Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1999-08-18
2002-04-30
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S504120, C310S329000
Reexamination Certificate
active
06378368
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to oscillation gyroscopes having PZT (lead (Pb) Zirconate Titanate) thin films.
A conventional tuning-fork type oscillation gyroscope is shown in
FIG. 8
, while a vibrating reed type gyroscope is shown in FIG.
9
. As shown in
FIG. 8
, the tuning-fork type oscillation gyroscope
21
includes a pair of driving piezoelectric ceramic plates
23
, which are arranged on the ends of a connection plate
22
. The piezoelectric ceramic plates
23
are parallel to each other and their planes are normal to the X-axis. A detecting piezoelectric ceramic plate
24
is formed integrally with each piezoelectric ceramic plate
23
extending upward from the top center of the ceramic plate
23
. The ceramic plates
24
lie in a plane normal to the Y-axis. The X-axis and the Y-axis are perpendicular to each other.
When an alternating voltage is applied to the piezoelectric ceramic plates
23
, the piezoelectric ceramic plates
23
oscillate in the direction of X-axis. If torque is applied to the oscillation gyroscope
21
about the Z-axis, the piezoelectric plates
24
distort and produce a voltage corresponding to the distortion. The voltage is detected to obtain the force applied to the piezoelectric plates
24
. The force is referred to as Coriolis force Fc and is generally represented by the following formula (1):
Fc=2mV×&OHgr; (1)
In the formula, m indicates the mass of the oscillation gyroscope
21
, V indicates the vibrational speed, and &OHgr; indicates the angular velocity of the oscillation gyroscope
21
about the Z-axis. The angular velocity &OHgr; is obtained when the mass m, the vibrational speed V, and the force Fc have been obtained.
As shown in
FIG. 9
, a vibrating reed type oscillation gyroscope
21
includes a rectangular column-like vibrating reed type vibrator
26
, which is made of a constant elasticity metal. A pair of driving piezoelectric ceramic plates
27
(only one shown in the drawing) are adhered to opposing side surfaces, which are separated by 180 degrees, of the vibrator
26
. A pair of detecting piezoelectric ceramic plates
28
are adhered to the remaining two side surfaces (only one shown in the drawing). The application of an alternating voltage to the piezoelectric ceramic plates
27
vibrates the vibrating reed type vibrator
26
in the X-axis direction. When torque is applied to the oscillation gyroscope
21
about the Z-axis, the detecting piezoelectric ceramic plates
28
distort and generate a voltage corresponding to the distortion. The voltage is detected to obtain the Coriolis force applied to the piezoelectric ceramic plates
28
.
The piezoelectric plates
23
,
24
,
27
,
28
are formed from bulk PZT (lead zirconate/titanate, or ceramics containing a solid solution of lead titanate and lead zirconate). However, it is difficult to form bulk PZT into thin components and thus difficult to reduce the entire size of the oscillation gyroscope.
Additionally, when adhering the piezoelectric ceramic plates
27
,
28
to form the oscillation gyroscope like the vibrating reed type oscillation gyroscope
25
, the adhering of the piezoelectric ceramic plates
27
,
29
adds to the number of manufacturing steps. Furthermore, the adhering accuracy, or the precision of the adhering position is low. This affects the sensitivity of the oscillation gyroscopes
21
,
25
. Thus, it is difficult to manufacture oscillation gyroscopes having uniform accuracy. If the vibrator has a three-dimensional structure, it is difficult to attach the bulk PZT to an arbitrary location. This restricts the locations where the bulk PZT can be attached.
As apparent from formula (1), an increase in the mass m of the oscillation gyroscope increases the Coriolis force Fc. This increases the distortion amount of the detecting piezoelectric ceramics and increases the detecting voltage of the oscillation gyroscope. In other words, the detecting sensitivity of the oscillation gyroscope increases. It is thus preferred that the oscillation gyroscope have a greater mass to obtain a higher sensitivity. However, if the oscillation gyroscope employs bulk PZT, the mass cannot be increased unless the size of the substrate, which forms the bulk PZT, is increased. Hence, there is a limit to an increase in the sensitivity.
In addition, as apparent from formula (1), an increase in the vibrational speed V increases the Coriolis force Fc. This increases the distortion amount of the detecting piezoelectric ceramics and increases the detecting voltage of the oscillation gyroscope, which in turn, increases the detecting sensitivity of the oscillation gyroscope. However, for example, in the case of a vibrating reed type oscillation gyroscope, if the substrate of the bulk PZT is made thinner, the rigidity of the substrate decreases. Hence, the piezoelectric device is apt to twist and interfere with accurate oscillations. Furthermore, accurate detection is hindered when the detecting piezoelectric device is distorted and twisted.
Accordingly, an oscillation gyroscope
31
, which is compact, resists twisting, and increases sensitivity, has been proposed as shown in FIG.
7
. The oscillation gyroscope
31
has a rectangular column-like shape and is made of an elastic metal. An opening
34
extends through the lower side (fixed side) of the gyroscope
31
, while a perpendicular opening
35
extends through the upper side (free side) of the gyroscope
31
. The gyroscope
31
has a first parallel plate portion
32
corresponding to the opening
34
and a second parallel plate portion
33
corresponding to the opening
35
. Titanium films are formed on the surfaces of the first and second parallel plate portions
32
,
33
, while PZT thin films
36
are formed on the titanium films. A plurality of electrodes
37
, preferably made of aluminum, are formed on each PZT thin film
36
, with a lead wire (not shown) connected directly to each electrode
37
. The first parallel plate portion
32
serves as a driving portion for producing vibrations, while the second parallel plate portion
33
serves as a detecting portion. Voltage is applied to the first parallel plate portion
32
to produce vibrations and cause the PZT thin films
36
of the second parallel plate portion
33
to generate a voltage, which is output via the lead wires (not shown) that are connected to the electrodes
37
.
However, the connection of the lead wires changes the rigidity of the second parallel plate portion
33
. This affects the output voltage generated by the PZT thin films
36
. This leads to a shortcoming in which the detecting characteristics cannot be stabilized. The connection of the lead wires also affects the vibrating characteristics of the first parallel plate portion
32
. This leads to a shortcoming in which the driving characteristic cannot be stabilized.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide an oscillation gyroscope having a PZT thin film with uniform characteristics.
To achieve the above objective, an oscillation gyroscope according to the present invention comprises a substrate made of an elastic metal and having a substantially rectangular shape, the substrate having first to fourth side surfaces arranged in the circumferential direction, wherein the first side surface and the third side surface, and the second side surface and the fourth side surface are located on opposite sides, the substrate having a fixed end for fixing the oscillation gyroscope, and a free end located on the opposite side of the fixed end, the substrate having a first opening extending from the first side surface to the third side surface at the fixed end side, a first parallel plate portion located on both sides of the first opening and having a pair of side plates including the second and fourth side surfaces, the substrate having a second opening extending from the second side surface to the fourth side surface at the free end side, a second parallel plate portion located on both sides of the second opening and
Itoigawa Koichi
Iwata Hitoshi
Buyan Robert D.
Kabushiki Kaisha Tokai Rika Denki Seisakusho
Kwok Helen
Stout, Uxa Buyan & Mullins, LLP
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