Optics: measuring and testing – Angle measuring or angular axial alignment – With photodetection remote from measured angle
Patent
1995-11-09
1998-07-28
Buczinski, Stephen C.
Optics: measuring and testing
Angle measuring or angular axial alignment
With photodetection remote from measured angle
250342, 356153, 3561411, G01J 502, G01B 1126
Patent
active
057868891
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of monitoring the coalignment of a sighting or surveillance sensor suite including a laser and a sensor coaligned with the laser bean. The invention also relates to apparatus for monitoring the coalignment of a sensor suite.
Modern military sighting and surveillance sensor suites are often required to have accurate coalignment of the sensors within the system and, in such cases where weapons are to be aimed or guided, to the point of impact of the weapon. Coalignment is achieved by one of several methods: the system may be factory set and coalignment retained by design; or in the case of a gun or rocket, the aiming device may be set by firing several practice rounds and adjusting the sighting system point of reference to the point of impact.
Maintaining alignment in a factory set system tends to result in over engineering of the aiming system to achieve the necessary long term stability, leading to cost and size/weight penalties. Also, an assumption that factory coalignment settings have been retained may result in problems and, in the case of a weapon system, the user is unable to determine how accurate his shot will be until he engages a target. The impact on a surveillance system may not be as immediate, but relying on inaccurate target location data could have serious repercussions.
Adjustment to sighting systems through monitoring the point of impact of practice rounds allows coalignment to be checked, though of course this involves the deployment of ordinance. This requires provision of a safe clear area in which coalignment tests can be conducted, and may be time consuming, precluding use in theatre. Also, if the ordinance is costly, such as missiles or smart bombs, then such trials are economically unacceptable. Further, this form of trial requires the operator to possess a considerable degree of skill to adjust the system and provide a subjective assessment of the error between the intended target and the actual point of impact of the projectile.
Increasingly, a greater number of weapons are laser guided, or have targets illuminated by laser designators, and these systems depend heavily on high accuracy sensor coalignment. In such systems, the laser is the system reference and it is to the laser beam that the other sensors are coaligned.
One of the most popular lasers currently in use is the Nd: YAG laser. Lasers of this type are compact, solid state lasers emitting at 1064 nm. They are capable of producing good energy output (500 mj), at high repetition rates (20 HZ and over), for typically, 15 ns pulse durations. However, in direct view sighting systems it is impossible to show the user the path of the laser in order to effect coalignment because not only is 1064 nm radiation invisible to the human eye, but can also cause serious eye damage.
Another difficulty in utilising laser based sighting or surveillance sensor suites is that, as mentioned above, the most popular lasers can potentially cause serious eye damage. However, the requirement to train military personnel in the operation of laser based weapons systems in as near real situation as possible requires use of such systems in exercises. To minimise the possibility of eye damage eye-safe lasers have been developed for training purposes. The most popular wavelength of eye-safe laser operation is 1540 nm, as produced by erbium glass lasers. However, in a sighting system utilising CCD TV cameras it is not possible to produce a coalignment checking system using 1540 nm energy direct onto the CCD as silicon, the basis for current CCD camera detectors, does not absorb 1540 nm photons and therefore has no response to this wavelength.
A number of techniques have been used to render lasers "visible" to such sensors, and the human eye, the most popular of which relies on focusing the laser onto a target formed of a material which absorbs the laser energy and ablates to produce a visible spot. However, there are a number of problems associated with such a system. Firstly, as the target ablates, it has a limited lif
REFERENCES:
patent: 4091412 (1978-05-01), Salonimer
patent: 4422758 (1983-12-01), Godfrey et al.
patent: 5291263 (1994-03-01), Kong
Crook Grahame Stewart
Pope Stephen John
Buczinski Stephen C.
Pilkington P E Limited
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