Error message 2852 "MDR: PTP Not allowed while motion driver base active"

Just got a call from a customer that they've started having this message while they're trying to teach points. This is new, even though the robot in question has been in production for a while, and they've taught a dozen new parts successfully over the past few months.

My System Messages manual has... zero details about this message.

Robot is a KRC4 with KSS 8.3.17. It uses ConveyorTech to pick up parts off of a conveyor, but they're getting this error when they try to teach points at the Drop position. My first thought was that they were trying to teach the Dropoff without having executed the CONV_QUIT function, but the teaching program (and the new-part teaching procedure) is structured to make that really difficult. Plus, like I said, they have experience teaching new parts in this robot successfully, so that explanation seems unlikely.

Anyone know anything about this error and what can cause it?

Yeah, that's the weird thing -- it shouldn't have been possible for them to get to the moves they were trying to touch up without completing the CT motion and exiting it with CONV_QUIT.

Anyway, they started over and say everything's fine now. So I'm guessing they did a block select and didn't realize it.

I don't know for certain, but if I had to guess, I would say that it's due to the way that the KRC handles PTP vs LIN motions, and how the system integrates the conveyor motion into the path planner.

Basically, a PTP motion pre-checks its destination for reachability, and executes. The motion cannot be altered once it starts.

A LIN motion, OTOH, is basically a continuous chain of very tiny (sub-mm) PTP motions. This allows the path planner to inject shifts to $BASE, from the conveyor encoder, "in between" each tiny PTP motion that makes up the LIN. This makes it possible for the LIN motion to be constantly updated to follow the moving conveyor, even as the conveyor speed varies.