Lead-free programmable multistable piezo-thermal actuators (LEAP)

我们的目标是开发新的多稳态和可编程驱动器的基础上结合压电和热致动。与现有压电致动器相比，我们在总体上创造了新的性能和功能的同时，还解决了实现传统锆钛酸铅（PZT）基陶瓷的无铅替代品的关键挑战：由于铅具有高度毒性，并且可能在环境中积累（例如，由于不适当的回收和处置），因此一般禁止在电子产品中使用铅，PZT依赖于暂时的ROHS豁免。无铅压电材料、压电致动和热致动本身带来了以下一系列问题和限制，我们的目标是克服这些问题和限制：a） 位移通常通过杠杆机构-弯曲和屈曲-来增强，但以减小力为代价，保持其乘积近似恒定。B） 无铅压电材料具有比PZT低得多的电荷系数。 热致动器具有高功耗，特别是在保持位置时。 屈曲致动器通常只有一个基态，而不是真正的多稳定性，其中在没有施加电信号的情况下保持位置。 除了想要的或不想要的变形之外，温度影响压电响应，并且可能使压电材料在居里温度以上发生形变。 无铅压电材料的居里温度也比PZT低。 一个关键的概念是机械多稳态设计，使用热致动结合压电致动在不同的稳定状态之间切换，使我们能够设计出更高的能量屏障，而这是单独的压电致动无法克服的（d）。这保持了低功耗（c），并且它实现了更大的力和更大的位移（a）和（B）。压电致动，然后用于提供一个稳定点周围的微调，我们的目标是开发系统的微调范围在不同的稳定状态重叠，提供连续的位移。第二个关键概念是用不同的微极化图案对压电材料进行重新极化，其中通过加热到居里温度来辅助压电片的面内和面外极化的组合-将（e）和（f）转变为优点。然后，剩余位移限定附加的稳定状态，并且致动器可以被重新编程以具有不同的机电响应。虽然这将提供额外的功能，但它也将增加压电材料的应变的总体范围。在力学上，我们将使用组合弯曲和屈曲，并旨在开发具有非平凡阶屈曲状态和这些状态之间的过渡的预拉伸平面弹簧系统。为了避免单独的加热层，我们的目标是使用压电材料用超声波加热。遵循结构简单的想法，我们将通过压电致动器的频率依赖性阻抗来探索自感知。

We aim to develop novel multistable and programmable actuators based on the combination of piezoelectric and thermal actuation. Whilst generally creating new performance and functionality compared to present piezo actuators, we address the key challenge of implementing lead-free alternatives to conventional lead-ziconate-titanate (PZT) based ceramics: As lead is highly toxic and can accumulate in the environment (e.g. due to improper recycling and disposal), it is generically banned from electronic products and PZT relies on a temporary ROHS exemption. Lead-free piezo materials, piezo actuation and thermal actuation alone pose the following set of problems and limitations that we aim to overcome:a) The displacement is typically enhanced with lever mechanisms - bending and buckling - but at the cost of reduced force, keeping their product approximately constant. b) Lead free piezo materials have much lower charge coefficients than PZT.c) Thermal actuators have a high power consumption, in particular also when holding a position.d) Buckling actuators typically have only one ground state, not true multistability where a position is held without an applied electric signal.e) In addition to wanted or unwanted deformations, the temperature affects the piezoelectric response and may depolarize the piezo material above the Curie temperature.f) Lead-free piezo materials also have a lower Curie temperature than PZT. One key concept are mechanically multistable designs that use thermal actuation in combination with piezo actuation to switch between the different stable states, allowing us to design higher energy barriers that would not be overcome by piezo actuation alone (d). This keeps the power consumption low (c) and it enables higher forces and larger displacements, (a) and (b). Piezo actuation is then used to provide fine tuning around a stable point, and we aim to develop systems where the fine tuning range around different stable states overlaps, providing continuous displacement. The second key concept is to re-pole the piezo material with different micro-polarization patterns with a combination of in- and out-of-plane polarization of the piezo sheets assisted by heating to the Curie temperature - turning (e) and (f) into virtues. The remnant displacement then defines additional stable states, and the actuators can be re-programmed to have different electromechanical responses. While this will provide additional functionality, it will also increase the overall range of strains of the piezo material. Mechanically, we will use combined bending and buckling and aim to develop pre-tensioned planar spring systems with non-trivial order buckling states and transitions between these states. To avoid separate heating layers we aim to heat with ultrasound using the piezo material. Following the idea of structural simplicity, we will explore self-sensing through the frequency-dependent impedance of the piezo actuators.