Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-05-04
2002-08-27
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S379010
Reexamination Certificate
active
06439052
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a gyroscope and an input apparatus having the gyroscope, more particularly relates to a gyroscope that detects the displacement of a leg of a tuning fork caused particularly when the angular velocity is supplied in the form of change in capacitance and an input apparatus having the gyroscope.
2. Description of the Related Art
Heretofore, the gyroscope having a tuning fork formed of conductive material such as silicon has been known. The gyroscope of this type detects the vibration in the direction perpendicular to the vibration direction caused by Coriolis force when a leg of a tuning fork is vibrated in one direction and the angular velocity with the center axis in the longitudinal direction of the leg is supplied during vibration. Because the magnitude of the vibration caused by the Coriolis force corresponds to the magnitude of the angular velocity, the gyroscope can be used as an angular velocity sensor, it can be applied to, for example, the coordinate input apparatus of a personal computer.
FIG. 19
is a diagram for illustrating the structure of a tuning fork that is the main component of the conventional gyroscope. As shown in
FIG. 19
, the tuning fork
100
of this example has three legs
101
and a support
102
which connects the three legs to base ends of each leg
101
and is formed of silicon that has been rendered conductive. The tuning fork
100
is fixed to a substrate
103
with the support
102
, and driving electrodes (not shown in the drawing) are provided under the corresponding legs
101
respectively. As the result, the electrostatic attractive force caused when a voltage is applied to a driving electrode causes vibration of each leg
101
in the vertical direction.
In this gyroscope, the angular velocity having the rotation axis in the longitudinal direction of the leg
101
supplied to the leg during vibration in the vertical direction causes the vibration in the horizontal direction, the vibration in the horizontal direction is detected by means of a pair of detecting electrodes
104
disposed on both sides of each leg
101
. In detail, when the gap between the detecting electrode disposed on one side of a leg
101
and the leg
101
is narrowed and a gap between a detecting electrode
104
disposed on the other side of the leg
101
and the leg
101
is widened concomitantly with horizontal displacement of the leg
101
, two pairs of electrostatic capacitance formed by the detecting electrodes
104
and legs
101
are changed. The magnitude of input angular velocity is detectable based on the electrostatic capacitance change.
In the case of the gyroscope having the structure described herein above, the gap between a leg
101
and an adjacent leg
101
(referred to as inter-leg gap hereinafter) cannot be narrowed unlimitedly because detecting electrodes are provided on both sides of each leg
101
. The inter-leg gap is G=2x
1
+3x
2
wherein the width of a detecting electrode
104
is denoted by x
1
and the gap between a detecting electrode
104
and a leg
101
and the gap between detecting electrodes adjacent each other are denoted by x
2
. Because of work limit of x
1
and x
2
in silicon work to which general semiconductor device fabrication technique is applied, the narrow inter-leg gap G has been limited.
On the other hand, it has been found that the reduction of the inter-leg gap G of a three-leg tuning fork leads to the increased “Q value” that is the performance index for representing the magnitude of resonance of a device of this type. The increased Q value contributes not only to improvement of detection sensitivity of angular velocity but also to improvement of conversion efficiency from the electric energy supplied to a device to the vibration energy, and as the result the driving voltage can be reduced.
However, though it is estimated that the reduced inter-leg gap is advantageous in miniaturization of a device, improvement of detection sensitivity, and reduction of driving voltage, because of the limitation on the reduction of the inter-leg gap of the conventional gyroscope, the increased Q value has not been realized.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above-mentioned problem, and it is the object of the present invention to provide a high-quality and low-cost gyroscope that is variously advantageous as described herein above and an input apparatus that uses the gyroscope.
To achieve the above-mentioned object, a gyroscope of the present invention is characterized by comprising a tuning fork formed of conductive material having vibrators and a support for connecting the base ends of the vibrators, driving electrodes for driving the vibrators in capacitance coupling with the vibrators, and at least one detecting electrode for each vibrator disposed correspondingly to the vibrator so as to face at least partially to the end face of the vibrator in the extending direction for detecting the capacitance formed between the detecting electrode and the end face.
The gyroscope of the present invention operates based on the detection principle that the vibration of a vibrator (corresponding to the above-mentioned “leg”) of a tuning fork is detected in the form of capacitance change like the conventional gyroscope. Usually, the capacitance C is represented as shown in the following.
C=&egr;·
(
S/d
) (1)
wherein &egr; denotes a dielectric constant, S denotes the surface of an electrode, and d denotes the gap between electrodes.
In the case of a conventional gyroscope, the change of the gap between a leg and a detecting electrode concomitant with vibration, namely capacitance change due to the change of the gap between electrodes d in the above-mentioned equation (1), is detected. On the other hand, in the case of a gyroscope of the present invention, the change of the facing area of a leg to a detecting electrode concomitant with vibration, namely capacitance change due to the change of the electrode area S in the above-mentioned equation (1) is detected. The detection in the conventional gyroscope is different from the detection in the gyroscope of the present invention in that point.
In other words, the gyroscope of the present invention is structurally featured in that a detecting electrode at least partially facing to the end face of a vibrator in the extending direction to form a capacitance between the detecting electrode and the end face of the vibrator is provided. Because of the structure, the vibrators of the tuning fork are vibrated when a voltage is applied to the driving electrode, and when the angular velocity having the rotation axis in the longitudinal direction of the vibrator is supplied in that state, vibration in the direction perpendicular to the above-mentioned vibration direction is caused. At that time, because the end face of the vibrator is facing to the detecting electrode, and the facing area of the end face to the detecting electrode changes concomitantly with vibration of the vibrator, the capacitance change is caused. The angular velocity can be detected by detecting the capacitance change.
Therefore, in the case of the gyroscope of the present invention, the detecting electrode may be provided on the extension line in the longitudinal direction of the vibrator, and it is not necessary to provide the detecting electrode between a leg and an adjacent leg unlike the conventional gyroscope. As the result, the inter-leg gap can be minimized to the work limit of the material of the tuning fork, for example, work limit of silicon, and Q value is thereby increased, the detection sensitivity is improved, and the driving voltage is reduced. Of course, the device is miniaturized.
At least one detecting electrode may be provided for each vibrator. In other words, in the case that one detecting electrode is provided, the capacitance change of one capacitor involving one detecting electrode and one vibrator may be detected. In the case that two detecting electrodes are prov
Abe Munemitsu
Esashi Masayoshi
Murata Shinji
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Kwok Helen
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