Compact driver sets legs in motion

Edited by the Engineeringtalk editorial team Jun 17, 2005

A small footprint driver is now available for the innovative Piezo Legs linear motor introduced to UK designers and technologists last year by Unimatic Engineers.

A small footprint driver is now available for the innovative Piezo Legs linear motor introduced to UK designers and technologists last year by Unimatic Engineers in London.

Designated the PiezoMotor Driver PDA 3.1, its main function is to control the speed of the motor via a +/-10V analogue voltage signal and is particularly aimed at industrial users.

"Piezo Legs is such a radical new technology that interest is being shown in virtually every field of engineering design", says Jon Harding of Unimatic.

"People from an industrial background automatically expect to see the controller supplied as a stand-alone enclosed module, and this is what we are now able to supply".

Other sectors, such as medical device manufacturers, prefer an open board controller which they integrate into their machines' operator panels.

Piezo technology is based on a laminate of ceramic layers, each of which expands by a different amount when subjected to a tiny electrical charge.

Because the layers are bonded one to another, the differential expansion between the layers causes deflection out of the plane of lamination, in a manner similar to a bimetallic strip.

Thus a piezoelectric leg can be made to flick back and forth, similar to walking, to create precision linear motion.

The voltages involved are so tiny that they pose no danger to operators, nor could they even cause a spark so are ideal for hazardous area applications.

Similarly the legs of the piezo motor are miniscule, but speeds up to tens of millimetres per second can be achieved because they can swing at 10,000step/s or more.

This also allows accuracy and resolution of positioning to 2nm.

The PDA 3.1 is little bigger than a matchbox (74 x 69 x 17mm) and is self-calibrating when it is first connected to a motor - crucial as many of the motors are custom designed for their application.

It is powered by a 0.3A power supply and produces a trapezoidal waveform in the 0-700Hz frequency range.

It functions by converting the analogue signal into discrete (0.32V) speed channels, giving high resolution and thus allowing incredibly accurate positioning to be achieved.

For longer movements where high speed is desirable several signals can be combined; this temporarily reduces the resolution, but positional corrections at the end of stroke can be performed by reverting to a single channel.

Installation of the PDA 3.1 is plug and play and operation is simplicity itself.

A single pushbutton will calibrate or recalibrate the driver, an LED flashes to indicate that recalibration is required, whereas steady illumination indicates "system ready".

The power to weight ratio is such that Piezo Legs motors are regularly used to in applications where they lift 1000 times their own weight.

This makes them ideal for medical implants, in-car and in-plane uses and other applications where weight and space are often critical.

Explosive atmosphere deployment is possible due to the nonsparking characteristic.

The unitary construction means there is virtually no failure through wear, making Piezo Legs suitable for high reliability and long life applications.