Automatic correction of key error sources in an inertial navigator
First Claim
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1. An inertial navigator, comprising:
- a plurality of gyros, said gyros providing a north gyro input signal, an east gyro input signal, and a down gyro input signal;
a plurality of accelerometers;
means for converting measurements from said accelerometers to a system east velocity and a system north velocity; and
a control system comprising a first control loop and a second control loop;
wherein said first control loop comprises a first rate damping control block responsive to said system east velocity and an external east velocity measurement, said first control loop generating an observable signal proportional to a north gyro drift rate when said accelerometers and said gyros are at rest and the first control loop is in a steady state;
wherein said second control loop comprises a second rate damping control block responsive to said system north velocity and an external north velocity measurement, said second control loop generating an adjusted system north velocity using an output of said second rate damping control block; and
wherein said second control loop is connected to an integral control block responsive to a difference between said adjusted system north velocity and said external north velocity measurement, said integral control block outputting an observable signal proportional to a down gyro drift rate when the second control loop is in a steady state.
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Abstract
Processes and algorithms to determine and correct key error sources in an inertial navigator. These key error sources are azimuth misalignment error and all gyro drift rate errors ("North", "East" and "Down"). Thus the invention provides improved directional accuracy and improved navigation performance. The processes and algorithms can be implemented within the system computer to determine and correct for the system error sources thus determined automatically.
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Citations
18 Claims
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1. An inertial navigator, comprising:
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a plurality of gyros, said gyros providing a north gyro input signal, an east gyro input signal, and a down gyro input signal; a plurality of accelerometers; means for converting measurements from said accelerometers to a system east velocity and a system north velocity; and a control system comprising a first control loop and a second control loop; wherein said first control loop comprises a first rate damping control block responsive to said system east velocity and an external east velocity measurement, said first control loop generating an observable signal proportional to a north gyro drift rate when said accelerometers and said gyros are at rest and the first control loop is in a steady state; wherein said second control loop comprises a second rate damping control block responsive to said system north velocity and an external north velocity measurement, said second control loop generating an adjusted system north velocity using an output of said second rate damping control block; and wherein said second control loop is connected to an integral control block responsive to a difference between said adjusted system north velocity and said external north velocity measurement, said integral control block outputting an observable signal proportional to a down gyro drift rate when the second control loop is in a steady state. - View Dependent Claims (2)
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3. An inertial navigator, comprising:
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a plurality of gyros, said gyros providing a north gyro input signal, an east gyro input signal, and a down gyro input signal; a plurality of accelerometers from which velocity measurements can be derived; and a control system comprising a plurality of control loops, said control loops including an east velocity control loop and a north velocity control loop receiving as inputs said velocity measurements from said accelerometers, said control system generating an observable signal proportional to a north gyro drift rate when said accelerometers and said gyros are at rest and said east velocity control loop is in a steady state, and generating an observable signal proportional to a down gyro drift rate when said accelerometers and said gyros are at rest and said north velocity control loop is in a steady state. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10)
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11. A method for determining and correcting error sources in an inertial navigator, said method comprising the steps of:
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placing the inertial navigator in an aided navigation mode; deriving a system cast velocity from an east accelerometer; generating a north gyro input signal from said system east velocity and from an east velocity measurement provided from an external navigation aid, said step of generating a north gyro input signal comprising the step of applying said system east velocity and said east velocity measurement to a first rate damping block; deriving a system north velocity from a north accelerometer; generating an east gyro input signal from said system north velocity and from a north velocity measurement provided from said external navigation aid, said step of generating an east gyro input signal comprising the step of applying said system north velocity and said north velocity measurement to a second rate damping block; generating a down gyro input signal, said step of generating a down gyro input signal comprising the step of applying an output of said second rate damping control block and said north velocity measurement to an integral control block; waiting a period of time of sufficient duration after placing the inertial navigator in the aided navigation mode to allow an output of said first rate damping block and the output of said second rate damping block to settle into a steady state; reading said north gyro input signal when in said steady state, and deriving a north gyro drift rate therefrom; reading said down gyro input signal when in said steady state, and deriving a down gyro drift rate therefrom; and correcting said inertial navigator for said north gyro drift rate and said down gyro drift rate. - View Dependent Claims (12, 13, 14, 15, 16, 17)
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18. A method for determining and correcting error sources in an inertial navigator, said method comprising the steps of:
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placing the inertial navigator in an aided navigation mode; deriving a system east velocity reading and a system north velocity reading from a plurality of accelerometers; calculating a north gyro drift rate using an east accelerometer Schuler loop with rate damping, with the east accelerometer Schuler loop in a stead state condition; calculating a down gyro drift rate using a north accelerometer Schuler loop with rate damping and an azimuth loop with integral control, with the north accelerometer Schuler loop and the azimuth loop in a steady state condition; and correcting the inertial navigator for said north gyro drift rate and said down gyro drift rate.
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Specification