Strapped-down attitude reference system

Claim 2

A strapped-down attitude reference system, including an azimuth reference system for maintaining a vector aligned with the geomagnetic field and continuously computing its components m1, m2 and m3 with respect to a vehicle-fixed reference frame (x, y, z), comprising: a toroidal magnetometer pair for measuring signals corresponding to the components Bx, By, and Bz of the geomagnetic vector with respect to the vehicle-fixed reference frame; roll, pitch and yaw gyros, for developing signals p, q, and r, respectively, which are the components of the vehicle''s angular velocity with respect to the x, y, and z axes, respectively; means for combining signals proportional to the components p, q, and r and the signals proportional to the components Bx, By, and Bz in accordance with the following set of equations: m1 rm2 - qm3 + k(Bx - m1), m2 pm3 - rm1 + k(By - m2), m3 qm1 pm2 + k(Bz - m3), where the dot iS a symbol for a derivative and k is a constant < OR = 0.1, to thereby compute the components m1, m2, and m3, of the reference vector aligned with the geomagnetic field.

Claim 3

A strapped-down attitude reference system according to claim 1, wherein the means for combining the signals comprises circuitries for a first, m1, second, m2, and third, m3, magnetic component, having as one of its inputs a signal from the magnetometer pair proportional to the Bx, By, and Bz components, respectively, and as two other inputs, signals proportional to the outputs r and q from the yaw and pitch gyros, signals proportional to the outputs p and r from the roll and yaw gyros, and signals proportional to the outputs q and p from the pitch and roll gyros, respectively, each circuitry for a magnetic component comprising: a first amplifier means, whose input is connected to the output of the magnetometer pair for amplifying the output signal corresponding to the Bx, By, or Bz component, and the output signal, m1, m2, or m3, of its circuitry for a magnetic component; a pair of multiplier means, each means having as inputs the output m1, m2, or m3, of one of the circuitries for one of the other magnetic components and the output of one of the gyros; a second amplifier means, whose input is connected to the output of one of the multiplier means and to the output of the first magnetic component amplifier means, for amplifying its input signals; an integrating circuit, whose inputs are the outputs of the second magnetic component amplifier means and one of the multiplier means, for obtaining the desired computed azimuth reference vector component, m1, m2, or m3; the elements of the three circuitries being so arranged as to implement the said set of equations.

Claim 4

A strapped-down attitude reference system according to claim 2, further comprising a vertical reference system which maintains a vector having components g1, g2, and g3 aligned with the earth''s gravity vector, the vertical reference system further comprising: accelerometers which produce acceleration signals ax, ay, and az, with respect to the vehicle-fixed reference frame; means for combining signals proportional to the acceleration signals ax, ay, and az and the signals proportional to the components p, q and r, in accordance with the following set of equations: g1 rg2 - qg3 + c(ax - g1) g2 pg3 - rg1 + c(ay -g2) g3 qg1 - pg2 + c(az - g3) where the dot over the letter g indicates differentiation, and c < or = 0.1.

Claim 5

A strapped-down attitude reference system according to claim 3, wherein the second-named means for combining signals comprises: circuitries for the first, second and third gravity components, g1, g2, and g3, each circuitry having as an input signal the output signal, -ax, -ay, or -az, from an x-component, y-component, or z-component accelerometer, respectively, x, y, and z assumed to correspond to the cyclical sequence numbers 1, 2, 3, each circuitry for a gravity component also having two input signals corresponding to the other two gravity components; and wherein the roll rate gyro developes a roll rate signal p which is fed into the circuitries for the second and third gravity components; the pitch rate gyro developes a pitch rate signal q which is fed into the circuitries for the first and thirD gravity components; the yaw rate gyro developes a yaw rate signal r which is fed into the circuitries for the first and second gravity components; the roll, pitch and yaw gyros assumed to correspond to the cyclical sequence 1, 2, and 3, respectively; each of the three circuitries for a gravity component of the vertical reference system comprising: a first amplifier means, whose two inputs are the output signal from one of the three accelerometers and a signal corresponding, to one of the gravity components, the cyclical sequence numbers of the accelerometer, the circuitry, and the gravity component being the same; a controllable switch, connected to the output of the first gravity component amplifier means, for disabling the accelerometer output signal during a period of time when the vehicle is undergoing excessive acceleration; a first gravity component multiplier having two inputs: (1) a signal corresponding to that one of the gravity components g1, g2, or g3, having the next higher cyclical sequence number, and (2) a signal from that gyro which has the next lower cyclical sequence number; a second gravity component amplifier means having two inputs, a signal from the output side of the switch and the output signal from the first gravity component multiplier; a second gravity component multiplier having two inputs: (1) a signal corresponding to that one of the gravity components having the next lower cyclical sequence number; and (2) a signal from the gyro which has the next higher cyclical sequence number; a gravity component integrator having as its two inputs the outputs of the second gravity component amplifier and of the second gravity component multiplier, and for its output the gravity component having the same cyclical sequence number as that of its circuitry.