Problem using analog feedback on pix7340

[toni939]

Hi,

I am trying to use analog force feedback on one of my axis on pxi 7340. The problem is that MAX always uses encoder as feedback even if i configure it to be analog. In MAX i disabled encoder and enabled the appropriate ADC for the axis and set the position to few hundred counts so the controler stops the axis when force is above a small value (around 1V). If i start motion it moves the same as if the feedback was encoder (for few hundred counts). I dont know what is happening. I red the motion manual and if i understood it correctly the axis should move at the configured speed until the force is larger as value i set in position field.


Thanks

[Jochen]

Hi toni939,

please have a look at this document to get a full understanding how analog feedback works with NI motion control boards. I have also gathered all discussions with my involvement about analog feedback under the AnalogFeedback tag.

Kind regards,

Jochen Klier

National Instruments

Message Edited by Jochen on 02-03-2010 04:20 PM

[toni939]

Hi, Jochen   Thanks for the fast reply. The only difference that i see between your and mine configuration of axis is i am using stepper output to control servo drive. I am new to motor control and i dont know if it is posible to use force feedback with stepper output. I wanted to try with large s-curve values to somewhat control torque of the servo.

[Jochen · Accepted solution]

Ok, this explains the behavior. To use analog feedback properly you need to configure the axes as servo axes with analog output. In closed loop stepper mode the board doesn't run a PID loop, but it checks at the end of the move if the target position was reached. If not it does a pull-in move.

This works fine for positioning stepper motors, but it doesn't work at all with analog feedback.

Please configure your drive in current mode with analog commad input if possible.

Kind regards,

Jochen

[toni939]

Thank you very much.