What are piezo actuator creep and drift?

Piezo actuators exhibit a linear* relationship between applied voltage and displacement, responding almost instantly to any change in voltage. But they also experience creep — a phenomenon in which the actuator continues to expand or contract even after the voltage change is complete.

Piezo actuator creep

发生蠕变，因为压电材料具有不对称的电荷分布，其产生偶极子。这些偶极子形成本地域，每个域都有一个偶极矩- 电子的不平等分布。

当施加电场时，与电场膨胀的畴膨胀，因此材料在电场的方向上延长或膨胀。但这不会立即发生 - 它需要偶极子时间来重新定向并达到稳态状态，而且，又将材料继续扩展（或收缩）一段时间。

Piezo开环蠕动 — In an open-loop system, creep can be several percent of the intended motion after an extended period of time.
*Image credit: piezosystem jena*

Creep always occurs in the same direction as that produced by the change in applied voltage. And although creep is a function of time, the rate of creep decreases logarithmically. 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.

可以在数学上确定在给定的时间量之后发生的蠕变量：

ΔL.(t) = displacement at time, t (m)

ΔL._t=0.1s= displacement at 0.1 s after the voltage change is complete (m)

γ=蠕变因子，取决于材料

Piezo执行器漂移

一些制造商使用术语蠕变并互换漂移，但在某些情况下，术语“漂移”用于描述当施加的电压是时发生的现象删除。

When voltage is removed from a piezo material, the偶极子放松,或调整随机,因此他们的极化is zero. But this reorientation takes some time and causes the piezo material to continue expanding (or contracting) until the dipoles reach a steady state.

Drift can also refer to thermal drift of temperature drift, which is a change in position of the actuator due to a change in temperature.

*尽管控制压电行为的方程预测施加电压和位移之间的线性关系，但在现实世界应用中，关系不纯线性。这是因为压电材料展示滞后— 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.