When programming the robot you might experience sometime the robot is stopping with a safety stop called “Joint Limit Violation” or similar error messages. And you can observe the robot was trying to reach a Waypoint you had set, but it was not possible due to mathematically and physical limitations. This can especially happen in MoveL (linear mode) programming. It does not mean that the robot cannot go to the Waypoint you have defined, but it cannot reach there in the way programmed.
Consider you arm and reaching for a coin that is in between your elbow and wrist. If you are not allowed to move you body posture – then it is very difficult to reach and grab the coin. But when you can move you body posture then it is very easy to pick the coin.
Similar situation can occur during programming the robot where it will be impossible for the robot to take a linear move from where it was to reach and grab the coin. The robot will attempt and you will se a rapid increase in speed and very fast thereafter the robot stop with joint error messages in order not to spoil the robot.
Just reposition the robot posture and waypoints and the robot can reach the target.
Sometimes you will see the robot accelerate and then suddenly stop with a safety stop. This is also Singularity when the robot reaches a point where the mathematic is nearing an illegal calculation e.g. like divide with zero. In the example of dived by zero the robot control might reach values that is only fraction e.g. 0.0000000000x which is virtual a zero and therefore the robot will stop with a Safety stop if the programming reach such value.
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By Zacobria Lars Skovsgaard
Accredited Universal Robots support Centre and Forum.