Efficient Plant February 2018 - 26

feature | human/machine safety
Safety light
curtains protect
personnel in
the vicinity of
point-of-operation hazards.

potentially whip up as bending occurs.
A second approach involves pull-backs
and restraints. These types of devices are
restrictive and have limitations-and operators hate them. Both shackle the operator to
a machine and restrict mobility.
The two-hand, down/foot-through device
is yet another approach. While this method
will work in some cases, it raises ergonomic
issues and is very slow.
Then there are light curtains and laser
active-optic protective devices (AOPDs).
They represent more advanced press-brake
safeguarding options. The diagram in Fig. 1
(p. 25) shows how these technologies work.

SHEDDING LIGHT ON SAFETY
Light curtains started out as simple product
detection devices, then developed into
machine-guarding solutions. Early versions
used incandescent lamps strung together
with a corresponding line of light detectors.
Presses were one of the first machine-safety
applications where safety light curtains were

26

| EFFICIENTPLANTMAG.COM

used. A light curtain is a photoelectric
presence-sensing device. It protects against
access into hazardous points and areas.
These solutions range from very compact
to larger, more robust and resistant models
that can withstand demanding ambient conditions. Note that a stop-time measurement
(STM) device is needed to calculate the
safety distance on a regular basis, just as it is
needed with two-hand controls.
Safety light curtains safeguard personnel
in the vicinity of point-of-operation hazards. This is done with an LED transmitter
and receiver. Any interruption of the plane
of light by an object equal to/or larger than
the "minimum object sensitivity" initiates
an output signal. That could be a hand or a
finger or a misplaced tool, and it causes the
machine to stop or it doesn't allow a cycle
until the blockage is removed. To not initiate this output signal, the operator must be
outside the protected area through the entire stroke of the press-brake ram. The safety
distance between the light curtain and the

machine depends on the application, the
type of light curtain, and the machine's
stopping performance.
OSHA has established the following set of
regulations for light curtains:
1. The machine must be able to stop the
movement of the ram anywhere in the
stroke.
2. The stopping time of the ram must be
known.
3. The stopping time of the ram must be
monitored for deviation in stopping
time on each stroke.
4. The minimum distance the light curtains can be located to the pinch point
must be known.
5. The light curtains must be control
reliable.
6. The machine stop circuit, with which
the light curtains are interfaced, must
be control reliable.
7. The light curtains must be self
checking for proper operation on
each stroke.

FEBRUARY 2018


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Table of Contents for the Digital Edition of Efficient Plant February 2018

Maximize CMMS, EAM Use
Tribology Program Fills Skills Gap
Caring For Bearings In Extreme Environments
Press-Brake Safeguarding Matters
Oil Systems Need To Breathe
SAP: Kicking Bad Habits
Advice For Automated Substations
Good BOMs Boost Maintenance Efficiency
Smarten Up About Rotor Analysis
Heed These Signs of Inefficiency
Implementations
IIoT
Efficiency Insight
Editorial
On The Floor
Solution Focus
Products
Showcase
Efficient Plant February 2018 - Cover1
Efficient Plant February 2018 - Cover2
Efficient Plant February 2018 - 1
Efficient Plant February 2018 - 2
Efficient Plant February 2018 - 3
Efficient Plant February 2018 - 4
Efficient Plant February 2018 - 5
Efficient Plant February 2018 - Editorial
Efficient Plant February 2018 - 7
Efficient Plant February 2018 - Implementations
Efficient Plant February 2018 - 9
Efficient Plant February 2018 - Maximize CMMS, EAM Use
Efficient Plant February 2018 - 11
Efficient Plant February 2018 - 12
Efficient Plant February 2018 - 13
Efficient Plant February 2018 - Tribology Program Fills Skills Gap
Efficient Plant February 2018 - 15
Efficient Plant February 2018 - 16
Efficient Plant February 2018 - 19
Efficient Plant February 2018 - 20
Efficient Plant February 2018 - Caring For Bearings In Extreme Environments
Efficient Plant February 2018 - 22
Efficient Plant February 2018 - 17
Efficient Plant February 2018 - 18
Efficient Plant February 2018 - 19
Efficient Plant February 2018 - 20
Efficient Plant February 2018 - Caring For Bearings In Extreme Environments
Efficient Plant February 2018 - 22
Efficient Plant February 2018 - 23
Efficient Plant February 2018 - Press-Brake Safeguarding Matters
Efficient Plant February 2018 - 25
Efficient Plant February 2018 - 26
Efficient Plant February 2018 - 27
Efficient Plant February 2018 - Oil Systems Need To Breathe
Efficient Plant February 2018 - 29
Efficient Plant February 2018 - 30
Efficient Plant February 2018 - SAP: Kicking Bad Habits
Efficient Plant February 2018 - Advice For Automated Substations
Efficient Plant February 2018 - Good BOMs Boost Maintenance Efficiency
Efficient Plant February 2018 - Smarten Up About Rotor Analysis
Efficient Plant February 2018 - Heed These Signs of Inefficiency
Efficient Plant February 2018 - On The Floor
Efficient Plant February 2018 - 37
Efficient Plant February 2018 - IIoT
Efficient Plant February 2018 - Solution Focus
Efficient Plant February 2018 - 40
Efficient Plant February 2018 - Products
Efficient Plant February 2018 - 42
Efficient Plant February 2018 - 43
Efficient Plant February 2018 - 44
Efficient Plant February 2018 - Showcase
Efficient Plant February 2018 - 46
Efficient Plant February 2018 - 47
Efficient Plant February 2018 - Efficiency Insight
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