The Study On The Automatic Tracking System Of The Welding Torch Height With Arc Sense

The aim of this thesis is that simultaneously tracking and controlling of the height of torch in the welding processing of the irregular surface, which can effectively guarantee the welding quality. Many advanced optical sensor were not used in the processing of the short-circuiting transfer CO₂ preventive welding, this is because that the much dust is intensively splashed and the intensity of arc is very much in this welding processing. Therefore, arc-sensor is used in this thesis, which can get the signal directly from the changes of the arc parameters when the distance between torch and the sample surface changes and eliminate the effect of arc, dust and its splashing. Average current sensor, arc time rate sensor and wire extension sensor extensionally adopted were investigated, and the comparably results were analyzed. The results shows that all the signal of these sensors can display the change of the height of torch, especially wire extension sensor which can most directly and truly reflect the changes between the controlled parameter and detected parameter, and improve the veracity and stability of the torch tracking system in short-current CO₂ preventive welding.The welding direction is controlled by a direct current motor and a one-way bridge type of rectification circuit. The DSP and the power of stepping motor driver were used to readjusting the height of the torch. In addition, the chip of CH250 and big power triode transistors in stepping motor were designed to build a set of step motor driving circuits, which can control the stepping motor using the CP pulse and DIR signals from the event management unit (EVB).The arc signals were acquired by High properties, high velocity and multi-functional PCL-818L acquisition system, which has all most data acquisition function (i.e. A/O, D/A) and fits the low-cost, high velocity 12-bit data acquisition system. The arc was alternatively acted in the burning arc and short circuiting processing in the short-current welding processing, leading to the arc current intensively changing and forming the spike pulse that had a deteriorative effect on the veracity of the data. In order to eliminate this spike pulse, the arc signals acquired were treated by median filter, which is a representative non-linear filter widely applied in image processing and has many traits, such as stability, immobile point and local readjusting etc, as a special order statistics.The logic unit that control system adopts is the high-powered chip, DSP-TMS320F2812, which is 32-bit high-powered. The frequency is up to 150MHz and it can enhance higher operational precision greatly of the control system. Moreover, the DSP integrate plenty of function circuit units, the optimized event manager which include pulse width modulate (PWM) and 12-bit analog to digital conversion (ADC), which makes the systematic hardware circuit we design simply and raises the reliability that system runs. Besides, its powerful and flexible multistage interrupt system provides convenience and guarantee to the real time of the tracking system. The function of the DSP completion includes mainly below: A function is the sampling of weld current using the A/D in the DSP, at the same time finishing the digital smooth filter and DFT operation; Another function is to carry out operation to the warp that we gets according to certain control pattern, and sends control instruction according to operational result.As best as possible the DSP resources were occupied, the software design is based on module design theory. As a kind of advanced language, C is much easier to process the deviation signal of arc sensor, so C were adopted to make united programming in the course of analyzing and controlling.Fuzzy control, which is a new control technique, is the controlling kernel in the tracking system of the height of torch. It can solve much problem, such as the complexity of the system, the inveracity of the detecting, the uncertain of the mathematics model and the strong coupling of the system, etc. Fuzzy control could intelligent control the data, namely the control experience of men and its readjusted version were putted in the controller to control the data, it can satisfy the tracking system of the torch's height in the in short-current CO₂ preventive wielding processing, solve all kinds of the uncertain problem caused by many influence factor in the welding and get the preferable control results.