fo r wo rkp iece h an d lin g an d d ie ch an gin g, are p ro gram m ed u sin g seq u en t ial p ro gram m in g m et h o d s. W h ere fast resp o n se t im es are called
fo r, t h e relevan t PLC in p u t sign als are d efin ed as in t erru p t in p u t s wh ich , as t h e n am e su ggest s, in t erru p t cyclically p ro cessed co n t ro l so ft -
ware fu n ct io n s an d t rigger a resp o n se p ro gram wh ich resp o n d s t o ext er- n al even t s in an ext rem ely sh o rt t im e.
3.5.9 Future outlook
Pro gram m able lo gic co n t ro llers are id eally su it ed t o t h eir resp ect ive ap p licat io n as sin gle-p u rp o se syst em s. Th ey are p art icu larly well su it ed
fo r t h e p ro cessin g o f lo gic o p erat io n s. Th e t ren d is t o ward s eq u ip p in g syst em s wit h ever m o re ext en sive, co st -in t en sive p ro cessin g cap abilit y.
Develo p m en t o f p ro gram m in g lan gu ages, o n t h e o t h er h an d , h as slo wed d o wn alm o st t o a h alt . Pro gram s are st ill bein g writ t en in t h e
fo rm o f lad d er d iagram s an d in st ru ct io n list s, wh ich are co m p arable t o
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Fig. 3.5.6 PLC American
manufacturer
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
an assem bler lan gu age. Th ese o rigin ally ap p licat io n -o rien t ed p ro gram - m in g lan gu ages are n o w bein g u sed fo r ach ievin g visu al d isp lay, d at a
p ro cessin g, d at a m an agem en t an d co m m u n icat io n fu n ct io n s. Th e co n seq u en ces o f t h is t ren d are h igh so ft ware d evelo p m en t an d
m ain t en an ce co st s, n o n -t ran sp aren t p ro gram s – wh ich n o t even p ro - gram d esign st an d ard izat io n can m ake an y easier t o u n d erst an d – an d
lo n g lead t im es t o p u t t h e p ress in t o o p erat io n . To p erm it t h e in t egra- t io n o f t h is t yp e fu n ct io n , t h e PLC h as t o be eq u ip p ed wit h ad d it io n al
exp en sive h ard ware m o d u les. In co m p ariso n , in d u st rial co m p u t ers, fo r exam p le PCs, o ffer t h e ben -
efit s o f grap h ic u ser in t erfaces, d at a p ro cessin g cap abilit y an d facilit y fo r o bject -o rien t ed p ro gram m in g t h ro u gh t h e u se o f p o werfu l p ro -
gram m in g t o o ls. Th e basic req u irem en t s im p o sed o n a fu t u re-o rien t ed p ress co n t ro l syst em , i. e. t h e abilit y t o access as m an y fu n ct io n s an d as
m u ch in fo rm at io n as p o ssible d irect ly at t h e m ach in e, are o n ly ach iev- able in t h e fu t u re t h ro u gh t h e u se o f great er in t elligen ce an d m o re co m -
p u t in g cap acit y. In ad d it io n , m o d ern au t o m at io n en gin eerin g calls fo r
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Press control systems
Fig. 3.5.7
Sw itch cabinet w ith components for main press drive
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
co n t ro l syst em s wit h great er n et wo rkin g cap abilit y t h ro u gh st an d ard n et wo rks fo r t h e exch an ge o f co n t ro l, p ro d u ct io n an d p ro cess d at a as
well as t h e cap abilit y fo r d iagn o sis an d in t erven t io n in t h e co n t ro l sys- t em t h ro u gh p u blic t eleco m m u n icat io n n et wo rks. Th e PLC alo n e is n o t
able t o co p e wit h t h ese d em an d s, alt h o u gh it s co n t in u ed exist en ce as a su bo rd in at e, fast m ach in e co n t ro l co n cep t is st ill ju st ified .
Pract ically all t h e co m p o n en t s req u ired fo r realizat io n o f t h e abo ve fu n ct io n s are available in t h e in d u st rial co m p u t er. Alo n gsid e it s co m -
p u t in g p erfo rm an ce, t h e in d u st rial co m p u t er also p ro fit s fro m t h e o p en -en d ed so ft ware wo rld . Fu rt h erm o re, d esp it e t h e st ead y rise in p er-
fo rm an ce lim it s, t h e co st s o f t h e t ech n o lo gy are fallin g in m an y cases. In view o f t h is t ren d , co n t ro l st ru ct u res feat u rin g d ist ribu t ed in t elli-
gen ce an d h igh er-level in d u st rial co m p u t ers in t erlin ked wit h fast co m - m u n icat io n syst em s are cert ain t o gain in creasin gly in p o p u larit y.
Ad d ed t o t h is is t h e in creased u se o f d ist ribu t ed in p u t o u t p u t m o d u les an d sen so r act u at o r co m m u n icat io n syst em s wit h a view t o red u cin g
t h e n ecessary in st allat io n an d wirin g in p u t . Met h o d s o f p ro gram m in g t h e co n t ro l so ft ware will beco m e m o re st an d ard ized an d sim p lified in
t h e fu t u re, fo r exam p le by t h e in t ro d u ct io n o f t h e in t ern at io n al st an - d ard IEC 1131.
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Fundamentals of press design
Fig. 3.5.8
Components of a servo drive system
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
O t h er ap p ro ach es exist in t h e fo rm o f p ro gram m in g t h ro u gh t h e u se o f st at u s grap h s, ap p licat io n “o bject ” o rien t ed p ro gram m in g an d u ser
lan gu age. In t h is case, reu sable m o d u les wit h an y d egree o f co m p lexit y can be gen erat ed an d st o red in a u ser-sp ecific m acro library. Th e p re-
p ared o bject s in t h e library are in p aram et ric fo rm an d can be gro u p ed wit h a m in im u m o f co m p licat io n t o co ver a large n u m ber o f t h e p ress
o r m ach in e fu n ct io n s. All t h at is n ecessary t o t h en jo in t h e in t erfaces fo r d at a exch an ge.
In fo rm at io n t ech n o lo gy is bein g in t egrat ed t o an ever great er d egree in t o t h e p lan t s o r m ach in es t h em selves.
As in tern ation ally stable “in form ation h igh ways” becom e available, n ew form s of fau lt diagn ostics an d m ain ten an ce back-u p will n atu rally
develop , allowin g p ossible fau lts an d op eratin g errors to be ascertain ed an d m ech an ical fau lts to be traced u sin g video tech n ology or m icro-
p h on es, so realizin g a system of tem p orary or con tin u ou s on -lin e m on i- torin g.
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3 Fundamentals of press design
3.6 Press safety and certification 3.6.1 Accident prevention
