JPH11202676A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device which suppresse the rush current, stably executes the conduction/shut off control of a heater lamp, is free of electric power loss and does not give rise to unequal fixing. SOLUTION: The electric power outputted from an AC power source 1 is rectified by a full-wave rectifier 3 and the current value of the electric power is detected by a current-voltage converter 5. The conduction/shut off of the heater lamp 2 are executed via a switching element 6 by a control circuit 7 in synchronization with the rise of the voltage waveform of the rectified electric power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrophotographic apparatus such as a laser beam printer and a copying machine.

[0002]

2. Description of the Related Art First, a fixing device will be described with reference to FIG. In order to fix the toner on which the image is formed on the recording material 13, a heat roll 11 having a built-in heater lamp 2 is generally used in a heat fixing type laser beam printer, copying machine, or the like.
The toner on which the image has been formed is melted and fixed on the recording material 13 by the heat effect of the pressure roller 12 and the pressure of the pressure roll 12.

As the heater lamp 2, a halogen lamp or the like is generally used. Halogen lamps are
Since the resistance is extremely low in a cold state, when an AC power supply is connected to the heater lamp 2, an extremely large current called an inrush current flows. Therefore, the heater drive circuit has been devised to suppress this rush current.

FIG. 3 shows an example of a conventional heater drive circuit to which a circuit for suppressing an inrush current is added. Heater lamp 2
Are connected to the AC power supply 1 through a triac 15 that is turned on / off by a soft start signal from the AC power supply 1, a soft start resistor 14 connected in parallel to the triac 15, and a triac 16 that is turned on / off by a heater drive signal. ing. In this configuration, for example, the triacs 15 and 16 are turned on when the soft start signal and the heater drive signal, which are the respective gate signals, are at logic "1", and are cut off at logic "0".

Next, the operation of the conventional heater drive circuit will be described with reference to FIG. First, the triac 16 is turned on by setting the heater drive signal to logic "1", the triac 15 is turned off by setting the soft start signal to logic "0", and the heater lamp 2 is turned on through the soft start resistor 14. To supply power to
Even when the heater lamp 2 is in a cold state, that is, when the resistance is low, the current is suppressed by the soft start resistor 14, so that the rush current is suppressed low. Here, when power is supplied without passing through the soft-start resistor 14, the current is increased by Id1 as shown in FIG. 4C, as compared with the case where the rush current is suppressed by the soft-start resistor 14. Will flow.

Next, after electric power is supplied from the AC power supply 1 to the heater lamp 2, the temperature of the heater lamp 2 rises,
For example, a time until the resistance value of the heater lamp 2 becomes substantially equal to the resistance value of the soft start resistor 14 is defined as t1.
After this time t1, as shown in FIG. 4 (b), the triac 15 is turned on by setting the soft start signal to logic "1", and the heater lamp 2 is turned on without passing through the soft start resistor 14.
Power to Here, if the triac 15 is not made conductive and only the triac 16 is made conductive and power is constantly supplied to the heater lamp 2 via the soft start resistor 14, the power is consumed by the soft start resistor 14. The current flowing through the lamp 2 is reduced by Id2 as shown in FIG. 4C, as compared with the case where power is supplied to the heater lamp 2 without passing through the soft start resistor 14. That is, if power is always supplied to the heater lamp 2 via the soft-start resistor 14, a larger amount of power is required to obtain the same amount of heat as compared to a case where no power is supplied via the soft-start resistor 14.

By the above method, the rush current when the heater lamp 2 has a low resistance is suppressed. When the heater lamp 2 is no longer low in resistance, the soft start resistor 14
The power loss is suppressed by supplying power to the heater lamp 2 without going through.

[0008]

Generally, in a heat fixing device, there are two situations in which the heater lamp 2 is turned on / off. One is that, in FIG. 2, for example, after turning on the power of a printer, a copying machine, or the like, it is necessary to supply power to the heater lamp 2 and heat the temperature of the heat roll 11 to a specified value or more until heat fixing becomes possible. This is called warm-up. Another is a situation in which the temperature of the heat roll 11 is generally detected in order to keep the temperature of the heat roll 11 constant during printing, and the conduction / interruption of the heater lamp 2 is constantly repeated within the upper and lower limits of the temperature. In addition, the temperature of the heating roll 11 during printing varies depending on the width, thickness, and the like of the recording material 13, and thus the conduction / interruption cycle of the heater lamp 2 varies in various ways.

First, in the configuration shown in FIG. 3, for example, intermittent printing, a situation in which the width and thickness of the recording material 13 are small, and the temperature of the heat roll 11 is not easily deprived by the recording material 13 will be described.
In this case, after the temperature of the heat roll 11 reaches the upper limit and the heater lamp 2 is shut off, the temperature of the heat roll 11 decreases relatively slowly. Heat roll 11 and heater lamp 2 at this time
FIG. 5 shows the temperature relationship. FIG. 5A shows the heat roll 11.
FIG. 5 (b) shows the state of conduction / interruption of the heater lamp 2, and when the logic is "1", the conduction state is set. FIG. 5C shows the temperature of the heater lamp 2. First, at the time of warm-up, only the triac 16 is turned on, and power is supplied to the heater lamp 2 via the soft start resistor 14. Thereafter, the triac 15 is turned on to supply power to the heater lamp 2 without passing through the soft start resistor 14. Heat roll 11 heated by heater lamp 2
When the temperature exceeds the lower limit shown in FIG. 5A, printing is possible. When printing is started and the temperature of the heat roll 11 reaches the upper limit, the triac 16 is shut off, and power supply to the heater lamp 2 is stopped. Generally, the heater lamp 2 is a heat roll 1
If the temperature of the heat roll 11 reaches the lower limit and the power is again supplied to the heater lamp 2, the temperature of the heater lamp 2 becomes less than the rush current when the temperature of the heat roll 11 reaches the lower limit value and is slower than that of the rush current 1. Since the temperature drops below the temperature T1 at which suppression is required, it is necessary to suppress the inrush current using the soft start resistor 14 even when the heater lamp 2 is turned on / off during printing.

However, if the soft start resistor 14 is always used during printing, for example, when the width or thickness of the recording material 13 is large, the following problems occur. In this case, since the temperature of the heat roll 11 is easily taken away by the recording material, the temperature of the heat roll 11 reaches the upper limit and the heater lamp 2
Is cut off, the temperature of the heat roll 11 decreases faster.
FIG. 6 shows the relationship between the temperature of the heat roll 11 and the temperature of the heater lamp 2 at this time. FIG. 6A shows the temperature of the hot roll 11, FIG.
(B) shows the conduction / interruption state of the heater lamp 2, and when the logic is "1", the heater lamp 2 is rendered conductive. FIG. 6C shows the temperature of the heater lamp 2. At the time of warming-up, a transition is made to a printable state in the same manner as in the case where the temperature of the heat roll 11 decreases slowly. When printing is started and the temperature of the heat roll 11 reaches the upper limit, the triac 16
Is shut off, and the power supply to the heater lamp 2 is stopped. When the temperature of the heat roll 11 decreases rapidly, the temperature of the heater lamp 2 becomes the temperature at which the rush current needs to be suppressed before the temperature of the heat roll reaches the lower limit value and power is supplied to the heater lamp 2 again.
Since it does not fall below T1, it is not necessary to suppress the inrush current using the soft start resistor 14 for the conduction / interruption of the heater lamp 2 during printing. On the contrary, when the temperature of the heat roll 11 decreases rapidly, if the heater lamp 2 is turned on / off using the soft start resistor 14 during printing, unnecessary power is consumed by the soft start resistor 14. Further, when the recording material 13 remarkably deprives the temperature of the heat roll 11, when the temperature of the heat roll 11 reaches the lower limit and power is supplied to the heater lamp 2 again, unnecessary power is consumed by the soft start resistor 14. As a result, the temperature of the heat roll 11 drops below the lower limit value, causing a problem of causing uneven fixing of the image on the recording material 13.

Therefore, in the conventional heater drive circuit, if conduction / interruption of the heater lamp 2 during printing is always performed without using the soft start resistor 14, a problem of an inrush current occurs when the temperature of the heat roll 11 slows down. In addition, if conduction / interruption of the heater lamp 2 during printing is always performed by using the soft start resistor 14, there is a problem that when the temperature of the heat roll 11 drops rapidly, fixing unevenness occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fixing device which suppresses an inrush current, stably controls conduction / cutoff of a heater lamp 2, does not lose power, and does not cause fixing unevenness.

[0013]

The above object is achieved by the following means.

Means for rectifying the AC power supply and switching means for detecting the current value of the rectified power and for turning on / off the heater lamp.

Means for synchronizing the timing of turning on / off the heater with the voltage waveform of the rectified power.

[0016]

FIG. 1 shows an example of a heater drive circuit according to an embodiment of the present invention. First, the configuration of the heater drive circuit of FIG. 1 will be described. The heater lamp 2 is connected to the AC power supply 1 and the full-wave rectifier 3, and is connected to the AC power supply 1 from the full-wave rectifier 3 via the fuse 4 for overcurrent protection. The full-wave rectifier 3 is connected to a control circuit 7 via resistors 8 and 9 and a Zener diode 10 for constant voltage, and further via a current-voltage converter 5 to a switching element 6.
Is also connected. Here, the resistors 8 and 9 perform voltage division for converting a voltage value of the AC power supply 1 to a voltage for a control signal. The fuse 4 is a protection element that blocks a large current from flowing when the circuit is broken and the AC power supply 1 is short-circuited. The output side of the current-voltage converter 5 is connected to the reset terminal of the control circuit 7, and the output terminal of the control circuit 7 is connected to the switching element 6, for example, IGBT or power M.
It is connected to a gate terminal such as an OS FET. Also,
The switching element 6 becomes conductive when logic "1" is input to the gate terminal, and is cut off when logic "0" is input. The current-voltage converter 5 converts a current flowing through the heater lamp 2 into a voltage and outputs the voltage as a control signal. The control circuit 7 outputs a signal from an output terminal in synchronization with a signal input to the drive terminal and a rising edge of a waveform input to the trigger terminal. For example, when logic "1" is input to the drive terminal of the control circuit 7, the logic "1" is output to the output terminal in synchronization with the rise of the waveform input to the trigger terminal. The same applies to the case of logic "0". The reset terminal detects the rise of the signal output from the current / voltage converter 5, and sets the output terminal to logic "0".

Next, the operation of the heater drive circuit according to one embodiment of the present invention will be described. In this configuration, the AC power supply 1 outputs the voltage waveform shown in FIG. 7A, and the voltage waveform rectified by the full-wave rectifier 3 is shown in FIG. 7B. The full-wave rectified voltage is converted into a control signal voltage by the voltage dividing resistors 8 and 9, and a voltage equal to or higher than a certain potential is cut by the Zener diode 10. The voltage waveform applied to the trigger terminal of the control circuit 7 at that time is as shown in FIG. Here, assuming that the heater drive signal is logic “1” as shown in FIG. 7D, the output terminal of the control circuit 7 is synchronized with the rising of the voltage waveform input to the trigger terminal as shown in FIG. A logic "1" voltage waveform is output. The voltage waveform output from the output terminal of the control circuit 7 is input to the gate terminal of the switching element 6, and the switching element 6 becomes conductive. Then, the current that has been full-wave rectified by the full-wave rectifier 3 from the AC power supply 1 through the heater lamp 2 flows into the switching element 6 via the current-voltage converter 5 as shown in FIG. . Therefore, the current-voltage converter 5 converts the current flowing through the heater lamp 2 into a voltage and outputs the voltage to the reset terminal of the control circuit 7. When the voltage value reaches a certain value I1 or more, the control circuit 7 sets the output of the output terminal to logic "0" and the switching element 6 cuts off the current, so that the heater lamp 2 is not supplied with power. A dotted line portion of the current waveform in FIG. 7F indicates a current flowing when the switching element 6 is not cut off. Next, the switching element 6 is turned on in synchronization with the voltage waveform diagram (c) input to the trigger terminal, and power is supplied to the heater lamp 2. That is,
As shown in FIG. 7 (g), this cycle is repeated, and when the inrush current falls below a certain value I1, the voltage output from the current-voltage converter 5 also falls below a certain value. The interruption operation is not performed, and a current without phase loss flows. That is, the heater lamp 2
When the heater lamp 2 is cold and has a low resistance, the rush current is suppressed. When the heater lamp 2 is warm and the resistance is not low, the rush current is not suppressed and the heater lamp 2 has no loss.
Can be fed to Further, by synchronizing the rise of the full-wave rectified waveform with the conduction of the switching element 6, the heater lamp 2 is always supplied with a low sine wave voltage value output from the AC power supply 1. An increase in current value due to overshoot can also be suppressed.

[0018]

As described above, according to the present invention, there is provided a fixing device which suppresses inrush current, stably controls conduction / cutoff of a heater lamp, does not lose power, and does not cause fixing unevenness. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a fixing device.

FIG. 3 is a block diagram showing a conventional circuit configuration.

FIG. 4 is a timing chart showing a conventional circuit operation.

FIG. 5 is a timing chart showing a problem in a case where the temperature drop of the hot roll is slow.

FIG. 6 is a timing chart showing a problem in a case where the temperature of the hot roll rapidly decreases.

FIG. 7 is a timing chart showing a circuit operation according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... Heater lamp 3 ... Full-wave rectifier 4 ... Fuse 5 ... Current-voltage converter 6 ... Switching element 7
... Control circuit 8, 9 ... Resistance 10 ... Zener diode 11
... Heat roll 12 ... Pressure roll 13 ... Soft start resistance
15 ... Triac

Claims (2)

[Claims] 1. A fixing device for fusing an image-formed toner and fixing it on a recording material by a heat effect of a heat roll having a built-in heater lamp and a pressure of a pressure roll, etc. And a switching unit for turning on / off the heater lamp. 2. The fixing device according to claim 1, wherein conduction / interruption of said heater lamp is performed in synchronization with a rise of a voltage waveform of rectified power.