3 Fundamentals of press design

Press control systems
The communication system connects the PLC, and provides data
exchange with the visual displays within the machine and also communication
with external systems.
3.5.5 Functional structure of the control system
Depending on the type of machine or press, the control system is broken
down according to the following functional groupings:
– feed,
– main drive system,
– safety control,
– slide functions (interlocking, overload safeguard, weight compensation,
die clamping system, adjustment),
– draw cushion or blank holder functions (pressure control, adjustment),
– moving bolster functions (traversing, lifting/lowering, clamping),
– functions of the workpiece transport devices and dies,
– hydraulic, pneumatic, lubrication functions,
– special die changing functions.
Cam operated limit switches play a special role in press control systems.
These press-specific functional units generate switching signals for certain
functions depending on the position of the crank angle. A difference
must be drawn between electromechanical rotating cam limit
switches (Fig.3.5.4), which are used for safety-relevant functions, and
electronic cam switches that are programmable. The latter comprise a
measuring system for the crank angle of the press and an electronic
evaluating module.
In contrast to mechanical presses, valves for the downstroke and
upstroke of the slide are separate in a hydraulic press, so eliminating the
need for a cam operated safety device.
3.5.6 Major electronic control components
Safety control systems used in Europe are generally still the dual-channel,
self-monitoring conventional type using contactors. In contrast,
since the mid-eighties, the safety control systems used in large-panel
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