JP4332274B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention, PaintingThe present invention relates to an image forming apparatus.
[0003]
[Prior art]
  An image heating and fixing apparatus as an image heating apparatus in an image forming apparatus such as an electrophotographic copying machine, a printer, and a fax machine will be described as an example. The image heating and fixing apparatus is undetermined that is formed directly or indirectly on the surface of a recording material using toner made of heat-meltable resin or the like by appropriate image forming process means such as electrophotography, electrostatic recording, and magnetic recording. Wear toner image on recording materialHardThis is a device for heat fixing processing as a received image.
[0004]
Conventionally, a heat roller type device has been widely used as an image heating device typified by a heat fixing device. This consists of a rotating roller pair of a fixing roller (heat roller) and a pressure roller that are heated and adjusted to a predetermined fixing temperature by incorporating a heat source such as a halogen lamp, and a pressure nip (fixing nip) of the roller pair. In this case, an unfixed toner image is heated and fixed on the surface of the recording material by introducing a recording material on which an unfixed toner image is formed and supported as a material to be heated and sandwiching and conveying the recording material.
[0005]
In addition to the heat roller type fixing device as described above, a contact heating type device such as a film heating type is also used. The apparatus of the film heating system has a heating body and a film whose one surface slides on the heating body and the other surface moves in contact with the recording material, and the heat of the heating body is recorded via the film. Is an apparatus that heats and fixes an unfixed toner image on a recording material surface.
[0006]
On the other hand, Japanese Utility Model Laid-Open No. 51-109737 discloses an induction heating fixing device (electromagnetic induction heating method, IHF method) that induces a current in a fixing roller by magnetic flux and generates heat by Joule heat. This makes it possible to directly heat the fixing roller by using the generation of the induced current, and achieves a fixing process that is more efficient than a heat roller using a halogen lamp.
[0007]
In addition, US Pat. No. 5,278,618 discloses an example in which a fixing film having a small heat capacity is used to heat a fixing roller by an exciting member in the vicinity of the nip.
[0008]
Further, a fixing device has been devised in which the heating efficiency of the fixing device is further improved by heating the fixing film outside the nip region by induction heating.
[0009]
[Problems to be solved by the invention]
However, in the conventional image heating apparatus using a halogen heater, a ceramic heater or the like as a heat source, there is a problem that heat is transferred to a film or a fixing roller, so that loss is large and energy cannot be effectively used.
[0010]
In the image heating apparatus disclosed in Japanese Utility Model Publication No. 51-109737, there is a problem that it takes a long time to raise the temperature to a temperature at which the image heating apparatus functions in order to heat the fixing roller having a large heat capacity. there were
Further, in the fixing device disclosed in US Pat. No. 5,278,618, it is necessary to supply a large current to the exciting member in order to heat the fixing film at the fixing nip portion. A decline was inevitable. In the case of a fixing device that requires a rubber layer or the like on the surface of the fixing film, in order to maintain the surface temperature by heating in the fixing nip region, the temperature of the interface between the rubber layer and the heating element is increased. There was a problem that the lifetime was significantly shortened.
[0011]
The fixing device for heating the fixing film outside the nip area can solve the problems of the fixing device, but the following problems occur.
[0012]
That is, the fixing film is generally rotationally driven by friction, and slip may occur when the driving frictional force decreases or the rotational torque of the fixing film increases. In the fixing device that heats the fixing film outside the nip region, there is a problem that when the slip occurs, the fixing film becomes an abnormally high temperature and the fixing film is damaged.
[0013]
  Therefore, the object of the present invention is toImprove fusing unit failure accuracy and suppress frequent operation errorsThere is.
[0014]
[Means for Solving the Problems]
  The present invention is characterized by the following means configuration.PaintingAn image forming apparatus.
[0015]
  An image forming unit for forming an image on a recording material;
  A cylindrical fixing film having a conductive layer; a film guide provided on the inner peripheral surface side of the fixing film for guiding rotation of the fixing film; and the surface of the film contacting the outer peripheral surface of the fixing film. A pressure roller that sandwiches the fixing film together with a guide and drives the fixing film by a frictional force acting between the surface of the fixing film and a region of the peripheral surface of the fixing film that the pressure roller contacts And an exciting coil that generates eddy currents in the conductive layer at a position upstream of the fixing film rotation direction to generate heat. The grease is applied between the fixing film and the film guide. A recording material utilizing heat generated in the conductive layer while nipping and conveying the recording material carrying an image between the fixing film and the pressure roller. A fixing unit for fixing the image,
  In an image forming apparatus having
  A rotation detecting means for detecting the rotation of the fixing film; and a safety device for determining whether or not the fixing means is out of order;A temperature detecting element for detecting the temperature of the fixing film;And when the rotation of the fixing film is detected by the rotation detection unit after the pressure roller is started to be driven by the driving unit in the image formation standby state, power supply to the excitation coil is started. The safety device determines that the fixing film has not started rotating by the rotation detecting means, andBased on the detection temperature of the temperature detection elementWhen it is determined that the grease is below a predetermined determination temperature for ensuring lubricity, rotation detection of the fixing film is continued without determining that the fixing unit has failed, and rotation of the fixing film is started by the rotation detection unit. An image forming apparatus comprising: determining that the fixing unit has failed when it is determined that the grease is higher than the determination temperature.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment (FIGS. 1 to 9)
(1) Image forming apparatus
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present exemplary embodiment. The image forming apparatus of this example is a four-color image forming apparatus (electrophotographic full-color printer) having a maximum sheet passing width of A4 size paper and a printing speed of four sheets per minute.
[0040]
Reference numeral 11 denotes an electrophotographic photosensitive drum (an image carrier, hereinafter referred to as a photosensitive drum) made of an organic photosensitive member, which is rotationally driven at a predetermined process speed (circumferential speed) in the clockwise direction of an arrow.
[0041]
The photosensitive drum 11 is subjected to a uniform charging process with a predetermined polarity and potential by a charging device 12 such as a charging roller during the rotation process.
[0042]
Next, the charged surface is subjected to scanning exposure processing of target image information by laser light L output from a laser optical box (laser scanner) 13. The laser optical box 13 outputs a laser beam L modulated (on / off) in accordance with a time-series electric digital pixel signal of target image information from an image signal generator such as a computer (not shown) to output the photosensitive drum surface. In this scanning exposure, an electrostatic latent image corresponding to target image information scanned and exposed on the surface of the photosensitive drum 11 is formed by this scanning exposure. A mirror 13 a reflects the output laser beam from the laser optical box 13 to the exposure position of the photosensitive drum 11.
[0043]
In the case of full-color image formation, scanning exposure and latent image formation are performed on a first color separation component image of a target full-color image, for example, a yellow component image, and the latent image is a yellow developing unit of the four-color developing device 14. 14Y is developed as a yellow toner image.
[0044]
The yellow toner image is transferred onto the surface of the intermediate transfer drum 16 at the primary transfer portion T1 which is a contact portion (or proximity portion) between the photosensitive drum 11 and the intermediate transfer drum 16.
[0045]
The surface of the photosensitive drum 11 after the transfer of the toner image to the surface of the intermediate transfer drum 16 is cleaned by the cleaner 17 after removal of adhered residues such as transfer residual toner.
[0046]
The process cycle of charging, scanning exposure, development, primary transfer, and cleaning as described above is performed when the target full-color image is second (for example, magenta component image, magenta developing unit 14M is activated), and third (for example, cyan component image, Cyan developing unit 14C is operated) and fourth (for example, black component image, black developing unit 14BK is operated) color separation component images are sequentially executed, and a yellow toner image, a magenta toner image, cyan on the surface of intermediate transfer drum 16 The four color toner images, a toner image and a black toner image, are sequentially superimposed and transferred to form a color image corresponding to the target full-color image.
[0047]
The intermediate transfer drum 16 has a middle-resistance elastic layer and a high-resistance surface layer on a metal drum. The intermediate transfer drum 16 is in contact with or close to the photosensitive drum 11 at the same peripheral speed as that of the photosensitive drum 11. The toner image on the side of the photoconductor drum 11 is transferred to the surface of the intermediate transfer drum 16 by a potential difference from the photoconductor drum 11 by applying a bias potential to the metal drum.
[0048]
The color toner image synthesized on the surface of the intermediate transfer drum 16 is not shown on the secondary transfer portion T2 in the secondary transfer portion T2 which is a contact nip portion between the intermediate transfer drum 16 and the transfer roller 15. Are transferred onto the surface of the recording material (transfer material) P sent out from the paper feeding unit at a predetermined timing.
[0049]
The transfer roller 15 supplies a charge having a polarity opposite to that of the toner from the back surface of the recording material P, thereby sequentially transferring the combined color toner images sequentially from the surface of the intermediate transfer drum 16 to the recording material P side.
[0050]
The recording material P that has passed through the secondary transfer portion T2 is separated from the surface of the intermediate transfer drum 16 and introduced into a heat fixing device 10 that is an image heating device, and undergoes a heat fixing process for an unfixed toner image to form a color image. The formed product is discharged to a discharge tray (not shown) outside the apparatus. The fixing device 10 will be described in detail in the next section (2).
[0051]
The intermediate transfer drum 16 after the color toner image has been transferred to the recording material P is cleaned by the cleaner 18 after removal of adhering residues such as transfer residual toner and paper dust.
[0052]
The cleaner 18 is always held in a non-contact state with the intermediate transfer drum 16, and is brought into contact with the intermediate transfer drum 16 during the secondary transfer of the color toner image from the intermediate transfer drum 16 to the recording material P. Retained.
[0053]
In addition, the transfer roller 15 is always held in a non-contact state with the intermediate transfer drum 16 and is in contact with the intermediate transfer drum 16 during the secondary transfer of the color toner image from the intermediate transfer drum 16 to the recording material P. Kept in a state.
[0054]
(2) Fixing device 10
A) Overall schematic configuration of the fixing device
FIG. 2 is a schematic cross-sectional view of the fixing device 10 according to the present embodiment, and FIG.
[0055]
The fixing device 10 of this embodiment is a pressure roller driving type (pressure member driving type) and electromagnetic induction heating type image heating apparatus using a cylindrical electromagnetic induction heat generating film.
[0056]
Reference numeral 1 denotes a cylindrical curvature variable (flexible) electromagnetic induction heat generating film (hereinafter referred to as a fixing film) as a rotary heating member. The layer structure of the fixing film 1 will be described in detail in section B).
[0057]
Reference numeral 105 denotes a cylindrical film guide, which is an insulating member that does not hinder the passage of magnetic flux. The cylindrical fixing film is loosely fitted on the film guide 105.
[0058]
Reference numerals 201 and 202 denote exciting coils and ferrite cores as heating means (magnetic field generating means) for electromagnetically heating the fixing film 1. The exciting coil 201 and the ferrite core 202 are disposed on the right half side of the inner space of the cylindrical film guide 105. The heating means 201 and 202 will be described in detail in section C).
[0059]
Reference numeral 3 denotes a pressure roller as a rotary pressure member, which is a heat-resistant / elastic roller in which a core metal 301 is covered with 2 mm of silicone rubber 302 to give elasticity.
[0060]
The pressure roller 3 is arranged such that both end portions of the core metal 301 are rotatably supported by bearings between chassis side metal plates (not shown) of the apparatus. A film guide member 105 having the fixing film 1 fitted thereon is disposed on the upper side of the pressure roller 3, and is disposed at both ends of the pressure rigid stay 4 inserted through the film guide and a spring receiving member on the apparatus chassis side. A pressing force is applied to the pressurizing rigid stay 4 by contracting a pressurizing spring (not shown) between each press (not shown). As a result, the lower surface of the film guide 105 and the upper surface of the pressure roller 3 are pressed against each other with the fixing film 1 interposed therebetween to form a nip (fixing nip portion) N having a predetermined width.
[0061]
The pressure roller 3 is rotationally driven in the counterclockwise direction indicated by the arrow by the driving means M. By the rotational driving of the pressure roller 3, a rotational force acts on the fixing film 1 by the frictional force between the pressure roller 3 and the outer surface of the fixing film 1 at the nip N, and the inner peripheral surface of the fixing film 1 is the film at the nip N. While rotating in close contact with the lower surface of the guide 105, the outer periphery of the film guide 05 is rotated in the clockwise direction indicated by the arrow at a peripheral speed substantially corresponding to the peripheral speed of the pressure roller 3 (pressure roller drive system). The film guide 105 supports the exciting coil 201 and the ferrite core 202 and also serves to improve the conveyance stability of the rotating fixing film 1. In order to rotate the fixing film 1 smoothly, heat resistant grease is generally applied to the inner surface of the fixing film 1.
[0062]
Thus, the pressure roller 3 is rotationally driven, and the fixing film 1 is rotated accordingly, and the fixing as a rotary heating member is performed by the action of a magnetic field generated by power supply from the excitation circuit 601 (FIG. 3) to the excitation coil 201. The film 1 generates heat by electromagnetic induction. In FIG. 2, F represents a part of the generated alternating magnetic flux.
[0063]
Reference numeral 5 denotes an NTC element as a temperature detection element that is fixedly disposed on the outer surface of the film guide 105 at a position near the nip N on the downstream side of the nip N in the rotation direction of the fixing film 1. The NTC element 5 is in contact with the back surface of the rotating fixing film 1, converts the temperature of the fixing film 1 into a voltage, and transmits it to a control circuit (microcomputer) 603. A rectangular wave generation circuit 602 controls the switching element in the excitation circuit 601 by changing the duty ratio of the rectangular wave depending on information from the control circuit 603.
[0064]
That is, the temperature of the nip N or the temperature of the fixing film 1 is a predetermined temperature by the temperature control systems 603, 602, and 601 including the NTC element (Negative Temperature Coefficient) 5 described above, and in this embodiment, the fixing film 1 is the fixing temperature. In a state where the temperature control is performed at 180 ° C., the recording material P on which the unfixed toner image T conveyed from the image forming unit is formed has an image surface between the fixing film 1 and the pressure roller 3 in the nip N. It is introduced upward, that is, opposite to the fixing film surface, and in the nip N, the image surface is brought into close contact with the outer surface of the fixing film 1 and is nipped and conveyed together with the fixing film 1. In the process in which the recording material P is nipped and conveyed through the nip N together with the fixing film 1, the fixing film 1 is heated by electromagnetic induction heat and the unfixed toner image T on the recording material P is heated and fixed.
[0065]
  When the recording material P passes through the nip N, it is separated from the outer surface of the rotary fixing film 1 and is discharged and conveyed. The heat-fixed toner image on the recording material P is cooled after passing through the nip N.HardIt becomes an image.
[0066]
Reference numeral 5B denotes an optical sensor as rotation detecting means for detecting the rotation operation of the fixing film 1. This will be described in detail in section D).
[0067]
B) Fixing film 1
FIG. 4 is a model diagram of the layer structure of the fixing film 1 in this embodiment.
[0068]
The fixing film 1 of this example includes a heat generating layer 101 made of a resistor such as a metal film as a base layer of an electromagnetic induction heat generating fixing film, an elastic layer 102 laminated on the outer surface, and a release layer laminated on the outer surface. This is a composite structure of the mold layer 103.
[0069]
For adhesion between the heat generating layer 101 and the elastic layer 102 and adhesion between the elastic layer 102 and the release layer 103, a primer layer may be provided between the respective layers.
[0070]
In the fixing film 1 having a cylindrical shape, the heat generating layer 101 is on the inner surface side, and the release layer 103 is on the outer surface side. When the alternating magnetic flux acts on the heat generating layer 101, an eddy current is generated in the heat generating layer 101, and the heat generating layer 101 generates heat. The heat generated by induction in this layer heats the entire fixing film 1 through the elastic layer 102 and the release layer 103, and heats the recording material P that is passed through the nip N to heat and fix the toner image T. .
[0071]
a. Heat generation layer 101
The heat generating layer 101 is, for example, a nickel layer having a thickness of 50 μm. 10 besides nickel^-Five-10^-Ten Any metal, metal compound, or organic conductor that is a good electrical conductor of Ω · m may be used. More preferably, a metal such as iron or cobalt or a compound thereof exhibiting ferromagnetism with high magnetic permeability can be used.
[0072]
If the thickness of the heat generating layer 101 is reduced, a sufficient magnetic path cannot be secured, the magnetic flux leaks to the outside and the heat generation energy of the heat generating layer itself may be reduced, and if the thickness is increased, the heat capacity increases and the time required for temperature increase becomes longer. Tend to be. Therefore, the thickness of the heat generating layer 101 has an appropriate value depending on the specific heat, density, magnetic permeability, and resistivity of the material used for the heat generating layer. In this example, a temperature increase rate of 3 ° C./sec or more could be obtained in a thickness range of 10 to 100 μm.
[0073]
b. Elastic layer 102
The elastic layer 102 is made of silicone rubber, fluorine rubber, fluorosilicone rubber, or the like, and is a material having good heat resistance and thermal conductivity.
[0074]
The thickness of the elastic layer 102 is preferably 10 to 500 μm. The elastic layer 102 has a thickness necessary for assuring the fixed image quality.
[0075]
When a color image is printed, a solid image is formed over a large area on the recording material P, particularly in a photographic image. In this case, if the heating surface (release layer 103) cannot follow the unevenness of the recording material P or the unevenness of the toner layer T, heating unevenness occurs, and gloss unevenness occurs in the image where the heat transfer amount is large and small. A portion with a large amount of heat transfer has a high glossiness, and a portion with a small amount of heat transfer has a low glossiness.
[0076]
If the thickness of the elastic layer 102 is 10 μm or less, the unevenness of the recording material or the toner layer cannot follow and unevenness of image gloss occurs. On the other hand, when the elastic layer 102 is 1000 μm or more, the thermal resistance of the elastic layer increases and it is difficult to realize a quick start. More preferably, the thickness of the elastic layer 2 is 50 to 500 μm.
[0077]
If the hardness of the elastic layer 102 is too high, the unevenness of the recording material P or the toner layer T cannot be fully followed and unevenness in image gloss will occur. Therefore, the hardness of the elastic layer 102 is 60 ° (JIS-A: JIS-KA type tester) or less, more preferably 45 ° or less.
[0078]
Regarding the thermal conductivity of the elastic layer 102, 6 × 10^-Four~ 2x10^-3[Cal / cm ・ sec ・ deg_.] Is good. Thermal conductivity λ is 6 × 10^-Four[Cal / cm ・ sec ・ deg_.], The thermal resistance is large, and the temperature rise in the surface layer (release layer 103) of the fixing film 1 is delayed. Thermal conductivity λ is 2 × 10^-3[Cal / cm ・ sec ・ deg_.], The hardness becomes too high or the compression set deteriorates. Therefore, the thermal conductivity λ is 6 × 10.^-Four~ 2x10^-3[Cal / cm ・ sec ・ deg_.] Is good. More preferably 8 × 10^-Four~ 1.5 × 10^-3[Cal / cm ・ sec ・ deg_.] Is good.
[0079]
c. Release layer 103
As the release layer 103, in addition to fluorine resins such as PFA, PTFE, and FEP, a material having good release properties and heat resistance such as silicone resin, silicone rubber, and fluorine rubber can be selected.
[0080]
The thickness of the release layer 103 is preferably 20 to 100 μm. If the thickness is less than 20 μm, there arises a problem that a poorly releasable part is formed due to coating unevenness of the coating film or the durability is insufficient. Further, when the release layer exceeds 100 μm, there arises a problem that heat conduction is deteriorated. In particular, in the case of a resin release layer, the hardness becomes too high and the effect of the elastic layer 102 is lost.
[0081]
d. Thermal insulation layer 104
Further, as shown in FIG. 5, in the configuration of the fixing film 1, a heat insulating layer 104 may be provided on the free surface side of the heat generating layer 101 (the surface opposite to the elastic layer 102 side of the heat generating layer 101).
[0082]
The heat insulating layer 104 is preferably a heat resistant resin such as a fluororesin, a polyimide resin, a polyamide resin, a polyamideimide resin, a PEEK resin, a PES resin, a PPS resin, a PFA resin, a PTFE resin, or an FEP resin.
[0083]
Moreover, as thickness of the heat insulation layer 104, 10-1000 micrometers is preferable. When the thickness of the heat insulation layer 104 is smaller than 10 μm, the heat insulation effect cannot be obtained and the durability is insufficient. On the other hand, if it exceeds 1000 μm, the distance from the high permeability core 202 and the exciting coil 201 to the heat generating layer 101 increases, and the magnetic flux is not sufficiently absorbed by the heat generating layer 101.
[0084]
In the case where the heat insulating layer 104 is provided, since the temperature of the exciting coil 201 can be prevented from being increased by the heat generated in the heat generating layer 101, stable heating can be performed.
[0085]
C) Heating means (magnetic field generating means) 201 and 202
The exciting coil 201 for generating the alternating magnetic flux must generate an alternating magnetic flux sufficient for heating. For this purpose, it is necessary to make the resistance component low and the inductance component high. In this embodiment, a ferrite core 202 is used as the core wire of the exciting coil 201 by using a high frequency wire having a bundle wire diameter φ2 of 3 mm by bundling a thin wire having a heat resistant insulation coating on a copper wire having a wire diameter φ1 of 0.2 mm. It is wound 10 times so as to go around.
[0086]
The ferrite core 202 is a high magnetic permeability magnetic member for efficiently guiding the magnetic flux generated by the exciting coil 201 to the fixing film 1. Ferrite core 202 is M_xZ_n1-xFe₂ O_Four A metal oxide having the composition described above is added with a small amount of an additive, and has a characteristic that it exhibits a very high specific resistance as compared with other high magnetic permeability materials and has a small loss due to eddy current. In general, when the metal element M, the composition x, and the additive are different, the magnetic permeability, the Curie temperature, the holding power, etc. representing the performance of the ferrite are different. In this example, a material having a relative permeability of 2500 and a Curie temperature of 205 ° C. (Tokin 2500B) is used.
[0087]
The exciting coil 201 generates an alternating magnetic flux by the alternating current supplied from the exciting circuit 601, and the alternating magnetic flux generates an eddy current in the heat generating layer 101 of the fixing film 1. This eddy current generates Joule heat (eddy current loss) due to the specific resistance of the heat generating layer 101, and the recording material P and the toner on the recording material conveyed to the nip N through the elastic layer 102 and the release layer 103. T can be heated. As shown in FIG. 2, the heat generation areas H and H are obtained centering on the portion facing the exciting coil 201, and in this configuration, the fixing film 1 is heated outside the nip N area.
[0088]
FIG. 6 schematically shows how the alternating magnetic flux is generated. F represents a part of the generated alternating magnetic flux. The alternating magnetic flux F guided to the ferrite core 202 generates an eddy current in the electromagnetic induction heat generating layer 101 of the fixing film 1 to generate Joule heat. The calorific value Q here is determined by the density of the magnetic flux passing through the heat generating layer 101 and shows a distribution as shown in the graph of FIG. In the graph of FIG. 6, the vertical axis indicates the circumferential position in the fixing film 1 represented by an angle x where the center of the ferrite core 202 is 0, and the horizontal axis indicates the amount of heat generated Q in the heat generating layer 101 of the fixing film 1. Indicates. Here, when the maximum heat generation amount is Q, the heat generation region H is defined as a region where the heat generation amount is Q / e or more. This is a region where the amount of heat generated for fixing can be obtained.
[0089]
D) Device control
a. Temperature control
Since the heat energy generated in the heat generating layer 101 of the fixing film 1 is proportional to the square of the magnitude of the eddy current, and the magnitude of the eddy current is proportional to the energy of the alternating magnetic flux, excitation is required when the temperature of the fixing film 1 is increased. If the magnetic field energy to the coil 201 is increased and the temperature is decreased, the magnetic field energy may be decreased.
[0090]
The magnetic field energy may be increased or decreased by adjusting the voltage applied to the exciting coil 201 or by adjusting the current. When using a normal power line, it is considered as a constant voltage source. Therefore, it is preferable to adjust the current flowing through the exciting coil 201 in order to configure the circuit at a low cost.
[0091]
When these electromagnetic circuits are considered in a range satisfying the resonance condition, the above-described current increase / decrease can be controlled by the length of application time of the voltage applied to the exciting coil 201. That is, the temperature of the fixing film 1 can be changed by switching in synchronization with the vibration period of the magnetic field in the electromagnetic circuit and changing the voltage application time a and the release time b shown in FIG. In this example, the release time b is fixed to 6 ms, and the voltage application time a can be controlled between 1 to 15 ms. Therefore, in this example, the alternating voltage supplied to the exciting coil 201 has a frequency with the sum of the voltage application time a and the release time b as one cycle, and is variable control of about 47 to 143 KHz.
[0092]
The control circuit (microcomputer) 603 samples the temperature of the fixing film 1 obtained from the NTC element 5 at a constant period, calculates the voltage application time a for this information, and outputs it from the rectangular wave generation circuit 602. As a method of calculating the voltage application time a, when the difference between the appropriate temperature (fixing temperature) enabling image heating and the sampled temperature is Δk−2, Δk−1, Δk in time order, For the previous voltage application time ak
(1). β △ k ・ ・ ・ ・ ・ Proportional controlled variable
(2). γ (Δk-1−Δk) ... Differential control amount
(3). δ (Δk−2 + Δk−1 + Δk)... integral control amount
So-called PID control (Proportional Integral Differential) that determines the current application time a by adding and subtracting is used. By appropriately setting β, γ, and δ in this control, for example, when the temperature of the fixing film 1 is low, the proportional control amount is increased, the application time a is lengthened, and the system is cooled. When the temperature of the fixing film 1 is not easily raised by other members, even if the temperature is approaching the fixing temperature, the differential control amount is increased and the application time a can be set longer.
[0093]
b. Control by optical sensor 5B
Next, detection of rotation and stop of the fixing film 1 by the optical sensor 5B serving as rotation detection means of the fixing film 1 and power supply control will be described with reference to FIGS.
[0094]
As shown in FIG. 8, detection marks C for rotation detection arranged in a circumferentially different color and at equal intervals are provided on the outer peripheral surface on one end side of the cylindrical fixing film 1. . The optical sensor 5B is disposed at a position corresponding to the detection mark C of the fixing film.
[0095]
The optical sensor 5 </ b> B includes a light emitting element 51 and a light receiving element 52, and the light emitted from the light emitting element 51 is reflected by the fixing film 1 and is detected by the light receiving element 52. The detection marks C provided on the fixing film 1 are arranged in white 3 mm square and equally spaced (about 3 mm), and the intensity of the reflected light periodically changes due to the rotation of the fixing film 1. The sensor 5B converts this into an electrical signal and outputs it to the control circuit 603.
[0096]
In the present embodiment, this period is compared with a predetermined value, and if it is longer, it is determined that the fixing film 1 is stopped, and power supply from the excitation circuit 601 to the excitation coil 201 is stopped. Such rotation detection of the fixing film 1 is started together with the driving of the pressure roller 3 as shown in the control flowchart of FIG. 9, and is constantly monitored during the operation of the apparatus.
[0097]
In the present embodiment, when the detected cycle becomes shorter than a predetermined value, the power supply to the exciting coil 201 is resumed. As a result, the temperature of the fixing film 1 can be raised so that the fixing operation can be performed.
[0098]
The fixing film 1 is frictionally driven by the pressure roller 3, and particularly when the fixing device 10 is not warmed, the lubricity of the grease applied to the inner surface of the fixing film 1 is lowered and the above-described slip is likely to occur.
[0099]
In the conventional image heating apparatus and image forming apparatus, it is general that an excessive temperature rise of the fixing film 1 due to the slip is detected by a safety device (not shown) and handled as an apparatus failure, and an image having on-demand characteristics. In the heating device, since the fixing device 10 is cooled to near room temperature during standby, there is a high possibility that the device failure will occur.
[0100]
According to this example, the temperature at which grease lubricity is ensured is provided as the determination temperature (FIG. 9), and when it is equal to or lower than this determination temperature, the image forming operation is continued without causing an apparatus failure even when the slip occurs. Thus, high reliability can be ensured.
[0101]
Although the fixing device 10 of this example is interposed through the elastic layer 102 and the release layer 103, its thermal resistance is smaller than that of a heat roller type fixing device including a halogen heater, and the heat of the heating element is directly applied. Even when a full-color image with a large amount of toner is consumed in the above-described configuration, the toner image can be sufficiently melted and a high-quality image forming apparatus can be obtained. Further, since the heat capacity of the fixing device is small, on-demand fixing is possible, and power consumption during standby can be significantly reduced.
[0102]
Second Embodiment (FIGS. 10 and 11)
This embodiment uses a speed detection roller 5C and an encoder 5D as shown in FIG. 10 in place of the optical sensor 5B as the rotation detection means of the fixing film 1 in the fixing device configuration of the first embodiment described above. Then, the rotation speed of the fixing film 1 is detected, and power supply control to the exciting coil 201 is performed.
[0103]
The speed detection roller 5C is a driven roller whose surface is coated with silicone rubber, and is in contact with the non-image area on the surface of the fixing film 1. The encoder 5D coaxial with this roller 5C accurately detects the rotational speed of the speed detection roller 5C. it can. Detection information of the encoder 5D is input to the control circuit 603 (FIG. 3).
[0104]
The power supply control in this embodiment is not only ON / OFF, but also adjusts the power supplied according to the rotation speed of the fixing film 1 as shown in the control flow chart of FIG. The electric power is controlled by changing the voltage application time a and the open time b of the excitation voltage described in the first embodiment.
[0105]
Specifically, when starting from room temperature, that is, until the temperature of the fixing film 1 reaches the determination temperature, the electric power W supplied to the rotational speed V of the fixing film 1 is
W = αV + β
β is the minimum power that does not overheat even when the fixing film stops,
α is the maximum supply power when V is the image forming speed
Select to be
[0106]
As a result, at a low temperature at which the fixing film 1 is likely to slip, the fixing film 1 is warmed with a weak electric power (minimum is β) to prevent slipping, and the supply power is increased as the rotational speed is increased. The amount of heat (energy) given to the unit area is controlled to be substantially constant.
[0107]
Therefore, according to this example, since the continuous power supply to the fixing film 1 is always possible, the start-up time can be shortened at the same time as the slip prevention.
[0108]
<Third embodiment> (FIG. 12)
In this embodiment, as shown in FIG. 12, an NTC element 5E is provided in the heat generation area H separately from the NTC element 5 for temperature control of the fixing film 1, and thereby the temperature of the heat generation area H of the fixing film 1 is set. The temperature rise rate is detected and monitored. When the temperature increase rate exceeds a predetermined value, it is determined that the fixing film 1 is stopped, and the power supply to the exciting coil 201 is stopped.
[0109]
This specific control method is the same as that described in the first embodiment.
[0110]
In this embodiment, the rotation state of the fixing film 1 is monitored by the temperature rise speed, and a simple configuration can be realized. Therefore, an inexpensive and highly reliable image forming apparatus can be realized.
[0111]
<Fourth Embodiment> (FIG. 13)
Although the four-color image forming apparatus has been described in the first to third embodiments, the image forming apparatus may be a monochrome or one-pulse multi-color image forming apparatus. In this case, the elastic layer 102 in the fixing film 1 of the fixing device 10 can be omitted.
[0112]
It is a schematic block diagram of an example of a monochrome image forming apparatus. The apparatus of this example is a schematic cross-sectional view of a laser beam printer using an electrophotographic process and detachable from a process cartridge.
[0113]
The intensity of the laser beam L from the scanner 13 is modulated by an image information signal sent from a host computer (not shown), and an electrostatic latent image is created on the photosensitive drum 11.
[0114]
The intensity of the laser beam L and the irradiation spot diameter are appropriately set according to the resolution of the image forming apparatus and the desired image density, and the electrostatic latent image on the photosensitive drum 11 is a bright portion where the laser beam L is irradiated. The other portion is formed at the potential VL by being held at the dark portion potential VD charged by the primary charger 12.
[0115]
The photosensitive drum 11 rotates in the direction of the arrow, and the electrostatic latent image is sequentially developed by the developing device 14. The toner in the developing device 14 is controlled in toner height and tribo by a developing sleeve 14a and a developing blade 14b which are toner supply rotating bodies, and a uniform toner layer is formed on the developing sleeve 14a. The developing blade 14b is usually made of metal or resin, and the resin blade is in contact with the developing sleeve 14a with an appropriate contact pressure.
[0116]
The toner layer formed on the developing sleeve 14a faces the photosensitive drum 11 as the developing sleeve 14a itself rotates, and is generated by the voltage Vdc applied to the developing sleeve 14a and the electric field formed by the surface potential of the photosensitive drum 11. Only the portion of VL is visualized selectively.
[0117]
The toner image on the photosensitive drum 11 is sequentially transferred onto the paper P sent from the paper feeding device 19 by the transfer device 15. Reference numeral 17 denotes a cleaning device for the surface of the photosensitive drum after the toner image is transferred to the paper P.
[0118]
  The paper P onto which the toner image has been transferred is sent to the fixing device 10 along with the rotation of the photosensitive drum 11, and is heated and pressed.SolidIt becomes a constant image. The fixing device 10 is, for example, the fixing device shown in the first to third embodiments.
[0119]
The paper P that has undergone the toner image fixing process is discharged by a paper discharge roller 20 to a paper discharge tray 21 outside the apparatus.
[0120]
The PC is a process cartridge that can be attached to and detached from the printer body. The present embodiment includes four process devices, that is, a photosensitive drum 1, a charger 12, a developing device 14, and a cleaning device 17, and these are collectively processed as a process cartridge that can be attached to and detached from the printer main body. is there.
[0121]
<Others>
1) Magnetic field generating means 201 and 202 as heating means for the cylindrical fixing film 1 which is a rotary heating member may be disposed outside the cylindrical fixing film 1.
[0122]
2) The fixing film 1 as a rotary heating member has an apparatus configuration in which an endless belt-like member is stretched between two or more members and is frictionally driven by a pressure roller or a drive member other than the pressure roller. May be.
[0124]
  3) In addition to the roller, the rotary pressure member can be a rotating body such as a belt member.
[0126]
  4)In the image forming apparatus, the principle and process of image formation on the recording material P are arbitrary.
[0127]
【The invention's effect】
  As described above, according to the present invention,The determination accuracy of the fixing unit failure is improved, and frequent occurrence of operation errors can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.
FIG. 2 is a cross-sectional schematic diagram of the fixing device.
FIG. 3 is a cutaway perspective view of a main part of the fixing device and a block diagram of a control system.
FIG. 4 is a model diagram of a layer structure of a fixing film (part 1).
FIG. 5 is a model diagram of a layer structure of a fixing film (part 2).
FIG. 6 is an explanatory diagram of magnetic field generation means and calorific value / heat generation area.
FIG. 7 is an explanatory diagram for controlling the alternating voltage supplied to the exciting coil.
FIG. 8 is an explanatory diagram of an optical sensor as a rotation detection unit of the fixing film.
FIG. 9 is a flowchart of apparatus control by fixing film rotation detection means.
FIG. 10 is a schematic cross-sectional view of a fixing device according to a second embodiment.
FIG. 11 is a flowchart of apparatus control by fixing film rotation speed detection means.
FIG. 12 is a schematic cross-sectional view of a fixing device according to a third embodiment.
FIG. 13 is a schematic cross-sectional view of an image forming apparatus according to a fourth embodiment.
[Explanation of symbols]
1 .. Fixing film (rotary heating member) 20, 202 .. Magnetic field generating means (heating means) 3 .... Pressure roller (rotating pressure member) 5,5E..NTC element, 5B..Rotation detection Member (optical sensor), 5C ・ ・ Rotational speed detection roller, 5D ・ ・ Encoder

Claims (1)

An image forming unit for forming an image on a recording material;
A cylindrical fixing film having a conductive layer; a film guide provided on the inner peripheral surface side of the fixing film for guiding the rotation of the fixing film; and the surface contacting the outer peripheral surface of the fixing film. A pressure roller that sandwiches the fixing film together with a guide and drives the fixing film by a frictional force acting between the surface and the surface of the fixing film; and a region of the peripheral surface of the fixing film where the pressure roller contacts And an exciting coil for generating an eddy current in the conductive layer at a position upstream of the fixing film rotation direction to heat the conductive layer, and grease is applied between the fixing film and the film guide. A recording material utilizing heat generated in the conductive layer while nipping and conveying the recording material carrying an image between the fixing film and the pressure roller. A fixing unit for fixing the image,
In an image forming apparatus having
A rotation detection unit that detects rotation of the fixing film; a safety device that determines whether or not the fixing unit is out of order; and a temperature detection element that detects a temperature of the fixing film. After the pressure roller is started to be driven by the driving means, when the rotation detecting means detects the rotation of the fixing film, power supply to the exciting coil is started, and the safety device is driven by the rotation detecting means. If it is determined that the fixing film has not started rotating and it is determined that the grease is equal to or lower than a predetermined determination temperature that ensures lubricity based on the temperature detected by the temperature detecting element, it is not determined that the fixing means has failed. The rotation detection of the fixing film is continued, and it is determined by the rotation detection means that the fixing film has not started rotating, and the grease is at the determination temperature. An image forming apparatus and determines that the fixing unit failure if it is determined to be high.

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