JP2006133399A - Fixing device, image forming apparatus, and driving method for fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent meandering of a belt in a fixing device of a belt nip system. <P>SOLUTION: The spacing L0 (mm) between projecting meandering regulation members provided on both end sides on an inner peripheral surface of the belt suspended between a plurality of support rollers, the length L1 (mm) in the axial direction of rotation of a first pressing roller arranged on an upstream side in the conveyance direction of a recording medium, and the L2 (mm) in the axial direction of rotation of a second pressing roller arranged on a downstream side in the conveyance direction of the recording medium are so set as to satisfy the relation L0>L2>L1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device that contacts and fixes an unfixed toner image on a recording sheet in an image forming apparatus such as a copying machine, a printer, and a facsimile, an image forming apparatus including the same, and a driving method of the fixing device. .

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus (printing apparatus) such as a copying apparatus, a printer, or a facsimile apparatus is provided with a photosensitive drum, a charging device, an exposure device, a developing device, a transfer device, a fixing device, and the like. .

  In such an image forming apparatus, the exposure surface exposes the photosensitive surface (electrostatic latent image surface) of the photosensitive drum charged by the charging device to form an electrostatic latent image. Then, the formed electrostatic latent image is developed with toner (developer) in a developing device to generate a toner image (visible image). Then, the toner image is set to be fixed by a fixing device after being transferred onto a recording paper (recording material; a printing medium such as plain paper or OHP recording paper) by a transfer device.

  The fixing device fixes toner onto a recording medium such as recording paper by heating or pressing. The fixing device includes a plurality of support rollers, a belt (endless belt) rotatably stretched around each support roller, and a fixing roller that forms a belt nip in contact with the belt. 2. Description of the Related Art A belt nip type fixing device is known in which a recording paper on which a contact toner image is formed is passed and fixing is performed by pressure and thermal energy in the belt nip.

  However, in such a belt nip type fixing device, the surface shape of the support rolls over which the belt is stretched is uneven, the parallelism between the support rolls is not uniform, and the belt circumferential length is not uniform in the belt width direction. There is a problem that the position of the belt is likely to become unstable during the fixing operation due to imbalance in the belt width direction of the pressure contact force between the fixing roller and the belt. That is, the belt nip type fixing device is prone to the phenomenon that the belt is displaced in the width direction (belt shift), the belt is wavy in the width direction (belt undulation), and the recording paper is wrinkled. There is.

  For this reason, for example, in Patent Document 1, in order to solve the problem of belt misalignment, the belt is stretched by three or more rolls, one of which is a displacement roll, and the other two or more. A technique for setting a fixed roll and performing a belt nip between the fixed rolls is described. Further, it is described that the waviness and wrinkles of the belt can be prevented by displacing one end of the shaft of the displacement roll along an elliptical orbit centering on the central axis of the two fixed rolls.

  Further, in Patent Document 1, in a fixing device using a belt nip method, an upstream side of a pressure roll is covered with an elastic body in order to suppress an image shift that occurs when a fixing roll covered with an elastic body is used. Techniques for providing pressure assist rolls are described.

  Further, for example, in Patent Document 2, in order to prevent the belt from meandering, a meshing portion provided on the endless belt is fitted into a groove provided at the end of the support roll of the endless belt, and the meandering in the axial direction of the support roll is performed. The technology to suppress the force is described.

  Further, for example, Patent Document 3 includes a heating belt, two inner rollers that are arranged in the heating belt and support the heating belt, and a pressure roller that presses against the heating belt. Among the two rollers, the inner roller on the upstream side in the recording material conveyance direction is used as a heating roller, and the rotational force is transmitted to the heating belt by the inner roller on the downstream side so that the heating belt is pulled at the nip portion. And a technique for preventing sagging and lifting of the heating belt at the nip portion. Patent Document 3 describes a technique for preventing meandering of the heating belt by providing a convex portion on the heating belt and an engaging concave portion on the pressure roller, and engaging both of them.

  Further, for example, as described in Patent Document 1 described above, in the configuration in which the end of the shaft of the support roll (displacement roll) that supports the belt is displaced to prevent the belt from wavy or wrinkled, the support roll and the belt are worn. The amount of wear increases, and wear (powder) adheres unevenly to the inner surface of the belt and the support roll, increasing the variation in frictional resistance. This may cause deviations in the belt axial direction and damage to the belt. is there.

Therefore, for example, in Patent Document 4, an endless belt is wound around three support rolls, and two of the support rolls are used as press contact support rolls that press the belt outer peripheral surface against a heat fixing roll. In the meantime, there is provided a pressure applying member that presses the outer peripheral surface of the belt against the heat fixing roll, and a lubricant applying member that contacts the inner peripheral surface of the belt in the vicinity of the pressure applying member and applies a lubricant, thereby reducing frictional resistance. Thus, there is described a technique for reducing the belt offset and preventing meandering.
Japanese Patent No. 3084692 (issued on September 4, 2000) JP 60-151678 A (publication date: August 9, 1985) JP 2000-172103 A (publication date: June 23, 2000) Japanese Patent Laid-Open No. 11-45018 (Publication date: February 16, 1999)

  However, in the technique disclosed in Patent Document 1, image quality such as image shift and image loss may occur depending on the configuration and positional relationship of each roller, process speed (fixing processing speed), and the like. For example, the toner image on the recording medium may adhere to the fixing roll in an area where the belt is in contact with the fixing roll without applying pressure by the pressure roll or the auxiliary pressure roll. Then, if the position where the adhered portion re-contacts the recording medium deviates from the original position, image misalignment may occur. Further, when the recording medium is peeled off from the fixing roll, the toner image may adhere to the fixing roll and cause an image defect. Further, since there is no belt tension adjusting mechanism, separation / contact mechanism, etc., the belt tension is always constant, and the belt is likely to meander or wrinkle.

  Furthermore, the technology that prevents the wavy and wrinkle of the belt by displacing one end of the shaft of the support roll (displacement roll) that supports the belt complicates the structure and its control system, and increases the size of the apparatus. There is a problem of inviting.

  Moreover, in the technique of patent document 2, the engagement part provided in the endless belt comes off from the groove | channel provided in the edge part of the support roll of an endless belt, gets on a support roll, and a support roll or a meshing part is damaged. There is a case.

  Moreover, in the technique of patent document 3, although a heating belt is wound around a heating roller, in such a structure, there exists a problem that the driveability of a belt falls. That is, the heating roller has a larger deformation amount than the other rollers, and this may cause a running failure such as the belt meandering due to a deviation in parallelism with the other roller on which the heating belt is suspended. is there. In addition, the convex portion provided on the heating belt may get over the engaging concave portion of the pressure roller, and the convex portion provided on the pressure roller, the heating roller or the belt, or the belt itself may be damaged.

  Moreover, in the technique of patent document 4, since the lubricant application member is arrange | positioned in the vicinity of the pressure provision member used as high temperature / high pressure conditions, there exists a problem that it is difficult to supply a lubricant stably over a long period of time. . In addition, if the amount of lubricant applied to the inner surface of the belt is too large, or if the lubricant wraps around the outer peripheral surface of the belt, the belt may slip.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to appropriately prevent the meandering of the belt and extend the life of the belt in the belt nip type fixing device. is there.

  In order to solve the above-described problem, the fixing device of the present invention includes a heating roller that is heated to a predetermined temperature, a belt that contacts the part of the heating roller, and a plurality of belts on which the belt is suspended. And two of the plurality of support rollers are used as pressure rollers that press both ends of a portion of the belt that wraps around a part of the heating roller to the heating roller. A fixing device for fixing an unfixed toner image formed on a recording medium by passing the recording medium between the belt and the belt, wherein the belt is in contact with the support rollers when suspended. A meandering restricting member that protrudes in a direction substantially perpendicular to the contact surface of the belt with each of the support rollers on both ends of the circumferential surface of the support roller in the rotation axis direction; The distance L0 (mm) between the meandering restricting members provided on both ends of the recording belt and the first pressing roller in the first pressing roller that presses the heating roller and the belt on the upstream side in the conveyance direction of the recording medium. The length L1 (mm) of the roller in the rotation axis direction and the length of the second pressure roller in the rotation axis direction of the second pressure roller that presses the heating roller and the belt downstream in the conveyance direction of the recording medium. L2 (mm) satisfies the relationship L0> L2> L1, and the meandering restricting member abuts against the end of the second pressing roller in the rotation axis direction, thereby preventing meandering of the belt. It is characterized by doing.

  In general, when a belt is suspended by a plurality of support rollers, there is a problem that the belt meanders because the parallelism of the rotation shafts of the support rollers is slightly different. In order to solve this problem, a technique in which a convex portion is provided at the belt end portion and a concave portion that engages with the convex portion at the belt end portion is provided on the roller on which the belt is suspended is described in, for example, the above-described patent document. 2 and Patent Document 3. However, these techniques have a problem in that the convex portion provided at the end of the belt passes over the concave portion of the suspension roller, causing belt running failure.

  On the other hand, according to the above configuration, the meandering restricting members provided at both ends of the belt are arranged on the downstream side in the recording medium conveyance direction among the pressing rollers that form the fixing nip portion with the heating roller. The belt meandering is prevented by coming into contact with the end of the pressing roller positioned in the rotational axis direction. Thereby, the problem that the meandering restricting member provided on the belt runs on the support roller can be prevented, and the support roller or the heating roller due to the meandering restricting member riding on the support roller can be prevented.

  The meandering restricting members may be provided on the inner peripheral surface of the belt over the entire circumference. In this case, when the belt rotates along the support rollers, a stable meandering prevention effect can be obtained regardless of the position in the rotation direction.

  Further, the interval L0 (mm) between the meandering regulating members and the length L2 (mm) in the rotation axis direction of the second pressing roller may be 4 mm> L0-L1> 2 mm.

  According to the above configuration, for example, even when the belt or the pressing roller is thermally deformed by heat from the heating roller, the interval between the meandering restriction member and the end of the pressing roller can be appropriately maintained. . Therefore, when the belt is running normally without trying to meander, the meandering restricting member and the pressing roller do not come into contact with each other, so that no frictional force is generated between them. The life of the pressing roller can be extended. On the other hand, when the belt tries to meander, the meandering restricting member and the end of the pressing roller come into contact with each other, thereby properly regulating the meandering of the belt.

  In order to solve the above-described problem, the fixing device of the present invention includes a heating roller that is heated to a predetermined temperature, a belt that contacts the part of the heating roller, and a plurality of belts on which the belt is suspended. And two of the plurality of support rollers are used as pressure rollers that press both ends of a portion of the belt that wraps around a part of the heating roller to the heating roller. A fixing device for fixing an unfixed toner image formed on a recording medium by passing the recording medium between the belt and an inner peripheral surface of the belt at a position away from the heating roller in the belt It is characterized by having a lubricant application means for applying a lubricant to

  Generally, a fixing device in which a belt is suspended by a plurality of support rollers has a problem that the belt meanders while the belt is rotating (running). For this reason, a method has been proposed in which the slip force that causes meandering is reduced by applying a lubricant to the inner surface of the belt to improve such a problem. However, when the lubricant is applied to the inner surface of the belt, if the amount of application is too large, the lubricant may wrap around the outer peripheral surface of the belt and cause the belt to slip. However, in the case of the configuration in which the lubricant is supplied to the belt at a position close to the heating roller, it is difficult to stably supply the lubricant over a long period of time because of the high temperature and high pressure conditions, resulting in excessive or insufficient lubricant. End up.

  On the other hand, according to said structure, a lubricant can be apply | coated in the position where ambient temperature is low by apply | coating a lubricant in the position away from the heating roller. For this reason, the amount of lubricant applied can be stabilized, and an appropriate amount of lubricant can be supplied to the inner peripheral surface of the belt.

  In addition, at least one of the plurality of support rollers has a contact surface with the belt formed of a porous layer, and a lubricant impregnated in the porous layer is applied to the inner peripheral surface of the belt. It is good also as a structure which functions as a lubricant application means.

  According to the above configuration, the lubricant is impregnated on the inner peripheral surface of the belt by impregnating the porous layer formed on the support roller with the lubricant and bringing the belt into contact with the porous layer impregnated with the lubricant. Supply. Thereby, an appropriate amount of lubricant can be applied to the inner peripheral surface of the belt.

  The support roller functioning as the lubricant application means comprises a hollow core material provided with a number of holes on the surface and the porous layer covered with the core material, and is provided on the core material. The porous layer may be impregnated with a lubricant through a large number of holes.

  According to the above configuration, the porous layer is impregnated with the lubricant retained in the core material through the numerous holes. Thereby, a lubricant can be stably supplied to the porous layer.

  In addition, the porous layer is provided with a smoothing means that makes contact with the porous layer substantially uniformly along the rotation axis direction of the support roller provided with the porous layer, and smoothes the state of the porous layer impregnated with the lubricant. It is good also as a structure.

  According to said structure, the lubricant impregnation state of the said porous layer can be smooth | blunted, and a lubricant can be apply | coated uniformly to the internal peripheral surface of the said belt.

  Further, the support roller functioning as the lubricant application means supports the position on the lowermost side of the belt in the direction of gravity action, and the length of the support roller in the rotational axis direction of the belt is the support length. A direction that is longer than the length of the roller in the rotation axis direction and substantially perpendicular to the contact surface of the belt with the support roller at both ends of the support roller on the inner peripheral surface of the belt in the rotation axis direction It is good also as a structure provided with the lubricant outflow prevention member which protrudes.

  According to the above configuration, the lubricant impregnated in the porous layer can be suppressed / prevented from flowing out. That is, even if the lubricant impregnated in the porous layer is about to flow out, the lubricant outflow prevention members provided at both ends of the belt can be blocked and prevented from flowing out.

  In order to solve the above-described problem, the fixing device of the present invention includes a heating roller that is heated to a predetermined temperature, a belt that contacts the part of the heating roller, and a plurality of belts on which the belt is suspended. And two of the plurality of support rollers are used as pressure rollers that press both ends of a portion of the belt that wraps around a part of the heating roller to the heating roller. A fixing device that fixes an unfixed toner image formed on a recording medium by passing the recording medium between the belt and a belt, and is suspended by the plurality of support rollers when a fixing operation is not performed. It is characterized by relieving the tension of the belt.

  According to the above configuration, it is possible to prevent the winding belt from being formed by constantly applying tension to the belt, and thus it is possible to reduce the shifting force generated on the belt by the winding rod. Thereby, the load concerning the said belt can be reduced. Further, it is possible to prevent a change in the partial shift direction and the shift force in the belt circumferential direction due to the winding rod, and the running performance is improved. In addition, when the meandering restriction member is provided on the belt, it is possible to reduce the load applied to the meandering restriction member and the pressure roller that forms the second nip portion. Therefore, the life of the belt and the pressure roller can be extended.

  Moreover, it is good also as a structure which relieve | moderates the tension | tensile_strength of the said belt by changing the relative position of each said support roller. In this case, the tension relaxation means can be realized with a simple configuration.

  In order to solve the above-described problem, the fixing device of the present invention includes a heating roller that is heated to a predetermined temperature, a belt that contacts the part of the heating roller, and a plurality of belts on which the belt is suspended. And two of the plurality of support rollers are used as pressure rollers that press both ends of a portion of the belt that wraps around a part of the heating roller to the heating roller. A fixing device for fixing an unfixed toner image formed on a recording medium by passing the recording medium between the belt and the belt, and when the fixing operation is not performed, the belt is separated from the heating roller. It is characterized by letting.

  According to the above configuration, by moving the belt away from the heating roller when the fixing operation is not performed, the shifting force acting on the belt and the meandering prevention member provided in the belt can be reduced. That is, when the belt is rotated while being always wound around the heating roller, the offset force acting on the belt is always maximized. Therefore, a maximum load is always applied to the belt and the meandering prevention member provided on the belt. This was one of the factors that shortened the belt life. Therefore, as described above, by making the belt detachable, the load on the belt can be reduced and the life of the belt can be extended.

In addition, a rotation driving unit that rotates the support roller and a pressure roller that forms a first nip portion where the heating roller and the belt are in pressure contact with each other on the upstream side in the conveyance direction of the recording medium are moved to move the first nip. A first separation / contact means for bringing the belt into contact with or separated from the heating roller, and a pressure roller forming a second nip where the heating roller and the belt are in pressure contact with each other on the downstream side in the conveyance direction of the recording medium The second separation / contact means for moving the belt at the second nip portion to contact or separate the belt from the heating roller, and the operation of the rotation drive means, the first separation / contact means, and the second separation / contact means Control means for controlling
The control means, when performing the fixing operation, the first process of bringing the belt into contact with the heating roller at the second nip portion by the second separating / contacting means, and after the first process, A second process of rotating the support roller by a rotation driving means to rotate the belt along each of the support rollers, and after the second process, the first nip is rotated with the belt rotated. It is good also as a structure which performs the 3rd process which makes the said belt contact | abut the said heating roller in a part.

  According to the above configuration, after the belt is brought into contact with the heating roller in the second nip portion, the belt is rotated, and the belt is brought into contact with the heating roller in the first nip portion while the belt is rotating. As a result, it is possible to prevent the belt from sagging or wrinkling at the portion where the belt is wound around the heating roller. Therefore, the running property (rotation property) of the belt can be stabilized.

  That is, when the belt is wound around the heating roller, the pressing roller that forms the first nip portion and the pressing roller that forms the second nip portion are simultaneously brought into contact with the fixing roller 41, or the belt is tensioned. In the case where it is not possible to wind the tarmi while winding it, the first nip portion and the second nip portion serve as a restraint point of the belt position, and wrinkles and sagging tend to occur in the belt portion suspended therebetween. If the belt is rotated in a state where there is such wrinkles or sagging, belt running performance is deteriorated and the belt is cracked. On the other hand, by causing the belt to contact the heating roller in the order of the above configuration and winding the belt around the heating roller, it is possible to prevent the belt from sagging and wrinkles and stabilize the running performance of the belt. Can do.

  Further, the rotation driving means for rotating the support roller, and the pressing roller forming the first nip portion first nip where the heating roller and the belt are pressed against each other on the upstream side in the conveyance direction of the recording medium are moved to A first separation / contact means for contacting or separating the belt from the heating roller at the first nip portion, and a second nip where the heating roller and the belt are pressed against each other on the downstream side in the recording medium conveyance direction are formed. A second separating / contacting means for moving the pressing roller to contact or separate the belt from the heating roller at the second nip portion, the rotation driving means, the first separating / contacting means, and the second separating / contacting means. Control means for controlling the operation of the means, and the control means rotates the belt and stops the belt at the first nip portion when stopping the fixing operation. A fourth process for separating the belt from the heating roller, and a fifth process for stopping the rotation of the belt by stopping the rotation of the support roller by the rotation driving means after the fourth process, After the fifth process, the second process may be configured to perform a sixth process in which the belt is separated from the heating roller at the second nip portion by the second separation unit.

  According to the above configuration, with the belt rotated, the belt is separated from the heating roller at the first nip portion, and then the rotation of the belt is stopped. Thereafter, the belt is removed from the heating roller at the second nip portion. Separate. As a result, as in the case where the belt is not in contact with the heating roller during the fixing operation described above, the belt can be prevented from sagging or wrinkling at the belt winding portion with respect to the heating roller. The running performance of the belt can be stabilized.

  Further, when performing the fixing operation, the control unit performs a warm-up operation in a state in which the support roller is rotated at a speed slower than the speed at the time of the fixing operation by the rotation driving unit before the first processing. May be performed.

  According to the above configuration, the warm-up operation can be performed while the belt is separated from the heating roller and the belt is rotated at a speed slower than the rotation speed during the fixing operation. In this case, since the number of rollers in contact with the belt is smaller than that during the fixing operation, the shifting force acting on the belt is reduced, and the force acting on the belt and the meandering prevention member provided on the belt can be reduced. Further, the shifting force can be further reduced by rotating the belt at a speed slower than the speed during the fixing operation (fixing processing speed).

  In order to solve the above problems, an image forming apparatus of the present invention includes any one of the above-described image forming apparatuses. For this reason, the same effects as those of the image forming apparatuses described above can be obtained.

  In order to solve the above-described problems, the fixing device driving method of the present invention includes a heating roller that is heated to a predetermined temperature, a belt that contacts the part of the heating roller so as to be wound, and the belt is suspended. A plurality of support rollers, and two of the plurality of support rollers are used as pressure rollers that press both ends of a portion of the belt that wraps around a part of the heating roller to the heating roller. A fixing device driving method for fixing an unfixed toner image formed on a recording medium by passing the recording medium between a roller and the belt, and when the fixing operation is not performed, It is characterized by being separated from the heating roller.

  According to the above method, by moving the belt away from the heating roller when the fixing operation is not performed, it is possible to reduce the shifting force acting on the belt and the meandering prevention member provided on the belt. That is, when the belt is rotated while being always wound around the heating roller, the offset force acting on the belt is always maximized. Therefore, a maximum load is always applied to the belt and the meandering prevention member provided on the belt. This was one of the factors that shortened the belt life. Therefore, as described above, by making the belt detachable, the load on the belt can be reduced and the life of the belt can be extended.

  Further, when performing the fixing operation, a first step of bringing the belt into contact with the heating roller by the pressing roller provided on the downstream side in the conveyance direction of the recording medium, and after the first step, A second step of rotating the belt along each of the support rollers; and after the second step, the belt is rotated by the pressing roller provided on the upstream side in the conveyance direction of the recording medium. And a third step of bringing the belt into contact with the heating roller.

  According to the above method, after the belt is brought into contact with the heating roller at the pressure contact portion (first nip portion) on the downstream side in the conveyance direction of the recording medium, the belt is rotated and the recording medium is rotated. The belt is brought into contact with the heating roller at the pressure contact portion (second nip portion) on the upstream side in the transport direction. As a result, it is possible to prevent the belt from sagging or wrinkling at the portion where the belt is wound around the heating roller. Therefore, the running property (rotation property) of the belt can be stabilized.

  That is, when the belt is wound around the heating roller, the pressing roller that forms the first nip portion and the pressing roller that forms the second nip portion are simultaneously brought into contact with the fixing roller 41, or the belt is tensioned. In the case where the nip is not wound while winding up the tarmi, the first nip portion and the second nip portion serve as a restraint point of the belt position, and wrinkles and sagging tend to occur in the belt portion suspended therebetween. If the belt is rotated in a state where there is such wrinkles or sagging, belt running performance is deteriorated and the belt is cracked. On the other hand, by causing the belt to contact the heating roller in the order of the above configuration and winding the belt around the heating roller, it is possible to prevent the belt from sagging and wrinkles and stabilize the running performance of the belt. Can do.

  Further, in order to make the belt contact with the heating roller while winding up the belt, after contacting the pressure roller constituting the first nip, contact the heating roller while rotating the pressure roller constituting the second nip. You may take the procedure to make it.

  Further, when the fixing operation is stopped, in a state where the belt is rotated, the pressure roller provided on the upstream side in the conveyance direction of the recording medium is moved to move the belt pressed by the pressure roller. A fourth step in which a part is separated from the heating roller, a fifth step in which the rotation of the belt is stopped after the fourth step, and a conveyance of the recording medium after the fifth step. And a sixth step of moving the pressing roller provided on the downstream side in the direction so that a part of the belt pressed by the pressing roller is separated from the heating roller.

  According to the above method, after the belt is rotated, the belt is separated from the heating roller at the pressure contact portion on the upstream side in the recording medium conveyance direction, and then the rotation of the belt is stopped, and then the recording medium is conveyed. The belt is separated from the heating roller at the pressure contact portion on the downstream side in the direction. As a result, during the fixing operation described above, it is possible to prevent the belt from sagging or wrinkling at the belt wrapping portion with respect to the heating roller, as in the case where the belt is not in contact with the heating roller and transitions to the contact state. And the running performance of the belt can be stabilized.

  In addition, when performing the fixing operation, the control unit performs a warm-up operation in a state where the support roller is rotated at a speed slower than the speed during the fixing operation by the rotation driving unit before the first step. May be performed.

  According to the above configuration, the warm-up operation can be performed while the belt is separated from the heating roller and the belt is rotated at a speed slower than the rotation speed during the fixing operation. In this case, since the number of rollers in contact with the belt is smaller than that during the fixing operation, the shifting force acting on the belt is reduced, and the force acting on the belt and the meandering prevention member provided on the belt can be reduced. Further, the shifting force can be further reduced by rotating the belt at a speed slower than the speed during the fixing operation (fixing processing speed).

  In the fixing device of the present invention, the belt is contacted with each of the support rollers on the inner circumferential surface of the belt in contact with each of the support rollers when the belt is suspended. A meandering-restricting member that protrudes in a direction substantially perpendicular to the contact surface, and the distance L0 (mm) between the meandering-restricting members provided on both ends of the belt and the upstream side in the conveyance direction of the recording medium A length L1 (mm) of the first pressing roller in the rotation axis direction of the first pressing roller that presses the heating roller and the belt, and the heating roller and the belt on the downstream side in the conveyance direction of the recording medium. The length L2 (mm) of the second pressing roller in the direction of the rotation axis of the second pressing roller that press-contacts satisfies the relationship of L0> L2> L1, and the meandering restricting member includes the second pressing roller By abutting the end portions of the rotation axis direction of the over la, thereby preventing meandering of the belt.

  Therefore, the problem that the meandering restricting member provided on the belt rides on the support roller can be prevented, and the support roller or the heating roller due to the meandering restricting member riding on the support roller can be prevented.

  The fixing device of the present invention includes a lubricant application unit that applies a lubricant to the inner peripheral surface of the belt at a position away from the heating roller in the belt.

  Therefore, by applying the lubricant at a position away from the heating roller, the lubricant can be applied at a position where the ambient temperature is low, so that the amount of lubricant applied is stabilized and an appropriate amount of lubricant is applied to the inner circumference of the belt. Can be supplied to the surface.

  The fixing device of the present invention relaxes the tension of the belt suspended on the plurality of support rollers when the fixing operation is not performed. Therefore, the load applied to the belt can be reduced, and the life of the belt can be extended.

  In the fixing device of the present invention, the belt is separated from the heating roller when the fixing operation is not performed. Therefore, by moving the belt away from the heating roller when the fixing operation is not performed, the shifting force acting on the belt can be reduced, and the life of the belt can be extended.

  The image forming apparatus of the present invention includes any one of the image forming apparatuses described above. For this reason, the same effects as those of the image forming apparatuses described above can be obtained.

  In the driving method of the fixing device of the present invention, the belt is separated from the heating roller when the fixing operation is not performed. Therefore, by moving the belt away from the heating roller when the fixing operation is not performed, the shifting force acting on the belt can be reduced, and the life of the belt can be extended.

Embodiment 1
An embodiment of the present invention will be described with reference to the drawings.

(Image forming device)
FIG. 2 is a cross-sectional view showing the internal structure of the image forming apparatus provided with the fixing device according to the present embodiment. This image forming apparatus is a dry electrophotographic color image forming apparatus, for example, on a predetermined recording paper (recording medium) based on image data transmitted from a terminal device connected via a network. A multi-color or single-color image is formed.

  As shown in FIG. 2, the image forming apparatus includes a visible image forming unit 10, a recording paper transport unit 30, a fixing device (heating device) 40, and a supply tray 20.

  The visible image forming unit 10 includes four visible image forming units 10Y, 10M, 10C, and 10B corresponding to the colors of yellow (Y), magenta (M), cyan (C), and black (B). It is installed side by side. That is, the visible image forming unit 10 includes four visible image forming units 10Y, 10M, 10C, and 10B. The visible image forming unit 10Y forms an image using yellow (Y) toner, and the visible image is formed. The forming unit 10M forms an image using magenta (M) toner, the visible image forming unit 10C forms an image using cyan (C) toner, and the visible image forming unit 10B is black (B). An image is formed using the toner. Specifically, four sets of visible image forming units 10Y, 10M, 10C, and 10B are arranged along a recording paper conveyance path that connects the supply tray 20 that feeds the recording paper and the fixing device 40. The so-called tandem type.

  The visible image forming units 10Y, 10M, 10C, and 10B have substantially the same configuration. That is, the photosensitive drum 11, the charger 12, the laser beam irradiation means 13, the developing device 14, the transfer roller 15, and the cleaner unit 16 are respectively provided, and each color toner is multiplex-transferred onto the conveyed recording paper. .

  The charger 12 uniformly charges the surface of the photosensitive drum 11 to a predetermined potential. The laser beam irradiation means 13 exposes the surface of the photosensitive drum 11 charged by the charger 12 according to the image data input to the image forming apparatus, and forms an electrostatic latent image on the surface of the photosensitive drum 11. Is. The developing device 14 visualizes the electrostatic latent image formed on the surface of the photosensitive drum 11 with toner of each color. The transfer roller 15 is applied with a bias voltage having a polarity opposite to that of the toner, and transfers the toner image formed on the photosensitive drum 11 onto the recording paper conveyed by the recording paper conveying means 30. The cleaner unit 16 removes and collects the toner remaining on the surface of the photosensitive drum 11 after the developing process by the developing device 14 and the transfer process by the transfer roller 15. The surface of the photosensitive drum 11 is charged by the charger 12, an electrostatic latent image is formed on the charged surface by the laser light irradiation unit 13, and the formed electrostatic latent image is developed by the developing device 14. The transferred toner image is transferred onto the recording paper by the transfer roller 15, and the toner image remaining on the surface after the transfer is removed and collected by the cleaner unit 16.

  Then, the transfer of the toner image onto the recording paper is performed in each color visible image forming unit. That is, since the toner image is transferred to the recording paper for the four colors, the same process is repeated four times.

  The recording paper conveying means 30 includes a driving roller 31, an idling roller 32, and a conveying belt 33, and conveys the recording paper so that the visible image forming unit 10 forms a toner image on the recording paper. The drive roller 31 and the idling roller 32 stretch the endless transport belt 33. The drive roller 31 is rotated by being controlled at a predetermined peripheral speed, thereby rotating the endless transport belt 33. Yes. The conveyance belt 33 generates static electricity on the outer surface, and conveys the recording paper while electrostatically adsorbing the recording paper.

  In this way, the recording sheet is transferred to the toner belt (unfixed toner image) while being transported to the transport belt 33, and then peeled off from the transport belt 33 by the curvature of the drive roller 31 and transported to the fixing device 40. . The fixing device 40 applies moderate heat and pressure to the recording paper, dissolves the toner transferred onto the recording paper, and fixes the toner on the recording paper, thereby forming a robust image on the recording paper.

(Fixing device)
Next, the fixing device 40 will be described with reference to FIG. FIG. 3 is a cross-sectional view illustrating a schematic configuration of the fixing device 40.

  As shown in this figure, the fixing device 40 includes a fixing roller (heating roller) 41, a plurality of pressing members (pressure roller 42 and peeling roller 43), and a belt 44.

  In the fixing roller 41, an elastic layer 41b and a release layer 41c are formed in this order on a cored bar 41a, and a halogen lamp is installed as a heating source (heating means) Q inside the cored bar. Yes.

  The core metal 41a is made of hollow aluminum having an outer diameter of 47 mm. However, the material of the cored bar 41a is not limited to this, and may be made of, for example, iron metal. Further, the size of the cored bar 41a is not particularly limited.

  The elastic layer 41b is made of a silicone rubber having a heat resistance of 1.5 mm in thickness. The release layer 41c is made of a PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) tube having a thickness of about 30 μm. The material of the release layer 41c is not limited to PFA as long as it has excellent heat resistance and durability and excellent release properties from the toner, and other fluorine-based materials such as PTFE (polytetrafluoroethylene), for example. Materials may be used. The fixing roller 41 according to the present embodiment has an outer diameter of about 50 mm and a surface hardness of 75 ° (Asker C hardness).

  The pressure roller (sponge roller, support roller) 42 is obtained by laminating an elastic layer 42b and a release layer 42c on a cored bar 42a. The pressure roller 42 applies a pressing force toward the fixing roller 41 toward the fixing roller 41 by an elastic member (spring or the like) (not shown) to press the belt 44 against the fixing roller (heating roller) 41. A fixing nip portion (first nip portion) is formed between the fixing roller 41 and the fixing roller 41 via a belt 44. That is, the first nip portion is a contact portion between the outer peripheral surface of the belt 44 applied with the pressing force toward the fixing roller 41 by the pressure roller 42 and the fixing roller 41, and is the most upstream in the recording paper conveyance direction. This is a fixing nip portion formed on the side. The pressure roller 42 plays a role of pressing the recording sheet against the fixing roller 41 when the recording sheet is passed through the first nip portion, so that heat can be transmitted to the toner on the recording sheet. .

  Here, the core metal 42a of the pressure roller 42 is made of iron and has an outer diameter of 13 mm. However, the material and size are not limited to this, and are made of, for example, stainless steel or aluminum. May be.

  The elastic layer 42b of the pressure roller 42 is for uniformly pressing the recording paper and sufficiently transferring the heat of the fixing roller 41 to the recording paper to melt the toner on the recording paper. 8.5 mm heat-resistant silicone sponge rubber is used. However, the material and thickness are not particularly limited as long as such a function is achieved.

  Similar to the release layer 41c of the fixing roller 41, the release layer 42c of the pressure roller 42 is made of, for example, PFA or PTFE.

  Each layer of the pressure roller 42 is firmly adhered, and the outer diameter of the pressure roller 42 is 30.0 mm. Further, the nip width (the length in the recording paper conveyance direction) of the first nip portion formed by pressing the belt 44 against the fixing roller 41 by the pressing force of the pressure roller 42 changes the load of the elastic member. Can be adjusted.

  The peeling roller (supporting roller) 43 further pressurizes the toner image on the recording paper heated at the first nip portion against the fixing roller 41 via the belt 44, thereby further heating the toner image. This is to secure a sufficient fixing strength and at the same time to peel off the recording paper from the surface of the fixing roller 41. The core metal 43a made of stainless steel is coated with an elastic layer 43b and a release layer 43c in this order. . Similarly to the pressure roller 42, the peeling roller 43 applies a pressing force in the direction of the fixing roller 41 to the belt 44 by an unillustrated elastic member (spring), thereby pressing the belt 44 against the fixing roller 41 and fixing roller 41. A fixing nip portion (second nip portion) is formed between the belt 44 and the belt 44. That is, the second nip portion is a contact portion between the fixing roller 41 and the outer peripheral surface of the belt 44 applied with the pressing force toward the fixing roller 41 by the peeling roller 43, and a pressing member that forms the first nip portion. This is a fixing nip portion formed by a pressing member (peeling roller 43) disposed adjacent to the (pressing roller 42) in the recording paper conveyance direction.

  In the present embodiment, a peeling roller 43 having an outer diameter of 15 mm is used. The surface hardness of the peeling roller is preferably higher than the surface hardness of the fixing roller 41. This is because the nip shape in the second nip portion formed by press-contacting the fixing roller 41 and the belt 44 can be made downward, so that when the color image is fixed, self-peeling (forced peeling assisting means such as a peeling nail) This is because it can be easily peeled off at the waist of the paper without being required, and can be peeled off without depending on the peeling nails as much as possible. On the other hand, when the surface hardness of the peeling roller 43 is lower than the surface hardness of the fixing roller 41, the nip shape of the second nip portion is upward, so that the paper discharged from the second nip portion follows the surface of the fixing roller 41. Discharged. For this reason, sufficient self-peeling performance cannot be obtained.

  The belt 44 includes a belt base material and a release layer (both not shown), and is suspended from the pressure roller 42 and the peeling roller 43. Similar to the release layer 41c of the fixing roller 41, the release layer of the belt 44 is provided for the purpose of preventing toner adhesion, and is made of, for example, PFA or PTFE. Further, the material of the belt base material is not particularly limited, but is made of, for example, PI (polyimide). The surface hardness of the belt 44 is preferably higher than the surface hardness of the fixing roller 41 as in the case of the peeling roller 43.

The pressure roller 42 and the peeling roller 43 press the belt 44 against the surface of the fixing roller 41 by a biasing means such as a spring (not shown). As a result, as shown in FIG. 1, the first nip portion (fixing nip portion) where the fixing roller 41 and the belt 44 abut (pressure contact), and the second nip portion where the fixing roller 41 and the belt 44 abut (pressure contact). A nip portion (fixing nip portion, belt winding portion) that is a region where no pressure contact means (pressing roller) is provided between the nip portion (fixing nip portion) and the first nip portion and the second nip portion. Is formed. That is, the virtual nip portion is a low-pressure portion that is sandwiched between the first nip portion and the second nip portion and is not provided with a pressing roller.
A region from the front end of the first nip portion to the rear end of the second nip portion is defined as a total nip portion. The first nip portion is a fixing nip portion that is formed first from the paper entry side, and the second nip portion is formed on the paper discharge side relative to the first nip portion.

  In the fixing device 40, the surface of the fixing nip is not yet determined in each of the fixing nips, that is, the region sandwiched between the fixing roller 41 heated to a constant temperature by a heating unit (not shown) and the pressing member (the pressure roller 42 and the peeling roller 43). By passing the recording paper (heated material) P to which the adhered toner adheres, the toner is melted and pressed against the recording paper to fix the image on the recording paper. Note that after fixing, the toner is welded to the recording paper, and gloss is obtained.

  In the virtual nip portion, the fixing roller 41 and the belt 44 are in contact with each other. For this reason, the conveyance failure of the recording paper can be prevented. In addition, although there is no pressing member in the virtual nip portion, since the fixing roller 41 and the belt 44 are in contact with each other, the heat of the fixing roller 41 can be appropriately transferred to the recording paper. Can be improved.

  In the fixing device 40 according to the present embodiment, the process speed Vp in the fixing device 40, that is, the moving speed of the surface of the fixing roller 41 due to the rotation of the fixing roller 41 is set to 350 mm / second. The fixing temperature T of the fixing roller 41, that is, the temperature of the surface of the fixing roller 41 at each nip portion is set to 170 ° C. In the present embodiment, the unfixed toner image that is subjected to the fixing process by the fixing device 40 is formed using toner having a toner outflow start temperature Ti of 99 ° C.

  In the fixing device 40, the nip width a1 of the first nip portion formed by the pressure roller 42, the belt 44, and the fixing roller 41 satisfies a1 / Vp ≧ 0.02 with respect to the process speed Vp. The nip width b of the virtual nip portion formed between the nip portion and the second nip portion is set so as to satisfy b / Vp <0.1 with respect to the process speed Vp. Note that the nip width a2 of the second nip portion formed by the peeling roller 43 and the belt 44 and the fixing roller 41 is arbitrarily set. For example, the nip width a1 of the first nip portion is set to 7.3 mm, the nip width b of the virtual nip portion is set to 9 mm, the nip width a2 of the second nip portion is set to 3 mm, and the total nip width (a1 + b + a2) is set to 19.3 mm. Yes.

  Thus, in the fixing device 40, the process speed Vp is 350 mm / second, the fixing temperature T is 170 ° C., the toner outflow start temperature Ti is 99 ° C., and the nip width a1 of the first nip portion is a1 / Vp ≧ 0. .02 is set to satisfy. As a result, the toner can be sufficiently heated at the first nip portion to such an extent that no low temperature offset occurs. For this reason, since the occurrence of the low temperature offset phenomenon can be prevented, it is possible to reliably prevent the image shift as described above from occurring.

  That is, if the length of the nip width a1 of the first nip width is short, unfixed toner on the recording paper in a state where the toner is not sufficiently melted in the first nip portion (a state where the toner is not sufficiently adhered to the recording paper). Is transported to the virtual nip portion. In this case, since the pressing force by the pressing member is not applied to the virtual nip portion, a pressure fluctuation occurs, and a so-called low temperature offset phenomenon that unfixed toner on the recording paper adheres to the fixing roller 41 may occur. . When the toner adhering to the fixing roller 41 comes into contact with the recording paper again, it may be displaced from the original position on the recording paper, resulting in image displacement.

  On the other hand, by setting the nip width a1 of the first nip portion as described above, the toner can be sufficiently heated in the first nip portion to the extent that no low temperature offset occurs. For this reason, since the occurrence of the low temperature offset phenomenon can be prevented, it is possible to reliably prevent the image shift as described above from occurring.

  In the fixing device 40, the process speed Vp is 350 mm / second, the fixing temperature T is 170 ° C., the toner outflow start temperature Ti is 99 ° C., and the nip width b of the virtual nip portion is set to b / Vp <0.1. It is set to meet. Thereby, in the virtual nip portion, the temperature of the toner can be maintained at a temperature at which high temperature offset does not occur.

  That is, the fixing roller 41 and the belt 44 are in contact with each other at the virtual nip portion. For this reason, although there is no pressing member in the virtual nip portion, the heat of the fixing roller 41 is transferred to the recording paper due to the contact between the fixing roller 41 and the belt 44. When the amount of heat transfer is appropriate, the fixing property of the toner can be improved. However, when the amount of heat transfer is too large, the toner is heated too much and melts more than necessary, and the recording paper is detached and attached. At this time, toner may remain on the surface of the fixing roller 41, which may cause a so-called high temperature offset. That is, if the nip width of the virtual nip portion is too long, the toner (toner surface) on the recording paper is excessively heated, and image loss due to high temperature offset may occur.

  In contrast, by setting the nip width b of the virtual nip portion as described above, the temperature of the toner can be maintained at a temperature at which no high temperature offset occurs in the virtual nip portion.

  In the above description, the case where the process speed Vp is 350 mm / second, the fixing temperature T is 170 ° C., and the toner outflow start temperature Ti is 99 ° C. has been described, but the present invention is not limited to this. When the process speed Vp, the fixing temperature T, and the toner outflow start temperature Ti are different from the above conditions, the toner can be sufficiently heated to the extent that no low temperature offset occurs in the first nip portion according to each condition. Thus, the nip width a1 of the first nip portion may be set, and the nip width b of the virtual nip portion may be set so that no high temperature offset occurs in the virtual nip portion.

  Here, when the process speed Vp, the fixing temperature T, and the toner outflow start temperature Ti are different, the nip width of the first nip portion required to sufficiently heat the toner in the first nip portion to the extent that the low temperature offset does not occur. In order to investigate a1, an experiment shown in (Experimental example) described later and an analysis shown in (Analytical example) were performed.

  As a result, it was confirmed that the occurrence of low temperature offset can be prevented by heating the toner temperature at the outlet of the first nip portion to a temperature equal to or higher than the toner outflow start temperature.

When the nip passage time for the recording paper to pass through the first nip portion is tn, the toner outflow start temperature is Ti, and the fixing temperature is T,
tn ≧ 0.0006Ti−0.00024T + 0.0015
It was found that if the nip passage time tn of the first nip portion is set so as to satisfy the condition, the toner can be heated to the toner outflow start temperature Ti or higher at the first nip outlet, and low temperature offset can be appropriately prevented. .

Note that the nip passage time tn of the first nip portion is expressed by tn = a1 / Vp using the nip width a1 of the first nip portion and the process speed Vp. Therefore,
a1 ≧ (0.0006Ti−0.00024T + 0.0015) × Vp
If the nip width a1 is set so as to satisfy the condition, the temperature of the toner at the outlet of the first nip portion becomes equal to or higher than the toner outflow start temperature, so that the occurrence of a low temperature offset can be prevented and image displacement can be prevented.

(Experimental example)
Using the above-described fixing device 40, the fixing condition such as toner type, fixing temperature and nip passage time is changed, and other conditions are kept constant, and a recording paper (unfixed toner image) is placed on the recording paper ( An unfixed image sample) was passed through and an experiment was conducted to evaluate the image shift of the sample after fixing.

  As an unfixed image sample, an unfixed image formed on a recording paper using two kinds of color oilless toners (toner A: polyester resin, toner B: styrene acrylic resin) having different thermal characteristics was used.

As a result of measuring the thermal characteristics of the toner with a flow tester (fluidity evaluation apparatus), the outflow start temperature Ti of the toner A was 99 ° C., and the 4 mm drop temperature T _{4 mm} was 120 ° C. Toner B outflow start temperature Ti = 91 ° C., 4 mm drop temperature T _{4 mm} = 115 ° C.

The toner particle diameter is 6.5 μm for both toners A and B, and the amount of both toners adhered to the recording paper per unit area is 0.5 mg / cm ² . As the recording paper, 65 g of plain paper was used. The process speed was 350 mm / s (seconds).

  First, image deviation evaluation for each of toner A and toner B is performed using the surface temperature (fixing temperature) of the fixing roller 41 facing the pressure roller 42 and the nip width (first nip width) of the first nip portion as parameters. The experiment was conducted. More specifically, for each of toners A and B, the first nip width is changed in three stages of 5.6 mm, 6.4 mm, and 7.3 mm, and the fixing temperature is 160 ° C. for each first nip width. An evaluation test was performed by changing the temperature to 170 ° C and 180 ° C. The fixing temperature was measured by a temperature sensor (not shown) provided on the surface of the fixing roller 41. Further, the nip width (second nip width) of the second nip portion was constant at 3 mm in both cases of the toners A and B. The process speed was fixed at 350 mm / s.

  The results of an image shift evaluation experiment with toner A are shown in Table 1 below, and the results of an image shift evaluation experiment with toner B are shown in Table 2 below. The evaluation of image shift was performed by measuring the density of the sample after passing the unfixed image sample through the fixing device 40 and fixing it, and evaluating the image quality subjectively. More specifically, a sample fixed by a conventionally used roller pair type fixing device was prepared as a comparative example (standard sample), and a relative evaluation with respect to the standard sample was performed. In Tables 1 and 2, “○” if there is no problem in image density and image quality, there is no problem in image density, but the image quality is slightly inferior (there is no problem on the product, but when enlarged and observed, the comparison example The case where the density unevenness is present is indicated by “Δ”, and the case where the image density is lowered and the image quality is inferior (the image shift is clearly noticeable as compared with the comparative example) is indicated by [×].

  As shown in Table 1, in the toner A, when the first nip width was 5.6 mm, the evaluation was “x” at the fixing temperatures of 160 ° C. and 170 ° C., and “Δ” at the fixing temperature of 180 ° C. When the first nip width was 6.4 mm, the evaluation was “x” at a fixing temperature of 160 ° C., “Δ” at a fixing temperature of 170 ° C., and “◯” at a fixing temperature of 180 ° C. When the first nip width was 7.3 mm, the evaluation was “Δ” at a fixing temperature of 160 ° C., and “◯” at a fixing temperature of 170 ° C. and 180 ° C.

  On the other hand, as shown in Table 2, when the first nip width was set to 5.6 mm, toner B was evaluated as “Δ” at a fixing temperature of 160 ° C., and “◯” at fixing temperatures of 170 ° C. and 180 ° C. It was. When the first nip width was 6.4 mm and 7.3 mm, the evaluation was “◯” at any fixing temperature of 160 ° C. to 180 ° C.

  From this result, it can be seen that toner A is more likely to cause image displacement than toner B. It can also be seen that the image shift improves as the fixing temperature is higher and the first nip width is wider.

  Next, an experiment similar to the above was performed for the toner A in which image misalignment is likely to occur, with the first nip width fixed at 5.6 mm and the second nip width as a parameter instead. That is, as shown in Table 3 below, the second nip width is changed in three stages of 3 mm, 3.8 mm, and 4.6 mm, and the fixing temperature is 160 ° C., 170 ° C., and 180 ° C. for each second nip width. It was changed in three stages. The results are shown in Table 3. In this table, “◯”, “Δ”, and “×” represent evaluation results using the same evaluation criteria as in Tables 1 and 2.

  As shown in this table, when the second nip width is 3 mm, 3.8 mm, or 4.6 mm, the evaluation is “x” at the fixing temperatures of 160 ° C. and 170 ° C. The evaluation was “△”.

  From this result, it can be seen that even if the second nip width is widened, the image shift is not improved so much. Considering the results of Table 1 together, it is presumed that the main cause of image shift is not closely related to the second nip portion but closely related to the first nip portion.

  Therefore, in order to examine the cause of the image displacement in more detail, the peeling roller 43 and the belt 44 are removed from the fixing device 40 shown in FIG. 3 to obtain the same configuration (model) as that of the conventional roller pair type fixing device. The fixed image after passing through one nip portion was examined. More specifically, the peeling roller 43 and the belt 44 are removed from the fixing device 40, and the fixing temperature is 160 ° C., 170 ° C., 180 ° C., and the first nip width is 5. under a process speed of 350 mm / s (seconds). Unfixed image samples were passed through three stages of 6 mm, 6.4 mm, and 7.3 mm, and the fixability was evaluated by a bending test. In this configuration, since the self-peeling property cannot be secured, oil is applied to the surface of the fixing roller 41 to secure the self-peeling property.

  As a method for evaluating the fixability, after lightly bending the fixed sample so that the printed surface is on the inside, a predetermined load is applied to the bent portion, and the width of the toner drop-off portion generated at the fold portion is measured. Based on the evaluation.

  The evaluation results are shown in Table 4. In this table, “×” is used when the low temperature offset occurs entirely, “△” is used when the low temperature offset is partially generated, and “◯” is used when the low temperature offset is not generated. . When the fixing strength is insufficient, “NG” is indicated, and when the fixing strength is sufficient, “OK” is indicated.

  As shown in Table 4, regarding the low temperature offset, when the first nip width was 5.6 mm, the evaluation was “x” at a fixing temperature of 160 ° C. and 170 ° C., and “Δ” at a fixing temperature of 180 ° C. . When the first nip width was 6.4 mm, the evaluation was “x” at a fixing temperature of 160 ° C., “Δ” at a fixing temperature of 170 ° C., and “◯” at a fixing temperature of 180 ° C. When the first nip width was 7.3 mm, the evaluation was “Δ” at a fixing temperature of 160 ° C., and “◯” at a fixing temperature of 170 ° C. and 180 ° C. Further, the fixing strength was insufficient (NG) in any measured case.

  From this result, it can be seen that although the low temperature offset occurs when the fixing temperature is low and the first nip width is narrow, the low temperature offset is improved by increasing the fixing temperature or widening the first nip width. It can also be seen that the fixing strength is insufficient (NG) even under conditions where low temperature offset does not occur. Further, comparing the results of Tables 1 and 4, it can be seen that the conditions for causing the image shift and the conditions for the low temperature offset completely coincide.

  From the above results, the cause of the image shift can be explained as follows. That is, a plurality of fixing nip portions (here, the first nip portion and the second nip portion) are formed on the fixing member (here, the fixing roller 41) by a plurality of pressing members (here, the pressure roller 42 and the peeling roller 43). In the case of the fixing device, a nip portion (virtual nip portion) in which almost no fixing pressure is applied is formed between the first nip portion and the second nip portion. That is, in the case where the belt 44 is not provided, there is no means for applying a fixing pressure, so that a fixing nip is not formed, and the belt (pressure belt) 44 is apparently fixed as in the fixing device 40 according to the present embodiment. Even if the nip is formed, only the pressure due to the tension of the belt 44 is applied, so that a nip portion (virtual nip portion) in which almost no fixing pressure is applied is formed.

  Accordingly, the toner image on the recording paper is in contact with the fixing member (fixing roller 41), the toner, and the recording paper by the pressing member at the first nip portion, but after passing through the first nip portion, the toner image on the second nip portion. Since there is no pressing member in the entire virtual nip portion, a slight gap is generated between the fixing roller 41 and the recording paper. At this time, if the melting state of the toner in the first nip portion is insufficient, a part of the toner image adheres to the fixing roller 41 side due to the low temperature offset phenomenon. Thereafter, when a slight misalignment occurs between the fixing roller 41 and the recording paper at the virtual nip portion, the fixing roller 41 and the recording paper are adhered to the fixing roller 41 again at the second nip portion. The position of the toner image with respect to the recording paper is displaced, and image displacement occurs.

  In other words, in order to prevent image misalignment in a fixing device having a plurality of fixing nip portions as shown in this embodiment, an unfixed image sample has a toner image that does not cause a low-temperature offset immediately after passing through the first nip portion. It can be seen that it is necessary to set the fixing conditions at the first nip portion so that is melted by heating.

  Note that the fixing conditions set at the first nip portion do not necessarily satisfy the fixing strength. That is, the image sample immediately after passing through the first nip portion has insufficient fixing strength, but it is only necessary to supply heat while passing through the virtual nip portion and the second nip portion and satisfy the fixing strength.

(Analysis example)
Next, in order to examine the relationship between the toner temperature at the first nip exit and the image shift, the fixing device 40 shown in FIG. 3 is modeled as one-dimensional heat conduction as shown in FIG. 4 to analyze the heat transfer state. Went. That is, as shown in FIG. 4, the heating source Q provided inside the cored bar 41a of the fixing roller 41, the cored bar (aluminum) 41a of the fixing roller 41, the elastic layer (silicone rubber) 41b, the release layer (PFA). 41c, the first air layer (air layer) air1 formed between the release layer 41c and the toner on the recording paper, the toner, the recording paper, formed between the recording paper and the release layer 44a of the belt 44. A model in which a belt base material 44b composed of a second air layer (air layer) air2, a release layer 44a, and PI is arranged in this order is created, and a cross-sectional depth direction of the fixing roller 41 (pressing from the heating source Q) The heat transfer in the direction of the roller 42) was analyzed.

  In the above model, the air layers air1 and air2 are provided in the boundary region between the fixing roller 41 and the toner surface and in the boundary region between the release layer 44a of the belt 44 and the recording paper. This is because the surface of the recording paper has a certain degree of surface roughness, and the gap caused by the surface roughness is modeled as air layers air1 and air2. Also, considering the microscopic behavior, the temperature distribution is different among the layers, so that the layers of the elastic layer 41b, the release layer 41c, the toner, and the recording paper of the fixing roller 41 are finely divided in the heat transfer direction. Using this model, the lowermost layer temperature, which is the temperature of the layer (side) in contact with the recording paper, of the toner of the unfixed image (unfixed toner image) printed on the recording paper immediately before the first nip exit was calculated. .

  As analysis conditions, the thickness, initial temperature, specific heat, specific gravity, thermal conductivity, and other necessary physical properties of each layer shown in Table 5 were given. Regarding the elastic layer 41b of the fixing roller 41, the elastic layer 41b is divided into 15 layers. The initial temperature of each of the divided layers is 160 ° C. for the layer in contact with the release layer 41c and 188 ° C. for the layer in contact with the cored bar 41a. It was. Moreover, the initial temperature of the layer during the division was set to a value increased by 2 ° C. from the layer close to the release layer 41c.

  The analysis conditions shown in Table 5 are the settings (conditions) when the fixing temperature is 160 ° C. When calculating the fixing temperature at 170 ° C., the layers set by the fixing roller 41 (release layer 41c, elastic layer 41b). The initial temperature of the cored bar 41a) is increased by 10 ° C. Similarly, when calculating at a fixing temperature of 180 ° C., the temperature of each layer of the fixing roller 41 is further increased by 10 ° C.

  The calculation formula used for the analysis will be described. As shown in FIG. 5, in the layers adjacent in order of the a layer, the b layer, and the c layer, the temperature T (b, t + τ) after τ seconds from a certain time t of the b layer is expressed by the following equation.

T (b, t + τ) = T (b, t) + τ / (ρ _b × C _b × H _b ) × [{T (a, t) −T (b, t)} / (h _a / 2λ _a + h _{b / 2λ b) + {T} (c, t) -T (b, t)} / (h b / 2λ b + h c / 2λ c)] ··· equation (1)
Here, h is the layer thickness, T is the temperature, λ is the thermal conductivity, ρ is the specific gravity, and C is the specific heat. The subscripts a, b, and c are the values of the a layer, b layer, and c layer, respectively. It is shown that.

  Using this equation, the temperature of each layer after a minute time τ has been calculated, and the calculation is repeated until the time immediately before completion of the nip passage (the value obtained by dividing the nip width by the process speed).

  Table 6 shows the results of calculating the toner bottom layer temperature at the first nip outlet under the above analysis conditions using the fixing temperature and the first nip width as parameters.

  As shown in this table, when the first nip width was 5.6 mm, the lowest toner layer temperature was 87 ° C. at a fixing temperature of 160 ° C., 91 ° C. at a fixing temperature of 170 ° C., and 95 ° C. at 180 ° C. When the first nip width was 6.4 mm, the fixing temperature was 91 ° C. at 160 ° C., the fixing temperature was 170 ° C., 95 ° C., and 180 ° C. was 99 ° C. When the first nip width was 7.3 mm, it was 95 ° C. at a fixing temperature of 160 ° C., 99 ° C. at a fixing temperature of 170 ° C., and 103 ° C. at 180 ° C.

  From the results of Tables 1 and 6, it can be seen that when the toner A lowermost layer temperature at the nip outlet reaches 99 ° C. or more, a good image without image displacement is obtained in the toner A. That is, it is understood from the thermal analysis that when the temperature of the lowermost layer of the toner at the first nip outlet reaches or exceeds the outflow start temperature of toner A (99 ° C.), no image shift has occurred.

  Similarly, from the results of Tables 2 and 6, when the toner bottom layer temperature at the nip outlet reaches 91 ° C. or higher in the toner B, a good image without image displacement can be obtained. In other words, even if the physical property value of the toner is changed, the image shift can be improved by setting the fixing conditions (fixing temperature, first nip width) so as to be equal to or higher than the toner outflow start temperature in the first nip portion. it can.

  Incidentally, the amount of heat given to the toner in the first nip portion is determined by the fixing temperature and the nip passage time (nip passage time = nip width / process speed) calculated from the relationship between the first nip width and the process speed. Accordingly, if the nip passage time (here, the nip passage time at the first nip portion) is set so that the toner bottom layer temperature becomes equal to or higher than the toner outflow start temperature at a certain fixing temperature, the image shift is improved. It is also considered.

  Here, the toner A was used to evaluate image misregistration using the process speed and the first nip width as parameters at a fixed fixing temperature (170 ° C.). Further, the toner bottom layer temperature just before completion of the nip passage was calculated by thermal analysis. The results are shown in Table 7. Note that the evaluations “◯”, “Δ”, and “×” of image shift are based on the same evaluation criteria as in Tables 1 and 2.

  As shown in Table 7, the image shift has a correlation with the toner bottom layer temperature immediately before the completion of the nip passage. The lowest toner layer temperature immediately before completion of the nip has a correlation with the nip passage time. It can also be seen that image misalignment does not occur if the nip passage time is such that the lowest temperature of the toner is equal to or higher than the outflow start temperature (99 ° C. for toner A).

  Note that the nip passage time required for setting the lowest layer temperature of the toner immediately before completion of the nip to be equal to or higher than the toner outflow start temperature varies depending on the fixing temperature. FIG. 6 is a graph showing the relationship between the toner bottom layer temperature Tb immediately before passing through the nip and the nip passing time Tn at each fixing temperature when the fixing temperatures are 160 ° C., 170 ° C., and 180 ° C. This graph is plotted based on the data shown in Table 6 for each fixing temperature described above, with the horizontal axis representing the lowest layer temperature of the toner reached immediately before completion of nip passage, and the ordinate representing the nip passage time at that time. The results and their approximate lines are represented by solid lines.

  Thus, for each fixing temperature condition, there is a proportional relationship between the lowest layer temperature Tb of the toner immediately before passing through the nip and the nip passing time tn, and as a linear function as shown in the following equation (2). Can be represented.

tn = α × Tb + β (2)
Α and β are constants.

  When considered as a linear function, since the graphs at the respective fixing temperatures are almost parallel, only the intercept β is different, and the inclination thereof is almost constant regardless of the fixing temperature (a = 0.006). is there. In this graph, when the intercept β (value of tn when Tb = 0) is considered as a function f (T) having the fixing temperature T as a parameter, the nip passage time tn is expressed by the following relational expression ( It can be approximated by equation (3).

tn = 0.006 × Tb + f (T) (3)
FIG. 7 is a graph showing the relationship between the fixing temperature T and the intercept β (function f (T)). That is, when the approximate line of each fixing temperature shown in FIG. 6 is represented by the function of the above formula (2), the horizontal axis is plotted as the fixing temperature T, the vertical axis is plotted as the intercept β, and the approximate line is represented. It is. Thus, the approximate line can be expressed as a linear function shown in the following equation (4).

β = −0.00024T + 0.0015 Formula (4)
From the above equations (3) and (4), the relationship between the nip passage time tn, the toner bottom layer temperature Tb, and the fixing temperature T can be expressed by the following equation (5).

tn = 0.006Tb−0.00024T + 0.0015 (5)
Here, as the nip passage time tn becomes longer, the toner bottom layer temperature Tb immediately before the completion of the nip passage becomes higher. Therefore, the first nip passage time (that is, at a certain process speed) is satisfied so as to satisfy the following equation (6). If the first nip width) is set, an image without image displacement can be obtained. That is, by setting the nip passage time tn so as to satisfy the following expression (6), the toner bottom layer temperature Tb becomes higher than the toner outflow start temperature Ti, and image shift can be prevented.

tn ≧ 0.0006Ti−0.00024T + 0.0015 Formula (6)
By using the above formula (6), it is possible to calculate the fixing temperature and the nip width (first nip width) necessary for preventing image misalignment in a toner having a certain thermal characteristic without obtaining it by experiment or analysis. . That is, by setting the fixing temperature T and the nip passage time (nip width) tn satisfying the above formula (6), it is possible to realize a fixing device that prevents image shift without performing an experiment.

  As described above, the toner bottom layer temperature can be obtained by theoretical calculation using the fixing device 40 as a model. By setting the fixing temperature and the nip passage time based on the result of theoretical calculation, for example, in a toner having an arbitrary thermal characteristic, the fixing condition in which the toner bottom layer temperature at the first nip exit is equal to or higher than the toner outflow start temperature. The (fixing temperature and nip passage time) can be calculated without being obtained through experiments or analysis, and image misalignment can be prevented appropriately.

  Note that the pressure roller 42 as the first pressing member in the fixing device 40 is an elastic roller in which an elastic layer 42b is coated on a cored bar 42a. Thus, by using the pressure roller 42 that forms the first nip portion as an elastic roller, the nip width of the first nip portion can be set sufficiently wide. Therefore, it is possible to easily realize the fixing conditions required at the first nip portion.

  In the fixing device 40, a belt 44 suspended from a plurality of support rollers (the pressure roller 42 and the peeling roller 43) is provided, and a plurality of nip portions are formed between the belt 44 and the fixing roller 41. Has been. That is, the belt 44 is pressed against the fixing roller 41 by a plurality of support rollers (pressing members; the pressure roller 42 and the peeling roller 43).

  When the belt 44 is not provided, there is a gap between the nip portion (first nip portion) formed by the first pressing member and the nip portion (second nip portion) formed by the second pressing member. Since there is nothing that regulates the conveyance direction, the conveyance direction of the recording paper changes until the recording paper enters the second nip portion, and the conveyance property such that the recording paper cannot enter the second nip portion. Problems can arise. Therefore, by providing the belt 44, the recording paper discharged from the first nip portion is conveyed while being sandwiched between the belt 44 and the fixing roller 41 (regulating the conveyance direction), thereby preventing conveyance failure. be able to.

  Further, for example, in addition to the pressure roller 42 and the peeling roller 43, one or more tension rollers (support rollers, not shown) may be provided for the purpose of maintaining the tension of the belt 44. The fixing device 40 includes a pressure roller 42 and a peeling roller 43 as support rollers for the belt 44, and the belt 44 is pressed against the fixing roller 41 by all the support rollers (the pressure roller 42 and the separation roller 43). However, the configuration is not limited thereto, and the belt 44 may be pressed (pressed) toward the fixing roller 41 by all or a part of the plurality of support rollers.

  In the above description, the configuration including the pressure roller 42 and the peeling roller 43 as the support roller for supporting the belt 44 has been described, but the number of support rollers is not limited thereto. For example, in addition to the pressure roller 42 and the peeling roller 43, a tension roller 47 may be provided as shown in FIG. Alternatively, a larger number of support rollers may be provided. However, if the number of support rollers is increased too much, the belt length of the belt 44 becomes longer, and the number of contact points between the belt 44 and each support roller increases, so that the amount of heat released from the belt 44 increases, and the fixing roller Since the power consumption for heating 41 may increase, the number of support rollers is preferably two or three.

  The fixing device 40 or the image forming apparatus further includes a fixing condition calculation unit that calculates fixing conditions (fixing temperature and nip passage time) for setting the toner bottom layer temperature at the outlet of the first nip portion to be equal to or higher than the toner outflow start temperature. The fixing temperature and / or the nip passage time may be controlled based on the calculated fixing conditions.

  For example, the temperature of a heating source (heating means) Q for heating the fixing roller 41 is variable, and a temperature control means (not shown) for controlling the temperature of the heating source Q is provided in the image forming apparatus or the fixing apparatus, and the fixing is performed. You may make it control the temperature of the heating source Q based on the calculation result of a condition calculation means.

  Further, a nip width control means for controlling the nip width may be provided, and the nip passage time may be controlled by controlling the nip width based on the calculation result of the fixing condition calculation means. For example, a plurality of pressure pads or pressure rollers having different widths can be selected, and the pressure pad or pressure roller used for the first nip portion is selected based on the calculation result of the fixing condition calculation means. Also good. Further, the nip width may be controlled by controlling the pressing force applied to the pressure roller 42, but in this case, the fluctuation range of the pressing force is caused by the deflection of the roller, and the nip width is equal to that of the roller. It is preferable to set the degree of non-uniformity in the rotation axis direction.

  Further, the nip passage time may be controlled by making the process speed variable and controlling the process speed based on the calculation result of the fixing condition calculation means.

  In addition, the toner outflow start temperature may be input by a user via an input unit (not shown), or a measurement unit that measures the toner outflow start temperature of the toner to be used may be additionally provided. Alternatively, the toner outflow start temperature may be specified by providing a mark or the like that can identify the type of toner (toner outflow start temperature) in a container (cartridge, replacement container) in which toner is stored, and reading the mark.

  In the present embodiment, the fixing condition (fixing temperature and nip passage time) for setting the toner bottom layer temperature at the outlet of the first nip portion to be equal to or higher than the toner outflow start temperature is obtained by one-dimensional heat transfer analysis. Although explained, it is not limited to this. For example, an analysis considering a two-dimensional or three-dimensional shape may be performed, or an analysis considering a time change may be performed.

  In this embodiment, a color image of a dry electrophotographic system that forms a multicolor or single color image on a predetermined recording sheet based on image data transmitted from a terminal device connected via a network. Although the case where the forming apparatus includes the fixing device of the present invention has been described, the present invention is not limited to this. For example, the present invention may be applied to a copying machine (image forming apparatus) that includes an image reading apparatus and forms a read image on a recording sheet, or an image forming apparatus that has multiple functions such as a facsimile machine, a copying machine, and a printer. Good.

  In this embodiment, the unfixed toner image is heated to a temperature at which the low temperature offset does not occur at the first nip portion. However, at this time, the temperature is preferably set to a temperature at which the high temperature offset occurs. That is, if the toner becomes too high, image loss may occur due to so-called high temperature offset. Therefore, the temperature of the toner at the first nip portion outlet is set between each fixing nip portion and each fixing nip portion (each virtual nip portion). It is preferable to set the fixing temperature and the nip passage time so that a low temperature offset does not occur and a high temperature offset does not occur.

[Embodiment 2]
Another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those provided in the image forming apparatus and the fixing device in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and description thereof is omitted. Moreover, about the member which attached | subjected the same code | symbol, unless otherwise indicated, the same change as Embodiment 1 shall be possible.

FIG. 9 is a cross-sectional view illustrating a schematic configuration of the fixing device 50 according to the present embodiment.
As shown in this figure, the fixing device 50 is suspended from a fixing roller 41, a plurality of support rollers (a pressure roller (pressing member) 42, a peeling roller (pressing member) 43, a tension roller 47), and each support roller. (Stretched) belt 54. In the fixing device 50, the belt 44 is changed to the belt 54 in the fixing device 40 shown in FIG. 8 in the first embodiment, and the lengths of the pressure roller 42 and the peeling roller 43 in the rotation axis direction will be described later. It is stipulated in. The fixing device 50 is provided in place of the fixing device 40 in the image forming apparatus of the first embodiment.

  FIG. 10 is a cross-sectional view of the belt 54. As shown in this figure, the belt 54 is an endless belt composed of a belt base material 54a and a release layer 54b, and each support roller (the pressure roller 42, the peeling roller 43, and the tension roller 47) has a belt base material 54a. It is suspended so that the side becomes the inner peripheral surface. Similar to the release layer 41c of the fixing roller 41, the release layer 54b of the belt 54 is provided for the purpose of preventing adhesion of toner, and is made of, for example, PFA or PTFE. The material of the belt base material 54a is not particularly limited, but is made of, for example, PI (polyimide). The surface hardness of the belt 54 is preferably higher than the surface hardness of the fixing roller 41 as in the case of the peeling roller 43.

  Further, as shown in FIG. 10, the belt 54 has belt bases at both ends (both ends arranged in the rotation axis direction of each support roller) of the inner circumferential surface when suspended by the support rollers. Ribs (meandering restricting members) 55 and 55 projecting in a direction substantially perpendicular to the material surface are provided. The ribs 55 and 55 are provided on both ends of the belt 54 that is an endless belt over the entire circumference. The material of the ribs 55 and 55 is not particularly limited, but is preferably an elastic member, and is formed of the same material as the belt base material 54a, for example. In addition, as shown in FIG. 10, let the space | interval between both rib 55 * 55 (distance between the inner walls of both rib 55 * 55) be rib space | interval L0.

  FIG. 11 is a perspective plan view of the pressure roller 42 and the peeling roller 43 as seen from the fixing roller 41 side. In this figure, the belt 54 suspended on the pressure roller 42 and the peeling roller 43 is indicated by broken lines.

As shown in this figure, in this embodiment, the pressure roller length (the length of the pressure roller 42 in the contact portion with the belt 54 in the rotation axis direction of the roller) L1 and the separation roller length (the separation roller 43). The length of the roller in the rotation axis direction) L2 and the rib interval L0.
L0>L1> L2
It is set to satisfy the relationship.

  In general, when a belt is suspended by a plurality of support rollers, there is a problem that the belt meanders because the parallelism of the rotation shafts of the support rollers is slightly different. In order to solve this problem, a technique in which a convex portion is provided at the belt end portion and a concave portion that engages with the convex portion at the belt end portion is provided on the roller on which the belt is suspended is described in, for example, the above-described patent document. 2 and Patent Document 3, however, these techniques have a problem in that the convex portion provided at the belt end portion passes over the concave portion of the suspension roller, causing belt running failure.

  On the other hand, in the fixing device 50 according to the present embodiment, the ribs 55 provided at both ends of the belt 54 form the fixing nip portion with the fixing roller 41, among the supporting rollers in the recording paper conveyance direction. The belt 54 is prevented from meandering by coming into contact with both ends in the rotation axis direction of the peeling roller 43 which is a support roller located on the downstream side. That is, both ends of the peeling roller 43 that forms the second nip portion downstream of the pressure roller 42 that forms the first nip portion upstream of the recording paper conveyance direction are provided at both ends of the belt 54. By abutting against the formed rib 55, it functions as meandering prevention means for preventing meandering of the belt.

  In this way, the meandering restriction roller (suspension roller) that restricts the meandering of the belt is not a roller (heating roller nip inlet side) that forms the fixing nip portion on the most upstream side in the recording paper conveyance direction. By using a roller that forms a fixing nip portion on the downstream side in the direction (roller on the exit nip side), it is possible to prevent the rib 55 provided on the belt 54 from riding on the meandering restriction roller. Accordingly, it is possible to prevent the heating roller from being damaged due to the belt riding on the meandering restriction roller.

  The distance between the ribs 55 and 55 provided at the end of the belt 54 and both ends of the peeling roller 43 is, for example, 1 mm to when the distance between each rib 55 and each end of the peeling roller 43 is equal. What is necessary is just to set so that it may be set to 2 mm. That is, it may be set so that 4 mm> L0−L1> 2 mm. Thereby, even when the belt 54 or the peeling roller 43 is thermally deformed by the heat from the fixing roller 41, the distance between the ribs 55 and 55 and both ends of the peeling roller 43 can be appropriately maintained. That is, when the belt 54 is running normally, the peeling roller 43 and the ribs 55 and 55 are not in contact with each other, so that no frictional force is generated between them, and the life of the belt 54 and the peeling roller 43 is extended. Can be planned. On the other hand, when the belt 54 is meandering, the rib 55 and the end portion of the peeling roller 43 come into contact with each other, whereby the meandering of the belt 54 can be appropriately regulated.

  Further, not only the peeling roller 43 but also the tension roller 47 may function as a meandering restricting member like the peeling roller 43.

  In the present embodiment, the configuration in the case where there are three support rollers (the pressure roller 42, the peeling roller 43, and the tension roller 47) on which the belt 54 is suspended has been described, but the present invention is not limited to this. The number of may be two, or four or more. However, if the number of support rollers is increased too much, the belt length of the belt 54 becomes longer, and the number of contact points between the belt 54 and each support roller increases, so that the amount of heat released from the belt 54 increases, and the fixing roller Since the power consumption for heating 41 may increase, the number of support rollers is preferably three.

  In this embodiment, the pressure roller 42 is provided with a release layer 42c made of PFA, PTFE or the like for improving slipperiness on the surface of a solid stainless steel roller having an outer diameter of 15 mm, in which the elastic layer 42b is omitted. Alternatively, the same effect can be obtained by using the pressure roller 42 with the stainless steel exposed on the surface. Further, a stainless steel roller having the same specifications as the pressure roller may be used as the peeling roller 43.

  Even when a high-humidity roller such as stainless steel is used for the pressure roller 42 and the peeling roller 43, the fixing roller and the roller pressing force are set so that the passage conditions of the first nip and the second nip are set as in the first embodiment. By setting these, image quality defects such as image misalignment and fixing defects can be prevented as in the first embodiment.

[Embodiment 3]
Another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those provided in the image forming apparatus and the fixing device in the first and second embodiments are denoted by the same reference numerals as those in the first and second embodiments, and the description thereof is omitted. Moreover, about the member which attached | subjected the same code | symbol, unless otherwise indicated, the same change as Embodiment 1 and 2 shall be possible.

  FIG. 12 is a cross-sectional view illustrating a schematic configuration of the fixing device 60 according to the present embodiment. The fixing device 60 is provided in the above-described image forming apparatus instead of the fixing device described in each of the above embodiments. As shown in this figure, the fixing device 60 includes a fixing roller 41, a plurality of support rollers (a pressure roller 42, a peeling roller 43, and a tension roller 67), and a belt 54 suspended (stretched) on each support roller. It consists of. As shown in this drawing, the fixing device 60 has substantially the same configuration as the fixing device 50 shown in FIG. 9 in the second embodiment. However, it differs from the fixing device 50 in that a tension roller 67 that functions as a lubricant applying means for applying a lubricant to the inner peripheral surface of the belt 54 is provided instead of the tension roller 47 in the fixing device 50.

  FIG. 13A is a perspective view of the tension roller 67, and FIG. 13B is a cross-sectional view showing a part of the tension roller 67.

  As shown in FIGS. 13A and 13B, the tension roller 67 includes a hollow cored bar (core material) 67a and a ceramic or the like provided so as to cover the outer peripheral surface of the cored bar 67a. The porous layer 67b. A large number of minute holes (not shown) are provided on the outer peripheral surface of the cored bar 67a, whereby lubricant that is filled and supplied into the cored bar 67a is provided in the cored bar 67a. It is discharged to the porous layer 67b through the holes, and the porous layer 67b is impregnated with the lubricant. As a result, the lubricant impregnated on the surface of the tension roller 67 is applied to the inner peripheral surface of the belt 54.

  Note that both end portions of the cored bar 67a are formed in a cylindrical shape having a smaller diameter than the center portion, and these both end portions function as a rotation shaft of the tension roller 67. Further, in the cored bar 67a, a lubricant is replenished into the cored bar 67a as needed from a lubricant supply means (not shown) provided outside the tension roller 67 via both ends functioning as the rotating shaft. It has become so.

  Further, as described above, ribs (beads) 55 and 55 are provided at both ends of the inner peripheral surface of the belt 54. Thereby, the lubricant applied to the inner peripheral surface of the belt 54 is prevented from flowing around the outer peripheral surface of the belt 54.

  As described above, in the fixing device 60, the lubricant is applied (supplied) to the inner peripheral surface of the belt 54 in the tension roller 67 which is a support roller disposed at a position far from the fixing roller (heating roller) 41. In this way, by applying the lubricant at a position far from the fixing roller (heating roller) 41 as a heat source, the lubricant can be applied at a position where the ambient temperature is low. The lubricant can be supplied to the inner peripheral surface of the belt 54.

  That is, generally, a heating device (fixing device) in which a belt is suspended by a plurality of rollers has a problem that the belt meanders during rotation. Therefore, a method has been proposed for improving such a problem by applying a lubricant to the inner surface of the belt to reduce the shifting force that causes the meandering. However, when applying a lubricant to the inner surface of the belt, if the amount of application is too large or if the lubricant wraps around the outer periphery of the belt, the belt will slip. It is necessary to prevent sneaking into the surface. However, when the lubricant is supplied to the belt at a position close to the heating source, it is difficult to stably supply the lubricant over a long period of time because of the high temperature and high pressure conditions. Therefore, the supply amount of the lubricant becomes unstable, and the excess or deficiency of the lubricant occurs. Therefore, as in this embodiment, by applying the lubricant at a position far from the fixing roller (heating roller) 41 that is a heat source, the lubricant can be applied at a position where the ambient temperature is low. It can be stabilized.

  In the fixing device 60, a tension roller 67 having a porous layer 67b on the surface is used as a lubricant application means (supply member) for supplying a lubricant. In this way, for example, a porous layer made of ceramic or the like is impregnated with a lubricant, and the belt is brought into contact with the porous layer impregnated with the lubricant to supply the lubricant to the inner peripheral surface of the belt. Thus, an appropriate amount of lubricant can be supplied to the inner surface of the belt. The material of the porous layer is not limited to ceramic, and may be any material that can be appropriately impregnated with a lubricant and has an appropriate strength as a support roller for suspending the belt 54.

  In the fixing device 60, ribs (beads) 55 are provided at both ends of the inner peripheral surface of the belt 54. Thereby, it is possible to prevent the lubricant applied to the inner peripheral surface of the belt 54 from entering the outer peripheral surface of the belt 54. Therefore, it is possible to prevent adverse effects such as slipping of the belt due to the lubricant flowing around the outer peripheral surface of the belt.

  In the fixing device 60, the tension roller 67 is disposed at the lowermost position among the plurality of support rollers that support the belt 54. That is, the tension roller 67 supports the position on the lowermost side (the lowest side with respect to the direction of gravity action, the ground side) of the belt 54 suspended by a plurality of support rollers. Thereby, it is possible to prevent the lubricant impregnated in the tension roller 67 from flowing out. That is, as shown in FIG. 13 (b), even if the lubricant impregnated in the tension roller 67 tries to flow outside, the lubricant is blocked by the ribs 55 and 55 provided at both ends of the belt 54, so that There is no leakage. In addition, a lubricant outflow prevention member for preventing outflow of a lubricant having substantially the same configuration as that of the ribs 55 and 55, for example, may be separately provided on both end sides of the ribs 55 and 55 as meandering prevention members in the belt 54. Good. Alternatively, the ribs 55 and 55 as the meandering prevention member may not be provided, and only the lubricant outflow prevention member may be provided.

  Further, for example, as shown in FIGS. 14A and 14B, a blade that substantially uniformly contacts a part of the surface of the tension roller 67 (porous layer 67b) along the rotation axis direction of the roller. (Smoothing means) 61 may be provided. Thereby, the lubricant impregnation state (condition of the contact surface) of the contact surface with the belt 54 in the tension roller 67 can be made constant (smoothed), and the lubricant can be applied more evenly.

  Further, the description has been given of the fixing device 60 provided with the tension roller 67 as the lubricant application unit in place of the tension roller 47 in the fixing device 50 shown in FIG. 9 in the second embodiment. It is not limited. For example, in the fixing device 40 shown in FIG. 8 in the first embodiment, the tension roller 47 may be replaced with the tension roller 67.

  In the present embodiment, the case where the number of support rollers on which the belt 54 is suspended is three (the pressure roller 42, the peeling roller 43, and the tension roller 67) is not limited to this, and the number of support rollers is as follows. There may be more. However, if the number of support rollers is increased too much, the belt length of the belt 54 becomes longer, and the number of contact points between the belt 54 and each support roller increases, so that the amount of heat released from the belt 54 increases, and the fixing roller Since the power consumption for heating 41 may increase, the number of support rollers is preferably three. Even when four or more support rollers are provided, it is preferable that the tension roller 67 is disposed so as to support the lowermost position (the lowest position with respect to the direction of gravity action) of the belt 54.

[Embodiment 4]
Another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those provided in the image forming apparatus and the fixing device according to Embodiments 1 to 3 are denoted by the same reference numerals as those of the embodiments, and description thereof is omitted. Moreover, about the member which attached | subjected the same code | symbol, unless otherwise indicated, the same change as each embodiment shall be possible.

  FIGS. 15A and 15B are cross-sectional views illustrating a schematic configuration of the fixing device 70 according to the present embodiment. The fixing device 70 is provided in the above-described image forming apparatus instead of the fixing device described in each of the above embodiments. As shown in these drawings, the fixing device 70 includes a fixing roller 41, a plurality of support rollers (a pressure roller 42, a peeling roller 43, and a tension roller 47), and a belt suspended (stretched) on each support roller. 54. In addition, the fixing device 70 supports a spring (biasing means) 75 that applies an urging force in a direction in which the tension is applied to the belt 54 with respect to the tension roller 47, and one end of the spring 75. And an eccentric cam 77 that generates a pressing force in the direction in which the ineffective force is applied to the urging frame 76.

  As shown in FIG. 15A, during the fixing operation, a pressing force from a driving source (not shown) is applied to the biasing frame 76 by the eccentric cam 77 in a direction (downward) to contract the spring 75. The roller 47 moves downward and comes into pressure contact with the belt 54, and tension is applied to the belt 54 (the tension state is established).

  On the other hand, when the fixing operation is not performed, as shown in FIG. 15B, the eccentric cam 77 rotates about 180 ° C. with respect to the fixing operation, so that the pressing force against the urging frame 76 is released, and the tension roller 47 Therefore, the tension roller 47 moves upward. Accordingly, the tension of the belt 54 is released and the belt is in a free tension state.

  FIG. 16 is a block diagram illustrating a configuration of the fixing device 70. As shown in this figure, the fixing device 70 includes an input unit 71, a control unit 72, a roller rotation driving unit 73, and a roller movement driving unit (tension roller movement driving unit) 74.

  The input unit 71 receives an instruction regarding on / off of a fixing operation from an image forming apparatus provided with the fixing device 70, and transmits the instruction to the control unit 72.

  The control unit 72 controls all operations in the fixing device 70, and includes a heating control unit 72a, a rotation control unit 72b, and a tension roller movement control unit (movement control unit) 72c. The control unit 72 may be provided in the control unit of the image forming apparatus.

  The heating controller 72a controls the heating source Q provided in the fixing roller 41, and controls the surface temperature of the fixing roller 41, that is, the fixing temperature. A temperature sensor (not shown) for detecting the surface temperature of the fixing roller 41 may be provided, and the heating controller 72a may control the heating source Q according to the detection result of the temperature sensor.

  The rotation control unit 72 b controls the operation of the rotation driving unit 73. The rotation drive unit 73 rotates each roller, and includes, for example, a drive source such as a motor and a transmission unit that transmits a driving force generated by the drive source to the rotation shaft of each support roller. Note that this transmission means does not necessarily have to transmit the driving force to all the support rollers, and by transmitting the driving force to some of the support rollers (for example, the pressure roller 42) and rotating the belt, 54 may be rotationally driven along each support roller, thereby rotating the other support rollers (for example, the peeling roller 43 and the tension roller 47).

  The tension roller movement control unit 72 c controls the operation of the roller movement driving unit 74. The roller movement drive unit 74 drives the eccentric cam 77 to rotate. By rotating the eccentric cam 77, the urging frame 76 and the tension roller 47 are moved, and the tension acting on the belt 54 is changed to a tension state ( Switch between tension application state and free tension state (tension release state). The roller movement drive unit 74 includes a drive source such as a motor and a transmission unit that transmits the drive force of the drive source to the eccentric cam 77.

  When the signal input from the control unit of the image forming apparatus to the control unit 72 via the input unit 71 is an instruction to perform the fixing operation, the tension roller movement control unit 72c controls the operation of the roller movement driving unit 74. The eccentric cam 77 is rotated to a position where a pressing force is applied to the biasing frame 76 in a direction in which the spring 75 is contracted (downward). As a result, as shown in FIG. 15A, the tension roller 47 moves downward and comes into pressure contact with the belt 54, and tension is applied to the belt 54 to enter a tension state.

  On the other hand, when the signal input from the control unit of the image forming apparatus to the control unit 72 via the input unit 71 is an instruction to stop the fixing operation, the tension roller movement control unit 72c operates the roller movement driving unit 74. And the eccentric cam 77 is rotated to a position where the pressing force against the urging frame 76 is released. As a result, as shown in FIG. 15 (b), the tension roller 47 is moved upward because no ineffective force is applied to the tension roller 47. Accordingly, the tension of the belt 54 is released and the belt is in a free tension state.

As described above, the fixing device 70 according to the present embodiment releases the tension of the belt 54 to be in a free tension state when the fixing operation is not performed. As a result, it is possible to prevent the belt from being curled, so that the shifting force generated on the belt by the curled hair can be reduced. Therefore, the meandering prevention mechanism, that is, the load on both ends of the ribs 55 and 55 provided on the belt 54 and the peeling roller 43 can be reduced, and the life of the belt 54 can be extended (long life). The configuration in which the position of the tension roller 47 is movable in the direction in which the tension of the belt 54 is increased or decreased has been described, but the present invention is not limited to this. For example, instead of the tension roller 47, the tension roller 67 described in the third embodiment may be used, and the position of the tension roller 67 may be moved in the same manner as the tension roller 47. Alternatively, instead of the belt 54, the belt 44 described in the first embodiment may be used.

  In this embodiment, the tension of the belt 54 is controlled by moving the position of the tension roller 67. However, the present invention is not limited to this, and other support rollers (for example, the pressure roller 42 and / or the pressure roller 42) are used. The tension of the belt 54 may be controlled by moving the peeling roller 43).

  In this embodiment, the case where the number of support rollers supporting the belt 54 is three (the pressure roller 42, the peeling roller 43, and the tension roller 47) is described. However, the present invention is not limited to this, and a larger number of support rollers are provided. Alternatively, the support roller may have two configurations. In this case, the tension of the belt 54 may be switched by making the rotation shaft of any one of the support rollers movable. In addition, the number of support rollers that can move the position of the rotation shaft is not necessarily one, and the tension of the belt 54 may be switched by moving the positions of a plurality of support rollers.

  In the present embodiment, the eccentric roller 77, the biasing frame 76, and the spring 75 are provided as means for moving the tension roller 47. However, the present invention is not limited to this, and the position of the tension roller 47 is appropriately set. Any configuration can be used as long as it can be controlled.

  In this embodiment, the tension of the belt 54 is released when the fixing operation is not performed. However, the present invention is not limited to this. That is, it is not always necessary that the tension is completely applied, and the tension of the belt 54 may be reduced more than that during the fixing operation.

[Embodiment 5]
Another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those provided in the image forming apparatus and the fixing device according to Embodiments 1 to 4 are denoted by the same reference numerals as those of the embodiments, and description thereof is omitted. Moreover, about the member which attached | subjected the same code | symbol, unless otherwise indicated, the same change as each embodiment shall be possible.

  FIG. 17 is a side view showing a state during the fixing operation in the fixing device 80 according to the present embodiment. FIG. 18 is a plan view of the fixing device 80 as viewed from below (the ground side). The fixing device 80 is provided in the above-described image forming apparatus instead of the fixing device described in each of the above embodiments.

  As shown in FIGS. 17 and 18, the fixing device 80 includes a fixing roller 41, a plurality of support rollers (pressure roller 42, peeling roller 43, tension roller 47), belt 54, driving gear 81a, driven gear 81b, movable A side frame 82, a guide member 83, an eccentric cam 84, an eccentric cam 85, a spring (biasing means) 84, a spring (biasing means) 85, a spring (biasing means) 75, and an urging frame 76 are provided.

  The drive gear 81a transmits a rotational drive force from a drive source (not shown) to the driven gear 81b. The driven gear 81b is fitted to a rotation shaft (pressure roller shaft, cored bar) 42a of the pressure roller 42, and rotates the pressure roller 42 by a rotational driving force transmitted from the drive gear 81a.

  The movable side frame 82 rotatably supports the rotation shaft 42a of the pressure roller 42 and the rotation shaft (peeling roller shaft, cored bar) 43a of the peeling roller 43, and is provided at both ends of both rollers. .

  As shown in FIG. 17, a protruding portion 82 a is provided at the end of the movable side frame 82 on the pressure roller 42 side, and a protruding portion 82 b is provided at the end of the peeling roller 43 side. A spring 86 that urges the protrusion 82 a in the direction of the fixing roller 41 is provided below the protrusion 82 a, and the protrusion 82 b is urged in the direction of the fixing roller 41 below the protrusion 82 b. A spring 87 is provided.

  Further, an eccentric cam 84 is provided on the upper part of the protrusion 82a, and an eccentric cam 85 is provided on the upper part of the protrusion 82b. The rotating shafts (eccentric shafts) of the eccentric cams 84 and 85 are connected to driving means (not shown). The eccentric cam 84 moves the position of the rotation shaft 42a of the pressure roller 42 to change the contact state of the belt 54 with the fixing roller 41 between the pressure roller 42 and the fixing roller 41. And switch to disconnected state. Further, the eccentric cam 85 moves the position of the rotation shaft 43a of the peeling roller 43 to change the contact state of the belt 54 with the fixing roller 41 between the peeling roller 43 and the fixing roller 41 from the contact state. Switch to contact state. During the fixing operation, the eccentric cams 84 and 85 are moved away from the projecting portions 82a and 82b by moving means (not shown). Alternatively, when the drive gear 81a is rotationally driven, it moves toward the fixing roller 41 along the rotation shaft 42a guide hole 83a of the pressure roller 42, whereby the eccentric cams 84 and 85 are separated from the protrusions 82a and 82b. You may make it contact.

  FIG. 19 is a block diagram illustrating a configuration of the fixing device 80. As shown in this figure, the fixing device 80 includes an input unit 71, a control unit 90, a roller rotation driving unit 94, a pressure roller movement driving unit 95, a peeling roller movement driving unit 96, and a tension roller movement driving unit 74. ing.

  The input unit 71 receives an instruction from an image forming apparatus provided with the fixing device 80 and transmits the instruction to the control unit 90.

  The control unit 90 controls all operations in the fixing device 80, and includes a heating control unit 72a, a rotation control unit 72b, and a movement control unit 91. The control unit 90 may be provided in the control unit of the image forming apparatus.

  The heating controller 72a controls the heating source Q provided in the fixing roller 41, and controls the surface temperature of the fixing roller 41, that is, the fixing temperature. A temperature sensor (not shown) for detecting the surface temperature of the fixing roller 41 may be provided, and the heating controller 72a may control the heating source Q according to the detection result of the temperature sensor.

  The rotation control unit 72 b controls the operation of the rotation driving unit 73. The rotation driving unit 73 drives each roller to rotate. For example, a driving source such as a motor and a driving force generated by the driving source are applied to a driven gear 81b fitted to the rotating shaft 42a of the pressure roller 42. It transmits to the drive gear 81a to transmit.

  The movement control unit 91 includes a pressure roller movement control unit 92, a peeling roller movement control unit 93, and a tension roller movement control unit 72c.

  The pressure roller movement control unit 92 controls the operation of the pressure roller movement drive unit 95. The pressure roller movement drive unit 95 drives the eccentric cam 84 to rotate. By rotating the eccentric cam 84, the protrusion 82 a of the movable side frame 82 is moved and the position of the pressure roller 42 is moved. . The pressure roller movement drive unit 95 includes a drive source such as a motor and a transmission unit that transmits the drive force of the drive source to the eccentric cam 84.

  The peeling roller movement control unit 93 controls the operation of the peeling roller movement driving unit 96. The peeling roller movement control unit 96 rotates and drives the eccentric cam 85, and the eccentric cam 85 rotates to move the protruding portion 82 b of the movable side frame 82 and move the position of the peeling roller 43. The peeling roller movement drive unit 96 includes a drive source such as a motor and a transmission unit that transmits the drive force of the drive source to the eccentric cam 85.

  The tension roller movement control unit 72 c controls the operation of the tension roller movement driving unit 74. The tension roller movement drive unit 74 drives the eccentric cam 77 to rotate. By rotating the eccentric cam 77, the urging frame 76 and the tension roller 47 are moved, and the tension acting on the belt 54 is changed to the tension state. Switch between (tension applied state) and free tension state (tension released state). The tension roller movement drive unit 74 includes a drive source such as a motor and a transmission unit that transmits a drive force of the drive source to the eccentric cam 77.

  Next, the operation of the fixing device 80 will be described. First, the operation when the fixing operation is stopped and the belt 54 is separated from the fixing roller 41 from the state during the fixing operation shown in FIG. 17 will be described. FIG. 20 is a flowchart showing an operation flow in this case.

  When the input unit 71 receives an instruction to stop the fixing operation from the image forming apparatus (S1), the control unit 90 moves the pressure roller 42 away from the fixing roller 41 (S2). More specifically, the pressure roller movement control unit 92 in the control unit 90 controls the pressure roller movement driving unit 95, and the eccentric cam 84 is moved from the state during the fixing operation as shown in FIG. Rotate about 180 degrees. As a result, the protruding portion 82a of the movable side frame 82 is pushed down, and the pressure roller 42 moves in a direction away from the fixing roller 41 along the guide hole 83a. Accordingly, a part of the belt 54 that is in pressure contact with the fixing roller 41 by the pressing force of the pressure roller 42 is separated from the fixing roller 41. That is, the pressure roller 42 that has been in contact with the fixing roller 41 via the belt 54 comes into contact with and separates from the fixing roller 41.

  Next, the control unit 90 stops the rotational driving of the pressure roller 42 (S3). That is, the rotation control unit 72b in the control unit 90 controls the operation of the roller rotation drive unit 94 to stop the rotation drive of the drive gear 81a. As a result, the rotational driving force transmitted from the drive gear 81a to the pressure roller 42 via the driven gear 81b is not applied, and the rotation of the pressure roller 42 is stopped. In addition, the rotation (movement) of the belt 54 is stopped by stopping the rotation of the pressure roller 42 that is a driving roller, and the rotations of the peeling roller 43 and the tension roller 47 that are driven rollers are also stopped.

  Next, the controller 90 separates the separation roller 43 from the fixing roller 41 (S4). More specifically, the peeling roller movement control unit 93 in the control unit 90 controls the peeling roller movement driving unit 96 to rotate about 180 degrees from the state of FIG. 21A as shown in FIG. Let As a result, the projecting portion 82 b of the movable side frame 82 is pushed down, and the peeling roller 43 moves away from the fixing roller 41. Therefore, the belt 54 that is in pressure contact with the fixing roller 41 by the pressing force of the peeling roller 43 is separated from the fixing roller 41. That is, the pressure roller 42 that has been in contact with the fixing roller 41 via the belt 54 comes into contact with and separates from the fixing roller 41. As a result, the belt 54 is separated from the fixing roller 41.

  Next, the control unit 90 moves the tension roller 47 to release the tension of the belt 54 and put it in a free tension state (S5). More specifically, the tension roller movement control unit 72c in the control unit 90 controls the operation of the tension roller movement driving unit 74, and pushes the eccentric cam 77 against the biasing frame 76 as shown in FIG. Rotate to a position to release pressure. As a result, a state where no inferior force is applied to the tension roller 47 is provided, so that the tension roller 47 moves upward. In other words, the tension roller 47 is forcibly moved downward during the fixing operation to apply tension to the belt 54. By releasing the forced movement from this state, the tension of the belt 54 is released and free tension is applied. State. Thereby, the separation / contact operation of the belt 54 is completed.

  Next, the operation when the belt 54 is switched from the separated state to the contact state will be described. FIG. 22 is a flowchart showing an operation flow in this case.

  When the input unit 71 receives an instruction to start the fixing operation from the image forming apparatus (S11), the control unit 90 moves the tension roller 47 to apply tension to the belt 54 (S12). More specifically, the tension roller movement control unit 72 c in the control unit 90 controls the operation of the tension roller movement driving unit 74 and rotates the eccentric cam 77 to a position where a pressing force is applied to the urging frame 76. . That is, the eccentric cam 77 is rotated to a position where the tension roller 47 is forcibly moved downward. As a result, the fixing device 80 is in the state shown in FIG. 21B, and tension is applied to the belt 54. For example, when the fixing device 80 is activated, a warm-up operation (preheating operation) may be performed in this state. In this case, the rotation speed of the pressure roller 42, that is, the rotation speed of the belt 54 may be rotated at a speed slower than that during the fixing operation.

  Next, the controller 90 brings the peeling roller 43 into contact with the fixing roller 41 (S13). More specifically, the peeling roller movement control unit 93 in the control unit 90 controls the peeling roller movement driving unit 96 to rotate about 180 degrees from the state of FIG. 21B as shown in FIG. Let As a result, the protrusion 82 b of the movable side frame 82 is pushed up by the spring 87, and the peeling roller 43 moves in the direction of the fixing roller 41. Accordingly, the belt 54 comes into contact (pressure contact) with the fixing roller 41 by the pressing force of the peeling roller 43. That is, the pressure roller 42 contacts the fixing roller 41 through the belt 54.

  Next, the control unit 90 starts to rotate the pressure roller 42 (S14). That is, the rotation control unit 72b in the control unit 90 controls the operation of the roller rotation drive unit 94 to start the rotation drive of the drive gear 81a. As a result, the rotational driving force is transmitted from the drive gear 81a to the pressure roller 42 via the driven gear 81b, and the rotation of the pressure roller 42 is started. In addition, the rotation (movement) of the belt 54 is started by starting the rotation of the pressure roller 42 that is a driving roller, and the rotation of the peeling roller 43 and the tension roller 47 that are driven rollers is also started.

  Next, the controller 90 brings the pressure roller 42 into contact with the fixing roller 41 (S15). More specifically, the pressure roller movement control unit 92 in the control unit 90 controls the pressure roller movement drive unit 95, and the eccentric cam 84 is moved from the state of FIG. Rotate 180 degrees. As a result, the protruding portion 82a of the movable side frame 82 is pushed up by the spring 86, and the pressure roller 42 moves in the direction of the fixing roller 41 along the guide hole 83a. It contacts (presses) the fixing roller 41. Therefore, a fixing operation is possible.

  As described above, in the fixing device 80 according to the present embodiment, when the fixing operation is not performed, the belt 54 is separated from the fixing roller 41 and is contacted when the fixing operation is performed. As described above, the belt 54 and the rib (meandering prevention means) 55 provided on the belt 54 are reduced by moving the belt 54 away from the fixing roller 41 when the fixing operation is not performed. it can.

  That is, when the belt is rotated while being constantly wound around the fixing roller, the shifting force acting on the belt is always maximized. Therefore, the maximum load is always applied to the meandering prevention mechanism (for example, a rib (bead)) provided on the belt. This was one of the factors that shortened the belt life. Therefore, as in the present embodiment, by making the belt 54 detachable, the load on the belt 54 can be reduced and the life of the belt 54 can be extended.

  Further, the belt 54 may be separated from the fixing roller 41 during the heating operation (warming up) of the fixing roller 41. In this state, the fixing roller 41 and the belt 54 may be heated while rotating the belt 54 at a speed slower than the fixing speed. In this case, the number of rollers in contact with the belt 54 is smaller than that during the fixing operation, so that the shifting force acting on the belt 54 is reduced, and the force acting on the belt 54 and the meandering prevention member provided on the belt 54 is also reduced. Further, the rotational force can be further reduced by rotating at a speed slower than the fixing processing speed.

  In the fixing device 80, when the belt is stopped, the tension roller 47 is moved so that the tension of the belt 54 becomes low, and the tension of the belt 54 is released. Thereby, it is possible to prevent the belt 54 from being curled and to reduce the shifting force due to the curl. In this embodiment, the tension of the belt 54 is released by moving the position of the tension roller 47. However, the present invention is not limited to this, and the position of each support roller (belt suspension roller) that suspends the belt 54 is not limited thereto. Any structure may be used as long as the (phase position) relationship can be appropriately adjusted.

  Further, in the fixing device 80, when the belt 54 shifts from the state where the belt 54 is not in contact with the fixing roller 41 to the contact state during the fixing operation, first, (1) the tension roller 47 is moved to apply tension to the belt 54. (2) The belt 54 is brought into contact with the fixing roller 41 by the peeling roller 43, (3) the belt 54 is rotated (conveyed) in this state, and (4) the belt 54 is rotated by the pressure roller 42. The belt 54 is brought into contact with the fixing roller 41. As a result, it is possible to prevent the belt 54 from sagging and wrinkles at the portion where the belt 54 is wound around the fixing roller 41, and to stabilize the running property (rotation property) of the belt 54.

  That is, when the belt 54 is wound around the fixing roller (heating roller) 41 and the pressure roller 42 and the peeling roller 43 (a plurality of backup rollers) are simultaneously brought into contact with the fixing roller 41, the pressure roller The abutting portion of the belt 42 and the peeling roller 43 (each backup roller) with respect to the fixing roller 41 becomes a restraint point of the belt position, and the belt portion suspended therebetween is likely to wrinkle or sag, and the belt running performance is deteriorated or the belt It was a cause of cracking. On the other hand, as in the present embodiment, the belt 54 is brought into contact with the fixing roller 41 in the above-described order, and the belt 54 is wound around the fixing roller 41, thereby causing the belt 54 to sag and wrinkle. This can prevent the belt 54 from running (stable).

  In the fixing device 80, when performing the operation of separating the belt 54 from the fixing roller 41 from the state in which the belt 54 is in contact with the fixing roller 41, first, (a) the belt 54 is rotated and applied. The pressure roller 42 is moved away from the fixing roller 41, (b) the rotation of the belt 54 is stopped, (c) the peeling roller 43 is moved away from the fixing roller 41, and (d) the tension roller 47 is moved to move the belt 54. Release the tension.

  This prevents the belt 54 from sagging and wrinkles at the wrapping portion of the belt 54 with respect to the fixing roller 41, as in the case where the belt 54 shifts from the state where the belt 54 is not in contact with the fixing roller 41 to the contact state. It is possible to stabilize the running performance (rotation).

  In the present embodiment, the configuration in which the contact state of the belt 54 with the fixing roller 41 is switched by moving the positions of the pressure roller 42 and the peeling roller 43 is not limited to this. For example, by making the position of the fixing roller 41 movable, the contact state of each roller similar to the present embodiment may be realized.

  Further, in place of the tension roller 47, the tension roller 67 described in the third embodiment may be provided. In this case, since the lubricant can be appropriately applied to the inner peripheral surface of the belt 54, the driving of the belt 54 can be further stabilized.

  In this embodiment, the tension roller can be moved to release the tension between the bell and 54. However, the present invention is not limited to this. For example, the tension of the belt 54 may not be released, and only the contact state of the belt 54 with the fixing roller 41 may be controlled as described above. Further, the configuration is not limited to the configuration in which the tension of the belt 54 is completely released, and the configuration in which the tension of the belt 54 is reduced as compared with that during the fixing operation may be employed.

  In this embodiment, the case where the number of support rollers supporting the belt 54 is three (the pressure roller 42, the peeling roller 43, and the tension roller 47) is described. However, the present invention is not limited to this, and a larger number of support rollers are provided. Alternatively, the support roller may have two configurations.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be applied to any fixing device in which a plurality of fixing nip portions are formed by a fixing roller and a belt contacting the fixing roller.

FIG. 4 is a cross-sectional view showing a nip portion formed by a fixing member and a pressing member in the fixing device according to the embodiment of the present invention. 1 is a cross-sectional view showing an internal structure of an image forming apparatus provided with a fixing device according to the present invention. 1 is a cross-sectional view illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. It is a figure which shows the model of the one-dimensional heat transfer analysis performed in one Embodiment of this invention. It is a figure for demonstrating the heat transfer between several layers in the one-dimensional heat transfer analysis performed in one Embodiment of this invention. 6 is a graph showing the relationship between the toner bottom layer temperature immediately before passing through the nip and the nip passing time at each fixing temperature when the fixing temperature is set to 160 ° C., 170 ° C., and 180 ° C. 6 is a graph showing the relationship between the intercept of the linear function and the fixing temperature when the nip passage time is expressed as a linear function of the toner bottom layer temperature. FIG. 9 is a cross-sectional view showing a modification of the fixing device according to the embodiment of the present invention. It is sectional drawing of the fixing device concerning other embodiment of this invention. FIG. 10 is a cross-sectional view of a belt provided in the fixing device of FIG. 9. FIG. 10 is a plan view showing a part of the fixing device of FIG. 9. FIG. 6 is a cross-sectional view of a fixing device according to still another embodiment of the present invention. FIG. 13A is a perspective view of a lubricant application unit provided in the fixing device of FIG. 12, and FIG. 13B is a cross-sectional view showing a part of the lubricant application unit. (A) is sectional drawing which shows the modification of the lubricant application | coating means of FIG. 13, (b) is sectional drawing of a fixing device provided with it. (A) is sectional drawing which shows the state at the time of fixing operation | movement in the fixing device concerning further another embodiment of this invention, (b) is sectional drawing which shows the state at the time of the said fixing device stop. FIG. 16 is a block diagram illustrating a configuration of the fixing device illustrated in FIGS. 15A and 15B. FIG. 9 is a cross-sectional view showing a state during a fixing operation in a fixing device according to still another embodiment of the present invention. FIG. 18 is a plan view illustrating a part of the fixing device illustrated in FIG. 17. FIG. 18 is a block diagram illustrating a configuration of the fixing device illustrated in FIG. 17. FIG. 18 is a flowchart showing a flow of operation when the belt is separated from the fixing roller in the fixing device shown in FIG. 17. FIG. 18A is a cross-sectional view illustrating a state in which the operation of bringing the belt into contact with or separating from the fixing roller is performed in the fixing device illustrated in FIG. 17, and FIG. (B) is the state where the pressure roller and the peeling roller are separated from each other, and the belt is under tension. (C) is the state where the pressure roller and the separation roller are separated from each other, and the belt tension is released. Shows the state. FIG. 18 is a flowchart showing an operation flow when the belt is brought into contact with the fixing roller in the fixing device shown in FIG. 17.

Explanation of symbols

40, 50, 60, 70, 80 Fixing device 41 Fixing roller (heating roller)
42 Pressure roller (support roller, pressure roller)
43 Peeling roller (support roller, pressing roller, meandering regulating member)
44, 54 Belt 47 Tension roller (support roller)
55 Ribs (Meandering restriction member, Lubricant outflow prevention member)
67 Tension roller (support roller, lubricant application means)
67a Core metal (core material)
67b Porous layer 72, 90 Control part (control means)
72b Rotation control unit 72c Tension roller movement control unit 73 Roller rotation drive unit 74 Tension roller movement drive unit 75 Spring 76 Energizing frame 77 Eccentric cam 86, 87 Spring 84, 85 Eccentric cam 81a Drive gear 81b Driven gear 82 Movable side frame 82a , 82b Projection part 83 Guide member 83a Guide hole 91 Movement control part 92 Pressure roller movement control part 93 Peeling roller movement control part 94 Roller rotation driving part 95 Pressure roller movement driving part 96 Peeling roller movement driving part a1 First nip width a2 Second nip width b Virtual nip width L0 Rib interval L1 Pressure roller length L2 Release roller length Q Heating source T Fixing temperature Tb Toner bottom temperature Ti Toner spill start temperature Tn Nip passage time tn Nip passage time Vp Process speed

Claims (19)

A heating roller that is heated to a predetermined temperature; a belt that comes into contact with a part of the heating roller; and a plurality of support rollers on which the belt is suspended; two of the plurality of support rollers Is used as a pressure roller that presses both ends of a portion of the belt that wraps around a part of the heating roller, and the recording medium is passed between the heating roller and the belt by passing the recording medium between the heating roller and the belt. A fixing device for fixing an unfixed toner image formed on
When the belt is suspended, the belt is substantially perpendicular to the contact surfaces of the belt with the support rollers at both ends in the rotation axis direction of the support rollers on the inner peripheral surface that contacts the support rollers. A meandering restricting member protruding in any direction,
The distance L0 (mm) between the meandering restricting members provided on both ends of the belt and the first pressing roller in the first pressing roller that presses the heating roller and the belt upstream in the conveyance direction of the recording medium. The length L1 (mm) of the roller in the rotation axis direction and the length of the second pressure roller in the rotation axis direction of the second pressure roller that presses the heating roller and the belt downstream in the conveyance direction of the recording medium. L2 (mm) satisfies the relationship L0>L2> L1,
The fixing device according to claim 1, wherein the meandering restricting member is in contact with an end of the second pressing roller in the rotation axis direction, thereby preventing meandering of the belt.   The fixing device according to claim 1, wherein each of the meandering restricting members is provided on the inner peripheral surface of the belt over the entire circumference.   The distance L0 (mm) between the meandering regulating members and the length L2 (mm) of the second pressing roller in the rotation axis direction satisfy 4 mm> L0-L1> 2 mm. 3. The fixing device according to 2. A heating roller that is heated to a predetermined temperature; a belt that comes into contact with a part of the heating roller; and a plurality of support rollers on which the belt is suspended; two of the plurality of support rollers Is used as a pressure roller that presses both ends of a portion of the belt that wraps around a part of the heating roller, and the recording medium is passed between the heating roller and the belt by passing the recording medium between the heating roller and the belt. A fixing device for fixing an unfixed toner image formed on
A fixing device comprising: a lubricant application unit that applies a lubricant to an inner peripheral surface of the belt at a position away from the heating roller in the belt.   At least one of the plurality of support rollers has a contact surface with the belt formed of a porous layer, and lubrication is performed by applying a lubricant impregnated in the porous layer to the inner peripheral surface of the belt. The fixing device according to claim 4, wherein the fixing device functions as an agent application unit. The support roller that functions as the lubricant application means comprises a hollow core material having a number of holes on the surface, and the porous layer covered with the core material,
The fixing device according to claim 5, wherein the porous layer is impregnated with a lubricant through a large number of holes provided in the core material.   A smoothing means for smoothly contacting the porous layer with the lubricant impregnated state by contacting the porous layer substantially uniformly along the direction of the rotation axis of the support roller comprising the porous layer; The fixing device according to claim 5 or 6. The support roller that functions as the lubricant application means supports the position on the lowermost side in the direction of gravity in the belt,
The length of the support roller in the rotation axis direction of the belt is longer than the length of the support roller in the rotation axis direction, and the both ends of the belt in the rotation axis direction of the support roller on the inner peripheral surface of the belt. The fixing device according to claim 5, further comprising a lubricant outflow prevention member that protrudes in a direction substantially perpendicular to a contact surface of the belt with the support roller. A heating roller that is heated to a predetermined temperature; a belt that comes into contact with a part of the heating roller; and a plurality of support rollers on which the belt is suspended; two of the plurality of support rollers Is used as a pressure roller that presses both ends of a portion of the belt that wraps around a part of the heating roller, and the recording medium is passed between the heating roller and the belt by passing the recording medium between the heating roller and the belt. A fixing device for fixing an unfixed toner image formed on
A fixing device that relaxes the tension of the belt suspended on the plurality of support rollers when a fixing operation is not performed.   The fixing device according to claim 9, wherein the tension of the belt is relaxed by changing a relative position of each of the support rollers. A heating roller that is heated to a predetermined temperature; a belt that comes into contact with a part of the heating roller; and a plurality of support rollers on which the belt is suspended; two of the plurality of support rollers Is used as a pressure roller that presses both ends of a portion of the belt that wraps around a part of the heating roller, and the recording medium is passed between the heating roller and the belt by passing the recording medium between the heating roller and the belt. A fixing device for fixing an unfixed toner image formed on
A fixing device, wherein the belt is separated from the heating roller when a fixing operation is not performed. In the first nip portion, a rotation driving means for rotating the support roller and a pressure roller that forms a first nip portion where the heating roller and the belt are pressed against each other on the upstream side in the conveyance direction of the recording medium are moved. A first separating / contacting means for bringing the belt into contact with or separating from the heating roller, and a pressing roller forming a second nip where the heating roller and the belt are in pressure contact with each other on the downstream side in the conveyance direction of the recording medium are moved. And controlling the operation of the second separating / contacting means for bringing the belt into contact with or separating from the heating roller at the second nip portion, the rotation driving means, the first separating / contacting means, and the second separating / contacting means. Control means for
When the control means performs the fixing operation,
A first process of bringing the belt into contact with the heating roller at the second nip portion by the second separation / contact means;
After the first process, a second process of rotating the support roller by the rotation driving means and rotating the belt along the support rollers;
The third process of performing a third process of contacting the belt with the heating roller at the first nip portion while the belt is rotated after the second process is performed. The fixing device described. Rotation driving means for rotating the support roller, and a first nip portion where the heating roller and the belt are in pressure contact with each other on the upstream side in the conveyance direction of the recording medium are moved to move the first roller. A first separation / contact means for bringing the belt into contact with or separated from the heating roller at the nip portion, and a pressure for forming a second nip where the heating roller and the belt are in pressure contact with each other on the downstream side in the conveyance direction of the recording medium A second separating / contacting means for moving the roller so that the belt contacts or separates from the heating roller at the second nip, and the rotation driving means, the first separating / contacting means, and the second separating / contacting means. Control means for controlling the operation,
When the control means stops the fixing operation,
A fourth process of separating the belt from the heating roller at the first nip portion while the belt is rotated;
After the fourth process, a fifth process for stopping the rotation of the belt by stopping the rotation of the support roller by the rotation driving unit;
13. The sixth process according to claim 11, wherein after the fifth process, a sixth process is performed in which the belt is separated from the heating roller at the second nip portion by the second separation unit. The fixing device described.   When performing the fixing operation, the control unit performs a warm-up operation in a state in which the support roller is rotated at a speed slower than the speed during the fixing operation by the rotation driving unit before the first processing. The fixing device according to claim 12.   An image forming apparatus comprising the fixing device according to claim 1. A heating roller that is heated to a predetermined temperature; a belt that comes into contact with a part of the heating roller; and a plurality of support rollers on which the belt is suspended; two of the plurality of support rollers Is used as a pressure roller that presses both ends of a portion of the belt that wraps around a part of the heating roller, and the recording medium is passed between the heating roller and the belt by passing the recording medium between the heating roller and the belt. A fixing device driving method for fixing an unfixed toner image formed on
A fixing device driving method, wherein the belt is separated from the heating roller when a fixing operation is not performed. When performing the fixing operation,
A first step of bringing the belt into contact with the heating roller by the pressing roller provided on the downstream side in the conveyance direction of the recording medium;
A second step of rotating the belt along the support rollers after the first step;
After the second step, in a state where the belt is rotated, a third step of bringing the belt into contact with the heating roller by the pressing roller provided on the upstream side in the conveyance direction of the recording medium, The driving method of the fixing device according to claim 16, wherein the fixing device is driven. When stopping the fixing operation,
In a state where the belt is rotated, the pressing roller provided on the upstream side in the conveyance direction of the recording medium is moved so that a part of the belt pressed by the pressing roller is separated from the heating roller. A fourth step;
A fifth step of stopping the rotation of the belt after the fourth step;
After the fifth step, the pressing roller provided on the downstream side in the recording medium conveyance direction is moved, and a part of the belt pressed by the pressing roller is separated from the heating roller. 18. The fixing device driving method according to claim 16, wherein the step 6 is performed.   When performing the fixing operation, the control unit performs a warm-up operation in a state where the support roller is rotated at a speed slower than the speed during the fixing operation by the rotation driving unit before the first step. The method for driving a fixing device according to claim 16.

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