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The Components of the
Elliptec Motor
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The Elliptec Piezoelectric
Resonant Motor
Elliptec motors quickly and precisely position stages and mounts while never seeming to move. Their
microscopic movements occur at ultrasonic frequencies and are invisible to the naked eye.
The Elliptec™ Piezoelectric Resonant Motor
Thorlabs' Elliptec™ piezo resonant motor, shown at right, is lightweight, with a mass of 1.2 g,
and compact: the dimensions of the resonator housing, excluding the spring, are 8 mm x 4
mm x 20 mm.
Components of the Motor
The components that compose the motor are shown at far-right. The piezoelectric element is press fit into the aluminum
resonator, which has been precisely designed and machined to produce the desired elliptical motion at the tip and to interface optimally with the driven
module. The free ends of the spring are integrated with the resonator housing. The wires, which are soldered to the top and bottom of the piezoelectric
element, deliver the voltage signal that induces the piezoelectric element to vibrate at ultrasonic frequencies.
When the motor is built into a system, the open loop of the spring is bolted to a sturdy surface that is stationary with respect to the item to be driven, and the
tip of the resonator is placed in contact with the item. The purpose of the spring is to maintain constant contact between the tip of the resonator and the driven
item, and the direction of motion is determined by the resonance frequency at which the piezo element is driven.
Elliptical Motion and Comparison with Conventional Motors
The motor is operated by driving it at one of its two
resonance frequencies. A voltage signal oscillating
at an ultrasonic frequency is applied to the
piezoelectric chip, which responds by expanding
less than a micron and then contracting back to its
original dimensions at the frequency of the driving
signal. This rapid-cycling change in the chip's
dimensions causes a vibration in the aluminum
resonator housing. When the vibration is at one of
the housing's resonance frequencies, a pushing
motion results at the tip of the motor. When
the vibration is at the other resonance frequency a
pulling motion results.
As illustrated in the video, the pulling and pushing
motions result from the tip of the motor tracing an
elliptical path in space when the motor operates at
resonance. The selected resonance frequency
controls the direction of the cyclical motion. The
motor's tip traces one half of the ellipse as it
expands and the other half as it contracts. When
the motor pushes the driven item, the motor's tip is in contact with the item while the tip expands; the two are not in contact while the tip contracts. The
converse is true when the motor pulls the driven item in the opposite direction. The total displacement at the tip of the motor is a function of both the
mechanical load it is driving and the voltage supplied to the piezo element. The maximum displacement can be up to a few microns when the peak driving
voltage is 5 V.
The motor behaves in many ways like a DC or electromagnetic stepper motor, but it does not suffer from many of the drawbacks of these conventional motors.
Unlike conventional electromagnetic motors, which must overcome inertial delays to come to a stop, the highly dynamic Elliptec motor can stop within
microseconds. As it has no gears, it does not exhibit backlash. Since it possesses no magnets, it is compatible with use in environments sensitive to
electromagnetic interference. The motion of the driven element is continuous and smooth. As the tip of the motor must be in contact with the driven item to
induce motion, the motor possesses the safety feature of an inherent friction brake. When in contact with a plastic surface, the motor operates virtually silently.
For OEM applications, the motor can be manufactured in volume at low cost, and it can be driven by inexpensive analog electronics. It does not require
microprocessors or software; however it is compatible for use with them.
T H E E L L I P T E C ™ M O T O R
Software for Devices Driven by Elliptec™ Piezoelectric Resonant Motors
All devices based on the Elliptec™ resonant piezo motor may be controlled by the Elliptec system software,
S O F T W A R E
