JPS617589A - High frequency heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a method of varying the high frequency output of a high frequency heating device.
The present invention relates to a method for controlling a switch used as a means for opening and closing a primary line of a power transformer.

Conventional configurations and their problems In high-frequency heaters, it has become common practice to set the high-frequency output to an appropriate level depending on the type, quality, and finish of the food to be cooked, and this has improved cooking performance. It's helpful. In this way, as a means of changing the high frequency output to an appropriate level, there are two methods: intermittent high voltage power supply to the high frequency output oscillator, and intermittent method on the power supply side of the power transformer (hereinafter referred to as 1).
The first-order intermittent method has been developed, and the first-order intermittent method has become mainstream from the viewpoint of cost, insulation performance, and configuration.

FIG. 1 shows a circuit diagram of a conventional example.

Triacs and power relays are used as means for connecting and disconnecting the power supply side of a power transformer that supplies power to a high-frequency oscillator. (Figure 1 shows an example in which a triac is used.) As in the conventional example shown in Figure 1, with the means using a triac, it is difficult to control the power-on phase when power is applied to the power transformer. Although it has the advantage of being highly accurate and keeping the inrush current of the power transformer low, the CiTRIAC is easily damaged by static electricity coming in from outside the high-frequency heating device, induced lightning by lightning, and surge voltage generated inside the device. There is a high risk that the damaged mote will go into short-circuit mode, constantly supplying power to the power transformer and oscillating at high frequencies, which is a dangerous situation, and the ability to vary the high-frequency output will also be lost. Further, in order to separate and insulate the AC power supply circuit and the control circuit, auxiliary parts such as photocouplers are also required, making the configuration complicated.

On the other hand, with the method of using a power relay, static electricity from outside the main unit, induced lightning, and surge voltage inside the main unit can be
Although this solved the problem with the triac mentioned above, the precision of the phase control when the power transformer was turned on was poor, and it was not possible to keep the inrush current value low when the power was turned on. For this reason, there is a high risk that the power relay's contacts will be welded due to an inrush current that is nearly 10 times the steady current, creating a dangerous situation similar to the case with the triac mentioned above, and also losing the output variable function. It is.

OBJECTS OF THE INVENTION The present invention is intended to eliminate the above-mentioned conventional drawbacks, and aims to prevent drawbacks such as welding of contacts due to rush current by utilizing highly efficient means.

Structure of the Invention In order to achieve the above object, the present invention includes a high-frequency oscillator as a high-frequency output source and a power transformer that supplies power to the oscillator. A relay is provided, a control unit is provided to control the on/off of this power relay, and a means for detecting the ON/OFF phase of the contact of this power relay is provided, and this detected ○N10FF phase information is fed back to the control unit. This configuration automatically controls the optimum phase of the power relay to eliminate inrush current, improves the durability of the power relay's contacts, greatly increases its reliability, and eliminates variations in power relay operating time and power supply. Even if there is a voltage fluctuation, the shifted phase can be automatically corrected and the optimum closing phase can be reset.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows an external view of one embodiment.

Reference numeral 1 denotes a main body of a high-frequency heater, and a heating chamber 2 made of a ferromagnetic material is provided within this main body 1.

The opening of the heating chamber 2 is provided with a door 3 that can be opened and closed freely to take in and take out the food in the heating chamber 2, and the front of the main body 1 has operations for setting and displaying cooking time, output, etc. A section 4 is provided.

In FIG. 3, a circuit diagram of one embodiment is shown. A high frequency oscillator 5 for irradiating high frequency output into the entire heating chamber 2, and a power transformer 6 for supplying power to the high frequency oscillator 5 are provided. A power relay 7 is provided on the power source side of the power transformer 6, and the high frequency output is changed by opening and closing the power relay 7 and turning on and off the power to the power transformer 6.

A core 9 is provided to detect the open/close phase of the contacts of the power relay 7, and a part of the power line is connected to the core 9.
It is wrapped around. By doing so, changes in the current flowing through the power supply line can be input to the control unit 8 via the core 9. Regarding the opening/closing timing of the power relay 7, phase control, correction to the optimum phase, etc.,
The microcomputer 8a in the control section 8 performs control according to procedures stored in advance. Next, the circuit of the control section 8 will be shown. The control unit 8 includes a microcomputer 8a, and performs various controls according to programs stored therein. Next, the circuit configuration of the control section will be explained based on FIG. 4. The commercial power source is stepped down by a low voltage transformer 10 to approximately 30V AC.

Then, this AC voltage is half-wave rectified by a rectifier diode 11 and a smoothing capacitor 12. The voltage after this rectification is
This becomes the operating coil voltage of the power relay 7. Further, a block 13 indicated by a dotted line in the figure is a power supply circuit for the microcomputer 8a.

To the input port 2 of the microcomputer 8a is the power supply clock generation circuit 1111 from the block 14 shown by the dotted line in the figure.
．． A "0" signal is input, and the power supply phase timing of the commercial power source is detected. On the other hand, the power relay 7 is controlled via a transistor according to the output port R1 of the microcomputer 8a.

Next, a circuit for extracting changes in the primary current of the high-rise transformer 6 will be described. As shown in the figure, when the main current flows, the change in current induces a current in the coil wound around the core 9 on the control unit side, which acts as a current transformer. This current is transmitted to the electronic circuit of the control section via the pulse transformer 15, the transistor 16 is kept fully conductive while the main current is flowing, and the 11011 signal of one port is input to the microcomputer 8a.

The effects of the above configuration will be explained below.

Is there something to cook in heating chamber 2? When the cooking condition is set and cooking is started, the control unit 8 sends a signal to the power relay 7 to close the power circuit of the power transformer 6, the power relay 7 closes, and the power transformer A voltage is applied to 6, power is supplied to the high frequency oscillator, and high frequency output is obtained. When varying the high frequency output, the control unit 8 outputs an opening/closing operation signal for the power transformer 6, the power relay 7 repeats the opening/closing operation, and the high frequency oscillator 5 repeats oscillation, stopping and oscillation, and then outputs the high frequency. Make variable.

Next, with reference to FIG. 5, the waveforms of each part when closing the contacts of the power relay 7 will be explained. The microcomputer 8a serves as the starting point for controlling all the zero-cross pointers of the output voltage waveform of the low-voltage transformer from negative to positive. This zero cross signal is input to the second port of the microcomputer 8a. Then, when closing the power relay 7,
After counting for 7 hours using the internal timer function of the microcomputer 8a, a ''1' signal is output to the R1 port which is the control port of the power relay 7. By the way, the power relay 7 generally has an operation delay of 8 hours Td from when voltage is applied to its operating coil until its contacts actually close. In the case of this embodiment, it is about 10 m5ec. (This relay operation amount time Td fluctuates by about ±50% depending on the voltage applied to the operating coil.) Therefore, as shown in FIG. There is a time Td before the contact closes. Then, as shown in Fig. 5(d) K, the contact closes and the main current begins to flow. In Figure 5(d), the main current.

The reason why the initial peak value of is large is that an inrush current is flowing. This change in main current is caused by the aforementioned core 9'
ff: is transmitted to the control unit via 11111 and gives an "o" signal to the input port x1 of the microcomputer 8a. By checking the falling waveform of one port on this, the microcomputer 8a can know the closing phase of the contact of the power relay 7. That is, since the phase of the power supply voltage waveform is detected indirectly from the time T0Td, it is important to turn on the voltage at its maximum phase in order to keep the inrush current low. In terms of tp in Figure 5, (T+Td)-15msec (however, 50H2
). However, as mentioned above, since the relay operation delay time Td is large during fluctuations, it can be seen that it is sufficient to correct it by T in order to maintain it at T0Td = 15m5ec. That is, based on the measurement result of the operation delay time Td, feedback is activated to correct the internal timer setting time so that it becomes greater than T+Td-15tnseC. This feedback function is
It is executed by software using a program stored inside the computer.

FIG. 6 shows a control program flow diagram of this embodiment. In the case of this embodiment, since interrupt processing is performed using an internal timer function, the control flow has a dual structure of a main program and a subprogram that is a processing program when an internal timer interrupt occurs. There is. first,
The microcomputer 8ai power supply clock is taken in and the zero phase of the power supply waveform is used as the base point for relay control. Next, is it necessary to operate the power relay contact from OFF to ON?
Check, if necessary, whether all internal timers are currently running. , If the internal timer is not running, set the internal timer. At this time, as mentioned above, T+Td=15m5ec
(However, the internal timer setting time Tk is determined based on the value of Td measured so that it becomes 50H2 hours). After setting the internal timer, start the timer and wait for the time set in the internal timer to elapse while performing other processing within the main program. When the set time has elapsed, the processing is forcibly transferred from the main program to the subprogram, and within the subprogram, a signal to close the contacts of the power relay is output from the R1 port of the microcomputer 8a. Thereafter, a counter for counting the relay operation delay time Td' is started, and the time from when the 1 point signal of the microcomputer 8a falls from +i 1 t+ to it On is counted. The above is a series of relay control flows.

In this way, according to this embodiment, in the means for varying the high frequency output, it is possible to eliminate the inrush current that occurs due to the opening and closing operations of the power relay that fully opens and closes the power supply of the power transformer, and the contact of the power relay The power relay, which has improved durability and excellent insulation performance and anti-noise performance, can be used as an element for switching on and off the power supply of a power transformer, thereby realizing an inexpensive configuration. In addition, the heating chamber and the like made of ferromagnetic material can prevent vibration noise caused by magnetic leakage of the power transformer due to the rush current, which also has the effect of eliminating discomfort for the user. As a result, the vibration isolating plates, etc. that were provided to prevent these magnetic vibrations are no longer necessary, and the overall configuration can be simplified.1 This has the effect of increasing the degree of design freedom in the placement of power transformers, etc. have.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained.

(1) By constantly performing optimal relay control for all power supply conditions for all relays, inrush current can be eliminated and the durability of power relay contacts can be significantly improved. Ta.

? ) As described above, since variations in relay operation delay time can be corrected, there are no restrictions on the operation time of the power relay, and as a result, the cost of the power relay can be reduced. Furthermore, there is no need for a constant voltage source for the operating coil voltage, which has been conventionally employed, and high quality regulation of the operating coil power source including a low voltage transformer is no longer required.

Therefore, this led to a significant cost reduction overall.

(3) Since inrush current can be eliminated, it is possible to eliminate vibration-proofing materials installed in heating chambers, etc. made of ferromagnetic materials, and vibrations in heating chambers, etc., which can cause discomfort, can be removed. I was able to eliminate the sound.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional example, Fig. 2 is an external view of a high-frequency heater which is an embodiment of the present invention, Fig. 3 is a circuit diagram of the same, Fig. 4 is a circuit diagram of the same control section, and Fig. 5 is a circuit diagram of the same control section. The figure is a relationship diagram between voltage phase and microcomputer terminal waveform in the control section, and FIG. 6 is a control flow diagram of this embodiment. 1...Main body, 5...High frequency oscillator, 6
...Power transformer, 7...Power relay, 8...Control unit, 9a...Microcomputer, 9...-z-r- (change ii), 1s...
・Pulse transformer. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 5 Figure 6

Claims (1)

[Claims] A heating chamber that stores food, a high-frequency oscillator that supplies high-frequency output to this heating chamber, a power transformer that supplies power to this, a power relay that switches on and off the power on the power side of this power transformer, and this power It has a control unit that controls the ON/OFF timing of the relay, and a means for detecting the ON/OFF phase of the contacts of the power relay, and the information from the means for detecting the ON/OFF phase of the contacts of the power relay is A high-frequency heating device configured to provide feedback to a control unit for ON/OFF timing of a power relay.