Rockwell Automation 445L GuardShield Safe 4 and Safe 4 PAC Safety Light Curtains User Manual - Manual (Page 9)

R
GuardShield™ Safe 4 Safety Light Curtain User Manual
7
Original instructions
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 in inches
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
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.
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
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 object sensitivity of the safety light curtain. Object
sensitivity is the smallest diameter object which will always
be detected anywhere in the sensing field.
Example:
In opto-electronic safeguarding, such as with a perpendicular
safety light curtain applications with object sensitivity (effective
resolution) less than 2.5 inches, the D
pf
can be approximated
based on the following formula:
D
pf
(inches) = 3.4 × (Object Sensitivity – 0.276),
but not less than 0.
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, e.g. GuardShield
Safe 4 (for “Response Time” see page 6).
• Reach or approach speed.
• Resolution of the light curtain and/or beam separation.
Figure 3: Safety distance from the point of danger
How to Calculate the Safety Distance S for GuardShield Safe 4 Systems
with a resolution
40 mm. According to EN ISO 13855 and EN ISO 13857:
-> First, calculate S using the following formula:
S = 2000 × T + 8 × (d – 14) [mm]
Where …
T = stopping/run-down time of the machine
+ response time of the protective device [s]
Safety distance S (D
s
)
Protective field height
Point
Distance to avoid standing behind
of
danger
the safety curtain 75mm