Pneumatics powers a rum do in Cumbria

Visitors to a recently opened tourist attraction in Cumbria can watch an animated version of rum being made in the West Indies and transported to Britain, depicted on a 5m-high "kinetic clock".

The clock is the centrepiece of the £3m Rum Story centre in Whitehaven, which has historic ties to the rum trade and was once Britain`s third busiest port. Twice an hour, the clock springs into life - flags wave, parrots fly, and the sugar cane grows, is cut and falls into grinding wheels. The resulting rum is transported across dancing waves in a rocking and pitching boat, to its destination where it is transferred into copper measures and holding casks, ready for bottling and labelling.

Behind the historic scenes depicted in the tableau, is some modern technology in the form of pneumatics, electric motors and PLC controls. Most of the movements are achieved by pneumatic linear and rotary actuators, pushing on levers or turning cogs attached to parts of the display. Sections requiring continuous rotation are driven by motors.

The drive mechanism is the work of Ian Stephenson, former managing director of Copeland Fluid Power, who now works as a freelance fluid power specialist and training consultant.

A dozen air cylinders produce the clock`s smaller, linear movements while three rotary actuators provide twisting motions for the flags and knives. A rodless cylinder helps the sugar cane to "grow". Two synchronous motors power the grinding wheels and a turntable, while an electric pump delivers the "rum" into the copper measures.

The control system is based on an 84 I/O programmable controller, linked to an electropneumatic valve bank, undirectional speed controls and an HMI (human-machine interface). There are no sensors and all of the movements are time-based using the PLC`s timers and counters.

Picking the air compressor proved to be a challenge because its size could not be determined until the clock was being tested. It also had to be as quiet as possible and had to operate from a single-phase 20A supply. Stephenson chose a medical device that delivered high-quality air though a coalescing filter.

"It has been a valuable and interesting experience," reports Stephenson, "especially during the test and commissioning stages when I was using my laptop computer on site to download the PC-generated sequence control programs."