Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1979-09-12
1982-09-07
McGraw, Vincent P.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
G01C 1964
Patent
active
043481132
DESCRIPTION:
BRIEF SUMMARY
Specialists in Laser Rate gyros know that, because of certain defects inherent in the construction of these devices (backscatter from the mirrors in particular), the two laser beams rotating in opposite directions will tend to more or less completely couple together.
As a result of this, the beat frequency obtained by using currently known methods, that is, by making a part of each of the two beams colinear, will not be proportional to the speed of rotation of the rate gyro.
However, the representative curve of the beat frequency with respect to the angular speed of rotation of the rate gyro will remain symmetrical with respect to the origin.
Because of this symmetry, the well known principle of linearization by scanning can be used to correct the defect resulting from the coupling of the two laser beams.
The principle of this system of linearization is clearly set out by Mr. ARONOWITZ in "Laser Applications", volume 1, published by Monte Ross Academic Press of New-York and London.
The majority of the known procedures used for attenuating linearity errors in a ring type laser rate gyro consist of linearization by scanning, that is, superimposing a symmetrical angular oscillation onto the angular movement to be measured.
One of the known methods used consists of causing the entire rate gyro assembly to oscillate about an axis parallel to its detection axis.
The disadvantage of this procedure, however, is that a significant amount of energy is necessary to oscillate the rate gyro, in view of the mass that has to be set in motion.
Additionally, the oscillations of such a mass give rise to a significant reaction against the support elements, which can, in turn, transmit unwanted movement to other components in the installation, such as rate gyros or accelerometers for example.
The principal feature of the invention for attenuating linearity errors in a ring type laser rate gyro using N mirrors that are arranged in such a way that the laser beams travel along two identical polygons in opposite directions is the fact that at least one of the N mirrors which determine the trajectory of the laser beams mentioned above is oscillated angularly with respect to the body of the rate gyro, about an axis perpendicular to the plane defined by these beams. The rotation axis of each of the oscillating mirrors being, for preference, as close as possible to the perpendicular to the mirror being considered, that passes through the point where the laser beams come into contact with the mirror in question.
Other characteristics of the invention will become more fully apparent as the description which follows is read in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic representation of a three-Mirror laser rate gyro, in which, according to the invention, an oscillating motion is given to one or more mirrors.
FIGS. 2 and 3 show a method for creating the oscillating mirror.
FIGS. 4 and 5 show a method for creating an oscillation generator for oscillating the mirror.
FIGS. 6 and 7 show a variant of the method for creating the above mentioned oscillation generator.
FIG. 8 is an illustration of a ring type laser rate gyro incorporating an oscillating mirror according to the invention.
FIG. 1 illustrates as an example, which is not exhaustive, a laser rate gyro with three mirrors, M1, M2, M3, which are arranged on an equilateral triangle.
ABC is the trajectory followed by one laser beam, in one direction and CAB is a similar trajectory followed by a second laser beam in the opposite direction.
The detection axis of this rate gyro is perpendicular to the plane of FIG. 1.
In the procedure which is the subject of this invention, Mirror M1 oscillates about an axis which is parallel to the detection axis of the rate gyro.
It will be an advantage if this oscillation axis passes through the plane of the figure close to the line HH' which bisects the angle made by the laser beams reflected by this mirror.
Each of mirrors M2 and/or M3 can also be given an oscillating movement, the respective oscillation axes of which
REFERENCES:
patent: 3533014 (1970-10-01), Coccoli et al.
patent: 3581227 (1971-05-01), Podgorski
patent: 3786368 (1974-01-01), Bjorkholm et al.
patent: 4113387 (1978-09-01), Shutt
Aronowitz, F., "The Laser Gyro", pp. 153-163, Laser Applications, edited by Ross, M., Academic Press, N.Y. & London, 1971.
Boot, H. A. H. et al., "Ring-Laser Bias Using Reciprocal Optical Components", Electronics Letters, vol. 5, No. 15, Jul. 24, 1969, pp. 347-348.
McGraw Vincent P.
Societe Francaise d'Equipements pour la Navigation Aerienne
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