Significant effort goes into the cutting, polishing and treatment of every lens. Given the importance of ensuring the correct prescription, and the proximity of the lens to the wearer’s eye, any sort of defect simply cannot be countenanced.
One UK manufacturer of bespoke lenses, and a partner of 20 years plus to many of the leading names in the dispensing optician sector, is Vision Labs. Its specialist facility at Kidderminster in Worcestershire processes millions of lenses every year, each one tailored to the needs of the individual customer.
In its facility, raw plastic material is cut to the required geometry by CNC milling and turning equipment, before a high-speed polishing process smooths the lens and removes any remnants from the milling and turning processes. Each lens then undergoes a visual inspection and verification against the patient’s prescription, before undergoing any treatments required, such as tinting, UV protection and the application of scratch- resistant coatings and the latest multi-layer anti-reflection coatings, as needed.
Anthony Woodhouse, technical manager of Vision Labs, explains: “Given the volume of lenses we process, any defect with a lens or issue with production needs to be identified and remedied quickly, or we face a backlog in production which can impact on our delivery schedules and overall service to customers.
“All of our processing equipment is calibrated to very tight tolerances – as little as two microns – to ensure the best possible product quality and life cycle for consumables. However, all CNC equipment can be prone to positioning errors over time, emanating from natural wear and tear, or moving parts which are coming to the end of their lives and require replacement.
“During manufacture, each lens is subject to various levels of stress and heat. If these are not managed correctly, issues may arise which mean the lens may be rejected. In that event, we have to spend time investigating what has happened to determine the root cause then take any remedial action needed.
Machining accuracy is vital
“Key to minimising the risk of defects is ensuring optimal machining machine tool accuracy. Previously we assessed this based in tool displacement using an eyeglass with a scale. However, this method has limitations, even for the highly experienced tool setters within our team,” says Woodhouse.
Because of these challenges, the management team at Vision Labs sought another solution, and it came in the form of a Keyence VHX-7000 digital microscope.
The system’s high magnification and 4,000 pixel count, combined with two-dimensional edge detection software which snaps to the lines of contrast -- meaning the risk of differences between users is eliminated -- allows calibration tolerances as low as 0.1 microns.
Meanwhile, the glare removal feature and rapid 3D depth composition, combined with the VHX’s easy-to-use of software, meant that wear on diamond cutting tools can be rapidly assessed to ensure they are replaced only when needed, creating cost savings for Vision Labs.
Perhaps the greatest benefit has come in the area of analysing coatings, where the VHX’s optical shadow effect mode (OPT-SEM) allows these transparent features to be viewed more readily and so defects identified more rapidly. That feature is said to be a world-first. The multi-lighting feature, allowing immediate change between ring, coaxial, polarised and transmitted lighting, also assists the clarity of view.
Woodhouse continues: “The Keyence microscope is easy to use and gives us incredibly accurate and detailed information. removes the issues associated with the previous visual testing, as it enables us to calibrate our machines extremely accurately and counter any issues in our processes. It has enabled us to view defects in a way that was not possible before, equipping us with a better understanding of how they occur – and how we can minimise the risk of defects.
“This latest investment in Keyence equipment has resulted in higher-quality products, fewer interruptions to production and enhanced cutting tool lifetimes – meaning a significant impact on our productivity, service and the bottom line.”