| 摘要 |
<p>To guarantee quick and free-of-overshoot rise up of welding current for any resistance welding machines and for any welding operations. The combination of a current sensor 30, a primary current measuring circuit 32, an analog-to-digital converter 34. a CPU 38 and an inverter driver circuit 36 defines a pulse-width-modulation constant-current control circuit for an inverter resistance welding machine involved. The constant-current control circuit includes a feedback loop and controls switching (PWM operation) of an inverter circuit 18 so as to generally maintain a primary current I1 near a selected current value ÄIsÜ. According to programs stored in ROM 40. CPU 38 performs required processing. In particular, when a maximum allowable current value of the resistance welding machine involved has been entered and a selected current value of a particular welding operation has been entered. CPU 38 computes an initial pulse width of a control pulse CP from the maximum allowable current value and the selected current value. In a first cycle of the welding operation, CPU 38 supplies a first control pulse CP1 having the initial pulse width to the inverter circuit 18 to thereby start the welding operations. The initial control pulse width is determined as a function of a machine current capacity and the desired current level of a welding operation, and may be made in proportion to a relative magnitude (ratio) of the desired current to the machine current capacity. In the subsequent cycles of the welding operation. CPU 38 reads the measured current value of each cycle and compares with selected current value to compute the deviatio of the measured current value. Based on the deviation, CPU determines a next pulse width in order that the deviation will be cancelled. <IMAGE></p> |
