135 Piezoelectric Actuators and F uture Motors for C ryogenic Applications in S pace  

Christian Belly *, Francois Barillot * and Fabien Dubois*  

Abstract  

The purpose of this paper is to present the current investigation and advancements with piezo actuators  or motors in a cryogenic environment especially from the space application point of view. Established  performances obtained on cryo- dedicated Amplified Piezo Actuators ( APA®) are given and extension of  their capabilities is detailed using piezo motors , or Stepping Piezo Actuator . The Stepping Piezo Actuator  (SPA) principle is shown  in two innovative configurations, fully compatible with a cryogenic environment . 

Introduction  

High-preci sion piezoelectric -based mechanisms have already proven their capability to meet  requirements for space applications in common temperature ranges. A new step is now underway to  improve their operational  range down to temperatures nearing absolute zero. Bas ed on the latest  experimental results, this paper presents this emergi ng capability for piezoelectric -based actuators,  motors and mechanisms to meet this need.    First, Amplified Piezo Actuators are presented, and especially their cryo- dedicated version, wi th  measurements down to 40K. Then,  APA ® integration within  a piezo motor is shown, and experimental  data, including low temperature (90K) experiments , are prese nted. After that, two new motor   configurations are presented, with ambient behavior explanation before setting the perspectives offered by those newly available technologies.  

Piezo Actuators in a Cryogenic Environment 

Amplif ied Piezo Actuators   Amplified Piezoelectric Actuators (APA®) are linear actuators offering large deformations (from 1 to 10%)  and medium strokes (up to 1 mm) [ 1]. They have been designed with an efficient mechanical amplifier  and a pre- stress applied to the piezo ceramics. This design choice was performed initially to meet space  requirements in order to offer a good ability to wi thstand exter nal vibrations (due to launch). As a  consequence of their pre- stress, they can perform the full strokes not only in static conditions but also in  dynamic conditions including resonance and fast transient motion. As additional benefit , they are   extremely reliable (lifetime is more than 1010 cycles), they have passed many aerospace qualifications ,  and they are selected in many EU and U .S. space missions [ 2]. Using the ability of APA® for dynamic  motions, various mechanisms have been built:  fast piezo shutters , fast tool servo,  circuit breakers, micro  scanners , proportional piezo  valves, and piezo generators . APA® samples are visible on Figure 1.  

Cryo Performance of Dedicated Amplified Piezo Actuator s  The ability of piezoelectric ceramics and stacks to work in a cryogenic environment has already been  shown in previous work [3]. Acquired knowledge has been used in order to design cryo- dedicated  actuators, using an ingenious combination of materials in order t o control thermos -mechanical behavior.  In this study, s everal actuator  charact eristics, such as stroke, capacitance and creep are studied versus  temperature, in a temperature range going from ambient to 40K. The interest in this knowledge is mainly  valuabl e in terms  of cryogenic -dedicated design.  

                                                  * Cedrat Technologies, Meylan, France  

Proceedings of the 43rd Aerospace Mechanisms Symposium, NASA Ames Research Center, May 4-6, 2016