Optic design of head-up displays with freeform surfaces specified by NURBS

Abstract

The imaging system of a head-up display of production-vehicles in automobile industry includes the windshield which is different for each automobile type. Thus, the the imaging system has to be matched to it. This requires an effcient optic design procedure in order to minimize the development costs. One challenge is the layout of the freeform surfaces of the imaging reflectors because there is a lack of procedures comparable to classical imaging systems like first order design or aberration theory. Additionally, reference systems are not published. Onother big issue is consistent data management. It is usual practice in automotive industriy that the surface data of the imaging surfaces will be imported in CAD systems. Often, from these systems manufacturing code is automaticall generated. Importing surface date is delicate, because the surface describtion in CAD systems is done by NURBS (non-uniform rational B-Splines) which are not or insufficently implemented in commercial optic design software. Thus, a conversion of the surface is performed by the software tools. This conversion is normally not much documented and problems with e.g. accuracy, surface continuity often arrise.In this contribution some methods for the design of an imaging reflector for a head-up display and some resulting designs are presented. Additionally it is shown that already in the design phase the freeform surface can be described by NURBS without any lack of performance. This kind of describtion can then easily be transfered to CAD systems by standardized formats like IGES or STEP without any error-prone conversion.

Exploring Design Parameters for a 3D Head-Up Display

“…Nowadays, automotive HUDs typically present a virtual image approximately 2 m in front of the driver [7]. Ott et al show the functionality of a HUD system [8]. Currently, AR HUDs are developed that allow displaying information at larger projection distances of more than 10 m due to their particular optical design.…”

Free-form illumination of a refractive surface using multiple-faceted refractors

“…To fit the final free-form refractive surface, one point was chosen from each faceted refractor. Many smooth surface description methods have been proposed and developed to fit an optical surface, such as Zernike polynomials [30], nonuniform rational basis spline (NURBS) [31,32], and Forbes polynomials [33,34]. Each model may have merit in different aspects, such as designing or manufacturing, which has been discussed in detail in previous works.…”

Data processing method based on surface and tangent vector deviations for freeform surface

“…Freeform surfaces are different from spherical and aspheric surfaces, without symmetry axis and rotational symmetry, owning multiple degree of freedom [12][13] . Common kinds of freeform surfaces are XY polynomial, Zernike polynomial, NURBS surface, etc.…”