Rockwell Automation 440L GuardShield Type 4 and Remote Teach User Manual - Manual (Page 12)

GuardShield™ Safety Light Curtain User Manual
10
R
Original instructions
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
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.
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 (for
“Response Time” see page 9).
• Reach or approach speed.
• Resolution of the light curtain and/or beam separation.
Figure 4: Safety distance from the point of danger
How to Calculate the Safety Distance S
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]
d = resolution of the light curtain [mm]
S = safety distance [mm]
The reach/approach speed is already included in the formula.
If the result S is ≤ 500 mm (19.6 in.), then use the
determined value as the safety distance.
Point
of
danger
Protective field height
Safety distance S (D
s
)
Distance to avoid standing behind
the safety curtain ≤ 75 mm