JP2718625B2 - High frequency dielectric heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drying an object to be heated, such as wood or dyed fiber (yarn wound on a bobbin), whose moisture content decreases with heating by high frequency dielectric heating. Or a high-frequency dielectric heating device for heating.

[0002]

2. Description of the Related Art When drying wood using high frequency, it is necessary to supply electric power in accordance with the water content contained in the wood in consideration of dielectric breakdown and corona discharge caused by a decrease in the water content. Is known to be important. Conventionally,
A high-frequency dielectric heating device considering this point has been proposed (Japanese Patent Laid-Open No. 59-121794). This device is based on the finding that from the relational expression of the high-frequency power absorbed inside the wood, if the voltage between the electrodes is detected, it is possible to estimate the change tendency of the water content that greatly affects the dielectric constant of the wood. For a predetermined period of time at the beginning of high-frequency application, constant power control is performed.After that, when the water content reaches a level at which dielectric breakdown or corona discharge occurs when the moisture content becomes equal to or less than the threshold, the voltage is switched to constant voltage control at that time, It is intended to dry wood efficiently and efficiently.

[0003]

The conventional high-frequency induction heating apparatus employs a fixed control method in which the first half employs constant power control, while the second half employs a constant control method of constant voltage control. Can be driven only at a voltage level that can be expected to be sufficiently safe even if the constant voltage control is continued at the final voltage in the above.While safe drying of wood can be secured to some extent, there is a limit in efficiency. I had to say that there was.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and detects an insulation breakdown (spark) in an object to be heated, and lowers, raises or lowers the voltage between electrodes according to the state of occurrence of the spark. Therefore, it is an object of the present invention to provide a practical, safe, and more efficient high-frequency dielectric heating apparatus suitable for actual drying and heating.

[0005]

According to the present invention, there is provided an electrode for supplying high frequency power to be absorbed by an object to be heated, a high frequency generating means for applying a required level of high frequency power to the electrode,
Inter-electrode voltage detection means for detecting the voltage of the electrodes, and voltage stabilization means for controlling high-frequency power applied to the electrodes so that the voltage detected by the inter-electrode voltage detection means is substantially constant at a predetermined level, 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). .

In addition, the present invention further comprises a timer for repeatedly counting a preset time, and the voltage changing means detects the spark while the timer elapses the set time, and the voltage changing means detects the spark at the time of the detection. The inter-electrode voltage is lowered by the first level and the timer is reset and started (claim 2).

[0007] In addition, the present invention further comprises a timer for repeatedly counting a preset time, and wherein the voltage changing means includes a timer for measuring the preset time when the timer does not detect a spark while the preset time elapses. When the time elapses, the inter-electrode voltage may be increased by a predetermined second level, and the timer may be reset and started (claim 3).

[0008] Further, in claim 1, further comprising a timer for repeatedly counting a preset time, wherein the voltage changing means detects the spark while the timer elapses the set time, and the voltage changing means detects the spark at the time of the detection. The inter-electrode voltage is decreased by the first level, and if no spark is detected while the set time is measured, 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).

It is desirable that the operation of the voltage changing means be stopped for a predetermined time from the start of the supply of the high-frequency power.

[0010]

According to the first aspect of the invention, when high-frequency power is supplied to the object to be heated interposed between the electrodes, the voltage between the electrodes at this time is detected, and the detected voltage is set 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 spark between the electrodes is detected, the voltage between the electrodes is compared with the current level by a predetermined first value.
The spark is prevented from being generated by lowering the inter-electrode voltage by a required level by lowering the voltage only by the level.

According to the second aspect of the present invention, if spark is detected while the timer elapses the set time, the voltage between the electrodes drops by the first level at the time of the detection and the timer is reset and started. 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 spark is not detected while the timer elapses the set time, the inter-electrode voltage is increased by a predetermined second level when the set time elapses, and the timer is activated. A reset is started, and the occurrence of spark within the next set time is monitored by the reset start.

According to the present invention, when a spark is detected while the timer elapses the set time, the voltage between the electrodes is reduced by the first level at the time of the detection, and the timer is reset and started. On the other hand, if spark is not detected while the timer elapses the set time, the inter-electrode voltage is increased by a predetermined second level when the set time elapses, and the timer is reset-started. Monitoring of the occurrence of spark in time is performed.

According to the fifth aspect of the present invention, since the water content of the object to be heated is considered to be high for a certain period of time after the start of the supply of the high-frequency power, the voltage between the electrodes can be maintained at a predetermined level without particularly controlling the voltage between the electrodes. Power is supplied.

[0015]

FIG. 1 is a block diagram showing a high-frequency dielectric heating apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a high-frequency generator connected to a power supply to generate a high-frequency signal of a required frequency and a required level. A high-frequency output from the generator 1 is supplied to a matching circuit 2 for impedance matching with a load.
, And supplied to the electrode 4.

The electrode 4 is composed of a pair of electrode plates 41 and 42. Preferably, the upper electrode plate 41 is moved up and down so that an object to be heated, for example, wood 3 for drying, is interposed therebetween. It can be moved up and down in the following drying chamber (not shown). The wood 3 for drying has a required thickness, for example, is mounted on a truck, and can be transported through a door to a drying chamber which is evacuated 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 carriage conveying rail or the like. Further, if both the electrode plates 41 and 42 are not grounded and high-frequency power is supplied by a balanced power supply method, more uniform drying can be achieved.

Reference numeral 5 designates an inter-electrode voltage detecting circuit which is connected to an appropriate position of the upper and lower electrode plates 41 and 42 of the electrode 4 and detects an inter-electrode voltage. The detected voltage is rectified or smoothed and guided to the control circuit 6. Has become. 7 is an upper and lower electrode plate 41 of the electrode 4,
42 is a spark detection circuit that is connected to an appropriate position and detects a short circuit that occurs when insulation 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 for elapse of time T1, T0, and the like described later, and for elapse of the drying time T as necessary. Reference numeral 9 denotes a counter for counting the number of occurrences of spark detected by the spark detection circuit 7, which is set in advance to an allowable number, for example, two to several times, to prevent erroneous detection. Note that the counter 9 is not particularly necessary when the control circuit 6 performs control if a spark occurs even once.

The control circuit 6 has an operation section necessary for driving the 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 furthermore, the constant voltage is raised or lowered 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 apparatus according to the present invention. The time chart of FIG. 2 shows changes in the water content, the high-frequency power, and the inter-electrode voltage with respect to the drying time on the horizontal axis. For 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 voltage between electrodes shows a tendency to increase), and thereafter, the mode is switched to constant voltage control. I have. This constant voltage control is basically controlled in a span of a fixed time T0.
In accordance with the spark generation state 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. Just being down.

In FIG. 2, after being switched to the constant voltage control, the V1 level is increased by two times in the span of time T0, and further increased by the V1 level at time t1.
Immediately after this, at time t2, a spark occurs (spark abnormality), and the level is reduced by the V2 level. Further, at time t3 immediately after this, the voltage is lowered by the V2 level. After this, it can be seen that V1 levels are sequentially increased again. Then, when a predetermined drying time T has elapsed, the drive of the present apparatus is stopped. The water content gradually decreases over time.

The predetermined time T1 may be set in advance, or may be terminated when the voltage between the electrodes reaches a predetermined level, and the control may be shifted to the constant voltage control. As described above, when the predetermined time T1 is determined based on the voltage between the electrodes, a suitable time can be set according to the actual drying operation.
Also, the reason why the level V2 at the time of the down is made larger than the level V1 at the time of the up is that the voltage is gradually increased until the spark is generated, while the spark is stopped immediately when the spark is generated. This is to suppress spark generation as much as possible by lowering to a level that can be performed.

Further, the drying time may be controlled when another factor, for example, the level of the supplied electric power drops to a predetermined level. Alternatively, the measurement may be performed using a weighing scale, a moisture meter, or the like. In the case of using a weighing scale, it is possible to set the amount of change in weight of the object to be heated due to the decrease in moisture.In the case of using a moisture meter, the water content of the object to be heated is sequentially grasped as a dielectric constant, and the It can be set at a reduced level, or can be set based on the relationship between the amount of water stored and the initial water content by guiding the moisture that escapes with heating and drying to the outside with a vacuum pump.

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

When power is turned on after an object to be heated such as wood 3 is interposed between the electrodes 4, first, constant power control is performed for a predetermined time T1 (step S2). Then, when the predetermined time T1 has elapsed, the control is subsequently switched to the constant voltage control based on the voltage between the electrodes at that time (step S4),
Next, the elapse of the predetermined time T0 by the timer 8 is started (step S6). During this elapse of time, the presence / absence of spark generation is detected by the spark detection circuit 7 (step S8).
Is counted (step S10). When the count value reaches a preset value (YE in step S12).
S), a signal for instructing the control circuit 6 to decrease the voltage is output. 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 inter-electrode voltage by V2 (step S14).

On the other hand, if spark does not occur or the number of occurrences is equal to or less than the predetermined number during the period when the timer 8 passes the predetermined time T0 (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-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 performed. As a result, when the occurrence of spark is detected a predetermined number of times within the fixed time T0,
At that point, the voltage is lowered by the V2 level, and if no spark occurs within a predetermined time T0 or if it is less than a 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 embodiment, wood drying was described as an example. However, the present invention is not limited to this, and it can be used for drying and heating of a heating target containing water by using high frequency dielectric heating. Yes, and the necessity of the vacuum container is set according to the use object.

In this embodiment, the time T0 is fixed. However, the time T0 is shortened sequentially according to the elapse of the drying time, for example, according to the number of times of the voltage change control, or, for example, according to the level of the current inter-electrode voltage. The higher the level, the shorter the time can be set, so that the safety can be enhanced.

[0030]

As described above, according to the present invention, when a spark is detected between the electrodes, the voltage between the electrodes is decreased by a predetermined first level. It is possible to provide a practical, safe, and efficient high-frequency dielectric heating apparatus that is suitable.

According to the second aspect of the present invention, when the timer detects a spark while the set time elapses, the voltage between the electrodes is decreased by the first level at the time of the detection. In this span, safety is ensured, and efficient drying and heating control can be performed.

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

According to the fourth aspect of the invention, when the timer detects a spark while the set time elapses, the voltage between the electrodes is decreased by the first level at the time of the detection.
When the spark is not detected during the set time, the voltage between the electrodes 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 present invention, the constant current control is performed for a fixed time from the start of the supply of the high frequency power, so that efficient control according to the moisture content in the initial stage of drying and heating can be performed. .

[Brief description of the drawings]

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

FIG. 2 is a time chart in wood drying 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]

 DESCRIPTION OF SYMBOLS 1 High frequency generator 2 Matching circuit 3 Wood 4 Electrode 41 Upper electrode plate 42 Lower electrode plate 5 Voltage detection circuit between electrodes 6 Control circuit 7 Spark detection circuit 8 Timer 9 Counter

Claims (5)

(57) [Claims] An electrode for supplying high-frequency power absorbed by an object to be heated, a high-frequency generator for applying a required level of high-frequency power to the electrode, an inter-electrode voltage detector for detecting a voltage of the electrode, Voltage stabilizing means for controlling high-frequency power applied to the electrodes so that the voltage detected by the inter-electrode voltage detecting means is substantially constant at a predetermined level; spark detecting means for detecting sparks generated between the electrodes; A high-frequency induction heating device comprising: voltage changing means for lowering the inter-electrode voltage by a predetermined first level when a spark is detected. 2. The high-frequency induction heating apparatus according to claim 1, further comprising a timer for repeatedly counting a preset time, and wherein said voltage changing means detects a spark while said timer passes said set time. Then, at the time of the detection, the inter-electrode voltage is reduced by the first level and the timer is reset and started. 3. The high-frequency induction heating apparatus according to claim 1, further comprising a timer for repeatedly counting a preset time, and wherein said voltage changing means detects a spark while said timer passes said set time. 3. The system according to claim 2, wherein when not set, the inter-electrode voltage is increased by a predetermined second level when the set time has elapsed, and the timer is reset and started.
The high-frequency dielectric heating device according to claim 1. 4. The high-frequency induction heating apparatus according to claim 1, further comprising a timer for repeatedly counting a preset time, and wherein said voltage changing means detects a spark while said timer passes said 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 the set time is measured, 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. 5. The high-frequency dielectric heating apparatus according to claim 1, wherein the operation of the voltage changing means is stopped for a predetermined time from the start of the supply of the high-frequency power.