JP2011039281A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which is stably actuated without causing icicle-like fixing irregularity and without causing an increase in load torque by solving a problem that, in a belt fixing type fixing device where a fixing belt is pressed on a fixing member by a pressing member, it is necessary to bring a separation roller that presses the fixing belt on the fixing member with the pressing member close to the pressing member, however, if they are excessively close to each other, torque exerted on a driving means for driving a fixing roller is increased. <P>SOLUTION: A positional relation between the pressing member that presses the fixing belt on the fixing member and the separation roller can be varied. Thus, the positional relation can be always kept appropriate, and excellent fixing is stably maintained over a long term. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device in an image forming apparatus that forms an image by electrophotography.

  A belt-fixing type fixing device that pinches and conveys a recording material between a fixing member and a fixing belt and fixes a toner image has been developed and put into practical use.

The belt fixing type fixing device has the following advantages because the fixing nip for heating the toner image can be lengthened.
(1) The speed can be increased.
(2) A fixing member such as a heating roller can be made of a small diameter and the heat capacity of the fixing member can be reduced, so that the warm-up time can be shortened.
(3) Suitable for fixing a color image having a large amount of toner for forming an image.

  Patent Documents 1 to 3 disclose a belt fixing type fixing device in which a pressing member that presses the fixing belt against the fixing member is used, and a separation roller that separates the recording material from the fixing member is disposed downstream of the pressing member. Has been. Patent Document 3 discloses that a lubricant is applied to the inner peripheral surface of the fixing belt in order to reduce the sliding resistance between the fixing belt and the pressing member.

JP-A-11-45018 JP 2007-79036 A JP 2007-199285 A

  The fixing device in which the pressing member that presses the fixing belt against the fixing member and the separation roller that separates the recording material downstream of the pressing member have the following problems.

  The pressing member and the separating member press the fixing belt against the fixing member, but there is nothing that presses the fixing belt between the pressing member and the separating roller. Therefore, in the fixing nip between the pressing member and the separation roller, the recording material is pressed against the fixing member only by the tension of the fixing belt.

  As a result, the pressure for pressing the recording material between the pressing member and the separation roller is weakened or no pressure is applied.

  As a result, the pressure applied to the recording material at the fixing nip from the pressing member to the separation roller is not uniform not only in the recording material conveyance direction but also in the width direction perpendicular to the conveyance direction. This uneven pressure may cause uneven fixing. That is, icicle-shaped gloss unevenness extending in the conveyance direction of the recording material is formed on the image surface, thereby degrading the image quality.

  As a result of studies to prevent such a decrease in image quality, it has been found that image quality deterioration can be prevented by shortening the length of the low pressure section between the pressing member and the separation roller.

  However, it has been found that if the pressing member and the separation roller are too close, a new problem arises that the torque applied to the driving means for driving the fixing belt increases. When the increase in the torque is significant, the operation may fail. The increase in torque due to the close proximity between the pressing member and the separation roller is caused by the abrasion of the sliding member, which is a component of the pressing member, due to the contact between the pressing member and the separation roller. Occurs. In Patent Document 3, the sliding resistance of the fixing belt is reduced by a lubricant, but the positional relationship between the pressing member and the separation roller is always constant and does not change. For this reason, when the pressing member and the separation roller are too close to each other, the problem caused by the contact between the pressing member and the separation roller cannot be solved. That is, the increase in the torque cannot be sufficiently reduced depending on the lubricant.

  The present invention prevents image quality deterioration due to uneven fixing in a belt fixing type fixing device, solves the problem of increase in torque applied to a fixing belt driving means, and stably performs good fixing over a long period of time. An object of the present invention is to provide a belt fixing type fixing device.

  The object is achieved by the following invention.

1. A fixing member that heats and fixes the toner image to the recording material;
A fixing belt,
A pressing member that presses the fixing belt against the fixing member;
A separation roller disposed downstream of the pressing member with respect to the recording material conveyance direction and pressing the fixing belt against the fixing member;
In a fixing device having
A fixing device, wherein a positional relationship between the pressing member and the separation roller is changeable.

  2. 2. The fixing device according to 1, further comprising: a first displacement mechanism that displaces the pressing member, wherein the first displacement mechanism changes the positional relationship by displacing the pressing member.

  3. 2. The fixing device according to claim 1, further comprising a second displacement mechanism that displaces the separation roller, wherein the second displacement mechanism changes the positional relationship by displacing the separation roller.

  4). The fixing member includes a fixing roller, and the positional relationship is changed by the displacement of the pressing member or the separation roller, and the pressing member or the separation roller can be displaced on a concentric circle on the outer peripheral surface of the fixing roller. The fixing device according to any one of the above items 1 to 3, wherein the fixing device is provided.

  5. The pressure member includes a pressure pad that presses the fixing belt against the fixing member, a sliding member that covers the pressure pad, and a support member that supports the pressure pad. The fixing device according to any one of the above.

  In the present invention, the positional relationship between the pressing member that presses the fixing belt against the fixing member and the separation roller can be changed. As a result, the positional relationship can always be made appropriate, and good fixing can be stably maintained over a long period of time.

1 is a diagram illustrating a color image forming apparatus using a fixing device according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of a fixing device 100 according to an embodiment of the present invention. It is a figure which shows the press member. 3 is a graph showing pressure for pressing a recording material against a fixing roller 101 at a fixing nip. It is a figure which shows the 1st example which changes the positional relationship of the pressing member and the separation roller. It is a figure which shows the 2nd example which changes the positional relationship of the pressing member and the separation roller. It is a figure which shows the 3rd example which changes the positional relationship of the pressing member and the separation roller. It is a figure which shows the displacement mechanism which changes the positional relationship of the pressing member and the separation roller.

  FIG. 1 shows a color image forming apparatus using a fixing device according to an embodiment of the present invention. The color image forming apparatus shown in FIG. 1 transfers a toner image formed on a photosensitive member onto an intermediate transfer member and superimposes it, and transfers the superimposed toner images onto a recording material all at once. The image forming unit is constituted by an image reading unit SC and an image forming unit A, and a plurality of image forming units 10Y, 10M, 10C, and 10K, an intermediate transfer unit 7, a sheet feeding and conveying device, and a fixing device. 100.

  An image forming unit 10Y that forms a yellow image includes a photoreceptor 1Y, and includes a charging device 2Y, an exposure device 3Y, a developing device 4Y, a primary transfer device 5Y, and a cleaning device 6Y disposed around the photoreceptor 1Y. Have. An image forming unit 10M that forms a magenta image includes a photoreceptor 1M, and includes a charging device 2M, an exposure device 3M, a developing device 4M, a primary transfer device 5M, and a cleaning device 6M disposed around the photoreceptor 1M. Have. An image forming unit 10C for forming a cyan image has a photoreceptor 1C, and includes a charging device 2C, an exposure device 3C, a developing device 4C, a primary transfer device 5C, and a cleaning device 6C arranged around the photoreceptor 1C. Have. The image forming unit 10K that forms a black image includes a photoreceptor 1K, and also includes a charging device 2K, an exposure device 3K, a developing device 4K, a primary transfer device 5K, and a cleaning device 6K disposed around the photoreceptor 1K. Each image forming unit 10 is charged, exposed, and developed to form an image of each color on the photoreceptor.

  The intermediate transfer unit 7 includes a semiconductive endless belt-shaped intermediate transfer body 70 that is wound around a plurality of rollers and is rotatably supported.

  The toner images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are transferred onto the rotating intermediate transfer body 70 by the primary transfer devices 5Y, 5M, 5C, and 5K, and are sequentially superimposed and combined. A color toner image is formed. The recording material P accommodated in the paper feeding cassette 20 is fed by the paper feeding device 21 and is conveyed to the secondary transfer device 5A through a plurality of intermediate rollers 22A, 22B, 22C, 22D and a registration roller 23. The color toner images superimposed on the recording material P are collectively transferred. The recording material P onto which the color toner image has been transferred is fixed by the fixing device 100, is sandwiched between the paper discharge rollers 25, and is placed on a paper discharge tray 26 outside the apparatus.

  On the other hand, after the color toner image is transferred to the recording material P by the secondary transfer device 5A, the residual toner is removed by the cleaning device 6A from the intermediate transfer body 70 which has separated the curvature of the recording material P.

  During the image forming process, the primary transfer device 5K is always in pressure contact with the photoreceptor 1K. The other primary transfer devices 5Y, 5M, and 5C are in pressure contact with the corresponding photoreceptors 1Y, 1M, and 1C, respectively, only during color image formation.

  The secondary transfer device 5A comes into pressure contact with the intermediate transfer member 70 only when the recording material P passes through the secondary transfer device 5A and secondary transfer is performed.

  As a fixing device for fixing a toner image, a belt fixing type fixing device 100 is used in which a recording material is nipped and conveyed by a fixing belt and a fixing member, and the toner image is heated and fixed on the recording material during nipping and conveying. FIG. 2 is a diagram showing a configuration of the fixing device 100 according to the embodiment of the present invention.

  The fixing device 100 includes a fixing roller 101 as a fixing member that heats and fixes a toner image, and a fixing belt 105 that sandwiches and conveys the recording material P by the fixing roller 101.

  The fixing roller 101 includes a cored bar 101a made of a metal pipe having high thermal conductivity such as aluminum, an elastic layer 101b made of silicon rubber formed on the cored bar 101a, and an elastic layer 101b formed on the elastic layer 101b (not shown). It consists of a releasable surface layer made of PFA.

  As shown in FIG. 2B, the fixing belt 105 includes a base layer 105a of a heat-resistant resin film such as PI (polyimide), an elastic layer 105b made of silicon rubber formed on the base layer 105a, and an elastic layer 105b. And a surface layer 105c made of PFA formed thereon. The surface layer 105c contacts the recording material P.

  The fixing belt 105 is stretched around the entrance roller 102, the separation roller 103, and the steering roller 104.

  The entrance roller 102, the separation roller 103, and the steering roller 104 are each made of SUS. The separation roller 103 and the steering roller 104 are non-hollow rod-like members as shown in the figure, but the inlet roller 102 is a pipe-like member, and a heater 107 is provided in the inlet roller 102 to heat the recording material P. . The separation roller 103 presses the fixing belt 105 against the fixing roller 101 to deform the elastic layer 101 b and bites into the fixing roller 101.

  Below the fixing roller 101, the pressing member 106 presses the fixing belt 105 against the fixing roller 101, and the pressing member 106 and the separation roller 103 form a fixing nip N.

  The pressing member 106 includes a support member 106a, a spacer 106b, a pressing pad 106c, and a base member 106d. As shown in FIG. 3, the pressing pad 106c is covered with a sliding member 106e made of a PI sheet. The portion where the pressing pad 106 c contacts the fixing roller 101 is formed in a curved shape that matches the outer periphery of the fixing roller 101 as shown in the figure. The recording material P is provided with a rod-like member 106f at a portion away from the pressing pad 106c, that is, at the upper left end of the pressing pad 106c in FIG. The rod-shaped member 106f is made of SUS, and is formed integrally with the pressing pad 106c by insert molding. The base member 106d is made of aluminum, and the base member 106d is also formed integrally with the pressing pad 106c at the time of molding. As shown in FIG. 3, the sliding member 106e covers the pressing pad 106c and the rod-shaped member 106f.

  The downstream end of the pressing member 106 formed by the rod-shaped member 106 f is close to the separation roller 103. For example, the pressing member 106 is arranged with respect to the fixing roller 101 so that the distance D between the upstream end of the nip formed by the fixing roller 101 and the separation roller 103 and the center of the rod-shaped member 106f is about 2 to 4 mm. The

  The fixing roller 101 and the separation roller 103 are connected by a power transmission mechanism, and rotate as indicated by an arrow by driving a motor (not shown) as a driving unit. The entrance roller 102, the steering roller 104, and the fixing belt 105 are driven by the fixing roller 101 and the separation roller 103.

  A heater 108 is a halogen lamp that heats the fixing roller 101, and the toner image is fixed by the fixing roller 101 heated by the heater 108.

  In the image formation, the recording material P is introduced into the fixing device 100 as indicated by an arrow W1, and the fixing roller 101 and the separation roller 103 rotate as indicated by an arrow to sandwich and convey the recording material P.

  The toner image is heated and fixed on the recording material P at a fixing nip N between the fixing roller 101 and the fixing belt 105.

  The recording material P after the fixing process is separated from the fixing roller 101 by the straightness of the recording material P because the radius of curvature of the separation roller 103 is small. That is, since the separation roller 103 bites into the fixing roller 101, the recording material P advances in a direction away from the fixing roller 101 when it leaves the fixing nip N and is reliably separated from the fixing roller 101.

  The fixing nip N is formed in a section where the pressing member 106 and the separation roller 103 press the fixing belt 105 against the fixing roller 101. In the fixing nip N, there is no pressing action of the pressing member 106 and the pressing action of the separation roller 103 between the pressing member 106 and the separation roller 103, and the section in which the recording material P is held only by the tension of the fixing belt 105. There is. In this section, the pressure for pressing the recording material P is smaller than in the sections before and after the section.

  FIG. 4 shows a pressure distribution for pressing the recording material against the fixing roller 101 at the fixing nip N. As shown in FIG. 4, the pressure for pressing the recording material P against the fixing roller 101 in the section Na where the pressing member 106 is not pressed and the separation roller 103 is not pressed is low.

  When the distance Na of the section where the pressing action of the pressing member 106 in the fixing nip N and the pressing action of the separation roller 103 is not long, the phenomenon that the fixing property becomes uneven and the image quality is deteriorated occurs. That is, a non-uniform portion of glossiness that extends in an icicle shape in the recording material conveyance direction is formed. This phenomenon is considered to be caused by the vapor generated by heating evaporating unevenly in the section where the pressure is low.

  On the other hand, if the pressing member 106 and the separation roller 103 are too close, there is a problem that the rotational torque of the fixing roller 101 and the separation roller 103 increases due to the contact between the pressing member 106 and the separation roller 103. Causes malfunction. In the illustrated embodiment, the fixing roller 101 and the separation roller 103 are driven by a single motor which is a common driving unit. Therefore, an increase in rotational torque of the fixing roller 101 and the separation roller 103 is an increase in load torque applied to the motor.

  As described above, the distance D is set to about 2 to 4 mm, but this value is a value at which good fixing is performed without causing the deterioration of the image quality described above. The distance D, that is, the distance between the upstream of the nip formed by the separation roller 103 and the center of the rod-like member 106f is set to various values depending on the shape of the pressing member 106, the shape of the separation roller 103, etc. It is important to maintain the correct value. In other words, it is important that the value is set so that good fixing can be performed without causing deterioration in image quality throughout the operation period of the fixing device 100. In addition, although the description has been given assuming that the distance D is set to an appropriate value, in an accurate sense, good fixability is maintained by appropriately setting the positional relationship between the pressing member 106 and the separation roller 103. That is, the positional relationship can be changed by changing the relationship between the height of the pressing member 106 and the separation roller 103, the angle of the pressing member 106, and the like together with the distance D. The pressing member 106 includes a supporting member 106a that is not deformed, a pressing pad 106c that is deformed by pressing, and a sliding member 106e. Changing the positional relationship PR means changing the positional relationship between a member that does not deform, that is, the 106a and the separation roller 103, and changing the positional relationship PR means fixing the recording material P. This is a change in the positional relationship between the separation roller 103 and the pressing member 106 in the 100 operating state.

  The change in the positional relationship between the pressing member 106 and the separation roller 103 is changed by changing the position, height or angle of the support member 106 a or the position or height of the separation roller 103.

  When the fixing device 100 is operated for a long time, the sliding member 106e is drawn to the downstream side in the recording material conveyance direction, so that the sliding member 106e comes into contact with the separation roller 103, and the load torque described above changes. In addition, the load torque applied to the motor for driving the fixing roller 101 and the separation roller 103 is rapidly increased.

  In such a case, such a change in load torque can be avoided by changing the positional relationship between the pressing member 106 and the separation roller 103. Needless to say, the positional relationship between the pressing member 106 and the separation roller 103 is changed so that the distance D is too long to cause uneven fixing. The positional relationship is not necessarily constant and may change corresponding to the operation time of the fixing device, but the positional relationship corresponding to the operation time of the fixing device can be obtained in advance by experiments. Therefore, by storing and reading out the positional relationship corresponding to the operation time of the fixing device in a nonvolatile memory, it becomes possible to appropriately set the positional relationship in the entire operation period of the fixing device.

  Further, in the maintenance of the fixing device 100, the proper positional relationship between the pressing member 106 and the separation roller 103 can be obtained, and the obtained positional relationship can be set. As described above, the positional relationship between the pressing member 106 and the separation roller 103 can be changed, and by appropriately setting the appropriate positional relationship, variations in the positions of the pressing member 106 and the separation roller 103 are appropriately corrected. Thus, the positions of these members can be set with high accuracy.

  FIG. 5 shows a first example of changing the positional relationship.

  In FIG. 5, a long hole 110 indicated by hatching is a long hole formed in a support member (not shown). The pin 106g provided on the pressing member 106 is fitted into the long hole 110, and the pressing member 106 is guided by the long hole 110 and moves, for example, from the position indicated by the solid line to the left and right as indicated by the dotted line. . By moving the pressing member 106 along the surface of the fixing roller 101 as shown in the figure, the distance D is always set to an appropriate value, and good fixing is performed without causing an increase in the torque.

  FIG. 6 shows a second example of changing the positional relationship.

  The long hole 110 in FIG. 5 is linear, but the long hole 110 a in FIG. 6 is an arc centered on the shaft 101 c of the fixing roller 101, that is, an arc shape concentrically formed with the outer peripheral surface of the fixing roller 101. It is a hole. By moving the pressing member 106 along the elongated hole 110a, the pressing pad 106c presses the fixing belt 105 against the fixing roller 101 with a pressure that does not change even after the position is changed.

  FIG. 7 shows a third example for changing the positional relationship.

  In the third example, the position of the pressing member 106 does not change, and the distance D in FIG. 3 is changed by changing the position of the separation roller 103. The separation roller 103 is guided by a long hole 110b formed on a concentric circle 101d with the outer peripheral surface of the fixing roller 101, and is displaced from a solid line position to a dotted line position, for example. The distance D is changed by this displacement. Even if the separation roller 103 is displaced as shown in FIG. 7, the distance between the shaft 101c of the fixing roller 101 and the separation roller 103 does not change. Therefore, even when the separation roller 103 is displaced, the fixing property and the separation property of the recording material P do not change.

  FIG. 8 shows an example of a displacement mechanism that changes the positional relationship.

  A screw 106 h is fixed to the pressing member 106. By rotating the nut 111 as the first displacement mechanism rotatably attached to the fixing portion of the fixing device 100 as indicated by the arrow W2, the pressing member 106 is displaced from the position of the solid line to the position of the dotted line, for example, and the distance is changed. D is changed. Although not shown, also in the case of the third example shown in FIG. 7, the position of the separation roller 103 can be changed using a second displacement mechanism such as a cam.

  The positional relationship is changed by an appropriate method such as a manual change by the user or a change every time the operation time of the image forming apparatus reaches a predetermined value.

DESCRIPTION OF SYMBOLS 100 Fixing device 101 Fixing roller 102 Entrance roller 103 Separating roller 104 Steering roller 105 Fixing belt 106 Pressing member 107, 108 Heater

Claims (5)

A fixing member that heats and fixes the toner image to the recording material;
A fixing belt,
A pressing member that presses the fixing belt against the fixing member;
A separation roller disposed downstream of the pressing member with respect to the recording material conveyance direction and pressing the fixing belt against the fixing member;
In a fixing device having
A fixing device, wherein a positional relationship between the pressing member and the separation roller is changeable.   The fixing device according to claim 1, further comprising a first displacement mechanism that displaces the pressing member, wherein the first displacement mechanism changes the positional relationship by displacing the pressing member.   The fixing device according to claim 1, further comprising: a second displacement mechanism that displaces the separation roller, wherein the second displacement mechanism changes the positional relationship by displacing the separation roller.   The fixing member includes a fixing roller, and the positional relationship is changed by the displacement of the pressing member or the separation roller, and the pressing member or the separation roller can be displaced on a concentric circle on the outer peripheral surface of the fixing roller. The fixing device according to claim 1, wherein the fixing device is provided.   2. The pressing member includes a pressing pad that presses the fixing belt against the fixing member, a sliding member that covers the pressing pad, and a support member that supports the pressing pad. 5. The fixing device according to any one of 4 above.

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