Crane Services faced a number of challenges when asked to design a gantry system with a gripper mechanism for transporting blocks of polystyrene panels.
The blocks come in packs measuring up to 2700 by 1200 by 600mm, and can weigh from 13kg up to 100kg and the gantry system transports the finished packages to an automated pallet stacking station.
‘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.’
Crane Services considered pneumatic operation as an alternative way of actuating grabber mechanism. This method would apply constant pressure to the ends of the packs, regardless of the pack length. It also meant that the system could be safely operated to a stall condition whilst gripping the packs, which can cause problems of ‘burn out’ with electric motors.
However, the operation of two conventional pneumatic cylinders to operate the grab paddles presented another problem in that engineers couldn’t be sure that the cylinders would operate at the same speed and travel the same distance, so the polypacks wouldn’t be centrally picked.Crane Services’ solved these problems by building around Hoerbiger-Origa’s BHD heavy-duty linear belt drive. 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.
Their modular design and shared external dovetail profile meant that the pneumatic actuators could be close coupled to the BHD drives using a standard ‘multiplex’ mounting arrangement. Operating in parallel, two BHD units now form the main construction of the grabber unit, providing a stroke of 1450mm. Each is powered by two OSP-P 32x300mm pneumatic rodless cylinders.
‘The arrangement offers simple control, with a single 5/2 valve operating all the cylinders,’ says Lewis. ‘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.’