This paper presents the experimental results of investigating the performances of an air-bearing displacement sensor for surface form measurement of micro-structures, such as micro-lenses, on an ultra-precision machine tool. The sensor consists of a stylus for contacting the surface, a shaft for mounting the stylus, an air-bearing for suspending the shaft and a blade spring for applying the measuring force against the surface. At first, experiments were conducted on a vibration isolated table to identify the basic performance of the sensor for displacement measurement. Then, the sensor was mounted on a diamond turning machine for evaluating the performance of the sensor for on-machine surface form measurement of micro-lenses. A roll workpiece, on which a micro-lens array was fabricated by using a fast tool servo on the diamond turning machine, was employed as the specimen for the on-machine experiment of surface profile measurement.

This paper presents the dynamic response of an air-bearing displacement sensor for on-machine surface form measurement of micro structures. The on-machine measurement system has some merits in terms of measurement efficiency and re-machining for error compensation after measurement. On the other hand, the performance of the contact type measurement system based on stylus methods is dominated by the dynamic characteristics of the system because the system is subject to random vibrations of the machine tool including the spindle during measurement. Therefore, the dynamic response of the system is useful for analyzing the mechanical vibrations of the practical on-machine measurement system. In this paper, the equation of motion for the air-bearing displacement sensor to the excited input displacement is derived and the displacement behavior of the system by using a PZT actuator is investigated within certain frequency ranges experimentally for identifying the dynamics of the system.

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A contact stylus-type displacement sensor is proposed for a surface form measurement of micro-structures. The stylus is supported by an air-bearing, thus it can be moved smoothly without friction between the stylus and the air-bearing. In order to reduce the measurement force, a novel controlling technique of a contact force has been developed. During the measurement one edge of the stylus is maintained contact with the measured surface by its own weight. Another end of the stylus is connected with a counter weight by a string and the stylus is hanging on the string in order to reduce the contact force between the edge of the stylus and the measured surface. Measuring force is estimated to confirm the effectiveness of the counter weight. Surface measurement of a steel ball is carried out using the developed air-bearing displacement sensor.