Strap-down attitude and heading reference system

• US 4,254,465 A
• Filed: 08/03/1978
• Issued: 03/03/1981
• Est. Priority Date: 08/03/1978
• Status: Expired due to Term

• Current Assignee: Dynamic Sciences International, Inc.
• Original Assignee: Dynamic Sciences International, Inc.
• Inventors: Land, Robert P.
• Primary Examiner(s): Smith, Jerry
• Application Number:
  US05/930,672
• Time in Patent Office: 943 Days
• Field of Search: 364/453, 364/454, 340/27 R, 340/27 AT, 340/27 NA, 73/178 R, 244/17 S
• US Class Current: 701/220
• 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

Estimators of a vehicle'"'"'s position and attitude with respect to the earth are generated continuously by integrating the outputs of translational and rotational accelerometers that are attached to the vehicle. These estimators are corrected by comparing them to corresponding reference dynamic variables measured independently by instruments onboard the vehicle. The estimators are modified by slowly responding servo loops to equal their corresponding reference variables. Differences between certain of the estimators and their corresponding reference dynamic variables are used in generating feedback signals for correcting other of the estimators. By combining various of the estimators, system outputs representing sideslip angle and change in cross-track velocity can be generated.

Claims

1. An attitude reference system for use in a moving vehicle to provide signals representing estimates of earth-oriented motion-related variables, and to correct predetermined ones of those estimator signals by comparing them with corresponding applied reference variable signals, said attitude reference system comprising:

attitude rate sensing means for producing output signals which are independent of the heading of the vehicle and represent pitch and roll components of the angular velocity of the vehicle about a set of earth-oriented locally level axes;

acceleration sensing means for producing output acceleration signals representing linear accelerations of the vehicle along earth-oriented axes;

integrating means connected to said attitude rate sensing means and said acceleration sensing means for integrating their output signals to produce estimator signals representing estimates of predetermined earth-oriented motion-related variables; and

,

feedback means responsive to the applied reference variable signals and connected to said integrating means for comparing each estimator signal with a corresponding reference variable signal and for generating a feedback signal dependent on their difference and applying the feedback signal to said integrating means to cause the estimator signal to become substantially equal to its corresponding reference variable signal.

2. The system of claim 1 wherein said estimator signals include signals representing estimates of the attitude angles of the vehicle.

3. The system of claim 1 wherein said estimator signals include signals representing estimates of the position and velocity components of the vehicle.

4. The system of claim 1 wherein an estimator signal representing lateral vehicle velocity is compared to a reference variable signal representing lateral vehicle velocity.

5. The system of claim 1 wherein an estimator signal representing vehicle altitude is compared with a reference variable signal which represents the barometric altitude of the vehicle.

6. The system of claim 1 which said attitude rate sensing means further comprise an angular accelerometer attached to the vehicle for sensing angular accelerations of the vehicle in vehicle-oriented coordinates and for producing output signals representing those angular accelerations.

7. The system of claim 6 in which said attitude rate sensing means further comprise integrators responsive to the output signals of said angular accelerometers for producing output signals representing angular rates.

8. The system of claim 1 in which said acceleration sensing means further comprise a linear accelerometer attached to the vehicle for sensing translational accelerations of the vehicle in vehicle-oriented coordinates and for producing an output signal representing those translational accelerations.

9. A system for use in a moving vehicle to provide at least one signal representing an estimate of an earth-oriented motion-variable, and to correct at least one predetermined estimator signal by comparing it with a corresponding applied reference variable signal, said system comprising:

attitude rate sensing means for producing at least one output signal which is independent of the heading of the vehicle and represents a pitch or roll component of the angular velocity of the vehicle about an earth-oriented locally level axis;

acceleration sensing means for producing at least one output signal representing a linear acceleration of the vehicle along an earth-oriented axis;

integrating means connected to said attitude rate sensing means and said acceleration sensing means for integrating their output signals to produce at least one estimator signal representing at least one estimate of a predetermined earth-oriented motion-related variable; and

,

feedback means responsive to at least one applied reference variable signal and connected to said integrating means for comparing said at least one estimator signal with at least one corresponding reference variable signal and for generating a feedback signal dependent on their difference and applying the feedback signal to said integrating means to cause each of said at least one estimator signals to become substantially equal to its corresponding reference variable signal.

10. An attitude reference system for use in a moving vehicle, said system comprising:

attitude rate detecting means attached to the vehicle for producing angular rate output signals representing the angular body rates of the vehicle about a set of vehicle-fixed yaw, pitch and roll axes of the vehicle;

acceleration detecting means attached to the vehicle for producing output linear acceleration signals representing linear accelerations of the vehicle along said vehicle-fixed yaw, pitch and roll axes of the vehicle;

estimator means for operating upon said angular rate output signals to produce pitch and roll attitude estimator signals which are independent of the heading of the vehicle and are representative of estimates of predetermined functions of the roll attitude and pitch attitude of the vehicle with respect to the local level, said estimator means including integrating means for integrating said angular rate output signals;

said estimator means further including pitch error feedback means responsive to the roll axis linear acceleration signal for producing a pitch comparison signal, said pitch error feedback means including comparison means for comparing said pitch comparison signal and said pitch attitude estimator signal to produce a pitch error signal and applying said error signal to correct said pitch attitude estimator signal; and

said estimator means further including roll error feedback means responsive to the pitch axis linear acceleration signal for producing a roll comparison signal, said roll error feedback means including roll comparison means for comparing said roll comparison signal and said roll attitude estimator signal to produce a roll error signal and applying said roll error signal to correct said roll attitude estimator signal.

11. An attitude reference system for use in a moving vehicle, said system comprising:

a plurality of angular accelerometers attached to the vehicle for sensing angular accelerations of the vehicle about vehicle-fixed coordinate axes and for producing angular acceleration output signals representing those angular accelerations;

conversion means responsive to applied estimator signals representative of the pitch and roll attitude of the vehicle with respect to the local level for converting the angular acceleration output signals representing the sensed angular accelerations of the vehicle in vehicle coordinates to output signals which are independent of the heading of the vehicle and represent the angular accelerations of the vehicle about earth-oriented locally level coordinate axes;

integrating means for integrating said converted output signals to produce estimator signals representing estimates of the pitch and roll attitudes of the vehicle with respect to the earth-oriented axes;

feedback means responsive to applied comparison variable signals and connected to said integrating means for comparing each estimator signal with a corresponding comparison variable signal and for generating a feedback signal dependent upon their difference and applying the feedback signal to said integrating means to correct the estimator signal;

linear acceleration detecting means attached to the vehicle for producing output linear acceleration signals representing linear accelerations of the vehicle along said vehicle-fixed axes of the vehicle; and

comparison signal generating means responsive to said output linear acceleration signals for producing and applying to said feedback means at least one of said comparison variable signals.