Collaborative Robot Safety
PreciseFlex™ DDR Collaborative Robots
P/N: PFD0-DI-00010, Rev 5.0.0, April 9, 2022
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Copyright © 2022, Brooks Automation, Inc.
force sensor is fixed to a rigid surface.
Based on the ISO/TS 15066 standard, Precise has selected
280N for short term (less than 500ms) impact forces against a rigid surface.
Pinch points. If a robot has pinch points, a full speed impact in these pinch points should not exceed the
quasi-static force above.
Pressure, or force per unit area, may be derived from the above tests and is not tested directly,
since it will depend on the application, including the end effector design.
It is desirable to eliminate
sharp edges or points on the robot or end effector that can result in high pressures. In some case foam
padding or spring-loaded end effectors may be used to limit pressure during a collision. Rounded covers
and compliant covers (plastic) are helpful in limiting pressure during clamping or impact collisions.
Precise has tested, and TUV has verified (pending) the forces for the PFDD robots (See Appendix
B of this section). This data is intended to aid the integrator in performing a Performance Level
Assessment for determining whether collision forces in a particular workcell may cause operator
injury.
An example PLr workcell application assessment based on ISO 13849-1:2006 is given for a PF400
workcell in Appendix A of this section.
Controller Requirements
Early industrial robots were often large, powerful machines with payloads that could exceed 100kg. As a
result, the industrial robot safety standards such as ISO 10218-1 often specified a Category 3 control
system for these machines, see ISO 10218-1:2011 5.4.2 and 10218-2:2011 5.2.2. However, these
standards now recognize that not all robots are large, dangerous machines and include clauses that allow
less expensive controllers to be used if a risk assessment justifies this. 10218-1:2011 5.4.3 states “The
results of a comprehensive risk assessment performed on the robot and its intended application may
determine that a safety-related control system performance other than that in 5.4.2 is warranted for the
application”. 10218-2:2011 5.2.3 makes a similar statement. Note that in performing a risk assessment
under ISO 13849, the first determination, S1 or S2, is made based on whether an operator may sustain a
serious or non-recoverable injury. For large, heavy payload robots, S2 is typically selected and this
immediately directs the evaluation result to a PLr of c, d, or e, which indicate a Cat 3 controller. For low
payload robots, S1 is typically selected which directs the evaluation to a PLr of a, b, or c. The PFDD
robots have Cat 3 safety circuits.
Possible Precise Controller Faults and Controller Testing
Precise controllers are designed so that no single failure can disable the safety features in the controller
and cause an uncontrolled motion.
Safety circuits, Failure Modes, and TUV Testing for the PFDD robots. (Appendix D)
1.
Force Limits by Design or Control.
The PFDD robots are medium power robots and have
force limits set by inherent design and control. For all axes
except the Z axis
, the maximum forces
that can be applied by the motors, multiplied by the transmission are well under 140N as can be
seen in the manual control and low speed collision table entries.
