Test of 7 piezo electric bimorph cantilever beam actuators at 1 Hz, 0-300V. These are wired in parallel and held with ceramic tweezers to prevent shorting.
The bimorph actuators are a laminate consisting of three layers: the top layer is PZT, the middle layer is carbon fiber, and the bottom layer is PZT. They can be thought of as two capacitors in series; on the top side, the PZT-to-carbon fiber represents one capacitor, while the carbon fiber-to-PZT represents the second capacitor on the bottom side. The ‘directionality’ or poling of the PZT depends on the manufacture of the PZT material – meaning that the electric field applied to them should always be in the direction of their alignment (you can’t simply put an AC waveform to them). These actuators are configured to run in “simultaneous drive”, which means that the top-most surface of the top PZT layer is charged at a constant ‘bias’ voltage, the bottom-most pzt surface is held at ground potential, and the carbon fiber layer is given a varying signal in this case a 1Hz sinusoid from 0V to 300V. This arrangement ensures that the signal applied to each ‘capacitor’ unit is always positive. For example, if at one moment the ‘bias’ was 300V and the and carbon fiber was at 150V, then each capacitor would be strained the same amount and the actuator as a whole would be in a neutral position. On the other hand, if the bias was 300V and the carbon fiber layer was held at 50V, then the top PZT would be more strained than the lower PZT, causing the actuator to deflect. In both cases, the polarity of each ‘capacitor’ is respected. There are different types of arrangements for driving actuators, such as the ‘alternating drive’ topology.
Post time: Jun-12-2017