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Tuning OLD servo board, Allen Bradley Bandit 3, KFLOP/Kanalog retrofit

Nick W

May 25, 2007
Milford, CT
I'm replacing the original Bandit 3 CNC controller with a PC/KFLOP/Kanalog setup on my early 80's YCM-30 mill. I have all the encoders working, and the motor moving. When I tell it to move one inch, it successfully moves one inch in any direction, both measured by the encoders and actually distance. So that was a success.
I'm fairly knowledgeable about electronics, but not an expert in this stuff.
The motors 'drift' quite a bit. If I have the servos enabled with no signal from the controller all the axis move slowly in a direction. If I power up the controller it holds it at position. With the Kmotion software I can monitor the -10v/+10v outputs going to the servo. Each one is outputting a small voltage that is essentially balancing out the drift. In my research I see I need to adjust the Balance on the servo board. Luckily there is a trimmer pot labeled Balance for each axis. I think my approach will be to have the system running and adjust the pot until the voltage that the Kanlog controller is sending the servo is zero, or as close to zero as I can. This would mean there is no movement detected by the encoder and there is no need for the controller to send a correction signal. Then to verify I will jog in each direction and make sure the voltage output is the same value but opposite polarity. Is that a reasonable approach to setting the balance?

The other adjustments on the board are labeled Lead, Tach and Sig.

In my reading the Sig is typically adjusted to a specific voltage at a a specific feed rate. If I'm understanding this, set the machine to a feed rate, the voltage sent from the controller to obtain the feed rate will be based on the return signal from the encoders. You set the Sig so that the output from the controller is a specific voltage for that specific feed rate. Am I understanding that correct? The example I saw was 40IPM feed rate set to .8v. Is this setting universal or does every servo have different targets?

I'm not sure what Lead means, is that the same as Gain? Any tips on adjusting this for my servo?

I saw that you adjust the Tach if you can't obtain the proper adjustment on the Sig?

I do have an oscilloscope if that makes setting any of these easier. Also, there is a high pitch noise when the machine is on, I'm assuming it will go away once everything is adjusted right.


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