JP4272879B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly, to an image forming apparatus including a fixing device that heats a fixing member from the outside.
[0002]
[Prior art]
[Patent Document 1]
JP-A-9-54510 [Patent Document 2]
An electrophotographic image forming apparatus includes a fixing device for fixing an unfixed toner image transferred onto a recording medium. Conventionally, a heat roll type fixing device has been widely used as the fixing device.
[0003]
In a heat roll type fixing device, a pressure roller is pressed against a fixing roller having a heat source such as a halogen heater inside to form a nip, and a recording material is passed through the nip to fix an unfixed toner image. Since the fixing roller has a relatively large heat capacity, the rise time required to heat the fixing roller from room temperature to a set temperature becomes long.
[0004]
Therefore, a belt fixing method having advantages such as a wide nip width and a short rise time compared to the heat roll method has been proposed and put into practical use. Although the rise time can be considerably shortened in the belt fixing method, the conventional belt fixing device has a heat source for heating the fixing belt disposed in the loop of the belt. Because there is a loss of time. As a result, there is a problem that it takes time to recover from a temperature drop during paper feeding, which cannot cope with further shortening of the rise time.
[0005]
As a countermeasure, an external heating method has been proposed in which a heat source is arranged on the front side (outside) of a fixing member such as a fixing roller or a fixing belt, and the surface of the fixing member is directly heated. For example, Patent Document 1 discloses a heat fixing roller device including a surface heating device provided close to the outer peripheral surface of the heat roller. In this heat fixing roller device, the surface heating device is configured to heat the heat roller with electromagnetic waves radiated from the discharge tube.
[0006]
In the external heating method, only the surface layer of the fixing member that really needs to be heated is heated, so that the rise time is very fast, and the response from the temperature drop at the time of paper feeding is excellent.
[0007]
Incidentally, the fixing device has a problem of stably controlling the temperature of the fixing member. In the conventional fixing device, the surface temperature of the fixing member is detected by a temperature detection means such as a thermistor. When the detected temperature is lower than a predetermined temperature, the fixing heater is turned on, and when the detected temperature is higher than the predetermined temperature, the heater is turned off. The fixing member is controlled to a set temperature by ON / OFF control.
[0008]
In this ON / OFF control, in the case of a fixing roller or a belt fixing device having a heat source inside, the base and the elastic layer reach the set temperature because the substrate and the elastic layer reach the set temperature. Since the heat stored in the material and the elastic layer is transmitted to the surface layer, the temperature drop is gradual. Even when the heater is turned on, the temperature change is not abrupt because heat is transferred through the base material and the elastic layer.
[0009]
However, in the external heating method, only the surface of the fixing member having a small heat capacity is heated. Therefore, when the heater is turned on, it is heated to the set temperature or more at once, and when the heater is turned off, the temperature is lowered immediately. In the control, the fixing member could not be stably maintained at the set temperature. For this reason, there is a problem that the temperature of the fixing member is uneven, and partial fixing failure corresponding to the temperature unevenness, uneven gloss, and hot offset occur.
[0010]
[Problems to be solved by the invention]
However, Patent Document 1 does not specifically describe a method for stably controlling the temperature of the heat roller, and a temperature ripple of the fixing member may occur in the external heating type fixing device. There was a problem.
[0011]
In Patent Document 2, a power supply voltage obtained by rectifying a power supply AC with a rectifier is supplied to an inverter in which a switching element is connected in series to a load of a halogen heater or a halogen lamp, and the power control includes a PWM control unit and a phase control unit. What comprises an apparatus is disclosed. In this device, the PWM control unit and the phase control unit are switched in accordance with the pulse voltage of the rectifier. In addition, there are many applications for power control using a combination of a halogen heater and an inverter circuit. However, there are many applications where reduction of noise and inrush current during energization is a problem. There was a problem that the temperature ripple could not be reduced effectively.
[0012]
The present invention solves the above-described problems in the conventional external heating type fixing device, enables stable temperature control of the fixing member, has a short rise time, and has high heating efficiency, and an image forming apparatus having the same It is an issue to provide.
[0013]
[Means for Solving the Problems]
According to the present invention, there is provided a fixing member, a pressure member to which the fixing member is pressed, an external heating unit for heating the fixing member from the outside of the fixing member, and detecting the temperature of the fixing member. A temperature detection unit, and a power control unit that controls power supplied to the external heating unit based on a detection signal of the temperature detection unit, and records in a fixing nip formed by the pressure contact between the fixing member and the pressure member. In the fixing device for fixing the unfixed toner through the material, the external heating means includes a planar heating element disposed along an outer surface of the fixing member, and the planar heating element and the fixing member. An endless belt which can be rotated by being interposed therebetween, and a generator which is disposed in a loop of the endless belt and generates electric power by rotation of the belt, and is provided between the power control means and the external heating means. The power generation It is solved by Rukoto a switch means for closing the circuit by the power from.
[0014]
Further, in order to solve the above-mentioned problem, the present invention provides that the power control means rectifies commercial AC power using a rectifier circuit, and supplies the output of the rectifier circuit to the planar heating element via an inverter circuit. It is proposed to continuously change the power supplied to the planar heating element by driving the switching element of the inverter circuit by PWM control.
[0017]
In order to solve the above problems, the present invention is arranged such that the temperature detecting unit is not directly received by the heating unit, and the temperature detecting position of the fixing member by the temperature detecting unit is the position of the heating unit. It is proposed that it is set to a position that does not receive heat directly.
[0018]
In order to solve the above problems, the present invention proposes that the fixing member has a structure in which a heat insulating layer, a heat storage layer, and a release layer are sequentially laminated on a base material.
In order to solve the above problems, the present invention provides a recording material detection means for detecting that the recording material has passed through the nip, and the power is detected when the recording material detection means detects the passage of the recording material. It is proposed to control the power supplied to the heating element by the control means.
[0019]
In order to solve the above problems, the present invention proposes that the recording material detection means is a temperature detection means for detecting the temperature of the fixing member in the vicinity of the exit of the nip.
[0020]
Further, in order to solve the above problems, the present invention is configured as a member in which the fixing member rotates or rotates, and the power supply to the heating element is cut off when the rotation or rotation of the fixing member is stopped. Propose to be done.
[0021]
In addition, according to the present invention, the above problem is solved by an image forming apparatus comprising the fixing device according to any one of claims 1 to 7 .
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus equipped with an example of a fixing device according to the present invention. As the overall configuration and operation of the image forming apparatus will be described later, the fixing apparatus will be described first.
[0023]
FIG. 2 is a cross-sectional view showing the main configuration of the fixing device 10A according to the first embodiment. A fixing device 10A shown in this figure includes a fixing member 11 configured as a fixing roller, a pressure member 12 configured as a pressure roller, an external heating means 15, temperature detection elements 16, 17 and the like, which are not shown. Located in the fixing casing.
[0024]
In this example, the external heating unit 15 is configured as a heating unit that is not in contact with the fixing roller 11, and includes a radiation heater 13 and a reflection plate 14. The radiant heater 13 heats the fixing roller 11 from the outside by radiant heat. A reflector 14 is provided so that the radiant heat of the radiant heater 13 is reflected toward the fixing roller 11 side. A general halogen heater can be used as the radiant heater 13, but the life of the heater can be extended by using a carbon lamp heater mainly composed of carbon that is difficult to evaporate as a filament. The fixing roller 11 and the pressure roller 12 are pressed against each other to form a fixing nip. The fixing roller 11 is rotated clockwise in the drawing, and the pressure roller 12 is rotated counterclockwise in the drawing, and the recording paper P is passed through the fixing nip, thereby fixing the unfixed toner image on the recording paper on the paper.
[0025]
The fixing roller 11 and the pressure roller 12 are configured by laminating a heat insulating layer, a heat storage layer, and a release layer on a metal core. The heat insulating layer preferably includes an air layer, and a high heat insulating effect can be obtained by using a resin or elastomer foam, a hollow capsule or thread layered, or a resin or elastomer mixed therein. As the heat storage layer, a thin metal sleeve or solid elastomer can be used. However, when dealing with color images, it is necessary to improve the adhesion between the toner layer and the fixing roller. Is suitable. As the release layer, a tube or coating of a fluorine resin is generally used. By configuring the roller in this way, the heat supplied from the surface side is transferred to the release layer and heat storage layer, so that heat is not transferred to the heat insulation layer and the core metal, and the rise time is shortened. Can do.
[0026]
The temperature detection element 16 disposed in the vicinity of the entrance of the fixing nip is for detecting the temperature of the fixing roller 11, and for example, a contact type thermistor, a thermocouple, or a non-contact type infrared sensor can be used. When the temperature detecting element 16 directly receives the radiant heat of the external heating means 15, the temperature of the fixing roller 11 cannot be measured accurately. Therefore, the position becomes a blind spot from the external heating means 15 including the radiant heater 13 and the reflecting plate 14. Further, a temperature detection element 16 is provided.
[0027]
By the way, when the temperature of the fixing roller 11 is detected only by the temperature detecting element 16 arranged in the vicinity of the nip entrance, the fixing roller is rotated about one rotation to detect the temperature drop of the fixing roller 11 due to the recording material passing through the nip. A time lag occurs. In order to prevent fixing failure due to this time lag (due to heating delay), a detection element 17 for detecting the passage of the recording material is provided on the nip exit side in this example. In the case of this example, as the recording material passage detection means, a temperature detection element that detects the surface temperature of the fixing roller 11 is used, and the passage of the recording material is detected at the timing when the temperature of the fixing roller 11 decreases. Yes. Based on the temperature decrease timing and the decreased temperature value based on the detection signal of the recording material passage detection element 17, the power supplied to the radiant heater 13 by the power control circuit 30 (the amount of increase in power when the temperature decreases) is increased. Timing). In this example, since the temperature detection element is used as the recording material passage detection element 17, the recording material passage detection element 17 is also arranged at a position that becomes a blind spot from the external heating means 15.
[0028]
FIG. 3 is a block diagram schematically showing the configuration of the fixing device and its power control unit. As shown in this figure, a commercial AC power source 36 is rectified by a rectifier circuit 35, and the output is supplied to the heating element 13 of the external heating means via the switching element 32 of the inverter circuit 31. The inverter circuit 31 includes the switching element 32 and the PWM control circuit 33. The inverter circuit 31 receives signals from the temperature detection elements 16 and 17 (the temperature detection element 16 and the temperature detection element 17 as the recording material passage detection element) of the fixing device. Based on the PWM control of the switching element 32 by the control circuit 34, the power supplied to the radiation heater 13 can be continuously changed.
[0029]
In this embodiment, since the electric power supplied to the radiation heater 13 of the external heating means for heating the fixing member (fixing roller 11) from the outside is continuously changed, the fixing member is also used in the method of heating the fixing member from the outside. It is possible to prevent the temperature from rapidly becoming higher than the set temperature and to rapidly reduce the temperature, and to stably maintain the fixing member at the set temperature. For this reason, it is possible to prevent occurrence of partial fixing failure, gloss unevenness or hot offset due to temperature unevenness of the fixing member.
[0030]
FIG. 4 is a cross-sectional view showing the main configuration of the fixing device 10B of the second embodiment. The fixing device 10B shown in this figure is different from the fixing device 10A of the first embodiment in the configuration of the external heating means. Since the configuration other than this is the same, redundant description is omitted.
[0031]
As shown in FIG. 4, in the fixing device 10B of the second embodiment, a contact-type external heating device 20 is used for the fixing member as an external heating means for heating the fixing member (fixing roller 11) from the outside. The external heating device 20 includes a planar heating element 21, an endless belt (heating belt) 22, a generator 23, a relay 24, and the like.
[0032]
The planar heating element 21 is in contact with the fixing roller 11 via the heating belt 22 and heats the fixing roller 11 from the outside by heat conduction. The heating belt 22 is configured to rotate following the fixing roller 11, and a generator 23 disposed in the loop of the heating belt 22 generates power by the rotation of the belt 22. Further, the relay 24 is configured to be closed by the electromotive force generated by the generator 23 when the belt 22 rotates. When the relay 24 is open, power from the power control circuit 30 is not supplied to the planar heating element 21, and power is supplied to the planar heating element 21 only when the relay 24 is closed. ing. That is, in this embodiment, the heating element 21 of the external heating device is configured to generate heat only when the fixing roller 11 rotates (= when the heating belt 22 rotates). The generator 23 may generate power by rotating the shaft of the fixing roller 11 instead of the belt 22.
[0033]
Although the sheet heating element 21 can be provided so as to be in direct contact with the fixing roller 11, the heating belt 22 and the fixing roller 11 are brought into contact with the fixing roller 11 via the endless (loop-shaped) heating belt 22. Rotate each other to prevent wear of the fixing roller 11 (when the sheet heating element 21 is brought into direct contact with the fixing roller 11, the surface of the fixing roller 11 is rubbed by the fixed sheet heating element 21. ).
[0034]
FIG. 5 is a block diagram schematically showing the configuration of the fixing device and its power control unit in this embodiment. As shown in this figure, a relay 24 is arranged between the switching element 32 and the sheet heating element 21. When the rotation of the fixing roller 11 is stopped, no electromotive force is generated by the generator 23, and the relay 24 is opened. Thus, the energization to the sheet heating element 21 is interrupted.
[0035]
In the external heating method, if the heating element is energized while the rotation of the fixing roller is stopped, the fixing roller is locally heated and excessively heated in a few seconds. However, in this embodiment, the fixing roller 11 rotates as described above. Since the heating element 21 of the external heating device generates heat only when the fixing roller 11 stops rotating, the energization to the sheet heating element 21 can be reliably cut off.
[0036]
The non-contact type external heating device 15 of the first embodiment also has a configuration in which the power supply to the heater 13 is cut off when the fixing roller 11 stops, for example, fixing in the same manner as in the second embodiment. It is possible to provide a configuration in which the generator 23 generates power by the rotation of the roller 11 and closes the relay (when the rotation of the fixing roller 11 stops, the relay opens).
[0037]
FIG. 6 is a cross-sectional view showing the main configuration of the fixing device 10C of the third embodiment. The fixing device 10C shown in this figure is of the belt fixing type, and the same non-contact type external heating device 15 as the fixing device 10A of the first embodiment is used as the external heating means. A description of the same parts as those of the fixing device 10A of the first embodiment will be omitted, and different parts will be mainly described.
[0038]
As shown in FIG. 6, the fixing belt 26 is stretched between the fixing roller 11 and the heat insulating roller 25. A first external heating device 15 a is provided outside the loop of the fixing belt 26 so as to face the heat insulating roller 25. The second external heating device 15b is also provided outside the roller for the pressure roller 12 that is pressed against the fixing roller 11. The configurations of the fixing roller 11, the pressure roller 12, and the external heating device 15 are the same as those of the fixing device 10A of the first embodiment.
[0039]
In the fixing device of this embodiment, the fixing belt 26 is heated by the first external heating device 15a, and the pressure roller 12 is heated by the second external heating device 15b, so that the fixing belt 26 and the pressure roller 12 are pressed against each other. Then, the recording material P is passed through the fixing nip formed in this way to perform fixing. Although not shown, in this embodiment, temperature detection elements 16 and 17 (temperature detection element 16 and temperature detection element 17 as a recording material passage detection element) are provided near the entrance and exit of the fixing nip. is there.
[0040]
The first and second external heating devices 15a and 15b are controlled by a power control circuit 30 (see FIGS. 3 and 5) similar to that of the fixing devices of the first and second embodiments. The power supplied to the radiant heaters 13 and 13 of the external heating devices 15a and 15b can be continuously changed by PWM-controlling the switching element based on the above signal.
[0041]
In this embodiment, the contact-type external heating device 20 of the second embodiment can be used as the external heating device. Further, when the rotation of the fixing belt 26 and the pressure roller 12 is stopped, it is possible to provide a configuration for cutting off the power supply to the radiation heaters 13 of the first and second external heating devices 15a and 15b.
[0042]
Finally, as an example of an image forming apparatus in which the fixing device of each of the embodiments can be mounted, the schematic configuration and operation of the printer in FIG. 1 will be briefly described. In FIG. 1, it is assumed that the fixing device 10A of the first embodiment shown in FIG. 2 is provided.
[0043]
In FIG. 1, an image forming section centered on the photosensitive drum 1 is disposed at a substantially central portion of the printer main body. Around the photosensitive drum 1, a charging unit 2, a developing device 3, a transfer unit 4, a cleaning unit 5, and a charge eliminating unit 6 are disposed. A known optical writing device 8 is provided above the image forming unit. A paper feed cassette 9 is disposed below the image forming unit. Further, the fixing device 10 (10A) is disposed on the left side in the drawing of the image forming unit. A transfer belt 7 communicates between the transfer unit 4 and the fixing device 10. Instead of the fixing device 10A, the fixing devices of the second and third embodiments can be used.
[0044]
In the printer configured as described above, a signal for writing is sent from a host machine (not shown) such as a computer. The exposure device 8 is driven based on the received image signal, and the light from the laser light source of the exposure device is scanned by a polygon mirror that is rotationally driven by a motor, and is uniformly charged by the charging means 2 through the mirror and the like. The photosensitive drum 1 is irradiated to form a latent image corresponding to the writing information on the photosensitive member 1. The latent image formed on the photosensitive drum 1 is developed by the developing device 3 and is formed and held on the surface of the photosensitive drum 1 as a toner image.
[0045]
On the other hand, the uppermost sheet of the sheet bundle stored in the sheet feeding cassette 9 is fed by the sheet feeding roller 41, and is sent out by the registration roller 42 in timing with the toner image on the photosensitive drum 1.
[0046]
The toner image on the photosensitive drum 1 is transferred onto the paper by the transfer unit 4. The toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image is cleaned by the cleaning unit 5, and then the photosensitive drum 1 is discharged by the discharging unit 6 to prepare for the next image forming cycle.
[0047]
The paper after transfer of the toner image is sent to the fixing device 10 by the conveying belt 7 and the toner image is fixed on the paper by heat and pressure. The paper after the toner image is fixed is discharged onto the tray 44 by the paper discharge roller 43 and stacked.
[0048]
The present invention has been described with reference to the illustrated examples. However, the present invention is not limited to this, and appropriate modifications can be made within the scope of the present invention. For example, the configuration of the external heating means may be an appropriate configuration. In addition, a configuration in which the energization to the heating unit is interrupted when the fixing member is stopped is arbitrary. Of course, it goes without saying that the image forming apparatus may be a printer or facsimile other than a copying machine.
[0049]
【The invention's effect】
As described above, according to the fixing device and the image forming apparatus of the present invention, the switch means is closed only when the endless belt interposed between the sheet heating element and the fixing member rotates, and the external heating means is powered. Therefore, local heating of the fixing member is prevented, and excessive temperature rise can be prevented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus equipped with an example of a fixing device according to the present invention.
FIG. 2 is a cross-sectional view illustrating a main configuration of the fixing device according to the first embodiment.
FIG. 3 is a block diagram schematically illustrating a configuration of a fixing device and a power control unit in the embodiment.
FIG. 4 is a cross-sectional view illustrating a main configuration of a fixing device according to a second embodiment.
FIG. 5 is a block diagram schematically illustrating a configuration of a fixing device and a power control unit in the embodiment.
FIG. 6 is a cross-sectional view illustrating a main configuration of a fixing device according to a third embodiment.
[Explanation of symbols]
10 Fixing Device 11 Fixing Roller (Fixing Member)
12 Pressure roller (pressure member)
13 Radiation heater 14 Reflector 15 External heating means 16 Temperature detection element 17 Recording material passage detection element (temperature detection element)
20 External heating device 21 Planar heating element 22 Endless belt (heating belt)
23 Generator 24 Relay 25 Heat insulation roller 26 Fixing belt 30 Power control circuit 31 Inverter circuit 32 Switching element

Claims (8)

A fixing member, a pressure member to which the fixing member is pressed, an external heating unit for heating the fixing member from the outside of the fixing member, a temperature detecting unit for detecting the temperature of the fixing member, and the temperature detecting unit Power control means for controlling the power supplied to the external heating means based on the detection signal, and the recording material is passed through a fixing nip formed by the pressure contact between the fixing member and the pressure member, and unfixed toner is supplied. In a fixing device for fixing,
The external heating means includes a sheet heating element disposed along an outer surface of the fixing member, an endless belt that is rotatable between the sheet heating element and the fixing member, and the endless belt. A generator that is disposed in the loop of the belt and generates power by rotation of the belt,
A fixing device comprising: a switch unit that closes a circuit with electric power from the generator between the power control unit and the external heating unit . The power control means rectifies commercial AC power by a rectifier circuit, supplies the output of the rectifier circuit to the planar heating element via an inverter circuit, and drives the switching element of the inverter circuit by PWM control. The fixing device according to claim 1, wherein electric power supplied to the planar heating element is continuously changed. The temperature detection unit is disposed at a position where the heat of the heating unit is not directly received, and the temperature detection position of the fixing member by the temperature detection unit is set to a position where the heat of the heating unit is not directly received. The fixing device according to claim 1 or 2 .   The fixing device according to claim 1, wherein the fixing member has a configuration in which a heat insulating layer, a heat storage layer, and a release layer are sequentially laminated on a base material.   Recording material detection means for detecting that the recording material has passed through the nip is provided, and when the recording material detection means detects the passage of the recording material, the power control means controls the power supplied to the heating element. The fixing device according to claim 1, wherein: The fixing device according to claim 5 , wherein the recording material detection unit is a temperature detection unit configured to detect a temperature of the fixing member in the vicinity of an exit of the nip.   The power supply to the heating element is cut off when the fixing member is configured as a member that rotates or rotates, and the rotation or rotation of the fixing member is stopped. Fixing device. Characterized in that it comprises a fixing device according to any one of claims 1 to 7, an image forming apparatus.

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