JP2000337882A - Angular velocity sensor - Google Patents

Abstract

(57) [Problem] To provide an angular velocity sensor effective for a vehicle body control system, a navigation system, and the like in a vehicle or the like, which is relatively inexpensive and has high sensitivity and high detection accuracy. SOLUTION: Piezoelectric element material 1 such as quartz or ceramics
1, the prisms 11a, 11b, 11c are cut out integrally with the base 12, and electrodes A, B, C, D are provided on the side surfaces of the respective prisms, and an AC voltage is applied to drive the electrodes in the direction of their arrangement to make an excitation state. A small gap is formed between the prism 11b and the side electrode B parallel to the excitation direction by the spacer 15, and the opposing electrode 13 provided with an electret material 14 made of a polymer material such as Teflon on the surface is provided. The Coriolis force is detected as a voltage change by an electric impedance converter (FET) based on the capacitance change in the air gap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an angular velocity sensor for detecting an angular velocity effective for a vehicle body control system, a navigation system and the like in a vehicle or the like, and more particularly to an electret condenser type angular velocity sensor.

[0002]

2. Description of the Related Art FIG. 7 shows a configuration example of a conventional angular velocity sensor. In FIG. 7A, reference numeral 1 denotes a U-shaped metal diaphragm, which has two metal diaphragms 2 and 3 arranged at right angles to the upper portion thereof. 3, the piezoelectric elements 1a, 1b, 2a, 3a are fixed by an adhesive or the like. Reference numeral 4 denotes a fixed shaft for fixedly supporting these diaphragms, that is, the metal diaphragm constitutes a tuning fork state.

The piezoelectric element 1a drives (excitations) this tuning fork.
And is driven by application of an AC voltage. Although 1b may be used for driving, it is generally used for monitoring to stabilize vibration using this output. The driving frequency is to increase the amplitude,
In general, driving is performed in accordance with the resonance frequency of the metal diaphragm, and vibration can be obtained in directions such as 5. Reference numeral 6 denotes a rotation detection axis. If rotation is given in a clockwise direction as shown in the figure, a Coriolis force Fc as shown in FIG. 7B is generated and the metal vibration plates 2 and 3 vibrate. The electromotive force of the opposite phase is obtained in each of the piezoelectric elements 2a and 3a. Therefore, an output proportional to the angular velocity can be obtained by taking the difference between the respective detection outputs. In general, the output due to the Coriolis force is very small, and in order to obtain as large an output as possible, the resonance frequency of the metal diaphragm at which the Coriolis force is generated is adjusted to match the tuning fork frequency of the driving unit metal diaphragm. In FIG. 7, ω is the angular velocity, v is the vibration velocity, and m is the mass of the diaphragm.

[0004]

However, the conventional angular velocity sensor has the following problems. 1. Although the metal diaphragm for tuning fork drive and the metal diaphragm for Coriolis force detection are made of the same structure, the drive unit and the detection unit are not the same metal diaphragm. It is very difficult to increase the detection sensitivity. 2. Since the shape of the metal diaphragm is complicated, high processing accuracy is required, and cost increases and variations in detection accuracy are unavoidable. 3. Since the piezoelectric element is fixed to the metal vibration plate with an adhesive or the like, the fixing variation is large and easily affects detection accuracy, temperature characteristics, and the like. 4. Since there are two metal diaphragms in the detection unit, the deformation in the same direction due to vibration cancels out differentially, but the deformation in the opposite direction equivalent to the Coriolis force is detected as an output. Therefore, there is a weak point against vibration noise accompanied by a rotational moment.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a relatively inexpensive, high-sensitivity, high-accuracy and excellent angular velocity sensor.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to form a piezoelectric element material such as quartz or ceramic by cutting it into prisms, and to form one or more prisms on a straight line (in a tuning fork state). Fixed on a stand made of a separate material from the piezoelectric element or on a separate material, electrodes are formed on each side of the prism, and by applying an AC voltage to the electrodes of each part, the electrodes are driven in the direction in which the prisms are arranged, and are excited. One of the side electrodes of the located prism
A counter electrode in which an electret material made of a polymer material such as Teflon is fixed to the surface by fusing or the like so as to insulate a slight gap between each of the plurality of or each electrode surface, It is configured to take out the output due to Coriolis force via an electric impedance converter (FET) that takes out the capacitance change as a voltage change, and the vibrating body is the piezoelectric element itself such as quartz / ceramic, The drive and the detection are configured by the same vibrator.

With the above configuration, it is relatively easy to make the resonance frequencies of driving and detection coincide with each other, there is no fixation with an adhesive or the like, and the processing accuracy is only cutout processing, and it is possible to suppress harassment. In addition, a piezoelectric element having a high Q and high excitation efficiency is used for driving, and an electret capacitor system with a high conversion efficiency and a simple configuration is used for detecting the Coriolis force. High sensitivity and high detection accuracy can be obtained. Regarding the influence of vibration, the influence of vibration noise is likely to occur to some extent with respect to the vibration in the Coriolis direction, but the influence is small in the direction of excitation. In addition, since the resonance frequency can be set higher than that of the conventional product due to the configuration, there is an advantage that it is hardly affected by vibration.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION
A piezoelectric element material in which one or a plurality of prisms are linearly arranged on a table, electrodes provided on each side surface of the prisms, and driven by a AC voltage to drive in the direction in which the prisms are arranged, and an electrode; A counter electrode provided so as to form a slight gap between one or more of the electrode surfaces provided on a side surface parallel to the excitation direction, and a gap connected to the counter electrode; This is an angular velocity sensor equipped with an electrical impedance converter that detects the Coriolis force by taking out the capacitance change of the voltage as a voltage change.Since the drive and detection are composed of the same vibrator, each resonance frequency is easy to match, so Coriolis Efficient conversion of the high Q amplitude of the piezoelectric element for force detection and the use of an electret capacitor system with a simple configuration make it relatively inexpensive and provide high sensitivity and high detection accuracy. To.

In the invention according to a second aspect of the present invention, the opposing electrode forms a slight gap between the plurality of electrode surfaces provided on both side surfaces parallel to the excitation direction of the prism. The angular velocity sensor according to claim 1, wherein an output of a capacitance change of the air gap by an electric impedance converter connected to each of the opposed electrodes is taken out through a differential circuit. This has the effect that the output level of the Coriolis force can be further increased. .

The invention according to claim 3 of the present invention is the angular velocity sensor according to claim 1 or 2, wherein the prism is formed by cutting out a piezoelectric element material.
Since the cutting process is performed, the processing accuracy is good and the variation is small.

The invention according to claim 4 of the present invention is characterized in that it is housed in a metal case and is kept substantially sealed, and an output can be taken out by an output terminal provided in the case. An angular velocity sensor according to item 1, 2, or 3, which has an effect that high reliability can be obtained.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a perspective view of an electret condenser type angular velocity sensor according to a first embodiment of the present invention, and FIG. 2 is a side view of FIG.
In the present embodiment, a case where a single crystal piezoelectric element material such as quartz is used as the piezoelectric element material will be described as an example.However, even when a ceramic piezoelectric element or the like is used, by changing the electrode configuration and circuit configuration, etc. Similar effects can be obtained.

In FIGS. 1 and 2, X is an electric axis generally used in the case of quartz or the like, and it is desirable to carry out cutting processing in consideration of the axial direction. Reference numeral 11 denotes a piezoelectric element material formed by cutting out three prisms 11a, 11b, and 11c integrally with the base 12, and the base 12 is a prism 11
It is also possible to create and fix it separately from the members a, 11b and 11c, instead of using a single member. The reason for forming a plurality of prisms is to create a tuning fork state, maximize the effect of driving and excitation, and obtain a large amplitude. For example, even a single prism is included in the present invention. Although it is large or small, practical application is also possible.

The electrodes (hatched portions) A, B, C, and D are formed on each surface of each of the prisms 11a, 11b, and 11c by printing, vapor deposition, plating, and the like. The circuit connection of each electrode is shown in FIG. As shown in the connection of FIG. Reference numeral 13 denotes a counter electrode, on the surface of which an electret material 14 made of a polymer film such as Teflon is fixed by fusion or the like, and a side surface positioned parallel to the driving / excitation direction 16 of each prism by a spacer 15 or the like. A small gap is insulated from the electrode B. Table 12 and counter electrode 1
3 is fixed in some way. P indicates the pitch of the center of gravity of the prism, and the change in the resonance frequency, the excitation efficiency, etc. also occur with this pitch configuration.
The optimal dimensions are set.

FIG. 3 is a circuit diagram showing connections in the angular velocity sensor shown in FIG. 1, where R indicates a resistor and OSC indicates an oscillator. 21 is an example of the direction of the electric field, and 22 is an electric impedance converter for converting the electric impedance and extracting a voltage output because the spatial capacitance Co of the electret capacitor is very small and the impedance is very high. For example, an FET or the like is used. Electrodes A and C of prisms 11a and 11c and prism 11b
Electrodes B and D are connected to one end of the oscillator OSC, respectively, and electrodes B and D of prisms 11a and 11c and prism 11b
Electrodes A and C are respectively connected to the other end of the oscillator OSC by a resistor R.
Connected through. The counter electrode 13 is connected to the electric impedance converter 22, and a detection output is taken out between the output of the electric impedance converter 22 and the ground.

Next, the operation of this embodiment will be described. Each electrode A of each prism 11a, 11b, 11c,
When B, C and D are driven by the oscillator OSC, each prism l
1a, 11b and 11c vibrate in the direction indicated by arrow 16. On the other hand, the electret material 14 is charged with a charge Q (in this example, minus). That is, a space capacitance Co is formed between the counter electrode 13 and the electrode surface B of the prisms 11a, 11b, 11c.
When b and 11c vibrate in a direction perpendicular to the excitation direction 16 (Coriolis force generation direction 17), the capacitance changes by ΔC, and the electret charge causes a voltage change ΔV as described below. ΔV = Q / ΔC That is, an electret condenser type detection method is realized, and this method is known to have high conversion efficiency.

FIG. 4 is a perspective view when the angular velocity sensor 30 configured as described above is housed in a metal case 31. FIG. 4A shows an example of a vertical type, and FIG. 4B shows an example of a horizontal type.
The metal case 31 is provided with an output terminal 32 and the like, and is configured to keep a substantially sealed state. The drawbacks of the electret type are that it is susceptible to water and moisture, and that it adsorbs small dirt and the like, thereby deteriorating its reliability. However, by accommodating in the case as described above, it is possible to operate without any problem.

As described above, according to the first embodiment,
Three prisms 11a, 11b, 11c cut out from the piezoelectric element material 11 together with the base 12 are arranged on a straight line, and oscillators O are provided to electrodes A, B, C, D provided on the side surfaces of these prisms.
SC is connected and excited, and prism 11b in the middle
A small gap is formed by the spacer 15 between the electrode B provided on one side surface of the counter electrode 13 and the opposing electrode 13 is arranged via the electret material 14. The electric impedance converter 22 is connected to the opposing electrode 13. Since the Coriolis force is detected by extracting the capacitance change of the air gap as a voltage change, it is relatively easy to match the resonance frequencies of driving and detection, and there is no need to fix with an adhesive or the like. In addition, the processing accuracy is only cutout processing, and it is possible to suppress harassment, and use a piezoelectric element that has a high Q for driving and high excitation efficiency, and converts the high Q amplitude of the piezoelectric element for Coriolis force detection to conversion efficiency Since the electret condenser method, which is high in cost and simple in configuration, is used, relatively low cost and high sensitivity and high detection accuracy can be obtained.

(Embodiment 2) FIG. 5 is a perspective view showing a second embodiment of the present invention, and the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals. The second embodiment is different from the first embodiment in that the opposing electrode 13 via the electret material 14 is disposed so as to face both electrode surfaces B and D parallel to the excitation direction of the center prism 11b. As shown in FIG. 6, an electric impedance converter 22 is connected to the opposing electrode 13a arranged on the electrode B side, and a similar electric impedance converter 23 is connected to the opposing electrode 13b arranged on the electrode D side. And both electric impedance converters 2
The output difference between phases 2 and 23 is taken out from the differential circuit 24, which has the advantage that the output of the Coriolis force can be taken out further.

In each of the above embodiments, the prism is 11a,
11b and 11c. In the case of a plurality of components, various configurations are conceivable depending on the number and direction, and the output of the Coriolis force is not taken out from one piece but taken out from a plurality of pieces and combined. Can also. However, considering the efficiency including the cost, the prisms 11a, 11b, 11
It is considered appropriate to form three tuning forks with c and detect from the center prism 11b. Note that it becomes difficult to find the optimum point as the number of detection electrodes increases. According to the experiment, it was found that the smaller the pitch P (center of gravity pitch) of the prisms 11a, 11b, and 11c, the easier the resonance frequency in the excitation direction and the Coriolis force direction were to match, and the higher the pitch, the higher the efficiency.

[0021]

As described above, according to the present invention, a piezoelectric element material such as quartz or ceramic is cut into a prism and formed, and the prism is integrated with or separate from the piezoelectric element on one or more (tuning fork) straight lines. An electrode is formed on each side surface of the prism, and an AC voltage is applied to each electrode to drive the prism in the direction in which the prisms are arranged to be in an excited state, and the side electrodes of the prism located in parallel with the excitation direction are fixed. An opposing electrode having an electret material made of a polymer material such as Teflon fixed to the surface by fusing or the like is provided so as to insulate a slight gap between one or more electrode surfaces. Electric impedance converter (F
ET) through which the output by Coriolis force is taken out. The vibrating body is the piezoelectric element itself such as quartz or ceramic, and the driving and detecting are configured by the same vibrating body. It is relatively easy to make the resonance frequencies match, there is no fixation with an adhesive or the like, and the processing accuracy is only cutout processing, and it is possible to suppress harassment. In addition, a piezoelectric element having a high Q and high excitation efficiency is used for driving, and an electret capacitor system with a high conversion efficiency and a simple configuration is used for detecting the Coriolis force. High sensitivity and high detection accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view of an angular velocity sensor according to Embodiment 1 of the present invention.

FIG. 2 is a side view of the angular velocity sensor according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram of the angular velocity sensor according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing (a) a vertical type and (b) a horizontal type in which an angular velocity sensor according to the present invention is accommodated in a case.

FIG. 5 is a perspective view of an angular velocity sensor according to Embodiment 2 of the present invention.

FIG. 6 is a circuit diagram of an angular velocity sensor according to Embodiment 2 of the present invention.

FIG. 7A is a perspective view of a conventional angular velocity sensor.
And operation explanatory diagram (b)

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Piezoelectric element material 11a, 11b, 11c 12 prisms 13 Counter electrode 14 Electret material 15 Spacer 16 Drive / excitation direction 17 Coriolis force generation direction 21 Electric field direction 22, 23 Electrical impedance converter 24 Differential circuit 30 Angular velocity sensor 31 Case 32 Output terminal A, B, C, D electrode P pitch

Claims (4)

[Claims] 1. A piezoelectric element material in which one or more prisms are linearly arranged on a table, and are provided on each side surface of the prism, and are driven and excited in an arrangement direction of the prisms by applying an AC voltage. An opposing electrode provided so as to form a slight gap between the electrode and one or a plurality of the electrode surfaces provided on a side surface parallel to the excitation direction of the prism, and connected to the opposing electrode; An electrical impedance converter for detecting the Coriolis force by taking out the capacitance change of the air gap as a voltage change. 2. The opposing electrode is provided so as to form a slight gap between the plurality of electrode surfaces provided on both sides parallel to the excitation direction of the prism. 2. The angular velocity sensor according to claim 1, wherein an output of a change in capacitance of the air gap by an electric impedance converter connected to an electrode is taken out via a differential circuit. 3. The angular velocity sensor according to claim 1, wherein the prism is formed by cutting out a piezoelectric element material. 4. An apparatus according to claim 1, wherein said casing is housed in a metal case and is kept in a substantially sealed state, and output can be taken out by an output terminal provided in said case.
Or the angular velocity sensor according to 2 or 3.