Advanced Manufacturing Technologies for Light-Weight, Post Polished, Snap-together Reflective Optical System Designs
ABSTRACT: Fast, lightweight, off-axis, aspheric, reflective optical designs are increasingly being designed and built for space-based remote sensing, fire control systems, aerial reconnaissance, cryovac instrumentation, and laser scanning. Diamond point turning (DPT) is the technology of first resort for many of these applications. In many cases, the best diamond machining technologies available cannot meet the desired requirements for system wavefront error and scatter. Aluminum, beryllium, AlBeMet, and silicon carbide mirrors, layered with thin films of electroless nickel, silicon, or CVD SiC can be first diamond machined or precision ground and then post polished to achieve greatly enhanced performance levels for surface scatter wavefront error (WFE), and alignment registration. By application of manual or computer-controlled post polishing, and by using precise null testing techniques, the objectives of snap-together, or limited compensation alignment of aggressive reflective optical systems can be achieved that are well beyond the performance envelope achievable by diamond machining alone. This paper discusses the tradeoffs among materials and process selection for post polished reflective systems and illustrates actual applications including telescopes for earth and Mars orbit, and a commercial, high speed, flat field scan engine.
Author: Michael Sweeney
Application and Testing of Additive Manufacturing for Mirrors and Precision Structures
ABSTRACT: 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. CMM Optic 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 light-weighted, 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.
Authors: Michael Sweeney, Thomas Vettese
Design Considerations for Fast Steering Mirrors (FSMs)
ABSTRACT: The single-axis and two-axis, flexure mounted, fast steering mirror (FSM) represents a compact, low-cost, high-performance design solution for a variety of emerging optical scanning and beam stabilization applications. Such devices are used to correct for polygon cross scan errors in prepress photography, acquire and lock beams within free space laser telecom systems, modulate tilt and cavity control in interferometers, maintain beam stabilization in the presence of thermal drift and vibration, and provide general two-axis beam scanning. This paper discusses the tradeoffs among the range of motion, spring selection, actuator types, mirror designs, and control systems. Actual product design and performance data are presented for a single axis FSM used for polygon cross scan error correction, and a dual-axis FSM used for free space laser telecom.
Author: Michael Sweeney
Design Considerations for Optical Pointing and Scanning Mechanisms
ABSTRACT: Optical pointing and scanning mechanisms require inter-related optical, mechanical, and electrical engineering and manufacturing disciplines. Such devices are employed in extremely diversified fields of photographic imaging, laser projection displays (LPD), remote sensing for weather prediction, mapping, and earth resources study, and free-space laser telecom. The degrees of freedom commonly applied include rotary scanning, raster, and vector scanning, and limited angle gimbals. Support systems include flexures, ball bearings, and gas bearings. The performance of the optical payload supported by the pointing or scanning mechanism is paramount and dominates the process of materials selection, structural analysis, actuator selection, and control system development. This paper introduces the tradeoffs among range and type of motion, actuator types, angular sensor types, bearing types, and control systems applied to these types of systems. Actual product design and performance data is presented for a high-speed rotary scanner, a fast “nodding” scanner, a flexure supported fast steering mirror (FSM), and several ball bearing and gas bearing gimbal designs.
Author: Michael Sweeney
Design and Manufacturing Considerations for High-Performance Gimbals Used for Land, Sea, Air, and Space
ABSTRACT: 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.
Authors: Mike Sweeney, Tom Vettese