Large stroke and nanometer-resolution giant magnetostrictive assembled actuator for driving segmented mirrors in very large astronomical telescopes

Abstract

High-precision-positioning technology with nanometric resolution plays a vital role in driving segmented mirrors in very large astronomical telescopes (VLAT). Current positioning actuators in VLAT are generally based on hydraulic technology, flexible-hinge principle and motor-reducer approaches. Although these actuators have their own merits in their specific applications, they cannot satisfy the high-precise-positioning requirements in active and adaptive optics because of their inherent drawbacks such as hydraulic leakage, lagging, solid friction and insufficient accuracy. To improve the performance of actuators and meet the needs for positioning resolution and accuracy in active and adaptive optics in VLAT, this paper presents the design and implementation of a giant magnetostrictive assembled actuator (GMAA). The actuator features stable nano-resolution positioning, large stroke, instant response, and high load capacity. The design is based on a combination of dual level, i.e. coarse and fine drive regimes. A new large stroke, nanometric positioning GMAA is realized. In this paper the integrated design of the actuator, the control system and the test results from the prototype are presented. The test results prove not only the capacity and positioning accuracy of the actuator in large strokes, but also the effectiveness of the control system and the control method. The tests performed on a single GMA show that when its stroke is 0.6mm, its positioning accuracy may reach to ±30nm and the GMAA positioning accuracy may reach up to ±90nm. The tests performed on the entire GMAA verify that it is able to perform a stroke of 2.2mm with approximately 60nm of displacement resolutions when 600N of external load is applied.