Open Loop Command

Moderators: TomKerekes, dynomotion

Post Reply
Chevvron
Posts: 2
Joined: Mon Apr 22, 2019 9:26 pm

Open Loop Command

Post by Chevvron » Thu Sep 05, 2019 7:47 pm

Tom,
We have a linear axis with linear scale position feedback driven by an analogue servo drive and brushless motor with velocity feedback using +/10 volt command input.
Our initial setup would be to adjust the amplifier volts/rpm so that 9 volts analogue command input = our desired maximum axis velocity as an open loop motion move.
How do you use the Step response screen to command an open loop motion profile move so that we can set the +/-10 volt servo amplifier speed reference before then closing the position loop using the KFlop and tuning using the PID gains ?
Regards,
Tim

User avatar
TomKerekes
Posts: 661
Joined: Mon Dec 04, 2017 1:49 am

Re: Open Loop Command

Post by TomKerekes » Thu Sep 05, 2019 8:59 pm

Set the PID parameters to zero. Command a Move of your desired maximum velocity. Adjust the Velocity Feed Forward until you get a 9V output (9/10 x 2047 = 1842 DAC counts). Or, compute VFF from Output = VFF x Velocity. See:


Image
Regards,

Tom Kerekes
Dynomotion, Inc.

Chevvron
Posts: 2
Joined: Mon Apr 22, 2019 9:26 pm

Re: Open Loop Command

Post by Chevvron » Thu Sep 05, 2019 9:23 pm

Thanks Tom.
I now understand VFF = DAC counts with PID gains all zero.
Tim

User avatar
TomKerekes
Posts: 661
Joined: Mon Dec 04, 2017 1:49 am

Re: Open Loop Command

Post by TomKerekes » Thu Sep 05, 2019 10:06 pm

Hi Tim,

Actually it is DAC = VFF x Current Velocity. So for example if the Profile Velocity goes to 100000 counts/second and VFF = 0.01 then the DAC will be 1000 counts. Here is another related article.
Regards,

Tom Kerekes
Dynomotion, Inc.

Post Reply