3 Fundamentals of press design

100 Fundamentals of press design
Fig. 3.5.4 Electromechanical rotary cam switch
presses for example in the US market have been frequently designed to
use two PLC systems, each monitoring the other. American PLC manufacturers
have offered suitable solutions for this type of application for
some time. In Germany too, press safety control solutions based on
redundant PLC systems are becoming increasingly popular.
The systems used are standard commercially available PLCs
(Figs. 3.5.5 and 3.5.6). They are adapted to the functional requirements
of the press by means of intelligent modules such as rotating cam limit
switches, fast positioning modules, fast and conventional communication
modules and, where required, by independently operating taskspecific
control systems.
Operations involving critical real-time functions and complex data
processing tasks which are not suitable for the PLC are processed by
independent subsystems. These include the control of the draw cushions
and multiple-axis part transport devices or fast feed systems, acquisition,
processing and display of sensor outputs associated with the
drawing process as well as acquisition and evaluation of machine and
production data. Hydraulic presses, for example, are equipped with
quick-acting pressure systems to control the parallelism of the slide.
Digital rectifiers and DC or three-phase asynchronous motors are used
for main, transfer and ancillary drive systems (Fig. 3.5.7). Workpiece handling
systems are being increasingly equipped with dynamic digital servo
drive systems, in which control intelligence is often integrated into
the drive system electronics (Fig. 3.5.8).
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998