A pair of glasses can be a life-transforming product, but hundreds of millions of people in the developing world
live without the glasses they need because there are no optometrists to test their eyesight and provide prescription glasses. The Oxford-based company Eyejusters believed that there had to be a way to address this problem and make glasses available to everyone, so it set out to develop a range of adjustable spectacles.

The journey from a simple objective to a high-quality production-ready range of spectacles drew heavily on the expertise in injection moulding and robotics of Coventry-based Fanuc UK Ltd (www.fanuc.eu). The project also relied on input from Hi-Tech Automation, which contributed 3-D simulation and its experience in defining a robust production automation concept.

At the heart of the Eyejusters product is its SlideLens technology — a lens with a special profile containing both ‘positive and negative power areas’. When two of these lenses are placed together, the positive and negative power areas cancel each other out, but when one lens is then moved across the other, the amount by which they cancel each other out varies, changing the focus.

Producing optical lenses by injection moulding is invariably a challenging process, but the Eyejusters design presented problems that required in-depth product and process development to overcome. The key objective was to produce optically perfect lenses, but for the Eyejusters design to work, it was essential that they were also as thin as possible, so that the two lenses and their protective rear cover remained aesthetically neat and compact.

Moulding challenges

Because the Eyejusters lenses have profiles of varying thickness, it is almost impossible to mould them using conventional injection moulding techniques. This is because the injection ‘melt front’ tends to move around the thicker sections before completing the fill at the thin sections, which in this case are located in the centre of the lens. With conventional techniques, it was highly likely that problems with quality, such as hairline marks and air traps, would be present — blemishes that are unacceptable in an optical lens.

To eliminate problems such as these and develop a robust production solution, Fanuc ran a series of moulding development tests over an extended period. At the same time, Eyejusters worked on perfecting the tool design so that it could operate with a Fanuc Roboshot electric CNC injection moulding machine and achieve the thinnest-possible and highest-quality lenses.

The outcome of this development exercise was a final production solution comprising a patented mould design that worked in combination with the Roboshot machine’s ‘Pre Injection/Compression’ function. This sees the material injected into the tool under reduced clamp force; then, at a precise injection point, full clamp force is applied to compress the moulding, as the injection process is completed. The design of the Roboshot machine and its CNC system mean that selected positions to control the process are repeatable within 0.001mm.

Production solution

With the lens moulding techniques and processes fully defined, the next stage was to consider the integration of the injection moulding process within a production cell. This would also need to contain the additional technologies and processes required to assemble and finish the lens modules. It was at this point that the long-standing partnership between Fanuc and Hi-Tech became an essential element of the finished product. Hi-Tech has amassed years of experience in the plastics sector; and as a Fanuc Strategic Partner, the company has an in-depth knowledge of Fanuc’s robot range.

Hi-Tech’s initial task was to develop a working specification for each of the production processes and steps. This required daily liaison with Eyejusters personnel to review each step and make decisions on processes, specifications and parameters. The first step was to determine how best to remove the individual mouldings from the tool. In this instance, the team decided it would be beneficial to have the individual moulded parts attached to a runner/sprue for handling and orientation purposes, as this would allow the parts to be removed, transported and handled safely through subsequent processes without touching the optical surfaces. The robot gripper systems were designed accordingly.

The team next turned its attention to the subsequent processes, including lens coating, component de-gating, ultrasonic welding and final packing into thermo-formed trays. Hi-Tech used Fanuc’s RoboGuide simulation software to design, model and create the layout virtually, before any equipment was ordered or manufactured. Further benefits included the ability to evaluate and determine cycle times and generate the robot programs off-line.

As with any optical product, cleanliness is a key consideration; the techniques used for de-gating and welding needed to eliminate the potential for the contamination of the lens components by particulate matter. Hi-Tech selected laser de-gating and ultrasonic welding processes to perform these delicate operations, because they were clean and precise.With the automation cell built and operational, Hi-Tech next built a Class 5 clean room around the cell.

Each of the partners in this venture has since been recognised for its individual contribution and commitment at the Plastic Industry Awards 2016. Fanuc received the award for Supplier Partnership — Prime Machinery, and Hi-Tech received the Automation for Supplier Partnership — Ancillary Machinery award. Eyejusters also received the award for Best Business Initiative of the Year.