Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1973-01-29
2001-03-06
Buczinski, Stephen C. (Department: 3662)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C244S003160, C250S236000
Reexamination Certificate
active
06198564
ABSTRACT:
BACKGROUND OF THE INVENTION
In gyro-optical objective systems and other optical telescope applications, it is frequently desirable to scan the field of the optical objective system with a radiation detector, to determine the orientation of a radiation source relative to the optical axis of the objective system. Of the various scanning patterns available, the rosette scan is particularly advantageous in that the relatively small field of view of a radiation detector can be scanned across the entire field of the optical objective to produce a circular search pattern with a relatively large field of view.
There are a number of principal disadvantages to prior art methods of rosette scan generation. Because the pattern is the result of the addition of two concentric co-rotating or counter-rotating vectors, the magnitude of each must be established accurately by fixed mechanical parameters of the separate optical components responsible. For example, a greater or smaller deflection than desired will produce an overlapped or incomplete closure of the center of the scan pattern, effects which are generally unacceptable for optimum operation of the system.
Although minor changes can be made to the cant angle of a mirror, such changes are limited to execution during the assembly process of the optical system and, in the case of a prismatic component, the deviation is a completely fixed function which permits virtually no freedom for such adjustments. Again, the use of a refractive prismatic element for even just one of the deflection components can introduce chromatic and other aberrations which are largely uncorrectable due to the rotational nature of the principal axes of these aberrations.
For similar reasons, the use of refractive elements tends to considerably restrict the wavelength regions over which the objective system may be required to operate, and introduces excessive expense when esoteric materials are used to overcome such restrictions. Additionally, the optical design becomes unduly complex when such systems embody, for mechanical or optical convenience or performance, a combination of both refractive and reflective elements of which two are involved in the process of rosette vector generation. Furthermore, if such a system is required to be gimballed, as in a missile seeker, the use of a non-gimballed prismatic element can additionally degrade the optical resolution of the total system by the introduction of largely uncorrectable comatic effects at substantial look angles.
Yet a further difficulty lies in the necessity to provide mechanical counter-rotating drive systems for the elements concerned, and in the packaging of such systems within practical dimensions. Not only is the power requirement a significant factor, but the complex electromagnetic field structure surrounding, for example, a prism drive motor, can introduce significant noise voltages into the radiation detector and its amplifying circuits which could considerably degrade the total performance of the seeker system. Electrostatic charges, developed by the high rotational speeds of the elements concerned, can also produce similar effects.
A further requirement for correct target signal processing is a reference system for deriving continuous and precise angular information concerning the positions of the vector-producing components. This may involve the use of optical or electromagnetic transducers as pick-off elements to determine the precise position and rotational velocity of an optical element drive shaft, thereby adding to the weight and complexity of the system.
It is therefore desirable to have a scanning optical system that is relatively simple in construction, light in weight, and which produces an inherently accurate scan without inducing undesirable optical aberrations, and which facilitates the reduction of data relative to the orientation of a detected target with respect to the optical axis of the system.
SUMMARY OF THE INVENTION
This invention pertains to means for scanning the field of an optical objective or telescope and, more particularly, to apparatus for determining the direction, spatial origin, or spatial characteristics of a radiation source or radiation distribution pattern relative to the axis of the said objective or telescope system. It will be shown that the method used to secure the specific scanning action by mirror means is inherently simple in nature, and particularly so in comparison with existing methods used to achieve a similar result.
It will also be shown that by using means which do not disturb the basic optical alignment of the system the type of scanning pattern can be quickly changed or modified by external command to perform other specific scanning functions, examples and applications of which will be described hereinafter.
With specific application to a gyro-optical objective system used in the guidance of a radiation-seeking missile, the proposed invention can be made to execute a scanning pattern known as a “rosette”. With this type of scan, the comparatively small instantaneous field of view formed by the radiation detector in conjunction with the focal length of the objective, is caused to describe rapid and repetitive sinusoidal excursions forming “leaves”, which are displaced angularly at a relatively slower rate to constitute a circular geometrical search pattern having a comparatively large field of view. The rosette pattern is analogous to the path scanned by the radiation detector projected into space in the form of a narrow beam by the objective system. A radiation-emitting target entering the search field stimulates the radiation detector to produce electrical pulse signals whenever the detector's field of view coincides with it. These signals, in turn, provide error information to permit an auxiliary precession system to properly move the gyro-optical axis and, thereby, return the target image to the center of the scanned rosette field.
A particularly significant virtue of the rosette scan lies in the fact that the maximum information sampling or data rate exists at the center of the pattern, which renders the system inherently less sensitive to the effects of spurious targets or confusing spatial radiation pattern distributions.
It is therefore an object of the invention to provide a new and improved optical scanning system.
It is another object of the invention to provide a new and improved optical scanning system which is primarily reflective in nature.
It is another object of the invention to provide a new and improved optical scanning system which has mechanical simplicity.
It is a further object of the invention to produce a new and improved scanning system which is small in size.
It is another object of the invention to produce a new and improved optical scanning system which is light in weight.
It is another object of the invention to provide a new and improved optical scanning system which is more reliable in operation.
It is another object of the invention to provide a new and improved optical scanning system with reduced chromatic and other optical aberrations.
It is another object of the invention to provide a new and improved optical scanning system with a simplified vector reference system.
It is an additional object of the invention to provide a new and improved optical scanning system which permits the selection of a variety of scanning patterns.
It is a further object of the invention to provide a new and improved optical scanning system with a lower signal to noise ratio.
Other objects and many attendant advantages of the invention will become more apparent upon a reading of the following detailed description together with the drawings in which like reference numerals refer to like parts throughout.
REFERENCES:
patent: 2855521 (1958-10-01), Blackstone
patent: 3054899 (1962-09-01), McKnight et al.
patent: 3330958 (1967-07-01), Kaisler et al.
Buczinski Stephen C.
Collins David W.
Lenzen, Jr. Glenn H.
Raytheon Company
Rudd Andrew J.
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