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Asynchronous following error
I just did a measurment that I don't understand.
I have a set of 2 signals one is a 1KHz pulse signal , the other one is a 256KHz quadrature signal perfectly synchronized with the 1KHz

I plugged the 256K signal on a motor A B channel and the 1K on the C channel

Then I setup the trigger for this motor to react on a up level of the C channel, I then built a plc to read and rearm automatically the trigger and give me the difference in position between 2 triggers.
I get a perfect 256 all the time. so the triggering plc seems OK

I now plug the 1K signal to the C channel of an other motor, a real motor.
and I did the exact same.
I jog my axis at 5um/ms and I read the difference of position between 2 triggers..

what I obtain is a really noisy signal centered on 5um but with a big jitter (+ or - 2 um) so I get distances between 2 pulses varying from 3 to 7 um

what bothers me is that it does not relate to my following error, indeed, when I plot the following error at the same time, it only varies of + or - 300 nm .
so my expectation was that I could have a maximum of twice the following error in my difference , so never more than 600 nm...

The only explanation I can come up with is that pmac the following error showed by PMAC is good because it is sampled at the same rate as the reaction time of the servo loop. but what happens between 2 servo cycles can be much more dramatic than the following error !

but this is scary, could it mean that every time I manage to regulate a motor down to 200 nm of following error, I can actually have 2 um without knowing it ?

I am doing this because I am studying a setup to use an external clock (so fundamentally asynchronous) to command a position on a motor. (the motor has to be at a designated position at every tic of the clock without making stops (as if the move was linear))

Messages In This Thread
Asynchronous following error - jsinoir - 12-05-2018, 02:41 AM
RE: Asynchronous following error - Tony - 12-05-2018, 03:51 AM
RE: Asynchronous following error - jsinoir - 12-06-2018, 01:57 AM
RE: Asynchronous following error - jsinoir - 12-06-2018, 02:06 AM
RE: Asynchronous following error - jsinoir - 12-07-2018, 12:22 AM

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