Abstract: A new method on measure of pistons with middle-bulged varying ellipse shape is presented. The method is to measure pistons on the machine tool. The hardware system and software system for pistons measure are designed. In order to rectify the nonlinear of the system, the inverse function method is introduced. It can assure the measure accuracy perfectly. A thorough study on how to deal with the collected data is conducted. Its application in factories shows that the measure system can satisfy the requirements perfectly.

Key words: Middle-bulged varying ellipse, Piston Measure