초록 ▼

The 6-axis position and attitude of an imaging vehicle's detector assembly is measured by mounting the detector assembly on a compliant isolator and separating the main 6-axis IMU on the vehicle from a secondary IMU comprising at least inertial rate sensors for pitch and yaw on the detector assembly

The 6-axis position and attitude of an imaging vehicle's detector assembly is measured by mounting the detector assembly on a compliant isolator and separating the main 6-axis IMU on the vehicle from a secondary IMU comprising at least inertial rate sensors for pitch and yaw on the detector assembly. The compliant isolator couples low-frequency rigid body motion of the vehicle below a resonant frequency to the isolated detector assembly while isolating the detector assembly from high-frequency attitude noise above the resonant frequency. A computer processes measurements of the 6-axis rigid body motion and the angular rate of change in yaw and pitch of the isolated detector assembly to mitigate the drift and noise error effects of the secondary inertial rate sensors and estimate the 6-axis position and attitude of the detector assembly.

대표청구항 ▼

1. An imaging vehicle, comprising: a frame;a propulsion system mounted to the frame;a main IMU coupled to measure 6-axis rigid body motion of the vehicle's frame, said 6-axis rigid body motion including linear accelerations in x, y and z directions and angular rates of change of roll, pitch and yaw

1. An imaging vehicle, comprising: a frame;a propulsion system mounted to the frame;a main IMU coupled to measure 6-axis rigid body motion of the vehicle's frame, said 6-axis rigid body motion including linear accelerations in x, y and z directions and angular rates of change of roll, pitch and yaw about the respective x, y and z axes;a compliant isolator mounted to the frame;a detector assembly for capturing images of scene, said assembly including an isolated sub-assembly comprising a telescope and a detector mounted on said compliant isolator, said isolator and isolated sub-assembly having a resonant frequency between 5 Hz and 5 kHz to partially isolate said sub-assembly from attitude noise of the rigid body motion of the frame, said isolation inducing a pseudo-motion in yaw and pitch between the detector assembly and the frame;at least two secondary rate sensors that exhibit a time-varying drift in their measurements, said secondary rate sensors coupled to output secondary measurements of the angular rate of change in yaw and pitch of the isolated sub-assembly, said secondary measurements comprising a rigid body motion component, a time-varying drift component and a pseudo-motion component; anda computer that uses the main IMU's yaw and pitch measurements as a reference to remove the rigid body motion component from the secondary measurements of yaw and pitch to generate yaw and pitch difference signals, implements an estimator that processes the difference signals to generates estimates of the time-varying drift component for yaw and pitch, and subtracts the estimates from the secondary measurements of yaw and pitch to produce corrected secondary measurements of yaw and pitch that include the rigid body motion component and pseudo-motion component, said computer processing measurements of the 6-axis rigid body motion and the corrected measurements of the angular rate of change in yaw and pitch of the isolated sub-assembly to estimate a 6-axis position in x, y and z and attitude in roll, pitch and yaw of the isolated sub-assembly. 2. The imaging vehicle of claim 1, wherein said compliant isolator couples low-frequency rigid body motion of the vehicle frame below the resonant frequency to the detector assembly and isolates the sub-assembly from high-frequency attitude noise above the resonant frequency. 3. The imaging vehicle of claim 1, wherein said isolated sub-assembly comprises only the imaging components of said telescope and said detector, said detector assembly further comprising a non-isolated sub-assembly comprising one or more non-imaging components, said isolated sub-assembly configured to minimize the isolated mass. 4. The imaging vehicle of claim 1, wherein estimator comprises a low pass filter that removes pseudo-motion component. 5. The imaging vehicle of claim 1, wherein estimator comprises an integrator. 6. The imaging vehicle of claim 1, wherein estimator comprises a Kalman filter. 7. The imaging vehicle of claim 1, wherein estimator estimates the time-varying drift component in either angular rate of change or accumulated angle in yaw or pitch. 8. The imaging vehicle of claim 1, wherein said at least two secondary rate sensors exhibit a specified drift performance over a first time period, said main IMU exhibiting a specified drift performance over a second time period, said second time period being at least 10 times longer than said first time period. 9. The imaging vehicle of claim 1, wherein said at least two secondary rate sensors exhibit a first specified drift performance over a time period, said main IMU exhibiting a second specified drift performance over the time period, said second specified drift performance being at most one-tenth said first specified drift performance. 10. The imaging vehicle of claim 1, wherein said main IMU comprises a ring laser gyroscope, a fiber gyroscope or a hemispheric resonator gyroscope that provide 6-axis measurements and said at least two secondary rate sensors each comprise a MEMS angular rate sensor. 11. The imaging vehicle of claim 1, wherein said secondary rate sensors comprise an angular rate sensor that directly measures angular rate of change or a linear acceleration sensor that measures linear accelerations that coupled through a finite lever arm between the vehicle's center of gravity and the sensor produces a measurement of angular rate of change. 12. The imaging vehicle of claim 1, further comprising a cluster of secondary rate sensors, said cluster including a first plurality of said secondary rate sensors to measure angular rate of change in yaw and a second plurality of said secondary rate sensors to measure angular rate of change in pitch, said computer processing said plurality of measurements to increase the signal-to-noise ratio. 13. The imaging vehicle of claim 12, wherein said secondary rate sensors comprise MEMS sensors. 14. A kinetic energy kill vehicle (KV), comprising: a frame;divert and attitude control thrusters mounted to the frame to alter the trajectory of the KV;a main IMU coupled to measure 6-axis rigid body motion of the KV, said 6-axis rigid body motion including linear accelerations in x, y and z directions and angular rates of change of roll, pitch and yaw about the respective x, y and z axes;a compliant isolator mounted to the frame;a seeker for capturing images of scene, said seeker including an isolated sub-assembly comprising a telescope and a detector mounted on said compliant isolator, said isolator and isolated sub-assembly having a resonant frequency between 5 Hz and 5 kHz to couple low-frequency rigid body motion of the KV below the resonant frequency to the seeker and to partially isolate said sub-assembly from high-frequency attitude noise above the resonant frequency, said isolation inducing a pseudo-motion in yaw and pitch between the detector assembly and the frame;at least two secondary rate sensors that exhibit a time-varying drift in their measurements, said secondary rate sensors coupled to output secondary measurements of the angular rate of change in yaw and pitch of the isolated sub-assembly, said secondary measurements comprising a rigid body motion component, a time-varying drift component and a pseudo-motion component; anda computer that uses the main IMU's yaw and pitch measurements as a reference to remove the rigid body motion component from the secondary measurements of yaw and pitch to generate yaw and pitch difference signals, implements an estimator that processes the difference signals to generates estimates of the time-varying drift component for yaw and pitch, and subtracts the estimates from the secondary measurements of yaw and pitch to produce corrected secondary measurements of yaw and pitch that include the rigid body motion component and pseudo-motion component, said computer processing measurements of the 6-axis rigid body motion and the corrected measurements of the angular rate of change in yaw and pitch of the isolated sub-assembly to estimate a 6-axis position in x, y and z and attitude in roll, pitch and yaw of the isolated sub-assembly. 15. The KV of claim 14, wherein estimator comprises one of a low pass filter, an integrator, a Least Squares Estimator and a Kalman filter. 16. The KV of claim 14, wherein said at least two secondary rate sensors exhibit a first specified drift performance over a time period, said main IMU exhibiting a second specified drift performance over the time period, said second specified drift performance being at most one-tenth said first specified drift performance. 17. The KV of claim 14, further comprising a cluster of secondary rate sensors, said cluster including a first plurality of said secondary rate sensors to measure angular rate of change in yaw and a second plurality of said secondary rate sensors to measure angular rate of change in pitch, said computer processing said plurality of measurements to increase the signal-to-noise ratio. 18. The imaging vehicle of claim 17, wherein said secondary rate sensors comprise MEMS sensors. 19. A method of measuring 6-axis position and attitude of a detector assembly on an imaging vehicle, said vehicle comprising a propulsion system mounted to a frame and a main IMU coupled to measure 6-axis rigid body motion of the vehicle's frame, said 6-axis rigid body motion including linear accelerations in orthogonal x, y and z directions and angular rates of change of roll, pitch and yaw about the respective x, y and z axes, said detector assembly including an isolated sub-assembly comprising a telescope and a detector, said method comprising: mounting the isolated sub-assembly on a compliant isolator to provide a resonant frequency between 5 Hz and 5 kHz for yaw and pitch, said compliant isolator coupling low-frequency rigid body motion of the vehicle below the resonant frequency to the isolated sub-assembly and isolating the isolated sub-assembly from high-frequency attitude noise above the resonant frequency;using at least two secondary rate sensors that exhibit a time-varying drift to measure the angular rate of change in yaw and pitch of the isolated sub-assembly, said secondary measurements comprising a rigid body motion component, a time-varying drift component and a pseudo-motion component;using the main IMU's yaw and pitch measurements as a reference to remove the rigid body motion component from the secondary measurements of yaw and pitch to generate yaw and pitch difference signals;processing the difference signals to generate estimates of the time-varying drift component for yaw and pitch;subtracting the estimates from the secondary measurements of yaw and pitch to produce corrected secondary measurements of yaw and pitch that include the rigid body motion component and pseudo-motion component; andprocessing measurements of the 6-axis rigid body motion and the corrected measurements of the angular rate of change in yaw and pitch of the isolated sub-assembly to estimate a 6-axis position in x, y and z and attitude in roll, pitch and yaw of the isolated sub-assembly. 20. The method of claim 19, wherein a cluster of secondary rate sensors are used to measure the angular rate of change in yaw and pitch, said cluster including a first plurality of MEMS sensors to measure angular rate of change in yaw and a second plurality of MEMS sensors to measure angular rate of change in pitch.