Transcript Outline - 123SeminarsOnly.com

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The major advantages of USMs are:
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4.
5.
6.
7.
8.
Compact, lightweight, flexible and robust.
High positioning accuracy.
High low-speed torque and holding torque.
Unaffected by external electric or magnetic fields.
Quiet drive system.
Hard brake with no backlash.
Variable stroke.
Quick response.
 USMs can be classified in the following ways:
 One thing all USMs have in
common is their use of
piezoelectric material to
transform electrical energy to
mechanical energy.
• USMs typically use ceramics derived from lead-zirconate titanate
(abbreviated PZT).
• After the PZT ceramic is shaped and fired, it is then electric field
polarized. This allows the material to deform with a changing electric
field.
 Here we will discuss the operation of a ring type USM. Like
traditional motors, USMs have a stator and a rotor
• Some USMs use a toothed
stator to increase the holding
torque. Other motors simply
rely on frictional forces.
• As shown in the illustration
on the right, the bottom layer
of the stator is composed of
the PZT material mentioned
earlier.
 Two electrical signals with orthogonal modes (like sin(wt) and
cos(wt)) are introduced in the stator material.
 If a constant phase difference exists between the two modes a
traveling wave is created in the stator. Otherwise the wave is
standing.
 The repeated rolling motion of the stator creates microscopic
orbit of the stator’s surface particles (much like water drops in a
water wave. These small movements move the rotor forward.
 Thus, the traveling wave in the flexural stator material moves in
the opposite direction of the rotor spin.
 The stator may drive the rotor using tiny teeth or simply the
force of friction.
 While the angular velocity of the rotor is proportional to the
frequency of the traveling wave, that does not mean they are
equal. The traveling wave may pass through the stator several
times for a single rotation of the rotor.
 Linear USMs, sometimes called “tube” or “rod” USMs,
also use piezoelectric metals or ceramics for
actuation.
 Show here is a picture of New Scale Technologies tiny
“Squiggle” motor.
 The Squiggle motor weighs
about 30gm and boasts a stall
force of 10N. Micro
deformations also give
resolutions as high as 1nm,
and max speeds of 15mm/sec
 The Piezo LEGS motor, developed by MicroMo
Electronics Inc., illustrates one popular technique for
linear USM actuation.
• Like other USMs, the LEGS
motor generates motion in
discrete steps.
• 4 bimetallic metal/ceramic
“legs” are positioned around a
single nut on a threaded rod.
 Applying voltage to a PZT
leg causes it to change
shape. This strain in the leg
causes the nut to bend and
shift on the threaded rod.
• By synchronizing the 4 legs an elliptical force pattern
moves the rod in either the forward or reverse direction.
• Because deformations are small, several thousand
pulses/sec are needed.
 Spherical USMs may be employed when more than one degree of
freedom is needed. Potential applications include surgical robots
or robotic eyes
 The concept of a spherical
USM is simple. Three
separate ring USMs control
actuation in the x, y and z
directions. Thus, the sphere
can be given any orientation
in 3 space
 USMs have lots of potential
for use in medical
applications. One very
promising research area is in
medical diagnostic
instruments.
 The Robotics Institute of Carnegie Mellon University and
the Division of Cardiac Surgery at the University of
Pittsburgh are teaming up to create a tiny robot called the
HeartLander
 The Heart Lander is a tiny
robot that surgeons could
insert into a patient’s chest
cavity through a minimally
invasive incision. This tiny
robot could then move along
the surface of the heart and
perform interventions.
The surgeon would be able to control every movement via a
controller and monitor external to the patients body.
 Canon. (2007). Using UltrasonicVibrations to Drive Focus and
Zoom Lenses. Retrieved March 2, 2009, from Canon:
www.canon.com
 Carnegie Mellon University. (2007). HeartLander. Retrieved
February 22, 2009, from CMU:
www.cs.cmu.edu
 Toyama, D. S. (2008, April). Sherical ultrasonic motor,
piezoelectric actuator, spherical sensing system. Retrieved March
www.tuat.ac.jp