Introduction to the Hardware
15
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 (Appendix C) based on extensive ergonomic testing of
both pressure (force per unit area) and forces on various parts of the human body. The reader is referred
to this document for detail, but a rule of thumb for maximum pressure to avoid injury is less than
200N/cm
2
, and the maximum crushing force against a rigid surface (quasi-static) to avoid injury ranges
from 65N for the face to 200N for less sensitive parts of the body, with
130-150N
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
260-300N
.
Note that there are other well established references for force levels that will not cause injury to humans.
These include:
Automotive Power Windows:
135N
(1)
Power Operated Pedestrian Doors:
180N
(2)
Elevator Door Maximum Closing Force:
135N
(3)
Note also that 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. For impact forces with blunt
surfaces with the human maxilla (upper jaw bone) must reach 600N to break the bone. This can require
a velocity of over 2 meters/sec.
4
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
2
below summarizes their findings, which has contributed to the current draft 15066 standard. Note in
particular the column for CC, or compression constant, for various parts of the body. This data is useful in
determining the stiffness or compliance for force sensors when taking collision data. If a rigid robot part is
driven into a rigid sensor the forces will be unrealistically high when compared to bumping into a more
compliant human.
A useful number that may be extracted from this data for testing is a
compression constant of 75N/mm
,
which is consistent with the hand and the face. For collisions, a higher compression constant will
generate higher collision forces. It is interesting to note that while front of the neck has a fairly low impact
force pain threshold of 35N, the neck must be compressed 3.5mm to reach this force, while in the case of
the hand, which has an impact force pain threshold of 180N, the compression distance is less, at 2.4mm
even though the force is much higher.
In considering the design and testing of a robot that meets these “Collaborative” standards, the likelihood
of an impact to a particular area should be considered. The hand is most likely to be pinched in any pinch
points, whereas the skull is less likely to be pinched as most operators that may be extending their hands
into the workspace will be quite wary of getting their heads between a moving robot and a hard surface.
(1) 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
(2) ANSI/BHMA A156.10-1999 American National Standard for Power Operated Pedestrian Doors
(3) Department of Public Safety Division 40 Chapter 5 Elevators
(4) 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
Summary of Contents for PF3400
Page 8: ......
Page 32: ...PreciseFlex_Robot 24 Appendix B TUV Verification of PF400 Collision Forces...
Page 33: ...Introduction to the Hardware 25...
Page 34: ...PreciseFlex_Robot 26...
Page 35: ...Introduction to the Hardware 27...
Page 37: ...Introduction to the Hardware 29 Appendix C Table A2 from ISO TS 15066 2016...
Page 38: ...PreciseFlex_Robot 30 Table A2 Continued...
Page 41: ...Introduction to the Hardware 33 PF400 500gm Safety Circuits PF3400 3kg Safety Circuits...
Page 45: ...Installation Information 37...
Page 46: ...PreciseFlex_Robot 38...
Page 47: ...Installation Information 39...
Page 48: ...PreciseFlex_Robot 40...
Page 54: ...PreciseFlex_Robot 46 Schematic System Overview...
Page 55: ...Hardware Reference 47 Schematic FFC Boards Revision B PF400...
Page 56: ...PreciseFlex_Robot 48...
Page 57: ...Hardware Reference 49 Schematic FFC Boards Revision C PF400...
Page 58: ...PreciseFlex_Robot 50 Schematic FFC Boards 3kg PF400...
Page 59: ...Hardware Reference 51...
Page 60: ...PreciseFlex_Robot 52 Schematic Safety System Overview PF400 CAT3...
Page 61: ...Hardware Reference 53...
Page 62: ...PreciseFlex_Robot 54 Controller Power Amplifier Connectors Control Board Connectors...
Page 63: ...Hardware Reference 55 Gripper and Linear Axis Controller Connectors...
Page 64: ...PreciseFlex_Robot 56...
Page 65: ...Hardware Reference 57...
Page 66: ...PreciseFlex_Robot 58 Schematic Slip Ring for 60N Gripper...
Page 67: ...Hardware Reference 59...
Page 68: ...PreciseFlex_Robot 60...
Page 69: ...Hardware Reference 61...
Page 70: ...PreciseFlex_Robot 62...
Page 71: ...Hardware Reference 63...
Page 72: ...PreciseFlex_Robot 64...
Page 73: ...Hardware Reference 65 Motor 60N Gripper...
Page 74: ...PreciseFlex_Robot 66...
Page 106: ...PreciseFlex_Robot 98 b The CALPP application takes about 1 minute to run...
Page 124: ...PreciseFlex_Robot 116 Wiring for 60N Gripper with Battery Pigtail Wiring for Pneumatic Gripper...
Page 125: ...117 Wiring for Vacuum Gripper Wiring for Vacuum Pallet Gripper...