Aeronautics and astronautics – Missile stabilization or trajectory control
Reexamination Certificate
2000-04-10
2001-09-11
Gregory, Bernarr E. (Department: 3662)
Aeronautics and astronautics
Missile stabilization or trajectory control
C244S003150, C244S075100, C244S07600R, C073S570000, C073S584000, C073S649000, C701S003000, C701S004000, C701S011000
Reexamination Certificate
active
06288380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to apparatus for compensating for the structural vibration of a missile in flight. More particularly, the present invention relates to an adaptive body-bending estimator which will substantially reduce the amount of undesirable energy passed through the autopilot during flight.
2. Description of the Prior Art
During flight a missile passively vibrates at its structural natural frequencies. Generally, this passive vibration is not a problem, unless the missile's autopilot couples the missile body sensors with the control actuation system of the missile. The missile's autopilot coupling of the sensors with the actuators generates a feedback loop which actively amplifies missile vibrations. The amplified missile vibration can adversely affect missile performance during flight which may result in the missile missing its target. For example, missile vibrations can cause degradation in seeker performance, reduction in the range of the missile, and accelerated consumption of the missile actuation system's energy source.
A solution used in the past to solve this problem is to utilize notch filters to reduce the amount of undesirable energy passed through the autopilot. This approach, however, requires either (1) a prior knowledge of the structural frequencies of the missile, or (2) an estimation technique to identify the correct frequencies during the missile's flight.
Adjustable notch frequencies scheduled as a function of time generally work whenever a missile's structural frequencies are known and well characterized. Unfortunately, accurate predictions of the missile's structural frequencies are generally not available. This is especially true for missile developmental programs which may include uncertainties in the frequency profile due to inadequacies in testing and computer modeling.
Accordingly, there is a need for an adaptive body-bending estimator which compensates for the undesirable coupling of a missile's structural vibration through the missile autopilot which, in turn, adversely effects the missile performance during flight.
SUMMARY OF THE INVENTION
The present invention overcomes some of the disadvantages of the past, including those mentioned above, in that it comprises a relatively simple yet highly efficient and effective adaptive body bending estimator.
The adaptive body bending estimator comprises a band pass filter which receives a yaw accelerometer (BEND_ACCEL) signal from a missile's yaw accelerometer. The band pass filter, which has a bandpass of 25-70 hertz, rejects frequencies which are not of interest. The band-passed signal is then supplied to a notch filter bank comprising six logrithmically-spaced notch filters within a frequency range of between 42 hertz and 55 hertz. The six notch filters of the notch filter bank are centered at different frequencies, the frequencies being 42 Hz, 44.32 Hz, 46.78 Hz, 49.37 Hz, 52.11 Hz and 55.00 Hz. The notch filters reject signals at these frequencies. The signals from the filter bank are supplied to an absolute value generator which provides an absolute value for each of the six signals. The absolute value of each signal is passed through a low pass filter bank. The low pass filter bank processes these absolute value signals providing a time weighted average for each signal. The low pass filter bank provides its output signals to a find frequency module. The find frequency module weights each signal from low pass filter bank by its corresponding notch filter center frequency and then takes an average to determine an estimated frequency at which undesirable coupling of missile structural vibrations through the missile's autopilot will occur. The estimated frequency is then supplied to the missile's autopilot which selects the internal notch filter coefficient within the autopilot to reject this frequency.
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Gregory Bernarr E.
Kalmbaugh David
The United States of America as represented by the Secretary of
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