Can I use Mesa 5I20 + 7I47S + 7I42TA for AC Servo?

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24 Apr 2013 05:32 #33098 by Maglin
Hello I had purchased the Mesa 5I20 + 7I47S + 7I42TA for a different project using DC Servo's and I recently purchased AC servo's and am wondering if I can drive them with my current cards. The drives I have are 1x SDB50NK5 for using a 3.8KW servo as a spindle drive and 3x SDB20NK3 drives for driving three 1.8KW servo's for motion control. The drive can do step/dir and Speed/Torque control modes. In the speed control mode only the Z phase part of the encoder is showing as being able to be output. Here is the manual for my series of drives. If I use step/dir I can still output the A/B/C/Z encoders to LinuxCNC but would having the drive also using it's PID loop throw a wrench into the mix?

What would be my best approach at connecting these drives and using LinuxCNC with it? If I need new daughter cards which one should I get? I know the 7I77 is for velocity mode servo control. All help is appreciated.

Thank you,
Jeremiah

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24 Apr 2013 07:20 #33108 by PCW
You should be able to do step/dir control including encoder feedback
(either for monitoring or PID control) with what you have.

It seems strange that you cannot get encoder feedback in the velocity or torque modes,
as those modes _need_ encoder feedback for position control

If you can figure out how to get encoder outputs in velocity or torque modes
a 7I33TA will give you 4 analog channels and encoder inputs (replacing the 7I47S)

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24 Apr 2013 18:49 #33132 by andypugh

In the speed control mode only the Z phase part of the encoder is showing as being able to be output.

I have looked through the manual, and I rather suspect that they just forgot to mention the encoder feedback in the speed control diagram.
I would suggest putting the drive in speed mode, and seeing what comes out of the encoder feedback pins.
The table on page 14 makes no mention of the encoder not working in speed mode, it may be that the diagram is just of an example configuration for steady-speed operation.

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24 Apr 2013 20:37 #33136 by Maglin
Andy I was thinking the same thing. Thank you for looking at it. I'm going to try it out this weekend to see if I get feedback out of the drive in speed mode. If I do I'll pick up a 7I33 card to hook up the servo's with.

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24 Apr 2013 20:44 #33137 by andypugh
Also note that the analogue command goes to CN1-4 and that isn't shown in any of the diagrams.

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