Closed Loop Stepper System?

Hi all,

I've searched, but haven't really found anything definitive in answer, so am asking here. Using Mesa cards and Vexta drivers with the OEM 5 phase steppers in an Emco turning center, is it possible/feasible to have a closed loop system utilizing encoders? Is there anything needing to be made aware of or precautions taken when selecting components to do so? Thanks.

BigJohnT wrote:

It is my understanding that closed loop with steppers can only work in unique situations. The problems are you can't increase the power to a stepper like a servo to catch up. You can't really tune a step like you can tune a PID loop for a servo. IIRC a few have used encoders to trigger a following error but this seems wrong too. IIRC someone reported success with this by having the encoder counts much higher than the step pulses. Many try to do this as it seems easy to do.
JT

John, thanks for the reply.
Yes, one of the search results yielded a similar discussion.
Now, this may just be my naivete and ignorance in play, but I was thinking more along the lines of not trying to force the step
with increasing power, but rather to ( on a level of a fraction of a second ) pause everything until that step can be "replaced".

Dumb idea?

PS - senchoo email

Hi John,

I'm okay with it not being trivial. I am interested in learning about what it takes. I haven't been able to find the successful ones. Can you point me in the right direction?

I'm not married to the steppers in the machine right now but would like to make some manner of educated decision on my choices over the next few weeks. One the one hand, the step motors are in there already and I just need to buy drivers. On the other, I have 5 or 6 nice brushed servo drives sitting about as well, so would be open to the prospect of buying suitable servos to replace the steppers.

Thanks.

John,

Yes, it is an EmcoTurn 220P. The drivers are easy and I've sourced a bunch of them already. The problem is that I have no idea of the torque rating of the OEM steppers so have no idea of what servos to look for to replace them if I decide to go that way.