Additive Manufacturing (aka AM, and 3-D printing) is widely touted in the media as the foundation for the next industrial revolution. Beneath the hype, AM does indeed offer profound advantages in lead-time, dramatically reduced consumption of expensive raw materials, while enabling new and innovative design forms that cannot be produced by other means. General Dynamics and their industry partners have begun to embrace this technology for mirrors and precision structures used in the aerospace, defense, and precision optical instrumentation industries. Aggressively lightweighted, open and closed back test mirror designs, 75-150 mm in size, were first produced by AM from several different materials. Subsequent optical finishing and test experiments have exceeded expectations for density, surface finish, dimensional stability and isotropy of thermal expansion on the optical scale of measurement. Materials currently under examination include aluminum, titanium, beryllium, aluminum beryllium, Inconel 625, stainless steel/bronze, and PEKK polymer.
High performance stabilized EO/IR surveillance and targeting systems are in demand for a wide variety of military, law enforcement, and commercial assets for land, sea, air, and space. Operating ranges, wavelengths, and angular resolution capabilities define the requirements for EO/IR optics and sensors, and line of sight stabilization. Many materials and design configurations are available for EO/IR pointing gimbals depending on trade-offs of size, weight, power (SWaP), performance, and cost. Space and high performance military aircraft applications are often driven toward expensive but exceptionally performing beryllium and aluminum beryllium components. Commercial applications often rely on aluminum and composite materials. Gimbal design considerations include achieving minimized mass and inertia simultaneous with demanding structural, thermal, optical, and scene stabilization requirements when operating in dynamic operational environments. Manufacturing considerations include precision lapping and honing of ball bearing interfaces, brazing, welding, and casting of complex aluminum and beryllium alloy structures, and molding of composite structures. Several notional and previously developed EO/IR gimbal platforms are profiled that exemplify applicable design and manufacturing technologies.
Recently there has been resurging interest in beryllium telescopes ranging in aperture from 0.25-1.5 meter for various NASA space missions. The central theme for this discussion is axially symmetric, all beryllium telescope design forms that are part of advanced LIDAR altimetry systems used to measure the topography and relative density of surface and atmospheric features on the earth and on other planetary bodies. Similar NASA LIDAR missions have previously been sent to Earth’s orbit, the Moon, Mars, and are under consideration for other surveys within the solar system. Design considerations include achieving minimized mass simultaneous with demanding structural, thermal, and optical requirements on orbit after sustaining the rigors of space launch. Modern analysis tools and modeling techniques enable simulation of telescope wavefront errors resulting from environmental effects and the influences of bi-metallic bending from platings. Manufacturing considerations include progressive machining, diamond point turning, coordinate measurement machine profilometry, computerized grinding and polishing, brazing of complex beryllium structures, very thin electroless nickel plating, and other advanced manufacturing technologies imperative to successful visible–infrared optical performance. Recent design and manufacturing efforts on 0.60, 0.80, and 1.0 meter beryllium telescopes are profiled to illustrate the confluence of applicable design and manufacturing technologies.
The advances in the digital data processing and in design and manufacturing of high-performance single-facet scanning devices have made large scan-angle, high-speed/high-resolution digital imaging on cylindrical surfaces possible. Single facet deflectors operating at high speeds in open air tend to be noisy (70+ dBA at 30,000 rpm), collect contaminants (hence requiring frequent cleaning), and require high power to overcome the windage (hence high heat dissipation). For converging laser beam systems, flat and cylindrical window enclosures cannot be used as they induce astigmatism. A spherical window enclosure introduces power and spherical aberration. However, when a spherical window enclosure is used with a spherical lens before the deflector, power and spherical aberration can be eliminated.
Advances in lasers, solid state detectors, electronics, and computational and display capabilities have made a reality of filmless recording, precision dynamic testing, and real-time processing of optical interference fringe patterns. Stroboscopically produced fringe patterns of the mirror-facet surface of a cylindrically shaped and a conically shaped scanner heat for `monogonal' scanners correlate with the predicted dynamic deformations from finite element analysis (FEA) at rotational speeds of 10 krpm and 20 krpm.
Random jitter of the rotational axis in scanners produces scan-line tracking errors that are unacceptable in the laser typesetting and printing industry. The design of the Butterfly scanning device nullifies scan-line cross-scan tracking errors stemming, in part, from bearing wobble. Terms and expressions associated with types of line scanning systems and reflective rotary scanning devices are defined. The essential features of an Axe-Blade scanner, a two- facet scanning device, and the principles of a Butterfly scanner, a two piece, four-facet scanning device, are described. The symmetry of the Butterfly scanner simplifies its design and construction, its alignment and dynamic balancing; and leads to a compact unit. The design uses commercially available bearings, and achieves scanned beam accuracies in the arcsecond and the subarcsecond ranges that, in general, require gas bearings.
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