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Mach Discussion => General Mach Discussion => Topic started by: Chips on May 09, 2012, 02:28:58 PM

Title: Mach Mill adjusting feed to overcome inconstant spindle rpm
Post by: Chips on May 09, 2012, 02:28:58 PM

Hello,

My mill has a rather poor spindle motor drive. It's not always able to maintain the proper speed. Until I can replace the motor and drive.

I am wondering if Mach Mill has the capability if I put a tach on the spindle to notify it if the spindle speed drops. That Mach can reduce the feed until the spindle catches up. A sort of like constant surface feet per min. in Mach turn

Good day.

Title: Re: Mach Mill adjusting feed to overcome inconstant spindle rpm
Post by: Hood on May 09, 2012, 04:09:46 PM

You may manage by having the macropump look at the true spindle speed and reduce the feedrate override accordingly but it would not be that easy as it would need to know what it is meant to be. Suppose you could have it look at the commanded spindle speed and have that as 100%.
Hood

Title: Re: Mach Mill adjusting feed to overcome inconstant spindle rpm
Post by: BR549 on May 10, 2012, 04:25:21 PM

Hood has the idea, I did that long ago. The Macropump watches the commanded speed and compares the actual speed actual /commanded =% of the commanded and have the Macropump adjust the FRO the same %.
I have the code here somewhere if you want I can look for it. I may have done it in a brain as well.  I called it CruseControl in attempt to make a none stallable stepper setup. IF the spindle loaded up the machine would slow the feedrate to allow it to catch back up.

(;-)TP

Title: Re: Mach Mill adjusting feed to overcome inconstant spindle rpm
Post by: HimyKabibble on May 10, 2012, 09:16:55 PM

You're forgetting that FRO will only affected NEW commands, not those that are already in the buffer.  This means it could take several seconds for the FRO to change anything.  That will create a feedback loop with a VERY long, and VERY variable time constant, which will make it extremely difficult to control.

Regards,
Ray L.

Title: Re: Mach Mill adjusting feed to overcome inconstant spindle rpm
Post by: BR549 on May 11, 2012, 04:15:41 PM

YOU need to uncheck "no FRO on que" in genconfig (;-)  IF you have that checked in GEN CONFIG then you are correct it does not effect qued data. IF it is unchecked then it SHOULD run instantly. AND yes there must be a small deadband in the routine.

(;-) TP

Title: Re: Mach Mill adjusting feed to overcome inconstant spindle rpm
Post by: Chips on May 12, 2012, 05:58:06 PM

Thank you all for the info..

I was wondering about response time and potential feedback loops.

BR549 I would very much like to look at your code. Any caveats aside from uncheck "no FRO on que". How well did it work?

Kind regards,

Good day to all.