servodrive drift in actual position

we have a small drift in the knives actual position, as viewed with the eye on a stroboscope.

it is more visible at high speeds.

the knives are all following one common virtual master.

we monitored the position following error in scout, it is close to zero.

we are using below siemens simotion.

appreciate your ideas.



6AU1455-2AD00-0AA0
SIMOTION Drive-based Control Unit D455-2 DP/PN; programmable motion controller; ULTRA-HIGH performance; interfaces: 12 DI, 16 DI/DO, 6 DRIVE-CLiQ, 2 PROFIBUS, 3 PROFINET ports, 2 ethernet, 2 USB, 1 option slot; incl. dual fan / battery module and battery

Is what you are seeing really the truth?

If you look at the master with the stroboscope does it hold it's position?

Is the knives constantly drifting?


Next thing to look at is mechanics. Do you have any gears or anything else between the motor and the knives?
Can you see and use the stroboscope on the shafts of the servomotors?

If your position error is near zero in Scout, it makes me think that you have a mechanical issue.

What type of system are you using? Ball screw? Systems I typically see use a rack and pinion setup. I've seen the gear work it's way loose before on the gearbox shaft, causing positioning issues.

Sounds like the virtual master is giving it the wrong position, or more likely, the scaling is off somewhere. Are you using actual ratios or nominal ratios for your scaling?

we checked with Siemens, all our project looks ok.
it is most probably a problem in the stroboscope...
thank you all