JPH0658226B2 - Angular velocity sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration type angular velocity sensor having a tuning fork structure using a ceramic piezoelectric material.

2. Description of the Related Art A conventional angular velocity sensor is mounted as shown in FIG. In FIG. 7, 1 is a metal case in which the main body of a vibration type angular velocity sensor having a tuning fork structure is incorporated, 2 is a support metal fitting, and 3 is a support such as a casing or a circuit board. The angular velocity detection direction is the direction indicated by the arrow in FIG.
Of the angular velocity sensor and the output signal of the angular velocity sensor are made to coincide with each other and are firmly fixed by using the support fitting 2.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, since the vibration type angular velocity sensor of this type has the element vibrating at a constant frequency, malfunction will occur if disturbance vibration including a frequency component close to this frequency is applied. . Also, since the ceramic piezoelectric body is weak against shock,
Cracks may be caused by a slight impact from the outside,
Since it would be destroyed, it could not be used in a place where there is a great deal of vibration and shock in automobiles.

Means for Solving the Problems In order to solve the above problems, the present invention provides a first vibrating unit in which a driving piezoelectric bimorph element and a first detection bimorph element are orthogonally joined to each other, and a monitoring piezoelectric bimorph. A second vibrating unit in which an element and a second detecting bimorph element are orthogonally joined to each other, and the first and second vibrating units are arranged to be parallel to each other along a detection axis. A sensor main body having a tuning fork structure in which the free ends of the piezoelectric bimorph element and the monitor piezoelectric bimorph element are connected by a connecting plate, a metal case that houses the sensor main body and is connected to the ground potential, and an outer circumference of the metal case. A weight mounted on the support, a support for supporting the weight or the metal case, and a collision arranged between the support and the weight or the metal case. It is composed of a shock absorber.

Action The action of this technical means is as follows.

The weight attached to the outer circumference of the metal case allows the apparent mass of the sensor itself to be freely set, and the resonance frequency determined by this mass, the elastic constant of the shock absorber, and the thickness and area affects the electrical resonance frequency of the sensor. It can be set to a frequency that is difficult to do.

Further, in the case of a normal shock absorbing structure, the shock is absorbed while being damped and vibrated when a shock is applied to the shock from the outside, but it can be brought into a braking state close to critical braking even if the vibration is minimized.

Embodiment An embodiment of the angular velocity sensor according to the present invention will be described below with reference to the drawings.

First, a vibration type angular velocity sensor using a ceramic piezoelectric material will be described with reference to FIGS.

The sensor body of the angular velocity sensor has a structure as shown in FIG. 4, and is mainly composed of a drive element, a monitor element, and first and second sensing elements each composed of four piezoelectric bimorphs.
The driving element 101 and the first sensing element 103 are joined to each other at a joint portion 105
The connecting plate 107 connects the first vibrating unit 109, which is orthogonally joined by the connecting means 107, and the second vibrating unit 110, which is the orthogonal joining of the monitor element 102 and the second detecting element 104, by the joining portion 106.
Has a tuning fork structure in which the connecting plate 107 is supported at one point by a supporting rod 108.

When a sinusoidal voltage signal is applied to the driving element 101, the first vibrating unit 109 starts vibrating due to the inverse piezoelectric effect, and the second vibrating unit 110 also starts vibrating due to the tuning fork signal. Therefore, the electric charge generated on the element surface by the piezoelectric effect of the monitor element 102 is proportional to the sinusoidal voltage signal applied to the driving element 101. Stable tuning fork vibration can be obtained by detecting the charge generated in the monitor element 102 and controlling the sine wave voltage signal applied to the drive element 101 so that the charge has a constant amplitude.

The mechanism by which this sensor produces an output proportional to the angular velocity will be described with reference to FIGS. 5 and 6.

FIG. 5 is a top view of the angular velocity sensor shown in FIG. 4, and when the angular velocity ω is applied to the sensing element 103 vibrating at the velocity υ, “Coriolis force” is applied to the sensing element 103.
Occurs. This "Coriolis force" is perpendicular to the velocity υ and its magnitude is 2mυω. Since the sensing element 103 is vibrating in the tuning fork, if at some point the sensing element 103 is vibrating at a speed υ, the sensing element 104 is vibrating at a speed −υ and the “Coriolis force” is −2 mυω. Is. Therefore, the sensing elements 103 and 104 are deformed in the direction in which the “Colioca force” acts on each other as in the seventh example, and electric charges are generated on the element surface by the piezoelectric effect. Here upsilon is a movement caused by vibration of the tuning fork, fork vibration _{υ = a · sinω 0 t a} : amplitude of the tuning fork vibration omega _0: if the period of the tuning fork "Coriolis force" is F c ₌ a · ω · sinω ₀ t becomes, is proportional to the angular velocity omega and fork amplitude a, the force for deforming the sensing elements 103 and 104 in the planar direction. Therefore, the surface charge amount Q of the detection elements 103 and 104 becomes Q∝a · ω · sinω ₀ t, and if the tuning fork amplitude a is controlled to be constant, it becomes Q∝ω · sinω ₀ t, and the detection elements 103 and 104 The amount of surface charge Q generated at is obtained as an output proportional to the angular velocity ω. If this signal is synchronously detected at ω ₀ t, a DC signal proportional to the angular velocity ω is obtained. Even if a translational motion other than the angular velocity is applied to this sensor, electric charges of the same polarity are generated on the two element surfaces of the detection element 103 and the detection element 104, so when converting to a DC signal,
They cancel each other out so that no output is output.

However, due to variations in the sensor assembly process, for example, the driving element 101 and the first sensing element 103
In the case where the angle of the orthogonal junction of 1 is slightly deviated, or the performances of the first sensing element 103 and the second sensing element 104 are slightly deviated, this is a problem that can occur in reality. Since it is not possible to completely cancel the influence of disturbance vibration and output is generated, it is desirable to use a supporting method that does not transmit translational motion other than angular velocity to the sensor part as much as possible. In particular, it is desirable that the resonance frequency of the support be sufficiently lower than ω ₀ because vibrations including a period ω _{0 of} tuning fork vibration or a component including a frequency component of an integral multiple of ω ₀ are likely to malfunction. Further, when a large impact is applied, the ceramic element is cracked and destroyed or its characteristics are deteriorated. Therefore, a supporting method that makes it difficult for the sensor body to be transmitted to the impact is desirable.

FIG. 1 is a diagram showing an embodiment of the angular velocity sensor according to the present invention, and 11 is a metal case connected to the ground potential, which internally houses the sensor body shown in FIG. 12
Is a support fitting, 13 is a support, 14 is a weight, and 15 is a shock absorber.

FIG. 1 is a conceptual representation of FIG. 2. In FIG. 2, the sensor of mass m is supported by a shock absorber 15 having an elastic constant C, and the equation of motion is c: Elastic constant of shock absorber: Thickness of 〃 s: Area of 〃 x: Vibration amplitude m: Mass This motion is a simple vibration, Then, it can be expressed as x = Acos (ωt + β) (2). Cycle is Therefore, the resonance frequency in this supporting method depends on the capacity of the weight 14 and the area of the shock absorber 15. It can be seen that it is determined by the thickness and elastic coefficient. Usually, in this type of angular velocity sensor, since the element is used while vibrating at around 1 KHz, the resonance frequency on the support 13 is sufficiently lower than 1 KHz, for example, it is desirable to set it at around 10 Hz. As a result, vibration of frequency components above 10 Hz can be cut without being transmitted to the sensor.

Consider further the case where an impulse-like impact is applied. In general, when an object is subjected to an impact, damping vibration as shown in Fig. 3 occurs, and its equation of motion is Becomes

Here, 2 mK is a convenient attenuation term.

Therefore, Putting that, equation (4) is This is the equation of damped oscillation.

The solution of this differential equation is generally divided into the following three cases.

First, the solution of equation (5) when k ² −ω ² <0 is This can be interpreted as a simple vibration whose amplitude is decreasing according to ae- ^kt .

Next, the solution for k ² −ω ² > 0 is Is non-periodic.

Finally, the solution when k ² −ω ² = 0 becomes x = (At + B) e ^−kt (8), and this state is called critical braking.

The braking state suitable for the angular velocity sensor is preferably critical braking, and the impact absorber 15 converts the impact energy from the outside into the thermal energy earliest, so that the sensor can be protected.

Based on the above theory, it is possible to select the most suitable support condition for the vibration type angular velocity sensor having the tuning fork structure. That is, m, s, so that the resonance frequency ω does not affect the vibration frequency of the sensor and is in a critical braking state against an external impact.
The values of k and c can be set.

EFFECTS OF THE INVENTION As described above, according to the present invention, the resonance frequency of the support can be arbitrarily set to a low frequency sufficiently separated from the vibration frequency of the sensor, and the accuracy is close to critical braking against external impact. It is possible to easily obtain a condition that can satisfy such two conditions at the same time.

As a result, it is possible to overcome the problem that the vibration type angular velocity sensor is vulnerable to disturbance vibration including a frequency component close to the vibration frequency of the sensor, which is a weak point of the vibration type angular velocity sensor.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an angular velocity sensor according to the present invention, FIGS. 2 and 3 are conceptual views for explaining the operation of the sensor, and FIG. 4 is a perspective view of a tuning fork structure vibration type angular velocity sensor. ,
5 and 6 are operation explanatory views of the sensor, and FIG. 7 is a perspective view showing a conventional angular velocity sensor. 11 ... Metal case, 12 ... Support metal fittings, 13 ... Support body, 1
4 ... weight, 15 ... shock absorber, 102 ... monitor element,
103 ... 1st sensing element, 104 ... 2nd sensing element, 1
05, 106 ... Joining portion, 107 ... Connecting plate, 109 ... First
Vibration unit, 110 ... second vibration unit.

Front page continued (72) Inventor Jiro Terada 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Takahiro Manabe, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Invention Person Takenaka Hiroshi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Wako Ueda, Kadoma City, Osaka Prefecture 1006 Kadoma Matsushita Electric Industrial Co., Ltd. (72) Hiroshi Senda, Kadoma City, Osaka Prefecture Kadoma 1006, Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-62-188908 (JP, A) Actually opened 63-181913 (JP, U)

Claims (1)

[Claims] 1. A first vibrating unit in which a driving piezoelectric bimorph element and a first detection bimorph element are orthogonally joined to each other, and a monitoring piezoelectric bimorph element and a second detection bimorph element are orthogonal to each other. Second joined
Of the driving piezoelectric bimorph element and the monitoring piezoelectric bimorph element are connected by a connecting plate so that the first and second vibrating units are parallel to each other along the detection axis. A sensor body having a tuning fork structure, a metal case accommodating the sensor body and connected to the ground potential, a weight mounted on the outer periphery of the metal case, and a support for supporting the weight or the metal case. An angular velocity sensor composed of this support and a shock absorber arranged between a weight or a metal case.