The piezo electric effect is useful even at temperatures as low as 4 Kelvin. They also have no mechanisms that bind or freeze at low temperatures. This makes them low maintenance and clean and means they are compatible with vacuum environments. Consequently, they have very long lives with little or no wear. In fact, the solenoid is about twice the length of the piezo, but the force generated by this piezo actuator is over 300 times (!) that of the solenoid.īecause the piezoelectric effect is creating motion on the molecular level, there are really no moving parts in many piezo actuators. While their displacement, or stroke, may be small the forces generated by piezo actuators can be astounding, as shown in figure 5 on the left we see a piezo actuator and on the right side, we see an electromagnetic solenoid actuator of roughly comparable size. A piezo actuator holds its displacement with very high blocking force with no power dissipation.In fact, once the actuator is displaced, you could completely disconnect the electrodes and the piezo can maintain its displacement for weeks until leakage bleeds the charge from our capacitive structure. Nor are they influenced by magnetic fields.Because the piezoelectric effect is electrostatic in nature, their use does not generate magnetic fields.With these techniques different types of piezo actuators can be created, each with their individual shape:Īside from all the physical implementations of the piezo actuators, there are other beneficial properties that make these actuators particularly useful: Even with a stacked configuration, the voltage requirements can range from 60V to several kilovolts. By keeping our fields stronger, a piezo stack can have stroke or displacement of up to 2% of its length. If, however, we interleave the electrodes and crystals, we can maintain a higher electric field with lower voltages. This can quickly become unpractical, and we are further limited by the maximum allowable voltage of the piezoceramic material. The voltage required to maintain the electric field strength grows with the distance between electrodes. There are cost and manufacturability consequences to creating large monolithic piezoceramic structures, and as we increase the length of our device, the electrodes become further apart. So, to get an expansion of 0.1mm from a monolithic structure we need a device in the order of 1 meter in length. When we apply a voltage to the electrodes of our piezo device and create an electric field, a typical monolithic piezo crystal element will expand by only 0.01% of its overall length. As we will see a bit later, a piezo actuator does not behave as a pure capacitance, and this will have a direct effect on our control circuits and coaxing our desired motion out of these devices. Remarkably, the common symbol for a piezo device looks a lot like two electrodes with a block in between (see figure 2, Construction piezoelectric device).Įlectrically, two electrodes separated by a non-conducting – or dielectric – material is, by definition, a capacitor and as a first order approximation this is what we get with a piezo. Now, in order to more easily control the electric field, we add electrodes. That is, a crystalline structure that creates an electric field in response to mechanical forces or will expand or contract in the presence of an electric field. We start with bulk ceramic material with piezoelectric properties. Let’s briefly look at the construction of a piezoelectric device. In converting energy from electrical into mechanical, the device behaves as an actuator (see figure 1, Energy conversion). In converting energy from mechanical into electrical, the device behaves as a sensor. That is, a piezoelectric device can convert mechanical energy into electrical and vice versa. The piezoelectric effect is one of energy transduction. A simple example is a gas lighter used to light your barbeque.įor industrial use and especially in motion control, it is a bit more complicated: Piezoelectricity means electricity as a result of pressure. In this TOP Tech Talk we explain how to use them.ĭriving piezo actuators with linear amplifiers The piezo basics The solution to this problem is the use of power-operational amplifiers. However, the capacitive character, the required high voltages and currents make the control of piezo actuators difficult. Large forces can be produced at precise and small movements. They are available in all kinds of shapes and relatively cheap. Piezo actuators are widely used in today's applications. Driving piezo actuators with linear amplifiers
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