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A novel method for achieving closed loop control between the steering mirrors of a dual channel free space optical communications terminal is presented. By modifying an off-the-shelf open loop stick-slip actuator, the control system achieves a pointing resolution of 0.002° with under a 15% increase in mass, resulting in a light weight solution suitable for small satellites.
This paper investigates the potential of leveraging Additive Manufacturing (AM) and Topology Optimization (TO) for ultra-precision machining applications, with a specific focus on single-point diamond machining. The primary objective is twofold: to concurrently diminish fixture weight and increase stiffness. This dual approach aims to mitigate deformations induced by rotational and cutting forces, two effects known for their influence on the mirror surface form error and consequently on the optical performance. Using Finite Element Analysis (FEA), the study systematically compares fixtures produced through conventional machining (CM) with those employing AM and TO techniques. The results underscore a remarkable 68% reduction in weight for fixtures designed through TO. This substantial weight reduction renders the assembly of a machining fixture with four deployable segments of diameter 600mm when deployed, manageable by a single operator without the necessity for specialised lifting equipment. Additionally, these designs contribute to significant reductions of up to 87% and 37% in deformation caused by rotational and cutting forces, respectively. Overall, these advantages offer a promising perspective for overcoming limitations in space astronomical or Earth Observation telescope apertures.
This paper explores the application of HIP on printed aluminium substrates intended for mirror production using single point diamond turning (SPDT). The objective of the HIP is to reduce porosity whilst targeting a small grain growth within the aluminium, which is important in allowing the SPDT to generate surfaces with low micro-roughness. For this study, three disks, 50 mm diameter by 5 mm, were printed in AlSi10Mg at 0◦, 45◦, and 90◦ with respect to the build plate. X-ray computed tomography (XCT) was conducted before and after the HIP cycle to confirm the effectiveness of HIP to close porosity. The disks were SPDT and the micro-roughness evaluated. Mechanical testing and electron backscatter diffraction (EBSD) was used to quantify the mechanical strength and the grain size after HIP.
The parametric study could be analyzed with the sensitivity study, response surface, and optimization. The results show the parameters that have the most impact on performance and show its effect on performance in various conditions such as manufacturing load, grounded based stability with screw pressure, natural frequency, thermal load, and gravity release. The optimization process can lead to the improvement of the optical design. This study improves understanding of opto-mechanical design of the flexible pads in metallic mirrors, which can be applied to other metallic mirror designs.
This paper will describe the design, manufacture and metrology of mirror prototypes from the Active Deployable Optical Telescope (ADOT) 6U CubeSat project. The AM mirror is 52mm in diameter, 10mm deep, with a convex 100mm radius of curvature reflective surface and deploys telescopically on three booms. The objectives of the designs were to combine the boom mounting features into the mirror and to lightweight both prototypes by 50% and 70% using internal, thin-walled lattices. Four final lattice designs were downselected through simulation and prototype validation. Prototypes were printed in the aluminium alloy AlSi10Mg using powder bed fusion and fused silica using stereolithography. Aluminium mirrors were single point diamond turned and had surface roughness measurements taken. Fused silica designs were adapted from the aluminium designs and have completed printing.
Free form surfaces are now commonly used components in optics applications and can be widely found in fields such as ophthalmics, car illumination and head-up display systems and laser optics. The machining of free form optics on a 3-axis diamond turning machines is made possible with the use of tool servo machining which synchronises either or both the axial and radial motions of the tool and surface positions (X and Z axes) to the angular position of the spindle (C axis).
However, the machining of surfaces with non-zero gradient at the surface centre is particularly troublesome because the tool is still subject to a relatively large amplitude motion when reaching the central area of the surface. As a result, a small tool offset in either X (radial) or Y (height) creates a particular central signature that can be readily identified, measured and subsequently corrected by the machine operator.
In this paper, we report on a method to optimise the tool offset (X axis) in the particular case of non-zero central gradient and illustrate our discussion with simulation and measurement results.
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