ABSTRACT
The monitoring of the working conditions of a system is becoming an increasingly important issue in its automation. Despite many successful results, this area is still not mature enough to be used for complete unmanned automation. With the advantages of noncontact and the remote sensing approach, an optical sensing or monitoring technique such as light projection, light focusing, light detection, etc. is the most promising method when compared with other approaches. However, the problem with the optical approach is its reliability and repeatability, because it generally provides a high measuring resolution and is easily affected by disturbances. Among the optical techniques a laser beam is traditionally a major tool for sensing and monitoring and has often been used in conjunction with a CCD camera in processes such as machining, assembly, welding, textile fabrication, quality inspection, etc. The results of this method are normally satisfactory when the disturbance is not serious and a certain countermeasure is sometimes implemented to withstand the disturbance. An incandescent light is sometimes used instead of a laser light, but the application is limited because of a low sensitivity and narrow measuring range. The CCD camera itself is also a major tool for detection and often used as a machine vision or vision sensor. This approach uses an image-processing technique that generally is burdened by low-speed detection (recognition). An optical fiber sensor has basically two functions-light projection and light detection-depending on the application. It is often used with a laser beam as a light source.
