Development of a pneumatic ball probe (1st report) - Basic construction

The ability to measure the diameter of a small hole with low measuring forc e and high resolution is one of the key issues in product evaluation in the semiconductor and micro machining industry. Currently there is no popular sensing system for this type of measurement, so we have developed a novel p neumatic sensing system to solve this problem. The sensor consists of a sma ll ball, a thin pipe, a vacuum generator and a differential pressure gauge. In this sensor, the small ball is kept at the center of the thin pipe by t he vacuum pressure. When the ball touches a wall of a small hole, the ball is shifted from the center of the pipe, which causes air to flow from the o utside to the inside of the pipe. The differential pressure gauge detects t he airflow, and the sensor registers the contact between the small ball and the wall of the small hole. A first prototype of the pneumatic ball probe has been made and tested. Based on the theoretical analysis and the results of experimental tests, it appears that the probe can detect the contact of the ball.