Analogue Servo Open Loop Control - 7i77

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28 Sep 2022 13:57 - 28 Sep 2022 14:07 #252939 by jlennox
Hey Guys

I am currently converting a 86 Mazak VQC-20/40B and am slowly converting it as the M2 control died. I purchased a 7i77 with the intent of swapping out the stock resolvers on the ballscrews to encoders. I am currently ready to power the machine under linuxcnc and would like to know if it is possible to run the analogue servos in open loop to test the machine? To claify I want to run the machine open loop for some time to test the machine thoroughly before throwing more money at it, the open loop control in the pncconf will not cut it.

I have searched the forums high and low on how to do this to no avail and pncconf will not allow you to setup a 7i77 without encoders attached, atleast it did'nt for me anyway.

I have attached a mock hal and ini file I am using for the machine.
Attachments:
Last edit: 28 Sep 2022 14:07 by jlennox.

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28 Sep 2022 14:44 #252941 by PCW
If by open loop you mean just set analog voltages and check the
motor speeds and directions, you can do this with halshow if you
disconnect the analog out pin from the x-output pin, that is,
comment out this line: (for x)

net x-output => hm2_7i92.0.7i77.0.1.analogout0

Then you can directly set the hm2_7i92.0.7i77.0.1.analogout0 pin with halshow
or halcmd

Note that this should be done with the motors disconnected from the linear axis
to prevent a crash

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28 Sep 2022 14:47 #252942 by Todd Zuercher
I know nothing about your Mazak, but it is common for servos that use resolvers to have the drive read the resolver and then the servo drive creates a quadrature encoder signal that is sent to the control for feedback. Are you sure that your old system didn't do this?

Not sure what your expectations are. I really don't think it would be possible to "run" an analog servo machine open loop with no feedback to Linuxcnc. It may be possible to make motors move some for simple testing, but the motion would be very uncontrolled and potentially dangerous. Certainly not good enough to "run" the machine.

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28 Sep 2022 17:45 #252959 by tommylight
I agree with Todd, having open loop servos on motors attached to the machine is not good, it will break something.
What spindle and servo drives does it have?
Mine has Mitshubishi everything so i already figured the wiring for the spindle.
Have a read through this to get an idea on how to wire and test stuff step by step:
forum.linuxcnc.org/10-advanced-configura...ning-detailed-how-to

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28 Sep 2022 18:16 #252961 by Todd Zuercher

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29 Sep 2022 12:23 #253026 by jlennox
PCW: I remember reading some time ago one of your posts about doing this exact thing, thanks for reminding me. This will be one of my firsts test and makes life easy by just using halshow.

Todd: My machine has the old DC servos and drives, no quadrature ouput sadly. Thanks for your comments, my objective would be to jog the axis to check paralellism, perpendicularity, flatness, etc.

Tommy: Like watching your youtube vids. The servo motors themselves are closed loop to the drive with resolvers, just open loop till i get the encoders to swap with the resolvers on the ballscrew. My machine has the SJ-5.5A motor with FR-SE spindle drive.

Cheers for the link guys, for my build I have relied heavily on other peoples conversions of VQC-15/40s. I'm just adding gear functionality and high/low gear orient now. Appears I will need the encoders to do proper movements.

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