JPH08286542A - Electromagnetic induction type fixing device - Google Patents

Abstract

PURPOSE: To provide an electromagnetic induction type fixing device capable of detecting a temperature with excellent responsiveness and accuracy and preventing the overrising of the temperature, so as not cause the burning of a transfer paper and smoking by detecting the Curie point of the magnetic material of a fixing roller and using the Curie point for the prevention of the overrising of the temperature, so that the fixing device can hardly affected by dispersion in parts, a set position for attaching, a set environment, etc. CONSTITUTION: The electromagnetic induction type fixing device is provided with a primary coil part 4 interlinked with an external magnetic circuit part 3 for forming a magnetic loop on both end parts of the internal magnetic circuit part 2 of the fixing roller 1, a secondary coil part 5 formed outside the internal magnetic circuit part 2 and a power supply part for feeding power to the primary coil part 4. The Curie point of the magnetic material of which the internal magnetic circuit part 2 is made is set higher than a carry-over temp. at the time of keeping the fixing roller 1 at a fixable temp. and lower than the carry- over temp. when the fixing roller 1 has thermorunaway at the time of occurrence of abnormality and reaches a temp. requiring protection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in image forming apparatuses such as printers, electrophotographic copying machines and fax machines, and more particularly to an image forming apparatus equipped with an electromagnetic induction type fixing device.

[0002]

2. Description of the Related Art As a conventional electromagnetic induction type fixing device, an electric current is caused to flow through a fixing roller forming a secondary coil by electromagnetic induction to heat the fixing roller due to resistance loss to obtain energy required for fixing. A type of fixing device for fixing is known (Japanese Patent Application No. 6-267339).
In such an electromagnetic induction type fixing device, in order to prevent the temperature of the fixing roller from rising excessively, a heating supply circuit such as a thermostat and a temperature fuse is used as in the conventional fixing device in which the fixing roller is heated by a lamp. It has been common to employ a method of cutting or cutting the heating supply circuit by detecting the heating temperature with a temperature detecting element such as a thermistor.
However, in this method, variations in sensitivity characteristics due to differences in precision of parts, variations in mounting setting position, displacement in mounting position, differences in contact conditions such as cooling air depending on the setting environment,
The accuracy of temperature detection is greatly affected by the attachment of dust and the like, the clogging of paper scraps and paper pieces, and as a result, the transfer paper burns or smokes when the apparatus is abnormal.

[0003]

SUMMARY OF THE INVENTION In the above-mentioned conventional techniques, there are variations in the temperature sensitivity characteristics of components such as thermostats, temperature fuses and thermistors used to prevent overheating of the temperature, variations and deviations in the mounting setting position, and wind caused by the setting environment. The accuracy of temperature detection is greatly affected by the difference in hitting condition, the attachment of dust, the clogging of paper scraps and paper pieces, and there is a problem that the transfer paper is scorched or smoked when the apparatus is abnormal.

[0004]

SUMMARY OF THE INVENTION Therefore, in the present invention, when the fixing device operates abnormally and the temperature of the fixing roller rises excessively to reach the limit temperature, the temperature reached by the magnetic material forming the magnetic circuit of the fixing roller is magnetic. By selecting the material composition so that it becomes the Curie point of the material, when the magnetic material reaches the Curie point, the leakage magnetic flux of the magnetic loop composed of the magnetic circuit inside and outside the fixing roller is reduced. In a very large state, most of the magnetic flux does not intersect with the secondary coil, power transmission to the fixing roller side is stopped, and the temperature rise of the fixing roller is automatically stopped. In addition, if the magnetic material reaches the Curie point and is used to prevent overheating, the physical properties of the material can be used for detection, resulting in variations in parts, installation setting positions, setting environments, dust, etc. It is not easily affected by adhesion, paper scraps, paper jams, etc., and it is now possible to detect temperature with high responsiveness and accuracy, and to prevent overheating of the transfer paper without burning or smoking. An electromagnetic induction type fixing device can be provided.

[0005]

In order to achieve the above object, the invention according to claim 1 has an internal magnetic circuit portion integrally formed with the fixing roller, and the fixing roller at both ends of the internal magnetic circuit portion. A fixed external magnetic circuit part that forms a magnetic loop with the internal magnetic circuit part, and a primary coil part that interlinks with the external magnetic circuit part. It has a secondary coil part formed outside the circuit part and a power supply part for supplying power to the primary coil part, and the Curie point of the magnetic material forming the internal magnetic circuit part is maintained at a temperature at which the fixing roller can fix. The temperature is higher than the temperature reached by the internal magnetic circuit when the temperature is high, and the fixing roller is runaway by heat in the event of an abnormality, and when the temperature reaches the temperature to be protected, the temperature is lower than the temperature reached by the internal magnetic circuit. To be The most important feature. According to a second aspect of the invention, in the electromagnetic induction fixing device according to the first aspect, the internal magnetic circuit section is detected by detecting a current value supplied from the power source section to the primary coil section or a phase difference between the current and the voltage. The main feature is that the electromagnetic induction type fixing device is provided with a Curie point first detecting means for detecting that the toner has reached the Curie point.

According to a third aspect of the present invention, in the electromagnetic induction fixing device according to the first aspect, the magnetic flux in the magnetic coupling portion between the internal magnetic circuit portion and the external magnetic circuit portion is detected to detect the internal magnetic circuit portion. The main feature is that the electromagnetic induction type fixing device is equipped with a second Curie point detecting means for detecting that the toner has reached the Curie point. According to a fourth aspect of the invention, in the electromagnetic induction fixing device according to the second and third aspects, when the Curie point of the internal magnetic circuit section is detected, the current supplied from the power source section to the primary coil section is limited. Alternatively, the main feature is that the fixing device is an electromagnetic induction type, which is provided with a power supply limiting unit that outputs an alarm while limiting the current.

According to the invention of claim 5, the above-mentioned items 1, 2 and
The electromagnetic induction fixing device according to the third aspect is mainly an electromagnetic induction fixing device including current limiting means for limiting the current of the primary coil portion when the internal magnetic circuit portion reaches the Curie point. Characterize. According to a sixth aspect of the present invention, in the electromagnetic induction fixing device according to the fourth and fifth aspects, the temperature rise is prevented so that the temperature of the surface of the fixing roller or the vicinity of the surface does not exceed a predetermined temperature. The main feature of the electromagnetic induction fixing device is that it does not include a prevention unit.

[0008]

According to the first aspect of the invention, in the electromagnetic induction type fixing device configured as described above, the internal magnetic circuit portion formed integrally with the fixing roller and the magnetic loop together with the internal magnetic circuit portion are formed. It has an external magnetic circuit section, a primary coil section that links the external magnetic circuit section, a secondary coil section formed outside the internal magnetic circuit section, and a power supply section that supplies power to the primary coil section. The Curie point of the magnetic material that constitutes the circuit section is higher than the temperature reached by the internal magnetic circuit section when the fixing roller is maintained at a temperature at which it can be fixed. When the temperature is reached, the temperature is lower than the temperature reached by the internal magnetic circuit, so the temperature control function of the fixing roller becomes abnormal,
The temperature of the fixing roller rises rapidly, and the temperature of the magnetic circuit inside the fixing roller also rises due to heat transfer from the fixing roller.
When the Curie point of the magnetic material is reached, the magnetic permeability (μ), which is a magnetic property, suddenly decreases, and the property as a magnetic material is lost. As a result, a part of the magnetic loop that is formed by the magnetic circuit section inside and outside the fixing roller loses its function, and the magnetic flux formed by exciting the primary coil is It is not limited to the inside of the magnetic circuit part and exists in the surrounding space. In other words, there is a large amount of magnetic flux leakage. The fact that the leakage magnetic flux becomes very large means that most of the magnetic flux generated by the primary coil does not intersect with the secondary coil, and the function of the transformer composed of the magnetic circuit of the primary coil and the secondary coil is lost. Means that. As a result, electric power cannot be transmitted from the primary coil to the secondary coil, and the temperature rise of the fixing roller on the secondary coil side is stopped.
That is, it can function as an overheat prevention device in which the temperature rise stops at the Curie point. Further, if the Curie point of the magnetic material can be detected, it can be understood that the temperature of the fixing roller has become abnormal and has reached the temperature to be protected.

According to a second aspect of the invention, in the electromagnetic induction fixing device according to the first aspect, the current value or the current supplied from the power source to the primary coil in order to detect the Curie point of the internal magnetic circuit. Since a Curie point first detecting means capable of detecting the phase difference between the voltage and the voltage is provided, when the temperature of the fixing roller becomes abnormally high and the magnetic material of the internal magnetic circuit section reaches the Curie point, the primary coil section is formed. The input impedance of the primary coil section is greatly reduced and a large current flows. Therefore, it is possible to know the time when the Curie point is reached by detecting the change in the value of the current supplied from the power source section to the primary coil section by the Curie point first detecting means. Further, when the Curie point of the magnetic material is reached, the leakage magnetic flux increases, the reactance component of the input impedance of the primary coil increases, and the phase of the input current lags the phase of the input voltage.
Therefore, if the Curie point first detecting means detects the phase difference between the current and the voltage, the Curie point of the magnetic material can be detected,
It is possible to reliably know the time when the temperature at which the fixing roller should be protected is reached.

According to a third aspect of the present invention, in the electromagnetic induction fixing device according to the first aspect, in order to detect a Curie point of the internal magnetic circuit section, a magnetic coupling section between the internal magnetic circuit section and the external magnetic circuit section. Since the magnetic material of the internal magnetic circuit section reaches the Curie point when the temperature of the fixing roller becomes abnormally high, the magnetic resistance of the internal magnetic circuit section suddenly increases because it has the second Curie point detection means. And the magnetic flux leakage increases. Therefore, the Curie point second detecting means can detect the change of the magnetic flux in the magnetic coupling portion between the internal magnetic circuit section and the external magnetic circuit section to detect the Curie point of the magnetic material, and the fixing roller reaches the overheated temperature. You can know exactly when you did.

According to a fourth aspect of the present invention, in the electromagnetic induction fixing device according to the second and third aspects, when the Curie point of the internal magnetic circuit section is detected, a current supplied from the power source section to the primary coil section is supplied. Since the power supply limiting means for issuing an alarm is provided at the same time as limiting or limiting the current, the Curie point of the magnetic material is detected by the Curie point first detecting means or the Curie point second detecting means to supply the electric power. The limiting unit limits the current supplied from the power supply unit to the primary coil unit, or the current can be limited and an alarm can be issued at the same time, so that the temperature of the fixing roller becomes abnormally high and reaches the temperature to be protected. At that time, it is possible to provide an electromagnetic induction type fixing device that surely prevents temperature rise.

According to the invention of claim 5, the above-mentioned items 1 and 2 are
In the electromagnetic induction type fixing device according to the items (3) and (3), when the internal magnetic circuit unit reaches the Curie point, a current limiting unit for limiting the current of the primary coil unit is provided. The second Curie point detecting means detects that the magnetic material has reached the Curie point, and the current limiting means can limit or completely cut off the current in the primary coil portion, so that the temperature of the fixing roller is abnormally high. Therefore, it is possible to provide an electromagnetic induction type fixing device capable of reliably performing overtemperature prevention when the temperature reaches the temperature to be protected.

According to a sixth aspect of the present invention, in the electromagnetic induction fixing device according to the fourth and fifth aspects, a temperature for preventing the temperature of the surface of the fixing roller or the vicinity of the surface from being higher than a predetermined temperature. Since the constitution is not provided with the excessive temperature rise preventing means, it is not redundantly provided with the temperature excessive temperature rise preventing means by the Curie point first detecting means or the Curie point second detecting means.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 illustrates an example of an electrophotographic copying machine as an image forming apparatus, but since the configuration and function are known, only an outline will be described. The reading optical system 51 includes a light source 52 for irradiating a document with light, a mirror group 54 for guiding reflected light from the document placed on a contact glass on the upper surface of the apparatus main body to a condenser lens 53, and a collection. It comprises an image reading element 55 for reading the reflected light. In the writing optical system 56, the light is reflected by a polygon mirror 57 that rotates in synchronization with light from a light emitting source (not shown), is condensed by a lens group 58, and is then reflected by a mirror 59 in a predetermined direction. The photoconductor drum 6 which is already charged by the charging charger 60 after being reflected by
It leads to the surface of No. 1 and creates an electrostatic latent image that matches the read image. The electrostatic latent image is visualized by the toner carried by the developing roller 62.

On the other hand, the transfer paper in the paper feed cassette 63 is fed to a predetermined position of the photoconductor drum 61 by the paper feed roller 64, and is moved in synchronization with the rotation of the photoconductor drum 61 (in the arrow direction). After the toner image visualized by the transfer charger 65 is transferred onto the transfer paper, the charge given to the transfer paper is removed by the separation charger 66 to separate the transfer paper from the photoconductor drum 61 and to fix it. The toner image is thermally fixed on the transfer paper by the fixing device 50 including the roller 1 and the backup roller 14 that is in pressure contact with the fixing roller 1. Further, the toner remaining on the surface of the photosensitive drum 61 after the toner image is transferred onto the transfer paper is removed by the cleaning unit 67, and the next photosensitive and electrostatic latent image formation is refrained. The present invention relates to prevention of excessive temperature rise of a fixing device 50 that plays an important part in an image forming apparatus.

FIG. 2 shows the structure of the main part of an embodiment of the fixing device of the present invention. The fixing roller (heating roller) 1 is coated on the conductor cylinder forming the secondary coil part 5 and its surface. And a release layer that plays an important role in fixing the toner, and an internal magnetic circuit section 2 forming a magnetic circuit is integrated with the inner surface of the secondary coil section 5 by a cylindrical magnetic material. Further, the left and right journals 12 and 13 are fixed via the internal magnetic circuit unit 2. The fixing roller is fixed to the image forming apparatus by bearings (not shown), gears, etc. attached to the left and right journals 12, 13. When fixing the unfixed toner image on the transfer paper, the fixing roller is driven by a driving source (not shown).

The backup roller 14 is a roller having a soft layer of silicon rubber or the like on its surface, and the left and right end journals 1 are provided at both left and right ends in the axial direction in the same manner as the fixing roller 1.
5, 5 and 16 are attached, and the image surface of the transfer sheet to be fixed is pressed against the fixing roller 1 with a predetermined force, and is rotated at a roller surface speed substantially equal to that of the fixing roller 1. Therefore, the shaft of the backup roller 14 is provided with a pressing means so that a pressing force is applied in the direction of the fixing roller 1. The backup roller 14 has the same structure as the roller of a conventional electromagnetic induction type or other fixing device. The toner image on the transfer sheet is heated when passing between the rotating fixing roller 1 and the backup roller 14, and the melted toner is pressed against the transfer sheet to be fixed.

The external magnetic circuit portion 3 located outside the fixing roller 1 has a magnetic material 3a penetrating the inside of the primary coil portion 4 parallel to the fixing roller 5 and the axial direction of the internal magnetic circuit portion 2 inside the fixing roller 1. The magnetic circuit is composed of a coupling portion 3b that magnetically couples with the circuit portion 2 at both ends, and together with the internal magnetic circuit portion 2 constitutes a magnetic circuit that goes around. When the primary coil unit 4 is excited by an AC power supply (not shown), a magnetic flux is formed in the loop of this magnetic circuit, and a current is applied to the secondary coil unit 5 of the fixing roller 1 configured to intersect with this magnetic flux. Heat is generated due to flow and resistance loss.

As described above, the fixing roller 1 has a cylindrical portion of a magnetic material forming the internal magnetic circuit portion 2, a secondary coil portion 5 formed on the surface of the cylindrical portion, and a secondary coil portion 5 on the secondary coil portion 5. It is composed of a release layer coated on. The magnetic material forming the cylindrical portion 2 is ferrite, the secondary coil portion 5 is an aluminum cylinder, and the secondary coil portion 5 is fixed to the ferrite by adhesion. It is also possible to form a secondary circuit by applying a conductive material to the surface of the magnetic material, vapor deposition, or the like. Further, the magnetic coupling between the internal magnetic circuit unit 2 and the external magnetic circuit unit 3 is configured so as not to change due to the rotation of the fixing roller 1, and the both are arranged to face each other.

3A and 3B show the fixing roller 1 of FIG.
FIG. 3 shows a part of the modified example of FIG. 1, in which the internal magnetic circuit portion 2 of the fixing roller 1 is formed of a columnar magnetic material, the secondary coil portion 5 is formed on the surface of the internal magnetic circuit portion 2, and the surface of the secondary coil portion 5 is released from the mold. The left journal 12 (13 in the case of the right journal) is attached by sequentially laminating layers, forming holes in both ends of the cylindrical magnetic material 2, and adhering while positioning the holes by the holes. A coupling portion 3 for magnetically coupling the magnetic circuit between the journal mounting portion and the secondary coil portion 5 with the cylindrical surface 3b '.
b and the magnetic material 3a which penetrates the inside of the primary coil part 4 face b, and comprise a magnetic loop.

The magnetic coupling surface on the cylindrical surface also has a function of forming a loop of a magnetic circuit while absorbing thermal expansion of the magnetic material, displacement of the mounting position and the like. Therefore, the slide surface 3 where the magnetic material 3a and the coupling portion 3b in the figure are joined
Although c is not necessary for coping with thermal expansion, it is separated by a surface which is a slide surface 3c for convenience of attaching the primary coil portion 4 (not shown) to the external magnetic circuit portion 3 in this embodiment. Allowed and fixed without sliding.

In the embodiment shown in FIGS. 2 and 3, the Curie point of the magnetic material forming the internal magnetic circuit section 2 of the fixing roller 1 is set to the normal temperature reached by the internal magnetic circuit section 2 in the normal use state of the fixing device. Higher Curie point temperature,
Due to some abnormality, the temperature of the fixing roller 1 cannot be controlled, the temperature of the surface of the fixing roller 1 rises above the fixing temperature, and the apparatus is damaged, smoke is emitted, and the transfer sheet is smoked.
The Curie point temperature is set to be lower than the limit temperature reached by the internal magnetic circuit unit 2 when the temperature rises to a temperature that may cause ignition.

In order to prevent damage to the apparatus, to prevent smoke from the apparatus, to prevent ignition of the apparatus, to prevent smoking of the transfer sheet, to prevent ignition of the transfer sheet, and to protect the transfer sheet. The allowable temperature of the fixing roller 1 at the time of abnormality varies depending on the purpose. Therefore, it is necessary to use different Curie points of the magnetic material forming the internal magnetic circuit section 2 depending on the purpose to be protected. For example, in order to prevent the release layer on the surface of the fixing roller 1 from being damaged, the temperature that the release layer can withstand is usually 230 ° C.
Therefore, the temperature of the surface of the fixing roller 1 needs to be kept below the abnormal temperature, so that the Curie point of the magnetic material of the internal magnetic circuit section 2 needs to be as low as about 230 ° C. Further, when the purpose is to prevent smoking of the transfer paper, the surface temperature of the fixing roller is set to 350
Since it is only necessary to keep the temperature at about ℃, it is possible to use a magnetic material having a higher Curie point than that for the purpose of protecting the release layer. Moreover, since the Curie point of ferrite, which is a magnetic material that is normally used, is often 300 to 450 ° C., the material is easily available.

In the embodiment shown in FIG. 2, the internal magnetic circuit portion 2 of the fixing roller 1 has a cylindrical shape (hollow cylindrical shape) and is in close contact with the fixing roller 1, and the heat between the fixing roller 1 and the internal magnetic circuit portion 2 is increased. The transmission is good, and when the cylinder is thin, the fixing roller 1
The temperature difference between the surface and the internal magnetic circuit portion 2 is small, and a magnetic material having a Curie point close to the temperature for limiting the surface temperature of the fixing roller 1 may be selected. When the thickness of the cylinder is large, or when the internal magnetic circuit portion 2 is cylindrical (non-hollow) as in the embodiment of FIG. 2, the surface temperature of the fixing roller 1 which is the heat generating portion and the internal magnetic field A difference in temperature occurs between the circuit section 2 and the circuit section 2.

However, in the portion where the temperature of the magnetic material of the fixing roller 1 reaches the Curie point, the magnetic characteristics are lost and the magnetic resistance is greatly increased. When the magnetic reluctance becomes high, it becomes difficult for the magnetic flux to pass through that portion, and the magnetic flux concentrates on other portions that have not reached the Curie point. As a result, the magnetic flux density of the portion that has not reached the Curie point increases. As the cross-sectional area of the magnetic circuit in the portion reaching the Curie point increases, the magnetic flux density in the portion not reaching the Curie point increases and finally reaches the saturation magnetic flux density. Therefore, even if the temperature of the magnetic material is equal to or lower than the Curie point, if the magnetic flux density reaches the saturation magnetic flux density, the magnetic resistance is significantly increased as in the case where the Curie point is reached. The function as a transformer for transmitting energy to the part 5 is lost,
Energy cannot be transmitted to the fixing roller 1 forming the secondary coil portion 5, and the temperature rise stops.

In the actual design, for example, the magnetic flux density of the magnetic circuit in a normal use condition is set to 90% of the saturation magnetic flux density.
%, The fixing roller 1 of the internal magnetic circuit unit 2
If the temperature of the magnetic material from the portion in contact with the position of 10% of the cross-sectional area of the magnetic circuit exceeds the Curie point, the temperature rise of the fixing roller 1 can be suppressed. That is, if the entire internal magnetic circuit portion 2 does not reach the Curie point and the magnetic circuit portion of a predetermined portion near the fixing roller 1 reaches the Curie point, abnormal heating of the fixing roller 1 can be protected, so that the internal magnetic circuit portion can be protected. The Curie point of the magnetic material 2 can be set to a value close to the temperature of the surface of the fixing roller 1 to be protected. Further, since the entire internal magnetic circuit section 2 can be protected by reaching a Curie point, it has a function as a protective device with a quick response.

In the embodiment shown in FIG. 3, the internal magnetic circuit portion 2 of the fixing roller 1 has a cylindrical shape, has a longer axial length than the fixing roller 1 which is a heat generating portion, and protrudes at both ends. Therefore, the heat received from the fixing roller 1 at both ends is small and the amount of heat radiated to the surroundings is large, so that the temperature rise at the time of abnormality is small and the time required for the rise is large. However, in the abnormal temperature rise prevention method of the present application, it is not always necessary that all of the internal magnetic circuit unit 2 of the fixing roller 1 reach the Curie point, and if a part of the magnetic path reaches the Curie point and the magnetic resistance increases, the leakage flux will increase. Is increased, power cannot be transmitted from the primary coil unit 4 to the secondary coil unit 5, and further heating of the fixing roller 1, which is the secondary coil unit 5, is prevented. In this embodiment, the vicinity of the central portion of the fixing roller 1 in the axial direction is most unaffected by heat radiation to the surroundings at both end portions, so the temperature rises abnormally at a high rate, the rate of rise is large, and the Curie point is the fastest. Reached, and at that time the function of limiting the abnormal temperature rise worked.

To summarize the above description, in the system of the present application, if the Curie point is exceeded in the longitudinal direction (axial direction) of the internal magnetic circuit portion 2 of the fixing roller 1, that is, in a part of the magnetic flux recirculation direction, that part of the part will be generated. Magnetic resistance increases, leakage magnetic flux increases,
At least the magnetic flux interlinking with the secondary coil portion 5 corresponding to that portion is drastically reduced. As a result, heat generation of the fixing roller 1 corresponding to that portion is suppressed. At this time, even if the Curie point is not exceeded over the entire cross section of the magnetic material, the magnetic flux density in the portion not exceeding the Curie point is increased. As a result, if the saturation magnetic flux density of the magnetic material is exceeded, the The increase in resistance causes the function of limiting the abnormal temperature rise at that time. That is, when the portion of the magnetic material corresponding to the portion where the temperature rises most rapidly during an abnormality reaches the Curie point, the function of limiting the abnormal temperature rise works at that point. If the temperature of only a part of the magnetic material reaches the Curie point, the function of limiting the abnormal temperature rise works at that time, so that the response speed is fast.

Further, if only the magnetic material near the contact portion of the fixing roller 1 to be protected when the abnormal temperature rises reaches the Curie point, the protective function works, so that the temperature of the fixing roller 1 during the protective function operation and The temperature difference of the Curie points of magnetic materials is small. Therefore, it is easy to determine the Curie point of the magnetic material that suits the temperature of the fixing roller 1 to be protected. A portion where the temperature of the fixing roller 1 rapidly rises or a portion where the temperature rises significantly at the time of abnormality can be predicted in advance. The same protection function can be achieved even with the magnetic material of.

FIG. 4 shows an example in which the structure of the fixing roller 1 shown in FIGS. 2 and 3 is represented by electrical symbols. The power supply unit 6 supplies electric power for raising the fixing roller 1 to a required temperature, and the power supply switch 21 has a function of controlling connection of the power supply unit 6. The converter 22 converts the commercial frequency power received from the power supply unit 6 into a direct current, converts the direct current power into an alternating current having a frequency higher than the commercial frequency, and converts the primary coil 2 into a direct current.
5, to the primary coil 25 of the transformer 23 constituted by the secondary coil 26 and the core 28. The frequency of the power to be supplied is set to several KHz to several 100 KHz in order to make the device compact. Since the cross-sectional area of the core 28 of the transformer 23 is inversely proportional to the frequency used, a thinner and smaller core can be used as the frequency becomes higher, which saves materials and the fixing roller 1 can also be made thinner, thereby lowering the heat capacity. Therefore, it is effective to accelerate the temperature rise of the fixing roller 1.

Primary coil 25, secondary coil 26, core 2
Reference numeral 8 is a magnetic circuit loop formed by the primary coil unit 4 of FIG. 1, the secondary coil unit 5 of the fixing roller 1, the internal magnetic circuit unit 2 and the external magnetic circuit unit 3, respectively, indicated by symbols in the circuit diagram. . The equivalent circuit 24 including the secondary coil 26 and the resistor 27 is a circuit symbol that is obtained by disassembling the fixing roller 1 further finely. The resistance 27 is an equivalent resistance of the conductive cylinder forming the secondary coil portion 5 of the fixing roller 1 in the circumferential direction. The output of the temperature detector 30 that detects the temperature of the surface of the fixing roller 1 is connected to the temperature controller 31.

The temperature controller 31 is connected to the converter 22 and exchanges signals with a control device (not shown) via the communication path 29. The temperature controller 31 compares a preset target temperature with the output of the temperature detector 30 and controls the converter 22 based on the comparison result to set and maintain the temperature of the fixing roller 1 at the target value. To do. Further, the temperature controller 31 has a function of stopping the heating of the fixing roller 1 in response to a command from the controller, and controls the image forming apparatus when the heating of the fixing roller 1 is instructed to reach a target temperature when the temperature is low. It also has a function of sending a signal to the apparatus indicating that the temperature of the fixing device has risen, and a function of sending a signal indicating an abnormality such as disconnection of the temperature detector 30.

FIG. 5 shows another embodiment, which is the Curie point first detection for detecting the time point at which the value of the current supplied to the primary coil 25 or the phase difference between the current and the voltage greatly changes in the circuit of FIG. The difference is that means 7 is added. Since the constituent elements other than the Curie point first detecting means 7 are the same as those in FIG. 4, description thereof will be omitted, and only the Curie point first detecting means 7 indicated by the one-dot chain line will be described.

First, the current detector 7a is inserted in series with the primary coil 25, and information about the value of the current detected by the current detector 7a is sent to the Curie point discriminator 7c. Further, a voltage detector 7b is provided in parallel with the primary coil 25, and voltage information is sent to the Curie point discriminator 7c. In addition, in the Curie point first detecting means 7 for detecting the Curie point from the change of the current value supplied to the primary coil 25,
The voltage detector 7b can be omitted. When the control of the fixing device 50 is lost due to some abnormality, the temperature of the fixing roller 1 goes into a runaway state, and the temperature of the internal magnetic circuit portion 2 of the fixing roller 1 reaches the Curie point, the internal magnetic circuit portion 2 is configured. The characteristic of high magnetic permeability, which is a characteristic of magnetic materials, is lost. When the magnetic permeability is lost, the magnetic resistance of the magnetic circuit rapidly increases and the leakage magnetic flux increases. When the leakage magnetic flux increases, the electromagnetic coupling between the primary coil 25 and the secondary coil 26 becomes extremely small, and electrical energy cannot be transmitted from the primary coil 25 to the secondary coil 26.
Further temperature increase of 6 is prevented.

However, unless the temperature rise is detected by any detecting means, the apparatus is used in this state, and it is used at a high temperature which is not suitable for fixing. In this embodiment, when the internal magnetic circuit unit 2 reaches the Curie point, the input impedance of the primary coil 25 of the transformer 23 is greatly reduced and a large current flows, so that the current detector 7a detects the input current value. Then, by sending the current value information of the primary coil 25 to the Curie point discriminator 7c, it is detected that the internal magnetic circuit unit 2 has reached the Curie point. The detected result is sent to the control unit of the image forming apparatus (not shown) so that the control unit can perform appropriate abnormality processing and abnormality display. As a current detection method by the current detector 7a, a detection resistor having a small resistance value is provided and detection by a voltage drop method at both ends thereof is generally used. However, a method using a current transformer or a magnetic field generated by a current is detected. It is also possible to use the method.

The Curie point first detecting means 7 for detecting the Curie point from the change in the phase difference between the voltage and the current of the primary coil 25 is provided with the current detector 7a and the voltage detector 7b.
As shown in FIG. 5, the Curie point first detection means 7 is a current detector 7.
a, a voltage detector 7b, and a Curie point discriminator 7c. When the temperature of the fixing roller 1 rises due to some abnormality and the internal magnetic circuit unit 2 of the fixing roller 1 reaches the Curie point, the leakage magnetic flux increases, the reactance component of the input impedance of the primary coil 25 increases, and the phase of the input voltage changes. On the other hand, the phase of the input current will be delayed. In this embodiment, the Curie point discriminator 7c determines the phase difference between the input voltage and the current based on the detection information of the current detector 7a and the voltage detector 7b.
By detecting the change in the phase difference with, it is possible to more reliably detect that the magnetic circuit has reached the Curie point.
As described above, the detected result is sent to the control unit of the image forming apparatus (not shown) so that the control unit can appropriately perform the abnormality processing and the abnormality display.

FIG. 6 shows another embodiment of the present invention, in which leakage magnetic flux is detected near the magnetic coupling portion of the internal magnetic circuit portion 2 and the external magnetic circuit portion 3 in comparison with the embodiment of FIG. The configuration in which the second Curie point detecting means 8 is added is different. Since the constituent elements other than the Curie point second detecting means 8 are the same as those in FIG. 4, description thereof will be omitted, and only the characteristic features of this embodiment will be described. That is, when the temperature of the fixing roller 1 excessively rises due to some abnormality and the internal magnetic circuit portion 2 of the fixing roller 1 reaches the Curie point, the leakage magnetic flux increases. In this embodiment, the increasing magnetic flux leakage is directly detected by the Curie point second detecting means 8. By directly detecting the leakage magnetic flux, it is surely detected that the internal magnetic circuit unit 2 has reached the Curie point. The detected result is sent to a control unit (not shown) of the image forming apparatus so that the control unit can perform appropriate abnormality processing and abnormality display. Hall elements, magnetoresistive elements, detection coils, etc. are generally used as the magnetic sensor.

FIG. 7 is a combination of the embodiment of FIG. 5 and the embodiment of FIG. That is, in this embodiment, the Curie point first detecting means 7 or the Curie point second detecting means 8 detects that the internal magnetic circuit portion 2 of the fixing roller 1 has reached the Curie point, and the information is limited in power supply. A characteristic is that the converter 22 is controlled so as to limit the current received by the means 9 and supplied to the primary coil 25 of the transformer 23. Although not shown, the power supply limiting means 9 can also issue an alarm at the same time as limiting the current. The advantage of this embodiment is that the temperature detector 30
Is separated from the fixing roller 1 for some reason, or has failed, and although the temperature of the fixing roller 1 is actually high, a temperature runaway occurs due to a low detected temperature value obtained from the temperature detector 30, As a result, when the internal magnetic circuit unit 2 reaches the Curie point, the primary coil 2 of the transformer 23
5 has a function of preventing an accident such as overheating and eventually burning out, which is an embodiment corresponding to claim 4.

FIG. 8 shows an embodiment corresponding to claim 5, in which when the internal magnetic circuit section 2 reaches the Curie point, the input impedance of the transformer 23 is lowered, and when an excessive current flows therethrough, The temperature of the primary coil 25 rises,
To prevent the situation such as burnout, the primary coil 2
5 is provided with a current limiting means 10 for limiting the current in series. The current limiting means 10 may be of a self-operating type such as a fuse or a thermoswitch that blows, or it receives a detection output of the first Curie point detecting means 7 or the second Curie point detecting means 8 to perform an interruption operation. It may be like a relay. Even if the installation location is in series with the primary coil 22 as shown in the figure, the power supply unit 6 and the converter 22
It may be installed between and.

In the fourth or fifth embodiment, the power supply limiting means 9 or the current limiting means 10 is provided to prevent the temperature of the fixing roller from overheating. It is possible to omit the overheat prevention means for detecting the temperature of the surface or the vicinity of the surface to prevent the overheat, and to overlap with the overheat prevention means by the Curie point first detecting means or the Curie point second detecting means. I will not have it. As a result, cost increase due to duplication of the detection means is prevented, and the structure and wiring near the fixing roller are simplified.

Conventionally, in the normal fixing device 50, a thermo switch or a temperature fuse is installed in the vicinity of the fixing roller 1 in order to prevent heating in case of emergency. This is done by using various means for the fixing device to prevent temperature runaway and accidents such as burnout, and even when a failure occurs such that these protection means do not operate, a fire or the like occurs. It is provided as a final protection measure to prevent the above. These also comply with safety requirements such as the Electrical Appliance and Material Control Law and UL, and thermo switches and temperature fuses used at that time are those that comply with respective safety standards. By adopting the current limiting means 10 described in FIG. 8 which complies with the safety standard, a conventional thermoswitch (not shown) or a thermal fuse, which is arranged near the fixing roller 1, can be omitted. .

[0042]

As described above, according to the first aspect of the present invention, even when the control function of the fixing device is lost and an abnormality such as temperature heating occurs, the temperature of the Curie point is directly dependent on the property of the magnetic material. Since it is now possible to prevent excessive temperature rise, it is unlikely to be affected by variations in parts such as temperature detection, differences in installation setting position and setting environment, dust adhesion, paper scraps and paper jams, etc. As a result, it is now possible to provide an electromagnetic induction type fixing device in which the transfer paper is not burnt or does not emit smoke and in which safe overheating is prevented.

According to a second aspect of the present invention, the Curie point first detecting means detects the current value or the phase difference between the current and the voltage supplied from the power source section to the primary coil section at the Curie point of the magnetic material of the fixing roller. Since it was possible to detect the time when the temperature greatly changed, and to know the time when the temperature of the fixing roller became abnormally high and reached the temperature to be protected, from the judgment of the output state of the Curie point first detecting means, Since it is now possible to take immediate action when the fixing roller is in an abnormal state, it is possible to provide an electromagnetic induction type fixing device with responsiveness and accuracy, and safe overheat prevention. It was

According to a third aspect of the present invention, the Curie point second detecting means detects the time point at which the magnetic flux of the internal magnetic circuit section greatly changes at the Curie point of the magnetic material of the fixing roller to detect the temperature of the fixing roller. Since it is possible to know for sure when the temperature has risen abnormally and reaches the temperature to be protected, it is possible to quickly take action when the fixing roller is in an abnormal state from the judgment of the output state of the Curie point second detecting means. As a result, it is possible to provide an electromagnetic induction type fixing device which is safe and has high responsiveness and accuracy, and which prevents excessive temperature rise.

The invention according to claim 4 is the above item 2 and
In the electromagnetic induction type fixing device of paragraph 3, when the Curie point first detecting means or the Curie point second detecting means detects the Curie point of the magnetic material of the fixing roller, the power supply limiting means supplies power from the power supply section to the primary coil section. It is now possible to limit the current to be applied, or to issue an alarm at the same time as limiting the current, so when the temperature of the fixing roller becomes abnormally high and reaches the temperature to be protected, each component It is now possible to provide an electromagnetic induction type fixing device that protects the above and securely prevents overheating.

The invention according to claim 5 is the above-mentioned item 1, item 2,
And in the electromagnetic induction fixing device according to the item 3, by the Curie point first detecting means or the Curie point second detecting means,
When the Curie point of the magnetic material of the fixing roller is detected, it becomes possible to limit the current of the primary coil part or completely cut it off by the current limiting means, so that the temperature of the fixing roller becomes higher than that. , The fixing roller and each component cannot be used, the transfer paper is burnt,
It is now possible to eliminate problems such as smoking.

According to a sixth aspect of the invention, in the electromagnetic induction type fixing device according to the fourth and fifth aspects, a power supply limiting means or a current limiting means is provided to prevent the temperature of the fixing roller from rising excessively. As a result, it is possible to omit the overheat prevention means for detecting the temperature of the surface of the fixing roller or the vicinity of the surface to prevent the temperature from rising, preventing the cost increase due to the duplication of the detecting means, and the structure near the fixing roller. The effect of simplifying the wiring has come to be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of an image forming apparatus showing an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a fixing roller of an image forming apparatus showing an embodiment of the present invention.

3A is a side view of a main part of a fixing roller of an image forming apparatus showing an embodiment of the present invention, and FIG. 3B is a front view of a main part of a fixing roller of an image forming apparatus showing the embodiment of the present invention. Fig.

FIG. 4 is an explanatory diagram illustrating an equivalent circuit of a main portion of a fixing roller of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 5 is an explanatory diagram illustrating, with an equivalent circuit, a main part of a fixing roller to which a Curie point first detecting unit according to an embodiment of the present invention is added.

FIG. 6 is an explanatory diagram illustrating, with an equivalent circuit, a main part of a fixing roller to which a second Curie point detecting means according to an embodiment of the present invention is added.

FIG. 7 is an explanatory diagram illustrating an equivalent circuit of a main portion of a fixing roller to which a power supply limiting unit according to an exemplary embodiment of the present invention is added.

FIG. 8 is an explanatory diagram illustrating an equivalent circuit of a main part of a fixing roller to which a current limiting unit according to an embodiment of the present invention is added.

[Explanation of symbols]

1 ... Fixing roller, 2 ... Internal magnetic circuit part, 3 ...
External magnetic circuit part, 3a ... Magnetic material, 3b ... Coupling part, 4 ... Primary coil part, 5 ... Secondary coil part,
6 ... Power supply section, 7 ... Curie point first detecting means, 7
a ... current detector, 7b ... voltage detector, 7c ...
Curie point discriminator, 8 ... Curie point second detecting means, 9 ... power supply limiting means, 10 ... current limiting means,
11 ... Excess temperature rise prevention means, 12 ... Left journal, 13 ... Right journal, 14 ... Backup roller, 15 ... Left end journal, 16 ... Right end journal, 21 ... Power supply Switch, 22 ... converter, 23 ... transformer, 24 ... fixing roller section,
25 ... Primary coil, 26 ... Secondary coil, 27 ...
..Resistance, 28 ... Core, 29 ... Communication path, 30 ...
..Temperature detectors, 31 ... Temperature control devices, 32 ...
Current detector, 33 ... Voltage detector, 34 ... Magnetic detector, 35 ... Fuse, 36 ... Thermoswitch, 50 ... Fixing device, 51 ... Reading optical system,
52 ... Light source, 53 ... Condensing lens, 54 ... Mirror group, 55 ... Image reading element, 56 ... Writing optical system, 57 ... Polygon mirror, 58 ... Lens group , 59 ... Mirror, 60 ... Charger, 61 ... Photosensitive drum, 62 ... Developing roller,
63 ... Paper feeding cassette, 64 ... Paper feeding roller, 65
... Transfer charger, 66 ... Separation charger, 6
7 ... Cleaning unit, 68 ... Thermo switch, 69 ... Magnetic detector, 70 ... Fuse, 7
1 ... Thermo switch.

Claims (6)

[Claims] 1. An internal magnetic circuit portion integrally formed with a fixing roller and an axially opposite end portion of the internal magnetic circuit portion face each other in such a manner that magnetic coupling does not change due to rotation of the fixing roller, and A fixed external magnetic circuit part forming a magnetic loop with the internal magnetic circuit part, a primary coil part interlinking with the external magnetic circuit part, and a secondary coil part formed outside the internal magnetic circuit part. And a power supply unit for supplying power to the primary coil unit, and the Curie point of the magnetic material forming the internal magnetic circuit unit is the internal magnetic field when the fixing roller is maintained at a normal temperature at which fixing is possible. An electromagnetic induction type fixing device characterized in that the temperature is higher than the temperature reached by the circuit section, and is lower than the temperature reached by the internal magnetic circuit section when the fixing roller thermally overruns to reach an excessively high temperature in an abnormal state. 2. A Curie point for detecting that the internal magnetic circuit section has reached the Curie point by detecting a current value supplied from the power source section to the primary coil section or a phase difference between current and voltage. The electromagnetic induction fixing device according to claim 1, further comprising a first detecting unit. 3. Curie point second detection for detecting that the internal magnetic circuit portion has reached the Curie point by detecting a magnetic flux in a magnetically coupled portion of the internal magnetic circuit portion and the external magnetic circuit portion. An electromagnetic induction type fixing device according to claim 1, further comprising means. 4. When the internal magnetic circuit section detects that the Curie point has been reached, the current supplied from the power supply section to the primary coil section is limited, or the current is limited and an alarm is issued at the same time. The electromagnetic induction fixing device according to claim 2, further comprising a limiting unit. 5. The electromagnetic induction type as claimed in claim 1, further comprising a current limiting means for limiting a current of the primary coil portion when the internal magnetic circuit portion reaches a Curie point. Fixing device. 6. The constitution according to claim 4 or 5, characterized in that the fixing roller is not provided with a temperature excessive rise preventing means for preventing the temperature of the surface of the fixing roller or the vicinity of the surface from exceeding a predetermined temperature. Electromagnetic induction type fixing device.