Design Of ARM Controlled Servo Gun For Spot Welding

Electrode pressure is one of the main factor of resistance spot welding,whoes stablility and convertibility are very important to assuring good welding quality.But air-driven welding gun which is widely used in factories can not change electrode pressure at all. So this paper tends to design a new type of hanging spot welding sevo gun, which is capable of changing the electrode pressure in real time during welding process, in order to carry out complex welding circles and improve welding quality.The gun is driven by servo motor and has a ball screw as its main transmission part. It is designed simply and compactly and moves smoothly and fexiblely.The system empolys 32-bit ARM micro-controller as the controlling core. Compared to using traditional MCU, the system is provided with much higher frequnency and more powerfull hardware. More over, real-time operating system uC/OS-II is migrated into the system, base on which a layed, multi-tasks and message-driven software system is founded, which fully makes good use of the advantage of ARM and brings better stability and more rapid response.During spot welding, servo motor is working in the torque mode. Electrode's pressure and moving speed can be controlled by analog voltage input. Electrode's pressure and position can be measured by the feedback signal from the motor drive. And the welding current can be controlled by common I/O.Thus an open loop controlling system is formed.Experimental results prove that the gun's accuracy and response time can all meet the welding needs and it has many more functions, such as high-speed reaching, low-speed crawling, gently electrode touching, short-time pre-pressing and so on., which are very important to expand electrode life and improve welding efficiency. Further more, the servo gun can offer saddle shaped electrode pressure in the mild steel welding experiment. In comparison with constant electrode pressure, it can efficiently reduce welding expulsion, improve the weld's intension and plasticity, and obviously improve the welding quality.