JP2012103549A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device shortening warm-up time and preventing an excessive temperature rise of a metallic pipe.SOLUTION: In a fixing device 20 including: an endless fixing belt 21 having flexibility; a pressure roller 31 arranged on an outer peripheral side of the fixing belt 21 so that the fixing belt 21 can be pressured; a metallic pipe 22 fixed adjacently to an inner peripheral side of the fixing belt 21; drive means for driving the fixing belt 21 in a normal rotation direction and in a reverse direction; and a halogen heater 25 for heating the metallic pipe 22 and the fixing belt 21 to perform thermal fixing by passing a sheet carrying an unfixed toner image through a nip part formed by pressure contact of the fixing belt 21 and the pressure roller 31, the fixing belt 21 is heated in a non-rotation state during a warm-up operation, and a normal rotation control for driving the fixing belt 21 in the normal rotation direction is performed after a reverse control for driving the fixing belt 21 in the reverse direction by the driving means when the reverse control is performed.

Description

  The present invention relates to a fixing device and an image forming apparatus. More specifically, the present invention relates to a fixing device that fixes a toner image formed on an image carrier onto a recording medium, and an image forming apparatus including the fixing device.

  Various image forming apparatuses using an electrophotographic system have been devised as image forming apparatuses such as copiers, printers, facsimiles, and their combined machines, and are well known in the art. In the image forming process, an electrostatic latent image is formed on the surface of the photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner as a developer to be visualized and developed. The image is formed by a process in which the transferred image is transferred onto a recording paper (also referred to as paper, recording material, or recording medium) by a transfer device to carry the image, and a toner image on the recording paper is fixed by a fixing device using pressure, heat, or the like. Yes.

  In the fixing device, a fixing member and a pressure member constituted by opposing rollers or belts or a combination thereof are disposed so as to contact each other to form a nip portion. And a pressure is applied to fix the toner image on the recording paper.

  For example, a fixing device of a belt fixing system as shown in FIG. 11 includes a fixing roller 79 including a heating roller 74 having a heater 76 as a heat source, a fixing roller 72 having a rubber layer on the surface, and a fixing belt 79. The transferred toner image is heated and pressed and fixed in the process of passing the recording paper P onto which the toner has been transferred through a nip portion (fixing nip portion) formed by the pressure roller 71 in contact with the toner.

  Further, Patent Document 1 discloses a film heating type fixing device. For example, as shown in FIG. 12, such a film heating type fixing device has a heat resistant film (fixing film 84) between a ceramic heater 81 as a heating element and a pressure roller 71 as a pressure member. Is formed between the film 84 and the pressure roller 71 in the fixing nip portion, and the recording paper P to which toner has been transferred is interposed between the film 84 and the film 84 so as to be nipped and conveyed. The heat of the ceramic heater 81 is applied to the recording paper through the film 84 at the portion, and the unfixed toner image is fixed to the recording paper surface by heat and pressure with the applied pressure of the fixing nip portion.

  Such a film heating type fixing device can constitute an on-demand type device using a ceramic heater and a low heat capacity member as a film, and a ceramic heater as a heat source only when image forming of the image forming apparatus is executed. It is sufficient to energize the printer and heat it up to the specified fixing temperature. The waiting time from turning on the image forming apparatus to the image forming executable state is short (quick start), and the power consumption during standby is greatly increased. There are advantages such as small (power saving).

  Patent Document 2 discloses a pressure belt type fixing device. This fixing device is disposed with a rotatable heat-fixing roller whose surface is elastically deformed, an endless belt that can run while being in contact with the heat-fixing roller, and a non-rotating state inside the endless belt to heat-fix the endless belt A belt nip that allows the recording paper to pass between the endless belt and the heat fixing roller is provided between the endless belt and the heat fixing roller, and a pressure pad that elastically deforms the surface of the heat fixing roller is provided. By increasing the contact area between the recording paper and the roller, the heat conduction efficiency is greatly improved, energy consumption is reduced, and at the same time, miniaturization is realized.

  However, the fixing device described in Patent Document 1 has a problem of durability and a problem of belt temperature stability. In other words, the wear resistance due to the sliding of the ceramic heater that is the heat source and the inner surface of the belt is insufficient, and the surface that repeats continuous friction becomes rough and the frictional resistance increases when operated for a long time, and the running of the belt becomes unstable. There is a problem that a phenomenon such as an increase in driving torque of the fixing device occurs (issue 1).

  As a result, there has been a problem that the recording paper forming the image slips and the image shifts, or the stress applied to the drive gear increases and the gear is damaged.

  In the film heating type fixing device, since the belt is locally heated at the nip, when the rotating belt returns to the nip entrance, the belt temperature becomes the coldest, especially at high speed. However, there is a problem that fixing failure is likely to occur (Problem 2).

  On the other hand, as means for improving the problem of slidability between the belt inner surface and the fixing member, in the above-mentioned Patent Document 2, a glass fiber sheet obtained by impregnating PTFE as a low friction sheet (sheet-like sliding material) on the surface layer of the pressure pad A method using (PTFE-impregnated glass cloth) is disclosed, and it is shown that slidability is improved.

  However, such a pressure belt type fixing device has a problem that it takes a long time to warm up because the heat capacity of the fixing roller is large and the temperature rise is slow (Problem 3).

  As a technique for solving all of the above problems 1 to 3, in Patent Document 3, a pipe-shaped metal heat conductor is fixed inside an endless belt (fixing belt) so as to guide the movement of the endless belt. A fixing device including a pressure roller that heats an endless belt via a metal heat conductor by a heat source in the metal heat conductor and further contacts the metal heat conductor via the endless belt to form a nip portion is disclosed. ing. According to the invention of Patent Document 3, it is possible to warm the entire endless belt constituting the fixing device, to reduce the first print time from the heating standby time, and to solve the shortage of heat at the time of high-speed rotation. Can do.

  However, for example, in a fixing device using a low-heat-capacity thermal fixing method as in Patent Document 3, when the pressure member and the fixing member are driven to rotate forward by the driving means, the fixing member is disposed downstream of the fixing member in the rotation direction. In some cases, belt lifting may occur between metal pipes (see FIG. 3). Similarly, when the pressure member and the fixing member are driven in reverse, the belt may float on the downstream side in the rotation direction of the fixing member (see FIG. 5).

  If a warm-up operation is performed in such a state that the belt is lifted and the fixing member is in a non-rotating state, heat is not sufficiently transferred to the fixing belt, and only a long time is required for the warm-up operation. In addition, the metal pipe may be overheated.

  Therefore, the present invention eliminates belt lifting that occurs between the fixing member and the metal pipe by once performing forward rotation after the reversal control of the fixing device, thereby shortening the warm-up time and overheating the metal pipe. It is an object of the present invention to provide a fixing device capable of preventing the above and an image forming apparatus including the same.

  In order to achieve such an object, the fixing device according to claim 1 includes an endless fixing member having flexibility, and a pressure member arranged to be able to press the fixing member on the outer peripheral side of the fixing member. A pipe-shaped metal heat conductor fixed in the vicinity of the inner peripheral side of the fixing member, a driving means for driving the fixing member in a normal direction and a reverse direction, and a heating means for heating the metal heat conductor and the fixing member. A fixing device that heats and fixes a sheet carrying an unfixed toner image through a nip portion between the fixing member and the pressure member formed by pressure contact between the fixing member and the pressure member. During the warm-up operation of the fixing device, the fixing member is heated in a non-rotating state, and when the reversing control is performed to reversely drive the fixing member by the driving unit, the normal rotation control is performed to drive the fixing member forward after the reversing control. Is what you do.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the reverse control is performed when a jam occurs in the nip portion, and the warm-up operation is performed after the forward rotation control.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, at the time of forward rotation control after the reversal control, the fixing member is rotated at a rotation speed slower than the rotation speed at the time of printing. It is intended to rotate.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the fixing device includes a temperature detecting unit that detects a temperature of the fixing member, and the forward rotation control after the reverse control is performed. The rotation speed is determined based on the temperature detected by the temperature detecting means.

  According to a fifth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the fixing device includes a torque detecting unit that detects a torque applied to the driving unit, and the forward rotation control after the reverse control is performed. The rotation speed is changed based on the detection result by the torque detection means.

  According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, the rotation amount of the fixing member during the forward rotation control after the reverse control is equal to or greater than the rotation amount in the reverse control. To do.

  According to a seventh aspect of the present invention, in the fixing device according to any one of the first to sixth aspects, the reversal control and the normal rotation control are repeated a plurality of times.

  An image forming apparatus according to an eighth aspect includes the fixing device according to any one of the first to seventh aspects.

  According to the present invention, it is possible to shorten the warm-up time and prevent an excessive temperature rise of the metal pipe.

1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment. 1 is a schematic configuration diagram of a fixing device according to an exemplary embodiment. FIG. 2 is a schematic configuration diagram of a fixing device when forward rotation is stopped. It is a flowchart (1) at the time of inversion control. FIG. 2 is a schematic configuration diagram of a fixing device when reversal is stopped. It is a flowchart (2) at the time of inversion control. It is a flowchart (3) at the time of inversion control. It is a flowchart (4) at the time of inversion control. It is a flowchart (5) at the time of inversion control. FIG. 3 is a schematic configuration diagram of a fixing device showing when a lubricant pool is generated. 1 is a schematic configuration diagram of a belt fixing type fixing device. 1 is a schematic configuration diagram of a film heating type fixing device.

  Hereinafter, a configuration according to the present invention will be described in detail based on the embodiment shown in FIGS. The fixing device (20) according to the present embodiment includes an endless fixing member (fixing belt 21) having flexibility, and a pressure member (pressurizing member) disposed on the outer peripheral side of the fixing member so as to be able to press the fixing member. A pressure roller 31), a pipe-shaped metal heat conductor (metal pipe 22) fixed in the vicinity of the inner peripheral side of the fixing member, driving means for driving the fixing member to rotate forward and reverse, and metal heat A heating means (halogen heater 25) for heating the conductor and the fixing member, and an unfixed toner image is formed on the nip portion between the fixing member and the pressure member formed by the pressure contact between the fixing member and the pressure member. In a fixing device that heats and fixes a sheet that has been carried through, during the warm-up operation of the fixing device, the fixing member is heated in a non-rotating state, and when the reversing control is performed so that the fixing member is driven in reverse by the driving means. , Fixing after the reversal control And it performs normal rotation control for forward drive the wood.

(Configuration and operation of image forming apparatus)
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes an apparatus main body of a copying machine as an image forming apparatus, 2 an original reading unit that optically reads image information of an original D, and 3 an exposure light L based on image information read by the original reading unit 2. Is exposed to the photosensitive drum 5, 4 is an image forming unit for forming a toner image (image) on the photosensitive drum 5, and 7 is a toner image formed on the photosensitive drum 5 on the recording medium P. A transfer unit 10 for transferring, a document transport unit for transporting the set document D to the document reading unit 2, 12 to 14 a paper feed unit storing a recording medium P such as transfer paper, and 20 on the recording medium P A fixing device for fixing an unfixed image, 21 is a fixing belt as a fixing member installed in the fixing device 20, and 31 is a pressure roller as a pressure member installed in the fixing device 20.

  An operation during normal image formation in the image forming apparatus shown in FIG. 1 will be described. First, the document D is conveyed from the document table in the direction of the arrow in the drawing by the conveyance roller of the document conveyance unit 10 and passes over the document reading unit 2. At this time, the document reading unit 2 optically reads the image information of the document D passing above.

  Then, the optical image information read by the document reading unit 2 is converted into an electric signal and then transmitted to the exposure unit 3 (writing unit). Then, exposure light L such as laser light based on the image information of the electrical signal is emitted from the exposure unit 3 toward the photosensitive drum 5 of the image forming unit 4.

  On the other hand, in the image forming unit 4, the photosensitive drum 5 is rotated in the clockwise direction in the drawing, and image information is transferred onto the photosensitive drum 5 through a predetermined image forming process (charging process, exposure process, development process). An image (toner image) corresponding to is formed. Thereafter, the image formed on the photosensitive drum 5 is transferred by the transfer unit 7 onto the recording medium P conveyed by the registration roller.

  On the other hand, the recording medium P conveyed to the transfer unit 7 operates as follows. First, one of the plurality of paper feeding units 12, 13, and 14 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 12 is selected). To do). Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 12 is conveyed toward the position of the conveyance path K.

  Thereafter, the recording medium P passes through the conveyance path K and reaches the position of the registration roller. Then, the recording medium P that has reached the position of the registration roller is conveyed toward the transfer unit 7 at the same timing in order to align with the image formed on the photosensitive drum 5.

  After the transfer process, the recording medium P passes through the position of the transfer unit 7 and then reaches the fixing device 20 through the conveyance path. The recording medium P that has reached the fixing device 20 is fed between the fixing belt 21 and the pressure roller 31, and the image is fixed by heat received from the fixing belt 21 and pressure received from both members. The recording medium P on which the image has been fixed is delivered from between the fixing belt 21 and the pressure roller 31 (nip portion) and then discharged from the image forming apparatus main body 1. Thus, a series of image forming processes is completed.

(Configuration of fixing device)
Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail. As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing member, a metal heat conductor (also referred to as a metal pipe or a heating pipe) 22, a support body 23, a halogen heater 25, a nip forming member 26, a pressurizing member. It comprises a pressure roller 31 as a member, a temperature detection means 40, a torque detection means (not shown), and the like.

[Fixing belt]
The fixing belt 21 as a fixing member is a thin and flexible endless belt (or film), and rotates together with an external roller. In the example shown in FIG. 2, the pressure roller 31 is rotated by a driving unit (not shown), and the driving force is transmitted to the belt at the nip portion, whereby the fixing belt 21 is rotated.

  The fixing belt 21 is formed by sequentially laminating an elastic layer and a release layer on a base material, and the entire thickness thereof is set to 1 mm or less. The base material of the fixing belt 21 has a layer thickness of 30 to 50 μm and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide.

  The elastic layer of the fixing belt 21 has a layer thickness of 100 to 300 μm and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber. When there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed image is crushed and fixed, minute irregularities on the belt surface are transferred to the image and the image has a crusty skin-like shape. There is a problem that marks remain. On the other hand, by providing the elastic layer, minute irregularities on the surface of the fixing belt 21 in the nip portion are not formed, and heat is uniformly transmitted to the toner image on the recording medium P, thereby preventing the generation of a scum skin image.

  The release layer of the fixing belt 21 has a layer thickness of 10 to 50 μm, such as PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), and the like. Made of material. By providing the release layer, the releasability (peelability) for the toner image is secured.

  In the present embodiment, the diameter of the fixing belt 21 is set to 30 mm. Inside the fixing belt 21 (inner peripheral surface side), a metal heat conductor 22, a support 23, a halogen heater 25, a nip forming member 26, and the like are fixed.

[Nip forming member]
The nip forming member 26 is fixed on the inner peripheral surface side of the fixing belt 21, and abuts against the pressure roller 31 through the fixing belt 21 to form a nip portion. Note that it is preferable to form the sliding contact surface of the nip forming portion 23 with a material having a low friction coefficient so that the wear of the fixing belt 21 is reduced even if the nip forming member 26 and the fixing belt 21 are in sliding contact. Further, a sliding sheet may be provided between the nip forming member 26 and the inner peripheral surface of the fixing belt 21.

  In the example shown in FIG. 2, the shape of the nip portion is the concave shape 26a, but may be a flat shape or other shapes. By setting the shape of the nip portion to the concave shape 26a, the discharge direction of the leading end of the recording paper is closer to the pressure roller, the separation property is improved, and the occurrence of jam can be suppressed.

[heater]
The heat source is a halogen heater 25, and both ends thereof are fixed to a side plate (not shown) of the fixing device 20. Then, the metal heat conductor 22 is heated by the radiant heat of the halogen heater 25 whose output is controlled by the power supply unit of the image forming apparatus 1. Further, the fixing belt 21 is entirely heated by the metal heat conductor 22, and heat is applied to the toner image on the recording medium P from the surface of the heated fixing belt 21.

  The output control of the halogen heater 25 is controlled based on the detection result of the belt surface temperature by the temperature detection means 40 such as a thermistor facing the surface of the fixing belt 21. Further, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature by such output control of the halogen heater 25.

  In the example shown in FIG. 2, the halogen heater 25 is used as a heat source. However, the present invention is not limited to this, and an induction heating means (IH coil), a resistance heating element, a carbon heater, or the like may be used as a heat source. good.

[Metal heat conductor]
The hollow metal heat conductor 22 is fixed so as to face the inner peripheral surface of the fixing belt 21 at a position excluding the nip portion, and is heated by the radiant heat of the halogen heater 25 to heat the fixing belt 21 (heat). ). In addition, as a material of the metal thermal conductor 22, a material having thermal conductivity such as aluminum, iron, and stainless steel can be used. In this embodiment, SUS having excellent strength is used. In the example shown in FIG. 2, the metal heat conductor 22 has a circular shape, but is not limited to this, and has other cross-sectional shapes such as a circular shape or a square shape whose top portion is crushed. May be.

  Even if the speed of the apparatus is increased because the fixing belt 21 is heated over a wide range in the circumferential direction by the metal heat conductor 22 without locally heating only a part of the fixing belt 21. The fixing belt 21 is sufficiently heated to prevent the occurrence of fixing failure.

  Further, even when the metal heat conductor 22 is thinned to improve the heating efficiency of the fixing belt 21, the metal heat conductor 22 is separated from the nip forming member 26 that receives pressure from the pressure roller 31. Therefore, a problem that the metal heat conductor 22 is bent and the inner peripheral surface of the fixing belt 21 is rubbed strongly, a problem that the metal heat conductor 22 is bent and the driving torque of the fixing belt 21 is increased, and the like are suppressed. The

  As described above, the fixing device 20 is configured such that only the part of the fixing belt 21 is not locally heated and the fixing belt 21 is heated over a wide range in the circumferential direction by the metal heat conductor 22. Even when the speed is increased, the fixing belt 21 is sufficiently heated to prevent the occurrence of fixing failure. That is, since the fixing belt 21 can be efficiently heated with a relatively simple configuration, the warm-up time and the first print time are shortened, and the size of the apparatus is reduced.

  The difference in outer diameter between the fixing belt 21 and the metal heat conductor 22 is preferably within 1 mm. As a result, the area in which the metal heat conductor 22 and the fixing belt 21 are in sliding contact with each other is increased, and the problem that the wear of the fixing belt 21 is accelerated is suppressed, and the metal heat conductor 22 and the fixing belt 21 are separated from each other too much. A problem that the heating efficiency of the belt 21 is reduced can be suppressed. Furthermore, since the metal heat conductor 22 is placed close to the fixing belt 21, the circular posture of the flexible fixing belt 21 is maintained to some extent, so that deterioration and breakage due to deformation of the fixing belt 21 can be reduced. Can do.

  Further, the sliding surface of the metal heat conductor 22 may be formed of a material having a low friction coefficient so that the wear of the fixing belt 21 is reduced even if the metal heat conductor 22 and the fixing belt 21 are in sliding contact. good. Further, a lubricant such as silicone oil or fluorine grease is applied to the interface between the fixing belt 21 and the metal thermal conductor 22.

[Support]
It is also preferable to provide a support 23 that supports the nip forming member 26 in the nip portion and reinforces the strength inside the metal heat conductor 22. Moreover, when the support body 23 is heated by the radiant heat of the halogen heater 25, etc., it is also preferable to heat-insulate or mirror-treat the surface. Thereby, excessive heating can be prevented and useless energy consumption can be suppressed.

[Pressure roller]
The pressure roller 31 as a pressure member has a diameter of 30 mm and is formed by forming an elastic layer on a hollow cored bar. The elastic layer of the pressure roller 31 is made of a material such as foamable silicone rubber, silicone rubber, or fluororubber. A thin release layer made of PFA, PTFE, or the like can be provided on the surface layer of the elastic layer. The pressure roller 31 is pressed against the fixing belt 21 by a spring or the like, and the rubber layer is crushed and deformed to form a desired nip portion between both members.

  Note that when the elastic layer of the pressure roller 31 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the nip portion can be reduced, so that the bending that occurs in the metal heat conductor 22 is reduced. Can be further reduced.

  In this embodiment, the fixing belt 21 has a diameter equal to that of the pressure roller 31, but the fixing belt 21 has a diameter smaller than the pressure roller 31. You can also. In that case, since the curvature of the fixing belt 21 in the nip portion is smaller than the curvature of the pressure roller 31, the recording medium P sent out from the nip portion is easily separated from the fixing belt 21.

  The pressure roller 31 is rotated by a driving force transmitted from a driving unit such as a motor through a gear. Further, the pressure roller 31 may be a solid roller, but the hollow roller may have a smaller heat capacity. Further, a heat source such as a halogen heater may also be provided on the pressure roller 31 side. If there is no heater inside the pressure roller, sponge rubber may be used. Sponge rubber is more desirable because it increases heat insulation and makes it difficult for the fixing belt to lose heat.

(Fixing device control)
As described above, in the fixing device 20, the fixing belt 21 is rotated in the clockwise direction by the driving unit, and the driving force is transmitted to the fixing belt 21 at the nip portion. Rotate clockwise. The fixing belt 21 is sandwiched and rotated at the nip portion, but is guided by the metal pipe 22 outside the nip portion, so that the position of the fixing belt 21 is not separated from the metal pipe 22 beyond a certain distance. Has been.

  Here, when the forward rotation control in which the pressure roller 31 rotates in the clockwise direction and the fixing belt 21 rotates in the counterclockwise direction is stopped (when forward rotation is stopped), the rotation of the fixing belt 21 is performed as shown in FIG. A belt float (indicated by reference numeral 21a) may occur between the fixing belt 21 and the metal pipe 22 on the downstream side in the direction.

  Further, in the fixing device, generally, when a winding jam or the like occurs, inversion control of the driving unit is performed in order to eliminate the jam. The reversal control is a control in which the fixing belt 21 is rotated in the clockwise direction by rotating the pressure roller 31 in the opposite direction (counterclockwise) to the normal rotation by the driving unit.

  Here, the wrapping jam causes the sheet to be wound around the fixing roller 21 and the pressure roller 31 and the sheet is not discharged from the fixing device, so that it is difficult for the user to find and remove the sheet on which the jam has occurred. Therefore, in the conventional fixing device, as shown in the flowchart of FIG. 4, when a jam is detected, reversal control is performed for a predetermined time (for example, 500 ms) (S10), and the reversal control rotates before all the paper is wound. Stops (S11). In this way, the user can recognize the jammed paper by ejecting the paper to the nip entrance side.

  Further, when this reversal control is stopped (referred to as reverse reversal), as shown in FIG. 5, the fixing belt 21 and the metal pipe 22 are located downstream in the rotation direction of the fixing belt 21 as in the case of normal rotation stop. A belt float 21a may occur between them. Usually, the pressure is released once during the jam processing, but the floating between the fixing belt 21 and the metal pipe 22 is maintained even if the pressure is applied thereafter.

  When the warming-up operation of the fixing device that heats the fixing belt 21 and the like in a non-rotating state is performed from the reverse stop state shown in FIG. 5, the air between the fixing belt 21 and the metal pipe 22 serves as a heat insulating material, and the metal pipe The temperature will rise too much. In addition, since heat is not easily transmitted to the fixing belt 21, it takes time for the warm-up operation.

  Further, as described above, a lubricant such as grease is applied to the inner peripheral surface of the fixing belt 21 in order to improve the slidability. However, the heater is in an off state during normal rotation after the reversal control. Therefore, the temperature of the fixing device is low, and at low temperatures, the lubricant is poor in slidability, so that the torque is also increased.

  Therefore, as shown in the flowchart of FIG. 6, the fixing device 20 according to the present embodiment performs the forward rotation control (S21) after the reverse control (S20), thereby changing the state of the fixing belt 21 when the forward rotation is stopped. It returns to the state (S22).

  As described above, when the fixing belt 21 on the nip entrance side floats from the metal pipe 22 after the reversal control at the time of occurrence of the winding jam or the like, it is generated on the nip entrance side by performing the forward rotation control once. It is possible to eliminate the belt lift 21a and perform the warm-up operation in a state where the fixing belt 21 is in close contact with the metal pipe 22.

  Accordingly, it is possible to prevent an excessive temperature rise of the metal pipe during a warm-up operation performed by non-rotational heating after the reversal control, and a safe fixing device can be obtained. Further, by performing the forward rotation control, the fixing belt 21 can be brought into close contact with the metal pipe 22, so that the time required for the warm-up operation can be shortened as compared with the state in which the fixing belt 21 is lifted.

  Hereinafter, other embodiments of the image forming apparatus according to the present invention will be described. In addition, the description about the same point as the said embodiment is abbreviate | omitted.

(Second Embodiment)
Further, it is preferable that the driving means rotate at a rotation speed slower than a rotation speed (also referred to as a printing speed) at the time of printing (at the time of paper feeding) during the forward rotation control after the reversal control. The control in this case is shown in the flowchart of FIG. In this case, after the reversal control (S30), the forward rotation control is performed at a rotational speed slower than the rotational speed at the time of paper feeding (S31), and the state of the fixing belt 21 is returned to the state at the time of the forward rotation stop ( S32).

  In this way, by reducing the normal rotation speed in the forward rotation control after the reverse control, the torque is lowered to prevent the occurrence of a malfunction such as a mechanical failure due to the torque increase. Temperature rise can be prevented and a safe fixing device can be obtained.

(Third embodiment)
Moreover, it is preferable to determine the rotation speed at the time of forward rotation control after reversal control based on the temperature detected by the temperature detection means 40. The control in this case is shown in the flowchart of FIG. In this case, after the reversal control (S40), the temperature detecting means 40 detects the temperature of the fixing belt surface (S41), and based on the detected temperature, the rotational speed in the subsequent forward rotation control is determined (S42). The forward rotation control is performed according to the speed (S43), and the state of the fixing belt 21 is returned to the state at the time of stopping the forward rotation (S44).

  In the present embodiment, with reference to the rotation speed (driving amount of the driving unit) of the fixing belt 21 when the paper is passed as a reference (100%), “speed 1” is 80% and “speed 2” is the rotation speed during forward rotation control. "Is set to 50% and" Speed 3 "is set to 20%. A list of these settings is shown in Table 1.

  Table 2 is a list of correspondence tables of detected temperatures by the temperature detecting means 40 and rotation speeds corresponding to the detected temperatures. For example, the correspondence table may be stored in advance in the storage unit of the image forming apparatus. Based on Table 1 and Table 2, the rotational speed of the forward rotation control according to the detected temperature is determined (S42).

  Thus, in the forward rotation control after the reverse control, it is possible to rotate with the optimum torque by selecting and changing the rotational speed at the forward rotation control according to the fixing belt temperature before the rotation. It is possible to more effectively prevent the occurrence of troubles such as a mechanical failure and to prevent an excessive temperature rise of the metal pipe at the time of warm-up after the reversal control, thereby providing a safe fixing device.

(Fourth embodiment)
Moreover, it is preferable to determine the rotation speed at the time of forward rotation control after reversal control based on the torque concerning the drive means detected by the torque detection means. As the torque detection means, a known or new torque measuring device or the like may be used, and it is not particularly limited.

  The control in this case is shown in the flowchart of FIG. In this case, the forward rotation control (S51) is performed after the reverse control (S50), and the rotation speed at this time is feedback controlled based on the torque applied to the drive means detected by the torque detection means during the reverse control. (S52-S53). After the forward rotation control, the state of the fixing belt 21 is returned to the state when the forward rotation is stopped (S54).

  Table 3 is a list of correspondence tables between the detection results by the torque detection means and the rotation speeds corresponding to the detection results when the rotation torque at the time of passing paper is set as a reference (100%). Based on Tables 1 and 3, the rotational speed of the forward rotation control is changed.

  In this way, in forward rotation control after reverse rotation control, the torque during rotation is directly detected, and when the preset value is exceeded, the rotational speed is slowed down so that the torque can be reduced and the rotation can be performed more accurately. In addition to preventing the occurrence of a mechanical failure due to torque, it is possible to prevent an excessive temperature rise of the metal pipe at the time of warm-up after the reversal control, and to provide a safe fixing device.

(Fifth embodiment)
Further, it is preferable that the rotation amount (forward rotation distance) of the fixing belt in the forward rotation control after the reverse control is larger than the rotation amount (reverse distance) of the fixing belt in the previous reverse control.

  The lubricant applied to the inner surface by the positive rotation of the fixing belt 21 accumulates in a form that is dammed to the low friction sheet on the surface layer of the nip forming member. The lubricant that has been dammed up and accumulated on the upstream side of the nip portion is rotated by the fixing belt 21 and moved to the upstream side of the nip by performing reversal control, and as shown in FIG. A pool 50 can occur. When a warm-up operation is started from a state in which a large amount of lubricant is present on a part of the inner surface of the belt, heat is not transmitted to the fixing belt 21 during non-rotational heating during warm-up, and the warm-up time is reduced. It becomes long and leads to abnormal temperature rise of the metal pipe.

  Therefore, in this embodiment, the warm-up time is set by returning the lubricant 50 to the original position by setting the forward rotation distance to be equal to or more than the previous reverse distance so that the heat conduction between the fixing belt 21 and the metal pipe 22 does not deteriorate. Can be prevented, and an excessive temperature rise of the metal pipe can be prevented, so that a safe fixing device can be obtained.

  It is also preferable to repeat the inversion control and forward rotation control described above a plurality of times. Thus, by repeating the reverse control and the normal rotation control, the lubricant 50 can be made more familiar, and the rotational torque can be reduced.

  By using the image forming apparatus (FIG. 1) including the fixing device 20 having the above-described configuration, a safer image forming apparatus can be provided by using the fixing device having the above-described effects.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, in the above-described embodiment, the fixing device using the pressure roller 31 as the pressure member has been described as an example. However, the fixing device is not limited thereto. For example, a pressure belt or a pressure pad is used as the pressure member. It is also preferable.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Original reading part 3 Exposure part 4 Image forming part 5 Photosensitive drum 7 Transfer part 10 Original conveyance part 12, 13, 14 Paper feeding part 20 Fixing apparatus 21 Fixing belt 21a Belt floating 22 Metal thermal conductor (metal) pipe)
23 Support 25 Halogen heater 26 Nip forming member 26a Concave shape 31 Pressure roller 40 Temperature detecting means 50 Lubricant 71 Pressure roller 72 Fixing roller 73 Separation claw 74 Heating roller 75 Fixing cover 76 Heater 77 Tension roller 78 Spring 79 Fixing belt 80 Thermistor 81 Ceramic heater 82 Stay 83 Holder 84 Fixing film D Document K Transport path L Exposure light P Recording medium

JP-A-4-44075 JP-A-8-262903 JP 2007-334205 A

Claims (8)

An endless fixing member having flexibility;
A pressure member arranged to be able to press the fixing member on an outer peripheral side of the fixing member;
A pipe-shaped metal heat conductor fixed in the vicinity of the inner peripheral side of the fixing member;
Driving means for driving the fixing member in a normal rotation direction and a reverse rotation direction;
Heating means for heating the metal heat conductor and the fixing member,
In a fixing device that heats and fixes a sheet carrying an unfixed toner image through a nip portion between the fixing member and the pressure member formed by pressure contact between the fixing member and the pressure member,
During the warm-up operation of the fixing device, the fixing member is heated in a non-rotating state,
When the reversing control for reversing the fixing member by the driving unit is performed, the fixing device performs normal rotation control for normally driving the fixing member after the reversing control. The reversal control is performed when a jam occurs in the nip portion,
The fixing device according to claim 1, wherein the warm-up operation is performed after the forward rotation control.   3. The fixing device according to claim 1, wherein the fixing member is rotated at a rotation speed slower than a rotation speed during printing during the forward rotation control after the reversal control. Temperature detecting means for detecting the temperature of the fixing member;
The fixing device according to claim 1, wherein a rotation speed at the time of the forward rotation control after the reversal control is determined based on a temperature detected by the temperature detection unit. Torque detecting means for detecting torque applied to the driving means;
The fixing device according to claim 1, wherein a rotation speed at the time of the forward rotation control after the reversal control is changed based on a detection result by the torque detection unit.   6. The fixing device according to claim 1, wherein a rotation amount of the fixing member at the time of the forward rotation control after the reversal control is equal to or larger than a rotation amount in the reverse rotation control.   The fixing device according to claim 1, wherein the inversion control and the forward rotation control are repeated a plurality of times.   An image forming apparatus comprising the fixing device according to claim 1.