JPH08122172A - Force sensor - Google Patents

Abstract

PURPOSE: To perform drive in a stable resonant mode by constituting a specific relation between the entire length of a resonator, an excitation piezoelectric element and the length of a receiving piezoelectric element. CONSTITUTION: A dynamic amount sensor comprises an inertia body 100, a support beam 101, vibrator 102, and piezoelectric elements are provided on the both ends of the vibrator 102, which is constituted of exciting part 103, a propagation part 104 and a receiving part 105. And when acceleration is applied, the inertia body 100 moves up and down, a supporting beam 101 bends and the vibrator 102 expands and contracts. Therefore, when a force is applied, a resonant frequency of the vibrator 102 is changed, and the acceleration can be measured by detecting the frequency change. In addition, the vibrator resonates in various vibration mode. Likelihood of occurrence of the vibration mode is closely related with the length (a) of the exciting part 103, the length (b) of the receiving part 105 and the entire length l of the vibrator 102, and the force sensor can be driven in a stable resonant mode by setting them 0.2<=a/l<0.5, 0.2<=b/l<0.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for detecting mechanical quantities such as acceleration, weight, pressure applied to an object.

[0002]

2. Description of the Related Art In recent years, an airbag system for protecting safety in an automobile accident, a navigation system for guiding a road, and the like have been actively developed, and accordingly, sensors such as an acceleration sensor and a vibration gyro have been developed.

As a conventional force detecting element, for example, Japanese Patent Publication No.
As shown in Japanese Patent Publication No. 3-1330, the structure shown in FIG. 9 or 10 is known. In FIG. 9, two piezoelectric vibrating plates 2 and 3 each having an electrode 1 attached thereto
Of the piezoelectric vibrating plates 2 and 3 are fixed to the substrate 4 and the other ends thereof are rigidly coupled by the spacing plate 5. When a force F is applied to the free ends of the piezoelectric vibrating plates 3 and 3, the change in each natural frequency of the piezoelectric vibrating plates 2 and 3 is measured based on the displacement received by the piezoelectric vibrating plates 2 and 3 at this time. The force F is measured. Further, FIG. 10 shows a step portion 7 and a groove 8 formed on the upper and lower surfaces of the cantilever 6, and the two piezoelectric vibrating plates 10 and 11 to which electrodes 9 are attached are fixed by bridging the groove 8. Piezoelectric diaphragm 1 when force F is applied to the free end of cantilever 6
The force F is measured by detecting the difference between changes in natural frequencies 0 and 11.

[0004]

However, in the piezoelectric vibrating plates 2, 3, 10 and 11 having the above-mentioned conventional structure, natural vibrations of various modes occur. That is, there are vertical and horizontal vibration modes and their higher-order resonances, natural vibration modes of the entire beam, torsional vibrations, etc., which are clearly separated and separated, and only the natural vibration mode to be used is distinguished from others. It was difficult to stably take out and maintain the resonance state.

The present invention is to solve the above-mentioned problems of the prior art, and by applying a force, the natural vibration mode of the vibrating body whose natural frequency changes can be completely separated from other unnecessary resonance modes and is always constant. An object of the present invention is to provide a mechanical quantity sensor that can maintain a stable resonance state.

[0006]

In order to achieve this object, the present invention firstly provides an inertial body movable by the action of a mechanical quantity, a support beam for supporting the inertial body, and a support beam provided on the support beam. A vibrating body having both ends fixed to the support beam, a piezoelectric element for excitation that is joined near one end of the vibrating body to excite the vibrating body, and joined near the other end of the vibrating body. A receiving piezoelectric element for receiving the vibration of the vibrating body, and between the total length 1 of the vibrating body and the length a of the exciting piezoelectric element and the length b of the receiving piezoelectric element, It is characterized by having a relationship of 0.2 ≤ a / l <0.5 or 0.2 ≤ b / l <0.5. Also the second
Further comprising: an inertial body that is movable by the action of a mechanical quantity; a support beam that supports the inertial body; and a vibrating body that is provided on the support beam and has both ends fixed to the support beam. The primary resonance frequency of is equal to or more than 10 times the primary resonance frequency of the inertial body and the support beam. Thirdly, an inertial body that is movable by the action of a mechanical quantity, a support beam that supports the inertial body, a vibrating body that is provided on the support beam and has both ends fixed to the support beam, and the vibrating body. A piezoelectric element bonded to the upper side and a pair of electrodes divided in a direction intersecting the longitudinal direction of the vibrating body on the surface of the piezoelectric element are provided, and one of the pair of electrodes excites the vibrating body. The excitation electrode and the other are reception electrodes for receiving the vibration of the vibrating body.

[0007]

According to the present invention, with the above structure, first, the resonance peak of the higher-order mode is lowered or eliminated, and the resonance frequency of the lower-order mode of the vibrating body clearly shows the peak, and the driving in the stable resonance mode is performed. Is possible. Secondly, the primary resonance frequency of the vibrating body is 10 times or more the primary resonance frequency of the inertial body and the supporting beam, and the vibrating body is stabilized without being affected by the resonant frequency of the entire beam. And can resonate. Thirdly, since it is possible to generate only the primary resonance frequency of the vibrating body, it is possible to always generate the first mode of the same mode.
Stable driving is possible at the second resonance, and a sensor with few malfunctions can be realized.

[0008]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings.

1A and 1B are a sectional view and a plan view of a mechanical quantity sensor according to an embodiment of the present invention. In FIG. 1A, 100 is an inertial body, 101 is a support beam, and 102 is a vibrating body, and the vibrating body 102 is composed of an exciting unit 103, a propagating unit 104, and a receiving unit 105.

In FIG. 1, when acceleration is applied, the inertial body 100 moves up and down, the support beam 101 bends, and the vibrating body 102 expands and contracts. Therefore, when a force acts, the resonance frequency of the vibrating body changes, and the acceleration can be measured by detecting this frequency change. For example, if it can be assumed that the vibration of the vibrating body is the vibration of the yarn, the resonance frequency f is represented by (Equation 1).

[0011]

[Equation 1]

Here, 1 is the length of the yarn, S is the tension of the yarn, ρ is the mass per unit length of the yarn, and n is the order of vibration. According to (Equation 1), the resonance frequency f changes in proportion to the square root of the thread tension, and if the structure changes the tension of the vibrating body when a force is applied, the dynamics of acceleration, pressure, force, etc. It turns out that the quantity can be measured.

FIG. 2 shows an example of characteristics in the configuration of FIG.
The vertical axis represents the resonance frequency f of the vibrating body, and the horizontal axis represents the applied acceleration. According to this, the resonance frequency when the acceleration is 0 is 22 kHz, but rises to 27 kHz when the acceleration of 120 G is applied. About 40 per 1G
There is a change in Hz, the rate of change is 0.2% / G, and it is possible to measure up to a very large acceleration as shown in the figure,
An acceleration sensor with a wide dynamic range was realized. In the structure of FIG. 1, the sensitivity varies depending on the ratio of the mass of the inertial body to the mass of the supporting beam portion. However, in the case of the data of FIG. 2, the inertial body has a structure seven times as large as that of the supporting beam portion. It is considered that the small deflection of the supporting beam acted as a large tension on the vibrating body, and a large sensitivity could be output.

One of the structural features of this embodiment is the structure of the vibrating body, which is composed of an exciting section, a propagating section, and a receiving section. Generally, in the case where the piezoelectric ceramic is resonated and the thickness of the piezoelectric ceramic itself vibrates, there is a method of detecting the impedance change of the piezoelectric ceramic itself to know the resonance point. However, like the present invention,
When the vibrating body is a bonded body of a piezoelectric ceramic and another structural member, a large impedance change does not always occur at the resonant frequency of the bonded body, and the resonance point cannot be detected with good sensitivity in many cases. On the other hand, in the present invention, since the vibration of the vibrating body which is the bonded body is directly detected by the receiving unit, it becomes possible to accurately detect all the vibrations of the vibrating body, and it is possible to obtain an appropriate vibrating body structure. In designing, the degree of freedom in dimensions becomes extremely large.

FIG. 3 is for explaining the vibration state of the vibrating body 102 of FIG. 3A and 3B are a plan view and a cross-sectional view in which a portion of the vibrating body 102 is enlarged and illustrated. The vibrating body 102 has piezoelectric elements provided at both ends,
The excitation unit 103 is formed at the left end, and the reception unit 105 is formed at the right end. Such a vibrating body is generally shown in FIGS.
Resonates in various vibration modes as shown in FIG. The vibration frequency at which these resonance modes occur is uniquely determined by the thickness and length of the vibrating body and the Young's modulus of the material forming the vibrating body, and does not depend on the width h of the vibrating body.

The easiness of occurrence of the resonance mode as described above is
The vibrating body, which is closely related to the length a of the excitation unit 103, vibrates due to the stretching vibration of the piezoelectric element of the excitation unit 103, and when the excitation frequency matches the frequency at which the resonance mode occurs, the vibration in the resonance mode occurs. Will occur. Here, in order to consider the relationship between the length a of the excitation part and the vibration mode that is likely to occur, the length between the nodes in the fourth resonance mode in FIG. Since the exciting part is deformed by the expansion and contraction of the piezoelectric element, the natural deformed state of the exciting part is considered to be a bow shape having nodes at both ends of the exciting part 103. Therefore, it is considered that a resonance mode in which a and x are substantially equal to each other is likely to occur. For example, when x is about half of a, the piezoelectric element of the excitation part has both an expanding part and a contracting part.
It is very difficult to generate such a vibration mode by forced vibration.

Similarly, the length b of the receiver 105 and FIG.
The same applies to the length y in (f),
When b≈y, a sufficient output signal is obtained because the piezoelectric element of the receiving unit 104 receives strain in the same direction on the entire surface, but y
Becomes smaller than b, the piezoelectric element of the receiving unit 104 has a portion where reverse distortion occurs, and a positive charge is generated in a certain portion and a negative charge is generated in another portion. Will be reduced.

FIG. 4 is an experimental result showing the frequency characteristic of the output signal output from the receiving unit 105 when the dimensions of the exciting unit 103 and the receiving unit 105 are changed. The horizontal axis represents the frequency of the sinusoidal input signal applied to the piezoelectric element of the exciting unit 103, and the vertical axis represents the output voltage from the piezoelectric element of the receiving unit at that time. For example, the excitation unit 103
When a signal voltage of several V is applied to the receiver, an output voltage of several mV to several hundreds of mV is obtained from the receiver, but the value sharply increases at the resonance frequency, so that the horizontal axis indicates the frequency as shown in FIG. If is taken, a curve having a peak at the resonance frequency is obtained. Here, the vibrating body 102 was manufactured by adhering a piezoelectric element (Sumitomo Metallic H5D) to a 4-2 alloy, and the thickness of the 4-2 alloy and the piezoelectric element was 80 μm. In FIG. 3, h = 2 mm and l = 10 mm, and the dimensions a and b of the excitation unit 103 and the reception unit 105 are equal values, a and b
Was changed.

In FIG. 4A, a and b are relatively large, and
The frequency characteristics when /l=0.45 is shown.
Peaks in the third and third resonance modes are seen, and no further peaks in the fourth and fifth resonance modes are seen. These higher-order resonance modes appear as a and b become smaller,
For example, as shown in FIG. 4B, when a / l = 0.2, a 6th-order resonance mode occurs. Further, FIG. 4 (c) shows a / l.
= 0.15 and a and b are made smaller,
It has been found that when a and b are too small, the first, second, and third low-order resonance modes disappear, and only the high-order resonance modes appear.

It is generally said that the low-order resonance mode is more stable than the high-order resonance mode. This is shown in Figure 3.
In the case of a vibrating body having such a shape, in addition to the vibration modes shown in FIGS. 3C to 3H, there are resonance modes in the width direction (h) and torsional vibration modes. It tends to appear near the frequency of the next resonance mode, and in terms of frequency characteristics, peaks of other modes occur near the peak of the higher resonance mode,
The reason is that it becomes difficult to constantly drive the circuit at the frequency of the peak point of the higher-order resonance mode on the circuit. Therefore, also in the configuration of the present invention, it is preferable to use the low-order resonance mode, and it is safe to select any one of the first-order, second-order, and third-order resonance modes. 3 of these
When the attention is paid only to the propagation part 104 of the vibrating body 102, the third resonance mode corresponds to the first resonance mode of the propagation part 104, and thus the second resonance mode can be considered as one of stable fundamental modes. When using any one of the first, second, and third resonance modes, from the result of FIG.
It can be seen that a structure satisfying ≦ a / l <0.5 or 0.2 ≦ b / l <0.5 is preferable.

Next, a force sensor having another structure will be described for comparison with this embodiment. FIG. 5A shows another structure of the vibrating body. 3 is different from FIG. 3 in that the piezoelectric element is bonded to the entire surface of the vibrating body, and the electrode on the piezoelectric element 51 is divided into an excitation electrode 52 and a reception electrode 53.
2 is used for excitation and the reception electrode 53 is used for reception. That is, the propagating portion 54 of the vibrating body is composed of the piezoelectric element 51 and the flat plate, and the exciting portion 55 and the receiving portion 5 are connected.
The structure is the same as that of No. 6 in thickness. In this structure, when the frequency characteristic of the output signal is measured, it becomes as shown in FIG. 5 (b), the peak value is lower than that in FIG. 3, many small peaks appear, and the resonance mode which seems to be a clear fundamental mode. It turned out to be difficult to cause. This is because the present embodiment shown in FIG. 3 vibrates near the boundary between the excitation unit 103 and the propagation unit 104 or the reception unit 105 and the propagation unit 104 due to the different thicknesses of the excitation unit 103 and the reception unit 105 and the propagation unit 104. It is assumed that the node is likely to occur and a peak such as a third resonance appears largely.

It should be noted that the excitation electrode and the reception electrode are replaced by 1
Even if 03 is a receiving unit and 105 is an exciting unit, the same effect can be obtained.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

1A and 1B are a sectional view and a plan view of a mechanical quantity sensor according to an embodiment of the present invention. Since the description of FIG. 1 is the same as that of the first embodiment, the description thereof is omitted.

In FIG. 1, a vibrating body 102 is an inertial body 1.
Although it is installed on the support beam 101 that bends with the movement of 00, the resonance mode exists for the entire beam including the inertial body 100 and the support beam 101. This resonance mode can be considered to be substantially the same as the vibration of a cantilever beam, but the inertial body moves well with a small force and the deflection of the support beam 101 is large,
Although the sensitivity as a sensor increases, the resonance frequency of the entire beam decreases accordingly. The resonance frequency of this entire beam is
It is related to the frequency range of the applied force that one wants to measure. That is, for example, in the case of an acceleration sensor for automobiles,
It is necessary to accurately measure the acceleration in the range of 0 to 500 Hz, but if the resonance frequency of the entire beam exists in this range,
It becomes difficult to accurately measure the acceleration near the resonance frequency. Therefore, the lower the resonance frequency of the entire beam, the higher the detection sensitivity, but it is desirable to design the resonance frequency to be a frequency range to be measured or higher, for example, 500 Hz or higher, and ideally 1 kHz.

The resonance frequency of the entire beam and the vibrating body 10
The two resonance frequencies are independent of each other and must not influence each other. In order to explain this, the experimental result of FIG. 6 is shown. The horizontal axis represents the frequency of the signal applied to the piezoelectric element of the excitation unit 103 of the vibrating body 102, and the vertical axis represents the output signal voltage from the reception unit 105. The data in FIG.
At, t1 = 0.4 mm, t2 = 0.8 mm, L1
= L2 = H = 5 mm, 1 = 5 mm in FIG. 3, a = b
= 1.5 mm, h = 1 mm. In the curve of FIG. 6, fc0, fc1, and fc2 are peaks of the resonance frequency of the entire beam, which correspond to the primary, secondary, and tertiary resonance frequencies, respectively. Further, fs0, fs1, and fs2 are resonance frequencies of the vibrating body 102, and are (c), (d), and
This corresponds to the primary, secondary, and tertiary resonance modes shown in (e). In FIG. 6, fc0, fc1, and fc2 are fs0.
It is in a position far away from. That is, the resonance frequency of the entire beam is located away from the resonance frequency of the vibrating body 102 and does not affect each other, so that it can be said that the structure is such that a very good result is obtained. However, when the frequencies fc0 and fs0 are relatively close to each other, a high-order resonance frequency (for example, fc4) may overlap with fs0 in the entire beam, and the resonance frequency of the vibrating body 102 can be accurately detected. Can't do it. Considering that the resonance of the entire beam includes a higher-order resonance mode, it is safe and good that the resonance frequency of the vibrating body 102 used and the primary resonance frequency of the entire beam are separated by one digit or more. A sensor can be realized.

It should be noted that the excitation electrode and the reception electrode are exchanged, and 1
Even if 03 is a receiving unit and 105 is an exciting unit, the same effect can be obtained.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings.

7 and 8 show the structure of the vibrating body of the third embodiment. The structure of the vibrating body shown in FIG. 3 is a structure in which higher-order resonance such as third-order resonance is relatively likely to occur, but if possible, a structure in which only simple primary resonance frequency is generated is desired. . 7 and 8 show a vibrating body structure that satisfies such requirements. In FIG. 7, the inertial body 100 and the support beam 101 are configured in the same manner as in FIG. 1, and a strip-shaped flat plate 106 is installed on the upper surface of the support beam 101 with both ends fixed,
The piezoelectric element 107 is joined to the upper part thereof. Flat plate 10
When 6 is an insulator, an electrode is provided between the piezoelectric element 107 and the flat plate 106, and when the flat plate 106 is a conductor, the flat plate 106 is used as an electrode so that a constant potential can be applied to the lower surface of the piezoelectric element. On the other hand, the upper surface of the piezoelectric element is divided into left and right sides with respect to a line connecting both ends of the flat plate 106.
8 and the receiving electrode 109 are provided.

FIG. 8 is an enlarged view of the vibrating body portion of FIG. In such a structure, the excitation electrode 108 is continuous from the fixed end to the fixed end of the vibrating body, and when an exciting voltage is applied to the exciting electrode, the vibrating body is expanded and contracted as shown in FIG. 8C. First-order resonance mode is most likely to occur 2
A resonance mode, such as a third-order resonance, in which a part of the vibrating body expands and a part of the vibrating part contracts, is not generated by the forced vibration. That is, regarding the sensor of FIG.
Taking the same data as above, only the resonance frequency fs0 clearly shows a peak, and the peaks at fs1 and fs2 disappear.

FIG. 8C shows the first-order resonance mode of the beam fixed at both ends. According to this, since both ends are fixed, it is understood that the bending direction of the central portion is opposite to the bending direction of the portion near the ends. Therefore, when the vibration of the primary resonance mode is used, if the receiving electrode 109 has the same area in any part of the beam, the charge generated in the central part and the charge generated in the end part have different signs. Therefore, they cancel each other out, resulting in a drawback that the output voltage decreases. Therefore, in the present invention, FIG.
As shown in (a), the excitation electrode 108 is wide at the central portion and narrow at the end portion, and the receiving electrode 109 is oppositely wide at the end portion and narrow at the central portion. With this configuration, the opposite sign component of the charge generated in the receiving electrode is reduced, the receiving sensitivity is increased, and the peak at the primary resonance frequency can be made sharp and high.

It should be noted that the excitation electrode and the reception electrode are replaced by 1
Even if 08 is a receiving electrode and 109 is an exciting electrode, the same effect can be obtained.

[0033]

As described above, according to the present invention, firstly, between the total length l of the vibrating body and the length a of the piezoelectric element for excitation and the length b of the piezoelectric element for reception, 0. By using a structure having a relationship of 2 ≤ a / l <0.5 or 0.2 ≤ b / l <0.5, the resonance peak of the higher order mode is reduced or eliminated, and the lower order mode of the vibrating body is reduced. It is possible to realize an excellent force sensor in which the resonance frequency of (1) clearly shows a peak and driving in a stable resonance mode is possible.

Secondly, the primary resonance frequency of the vibrating body is
An excellent force sensor that can stably resonate a vibrating body without being affected by the resonance frequency of the entire beam by a structure in which the primary resonance frequency of the inertial body and the supporting beam is 10 times or more. Is.

Thirdly, by providing a pair of electrodes divided on the surface of the piezoelectric element in a direction intersecting the longitudinal direction of the vibrating body, only the primary resonance frequency of the vibrating body can be generated. Therefore, stable driving can always be performed in the primary resonance of the same mode, and an excellent force sensor with few malfunctions can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view and a plan view of a force sensor according to a first embodiment of the present invention.

FIG. 2 is an acceleration-frequency characteristic diagram showing an example of measurement of acceleration in the first embodiment of the present invention.

FIG. 3 is an enlarged view of a vibrating body portion according to the first embodiment of the present invention and a schematic view showing various vibration modes.

FIG. 4 is a graph showing frequency characteristics in the first embodiment of the present invention.

FIG. 5 is a configuration diagram of a force sensor having another configuration for comparison with the first embodiment of the present invention.

FIG. 6 is a frequency characteristic diagram in the second embodiment of the present invention.

FIG. 7 is a sectional view and a plan view of the force sensor according to the third embodiment of the present invention.

FIG. 8 is an enlarged view of a vibrating body portion and a schematic view of a vibrating mode according to a third embodiment of the present invention.

FIG. 9 is a perspective view of a conventional force sensor.

FIG. 10 is a perspective view of a conventional force sensor.

[Explanation of symbols]

 100 Inertial Body 101 Support Beam 102 Vibrating Body 103 Exciting Section 104 Propagating Section 105 Receiving Section 107 Piezoelectric Elements 108, 109 Electrodes

Front page continuation (72) Inventor Shinichiro Aoki, 3-10-1, Higashisanda, Tama-ku, Kawasaki, Kanagawa Prefecture Matsushita Giken Co., Ltd. No. Matsushita Giken Co., Ltd.

Claims (4)

[Claims] 1. An inertial body that is movable by the action of a mechanical quantity, a support beam that supports the inertial body, a vibrating body that is provided on the support beam and has both ends fixed to the supporting beam, and the vibrating body. An exciting piezoelectric element that is joined near one end of the vibrating body to excite the vibrating body, and a receiving piezoelectric element that is joined near the other end of the vibrating body to receive the vibration of the vibrating body,
Between the total length l of the vibrating body and the length a of the excitation piezoelectric element and the length b of the reception piezoelectric element, 0.2 ≦ a / l <0.5 or 0.2 ≦ b A force sensor having a relationship of /l<0.5. 2. An inertial body movable by the action of a mechanical quantity, a support beam supporting the inertial body, and a vibrating body provided on the support beam and having both ends fixed to the support beam,
The force sensor, wherein the primary resonance frequency of the vibrating body is 10 times or more the primary resonance frequency of the inertial body and the support beam. 3. An inertial body movable by the action of a mechanical quantity, a support beam supporting the inertial body, a vibrating body provided on the support beam and having both ends fixed to the support beam, and the vibrating body. A piezoelectric element bonded to the upper side and a pair of electrodes divided in a direction intersecting the longitudinal direction of the vibrating body on the surface of the piezoelectric element are provided, and one of the pair of electrodes excites the vibrating body. A force sensor characterized in that it is an exciting electrode and the other is a receiving electrode that receives the vibration of the vibrating body. 4. A pair of electrodes dividedly provided on the piezoelectric element, one of which is wide in the central portion of the vibrating body and narrow near the fixed end, and the other of which is narrow in the central portion of the vibrating body and near the fixed end. The force sensor according to claim 3, wherein the force sensor has a wide shape.