Roundness error of axial rotary workpiece is an important index for evaluation of processing level of machine tools.Aiming at large axial workpiece is unable to adopt traditional roundness measuring instrument

theoretical basis and mathematical model of the three-point method measuring axial rotary workpiece roundness error are introduced.Non-contact capacitive sensor is used to detect micro displacement

structure of sensor and basic principle of measuring circuit are given.Hardware system suitable for roundness error measuring is set up based on capacitive sensor

and special measuring system is developed by virtual instrument technology to realize data acquisition

linear correction

error separation and evaluation.In the end

experiment is carried out

reliability and precision of measuring system are evaluated through analysis on datas by multiple measurements.