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ABB Low Voltage Industrial Products 0312
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Control devices
Why you should use control devices
for the machine operator to be able to directly start and
stop dangerous machine movement
Three-position device
Three-position devices, hold-to-run devices and enabling devices
are used during trouble-shooting, programming and test running
when no other safety components are possible or suitable. The
device is held in the hand and the operator can in an emergency
situation either press harder or entirely release the device to stop
the machine.
In an emergency situation the operator
can either press harder or release the
three-position device to
stop the machine.
Two hand control device
A two-hand control device is used when it must the guaranteed
that the operator's hands will be kept outside the risk area. If there
is a risk that someone else other than the operator can reach into
the machine without the operator seeing it, the safety device must
be supplemented by something more, e.g. a light beam.
To be able to operate the machine with the two-hand device, all
the buttons on the device have to be operated within 0.5 seconds
of each other. This is called concurrence. All the buttons also have
to be returned to their initial position before one can start again. If
any button is released during the machine movement the machine
will be stopped. Using the stopping time one can calculate the
necessary safety distance. A safety distance of less than 100 mm
must not be used.
The highest safety level is assured by connecting the buttons of
the two-hand device to a safety relay. The safety relay checks for
concurrence and that all the buttons have returned to their initial
position before a new start can be made. The safety relay also
gives a stop signal if any of the buttons are released.
The two-hand device protects against
"after-grasp"; if the operator by reflex tries
to enter or reach into a machine during
the dangerous machine movement.
Foot operated switches
A foot operated switch is used when the operator has to hold the
material during processing. The pedal must have a safety cover
to prevent unintentional start. For seated work one must also
have a foot support to facilitate the operator holding his foot in
the pedal´s off position.
The highest safety level is secured by monitoring the pedal with
a safety relay.
The foot operated switch is used when the
operator has to hold the material with both
hands during processing.