PLC makes hotel towels cleaner

PLC helps hotels, hospitals and other public facilities process their own roller towels rather than send them to commercial laundries.

Hotels, hospitals and other public facilities can now process their own roller towels rather than send them to commercial laundries, thanks to a redesign of the necessary plant by Ducker Engineering in Kendal.

The revised machines, named Revolution, unroll, soak, wash, rinse, dry and re-roll the towels in one continuous process.

One of the keys to Revolution is a controls package, supplied by Mitsubishi Electric, which ensures all aspects of the machine are running at optimum settings.

It also ensures that Revolution uses less energy, water and labour than earlier versions of the machine or conventional laundering methods.

In use, the roller towels, which are typically about 30m long, are stitched together end-to-end so the machine can operate continuously.

Initially about six or seven towels are stored in a buffer hopper, included so continuous operation can be ensured.

From here the main drive, operating through pinch rollers, periodically pulls a 200m length of towel into a soak tank containing hot water and detergent.

It stays there for a specified dwell time, as programmed into the Mitsubishi FX2N PLC at the heart of the control system.

After the soak programme, the main drive activates again to draw the towel through the pressure washing section, where eight bar jets of high temperature water blast away any ingrained dirt particles.

The main drive is one of six within Revolution, all of which are controlled by Mitsubishi variable speed inverters.

"Sectioning the drive was one of the major decisions in the redesign process," said Richard Lanagham, Ducker's Chief Electrical Engineer.

"Our original design, which dated back 25 to 30 years, had one big central drive".

"This wasn't particularly controllable or energy efficient by modern standards and created significant issues at installation and for maintenance planning".

"The sectioned arrangement is better in every respect and with today's inverter technology it is not a great problem to synchronise them".

After the pressure washing, a second drive pulls the towel through the rinse section which makes sure no residues of detergent are left.

The towel then proceeds to twin, independently driven drying drums.

The towel is laced over both drums and slowly travels across them, drying as it goes.

It comes out bone dry and relatively crease-free so does not need pressing.

Finally, it is rewound on rewind stands not dissimilar to those found in paper mills.

"We have to be very efficient at unpicking the stitching we used to join towels at the beginning of the process and swapping to a new stand for each towel," said Lanagham.

The FX PLC communicates constantly with the various inverters and also controls process variables such as water temperature, pressure and flow, timings, detergent inflow, towel tension and so on.

And it drives a number of Mitsubishi HMIs (human machine interfaces) at strategic places around Revolution.

Lanagham said: "We did the redesign using 3D modelling software and decided that, rather than file the virtual models away, we'd use them as graphics on the HMIs for local monitoring and control".

"We've had to overlay process variable readings, alarms and so on, but that was no more work than generating conventional schematics".

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