Variable Sampling Verification Protocols for High Rate MEMS Gyroscope Lots
Variable sampling verification for high-rate MEMS gyroscopes optimizes lot acceptance by deriving continuous quality indices from dynamic rate table test samples.
Direct Drive Rate Table
Precision Platform
A high performance motion simulator provides precise angular velocity and positioning for the calibration of inertial sensors. This direct drive rate table utilizes a brushless motor coupled directly to the rotation shaft without the use of gears or belts. It eliminates the mechanical backlash and friction typically associated with traditional drive systems.
The instrument delivers high torque and exceptional speed stability across a wide dynamic range. This capability is required for testing high grade gyroscopes and accelerometers used in aerospace applications. The operation of the system stops when the payload weight exceeds the bearing capacity or the torque limit.
Mechanical Control
Motion is governed by a high resolution optical encoder that provides feedback to a digital servo controller. When operating a direct drive rate table, the controller adjusts the current to the motor to maintain the commanded angular rate within a tight tolerance. The absence of gearing allows for high bandwidth response, which is useful for simulating complex motion profiles or vibration.
Calibration of the table involves verifying the rate accuracy and the wobbling of the axis relative to a known gravitational vector. Drift in the internal electronics is minimized through active thermal management of the motor and the drive electronics. Technicians use laser interferometers to measure the angular positioning accuracy during the qualification process.
This verification ensures that the sensor under test experiences a pure rotation without unwanted linear acceleration.
Test Environment
Challenges in the installation arise from the need for a stable and level foundation to prevent seismic noise from affecting the measurements. For a direct drive rate table, the floor must be isolated from building vibrations caused by air conditioning or heavy machinery. Interference from magnetic fields generated by the high torque motor is mitigated by specialized shielding and careful sensor placement.
The alignment of the table axis with the local vertical is verified using precision spirit levels or electronic inclinometers. A certificate of calibration for the table is issued by a metrology lab to attest to its traceability to national standards. Periodic maintenance involves checking the health of the bearings and the integrity of the electrical slip rings.
These components allow signals to pass from the rotating sensor to the stationary data acquisition system.
Qualification Boundary
Limits of the testing procedure are reached when the required acceleration exceeds the peak torque of the motor. While a direct drive rate table is ideal for steady state rate testing, its performance in high frequency oscillation is limited by the inertia of the tabletop. Integration of the table into an automated test station requires specialized software to synchronize the motion with the data collection.
The tolerance for rate jitter is set by the sensitivity of the sensor being qualified. Engineers use these tables to characterize the scale factor and bias of gyroscopes over their entire operating range. Final validation of the sensor performance depends on the table providing a repeatable and accurate motion reference.
The resulting data is used to generate the compensation coefficients for the navigation algorithms.