mechanical device, etc. The software system has been successfully developed with a Windows 98-based VCþþ. According to the CAD data of the test parts and interpolation methods, the scanning procedure is programmed, the atti- tude of the ultrasonic probes is controlled using the five-axis scan system, and the automatic scanning of complex surface parts, and the real-time acquiring ultrasonic data and auto- matic identifying of flaw signals, is realized. The system principle is shown in Fig. 1. The system can use immersion probes to inspect, and also can adopt the direct contact method. The principle of the system inspection is: firstly, to input the information of the test parts to control system; secondly, to control the system processes and translates the information, then to output the control signal to the servo system, upon which the servo system sends the driving signal to the mechanism system; and finally, the machine makes the probes scan along the scheduled scanning path. In the scanning process, the probes always superposes with the normal direction of the examined spot to establish the foundation for obtaining the correct ultrasonic signal. The scanning principle is shown in Fig. 2 (a) being the scanning path and (b) being the positional relationship of the parts to the probe.