The Study On The Controlling System Of Arc Sensor For Automatic Tracking In Welding Based On DSP

In order to insure welding quality, preciously automatic tracking of seam isnecessary. The sense way adopted is swing arc sensor. The welding direction iscontrolled by a direct current motor and a one-way bridge type of rectificationcircuit. Whole trigger electronic circuit is composed of comparison, integral anddifferential circuits. Regulating potentiometer W1 can change the phase of thetrigger pulse to adjust the rotation speed of the direct current motor. The output portwas isolated by the pulse transformer. The swing welding system is composed ofDSP2812 logic unit. The pulse of CP and signal of DIR in the driving system wereoutputted from the timer of the Event Management A(EVA). The chip of CH250and big power triode transistors were designed to build a set of step motor drivingcircuits. Only two signals of the DSP CP and DIR from EVB are needed for thecontrol of the step motor. The weld current is sampled by the A/D in the single chip,at the same time finishing the digital smooth filter and DFT operation.By doing DFT of weld current we can get the response of one time pendulumfrequency from which we can get the size and direction of warp as feedback.Because we need to do DFT of the one time pendulum frequency only, algorithm issimple to realize.The logic unit that control system adopts is the high-powered chip,DSP-TMS320F2812, which is 32-bit high-powered. The frequency is up to150MHz and it can enhance higher operational precision greatly of the controlsystem. Moreover, the DSP integrate plenty of function circuit units, the optimizedevent manager which include pulse width modulate (PWM) and 12-bit analog todigital conversion (ADC), which makes the systematic hardware circuit we designsimply and raises the reliability that system runs. Besides, its powerful and flexiblemultistage interrupt system provides convenience and guarantee to the real time ofthe tracking system. The function of the DSP completion includes mainly below: Afunction is the sampling of weld current using the A/D in the DSP, at the same timefinishing the digital smooth filter and DFT operation;Another function is to carryout operation to the warp that we gets according to certain control pattern, andsends control instruction according to operational result.As best as possible the DSP resources were occupied, the software design isbased on module design theory. As a kind of advanced language, C is much easierto process the deviation signal of arc sensor, so C were adopted to make unitedprogramming in the course of analyzing and controlling.The control pattern that this system adopts is the digital PID control. It candivide to the increment type PID algorithm and the postural type PID algorithm. Tothe whole system, the two types have no essential difference, but because of theimprovement of arithmetic, the increment type PID has the advantage itself. Forinstance, the computer output increment, so the infection from error iscomparatively less, the impulsion is low when we do the manus action/automatismswitch and it is convenience to do the no-harass switch. The account in thearithmetic only needs the lately sample, it can save the calculate time and memoryspace. So when we use the component that has unused function such as the stepmotor, we usually adopt the increment type PID algorithm. Based on therequirement of control index and the characteristic of object controlled, accordingthe experience algorithm to PID parameter, we work out a set of control parametersfurther.Using the integrated compile-debug environment of TI company andemulator ICETEK-5100PP, I compile the control program, debug the modules andmake entirely debug. We find out that tracking control system can reach the goalexpected.