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JPH07190782

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DESCRIPTION JPH07190782
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
vibration angular velocity meter, and more particularly to a compact and inexpensive
piezoelectric vibration angular velocity meter.
[0002]
2. Description of the Related Art In the piezoelectric vibration angular velocity meter utilizing the
positive and reverse piezoelectric effects, two types, the GE type and the Watson type, have been
the mainstream. In the GE type piezoelectric vibration angular velocity meter, as shown in FIG. 4,
a piezoelectric ceramic plate is bonded to a rod-like vibrator made of metal, thereby driving the
metal vibrator and detecting the Coriolis force generated as the vibrator rotates. Do. The mode of
vibration used is an unconstrained lateral vibration, usually fixing the transducer to the substrate
at the node of the vibration.
[0003]
In the Watson-type piezoelectric vibration angular velocity meter, as shown in FIG. 5, four
piezoelectric ceramic bimorphs are stacked in a crossover tuning fork shape so as to be
orthogonal to each other, and the entire tuning fork is excited by the driving bimorph. The
resulting Coriolis force is detected by a detection bimorph. These elements are applied as an
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angular velocity sensor, a camera shake sensor, etc. and have many results.
[0004]
However, these piezoelectric vibration angular velocity meters require complicated processes
such as bonding of ceramic plates and attachment of lead wires because the configuration and
fixing method of the vibrators are complicated. It was impossible to reduce the size and cost. An
object of the present invention is to solve these problems and to provide a compact and
inexpensive mass-produced vibration angular velocity meter.
[0005]
According to the present invention, there is provided a structure in which a vibrator has a
plurality of beam shapes formed in the same plane, one side of the plurality of beam shapes
being supported by a base and the other side supporting a weight. And In addition, the present
invention is based on the idea that the silicon processing process can be combined with the vapor
phase synthesis method of the piezoelectric / electrostrictive material, which has recently
become popular, as a means for producing a piezoelectric vibration angular velocity meter. The
vibrator is formed by the silicon processing process, and the thin film made of the piezoelectric
and electrostrictive material is formed thereon to form the piezoelectric vibration angular
velocity meter, and the vibrator is formed into a plurality of beam shapes formed in the same
plane. One side of the plurality of beam shapes is supported by the base and the other side is
supported by the weight.
[0006]
[Function] When applying an AC electric field of a frequency near the resonance frequency of the
horizontal vibration of a vibrator of the type supporting a silicon weight by a beam to a thin film
made of piezoelectric or electrostrictive material, the piezoelectric reverse effect is applied to the
vibrator. Natural vibration is excited. At this stage, when rotation occurs around the beam axis,
Coriolis force is generated in the direction perpendicular to both the axial direction and the
vibration direction of the beam. This force deforms the beam in the direction perpendicular to
the vibration caused by the drive electric field, and if this detects the induced charge generated
by the piezoelectric positive effect in the piezoelectric / electrostrictive thin film fixed to another
beam, it rotates according to the following relationship The angular velocity can be estimated.
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[0007]
Fc = 2 m [v · Ω] (1) Here, Fc is the Coriolis force, m is the mass of the oscillator, v is the
oscillation velocity of the oscillator, and Ω is the rotational angular velocity. In the case of a
vibrator with a weight, the Coriolis force is increased because the mass is increased as compared
with a vibrator with only a beam without a weight, and the sensitivity of the piezoelectric
vibration angular velocity meter is improved.
[0008]
A vibrator with a structure in which a weight is disposed at the center of four beams which are
orthogonal to each other provides stable resonance. The piezoelectric / electrostrictive thin film
formed on the pair of beams excites flexural vibration in which the four beams vibrate in the
direction perpendicular to the surface of the element centering on the weight. In this state, when
rotational movement occurs around the axis of another pair of beams on which the detection thin
film is formed, the beams bend in the element plane due to the Coriolis force. The output
generated by the Coriolis force is detected by the detection piezoelectric / electrostrictive thin
film fixed on the same beam as this bending.
[0009]
When a piezoelectric / electrostrictive thin film is formed on the weight part and used as a
driving thin film in the vibrator having the above-mentioned structure, all the piezoelectric /
electrostrictive thin films formed on the four beams are used as a detecting thin film I can do it.
When an alternating current of an appropriate frequency is applied to the piezoelectric /
electrostrictive thin film of the weight portion, resonance in which the weight moves in the
direction perpendicular to the element plane is excited. At this time, when rotation about a pair of
beams occurs, the Coriolis force causes the beam to bend in the element plane, and when
rotation about another pair of beams perpendicular thereto occurs, the beams likewise become
similar. To bend. By detecting a piezoelectric signal due to bending, it is possible to detect
rotational angular velocities about two mutually orthogonal axes with one element.
[0010]
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From the detection electrode, in addition to the piezoelectric signal caused by the Coriolis force,
an output in which the piezoelectric signal accompanying the vibration of the beam is added is
obtained. When Coriolis force is applied, the beam deflects in a direction perpendicular to the
vibration direction, and a compressive stress is applied to one side and a tensile stress to the
other side symmetrically with respect to the central plane of the beam. Here, if the detection
electrodes are arranged symmetrically with respect to the central axis of the beam, the
piezoelectric signals resulting from the Coriolis force obtained from both electrodes have the
same absolute value and the opposite sign. Since the piezoelectric signal based on the vibration
of the beam is equal at both electrodes, it is possible to obtain only the signal due to the Coriolis
force by taking the difference between the outputs obtained from both electrodes.
[0011]
The present invention will be described in more detail by way of the following examples. FIG. 1
shows an example of a piezoelectric vibration angular velocity meter according to the present
invention. A silicon-made weight (3) is fixed to a substrate (1) made of silicon by four beams (2)
made of silicon. When an alternating voltage near the resonance frequency of the vibrator is
applied to the driving piezoelectric / electrostrictive thin film (4), the weight and the beam
vibrate in the direction indicated by V in the figure. At this time, when rotation occurs around an
axis indicated by Ω, the Coriolis force represented by equation (1) is generated in the direction
of Fc. The deflection produced in the beam is detected as a piezoelectric signal by the detection
piezoelectric / electrostrictive thin film (6).
[0012]
FIG. 3 will be described in more detail focusing on the portion of the beam to which the
piezoelectric / electrostrictive thin film for detection is fixed. FIGS. 3-1 is the figure which looked
at the part of a base | substrate (1) and a beam (2) from diagonally. Both the base and the beam
are covered with silicon nitride (8) which is a protective film when etching silicon. A lower
electrode (9), a piezoelectric / electrostrictive thin film (6), and an upper electrode (10) are
formed thereon. FIG. 3B is a view of the element cut from above in the plane of the lower
electrode, and the lower electrode is divided into two. In the figure, when Coriolis force is applied
in the direction of Fc, a tensile stress is exerted on one side (9a) and a compressive stress is
exerted on the other side (9b). Assuming that the upper electrode is used as a ground, the voltage
detected between the detection electrode 6a and the ground is va, and the voltage detected
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between the detection electrode 6b and the ground is vb, both of the va and vb are Coriolis force.
In addition to the accompanying signals, the signals resulting from the vibrations of the beam are
detected in a combined manner. Since the signal due to the Coriolis force is different in sign
between va and vb, taking the difference va−vb between them cancels the signal due to the
cantilever vibration, so that only the signal due to the Coriolis force can be read.
[0013]
The structure of the beam to which the driving piezoelectric / electrostrictive thin film is fixed is
basically the same as that described above except that the lower electrode is not divided. FIG. 2
shows another example of the piezoelectric vibration angular velocity meter based on the present
invention. A silicon weight (3) is fixed to a silicon base (1) by four silicon beams (2), and a driving
piezoelectric / electrostrictive thin film (5) is formed on the upper surface of the weight It is
done. Piezoelectric / electrostrictive thin films for detecting rotational angular velocities of two
orthogonal axes are fixed on two orthogonal beams. When an alternating voltage near the
resonance frequency of the vibrator is applied to the piezoelectric / electrostrictive thin film for
driving, the weight and the beam vibrate in the direction indicated by V in the figure. At this time,
when rotation occurs around an axis indicated by Ω, the Coriolis force represented by equation
(1) is generated in the direction of Fc. The deflection generated in the beam in the Ω direction is
detected by the detection electrode (6a). Similarly, in the rotation around the beam in the
direction perpendicular to Ω, the deflection generated in the beam is detected by the detection
electrode (6b). By connecting an appropriate detection circuit, it is possible to detect rotational
speeds in two directions orthogonal to one element.
[0014]
The detailed structure of the piezoelectric / electrostrictive thin film for detection is the same as
that described in the first embodiment.
[0015]
As described above, according to the present invention, a very small and inexpensive
piezoelectric vibration angular velocity meter can be obtained.
In particular, the vibrator does not have a weight by forming a plurality of beam shapes formed
in the same plane, supporting one side of the plurality of beam shapes by the base and
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supporting the weight on the other side. Since the mass is increased in comparison, the Coriolis
force is increased, and the sensitivity is improved.
[0016]
The piezoelectric vibration angular velocity meter according to the present invention is not only
used alone, but can be incorporated into a small system such as a micromachine or a microrobot.
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