Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-10-25
2001-09-11
Le, Que T. (Department: 2871)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C369S044130
Reexamination Certificate
active
06288383
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a laser spot locating device and to a laser spot locating system including same. More particularly, the present invention relates to a scan-free, daylight operative, laser spot locating device and further to a system including same along with a laser designator.
Accurate location of a low frequency pulsed laser spot in a large field of view is typically effected by a four quadrant detectors device which further includes gimbals and a servo loop used to scan the four quadrant detectors of the device until the laser spot is located in the center of the field of view of the device.
This gimbals and servo loop based device demands a long chain of laser pulses for location, due to the gimbals and servo loop, it is very expensive to manufacture, it is cumbersome, and above all, it is relatively slow in locating laser spots, e.g., about 10 seconds per location.
In order to simplify the device by elimination of the gimbals and servo loop, defocusing of the spot to about a quarter of the field of view is employed. The position of the spot is thereafter determined by the ratio of the defocused spot on each quadrant detector, thereby obviating the need for the gimbals and the servo loop. However, due to defocusing, the accuracy of such a device is very low.
Charge transfer devices (CCDs, CIDs or active pixel devices), which also obviate the need for gimbals and servo loop due to their inherent array of radiation-sensitive elements, are usable for laser spot location only when employed in combination with strong CW lasers that consume a large amount of power, or with less powerful lasers when there is a very low background radiation, (as at night time or inside a machine). In daylight, however, such devices results in a very poor sensitivity (i.e., low signal-to-noise ratio), rendering such devices inoperative.
There is thus a widely recognized need for, and it would be highly advantageous to have, a daylight operable, scan-free laser spot locating device and system devoid of the above limitations.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a daylight operable, scan-free, laser spot locating device for locating a laser spot being pointed at an object, the device comprising (a) a laser spot detecting system including at least one laser spot detecting device and a first electronic system, the laser spot detecting system being for detecting the laser spot in its field of view; (b) a laser spot locating system including a charge transfer device, the charge transfer device featuring an array of radiation-sensitive elements and including snapshot and internal shutter functions, the laser spot locating system further including a second electronic system, the laser spot locating system being for locating the laser spot in its field of view; (c) an optical arrangement for simultaneously providing the laser spot detecting system and the laser spot locating system with substantially overlapping or substantially identical first and second frames, respectively; and (d) a communication medium for communicating between the first and second electronic systems, such that when the laser spot detecting system detects the laser spot in its field of view, the laser spot locating system is activated to locate the laser spot in terms of a deviation of the laser spot from a predefined location in its field of view.
According to another aspect of the present invention there is provided a daylight operable laser spot locating system comprising (a) a laser designator for pointing a laser spot at an object; and (b) a daylight operable, scan-free, laser spot locating device for locating the laser spot, the device including (i) a laser spot detecting system including at least one laser spot detecting device and a first electronic system, the laser spot detecting system being for detecting the laser spot in its field of view; (ii) a laser spot locating system including a charge transfer device, the charge transfer device featuring an array of radiation-sensitive elements and including snapshot and internal shutter functions, the laser spot locating system further including a second electronic system, the laser spot locating system being for locating the laser spot in its field of view; (iii) an optical arrangement for simultaneously providing the laser spot detecting system and the laser spot locating system with substantially overlapping or substantially identical first and second frames, respectively; and (vi) a communication medium for communicating between the first and second electronic systems, such that when the laser spot detecting system detects the laser spot in its field of view, the laser spot locating system is activated to locate the laser spot in terms of a deviation of the laser spot from a predefined location in its field of view.
According to yet another aspect of the present invention there is provided a method of locating a laser spot pointed at an object, the method comprising the steps of (a) detecting a presence of the laser spot via a laser spot detecting system including at least one laser spot detecting device; and (b) activating a laser spot locating system including a charge transfer device, the charge transfer device featuring an array of radiation-sensitive elements and including snapshot and internal shutter functions, to locate the laser spot by shortening an integration time employed thereby.
According to further features in preferred embodiments of the invention described below, the optical arrangement includes at least one focusing lens.
According to still further features in the described preferred embodiments the optical arrangement includes at least one focusing lens.
According to still further features in the described preferred embodiments the optical arrangement includes at least one filter for filtering out radiation outside a spectral region of the laser spot.
According to still further features in the described preferred embodiments the laser spot locating system has a first operation mode characterized in constant dumping of signal and a second operation mode characterized in moving the signals to an output shift register, whereas the laser spot locating system is activated to locate the laser spot in terms of the deviation of the laser spot from the predefined location in its field of view by switching from the first mode of operation to the second mode of operation.
According to still further features in the described preferred embodiments the short integration time is in a range of a duration of a single laser pulse generated by the laser designator.
According to still further features in the described preferred embodiments the short integration time is in a range of about 20-100 microseconds.
According to still further features in the described preferred embodiments the predefined location is a center.
According to still further features in the described preferred embodiments the laser spot detecting device includes a solid state laser detector.
According to still further features in the described preferred embodiments the solid state laser detector is of a material matching the wavelength of the laser, e.g., silicon, gallium arsenide, etc.
According to still further features in the described preferred embodiments the charge transfer device is selected from the group consisting of CCD, CID and an active pixel device.
The present invention successfully addresses the shortcomings of the presently known configurations by providing a daylight operable, scan-free, laser spot locating device and system characterized by high signal-to-noise ratio even under daylight background illumination, which device is based on pixels detection and therefore obviates the need for gimbals and servo loop, and which operates much faster as compared with prior art devices with similar performances (i.e., gimbals including devices).
REFERENCES:
patent: 4561081 (1985-12-01), Janssen et al.
Langer Thomas
Urbach Israel
Friedman Mark M.
Le Que T.
Rafael-Armament Development Authority Ltd.
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