Introduction to the Hardware
17
Robot Testing and Safety Circuits
While some robots have 6 or even 7 axes and can move in many directions, generally testing can be
done in the horizontal plane and in the vertical direction. Since gravity adds to the force in the
downwards vertical direction, and since in the horizontal plane forces are symmetric in opposite
directions, testing in +X, +Y, and –Z (downwards) is generally sufficient to characterize robot forces.
Precise uses a test stand, to which a certified force gage can be attached in either the vertical or
horizontal direction, for testing forces. A “compliance plate” assembly is attached to the robot to simulate
the compliance of the human hand of 75N/mm.
Clamping/squeezing force is measured by moving the robot slowly into the force gage until the robot
reaches its maximum force and generates an error. Based on Table A2 from ISO/TS 15066 (Appendix
C), Precise has selected the maximum clamping force (quasi-static) to be 140N for a collaborative
robot.
Transient impact force in free space is measured by moving the robot at its maximum permitted speed
and payload with the compliance plate impacting the force sensor when the force sensor is held by a
person in free space. Based on Table A2 from ISO/TS 15066, Precise has selected the maximum
impact force (transient force) in free space to be 280N for the hand and forearm and 130N for the
skull for a collaborative robot.
Impact force against a rigid surface (trapping) is measured by moving the robot at speeds up to its
maximum permitted speed and payload with the compliance plate impacting the force sensor when the
force sensor is fixed to 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 the forces for the PF400 robot (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.
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