Figure 12. Safety distance (minimum distance) and hard (fixed) guarding
Hard (fixed) Guarding
Reset Switch
Nearest Hazard Point
Robot
Turn-
Table
Hard (fixed)
Guarding
Safety Light Curtain/Screen
5.1.2 Formula and Examples
Notes:
1. The OSHA-recommended hand speed constant
K
has been determined by various studies and, although these
studies indicate speeds of 1600 mm/sec. (63 in/sec.) to more than 2500 mm/sec. (100 in/sec.), they are not
conclusive determinations. Consider all factors, including the physical ability of the operator, when determining the
value of
K
to be used.
2. The recommended hand speed constant
K
, derived from data on approach speeds of the body or parts of the body
as stated in ISO 13855.
3.
Ts
is usually measured by a stop-time measuring device. If the machine manufacturer's specified stop time is used,
at least 20% should be added to allow for possible clutch/ brake system deterioration. This measurement must take
into account the slower of the two MPCE channels, and the response time of all devices or controls that react to stop
the machine.
WARNING:
•
Stop time (Ts) must include the response time of all devices or controls that react to stop
the machine
•
If all devices are not included, the calculated safety distance (Ds or S) will be too short, which can
lead to serious injury or death.
•
Include the stop time of all relevant devices and controls in your calculations.
•
If required, each of the two machine primary control elements (MPCE1 and MPCE2) must be
capable of immediately stopping the dangerous machine motion, regardless of the state of the
other. These two channels of machine control need not be identical, but the stop time performance
of the machine (Ts, used to calculate the safety distance) must take into account the slower of the
two channels.
Calculations for US Applications
The Safety (Separation) Distance formula for U.S. applications:
Ds = K × (Ts + Tr) + Dpf
Ds
the Safety Distance, in inches
K
1600 mm per second (or 63 in per second), the OSHA 29CFR1910.217, and ANSI B11.19 recommended hand-
speed constant (see Note 1 below)
Ts
the overall stop time of the machine (in seconds) from the initial stop signal to the final ceasing of all motion,
including stop times of all relevant control elements (for example, IM-T-.. Interface Modules) and measured at
maximum machine velocity (see Note 3 below)
EZ-SCREEN
®
LS Basic Safety Light Curtain
22
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