Design and test of a novel cost-effective piezo driven actuator with a two-stage flexure amplifier for chopping mirrors

A fast chopping secondary mirror is the critical functioning assembly in an astronomical telescope for infrared observation. Normally, a chopping mirror is driven by precision high-load and high-stiffness linear actuators which are expected to be lightweight, compact and further cost-effective. The stroke of the actuator is typically required to up to several hundred microns with typical load capacity up to several hundred Newtons. We developed a novel piezo-based prototype linear actuator with a two-stage rhombic flexure amplifier. In this paper, first we present the detail design scheme of the actuator by analytical calculations with comprehensive Finite Element Analysis (FEA) verification. Afterwards, we also present the procedures and results of tests of linearity, load capacity, eigenfrequency, stability and repeatability. The selected piezoelectric drive unit is a block of 35x10x10 mm 3 with output force up to 4000 N. The two-stage displacement amplifier is simply integrated by two identical singular rhombic flexures orthogonally mounted together. Each stage, one rhombic flexure with a longer axis of 76 mm long, is designed with an ideal amplification ratio of 3, which leads to a final theoretical compound amplification ration of 9. In order to realize the basic triangular-amplification principle in a rhombic flexure, we introduced flexure joints at all the eight ends of its four edge bars. The singular rhombic flexures can be efficiently manufactured by electrical discharge wire-cutting process at a time in batch by being overlapped in layers. Afterwards we carried out related measurements to test its performance.