JPH07161467A - High frequency dielectric heating device - Google Patents

Abstract

PURPOSE:To practically and safely control device with high efficiency in response to the real drying and heating by lowering the electrode-to-electrode voltage by a required level when a spark is generated inside of an object to be heated. CONSTITUTION:Power from a high frequency generating device 1 is supplied to electrodes 4 through a matching circuit 2. A wood 3 is interposed between the electrodes 4, and when the heating for drying the wood 3 is started, after the constant current control is performed for a predetermined time, control is switched to the constant voltage control. A spark detecting circuit 7 detects the generation of spark. When the number of generation of spark counted by a counter 9 exceeds a predetermined value within a predetermined time set by a timer 8, the electrode-to-electrode voltage is lowered by V2 level in comparison with the real voltage on the basis of the control signal from the control circuit 6 to the matching circuit 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention dries high-frequency dielectric heating of an object to be heated, such as wood and dyed fibers (such as wool wound on a bobbin) whose water content decreases with heating. Or to a high-frequency dielectric heating device for heating.

[0002]

2. Description of the Related Art In the case of drying wood by using high frequency, in consideration of the dielectric breakdown and corona discharge which occur with the decrease of water content, power is supplied according to the water content contained in the wood. Are known to be important. Conventionally,
A high-frequency dielectric heating device in consideration of this point has been proposed (Japanese Patent Laid-Open No. 59-121794). This device, from the relational expression of the high-frequency power absorbed in the wood, by detecting the inter-electrode voltage, based on the knowledge that it is possible to estimate the change tendency of the water content that greatly affects the dielectric constant of wood, Constant power control for a predetermined time at the beginning of high frequency application, and after that, when the water content falls below a threshold value and reaches a level at which dielectric breakdown or corona discharge occurs, switching to constant voltage control by the voltage at that time, The wood is suitably and efficiently dried.

[0003]

The conventional high-frequency dielectric heating device employs a fixed control method in which the first half is subjected to constant power control while the latter half is uniformly controlled to constant voltage. Although it is possible to drive only at a voltage level at which the safety can be expected even if the constant voltage control is continued at the final voltage in the above, and safe drying of the wood can be secured to some extent, there is a limit to efficiency. I had to say that there was.

The present invention has been made in view of the above, and detects the dielectric breakdown (spark) in the object to be heated and lowers or raises or raises or lowers the inter-electrode voltage according to the occurrence state of the spark. Therefore, it is an object of the present invention to provide a practical, safe, and highly efficient high-frequency dielectric heating device that is suitable for actual drying and heating.

[0005]

According to the present invention, an electrode for supplying high frequency power absorbed by an object to be heated and a high frequency generating means for applying a required level of high frequency power to the electrode are provided.
An inter-electrode voltage detecting means for detecting the voltage of the electrodes, and a voltage stabilizing means for controlling the high frequency power applied to the electrodes so that the voltage detected by the inter-electrode voltage detecting means becomes substantially constant at a predetermined level, It is provided with a spark detecting means for detecting a spark generated between the electrodes and a voltage changing means for lowering the inter-electrode voltage by a predetermined first level when the spark is detected (claim 1). .

Further, according to the present invention, a timer for repeatedly measuring a preset time is provided, and the voltage changing means detects the spark while the timer elapses the set time, and at the time of detection, the voltage change means detects the spark. The inter-electrode voltage is decreased by the first level and the timer is reset and started (claim 2).

Further, according to the present invention, a timer for repeatedly measuring a preset time is provided, and the voltage changing means sets the set time when the timer does not detect a spark during the lapse of the set time. When the above condition elapses, the voltage between the electrodes may be increased by a predetermined second level and the timer may be reset and started (claim 3).

Further, according to the present invention, a timer for repeatedly measuring a preset time is provided, and the voltage changing means detects the spark while the timer elapses the set time, and at the time of the detection, the voltage is changed. The inter-electrode voltage is decreased by the first level, while if no spark is detected during the time setting, the inter-electrode voltage is increased by a predetermined second level and the inter-electrode voltage is changed. At this time, the timer may be reset and started (claim 4).

Further, it is desirable that the operation of the voltage changing means is stopped for a certain period of time from the start of supplying the high frequency power (claim 5).

[0010]

According to the first aspect of the present invention, when the high frequency power is supplied to the object to be heated interposed between the electrodes, the inter-electrode voltage at this time is detected, and the detected voltage is at a predetermined level. The high frequency power applied to the electrodes is controlled so as to be substantially constant. On the other hand, when the occurrence of sparks between the electrodes is detected, the inter-electrode voltage is compared with the current level to a predetermined first value.
By lowering the voltage only by the level and by lowering the voltage between the electrodes by a required level, sparks were prevented from occurring.

According to the second aspect of the present invention, when the spark is detected while the timer has elapsed the set time, the inter-electrode voltage is decreased by the first level and the timer is reset and started at the time of the detection. By this reset start, the occurrence of spark within the next set time is monitored.

According to the third aspect of the present invention, when the spark is not detected while the timer has elapsed the set time, the inter-electrode voltage is increased by the predetermined second level when the set time elapses, and the timer is activated. A reset start is performed, and the occurrence of sparks within the next set time is monitored by this reset start.

According to the fourth aspect of the present invention, when the spark is detected while the timer elapses over the set time, the inter-electrode voltage is decreased by the first level and the timer is reset and started at the time of the detection. On the other hand, when the spark is not detected during the elapse of the set time, the inter-electrode voltage is increased by the predetermined second level when the set time elapses, and the timer is reset and started. The occurrence of sparks in time is monitored.

According to the fifth aspect of the invention, since it is considered that the water content of the object to be heated is high for a certain period of time from the start of the supply of the high frequency power, the voltage between the electrodes does not have to be controlled to be lowered, and a predetermined level is maintained. Power is supplied.

[0015]

1 is a block diagram of a high frequency induction heating apparatus according to the present invention. In the figure, reference numeral 1 denotes a high frequency generator which is connected to a power source and generates a high frequency signal of a required frequency and a required level. The high frequency output from the generator 1 is a matching circuit 2 for impedance matching with a load.
And is supplied to the electrode 4 via.

The electrode 4 is composed of a pair of electrode plates 41 and 42, and preferably an upper electrode plate 41 is an elevating mechanism or the like so that an object to be heated, for example, the wood 3 for drying is interposed therebetween. It can be moved up and down in the following drying room (not shown). The drying wood 3 has a required thickness, and is placed on a carriage, for example, and can be transported through a door to a drying chamber that is brought into a vacuum state by an air compressor (not shown) or the like.

If the lower end member of the truck is used as the lower electrode 42, the work of interposing the wood 3 between the electrodes can be easily performed. In this case, the lower electrode plate 42 can be easily grounded via a rail or the like for transporting the carriage. Further, if the high frequency power is supplied by the balanced power supply method without grounding the both electrode plates 41, 42, more uniform drying can be achieved.

Reference numeral 5 denotes an inter-electrode voltage detection circuit which is connected to the upper and lower electrode plates 41 and 42 of the electrode 4 at appropriate positions and detects the inter-electrode voltage. The detection voltage is rectified or smoothed and guided to the control circuit 6. Has become. 7 is the upper and lower electrode plates 41 of the electrode 4,
It is a spark detection circuit that is connected to a proper place of 42 and detects a momentary short circuit that occurs when a dielectric breakdown or the like occurs in a part of the wood 3 and outputs a detection signal thereof. If both the instantaneous voltage short circuit and the rectified and smoothed inter-electrode voltage can be generated using the output of the inter-electrode voltage detection circuit 5, the spark detection function can also be used. Reference numeral 8 denotes a timer that elapses time T1, T0, etc., which will be described later, and elapses the drying time T as necessary. Reference numeral 9 is a counter that counts the number of sparks detected by the spark detection circuit 7, and is set in advance to an allowable number, for example, 2 to several times, to prevent erroneous detection. It should be noted that the counter 9 is not particularly necessary when the control circuit 6 performs control if the spark occurs even once.

The control circuit 6 has an operating section necessary for driving the present apparatus, and performs constant power control for a predetermined time T1 from the start of driving, and thereafter takes in the inter-electrode voltage from the inter-electrode voltage detection circuit 5. Then, a control signal is output to the matching circuit 2 or to the high frequency generator 1 to perform constant voltage control, and the constant voltage is changed up or down according to the outputs of the timer 8 and the counter 9.

FIG. 2 is a time chart in wood drying as an example of the control operation by the high-frequency dielectric heating device according to the present invention. The time chart of FIG. 2 shows changes in water content, high-frequency power, and inter-electrode voltage with respect to the drying time on the horizontal axis. At a predetermined time T1 from the start of driving, constant power control is performed so that the supplied power is maintained at a required constant level (the inter-electrode voltage shows an increasing tendency), and then the constant voltage control is switched to. There is. This constant voltage control is basically controlled by a span of a certain time T0,
Depending on the state of spark generation during that time, that is, if no spark occurs during that time, the current inter-electrode voltage is increased by V1 when the time T0 elapses, while if a spark occurs, the current inter-electrode voltage becomes V2 at that time. It's just down.

In FIG. 2, after switching to the constant voltage control, the voltage V1 level is increased twice only in the span of time T0, and the voltage V1 level is further increased at time t1.
Immediately after this, at time t2, a spark occurs (spark abnormality) and the V2 level is lowered. Further, at the time t3 immediately after this, it is down by the V2 level. After this, it can be seen that the V1 levels are sequentially increased. Then, when a predetermined drying time T elapses, the driving of the apparatus is stopped. The water content gradually decreases with the passage of time.

The predetermined time T1 may be set in advance, or may be finished when the inter-electrode voltage reaches a predetermined level and the constant voltage control may be started. In this way, when the predetermined time T1 is determined by the voltage between the electrodes, it is possible to set a suitable time in a form that matches the actual drying operation.
Also, the level V2 at the time of down is made larger than the level V1 at the time of up, so that the voltage is gradually increased until the spark occurs, while the spark generation stops quickly when the spark occurs. This is to suppress the occurrence of sparks as much as possible by lowering the level to a level that allows it.

Further, the drying time may be controlled when another factor, for example, the level of the supplied electric power is lowered to a predetermined level. Alternatively, a weight scale or a moisture meter may be used. In the case of using a weigh scale, it is possible to set by the amount of change in weight of the heating target due to the decrease in water content, and in the case of using a moisture scale, the water content of the heating target is grasped as a dielectric constant, It can be set at a reduction level, or it can be set from the relationship between the stored water amount and the initial water content by guiding the water escaping to the outside with heating and drying to a water storage tank with a vacuum pump.

Next, the control operation of the high frequency induction heating apparatus according to the present invention will be described with reference to the flowchart of FIG.

When the power source is turned on after the object to be heated such as the wood 3 is interposed between the electrodes 4, the constant power control is first performed for a predetermined time T1 (step S2). Then, when the predetermined time T1 has elapsed, the control is subsequently switched to constant voltage control based on the inter-electrode voltage at that time (step S4),
Then, the timer 8 starts elapse of a certain time T0 (step S6). During this lapse of time, the spark detection circuit 7 detects whether or not the spark is generated (step S8). When the spark is generated, the number of times is counted by the counter 9
Is counted (step S10). When the count value reaches a preset value (YES in step S12)
S), a signal instructing the voltage reduction is output to the control circuit 6. When the voltage down instruction signal is input, the control circuit 6 outputs a control signal to the matching circuit 2 to reduce the current electrode voltage by V2 (step S14).

On the other hand, if the above-mentioned timer 8 does not generate a spark within a period of time elapsing a predetermined time T0, or if the number of occurrences is a predetermined number or less (both N in steps S8 and S12).
O, and NO in step S6), the control circuit 6 outputs a control signal to the matching circuit 2 to increase the current inter-electrode voltage by V1 (step S16).

When the voltage change instruction is issued (step S
14, S16), the timer 8 is reset and started, and the counter 9 is reset (step S18).
Next, it is determined whether or not a predetermined drying time has elapsed. If not, the process returns to step S4 and steps S4 to S20 are repeatedly executed. As a result, if the occurrence of sparks is detected a predetermined number of times within a certain time T0,
At that time, the voltage is lowered by the V2 level, and if no spark is generated within the fixed time T0 or if it is less than the predetermined number of times, the voltage is raised by the V1 level and constant voltage control in consideration of efficiency and safety is performed.

In the above embodiments, wood drying is described as an example, but the present invention is not limited to this, and it can be used for drying and heating a heating object containing moisture by using high frequency dielectric heating. Yes, and the necessity of the vacuum container is set according to the usage target.

Further, in the present embodiment, the time T0 is set to be constant, but the time T0 is set to be shorter in accordance with the elapse of the drying time, for example, in accordance with the number of times of voltage change control, or in accordance with the level of the current inter-electrode voltage, The higher the level, the shorter the time can be set to improve the safety.

[0030]

As described above, according to the present invention, when the spark is detected between the electrodes, the voltage between the electrodes is lowered by the predetermined first level, so that the actual drying and heating operations can be performed. It is possible to provide a suitable, practical, safe, and highly efficient high-frequency dielectric heating device.

According to the second aspect of the present invention, when the timer detects the spark while the set time elapses, the inter-electrode voltage is decreased by the first level at the time of the detection. Safety is ensured in the span of, and efficient drying and heating control can be performed.

According to the third aspect of the invention, when the timer does not detect the spark during the elapse of the set time, the inter-electrode voltage is increased by the predetermined second level when the set time elapses. Therefore, efficient drying and heating control can be performed within the safe range.

According to the invention of claim 4, when the timer detects the spark while the set time elapses, the inter-electrode voltage is decreased by the first level at the time of the detection, and
When no spark is detected while the set time is being measured, the inter-electrode voltage is increased by the predetermined second level, so that extremely efficient drying and heating control can be performed.

According to the fifth aspect of the invention, the constant current control is performed for a certain period of time from the start of the high frequency power supply, so that efficient control can be performed according to the water content in the initial stages of drying and heating. .

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a high frequency dielectric heating device according to the present invention.

FIG. 2 is a time chart for drying wood as an example of a control operation by the high-frequency dielectric heating device according to the present invention.

FIG. 3 is a flowchart showing a control operation by the high-frequency dielectric heating device according to the present invention.

[Explanation of symbols]

 1 high frequency generator 2 matching circuit 3 wood 4 electrode 41 upper electrode plate 42 lower electrode plate 5 inter-electrode voltage detection circuit 6 control circuit 7 spark detection circuit 8 timer 9 counter

Claims (5)

[Claims] 1. An electrode for supplying a high-frequency power absorbed by an object to be heated, a high-frequency generating means for applying a high-frequency power of a required level to the electrode, an inter-electrode voltage detecting means for detecting a voltage of the electrode, and Voltage stabilizing means for controlling the high frequency power applied to the electrodes so that the voltage detected by the inter-electrode voltage detecting means becomes substantially constant at a predetermined level; spark detecting means for detecting sparks generated between the electrodes; A high-frequency dielectric heating device comprising: a voltage changing unit that lowers the inter-electrode voltage by a predetermined first level when a spark is detected. 2. The high frequency dielectric heating device according to claim 1, further comprising a timer for repeatedly measuring a preset time, and the voltage changing means detects a spark while the timer elapses the set time. Then, at the time of the detection, the inter-electrode voltage is decreased by the first level and the timer is reset and started. 3. The high frequency dielectric heating device according to claim 1, further comprising a timer for repeatedly measuring a preset time, and the voltage changing means detects a spark while the timer elapses the set time. If not, the inter-electrode voltage is increased by a predetermined second level and the timer is reset and started when the set time has elapsed.
The high frequency dielectric heating device described. 4. The high-frequency dielectric heating device according to claim 1, further comprising a timer for repeatedly measuring a preset time, and the voltage changing means detects a spark while the timer elapses the set time. Then, at the time of the detection, the voltage between the electrodes is decreased by the first level,
On the other hand, when no spark is detected while measuring the set time, the inter-electrode voltage is increased by a predetermined second level, and when the inter-electrode voltage is changed, the timer is reset and started. A high-frequency dielectric heating device characterized in that 5. The high frequency dielectric heating device according to claim 1, wherein the operation of the voltage changing means is stopped for a certain period of time from the start of supplying the high frequency power.