Royal Mint coins it in with new variable AC drives

After replacing its nine coin presses with DoL starters and AC variable drives, South Wales based Royal Mint has managed to improve the manufacturing output of each press by 50%. The new control equipment, supplied by Control Techniques, has enabled output to increase from 300 to 500 coins per minute, the rated maximum for the Grabener presses when new. And the refurbished presses are also now benefiting from reduced downtime, leading to savings in maintenance time and costs. “Many of our presses were not achieving their rated outputs,” explains Peter Evans, project engineer at Royal Mint. “So we embarked on a comprehensive upgrade of each machine. The most significant change has been a complete re-design of the control systems to incorporate variable speed drives.” The presses are being returned to their German manufacturers for refurbishing, with the Control Techniques drives being supplied and programmed by the company’s Drives Centre in Germany. So far, two presses have been upgraded with a further four still to be done. Each upgraded press now has two AC drives installed. On the Grabener presses for example, an 11kW Unidrive universal AC drive now controls the 9kW motor for the flywheel via a clutch and a 3:1 ratio gearbox, giving a maximum speed of 500rpm. A Commander GP (general purpose) 0.75kW AC drives provides speed control of the rotary feed bowl feeder to feed coin blanks from a hopper into a stack that feeds the press. Although the presses vary in their power requirements, one size of Unidrive and Commander GP has been chosen to encompass the range, to minimise spares requirements. Each press is under overall PLC control and the speed of each drive is adjusted from the operator’s control panel. The coin feed is set to ensure that the coin stack is always well filled, whilst the main Unidrive, under open-loop speed control, provides a direct adjustment of the coin output rate. As well the benefits in improved manufacturing output, it’s now easier to set up the machines for new coin runs. General maintenance is much easier too with a much tidier, more accessible control cubicle.