Motor keeps wheelchair users comfortable

An AC geared motor from Crouzet running off a battery-based DC supply is helping wheelchair users avoid pressure sores, following the transfer of mattress technology to smaller seat cushions.

An AC geared motor from Crouzet running off a battery-based DC supply is helping wheelchair users keep comfortable and avoid pressure sores, following the transfer of alternating mattress technology to smaller seat cushions.

Alternating mattresses were developed for immobile bed-bound patients to prevent bedsores, which can be a major problem for the long-term ill.

The mattresses work by inflating and deflating different patterns of air cells within the body of the mattress, so that pressure is never experience in the same places on the patients' body for too long.

Now GN Systems in Bolton is miniaturising the concept for wheelchair seat cushions.

They are working with Crouzet and a number of other suppliers to develop the technology for Karomed, a division of the health care specialists Verna Group Ltd.

GN is using the Crouzet motor to turn a rotating disc assembly which forms a two-position valve to select one of two inflation patterns within the cushion.

The cushion is made up of a number of separate air cells, and the rotates continually to change the inflation pattern, over a twenty minute cycle period The pressure within the cells is initially set to match each individual user.

On top of this there are user-selectable soft, medium or firm inflation options.

All these features mean there is a requirement for a degree of intelligence on-board the wheelchair, which GN achieves with a single chip solution.

"The chip we chose is so powerful," explains GN Director Gerry Russell, "that we also use it to control battery charging, to shutdown operations if the charge level falls too low and to indicate current operating status." "Of course, with a battery-based system the output is DC.

But the small mobile compressors that we use are AC - they work on the alternating armature principle rather than using a motor.

So we use the chip, again, to pulse the direct current output at 50Hz.

A small subsidiary inverter circuit ensures a true positive and negative sine wave output." The Crouzet motor, a 12 volt model was extensively tested during the 12 month development phase, to make sure it would stand up to long-term use with the battery supply.

Crouzet's drives specialist also advised that the motor be supplied in a protective control enclosure, as it would be exposed to rain, snow, vibration, shock loads etc.

Crouzet was also concerned to match the motor very carefully to its load for maximum long-term reliability.

After careful consideration it was decided to use a geared unit rather than direct drive, to generate the optimum speed and torque output from the smallest motor practical.

Russell says that the cushion has already been launched in Canada and Australia, to great acclaim.

It is now being introduced to UK health and care services, and the reaction is very positive.

"The question carers always ask is about reliability in the field", says Russell.

"With our careful development and Crouzet's design input on the critical drive system, we are certain we won't ever let anybody down.".

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