Rockwell Tools GUARDSHIELD SAFE 4 - Manual (Page 9)

Operation Manual GuardShield Safe 4
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
D
s
Safety Distance
63 Is the OSHA recommended hand speed
constant in inches per second
T
S
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 90
o 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
D
s
Minimum safety distance between the safe
guarding device and the nearest point of
operation hazard, in inches.
9
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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.”
T
s
Stop time of the machine tool measured at the
final control element.
T
c
Response time of the control system.
Note: T
S
and T
C
are usually measured by a stop time
measuring device.
T
r
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.
T
bm
Additional time allowed for the brake monitor to
compensate for variations in normal stopping
time.
D
pf
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.
5.1.3. Height of protective field
The protective field is clearly visible as the black
area with the optical lenses on the transmitter and
receiver.
In addition the height of the protective field A is found
on the label of each system and in the selection tables,
described in chapter 8.2 (resolution 14 and 30 mm).
ATTENTION
The laser beams of the ILAS are not
part of the protective field.
Use only the protective field as
mentioned on the product label.
Otherwise serious injury or death may
occur.
5.1.4. Response time – light curtain
The response time t
R
is found on the product label, or
from the selection tables 8.2.