JP2019120788A - Fixing device and image forming apparatus - Google Patents

Abstract

To avoid paper jam in a torque increase region occurring due to a reduction with time in temperature of a fixing belt.SOLUTION: When the cumulative travel distance of a fixing member or the cumulative number of fed recording medium exceeds a predetermined value, a fixing device sets a fixing member heat storage time required before a first recording medium after the start of paper feed enters a fixing nip longer than a fixing member heat storage time required before the predetermined value is reached. In other words, the fixing device sets a time t2 until the start of paper feed longer than before (than a t2 required before the cumulative travel distance or the cumulative number of fed recording medium reaches the predetermined time).SELECTED DRAWING: Figure 5

Description

The present invention relates to a fixing device and an image forming apparatus.

In an image forming apparatus such as a printer, copier or facsimile, an image is formed by an image forming process such as electrophotographic recording, electrostatic recording, magnetic recording, etc., and an unfixed toner image is a recording medium sheet by an image transfer method or a direct method. It is formed on a recording medium such as printing paper, photosensitive paper, electrostatic recording paper and the like. As a fixing device for fixing an unfixed toner image, fixing devices of a heat roller method, a belt fixing method, a film fixing method, etc. are widely adopted.

As such a fixing device, for example, those described in JP-A-2007-334205 (Patent Document 1), 2007-233011 (Patent Document 2), and JP-A-2016-71302 (Patent Document 3) are known. .

The thing of the said patent document 1 provides a pipe-like metal heat conductor and a heat source in the loop of an endless belt, and becomes a structure which heats an endless belt through a metal heat conductor. Furthermore, a pressure roller is provided which is in contact with the metal heat conductor via the endless belt to form a nip portion, and the endless belt is moved in the circumferential direction so as to be rotated with the rotation of the pressure roller.

Further, in the above-mentioned Patent Document 2, the endless belt is directly heated by a heat source by providing only a heat source with a member for forming a nip in a loop of the endless belt, a supporting member for supporting the member, and a nip It is configured to be formed.

Further, in Patent Document 3, an endless fixing belt having a heat source inside, a pressure roller disposed opposite to the fixing belt and forming a nip portion with the fixing belt, a traveling distance and recording of the fixing belt The linear velocity of the fixing belt is determined by determining the linear velocity of the fixing belt other than when the recording medium is transported from the relationship between the traveling distance and the number of sheets, and the linear velocity of the fixing belt is changed. And a linear velocity changing unit.

In the prior art configuration, in order to reduce the resistance between the fixing member (belt, film, etc.) and the nip forming member, a cloth or sheet-like member containing / coated with a lubricant or lubricating oil is nipped with the fixing member and the fixing member. It takes a configuration to be disposed between the forming members. In this configuration, a lubricant or lubricating oil having a reduced viscosity (hot) at the time of heating leaks out from the end face in the axial direction of the fixing member, or the lubricating oil is volatilized because the set temperature is high. As a factor, the increase in friction resistance over time = an increase in fixing device drive torque may occur. When the above-described increase in drive torque occurs, the fixing member may not rotate, and a sheet jam may occur, which may cause the recording material such as a sheet to be jammed, leading to a reduction in productivity due to the machine down.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device and an image forming apparatus capable of avoiding a paper jam in a region where a driving torque of a fixing member increases with time.

In order to solve this problem, according to the present invention, there is provided an endless fixing member, a heating source for heating the fixing member, a pressure member brought into contact with the fixing member, and the fixing member disposed inside the fixing member. A fixing device including a nip forming member that abuts against the pressing member via a member to form a fixing nip, wherein the cumulative traveling distance of the fixing member or the cumulative number of sheets of recording media exceeds a predetermined value; The fixing member heat storage time until the first sheet of recording medium enters the fixing nip is set to be longer than the fixing member heat storage time until the predetermined value is reached.

According to the present invention, it is possible to avoid the paper jam in the drive torque increase region caused by the temperature decrease of the fixing member with time. Further, paper jam can be avoided even if the driving torque of the fixing belt increases with time. As a result, machine down can be suppressed and productivity can be maintained, and a stable fixing device can be provided.

FIG. 1 is a cross-sectional view showing an example of an image forming apparatus equipped with a fixing device according to the present invention. FIG. 1 is a cross-sectional view showing an embodiment of a fixing device. 5 is a graph showing the relationship between the temperature of a fixing belt and driving torque in a new unit. 6 is a graph showing the relationship between the temperature of a fixing belt and driving torque when conventional control is applied to a time-dependent unit. 5 is a graph showing the relationship between the temperature of the fixing belt and the driving torque in the time-dependent unit in the present invention.

FIG. 1 is a cross-sectional view showing a schematic configuration of a color printer as an example of an image forming apparatus capable of mounting a fixing device according to the present invention. The configuration and operation of the image forming apparatus will be described later, and the fixing device will be described first.

FIG. 2 is a cross-sectional view showing an embodiment of a fixing device according to the present invention. The fixing device 20 shown in FIG. 2 includes a fixing belt 21 as a fixing member and a pressure roller 22 as a pressure member opposed to the fixing belt 21. A halogen heater 23, which is a heat source, is provided in the fixing belt 21, whereby the fixing belt 21 is directly heated by radiant heat from the inner peripheral side. Further, a pad (nip forming member) 24 for forming the pressure roller and the nip portion N via the fixing belt is disposed on the side facing the pressure roller 22 in the fixing belt 21.

In the fixing device of this embodiment, in order to slide the pad 24 and the fixing belt 21, a sliding sheet 28 impregnated with lubricating oil is provided. Thus, the inner surface of the fixing belt and the pad 24 come into sliding contact indirectly via the sliding sheet 28. In this example, the sliding sheet 28 is provided not only on the nip surface side of the pad 24 but also on both sides (side surfaces in the sheet conveyance direction) from the side opposite to the nip surface.

A cloth-like sheet in which fibers are woven can be suitably used as the lubricant / lubricant holding member (sliding sheet 28 in the illustrated example). As the lubricant or lubricating oil, silicone oil, silicone grease, fluorine grease or the like can be used. Further, the lubricant may be applied to the nip forming member (the pad 24 in the illustrated example) without using the lubricant holding member (the sliding sheet 28 in the illustrated example).

The fixing belt 21 as a fixing member is a thin and flexible endless belt member (including a film). Holders 26 are disposed at both axial end portions of the substantially cylindrical fixing belt 21 and rotatably support the fixing belt 21.

The pressure roller 22 as a pressure member includes a core, an elastic layer provided on the core, and a release layer provided on the surface of the elastic layer. The pressure roller 22 is pressed toward the fixing belt 21 by the pressure unit, and is in contact with the pad 24 via the fixing belt 21. At a portion where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor provided in the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate.

Both ends of the halogen heater 23 as a heating source for heating the fixing belt 21 are fixed to the side plate 27. The heating control of the halogen heater 23 is performed based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor. By such output control of the heater 23, the temperature (fixing temperature) of the fixing belt 21 can be set to a desired temperature. In addition to the halogen heater, an IH, a resistance heating element, a carbon heater or the like may be used as a heating source for heating the fixing belt 21.

The pad 24 is disposed longitudinally in the rotational axis direction of the fixing belt 21, and is fixed and supported by the stay 25 and positioned. The stay 25 of this example is composed of an upper stay 25-1, a lower stay 25-2, and a right stay 25-3. The stay 25 and the holder 26 are supported by the side plate 27.

At the time of the fixing operation, the pressure roller 22 is rotated clockwise in the figure by the drive mechanism, and the fixing belt 21 is driven. At the same time, the halogen heater 23 directly heats the fixing belt 21. Thereafter, when sufficient heat is accumulated, sheet passing is started, and the sheet (recording medium) P carrying the toner T is conveyed from the lower direction in FIG. 2 and passes through the nip portion N, and the toner is fixed on the sheet Ru.

At the time of the fixing operation, the lubricating oil exuded from the sliding sheet 28 spreads thinly on the inner surface of the fixing belt 21 rotating counterclockwise, and is recovered by the sliding sheet 28 when returning to the entrance of the pad 24. It is a cycle to return to the nip surface again.

FIG. 3 is a graph showing the relationship between the temperature of the fixing belt 21 and the driving torque in the new unit. As shown in the graph, the lower the fixing belt temperature, the higher the torque, and the higher the fixing belt temperature, the lower the torque.

During fixing operation, the temperature is increased at a low speed (linear speed lower than the sheet passing linear speed) until t1, and then the fixing belt is heated to a temperature higher than the target temperature at the sheet linear speed, and nipped at t2. Let the paper pass through.

The temperature rise at low speed until t1 is to lower the driving torque and operate by lowering the linear speed because the temperature of the fixing belt is low and the torque is high. Thereby, the torque at the time of low speed drive until t1 becomes low as shown by a broken line in the figure. In addition, when it is set as a paper-delivery linear speed until t1, as shown by a continuous line in a figure, a driving torque becomes high.

In addition, raising the belt temperature higher than the target temperature as in [a] means that the heater is fully turned on to start sheet passing as fast as possible, and the temperature does not easily rise immediately after sheet feeding starts This is to raise the temperature of the belt longitudinal end. Because of this effect, the temperature control may become unstable immediately after the start of sheet feeding, as in [b], the belt temperature may fall below the target temperature (to an extent that it does not affect the image).

FIG. 4 is a graph showing the relationship between the temperature of the fixing belt 21 and the driving torque when the conventional control is applied to the time-dependent unit. As shown in the graph, since the driving torque rises with time, when the temperature decreases in [b], the driving torque exceeds the slip torque as in [c] in the figure. In this case, the fixing belt can not rotate, causing a paper jam and the machine to go down.

Therefore, in the present embodiment, as shown in FIG. 5, the time t2 until the start of sheet passing is extended when the sheet passing distance exceeds a predetermined value and the number of sheets passing is exceeded. That is, the heat storage time of the fixing member until the first sheet of paper to be fed starts to enter the fixing nip is set longer than before. This eliminates the need to sharply raise the end temperature of the fixing belt, thereby lowering the temperature of the portion [a] and avoiding temperature instability, thereby reducing the temperature decrease width of the portion [b]. In addition, since the paper feed start is started (at timing t2 behind [b]) by avoiding the state of [b], the paper is passed in a state where the fixing belt temperature is high, and paper jam can be avoided. become able to.

The case where the sheet passing distance and the sheet passing number exceed the predetermined value is the case where the cumulative traveling distance of the fixing member (the fixing belt in the illustrated embodiment) or the cumulative sheet number of the recording medium exceeds the predetermined value. Do.

More specifically, the fixing device 20 controls the energization of the halogen heater 23 (heating source) based on the temperature detection means for detecting the temperature of the fixing belt 21 (fixing member) and the detected temperature. The control means, a sheet passing timing control means for determining the timing when the recording medium passes through the fixing nip, and a means for counting and recording the cumulative traveling distance of the fixing member or the accumulated number of sheets of the recording medium The timing control means determines the fixing member heat storage time (fixing member heating time by the heating source) until the first sheet of recording medium enters the fixing nip, and the cumulative traveling distance of the fixing member or The heat storage time is set to be longer than the time (the fixing member heat storage time until the predetermined value is reached) when the cumulative sheet number of the recording medium exceeds the predetermined value. .

Here, it is possible to use the control means of the image forming apparatus in which the fixing device 20 is mounted as the control means for controlling the above-mentioned energization, the sheet passing timing control means, the means for counting and recording, and the like.

As described above, in the present invention, it is possible to avoid sheet jamming in a region where driving torque increases due to temperature decrease of the fixing member over time, and it is possible to provide a stable fixing device.

In addition, since paper jam can be avoided even when the driving torque of the fixing belt increases with time, machine down can be suppressed and productivity can be maintained. Furthermore, the present invention can exhibit a particularly excellent effect in the configuration using a lubricating oil. In addition, in the configuration in which a lubricant holding member such as a sliding sheet is disposed between the nip forming member and the fixing member, a particularly excellent effect can be exhibited.

Finally, the configuration and operation of the image forming apparatus of FIG. 1 will be described. The image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided at the center of the apparatus main body. The image forming units 4Y, 4M, 4C and 4K contain developers of different colors of yellow (Y), magenta (M), cyan (C) and black (K) corresponding to color separation components of a color image. Other than the above, the configuration is the same.

Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photosensitive member 5 as a latent image carrier, a charging device 6 for charging the surface of the photosensitive member 5, and a surface of the photosensitive member 5. The developing device 7 that supplies toner, and a cleaning device 8 that cleans the surface of the photosensitive member 5 are provided. In FIG. 1, only the photosensitive member 5, the charging device 6, the developing device 7, and the cleaning device 8 provided in the black image forming unit 4K are denoted by reference numerals, and in the other image forming units 4Y, 4M, and 4C. The sign is omitted.

Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 for exposing the surface of the photosensitive member 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photosensitive member 5 with a laser beam based on image data.

The transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

The intermediate transfer belt 30 is an endless belt, and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is rotationally driven, the intermediate transfer belt 30 travels (rotates) in the direction indicated by the arrow in the drawing.

The four primary transfer rollers 31 respectively sandwich the intermediate transfer belt 30 with the respective photosensitive members 5 to form a primary transfer nip. Further, a power supply (not shown) is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) and / or an alternating voltage (AC) is applied to each primary transfer roller 31.

The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Further, similarly to the primary transfer roller 31, a power supply (not shown) is connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or an AC voltage (AC) is applied to the secondary transfer roller 36. It has become so.

The belt cleaning device 35 has a cleaning brush and a cleaning blade disposed to abut the intermediate transfer belt 30. A waste toner transfer hose (not shown) extended from the belt cleaning device 35 is connected to an inlet of a waste toner container (not shown).

In the upper part of the printer main body, a bottle storage portion 2 is provided, and four toner bottles 2Y, 2M, 2C, 2K containing toner for replenishment are detachably mounted in the bottle storage portion 2. Between the respective toner bottles 2Y, 2M, 2C, 2K and the respective developing devices 7 there is provided a supply path (not shown), and development is carried out from each toner bottle 2Y, 2M, 2C, 2K via this supply path. The toner is supplied to the device 7.

On the other hand, at the lower part of the printer main body, a sheet feeding tray 10 accommodating sheets P as a recording medium, a sheet feeding roller 11 for discharging the sheet P from the sheet feeding tray 10 and the like are provided. Here, the recording medium includes, in addition to the plain paper, thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, etc. Although not shown, a manual sheet feeding mechanism may be provided.

In the printer main body, a conveyance path R for discharging the sheet P from the sheet feed tray 10 through the secondary transfer nip and out of the apparatus is disposed. On the conveyance path R, on the upstream side of the position of the secondary transfer roller 36 in the sheet conveyance direction, a pair of registration rollers 12 as conveyance means for conveying the sheet P to the secondary transfer nip is disposed.

Further, a fixing device 20 for fixing the unfixed image transferred to the sheet P is disposed downstream of the position of the secondary transfer roller 36 in the sheet conveyance direction. Further, on the downstream side of the fixing device 20 in the sheet conveyance direction of the conveyance path R, a pair of sheet discharge rollers 13 for discharging the sheet to the outside of the apparatus is provided. Further, a sheet discharge tray 14 for stocking the sheets discharged to the outside of the apparatus is provided on the upper surface portion of the printer main body.

Subsequently, the basic operation of the printer according to the present embodiment will be described with reference to FIG. When the image forming operation is started, each photosensitive member 5 in each of the image forming units 4Y, 4M, 4C, 4K is rotationally driven clockwise by a driving device (not shown), and the surface of each photosensitive member 5 is charged. Is uniformly charged to a predetermined polarity. Laser light is irradiated from the exposure device 9 on the surface of each charged photosensitive member 5 to form an electrostatic latent image on the surface of each photosensitive member 5. At this time, the image information to be exposed on each photosensitive member 5 is monochrome image information obtained by decomposing a desired full color image into yellow, magenta, cyan and black color information. Thus, the electrostatic latent image is visualized (visualized) as a toner image by supplying toner to each electrostatic latent image formed on each photosensitive member 5 by each developing device 7 .

Further, when the image forming operation is started, the secondary transfer backup roller 32 is rotationally driven counterclockwise in the figure to cause the intermediate transfer belt 30 to run in the direction shown by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a reverse polarity to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed at the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

Thereafter, when the toner image of each color on the photosensitive member 5 reaches the primary transfer nip as the photosensitive member 5 rotates, the toner image on each photosensitive member 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photosensitive member 5 that can not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photosensitive member 5 is neutralized by a static elimination device (not shown) to initialize the surface potential.

At the lower part of the image forming apparatus, the sheet feeding roller 11 starts rotational driving, and the sheet P is fed from the sheet feeding tray 10 to the conveyance path R. The sheet P fed to the conveyance path R is timed by the registration roller 12 and is sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to that of the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, whereby a transfer electric field is formed in the secondary transfer nip.

Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 circulates, the toner image on the intermediate transfer belt 30 is generated by the transfer electric field formed in the nip. Are collectively transferred onto the sheet P. At this time, the residual toner on the intermediate transfer belt 30 which has not been transferred to the sheet P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container (not shown) and collected.

Thereafter, the sheet P is conveyed to the fixing device 20, and the toner image on the sheet P is fixed to the sheet P by the fixing device 20. Then, the sheet P is discharged to the outside of the apparatus by the sheet discharge roller 13 and is stocked on the sheet discharge tray 14.

The above description is an image forming operation for forming a full color image on a sheet, but one of four image forming units 4Y, 4M, 4C, and 4K is used to form a monochrome image, It is also possible to use two or three imaging units to form a two or three color image.

As mentioned above, although this invention was demonstrated based on the example of illustration, this invention is not limited to this, It can change suitably within the scope of the present invention. The basic configuration of the fixing device can adopt any configuration as long as the present invention is applicable.

Further, types and amounts of lubricants and lubricating oils, or materials and surface properties of sliding sheets, nip forming members, fixing belts, etc. may be used as long as the present invention can be practiced. The configuration of the image forming apparatus is also arbitrary, and the present invention is not limited to one using four color toners, but the present invention is applied to a full color machine using three color toners, a multicolor machine using two color toners, or a monochrome apparatus. can do. Of course, the image forming apparatus is not limited to a printer, and may be a copier, a facsimile, or a multifunction machine having a plurality of functions.

DESCRIPTION OF SYMBOLS 1 image forming apparatus 20 fixing device 21 fixing belt (fixing member) 22 pressure roller (pressing member) 23 halogen heater (heating source) 24 pad (nip forming member) 25 stay 26 holder (fixing member holding member) 28 sliding Sheet (lubricant holding member) 27 Side plate N Nip portion (fixing nip) P Paper (recording medium) T Toner

JP 2007-334205 A Japanese Patent Application Publication No. 2007-233011 JP, 2016-71302, A

Claims (8)

An endless fixing member, a heating source for heating the fixing member, a pressure member in contact with the fixing member, and the pressure member disposed in the fixing member and in contact with the pressure member via the fixing member And a nip forming member for forming a fixing nip, fixing the first recording medium to be started when the cumulative traveling distance of the fixing member or the cumulative number of sheets of the recording medium exceeds a predetermined value. A fixing device, wherein a fixing member heat storage time until entering a nip is set to be longer than a fixing member heat storage time until reaching the predetermined value. A temperature detection means for detecting the temperature of the fixing member, a control means for controlling energization of the heat source based on the detection result of the temperature detection means, and a sheet passing which determines the timing when the recording medium passes through the fixing nip. Timing control means; and means for counting and recording the cumulative travel distance of the fixing member or the cumulative number of sheets of recording media, and the sheet passing timing control means is configured to set the first recording medium for the first sheet to be passed. The fixing device according to claim 1, wherein the fixing member heat storage time until the toner enters the fixing nip is determined. A fixing member holding member configured to hold the fixing member at both ends; a pressing mechanism configured to press the pressing member against the nip forming member via the fixing member; and a rotation mechanism configured to rotate the pressing member. The fixing device according to claim 1, wherein the fixing device is provided. The fixing device according to any one of claims 1 to 3, wherein a lubricant is applied to the nip forming member. The fixing device according to any one of claims 1 to 4, wherein a lubricant holding member is disposed between the nip forming member and the fixing member. The fixing device according to claim 4, wherein the lubricant is silicone oil, silicone grease or fluorine grease. The fixing device according to claim 5, wherein the lubricant holding member is a cloth-like sheet in which fibers are woven. An image forming apparatus comprising the fixing device according to any one of claims 1 to 7.

Images