Sizing Your
System
The following
formula is an international draft guideline for the
proper positioning and application of safety mats for
machine guarding. This formula must be followed for all
safety mat applications supplied to the European
Community (CE) member nations. CEN is the European
Committee for Standardization. Final draft
#prEN999
The minimum
distance from the danger zone shall be calculated by
using the general formula: S=(K x T) +C
where:
S is the safety
mat minimum distance in inches/millimeters in a
horizontal plane, from the danger zone to the detecting
edge of the safety mat furthest from the danger
zone.
K is a parameter
in inches/millimeters per second, derived from data on
approach speeds of the body or parts of the body. K=63
inches/second or
1600mm/second.
T is the total
system stopping time performance in seconds, which
includes activating the safety mat, the mat controller
output signal switching device and the time required to
stop the machine and remove risk. The activation time of
the STTS Safety Mat System including controller is 35
msec (.035 seconds). This amount must be added to the
machine stopping time to fulfill the "T"
requirements.
C is an additional
distance in inches/millimeters, based on intrusion
towards the danger zone prior to actuation of the
protective safety mat equipment. C=48 inches or
1219mm.
Annex
B (informative)
Walking speeds and stride
lengths.
The positioning of equipment
which is activated by a person walking into the detection zone
by stepping onto a pressure sensitive mat is affected by speed
of approach and stride length. The walking speed and stride
length depend on the physical and anthropometric data of the
population.
Speed of
Approach
This standard
assumes the approach of persons towards the danger zone
will be at walking speed.
Stride
Length
Available
research data has shown the 95th percentile of two steps
(i.e., starting and finishing with the same foot)
measured from heel contact at walking speed is
approximately 75 inches/1900 mm. By dividing by 2 and
subtracting the 5th percentile shoe length, this gives a
stride length of 28 inches/700 mm. If it is assumed that
an allowance has to be made, for example, between the
detection zone and the stride length of 2 inches/50 mm,
this gives a minimum width of 30 inches/750 mm for the
detection zone.
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