Figure 3. Safety distance (minimum distance) and hard (fixed) guarding
Hard (fixed) Guarding
Reset Switch
Nearest Hazard Point
Robot
Turn-
Table
Hard (fixed)
Guarding
Safety Light Curtain/Screen
5.2.1 Formula and Examples
U.S. Applications
European Applications
The Safety (Separation) Distance formula for U.S. applications:
Ds = K × (Ts + Tr) + Dpf
The Minimum Distance formula for European applications:
S = (K × T) + C
Ds
the Safety Distance (in inches)
K
1600 mm per second (or 63 in per second), the OSHA
29CFR1910.217, and ANSI B11.19 recommended hand-speed
constant (see Note 1 below)
Ts
the overall stop time of the machine (in seconds) from the initial
stop signal to the final ceasing of all motion, including stop times of
all relevant control elements (for example, XS26-2 Safety
Controllers) and measured at maximum machine velocity (see Note
3 below)
Tr
the maximum response time, in seconds, of the S4B emitter/
receiver pair (depending on model)
Dpf
the added distance due to the depth penetration factor as
prescribed in OSHA 29CFR1910.217, and ANSI B11.19 for U.S.
applications. See Depth Penetration Factor (Dpf) table below or
calculate using the formula (in mm): Dpf = 3.4 × (S – 7) where S is
the resolution of the light curtain (for S ≤ 63 mm).
S
the Minimum Distance, in mm, from danger zone to light screen
center line; minimum allowable distance is 100 mm ( 175 mm for
non-industrial applications), regardless of calculated value
K
hand-speed constant (see Note 2 below);
2000 mm/s
(for Minimum
Distances < 500 mm)
1600 mm/s
(for Minimum Distances > 500
mm)
T
the overall machine stopping response time (in seconds), from the
physical initiation of the safety device and the machine coming to a
stop (or the hazard removed). This can be broken down into two
parts:
Ts
and
Tr
where
T
=
Ts
+
Tr
C
the additional distance, in mm, based on intrusion of a hand or
object towards the danger zone prior to actuation of a safety
device. Calculate using the formula (in mm):
C = 8 × (d - 14)
where
d
is the resolution of the light curtain (for
d
≤ 40 mm), or use
850 mm for C.
Table 1: Depth Penetration Factor (D
pf
)
30 mm Systems
78 mm (3.1 in)
S4B Safety Light Curtain
16
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