A force transducer in which a deflectable seismic mass is supported on a frame by support means is disclosed. The seismic mass at rest includes a plane and when the seismic mass is deflected by any force the mass always retains the plane parallel to the rest position. Any deflection of the seismic mass is purely topographically translational movement with no rotational movement allowed. The invention allows three identical structures to be etched onto a flat semiconductor wafer and yet can be used to determine accelerations in three perpendicular directions. As the structures deflect, the surfaces of their seismic masses always remain parallel to the wafer surface. This enables measurement of the deflection to be made easily, for example by depositing electrodes on the surfaces of the seismic masses and fixed surfaces (such as deflection stops) and measuring the change in capacitance between the electrodes. Cross coupling effects will be negligible since each transducer is stiff in all directions except the sensitive direction.
The accelerometer includes an inertial mass, a fixed base and at least one or more supports/sensors for supporting the mass from the base rendering the support system statically indeterminate. The supports/sensors are preferably double-ended dual beam tuning forks suspended between mounting pads and vibrated by an oscillator. By adding one or more supports/sensors beyond those supports/sensors necessary for a statically determinate support system, the support system is rendered statically indeterminate and therefore sensitive in one or more directions.
A method for calibrating a sensor includes providing a fixture that defines a first coordinate system, providing a chassis, and orienting a plurality of sensor elements to form a misaligned coordinate system, wherein the misaligned coordinate system axes are oriented at other than right angles with respect to each other. The method also includes coupling the sensor to be calibrated to the fixture and mathematically compensating the misaligned coordinate system to correspond with the first coordinate system.
A long-period weak-motion inertial sensor includes a frame having a frame mounting surface, a movable mass having a movable mass mounting surface, a transducer for sensing displacements of the movable mass with respect to the frame, and a monolithic flexure element for suspending the movable mass in the frame. The monolithic flexure element includes: a stiff frame integral clamp attachable to the frame mounting surface of the frame, a stiff movable mass integral clamp attachable to the movable mass mounting surface of the movable mass, and a stiffest flexible region for operatively connecting the frame integral clamp to the movable mass integral clamp. The frame and movable mass mounting surfaces do not overlap the stiffest flexible region, thereby minimizing the generation of creep and hysteresis noise. The variation in stiffness of the monolithic flexure element is controlled by varying thickness along the length of the flexure element.
A micromachined silicon tuned accelerometer gyro is formed out of silicon wafers, by micromachining. The top and bottom cover which include driver, forcer, tuning and guard ring elements mounted therein are micromachined in arrays on silicon-on-insulator (SOI) wafers. The center (driver and sensing) element between the top and bottom is micromachined in an array of four inch diameter silicon wafers. The driver and sensing structure is a tuned pendulum attached by flexure joints to a vibrating structure which is in then suspended by a parallelogram dither suspension. The pendulum is tuned by adjusting the magnitude of a d.c. signal to match the natural frequency of the pendulum to the natural frequency of the vibrating structure. The dither suspension flexures of the vibrating structure is uniquely defined and easily machined but yet provides a dither suspension that restrains the vibrating structure within its vibrating plane with no harmonic distortion.
