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new control cycle would occur only after three new non-filtered stand-off estimates
were obtained. This strategy was adopted in order to eliminate from the estimation the
effect of the stand-off estimates obtained before each control cycle, hence preventing
the control system from responding to an error that has already been acted upon. In
control terms, it could be called a "forgetting" property of the filter, without which an
oscillatory behaviour would result, as observed in the tuning trials.
6.4.2 Dependency of Power Ratio reference range with wire feed speed
According to the final form of the welding process controller
described in
section 4.2.1, the best performance for the dip mode of metal transfer was found to
occur when the allowed range of variation of the power ratio was considered as a
function of the wire feed speed. Figure 6.35 shows that this is in agreement with the
actual behaviour of the power ratio when different wire feed speeds are used.
Figure 6.36 shows the variation of the other monitoring indices with the wire
feed speed for stable dip mode of metal transfer. Note that TSI is the most affected
index, while TI and DCI remain fairly constant. Considering that TSI is used only for
a minor voltage trimming rule, the allowed range of variation was kept constant,
despite the observed dependency on the wire feed speed.
No pronounced trends in the monitoring indices were observed when varying
the wire feed speed in stable spray mode of metal transfer.
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