Profile Measurements of Micro-aspheric Surfaces Using an Air-bearing Stylus with a Microprobe

A novel scanning probe measurement system was developed to enable precise profile measurements of micro-aspheric surfaces. An air-bearing stylus with a microprobe was used to perform the surface profile scanning. The new system worked in a contact mode and had the capability of measuring micro-aspheric surfaces with large tilt angles and complex profiles. Due to limitations resulting from the contact mode, such as possible damage caused by the contact force and lateral resolution restrictions from the curvature of the probe tip, several system improvements were implemented. An air bearing was used to suspend the shaft of the probe to reduce the contact force, enabling fine adjustments of the contact force by changing the air pressure. The movement of the shaft was measured by a linear encoder with a scale attached to the actual shaft to avoid Abbe errors. A 50-㎛-diameter glass sphere was bonded to the tip of the probe to improve the lateral resolution of the system. The maximum contact force of the probe was 10 mN The shaft was capable of holding the probe continuously if the contact force was less than 40 mN, and the resolution of the probe could be as high as 10 ㎚. The performance of the new scanning probe measurement system was verified by experimental data.