抄録
Design information on a new type of aerostatic lead screw is proposed. To avoid the occurrence of pneumatic hammer, a surface restriction system is employed. The surface restriction can be provided by stepping the flank of the internal thread. The pressure distribution on the flank is analysed by using the Finite Element Method, and the virtual bearing area is calculated by integrating the pressure over the flank. It is shown that the virtual bearing area increases as the gas film thickness decreases. From the relationship between the virtual bearing area and the gas film thickness, the thrust stiffness of the lead screw is calculated. According to the proposed design method, an aerostatic lead screw with the following specifications is made ; outer diameter of the male screw 51 mm, flank angle 15° (trapezoidal thread), pitch 16 mm, flank width 8.28 mm, step width 3.86 mm and step depth 10 μm. The maximum thrust stiffness is 10.3 N/μm, where the air supply pressure is 0.49 MPa and the gas film thickness is 9 μm. Though the measured thrust stiffness is slightly lower than the calculated value, it is high enough for using the aerostatic lead screw as the lead screw of the feed drive devices.
