![]() ![]() Non-linearities - including hysteresis, creep, and drift - can be significantly reduced or eliminated through closed-loop control using a feedback device such as a capacitive sensor. With closed-loop control of a piezo actuator, hysteresis and creep (non-linear behaviors) can be virtually eliminated. This is because piezo materials exhibit hysteresis - essentially, a lag between the change in voltage and change in displacement, causing the actuator to follow different paths of expansion and contraction as voltage is applied and removed. *Although the equations governing piezoelectric behavior predict a linear relationship between applied voltage and displacement, in real-world applications, the relationship is not purely linear. But this reorientation takes some time and causes the piezo material to continue expanding (or contracting) until the dipoles reach a steady state.ĭrift can also refer to thermal drift of temperature drift, which is a change in position of the actuator due to a change in temperature. When voltage is removed from a piezo material, the dipoles relax, or re-orient randomly so that their polarization is zero. Piezoelectric actuators are electromechanical actuators that convert electrical energy into mechanical motion. Some manufacturers use the terms creep and drift interchangeably, but in some cases, the term “drift” is used to describe a phenomenon that happens when the applied voltage is removed. Γ = creep factor, depending on material Piezo actuator drift ΔL t=0.1s = displacement at 0.1 s after the voltage change is complete (m) The amount of creep that will occur after a given amount of time can be determined mathematically: For example, the amount of creep a piezo actuator experiences between 10 and 100 seconds is similar to the amount of creep experienced between 0 and 10 seconds. And although creep is a function of time, the rate of creep decreases logarithmically. In an open-loop system, creep can be several percent of the intended motion after an extended period of time.Ĭreep always occurs in the same direction as that produced by the change in applied voltage. But this doesn’t occur instantly - it takes the dipoles some time to re-orient and come to a steady-state condition, and, in turn, the material continues to expand (or contract) for some amount of time. When an electric field is applied, the domains that are aligned with the electric field expand, so the material lengthens or expands in the direction of the electric field. These dipoles form local domains, each with a dipole moment - an unequal distribution of electrons. ![]() Piezo actuator creepĬreep occurs because piezoelectric materials have an asymmetric charge distribution, which creates dipoles. But they also experience creep - a phenomenon in which the actuator continues to expand or contract even after the voltage change is complete. Piezo actuators exhibit a linear* relationship between applied voltage and displacement, responding almost instantly to any change in voltage.
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