Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2003-01-10
2004-06-01
Kwok, Helen C. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S504040, C073S504120
Reexamination Certificate
active
06742390
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an angular velocity sensor suitable for use in detecting an angular velocity.
2. Description of the Related Art
As a first example of a known angular velocity sensor, Japanese Unexamined Patent Application Publication No. 5-312576 discloses an angular velocity sensor which includes a substrate, a mass member which is retained by retaining beams attached to the substrate such that the mass member can move in two perpendicular directions, a vibration generator for vibrating the mass member in a vibration direction which is one of the two perpendicular directions that is parallel to the substrate, and an angular velocity detector which detects an angular velocity on the basis of a displacement of the mass member in a detection direction which is perpendicular to the vibration direction.
In such an angular velocity sensor, among X and Y axes which are parallel to the substrate and a Z axis which is perpendicular to the substrate, the mass member is vibrated in, for example, the X-axis direction with a predetermined amplitude. When an angular velocity about the Z axis is applied to the mass member while it is vibrating in the above-described manner, a Coriolis force is applied to the mass member in the Y-axis direction. Accordingly, the mass member moves in the Y-axis direction, and the angular velocity detector detects the displacement of the mass member on the basis of a capacitance change and outputs a detection signal corresponding to the angular velocity.
In this case, the mass member is retained by the retaining beams provided on the substrate in such a manner that the mass member can move (vibrate) in the X-axis direction. One end of each retaining beam is fixed to the substrate, and the other end is connected to the mass member. While the angular velocity sensor is activated, the retaining beams are deflected such that the mass member vibrates in the X-axis direction.
As a second example of a known angular velocity sensor, Japanese Unexamined Patent Application Publication No. 7-218268 discloses an angular velocity sensor which is called a tuning fork gyroscope, wherein a pair of mass members are arranged above a substrate and are vibrated in opposite phases, so that vibrations of the mass members transmitted to the substrate via retaining beams cancel each other.
In such a case, the retaining beams have a complex shape including a plurality of bent portions in order to retain each of the mass members at a predetermined position. One end of each retaining beam is split into two portions which are connected to the two mass members.
In the above-described first example, the mass member is connected to the substrate by the retaining beams. Therefore, when the mass member vibrates above the substrate, the vibration is easily transmitted to the substrate via the retaining beams.
Accordingly, when the angular velocity sensor is activated, vibration energy is transmitted to the substrate and the amplitude and the vibration velocity of the mass member are reduced. Thus, the Coriolis force due to the angular velocity is also reduced and the detection sensitivity decreases. In addition, when the vibration is transmitted to the substrate, the mass member may vibrate in the detection direction due to the vibration of the substrate even when no angular velocity is applied. Accordingly, the detected angular velocity often includes an error, and reliability of the angular velocity sensor decreases.
In the above-described second example, the mass members are vibrated in opposite phases so that the vibrations of the mass members transmitted to the substrate cancel each other. However, the mass members are retained by the retaining beams having a complex shape with bent portions, and it is difficult to manufacture the retaining beams having the same size, shape, deflection characteristics, etc.
Accordingly, in the second example, the mass members may vibrate in different manners due to the difference in size between the retaining beams, processing errors, etc. In such a case, the vibrations of the mass members transmitted to the substrate via the retaining beams cannot reliably cancel each other.
On the other hand, when an acceleration is applied to the angular velocity sensor in the Y-axis direction due to an external force, such as an impact force, while the angular velocity sensor is activated, the mass members may move in the Y-axis direction not only due to the Coriolis force caused by the angular velocity but also due to an inertial force caused by the acceleration. In such a case, although the detected displacement includes both an angular-velocity component and an acceleration component, the angular velocity is determined on the basis of the detected displacement.
Therefore, even a small impact applied to the angular velocity sensor causes an error corresponding to the acceleration component in the angular-velocity detection signal and decreases the accuracy in detecting angular velocity. Accordingly, it is difficult to ensure the reliability of the sensor.
If the acceleration applied to the angular velocity sensor includes a frequency component that is close to the vibration frequency of the mass members, the error due to the acceleration component cannot be reliably removed even by signal processing, such as synchronous detection, in which the detection signal is synchronously rectified at a period corresponding to the vibration frequency and integrated to separate the angular-velocity component.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a high-sensitivity, high-accuracy, and high-reliability angular velocity sensor which prevents vibrations of mass members from being transmitted to a substrate via retaining beams and in which the mass members vibrate in a stable vibrational state.
According to a preferred embodiment of the present invention, an angular velocity sensor includes a substrate, four mass members which face the substrate with a gap between each mass member and the substrate, the mass members being arranged along a Y-axis direction when X, Y, and Z axes that are perpendicular to each other are defined, retaining beams which connect the mass members such that the mass members can move in the X-axis direction, a fixing member disposed between the substrate and the retaining beams to fix the retaining beams to the substrate, a vibration generator which vibrates at least one of the mass members in the X-axis direction so that the adjacent mass members vibrate in opposite phases, and an angular velocity detector which detects an angular velocity on the basis of displacements of two of the four mass members which are disposed symmetrically about the central position in the Y-axis direction when the two mass members disposed symmetrically about the central position move in at least one of the Y and Z-axis directions by the angular velocity.
Accordingly, the four mass members can be connected to each other by the retaining beams along the Y-axis direction, which is perpendicular to the vibrating direction (X-axis direction). By vibrating at least one of the mass members by the vibration generator, the four mass members can be vibrated such that two adjacent mass members are in opposite phases. The retaining beams which connect the mass members are provided with vibration nodes, which are maintained at predetermined positions when the retaining beams vibrate along with the mass members.
Since the two mass members which are disposed symmetrically about the central position (at the central region or at the outside in the Y-axis direction) vibrate in opposite phases, these two mass members move in the opposite directions due to a Coriolis force when the angular velocity is applied, and move in the same direction due to an inertial force when an acceleration is applied. Therefore, the displacements thereof in the same direction (acceleration components) can be canceled by calculating the difference between the
Konaka Yoshihiro
Mochida Yoichi
Keating & Bennett LLP
Kwok Helen C.
Murata Manufacturing Co. Ltd.
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