HK1207018B

HK1207018B - Electric potential treatment device

Info

Publication number: HK1207018B
Application number: HK15107589.5A
Authority: HK
Inventors: 小川幸雄
Original assignee: 株式会社白寿生科学研究所
Priority date: 2012-06-26
Filing date: 2013-06-12
Publication date: 2017-04-07

Abstract

The present invention prevents electric shock to a treatment subject, secures the safety of the treatment subject, and easily obtains a sensation of stimulation and a sensation of treatment by means of an AC source. The electric potential treatment device (1), which performs treatment by means of placing the treatment subject within an electric field, is characterized by having: a primary electrode (2) disposed spaced from the treatment subject; a first contact electrode (3) and a second contact electrode (4) disposed in a state contacting the treatment subject; and a voltage generation unit (5) that, with respect to the electrodes, increases the voltage of the commercial power source voltage and supplies a predetermined AC voltage. The electric potential treatment device (1) is further characterized by a high AC voltage for treatment being imparted to the primary electrode (2) by means of the voltage generation unit (5), a low AC voltage being imparted to the first contact electrode (3) and the second contact electrode (4) by means of the voltage generation unit (5), and a weak current (i) being caused to flow through the treatment subject by means of the potential difference between the contact electrodes.

Description

Electric potential therapeutic instrument

Technical Field

The present invention relates to a potential therapeutic apparatus for therapy using an electric field, and more particularly, to a potential therapeutic apparatus which can provide a therapeutic feeling to a human body while ensuring safety of the human body.

Background

The electric potential therapy apparatus is an apparatus for applying a high electric potential to a human body insulated from the ground and performing therapy by utilizing a biostimulation effect by an electric field formed around the human body. That is, the potential therapeutic apparatus forms an electric field around the human body by a potential difference generated by applying an alternating voltage to the human body and the counter electrode. As a method of forming such an electric field, there are a method of grounding the counter electrode while setting the human body at a high potential, a method of grounding the human body while setting the counter electrode at a high potential, and a method of setting the human body at a high potential while setting the counter electrode at a high potential of an opposite phase.

As a method of setting the human body to a high potential, there is a method of providing a foot electrode on a pedal (foot rest) on which a person to be treated sits while putting his foot on a chair, setting the foot electrode to a high potential, and forming an electric field between the human body of the person to be treated and a peripheral wall portion or a counter electrode thereof (for example, see patent document 1). In order to prevent the subject from receiving an electric shock, a method of grounding the human body includes, for example, grounding a foot electrode (as a ground electrode) and setting a head electrode or a seat electrode facing the foot electrode at a high potential to form an electric field between the human body and each electrode (see, for example, patent document 2).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 5-123405

Patent document 2: japanese patent laid-open publication No. 2002-177402

Disclosure of Invention

Technical problem to be solved

However, in the technique described in patent document 1, since the person to be treated has a high potential, the person may receive an electric shock when the person comes into contact with another person or a peripheral object such as a wall portion, and feel uncomfortable with the electric shock. In addition, in the technique described in patent document 2, although the electric shock can be prevented by holding the person to be treated at the ground potential, there is a problem that the stimulation and therapeutic feeling due to the ac high voltage disappear because the potential difference with the surrounding object disappears.

Accordingly, an object of the present invention is to provide a potential treatment apparatus which can prevent a person to be treated from receiving an electric shock, eliminate discomfort of the person to be treated, and easily obtain stimulation and treatment feeling due to an ac high voltage.

(II) technical scheme

In order to achieve the above object, the invention according to claim 1 is a potential treatment apparatus for performing treatment by placing a subject in an electric field, the potential treatment apparatus including a main electrode disposed apart from the subject, a first contact electrode and a second contact electrode disposed in contact with the subject, and a voltage generating device for boosting a commercial power supply voltage and supplying a predetermined ac voltage to the main electrode, wherein the voltage generating device applies the ac voltage to the main electrode, the voltage generating device applies the ac voltages to the first contact electrode and the second contact electrode, respectively, and the voltage difference between the two contact electrodes causes a weak current to flow through the subject, and the phases of the ac voltages applied to the first contact electrode and the second contact electrode are inverted.

According to the present invention, a weak current is caused to flow through the human body of the person to be treated by the first contact electrode and the second contact electrode.

The present invention according to claim 2 is an electric potential treatment apparatus for performing treatment by placing a patient in an electric field, the electric potential treatment apparatus including a main electrode disposed apart from the patient, a first contact electrode and a second contact electrode disposed in contact with the patient, and a voltage generator for boosting a commercial power supply voltage and supplying a predetermined ac voltage to the main electrode, wherein the voltage generator applies the ac voltage for treatment to the main electrode, the voltage generator applies the ac voltage to each of the first contact electrode and the second contact electrode, and a weak current flows through the patient due to a potential difference between the two contact electrodes, so that the phases of the ac voltages applied to the first contact electrode and the second contact electrode are in phase, and the ac voltage applied to the main electrode and the ac voltages applied to the two contact electrodes are in phase The phase of (a) is set to be an opposite phase, the ac voltage applied to the first contact electrode is set to have a positive peak value larger than a negative peak value, and the ac voltage applied to the second contact electrode is set to have a negative peak value larger than a positive peak value.

(III) advantageous effects

According to the inventions described in claim 1 and claim 2, since the alternating voltage is applied to the first contact electrode and the second contact electrode, the human body of the person to be treated is not set to a high potential, and therefore the person to be treated hardly feels an electric shock even when the person is in contact with a wall or other grounded object. In addition, since a weak current flows through the human body due to the potential difference of the alternating voltage applied to the two contact electrodes, the person to be treated can easily understand that the person is in a treatment state by feeling the weak current.

According to the invention described in claim 1, the human body of the subject is not set to a high potential, and the phases of the ac voltages applied to the two contact electrodes are in opposite phases, so that the human body potential is "zero". That is, even if the person to be treated touches the wall portion or other object in a grounded state, the person does not feel an electric shock at all.

According to the invention described in claim 2, since the phases of the ac voltages applied to the first contact electrode and the second contact electrode are in the same phase and the phases of the ac voltage applied to the main electrode and the ac voltages applied to the two contact electrodes are in opposite phases, higher potential treatment can be performed on the subject. Further, since the ac voltage applied to the first contact electrode is set to have a positive peak value larger than a negative peak value and the ac voltage applied to the second contact electrode is set to have a negative peak value larger than a positive peak value, a weak current flows while the human body is kept at a low potential, and thus the person to be treated can easily understand that the person is in a treatment state by feeling the person.

Drawings

Fig. 1 is a schematic circuit diagram of an electric potential treatment apparatus according to embodiment 1 of the present invention.

FIG. 2 is a schematic diagram showing the electric potential of the electric potential treatment apparatus of FIG. 1.

Fig. 3 is a schematic circuit diagram of the electric potential treatment apparatus according to embodiment 2 of the present invention.

FIG. 4 is a schematic view showing the electric potential of the electric potential treatment apparatus of FIG. 3.

FIG. 5 is a waveform diagram showing the potential of the potential treatment apparatus of FIG. 3, wherein (a) shows a waveform of the first low potential, (b) shows a waveform of the second low potential, and (c) shows a waveform of the body potential.

Detailed Description

The present invention will be described below based on the illustrated embodiments.

(embodiment mode 1)

Fig. 1 and 2 show embodiment 1 of the present invention. The electric potential therapy apparatus 1 is an apparatus for applying an ac high voltage to a main electrode 2 and applying an ac low voltage of opposite phase to a first contact electrode 3 and a second contact electrode 4, and treating a person to be treated by placing the person in the electric field, and as shown in fig. 1, the electric potential therapy apparatus 1 mainly includes an electric potential treatment device 100, a main electrode 2 disposed on the electric potential treatment device 100, a first contact electrode 3, a second contact electrode 4, and a voltage generation unit 5, and the voltage generation unit 5 serves as a voltage generation device for supplying a voltage to the main electrode 2, the first contact electrode 3, and the second contact electrode 4.

In embodiment 1, the high ac voltage applied to the main electrode 2 is set to 9000V, for example, and the low ac voltage applied to the first contact electrode 3 and the second contact electrode 4 is set to 100V, for example, so that the main electrode 2 induces the high potential V1(9000V) and the first contact electrode 3 and the second contact electrode 4 induce the low potentials V2(100V) and V3(100V), respectively, for therapeutic application, and the application is performed for physical sensation.

The surface material of the electric potential treatment apparatus 100 is made of an insulator, and includes a chair 101 for treating a seat, a head cover 102, and a pedal (communicating plate) 103. The chair 101 is mainly composed of a seat, a backrest, and left and right side walls covering the side portions of the lower body of the person to be treated, and a remote controller for performing operations such as turning ON and OFF of the power is disposed ON the upper surface of the side walls.

Hood 102 is disposed above chair 101, is spaced above the head of the person to be treated in a state where the person to be treated is seated on chair 101, and incorporates main electrode 2 described later.

The pedal 103 is disposed on the floor in front of the chair 101, is sized and shaped to allow both feet of the person to be treated to rest thereon in a state of sitting on the chair 101, and incorporates a first contact electrode 3 and a second contact electrode 4, which will be described later.

In a state where the person to be treated sits on the electric potential treatment apparatus 100, the upper part of the body is covered with the head cover 102, the right and left parts of the body are covered with the side walls, and the lower part of the body is covered with the step plate 103.

The main electrode 2 is built in a head cap 102 (fig. 1) covered with an insulator, is connected to the voltage generating unit 5, and is applied with an ac high voltage V1 (fig. 2) for treatment.

The first contact electrode 3 is disposed on one side of the pedal 103, is covered with an insulator, and is in contact with the right foot of the person to be treated via the insulator. The first contact electrode 3 is connected to the voltage generation unit 5 so as to allow an inflow current (weak current) i to flow through the subject, and is applied with a first low voltage V2 of an alternating current.

The second contact electrode 4 is configured in the same manner as the first contact electrode 3, is disposed on the other side of the pedal 103, and is in contact with the left foot of the person to be treated via an insulator. The second contact electrode 4 is connected to the voltage generation unit 5 so as to allow a weak current i to flow through the subject, and is applied with a second low voltage V3 of alternating current.

The voltage generating unit 5 boosts the commercial power supply voltage and supplies a predetermined ac voltage to the main electrode 2 and the contact electrodes 3 and 4. As shown in fig. 1, the voltage generating unit 5 mainly includes a socket 51 for connecting a commercial power supply and switches 51SW1 and 51SW2, and includes a main electrode transformer 52, a first contact electrode transformer 53, and a second contact electrode transformer 54.

The switches 51SW1 and 51SW2 are used to switch between start (ON) and stop (OFF) of supply of electric power from the commercial power source to the electric potential treatment apparatus 1. The switches 51SW1 and 51SW2 are switched ON and OFF by a power button provided ON the remote controller of the electric potential treatment apparatus 100.

The main-electrode transformer 52 is for inducing a high potential V1 to the main electrode 2, and has one end of a primary winding 52a connected to the socket 51 via a switch 51SW2 and the other end connected to the socket 51 via a switch 51SW 1. One end of the secondary winding 52b of the main electrode transformer 52 is connected to the ground G, and the other end is connected to the main electrode 2 via the main electrode current limiting element 52R. The current limiting element 52R has a function of increasing the output impedance in order to prevent electric shock due to the main electrode 2. In the main electrode transformer 52, if the voltage generating unit 5 operates, a high potential (high potential) V1 is induced.

The first contact transformer 53 is used to induce the first low potential V2 in the first contact 3, and one end of the primary winding 53a is connected to the socket 51 through the switch 51SW2, and the other end is connected to the socket 51 through the switch 51SW 1. The secondary winding 53b of the first contact electrode transformer 53 has one end connected to the ground G and the other end connected to the first contact electrode 3 via the first contact electrode current rectifying element 53R. The current rectifying element 53R is connected to improve the safety of the first contact electrode 3. In the present embodiment, the current limiting element 53R is set so that the weak current i flowing through the human body of the subject is, for example, approximately 0.5 to 1 mA. In the first contact electrode transformer 53, if the voltage generation unit 5 operates, a low potential (first low potential) V2 is induced.

The second contact transformer 54 is used to induce the second low potential V3 in the second contact 4, and has the same structure as the first contact transformer 53, but one end of the primary winding 54a of the second contact transformer 54 is connected to the socket 51 through the switch 51SW1, and the other end is connected to the socket 51 through the switch 51SW 2. That is, the method of connecting the first contact electrode transformer 53 and the commercial power supply is the reverse of the method of connecting the second contact electrode transformer 54 and the commercial power supply. Specifically, the secondary winding 54b of the second contact electrode transformer 54 has one end connected to the ground G and the other end connected to the second contact electrode transformer 54 through the second contact electrode current rectifying element 54R. The current rectifying element 54R is connected to improve the safety of the second contact electrode 4, similarly to the current rectifying element 53R. In such a second contact electrode transformer 54, if the voltage generating unit 5 operates, the second low potential V3 opposite in phase to the first low potential V2 is induced.

As shown in fig. 2, the voltage generating unit 5 configured as described above induces a high potential V1 for potential treatment on the main electrode 2, induces low potentials V2 and V3 having opposite phases with the same voltage on the first contact electrode 3 and the second contact electrode 4, respectively, and forms a treatment electric field by the potential difference between the main electrode 2 and the first contact electrode 3 and the second contact electrode 4. Then, in a state where the person to be treated sits on the potential treatment device 100, the human body is placed in an electric field formed between the main electrode 2 positioned above the head and the contact electrodes 3, 4 whose both feet are in contact through the pedal 103.

Next, a method of using the electric potential treatment apparatus 1 having such a configuration and an operation thereof will be described.

First, as shown in fig. 1, when the person to be treated sits on a chair 101, the person to be treated is in a state where both feet are in contact with pedals 103 and the head is separated from a head cover 102.

When the person to be treated operates the remote controller ON the upper surface of the side wall and turns ON the power source of the electric potential treatment apparatus 1, the voltage generating unit 5 is operated. Thus, an ac high voltage (9000V) is applied to the main electrode 2, and ac low voltages V2 and V3(100V) are applied to the first contact electrode 3 and the second contact electrode 4, respectively, to form an electric field around the human body of the subject, thereby performing treatment using the electric field.

At this time, the first low potential V2 of the first contact electrode 3 and the second low potential V3 of the second contact electrode 4 are opposite in phase at the same voltage, and thus the human body of the person to be treated is set to the ground potential. As shown in fig. 2, a weak current i flows between the first contact electrode 3 and the second contact electrode 4, that is, between the right foot and the left foot in the human body of the person to be treated due to the potential difference between the first low potential V2 and the second low potential V3, and the body feels the weak current.

As described above, according to the electric potential treatment apparatus 1, since the alternating low voltages V2, V3 are applied to the first contact electrode 3 and the second contact electrode 4 by the voltage generating unit 5 without setting the human body of the person to be treated to a high electric potential, the person to be treated hardly feels an electric shock even if the person is in contact with a wall or other grounded object. In addition, since a weak current i flows through the human body by the potential difference of the ac low voltage applied to the two contact electrodes 3 and 4, the person to be treated can easily understand that the person is in a treatment state by sensing the current i. That is, the person to be treated can feel a sense of treatment while maintaining the safety of the electric potential treatment apparatus 1 at a high level. Further, since the human body of the person to be treated does not have a high potential, the electric field formed around the human body of the person to be treated is formed to be substantially the same as the electric field formed when the foot electrodes are grounded. That is, even if the first contact electrode 3 and the second contact electrode 4 are provided, the effect of the treatment is not impaired.

Further, since the contact electrode transformers 53 and 54 and the contact electrodes 3 and 4 are connected by the current limiting elements 53R and 54R, it is possible to control so as to prevent a weak current i exceeding an allowable value from flowing to the first contact electrode 3 and the second contact electrode 4, and it is possible to reduce the risk of electric shock while the person to be treated can feel a proper therapeutic feeling.

(embodiment mode 2)

Fig. 3 to 5 show embodiment 2 of the present invention. In this embodiment, the voltage generation unit 6 is different in structure from the voltage generation unit 5 in embodiment 1. Therefore, the same reference numerals or corresponding reference numerals are given to the same components as those in embodiment 1, and the description thereof will be omitted.

In the present embodiment, as shown in fig. 3 and 4, a high potential V11 for potential therapy is induced in the main electrode 2, and low potentials V12 and V13 having different maximum values of the same phase are induced in the first contact electrode 3 and the second contact electrode 4 with the same voltage. The high potential V11 is set to be opposite in phase to the low potentials V12 and V13.

The voltage generating means 6 makes the phases of the ac low voltages applied to the two contact electrodes 3 and 4 in the same phase, and makes the phases of the ac high voltage applied to the main electrode 2 and the ac low voltages applied to the two contact electrodes 3 and 4 in opposite phases. The voltage generating means 6 is set such that the positive peak value of the ac voltage applied to the first contact electrode 3 is larger than the negative peak value, and the negative peak value of the ac voltage applied to the second contact electrode 4 is larger than the positive peak value.

As shown in fig. 3, the primary winding 62a of the main electrode transformer 62 of the voltage generating unit 6 has one end connected to the switch 61SW1 and the other end connected to the switch 61SW 2. One end of the secondary winding 62b of the main electrode transformer 62 is connected to the ground G, and the other end is connected to the main electrode 2 via the current limiting element 62R. The current limiting element 62R is connected to the main electrode 2. In this way, if the voltage generating unit 6 operates in the main electrode transformer 62, a high potential (high potential) V11 is induced.

The primary windings 63a and 64a of the contact-electrode transformers 63 and 64 have one ends connected to the socket 61 via the switch 61SW1 and the other ends connected to the socket 61 via the switch 61SW 2. The secondary windings 63b and 64b of the contact-electrode transformers 63 and 64 have one end connected to the ground G and the other end connected to the contact electrodes 3 and 4 through the first current limiting elements 63R1 and 64R1, respectively.

The secondary windings 63b and 64b of the contact-electrode transformers 63 and 64 are connected in parallel to the rectifier elements 63c and 64c, one ends of the rectifier elements 63c and 64c are connected between the current limiting elements 63R1 and 64R1 and the first contact-electrode transformers 63 and 64, and the other ends of the rectifier elements 63c and 64c are connected to one ends of the secondary windings 63b and 64b through the second current limiting elements 63R2 and 64R2, respectively.

Then, the rectifier device 63c connected to the first contact electrode transformer 63 is connected in the forward direction, and the rectifier device 64c connected to the second contact electrode transformer 64 is connected in the reverse direction.

Thus, in the transformer 63 for the first contact electrode, the alternating-current voltage across the secondary winding 63b is divided by the ratio of the resistance value of the first current rectifying element 63R1 to the resistance value of the second current rectifying element 63R2, and the respective peak values are applied to the first contact electrode 3 in the relationship of | + V12p | > | -V12p | by the rectifying element 63c ((a) in fig. 5).

In the second contact electrode transformer 64, the ac voltage across the secondary winding 64b is divided by the ratio of the resistance value of the first current rectifying element 64R1 to the resistance value of the second current rectifying element 64R2, and the respective peak values are applied to the second contact electrode 4 in the relationship of | + V13p | < | -V13p | by the rectifying element 64c ((b) in fig. 5).

As shown in fig. 4, the voltage generating unit 6 configured as described above induces the ac high voltage V11 for potential therapy to the main electrode 2, and induces the ac low voltages V12 and V13 having the same phase and the maximum values different from each other as shown in (a) and (b) in fig. 5 to the first contact electrode 3 and the second contact electrode 4, respectively, with the same voltage, and since the ac high voltage applied to the main electrode 2 and the ac low voltages V12 and V13 applied to the respective contact electrodes 3 and 4 are in opposite phases, the electric field formed by these is stronger than the electric field formed between the main electrode 2 and the ground G (embodiment 1).

Further, as described above, a potential difference is generated between the first contact electrode 3 and the second contact electrode 4, and the person to be treated who has left and right feet placed on these contact electrodes 3 and 4 has a low potential close to the ground potential, so that burn due to electric shock or electric discharge when the person or object is in contact with the outside during treatment is prevented, and a weak current i flows in the human body, and the human body feels the weak current i as stimulation.

The weak current i is preferably set to a current value (1mA or less) that is not dangerous, and for this purpose, the ratio of the alternating voltage applied to each of the contact electrodes 3 and 4 to the resistance values of the first current rectifying element 63R1 or 64R1 and the second current rectifying element 63R2 or 64R2 is appropriately set. The value of the current flowing in the human body is controlled by setting the resistance value ratio, and the intensity of the current stimulus to the human body is adjusted.

Further, since the contact electrode transformers 63 and 64 and the contact electrodes 3 and 4 are connected by the current limiting elements 63R1 and 64R1, it is possible to prevent a weak current i exceeding an allowable value from flowing to the contact electrodes 3 and 4, and to reduce the risk of electric shock while the subject feels a moderate feeling of treatment.

While embodiments 1 and 2 of the present invention have been described above, the specific configuration is not limited to each of embodiments 1 and 2, and design changes and the like within a range not departing from the gist of the present invention are also included in the present invention.

For example, the alternating current voltage for treatment induced in the main electrode and the alternating current voltage for physical sensation induced in each touch electrode may be set to be substantially the same voltage, and 9000V may be induced in the main electrode, 9000V in the first touch electrode, and 9000V in the second touch electrode.

The phase between the therapeutic ac voltage induced to the main electrode and the bodily sensation ac voltage induced to each contact electrode is not limited to the combination of embodiments 1 and 2, and for example, the therapeutic ac voltage and the two bodily sensation ac voltages may be in the same phase. Specifically, 9000V is induced in the main electrode, 100V is induced in the first contact electrode, and 90V is induced in the second contact electrode. If the above arrangement is adopted, a weak current corresponding to the potential difference (10V) applied to the first contact electrode and the second contact electrode flows in the human body, and the person to be treated can receive electric field treatment while receiving the weak current.

Further, the phases of the ac voltages applied to the three electrodes may be shifted by 120 °, respectively.

In embodiments 1 and 2, two contact electrodes 3 and 4 are shown to be arranged on the left and right sides of the pedal 103, but the present invention is not limited to this, and the contact electrodes may be arranged on the armrest portion on which the left and right elbows are placed, or the contact electrodes may be arranged on the left and right sides of the seat portion of the chair 101. That is, it is sufficient to cause a weak current i to flow by bringing a part of the body of the subject into contact with the contact electrodes arranged at two positions, respectively.

Further, it is needless to say that the magnitude of the weak current i flowing through the human body can be adjusted by appropriately adjusting the current limiting elements 53R, 54R, 63R1, and 64R1, and the stimulation/therapeutic feeling can be adjusted according to the person to be treated.

Description of the reference numerals

1 electric potential therapeutic instrument

2 main electrode

3 first contact electrode

4 second contact electrode

5 Voltage generating Unit (Voltage generating device)

51 socket

51SW1 switch

51SW2 switch

52 main electrode transformer

52a primary winding

52b secondary winding

Current limiting element for 52R main electrode

53 transformer for first contact electrode

53a primary winding

53b secondary winding

53R Current rectifying element for first contact electrode

54 transformer for second contact electrode

54a primary winding

54b secondary winding

Current limiting element for 54R second contact electrode

High potential of V1

V2 first low potential

V3 second low potential

i weak current

6 Voltage generating Unit (Voltage generating device)

61 socket

61SW1 switch

61SW2 switch

62 transformer for main electrode

62a primary winding

62b secondary winding

62R current limiting element

63 transformer for first contact electrode

63a primary winding

63b secondary winding

63c rectifying element

63R1 first current limiting element

63R2 second current limiting element

64 second contact electrode transformer

64a primary winding

64b secondary winding

64c rectifier element

64R1 first current limiting element

64R2 second current limiting element

100 potential therapeutic equipment

101 chair

102 head cover

103 pedal (Universal station)

High potential of V11

V12 first low potential

V13 second low potential

i weak current

Claims

1. A potential therapeutic apparatus is characterized in that a person to be treated is placed in an electric field for treatment,

a voltage generating device having a main electrode disposed separately from the subject, a first contact electrode and a second contact electrode disposed in contact with the subject, and a voltage boosting device for boosting a commercial power supply voltage and supplying a predetermined ac voltage to the electrodes;

applying a therapeutic ac voltage to the main electrode by the voltage generating device;

applying alternating voltages to the first contact electrode and the second contact electrode by the voltage generating device, respectively, and causing a weak current to flow through the patient by a potential difference generated between the first contact electrode and the second contact electrode;

the phases of the alternating voltages applied to the first contact electrode and the second contact electrode are set to be opposite phases.

2. A potential therapeutic apparatus is characterized in that a person to be treated is placed in an electric field for treatment,

the phases of the ac voltages applied to the first contact electrode and the second contact electrode are set to be in the same phase, the phases of the ac voltage applied to the main electrode and the ac voltages applied to the first contact electrode and the second contact electrode are set to be in opposite phases, the ac voltage applied to the first contact electrode is set to have a positive peak larger than a negative peak, and the ac voltage applied to the second contact electrode is set to have a negative peak larger than a positive peak.