LIBRARY ı6ıul 0) - Cranfield University
LIBRARY ı6ıul 0) - Cranfield University
LIBRARY ı6ıul 0) - Cranfield University
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Table 4.8 - Final welding process control algorithm<br />
1 If PR < PRLOWDIP then AV = +BIGTRIM<br />
2 If PRLOWDIP 5 PR < minPRdi then AV = SMALLTRIMI<br />
3 If minPRdi 5 PR :5 maxPRdip then test rule (3. a)<br />
3. a If DCI < DCI-LOW then AV = -MICROTRIM<br />
else if DCI > DCI-HIGH then AV = MICROTRIM<br />
else test rule (3. b)<br />
3. b If TI > TI-HIGH then AV = MICROTRIM<br />
else if TI < TI-LOW then AV = -MICROTRIM<br />
else test rule (3. c)<br />
3. c IJTSI > TSI-HIGH or TSI < TSI-LOW then AV = -MICROTRIM<br />
else AV = ZEROTRIM<br />
4 If minPRdi < PR < PRHIGHDIP the,, AV = -1.5 x MICROTRIM<br />
5 If PRHIGHDIP < PR < PRLOWGLOBY then<br />
AV = -1.5 x SMALLTRIM<br />
6 If PRLOWGLOBY < PR < PRMEDGLOBY then<br />
AV = -1.5 x MEDTRIM<br />
7 I PRMEDGLOBY < PR < PRHIGHGLOBY there test rule (7. a)<br />
7. a If (I. < I, ) then AV<br />
R, = -1.5 xBI GTRIM<br />
else AV = BIGTRIM<br />
8 If PRHIGHGLOBY < PR < PRLOWSPRAY then AV = MEDTRIM<br />
9 I PRLOWSPRAY < PR < PRMEDSPRAY then AV = SMALLTRIM<br />
10 If PRMEDSPRAY < PR < PRHIGHSPRAY their AV = ZEROTRIM<br />
11 If PR > PRHIGHSPRAY then AV = -1.5 x SMALLTRIM<br />
MEMEMEEME ft<br />
Note that the controller shown above is intrinsically empirical. The stability<br />
limits for the power ratio and the other monitoring indices were also obtained<br />
empirically and the voltage correction values were suggested based on process<br />
previous knowledge and prior experience. Figure 4.2 shows the control algorithm in a<br />
schematic form with voltage trim directions. The rule based incremental controller<br />
developed above differed from the original structure presented by Luzeaux [ref. 194]<br />
in the sense that different increment sizes of the control variable were used, depending<br />
on how far the process was from the desired state. This characteristic can be<br />
considered as a fuzzyf cation of the rules<br />
An important element in the implementation of the these control algorithms is<br />
the response time of the power source to a change in the set-up parameters. This is<br />
dealt with in section 4.2.5.<br />
The control algorithm presented above has a fast response compared to the<br />
voltage controller developed by Won and Cho [ref. 201]. The work by Won and Cho<br />
was conceptually similar to the controller developed in this work, however the<br />
stability assessment<br />
was carried out using the arc stability index developed by Mita et<br />
al. [ref. 37] (see Section 2.1.5.3) and the voltage control commands were generated<br />
by a fuzzy-logic based controller. This controller was designed to iteratively seek a<br />
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