Hi pros,
Many clients are asking us about the motion that the UR robot is doing upon initialisation.
I tried to find some documentation that would explain this motion. The terms that I usually use to explain this step to clients is that there are no batteries in the robot arm that would allow the robot to remember encoder position upon startup. So the robot 'dances' a little upon initialisation to find out encoder positions values.
So the good side to this is that you cannot loose mastering values because of dead batteries (we know this happens quite often on other robots and it can be a pain to set this back up). However, the downside is that little dance motion needed upon startup.

Anyone can point me to some documentation or can add some details to this? Maybe you can @Stefan_Stubgaard

@Sebastien There is a difference between CB2 and CB3 robots:

CB2 robots uses incremental encoders. The system has no battery backup (thus avoiding the risk of dead batteries as you mention), this is why each joint needs to reference itself by finding a reference point on the encoder disk. A total of 20 reference points exists, meaning the max motion is 360/20 = 18 degreesper joint

CB3 robots uses "true" absolute encoders with a unique technology, which does not require batteries for remembering its position after being turned off, so you will never have the risk of dead batteries on CB3 either. When powering up, there is a slight motion for each joint, this is in order for the joint to be able to retract the brake pin (the clicking sound you might notice)