Hi AZ,

Adding some I (Integrator Gain) should force the average error to be exactly zero.  Start with a small number such as 0.00001.

 

Hello Tom:

I have been running those low current motors directly with the SnapAmp Peak current set to 10 and they work fine.  No excess jitter or other noise.  I did not add the parallel load resistors.

I have the Pgain set to 3. Dgain at 300 and this delivers very acceptable holding torque and stability with a 100 hz low pass gain filter.  These motors have ferrite beads on the motor leads and the beads do get warm to the touch.  The motors get warm also but just barely enough to feel the temp difference from ambient.

I do have a couple of other issues that came up.  The motor actual positions are offset by quite a bit when in position and this offset distance is consistent no matter the motor position.  If I DisableAxis, then EnableAxis the motor will shift the distance of this offset each time. On an analog drive I would simply adjust the input offset adjustment to take care of this but is there a way to adjust the SnapAmp output offset to eliminate this?

The second issue has to do with the EnableAxisDest(0,X) command

I am using version 4.32 now and have used  version 4.31 and 4.30 previously.

In 4.31 and 4.30 when I used this command, it would preset the current axis position to the value of (X) with no motion.  In 4.32 it commands a move to that position (X).  Am I missing something or did this change? 

Hi AZ,

Depends a lot on what you are trying to do and what is important to you.

The normal technique is to enable the axis and set the target destination to where the Encoder Position is currently reading with:

EnableAxisDest(0,ch0->Position);

This method maintains the correct Axis Position even after a crash, Drive disable, drift, manual movement, etc as the system will still maintain a valid Encoder position regardless of whether the axis follows the desired Commanded positions or not.  This is what EnableAxis(0); does for Servo Mode Axes by default.

This method should enable the axis gracefully avoiding any violent motion because the target servo position is set to where it actually is.

Adding the I gain should make the Commanded position and Measured Encoder position very close (average difference will be zero except for any servo dither).   But there still might be some movement depending on the servo dither, if/how long the axis has been disabled, drift, manual movement, etc...  If this is a problem you might save the last commanded destination, enable the axis, then perform a controlled movement back to the last commanded destination.  For example:

double SaveDest=ch0->Dest;  // Save where we were last commanded to be

EnableAxisDext(0, ch0->Position); // enable the axes where we are

Move(0,SaveDest);  // move back to where we were last commanded

while (!CheckDone(0)) ;  // wait for the motion back to complete

 

OK.  How can I preset the current axis position in Kflop without Kcnc running to a value other than zero?  I can't seem to find an example of this other than the G code fixture offsets in Kcnc.

 

Would I set the commanded position or set the actual current encoder position?

 Would I have to do it with the axis disabled especially considering that the actual motor position would jump to the offset as mentioned before?

AZ