Optics: measuring and testing – By light interference – Rotation rate
Reexamination Certificate
2000-01-06
2001-05-08
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Rotation rate
Reexamination Certificate
active
06229615
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to ring laser gyros (RLG), in particular techniques for controlling the dithering of RLGs.
BACKGROUND
It is known that the two laser beams in a ring laser gyro will lock on to each other if their frequency difference is too low, a condition that can occur at low input (rotation) rates, rendering the gyro (RLG) unable to detect low angular input rates. To eliminate this problem, a gyro can be mechanically modulated (“dithered”) a small amount by a dither motor.
An electric motor drive, such as a piezoelectric transducer operating on a torsion spring to which the gyro is mounted, may be used to dither the gyro and a similar transducer (dither pickoff) can be attached to the gyro to detect the dither motion as part of closed loop dither control to sustain spring oscillation at a desired amplitude that does not interfere with gyro operation.
In practice, however, the level of the signal seen at the dither pick off for a given dither level, known as the gain of the dither pickoff, can vary significantly between RLGs. Therefore, the same dither control electronics may not provide the same performance from one RLG to another. A manual way to use the same the basic electronics for all RLGS but customize the operation to each gyro for its dither pickoff gain can include using resistor or capacitor divider network to vary the gain of an amplifier producing the dither pickoff that is used to control the motor drive.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved technique for using the same dither electronics with different RLGs without the manual step of adjusting the gain.
According to the invention, the dither pick off is applied to an amplifier that controls the dither motor and the amplifier gain is varied as function of the gyro optical rate readout amplitude.
In the prior art, a gyro optical readout produces separate signals for clockwise (CW) and counterclockwise (CCW) motion. According to the invention these clockwise (CW) and counterclockwise (CCW) signals are counted up for an interval defined by a clock signal to produce a count C
1
within a defined period. The output from the dither amplifier is applied to a comparator to produce a signal that drives a counter which on reaching a selected value or count produces the clock signal, defining the defined period. The gain of the amplifier is selected between a plurality of values by a gain count, which is incremented if Cl is less than a stored minimum and decremented if C
1
is greater than a stored maximum. If it is neither, the operation of the gain select is inhibited and the gain is not changed.
According to one aspect of the invention, if the frequency of the motion quadrature signals is too high the gain select process is aborted
A feature of the invention is that if the CW and CCW signals are counted for a period that is exactly a integer multiple of the dither motion period, the filtering of gyro external motion is much more effective and the time period does not have to be as long. In fact, if there were no random noise modulation, which is present in all practical dithered RLGs, only exactly one dither period would be required to filter out the external motion. Waiting for multiple dither periods can be done to filter out the random noise modulation.
Other objects, benefits and features of the invention will be apparent from the following discussion of one or more embodiments.
REFERENCES:
patent: 4243324 (1981-01-01), Friedland
patent: 4255054 (1981-03-01), Freidland
Greenstien Robert E.
Honeywell International , Inc.
Turner Samuel A.
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