JP2001194950A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device equipped with a protective circuit which operates by detecting an AC power voltage applied to a fixing roller, even when an insulating layer of the fixing roller is in the middle of insulation deterioration. SOLUTION: In the fixing device equipped with a fixing roller 40 constituted by laminating a planar heating element 42 through an insulating layer 44 on the inside wall of a metal cylindrical body 43, and the protective circuit 51 for preventing overheating of the planar heating element 42 by a breakdown between the metal cylindrical body 43 and the planar heating element 42, the protective circuit 51 has a reference voltage generating circuit 36 which generates the reference voltage, a voltage detection circuit 34 which detects the voltage of the metal cylindrical body 43, an abnormality detection circuit 30 which outputs an abnormal detecting signal when a detection voltage exceeds the reference voltage by comparing a detection potential detected by the voltage detection circuit 34 and the reference voltage, and a cutoff circuit 22 which detects an abnormal detecting signal and intercepts an electric power supplied from a power source to the planar heating element 42.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device using a fixing roller in which a sheet heating element is laminated on an inner wall of a metal cylinder via an insulating layer, and more particularly, to a fixing device between a metal cylinder and a sheet heating element. The present invention relates to a fixing device provided with a protection circuit for preventing overheating of a sheet heating element due to dielectric breakdown of the fixing roller and protecting the fixing roller from red heat, fire spread, smoke generation, and the like.

[0002]

2. Description of the Related Art A fixing device incorporated in an electrophotographic image forming apparatus such as a copying machine has a fixing roller and a pressure roller, and passes a printing paper holding an unfixed toner image between the two rollers. Some fixation is carried out. The fixing roller has a built-in heating element such as an electric heater for melting unfixed toner and fixing the unfixed toner on printing paper. As this type of heating element, a linear heating element has been widely used, but in recent years, a fixing roller having a configuration in which a sheet heating element is laminated on an inner wall of a metal cylinder with an insulating layer interposed therebetween has been developed. But,
The insulating material used for the insulating layer that insulates the metal cylinder and the sheet heating element is high temperature generated by the sheet heating element,
Alternatively, deterioration is promoted as time passes because the device is placed under adverse conditions such as a heat cycle in which high and low temperatures alternate. If the insulating material of the insulating layer deteriorates and the insulating property decreases, a short circuit may occur between the metal cylinder and the sheet heating element. When a short circuit occurs at two or more locations, current does not flow between the short-circuit positions on the planar heating element, and current flows through the metal cylinder. As a result, in locations other than the short-circuit position of the sheet heating element, the resistance value calculated in all current paths is lower than usual, so that a larger current flows than usual. In this way, the current flowing through the planar heating element becomes abnormally large, and the planar heating element is overheated. For this reason, a recent fixing device has been provided with a protection circuit for detecting a short circuit between the sheet heating element and the metal cylinder. Hereinafter, a fixing device having a conventional protection circuit will be described.

FIG. 4 is a circuit diagram of a fixing device having a conventional protection circuit. AC (AC) input from commercial power supply 10
The AC power supply voltage such as 0 V is input to the fixing control circuit 10 and also to the primary side circuit (power supply circuit) 14. The AC power supply voltage input to the fixing control circuit 10 is supplied to the sheet heating element 42 in the fixing roller 40 via the relay RL1 and the triac TRC1, and the sheet heating element 4
2 to generate heat. The circuit including the capacitor C12 and the resistor R11 installed in parallel with the triac TRC1 is a snubber circuit for preventing the TRC1 from malfunctioning. The sheet heating element 42 is made of metal and is further laminated inside an insulating layer 44 laminated on the inner peripheral surface of a tubular metal cylinder 43. Therefore, in the normal state, the voltage supplied to the planar heating element 42 is cut off by the insulating layer 44 and is not transmitted to the metal cylinder 43 made of metal.
A conductive brush 20 is in contact with the surface of the metal cylinder 43 to remove static electricity. In the normal state as described above, the voltage supplied to the sheet heating element 42 is not applied to the metal cylinder 43, so the voltage supplied to the brush 20 is applied to the sheet heating element 42. Not even. On the other hand, the AC power supply voltage input to the primary side circuit 14 is full-wave rectified by the diode bridge BR1 and further smoothed by the capacitor C11. (DC)
Voltage. This DC voltage is turned on / off by the switching transistor Q1, and a pulse voltage is supplied to the primary winding N1 of the switching transformer T1 to generate a pulse output voltage on the secondary winding N2. In the secondary circuit 16, which receives the supply of the pulse voltage from the secondary winding N2, rectifies and smoothes the pulse voltage, and supplies it as a DC power supply voltage to each unit in the image forming apparatus. The protection circuit 50 receives the power supply voltage cutoff signal via the photocoupler PC2 through the abnormality detection circuit 18 that outputs a power supply voltage cutoff signal for instructing whether or not to cut off the AC power supply voltage supplied to the fixing roller 40.
And a power supply voltage cutoff circuit 22 for cutting off the C power supply voltage.

The abnormality detecting circuit 18 generates a power supply voltage cutoff signal by dividing the voltage on the surface of the metal cylinder 43 obtained from the brush 20 by the resistors R6 and R7 and smoothing the voltage by the capacitor C2. The power supply voltage cutoff circuit 22 receives the supply of the DC power supply voltage from the secondary side circuit 16 and cuts off the AC power supply voltage supplied to the fixing roller 40 by opening the relay RL1 in the fixing control circuit 10. The collector side of the photocoupler PC2 in the power supply voltage cutoff circuit 22 is connected to a DC power supply voltage via a resistor R21, and the emitter side of the photocoupler PC2 is grounded via a resistor R22. Thyristor SCR is connected between DC power supply voltage and ground.
1 has a resistor R23 on the cathode side and a resistor R24 on the anode side. The gate of the thyristor SCR1 is connected to the emitter side of the photocoupler PC2 and receives a power supply voltage cutoff signal. Note that the capacitor C
Reference numeral 21 prevents a malfunction of the thyristor SCR1 by smoothing the power supply voltage cutoff signal. A series circuit of the coil portion of the relay RL1 and the transistor Q2 is further provided between the DC power supply voltage and the ground. The collector of the transistor Q2 is connected to the coil of the relay RL1, the emitter of the transistor Q2 is connected to ground, and the base of the transistor Q2 is connected to the thyristor SCR1.
Connected to the cathode side. Power supply cutoff signal (ON)
Is input to the photocoupler PC2, the photocoupler P
C2 is turned on, the gate of thyristor SCR1 is turned high, and SCR1 is turned on. Then
The voltage between the DC power supply voltage and the ground is the resistance R23 and the resistance R
The voltage divided by 24 is applied to the base of the transistor Q2, turning on the transistor Q2. When the transistor Q2 is turned on, a current flows through the coil of the relay RL1, whereby the opening / closing portion of the relay RL1 is opened and the AC power supply voltage to the fixing roller 40 is cut off.
As described above, the protection circuit 51 of the conventional fixing device divides and detects the voltage output when the sheet heating element 43 and the metal cylinder 40 are short-circuited, and drives the photocoupler PC2 based on the detected voltage. By driving the relay RL1 to cut off the power supply to the sheet heating element 43, the abnormal current is prevented from flowing through the sheet heating element 43 so that the fixing roller 40
Is protected.

[0005]

However, in the above-described conventional protection circuit 51, the voltage detected by the brush 20 in contact with the surface of the metal cylinder 43 is divided and output to the photocoupler PC2. If a relatively high voltage was not detected by the brush 20, the protection circuit for the fixing device was not driven. Specifically, the photocoupler PC2 is driven unless the triac TRC1 is in the ON state and a high voltage is not detected due to the complete breakdown of the insulating material of the insulating layer of the fixing roller. As a result, a sufficient current did not flow, so that no abnormality was detected and the protection circuit of the fixing device was not driven. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described conventional problems, and detects an AC power supply voltage applied to a fixing roller even when the insulation layer of the fixing roller is in the process of insulation deterioration. It is an object of the present invention to provide a fixing device provided with a protection circuit to perform the fixing.

[0006]

According to one aspect of the present invention, there is provided a fixing roller comprising a sheet heating element laminated on an inner wall of a metal cylinder via an insulating layer. A fixing circuit for preventing overheating of the sheet heating element due to dielectric breakdown between the metal cylinder and the sheet heating element, wherein the protection circuit generates a reference voltage for generating a reference voltage; Circuit, a voltage detection circuit for detecting the voltage of the metal cylinder, and comparing the detection potential detected by the voltage detection circuit with the reference voltage, and detecting an abnormality when the detection voltage exceeds the reference voltage. An abnormality detection circuit that outputs a signal, and a shutoff circuit that detects the abnormality detection signal and shuts off power supplied from the power supply to the planar heating element. According to a second aspect of the present invention, in the fixing device according to the first aspect, the protection circuit includes a photocoupler for transmitting the abnormality detection signal from the abnormality detection circuit to the cutoff circuit, and drives the photocoupler. Power for controlling the power supplied from the power supply to the abnormality detection circuit is obtained not from the metal cylinder short-circuited to the sheet heating element due to dielectric breakdown. According to a third aspect of the invention, in the fixing device of the second aspect, the reference voltage generation circuit generates the reference voltage proportional to an input voltage of the fixing roller. According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the fixing device further includes a contact member that contacts the metal cylinder, and the contact member is connected to a primary side of the power supply circuit via a resistor. It is characterized by being connected to a virtual ground or the like of a circuit.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on illustrated embodiments. FIG. 1 is a block diagram of a fixing device showing an example of an embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of an abnormality detection circuit in FIG. 1, and FIG. 3 is a protection circuit and its periphery. FIG. 3 is a circuit diagram showing a circuit. 1 to 3, the same reference numerals are given to the same components as those of the conventional fixing device shown in FIG.
Duplicate description will be omitted as appropriate. As shown in FIGS. 1 to 3, in the fixing device of this embodiment, the configuration of the abnormality detection circuit 30 in the protection circuit 51 is different from the conventional one shown in FIG. The abnormality detection circuit 30 according to the present embodiment is configured as shown in FIG.
The power supply voltage is obtained from the winding N3 of the transformer T1 as shown in FIG.
Since the abnormal voltage on the three surfaces is the detected voltage and not the power supply voltage, the photocoupler PC2 can be driven regardless of the magnitude of the detected voltage. Further, as shown in FIG.
A rectifier circuit 32 that rectifies the power supply voltage obtained from the first winding N3 into a DC voltage, a reference voltage generation circuit 36 that generates an arbitrary reference voltage based on the DC voltage output from the rectifier circuit 32, and a brush. A voltage detection circuit 34 for dividing the voltage on the surface of the metal cylinder 43 obtained from the voltage detector 20 to detect the potential on the surface of the metal cylinder 43, and comparing the detected potential with a reference voltage to cause the fixing roller 40 to have an abnormality such as insulation breakdown. And an abnormal voltage detection circuit (abnormality detection circuit) 38 that detects the occurrence of a power failure and outputs a power supply voltage cutoff signal (abnormality detection signal).

Next, each circuit shown in FIG. 2 will be described in more detail with reference to FIG. The rectifier circuit 32 includes a transformer T
This circuit includes a diode D1 for rectifying a pulse voltage input from one winding N3 into a DC voltage, a resistor R1 for adjusting the DC voltage, and a capacitor C1 for smoothing the DC voltage. The rectifier circuit 32
Is composed of a resistor R4 and a resistor R5 that divide the DC voltage obtained in step (1) to generate a reference voltage. The metal cylinder voltage detection circuit 34 is provided in parallel with the resistors R6, R7, and R7 that divide the voltage on the surface of the metal cylinder 43 detected by the brush 20 to generate a detection voltage. Capacitor C for smoothing the detection voltage output to detection circuit 38
2 The abnormal voltage detection circuit 38 receives the reference voltage and the detection voltage, and outputs the power supply voltage cutoff signal to the photocoupler PC2 when the detection voltage becomes higher than the reference voltage.
, An operational amplifier IC1 that outputs to the input side anode, a resistor R9 that adjusts the output voltage of the operational amplifier IC1, and a resistor R8 that adjusts the voltage of a circuit that feeds back the output of the operational amplifier IC1 to the reference voltage. The brush 20 of the present embodiment is connected to the abnormality detection circuit 30 and a virtual ground (primary zero potential) of the primary circuit (power supply circuit) 14 via the metal cylinder voltage detection circuit 34. Therefore, the static electricity charged on the metal cylinder 43 by the paper passing flows to the virtual ground (primary zero potential) of the abnormality detection circuit 30 and the power supply circuit 14 and is discharged.

The operation of the abnormality detection circuit 30 of this embodiment is as follows. The rectifier circuit 32 always supplies the DC power supply voltage generated from the pulse voltage to each subsequent circuit, and the reference voltage generation circuit 36 always supplies the reference voltage generated from the DC power supply voltage to the inverting input terminal of the operational amplifier IC1. The voltage on the surface of the metal cylinder 43 obtained from the brush 20 is divided by the resistors R6 and R7, and
2, and becomes the detection voltage smoothed by the operational amplifier IC1.
Is supplied to the non-inverting input terminal of. If the input detection voltage does not exceed the reference voltage, a low level is output from the operational amplifier IC1, and a high level for driving the output side of the photocoupler PC2 is not output. However, when the input detection voltage exceeds the reference voltage, the output of the operational amplifier IC1 becomes a high level for driving the output side of the photocoupler PC2, and drives the power supply voltage cutoff circuit 22 at the subsequent stage. Then, the power supply voltage cutoff circuit 22 cuts off the AC power supply voltage supplied to the fixing roller 40 by opening the relay RL1 in the fixing control circuit 10. In the abnormality detection circuit 30 configured as described above, the reference voltage can be set to an arbitrary value. Even if an abnormal detection voltage is input to the abnormality detection circuit 30, the voltage is detected and the fixing roller 4
The power supply voltage supplied to 0 can be cut off.

In this embodiment, the detection voltage is A
The reference voltage generated from the output of the transformer T1 fluctuates in proportion to the AC input voltage.
The operational amplifier IC1 similarly calculates the difference between the detected voltage and the reference voltage which fluctuate in proportion, so that the noise component also fluctuates according to the fluctuation of the input detection voltage. Therefore, the S / N ratio does not change due to the change in the detection voltage. Further, in this embodiment, the static electricity charged in the metal cylinder 43 in the metal housing 40 flows from the brush 20 to the virtual ground via the resistors R6 and R7 and is discharged. Therefore, the static electricity charged on the metal cylinder 43 can be removed. In this embodiment, the operational amplifier IC1 is used for the abnormal voltage detection circuit 38, but a comparator may be used instead of the operational amplifier. Although the brush 20 is used to detect the voltage of the metal cylinder 43, the voltage may be detected directly from the metal cylinder 43 without using the brush 20.

[0011]

As described above, according to the first aspect of the present invention,
By appropriately setting and changing the value of the reference voltage, even if a small detection voltage such as that generated at the time of abnormality during the dielectric breakdown of the insulating layer of the fixing roller is input to the abnormality detection circuit, Since the voltage can be detected and the power supply voltage supplied to the fixing device can be cut off, the protection that operates by detecting the power supply voltage applied to the metal cylinder even if the insulation layer of the fixing roller is in the process of insulation deterioration. A fixing device including a circuit can be provided. According to the second aspect of the present invention,
In addition to claim 1, the power for driving the photocoupler for transmitting the abnormality detection signal from the abnormality detection circuit to the cutoff circuit is supplied from the power supply, not from the metal cylinder short-circuited to the sheet heating element due to insulation breakdown. Since the power supply to the detection circuit is obtained from the controlling power supply circuit, the photocoupler can be driven even if the sheet heating element of the fixing roller and the metal cylinder do not become completely short-circuited. , The protection circuit can be operated more reliably. According to the third aspect of the present invention, in addition to the second aspect, since the reference voltage is generated in proportion to the input voltage of the fixing roller, the variation of the S / N ratio due to the variation of the detection voltage can be suppressed. According to the fourth aspect of the present invention, since the contact member that contacts the metal cylinder is grounded via the resistor, static electricity charged on the metal cylinder is discharged from the contact member via the resistor and removed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a fixing device showing an example of an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an abnormality detection circuit in FIG. 1;

FIG. 3 is a circuit diagram showing a protection circuit and its peripheral circuits.

FIG. 4 is a circuit diagram showing a protection circuit of a conventional fixing device and its peripheral circuits.

[Description of Signs] 10: Fixing control circuit, 14: Primary circuit, 16
... Secondary circuit, 18, 30 ... Abnormality detection circuit, 2
0: brush (contact member), 22: power supply voltage cutoff circuit, 32: rectifier circuit, 34: voltage detection circuit,
36: reference voltage generation circuit, 38: abnormal voltage detection circuit, 40: fixing roller, 42: sheet heating element,
43: metal cylinder, 44: insulating layer, 50, 51
..Protection circuits

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 3/00 335 H05B 3/00 335 F term (Reference) 2H027 DA03 DA32 DE04 EA12 EC06 ED25 EF09 EK06 HA01 2H033 AA24 BA31 BB01 CA02 CA04 CA23 CA44 3K058 AA16 AA42 BA18 CA03 CA23 CA41 CA68 CD01 CD04 CE02 CE13 CE17 CE19 DA03 GA06 5H323 AA36 BB03 CA06 CB03 DA01 DB04 JJ03 MM02 NN01 QQ05 RR04 RR10 SS10 TT09 9A001 BB06 HKK

Claims (4)

[Claims] A fixing roller formed by laminating a sheet heating element on an inner wall of a metal cylinder via an insulating layer; and a fixing roller formed by laminating the sheet heating element due to dielectric breakdown between the metal cylinder and the sheet heating element. In a fixing device including a protection circuit for preventing overheating, the protection circuit includes a reference voltage generation circuit that generates a reference voltage, a voltage detection circuit that detects a voltage of the metal cylinder, and the voltage detection circuit. An abnormality detection circuit that compares the detected voltage detected by the above with the reference voltage, and outputs an abnormality detection signal when the detected voltage exceeds the reference voltage, and detects the abnormality detection signal and supplies a power to the surface. And a shutoff circuit for shutting off power supplied to the heating element. 2. The protection circuit according to claim 1, further comprising: a photocoupler for transmitting the abnormality detection signal from the abnormality detection circuit to the shutoff circuit, and supplying power for driving the photocoupler from the power supply to the abnormality detection circuit. 2. The fixing device according to claim 1, wherein the power supplied to the fixing device is obtained from a power supply circuit that controls the power supply to the fixing device. 3. The fixing device according to claim 2, wherein the reference voltage generation circuit generates the reference voltage proportional to an input voltage of the fixing roller. 4. The method according to claim 1, further comprising: a contact member that contacts the metal cylinder, wherein the contact member is connected to a virtual ground of a primary circuit via a resistor. The fixing device as described in the above.