Pneumatic grippers handle polystyrene with care

When Crane Services was asked to develop a gantry system with an enhanced gripper mechanism for transporting packs of polystyrene insulation panels, it knew it was facing a challenge.

When crane and gantry lifting systems specialist Crane Services was asked to develop a gantry system that would offer an enhanced gripper mechanism for transporting packs of polystyrene insulation panels, it knew it was facing a challenge, but found a solution in switching from an electrically powered gripper to pneumatic actuation.

The gantry system was required for picking up and transporting shrink wrapped polystyrene blocks, which are supplied to the construction industry as insulation materials.

With the new Part L Building Regulations requiring greater energy efficiency, more insulation than ever is bought and fitted.The moulded blocks of polystyrene come in shrink wrapped packs measuring up to 2700 x 1200 x 600mm, and can weigh anything from 13 to 100kg depending on the density of the polystyrene.

In production, blocks of polystyrene are taken from the moulding machine, passed through a hot wire cutter which cuts them into panels 15-50mm thick, and shrink wrapped ready for transportation.

The gantry system then comes into operation, transporting the finished packages to an automated pallet stacking station.

The loaded pallets are subsequently accumulated on a powered outlet roller conveyor for and removed by a forklift truck for storage and transportation.

With Crane Services' hoists and gantry actuation systems generally being electrically powered, electro-mechanical actuation had always seemed the natural choice to drive the gripper paddles.

But the problem presented in this case by the challenge of picking up the various sizes of shrink wrapped polystyrene blocks suggested to Crane Services that an alternative technology was needed.

"Our initial idea was to use electrically operated screw jacks to drive the gripper paddles to the ends of the packs", says Crane Services Managing Director Rob Lewis.

"But the wide variation in pack length caused problems, particularly with the jacks jamming".

Looking for an alternative means of actuating the grabber mechanism, the company considered pneumatic operation.

"Pneumatic operation looked attractive, because a constant pressure could be applied to the ends of the packs, regardless of the pack length", says Lewis.

"And it could be safely operated to a stall condition whilst gripping the packs - something which can cause problems of 'burn out' with electric motors".

"But against this, the operation of two simple, conventional pneumatic cylinders to operate the grab paddles presented a problem of its own, in that you could never be sure that the cylinders would operate at the same speed and travel the same distance, so the polypacks wouldn't be centrally picked".

The answer to the problem came in the form of an engineered solution built around Hoerbiger-Origa's BHD heavy duty linear belt drive, which offers the unique option of a bi-parting version.

Although normally powered by electric motors, Hoerbiger-Origa designed a system with the motive force supplied by four of its OSP-P rodless pneumatic cylinders.

Because of their modular design and shared external dovetail profile, the pneumatic actuators were able to be close coupled to the BHD drives using a standard "multiplex" mounting arrangement.

"We realised straight away that this would solve the problem", says Lewis.

Operating in parallel, two BHD units now form the main construction of the grabber unit, providing an effective stroke of 1450mm.

Each is powered by two OSP-P 32 x 300mm pneumatic rodless cylinders, with Hoerbiger-Origa also providing the speed control equipment, FRL equipment and all fittings, tubing and accessories.

"The design has eliminated a great deal of fabrication engineering, and because the units are mechanically coupled, we are assured of perfectly synchronous movement", says Lewis.

"On top of that, the arrangement is neat and compact, and offers simple control, with a single 5/2 valve operating all the cylinders".

"The grab force can easily be varied by adjusting the operating pressure, allowing the system to accommodate the density and resistance of wide range of different size and weight blocks being handled".

In the completed design, the grab system is mounted to an overhead gantry hoist.

The gantry is driven by an AC inverter, allowing speed and acceleration parameters to be optimised for peak performance.

The lowering and raising of the gripper is also controlled via AC inverter, which powers a winch reeling a four-wire rope that supports the gripper mechanism.

Four microswitches are mounted on the faces of the grab plates, to detect the package being gripped and to initiate the lift cycle.

"The operating speed of the system is now impressively quick", says Lewis, "with the pneumatically powered mechanism helping to provide a 48 second handling cycle per package.

"Highly effective, the system is particularly simple, compact, lightweight and attractive", Lewis concludes.

"And it's already generating interest from a number of our customers with handling problems of their own.

"We are increasingly becoming involved with turnkey automated handling systems of this type".

"The demand to eliminate mechanical handling inefficiencies from existing production processes is a key growth area for Crane Services and we believe that the balance of mechanical, electrical, pneumatic and electronic control technologies and innovative engineering used in this installation show cases our capabilities as an organisation".

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