[lcvette]

What does it sound like? Clicks at the jerk points? If so, I would guess that is your acceleration feedforward (aff) doing its job. Aff causes a current (force) to be output proportional to acceleration. Since you are running trapezoidal moves, Those acceleration curves have square edges. Its like hitting your ball screws with a little hammer. Since feedforward is not a closed loop thing, it's bandwidth is only limited by your current loop performance. So to calm down those clicks, you either need to back off on your aff and sacrifice following error performance on acceleration portions or change your trajectory so you aren't commanding square acceleration profiles. Or put a low pass on your speed loop output. It will limit performance, while reducing the clicking, but you might find a happy medium. However, it will limit your closed loop bandwidth. The one practical downside of those clicks is that they might show up as ringing in the surface finish because they excite the mechanical structure. Or it might not...

I think you are generally getting quite nice performance. You may even think about backing off your system bandwidth. I had an experience when doing servo tuning for a recognizable VMC manufacturer. -- Don't set your bandwidth too high or you will shake the head / column on higher jerk portions of your trajectory. I had come from a background of always shooting for maximum bandwidth / minimum following error, but with max servo bw, those high jerk sections would get the head / column moving, as the servo jerk was like hitting the mill with a hammer. When we backed off on the system bw, contouring tests would have drastically less ringing shown in the tool paths. It was a mixed bag -- I could clearly measure the increase in servo following error, but that was less objectionable than the ringing left in the cut. That ringing was absolutely not measurable by us and was absolutely invisible to running your fingernail over it, but it was easy to see.

I think that o am probably going to run open loop with the best servo drive tune due to the fact that the motion is smoothest. I can absolutely tell you that in full closed loop at this point in time that there is too much noise transferred into the machine from the control managing the following error corrections. what is causing it to me could be a number of things, as you stated, drives, trapezoidal acceleration, bandwidth, etc.. I'm still new to all of this and still learning, so each day brings more Information to work with. oddly enough, Clint has been running machine with a completely untuned drive since day one and if it is anything like mine the max following error was Astronomical.. yet he managed to make parts that were to tolerance. a mystery to me.

I have the accelerated feed forward in the drive set to zero because it made things worse. the position feed forward is set at 100% and position gain at Max but once position feed forward is at Max the gain plays less of a part it would seem. changes to it seemed to make little difference unless they were really big.

I have some direction from PCW at mess to try using the encoder as a low bandwidth feedback loop similar to a linear encoder, I'm researching now how to configure that in the Hal to test and will report the results! thanks for you input, very insightful!

Chris

Sent from my XT1585 using Tapatalk