Spherically Mounted Retroreflector Coupling for Interferometric Accuracy
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Solution Overview
Problem
Existing retroreflectors, both solid glass and hollow prisms, face challenges in high-precision 3D position measurement due to refraction, dihedral angle errors, and non-planarity, which affect interferometric distance measurement accuracy and are costly to produce.
Innovation Solution
A spherically mounted retroreflector design with a coupling element and carrier, allowing mechanical connection without adhesives, limiting translational movability along a single axis, and using a shim ball for precise alignment and temperature compensation, ensuring planarity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If hollow prism retroreflectors are built using molding process or gluing three reflective surfaces, then the retroreflector can be assembled, but the production becomes complex and costly
Solution Approach 1:
The retroreflector is divided into separate components: a carrier with cavity and an optic inlay with retroreflector. These segments are assembled together, allowing independent manufacturing and simplifying production while maintaining precision requirements only for the optic inlay itself
Solution Approach 2:
The optic inlay is positioned within the cavity of the carrier, creating a nested structure where the precision component (optic inlay) is housed within the supporting structure (carrier), simplifying the overall assembly process while protecting the precision elements
2Measurement precision
If three reflective surfaces are precisely oriented to avoid dihedral angle errors, then measurement accuracy improves, but manufacturing complexity and cost increase
Solution Approach 1:
The precision requirements for avoiding dihedral angle errors are extracted and concentrated solely in the optic inlay component. The carrier provides mechanical support without needing precision orientation, separating the precision function from the structural function and simplifying overall manufacturing
Solution Approach 2:
The coupling element acts as an intermediary between the carrier and optic inlay, providing precise positioning and orientation for the optic inlay while allowing the carrier to be manufactured with standard tolerances. This mediator component isolates the precision requirements to a small, manageable element
3Length of stationary object
If reflective surfaces have high degree of planarity, then interferometric measurement distance increases, but manufacturing precision requirements increase
Solution Approach 1:
The requirement for high surface planarity is extracted and applied only to the reflective surfaces of the optic inlay, while the carrier and coupling elements can be manufactured with standard tolerances. This concentrates precision requirements to the smallest necessary area
4Stability of the object's composition
If retroreflector is mounted on spherical carrier for stability and protection, then mechanical stability improves, but temperature changes induce dihedral angle errors
Solution Approach 1:
The design accounts for temperature-induced parameter changes by allowing controlled thermal expansion of the carrier and coupling element, while the optic inlay maintains its precision geometry. The coupling element's geometry is designed to compensate for thermal effects on the retroreflector's orientation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves cost-effective production with reduced dihedral angle errors and temperature-induced deformations, maintaining high measurement accuracy and constructively interfering light signals.
Implementation Method 1
hollow prisms used as retroreflectors typically comprise three reflective surfaces, wherein incoming light is reflected back along the opposite direction (opposite with respect to an incoming direction) by the hollow prism. The reflection is in general provided through direct reflection at the three reflective surfaces of the hollow prism.
Implementation Method 2
The optic inlay is connected to the carrier. The optic inlay comprises a coupling portion, and the spherically mounted retroreflector comprises a coupling element arranged between the optic inlay and the carrier, wherein the coupling portion and the coupling element are embodied so that they correspond and interact with each other in such a way that - when connected to one another in a purely mechanical manner - translational movability of the optic inlay relative to the coupling element is limited to movability along one movement axis
Implementation Method 3
the at least partly spherical outer surface has a sphere center, which sphere center coincides with the vertex
Data Source
Figure 1~2
Figure 3~4
Figure 5(a)~5(c)
AI summary
The invention relates to a spherically mounted retroreflector (1). The spherically mounted retroreflector (1) comprises 1) an optic inlay (2), the optic inlay (2) comprising a retroreflector having a vertex (9) and an axis of symmetry (11), and 2) a carrier (3) having an at least partly spherical outer surface and a cavity, wherein the optic inlay (2) is arranged in the cavity, and wherein the at least partly spherical outer surface has a sphere center, which sphere center coincides with the vertex (9), wherein the optic inlay (2) is connected to the carrier (3). The optic inlay (2) comprises a coupling portion (5), and the spherically mounted retroreflector (1) comprises a coupling element (4) arranged between the optic inlay (2) and the carrier (3), wherein the coupling portion (5) and the coupling element (4) are embodied so that they correspond and interact with each other in such a way that translationally the optic inlay (2) can at most be moved along a movement axis, in particular the axis of symmetry (11), away from the coupling element (4) in case the coupling portion (5) and the coupling element (4) are connected to one another in a purely mechanical manner.