Output/Input Scale Factor

["Laser"]

I have a high resolution stage used for a scanning application.  I'm using a pci-7344 to control the stage.  The system is marginally stable with kp=1 and various values set for ki and kd.  I have found several posts with the same issue:

http://forums.ni.com/t5/Motion-Control-and-Motor-Drives/tuning-servo-system/m-p/139507/highlight/tru...

http://forums.ni.com/t5/Motion-Control-and-Motor-Drives/Is-there-any-way-to-drcease-the-open-loop-ga...

http://forums.ni.com/t5/Motion-Control-and-Motor-Drives/MAX-Reducing-Encoder-Resolution/m-p/1030934/...

http://forums.ni.com/t5/Motion-Control-and-Motor-Drives/7344-PID-proportional-gain-1-but-actuator-st...

It is apparent that the gain needs to be set below one and the only current solutions (decrease encoder resolution or decreasing the output limits) are both unacceptable.  Encoders aren't free (and in my case extremely difficult to replace) and I want my stage to run as fast as possible.

Many other modern controllers allow the input and/or the output of the PID loop to be scaled (even if it's only by factors of two for non floating point dsp's) for exactly this reason.  This allows one to arbitrarily place the optimal kp value within the allowable integer range (i.e. 1<kp<32768).  Is there a way to do this on ni controllers?  If not is there a propper place to request features?

[MissFitt]

Unfortunately you can't scale the input or output of the PID loop. I am attaching two links below that discuss how to tune the servo motor and also where you can make product suggestions. I'm sorry I don't have better news for you, but please post your ideas to the idea exchange below so our developers can look at them. Thank you!

A Simple Method for Servo Motor Tuning

NI Idea Exchange

Mychal F

[Highland_Controls]

Is your drive matched to the motor?  An oversized drive can cause tuning problems, and require a low P gain.  Also, the analog input gain can often times be scaled in the drive.