Robotics/Components/Actuation Devices/Piezoelectric Actuators

Piezoelectric actuators are actuators that take advantage of the piezoelectric effect found in certain materials.

Piezoelectric Effect


Certain materials have a characteristic of generating an electric potential when compressed or expanded. The amount of potential across the surface is determined by the force of displacement.

Because an electric potential is created from a change in volume, a change in temperature also has the ability of generating an electric potential.

The piezoelectric effect also has an inverse effect. When a voltage is applied to a material with piezoelectric properties, the material expands or contracts depending on the polarity of the voltage applied. The inverse piezoelectric effect is the basis of piezoelectric motors.

Materials with the Piezoelectric properties
Piezoelectricity naturally occurs in symmetrical crystals. Piezoelectric materials can also be manufactured as ceramics.

Crystals Ceramics " All Crap"
 * Quartz
 * Tourmaline
 * Barium Titanate

More Materials can be found by going here, and filtering for the piezoelectric category.

Piezoelectric Actuators
The ability to change shape when a voltage is applied can be used to displace objects. This basically allows electrical energy to be converted to mechanical energy. This can be used to rotate motors or even

Linear
The concept behind a linear piezo motor is layering a stack of piezoelectric discs that will push on each other and eventually push on a surface at an angle which will propel the object forward. The distance the propeller pushes is limited, but the frequency can be very rapid. The input voltage can change the output speed and allows a great amount of accurate movements. The force exerted is minimal and lessens the worry of breaking smaller objects.

Rotary
A rotary motor can work in the same fashion as the linear motor, except when you apply this concept at a much steeper angle to an axle, the linear motion is turned into a rotational motion. Two of these linear motors applied on both sides of a disc in the same direction can spin the disc. This is the same concept in a pitching machine used to sling baseballs.

Stepper
Using a piezoelectric material for a stepper motor can give you better precision due to the short distances involved. By placing piezoelectric motors in opposing directions operating at frequencies that are slightly out-of-phase, the rotation is slight between the time when piezoelectric motors have the disc in a “hold” state. The slight movements and rapid response allow the rotation to be precise.

Squiggle Motor
New Scale Technologies has taken this concept and applied it to a nut and bolt to create a type of screwing effect. The vibrations caused by the piezoelectric material cause the nut to exhibit a “hula hoop” effect to the threads, moving the screw up or downward depending on polarity. This can be used to push an object on a small scale very accurately.

Robotics Applications
Piezoelectric motors have the benefit of being very precise at very fast frequencies. They can also operate on a very small scale allowing robots to become smaller. Piezoelectric motors have the benefit of being able to exert a large displacement with a low driving voltage. Another benefit is the minimal amount of EMI/RFI noise created.

They can be wired in such a way to be sensors as well. They can be used to determine the number of rotations, or if there is a force being exerted against a surface.