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Author Topic: RPM readout showing negative numbers . . suddenly . . . WTF??  (Read 8636 times)

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Offline simpson36

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RPM readout showing negative numbers . . suddenly . . . WTF??
« on: August 18, 2010, 05:08:48 AM »
I did a search on this and have not found and answer, but I am sure it must be something simple.

Currently I am  installing Mistubishi industrial AC servo drives and therefor have beed tinkering around in the control box and reconfiguring Mach, but I did not change the BOBs  nor any of the sensors or wiring related to the spindle speed. I don't know when the RPM readout went south so I can't say exactly what I was messing with that affected it.

The signal from the sensor shows strong and clean on a scope and the BOB has indicator LEDs  that are flashing regularly as the spindle rotates. The readout is not only negative, but the readings are low  . . no pun intended . . for example it reads -750 when the spindle is actually running about 2,000 RPM. The readout does change and follows the spindle speed, albeit inaccurately.
Re: RPM readout showing negative numbers . . suddenly . . . WTF??
« Reply #1 on: August 18, 2010, 06:43:02 AM »
i dont understand your issue.
you use servo motor for spindle,if yes then you can use speed monitor in Driver.


Amir
**Even a clock that does not work is right twice a day**

Offline simpson36

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Re: RPM readout showing negative numbers . . suddenly . . . WTF??
« Reply #2 on: August 18, 2010, 07:47:03 AM »
Thanks for the response.

Motor type is irrelevant in this instance. I am referring to Machs RPM screen readout (DRO) which is driven by a sensor (photointerruptor and shutter disk in my case) which is independent of the motor or drive type.

Offline Hood

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Re: RPM readout showing negative numbers . . suddenly . . . WTF??
« Reply #3 on: August 18, 2010, 07:53:23 AM »
 Never seen or heard about this before except with the driver a few revisions back and certain computers but unless you ave changed Mach Rev or Computer mobo then afraid I dont know :(
Hood

Offline simpson36

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Re: RPM readout showing negative numbers . . suddenly . . . WTF??
« Reply #5 on: August 18, 2010, 08:24:53 AM »
Never seen or heard about this before except with the driver a few revisions back and certain computers but unless you ave changed Mach Rev or Computer mobo then afraid I dont know :(
Hood

Thanks for the comment. Same computer, same sensor, same wiring, same operator (likely will prove ot be the problem ultimately). It is quite the mystery.

The only thing new is that I have introduced AC servo motors and 220V power, but even with all of that switched off, the DRO is still jazzed I went back to an older version of Mach and reinstalled including the pulse driver. Problem is still there. Next I guess I will delete the XML and reinstall again and reconfigure fro scratch.

My concern is that it is an interference issue and if so it may effect other more critical functions.

Incidentally, I am now an industrial AC servo drive convert. I just put an AC servo motor on my 4th axis that is about 1/3 the size of the DC servo and still has slightly more continuous torque rating. A little 200 watt AC servo motos on my X axis has more than twice the torque of the slightly bigger NEMA23 DC servo motor it replaced. Pretty impressive so far . . . .

Two words . . . AUTO . . .TUNING . . .  ;D


« Last Edit: August 18, 2010, 08:26:34 AM by simpson36 »

Offline Hood

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Re: RPM readout showing negative numbers . . suddenly . . . WTF??
« Reply #6 on: August 18, 2010, 08:39:42 AM »
Any way you can bypass the BOB and connect direct to the port or a second port? From what you say its working as far as the BOB inputs.

Yes AC servos are the mutts nuts, auto tuning is good but I find I can still get things sweeter with a further manual tune. Not sure of your drives software but the scope feature in mine makes tuning a lot easier, can monitor up to 4 things at a time although I usually only monitor the three. When Velocity tuning its commanded velocity, feedback velocity and error. For Positional tuning its  Position command, feedback and error.

Was messing around with the lathe the last day testing out my netbook with the USB to Serial adapter, monitored both axis and homed, count zeroed in software and commanded a positional G0 move via Mach, most I saw out of position, with probably 50 moves of varying amounts on each axis, was -1 count, not bad when there are 8000 per 5mm :)

Hood

Offline BR549

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Re: RPM readout showing negative numbers . . suddenly . . . WTF??
« Reply #7 on: August 18, 2010, 09:11:02 PM »
IF you want to try something try reloading a backup XML, not the autosave version but an original copy.

Offline simpson36

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Re: RPM readout showing negative numbers . . suddenly . . . WTF??
« Reply #8 on: August 19, 2010, 09:38:41 AM »
IF you want to try something try reloading a backup XML, not the autosave version but an original copy.


That's a good suggestion. Is there a way to distinguish between an autosave and and original backup?

Offline BR549

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Re: RPM readout showing negative numbers . . suddenly . . . WTF??
« Reply #9 on: August 19, 2010, 11:13:05 AM »
The autosaved versions are only reloadable from inside of mach. They have a differrent extension.  The original backup will be named exactly like the one being used only stored in a different directory.

AS a rule you should keep a backup copy of the XML stored away somewhere safe (off of the computer) just in case you need it

So far about 99% of the time I see strange things showing up in the dros it points back to a corrupt XML. Not saying that is YOUR problem but I would check it to be sure.

Just a thought, (;-)

PS:  YEP AC servos RULE (;-)

« Last Edit: August 19, 2010, 11:14:49 AM by BR549 »