PreciseFlex_Robot
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5.10.5 Power and force limiting by inherent design or control
“The power or force limiting function of the robot shall be in compliance with 5.4. If any parameter limit is
exceeded, a protective stop shall be issued.”
Section 5.4 requires the system designer to perform a Performance Level (PL) or Safety Integrity Level
requirement (SIL) check based on the robot AND the application tooling and workcell. For example, a
safe robot may still need safety interlock screening if it is moving a dangerous tool. This requires the
application designer to review the requirements of 10218-2:2011 which addresses robots in workcells.
Determining a Machine’s Required Performance Level (PLr). ISO 13849-1:2006 Annex A provides
tables and a worksheet to identify a machine’s Required Performance Level requirements. Figure 1 below
shows a flow chart for determining Performance Levels. Briefly these are: Select S1 for slight injuries
(normally reversible) and S2 for serious injuries or death. Select F1 for infrequent exposure to a hazard
(for example only from time to time) and F2 for frequent exposure (for example continuously entering
workcell). Select P1 for easily recognizing and avoiding a hazard (for example a repetitive motion) and
P2 for a hazard that may be difficult to avoid (for example a sudden, non-repetitive motion that may trap
an operator). An example of determining PL for a PF400 workcell is given in Appendix A of this section,
where it is shown that a PL of “a” is sufficient for the workcell.
Figure 1
In determining whether operators should be prevented from entering a workcell while a robot is moving,
the first question that must be answered when performing a risk assessment is determining the likely
severity of injury if a robot strikes a person. If the robot will not injure a person in the event of a collision,
and there is no other equipment in the workcell that can injure a person, then a person may be allowed to
enter the workcell while the robot is moving.
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