X20DC1073 position encoder via X2X/Powerling, Calculationg POS_CTRL_T_TOTAL & POS_CTRL_T_PREDICT

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1

Hello B&R Community,

given the following scenario:

I have a second encoder (Vss) for the position controller which is read by a X20DC1073 card on a X20BB80 Bus controller. The bus controller is connected to the PLC via Powerlink. The drive (acopos micro) is in the same powerlink network. The drive drives a servo motor. Currently i am struggling to fill in the correct values for the following parameters:

POS_CTRL_T_TOTAL
POS_CTRL_T_PREDICT

Is there a method to calculate these delays?

Thank you in advance!

2

Hello Dominik,

the best way to find POS_CTRL_T_PREDICT is by measuring it in the following way.

  1. Tune the speed controller (Autotuning)
  2. In the position controller, set POS_CTRL_T_PREDICT to 400 µs and “Proportional gain” to 0 (only speed feed forward is output)
  3. Do an absolute or additive move with a constant velocity phase and trace PCTRL_S_SET/PCTRL_S_ACT and/or PCTRL_V_SET/PCTRL_V_ACT and measure the time difference

Add the measured time difference to POS_CTRL_T_PREDICT.
I expect it to be 1 X2X cylce + 2 POWERLINK cycles

POS_CTRL_T_TOTAL must be the same or greater than POS_CTRL_T_PREDICT and is used for Master-Slave couplings, when the axes are on different drives. At the master POS_CTRL_T_TOTAL is set greater by the time of the network communication to the drive of the slave. This delays the set position for the master controller and both axis physical positions are synchronized.

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3

Hi Martin, thanks a lot for this detailed description! :slight_smile: I will give it a try :slight_smile: