Methods for determining an initial AINS heading

• US 20090326740A1
• Filed: 06/27/2008
• Published: 12/31/2009
• Est. Priority Date: 06/27/2008
• Status: Active Grant

• Current Assignee: Applanix Corporation, Inc.
• Original Assignee: Applanix Corporation, Inc.
• Inventors: Wang, Jau-Hsiung
• Granted Patent: US 8,019,543 B2
• Time in Patent Office: Days
• US Class Current: 701/3
• CPC Class Codes: G01C 23/00 Combined instruments indicating more than one navigational value, e.g. for aircraft; Combined measuring devices for measuring two or more variables of movement, e.g. distance, speed or acceleration

Abstract

Two methods for determining a best initial heading estimate for use in an AINS system, while recording position data values and in-motion data values, assigning incremental changes to indexed heading ψ_k, calculating a set of time indexed present AINS position values and a corresponding set of time indexed absolute horizontal position measurement residual values, recording the absolute maximum time indexed horizontal position measurement residual and the corresponding value of ψ_k returning to the step of assigning an incremental increase to a next value to indexed heading ψ_k up to 360 degrees, identifying the maximum time indexed horizontal position measurement residual and corresponding ψ_k, followed by identifying the ψ^k having the smallest absolute maximum horizontal position measurement residual as A_k Second method uses a circular array of AINS ENGINES each with a different ψ_k running in parallel and finding smallest horizontal position measurement residual for A_k.

Claims

1. a method for determining A_k (a best initial heading estimate) using serial computing for use with an alignment program running in an AINS (aided INS) computer in an AINS system, the method comprising the steps of:

A. powering up the AINS system, requesting movement of the AINS system and acknowledging movement when AINS system is moving,

B. receiving and recording N (a predetermined number of) time indexed records, each record having a corresponding sub-set of time indexed aiding position data values and a corresponding sub-sets of time indexed in-motion data values in a first array, and advancing to step C as the Nth (last) time indexed record is recorded in the first array,

C. assigning a value to an indexed heading ψ

_k,

D. selecting a record from the first array and using the assigned value of the indexed heading ψ

_k and the AINS algorithm calculating and recording an update for the position data,

E. calculating and recording a time indexed horizontal position measurement residual using record from the first array and the value of the indexed heading ψ

_k in a second array,

F. testing to see if all N records in the first array have been processed and if there are records in the first array that have not been processed, return to step D and E and if all N records in the first array have been processed then advance to step G,

G. selecting the maximum horizontal position measurement residual norm from those saved in the second array and the corresponding ψ

_k in a third array, and advance to step H.

H. test to see if ψ

_k is equal to 360 degrees and if not, return to step C, increment the value of ψ

_k and repeat steps D, E, F, G and if ψ

_k equals 360 degrees, advance to step I,

I. identifying the smallest maximum horizontal position measurement residual norm over the recorded maximum horizontal position measurement residual norms in the third array and designate the initial heading corresponding to the smallest horizontal position measurement residual norm in the third array as A_k for subsequent use in alignment.

2. The method of claim 1 at step B wherein the second sub-set time indexed in-motion data values received from the IMU further comprise:

a sequence of time indexed incremental Euler angles (pitch, roll and azimuth) and platform velocities from the IMU between each timed indexed aiding position data value.

3. The method of claim 1, wherein step C. is amended to have ψ

_k set to a value equal to Δ

y times k where Ay is a heading increment assigned by the user and k is 360/Δ

y.

4. The method of claim 1 wherein step E. further comprises the step of calculating and recording

a time indexed horizontal position measurement residual values using ψ

_k for each corresponding time indexed present position value in the first array using

an AINS Kalman filter horizontal position measurement residual computation process.

5. The method of claim 1 wherein step H is further characterized as comprising:

determining if index k=K where K is a predetermined constant characterized to prevent ψ

_k from exceeding 360 degrees, and if not, return to added step C, and if k=K, advancing to step I.

6. A method for determining A_k (a best initial heading estimate) for use with an alignment program running in an AINS (aided INS) computer in an AINS system using serial computing, the method comprising the steps of:

A moving the AINS system during a filter interval,

B. recording N pairs of GNSS position data and INS in-motion data as N records in a first array,

C. assigning a corresponding indexed heading ψ

_k characterizes a predetermined indexed heading selected from a circular set of K indexed headings extending in uniform spaced relation sequence from a first indexed heading to the last indexed heading,

D. processing each of the N records in the first array with the indexed heading ψ

_k to obtain N horizontal position measurement residuals and saving each of the respective N horizontal position measurement residuals with its corresponding indexed heading in a second array,

E. selecting the maximum value horizontal position measurement residual from the N horizontal position measurement residuals in the second array and save it with its corresponding index heading ψ

_k in a third array,

F. select the next indexed heading and if the next indexed heading is not the last indexed heading, return to step C and re-execute steps C, D, E, and F and if the next indexed heading is the last indexed heading, advance to step G and perform step G,

G. identify the smallest horizontal position measurement residuals from the recorded maximum horizontal position measurement residuals in the third array and select the corresponding value of ψ

_k in the third array as A_k, for use in the alignment program.

7. The method of claim 6 wherein the INS in-motion data further comprises:

a sequence of time indexed incremental Euler angles and platform velocities as state components of the in-motion data values in a second array.

8. The method of claim 6 wherein step C is further characterized to have indexed heading ψ

_k=Δ

ψ

×

k, with k being a stepped index value in a range of from one through a constant K, the step size of Δ

ψ and

the value of K being characterized to restrict the value of indexed ψ

_k to be less than 360 degrees.

9. The method of claim 6. wherein step D is further characterized to require that an AINS Kalman filter position measurement residual computation process and a horizontal position measurement residual computation process be used.

10. A system for determining A_k (a best initial heading estimate), running in an AINS (aided INS) computer in an AINS system using parallel computing, the system comprising:

an IMU coupled to

the AINS computer, the IMU being coupled to provide INS data to

a data bus from

a triax of accelerometers and data from

a triax of rate gyros,

an array of AINS engine computers coupled to the data bus to be responsive to the INS data, each AINS engine computer having

an alignment program initialized with an indexed heading ψ

_k characterizing a predetermined heading selected from a circular set of K indexed headings extending in a uniform spaced relation sequence from a first to a Kth or last indexed heading,

a GNSS for providing position data to the data bus,

each AINS engine computer being coupled to the data buss, the alignment program running in each respective AINS engine being, responsive to the INS data from the IMU, the position data from the GNSS the alignment program being further characterized to provide a series of time indexed horizontal position measurement residues in response to movement of the AINS,

a kth AINS engine producing the smallest sum of horizontal position measurement residuals being identified as the AINS engine having been initialized with an indexed heading ψ

_k closest in value to the A_k, best initial heading estimate.

11. The system for determining A_k of claim 10 further comprising:

a multiplexer, the multiplexer being coupled to receive and record the outputs of each respective AINS engine and to output only the output of the AINS engine having been initialized with an indexed heading ψ

_k closest in value to the A_k.

12. The system for determining Ak of claim 11 further comprising:

a switch controller coupled to interrupt the operation of all AINS ENGINES, but the AINS engine providing the smallest horizontal position measurement residuals.

13. The system for determining A_k of claim 12 wherein:

the switch controller is further characterized to be responsive to an output from the multiplexer to select the AINS engine providing the smallest horizontal position measurement residuals.

14. The system for determining Ak of claim 11 wherein the initial heading program running in the AINS computer is further characterized as having

a multiplexer function, the multiplexer function receiving time indexed horizontal position measurement residuals and blended navigation solution data pairs from each AINS engine in an AINS computer memory {ROM or RAM), the multiplexer function sums the time indexed horizontal position residues from each respective AINS engine in “

k”

corresponding registers during movement of the AINS after power up and after a predetermined time interval of N seconds, the multiplexer scans the sums of the horizontal position measurement residuals in each of the k respective registers and identifies the initial heading and the corresponding AINS engine that generated

a smallest sum of time indexed horizontal position measurement residuals.

15. The system for determining A_k of claim 14 wherein after the initial heading program running in the AINS computer has identified the AINS engine that generated the smallest sum of time indexed horizontal position measurement residuals, the multiplexer outputs all blended navigation solutions calculated after the Nth second from the AINS computer memory (ROM or RAM).

16. The system for determining Ak of claim 14 wherein after the initial heading program running in the AINS computer has identified the AINS engine that generated the smallest sum of time indexed horizontal position measurement residuals, the multiplexer outputs all blended navigation solutions calculated before the Nth second from the AINS computer memory (ROM or RAM).

17. The system for determining Ak of claim 15 wherein after the Nth second, the multiplexer provides a signal to the switch controller to interrupt the operation of all AINS ENGINES except the identified AINS engine that produced the smallest horizontal position measurement residuals sum.

18. The system for determining A_k of claim 16 wherein after the Nth second, the multiplexer provides a signal to the switch controller to interrupt the operation of all AINS ENGINES except the identified AINS engine that produced the smallest horizontal position measurement residuals sum.

19. The system for determining A_k of claim 10 wherein each AINS engine further comprises:

a dedicated inertial navigator computer, coupled to the data bus to be responsive to data from the IMU,

a dedicated error controller coupled to exchange data with the Kalman filter and to provide correction data to the inertial navigator computer, and

a Kalman filter coupled to receive GNSS position data from the GNSS and to be initialized with A_k from the initial heading program.