JP2718630B2 - Spark detection circuit of balanced feeding type high frequency 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 balanced power supply type high frequency heating apparatus for supplying high frequency power from a balanced power supply circuit to opposed first and second electrodes to heat an object to be heated interposed between the electrodes. In particular, the present invention relates to a spark detection circuit capable of detecting a short circuit between the first electrode and the ground, or a short circuit between the second electrode and the ground, in addition to the short circuit between the first and second electrodes.

[0002]

2. Description of the Related Art There is known a high-frequency heating apparatus in which high-frequency power is supplied from a power supply circuit to a facing anode electrode and a ground electrode to internally heat an object interposed between the electrodes by dielectric loss. Conventionally, in such an apparatus, a spark may be generated between the anode electrode and the earth electrode due to deformation of the object to be heated due to internal heating or outflow and movement of liquid or vapor such as water-containing moisture. If you leave
Repetitive sparks have resulted in partial alteration of the object to be heated, and deterioration and breakage of components constituting the apparatus.
Therefore, this type of apparatus is conventionally provided with a spark detection circuit for suitably detecting such a spark. The spark detection is performed by applying a bias voltage of a predetermined level between the anode electrode and the ground, and detecting a short-circuit current flowing due to a short-circuit of the applied voltage when a spark occurs between the electrodes.

[0003] In the drying of wood and the production of laminated veneers, it is known that a press plate for pressing is juxtaposed in the same row as the counter electrode.

[0004]

In recent years, as a high-frequency heating apparatus, an apparatus employing a balanced power supply circuit system has been provided from the viewpoint of further improving the uniformity of internal heating of an object to be heated. In the balanced power feeding method, since both electrodes are electrically floating above the ground, even if a spark detection circuit similar to that of the conventional unbalanced power feeding method is used, the spark between both electrodes can be detected properly as it is. I can't.

In a circuit of the balanced power supply system, it is necessary to treat a case where each of a pair of electrodes disposed opposite to each other is short-circuited to the ground as an abnormal occurrence. The detection circuit cannot cope with such a situation. In particular, in the case where a press platen (potentially grounded) is arranged close to the opposing electrodes, in addition to sparks between the electrodes, sparks generated between the respective electrodes and the press platen through materials and the like are used. In addition, it is necessary to detect it appropriately.

[0006] The present invention has been made in view of the above,
It is an object of the present invention to provide a spark detection circuit capable of reliably detecting all sparks generated between electrodes and between each electrode and ground in a high-frequency heating device of a balanced power supply system.

[0007]

SUMMARY OF THE INVENTION The present invention provides a balanced power supply type high frequency heating apparatus for supplying high frequency power from a balanced power supply circuit to opposed first and second electrodes to heat an object interposed between the electrodes. , A first voltage generating means for applying a bias voltage V1 between a first electrode and a ground, a second voltage generating means for applying a bias voltage V2 between a second electrode and a ground, and the first electrode and a ground First short-circuit detecting means interposed between the first voltage generating means and detecting short-circuit of the first voltage generating means;
And a second short-circuit detecting means interposed between the second electrode and the ground and detecting a short-circuit of the second voltage generating means.

The second voltage generating means is interposed between the first electrode and the second electrode, and applies a bias voltage of V2-V1, whereby the second electrode is grounded. On the other hand, this is equivalent to applying the bias voltage V2 (claim 2).

Further, the invention according to claim 2 further comprises a rectifying means interposed between the connection point of the first voltage generating means and the first electrode and a ground with a polarity opposite to the bias voltage V1. (Claim 3).

Further, in any one of the first to third aspects of the present invention, there is provided a power supply control means for stopping power supply when a short circuit is detected in at least one of the first and second voltage generation means. (Claim 4).

Further, in the invention of claims 1 to 4, the first,
Preferably, the second voltage generating means is configured to generate a bias voltage via an insulating circuit (claim 5).

Further, in the first to fifth aspects of the present invention, the bias voltage V2 may be set to twice the bias voltage V1 (claim 6).

[0013]

According to the first aspect of the present invention, the opposing first,
The high frequency power supplied from the balanced power supply circuit to the second electrode causes a dielectric loss inside the object to be heated interposed between the electrodes, so that the second electrode is heated. When a spark occurs between the first and second electrodes, a short-circuit current flows in a loop including the first and second voltage generating means, and a short circuit is detected by the first and second short-circuit detecting means. When a spark occurs between the first electrode and the ground,
The short circuit is detected by the first short circuit detecting means, while the second
When a spark is generated between the electrode and the ground, a short circuit is detected by the second short circuit detecting means.

According to the second aspect of the invention, the bias voltage V2 is applied to the second electrode with respect to the ground. Further, the second voltage generating means is connected to the first electrode and the second electrode.
By providing the interposition between the electrodes, there is a difference in the short-circuit detection operation from the first aspect. That is, first,
The spark between the second electrode is detected by the second short circuit detecting means, the spark between the first electrode and the ground is detected by the first short circuit detecting means, and the spark between the second electrode and the ground is first,
It is detected by the second short-circuit detecting means.

According to the third aspect of the present invention, since the rectifying means is provided between the connection point of the first voltage generating means and the first electrode and the ground with a polarity opposite to the bias voltage V1, the rectifying means is provided. The short circuit prevention of the first voltage generating means is ensured while securing the flow path of the short circuit current for the short circuit between the two electrodes and the ground. By providing this rectifying element, there is a difference in the short-circuit detection operation from the first aspect of the invention. That is, the spark between the first and second electrodes is detected by the second short-circuit detecting means, the spark between the first electrode and the ground is detected by the first short-circuit detecting means, and the spark between the second electrode and the ground is detected. It is detected by the second short-circuit detecting means.

According to the fourth aspect of the present invention, the first and the second are provided.
When the short circuit is detected by at least one of the short circuit detecting means, the supply of the power supplied to the first and second electrodes is stopped.

According to the fifth aspect of the present invention, it is not necessary to consider a high-level high-frequency potential when configuring the voltage generating means, and the circuit configuration is simplified accordingly.

According to the invention, the bias voltage applied between the first electrode and the ground is equal to the bias voltage applied between the first and second electrodes.

[0019]

FIG. 3 is an overall block diagram of a balanced feed type high frequency heating apparatus to which a spark detection circuit according to the present invention is applied. For example, the apparatus is manufactured by heating and bonding a long single plate laminate. FIG. 4 is a side view for explaining the operation of the apparatus. FIG. 5 is a schematic circuit diagram illustrating an example of a balanced power supply circuit.

In FIG. 3, reference numeral 1 denotes a control circuit for generally controlling the operation of the high-frequency heating apparatus. The control circuit 1 includes a microcomputer and the like, and controls power supply according to an operation instruction from the operation section 1a and detects a spark to be described later. Control for stopping power supply, and driving control of a control motor and a lifting mechanism. The control circuit 1 oscillates the high-frequency generation circuit 3 in the same phase, and applies a high-frequency electric field of the same phase to each of the electrode units 5 described later. Disturbance is prevented as much as possible, or the adjacent electrode portions are separated sufficiently as described below, and the disturbance of the electric field distribution pattern is at a level that hardly causes a problem. That's what we do.

The high-frequency supply circuit section is provided with n stages (two stages in FIG. 4 for convenience), and each stage comprises the same power supply circuit 2, high-frequency generation circuit 3, automatic tuning circuit 4, and electrode section 5. And a spark detection circuit 6 is provided.

The power supply circuit 2 receives power supply from, for example, a commercial AC power supply of 220 VAC, converts the power to a required level of DC through an AC-DC converter or the like, outputs the DC to a high frequency generation circuit 3, and detects a spark. The DC voltage E1, E2 of a required level is supplied to the circuit 6 as a bias voltage. The generation of the DC voltage for leading to the spark detection circuit 6 is performed separately through an insulating circuit such as a transformer. The high-frequency generation circuit 3 has an oscillator and the like inside and converts a DC power supply from the power supply circuit 2 into a high-frequency power of a required frequency. Depending on the thickness of the material, power of several KW to several tens of KW can be obtained. .

The automatic tuning circuit 4 performs power supply in a required matching state by matching with a load. In other words, the veneer laminated material, which is a load, has an appropriate moisture content, whereas when heated, the internal moisture evaporates and evaporates into steam to escape to the outside, and the dielectric constant, that is, the capacitance component changes. (Matching is displaced), the predetermined matching condition is always maintained accordingly.

FIG. 5 schematically shows a circuit of a balanced power supply system employed in the present apparatus. The unbalanced power supply method has the advantage that power control is easy, but the electric field distribution between the upper and lower electrode plates is unbalanced due to the structure around the ground side electrode, and usually the anode of the object to be heated is Temperature unevenness such as a higher temperature on the electrode plate side is likely to occur.
On the other hand, when the balanced power feeding method is adopted, the balance of the electric field distribution between the upper and lower electrode plates is improved, so that temperature unevenness is less likely to occur, and the temperature can be made uniform in the thickness direction of the object to be heated. This is particularly advantageous in the case of a thick heating object.

The electrode portion 5 is composed of electrode plates 51 and 52 which are arranged in parallel and opposed to each other. The two electrode plates 51 and 52 have the same rectangular plate shape, and the dimension in the left-right direction is set to L1. In addition, each of the electrode portions 5 is arranged in series adjacent to each other by a required size in consideration of insulation properties, for example, a distance L1 or an integer multiple thereof when applied to a single-plate laminated material heating device described later. Have been. The electrode plate 52 can be raised and lowered (contacted and separated) by the lifting mechanism 8 with respect to the electrode plate 51 by the electrode lifting mechanism 8A (see FIG. 3).

The adjacent electrode plate 52 (electrode plate 51)
For example, as shown in FIG.
A press platen section 9 composed of (lower press platen 91) is provided. The upper press platen 92 can be moved up and down (pressurized and depressurized) by a press plate lifting mechanism 8B, and the lower press platen 91 and the electrode plate 51 are arranged flush.

A transfer belt 10 is provided on the upper surface of the electrode plate 51 in the longitudinal direction. The transfer belt 10 is made of a thin insulating material, and a single-layer laminated material described later is placed on the transfer belt 10 and the transfer motor 7 is driven to drive the electrode plates 51 and 52 and the press plates 91 and 92. Between them in the longitudinal direction. The transfer belt 10 is provided so as to extend on both sides in the longitudinal direction of the electrode section 5 so that the loading and unloading of the veneer laminate can be reliably performed. Therefore,
Although not shown in the figure, a belt supporting board on which a belt transport roller 10 a having the same height as the electrode plate 51 is arranged on both sides in the longitudinal direction of the electrode portion 5. The transfer belt 10 is formed so as to be folded back to the installation surface (downward) side of the electrode unit 5 and endlessly or reciprocate.

The lifting mechanism 8 includes an electrode lifting mechanism 8A and a press plate lifting mechanism 8B, and includes a hydraulic cylinder, a hydraulic pump,
A known hydraulic system having an electromagnetic switching valve, a flow control valve, and the like is employed. The elevating mechanism 8 can apply a sufficient pressure so as to restrict the occurrence of warpage or the like of the laminated veneer laminated material.

The laminated veneer is formed by applying a thermosetting adhesive to the surface of a plurality of laminated veneers and laminating them. Generally, an alkali phenol or the like is used as the adhesive, and the required coating amount is applied uniformly or scattered over the entire surface. Almost half of the components of this adhesive are water, and it has been confirmed that a phenomenon occurs in which water vapor is generated by heating and a part of the adhesive moves in the longitudinal direction through the lamination surface. it is conceivable that.

Here, the basic operation of the heating and bonding process for the veneer laminate will be described with reference to FIG. FIG. 4 is a schematic diagram showing the relationship between the first heating operation and the second heating operation when the dimension between the electrode portions 5 is set to L1. FIG. 4A shows the first heat bonding, in which a high frequency is applied to the area sandwiched between the electrode portions 5 and the area of each press plate 9 is simply pressed. FIG. 4B shows a state in which the first heat bonding is completed, the electrode section 5 and the press board section 9 are separated from each other, and the veneer laminate is transferred by the L1 pitch. FIG. 4 (c) shows the second heat bonding.
A heating operation is performed on the portion pressed at the first time. The heating and bonding process is completed by these two heating operations,
The veneer laminate is transferred to the outlet side by the transfer belt 10,
It is carried out. The second heat bonding may be performed in a state where the press platen 9 is separated as shown in FIG.

FIG. 1 is a circuit diagram showing a spark detection circuit 6 and its peripheral circuits of a balanced power supply type high frequency heating apparatus according to the present invention. In the figure, high-frequency power is supplied to the electrode plates 51 and 52 from the high-frequency generation circuit 3 via the oscillation transformer and the automatic tuning circuit 4. The press plates 91 and 92 are both grounded.

The spark detection circuit 6 includes power supplies B1 and B2 for generating a bias DC voltage and relay coils RL1 and R2 constituting a relay as means for detecting a short circuit.
L2 and the like.

The power supplies B1 and B2 are configured from a commercial power supply of AC 100 V via a transformer T which is an insulating circuit. That is, commercial power is applied to the primary winding Lo of the transformer T, and the primary winding L1 and the second winding L2
The winding ratio is set so that a predetermined voltage, for example, 12 V AC is induced. The power supply B1 rectifies the output of the first winding L1 with a diode D1, smoothes it with a capacitor C1, and generates a predetermined DC bias voltage E1. The power supply B2 rectifies the output of the second winding L2 with a diode D2 and smoothes it with a capacitor C2 to generate a predetermined DC bias voltage E2 (E1 = E2 in this embodiment).

The power supply B1 and the relay coil RL1 are connected in series, the capacitor C1 is connected to the electrode plate 51, and the relay coil RL1 is connected to the ground. Between the capacitor C1 and the electrode plate 51, there are provided a variable resistor VR1 for limiting the current at the time of short-circuit, a filter LPF1 for blocking the high frequency from being mixed into the power supply, and a capacitor C10. A diode Do as a rectifier connected in reverse polarity to the generated voltage of the power supply B1 is interposed between the connection point between the variable resistor VR1 and the filter LPF1 and the ground, to prevent short-circuit of the power supply B1. I have.

The power supply B2 and the relay coil RL2 are connected in series, the relay coil RL2 side is connected to the electrode plate 52, and the capacitor C2 side is connected to the ground via the power supply B1, that is, equivalently connected to the electrode plate 51. . Therefore, the power supply B2 is equivalent to (E1 + E2) when viewed from the ground. Between the capacitor C2 and the electrode plate 51, a variable resistor VR2 for limiting the current at the time of short circuit is provided. In addition, a filter LPF2 and a capacitor C20 are provided between the electrode plate 52 and the relay coil RL2 to block high-frequency mixing into the power supply side. Note that the relay coil R
L1 and RL2 close their movable contact pieces (not shown) from a normally open state when a current flows through these coils. These movable contact pieces are connected in series, so that both relays constitute an OR circuit 1b as shown in FIG. Then, the relay coils RL1,
When a short-circuit current flows through at least one of the RLs 2 and a signal indicating the occurrence of a short-circuit is input to the control circuit 1 via the OR circuit 1b, the control circuit 1 instructs all the power supply circuits 2 to stop supplying power. It outputs a signal. If the OR circuit 1b is provided for each electrode unit 5, only the power supply circuit 2 corresponding to the short-circuited electrode unit 5 can be stopped.

As the short-circuit detecting means, other detecting means such as a photo-interrupter comprising a light emitting diode and a phototransistor can be adopted instead of the above-mentioned relay utilizing electromagnetic force. In addition, a normal current detection circuit can be used if insulation is not taken into consideration.

FIG. 2 shows only a DC circuit extracted from the spark detection circuit 6. The operation of detecting a short circuit will be described with reference to FIG. (1) When spark A is generated between the electrode plates 51 and 52 The spark A between the electrode plates 51 and 52 is caused by erroneous contact of moisture or conductive foreign matter in or around the object to be heated.
Further, it is conceivable that a spark line is generated due to local deterioration of the object to be heated. When the spark A occurs, the power supply B2 is short-circuited, and a short-circuit current flows as shown in a loop. Therefore, the occurrence of a short circuit is detected by the relay coil RL2.

(2) Electrode plate 51 and ground (press plate 9
In the case where a spark B occurs between the electrode plate 51 and the ground, especially the press plate 91 (92)
For example, in the case of a single-layer laminated material, the spark between them may be caused by the moisture in the adhesive flowing laterally on the laminated surface, or by erroneous contact of foreign matter. When the spark B occurs, the power supply B1 is short-circuited, and a short-circuit current flows as shown in a loop. Therefore, the occurrence of a short circuit is detected by the relay coil RL1.

(3) Electrode plate 52 and ground (press plate 9
In the case where spark C is generated during the same period (including), the spark C is generated for the same reason as the above (2). in this case,
Due to the presence of the diode Do, only the power supply B2 is short-circuited. Accordingly, a short-circuit current flows as shown in a loop, and thereby, the occurrence of a short-circuit is detected in the relay coil RL2.

As described above, not only between the electrode plates 51 and 52, but also between the electrode plates 51 and 52 and the ground can be detected, so that all possible sparks can be detected. This can be detected.

FIGS. 6 to 8 are modified examples of the spark detection circuit 6, and are circuit diagrams in which only the DC circuit is extracted. In addition, the resistance component for short-circuit current limitation is not shown.
Hereinafter, a short-circuit detection operation will be described for each modification.

FIG. 6 shows the circuit of FIG. 2 with the diode Do removed. In this case, the operation of sparks A and B is the same as that of FIG.
, Both the power supplies B1 and B2 are short-circuited as shown in a loop. Therefore, spark C is relay coil RL
1 and RL2.

FIGS. 7 and 8 differ from FIGS. 2 and 6 in that the power source B2 is configured with the ground reference. However,
In other respects, FIG. 7 basically corresponds to FIG. 2 and FIG. 8 basically corresponds to FIG.

In FIG. 7, a short circuit current as shown in a loop flows due to spark A, the occurrence of a short circuit is detected in relay coil RL2, a short circuit current as shown in a loop flows due to spark B, and a short circuit occurs in relay coil RL1. The occurrence is detected, a short-circuit current as shown in a loop flows by the spark C, and the occurrence of a short-circuit is detected in the relay coil RL2.

In FIG. 8, a short-circuit current as shown in a loop flows by the spark A, and the relay coils RL1, RL
2, the occurrence of a short circuit is detected, and a short circuit current as shown in a loop flows by the spark B, and the relay coil R
The occurrence of a short circuit is detected at L1, and a short circuit current as shown in a loop flows by the spark C, and the relay coil RL2
Detects the occurrence of a short circuit.

As shown in each of the above embodiments, in each spark detection circuit, the manner of detecting a short circuit by a relay coil for a spark between electrodes and between each electrode and the ground is different. It is possible to identify. By providing the notifying means for notifying the spark location in accordance with each short-circuit detection mode, it is easy to confirm the abnormal location, and the normal return operation can be performed quickly and easily.

[0047]

As described above, according to the first aspect of the present invention, a spark generated between the first and second electrodes is generated between the first electrode and the ground by the first and second short-circuit detecting means. Can be detected by the first short-circuit detecting means, and the spark generated between the second electrode and the ground can be detected by the second short-circuit detecting means, so that all of the sparks which may occur can be detected. .

According to the second aspect of the present invention, the second voltage generating means is provided between the first electrode and the second electrode, and
Since the configuration is such that the bias voltage of 2-V1 is generated, the bias voltage of the second voltage generating means can be reduced. In addition, the spark generated between the first and second electrodes is
The spark generated between the first electrode and the ground can be detected by the first short-circuit detecting means, and the spark generated between the second electrode and the ground can be detected by the first and second short-circuit detecting means. Therefore, all possible sparks can be detected.

According to the third aspect of the present invention, since the rectifying means is provided between the connection point of the first voltage generating means and the first electrode and the ground with a polarity opposite to the bias voltage V1, the rectifying means is provided. The short-circuit prevention of the first voltage generating means can be ensured while securing the flow path of the short-circuit current for the short-circuit between the two electrodes and the ground. The spark generated between the first and second electrodes is detected by the second short-circuit detecting means, and the spark generated between the first electrode and the ground is detected by the first short-circuit detecting means.
Then, since the spark generated between the second electrode and the ground can be detected by the second short-circuit detecting means, all of the sparks that can be generated can be detected.

According to the fourth aspect of the present invention, the first and the second
Power supply control means for stopping the power supply when a short circuit is detected in at least one of the voltage generation means. In addition, it is possible to prevent the occurrence of breakage or to ensure the safety of the object to be heated.

According to the fifth aspect of the present invention, the first and the second
Since the voltage generating means is configured to generate a bias voltage via an insulating circuit, there is no need to consider a high-level high-frequency potential, and the circuit configuration can be simplified.

According to the sixth aspect of the present invention, the bias voltage V2 is set to be twice the bias voltage V1, so that the bias voltage applied to the first electrode and the first and second bias voltages are set.
Since the bias voltage applied between the electrodes can be matched, the short-circuit detecting means can be shared from the viewpoint of the withstand voltage.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a spark detection circuit of a balanced power supply type high frequency heating apparatus according to the present invention and a peripheral circuit section thereof.

FIG. 2 is a circuit diagram in which only a DC circuit is extracted from the spark detection circuit of FIG.

FIG. 3 is an overall block diagram of a balanced-feed high-frequency heating device to which the spark detection circuit according to the present invention is applied.

4A and 4B are side views for explaining the operation of the high-frequency heating device, where FIG. 4A shows a first heating operation, FIG. 4B shows a material transfer operation, and FIG. 4C shows a second heating operation. ing.

FIG. 5 is a schematic circuit diagram illustrating an example of a balanced power supply circuit.

FIG. 6 is a circuit diagram in which only a DC circuit in another modified example of the spark detection circuit is extracted.

FIG. 7 is a circuit diagram in which only a DC circuit is extracted in still another modified example of the spark detection circuit.

FIG. 8 is a circuit diagram in which only a DC circuit is extracted in still another modified example of the spark detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Control circuit 1b OR circuit 2 Power supply circuit 3 High frequency generation circuit 4 Automatic tuning circuit 5 Electrode part 51,52 Electrode plate 6 Spark detection circuit 9 Press board part 91,92 Press board B1, B2 Power supply RL1, RL2 Relay coil Do, D1, D2 Diode T Transformer (insulation circuit) C1, C2 Smoothing capacitor LPF1, LPF2 Filter

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Koji Yamamoto, inventor, 1-3-3, Shibukawa-cho, Yao-shi, Osaka Yamamoto Vinita Co., Ltd. Yao factory

Claims (6)

(57) [Claims] 1. A balanced power supply type high frequency heating apparatus for supplying high frequency power from a balanced power supply circuit to opposed first and second electrodes to heat an object to be heated interposed between the electrodes. A first voltage generating means for applying a bias voltage V1 to the second electrode, a second voltage generating means for applying a bias voltage V2 between the second electrode and the ground, and a second voltage generating means interposed between the first electrode and the ground. A first short-circuit detecting means for detecting a short-circuit of the first voltage generating means, and a second short-circuit detecting means interposed between the second electrode and the ground for detecting a short-circuit of the second voltage generating means.
A spark detection circuit for a balanced power supply type high frequency heating device, comprising: 2. The apparatus according to claim 1, wherein said second voltage generating means is provided between said first electrode and said second electrode, and applies a bias voltage of V2-V1. The spark detection circuit of the balanced feeding type high frequency heating device as described in the above. 3. A spark detection circuit for a balanced power supply type high frequency heating apparatus according to claim 2, wherein a polarity opposite to a bias voltage V1 is applied between a ground between a connection point between said first voltage generation means and said first electrode and ground. A spark detection circuit for a balanced feeding type high frequency heating device, comprising a rectifying means interposed. 4. The spark detection circuit for a balanced-feed high-frequency heating device according to claim 1, wherein when a short circuit is detected in at least one of the first and second voltage generating means, power is supplied. A spark detection circuit for a balanced-feed high-frequency heating device, comprising: a power supply control unit for stopping supply. 5. The balanced power supply according to claim 1, wherein said first and second voltage generating means generate a bias voltage via an insulating circuit. Spark detection circuit of the high frequency heating device. 6. The apparatus according to claim 1, wherein the bias voltage V2 is set to twice the bias voltage V1.
6. A spark detection circuit for a balanced-feed high-frequency heating device according to any one of claims 1 to 5.