3-dimensional (3D/360) backside surfacing ?

[skirk1975]

I want a technical (and also a basic) explanation of 3-dimensional backside digital surfacing. Compared to previous technology used (2-axis?). What do you got?

[Darryl Meister]

You might find the following two articles useful:
Progress in the Spectacle Correction of Presbyopia (see Part 2)
The Optics of Free-Form Lenses

Also, "free-form" lenses are surfaced using computer-controlled, multi-axis (3-axis or more) generators. But most conventional lenses are also surfaced using computer-controlled, 3-axis generators. Older biaxial (2-axis) generators aren't used very often nowadays.

Free-form generators work in much the same way as the regular 3-axis generators used in traditional lens surfacing, although free-form generators rely on more sophisticated electronics and mechanial components that are capable of producing smoother surfaces of greater complexity compared to regular generators. This allows these machines to produce complex lens surfaces that require only a short polishing cycle using a soft lap tool.

Best regards,
Darryl

[shanbaum]

I want a technical (and also a basic) explanation of 3-dimensional backside digital surfacing. Compared to previous technology used (2-axis?). What do you got?

All surfacing is three dimensional.

[HarryChiling]

Every lens has an A size (x-axis) a B size (y-axis) and a thickness (z-axis) surfaceing requires that the equipment manipulate a cutter so that it removes stock from the lens at various thicknesses given any combination of x,y coordinates. Even the old school hand crank generators created 3 demensional lenses. The term digital as well doesn't apply accurately to the process since almost everything in the lab now adays are computer driven. Freefrom is the best description IMO because the term describes the type of surfaces being created by the processwing technique, these surfaces are "free" from any particular "form". Traditional generators (the old rotator cuff busters) believe it or not cut aspheric surfaces, we refered to it as elliptical error and used our steel or aluminum laps and abrasive pads to polish this inconsistency away, digital generators alleviated that problem and now the newer free form generators can create any amount of "elliptical error" the user can express in point data, includeing creating surfaces that are far more complex then a simple rotationally symetrical curve. These newer generators open up the realm of design to a unlimited number of possibilities. Instead of the cost of molding being a road block to a desing, it's all software driven now so prototyping a design can be done easier, and designs on the fly can be done, as well as older designs that faded aways such as blended bifocals which didn't have enough market share to be viable hav enow reemerged into the market.

[Darryl Meister]

Harry, You make elliptical error sound like a "good thing." ;) As opposed to an unwanted artifact caused by grinding a toric lens surface without enough degrees of freedom.

Best regards,
Darryl