JPH0690585B2 - Fixing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fixing device that controls the temperature of a fixing device or the like used in an image forming apparatus or the like.

[Prior art]

Various heat generating members are used in electronic devices. For example, a fixing device in an image forming apparatus (electronic copying apparatus) is an apparatus that fixes an unfixed toner image transferred on a transfer paper as a stable image on the transfer paper by using high temperature. In general, such a member is required to have a constant temperature, and a constant temperature required for fixing is maintained by controlling on / off of a heating element described later using a temperature sensitive element such as a thermistor. However, if a failure (disconnection) occurs in the above-mentioned heating element, not only fixing failure occurs, but also the apparatus itself is damaged.

In order to prevent this, various control circuits have been devised.

FIG. 4 shows a circuit diagram of a conventional fixing device provided with a circuit for detecting the disconnection of the heating element.

The circuit shown in the figure is a temperature control circuit composed of a bridge circuit composed of a thermistor TH and resistors R ₁ , R ₂ and R ₃ and a comparator Q ₁ , a trigger circuit 1, a transistor Q ₂ and resistors R _{4 to} R ₆ . TRIAC 2, heater H, AC power supply 3, current detection circuit 4
It is composed of a heater disconnection detection circuit.

This circuit normally connects the power supply voltage V _CC to the resistor R ₃ and the thermistor TH.
Voltage V _N divided by and reference voltage V ₁ divided by resistors R ₁ and R ₂
Are compared with the comparator Q ₁ , and the comparison output controls the on / off of the triac 2 via the transistor Q ₂ .
It is a circuit that conducts or interrupts an alternating current to the heater H.
Then, the operating current detection circuit 4 is operated by the comparator Q ₁
In the current detection circuit 4, when the output of the comparator Q ₁ is a high signal, if the current is not supplied from the AC power supply 3, the disconnection signal a is output and the heater H is disconnected. It is to inform that.

[Problems of conventional technology]

However, the conventional temperature control device can detect the breakage of the heater H, but since the current detection circuit 4 is connected to the AC power supply 3 which is a commercial power supply, the current detection circuit 4 can be detected.
Is required to be configured with a high voltage circuit, which is extremely disadvantageous in terms of cost. In addition, the power specifications for each exporting country must be met, and parts cannot be shared.

[Object of the Invention]

In view of the above-mentioned conventional drawbacks, the present invention detects the disconnection of a heater connected to a commercial power source only by a low-voltage control circuit, makes a current detection circuit common without being affected by the power source specifications of each country, and reduces the cost of the device. An object of the present invention is to provide a fixing device having a temperature control circuit that enables the temperature to be lowered.

[Main points of the invention]

In order to achieve the above object, the present invention provides a member to be heated which is heated by a heat source, a detecting means for detecting the temperature of the member to be heated, an output of the detecting means and a reference potential for setting a predetermined temperature. In a fixing device for fixing unfixed toner on a sheet, the predetermined temperature is lowered in synchronization with a timing of conveying the sheet after reaching the predetermined temperature. Inputting the potential changing means for changing the reference potential to switch to the side, the output of the potential changing means and the output of the control means,
It is characterized by having a judging means for judging the disconnection of the heat source on the condition of a signal output from the control means for heating the heat source when the reference potential is switched to the low temperature side.

Example of Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is an external view of the fixing device of the present invention. In the figure, 5 has a heat source 6 such as a heater inside, and Teflon (registered trademark) having heat resistance and toner releasability on the peripheral surface.
It is a heating roll coated with a resin 5a such as the above, and rotates in the direction shown. At the lower part of the heating roll 5, a pressure roll 7 having a peripheral surface coated with silicon rubber or the like having heat resistance and elasticity is pressure-contacted with an appropriate pressure to form a nip portion 8.
It cooperates with the heating roll 5 while being pressed against it.
Then, by nipping and passing the sheet on which the toner image is formed in the nip portion 8 in the direction of arrow A, the sheet is pinched and pressed, and at this time, by the heating action of the heat source 6 and the pressing action of the pressure roll 7, The toner image is heat-fused on the paper to perform the fixing work. The tip of the peeling claw 9 is brought into contact with the paper discharge side on the circumferential surface of the heating roll 5, the paper discharged from the nip portion 8 is peeled from the heating roll 5, and the paper is removed from the machine by a paper discharge roll 10. To discharge.

Further, a temperature detecting thermistor 11 is attached to the peripheral surface of the heating roll 5 in contact with the peripheral surface of the heating roll 5, and the thermistor 11 is attached to the arm 12. The arm 12 is rotatably provided around a shaft 12a.

The temperature control circuit shown in FIG. 1 is provided as a temperature control device in the fixing device having the above-described external configuration.

In the figure, a series circuit of a thermistor 11 which is a temperature sensitive element and a resistor R ₇ is connected in parallel with a series circuit of resistors R ₈ , R ₉ and R ₁₀ to form a bridge circuit. Also, the thermistor 11 and the resistor
The connection point of R ₇ is connected to the non-inverting input of comparator Q ₃ ,
A connection point between the resistor R ₈ resistor R ₉ is connected to the inverting input of the comparator Q _3. Also, the output of the comparator Q ₃ is the resistance R
It is connected to the connection point of ₁₁ and resistor R ₁₂ . The output of the comparator Q ₃ is also connected to the input of the AND gate 19 and the input port I ₀ of the microprocessor (MPU) 14. Resistance R
_A resistor R ₁₃ is connected to the dish at ₁₂ , and the resistors R ₁₁ and R ₁₂ ,
A series circuit is constructed with R ₁₃ . Also, with this resistor R ₁₂
The base terminal of the transistor Q ₄ is connected to the connection point of R ₁₃ . The emitter terminal of the transistor Q ₄ is grounded and the collector terminal is connected to the trigger circuit 15.

Further, the gate terminal of the triac 16 is connected to the trigger output of the trigger circuit 15, and the triac 16, the heater H '(heat source 6 in FIG. 2) and the alternating current 17 constitute a closed circuit.

On the other hand, the print button 1 is connected to the input port I ₁ of the MPU14 described above.
8 is input and is connected from the output port O ₀ to the input of the above-mentioned AND gate 19 via the inverter 20a. And A
The ND gate 19 outputs the disconnection signal b of the heater H'when the conditions described later are met. Furthermore, the output port O ₀ is also connected to the base terminal of the transistor Q ₅ via the resistor R ₁₄ . The collector terminal of the transistor Q ₅ is connected to the connection point of the resistors R ₉ and R ₁₀ which form the above-mentioned bridge circuit, and the emitter terminal is grounded.

Further, the MPU 14 further has an output port O ₁ , and the output of O ₁ is connected via an inverter 20b, which is a driver, to a solenoid 23 that rotates a paper feed roller in order to feed a sheet (not shown) from a cassette. There is. The MPU 14 controls the entire copying apparatus, but other input / output is omitted.

The circuit operation of the fixing device of this embodiment having the circuit configured as described above will be described below.

First, a switch (not shown) is turned on, power is supplied between the terminals 21 and 22, and this circuit is brought into an operating state. When the power is turned on, the surface temperature of the heating roll 5 is the same as room temperature. Therefore, the resistance of the thermistor 11 is high, and the voltage V _N ′ at the connection point between the resistance R ₇ and the thermistor 11 is the voltage at the connection between the resistances R ₈ and R _9.
Higher than V _I ′. Therefore, the output of comparator Q ₃ is
It becomes a high signal to turn on the transistor Q _4, the trigger circuit
Turn on 15 and supply a high signal to the gate of triac 16. By this series of operations, the triac 16 becomes conductive, and an alternating current flows through a closed circuit composed of the AC power supply 17, the heater H ′, and the triac 16. Therefore, the heater H '
The heating roll 5 is heated by the (heat source 6), and the peripheral surface temperature of the heating roll 5 gradually rises.

By this heating operation, the heating roll 5 is gradually heated, and when the thermistor 11 detects the temperature at which the toner can be fixed (about 180 ° C.), the temperature is previously determined by the ratio of the resistance value of the resistor R _{8 and} the resistance value of the resistor R _9. The voltage value (V _I ′) corresponding to 180 ° C is applied to the inverting input terminal of the comparator Q ₃ (However, as will be described later, the transistor Q ₅ turns on and one end of the resistor R ₉ is connected to ground potential. substantially identical is), the input voltage magnitude of V _N 'and V _I' of the comparator Q ₃ are the reverse of the foregoing, the output of the comparator Q ₃ are a low signal. Therefore, the transistor Q ₄ is turned off, the trigger circuit 15 is also turned off, and the AC current flowing through the closed circuit of the AC power supply 17, the heater H ′, and the triac 16 is cut off.

By this circuit operation, the heater H'stops the heating operation.
Heating operation of the heater H 'is stopped and the temperature detected by the thermistor 11 decreases, the output of the comparator Q ₃ again reversed,
The above operation is repeated to control the temperature of the heating roll 5 to a predetermined temperature (180 ° C.).

The circuit operation will be described below with reference to the time chart and temperature characteristic diagram of FIG. When the input to the input port I ₀ is switched from the high level to the low level (time T ₁ ), the MPU 14 judges the ready state of the fixing device. Print button after T ₁
When 18 is pressed, the output port O ₀ outputs low level for about 0.1 seconds. At this time, the transistor Q ₅ is turned off, and a series circuit of the resistor R ₉ and the resistor R ₁₀ is formed. Therefore, the reference voltage V _I ″ is applied to the inverting input terminal of the comparator Q _3. The reference voltage V _I ″ has a temperature of 150 ° C. detected by the thermistor 11.
It is set to the resistance value that the output of the comparator Q ₃ is inverted at the corresponding resistance value at ℃. Therefore, when the output of the output port O ₀ is a low signal, the comparator Q ₃ outputs a high signal only when the temperature of the heating roll 5 is 150 ° C. or lower. The temperature of the heating roll 5 becomes 150 ° C. or lower only when the heater H ′ is disconnected unless the power is turned off. For example, even when the transfer paper passes through the fixing device, the period T in FIG.
As shown in, the temperature of the heating roll 5 never drops below 150 ° C. Also, this temperature of 150 ° C is the minimum temperature required for the fixing device to heat-fix the toner, and is usually
About 180 ℃ is desirable for fixing toner, but 150 ℃
If it is above, there will be no particular problem such as defective fixing.

On the other hand, the AND gate 19 inputs the high or low signal of the comparator Q ₃ as well as the pulse signal from the output port O ₀ through the inverter 20a as described above, and the AND gate 19 outputs the high signal from the inverter 20a. When you type
Check the output of comparator Q ₃ . At this time, if the output of the comparator Q ₃ is a low signal, that is, if it is in the state of time T _{1 to} T ₃ in the time chart / temperature characteristic diagram of FIG. ₃ , the disconnection signal b is output from the AND gate 19. There is no such thing. If the disconnection signal b is not output at the time when the output of the output port O ₀ rises to the high level, the solenoid 23 is turned on, the sheet feeding roller (not shown) rotates, and the copying operation starts.
Output of output port O ₀ is reduced at each copy cycle.
Switch from the high level to the low level for 0.1 second and check the heater H'for disconnection. Since this copy cycle is about 8 seconds, the check is performed once every 8 seconds. If there is no abnormality at each check point, the set number of copies are completed and the copy operation ends. However, if the heater H ′ is broken at the time T _{2 in} the temperature characteristic curve B of FIG. 3, the time T ₂ → T ₃ → T ₄ elapses, and the temperature of the heating roll 5 decreases, At T ₄ , when the high signal output of the comparator Q ₃ is detected, the disconnection signal b is output from the AND gate 19.
Is output. This disconnection signal b is the input port I _{2 of} MPU14.
Is input to, and processing such as copy prohibition and error display is performed.

As described above, the temperature control device of the present embodiment is provided with the comparator.
Sets two reference voltage value corresponding to the fixable temperature and the normal fixing temperature in Q _3, to compare the temperature detected by the thermistor 11 to the comparator Q ₃ at a potential of fixable temperature at a predetermined timing, the heating at this time (if the comparator Q ₃ to output a high signal) if the roll 5 is less than a predetermined temperature, and outputs a disconnection signal b from the aND gate 19 is for detecting that the heater H 'is broken.

Further, in the present embodiment, the temperature of the heating roll 5 (the temperature detected by the thermistor 11) corresponding to the reference voltage compared by the comparator Q ₃ is set to 180 ° C. and 150 ° C. However, the temperature is not limited to these temperatures.

In the above-described embodiment, the temperature check is performed before the start of sheet feeding, but in addition to this, various operations performed in each copy cycle, such as the start of scanning of the optical system and the operation of the sheet discharge switch, are related. Is also good.

Further, the gist of the present invention can be applied to a temperature control device other than the fixing device, for example, a tube wall temperature control device of a fluorescent lamp.
Further, it is needless to say that the invention can be applied to an image forming apparatus other than a copying machine, for example, a fixing device of a page printer using an LED, a laser, a liquid crystal or the like as a print head.

[Effects of the Invention] According to the present invention as described in detail above, since the disconnection detection circuit of the heater can be detected by the configuration of only a simple low voltage circuit such as an AND gate, a high voltage circuit is not required as a circuit, The parts can be shared, and the cost of the device can be reduced. In addition, a single comparator can be used to compare two temperature values (2
Point voltage comparison) is possible.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a temperature control device of this embodiment, FIG. 2 is a configuration diagram of a fixing device in which the temperature control device of this embodiment is used, and FIG. 3 is a time chart and a time chart thereof. FIG. 4 is a circuit diagram of a conventional temperature control device, and FIG. 4 is a temperature characteristic diagram of the heating roll. 5 ... Heating roll, 6 ... Heat source, 11 ... Thermistor, 14 ... Microprocessor (MPU), 17 ... AC power supply, 18 ... Print button, 19 ... AND gate, H, H '... Heater , Q ₃ ... Comparator, Q ₅ ... Transistor.

Claims (1)

[Claims] 1. A heated member heated by a heat source, a detection means for detecting the temperature of the heated member, and an output of the detection means and a reference potential for setting a predetermined temperature are compared to each other. A fixing device for fixing unfixed toner on a sheet, which comprises a control unit for controlling energization, and the reference for switching the predetermined temperature to a low temperature side in synchronization with a timing of conveying the sheet after the predetermined temperature is reached. A signal for inputting the potential changing means for changing the potential and the output of the potential changing means and the output of the control means, and for heating the heat source from the control means when the reference potential is switched to the low temperature side. A fixing device, comprising: a determining unit that determines a disconnection of the heat source based on an output.