akd servo drive operation mode

[JhnEls]

I have an AKM servo motor and AKD servo drive that works great in the constant torque operation mode (mode that was recommended in the NI user manual).  However, I would like to operate the servo in a constant velocity mode.  I have tried adjusting the settings using the AKM software but the motor will not turn when using MAX (following error).  The operation mode is updated on the drive output from 00 (constant torque) to 01 (constant velocity).  This is the only parameter that I have changed.

Equpment being used:

Ni PXI-7344 motion controller

UMI-7774 motion interface

AKM42E-ANCNC-00 BLDC motor with SFD

Single Axis AKD drive, Analog, 3A continuous current, 120/240 VAC

PXIe-1078 express chassis

PIXIe-8102 controller

Labview 2011

Does anyone have any suggestions on why the motor will not turn in constant velocity mode?

Thank you for your time.

[Cameron-T]

You can control your servo motor in velocity mode by using the controller and driver (NI Motion). NI Motion has options to run in velocity mode. It works by using the feedback from the motor to determine the trajectory needed to keep a certain velocity. To do this, you would leave the drive in the suggested mode. Try running it in Measurement & Automation Explorer first, and then move to LabVIEW.

[JhnEls]

Thank you Cameron.  I have switched the operation mode setting in MAX to velocity but when the velocity is displayed in the MAX window titled "current trajectory data", the velocity will fluctuate by around 5%.   I would like the velocity to stay constant.  Any further ideas?

[Cameron-T]

Is it a consistent 5% regardless of the velocity you ask for? That would be good to check before we continue.

[Highland_Controls]

If you have the drive in velocity mode, then you must tune the velocity loop in the drive.  After that is done, then tune the position loop using MAX.

[JhnEls]

I have tried tuning Kv (ranged from 0 to 2500).  Anything greater than 1250, the motor did not operate properly.  For Kv ranging from 0 to 1250, the performance was nearly the same.  With the Kp = 275, Kd = 655, and Ki = 166, the following variations occurred:  RPM = 25, +/- 1; 50 +/- 5; 100 +/- 6; 150 +/- 2; 200 +/- 2 (range in RPM that I need for the experiment).  The aforementioned constants were obtained using the autotune function in MAX (does not repeat very well).  What variation should be expected when using a servo motor that is properly tuned?

[Highland_Controls]

If you have the drive in velocity mode, that means that the velocity loop is being closed in the drive and you have to tune using the drive software, not MAX.  Once you finish tuning in the drive, then you can use MAX to tune the position loop.  Not familiar with the AKD stuff, but you should also tune the current loop in the drive, unless the drive and motor come as a matched pair or the drive somehow knows what motor is connected to it.

[JhnEls]

I have tried tuning the motor in velocity mode using the software.  The system does not respond to the tuning - amplifier disable unexpectedly error appears and the current seems to reach its maximum.  I am not sure what is going on since the system will run out of MAX, although the position tuning is quite suspect as well. 

[Highland_Controls]

Does your motor move at all?  Can you change the tuning parameters to start off with a gently move?  Does your motor have a brake on it?

[JhnEls]

Yes, the motor will turn, but the velocity is not constant. I have tried a wide range of tuning parameters - some work better than others in terms of smoothness but the velocity is always erratic. No, the motor does not have a brake.