![]() In particularly the finishing of precise mirrors and lens used in semiconductor and astronomical applications. This novel characteristic has found applications in a number of areas. However, unlike ferrofluids it’s their viscosity that changes. Magnetorheological (MR) fluids are pretty awesome! Much like ferrofluids, MR fluids respond to changes in magnetic field strength. Unlike piezos they require relatively low voltages for operation and have found niche applications. However much like piezos it can also be used for high precision motion. We’ve been talking about magnetostriction quite a lot lately. Magnetostriction is the tendency of a material to change shape under a magnetic field. There are numerous other piezo configurations, but typically they are used to provide high force, high precision motion. Obligatory Imperial March demonstration is embedded here: Favorites include Stairway to Heaven, and not 1 but 2 versions of Still Alive (from Portal). Picomotors have resolutions of around 30 nanometer over a huge range of travel, typically 25mm, they’re typically used for optical focusing and alignment and can be picked up on eBay for 100 dollars or so. Oh and they can also be used to make music. The neat thing about this configuration is that it retains much of the piezo’s original precision. By inverting the process (extending quickly, then compressing slowly) the process is reversed and the screw is turned in the opposite direction. The screw can therefore be made to rotate. When extending slowing a jaw rotates a screw, but if the piezo stack is compressed quickly the screw will not return. The basic mechanism is shown in the figure below. This difference between static and dynamic friction is exploited in stick-slip actuators. ![]() Pull it quickly and there will be less friction and the crockery will remain in place. If you pull the cloth slowly there will be significant friction between the cloth and this crockery and they will be dragged along with the cloth. This is much like the tablecloth magic trick shown above. ![]() :))Īnother type of long travel piezo actuator uses the “stick-slip phenomenon”. The tablecloth trick (yes this one’s fake, the kid is ok don’t worry. And the LEGS (and similar Inchworm actuator) allows relatively quick, high force, and high resolution motion. However, piezos can move quickly (flexing thousands of times a second). The rod is therefore moved, in tiny nanometer steps. Rather than using this motion directly, LEGS uses this motion to “walk” along a rod, pushing it back and forth. As noted, Piezos only produce small (generally sub-millimeter) motion. The PiezoMotor LEGS actuator is shown to the above. Notably Inchworm, “LEGS”, and slip-stick actuators. There are a number of piezo configurations that allow this. Sometimes though you need high precision over a larger range of travel. Piezo stacks are ideal here (though hackers have also used cheap buzzers!). These often require sub-nanometer accuracy (less than 1000th of 1000th of 1 millimeter) in order to visualize individual atoms. ![]() The poster-boy application of piezo actuators is perhaps the scanning probe microscope. It is here that piezo actuators really shine. Not very much by normal standards! The PiezoMotor LEGS actuator “walks” along a rod, pushing it as it goes.įor some applications however resolution is of primary interest rather than range of travel. To gauge the motion of a buzzer I recently attempted to drive one with a 150 volt piezo driver, this resulted in a total deflection of around 0.1mm. While a buzzer will produce a clearly audible sound you can’t really see it flexing (as it does shown above). You’d usually drive these with less than 10 volts. The piezoelectric device you’re probably most familiar with is the humble buzzer. The catch of course is that it doesn’t move very much. ![]() Apply a voltage to a piezoelectric material and it will move, as simple as that. Piezoelectric materials sometimes seem magic. I’d love to hear about your favorite actuators and motors too, so please comment below! Piezo actuators and motors The flexing of a piezo buzzer from arcbotics In any case, their mechanisms are interesting in their own right! Join me after the break for a survey of piezo, magnetostrictive, magnetorheological, voice coils, galvonometers, and other devices. In this article, I’m going to look beyond these common devices and search out more esoteric and unusual electronic actuators that might just find a place in one of your projects. Motors are everywhere DC motors, AC motors, steppers, and a host of others. ![]()
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