Th e co m m u n icat io n syst em co n n ect s t h e PLC, an d p ro vid es d at a exch an ge wit h t h e visu al d isp lays wit h in t h e m ach in e an d also co m -
m u n icat io n wit h ext ern al syst em s.
3.5.5 Functional structure of the control system
Dep en d in g o n t h e t yp e o f m ach in e o r p ress, t h e co n t ro l syst em is bro - ken d o wn acco rd in g t o t h e fo llo win g fu n ct io n al gro u p in gs:
– feed , – m ain d rive syst em ,
– safet y co n t ro l, – slid e fu n ct io n s in t erlo ckin g, o verlo ad safegu ard , weigh t co m p en -
sat io n , d ie clam p in g syst em , ad ju st m en t , – d raw cu sh ion or blan k h old er fu n ction s p ressu re con trol, ad ju stm en t,
– m o vin g bo lst er fu n ct io n s t raversin g, lift in g lo werin g, clam p in g, – fu n ct io n s o f t h e wo rkp iece t ran sp o rt d evices an d d ies,
– h yd rau lic, p n eu m at ic, lu bricat io n fu n ct io n s, – sp ecial d ie ch an gin g fu n ct io n s.
Cam o p erat ed lim it swit ch es p lay a sp ecial ro le in p ress co n t ro l syst em s. Th ese p ress-sp ecific fu n ct io n al u n it s gen erat e swit ch in g sign als fo r cer-
t ain fu n ct io n s d ep en d in g o n t h e p o sit io n o f t h e cran k an gle. A d iffer- en ce m u st be d rawn bet ween elect ro m ech an ical ro t at in g cam lim it
swit ch es Fig. 3.5.4
, wh ich are u sed fo r safet y-relevan t fu n ct io n s, an d elect ro n ic cam swit ch es t h at are p ro gram m able. Th e lat t er co m p rise a
m easu rin g syst em fo r t h e cran k an gle o f t h e p ress an d an elect ro n ic evalu at in g m o d u le.
In co n t rast t o m ech an ical p resses, valves fo r t h e d o wn st ro ke an d u p st ro ke o f t h e slid e are sep arat e in a h yd rau lic p ress, so elim in at in g t h e
n eed fo r a cam o p erat ed safet y d evice.
3.5.6 M ajor electronic control components
Safet y co n t ro l syst em s u sed in Eu ro p e are gen erally st ill t h e d u al-ch an - n el, self-m o n it o rin g co n ven t io n al t yp e u sin g co n t act o rs. In co n t rast ,
sin ce t h e m id -eigh t ies, t h e safet y co n t ro l syst em s u sed in large-p an el
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p resses fo r exam p le in t h e US m arket h ave been freq u en t ly d esign ed t o u se t wo PLC syst em s, each m o n it o rin g t h e o t h er. Am erican PLC m an u -
fact u rers h ave o ffered su it able so lu t io n s fo r t h is t yp e o f ap p licat io n fo r so m e t im e. In Germ an y t o o , p ress safet y co n t ro l so lu t io n s based o n
red u n d an t PLC syst em s are beco m in g in creasin gly p o p u lar. Th e syst em s u sed are st an d ard co m m ercially available PLCs
Figs. 3.5.5 an d
3.5.6 . Th ey are ad ap t ed t o t h e fu n ct io n al req u irem en t s
o f t h e p ress by m ean s o f in t elligen t m o d u les su ch as ro t at in g cam lim it swit ch es, fast p o sit io n in g m o d u les, fast an d co n ven t io n al co m m u n ica-
t io n m o d u les an d , wh ere req u ired , by in d ep en d en t ly o p erat in g t ask- sp ecific co n t ro l syst em s.
O p erat io n s in vo lvin g crit ical real-t im e fu n ct io n s an d co m p lex d at a p ro cessin g t asks wh ich are n o t su it able fo r t h e PLC are p ro cessed by
in d ep en d en t su bsyst em s. Th ese in clu d e t h e co n t ro l o f t h e d raw cu sh - io n s an d m u lt ip le-axis p art t ran sp o rt d evices o r fast feed syst em s, acq u i-
sit io n , p ro cessin g an d d isp lay o f sen so r o u t p u t s asso ciat ed wit h t h e d rawin g p ro cess as well as acq u isit io n an d evalu at io n o f m ach in e an d
p ro d u ct io n d at a. Hyd rau lic p resses, fo r exam p le, are eq u ip p ed wit h q u ick-act in g p ressu re syst em s t o co n t ro l t h e p arallelism o f t h e slid e.
Digital rectifiers an d DC or th ree-p h ase asyn ch ron ou s m otors are u sed for m ain , tran sfer an d an cillary d rive system s
Fig. 3.5.7 . Workp iece h an -
d lin g system s are bein g in creasin gly eq u ip p ed with d yn am ic d igital ser- vo d rive system s, in wh ich con trol in telligen ce is often in tegrated in to
th e d rive system electron ics Fig. 3.5.8
.
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Fundamentals of press design
Fig. 3.5.4
Electromechanical rotary cam sw itch
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
3.5.7 Architecture and hardw are configuration
