Inertial GPS navigation system using injected alignment data for the inertial system

• US 20050060093A1
• Filed: 09/02/2004
• Published: 03/17/2005
• Est. Priority Date: 09/05/2003
• Status: Active Grant

• Current Assignee: Novatel Incorporated (Hexagon AB)
• Original Assignee: Novatel Incorporated (Hexagon AB)
• Inventors: Hamilton, Jason, Bobye, Michael, Ford, Thomas John
• Granted Patent: US 7,346,452 B2
• Time in Patent Office: Days
• US Class Current: 701/214
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial
• CPC Class Codes: G01S 19/49 whereby the further system is an inertial position system, e.g. loosely-coupled
• CPC Class Codes: G01S 19/55 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

An inertial (“INS”)/GPS receiver uses injected alignment data to determine the alignment of the INS sub-system when the receiver is in motion during start-up. The alignment data is determined from parameterized surface information, measured GPS velocity, and a known or predetermined angular relationship between the vehicle on which the receiver is mounted and an inertial measurement reference, or body, frame associated with the accelerometers and gyroscopes of the inertial measuring unit (“IMU”). The parameterized surface information, which provides a constraint, may be the orientation of the surface over which the vehicle that houses the receiver is moving. The receiver uses the initial GPS position to determine the location of the vehicle on the parameterized surface, and thus, the known surface orientation. The receiver then determines the roll, pitch and heading of the vehicle on the surface using the associated GPS velocity vector. Thereafter, the receiver uses the calculated roll, pitch and heading of the vehicle and the known or predetermined angular relationship between the vehicle and the IMU body frame to determine a rotation matrix that relates the IMU body frame to a computation or referenced frame used by the receiver.

Claims

1. An inertial/global positioning system (GPS) receiver including:

A. a GPS sub-system for providing correlation measurements associated with signals received from a plurality of GPS satellites;

B. an inertial sub-system with an inertial measurement unit for providing inertial measurements from a plurality of accelerometers and gyroscopes; and

C. a processor for calculating GPS position based on the correlation measurements and inertial position, velocity and attitude relative to the GPS position based on the inertial measurements, the processor aligning the inertial measurement unit when the receiver is in motion using a GPS position, a corresponding GPS velocity vector and alignment data associated with parameterized surface information.

2. The inertial/global positioning system receiver of claim 1 wherein the processor uses as the parameterized surface information a relative orientation of a planar surface that corresponds to the GPS position.

3. The inertial/global positioning system receiver of claim 2 wherein the processor

uses the GPS velocity vector in conjunction with the planar surface orientation information to determine pitch, roll and heading of a vehicle on which the receiver is mounted, and

determines an angular relationship between an inertial measurement unit body frame that is associated with the relative orientations of the accelerometers and gyroscopes and a computation or reference frame that is used by the receiver based on the angular relationship between the vehicle and the inertial measurement unit body frame.

4. The inertial/global positioning system receiver of claim 3 wherein the processor determines the pitch, roll and heading of the vehicle by

translating the GPS velocity vector to a vector in a planar section frame associated with the planar surface and determining pitch and roll vectors,

translating the pitch and roll vectors to corresponding vectors in a geographic or local level frame,

manipulating the components of the pitch and roll vectors parameterized in the local level frame to produce the pitch, roll and heading values.

5. The inertial/global positioning system receiver of claim 4 wherein the planar section frame has a triad of orthogonal axes with a z-axis normal to the surface, and

the z component of the GPS velocity vector parameterized in the planar section frame is set to zero to determine the pitch vector.

6. The inertial/global positioning system receiver of claim 5 wherein the roll vector parameterized in the planar frame section is determined by rotating the pitch vector about the z-axis.

7. The inertial/global positioning system receiver of claim 4 wherein the processor determines the angular relationship between the inertial measurement unit body frame and the reference frame by

calculating a rotation matrix R_v^l that relates a vehicle frame and the local level frame based on the pitch, roll and heading values,

calculating a rotation matrix R_b^v that relates the inertial measurement unit body frame to the vehicle frame based on the angular relationship between the vehicle and the inertial measurement unit body frame,

calculating a rotation matrix R_b^e that relates the inertial measurement unit body frame to the reference frame based on the calculated matrices R_v^l and R_b^v, and a known rotation matrix R_l^e that relates the local level frame to the reference frame.

8. The inertial/global positioning system receiver of claim 7 wherein the vehicle frame has the axes with a y-axis directed ahead of the vehicle, a z-axis directed up and an x-axis directed to the right of the driver.

9. The inertial/global positioning system receiver of claim 7 wherein the processor determines the angular relationship between the vehicle frame and the inertial measurement unit body frame based on data supplied by a user.

10. The inertial/global positioning system receiver of claim 7 wherein the processor determines the angular relationship between the vehicle frame and the inertial measurement unit body frame based on data gathered when the inertial sub-system was previously aligned and the vehicle was on a surface with a known orientation.

11. The inertial/global positioning system of claim 7 wherein the processor determines the angular relationship between the vehicle and the inertial measurement unit body frame by

calculating a rotation matrix R_v^l based on the GPS velocity vector, the y-axis of the vehicle frame being parallel to the GPS velocity vector and the x and y axes of the vehicle frame being parallel to the surface plane of the planar section, and

calculating R_b^v=R_l^vR_b^l where R_l^v is the transpose of R_v^l and R_b^l is known from the alignment.

12. The inertial/global positioning system receiver of claim 1 wherein the processor further determines the alignment of the inertial measuring unit when the receiver is stationary based on the measurements made by the inertial measurement unit.

13. A method of determining the alignment of an inertial measurement unit of an inertial/GPS receiver that is in motion at start-up, the method including:

A. receiving signals from a plurality of GPS satellites;

B. acquiring and tracking carriers and codes in the satellite signals;

C. determining a GPS position and an associated GPS velocity vector;

D. identifying a location on a surface model that corresponds to the GPS position and determining the relative orientation of a corresponding surface plane;

E. using the orientation of the surface plane and the GPS velocity vector to determine pitch, roll and heading of a vehicle on which the receiver is mounted; and

F. using the pitch, roll and heading information and information about an angular relationship between the vehicle and a measurement or body frame associated with the inertial measurement unit to determine an angular relationship between the inertial measurement unit body frame and a computational or reference frame.

14. The method of claim 13 further including in the step of determining pitch, roll and heading

translating the GPS velocity vector to a vector in a planar section frame associated with the surface plane and determining pitch and roll vectors in the planar section frame,

transforming the pitch and roll vectors from the planar section frame to a geographic or local level frame;

and

calculating the pitch, roll and heading values using the components of the pitch and roll vectors parameterized in the local frame.

15. The method of claim 14 wherein the planar section frame has a triad of orthogonal axes with a z-axis normal to the surface plane and the step of translating the GPS velocity vector further includes setting the z component of the GPS velocity vector parameterized in the planar section frame to zero to determine the pitch vector.

16. The method of claim 15 further including determining the roll vector parameterized in the planar frame section by rotating the pitch vector about the z-axis of the planar frame.

17. The method of claim 13 wherein the step of determining the angular relationship between the inertial measurement unit body frame and the reference frame includes

calculating a rotation matrix R_v^l that relates a vehicle frame and the local level frame based on the pitch, roll and heading values,

calculating a rotation matrix R_b^v that relates the inertial measurement unit body frame to the vehicle frame based on the angular relationship between the vehicle and the inertial measurement unit body frame,

calculating a rotation matrix R_b^e that relates the inertial measurement unit body frame to the reference frame based on the calculated matrices R_v^l and R_b^v, and a known rotation matrix R_l^e that relates the local level frame to the reference frame.

18. The method of claim 13 wherein the information about the relationship between the vehicle frame and the inertial measurement unit body frame that is used in the step of determining the angular relationship between the inertial measurement unit body frame and the reference frame is based on data gathered when the inertial measurement unit was aligned previously and the vehicle was on a surface with a known orientation.

19. The method of claim 13 wherein the information about the relationship between the vehicle frame and the inertial measurement unit body frame that is used in the step of determining a relationship between the inertial measurement unit body frame and the reference frame is based on information supplied by the user.

20. The method of claim 13 further including the step of determining a relationship between the inertial measurement unit body frame and the reference frame when the receiver re-starts in a stationary state using measurements made by the inertial measurement unit.

21. The method of claim 17 further including in the step of determining the angular relationship between the vehicle and the inertial measurement unit body frame the steps of

calculating a rotation matrix R_v^l based on the GPS velocity vector, with the y axis of the vehicle frame being parallel to the GPS velocity vector and the x and y axes of the vehicle frame being parallel to the surface plane, and

calculating R_b^v=R_l^vR_b^l where R_l^v is the transpose of R_v^l and R_b^l is known from the alignment.