JP3303570B2 - Heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copier or printer as a heat fixing device for fixing a developer (toner) transferred to a transfer material by heating with a heater to the transfer material. The present invention relates to a heating device used for the like.

[0002]

2. Description of the Related Art In electrophotographic copying machines and printers,
Generally, a thermal fixing device is provided for fixing the developer transferred to the transfer material to the transfer material by the heat of a heater. The heat fixing device includes a heater that generates heat by electric power supplied from a power supply, and a switch such as a relay or a triac for controlling on / off of the heater. The resistance value of the heater used in the thermal fixing device is usually low at room temperature immediately after power-on, and increases as the temperature of the heater rises after power-on. For this reason, an excessive rush current flows through the heater immediately after the power is turned on, and as a result, there is a possibility that the above-described welding of the relay contacts, breakage of the triac, power supply voltage fluctuation failure, and the like may occur.

As a countermeasure against this, Japanese Patent Application Laid-Open No. Sho 63-31058
Japanese Patent Application Publication No. 7 (1999) discloses measuring the temperature of a heater, connecting a resistor in series to the heater when the heater temperature is low, and short-circuiting the resistor when the heater temperature rises to a predetermined temperature. There is disclosed a technique for suppressing an inrush current at the time of turning on, and for eliminating the influence of the loss due to the resistance when the heater reaches a predetermined temperature.

In Japanese Patent Application Laid-Open No. 3-113519, a phase control means for controlling the phase of a supplied current is provided between a heater and an input power supply for supplying power to the heater. During the corresponding predetermined time, the current supplied from the power supply to the heater is supplied while controlling the phase so as to increase stepwise, and after the lapse of the predetermined time, the above-described phase control is stopped so that power over all phases is supplied. A technique is disclosed that suppresses the inrush current when the power is turned on and reduces the decrease in the rate of increase in the heater temperature.

[0005]

However, in the technique disclosed in Japanese Patent Application Laid-Open No. 63-310587, the time from when the power is turned on to when it is detected that the heater has reached a predetermined temperature is long. In order to suppress the inrush current over time, a resistor having a large rated power is required. Also,
When the temperature of the heater becomes higher than the predetermined temperature, the power is turned off once,
When the heater becomes lower than the predetermined temperature, the power is turned on again.When the power is turned on again, there is a rush current, and there is a possibility of a voltage fluctuation failure of the power supply, but the heater temperature is already at a somewhat high state. Therefore, the resistor is short-circuited immediately when the power is turned on again, and the rush current cannot be suppressed.

Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 3-113519, a phase control circuit is added to the conventional heater control method, so that the cost increases. Further, since the phase control is used, many harmonics are generated, and there is a possibility that the harmonic current may cause a failure in the power supply system. In view of the above circumstances, the present invention provides a heating device that can not only suppress a large inrush current when the heater is at low temperature, but also suppress an inrush current when the temperature of the heater is somewhat high, and prevent a voltage fluctuation failure of the power supply. The purpose is to provide.

[0007]

According to the present invention, there is provided a heating apparatus comprising: (1) a heater that generates heat by electric power supplied from a power supply; and (2) a heater disposed between the power supply and the heater. Power supply control means for controlling whether or not to supply power to the heater based on the temperature of the heater. (3) connected in series to the heater,
A resistor that suppresses a flowing current . (4) A resistor that has a predetermined time constant and is charged to a voltage corresponding to the voltage of the heater, and the voltage of the heater is higher than a predetermined voltage based on the voltage of the capacitor. (5) a second switch arranged in parallel with the resistor, wherein the heater voltage determining means determines that the voltage of the heater is higher than a predetermined voltage; And a resistor short-circuiting means for closing the second switch when the operation is performed and opening the second switch when the voltage of the heater is determined to be lower than a predetermined voltage. It is.

[0008]

According to the heating device of the present invention, it is determined whether the voltage of the heater is higher or lower than the predetermined voltage based on the voltage of the capacitor charged with a predetermined time constant to the voltage corresponding to the voltage of the heater. The second switch is closed and the resistor is short-circuited when the voltage of the heater is determined to be higher than the predetermined value by the resistor short-circuiting means, and the voltage of the heater is lower than the predetermined voltage. Is determined, the second switch is opened to connect the heater and the resistor in series.
In other words, based on the voltage of the capacitor charged to a voltage corresponding to the heater voltage with a predetermined time constant instead of the heater temperature, it is determined whether the resistor is short-circuited or connected in series with the heater. Even if the resistance is already high, the capacitor voltage is low immediately after the power is turned on again, and the resistor is not short-circuited until the predetermined time determined by the time constant elapses, and therefore, the excessive rush current when the heater is at low temperature Not only can be suppressed, but also the rush current when the temperature of the heater is high to some extent can be suppressed, thereby preventing a voltage fluctuation failure of the input power supply. Further, since the temperature control of the heater is performed by the power supply control means, the heater does not overheat.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a heating apparatus according to the present invention. FIG. 1 is a schematic diagram showing a schematic configuration of the heating device. The heater 2 of the heating device 50 is an example of a first switch according to the present invention, which controls whether or not power is supplied to the heater 2 and a rush current limiting resistor 5 that limits a rush current to the heater 2. . It is connected to an AC power supply 1 via a triac 3. Further, the heating device 50 includes a temperature sensor 6 for measuring the temperature of the heater 2, a heater control circuit 8 for outputting a signal for controlling on / off of the triac 3 based on the temperature of the heater, and a signal from the heater control circuit 8. Is provided, a drive circuit 10 for driving the triac 3 is provided, whereby the heater 2 is controlled so as to reach a predetermined temperature. A heater voltage detection circuit 9 is provided in parallel with the heater 2.
When the voltage applied to the power supply exceeds a predetermined voltage, a signal indicating that the heater voltage has exceeded the predetermined voltage is output from the heater voltage detection circuit 9 to the drive circuit 11, and the drive circuit 11 turns on the triac 4 by this signal. Thus, short-circuit control of the inrush current limiting resistor 5 is performed. The zero-cross detection circuit 7 turns on and off the triacs 3 and 4 by determining the zero-cross point (0 volt point) of the AC input voltage.
This is a circuit for reducing adverse effects on the power supply system due to sudden current fluctuations.

Referring to FIG. 2, details of each of the above circuits will be described. After the AC power supply 1 is turned on, the heater control circuit 8
Circuit 10 turns on the triac 3 by a signal from the AC power supply 1 to the heater 2 via the inrush current limiting resistor 5.
Is supplied, and the resistance value of the heater 2 starts to increase.
Thus, the inrush current immediately after the AC power supply 1 is turned on is
It is suppressed by the inrush current limiting resistor 5. When power is supplied to the heater 2, a rectified voltage of the voltage applied to the heater 2 is output from the rectifier diode 12 of the heater voltage detection circuit 9, and the voltage divided by the resistors R2 and R3 is converted to a capacitor C1 and a comparator. 13+ terminal. As the temperature of the heater 2 increases and the resistance value of the heater 2 increases, the voltage applied to the heater 2 also increases according to the voltage dividing ratio with the rush current limiting resistor 5. When the voltage applied to the heater 2 increases, both ends of the capacitor C1 and the comparator 1
The voltage applied to the + terminal of 3 also increases. Comparator 13
When the voltage at the + terminal increases and the voltage at the + terminal becomes higher than the V _REF voltage at the − terminal of the comparator 13 set to a predetermined value, a high signal is output from the comparator 13 to the drive circuit 11, and the drive circuit The triac 4 is turned on by 11 to short-circuit the rush current limiting resistor 5, the resistance loss of the rush current limiting resistor 5 is eliminated, and the voltage of the AC power supply 1 is applied to the heater 2 to accelerate the temperature rise of the heater 2.

When the temperature of the heater 2 further rises and this temperature exceeds a predetermined temperature set in the heater control circuit 8, the power supply from the heater control circuit 8 to the driving circuit 10 to the heater 2 is stopped. Is output, the triac 3 is turned off, and the supply of power to the heater 2 is stopped. When the triac 3 is turned off and the supply of power to the heater 2 is stopped, the electric charge of the capacitor C1 flows through the resistor R3, and the voltage of the capacitor C1 decreases. This is detected by the comparator 13 and the triac 4 is turned off.

After the supply of electric power to the heater 2 is stopped, when the temperature of the heater 2 falls and the temperature of the heater 2 becomes lower than a predetermined temperature set in the heater control circuit 8, the heater control circuit 8 drives the heater 2. An ON signal for supplying power to the heater 2 is output to the circuit 10, the triac 3 is turned on again, and power is supplied again from the AC power supply 1 to the heater 2 via the inrush current limiting resistor 5. Immediately after the power is turned on again, the resistance value of the heater 2 rises to near the predetermined temperature set in the heater control circuit 8 or exceeds the predetermined temperature. Therefore, the voltage applied to the heater 2 is high immediately after the power is turned on again. If the capacitor C1 is not connected, the comparator 13 instantaneously outputs H
The high signal is output to the drive circuit 11, and the triac 4 is turned on. In that case, even if the resistance value of the heater 2 is high, some rush current still flows through the heater 2. However, here, the capacitor C1 is connected in parallel with the resistor R3 to the + terminal of the comparator 13 of the heater voltage detection circuit 9, and a time constant circuit is formed with the resistors R2 and R3. Therefore, after the triac 3 is turned on again, the High signal is not output from the comparator 13 until the predetermined time determined by the time constant elapses, and the triac 4 remains off. Therefore, when the triac 3 is turned on again, the heater 2
Even if the resistance is already high, the rush current limiting resistor 5 is in a state of being inserted in series for a predetermined time, and the rush current at the time of re-input is prevented.

Here, the time from when the power is first turned on until the voltage at the + terminal of the comparator 13 exceeds the V _REF voltage at the − terminal is t ₁ , and the time when the power of the comparator 13 is turned off when the power is turned on again without the capacitor C1 is t ₁ . Terminal voltage is -terminal V
When the time to more than _REF voltage and t _2, constant t the time of the time constant circuit is set in the condition of _{t 1>t> t 2 ......} (1). Thereby, the rate of rise of the temperature of the heater 2 at the time of the first power-on is not reduced (the rise time is delayed), and even when the power is turned on again after the temperature of the heater 2 reaches the predetermined temperature, the instantaneous To triac 4
Is turned on and the rush current limiting resistor 5 is not short-circuited, and the AC power supply 1 is always supplied to the heater 2 via the rush current limiting resistor 5 for the time constant t each time. In this embodiment, in case that the inrush current limiting resistor 5 is overloaded due to an abnormality of the heater 2 or the heater voltage detecting circuit 9 and abnormal heat is generated, the circuit is cut off and danger such as smoke or ignition of the resistor is generated. In order to prevent a serious failure, a resistor having a built-in thermal fuse is used as the inrush current limiting resistor 5.

As described above, in the heating device 50, since the applied voltage of the heater, which changes in accordance with the heater resistance value causing the inrush current, is directly monitored, the temperature of the heater 2 is controlled using a temperature sensor. Rather than measuring the temperature, a decrease in the rate of rise of the heater temperature can be reduced, and the inrush current limiting resistance can be reduced. Further, since no phase control circuit is used, the apparatus is simple and relatively low in cost, there is no generation of harmonic current, and voltage fluctuation failure can be prevented.

FIG. 3 shows another embodiment. Figure 3 shows another implementation
FIG. 3 is a circuit diagram showing an example heating device, which is the same as the element in FIG.
Are indicated by the same reference numerals. Comparator of the heating device 50 shown in FIG.
The fixed V that is set at the negative terminal of the _REF Instead of
The heating device 60 shown in FIG.
11, rectifier diode 61, capacitor C2, transformer
62, an input power supply voltage detection circuit 14 having
The input power supply voltage is determined by the signal of the power supply voltage detection circuit 14.
Is changed, the voltage of the heater 2 changes.
The voltage V at one terminal of the comparator 13 at the same ratio
_REF Also changes, so that the heater 2
Turning triac 4 on and off based on resistance
it can. As a result, fluctuations in the input power supply voltage
The rate of temperature rise of the resistor 2 decreases,
A large secondary inrush current flows when a short circuit occurs
Can be prevented.

The same effect can be obtained by replacing the rush current limiting resistor 5 of the above embodiment with a reactor, or by providing a circuit for detecting the applied voltage of the rush current limiting resistor 5 in place of the heater voltage detecting circuit 9. .

[0017]

As described above, according to the heating apparatus of the present invention, (1) the rush current can be always limited, and the decrease in the rate of temperature rise of the heater can be reduced as compared with the control by measuring the heater temperature. (2) It is possible to use a rush current limiting resistor having a relatively smaller capacity than the control based on the measurement of the heater temperature. (3) No harmonic current is generated, and voltage fluctuation failure can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram schematically showing an embodiment of a heating device according to the present invention.

FIG. 2 is a circuit diagram showing details of the circuit shown in FIG. 1;

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 AC power supply 2 Heater 3, 4 Triac 5 Inrush current limiting resistor 6 Temperature sensor 7 Zero cross detection circuit 8 Heater control circuit 9 Heater voltage detection circuit 10 Drive circuit 1 11 Drive circuit 2 12 Rectifying diode 13 Comparator R1, R2, R3, R4 , R5, R6, R7, R8, R
9, R10, R11 resistors C1, C2 capacitors

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-49911 (JP, A) JP-A-3-12685 (JP, A) JP-A-4-360184 (JP, A) JP-A-4- 282588 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/20

Claims (1)

(57) [Claims] 1. A heater that generates heat by electric power supplied from a power supply, and a first switch disposed between the power supply and the heater, the electric power being supplied to the heater based on the temperature of the heater. a power supply control means for controlling whether to supply, before being connected in series with Kihi over data, electricity flowing through the heater
A resistor that suppresses current flow , and a capacitor that has a predetermined time constant and is charged to a voltage corresponding to the voltage of the heater, and the voltage of the heater is higher or lower than a predetermined voltage based on the voltage of the capacitor. And a second switch arranged in parallel with the resistor, wherein the heater voltage determining unit determines that the voltage of the heater is higher than a predetermined voltage. And a resistor short-circuit means for closing the second switch and opening the second switch when it is determined that the voltage of the heater is lower than a predetermined voltage.