Gyroscope and input unit using the same

Details Gyroscope and input unit using the same Gyroscope and input unit using the same

2001-05-22

2003-07-01

Kwok, Helen (Department: 2856)

Measuring and testing

Speed, velocity, or acceleration

Angular rate using gyroscopic or coriolis effect

C310S370000

Reexamination Certificate

active

06584843

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to gyroscopes and input devices using the gyroscopes. More specifically, the present invention relates to a gyroscope in which displacements of the tines of a tuning fork, which occur when an angular velocity is applied, are detected by using variations in capacitances, and to an input device using the gyroscope.
2. Description of the Related Art
Conventionally, gyroscopes in which a tuning fork formed of a conductive material such as silicon, etc., is used are known. In these types of gyroscopes, the tines of the tuning fork are vibrated in one direction, and vibrations thereof in the direction perpendicular to this direction, which occur due to Coriolis force when an angular velocity about the central axis parallel to the longitudinal direction of the tines is input, are detected. The vibrations which occur due to Coriolis force correspond to the angular velocity applied. Thus, the gyroscopes may be used as angular velocity sensors, and may be used in, for example, coordinate input devices for personal computers.
FIG. 15
is a schematic diagram showing a construction of a conventional gyroscope, which is disclosed in Japanese Unexamined Patent Application Publication No. 11-311520 which is assigned to the present assignee. As shown in
FIG. 15
, a gyroscope
100
includes a tuning fork
103
having three tines
101
and a supporting portion
102
which connects base ends of the tines
101
. The tuning fork
103
is formed of silicon which has electric conductivity. The supporting portion
102
is fixed on a substrate
104
formed of a glass, and drive electrodes
105
a
,
105
b
,
105
c
, and
105
d
, which are also formed of silicon, are disposed between and the tines
101
and outside the tines
101
at both ends. The drive electrodes
105
a
and
105
c
are electrically connected with each other, and the drive electrodes
105
b
and
105
d
are also electrically connected with each other. An alternating voltage having opposite phases is applied to the pair of drive electrodes
105
a
and
105
c
and to the pair of the drive electrodes
105
b
and
105
d
. Accordingly, electrostatic attractions occur when the voltage is applied to the drive electrodes
105
a
to
105
d
, and each of the tines
101
is vibrated in a direction parallel to the surface of the substrate
104
. This direction will be referred to as the lateral direction in the descriptions hereof.
In the gyroscope
100
, when an angular velocity about an axis parallel to the longitudinal direction of the tines
101
is input while the tines
101
vibrate in the lateral direction, vibrations of the tines
101
in the direction perpendicular to the substrate
104
occur. This direction will be referred to as the thickness direction in the descriptions hereof. The vibrations of the tines
101
in the thickness direction are detected by detection electrodes
106
, which are disposed under the tines
101
. The detection electrodes
106
are formed on the substrate
104
as metal films of chromium, etc. When the tines
101
vibrate in the thickness direction, the gaps between the tines
101
and the detection electrodes
106
vary, so that electrostatic capacitances between the tines
101
and the detection electrodes
106
also vary. Therefore, by obtaining the variations of electrostatic capacitances in terms of electric signals, the input angular velocity may be determined.
Generally, there are two types of such gyroscopes. In one type, which is referred to as a lateral direction driving type, the tines are driven in the lateral direction, and vibrations thereof in the thickness direction are used for the detection. In the other type, which is referred to as a thickness direction driving type, the tines are driven in the thickness direction and the vibrations thereof in the lateral direction are used for the detection. The gyroscope
100
shown in
FIG. 15
is of the former type.
In the gyroscopes having the above-described construction, the drive electrodes are disposed at both sides of each of the tines. Thus, gaps between the tines cannot be made sufficiently small. More specifically, when the width of the drive electrodes is x
1
, and the gap between the drive electrodes and the tines is x
2
, the gap G between the tines is calculated as G=x
1
+2x
2
. There are limits determined by silicon processes using typical technologies for manufacturing semiconductor devices regarding the amounts by which x
1
and x
2
can be reduced. Accordingly, there is also a limit to how much the gap G between the tines can be reduced.
On the other hand, it is known that in three-tine type tuning forks, a “Q value”, which indicates a degree of resonance in devices such as tuning forks, may be increased by reducing the gap G between the tines. When the Q value is increased, efficiency at which electric energy input to the device is converted into vibration energy is improved. Thus, in the lateral direction driving type gyroscope, a large driving force can be obtained using a small driving voltage. Therefore, the driving voltage can be reduced.
As described above, it is expected that various advantages can be obtained by reducing the gap between the tines; for example, the size of the device and the driving voltage can be reduced. In the conventional gyroscope, however, there is a limit to how much the gap between the tines can be reduced, and it has not been possible to achieve a reduction of the gap.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a low-cost, lateral direction driving type gyroscope in which the above-described various effect can be obtained, and an input unit using the gyroscope.
In order to attain the above-described object, according to an aspect of the present invention, a gyroscope includes a tuning fork having vibrating beams; a pair of substrates which are disposed one at each side of the tuning fork, at least the surfaces thereof being insulative; drive electrodes which are provided on each of the substrates in such a manner that parts of the drive electrodes oppose the vibrating beams and the remaining parts of the drive electrodes protrude from the vibrating beams, the drive electrodes being capacitively coupled to the beams and driving the vibrating beams in a direction parallel to the substrates; and detection electrodes which are capacitively coupled to the vibrating beams, and which detect displacements of the vibrating beams in a direction perpendicular to the vibrating direction of the vibrating beams.
The gyroscope of the present invention is assumed to be the lateral direction driving type. In addition, similar to the conventional type, the principle for driving the vibrating beams is based on an electrostatic attraction force. In the conventional gyroscope, vibrating beams (which corresponds to the above-described tines) of the tuning fork are driven by using attraction forces applied to the opposing surfaces of the vibrating beams and the drive electrodes. In contrast, in the gyroscope according to the present invention, the drive electrodes are disposed in such a manner that the parts thereof oppose the vibrating beams of the tuning fork and the remaining parts thereof protrude from the vibrating beams. Thus, when a voltage is applied between the vibrating beams and the drive electrodes, the vibrating beams are driven by forces applied in directions in which the opposing areas between the vibrating beams and the drive electrodes are increased.
In order to describe this more specifically, with reference to
FIG. 11
, a case is considered in which a vibrating beam and a drive electrode have surfaces which are shifted relative to each other in the horizontal direction (in
FIG. 11
) and which include opposing parts
1
and
2
. When the size of the surfaces in the direction perpendicular to the shifting direction thereof is g and the distance between the surfaces is d, the electrostatic attraction force F applied in a direction in which the area of the opposing

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