Is a Light Curtain.
Very simply, a Safety Light Curtain is a device used to
protect persons from dangerous machinery. A Safety Light
Curtain is made up of two electronic sensor bars (Transceivers),
which send and receive invisible infra-red beams between
each other. These transceivers are connected, as per Figure
A, to a Controller, which receives electronic signals
from the transceivers and from these signals decides whether
or not the area between the transceivers is clear or obstructed.
Safety Light Curtain is placed between a machine
operator and a dangerous machine as per Figure B,
so that if the operator puts any part of their body into
the machine, then some of the infra-red beams between
the Transceivers will have been obstructed. The Controller
will then send a stop signal to the machine, before the
operator can be injured.
Controllers can operate up to four curtains (see fig
C&D) with any mixture of sizes and ranges. This
can be a useful feature if you wish to guard four sides
of a machine.
Note, although 4 Curtains are controlled, the Controller
output will switch to stop the machine regardless of which
light curtain is obstructed.
The Light Curtain Controller is connected to each transceiver
using 4 core screened cable. The Controller determines
from the signals from each transceiver, if the curtain
area between the Transceivers is clear and provides outputs,
which are used to stop the dangerous motion of the machine
if the curtains are obstructed. This can be done by using
the outputs to close or open valves to brakes or cylinders
on the machine to stop the dangerous motion.
Interfacing with machinery
Light Curtain Reset inputs have several uses. Resets can
monitor the correct operation of the valves or other devices
which the Light Curtain Outputs are controlling. They
can be used with a push-button as a manual reset once
the light curtain has been obstructed. They can also provide
a very useful "anti-repeat" function, which
does not allow the machine to re-start on its own
once the curtain is unobstructed.
Light Curtain Mute inputs effectively bypass the Safety
Light Curtain. This can be useful for machine set up.
These inputs can also be automatically activated by the
machine during safe portions of a cycle, such as the opening
stroke of the power press as shown in Figure E. This would
allow the operator to step into the guarded area to remove
the work-piece whilst the press was opening. The Mute
inputs can also be used to make the Light Curtain UNIDIRECTIONAL,
in other words product may be allowed to exit through
the Light Curtain but nothing may enter through the Light
mirrors can be used to bounce the Light Curtain beams
around corners. This would allow you, for example, to
guard the application shown in the above Figure F with
two corner mirrors and four less transceivers. Note, mirrors
should not be used over distances totaling more than 12
metres. The main disadvantage of using mirrors is that
they can be very difficult to align. Any mountings for
mirrors should be very strong and robust. Mirrors are
not recommended for use in high traffic areas as they
will need constant re-alignment.
include Chemical wash-down enclosures, Power Supplies,
Dust Ignition Proof Enclosures, Pre-wired Cable assemblies