JPH0511653A - Heating device - Google Patents

Abstract

PURPOSE:To prevent the fault of heating and the damage of a device from occurring even when a voltage impressed on a power source is changed with respect to the rated electric power as for the film heating system heating device. CONSTITUTION:As for the heating device which gives heat energy to a body to be heated from a heating body side through a heat resistance film by contacting the material to be heated with an opposite side to the heating body side of the heat resistance film which is driven to travel in contact with the heating body 20 arranged to be fixedly supported and passing it through the position of the heating body, the power source 106 which supplies the electric power to the heating body 20, a detection means 108 which detects the voltage V impressed on the power source and a timer 107 which detects a successive power supply time (t) to the heating body are provided. Then, the value of the allowable maximum value (t0) of the successive power supply time (t) is changed according to the value of the voltage V and the power supply to the heating body is stopped when the value of the successive power supply time becomes the allowable maximum value (t0).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device of a system in which heat energy is applied to a material to be heated such as a recording material through a heat resistant film.

This device is an electrophotographic copying machine, printer,
An image heating and fixing device in an image forming apparatus such as a fax, that is, a recording material (electrofax sheet. A recording material carrying an unfixed toner image corresponding to the target image information formed on the surface of an electrostatic recording sheet, a transfer material sheet, a printing paper, etc. by a direct method or an indirect (transfer) method. It can be used as an image fixing device that performs heat fixing processing as a permanently fixed image on the surface.

Further, the present invention is not limited to the image fixing device, but is widely used as a means and a device for heat-treating a material to be heated such as an image carrier, such as a device for heating a recording material carrying an image to modify its surface property. Can be used.

[0004]

2. Description of the Related Art Conventionally, a heating device for a recording material, for example, for heating and fixing an image, includes a heating roller which is maintained at a predetermined temperature and a pressure roller which has an elastic layer and is in pressure contact with the heating roller. Accordingly, a heat roller method of heating the recording material while nipping and transporting the recording material is widely used.

Various methods and configurations such as a flash heating method, an oven heating method and a hot plate heating method are known and put into practical use.

A belt heating system is also known as disclosed in US Pat. No. 3,578,797. this is, . The toner image is brought into contact with a heating element web and heated to its melting point to be melted; After melting, the toner is cooled to a relatively high viscosity ,. It is a method of fixing without causing offset by passing through the process of peeling the toner from the heating body web in a state where the tendency of the toner to adhere to the heating body web is weakened.

Recently, a fixedly supported heating element (thermal heater, hereinafter referred to as a heater), a heat-resistant film (fixing film) conveyed while being pressed against the heater,
An unfixed image formed and carried on the surface of the recording material is formed on the surface of the recording material by applying heat of the heater to the recording material through the film. An apparatus (film heating method) having a method and structure for heating and fixing to a sheet has been devised.

According to the applicant's earlier proposal, for example, Japanese Patent Laid-Open No.
The system, apparatus, etc. disclosed in Japanese Patent Laid-Open No. 3-313182 belong to this, and a thin heat-resistant film (sheet), a moving driving means for the film, and a fixed support of one side of the film with the film inside. A heater disposed and a pressure member disposed on the other surface side so as to be in contact with the heater and to bring the developed image bearing surface of the recording material, on which the image is to be fixed, through the film into close contact with the heater, The film is moved at least at the same time as the recording material to be image-fixed which is conveyed and introduced between the film and the pressing member at the same speed at the time of image fixing, and the heater is pressed with the running moving film sandwiched. By passing through a fixing nip portion as a fixing portion formed by pressure contact with a member, the visible image bearing surface of the recording material is heated by the heater through the film to heat the visible image (unfixed toner image). Give energy Softened and allowed melt Te, then a heating means or apparatus which is based on that are spaced from each other by a separation point of the recording material and the film after fixing portion passes.

In such a film heating type device, since a low heat capacity heating element can be used as a heater, power consumption is reduced as compared with the conventional contact heating type heat roller type or belt heating type device. -It is effective because it has advantages such as shortening the wait time (quick start) and solving various drawbacks of other conventional heating system devices.

The heater as a heating element is an insulating substrate (base material) of ceramics or the like having low heat capacity and good heat resistance and good thermal conductivity.
A low heat capacity one having a low heat capacity energization heating resistor formed by coating it in a linear or strip shape is used, and the heater has a small heat capacity of the resistor and the substrate due to energization of the resistor. Therefore, the surface temperature rises rapidly to the required fixing temperature.

The heat-resistant film in contact with the heater also has a small heat capacity, and the heat energy on the heater side is effectively transmitted to the recording material side in a pressure contact state with the film through the film, so that the image is heat-fixed. It

The temperature control of the heater is carried out by detecting the heater temperature with a temperature detecting element and controlling the energization to the energization heating resistor by the temperature detection information to control the temperature of the heater to a predetermined fixing temperature. Is taken.

In this case, a temperature detecting element such as a thermistor having a low heat capacity and a high response is formed integrally with the heating body in order to control the temperature of the heating body having a low heat capacity with high accuracy and without response delay such as ripple. And is adhered to the heating element, or is pressed against the heating element or is disposed close to the heating element.

[0014]

However, since the heating rate is high in the film heating method, in the following cases, the heating element is continuously supplied with power for an excessively long time, and the heating element overheats. , The heating device may be damaged or, in the worst case, may ignite.

.. When the responsiveness of the temperature sensing element deteriorates For example, a. When the thermistor is adhered to the heating body, the thermistor peels off from the heating body due to deterioration of durability of the adhesive. B. When the thermistor is pressed against the heating body by the spring, elasticity of the spring is lost due to durability, and the thermistor and the heating body are separated from each other.

.. When the control circuit that controls the power supply to the heating element malfunctions due to the temperature detected by the temperature detection element, in order to prevent excessive heating of the heating element in such a case, continuous power supply time to the heating element has been conventionally used. A timer for detecting t is provided, and when the value of the time t reaches the maximum allowable value t ₀ , the power supply to the heating body is stopped regardless of the temperature detected by the temperature detecting element.

On the other hand, in this type of heating system, a normal AC
Power is supplied to the power source from the line, and power is supplied to the heating element from this power source. When a so-called stabilized power supply whose output power is constant regardless of the AC input voltage is used as the power supply, the size of the device is significantly increased. Therefore, the output voltage of this type of power supply is usually proportional to the input voltage. To do.

When a resistance heating element is used as the heating element, the power supplied to the heating element is proportional to the square of the output voltage of the power source.
Further, the rate of temperature rise of the heating body is approximately proportional to the power supplied to the heating body. Therefore, the heating rate of the heating element is proportional to the square of the input voltage of the power source. Then, when the power supply input voltage becomes, for example, 70% and 130% of the rated value, the heating rate of the heating element becomes 49% and 169% at the rated input, respectively.

At the time of rated input, the time required for the heating element to reach a predetermined heating operating temperature T _F from room temperature is t _1, and even if the temperature of the heating element reaches T _F , energization is continued and the heating element is kept at the predetermined temperature. when the time until damage occurs in the heating device when it is hot T _D and t _2, in order to prevent the heating body being damaged, the t ₁ <t ₀ <t ₂ becomes the time t ₀ is provided, continuous Then, it is assumed that a safety measure mechanism is provided so that the heating body is not energized for a time t ₀ or more. When the initial temperature of the heating element is higher than room temperature, the value of t ₀ can be set according to the initial temperature. Hereinafter, the description will be continued assuming that the initial temperature of the heating element is room temperature.

When the rated power is supplied to the heating element,
In the unlikely event that the temperature sensing element delays in response and the temperature sensed by the temperature sensing element becomes lower than the actual temperature of the heating element, the heating device is heated before reaching the damaged heating element temperature T _D. Power to the body is cut off.

On the other hand, when the input to the heating element is 70% of the rated value and the temperature detecting element is operating properly, the heating rate of the heating element is slow, so that heating is performed by continuous energization at time t _0. It is possible that the body may not reach the predetermined temperature T _F. In this case, the heat treatment of the recording material becomes insufficient.

Further, the power supply voltage to the heating element is 130% of the rated value.
% And the responsiveness of the temperature sensing element deteriorates, if the heating element is continuously energized for a time t ₀ , the heating element temperature T becomes T> T _D , and the heating device may be damaged. is there.

In view of the above, the present invention is directed to a film heating type heating device so that the above-mentioned heating failure and damage to the heating device do not occur even when the voltage applied to the voltage changes with respect to the rated power. To aim

[0024]

According to the present invention, a material to be heated is brought into close contact with a surface of a heat-resistant film which is driven to move in close contact with a heating body which is fixedly supported so as to be opposed to the heating body. A heating device for applying heat energy to the object to be heated from the side of the heating body through the heat resistant film by passing through the position of the heating body, and detecting a power supply for supplying power to the heating body and a voltage V applied to the power supply. And a timer for detecting the continuous power supply time t to the heating body, and changes the value of the maximum allowable value t ₀ of the continuous power supply time t according to the value of the voltage V. The heating device is characterized in that when the value of the continuous power supply time t reaches an allowable maximum value t ₀ , power supply to the heating body is stopped.

[0025]

Function: Even if the voltage V applied to the power source changes with respect to the rated power, the voltage state is detected by the detection means, and the detection voltage V
The value of the maximum allowable value t ₀ of the continuous power supply time t to the heating element is changed according to the value of, that is, when the value of V becomes large, the value of t ₀ becomes small and the value of V becomes small. Then, the value is changed in the direction of increasing the value of t ₀ to prevent overheating when the value of V is large and insufficient heating when the value of V is small.

In addition, the continuous power supply time t to the heating element
However, when the allowable maximum value t ₀ controlled according to the value of the voltage V is reached as described above, the power supply to the heating body is stopped to prevent damage to the device due to overheating.

[0027]

【Example】

(1) Example of image forming apparatus (FIG. 3) First, an example of an image forming apparatus using the heating device according to the present invention as a fixing device for an unfixed image will be described. The image forming apparatus of this example is a reciprocating type / rotating drum type / transfer type electrophotographic copying apparatus.

In FIG. 3, reference numeral 100 denotes an apparatus casing, 1 denotes a reciprocating type document placing table made of a transparent plate member such as a glass plate disposed on an upper surface plate 100a of the casing, and an upper surface plate of the casing. 100a is reciprocatingly driven to the right a and the left a'in the drawing at predetermined speeds.

Reference numeral G denotes an original document, which is placed on the upper surface of the original document table 1 with the image surface side to be copied facing downward according to a predetermined placement standard, and the original document pressure plate 1a is placed on the original document table 1a and pressed down. Is set.

Reference numeral 100b denotes a slit opening serving as a document illuminating section which is opened on the surface of the machine top plate 100a with the direction perpendicular to the reciprocating direction of the document placing table 1 (direction perpendicular to the paper surface) as the length. The downward image surface of the document G placed and set on the document placing table 1 sequentially passes through the position of the slit opening 100b from the right side to the left side in the forward movement process of the document placing table 1 to the right a. The light L of the lamp 7 is passed through the slit opening 100b and the transparent document placing table 1 and is illuminated and scanned during the passage. The light reflected from the document surface of the illumination scanning light is image-wise exposed on the surface of the photosensitive drum 3 by the short-focus small-diameter image-forming element array 2.

The photosensitive drum 3 is coated with a photosensitive layer such as a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer, and the central support shaft 3
It is rotationally driven in the clockwise direction indicated by the arrow b at a predetermined peripheral speed around a, and in the course of the rotation, it is subjected to uniform charging treatment of positive or negative polarity by the charger 4, and the uniformly charged surface is subjected to the above-mentioned By receiving the image formation exposure (slit exposure) of the document image, an electrostatic latent image corresponding to the image-formed and exposed document image is sequentially formed on the surface of the photosensitive drum 3.

This electrostatic latent image is sequentially visualized by a developing device 5 with toner made of resin or the like which is softened and melted by heating,
The toner image, which is the visible image, moves to a portion where the transfer discharger 8 as a transfer portion is provided.

Reference numeral S denotes a cassette in which transfer material sheets P as recording materials are stacked and housed, the sheets in the cassette are fed out and fed one by one by the rotation of the feeding roller 6, and then the drum 3 by the registration roller 9. When the tip of the upper toner image forming portion reaches the portion of the transfer discharger 8, the tip of the transfer material sheet P also arrives at the position between the transfer discharger 8 and the photosensitive drum 3, and the timing is adjusted so that they coincide with each other. It is then delivered synchronously. Then, the toner images on the photosensitive drum 3 side are sequentially transferred to the surface of the fed sheet by the transfer discharger 8.

The sheet to which the toner image has been transferred at the transfer portion 8 is sequentially separated from the surface of the photosensitive drum 3 by separating means (not shown), and is guided by a conveying device 10 to a fixing device 11, which will be described later, and is unfixed. The toner image is heat-fixed and discharged as an image-formed product (copy) onto the discharge tray 12 outside the apparatus. On the other hand, the photosensitive drum 3 after the toner image transfer
The surface is subjected to removal of adhering contaminants such as transfer residual toner by the cleaning device 13 and is repeatedly used for image formation.

(2) The fixing device 11 (FIG. 1) 24 is an endless belt-shaped fixing film, and is arranged on the left side driving roller 25, the right side driven roller 26, and below the driving roller 25 and the driven roller 26. The low-heat-capacity linear heating element 20 as the heating element is suspended and stretched between the three members 25, 26, 20 parallel to each other.

The driven roller 26 also serves as a tension roller for the endless belt-shaped fixing film 24.
The fixing film 24 is rotated at a predetermined peripheral speed in a clockwise direction with the clockwise rotation of the drive roller 25, that is, the image forming unit 8 is rotated.
The unfixed toner image Ta conveyed from the side is rotationally driven at the same peripheral speed as the conveying speed of the transfer material sheet P carrying the upper surface without wrinkles, meandering, or speed delay.

The driving roller 25 is a metal roller coated with a heat resistant material having a high friction coefficient with respect to the film 24, for example, silicon rubber, and the driven roller 26 is the driving roller 2.
5 is a metal roller having a lower friction coefficient than that of No.

Numeral 28 is a pressure roller having a rubber elastic layer having a good releasing property such as silicon rubber as a pressure member,
The endless belt-shaped fixing film 24 is sandwiched by the descending film portion, and is pressed against the lower surface of the heating body 20 by a biasing means (not shown) at a total pressure of 4 to 7 kg. The material sheet P rotates in the forward counterclockwise direction in the conveying direction.

The heating element 20 is a linear heating element having a low heat capacity and having a length in a direction (width direction of the film) intersecting with the plane movement direction of the film 24, and includes a heater substrate 21, an energization heating resistor (heating element) 22, It comprises a temperature measuring element 23 and the like, and is fixedly supported by being attached and held to the heater support 27.

The heater support 27 has a heat insulating property, a high heat resistance and a rigidity for heat-insulating and supporting the heating body 20 with respect to the fixing device 11 and the image forming apparatus. P
It can be composed of a high heat resistant resin such as I (polyimide), PEEK (polyether ether ketone), liquid crystal polymer, or a composite material of these resins and ceramics, metal, glass or the like.

The heater substrate 21 is a member having heat resistance, insulation, low heat capacity and high heat conductivity, and is, for example, an alumina substrate having a thickness of 1 mm, a width of 10 mm and a length of 240 mm.

The heating element 22 is the lower surface of the substrate 21 (film 2
4 (along the side facing 4) along the longitudinal direction, for example, A
An electric resistance material such as g / Pd (silver palladium) or Ta ₂ N is applied to the thickness of about 10 μm and a width of 1 to 3 mm by screen printing or the like, and a heat-resistant glass 21a as a surface protective layer thereon
Of about 10 μm.

A thermistor 23 having a low heat capacity as a temperature detecting element is adhered to a substantially central portion of the upper surface of the substrate 21 (the surface opposite to the surface provided with the heating element 22) with a silicone adhesive having good thermal conductivity. It is arranged.

In the case of the heating element 20 of this example, electricity is applied to the linear or strip heating element 22 from both ends in the longitudinal direction to cause the heating element 22 to generate heat over substantially the entire length. The power supply mechanism will be described in detail later in (5).

(3) Fixing Execution Operation The image forming start signal causes the apparatus to perform an image forming operation, and the unfixed toner image Ta transferred to the fixing apparatus 11 from the transfer section 8 is transferred as a material to be heated with the toner image Ta carried on the upper surface. The material sheet P is guided by the guide 29 and the fixing film 24 and the pressure roller 28 at the pressure contact portion N between the heating body 20 and the pressure roller 28.
And the fixing film 2 in which the unfixed toner image surface is rotated in the same direction at the same speed as the conveyance speed of the sheet P.
No. 4, which is in close contact with the lower surface of No. 4 and passes through the mutual pressure contact portion N between the heating body 20 and the pressure roller 28 while receiving a sandwiching pressure in the overlapping state with the fixing film 24 without causing surface deviation or wrinkling. .. Since the heating element 20 is electrically heated by the image formation start signal at a predetermined timing, the toner image T
A is heated at the press contact portion N and becomes a softened / melted image Tb.

The fixing film 24 has its running direction turned at a steep angle (the bending angle θ is about 45 °) at the edge portion S (having a radius of curvature of about 2 mm) of the heater support 27 having a large curvature. Therefore, the sheet P conveyed by passing through the pressure contact portion N in a state of being overlapped with the fixing film 24 is curvature-separated from the fixing film 24 at the edge portion S, and the discharge tray 12
The paper is discharged to. By the time the paper is discharged, the toner is sufficiently cooled and solidified and is in a state of being completely fixed on the sheet P (toner image Tc).

Since the toner used in this embodiment has a sufficiently high viscosity when heated and melted, even if the toner temperature at the time of separation from the fixing film 24 is equal to or higher than the melting point of the toner, the fixing force between the toners is fixed to the fixing film. It is much larger than the adhesive force of the toner. Therefore, when the fixing film 24 and the sheet P are separated from each other, toner offset to the fixing film 24 does not substantially occur.

Further, in the present example, the heat capacity of the heating element 22 and the substrate 21 of the heating element 20 is small, and since they are adiabatically supported by the support element 27, the surface temperature of the heating element 20 at the press contact portion N is Since the temperature is raised to a sufficiently high temperature with respect to the melting point of the toner (or the temperature at which the sheet P can be fixed) in a short time, it is not necessary to raise the temperature of the heating body 20 in advance (so-called standby temperature adjustment), which saves energy. This can be realized and the temperature rise inside the machine can be prevented.

(4) Fixing Film 24 The fixing film 24 has a total thickness of 100 μm or less, preferably 40 μm or less, such as heat resistance, releasability and durability in order to reduce the heat capacity and achieve quick startability. Single layer or multiple layer films can be used. FIG. 2 is a schematic diagram of the layer constitution of an example of the composite layer film, and this example is a two-layer constitution film. Reference numeral 24a is a heat-resistant layer as a base layer (base film) of the fixing film, and 24b is a release layer laminated on the outer surface (surface facing the toner image) of the heat-resistant layer 24a.

The heat-resistant layer 24a is made of polyimide, polyetheretherketone (PEEK), polyethersulfone (PES), polyetherimide (PEI), polyparabanic acid (PPA), or other high heat-resistant resin film. Those with excellent heat resistance can be used.

The release layer 24b is preferably a fluororesin such as PTFE (polytetrafluoroethylene) / PFA / FEP, or a silicon resin. The release layer 24b is laminated on the heat-resistant layer 24a by adhesive lamination of a release layer film. Laminating of release layer materials by electrostatic coating (coating), vapor deposition, CVD, etc.
The heat-resistant layer material and the release layer material can be coextruded to form a two-layer film.

Since the heat-resistant layer 24a is set thicker than the release layer 24b, the total thickness of the film can be reduced while maintaining the strength of the film, and the heat transfer efficiency from the heating element to the recording material is high. ..

The surface resistance of the release layer 24b is 10 ¹⁰ Ω.
The following are preferred. The resistance value of the surface of the release layer 24b may be lowered by a method of mixing a conductive agent such as carbon black, graphite, or a conductive whisker. In that case,
It is possible to prevent the toner contact surface of the fixing film 24 from being charged.
When the toner contact surface of the fixing film 24 is insulative, the surface of the fixing film is charged and disturbs the toner image on the sheet P, or the toner image is transferred to the fixing film 24 (so-called charge offset). In some cases, these measures can avoid these problems.

(5) Power Supply Mechanism FIG. 4 is a diagram for explaining a power supply mechanism of the heating element 20 to the heating element (energized heating resistor) 22.

Power is supplied to the heating element 22 from a power source 106 having a switching element such as a triac. Rating 100
A voltage detection circuit (according to a known circuit configuration) between the AC power supply 109 and the power supply 106, which has a power of 400 W when V is applied.
108 intervenes and constantly monitors the input voltage to the power supply 106. The control circuit 107 controls a switching element (not shown) of the power supply 106 according to the temperature detected by the thermistor 23 to supply a predetermined electric power to the heating element 22.

In the present invention, the time t during which the heating element 22 can be continuously energized in accordance with the detection voltage V of the voltage detection circuit 108.
₀ is changing.

FIG. 5 is a diagram in which the continuous energizable time t ₀ is plotted with respect to the detection voltage V. As the voltage V increases, t ₀ decreases. In addition,
The value of t ₀ in FIG. 5 is 20 ° C. before the energization of the heating element 22 is started, and is the value when the set temperature of the heating element is 200 ° C. The case where the initial temperature is higher than 20 ° C. will be described later.

In FIG. 5, together with t ₀ , the time t ₁ until the heating element 20 reaches the set temperature 200 ° C. and the heating element 2 are shown.
The time t ₂ from when the device emits smoke when the current is still applied even when 0 exceeds the set temperature is also plotted.

Here, when the maximum energizable time t ₀ is not changed according to the input voltage V and is fixed to a value of 9 sec at 100 V, the following problems occur.

.. When the voltage was 70 V, the energization was cut off before the heating element reached the set temperature, and heating failure occurred.

.. When the responsiveness of the thermistor became abnormally slow at a voltage of 130 V, smoke was emitted for 7.5 seconds before the energization was stopped for 9 seconds.

In this embodiment, the initial temperature of the heating element 20 is 20.
When the temperature is other than 0 ° C., the maximum energizable time t ₀ is changed according to the temperature as shown in FIG. That is, as shown in FIG. 7, the maximum energizable time t ₀ is changed using both the input voltage and the heating body initial temperature as parameters.

The heating body initial temperature may be detected by a thermistor. However, when the thermistor 23 is low in temperature and the accuracy is poor, a low temperature range of less than 200 ° C., especially 1 for measuring the heating body initial temperature.
Thermistor 2 is another thermistor with good accuracy at 00 ° C or less.
It may be installed near 3 and used.

(6) Other Examples FIG. 8 shows another example of the power feeding mechanism for the heating element 22 of the heating element 20. In this example, the circuit of FIG.
The temperature fuse 101, the first relay 102, and the second relay 103 are interposed in series between and the heating element 22.

The thermal fuse 101 is arranged in the approximate center of the upper surface of the substrate 21 close to the substrate 21 via a holder having a thickness of 1 mm, and is fused at 220 ° C.

In the first relay 102, the output of the thermistor 23 is detected by the external temperature detecting circuit 104, and the thermistor 2 is detected.
When the detected temperature of 3 exceeds a predetermined value, the power supply to the heating element 22 is forcibly cut off.

The second relay 103 has a voltage detecting circuit 10
8 and the external temperature detection circuit 104 are connected to an external timer 105.

The external timer 105 includes a voltage detection circuit 108.
The maximum energizable time t ₀ is set based on the input voltage to the power source 106 detected in step 1 and the heating element initial temperature detected by the external temperature detection circuit 104, and the control circuit 107 drives the power source 106 to start energizing the heating element 22. Measure the time since the start. If the current is continuously applied for time t ₀ , the second
The relay 103 is operated to cut off the power supply to the heating element 22.

In the case of this embodiment, even if the control circuit 107, which normally includes a microcomputer, malfunctions, the power supply to the heating element 22 can be reliably stopped before the device is damaged.

Still another embodiment will be described below.

(A) Instead of detecting the initial temperature of the heating element 20, the temperature of the heating element is detected a predetermined time after the start of energization, and the maximum energizable time t ₀ is determined from the value and the input voltage. May be. In the case of the present embodiment, since the thermistor output value when the heating body temperature is high, that is, when the heating body temperature is close to the heating operation temperature, the temperature detection accuracy is improved.

(B) Instead of the absolute value of the temperature of the heating element, the maximum energizable time t ₀ may be determined from the input voltage value and the rate at which the heating element temperature changes (rises) during a predetermined time.

(C) When the continuous energization time reaches t ₀ and the energization to the heat generating element 22 is cut off, it is advisable to inform the user of the occurrence of an abnormality by lighting a lamp or the like.

[0074]

As described above, according to the present invention, in the film heating type heating device, even if the voltage applied to the power source changes with respect to the rated power, the heating device is not suitable for heating or smoking during abnormal operation of the device. Damage is prevented from occurring.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a heating device according to an embodiment.

FIG. 2 Model diagram of layer structure of heat-resistant fixing film

FIG. 3 is a schematic configuration diagram of an example of an image forming apparatus incorporating the heating device as a fixing device.

FIG. 4 is a block diagram of an energizing circuit for a heating element.

FIG. 5 is a diagram showing a change in maximum energizable time with respect to an input voltage.

FIG. 6 is a diagram showing a change in maximum energizable time with respect to a heating element initial temperature.

FIG. 7: Selection diagram of maximum energizable time with input voltage and heating element initial temperature as parameters

FIG. 8 is a block diagram of another energizing circuit for the heating element.

[Explanation of symbols]

 20 heating element 22 heating element 23 thermistor 24 heat resistant film 28 pressure roller P recording material 106 power source 107 control circuit 108 voltage detection circuit 109 AC power source

Claims (1)

Claim: What is claimed is: 1. A heating element, wherein a material to be heated is brought into close contact with the surface of the heat-resistant film which is driven to move in close contact with a heating element which is fixedly supported. A heating device for applying heat energy to a heated object from a heating body side through a heat resistant film by passing through a position, a power supply for supplying power to the heating body, and a detection for detecting a voltage V applied to the power supply. And a timer for detecting a continuous power supply time t to the heating body, and changing the value of the maximum allowable value t ₀ of the continuous power supply time t according to the value of the voltage V, A heating apparatus characterized in that when the value of the continuous power supply time t reaches an allowable maximum value t ₀ , power supply to the heating body is stopped.