Optical lens production gets 20:20 vision

Built for one of the UK’s leading manufacturers of plastic moulded optical components, the novel configuration of the machine vision systems within this cell demonstrates the capabilities of the technology to both 'vision' inspect and 'optically' inspect a range of disposable tonometer optical lenses.

Tonometry is the procedure used by eye care professionals to check the intraocular pressure inside the eye. For these precision moulded parts to function correctly, it is essential that the optical surfaces are flat to within a few microns.

ATM's system uses two separate vision systems, one to vision inspect each component for contamination and correct laser de-gating, and the second to measure the flatness of each individual moulded lens surface in conjunction with structured lighting.

The first machine vision system is used to check for contamination and 'gate witness' on each individual lens. The lenses are indexed into the inspection station using a rotary table system and are backlit to allow the inspection checks to take place.

Any contamination detected that is greater than 0.3mm2 and/or having gate witness of 1.0mm, results in that lens being rejected from the system. Lenses passing these inspection checks are presented to the second vision system which is used to check optical flatness. This part of the system uses a special lighting arrangement, combined with a PC based machine vision system, to measure the flatness of the optical surface to micron level tolerances.

The vision inspection stations are just part of a full turnkey system that performs all operations from de-moulding with a 6-axis robot and part handling and transfer using dual rotary tables and several pick and place mechanisms.

A laser de-gating system was also incorporated as it allowed a non-contact method of gate removal, thus eliminating any potential for mechanical shock which could damage the lens. A further benefit was the super smooth finish achieved by the laser.