Royal Mint coins it in with upgraded drives

The upgrading of a series of nine coin presses at the Royal Mint in Pontyclun in South Wales has given each press a potential increase of a massive 50%.

The upgrading of a series of nine coin presses at the Royal Mint in Pontyclun in South Wales has given each press a potential increase of a massive 50%.

The replacement of the DoL starters with variable AC drives from Control Techniques was one of the significant reasons for this boost in performance.

Typically, on the Grabener presses, the output has been increased from 300 up to 500 coins per minute, the rated maximum for the presses when new.

As well as giving an improved output, the refurbished presses have a reduced machine downtime and there are significant savings in maintenance time and costs.

The Royal Mint, based at the Llantrissant Business Park in mid-Glamorgan, not only manufactures coins for the sterling market, but also coinage for over 100 countries, including many in the Euro zone.

Its presses range in size from 70 up to 200t rating, being flywheel driven, with each press having a maximum strike rate of between 500 and 750rev/min, representing 500 to 750 coins per minute.

A series of six presses have successfully been refurbished both mechanically and electrically.

"Many of our presses were not achieving their rated outputs", explains Royal Mint Project Engineer, Peter Evans, "and so we embarked on a comprehensive upgrade of each machine.

The most significant change has been a complete redesign of the control systems to incorporate state-of-the-art variable speed drives".

"We have used Control Techniques drives at other locations in the plant and have been impressed with their performance and reliability, as well as the back-up from the company, so chose Control Techniques AC drives for this application too".

The presses are being returned to their German manufacturer for refurbishing, with the Control Techniques drives being supplied and programmed by Control Techniques' Drives Centre in Germany.

At the time of writing, 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 11 kW Unidrive 'universal' AC drive now controls the 9kW motor for the flywheel via a clutch and a 3:1 gearbox, to give a maximum speed of 500rev/min.

A Commander GP (general purpose) 0.75kW AC drive provides speed control of the rotary 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.

The Unidrive range of AC drives spans capacities from 0.75kW to 1MW and five operating modes including servo mode.

With plug-in modules, the drive can be tailor made to fit a vast range of different applications, with most of the industry-standard network protocols, as well as RS232 serial communications, used in this application.

Each Unidrive was fitted with a UD71 coprocessor to provide an RS232 interface with the programming software for control and diagnostics purposes.

The Commander GP range (0.75 to 110kW) can be run in open loop V/F or open loop vector control to meet the majority of requirements for thousands of machinery control applications.

It features auto-tune setup with five macros - easy mode, motorised potentiometer, pre-set speeds, torque control or PID control - superb performance with full torque at very low speeds, quiet motor operation and tremendous flexibility of use.

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.

"We went on a three-day training course at Control Techniques in Newtown", adds Peter Evans, "to learn how to program and maintain the Unidrives.

We were very impressed with the drive's flexibility and versatility to take on almost any application.

Since the drives have been installed, our confidence in the reliability of Control Techniques drives has been borne out in experience".

The benefits of each upgrade have been an immediate increase in the output of each press, by up to 50%, easier setup for new coins and a dramatic drop in machine downtime.

General maintenance is much easier too, with a much tidier, more accessible control cubicle.

The Royal Mint continues as a department of government, but, although its primary responsibility remains the provision of the UK coinage, its reputation for the world's finest coins means that more than 100 countries have entrusted the striking of their national coins to the Royal Mint.

At present, over half of its output is for overseas customers and it is the world's leading exporting mint.

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