Freeform surface modelling is a technique for engineering freeform surfaces with a CAD or CAID system. CAD software packages use two basic methods for the creation of surfaces.
Freeform surface modelling is a technique for engineering freeform surfaces with a CAD or CAID system.
The technology has encompassed two main fields. Either creating aesthetic surfaces (class A surfaces) that also perform a function; for example, car bodies and consumer product outer forms, or technical surfaces for components such as gas turbine blades and other fluid dynamic engineering components.
CAD software packages use two basic methods for the creation of surfaces. The first begins with construction curves (splines) from which the 3D surface is then swept (section along guide rail) or meshed (lofted) through.
A surface being created from curves.
The second method is direct creation of the surface with manipulation of the surface poles/control points.
Surface edit by poles
From these initially created surfaces, other surfaces are constructed using either derived methods such as offset or angled extensions from surfaces; or via bridging and blending between groups of surfaces.
WHAT ARE THE BENEFITS OF FREEFORM ?
Since freeform technology requires only a semi-finished single vision to begin with, lens manufacturers require smaller production space and infrastructure allowing them to invest in R&D for new lens materials and coatings instead. Lens designers have the freedom to develop smarter and more intricate designs without the costly and lengthy process to cast, test, re-design and improve on their projects.
Freeform lens production benefits labs by reducing space and cost for semi-finished lens inventories, providing them with timely access to new designs and a more robust product offering for their clientele. The investment in digital machinery is well worth it.
Eye care professionals have access to the latest technologies to optimize vision correction for their patients. Specialized designs for complex prescriptions are more readily available. Eyeglass wearers receive an array of lens options with uncompromised performance for their specific lifestyle and work environment. Strong prescription patients are no longer limited in their frame selections and benefit from better looking, comfortable eyeglasses with a great range of view.
HOW DOES FREEFORM WORK ?
The freeform design package is made available to laboratories with digital surfacing equipment electronically. As the prescription is entered into their LMS, a lab job is created and the selected design file is pulled from the computer. The base design is adjusted based on the patients’ measurements, frame size and shape, and lens material. The specific combination of design, prescription, frame and face fit details create a design uniquely tailored for that patient. No other patient can use this same design because their measurements will be different.
For example: Design X is selected for 10 patients with the same prescription and same frame in the same lens material. Each job will have a slightly different design based on the individual back vertex distance, Pantoscopic tilt, and face bow measurements of each patient. If this same design is used in jobs for the same 10 patients, same prescription and lens material but different frames, the resulting lenses will vary even more due to different corridor lengths based on the frame size. Once lens material index variation enters the equation, the results are even more dissimilar.
This is especially important for patients with strong prescriptions, where lens thickness and aberrations are more pronounced in high minus and plus semi-finished lens blanks.
FREEFORM LENSES AND TECHNOLOGY
Computerized freeform production has the additional benefit of being more receptive to the incorporation of optical technologies to correct aberrations, smooth power progression, widen viewing fields, allow freelance placement of the design regardless of the lens blank’s optical centre, etc.