A Porous-Restricted Aerostatic Lead Screw Actuator for High Performance Microscale Machine Tools

Abstract

The design and manufacturing process for a porous-restricted aerostatic lead screw actuator (ALSA) is presented. The ALSA provides near-frictionless motion with submicron positioning accuracy, high stiffness at low inlet air pressures (<827 kPa), and a travel length of 50 mm. Porous graphite disk inserts are held in a helical pattern in an aerostatic nut housing against a lead screw thread to create multiple simultaneous air bearing surfaces. A wave spring flexure is inserted behind each graphite disk to provide a preload and ensure full contact between the porous graphite disk surface and the lead screw flank. When the wave spring flexures and graphite disks are potted in combination with a slow-curing epoxy, this creates a self-aligning method to consistently match all graphite disk insert surfaces to the helical profile of the lead screw thread. Experimental trials were performed to evaluate the performance of the manufactured ALSA. It was found that a stable nut with a per-thread stiffness of 9.7 N/μm was achievable with a 3.5 μm air gap and an overall permeability of 5.4 × 10−15 m2. Applications requiring higher stiffness may couple two or more single-threaded nuts to achieve the desired actuator stiffness.