Dynamic attitude measurement sensor and method

• US 6,421,622 B1
• Filed: 06/04/1999
• Issued: 07/16/2002
• Est. Priority Date: 06/05/1998
• Status: Expired due to Term

• Current Assignee: Aceinna Transducer Systems Company Limited
• Original Assignee: Crossbow Technology Incorporated (Moog Incorporated)
• Inventors: Rios, Jose A., Song, Jin, Horton, Michael A.
• Primary Examiner(s): Grimley, Arthur T.
• Assistant Examiner(s): Charioui, Mohamed
• Application Number:
  US09/326,738
• Time in Patent Office: 1,138 Days
• Field of Search: 702/151, 702/155, 702/141, 702/142, 702/95, 701/213, 701/214, 701/220, 701/11, 701/4, 342/95
• US Class Current: 702/95
• CPC Class Codes: G01C 21/185 for gravity
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems

Abstract

A method and system senses the attitude of an accelerating object. Attitude sensing is accomplished by measuring acceleration in three orthogonal axes and measuring angular rate about each such axis to compute attitude accurately relative to a vertical axis. The system includes accelerometers and angular rate sensors for sensing the acceleration and the angular rate, respectively, of the object. A processor updates a quarternion representation of attitude based upon the angular rate of the object and a corrective rate signal to obtain the attitude of the object. Temperature compensation and frequency compensation may also be performed to update the quarternion.

Claims

1. A method for determining an attitude of an accelerating object exclusively from acceleration and angular rate, comprising:

determining an angular rate of the object to obtain a quarternion representation of attitude;

converting the quarternion into a direction cosine matrix;

determining a level frame acceleration value of the object based upon the direction cosine matrix and an acceleration of the object;

generating a corrective rate signal based upon the level frame acceleration value; and

updating the quarternion representation based upon the determined angular rate of the object and the corrective rate signal, and converting the updated quarternion into a direction cosine matrix to obtain the attitude of the object.

2. The method of claim 1 further comprising:

extracting Euler Angles from the direction cosine matrix to represent the attitude of the object.

3. The method of claim 1 wherein the corrective signal includes a correction component to correct for a heading deviation of the object.

4. The method of claim 1 further comprising:

performing temperature corrections to the gyros and accelerometers which provide temperature compensated gyro data which directly updates the quarternion, and temperature compensated accelerometer data which provides accurate rate corrections to correct the quarternion update.

5. The method of claim 1 further comprising:

performing frequency compensation to the gyro sensor data which expand the operational bandwidth of the gyros to provide updates to the quarternion under dynamic conditions which the gyro sensor alone would not be able to track, or which compress (filter) the gyro and accelerometer bandwidth to reduce noise and to reduce vibration sensitivity in the quarternion calculation.

6. The method of claim 1 wherein the gain of the correction signal is adjustable.

7. The method of claim 1 wherein calibrated data is obtained by applying compensation parameters to the raw sensor data.

8. The method of claim 1 wherein an automated calibration procedure provides the compensation parameters used to compensate the raw sensor data.

9. The method of claim 1 whereby the quarternion differential equation is defined to be dependent on the angular rates measured by the gyros, and on the corrective rates determined from the accelerometer gravity reference algorithm, solved through integration, and then the quarternion is normalized.

14. The method of claim 1 further comprising:

using a local level-plane predefined maneuvering Kalman Filter algorithm to automatically estimate and provide gyro and accelerometer calibration coefficients.

10. A self-contained system capable of determining an attitude of an accelerating object exclusively from acceleration and angular rate, the system, comprising:

an acceleration sensor aligned with each of a plurality of orthogonally-oriented axes of rotation of the object for providing an acceleration value;

an angular rate sensor aligned with each of the plurality of orthogonally-oriented axes of rotation of the object for providing an angular rate value;

a processor for receiving the acceleration value from the acceleration sensor and the angular rate value from the angular rate sensor, and for executing a computer program that performs the steps of;

establishing a quarternion representation of attitude based on the angular rate value;

converting the quarternion into a direction cosine matrix;

determining a level frame acceleration value of the object based upon the direction cosine matrix and the acceleration of the object;

generating a corrective rate signal based upon the level frame acceleration; and

updating the quarternion representation based upon the angular rate of the object and the corrective rate signal to obtain the attitude of the object.

11. The system of claim 10 further comprising:

a temperature sensor, coupled to the processor, for providing temperature data used to compensate the gyros and accelerometers which provide the update and correction to the update of the quarternion.

12. The system of claim 10 further comprising:

a magnetic sensor, coupled to the processor, for providing heading data used to update the quarternion.

13. The system of claim 10 further comprising:

a frequency compensation stage for performing frequency compensation to the gyros and accelerometers which can provide enhanced dynamic response of, reduce the noise in, and reduce the sensitivity to vibration of the quarternion update.

15. A self-contained system for determining an attitude of an accelerating object exclusively from acceleration and angular rate, the system comprising:

a plurality of acceleration sensors configured to determine an acceleration rate of the accelerating object, each acceleration sensor being aligned with one of a plurality of orthogonally-oriented axes of rotation of the object;

a plurality of angular rate sensors configured to determine the angular rate of the accelerating object, each angular rate sensor being aligned with one of the plurality of orthogonally-oriented axes of rotation of the object;

wherein an initial calibration is performed for the plurality of acceleration sensors and angular rate sensors disposed about the orthogonally-oriented axes of rotation for producing calibration data;

a processor coupled to the acceleration sensors and the angular rate sensors and including a memory for storing calibration data, the processor configured to determine the attitude of the accelerating object by;

converting in one processing cycle the acceleration rate and the angular rate in time-sequenced share mode;

using the stored calibration data to calibrate the acceleration rate and angular rate of the accelerating object based upon temperature and misalignment of the plurality of sensors on the object;

computing a quaternion representation of attitude of the accelerating object based upon the angular rate and a corrective angular rate of the accelerating object, and normalizing the quarternion representation;

converting the quarternion representation into a direction cosine matrix;

multiplying the direction cosine matrix with a compensated acceleration rate to obtain a true acceleration of the object without tilt;

generating a corrective rate signal based upon the true acceleration of the object without tilt; and

extracting euler angles from the direction cosine matrix for producing a representative output.

16. The system of claim 15 further comprising:

a plurality of magnetic sensors coupled to the processor and configured to provide a correction rate for yaw axis acceleration.

17. A method of determining an attitude of an accelerating object exclusively from acceleration and angular rate, comprising:

performing an initial calibration of a plurality of sensors configured to sense the acceleration rate and the angular rate of an accelerating object;

sensing the acceleration rate and the angular rate of the accelerating object by use of the plurality of sensors;

converting in one processing cycle the acceleration rate and the angular rate in time-sequenced share mode;

using stored calibration data to calibrate the acceleration rate and angular rate of the accelerating object based upon temperature and misalignment of the plurality of sensors on the object;

computing a quarternion representation of attitude of the accelerating object based upon the angular rate and a corrective angular rate of the accelerating object, and normalizing the quarternion representation;

converting the quarternion representation into a direction cosine matrix;

multiplying the direction cosine matrix with a compensated acceleration rate to obtain a true acceleration of the object without tilt;

generating a corrective rate signal based upon the true acceleration of the object without tilt; and

extracting euler angles from the direction cosine matrix for producing a representative output.