Rockwell Automation 440L GuardShield PAC Type 4 Safety Light Curtain - Manual (Page 12)

GuardShield™ PAC Safety Light Curtain Installation Instructions
10
Original instructions
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 in. 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
in./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.
Example—Reach Over
In this example, the value of K is the hand speed constant of 63 in.
per second, the Ts machine stop time is 250 ms (0.250 sec), the
20% brake wear factor is 0.05 sec and the GuardShield PAC
response time is 20 ms (0.020 sec). The Dpf is 48 in. for reach over
applications.
IMPORTANT
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.
Ds= 63 in./sec X ( 0.250 + 0.050+ 0.02) + 48 in.
Ds = 20.16 in. + 48 in.
Ds = 68.16 in. from hazardous motion
The GuardShield three beam PAC should be mounted at least 68.2
in. from the closest reachable hazard point of the protected
machinery or equipment.
European Safety Distance Formula
A safety distance must be maintained between the light curtain
and the point of danger. This safety distance ensures that the
point of danger can only be reached after the dangerous state of
the machine has been completely removed.
The safety distance as defined in EN ISO 13855 and EN ISO 13857
depends on:
• Stopping/run-down time of the machine or system. (The
stopping/run-down time is shown in the machine
documentation or must be determined by taking a
measurement.)
• Response time of the protective device
• The person’s speed of approach
• Resolution of the light curtain and/or beam separation
When using the GuardShield PAC three beam with 400 mm beam
spacing, EN 999 requires that the first beam should be mounted
at 300 mm above the floor. When mounted in this configuration, it
is necessary to add 850 mm as the value for “C” in the safety
distance calculation equation.
Figure 7: Safety distance from the point of danger