roller 31 is the smallest. The pressurizing means 33 by the pressurizing lever 43, the support shaft 44, the movable plate 45, the tension spring 46, the pin 47, the rotating shaft 48, the cam 49, the gear 50, the disc 51, the detecting means 52, a pulse motor (not shown), etc. The pressure means 33 is configured to switch the pressure contact force of the pressure roller 31 against the fixing roller 30 in three stages. In this embodiment, the pressure contact force of the pressure roller 31 to the fixing roller 30 is switched to three stages. However, the pressure contact force of the pressure roller 31 to the fixing roller 30 can be further increased by changing the shape of the cam 49. It is possible to switch.

  In the above-described embodiment, an example in which a full-color electrophotographic copying apparatus is used as the image forming apparatus 1 is shown. However, the image forming apparatus to which the present invention is applicable is not limited to this, such as a facsimile, a printer, a multifunction peripheral, etc. The present invention can be applied to any image forming apparatus to which a fixing device that fixes a toner image transferred onto a transfer sheet by heating and pressing can be applied.

1 is a schematic front view of a main part of an image forming apparatus employing an embodiment of the present invention. 1 is a schematic diagram of a fixing device used in an embodiment of the present invention. 6 is a flowchart illustrating an operation of a fixing device used in an embodiment of the present invention. 6 is a chart showing an example of a control table of a fixing device used in an embodiment of the present invention. FIG. 6 is a schematic diagram illustrating the behavior of the transfer paper after passing through the fixing nip portion in an embodiment of the present invention. It is a schematic perspective view which shows an example of the pressurization means used for one Embodiment of this invention. It is the schematic explaining the behavior of the cam used for one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 18 Fixing apparatus 30 Fixing roller 31 Pressure roller 32 Heating means (heater)
33 Pressurizing means 34 Temperature measuring means 35 Paper thickness detecting means 36 Control means 37, 38 Separating member 49 Cam P Transfer paper

Claims (7)

A fixing roller made of an elastic material; a pressure roller made of an elastic material that presses against the fixing roller to form a fixing nip; a heating unit that heats the fixing roller; and the pressure roller pressed against the fixing roller. Pressure measuring means for measuring, temperature measuring means for measuring the temperature of the fixing roller, paper thickness detecting means for detecting the paper thickness of the transfer paper, measurement results of the temperature measuring means and detection results of the paper thickness detecting means. In response, a fixing device comprising a control means for controlling the operation of the heating means and the pressure means,
The control means controls the operation of the heating means and the pressurizing means according to the detection result of the paper thickness detecting means, and the heating means and the pressurizing means at the leading end portion and the central portion of the transfer paper. A fixing device characterized in that the operation of the fixing device is made different. The fixing device according to claim 1.
The control means calculates the basis weight of the transfer paper from the detection result of the paper thickness detection means and the size and quantity of the transfer paper, and controls the operation of the heating means and the pressure means according to the basis weight. A fixing device. The fixing device according to claim 2.
When the basis weight is 100 g / m ² or more, the control means makes the operation of the heating means and the pressurizing means the same between the leading end portion and the central portion of the transfer paper. . In the fixing device according to any one of claims 1 to 3,
A separation member that separates the transfer paper from the fixing roller and the pressure roller at a downstream side of the fixing nip portion in the transfer paper conveyance direction, and the leading end portion is at least a distance from the fixing nip portion to the separation member There is a fixing device. In the fixing device according to any one of claims 1 to 4,
The fixing device according to claim 1, wherein the pressing means is capable of switching the pressure contact force of the pressure roller to the fixing roller in a plurality of stages. The fixing device according to claim 5.
The fixing device according to claim 1, wherein the pressure unit includes a cam that switches a pressure contact force of the pressure roller to the fixing roller in a plurality of stages.   An image forming apparatus comprising the fixing device according to claim 1.

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