Determine The Safety Distance - Allen-Bradley GuardShield 440L-T2KA series Installation Instructions Manual

Resolution Protective Height [mm
[mm (in.)] (in.)]
30 (1.18) 160 (6.3)
30 (1.18) 320 (12.5)
30 (1.18) 480 (18.8)
30 (1.18) 640 (25.1)
30 (1.18) 800 (31.4)
30 (1.18) 960 (37.7)
30 (1.18) 1120 (44.0)
30 (1.18) 1280 (50.3)
30 (1.18) 1440 (56.6)
30 (1.18) 1600 (62.9)
30 (1.18) 1760 (69.2)
IMPORTANT Determine Stop Time: The measurement of stop time (T)
must include the stop times of all devices in the stop circuit. A
calculation T, which does not include all device and control
system elements results in an inaccurate safety distance
calculation.

Determine the Safety Distance

The light curtain must be mounted with proper safety distance
• From the point of danger
• From reflective surfaces
US Safety Distance Formula
ATTENTION: The GuardShield™ Type 2 safety light curtains must be
mounted at a sufficient distance from the pinch point or point of
operation hazard. A sufficient distance helps ensures that the
machine stops before a finger, hand, arm, or body reaches the hazard.
This distance, referred to as the safety distance, must be properly
calculated before determining the safety light-curtain protective-
height and mounting the light curtains on the machine. Failure to
calculate this safety distance accurately results in operator injury.
IMPORTANT According to EN ISO 13855, regardless of the calculated safety
distance, never mount GuardShield™ Type 2 safety light curtains
closer than 100 mm (4 in.) from the point of operation or pinch
point hazard.
In the United States, there are two formulas that are used to calculate
the safety distance. The first, the OSHA formula, is the minimum
requirement for the calculation of the safety distance. The second
formula, the one recommended by Rockwell Automation®, is the ANSI
formula, which incorporates additional factors to be considered when
calculating the safety distance.
OSHA Safety Distance Calculation Formula
The OSHA safety distance formula as specified in CFR Subpart O
1910.217 is as follows:
Ds = 63 X T
Number of
Beams Response Time
8 20 ms
16 20 ms
24 20 ms
32 20 ms
40 20 ms
48 20 ms
56 20 ms
64 20 ms
72 20 ms
80 20 ms
88 20 ms
Rockwell Automation Publication 440L-IN011B-EN-P - October 2017
Ds Safety Distance
63 Is the OSHA recommended hand speed constant in
inches per second
T Is the total stop time of all devices in the safety circuit,
which is measured in seconds. This value must include all
components that are involved to stop the hazardous
motion of the machinery. For a mechanical power press, it
is the stop time that is measured at approximately the 90º
position of the crankshaft rotation.
Note: The T number must include the response times of all devices,
including:
• Response time of the safety light curtain
• Safety light curtain controller (if used)
• Control circuit of the machine, and
• Any other devices that react to stop the hazardous motion
of the machinery.
WARNING: Not including the response time of a device or devices
in the stop time calculation results in insufficient safety distance
for the application, which results in operator injury.
The ANSI Safety Distance Formula
The ANSI safety distance formula, which is the Rockwell Automation®
recommended formula, is as follows:
D = K x (T + T
S S
Ds Minimum safety distance between the safe guarding device
and the nearest point of operation hazard, in inches.
K Hand-speed constant in inches per second. The ANSI
standard value is 1600.2 mm (63 in.) per second when the
operator begins reaching toward the point of operation
hazard from rest. NOTE: ANSI B11.19 2000 E8.3.2.3
and Annex D states "One of the accepted values for K is
the hand speed constant (it is usually considered as the
horizontal motion of the hand and arm while seated). The
common value of K is 1.6 m/s (63 in./s). Although other
values (typically greater) are also used. The hand speed
constant does not include other body movements, which
can affect the actual approach speed. Consideration of the
above factors should be included when determining the
speed constant for a given application. The employer
should consider all factors, including the physical ability of
the operator, when determining the value of K to be
used."
Ts Stop time of the machine tool that is measured at the final
control element. Measurement starts at maximum
machine velocity.
Tc Response time of the control system
Tr Response time of the presence sensing device (safety light
curtain) and its interface, if any. This value is stated by the
device manufacturer or it is measured by the user.
Tspm Additional time is allowed for the stop performance
monitor to compensate for variations in normal stopping
time Ts. Check ANSI B11.19 Annex D for details.
GuardShield Type 2 Safety Light Curtain
+ T + T ) + D
r spm pf
C
5