Apparatus for scanning a rotating gyroscope

An apparatus comprising, inter alia, gyroscope feedback circuitry which aw scanning the rotor magnet of a gyroscope disposed in an associated guided missile system so as to increase the seeker field thereof is disclosed. A signal from the cage coil of the gyroscope having an amplitude approximating a sine function of the angular position of the spin axis of the rotor magnet portion of the gyroscope with respect to the body axis of the associated guided missile is used to generate a constant amplitude drive signal for driving the precession coil of the gyroscope. Scanning, so as to drive the rotor magnet in a predetermined scan pattern is accomplished by phase shifting the signal from the cage coil as a function of its amplitude and then driving the precession coil with the aforementioned constant amplitude drive signal which is phased-locked to the phase shifted or processed cage coil signal.

CROSS-REFERENCE TO RELATED APPLICATION 
U.S. patent application Ser. No. 493,482, to Moran, entitled "An Electronic 
Phase Shifter Having A Constant Magnitude Output", filed May 11, 1983, and 
assigned to the same assignee as the present invention, contains related 
subject matter. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus for scanning a gyroscope, but 
more particularly the present invention relates to an apparatus for 
enlarging the scanning field of the gyroscope so as to improve target 
acquisition of an associated guided missile system. 
2. Description of the Prior Art 
Heretofore, various apparatuses and techniques have been advanced to 
improve the utility of gyroscopes in target searching, target acquisition 
and target tracking especially in guided missile systems. One such 
technique has been to control the nutation of a gyroscope so as to permit 
circular or elliptical scan patterns for target seeking purposes. Here, a 
fixed amplitude excitation at the natural frequency of a spinning mass 
portion of the gyroscope is introduced to cause nutation in the pitch and 
yaw axes of the gyroscope. In the absence of a negative rate feedback 
signal, maximum circular nutation is obtained. Nutation control is 
obtained by comparing the amplitudes of rate feedback and nutation command 
signals in a control circuit. The foregoing signals are used to generate 
torque control signals to cause the aforementioned spinning mass portion 
of the gyroscope to nutate. 
The present invention is contemplated for use with gyroscopes that generate 
a cage coil signal consisting of an amplitude and phase modulated waveform 
wherein the frequency of the carrier portion is the same as the inertial 
spin rate of a rotor magnet, i.e., spinning mass portion of the gyroscope. 
With the foregoing in mind, the previously mentioned technique does not 
include scanning by phase shifting the cage coil signal as a function of 
its amplitude and then driving a precession coil of the gyroscope with a 
constant amplitude signal which is phase-locked to the phase shifted cage 
coil signal. Consequently, there is a need in the prior art to configure 
an apparatus for scanning a rotating gyroscope using the foregoing 
technique. 
As additional background, target seekers using various types of sensors, 
including radiation types for generating error signals for precessing a 
particular gyroscope to align its axis with a desired target, have been 
disclosed in the prior art. Also, at least one technique for generating 
scanning patterns other than circular and elliptical, e.g., conical, is 
disclosed. 
The prior art and background, as indicated hereinabove, include some 
advances in gyroscope scanning apparatuses and techniques; however, 
insofar as can be determined, no prior art apparatus or technique 
incorporates all of the features and advantages of the present invention. 
OBJECTS OF THE INVENTION 
Accordingly, an important object of the present invention is to scan a 
rotating gyroscope by phase shifting the cage coil signal as a function of 
its amplitude in an improved manner. 
A corollary object of the present invention is to drive the precession coil 
of the gyroscope with a constant amplitude signal which is phase-locked to 
the phase shifted cage coil signal. 
Another object of the present invention is to eliminate transient and other 
noise problems due to the close proximity of the cage and precession 
coils. 
SUMMARY OF THE INVENTION 
In accordance with these and other objects and features of the present 
invention, an apparatus for scanning a rotating gyroscope is disclosed 
wherein scanning is accomplished by unique gyroscope feedback circuitry. 
The gyroscope feedback circuitry is characterized by having an 
amplifier/low-pass filter connected to a cage coil portion of the 
gyroscope to be scanned. A cage coil signal from the cage coil is 
amplified and filtered, and from one output of the amplifier/low-pass 
filter fed to the signal input of an electronic phase shifter. The other 
output of the amplifier/low-pass filter feeds an absolute value circuit. 
The output of the absolute value circuit drives one input of a 
differential amplifier. The other input of the differential amplifier is 
connected to a predetermined reference voltage. The output of the 
differential amplifier is connected to the control input of the electronic 
phase shifter. In turn, the output of the electronic phase shifter via a 
buffer/limiter drives a phase-locked loop. The free running frequency of 
the phase-locked loop is adjusted to be approximately equal to the spin 
frequency a rotor magnet portion of the gyroscope so that it will lock-up 
when driven by the electronic phase shifter. The output of the 
phase-locked loop, which is 180.degree. out of phase with its input, is 
filtered and inverted by an inverter/band-pass filter. The output of the 
inverter/bandpass filter, after being amplified in a precession coil 
driver, drives the precession coil of the gyroscope. 
An advantage of the foregoing embodiment of the present invention is that a 
large scanning field is possible which is useful in increasing the seeker 
field of an associated guided missile system. Another, advantage of the 
foregoing embodiment of the present invention that making the amplitude of 
the signal for driving the precession coil completely independent of the 
amplitude of the cage coil signal eliminates instability at certain 
frequencies caused by capacitive coupling between the cage and precession 
coils.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows an embodiment of gyroscope feedback circuitry 10 in which the 
present invention is employed, inter alia, to increase the seeker field of 
an associated missile system (not shown). Essentially, gyroscope feedback 
circuitry 10 comprises an amplifier/low-pass filter 12 which is connected 
at its input to a cage coil 14 disposed about a rotor magnet 16 of the 
gyroscope to be scanned. Also, as illustrated, a precession coil 18 is 
wound contiguously to and under the cage coil 14. The amplifier/low-pass 
filter 12 has two outputs. One output is connected to the signal input of 
an electronic phase shifter 20 and the other output is connected to an 
absolute value circuit 22. 
For purposes of the present invention, the electronic phase shifter 20 can 
be any phase shifter capable of substantially 180.degree. phase shift 
without affecting the magnitude of the signal at its input. Such a phase 
shifter is disclosed in the aforementioned related U.S. patent application 
Ser. No. 493,482, to Moran, entitled "An Electronic Phase Shifter Having A 
Constant Magnitude Output." In addition, the absolute value circuit 22 is 
configured as a full wave rectifier. More aspects of the foregoing will be 
discussed hereinafter in the "Statement of the Operation." 
Continuing with the block diagram representation of FIG. 1, the output of 
the absolute value circuit 22 is connected to one input of a differential 
amplifier 24 with the other input thereof connected to a predetermined 
reference voltage V.sub.ref. The output of the differential amplifier 24, 
which looks like a constant current source, is connected to the other 
input, i.e., the control input, of the electronic phase shifter 20. The 
output of the electronic phase shifter 20 via a buffer/limiter 26 drives a 
phase-locked loop 28. The phase-locked loop 28 includes a mixer 30, a 
low-pass filter 32 and a voltage-controlled oscillator 34. The 
phase-locked loop 28 is connected in the conventional manner with one 
input of the mixer 30 being the input to the phase-locked loop 28. The 
other input of the mixer 30 is connected to the output of the 
voltage-controlled oscillator 34, and the output of the mixer 30 is 
connected to the input of the low-pass filter 32. The junction of the 
other input of the mixer 30 and the output of the voltage-controlled 
oscillator 34 is also the output of the phase-locked loop 28. The output 
of the low-pass filter 32 is connected to the input of the 
voltage-controlled oscillator 34. This connection completes the loop. The 
output of the phase-locked loop 28 is connected to an inverter/band-pass 
filter 36 whose output is connected to the input of a precession coil 
driver 38. The output of the precession coil driver 38 is connected to the 
precession coil 18 of the gyroscope to be scanned. 
STATEMENT OF THE OPERATION 
Details of the operation, according to the present invention, are explained 
in conjunction with FIGS. 1 and 2 viewed concurrently. 
In operation, the cage coil signal, FIG. 2-A, from the cage coil 14 of the 
gyroscope to be scanned, is inputted to the amplifier/low-pass filter 12 
where it is amplified and filtered so as to sufficiently attenuate the 
noise present on the cage coil signal without appreciably shifting its 
phase. The cage coil 14 actually comprises two coils wound about the spin 
axis 40 of the rotor magnet 16 directly on top of the precession coil 18 
and contiguous thereto. Consequently, when the rotor magnet 16 is aligned 
with the missile body axis 42 of the associated guided missile system (not 
shown), no voltage is induced, and, accordingly, no cage coil signal is 
produced. The two coils aforementioned are wound as far apart as is 
practical, so that when the gyroscope to be scanned gimbals, the voltage 
induced in each of the coils will be significantly different. Also, the 
coils are connected in series opposing with the turns of one coil adjusted 
to cancel cross coupling from the precession coil 18. 
To continue, the amplitude of the cage coil signal, FIG. 2-A, is 
approximately a sine function of the angular position of the spin axis 40 
of the rotor magnet 16 with respect to the missile axis 42. When the cage 
coil signal is phase shifted 90.degree., the rotor magnet 16, and, 
accordingly, the gyroscope to be scanned will be precessed in a circle as 
depicted by a scan pattern 44. Phase shifting the cage coil signal less 
than 90.degree. will cause the rotor magnet 16 to spiral inwards towards 
the missile body axis 42. This action corresponds to a decrease in the 
amplitude of the cage coil signal. On the other hand, phase shifting the 
cage coil signal more than 90.degree. will cause the rotor magnet 16 to 
spiral outward. This action corresponds to an increase in the amplitude of 
the cage coil signal. 
Phase shifting is accomplished in the electronic phase shifter 20 by 
driving its signal input with the conditioned cage coil signal, FIG. 2-B, 
and its control input with a control signal, FIG. 2-C, that is directly 
proportional to the amplitude of the cage coil signal, FIG. 2-A. The 
control signal, FIG. 2-C, corresponds to a current generated by the 
differential amplifier 24 in response to the difference between the full 
wave rectified replica of the cage coil signal at the output of the 
absolute value circuit 22 and the predetermined reference voltage 
V.sub.ref. The predetermined reference voltage V.sub.ref is selected to 
set the scan diameter of the scan pattern 44. The phase shifted cage coil 
signal, FIG. 2-D, (shown shifted by 90.degree.) drives the buffer/limiter 
26 which operates as a high impedance buffer as well as as a limiter so as 
to prevent the input of the phase-locked loop from being over driven by 
the varying amplitude of the cage coil signal, FIG. 2-A. The output of the 
buffer/limiter 26 is illustrated in FIG. 2-E. This signal drives the 
phase-locked loop 28 which is used to isolate the precession coil drive 
signal, FIG. 2-G, from the aforementioned cage coil signal, FIG. 2-A. The 
free running frequency of the phase-locked loop 28 generated by its 
voltage-controlled oscillator 34 is adjusted to be approximately equal to 
the spin frequency of the rotor magnet 16 so that the loop will lock-up 
upon the application of the signal of FIG. 2-E. 
Still referring to FIGS. 1 and 2 as viewed concurrently, the output of the 
phase-locked loop 28 is a triangular waveform, FIG. 2-F, which is 
180.degree. out of phase with its input signal, FIG. 2-E, thereof. 
Accordingly, the triangular waveform is inverted and filtered slightly in 
inverter/bandpass filter 36 to produce the precession coil drive signal, 
shown in FIG. 2-G, after power amplification in the precession coil driver 
38. The output of the precession coil driver 38 drives the precession coil 
18. 
Thus, scanning is accomplished by phase shifting the cage coil signal, FIG. 
2-A, as a function of its amplitude and then driving the precession coil 
18 with a constant amplitude signal, FIG. 2-G, phase-locked to the phase 
shifted or processed cage coil signal, FIG. 2-D. 
To those skilled in the art, many modifications and variations of the 
present invention are possible in light of the above teachings. It is 
therefore to be understood that the present invention can be practiced 
otherwise than as specifically described herein and still be within the 
spirit and scope of the appended claims.