Brooks Automation 3. Collaborative Robot Safety
Part Number: PF40-DI-00010 Rev. A General Information
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.
EN/ISO 13849-1 defines a reliability level of any safety components in a machine by performance
level in terms of average probability of dangerous failure per hour. It then attempts to provide a
statistical method to compute this number for safety systems based on failure rates for various
system components to determine the actual Performance Level (PL), which can be compared to the
Required Performance Level (PLr).
Maximum Allowable Forces to Prevent Operator Injury
ISO/TS 15066 provides detailed force limitations (see Appendix H: Table A2 from ISO/TS 15066:
2016, Biomechanical Limits) based on extensive ergonomic testing of both pressure (force per unit
area) and forces on various parts of the human body. Refer to this document for detail, but a rule of
thumb for maximum pressure to avoid injury is less than 200 N/cm (see Power Operated Pedestrian
Doors: 180N ANSI/BHMA A156.10-1999 American National Standard for Power Operated
Pedestrian Doors ), and the maximum crushing force against a rigid surface (quasi-static) to avoid
injury ranges from 65 N for the face to 200 N for less sensitive parts of the body, with 130-150 N
being a good rule of thumb for any part of the body other than the face. Maximum free space
collision forces (transient forces) are typically two times the allowable crushing force and therefore
typically range from 260-300 N.
Note that there are other well established references for force levels that will not cause injury to
humans. These include:
l
Automotive Power Windows: 135N
National Highway Traffic Safety Administration, 49 CFR Part 571, [Docket No. NHTSA-2004-19032]
RIN 2127-AG36, Federal Motor Vehicle Safety Standards; Power-Operated Window, Partition, and Roof
Panel Systems
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Power Operated Pedestrian Doors: 180N
ANSI/BHMA A156.10-1999 American National Standard for Power Operated Pedestrian Doors
l
Elevator Door Maximum Closing Force: 135N
Department of Public Safety Division 40 Chapter 5 Elevators
Recent studies have shown that it is impact force, rather than moving mass, that determines
whether an unconstrained collision in free space will injure a person. Impact forces with blunt
surfaces with the human maxilla (upper jaw bone) must reach 600 N to break the bone. This can
require a velocity of over 2 meters/sec. (Safe Physical Human-Robot Interaction: Measurements,
Analysis & New Insights, 2010, Sami Haddadin, Alin Albu-Schaffer, Gerd Hirzinger, Institute of
Robotics and Mechatronics DLR e.V. - German Aerospace Center, P.O. Box 1116, D-82230
Wessling, Germany.)
Additional research for safety for collaborative robots is ongoing. The Institute for Occupational
Safety and Health (IFA) in Germany has surveyed the literature relating to crushing and impact
injuries. Figure 3-2 summarizes their findings, which has contributed to the current draft 15066
Copyright © 2023, Brooks Automation
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