Dynomotion

Group: DynoMotion Message: 11658 From: tapiolarikka Date: 6/7/2015
Subject: Servo tuning/step response?
Hi Tom!

After having built two systems I thought I had figured this out but now I'm more confused than ever by the max limits in step response screen.

1. Max output: should this be max value of encoder counts/sec at max dac value?

2. Max integrator: Max applied "amount of correction" ?

3. Max error: Manual says " max error that is allowed to pass though compensator"
                    Does this mean that corrective action is not taken until error is larger than this value?


the not understanding is most likely that english is not my native language but the confusion comes from trying to find examples. All examples I could find had these values in range 200-300, which are quite different from I ended up with.

Rgds,
Tapio
Group: DynoMotion Message: 11659 From: Tom Kerekes Date: 6/7/2015
Subject: Re: Servo tuning/step response?
Hi Tapio!

Regarding:

#1 - No.  Max Output is the Maximum value the Output is allowed to ever go up to (or magnitude down to) in DAC Counts.  Normally you would determine how many DAC counts are needed to go to your highest required speed.  Then set the Max Output to a value slightly higher.

#2 - Not really "correction".  It limits the Maximum amount of command output that the Integrator is allowed to create.   Using an Amplifier with a Velocity Command input (I assume this is your case) then when going at high speed the Integrator will be needed to supply all the output necessary to maintain zero error while in motion.  So the value is normally set equal to Max Output.

#3 - No.  Deadband can be used to not have any (or lower) corrective action for small errors.  It is more like the opposite.  As error increases larger corrective actions are normally made.  However if the current error exceeds the Max Error value it will be treated as if it was only the amount of Max Error and no larger corrective action will be made.  Normally when a system is working properly the errors should be fairly small (few mils).  You can then set the Max Error value to a bit larger than the maximum expected error.  In this way errors will be treated proportionally under normal conditions.  In the event of something abnormal such as a disabled amplifier, hitting an obstacle, etc where the error becomes abnormally large, then treating the error as a smaller error can help avoid an overly violent correction.  In most abnormal cases a following error should disable the axis anyway so Max Error in those cases will have no real value and can be set to infinity. 

HTH
Regards
TK


Group: DynoMotion Message: 11662 From: Tapio Larikka Date: 6/7/2015
Subject: Re: Servo tuning/step response?

Hi Tom,
 
So with 12 bit DAC increasing value above 2048 is practically useless or gives same result as 2048 ? (presuming that DAC's are signed 12bit)
Rgds,
Tapio
 
 
----- Original Message -----
Sent: Sunday, June 07, 2015 10:00 PM
Subject: Re: [DynoMotion] Servo tuning/step response?

 

Hi Tapio!

Regarding:

#1 - No.  Max Output is the Maximum value the Output is allowed to ever go up to (or magnitude down to) in DAC Counts.  Normally you would determine how many DAC counts are needed to go to your highest required speed.  Then set the Max Output to a value slightly higher.

#2 - Not really "correction".  It limits the Maximum amount of command output that the Integrator is allowed to create.   Using an Amplifier with a Velocity Command input (I assume this is your case) then when going at high speed the Integrator will be needed to supply all the output necessary to maintain zero error while in motion.  So the value is normally set equal to Max Output.

#3 - No.  Deadband can be used to not have any (or lower) corrective action for small errors.  It is more like the opposite.  As error increases larger corrective actions are normally made.  However if the current error exceeds the Max Error value it will be treated as if it was only the amount of Max Error and no larger corrective action will be made.  Normally when a system is working properly the errors should be fairly small (fe w mils).  You can then set the Max Error value to a bit larger than the maximum expected error.  In this way errors will be treated proportionally under normal conditions.  In the event of something abnormal such as a disabled amplifier, hitting an obstacle, etc where the error becomes abnormally large, then treating the error as a smaller error can help avoid an overly violent correction.  In most abnormal cases a following error should disable the axis anyway so Max Error in those cases will have no real value and can be set to infinity. 

HTH
Regards
TK


Group: DynoMotion Message: 11663 From: Tom Kerekes Date: 6/7/2015
Subject: Re: Servo tuning/step response?
Hi Tapio,

The Max Output for DACs should be 2047 reduced by any Output Offset that you may add (an Output Offset is not usually required).  DAC values greater than 2047 will wrap around and cause problems.

Regards
TK