Robots are increasingly being used in industry to perform various types of tasks. Some of the tasks performed by robots in industry are spot welding, materials handling, arc welding, and routing. The population of robots is growing at a significant rate in various parts of the world; for example, in 1984, a report published by the British Robot Association indicated a robot popula­ tion distribution between Japan (64,600), Western Europe (20,500), and the United States (13,000). This shows a significant number of robots in use. Data available for West Germany and the United Kingdom indicate that in 1977 there were 541 and 80 robots in use, respectively, and in 1984 these numbers went up to 6600 and 2623, respectively. Just as for other engineering products, the reliability and safety of robots are important. A robot has to be safe and reliable. An unreliable robot may become the cause of unsafe conditions, high maintenance costs, inconvenience, etc. Robots make use of electrical, mechanical, pneumatic, electronic, and hydraulic parts. This makes their reliability problem a challenging task because of the many different sources of failures. According to some published literature, the best mean time between failures (MTBF) achieved by robots is only 2500 hours. This means there is definite room for further improvement in robot reliability. With respect to safety, there have been five fatal accidents involving robots since 1978.