JP2000137394A - Heating device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stop the current conduction to a heating body before the temperature thereof becomes abnormally high and to prevent the heating body from being damaged by calculating the rising speed of the temperature of the heating body based on the output of a temperature detection element and stopping the current conduction to the heating body when the calculated value exceeds a fixed value. SOLUTION: The output of the temperature detection element 5 of every fixed time is fetched by a CPU 24 and the rising speed of the temperature is calculated by the CPU 24. Then, the calculated value is always compared with the previously set fixed value (reference value) for deciding the stop of the energizing. Since it is a normal time when the rising speed of the temperature calculated by the CPU 24 is smaller than the reference value, a normal temperature control action is executed. Since it is an abnormal time that excessive electric power is supplied to a resistance heating element 32 because of the short-circuit of a TRIACK 25 and the like when the rising speed of the temperature is larger than the reference value, a signal for cutting a relay 33 is outputted from the CPU 24 so as to stop the energizing of the element 32. Simultaneously, an error display is outputted so as to inform a user of the fault of a fixing device. Thus, the heating body 3 is prevented from being damaged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device suitable for a copying machine, a laser beam printer, and the like, and an image forming apparatus provided with the heating device.

[0002]

2. Description of the Related Art Conventionally, for example, for heat fixing of an image,
The recording material heating device includes a heating roller maintained at a predetermined temperature and a pressure roller pressed against the heating roller via an elastic layer to heat the recording material as a heating target while nipping and transporting the recording material. A heat roller method is frequently used.

In addition, a flash heating method,
Various methods and configurations such as an open heating method and a hot plate heating method are known and are in practical use.

Recently, instead of such a system, Japanese Patent Application Laid-Open Nos. 4-44075-44083, 4-204
As disclosed in Japanese Patent Application Laid-Open No. 980-204984 and the like, a fixedly supported heating element (heater), a heat-resistant film (fixing film) conveyed while being pressed against the heating element, and A pressure member (pressing roller) for bringing a recording material as a heated body into close contact with the heating member, and applying heat of the heating body to the recording material through the film to form and carry the recording material on the recording material surface An image heating and fixing device (heating device of a film heating type) having a method and a structure of heating and fixing an unfixed image on a recording material surface has been used.

In such a film heating type heating apparatus or image heating and fixing apparatus, a heating element having a low heat capacity can be used as the heating element. For this reason, it is possible to save power and shorten the wait time (quick start) as compared with a conventional apparatus such as a heat roller method or a belt heating method which is a contact heating method.

[0006]

In the above-described image forming apparatus using the heating fixing device of the fixing film heating method, the CP
Due to malfunction of the temperature control circuit such as runaway of U, short circuit of triac that controls the power supply to the heating element, etc., if the heating element is not temperature controlled and excessive power is supplied, the heating element and the substrate of the heating element A large temperature difference occurs in the width direction with a certain ceramic substrate. For this reason, a thermal stress exceeding the breaking strength is applied in the longitudinal direction of the ceramic substrate, causing a problem that the heating element is damaged (heater cracking).

Therefore, in the present invention, by monitoring the rate of temperature rise of the heating element, it is possible to prevent the heating element from being damaged by stopping energization before the temperature of the heating element becomes abnormally high. It is intended to provide an apparatus and an image forming apparatus.

[0008]

In order to achieve the above object, a heating apparatus and an image forming apparatus according to the present invention are characterized by having the following constitution.

[1] A heating device which has a heating element which generates heat when energized, and a temperature detecting element which detects the temperature of the heating element, and heats an image carried on a recording material by heat from the heating element. The heating apparatus according to claim 1, wherein a temperature rise rate of the heating element is calculated from an output of the temperature detecting element, and when the value exceeds a predetermined value, energization to the heating element is stopped.

[2]: a heating element that generates heat when energized, a temperature detecting element that detects the temperature of the heating element, a heat-resistant film that slides in contact with the heating element, and a recording material via the film. A pressure member that is brought into close contact with a heating member, and the nip formed by the heating member and the pressure member is conveyed while the fixing film and the recording material are sandwiched and conveyed onto the recording material. In a heating device for heating a carried image, a heating rate of the heating element is calculated from an output of the temperature measuring element, and when the value exceeds a certain value, the power supply to the heating element is stopped. apparatus.

[3] In the heating device according to [1] or [2], the temperature rising speed is compared with a constant value only when the temperature detecting element detects a temperature equal to or higher than a set target temperature of the heating device. A heating device, characterized in that:

[4]: In the heating device according to [1], [2] or [3], when the heating device is started up, the temperature rising speed is compared with a value different from a constant value used for comparison in normal times. When the temperature rise rate exceeds the value, the power supply to the heating body is stopped.

[5] An image forming apparatus using the heating device according to [1], [2], [3] or [4] as image fixing means.

<Operation> According to the heating device and the image forming apparatus having the above-described configuration, excessive power is supplied to the heating element due to runaway of the CPU, short-circuit of the triac, and the like.
Even when the temperature of the heating body rises rapidly, the temperature rising rate of the heating body is monitored. Can be stopped before the temperature reaches an abnormally high temperature, and damage to the heating element can be prevented.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a schematic structural view of an example of an image heating and fixing apparatus as a heating apparatus according to the present embodiment, in which a maximum sheet width of a film heating system is A3 size. This device is disclosed in Japanese Patent Application Laid-Open No. 4-44075-44083.
This is a so-called tensionless type device disclosed in Japanese Unexamined Patent Publication Nos. 4-204980-2044984.

In this tensionless type apparatus, an endless belt or cylindrical heat-resistant film is used, and at least a part of the peripheral length of the film is always tension-free (state in which tension is not applied).
The film is a device that is driven to rotate by the rotation driving force of the pressing member.

2 is an endless heat-resistant film,
It is externally fitted to a stay 1 which is a film guide member including a heating element 3 (heater). The inner peripheral length of the endless heat-resistant film 2 and the outer peripheral length of the stay 1 including the heating element 3 are larger, for example, by about 3 mm. Therefore, the film 2 is externally fitted with a margin in the circumference.

The film 2 has a film thickness of 10 to reduce the heat capacity and improve the quick start property.
0 μm or less, preferably 50 μm or less and 20 μm or more, heat-resistant single-layer film of PTFE, PFA, FEP, etc., or polyimide, polyamideimide, PEE
PTF on the outer peripheral surface of film such as E, PES, PPS
A composite layer film coated with E, PFA, FEP or the like can be used. In this example, a polyimide film having an outer peripheral surface coated with PTFE was used.

FIG. 2 is a schematic plan view of the heating element, with the middle part omitted and partly cut away. The heating element 3 is an elongated heat-resistant, insulating, and heat-conductive substrate 31 whose longitudinal direction is perpendicular to the conveying direction a of the heat-resistant film 2 or the recording material P as the object to be heated, and the surface of the substrate. Resistance heating element 32 formed at the center in the lateral direction of the side along the longitudinal direction of the substrate, a heat-resistant overcoat layer 34 protecting the surface of the heating element on which the resistance heating element is formed, and both longitudinal ends of the resistance heating element 32 The power supply electrodes 21 and 22 (FIG. 2) and the temperature sensor 5 such as a thermistor for detecting the temperature of the heating element are provided on the back side of the substrate.

The heating element 3 is fixedly arranged with the surface side on which the resistance heating element 32, which is the heating surface, formed and provided facing downward, held on the lower surface side of the rigid and heat-resistant stay 1. is there.

The heating substrate 31 is made of, for example, alumina, aluminum nitride, or the like having a thickness of 1 mm, a width of 10 mm, and a length of 33.
0 mm. The resistance heating element 32 is, for example, Ag
/ Pd (silver palladium), RuO ₂ , Ta ₂ N, etc., by screen printing or the like to a thickness of about 10 μm,
It is formed by coating in a line shape or a narrow band shape having a width of 1 to 3 mm. The power supply electrodes 21 and 22 are, for example, a screen printing pattern layer of Ag or the like. Overcoat layer 34
Is, for example, a heat-resistant glass layer having a thickness of about 10 μm.

Reference numeral 4 denotes a pressure roller as a film outer surface contact driving means for forming a pressure contact nip portion (fixing nip portion) N1 with the film 2 interposed between the heating member 3 and rotating the film 2. This film driving roller and pressure roller 4 is composed of a cored bar 4a, an elastic layer 4b made of silicon rubber or the like, and an outermost release layer 4c, and is provided with a predetermined pressing force by bearing means and urging means (not shown). The heating element 2 is disposed so as to be in pressure contact with the surface of the heating element 3. The rotational force acts on the film 2 by the frictional force between the roller and the outer surface of the film due to the rotational drive of the pressure roller 4.

The temperature of the heating element 3 rises as the resistance heating element 32 generates heat over its entire length by feeding power to the power supply electrodes 21 and 22 at both longitudinal ends of the resistance heating element 32. It is detected by. The output of the temperature detecting element 5 is A / D converted and taken into the CPU 24, and based on the information, the AC voltage of the AC power supply 26, which is energized to the resistance heating element 32 by the triac 25, is controlled by the phase control and the wave number control. Is controlled, the temperature of the heating element 3 is controlled. That is, by controlling the energization so that the temperature of the heating element 3 rises when the temperature detected by the temperature detecting element 5 is lower than a predetermined set temperature, and to lower the temperature when the temperature is higher than the predetermined temperature, the heating element 3 is heated.
Is fixed at the time of fixing.

When the temperature of the heating element 3 rises to a predetermined value and the rotation peripheral speed of the film 2 is stabilized by the rotation of the pressure roller 4, the heating element 3 and the pressure roller 4 and a pressure nip N1 formed by
The recording material P to be fixed as an object to be heated is introduced from an unillustrated image forming portion (transfer portion) between the film 2 and the pressure roller 4 and is nipped and conveyed together with the film 2. The heat of the heating element 3 is transferred to the recording material P via the film 2.
Unfixed image (toner image) T on the recording material P
Are heated and fixed on the surface of the recording material P. The recording material P that has passed through the pressure nip N1 is separated from the surface of the film 2 and conveyed.

In the image forming apparatus using the above-described fixing film heating type heat fixing device, if excessive power is supplied to the heating element 3 without temperature control due to a short circuit of the triac 25, etc., the resistance heating element 32 and heating element 3
A large temperature difference occurs in the width direction between the substrate and the ceramic substrate 31. For this reason, a thermal stress exceeding the breaking strength is applied in the longitudinal direction of the ceramic substrate 31, causing a problem that the heater is cracked.

Therefore, for safety measures, as means for detecting excess power supply to the heating element 3 and stopping energization to the heating element 3, the output of the temperature detecting element 5 using a CPU or a comparator is used. The temperature of the heating element 3 is monitored, and when it reaches a certain temperature, it is soft (CPU) or hard (comparator)
A method of stopping the current supply can be considered. However, since the energization is stopped only after the predetermined temperature is detected, the timing of the energization stop is delayed, and the heater may be broken before the detection or before the energization is stopped after the detection. Further, if the temperature of the abnormality detection is excessively lowered in order to advance the detection timing, an overshoot or the like at the time of normal startup may be erroneously detected.

In consideration of the above points, in the present embodiment, the temperature rise rate is monitored in order to quickly detect excess power supply to the heating element 3 at the time of failure. FIG. 3 shows a comparison diagram of the difference in the timing of abnormality detection between the case where the temperature is monitored and the case where the temperature rise speed is monitored.

In FIG. 3, T indicates a fixing temperature, T 'indicates an abnormality detection temperature for monitoring the temperature, and A indicates a point at which an abnormality has occurred. When monitoring the temperature rising speed, the temperature rising speed immediately after A is calculated, and it is determined that the temperature is abnormal at the point B, and the power supply to the heating element 3 is stopped.

On the other hand, when monitoring the temperature, no abnormality can be detected until the point C at which the detected temperature reaches T '. That is,
It can be seen that monitoring the temperature rise rate is faster than detecting the temperature, and the abnormality of the fixing device is detected faster and the possibility of cracking of the heater is reduced.

FIG. 4 shows a schematic diagram of a safety measure mechanism of the image forming apparatus according to the present embodiment. In this example, the output of the temperature sensing element 5 at regular intervals is taken into the CPU 24 and
At 24, the temperature rise rate is calculated, and the value is constantly compared with a predetermined value (reference value) for determining the stop of energization. When the temperature rise rate calculated by the CPU 24 is smaller than the reference value, it is a normal time, so that normal temperature control is performed. If the temperature rise rate is equal to or higher than the reference value, it is an abnormal time when excessive power is being supplied to the resistance heating element 32 due to a short-circuit of the triac 25 or the like. Stop energization. At the same time, an error message is displayed to notify the user of the fixing device failure.

Further, in this embodiment, in order to prevent a malfunction of the safety countermeasure mechanism at the time of normal startup, the reference value to be compared with the temperature rising speed at the time of startup is set to a value different from that at the time of normal temperature control. I have. For example, when the temperature of the heating element 3 is low, the temperature rising speed at the time of startup becomes fast, and therefore, the reference value is set to a value larger than that at the time of normal temperature control. Further, in order to prevent the detection temperature fluctuation from being erroneously detected during the normal temperature control, the temperature rise during the normal temperature control is performed only when the temperature detecting element 5 detects a temperature equal to or higher than the target fixing temperature of the heating device at that time. If an abnormality is detected based on the speed and the temperature at the time when the abnormality is detected at the same time does not greatly deviate from the target fixing temperature (for example, within 10 ° C.), no abnormality is determined.

The use of the image forming apparatus having the above-described configuration allows the resistance heating element 3 to be promptly supplied when excessive power is supplied to the resistance heating element 32 due to a short circuit of the triac 25 or the like.
By stopping the power supply to the heating element 2, the heating element 3 can be prevented from being damaged.

In the present embodiment, the temperature rise rate is monitored using the same temperature detecting element 5 as used in the normal temperature control. However, another temperature detecting element may be provided to perform control independent of the normal temperature control. good.

(Second Embodiment) FIG. 4 is a schematic diagram of a safety measure mechanism of an image forming apparatus according to the present embodiment. Other configurations of the image forming apparatus are the same as those of the first embodiment.

In the present embodiment, the rate of temperature rise is calculated by the differentiating circuit 35 based on the output of the temperature detecting element 5, and the value is constantly compared with the reference voltage 37 by the comparator 36. When the temperature rise rate calculated by the differentiating circuit 35 is smaller than the reference value, it is a normal time, so that normal temperature control is performed. The temperature control method is the same as that of the first embodiment.
The triac 25 controls the power supplied to the resistance heating element 32 based on the information.

If the temperature rise rate is higher than the reference value,
Since abnormal power is being supplied to the resistance heating element 32 due to runaway of the U24, short-circuiting of the triac 25, or the like, the comparator 33 turns off the relay 33 and stops supplying power to the resistance heating element 32. At the same time, an error message is displayed to notify the user of the fixing device failure.

As described in the first embodiment, the output of the temperature detecting element 5 and the reference voltage 37 are compared with each other by the comparator 36 (abnormal detection based on temperature). When the abnormality is detected at the temperature rising speed, the abnormality of the fixing device is detected earlier and the possibility of the heater cracking is reduced.

In the first embodiment, the CPU 24 calculates the temperature rise rate and detects an abnormality in the heating device.
When U24 becomes uncontrollable due to runaway or the like, it was impossible to stop energizing the resistance heating element 32.
However, in this embodiment, the differentiation circuit 35 and the comparator 36 detect the abnormality of the heating device independently of the CPU 24 and stop the energization to the resistance heating element 32.
24 abnormalities can be dealt with, and safety is further improved.

By using the image forming apparatus having the above-described configuration, when excessive power is supplied to the resistance heating element 32 due to runaway of the CPU 24, short-circuiting of the triac 25, etc., the power supply to the resistance heating element 32 is stopped as soon as possible. Can be prevented from being damaged.

(Third Embodiment) This embodiment has the safety countermeasures described in the first and second embodiments at the same time.
In addition, both are operated independently.

The schematic diagram of the safety countermeasure mechanism of the image forming apparatus according to this embodiment is the same as that of FIG. 4, and the other configuration of the image forming apparatus is the same as that of the first and second embodiments.

In the present embodiment, as in the first embodiment, the output of the temperature detecting element 5 is taken into the CPU 24 at regular time intervals, the temperature rise rate is calculated by the CPU 24, and the value is used as the preset power supply stop. Always compare with the reference value to determine. Further, similarly to the second embodiment, the temperature rise rate is calculated by the differentiating circuit 35 based on the output of the temperature detecting element 5, and the value is constantly compared with the reference voltage 37 by the comparator 36. Each abnormality detection method is the same as the method described in the first and second embodiments. If both of them do not detect abnormality, normal temperature control is performed. The normal temperature control method is the same as in the first and second embodiments. If an abnormality is detected at least on one side, the relay 33 is turned off by the CPU 24 or the comparator 36, and the energization to the resistance heating element 32 is stopped to prevent the heater from cracking. In addition, the reference value which determines each energization stop may be the same or different.

By using the image forming apparatus having the above-described configuration, when excessive power is supplied to the resistance heating element 32 due to runaway of the CPU 24, short-circuit of the triac 25, or the like, the power supply to the resistance heating element 32 is stopped as soon as possible. Can be prevented from being damaged. In the present embodiment, since two safety countermeasure mechanisms which operate independently are provided, the safety is further improved as compared with the first and second embodiments.

(Example of Image Forming Apparatus) FIG. 6 is a schematic structural view of an example of the image forming apparatus. The image forming apparatus of this embodiment is a laser beam printer using an electrophotographic process.

Reference numeral 41 denotes a rotary drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as a first image carrier.

[0046] The photosensitive drum 41 is rotated in the clockwise direction of arrow at a predetermined peripheral speed (process speed), uniformly charged to its by the primary charger 42 in the rotation process of a predetermined negative dark potential V _D Is done.

Reference numeral 43 denotes a laser beam scanner, which is a laser beam L modulated according to a time-series electric digital image signal of target image information input from a host device such as an image reading device, a word processor, and a computer (not shown). Is output, and the uniformly charged surface of the rotating photosensitive drum 41 is scanned and exposed. The exposed portion by this laser beam scanning exposure has a small potential absolute value and a bright potential V _L.
Therefore, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photosensitive drum 41.

Next, the latent image is reversely developed (toner adheres to the laser exposure light potential _VL portion on the surface of the photosensitive drum) with the negatively charged powder toner by the developing device 44 to be visualized as a toner image.

The developing device 44 has a developing sleeve 44a which is driven to rotate. The outer peripheral surface of the developing sleeve is coated with a thin layer of negatively charged toner, and faces the surface of the photosensitive drum 41. Value is photosensitive drum 4
Smaller than the dark potential V _D of the latent image of one side, by the development bias voltage V _DC is applied greater than the bright potential V _L, light of the latent image of the toner photosensitive drum 41 surface of the developing sleeve 44a The latent image is transferred only to the potential _VL and the latent image is visualized (reversal development).

On the other hand, a recording material P as a second image carrier loaded and set on a paper feed tray 45 is fed out one by one by the driving of a paper feed roller 46, and is conveyed by a transport guide 47a and a registration roller. The rotation of the photosensitive drum 41 via a transfer guide 47b to a transfer nip portion m, which is a press-contact nip portion between the photosensitive drum 41 and a transfer roller 49 as a transfer member to which a transfer bias is applied while being brought into contact with the photosensitive drum 41. The toner image on the surface of the photosensitive drum 41 is sequentially transferred onto the surface of the fed recording material P.

The recording material P that has passed through the transfer nip m is separated from the surface of the rotary photosensitive drum 41, introduced into the fixing device R shown in the first to third embodiments via the transport guide 47c, and then transferred to the fixing device R. After receiving the image fixing process, the discharge roller pair 5
0 is output onto the discharge tray 51.

After the separation of the recording material, the surface of the rotating photosensitive drum 41 is cleaned by a cleaning device 52 to remove the remaining photosensitive drum surface residue such as toner remaining after transfer, and is repeatedly used for image formation.

[0053]

As described above, according to the present invention, by monitoring the temperature rise rate of the heating element, the power supply is stopped before the heating element reaches an abnormally high temperature to prevent damage to the heating element. It is possible to provide a heating device and an image forming apparatus that can prevent the heating device.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a heating device (film heating type image heating and fixing device) based on the present invention.

FIG. 2 is a plan view showing a partially cut-out portion of a heating element and omitting an intermediate portion.

FIG. 3 is a diagram illustrating a comparison of the timing of abnormality detection when monitoring the temperature and when monitoring the temperature rise rate.

FIG. 4 is a schematic diagram of a security measure mechanism of the image forming apparatus according to the first embodiment.

FIG. 5 is a schematic diagram of a safety measure mechanism of the image forming apparatus based on the second embodiment.

FIG. 6 is a schematic diagram of the entire image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 stay 2 film 3 heating element 4 pressure member (film drive roller, pressure roller) 4 a cored bar 4 b elastic layer 4 c release layer 5 temperature sensing element 21 power supply electrode 22 power supply electrode 25 triac 26 power supply 31 heating element substrate (Ceramic substrate) 32 Resistance heating element 33 Relay 34 Overcoat layer 35 Differentiating circuit 36 Comparator 37 Reference voltage 41 Photosensitive drum 42 Primary charger 44a Developing sleeve 44 Developing device 45 Feed tray 46 Feed roller 47a Transport guide 47b Transfer guide 47c conveyance guide 48 registration roller pair 49 transfer roller 50 paper discharge roller pair 51 paper discharge tray 52 cleaning device L laser beam N1 pressure contact nip part P recording material R fixing device a conveyance direction m transfer nip part

Claims (5)

[Claims] 1. A heating device, comprising: a heating element that generates heat when energized; and a temperature detecting element that detects a temperature of the heating element, wherein the heating device heats an image carried on a recording material by heat from the heating element. A heating apparatus comprising: calculating a temperature rise rate of a heating element from an output of the temperature detecting element; and stopping the power supply to the heating element when the value exceeds a predetermined value. 2. A heating element that generates heat when energized, a temperature detecting element that detects a temperature of the heating element, a heat-resistant film that slides in contact with the heating element, and a recording material that is interposed between the heating element and the heating element. The fixing film and the recording material are held together on the recording material by the nip portion formed by the heating element and the pressure member being held and conveyed together. A heating apparatus for heating a heated image, wherein a rate of temperature rise of the heating element is calculated from an output of the temperature measuring element, and when the value exceeds a certain value, the power supply to the heating element is stopped. 3. The heating device according to claim 1, wherein the temperature rising speed is compared with a constant value only when the temperature detecting element detects a temperature equal to or higher than a set target temperature of the heating device. Heating equipment. 4. The heating device according to claim 1, wherein when the heating device is started up, the temperature rise speed is compared with a value different from a constant value used for comparison in a normal state, and the temperature rise speed is adjusted to the value. A heating device characterized in that when a value is exceeded, the power supply to the heating element is stopped. 5. An image forming apparatus using the heating device according to claim 1, 2, 3, or 4 as image fixing means.