Normal-Stressed Electromagnetic Triaxial Fast Tool Servo for Microcutting

Short strokes and complicated structures commonly degrade the operating performance of current piezo-actuated triaxial fast tool servos (FTSs). To overcome those deficiencies, we present a novel normal-stressed electromagnetic triaxial FTS for microcutting, which achieves a compact structure and a high resonant frequency with triaxial motions in hundreds of micrometers. The magnetic FTS has a single armature to provide the triaxial decoupled and noncontact driving forces, as well as a symmetric three-DOF corrugated compliant bearing to support and guide the decoupled outputs. With the parameters jointly optimized by an analytical and finite element model, the prototype showed a high degree of agreement with the design target for both static and dynamic performances. A linear active disturbance rejection control is implemented for the triaxial FTS, and an iterative learning scheme is further employed for the triaxial FTS to achieve fast and accurate trajectory tracking. The developed triaxial FTS is comprehensively demonstrated by fabricating a hexagonal spherical microlens array with each lenslet generated within 0.24 s. The practical error for the spatial trajectory tracking was within $ \pm$30 nm, and good surface quality with a form error of 63.66 nm and surface roughness of Sa = 2.05 nm is achieved.