QMT Features: March 2013
Imagine that!
Multisensor 3D measurement technology helps the world to see.

Imagine the iconic look of rock ‘n’ roll legend John Lennon - it would not be complete without his distinctive round-shaped glasses - a style now adopted by Oxford-based Adlens in developing and creating an award-winning, sight correcting range of variable focus eyewear using variable focus lens technology.  With the Adlens development breakthrough, allowing the power of each individual lens to be instantly adjusted at the turn of an intuitive dial, the eye’s natural dynamic behaviour can be quickly modelled and the important quality of vision restored.

For each pair of instant prescription glasses from The John Lennon Collection, sold complete with the trademarks of Yoko Ono Lennon, the company donates a pair of glasses to someone in the developing world as part of its ‘Buy One - Give One’ programme administered through its sister charity, Vision for a Nation.
For Adlens, the highest level of innovation and vision quality is the benchmark by which the variable focus eyewear specialist is judged, and the company’s highly qualified engineers apply the same parameters of capability in seeking methods of inspection and measurement.  Critical in the decision to install an OGP SmartScope ZIP 250 metrology platform from OGP UK in Foston, Derbyshire, was its versatility to incorporate multiple measuring techniques, switching from one to another as a seamless operation in a single settling.

The OGP machine, according to Adlens quality manager and test engineer Johannes Prins, could be used with one setting for touch probing, non-contact scanning of solid and transparent materials and surfaces and non-contact data capture in any plane due to the highly accurate 5-axis positioning of the part.  In addition, the high resolution video camera with 5:1 zoom optics and automatic calibration made detailed examination of the glasses frame a simple twist of the control.

The machine also has a programmable eight-sector SmartRing lighting source and a Rainbow light probe that is fully integrated and works seamlessly in all planes due to the rotary axis.  These features enable most components of the eyeglasses to be measured using five axes, to capture multi-face geometric dimensions and tolerances plus the determination of critical surface texture on the scratch-proof lenses, in a single data collecting cycle working from just one datum point setting.
Adlens spent three years in final development of two totally different types of variable focus lens for the Hermisphere and Emergensee product lines which is where the OGP SmartScope has proven to be so critical to achieve and 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, Hermisphere 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 to +3.5 until the eye achieves clear vision.  According to Johannes Prins:  “Without the SmartScope we would have had great difficulty in gathering realistic measurements that were consistent.”

Meanwhile, Emergensee, which are universal, whereby one size fits all, uses two textured polycarbonate lenses that move independently to focus one behind the other under screw adjustment from the edge of each frame.  Power ranges from 6 to 3D.  These glasses were developed for use in fluctuating circumstances such as following eye surgery by enabling immediate focal adjustment as the needs change or to temporarily overcome lost prescription glasses or contact lenses.
But most important in Adlens view is the ability to accommodate crisis situations and for inclusion in emergency packs for distribution following humanitarian catastrophes such as the recent earthquake and Tsunami in Japan when thousands were left with no access to sight correction.  Here, Adlens sprang to the rescue and shipped over 1,000 pairs of Emergensee™ glasses to help in the relief effort.

According to Johannes Prins, non-contact measurement was the only viable method to encompass all the elements of the new products in the pipeline of development.  This was driven by the company needing 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.

He said: “The bespoke design and complexity of the different shapes involved in progression of the product during development and the need to be very interactive using easy to grab qualification data on the different components meant we always needed to have consistency, be on-the-ball and ready to support our different departments. 

This applied across all stages of concept, development, tooling-up and production.”   He then reflects: “Without the SmartScope we would have seriously struggled with lead time to launch a proven product which could have resulted in the possibility of the business being seriously challenged.”

He then further qualified his statement by adding: “We needed to understand what was happening in the early life cycle of the product-track, the results of design changes, fine tuning and alterations to tooling and most important, 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.  Also, we would never have had everything under our control if we had to resort to the use of outside sources.”

Adlens is a global leader in the development of variable focus eyewear providing a cost-effective design and manufacture solution to refractive error - regarded as the greatest cause of poor vision.  Said Graeme MacKenzie, director of Industry Affairs for the company: “In sub-Saharan Africa alone, around 95 per cent of people who need eyeglasses do not own a pair.” 

This is qualified by taking Rwanda, for instance, where it is reckoned there are only 14 professional opticians for a population of over 10 million. Similarly, India, China and even Japan, without even considering the host of third world countries which all have comparable problems that affect a person’s education, way of life, employment and personal safety. 

The total versatility was so important in the decision to buy the OGP ZIP 250 SmartScope with its measuring volume using the optional 300 mm axis dimension in X, 150 mm in Y and 200 mm in Z.  This allowed Adlens to use the optional rotational axis to swing items such as the frames of the glasses to pick up measuring points and scan profiles in a single measuring cycle. It was also used in the injection moulding process.

Said Johannes Prins: “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 fitting and full integration within the video-based measuring routine of the OGP Rainbow probe, that is solely available from OGP, enables the optical spectrum of reflected light to determine any changes in surface heights within the 200 mm Z-axis travel.  Scanning the probe over surfaces such as the eyeglass lens quickly captures the profile with high 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 compared.

Mr Prins maintains the OGP machine really came into its own with regards to the injection moulding process, not only for checking profiles but also for developing the ultimate flow in the moulds to eliminate and improve areas where stresses could be created.

Most checking cycles involve between five and 10 batches of components however, the checking of a single part is not uncommon.  This means programming the cycle and maximising the effects of illumination with the camera lens is a common requirement for Adlens, especially on highly reflective surfaces such as the lens.  Here  Johannes Prinsmaintains the initial two-days training was very positive and set him on the road to quickly develop his own procedures.

Adlens is currently checking 13 components on Emergensee glasses, 40 on Hemisphere and, with another product under secret development, some 60 different parts are involved. Materials included ABS nylon, polycarbonate and some steel components.  In addition, on the Hemisphere and John Lennon eyeglass styles, sunglass lenses are available for outdoor use that have different levels of lens characteristics to be checked.  l 


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