20:20 vision on automation

System integrator Barr & Paatz has produced what is believed to be the first fully-automated contact lens manufacturing machine. Developed for Clearlab, the international supplier of daily disposable lenses, the new type of machinery integrates a complete lens manufacturing process — from injection molding to foil packaging — into a footprint just 8 m2. Moreover, by using highly flexible robotic handling arms to transfer products between the process stages, the machine can produce more than 24 million lenses a year.

HSP Handling Unit
The ready-integrated HSP handling unit is employed for high-speed pick-and-place, moving lens pallets between conveyors with the aid of a vacuum head. Right, pneumatic grippers pick carriers off the conveyor, so that they can be rotated to ensure an even distribution of the plastic monomer.

With seven major stations required to meet Clearlab’s process requirements — injection molding of a cast, plastic dosing, two stages of curing, hydration, packaging, and autoclaving — the physical size of the automation process was critical.

“Our focus in designing this machine was on implementing the best and smallest technical solution,” says Stirling Paatz of Barr & Paatz.

“We were looking for the optimum pneumatic components available to provide us with benefits in areas including real estate, performance and energy efficiency.”

More than 400 pneumatic actuators from Festo Corp. are used throughout the machine, organized into cells for each process stage. Each pneumatics cell — consisting of one or two valve terminals — operates semi-autonomously, as an I/O extension to the control system inside a Bosch Rexroth Corp.-supplied articulated robot. Nine robots perform the pick-and-place loading/unloading between the station and the conveyor. Profibus is used as the communications mechanism within the machine, for both the realtime I/O commands that control the cell’s operation, and the handshaking between robot arms that coordinate downstream and upstream handovers.

Barr & Paatz chose to base the pneumatics design exclusively on one manufacturer. With such a large number of pneumatic components, having common physical and interface standards that come with parts from a single supplier simplifies the construction of complete handling axes, the integration of accessories, and general system building.

A further advantage was the ability to choose optimized component designs. Among the examples found on the machine are numerous Festo compact-design cylinders, which are roughly 40% shorter than industrystandard parts. Other advanced components include VADM modules, which combine a vacuum pick-up function with a blow-off ejection mechanism. These parts save precious space in the front-end lens handling area and reduce air consumption through close-coupling and electronic control. Elsewhere, a pre-integrated X-Z axis handling unit known as HSP provides a ready-to-use solution for high speed pick-and-place operations between stations.

The sheer size of the pneumatics system made the choice of valve terminal critical. Here, Barr & Paatz selected the modular MPA valve, which provides a high flow capability in a width of just 10 mm. These valves are mounted on Festo’s high density CPX valve terminal backplane. The MPA portion accommodates up to 32 single- or dual-port valves — fitted with a Profibus interface for system integration. More than a dozen of these backplanes are distributed around the machine. In addition to controlling the pneumatics, the CPX backplanes also provide digital I/O expansion for the robot controllers. The result is a highly space-efficient and distributed solution for the electrical sensors and actuators required in the machine.

“Festo components have clever surface features and a common interface system that provide a very tidy way to build a large automation system,” adds Stirling Paatz. “This has saved a considerable amount of space, which in turn allows our client to increase manufacturing capacity within a very small footprint.”

Barr & Paatz was also able to use CAD models of the components to call off complete pneumatic subassemblies using a single part number, which greatly simplified purchasing and system building. This included the populated valve islands, which typically had a large number of digital I/Os, and a full complement of 32 valves — zoned into groups for vacuum, compressed air, or nitrogen services.

For more information, visit www.barr-paatz.co.uk or email [email protected].