Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-03-09
2001-11-27
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S504120
Reexamination Certificate
active
06321598
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of Japanese Patent Applications No. 11-66947 filed on Mar. 12, 1999, and No. 11-345134 filed on Dec. 3, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to angular velocity sensor devices such as an automotive control system, an automotive tipping detection system, a navigation system, and a hand-blurring preventing system for an optical instrument, which detect angular velocities.
2. Description of the Related Art
There is proposed an oscillation type angular velocity sensor device, which is produced by a micro-machine technique for purposes of size reduction and low cost. Such sensor device typically has a sensor element shown in FIG.
23
. The sensor element has a sensor chip produced using an SOI substrate to have a frame portion J
1
. An oscillator J
4
is supported by driving beams J
2
and detection beams J
3
to hang across the frame portion J
1
. An arrow a
0
indicates a drive oscillation direction of the oscillator J
4
and an arrow a
1
indicates a detecting oscillation direction of the oscillator J
4
, i.e., a direction in which a Coriolis force is produced.
The oscillator J
4
having a mass m is oscillated in the drive oscillation direction perpendicular to an angular velocity axis z, and the Coriolis force of 2 mV&OHgr;, which is generated in the direction perpendicular to the drive oscillation direction and the angular velocity axis z, is detected by displacement of the oscillator J
4
in the Coriolis force generating direction. Here, V represents a velocity of the oscillator J
4
, and &OHgr; represents an angular velocity.
In the angular velocity sensor device described above, however, material values such as a damping coefficient and a spring constant of the sensor element change in accordance with a change in ambient temperature and elapsed time. This may cause a drift of zero point of the angular velocity output value and a change in output sensitivity. To avoid these problems, the sensor device can have a function to monitor an amplitude of the oscillator J
4
to thereby oscillate the oscillator J
4
with a constant amplitude. The sensor device further can have a function to detect a temperature to adjust the sensitivity in accordance with the detected temperature. These functions, however, require an oscillation monitor, a temperature sensor, and circuits therefor, resulting in increased sensor size and increased cost.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above limitations. An object of the present invention is, in an oscillation type angular velocity sensor device, to prevent a drift of zero point of an angular velocity output value and a change in output sensitivity while achieving size reduction and low cost of the sensor device.
According to the present invention, an angular velocity sensor device has a sensor element including a movable portion. The movable portion is oscillated by driving on a specific plane and receives a Coriolis force generated in a specific direction parallel to the specific plane when an angular velocity is generated around an angular velocity axis perpendicular to the specific plane. The sensor device further has a circuit portion electrically connected to the sensor element to receive an output signal from the sensor element. The circuit portion determines the angular velocity by a first signal caused by the Coriolis force and a second signal not caused by the Coriolis force, based on the output signal.
The first signal and the second signal vary in accordance with a change in ambient temperature and elapsed time similarly to each other. Therefore, the angular velocity determined as an output value by the first signal and the second signal used as the reference is prevented from having a drift of zero point thereof and a change in sensitivity. Because it is not necessary to perform another correction by an additional circuit, size reduction and low cost of the sensor device can be achieved.
Preferably, the movable portion includes an oscillator, which is oscillated by the Coriolis force in a detecting direction non-parallel to the specific direction in which the Coriolis force is generated. Accordingly, a force component caused by the Coriolis force and a force component not caused by the Coriolis force are applied to the oscillator in the detecting direction, so that the sensor element outputs the output signal compound from the first signal and the second signal. More preferably, the movable portion includes first and second oscillators respectively oscillated by the Coriolis force in first and second detecting directions defining first and second angles larger than zero with the specific direction. In this case, the sensor element output first and second output signals corresponding to the first and second oscillators.
Preferably, the movable portion includes a first oscillator which is oscillated by driving in a drive direction and a second oscillator which is oscillated by the Coriolis force in a detecting direction defining a specific angle larger than zero with the specific direction. More preferably, the first oscillator is oscillated in the drive direction with a first resonance frequency and the second oscillator is oscillated in the detecting direction with a second resonance frequency approximately equal to the first resonance frequency. Accordingly, a magnitude of detecting oscillation can be increased, and the force components caused by and not caused by the Coriolis force and applied to the second oscillator in the detecting direction can be increased. The first signal and the second signal are enhanced, resulting in high sensitivity and high accuracy.
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patent: 5313835 (1994-05-01), Dunn
patent: 5329815 (1994-07-01), Dunn et al.
patent: 5359893 (1994-11-01), Dunn
patent: 5377544 (1995-01-01), Dunn
patent: 5511419 (1996-04-01), Dunn
patent: 5604312 (1997-02-01), Lutz
patent: 5734105 (1998-03-01), Mizukoshi
patent: 6070463 (2000-06-01), Moriya et al.
patent: 6-34375 (1994-02-01), None
patent: 8-114456 (1996-05-01), None
patent: 96/39615 (1996-12-01), None
patent: 97/02467 (1997-01-01), None
U.S. application No. 09/458,954, Higuchi et al., filed Dec. 10, 1999.
Ito Hiroaki
Iwaki Takao
Ohya Nobuyuki
Denso Corporation
Law Office of David G. Posz
Moller Richard A.
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