Air data aided inertial measurement unit

Patent metadata

Field	Value
Publication number	US-10101174-B2
Application number	US-201615243455-A
Country	US
Kind code	B2
Filing date	Aug 22, 2016
Priority date	Aug 22, 2016
Publication date	Oct 16, 2018
Grant date	Oct 16, 2018

Abstract

An inertial measurement unit (IMU) includes an inertial sensor assembly including a plurality of accelerometers and a plurality of rate gyroscopes, an inertial sensor compensation and correction module, and a Kalman estimator module. The inertial sensor compensation and correction module is configured to apply a set of error compensation values to sensed acceleration and rotational rate to produce a compensated acceleration and a compensated rotational rate of the IMU. The Kalman estimator module is configured to determine a set of error correction values based on a difference between a change in integrated acceleration of the IMU and a change in true airspeed of the IMU. The inertial sensor compensation and correction module is further configured to apply the set of error correction values to each of the compensated acceleration and the compensated rotational rate to output an error-corrected acceleration and an error-corrected rotation rate.

First claim

The invention claimed is:

1. An inertial measurement unit (IMU) comprising:
an inertial sensor assembly comprising:
a plurality of accelerometers, each of the plurality of accelerometers configured to sense acceleration of the IMU along one of a plurality of axes;
a plurality of rate gyroscopes, each of the plurality of rate gyroscopes configured to sense rotational rate of the IMU along one of the plurality of axes; and
a plurality of temperature sensors configured to sense temperature of an operating environment of the plurality of accelerometers and the plurality of rate gyroscopes;

an inertial sensor compensation and correction module configured to apply a set of error compensation values to acceleration sensed by the plurality of accelerometers and to rotational rate sensed by the plurality of rate gyroscopes to produce a compensated acceleration and a compensated rotational rate of the IMU, wherein the set of error compensation values comprises temperature-dependent error compensation values, and wherein the inertial sensor compensation and correction module is configured to apply the set of error compensation values by determining the temperature-dependent error compensation values based on sensed temperature from each of the plurality of temperature sensors; and
a Kalman estimator module configured to:
determine a change in integrated acceleration of the IMU over a time interval based on the compensated acceleration and the compensated rotational rate of the IMU;
determine a set of error correction values based on a difference between the change in the integrated acceleration of the IMU and a change in true airspeed of the IMU; and
provide the set of error correction values to the inertial sensor compensation and correction module;

wherein the inertial sensor compensation and correction module is further configured to:
apply the set of error correction values to each of the compensated acceleration and the compensated rotational rate to produce an error-corrected acceleration and an error-corrected rotational rate; and
output the error-corrected acceleration and the error-corrected rotational rate.

2. The IMU of claim 1 ,
wherein the Kalman estimator module is configured to determine the set of error correction values via an extended Kalman filter that utilizes the difference between the change in the integrated acceleration of the IMU and the change in the true airspeed of the IMU as input and produces the set of error correction values as output.

3. The IMU of claim 1 ,
wherein the temperature-dependent error compensation values comprise temperature-dependent scale factor error compensation values, temperature-dependent bias error compensation values, and temperature-dependent non-linearity error compensation values for each of the plurality of accelerometers and each of the plurality of rate gyroscopes.

4. The IMU of claim 3 ,
wherein each of the temperature-dependent scale factor error compensation values corresponds to an error in a slope of sensor output over a temperature range for a respective one of the plurality of accelerometers and the plurality of rate gyroscopes;
wherein each of the temperature-dependent bias error compensation values corresponds to a non-zero offset error of sensor output over the temperature range for a respective one of the plurality of accelerometers and the plurality of rate gyroscopes; and
wherein each of the temperature-dependent non-linearity error compensation values corresponds to a non-linearity of the sensor output over the temperature range for a respective one of the plurality of accelerometers and the plurality of rate gyroscopes.

5. The IMU of claim 1 ,
wherein the set of error compensation values comprises a non-orthogonality error compensation value corresponding to a non-orthogonality error of the plurality of axes.

6. The IMU of claim 1 ,
wherein the plurality of axes comprises a first plurality of axes defining a sensor axis reference frame; and
wherein the Kalman estimator module is configured to determine the change in the integrated acceleration of the IMU by:
transforming the compensated acceleration from the sensor axis reference frame to a body axis reference frame defined by a second plurality of axes aligned with respect to a moving body that includes the IMU; and
integrating the compensated acceleration in the body axis reference frame over the time interval.

7. The IMU of claim 1 ,
wherein the Kalman estimator module is further configured to determine the set of error correction values by removing an effect of gravity from the difference between the change in the integrated acceleration of the IMU and the change in the true airspeed of the IMU.

8. The IMU of claim 1 ,
wherein the Kalman estimator module is further configured to determine the set of error correction values by removing an effect of Coriolis acceleration forces from the difference between the change in the integrated acceleration of the IMU and the change in the true airspeed of the IMU.

9. The IMU of claim 1 ,
wherein the plurality of accelerometers comprises three accelerometers;
wherein the plurality of rate gyroscopes comprises three rate gyroscopes;
wherein the plurality of axes comprises three axes;
wherein each of the three accelerometers is aligned to sense the acceleration of the IMU along one of the three axes; and
wherein each of the three rate gyroscopes is aligned to sense the rotational rate of the IMU along one of the three axes.

10. A method comprising:
sensing acceleration of an inertial measurement unit (IMU) along a plurality of axes via a plurality of accelerometers of the IMU;
sensing rotational rate of the IMU along the plurality of axes via a plurality of rate gyroscopes of the IMU;
sensing temperature of an operating environment of the plurality of accelerometers and the plurality of rate gyroscopes via a plurality of temperature sensors of the IMU;
applying a set of error compensation values to each of the sensed acceleration and the sensed rotational rate to produce a compensated acceleration and a compensated rotational rate of the IMU, wherein the set of error compensation values comprises temperature-dependent error compensation values, and wherein applying the set of error compensation values comprises determining the temperature-dependent error correction values based on the sensed temperature from each of the plurality of temperature sensors;
determining a change in integrated acceleration of the IMU over a time interval based on the compensated acceleration and the compensated rotational rate of the IMU;
determining a set of error correction values based on a difference between the change in the integrated acceleration of the IMU and a change in true airspeed of the IMU;
applying the set of error correction values to each of the compensated acceleration and the compensated rotational rate to produce an error-corrected acceleration and an error-corrected rotational rate; and
outputting the error-corrected acceleration and the error-corrected rotational rate.

11. The method of claim 10 ,
wherein determining the set of error correction values comprises determining the set of error correction values via an extended Kalman filter that utilizes the difference between the change in the integrated acceleration of the IMU and the change in the true airspeed of the IMU as input and produces the set of error correction values as output.

12. The method of claim 10 ,
wherein the temperature-dependent error compensation values comprise temperature-dependent scale factor error compensation values, temperature-dependent bias error compensation values, and temperature-de

Assignees

• Rosemount Aerospace Inc

Inventors

• Ell Todd

Classifications

• G01P5/00

  Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft (application of speed-measuring devices for measuring volume of fluid G01F) · CPC title

• G01P21/00

  Testing or calibrating of apparatus or devices covered by the preceding groups · CPC title

• G01C25/00 Primary

  Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass (testing, calibrating or compensating compasses G01C17/38) · CPC title

• G01C21/16

  by integrating acceleration or speed, i.e. inertial navigation · CPC title

• G01C21/185

  for gravity · CPC title