Ultra-precision linear actuator for optical systems

The Ultra-Precision Linear Actuator presented in this paper was developed for the Next Generation Space Telescope's (NGST) primary mirror surface figure control. The development was a joint effort between Alson E. Hatheway, Inc (AEH) and Moog, Schaeffer Magnetics Division(SMD)(1). The goal of this project was to demonstrate an extremely light weight, relatively high stiffness actuator capable of operating uniformly well over the range of 20 degreesK to 300 degreesK and achieving diffraction-limited performance (+/-10 nm) in the optical band for weeks at a time, while consuming no electrical power and dissipating no heat. The essence of the design challenge was to develop a lightweight, high stiffness, low power, thermally stable linear positioning mechanism. Actuation systems with resolutions comparable to that of this design normally are operated in a closed-loop control system to compensate for any non-linearities and hysteresis inherent in their enabling technologies, such as piezoelectric and magnetostrictive transducers. These technologies require continuous application of power and therefore are not low power consumption devices. The development challenge was met through the use of Alson E. Hatheway's (AEH) patented Rubicon elastic transducer(2) which consists of two elastic elements; a soft spring and a stiff flexural member. Deflection of the soft spring applies a force input to the stiff flexure, which responds with a proportionally reduced output deflection. To maintain linearity, the displacements, and hence the stresses, developed in both elastic members are kept well below the elastic yield strength of the material. The AEH transducer is inherently linear and hysteresis free.