JP2002023758A - Keyboard device for electronic musical instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a key touch approximate to that of an acoustic piano without using an intricate mechanism and to prevent the deviation in the timing of a touch feel and generated tones in an electronic piano. SOLUTION: A capacitance type switch 15 disposed in a position where the switch abuts on a hammer 13 on a keyboard chassis 12 of the electronic piano is deflected by being depressed by a depressing part 13a of a hammer 13. This switch has an air flow part 30 in a flat planet part 22 of an elastic coating body 21 and when the switch is depressed and the deflection quantity attains the prescribed quantity or above after the increase of the elastic force of the elastic coating body 21, the elastic force decreases and the swift key touch resembling that of the acoustic piano is generated. Since the switch for the tone generation and the mechanism of the key touch generation are made the same, the deviation in the timing between the swift key touch and the generated tones can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a keyboard device for an electronic musical instrument such as an electronic piano.

[0002]

2. Description of the Related Art In an acoustic piano, when a key is pressed down, a pressing force shows a rapid change due to an escape mechanism near the end of a key stroke. That is, as shown in FIG. 11, in the key pressing curve, the pressing force is flat for a while after the key is started to be pressed, but then passes through a peak and a valley of the pressing force (a sudden decrease after the pressing force sharply increases). Finally, it shows a characteristic of suddenly rising again. On the other hand, in the keyboard device of the conventional electronic musical instrument, since there is no sharp peak or valley of the pressing force, it is not possible to obtain the feeling of coming off near the end of the key stroke of the acoustic piano.

In order to make the key touch of an electronic musical instrument close to the touch of an acoustic piano, several techniques have been proposed. For example, an elastic wedge body is provided between the arc portion provided at one end of the hammer and the lower surface of the key, and when the pressing force exceeds a certain value, the wedge body slides and is pushed out from between the arc portion and the lower surface of the key. By instantaneously reducing the pressing force, a sharp peak and a valley of the pressing force are formed immediately before the pressing operation of the pressing stroke is completed, and a sudden change portion such as a pressing curve of an acoustic piano is pseudo-added. There is a technique (JP-A-4-372991).

[0004] Further, by providing a hard angular collision member on the lower surface of the key and providing an elastic member having a corner temporarily engaged with the corner of the collision member on the keyboard chassis side, There is a technique in which a touch feeling similar to that of an acoustic piano can be obtained both when a key is pressed and when a key is released (Japanese Patent Laid-Open No. 6-43694).

[0005]

However, in the above-mentioned prior art, a complicated mechanism is provided separately from a switch for generating a sound in order to obtain a key touch close to that of an acoustic piano. There is a problem of becoming high. In Japanese Unexamined Patent Publication No. Hei 4-372991, the switch and the wedge body are provided in different parts, and the sliding operation of the wedge body occurs when the pressing force is further increased after the switch is operated. There is a problem that the timing of the generation of a touch sensation such as the sound generation due to the sound is largely shifted.

In Japanese Patent Application Laid-Open No. 6-43694,
Since a temporary touch between the key impact member and the elastic member, which is similar to that of an acoustic piano, is obtained through the temporary engagement and disengagement of the elastic member, it is necessary to secure and maintain a stable timing between the touch and the sound. Have difficulty.

Accordingly, the present invention provides a keyboard device for an electronic musical instrument that realizes a key touch close to that of an acoustic piano without using a complicated mechanism, and that does not cause a slipping touch feeling and a timing shift of a generated sound. The purpose is to:

[0008]

According to the present invention, there is provided a keyboard device for an electronic musical instrument having a key rotatably supported on a fulcrum provided on a keyboard chassis, the keyboard device being provided on the keyboard chassis. A switch and pressing means for pressing the switch when the key is rotated by a predetermined amount, the switch having an elastic covering for covering the electrode, and the elastic covering being pressed by the pressing means; The load was increased as the stroke progressed, and the load was reduced after reaching the maximum value. As a result, a key touch similar to that of an acoustic piano can be realized, and a shift in the timing of generated touch sound and generated sound can be prevented.

According to a second aspect of the present invention, the pressing means includes:
It is provided at a position facing the switch on the lower surface of the key,
In addition, the key is constituted by a projection which comes into contact with the switch when the key is turned. Thus, a key touch close to that of an acoustic piano can be obtained with a simple structure.

According to a third aspect of the present invention, there is provided an electronic musical instrument having a key rotatably supported on a fulcrum provided on a keyboard chassis, and a hammer engaged with the key and rotated in conjunction with pressing of the key. A keyboard device, wherein the keyboard chassis is provided with a switch that comes into contact with the hammer when the hammer rotates a predetermined amount, and the switch has an elastic covering member that covers an electrode. The load is increased as the stroke progresses by being pressed by the hammer, and the load is reduced after reaching the maximum value. Thus, a key touch closer to that of a real acoustic piano can be obtained.

According to a fourth aspect of the present invention, the elastic covering has a cup portion having a top portion facing a key or a hammer, and the electrode is accommodated in the cup portion.
Accordingly, when the pressing force of the switch exceeds a predetermined value, the elastic resistance is reduced due to the sudden deformation of the cup portion, and a touch feeling that the user comes off can be obtained.

According to a fifth aspect of the present invention, the elastic cover has a flat plate portion below the cup portion, and the flat plate portion has an air flow portion. This allows air to smoothly flow in and out of the cup portion, and a decrease in elastic resistance always occurs at a predetermined point in time, stabilizing the point at which a touch sensation such as escape occurs.

According to a sixth aspect of the present invention, the switch comprises:
The electrode covered with the elastic covering is opposed to the fixed electrode, and the capacitance is changed by deforming the elastic covering to change the capacitance. By using the capacitance type switch, the problem of the contact failure can be solved and the switching operation is always performed at a predetermined stroke position.

According to a seventh aspect of the present invention, the electrode covered with the elastic covering is a conical helical spring provided between a fixed electrode and a dielectric, and the helical spring is elastically coated. Due to the deformation due to the pressing of the body, the contact portion with the dielectric increases sequentially from the lower end side, thereby changing the capacitance between the fixed electrode and the fixed electrode. By using a conical helical spring for the electrode covered by the elastic coating, the change characteristic of the capacitance with respect to the depression stroke of the elastic coating by a key or a hammer is linearly proportional, and the capacitance is set. The value, that is, the setting of the operating point at which the switch is turned on can be arbitrarily set.

[0015]

Embodiments of the present invention will be described below with reference to examples. FIG. 1 is a sectional view showing the configuration of the electronic piano keyboard device of the first embodiment. This shows a cross section of one of a number of keys arranged on a keyboard chassis. The keyboard chassis 12 has a rising portion 12c at one end of a base 12e extending below the key 11.
And a short protrusion 12d extending parallel to the base 12e is formed at the upper end of the rising portion 12c. One end of the key 11 is rotatably supported by a shaft 12f at the tip of the overhang 12d. On the base 12e of the keyboard chassis 12, a support portion 12a is raised from an end opposite to the rising portion 12c at a position of about 1/3 of the length of the base 12e, and the upper end of the support portion 12a is turned. A metal hammer 13 is supported as a fulcrum.

The hammer 13 has a support portion 1 serving as a pivot point.
It has a first arm 13c extending from the support receiving portion 13b over the upper end of 2a to the rising portion 12c side and a second arm 13d extending in the opposite direction. 1st arm 1
3c is almost twice as long as the second arm 13d, and the tip of the first arm 13c is a base 12e in a natural state.
Sitting on the top, the tip of the second arm 13d is lifted. A projection 11a is formed on the lower surface near the free end of the key 11, and the projection 11a abuts on the tip of the second arm 13d of the hammer 13, so that the key 11 is substantially parallel to the base 12e in a natural state. Has become. Hereinafter, this state of the key 11 is referred to as a reference position as needed.

The key 11 is pushed down from the middle part of the key 11 so that the key 11 is moved to the shaft 12f at the tip of the overhang 12d.
Around the center. As a result, the second arm 13d of the hammer 13 is pushed down, and the first arm 13c is lifted. Since the first arm 13c is longer and heavier than the second arm 13d, the hammer 13 applies a reaction force as a pressing force when pressing a key, and applies a restoring force to the key 11 when releasing a key. The upper surface of the connection portion of the first arm 13c with the support receiving portion 13b is formed slightly below the rotation fulcrum at the upper end of the support portion 12a to form a stepped portion. A leaf spring 14 is provided between
The key 11 keeps the natural state at the reference position.

The base 12e of the keyboard chassis 12 is further provided with a second arm 13 of a hammer 13 by a support 12a.
A switch mounting portion 12b formed in a slope is provided on the d side. The switch mounting portion 12b has a hammer 13
A switch 15 of a capacitance type is attached to the second arm 13d. On the lower surface of the second arm 13d, there is formed a pressing portion 13a which can be brought into contact with a projection 25 described later of the switch 15 when the hammer 13 rotates.

When the key 11 is depressed, the hammer 13 pivots about the upper end of the support portion 12a in conjunction with the depression of the key 11, and the pressing portion 13a of the hammer 13 pushes the projection 25 to operate the switch 15. Then, the pronunciation starts. Then, the tip of the first arm 13c has an overhang 12d.
Is the stroke limit of the key 11 (see FIG. 2). In addition, when the hammer 13 is in a natural state and when the hammer 13 rotates, the tip of the first arm 13c respectively contacts the base 12
The shock absorbers 27a and 27b made of felt material are provided at the abutting portions of the e and the overhang portion 12d. Here, the hammer 13 having the pressing portion 13a capable of abutting on the switch 15 and the protrusion 11a formed on the lower surface near the free end of the key 11 and abutting on the tip of the hammer 13 constitute a pressing means. Make up.

Next, the structure of the switch 15 will be described with reference to FIG.
This will be described with reference to FIGS. FIG. 4A shows a free state,
(B) shows a state where the elastic covering 21 is deformed by being pressed by the hammer 13. In particular, as shown in FIG. 3, two semicircular fixed electrodes 1
7, 18 are formed facing each other. On the upper surfaces of the pair of fixed electrodes 17, 18, a polyester film dielectric 19 is adhered. A conic ring (conical helical spring) 20 is mounted on the dielectric 19 so as to cover the fixed electrodes 17 and 18, and the conic ring 20 is covered with an elastic covering 21.

The elastic covering 21 has a cup portion 23 which bulges from the flat plate portion 22 and has a generally bell-shaped shape along the conic ring 20, and a projection 25 having a flat upper surface at the top.
have. A small projection 24 is formed on the upper surface inside the cup portion 23, and the upper end of the conic ring 20 is fitted into the projection 24 to be stable. In particular, as shown in FIG. 5, on the surface of the flat plate portion 22 that is in contact with the printed circuit board 16, air circulation units 30 are provided in four directions.

As shown in FIG. 4, the flat plate portion 22 is screwed to the switch mounting portion 12b of the keyboard chassis 12 while being sandwiched between the printed board 16 and the holding plate 26. Depressed portion 13a of hammer 13 in conjunction with depression of key 11
Pushes the protruding portion 25 of the elastic covering 21, so that the conic ring 20 inside the elastic covering 21 has an increased contact portion with the dielectric 19 from the lower end side, so that the contact area sequentially increases.

That is, the switch 15 forms a so-called capacitor by interposing a dielectric between the opposed fixed electrodes 17 and 18 and the conic ring 20, and the conic ring 20 is deformed by the pressing of the elastic covering 21. Thus, a variable electrode whose area facing the fixed electrodes 17 and 18 changes. Thus, the switching operation is performed by changing the capacitance between the fixed electrodes 17 and 18 and the conic ring 20. Fixed electrode 1
Reference numerals 7 and 18 are connected to a control device (not shown).

Next, the operation of the switch 15 will be described. A predetermined voltage is applied between the fixed electrodes 17 and 18. In the state where the switch 15 is not pressed, FIG.
The conic ring 20 as a variable electrode as shown in FIG.
Is the dielectric 19 on the fixed electrodes 17 and 18 only at the lower end.
, The capacitance between the conic ring 20 and the fixed electrodes 17 and 18 is small, and therefore, the fixed electrodes 17 and 18 are electrically kept off.

When the projection 25 is pressed, the cup 23 is deformed and the conic ring 20 is compressed. Conic ring 20
Contacts the dielectric 19 on the fixed electrodes 17 and 18 in order from the lower end, and the capacitance increases with the increase of the contact area.
When the capacitance reaches a predetermined value, the switch is turned on. When the switch is turned on, the control device emits a predetermined sound corresponding to the key 11 on which the switch is installed.

When the switch 15 is depressed, it receives the elastic resistance of the elastic covering 21, and the reaction force, that is, the load increases as the stroke increases. However, when the pressing force exceeds a predetermined value, the elastic covering 21 undergoes rapid deformation as shown in FIG. 4B, and at this time, the elastic resistance is reduced. That is, as shown in the relationship between the load and the stroke in FIG. 6, when the switch 15 is pushed, the load increases as the stroke progresses, decreases after the load reaches the peak, and when the switch is further pushed, the bottom hits. Then, the characteristic becomes such that the load increases again.

Since the air in the cup portion 23 of the elastic covering 21 is discharged through the air circulation portion 30, the key 11
Does not hinder the movement of the elastic covering body 21 in conjunction with the pushing down. Therefore, the point at which the sudden deformation at which the elastic resistance decreases is stabilized. When the pressing is released, the cup portion 23 is released.
Returns to its original state by its elastic force. Therefore, the contact area of the conic ring 20 with the dielectric 19 on the fixed electrodes 17 and 18 decreases, and the state returns to the switch-off state. At this time, since air is supplied from outside through the air circulation unit 30, the movement of the elastic covering body 21 is not hindered.

Next, FIG. 7 shows a pressing curve when the key 11 is pressed down from the reference position. After the key depression is started, the pressing force is constant from M to N until the pressing portion 13a of the hammer 13 hits the top surface of the switch 15, that is, the projection 25 of the elastic covering 21. Thereafter, when the pressing portion 13a depresses the switch 15, the pressing force of the key rapidly increases due to the elastic resistance of the elastic covering member 21. When the pressing force exceeds a predetermined value, the pressing force decreases due to the rapid deformation of the elastic covering member 21, whereby a key touch similar to that of an acoustic piano and coming off after the pressing force increases can be felt at the fingertip. When the key 11 is further depressed, the tip of the first arm 13c of the hammer 13 comes into contact with the shock absorber 27b.
, And the bottom collides, and the pressing force increases again. At the point in time when the pressing force immediately after the peak load suddenly decreases (S in FIG. 7), the switch 15 has an area (contact area with the dielectric) facing the fixed electrodes 17 and 18 of the conic ring 20, which is the variable electrode.
And the capacitance is turned on when the capacitance exceeds a predetermined value, so that sound is generated at the same time.

The first embodiment is constructed as described above. In an electronic piano, a conic ring 20 as a variable electrode forming a capacitor is connected to a cup portion 2 of an elastic covering 21.
3, the switch 15 is configured to press the cup portion 23 in conjunction with the depression of the key, thereby obtaining a characteristic in which the pressing force of the key suddenly increases and then the pressing force decreases due to the sudden deformation of the cup portion 23. Thus, key touch similar to that of an acoustic piano can be realized.

Since the key touch feeling is generated by the switch 15 for sound generation, the timing corresponding to the so-called string striking when the switch is pressed to start sound generation, and the touch feeling that comes off at the end of key depression. Synchronizes with this, you can get the feeling of playing a real acoustic piano while being an electronic piano. Further, since the air circulating portion 30 is formed in the flat plate portion 22 of the elastic covering member 21, sudden deformation of the cup portion always occurs at a predetermined time,
The generation point of the touch feeling that comes off is stable.

Next, a second embodiment in which the hammer is omitted will be described with reference to the drawings. FIG. 8 is a sectional view showing the configuration of the second embodiment. The keyboard chassis 41
A step 41c having a switch mounting portion 41b is provided on a base 41a extending below the key 42, and a rising portion 41d is coupled to one end of the step 41c. One end of a key 42 is rotatably supported on a shaft 41f at the upper end of the rising portion 41d.

The key 42 is formed by a spring 43 provided between the key 42 and the step portion 41c near the shaft 41f.
It is urged to push up 2. This spring 43
However, like the hammer 13 in the first embodiment, a reaction force is applied as a pressing force when a key is pressed, and a restoring force is applied to the key 42 when the key is released.

A stopper 41e is provided on the base 41a, and a stopper 41g extending parallel to the base 41a toward the free end of the key 42 is provided at the tip of the stopper 41e.
Are formed. On the lower surface near the free end of the key 42, a catch portion 42a that engages with the pawl portion 41e extends downward, and a claw portion 42c that extends in the opposite direction to the stopper portion 41g is formed at the tip thereof. I have. When the claw portion 42c and the shock absorbing member 44a made of felt provided below the stopper portion 41g abut in the vertical direction, the pushing of the key 42 by the bias of the spring 43 is stopped. Therefore, in the natural state, the key 42 is
It is substantially parallel to the base 41a. The base 41
a, when the key 42 is rotated, the hook 42
The shock absorber 44b is also located at a position where the claw 42c of FIG.
Is provided.

The switch 15 of the capacitance type is mounted on the switch mounting portion 41b. This switch 15
The position of the key 42 facing the
The switch 1 is located below the position about 1/3 of the length of the switch 2.
A protrusion 42b for pressing the button 5 is formed. In addition,
The switch 15 is the same as the switch of the first embodiment.

When the key 42 is depressed, the key 42 is rotated about the shaft 41f, and the projection 42b directly presses the switch 15 to start sound generation. Then, as shown in FIG. 9, the point at which the claw portion 42c of the hook portion 42a contacts the shock absorber 44b provided on the base 41a is the stroke limit of the key 42. Here, the protruding portion 42b formed on the lower surface of the position of the key facing the switch 15 constitutes a pressing unit.

The second embodiment is constructed as described above. As in the first embodiment, the conic ring 20 as the variable electrode forming the capacitor is covered with the cup portion 23 of the elastic covering 21 and the projection is formed. By using the switch 15 (see FIGS. 3 and 4) in which the cup portion 23 is rapidly deformed when the pressing force applied to the portion 25 exceeds a predetermined value, a characteristic is obtained in which the pressing force decreases after the key pressing force sharply increases. Thus, key touch similar to that of an acoustic piano can be realized. Further, the switch 15 is directly pressed by the key 42 and the hammer is omitted, so that the structure of the entire device can be simplified and the manufacturing cost can be reduced.

In each of the embodiments, the shape of the cup portion of the elastic covering is a bell shape. However, by changing the shape, thickness, and material of the cup portion, the magnitude and position of the peak load can be variously changed. Can be set. For example, by forming the elastic covering into a thin bowl shape different from the bell shape as shown in FIG. 10 (a), as shown in FIG. 10 (b), the peak load shown in FIG. It is possible to obtain a characteristic in which the stroke is reduced to about 1/5 and the stroke until reaching the peak load is shortened. When the present invention is applied to another electronic musical instrument such as a synthesizer, and it is desired to eliminate as much as possible a touch feeling or a switching feeling, it can be achieved only by changing the shape of the elastic covering.

In the first embodiment, the hammer is made of metal. However, the hammer is not necessarily made of metal but may be made of a material having a sufficient mass. The rectangular leaf spring that urges the hammer and the key can be omitted depending on the mass of the hammer.

[0039]

According to the first aspect of the present invention, there is provided an acoustic piano which has an elastic covering for covering an electrode, and has a characteristic of reducing a load when a predetermined stroke is exceeded when pressed. It is possible to realize a key touch that is similar to the above. Further, since the switch for generating the sound and the mechanism for generating the key touch are the same, it is possible to prevent the touch feeling from coming off and the timing shift of the generated sound.

According to the second aspect of the present invention, in addition to the effect of the first aspect, the elastic covering is pressed by the projection provided on the lower surface of the key at a position facing the switch, so that the acoustic structure has a simple structure. A key touch similar to a piano can be obtained.

According to the third aspect of the present invention, in addition to the effect of the first aspect of the present invention, since the elastic covering is pressed via the hammer, a key touch closer to that of a real acoustic piano can be obtained.

According to the fourth aspect of the present invention, since the cup portion for accommodating the electrode is provided in the elastic covering member, when the pressing force of the switch exceeds a predetermined value, the sudden deformation of the cup portion reduces the elastic resistance. , A touch feeling that comes off.

According to the fifth aspect of the present invention, since the air circulating portion is provided in the flat plate portion of the elastic covering, air flows in and out of the cup portion smoothly and does not hinder the movement of the elastic covering. Decrease always occurs at a predetermined point in time, and the generation point of the touch feeling that comes off is stabilized.

According to the sixth aspect of the present invention, since the capacitance type switch is used, the problem of the contact failure can be solved and the switching operation is always performed at a predetermined stroke position.

According to the seventh aspect of the present invention, since the conical helical spring is used for the electrode covered by the elastic covering, the change characteristic of the capacitance with respect to the depression stroke of the elastic covering by the key or the hammer is obtained. It is linearly proportional and can arbitrarily set the set value of the capacitance, that is, the operating point at which the switch is turned on.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a state in which a key is depressed in the first embodiment.

FIG. 3 is an exploded perspective view of the capacitance type switch.

FIG. 4 is an enlarged sectional view showing a basic configuration of a switch mechanism.

FIG. 5 is a view taken in the direction of arrows AA in FIG. 4;

FIG. 6 is a characteristic diagram showing a relationship between a load of an elastic covering and a stroke.

FIG. 7 is a diagram showing a pressing curve of the present embodiment.

FIG. 8 is a sectional view showing the configuration of the second embodiment.

FIG. 9 is a diagram illustrating a state in which a key is depressed in the second embodiment.

FIG. 10 is a view showing another example of the elastic covering body.

FIG. 11 is a diagram showing a pressing curve of an acoustic piano.

[Explanation of symbols]

 11, 42 key 11a, 42b projecting part 12, 41 keyboard chassis 12a supporting part 12b, 41b switch mounting part 12c, 41d rising part 12d overhang part 12e, 41a base 12f, 41f shaft 13 hammer 13a pressing part 13b supporting receiving part 13c 1 arm 13d 2nd arm 14 leaf spring 15 switch 16 printed circuit board 17, 18 fixed electrode 19 dielectric 20 conic ring 21 elastic covering 22 flat plate 23 cup portion 24 projection 25 projection 26 holding plate 27a, 27b, 44a, 44b Shock absorber 30 Air circulation part 41c Step part 41e Stop part 41g Stopper part 42a Hook part 42c Claw part 43 Spring

Claims (7)

[Claims] 1. A keyboard device for an electronic musical instrument having a key rotatably supported on a fulcrum provided on a keyboard chassis, comprising: a switch provided on the keyboard chassis; and a switch provided when the key rotates a predetermined amount. The switch has an elastic coating covering the electrode, and the elastic coating is pressed by the pressing means to increase the load as the stroke progresses, and reaches a maximum value. A keyboard device for an electronic musical instrument, having a characteristic of reducing a load later. 2. The device according to claim 1, wherein the pressing means is provided on a lower surface of the key at a position facing the switch, and comprises a projection which comes into contact with the switch when the key is rotated. A keyboard device for an electronic musical instrument as described in the above. 3. A keyboard device for an electronic musical instrument, comprising: a key rotatably supported on a fulcrum provided on a keyboard chassis; and a hammer engaged with the key and rotated in conjunction with pressing of the key. ,
The keyboard chassis is provided with a switch that comes into contact with the hammer when the hammer rotates a predetermined amount, and the switch has an elastic covering that covers the electrodes, and the elastic covering is pressed by the hammer to move the stroke. A keyboard device for an electronic musical instrument, which has a characteristic of increasing a load as the load advances and reducing the load after reaching a maximum value. 4. The elastic coating body according to claim 1, further comprising a cup portion having a top portion facing a key or a hammer, and accommodating the electrode in the cup portion. 4. The keyboard device for an electronic musical instrument according to 3. 5. The electronic musical instrument according to claim 4, wherein the elastic cover has a flat plate portion below the cup portion, and the flat plate portion has an air flow portion. Keyboard device. 6. The switch according to claim 1, wherein the switch is an electrostatic capacitance type switch in which an electrode covered by an elastic covering is opposed to a fixed electrode, and the capacitance is changed by deformation of the elastic covering. 6. The keyboard device for an electronic musical instrument according to 2, 3, 4, or 5. 7. The electrode covered with the elastic covering is a conical helical spring provided with a fixed electrode and a dielectric material interposed therebetween, and the helical spring is deformed by pressing of the elastic covering. The contact portion with the dielectric increases sequentially from the lower end,
7. The keyboard device for an electronic musical instrument according to claim 6, wherein the capacitance between the fixed electrode and the fixed electrode is changed.