Mechanical equipment is becoming more and more large, complicated, high-speed and automatical.Once some parts of them fail, the severe or catastrophe consequences will be resulted in.

• 机械设备日益朝着大型化、复杂化、高速化、自动化等方向发展，一旦某一部分发生故障，往往会引起比较严重甚至是灾难性的后果。