Characterization of Multilayer Piezoelectric Actuators for Use in Active Isolation Mounts

Active mounts are desirable for isolating spacecraft science instruments from onboard vibrational sources such as motors and release mechanisms. Such active isolation mounts typically employ multilayer piezoelectric actuators to cancel these vibrational disturbances. The actuators selected for spacecraft systems must consume minimal power while exhibiting displacements of 5 to 10 μm under load. This report describes a study that compares the power consumption, displacement, and load characteristics of four commercially available multilayer piezoelectric actuators. The results of this study indicate that commercially available actuators exist that meet or exceed the design requirements used in spacecraft isolation mounts. Introduction Many spacecraft require vibration-suppression systems to isolate science instruments from vibrational disturbances such as mechanical motors or the release of spacecraft components on orbit. These disturbances are transmitted to the science instruments through the mounting hardware, thus affecting the accuracy of the science data that are gathered. One concept for vibration suppression uses active mounts to isolate science payloads from vibrational disturbances during science data collection (refs. 1 and 2). In a previous study at Langley Research Center, active isolation mounts that used piezoelectric actuators were tested by using the Earth Observing System Dynamic Test Bed (ref. 3). In the Langley study, each active mount was equipped with strain-gauge sensors, which provided feedback to a controller. The controller regulated voltage to the piezoelectric actuator in response to micrometer-scale disturbances. In the Langley design, each piezoelectric actuator was required to produce displacements between 5 and 10 μm under loads up to 9 kg. When these active mounts were used, the payload pointing error was reduced by 50 to 80 percent, thus demonstrating concept feasibility. The Langley active-isolation-mount concept employs multilayer piezoelectric ceramic actuators to reject vibrations. Multilayer actuators are produced by stacking thin layers of piezoelectric ceramics together either by adhesive bonding or by cofiring tape cast sheets (refs. 4 and 5). Depending on actuator size, multilayer stacks exhibit micrometer-scale displacements under loads up to several hundred kilograms. When multilayer piezoelectric actuators are used in spacecraft systems, the actuators should be selected to minimize power consumption while maintaining sufficient performance to meet design requirements. This report describes the results of a study comparing the power consumption, displacement, and load characteristics of four commercially available multilayer piezoelectric actuators. Experimental Procedure Test Specimens Based on the displacement and load requirements from the Langley design, multilayer actuators from four suppliers were evaluated. The supplier, part number, and dimensions of each actuator are provided in table I. Additionally, figure 1 shows a photograph of the components tested in this work. As shown in figure 1, all actuators tested had an insulating coating except for the Physik Instrumente (PI) components, which were enclosed in cylindrical stainless-steel housings. All actuators were supplied with electrical leads for applying voltage. Three actuators from each supplier were evaluated to determine the repeatability of their properties and to enable a statistical interpretation of the data. Power Consumption Because the majority of spacecraft vibrations occur at low frequencies, the capacitance and the dielectric dissipation of each actuator component were measured from 25 to 200 Hz by using an LCR meter. The power consumed during operation at each frequency was then determined using the relation (ref. 6)