JPH0866005A - Ac controller and imaging forming device employing the same - Google Patents

Abstract

PURPOSE: To enhance safety by providing means for detecting application of a voltage to a load between a zero-cross signal and a phase control signal to turn a switch off thereby protecting the entire system against failure or breakdown at the time of failure or breakdown of a thyristor. CONSTITUTION: A controller 6 outputs an AC input voltage as a phase control signal to turn a triac 2 on/off thus controlling (phase control) the voltage (effective voltage) being applied to a fixing heater 1 at a constant level. When the triac 2 is normal, a full-wave rectified voltage appears between X-Y of a rectifying section 3b connected across the fixing heater 1. When a fixing heater applying voltage is applied due to failure or breakdown of the triac 2, the controller 6 makes a decision that the triac 2 is abnormal based on the low level detection signals appearing between the AC input zero-cross signal and the phase control signal more than a predetermined times. A relay switch 4 is then turned off to interrupt power supply to the fixing heater 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for carrying out heat fixing by an AC load and an AC controller used for the image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using a ceramic heater as a heat generating means for fixing does not have a detecting means when a thyristor (triac) breaks down or is destroyed.

[0003]

Therefore, in the above-mentioned conventional example, when the thyristor fails or is destroyed, the fixing heater of the surf having a small heat capacity suddenly becomes high temperature, which may lead to the failure or destruction of the image forming apparatus. There is a nature.

The present invention has been made in order to solve the above-mentioned problems of the conventional example, and when the thyristor fails or breaks down, the power supply voltage is turned off to prevent the whole device from breaking down or failing to ensure safety. It is an object of the present invention to provide an image forming apparatus having improved performance and an AC control device used for the same.

[0005]

An AC control device of the present invention is an AC control device for phase-controlling an alternating current to a load by using a thyristor, and detecting a zero-cross point of the alternating voltage to detect a zero-cross signal. A zero-cross signal generating means, a phase control signal generating means for generating a signal for controlling the phase of the thyristor, a voltage detecting means for detecting a voltage across the load, and a switch for turning on / off a power supply voltage, The switch is turned off by detecting that the voltage is applied to the load by the voltage detection means between the zero-cross signal generated by the zero-cross signal generation means and the phase control signal generated by the phase control signal generation means. And a control means for controlling.

Further, the image forming apparatus of the present invention is equipped with the above-mentioned AC control device in which the load is a fixing heater.

[0007]

The AC control apparatus of the present invention is configured as described above, so that the power supply voltage is turned off when the thyristor fails, so that an excessive voltage is not applied to the load.

Further, the image forming apparatus of the present invention having the above-mentioned constitution can prevent the fixing heater from being abruptly heated and prevent the image forming apparatus from being damaged or destroyed.

[0009]

1 is a circuit diagram of an embodiment of the present invention.

In the figure, 1 is a heater for fixing the transfer paper, 2 is a triac for controlling the energization of the heater, and 3 is a voltage for detecting the voltage across the heater composed of a photocoupler 3a and a full-wave rectifier 3b. A detection device, 4 is a relay switch for turning ON / OFF the main power source, 5 is an AC input zero-cross signal generation circuit, and 6 is a controller for controlling the above-mentioned elements and the like.

The controller 6 includes means for setting the number of times of voltage detection as will be described later, and a phase control signal generation timer.

Next, the operation will be described.

When the operator presses a start key (not shown), energization of the heater 1 is started to fix the toner on the paper.

The heater 1 is a heater in which a resistor is printed on a ceramic substrate and has a very good thermal response. Therefore, in the normal ON / OFF control, the ripple becomes large with respect to the temperature control temperature, and the electric power is excessively applied to the heater, and the heater is damaged. Therefore, in this control, power control is performed so that a constant power is applied. Further, in order to reduce the ripple, control is performed such that the electric power is switched according to the temperature detected by the thermistor.

As an actual operation, an alternating current (A
C) The controller 6 of FIG. 1 outputs the phase control signal to the input voltage to turn the triac 2 of FIG. 1 ON / OF.
Then, the voltage (effective value voltage) applied to the fixing heater 1 is controlled (phase control) so as to be a predetermined constant value.

Normally, if the triac 2 is normal, the voltage between X and Y of the rectifier 3b connected to both ends of the fixing heater 1 becomes a full-wave rectified voltage as shown in FIG. The detection signal from the device 3 is as shown in FIG.

When the triac 2 fails or is destroyed for some reason and a fixing heater applied voltage as shown in FIG. 4D is applied, the detection signal from the voltage detection device 3 is shown in FIG. 4F. become that way.

At this time, the controller 6 judges that the triac 2 is abnormal when the low level of the detection signal between the AC input zero cross signal and the phase control signal exceeds a predetermined number of times, and turns off the relay switch 4, The energization of the fixing heater 1 is stopped.

Finally, flow charts showing the operation of this abnormality detecting means are shown in FIGS.

FIG. 5 is a main routine of the image forming apparatus, FIG. 6 is a zero cross signal interrupt subroutine, and FIG. 7 is a flow chart showing the contents of the abnormality detection processing.

When a power switch (not shown) is pressed and the power is turned on (S1), initialization is performed (the number of times of voltage detection is 0) (S2), and the processing for each load is repeated (S3).

The subroutine of the zero-cross signal interrupt detects the rising edge of the zero-cross signal (S4),
If the heater is ON (S5), the phase control signal generation timer (time from the rise of the zero cross to the output of the phase control signal) is set (S6), and the abnormality detection process (S7) is started. In the anomaly detection process, first, if the zero-cross signal falls (S9), the voltage detection of the arrow portion of FIG. 4 is started (S9).
10) If the voltage detection signal is at a low level (S1
1), 1 is added to the voltage detection number N (S13). If the voltage detection signal is not at the low level in step S11, the voltage detection number N is set to 0 (S12). Here, when the voltage detection number N reaches 10 (S14), the main power supply is turned off.
(S15).

Although the main power source is turned off when N = 10 here, the number may be changed to one or more.

The present invention can be used to control the voltage applied to the load even if the load is something other than the heater (lamp, motor, etc.).

The controlled object can be not only voltage but also current and power.

[0026]

As described above, according to the present invention,
Since an excessive current is not applied to the load, and in particular, the fixing heater is not abruptly heated in the second aspect of the invention, failure and destruction of the device can be prevented, so that safety is improved.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment.

FIG. 2 is a waveform diagram illustrating a heater applied voltage.

[Figure 3] Waveform diagram in normal state

[Fig. 4] Waveform diagram at the time of abnormality

FIG. 5 is a flowchart of a main routine

FIG. 6 is a flowchart of a zero-cross interrupt subroutine.

FIG. 7 is a flowchart of abnormality detection processing.

[Explanation of symbols]

 1 Fixing heater 2 Triac 3 Voltage detector 4 Relay switch 5 Zero cross signal generation circuit 6 Controller

Claims (2)

[Claims] 1. An AC control device for phase-controlling an alternating current to a load by using a thyristor, comprising: zero-cross signal generating means for detecting a zero-cross point of the alternating voltage and generating a zero-cross signal; and the thyristor. Phase control signal generation means for generating a signal for phase control, voltage detection means for detecting the voltage across the load, a switch for turning on / off the power supply voltage, a zero-cross signal generated from the zero-cross signal generation means, and An alternating current control device comprising: a control means for turning off the switch by detecting that a voltage is applied to the load by the voltage detection means between the phase control signal generated by the phase control signal generation means. 2. An image forming apparatus provided with the AC controller according to claim 1, wherein the load is a fixing heater.