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. 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. Piezotechnics is experienced in highly dynamic actuation.Driving piezo actuators with linear amplifiers Sufficient measures has be taken to avoid excessive temperatures:Ĭontact Piezotechnics if high power levels are required. Continuous dynamic operation can generate high losses and the piezo stack may rapidly heat up. Damping is effective in piezoelectric materials and in dynamic operation losses occurs with resulting heating of the Highly dynamic operation of a piezoelectric actuator results in high levels of mechanical (force x speed) and electrical The following equations illustrates the mechanical response quite below and beyond the mechanical The realizable displacement of an actuator in sinusoidal operation is given by theĮquilibrium of the piezoelectric force and the force needed to accelerate the effective mass. At higher frequencies the stroke is limited by the inertia of the effective actuator mass. The low frequency response of that basic actuator system is givenīy the free stroke. The actuator itself represents a spring mass system with low damping rate. The dynamic response of a piezo actuator and connected mechanical load to the electrically controlled piezoelectric force isĭetermined by masses, stiffness’s, and damping rates. The piezo in a fuel injector is used to generate several fast pulses during each ![]() Piezo is the superior actuator principle to control the injection process and superseded electromagnets. In modern car engines high-pressure fuel injectors are used to spray very precisely fuel into the combustionĬhamber. In dynamic actuation mode periodic (sine, square waves) or non-periodic waveforms (e.g.Ĭompensation of disturbances in a feedback control loop) are applied to the actuator.
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