Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1997-05-09
2001-06-26
Chapman, John E. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S504120
Reexamination Certificate
active
06250158
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to angular velocity sensors. More particularly, this invention pertains to a batch processed silicon beam array angular velocity sensor based upon the Coriolis sensing method.
2. Description of the Prior Art
Numerous arrangements exist for measuring rotation rate about a preselected axis in inertial space. Such apparatus, commonly designated a gyroscope, forms an essential element of any inertial navigation system. Gyroscopes include, for example, complex and difficult-to-manufacture gimballed spinning rotors, strapdown sensors such the ring laser and fiber optic gyroscopes. All of the above-named rate sensing devices are characterized by high cost, large size and power consumption, complexity of manufacture, expense of maintenance.
Other systems exist for measuring an input rotation rate about a preselected axis which are based upon the principle of the Focoult pendulum that was developed over one hundred years ago. A rate sensor based upon that principle, marketed under the trademark “GYROTRON”, was developed by the Sperry Gyroscope Corporation. The device, which, as all gyroscopes of the balanced resonant sensor or tuning fork type, provides significantly greater mechanical and operational simplicity than the above-mentioned types, operates on the principle that, when a tuning fork is rotated about its central axis, it possesses an angular momentum that is equal to the product of the rotation rate and the rotational moment of inertia. The reference motion of the tines of the tuning fork changes the moment of inertia cyclically. As a result, the rotation rate must change cyclically in a complementary fashion to conserve the angular momentum. Thus, the physical operation of the tuning fork type sensor is similar to that of a spinning ice skater who spins faster by pulling his arms in and slows down by extending them. Consequently, in a tuning fork sensor the outward-and inward radial vibration of the tines is converted into a rotational vibration whose amplitude is proportional to the input rate. A closed loop vibrating rotation rate sensor is disclosed in U.S. Pat. No. 5,056,366 of Samuel N. Fersht et al. entitled “Piezoelectric Vibratory Rate Sensor.”
Many useful applications exist for angular velocity sensors that do not require gyroscopic accuracy. Such applications are found in flight control systems, automobile skid control systems, video camera stabilization and virtual reality systems.
A type of angular velocity sensing device of lesser complexity whose operation also is based upon the measurement of Coriolis forces is disclosed in U.S. Pat. No. 3,520,195 of Stephen W. Tehon titled “Solid State Angular Velocity Sensing Device” and discussed by William D. Gates in an article titled “Vibrating Angular Rate Sensor May Threaten the Gyroscope”,
Electronics,
pp. 130-134 (Jun. 10, 1968). This device comprises a square metallic rod that is suspended at its nodal supports from a metal frame. The rod is driven at its fundamental frequency by a piezoelectric drive electrode fixed to one surface while a piezoelectric transducer that serves as a output signal pickoff is fixed to an orthogonal surface. While simple in design and concept, this device is not suitable for batch processing. Further, the piezoelectric elements that serve, inter alia, as drive and pickoff electrodes are bonded to the metallic surfaces of the vibrating rod by organic adhesive. Such adhesive materials absorb energy, causing a reduction in the Q of the vibrating rod. As a consequence, more energy must be input into the rod for the purpose of overcoming damping forces that work against vibration driving forces.
A variation of the VYRO is disclosed in an article by Brian Dance, “Piezoelectric Ceramic Elements for Compact Gyroscope”,
Design News,
pgs. 113, 114 (Sep. 20, 1993). The device described comprises an angular velocity sensor of Murata Ltd. of the United Kingdom whose sensing element is formed of “ELINVAR”, a nickel-chromium steel alloy. The bar may be of either circular or equilateral triangle cross section. A number of piezoelectric elements are fixed to the sensing element. Again, this device is not suitable for batch processing and is subject to performance degradation due to the presence of organic material for bonding the piezoelectric transducer elements to the vibrating sensor.
SUMMARY OF THE INVENTION
The preceding and other shortcomings of the prior art are addressed by the present invention which provides, in a first aspect, an angular velocity sensor. Such sensor includes an elongated beam. A frame has an internal aperture for accommodating the beam. Means are provided for suspending the beam within the aperture. Means, fixed to the beam, is provided for flexibly driving the beam as well as for detecting the presence and amplitude of magnitude of Coriolis force exerted thereupon. The beam, the means for suspending and the frame are an integral structure comprising silicon.
In a second aspect, the present invention comprises a monolithic angular velocity sensor. Such sensor including a plurality of sensor elements formed within a substantially planar silicon substrate. Each sensor element includes an elongated beam. The major axes of the elongated beam of the sensor elements are aligned parallel to one another.
In a third aspect, the present invention provides a monolithic angular velocity sensor for sensing rotation rates about two orthogonal axes. The sensor includes a first sensor element and a second sensor element formed within a silicon substrate. Each of such sensor elements includes an elongated beam. The major axes of the elongated beams of said sensor elements are aligned orthogonal to one another.
In a fourth aspect, the present invention provides a monolithic angular velocity sensor array for sensing rotation about two orthogonal axes. A first array of sensor elements includes a first plurality of elongated beams aligned parallel to one another. A second array comprises a second plurality of elongated beams aligned parallel to one another. The axes of the beams of the first array are aligned orthogonal to those of the second array. Each array is integral with a silicon substrate.
The foregoing and other features and advantages of this invention will become further apparent from the detailed description that follows. This written description will be accompanied by a set of drawing figures. Numerals of the drawing figures, corresponding to those of the written description, point to the various features of the invention. Like numerals point to like features of the invention throughout both the written description and the drawing figures.
REFERENCES:
patent: 3520195 (1970-07-01), Tehon
patent: 4836023 (1989-06-01), Oikawa
patent: 5056366 (1991-10-01), Fersht et al.
patent: 5505084 (1996-04-01), Greiff et al.
patent: 5675083 (1997-10-01), Nakamura
patent: 61-114123 (1986-05-01), None
patent: 5333038 (1993-12-01), None
patent: 07131280 (1995-05-01), None
patent: 08233582 (1996-09-01), None
William D. Gates, “Vibrating Angular Rate Sensor May Threaten the Gyroscope”,Electronics, pp. 130-134 (Jun. 10, 1968).
Brian Dance, “Piezoelectric Ceramic Elements for Compact Gyroscope”,Design News, pp. 113, 114 (Sep. 20, 1993).
D. L. Polla, “Integrated Ferroelectric Micromechanical Systems”,Science and Technology of Electroceramic Thin Films, pp. 413-426 (1995).
P. Schiller et al., “Integrated Piezoelectric Microactuators Based on PZT Thin Films”,Seventh International Conference on Solid-State Sensors and Actuators, pp. 154-157.
P. Muralt et al., “Fabrication and Characterization of PZT Thin Films For Micrometers”,Proceedings of The Eight International Conference on Solid-State Sensors and Actuators and Eurosensors IX, pp. 397-400 (Jun. 25-29, 1995).
Chapman John E.
Kramsky Elliott N.
Litton Systems Inc.
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