On-line technique for measuring thickness for three-dimensional braided composite material preforms

This paper presents an automatic method that can measure the thickness of three-dimensional (3-D) braided composite preforms. The thickness of 3-D braided composite material preform is an important parameter of 3-D braided composites. With the development of 3-D braided composite technology, an automated measurement technology for thickness of braided composite preform has become an importantgoal. The objective of this paper is to present an automatic measuring system. The system we devised consisted of a computer, a proximity sensor, a pressure sensor, an analog-to-digital converter and pulse motor, etc. The measuring principle and results are discussed in the paper. The system was tested on both carbon and glass fibre preforms. We obtained very encouraging results. Experiments showed the pressure and eddy current resistance value are important parameters for measuring the thickness of 3-D braided composite material preforms. The measuring precision is higher when the pressure value ranges from 0.6kg/cm2 to 0.8kg/cm2 and the eddy current resistance is 2kW for preforms made of carbon-fibre than of other substances.