Active trigonometry and its application to thickness measurement on reflective surface

The paper introduces a novel method to measure accurate thickness. On the basis of the principle of active trigonometry with vertically incident mode, an obliquely incident mode is proposed. The method is specially designed for a reflective surface of an object, such as a thin steel plate, to measure its thickness in real-time. The influence of the small deflection which is caused by mechanical vibrations is discussed and the manner to reduce this influence is given too.