Abstract: The module of pressure measure control circuit and the module of rotation speed measure control circuit based on the microcontroller P89C51RD2 are designed. The closed loop control system of pressure and rotation speed which are two key parameters of inertia friction welding is achieved. The electro-hydraulic proportional relief valve which has a perfect controllable property is used in the hydraulic pressure control system of the friction welding machine. The actual pressure signal sampled by a pressure sensor enters the module of pres-sure measure and control circuit. Through A/D conversion, computation and D/A conversion, the signal is inputted to the electro-hydraulic proportional relief valve, so that the pressure in friction welding process could be adjusted continuously. The transducer which has a perfect property of speed adjustment is used for main axes motor drive of the machine.The pulse signal of the main axes rotation speed sampled by a photoelectric rotary coder enters the module of rotating speed measure and control circuit. Through computation and D/A conversion, the signal is input to the transducer, so that the main axes rotation speed could be adjusted steadily and exactly. The application of practical production indicate that the control system of pressure and rotation speed is very steady in working, convenient in operating, and has a good effect in running.

Key words: Friction welding, Microcontroller Pressure measure and control, Rotational speed measure and control