JP2004054028A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device in which respective rollers are appropriately operated by eliminating a circumferential velocity difference between a fixing roller and a pressure roller. <P>SOLUTION: The fixing device 40 is provided with the fixing roller 41, a first heat roller 43 coming in press contact with the fixing roller 41 and having a halogen lamp inside, the pressure roller 42 coming in press contact with the fixing roller 41, a second heat roller 44 coming in press contact with the pressure roller 42 and having a halogen lamp inside, and a motor for driving the fixing roller 41 and the pressure roller 43. A one-way clutch gear 42f is arranged in the pressure roller 42. The outside diameter and the gear ratio of each roller are set so that the circumferential velocity of the pressure roller 42 is made lower than that of the fixing roller 41 and the rollers are gear-driven, and also, by allowing the pressure roller 42 to rotate more quickly than the one-way clutch gear, the pressure roller is driven following the fixing roller at the same velocity. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fixing device having a heating roller for externally heating a fixing roller and a pressure roller, and an image forming apparatus equipped with the fixing device.
[0002]
[Prior art]
2. Description of the Related Art In recent years, attention has been paid to energy saving in image forming apparatuses such as a PPC (Plain Paper Copier), a facsimile, a printer, and the like. One of the effective methods for saving energy of the fixing device is to shorten the warm-up time (the time required for the fixing roller or the like to rise to a predetermined temperature at which printing can be performed).
[0003]
For the purpose of shortening the warm-up time and reducing power consumption in the conventional heat roller fixing method, an external heating roller with a built-in heat source is pressed against the surface of the fixing roller or the pressure roller, and the fixing roller is pressed. And an external heat fixing system in which a pressure roller is heated from the surface. For example, Japanese Patent Application Laid-Open No. 4-116677 discloses a fixing roller 41 and a pressure roller 42 having no heating source therein, and a first heating roller which presses and heats the fixing roller 41 as shown in FIG. A fixing device is disclosed, which includes a fixing roller 43 and a second heating roller 44 that presses against and heats the pressure roller 42. As described above, the warm-up time is reduced by externally heating the fixing roller 41 and the pressure roller 42.
[0004]
The fixing roller 41 and the pressure roller 42 are provided with heat-resistant and heat-insulating elastic layers 41b and 42b such as silicon sponge around the metal cores 41a and 42a. For example, thin films 41d and 42d of a material in which rubber is filled with a high thermal conductive filler such as alumina or silica are provided, and PFA tube layers 41c and 42c are provided on the surface. Further, the first and second heating rollers 43 and 44 are constituted by metal rollers provided with heating elements 43b and 44b at the center.
[0005]
Therefore, the nip width formed between the fixing roller 41 and the pressure roller 42 is longer than when one of the metal rollers is used. Therefore, a large amount of heat can be given during paper passing. Further, since the fixing roller 41 and the pressure roller 42 are elastic bodies, there is an advantage that the unevenness of the toner 51 for forming an image can be easily followed. This is suitable for use in a color image forming apparatus having large irregularities due to a large amount of toner 51.
[0006]
[Problems to be solved by the invention]
In the above-described fixing apparatus disclosed in Japanese Patent Application Laid-Open No. 4-116677, the method of driving the four rollers includes a case where a heating roller is a driving roller and a case where a fixing roller (or a pressure roller) is a driving roller. Conceivable. When the heating roller is the driving roller, the fixing roller and the pressure roller that are in contact with the pressure roller are hard to follow, and a drive transmission unit is required. The advantage is that the heated roller in contact with the pressure roller can be sufficiently driven, and there is no need to separately provide a drive transmission means to the heated roller.
[0007]
However, when the fixing roller is used as a driving roller, the first heating roller 43 that is in pressure contact with the fixing roller can be sufficiently driven to rotate, but the pressure roller tends to slip, causing paper jams and image disturbance. There's a problem.
[0008]
Further, when the pressure roller is used as a drive roller, the second heating roller 44, which is in pressure contact with the pressure roller, can sufficiently rotate, but the fixing roller tends to slip, causing paper jams and image disturbance. There is a problem.
[0009]
It is possible to prevent both the fixing roller and the pressure roller from slipping by connecting the fixing roller and the pressure roller by gears fitted to each other and applying drive to one of the rollers. However, the fixing roller and the pressure roller have large thermal expansions, and their peripheral speeds are different between when they are cold and when they are heated.The rollers do not always stay at the same temperature during use. Then, a peripheral speed difference occurs between the fixing roller and the pressure roller. The load due to the peripheral speed difference may cause gear tooth skipping, abnormal noise, or drive damage, and it is desired to solve the problem.
[0010]
Furthermore, when the peripheral speed of the fixing roller and the pressure roller increases due to thermal expansion during heating, the paper transport speed passing through the fixing nip increases, and the paper transfer speed does not match the paper transport speed in the toner transfer unit. Causes disturbance.
[0011]
In view of the above problems, a first object of the present invention is to use a fixing roller and a pressure roller mainly composed of an elastic body and two external heating rollers mainly composed of metal in view of the above problems. In the fixing device and the fixing device using the same, the respective rollers are appropriately operated to prevent slip of the fixing roller and the pressure roller, and to prevent paper jam and image disorder. Further, a second object of the present invention is that even if the fixing roller and the pressure roller, which are mainly made of an elastic material, perform different thermal expansions at the time of heating, a load is generated due to a difference between the peripheral speeds of both rollers. , Abnormal noise and drive damage. Further, a third object of the present invention is to stabilize the paper transport speed passing through the fixing nip and synchronize with the paper transport speed in the upstream toner transfer unit to prevent image disturbance and stabilize the toner image. It is to plan.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a fixing roller, a first heating roller pressed against the fixing roller, a pressing roller pressed against the fixing roller, and a second heating roller pressed against the fixing roller. 2, a first gear mounted coaxially with the fixing roller, a second gear mounted coaxially with the pressure roller and fitted with the first gear, a pressure roller and a second gear. In a fixing device having a first one-way clutch interposed between gears, the first one-way clutch allows the pressure roller to rotate faster than the second gear, and also allows the rotation of the pressure roller to be faster than that of the second gear. Slow rotation of the pressure roller is prohibited, and the gear ratio of the first gear and the second gear is set so that the peripheral speed of the pressure roller does not exceed the peripheral speed of the fixing roller during cold and thermal expansion. It is characterized by being.
[0013]
According to the first aspect of the invention, the peripheral speed of the pressure roller is gear-driven lower than the peripheral speed of the fixing roller, and the first one-way clutch allows the pressure roller to rotate at a higher speed than the second gear. Therefore, the pressure roller can be driven to rotate by the fixing roller regardless of thermal expansion. As a result, the fixing roller rotates at substantially the same speed as the pressure roller, and the conveyance of the sheet is stabilized.
[0014]
Further, according to the present invention, a fixing roller, a first heating roller pressed against the fixing roller, a pressing roller pressed against the fixing roller, a second heating roller pressed against the pressing roller, A first gear mounted coaxially with the roller, a second gear mounted coaxially with the pressure roller and fitted with the first gear, and interposed between the fixing roller and the first gear; A fixing device including a second one-way clutch, wherein the second one-way clutch permits rotation of the fixing roller faster than the first gear and prohibits rotation of the fixing roller slower than the first gear; The gear ratio of the first gear and the second gear is set so that the peripheral speed of the fixing roller does not exceed the peripheral speed of the pressure roller at the time of cooling and thermal expansion.
[0015]
According to the second aspect of the invention, the peripheral speed of the fixing roller is not gear-driven faster than the peripheral speed of the pressure roller, and the second one-way clutch allows the fixing roller to rotate at a higher speed than the first gear. Since the fixing roller is permitted, the fixing roller can be driven and rotated regardless of the thermal expansion. As a result, the fixing roller rotates at substantially the same speed as the pressure roller, and the conveyance of the sheet is stabilized.
[0016]
According to a third aspect of the present invention, in the fixing device of the first or second aspect, a detecting unit for detecting a rotation speed of the first heating roller and the first gear or the second gear are driven. It is characterized by comprising a driving means and a control means for adjusting the rotation speed of the driving means when the rotation speed of the first heating roller is out of a predetermined range.
[0017]
According to a fourth aspect of the present invention, in the fixing device of the first or second aspect, a detecting unit for detecting the number of rotations of the second heating roller and the first gear or the second gear are driven. It is characterized by comprising a driving means and a control means for adjusting the rotation speed of the driving means when the rotation speed of the second heating roller is out of a predetermined range.
[0018]
According to the third and fourth aspects of the present invention, a change in the peripheral speed of the fixing roller and the pressure roller is detected based on the number of rotations of the heating roller, and the number of rotations of the driving means such as a motor is adjusted so as to cancel the change. , The peripheral speeds of the fixing roller and the pressure roller can be kept substantially constant. As a result, it is possible to stabilize the paper transport speed passing through the fixing nip, synchronize with the paper transport speed in the upstream toner transfer unit, prevent image disturbance, and stabilize the toner image.
[0019]
Further, an image forming apparatus according to the present invention includes the fixing device described above.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same components as those in FIG. 5 of the conventional example are denoted by the same reference numerals. FIG. 1 is a front view of a printer as an example of the image forming apparatus of the present invention. In FIG. 1, the housing of the cleaning device 18 is omitted. The printer 10 is a tandem-type full-color image forming apparatus. Inside the printer body housing 11, above the paper transport belt 12, from upstream to downstream in the transport direction (from right to left in FIG. 1). , Black, yellow, cyan, and magenta image forming units. Each image forming unit is provided with an amorphous silicon photosensitive drum 13 and a main charger 14, an LED exposing unit 15, a developing device 16, a transfer roller 17, and a cleaning device 18 around the photosensitive drum 13. I have.
[0021]
The cleaning device 18 includes a rubber cleaning roller 18a for adjusting the surface of the photoconductor drum 13, a discharge spiral 18b for discharging toner to a toner collection container (not shown), and a cleaning device for scraping off the toner on the photoconductor drum 13. And a blade 18c.
[0022]
The printer 10 also includes a paper feed mechanism 19 that feeds stored paper, a paper transport path 20 that transports paper from the paper feed mechanism 19, and drive rollers 21, 22, and 23 that drive the paper transport belt 12. A fixing device 40 for fixing an image formed by the image forming unit, a guide plate 24 for guiding a sheet from the sheet conveying belt 12 to the fixing device 40, a sheet conveying path 25 for conveying the sheet from the fixing device 40, The image forming apparatus includes a discharge unit 26 that discharges a sheet from the transport path 25 and toner supply containers 27M, 27C, 27Y, and 27B that supply toner to the respective developing devices 16.
[0023]
In the printer 10, the paper is transported from the paper feed mechanism 19 to the image forming unit via the paper transport path 20, and is transported by the transfer roller 17 while being transported between the photosensitive drum 13 and the paper transport belt 12. The positively-charged toner images of the respective colors on the surface of the photosensitive drums 13 are sequentially transferred to the paper side. The paper on which the toner has been transferred by all the photosensitive drums 13 is conveyed to a fixing device 40 where the toner is fixed, and a color image is formed. The sheet that has passed through the fixing device 40 is sent to the sheet transport path 25 and discharged to the discharge unit 26.
[0024]
FIG. 2 is an enlarged view of the vicinity of the fixing device 40 of FIG. The fixing roller 41 and the pressure roller 42 are pressed against each other to form a nip portion for fixing. A first heating roller 43 for externally heating the fixing roller 41 is in pressure contact with the fixing roller 41. Further, a second heating roller 44 for externally heating the pressure roller 42 is in pressure contact with the pressure roller 42. Further, the first heating roller 43 is provided with a tachometer 60 as a detecting means for detecting the number of revolutions, and the tachometer 60 is connected to a control unit 61 composed of a microcomputer or the like.
[0025]
The fixing roller 41 and the pressure roller 42 have the same structure, and are separated from iron cores 41a and 42a, and elastic layers 41b and 42b made of silicone rubber foam covering the surfaces of the cores 41a and 42a. PFA (tetrafluoroethylene-per-fluoroalkylvinyl ether copolymer) tube layers 41c and 42c that cover the surfaces of the elastic layers 41b and 42b to enhance the moldability. The elastic layers 41b and 42b preferably have an Asuka C hardness of 10 to 90 degrees, and more preferably have an Asuka C hardness of 25 degrees. At this time, the thickness of the elastic layers 41b and 42b is preferably 2 to 15 mm. The PFA tube layers 41c and 42c are not particularly limited as long as they have heat resistance and mold release properties. For example, PTFE (polytetrafluoroethylene), PVF (polyvinyl fluoride), and ECTFE (ethylene-chlorotrifluoroethylene) are used. Polymer) and the like. At this time, the thickness of the PFA tube layers 41c and 42c is preferably 20 to 100 μm.
[0026]
The first and second heating rollers 43 and 44 include roller bodies 43a and 44a made of aluminum and halogen lamps 43b and 44b inside the roller bodies 43a and 44a. The roller bodies 43a and 44a are not particularly limited as long as they are good heat conductors. For example, metals such as iron, nickel, and stainless steel can be used. At this time, the thickness of the roller main bodies 43a and 44a is preferably 0.2 to 2 mm. The halogen lamps 43b and 44b are not particularly limited as long as they are heating elements, and may be heating elements that can raise the surface temperatures of the fixing roller 41 and the pressure roller 42 to a maximum of about 220 ° C.
[0027]
In the present embodiment, the fixing roller 41 and the pressure roller 42 are driven by a motor (not shown) serving as a driving unit. Incidentally, both the fixing roller 41 and the pressure roller 42 may be driven by one motor, or the fixing roller 41 and the pressure roller 42 may be driven separately by using two motors. At this time, the first heating roller 43 is driven by the fixing roller 41, and the second heating roller 44 is driven by the pressure roller 42.
[0028]
Next, the role of the tachometer 60 will be described. The fixing roller 41 and the pressure roller 42 having the elastic layers 41b and 42b have a larger thermal expansion coefficient than the first and second heating rollers made of metal. Therefore, if the rotation speed of the motor that drives the fixing roller 41 and the pressure roller 42 is constant, the peripheral speed of the fixing roller 41 and the pressure roller 42 increases as the temperature increases, and the paper transport speed increases. As a result, sufficient heat and pressure are not applied to the image 51 at the time of fixing, and the fixing property is reduced.
[0029]
Therefore, the rotation speed of the first heating roller 43 detected by the tachometer 60 is given to the control unit 61, and the control unit 61 determines whether or not the rotation speed exceeds a rotation speed in a predetermined range set in advance. Judgment is made, and if it exceeds, control is performed so that the rotation speed of a motor (not shown) that drives the fixing roller 41 and the pressure roller 42 is reduced.
[0030]
As described above, by detecting an increase in the rotational speed of the first heating roller 43 having a small thermal expansion coefficient, that is, an approximately constant peripheral speed, an increase in the peripheral speed of the fixing roller 41 and the pressing roller 42 is estimated. Therefore, the peripheral speeds of the fixing roller 41 and the pressure roller 42 can be kept substantially constant by controlling the number of rotations of the motor. Therefore, sufficient heat and pressure can be applied to the image 51 at the time of fixing, and the fixing property can be maintained.
[0031]
Note that a tachometer 60 may be provided on the second heating roller 44. The type of the tachometer 60 is not particularly limited, and any of a non-contact type and a contact type can be used. For example, a light reflection type (stroboscopic type, photo reflector type, etc.), a method of providing a photo encoder, a magnetic head , A method using an AC generator, a method in which a rotating roller is brought into contact, and the like.
[0032]
FIG. 3 is a schematic side view of the fixing device 40, and FIG. 4 is a sectional view taken along line AA of FIG. In FIG. 3, for convenience of description, each roller is shown in a straight line. A fixing roller driving gear (first gear) 41f is provided on a fixing roller shaft 41e fixed to the fixing roller 41, and an input gear 70 for inputting driving from a motor meshes with the fixing roller driving gear 41f. A one-way clutch gear (in which the second gear and the first one-way clutch are integrated) 42f meshed with the fixing roller driving gear 41f is provided on the pressing roller shaft 42e fixed to the pressing roller 42. Is provided. Here, the outer diameter of the first and second heating rollers 43 and 44 is 25 mm, the outer diameter of the fixing roller 41 is 25 mm and the number of teeth is 23, the outer diameter of the pressure roller 42 is 24.5 mm and the one-way clutch gear 42f Can have 23 teeth. The outer diameter of the pressure roller 42 is not particularly limited as long as it is smaller than the outer diameter of the fixing roller 41, but it is necessary to maintain this relationship even during thermal expansion. When the outer diameter of the fixing roller 41 and the outer diameter of the pressing roller 42 are the same, the number of teeth of the pressing roller 42 is made larger than the number of teeth of the fixing roller 41, and the circumference of the pressing roller 42 is driven by a gear. The speed is set to be lower than the peripheral speed of the fixing roller 41, and the rotation speed of the pressure roller 42 is allowed to rotate faster than the one-way clutch gear so that the pressure roller can follow the fixing roller. I do.
[0033]
When the rotation of the pressure roller shaft 42e is relatively faster than the peripheral speed of the one-way clutch gear 42f, the drive from the one-way clutch gear 42f is not transmitted to the pressure roller shaft 42e and the one-way clutch gear 42f idles. Therefore, the pressure roller shaft 42e freely rotates. On the other hand, when the rotation of the pressure roller shaft 42f is relatively slower than the peripheral speed of the one-way clutch gear 42f, the drive from the one-way clutch gear 42f is transmitted to the pressure roller shaft 42e. Therefore, the pressure roller 42 rotates at the rotation speed of the one-way clutch gear 42f.
[0034]
In the normal driving state according to the present embodiment, since the outer diameter of the pressure roller 42 is smaller than that of the fixing roller 41, the number of rotations is larger than that of the fixing roller. On the other hand, since the one-way clutch gear 42f has the same number of teeth as the fixing roller 41, the number of rotations is the same. Therefore, as for the relationship between the pressure roller shaft 42e and the one-way clutch gear 42f, the rotation speed of the one-way clutch gear 42f is relatively reduced with respect to the pressure roller shaft 42e, and the one-way clutch gear 42f idles. As a result, the input gear 70 drives the fixing roller 41, and the fixing roller 41 drives the pressing roller 42 by the frictional force at the nip portion between the fixing roller 41 and the pressing roller 42.
[0035]
Further, when the slippage occurs between the fixing roller 41 and the pressure roller 42, the driving by the frictional force from the fixing roller 41 to the pressure roller 42 is stopped. At this time, the relationship between the pressure roller shaft 42e and the one-way clutch gear 42f is such that the rotation speed of the one-way clutch gear 42f becomes relatively large with respect to the pressure roller shaft 42e, and the drive from the one-way clutch gear 42f It is transmitted to the shaft 42e. Therefore, the pressure roller 42 rotates at the rotation speed of the one-way clutch gear 42f.
[0036]
As described above, even if the slippage occurs between the fixing roller 41 and the pressure roller 42 in the normal driving state, the pressure roller 42 rotates at substantially the same speed as the fixing roller 41, and the paper is conveyed. Stabilize.
[0037]
In the present embodiment, the one-way clutch gear 42f is used as the one-way clutch, but there is no particular limitation as long as it performs the same operation, and a belt or the like can be used in addition to the gear. In the above embodiment, the one-way clutch is provided on the pressure roller 42. However, the fixing roller 41 is provided with a one-way clutch gear (in which the first gear and the second one-way clutch are integrated). The same effect can be obtained even if the structures of the fixing roller 41 and the pressure roller 42 are reversed.
[0038]
Note that the image forming apparatus of the present invention can be widely used for PPC, facsimile, printer, and the like.
[0039]
【The invention's effect】
According to the present invention, a driving unit for driving the fixing roller and the pressure roller and a one-way clutch are provided on the pressure roller, and the peripheral speed of the pressure roller is gear-driven at a speed lower than the peripheral speed of the fixing roller. Because the first one-way clutch allows the pressure roller to rotate at a higher speed than the coaxial gear, the pressure roller can follow the fixing roller regardless of thermal expansion. As a result, the pressure roller rotates at substantially the same speed as the fixing roller, and the conveyance of the sheet is stabilized.
[0040]
Further, according to the present invention, a detecting unit for detecting the number of rotations of the first or second heating roller is provided, and the number of rotations of the driving unit is adjusted when the number of rotations is out of a predetermined range. Since the increase in the peripheral speed of the pressure roller can be estimated, the peripheral speeds of the fixing roller and the pressure roller can be kept substantially constant by controlling the rotation speed of the motor. Therefore, sufficient heat and pressure can be applied to the image at the time of fixing, and the fixing property can be maintained.
[Brief description of the drawings]
FIG. 1 is a front view of a printer as an example of an image forming apparatus of the present invention.
FIG. 2 is an enlarged view of the vicinity of the fixing device of FIG.
FIG. 3 is a schematic side view of the fixing device of the present invention.
FIG. 4 is a sectional view taken along line AA of FIG. 3;
FIG. 5 is a front view of the vicinity of a fixing device of a conventional printer.
[Explanation of symbols]
10 Printer (image forming device)
40 fixing device 41 fixing roller 41f fixing roller driving gear (first gear)
42 pressure roller 42f one-way clutch gear (integrated second gear and first one-way clutch)
43 first heating rollers 43b, 44b halogen lamp (heating element)
44 second heating roller 60 tachometer (detection means)
61 control unit (control means)

Claims (5)

A fixing roller,
A first heating roller pressed against the fixing roller;
A pressure roller pressed against the fixing roller,
A second heating roller pressed against the pressure roller,
A first gear mounted coaxially with the fixing roller;
A second gear mounted coaxially with the pressure roller and fitted with the first gear;
In a fixing device including a pressure roller and a first one-way clutch interposed between a second gear,
The first one-way clutch permits rotation of the pressure roller faster than the second gear, and inhibits rotation of the pressure roller slower than the second gear,
A fixing device wherein a gear ratio between a first gear and a second gear is set such that a peripheral speed of a pressure roller does not exceed a peripheral speed of a fixing roller at the time of cooling and thermal expansion. A fixing roller,
A first heating roller pressed against the fixing roller,
A pressure roller pressed against the fixing roller,
A second heating roller pressed against the pressure roller,
A first gear mounted coaxially with the fixing roller;
A second gear mounted coaxially with the pressure roller and fitted with the first gear;
A fixing device including a fixing roller and a second one-way clutch provided between the first gear;
The second one-way clutch allows rotation of the fixing roller faster than the first gear, and inhibits rotation of the fixing roller slower than the first gear,
A fixing device wherein a gear ratio of a first gear and a second gear is set such that the peripheral speed of the fixing roller does not exceed the peripheral speed of the pressure roller during cooling and thermal expansion. Detecting means for detecting the number of rotations of the first heating roller;
Driving means for driving the first gear or the second gear;
3. The fixing device according to claim 1, further comprising a control unit that adjusts the rotation speed of the driving unit when the rotation speed of the first heating roller is out of a predetermined range. Detecting means for detecting the number of rotations of the second heating roller;
Driving means for driving the first gear or the second gear;
The fixing device according to claim 1, further comprising a control unit configured to adjust a rotation speed of the driving unit when the rotation speed of the second heating roller is out of a predetermined range. An image forming apparatus comprising the fixing device according to claim 1.

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