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Electronic Design

Piezoelectric Motor Delivers Precise Positioning In Small Applications

Sometimes you need a really small motor, and stepper motors and voice coil motors just won't cut it. Try the Squiggle series of piezoelectric motors from New Scale Technologies. These devices can deliver 10-µm closed-loop repeatability. They're based on a linear actuator that generates ultrasonic vibrations at 115 kHz in a threaded nut.

This nut vibrates in an orbit that resembles a person's hips in a hulahoop motion. The microscopic motion causes the mating screw to rotate, creating precise, bidirectional linear motion. (To see an animation and a video of this motion, go to squiggle_overview.html.)

Instead of wasting power, thread friction drives the screw and holds it in position when the power is off. As a result, there is no backlash, and the motor has a very high stiffness. Also, the motor size can scale from as small as 2.4 by 2.4 by 6.5 mm to sizes with travel lengths as long as 50 mm (see the figure).

The piezo motor technology generates no magnetic fields. The motors can be made from nonferrous metals for use in MRI, scanning electron microscopy, and focused ion microscopy applications. Additional applications include autofocus and optical zoom mechanisms for mobile phone cameras, wearable and implantable medical devices, microfluidic pumps for automated drug discovery, and mirror alignment for cryogenic space telescopes. The motors can work in vacuum environments at levels down to 10-10 Torr as well.

Furthermore, the motor contains only a few parts. But it can replace complex electromagnetic gearhead motors (such as magnets, coils, and solenoids), which typically contain hundreds of parts. Motor positioning can be accurate to within 20 nm, while position speeds can range from 1 µm/s to 10 mm/s. The motor also can generate considerable force for its size—up to 5 Newtons.

To control the motor, New Scale developed an evaluation drive electronics package that ties into a computer via an RS-232 interface. The package also can be controlled manually. It can control up to six motors for multi-axis "set-and-hold" positioning.

A low-current 200-VRMS signal drives the motor with an on/off duty cycle of 0.1 ms. A smart connector on each Squiggle motor stores the motor's optimum drive parameters, including frequency, phase, and voltage. These parameters are downloaded to the driver when the motor is connected.

A developer kit is available for $850. In large volumes, the motor can cost less than $1 each.

New Scale Technologies Inc.

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