Single phase alternating current (AC) resistance spot welding (RSW) is an important method used in metalworking field and it has been used widely in industry. Nowadays there are some problems existed in the spot welding industry, which includes low welding precision, low welding quality, small welding range and low anti-disturbance capability. The problems are caused by a lot of elements, among these elements; the most important one is low precision of welding current control. So how to control the welding current accurately is the problem we need to solve....[ Read more ]

Single phase alternating current (AC) resistance spot welding (RSW) is an important method used in metalworking field and it has been used widely in industry. Nowadays there are some problems existed in the spot welding industry, which includes low welding precision, low welding quality, small welding range and low anti-disturbance capability. The problems are caused by a lot of elements, among these elements; the most important one is low precision of welding current control. So how to control the welding current accurately is the problem we need to solve.

Since 8bit microcontroller system and 32bit microcontroller have disadvantages in designing the RSW controller. 16bit microcontroller plus DSP is a cost-effective chip to design the RSW control platform, it can implement not only the close loop control but also the complex welding control algorithm. It satisfies the requirement to control output welding current accurately.

In this thesis the hardware system based on the 16bit digital signal controller (DSC) dsPIC30F6014 is designed and implemented, the system is comprised of signal input, signal output, user interface, communication, alarm and power six module. The hardware system is a cost-effective system that can implement the close loop control with complex algorithm.

The control algorithm includes the line voltage compensation and constant current control algorithm. The principle of constant current control is that measuring the current effective value in each cycle and altering the control angle next cycle according to α = f(I%) to keep the welding current percentage unchangeable. In a word. It is done by changing the control angle α (trigger time) to alter the output welding current. Line voltage compensation must be applied since line voltage fluctuation will affect the welding current.

Both hardware and software system of the AC RSW controller has been implemented successfully and the results prove it is able to control the welding control accurately and improve the welding quality greatly by comparing with other RSW control. Moreover, it provides a reliable and feasible platform for future development.