Abstract
Environmental effects typically limit the accuracy of large scale coordinate measurements in applications such as aircraft production and particle accelerator alignment. This paper presents an initial design for a novel measurement technique with analysis and simulation showing that that it could overcome the environmental limitations to provide a step change in large scale coordinate measurement accuracy. Referred to as absolute multilateration between spheres (AMS), it involves using absolute distance interferometry to directly measure the distances between pairs of plain steel spheres. A large portion of each sphere remains accessible as a reference datum, while the laser path can be shielded from environmental disturbances. As a single scale bar this can provide accurate scale information to be used for instrument verification or network measurement scaling. Since spheres can be simultaneously measured from multiple directions, it also allows highly accurate multilateration-based coordinate measurements to act as a large scale datum structure for localized measurements, or to be integrated within assembly tooling, coordinate measurement machines or robotic machinery. Analysis and simulation show that AMS can be self-aligned to achieve a theoretical combined standard uncertainty for the independent uncertainties of an individual 1 m scale bar of approximately 0.49 µm. It is also shown that combined with a 1 µm m−1 standard uncertainty in the central reference system this could result in coordinate standard uncertainty magnitudes of 42 µm over a slender 1 m by 20 m network. This would be a sufficient step change in accuracy to enable next generation aerospace structures with natural laminar flow and part-to-part interchangeability.
Highlights
A major technical challenge for large scale, high value manufacturing is to provide high accuracy measurements within a factory environment, typically involving large temperature variations and line-of-sight obstructions
This paper presents an initial design of a novel measurement system that has the unique capability to provide highly accurate coordinate measurements and datum structures without being affected by the surrounding environment
absolute multilateration between spheres (AMS) uses absolute distance laser interferometry to measure the distance between steel spheres
Summary
A major technical challenge for large scale, high value manufacturing is to provide high accuracy measurements within a factory environment, typically involving large temperature variations and line-of-sight obstructions. 28 (2017) 045005 of aerospace structures will require surface profile tolerances of less than 0.5 mm to achieve natural laminar flow and feature positions tolerances of less than 40 μm to achieve component interchangeability Proving conformance with these specifications requires measurement uncertainties of the order of 50 μm over 20 m and 4 μm over 4 m respectively [3]. This paper presents an initial design of a novel measurement system that has the unique capability to provide highly accurate coordinate measurements and datum structures without being affected by the surrounding environment. It can enable a step change reduction in measurement uncertainty for large scale industrial measurement. This system is referred to as absolute multilateration between spheres (AMS)
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