Rockwell Automation 442L SafeShield Safety Light Curtain Hardware - Manual (Page 22)

SafeShield Safety Light Curtain Hardware User Manual
22
• Resolution of the light curtain and/or beam separation
• Other parameters that are stipulated by the standard depending
on the application
Figure 19: Safety distance from the hazardous point
US Safety Distance Formula
This distance, referred to as the safety distance, must be properly
calculated prior to determining the safety light curtain protective
height and mounting the light curtains on the machine. Failure to
properly calculate this safety distance may result in operator injury.
In the United States there are two formulas that are used to
properly 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
S
Ds Safety Distance
63 Is the OSHA recommended hand speed constant in
inches per second
Ts Is the total stop time of all devices in the safety circuit,
measured in seconds. This value must include all
Safety distance S (D
s
)
Protective field height
Hazard-
ous
point
Distance to avoid standing behind
the light curtain ≤ 75mm
ATTENTION: The SafeShield safety light
curtains must be mounted at a sufficient
distance from the pinch point or point of
operation hazard to ensure that the machine
stops before a person’s finger, hand, arm(s),
or body reaches the hazard.
IMPORTANT: Regardless of the calculated safety
distance, SafeShield safety light curtains
should never be mounted closer than six
inches from the point of operation or
pinch point hazard.
components involved in stopping the hazardous motion
of the machinery. For a mechanical power press it is the
stopping time measured at approximately the 90º
position of the crankshaft rotation.
Note: The T
S
number must include the response times of all
devices, including the response time of the safety light
curtain, the safety light curtain controller (if used), the
machine’s control circuit and any other devices that react
to stop the hazardous motion of the machinery. Not
including the response time of a device or devices in the
stop time calculation will result in insufficient safety
distance for the application. This may result in operator
injury.
The ANSI Safety Distance Formula
The ANSI safety distance formula, which is the Rockwell
Automation recommended formula, is as follows:
D
S
= K x (T
S
+ T
C
+ T
r
+ T
bm
) + D
pf
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 63 inches per second when the
operator begins reaching toward the point of operation
hazard from rest. NOTE: ANSI B11.19 1990 E4.2.3.3.5
states “The value of the hand speed constant, K, has been
determined by various studies and although these studies
indicate speeds of 63 inches/second to over 100 inches/
second, they are not conclusive determinations. 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 measured at the final
control element.
Tc Response time of the control system
Note: T
s
and T
c
are usually measured by a stop time measuring
device.
Tr Response time of the presence sensing device (safety light
curtain) and its interface, if any. This value is generally
stated by the device manufacturer or it can be measured
by the user.
Tbm Additional time allowed for the brake monitor to
compensate for variations in normal stopping time.
Dpf Depth penetration factor. It is an added distance to allow
for how far into the protective field an object, such as a
finger or hand, can travel before being detected. D
pf
is
related to the safety light curtain’s object sensitivity.
Object sensitivity is the smallest diameter object which
will always be detected anywhere in the sensing field.
How to calculate the safety distance S according to EN 999
and EN 294:
Notes The following calculation shows an example calculation of
the safety distance. Depending on the application and the
ambient conditions, a different calculation may be
necessary.