The iconic look of John Lennon would not be complete without his distinctive round glasses — a style that has been adopted by Oxford-based Adlens for an award-winning range of eye-wear featuring variable-focus lens technology.
The Adlens development allows the power of each individual lens to be instantly adjusted at the turn of a dial. Moreover, for each pair of ‘instant-prescription’ glasses from the John Lennon Collection, the company donates a pair of glasses to someone in the developing world as part of its ‘Buy One — Give One’ programme, which is administered through its Vision for a Nation charity.
The high level of innovation and vision quality evidenced by Adlens’ variable-focus eye-wear is also reflected in the inspection and measurement of its products. In this regard, a key factor in the decision to install a SmartScope ZIP 250 bench-top metrology system —from Foston-based OGP UK
(www.ogpuk.com) — was the unit’s ability to incorporate multiple measuring techniques, switching seamlessly from one to another in a single setting.
The OGP machine can — in one setting — be used for touch probing, the non-contact scanning of solid and transparent materials and surfaces, and non-contact data capture in any plane — such is the highly accurate five-axis positioning of the part.
The machine also has a programmable eight-sector SmartRing lighting source and a Rainbow light probe, which is fully integrated and works seamlessly in all planes via the rotary axis. These features allow most components that make up the glasses to be measured using five axes to capture multi-face geometric dimensions and tolerances; they also allow the surface texture on the scratch-proof lenses to be determined.
Variable focus
Adlens spent three years developing two totally different types of variable-focus lens for its Hemisphere and Emergensee product lines, which enhance the accuracy of focus to correct for problems such as near- and far-sightedness.
Working much like binoculars, where focus is adjusted by way of a screw, Hemisphere uses a silicon oil injected between the rear lens and a flexible membrane. By varying the quantity of oil via two independent screw mechanisms (one for each eye), the fluid manipulates the membrane to vary the focus (between -4.5 and 3.5) until clear vision is achieved.
Adlens quality manager and test engineer Johannes Prins says: “Without the SmartScope, we would have had great difficulty gathering realistic measurements that were consistent.”
Meanwhile, Emergensee is universal (one size fits all) and features two textured polycarbonate lenses — one behind the other — that move independently and achieve the required focus via screw adjustment from the edge of each frame.
These glasses were developed to cope with fluctuating circumstances (such as following eye surgery) by providing immediate focal adjustment as needs change, or to temporarily overcome the inconvenience of lost prescription glasses or contact lenses.
Most important in Adlens’ view is the ability to accommodate crisis situations with the inclusion of its products in emergency packs for distribution following humanitarian catastrophes — such as the earthquake and Tsunami in Japan, when thousands of people were left with no access to sight correction (Adlens shipped over 1,000 pairs of Emergensee glasses to help in the relief effort).
Non-contact measurement
According to Mr Prins, non-contact measurement was the only viable method for assessing all the elements of the new products under
development. The company needed to ensure absolute precision to prevent any leakage of the special silicon fluid encased in the Hemisphere lens — not only as part of its construction during its early trials involving sealing the assembly using laser welding, but also during production.
“Without the SmartScope, we would have struggled to meet the lead time we had to achieve for the launch of a proven product. During the early life-cycle of the product, we needed to understand the effects of design changes and the alterations to the tooling — plus we needed to keep a detailed history in-house. This would have been very difficult using different types of measuring equipment and having to reset for different measurements.”
Adlens’ OGP ZIP 250 SmartScope features the optional 300mm X axis (the 150mm Y axis and 200mm Z axis are standard), which allows the use of a rotational axis to swing items —such as frames — to pick up measuring points and scan profiles in a single measuring cycle. It was also used as part of the injection moulding development process, not only for checking profiles but also for developing the optimum material flow and eliminating areas of stress.
Mr Prins said: “We could easily map all the surface data, which involved free-form surfaces with concave to convex profiles with respect to the lens and frame components, and immediately transfer the data for structure modelling and reference back to other areas of design.”
The full integration of the OGP Rainbow probe within the video-based measuring routine allows the optical spectrum of reflected light to determine any changes in surface heights within the 200mm Z-axis travel. Scanning the probe over surfaces such as the eye-glass lens quickly captures the profile with high levels of lateral and vertical resolution.
With the integration of the rotary axis, both profiles of the lens can be captured at the same setting from line scans and the data can be compared. Most checking cycles involve batches of between five and 10 components, although the checking of single parts is not uncommon.
Adlens is currently checking 13 components on Emergensee glasses, 40 on Hemisphere glasses and 60 on another product under development. The materials involved include ABS nylon, polycarbonate and steel.
Adlens background
Variable-focus glasses were invented in 1998 by Professor Joshua Silver, a physicist in the Department of Atomic and Laser Physics at Oxford University. In 2004, James Chen — a Hong Kong businessman and philanthropist — heard about fluid-injection lens technology and co-founded Adlens with Professor Silver.
Together, they set up the global headquarters in Oxford and the nearby Oxford Innovation Centre for design and development, where 38 people are based (most of them highly qualified engineers).
At the Innovation Centre, a process development laboratory has also been set up to develop and prove out assembly processes and automation for its production operations. The company also employs 12 people at offices in Tokyo (Japan) and Boston (USA).
Highlighting the importance of Adlens products, company director Graeme MacKenzie says: “In sub-Saharan Africa alone, around 95% of people who need glasses do not own a pair.
In Rwanda, for instance, it is reckoned that there are only 14 professional opticians for a population of over 10 million. It is a similar story in India and China — and even Japan — let alone the many third-world countries.”