Presence Sensing Devices are
one of the most common safeguards for automatic feed part revolution
clutch presses. They are designed to automatically stop the machine
stroke if the sensing field is interrupted. Proper use of presence
sensing devices provides protection not only for operators but also for
other employees in the area. They also minimize operator resistance to
these types of safety devices due to their nonrestrictive design.
Presence sensing devices are commonly
referred to as light curtains.
There are many requirements that must be met
before light curtains can be installed as point-of-operation
safeguards.
Presence
Sensing Requirements |
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Presence sensing devices can not be used on
machines using full revolution clutches. [29 CFR 1910.217(c)(3)(iii)(a)]
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A presence sensing device (PSD) must
protect the operator by preventing or stopping normal stroking
of the press if the operator's hands are inadvertently placed in
the point of operation. The PSD must also be interlocked into
the control circuit so that the slide motion will stop the
downstroke from continuing if any part of the operator's body is
within the sensing field at that time. [29 CFR 1910.217(c)(3)(iii)]
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Presence sensing device on part revolution clutch
Click on image to view
animation  |
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Should a failure occur within the system, the PSD must be constructed so that the normal stopping action is
still applied when required, but prevents the start of the next
stroke until the failure is corrected. The failure must be
indicated by the system. [29 CFR 1910.217(c)(3)(iii)(c)]
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"Muting"
or bypassing of the PSD during the upstroke of the press
slide is permitted for parts ejection, circuit checking, and
feeding. [29 CFR 1910.217(c)(3)(iii)(d)]
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The safety distance (Ds) from
the sensing field to the point of operation must be
greater than the distance determined by the safety distance formula. [29 CFR 1910.217(c)(3)(iii)(e)]
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Presence sensing field interrupted on the downstroke
Click on image to view video 
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Please do not consider using a
perimeter,
work-envelope safeguarding device in a point-of-operation type of application.
Perimeter light curtains have wider channel spacing to detect the whole body. Perimeter and single beam devices are designed
specifically for perimeter or area safeguarding. They can not be used
for point-of-operation safeguarding.
Presence sensing devices used for point-of-operation safeguarding must be
installed on a machine so that it protects operator's fingers and hands from
point-of-operation hazards. Regulations also state that "guards shall be
used to protect all areas of entry to the point of operation not protected by
the presence sensing device."
[29 CFR 1910.217(c)(3)(iii)(f)]]
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Presence
Sensing Device Images |
Point of operation light curtain |
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Point of
operation light curtain provides horizontal
pass-through protection |
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Point of operation light curtain provides horizontal pass-through protection |
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Single beam light curtain with mirrors |
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Perimeter light curtain for large work envelope safeguarding |
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Point of
operation and perimeter light
curtain
protection for power press and feeding system |
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