Freeform
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Freeform Xiangqian Jiang Centre for Precision Technologies, University of Huddersfield, Huddersfield, United Kingdom
Synonyms Complex geometry; Freeform optics
Freeform
metrology;
Definition Freeform is where the surface shape has no continuous translational or rotational symmetry about axes. Freeform surfaces belongs to the class of complex invariant surfaces (ISO 17450-1 2011).
Theory and Application Introduction Freeform surface is becoming ubiquitous in industrial products, either for functional or aesthetical reasons. The geometry of freeform surfaces cannot be described by a single universal equation and it has a great influence on the performances of a product (Jiang and Whitehouse 2012). Many types of surfaces are defined as freeform by industry: e.g., off-centred rotational
optics, toroidal, etc. These are mathematically not true freeform surfaces but they do have an axis, however this axis does not pass through the functional surface. What follows is also applicable to these quasi-freeform surfaces. Here there are described two types of freeform applications: freeform optics (see Fig. 1) and other freeform applications (see Fig. 2 for artificial knee joint). Each has its own design, manufacturing and measurement technologies, (Fang et al. 2013; Savio et al. 2007). Freeform Optics Leading-edge manufacturing has allowed the production of freeform optics to emerge in modern optics, bringing the advantages of excellent optical performance and system integration. Freeform optics is gradually maturing with broad use in imaging systems for green energy, illumination in automotive, aerospace, and biomedical engineering. Compared to traditional optical components, freeform optics has an increased range of manufacturable surfaces, giving optical designers more flexibility and scope for innovation; enhancing the optical system performance to the maximum extent. For instance, freeform optics enable optical performance that is otherwise impossible, such as simultaneously correcting aberrations, increasing depth of field and expanding the field of view. It can also simplify system structure with fewer surfaces, lower mass, lower cost, smaller package-size and reduced stray-light: realizing
# CIRP 2018 The International Academy for Production Engineering et al. (eds.), CIRP Encyclopedia of Production Engineering, https://doi.org/10.1007/978-3-642-35950-7_16854-1
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Freeform
Freeform, Fig. 1 Alvarez freeform lens design
Freeform, Fig. 2 Part of a measured artificial kneejoint
system integration easily, and reducing the difficulty in assembly. For example, multiple optical surfaces can be made on one freeform element. Although freeform optics have many advantages, the one disadvantage is that tolerances tend to be smaller than spherical optics and there is less leeway in correcting for manufacturing errors in the setup fixturing than spherical optics. Other Freeform Surfaces Other types of freeform surfaces are often called sculptured or curved surfaces. For example, in automotive (car bodies, headlights, panel displays,
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