JPS6358111A - Tuning fork type piezo-electric angular velocity sensor - Google Patents

Abstract

PURPOSE:To obtain an output signal of a detecting section which develops no undesired Y-axis low frequency vibration during the rotation of a sensor, by adjusting dimensions of parts of a tuning fork so as to set the Y-axis natural frequency higher than the X-axis drive frequency. CONSTITUTION:Piezo-electric plates 8 and 8' are driving are lined on the sides of detecting sections 2 and 2' of a tuning fork type vibrator 1. Then, when an AC voltage is applied between drive electrodes 8a and 8a' and 8b and 8b' separately, the detecting sections 2 and 2' to develop bending vibration in the X-axis. When a rotary angular velocity OMEGA is given around the Z-axis together with the X-axis drive at the same frequency as the X-axis natural frequency, the detecting sections 2 and 2' also to generate bending vibration in the Y-axis. On the other hand, the vibrator 1 is so formed that the X-axis natural frequency becomes less than the Y-axis natural frequency. With such an arrangement, in an output waveform after passing through a bandpass filter of a sensor, the difference V-Vc is proportional to the angular velocity OMEGA as obtained between the amplitude Vc with the sensor at rest and the amplitude V when a fixed angular velocity is given. As only the drive frequency is developed in the waveform, the angular velocity signal is demodulated easily with a detector.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an angular velocity generator using a piezoelectric material.

Conventional gyros for measuring angular velocity include rotational and vibrating gyros. The former has high performance, but has a large number of parts, requires high-precision processing, and is expensive.

The latter has a small shape, dimensions, 9 layers, etc., a simple structure, and is inexpensive, but it is still insufficient in terms of required performance, and improvements in performance are desired.

A vibrating gyro produces stiffness A when the angular velocity is increased to I on a vibrating object.
This is an application of the ability to generate force.

Various types of oscillators are used in the main part of this type of gyro to control the angular velocity, and various types and structures have been devised. For example, U.S. Special Consideration No. 2,544,
As in Specification No. 646, a vibrator in which two root-shaped piezoelectric bodies are orthogonally butt-joined at their ends so as to form a right angle to each other is used), and also in Specification No. 2,513,340 There is also one that uses a uni-shaped tuning fork vibrator.

In general, a tuning fork type vibrator can easily maintain a relatively stable resonance frequency and amplitude in both arms due to a phenomenon called coupled vibration, and is convenient for use in a vibrating angular velocity sensor.

FIG. 4 is a schematic diagram showing the vibration state of a general tuning fork-shaped vibrator.

The case where such a tuning fork-shaped vibrator is used in an angular velocity sensor will be explained with reference to the same figure.

Drive the arm of the tuning fork with a suitable driving means, such as the side (W)
(not shown), Figure 4 (a)
Both arms are excited so as to bend in opposite directions in the X-axis direction as shown in FIG. At this time, the driving frequency is determined by the width W and length a of the arm J: As shown in (b), the arm section receives the Coriolis force Fc and bends and vibrates in the Y-axis direction.This vibration mode has a natural frequency determined by the thickness t and length a of the arm. However, when the angular velocity Ω is actually increased by 15, Yi
The vibration frequency in the 1111 direction is equal to the drive frequency. Also, the amplitude of the arm in the Y-axis direction is the given angular velocity Ω
Therefore, the magnitude of the bending vibration in the Y-axis direction is detected by using an appropriate detection means, such as bonding a piezoelectric plate to the front surface (one surface) of the arm section.

As described above, the output signal waveform from the vibrating color speed sensor detection unit, not limited to the γ1-pronged vibrator, appears in the form of a modulated wave with the drive frequency as the carrier wave and the change in angular velocity as the signal wave.

Therefore, in order to determine the angular velocity from the output signal of a sensor that uses a piezoelectric material with a large output impedance as a detection means, an electric circuit is required to first amplify the output signal from the detection section and then pass it through a bandpass filter to eliminate noise and harmonics. Generally, the components are removed, demodulated by a detection circuit, and then low-frequency amplification is performed. Ultimately, an output characteristic having a linear relationship with changes in angular velocity is obtained.

Problems to be Solved by the Invention In many cases, the width W and thickness t of a tuning fork arm used in a conventional tuning fork type vibrator sensor are the same. Again lol
>t and w<t tuning forks are also used, but it was unclear what dimensions, including arm length a and base length b, would be suitable for an angular velocity sensor, so what is the optimum size tuning fork vibrator? I could not say it. FIG. 3 shows the output signal waveform of an angular velocity sensor using these conventional tuning fork vibrators.

This waveform is the waveform after passing through the aforementioned bandpass filter.

The range of △ in the figure is when the sensor is stationary, and the amplitude VI G
is output. The range B shows the output when rotating at a constant angular velocity, and the carrier wave of lm5 (1kHz) has a carrier wave of 6m5 (1kHz).
67H2) was obtained, and the low frequency components could not be removed using a bandpass filter alone.

Even if this waveform was detected and amplified at low frequency, accurate angular velocity could not be measured. The reason for this kind of waveform is that when the sensor is stationary, the image is captured only in the X-axis direction as shown in Figure 4 (a), and a noise component of amplitude V'C appears at the same frequency as the drive frequency, but when the sensor is rotating, The vibration shown in Fig. 4 (B) is generated (not P), but as shown in Fig. 4 (C), a large tt vibration occurs with a natural frequency determined by the total length l of the arm thickness 1 and 6 prongs. As a result, the equivalent 6m
This is because the low frequency component of s is output.

Means for Solving the Problems The present invention adjusts each radical method of the tuning fork in order to obtain an output signal of the detection section that is free from unnecessary low-frequency vibrations in the Y-axis direction when the sensor rotates. ) is characterized in that the natural frequency in the Y-axis direction is set higher than the driving frequency in the X-axis direction.

In this case, a noise component with a higher frequency than the carrier wave is visible in the modulated wave, but it can be easily removed by a band-pass filter, and the angular velocity signal wave can be easily detected by a simple demodulation circuit.

Embodiment An embodiment of the angular velocity sensor of the present invention is shown in FIG. 1
is a tuning fork-shaped vibrator consisting of two detection parts (arm parts) 2.2' and a base part 3, and the vibrator has piezoelectric plates 2a and 2b made of lead zirconate titanate, barium titanate, etc. It has a bimorph structure with layers separated by adhesive. That is, the piezoelectric plate 2a is polarized in the direction of arrow P.
There are detection electrodes 4 made of silver, gold, etc. on both the front and back surfaces of the arm.
, 4' and a center electrode 5.5' are provided, and the piezoelectric plate 2b, which is also polarized in the direction of arrow P', is also provided with 5, 5'.
The detection part electrodes 6, 6' are straddled with the central part electrodes 5 and 5' being shown as one layer in Fig. Electrode layer, adhesive layer.

It has a three-layer structure consisting of an electrode layer with an electric potential of tf < 2 b, and the contact layer is a thin layer of about a few μR1, so both electrode layers are electrically interconnected. "Shimei" (
P.

It is fixed to the support part 7 using the same method.

8. 8' is a drive electrode 8a made of silver or gold on both surfaces.

E'+b, 8'a, and 3'b are piezoelectric plates for driving, which are attached to both sides of the tuning fork-shaped vibrator 1 with adhesive to form a driving part.

When an AC voltage is applied between the drive electrodes 8a, 8'a and Bb, B'b, the drive piezoelectric plates 8 and 8' are aligned in the Z-axis direction, so the detection unit 2.2' This results in bending vibration in the X-axis direction. When a rotational angular velocity Ω around the Z-axis is applied while driving with excitation at the same frequency as the natural frequency in the X-axis direction, the detection parts 2 and 2' receive Coriolis and vibrate 4J (also 111 in the Y-axis direction). In other words, the trajectory of the tip of the y)-mu part of the tuning fork draws an elliptical orbit, but this rib, the detection part electrode 4
Between and 6 or between 4' and 6', an electric shock is generated due to a thunderstorm. The polarity is such that the detection part electrode 4 has a positive voltage I and 6'-b, and the detection part electrodes 4' and 6 have a negative polarity. Therefore, the detection part electrodes 4, 6' and 4'
and 6 are connected in parallel with external conductors (not shown) to extract the detection signal.1゜The tuning fork type vibrator for the angular velocity sensor of the present invention has a natural frequency in the 17J<It is characterized by a smaller covering than the natural frequency when bending and covering in the Y-axis direction.

An example thereof will be explained with reference to FIG. The figure shows the relationship between arm length and natural frequency obtained by division. The broken line (a) in the same figure is the natural frequency [f-△xw/a'l] in the X+11 direction when the width of the arm is w = 2 mm.
(Δ is a constant, the same as below j), and the straight line (b) is the natural frequency of the arm bending in the Y-axis direction when the arm's y-movement is t-4 mm [f = AX t,
/a 2 ko wo ho 1J.

The curves (bar 1) and (bar 2) have arm thickness t=
4mm, and the base length is 1)-8mm respectively.
and the natural frequency of Shidadoki [f-・Δ×t
, /(a0b)2].

In order to configure the r4 fork-shaped oscillation of the present invention, it is necessary to select the arm length a so that the broken line (a) = double line (bar 1> or (bar 2)). As shown in Figure 5i, the longer the base, the harder it is in the Y-axis direction.
Since the height is lower, the length of the arm is also quite appealing.
If shi', l-4J, 4f et al. 4. I know it's Z. Therefore, when the base fA a is set to b-8111m, the arm length a may be selected within the range shown by diagonal lines.

In the embodiment of the present invention, the arm width W-2. Thickness 1=4,
A tuning fork-shaped oscillator with length a = -41 and base length b = 8 (mm) was constructed (Q).
, the natural frequencies of each vibration mode (Figure 4) are different! 1001-l /', 7201-l Z, H1
It was assumed that the frequency would be 00H7, and when we actually measured the natural frequency, it turned out to be /C.

II III,: The output waveform after passing through the bandpass filter of the angular velocity sensor consisting of the high-pronged oscillation force of the XI method is expressed as the second
As shown in Figure 1, 1) 1'1, q) Same as Figure 3,
The range il+ of A in the figure is when Renly is at rest, and the amplitude V
c is output, giving a constant angular velocity [in the range of 3, the amplitude ■
The output (5 bows were made 1q. The magnitude of the amplitude V-Vc is
It shows an exact proportional relationship for a given angular velocity. In addition, the output signal waveform is 2 ms (500H
Since only the natural frequency in the X-axis direction of Z), that is, the driving frequency, appears, the angular velocity signal is easily demodulated by the next-stage detector, and a good angular velocity sen→no is obtained.

Effects of the Invention In the angular velocity sensor using the tuning fork vibrator of the present invention, the natural frequency of the bending vibration in the Y-axis direction, which is the detection direction of Coriolis, is higher than the fixed tT frequency in the X-axis direction and the tsunawara drive frequency. By doing so, the output signal waveform with a low frequency component is 4EJ'd, so it can be detected easily, and an extremely accurate angular velocity signal can be obtained by low frequency amplification. In addition, since the tuning fork vibrator itself can drive both arms with a constant amplitude using an extremely stable frequency, the output when not rotating is small compared to conventional vibrating angular velocity sensors other than the tuning fork type, and therefore the angular velocity II signal The signal-to-noise ratio was significantly improved. Furthermore, even if the sensor is affected by angular velocity or external vibration, it hardly appears in the output signal waveform of the detection section, making it possible to provide an extremely high-precision angular velocity sensor.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the angular velocity upper and lower using the tuning fork type vibrator of the present invention, and FIG. Figure 3 is a waveform diagram of the detection unit output signal of a conventional tuning fork type color speed sensor, Figure 4 is a schematic diagram showing the vibration mode of the tuning fork type vibrator, and Figure 5 is the arm length and natural frequency of the tuning fork type vibrator. FIG. 1...Tuning fork-shaped vibrator 2.2'...Detection section 1B Engraving of the drawing (no change in content):'X 7 Hard 2*5 Ya Chi Enkan 4-1 Concave (1) (b)
(c) Yukisu Y] ■ Mutsuyu 12 Down-1 δ'1 Application No. 20226 January 2,
Name of invention Tuning fork expansion piezoelectric material angular velocity pin number J- 〒601

Claims (1)

[Claims] Two arm parts of a bimorph-shaped tuning fork vibrator made by joining two piezoelectric plates are used as detection parts, and the arm parts are moved in the X-axis direction perpendicular to the Y-axis direction, which is the bending direction of the bimorph. In a tuning fork-shaped vibrator, which is made by fixing a piezoelectric material to the side surface of an arm portion having a quadrilateral cross section and using it as a driving portion, the tuning fork vibrator is driven at the natural frequency of the bending vibration in the X-axis direction of the arm portion so that the arm portion undergoes bending vibration. In addition, a tuning fork type piezoelectric angular velocity sensor characterized in that a natural frequency in the Y-axis direction is set on a higher frequency side than the above frequency.