Force the pace

From polishing high-end watch parts to moving water around more efficiently, the global growth of low-power drives looks set to continue. Colin Carter reports


With the cost and size of low-power drives coming down, they are increasingly being used in a wide variety of applications, from polishing machines in the watchmaking industry to improving the efficiency of a Cornish park’s water fountain.

And this growth looks set to continue, due to greater demand from emerging economies — especially Brazil, India, Russia, China and eastern Europe.

A recent report from the US-based advisory group ARC estimated the low-power drives market has a compounded annual growth rate of 9.8 per cent on a market valued at some $7bn (£4bn) in 2007.

One company at the forefront of this boom is Switzerland’s Crevoisier, which manufactures production machines for what is described as ‘the high-class watchmaking industry’. At the heart of Crevoisier’s Universal c-5001 lapping and polishing machine is Control Techniques’ Commander SK drive.

The machine, which polishes small parts to a precision of a micron for these high-end watches, has to be able to operate at constant torque at variable and accurate low speeds to get the required finish levels. The drive can be run between 250 and 3,750rpm and, as a bonus, is claimed to be quieter than the previous set-up.

Size was also a factor in choosing the Commander SK. It had to be set inside the table-top polisher as the polishing sequence is programmed directly into the drive, which saves using a programmable logic controller (PLC) both in terms of cost and space. The unit is controlled by a colour, touch-screen human machine interface (HMI) panel that stores settings for polishing different watch parts and materials.

But not all tasks require the minute precision of these watch-part polishing machines. At the other end of the size spectrum, the water industry often uses large drives to power pumps when moving liquids around. A refurbished water treatment plant at Clareville in Co Limerick, Ireland, for example, has installed Clyde Pumps’ high-lift Uniglide-e pumps, powered by 315kW WEG 6p induction motors, to pump treated water.

The double-entry pumps and motors are fitted with variable speed drives to both save energy and allow flexibility over various duty cycles. Energy savings accrue as the motors are not working flat out all the time — the savings are essential if water companies are to keep prices down and maintain energy efficiency.

While this is a neat solution for safety purposes, as the cost of power continues to rise the use of variable speed drives to cut electricity costs is now almost mandatory. The running costs of the Trenance Gardens boating lake fountain in Newquay, Cornwall, have been reduced to the extent that the fountain’s carbon footprint is claimed to be less than half its previous value.

An ABB variable speed drive and programmable controller alters the height of the fountain depending on the wind — thus ensuring passers-by do not get soaked — and reduces aerosol drift from the lake. On still, sunny days the fountain still reaches its maximum height, but when it is windy the height is reduced to two or three metres.

Wind speed data is fed to a PLC, which optimises the fountain height according to a 10-minute rolling average of the wind speeds. The control loop is designed to not react too quickly to one-off gusts, and can turn the fountain off completely if gale-force conditions occur.

On a slightly smaller scale, but also involving pumping water, Danfoss has supplied an AQUA drive to power a fire suppression system at the Central Lakes Co-operative Fertiliser plant in Altwater, Minnesota in the US.

The sprinkler system is pressurised with air to protect against the cold of the average Minnesota winter, with an air pressure transducer monitoring the system. If the pressure drops suddenly, the system identifies that the heads have encountered high heat conditions and the sprinkler relay is tripped.

The Danfoss drive then recognises the fire mode and starts a submersible pump, which pumps water into the system at almost five bar (70psi) at a flow rate of around 760gals (3.5kl)/min.

Outside of fire mode the pump can supply water at a much gentler rate to other areas of the plant for day-to-day activities such as filling tanks. This has the advantage that the pump stays active and the water in the reservoir doesn’t become stagnant.

Drives are also used in timber processing for heavy operations. The first part of the process, the cleaning and debarking of the logs, has been automated at Falkenberg Vida’s sawmill in Hjaltevad, Sweden.

Cleaning of the logs is carried out using chain-driven scrapers under a conveyor, which removes any debris that sticks to the logs. If a problem occurs — such as a log falling off the conveyor — the chain is protected by Emotron M20 shaft power monitors, which stop the scrapers immediately once chain tension is raised.

The debarking process is controlled by an Emotron FDU variable speed drive, which ensures the logs are fed at an even speed. This is powered by four 22kW motors jointly controlled by an FDU 1332kW variable speed drive. The ground bark is used to fuel the plant’s timber driers as well as for heating purposes.

So whether they are used to polish top-class watch parts, move water around more efficiently or begin the process of cleaning and preparing freshly-felled logs, motors and drives can save money and improve processes. And with new engineering projects around the world requiring high levels of automation, the future looks rosy for low-power drive and motor manufacturers.