Characterization of surface parallel mirror actuation using preloaded commercial lead zirconate titanate (PZT) stacks

The next generation of space telescopes will require large, segmented apertures for observations in the near ultraviolet through mid- and far-infrared regions to enable new science ranging from exoplanet characterization to precision astronomical observations that refine astrophysics models. To meet these challenges, we are developing instrumented (strain gauge) surface parallel actuators (SPAs) that are robust and can meet the stringent requirements of mass and cost per m2. We have developed a surface parallel mirror test piece and a set of flexured actuators that maintain compression in the piezoelectric stack elements at all times. The characterization work of these actuators is directed at understanding the performance of flexure piezoelectric multilayer stack actuator operation when embedded in the mirror. To determine the influence functions for each actuator position, we will report the measured stroke/strain and charge/capacitance versus voltage curves for all 42 preloaded actuators. Although designed to operate under close loop control via feedback from the strain gauge initial testing on bare lead zirconate titanate (PZT) stack actuators suggests that by driving the stack to a known domain state we could perform open loop control in the actuators to levels of  0.3 m. We will also report on creep for the actuators and cross actuation for each unique actuator position as well as discuss approaches to mitigating the effect on open loop control error. Thermal studies of flextensional actuators embedded in analog rib structures down to 100K will also be presented.

下一代空间望远镜需要大口径分段式孔径，以实现从近紫外到中红外及远红外波段的观测，从而推动涵盖系外行星表征至精密天文观测的前沿科学研究——这些观测将助力天体物理模型的优化。为应对这些挑战，我们正研发集成传感（应变计，strain gauge）的面并行致动器（surface parallel actuators，SPAs），此类致动器具备高鲁棒性，可满足每平方米质量与成本的严苛要求。我们已研制出一款面并行反射镜测试件及一套柔性致动器，后者可始终保持压电叠层元件处于压缩状态。这些致动器的表征工作旨在厘清柔性压电多层叠层致动器嵌入反射镜时的运行性能。为确定各致动器位置的影响函数，我们将报告所有42个预加载致动器的实测行程/应变曲线及电荷/电容-电压曲线。尽管此类致动器设计为通过应变计反馈实现闭环控制，但对裸露锆钛酸铅（lead zirconate titanate，PZT）叠层致动器的初步测试表明，通过将叠层驱动至已知畴态，我们可在致动器中实现±0.3 μm精度的开环控制。我们还将报告致动器的蠕变特性及各独特致动器位置的交叉致动现象，并探讨缓解其对开环控制误差影响的方法。此外，我们还将呈现嵌入模拟肋结构的弯张致动器在低至100开尔文（100K）环境下的热学研究结果。