Need help with servo/drive setup

[CreativeOffroad]

Hello all.

I am having a problem with my Mitek bed mill. My setup is listed below...

One of the servos was damaged in transport. The servo was a Glentek servo (GM4050-38). I was unable to locate a reasonably priced replacement, but did find an SEM MTS30U-42 to replace it. When I ordered the servo, I had them wire it the same as the Glentek servo per documents from Glentek.

When I hooked the servo up and started the machine, the servo ran uncontrolled until the controller errored out (I haven't mounted it yet).
I called tech support for the servo, and they told me to reverse the tach leads. I did, and after adjusting the balance on the servo amp, got the servo to stay still.

The problem now, is that the servo won't move. The controller shows the Z axis coordinates changing, but the servo isn't turning. It does register movement when I turn it by hand.

Any ideas? I know the BEMF (?) is different than the original servo, but thought I could adjust for it with the driver?

Thanks,
Scott

Mitek VBM50-F Bed Mill
Acramatic 2100 controller
Glentek SMA7115 Servo Amps
Glentek GM4050-38 Servos on X and Y axis'
SEM MTS30U-42

[Al_The_Man]

First power up normally and if the power is on the servo's, try turning the shaft of the motor, if it resists you, then the controller has command of the servo and means CNC is inputing a ±10vdc signal to the drive.
If you can turn the shaft, then measure the ±10vdc signal which should vary when you turn the motor shaft, this means the CNC is trying to command the drive but it is not responding.
Make sure the drive enable is on.
To trouble shoot the drive without the CNC controller, you can remove the ±10v signal and feed it with a 1.5~12v battery box.
Also to check the drive if all are the same size, temporarily swop two of the drives over.
Al.

[roseng]

also check to see if the current limiting pot on the drive is backed all the way off (counter clockwise) if so, apply a small drive signal, then slowly turn current limiting pot clockwise until motor turns.

Hope this Helps

[CreativeOffroad]

Thanks! I will try that. I cannot turn the servo shaft right now with the controller powered, but the motor will not turn by the controls.

I will try your tips, and post back this evening.

Thanks again,
Scott

[roseng]

Originally Posted by CreativeOffroad Thanks! I will try that. I cannot turn the servo shaft right now with the controller powered, but the motor will not turn by the controls. I will try your tips, and post back this evening. Thanks again, Scott

If you can't turn the shaft, then that rules out my current limiter theory.
have you tried reversing the analog speed command wires ?
if it uses a single ended command voltage, that would do it

[Al_The_Man]

Originally Posted by roseng have you tried reversing the analog speed command wires ? if it uses a single ended command voltage, that would do it

That usually causes a run away, in my experience.
If the controller is holding the motor in position, it appear the analogue signal is able to control the servo in position, but it appears there is no analogue move signal coming out.
Al.

[CreativeOffroad]

When I test across the two leads coming from the Acramatic to the servo amp, I get -10.35V on the Z axis (even witht the E-Stop pressed), and just a couple mv on the X and Y. It doesn't change with machine power applied either. Does that sound right?

[Al_The_Man]

Thats strange, with that type of input the motor should be running flat out.
Did you try swopping the drives to see if it transfers to another axis?
Al.

[CreativeOffroad]

It did run away until I stopped it with the balance pot. It does move to the Y axis when I swap. Sound like a problem with the Acramatic on the Z axis? Should I move the Z to the 4 axis? Is that an option?

[Al_The_Man]

I would trouble shoot it with the Control disconnected. If you disconnect the 10v analogue signal and jumper the two pins out you should be able to zero the drive with the balance pot, You should at this point find resistance to the shaft without runaway.
Once you have it stationary, apply 1.5v to the analogue in and you should be able to stop it by removing the battery and short the terminals together, do the same with the reverse polarity, if it runs continous in one direction, then swop the tach leads and try again.
You have to get this loop right before the CNC Loop.
Al.

[CreativeOffroad]

I get the -10.35 volts from controller even with it disconnected from the servo drive.

[Al_The_Man]

Originally Posted by CreativeOffroad I get the -10.35 volts from controller even with it disconnected from the servo drive.

That is because the motor/drive is not moving under the control of the analogue signal to move to zero (null) output.
Al.