US 4,791,573 AGranted

State-deviation-estimation circuit employing a phase-locked-loop phase reference

AssigneeSanders Associates, Inc.

InventorsPaul D. Zemany, Kirby A. Smith, John A. Smith

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Abstract

A system (34) for determining deviations in the state of motion of a projectile (10) from its intended state includes a comparison module (38) that receives the outputs S of a sensor array (36). The comparison module (38) converts the sensor outputs to a measurement vector Z.sub.m and computes the deviation of this measurement vector from an intended measurement vector Z.sub.0 received from a control system. The comparison module (38) then determines the difference E.sub.Z between this measured deviation and the deviation predicted by a Kalman filter (44, 46). In generating the measurement vector Z.sub.m from the outputs of the sensor array (36), the comparison module (38) "de-spins" the array outputs in accordance with the output of a phase reference (42), whose purpose is to indicate the phase with respect to gravity of the spin of the projectile (10) about its longitudinal axis. The Kalman filter's state-deviation estimator (46) weights the vector output of the comparison module (36) and adds it to the output of the Kalman filter's state-deviation predictor (44) to provide an updated state-deviation estimation E.sub.X (t:t), which the state-deviation predictor (44) then uses as a basis for its next cycle. The output of the comparison module (38) constitutes a measure of the performance of the state-deviation predictor (44) and is used as a correction factor for the phase reference (42) so that the system acts as a phase-locked loop to lock the phase reference (42) onto the projectile spin without the need for an external sensor to determine the direction of gravity.

Claims28

Dependent claims

In a projectile for executing ballistic motion under the influence of gravity, a guidance system for guiding the projectile in accordance with a target-vector indication supplied thereto, the guidance system comprising:

A. a movable control surface on the projectile for affecting the motion of the projectile in accordance with the orientation of the control surface;
B. a sensor array for sensing enough physical quantities to determine predetermined kinematic variables if the spin orientation of the platform with respect to gravity is known and for generating a sensor outlet representative of the sensed quantities;
C. computation means, connected to receive the sensor output and adapted for reception of the target-vector indication, for:
(i) establishing a phase reference representing an estimate of the spin phase of the platform with respect to gravity;
(ii) employing a mathematical model of the platform to calculate a predicted state deviation from an indication of the previous state deviation and to produce a predicted-deviation indication that represents the predicted state deviation;
(iii) producing from the sensor output, the predicted-deviation indication, and the target-vector indication a difference output representing the difference between (a) the deviation, from the values indicated by the target-vector indication, of the kinematic variables derived from the sensor array in accordance with the phase reference and (b) the deviation, derived from the predicted-deviation indication, of the kinematic variables from the values indicated by the target vector;
(iv) generating from the predicted-deviation indication and the difference output an estimated-deviation output consisting of the predicted-deviation indication adjusted in accordance with the difference output to represent the new deviation in the state of the platform and using the estimated-deviation output as the indication of the previous state deviation in the next calculation of the predicted state deviation;
and
(v) minimizing any misalignment of the phase reference with the direction of gravity by adjusting the phase reference in accordance with a component of the difference indication that results from misalignment of the phase reference with the direction of gravity, whereby the phase reference tends to be alignment with the force of gravity without the need for additional sensors;
and
D. a direction-control system for moving the control surface so as to control its orientation in accordance with the estimated deviation output.

8 more elements

For guiding a projectile that executes ballistic motion under the influence of gravity and includes a sensor array for sensing, and generating a sensor output representative of, enough physical quantities to determine predetermined kinematic variables if the spin orientation of the platform with respect to gravity is known and further includes moveable control surfaces for affecting the motion of the projectile in accordance with the orientation of the control surface, the method comprising the steps of:

A. establishing a phase reference representing an estimate of the spin phase of the platform with respect to gravity;
B. employing a mathematical model of the platform to calculate a predicted state deviation from an indication of the previous state deviation and to produce a predicted-deviation indication that represents the predicted state deviation;
C. producing from the sensor output, the predicted-deviation indication, and the target-vector indication a difference output representing the difference between (a) the deviation, from the values indicated by the target-vector indication, of the kinematic variables derived from the sensor array in accordance with the phase reference and (b) the deviation, derived from the predicted-deviation indication, of the kinematic variables from the values indicated by the target vector;
D. generating from the predicted-deviation indication and the difference output an estimated-deviation output consisting of the predicted-deviation indication adjusted in accordance with the difference output to represent the new deviation in the state of the platform and using the estimated-deviation output as the indication of the previous state deviation in the next calculation of the predicted state deviation;
E. minimizing any misalignment of the phase reference with the direction of gravity by adjusting the phase reference in accordance with a component of the difference lndication that results from misalignment of the phase reference with the direction of gravity, whereby the phase reference tends to be in alignment with the force of gravity without the need for additional sensors;
and
F. moving the control surface so as to control the orientation thereof in accordance with the estimated deviation output.

4 more elements

Dependencies are inferred from the claim text.