Development of a noncontact optical sensor for measuring the shape of a surface and thickness of transparent objects

This paper deals with a noncontact optical sensor to measure the shape and the thickness of transparent plates such as glass panels of liquid crystal displays. The conventional methods to obtain the shape or thickness of tran sparent plates depend on contact-type sensors such as linear variable diffe rential transformers. Due to the contact between the tip of the sensor and the surface of objects, the tip is abraded. In addition the casting of glas s at high temperature increases the size of the sensor body. The accuracy o f the sensor is degraded for these reasons. To overcome these problems, we proposed a low-cost and simple noncontact optical sensor that is composed o f a hologram laser unit (of the type used for optical pickup in CD players) and a plastic lens. To evaluate the performance of the proposed optical se nsor, a series of experiments were performed for various measurement condit ions. The proposed sensor shows excellent performance in measuring the shap e of transparent plates. (C) 2001 Society of Photo-Optical Instrumentation Engineers.