Rls encoder and vfd calibration

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nicolasjolliet
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Re: Rls encoder and vfd calibration

Post by nicolasjolliet »

Ok, thanks Marty.
the top speed i can set, it's the bottom speed i need to set in order to have a linear line at 45deg.
so if I set 5k to 5k, so 1k is 1k, 8k is 8k as well.
IMG_3422.jpg
martyscncgarage
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Re: Rls encoder and vfd calibration

Post by martyscncgarage »

nicolasjolliet wrote: Fri Oct 16, 2020 4:45 pm Ok, thanks Marty.
the top speed i can set, it's the bottom speed i need to set in order to have a linear line at 45deg.
so if I set 5k to 5k, so 1k is 1k, 8k is 8k as well.
IMG_3422.jpg
I'm sorry, I can't help you with that. The manual is pretty sparse.
In the Wizard Spindle Setup section, you DO have:
Spindle min speed high range set to 0
Spindle max speed in high range set to your max spindle speed
And you have left Medium Range Spindle Speed ratio at 1
Low range Spindle Speed ratio at 1

Correct?

Are you taking into consideration any spindle pulley ratios etc?

Just trying to throw out some ideas.
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
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martyscncgarage
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Re: Rls encoder and vfd calibration

Post by martyscncgarage »

I just looked at your report.
Looks like you have minimum spindle speed set to 600 and the max 8300.....
That means Acorn will never go to 0 volts on the bottom end.
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
nicolasjolliet
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Re: Rls encoder and vfd calibration

Post by nicolasjolliet »

Thanks Marty.
I was only working on the high range to get proper tuning first. And the pulleys ratio in high range are set within my settings.

Now , I set the minimum range very high, at 600, to see if it would have a play on my results. Turns out that It acts more as a threshold than a bottom scale factor (bias in PID parlance) Meaning that weather the minimum is set at 600 or zero, the 1k has the same offset against the encoder. In my case, when I tune 5k spindle to 5k encoder, m3 1k still will Spin at 800 rpm on the encoder instead of 1k, and 8k will spin at 9600 on the encoder. The wrong linear curve angle is not changed. I can not shift the linear scale’s angle regardless of the max and min speed in either acorn or the weird driver. I can only change its ratio (the height of the curve or the “gain”)

There is something I’M missing somewhere. But it doesn’t seem to be what you’re pointing at. Hard to be a beginner. I miss my hand drill :).
Muzzer
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Re: Rls encoder and vfd calibration

Post by Muzzer »

When you ask Acorn for 8000rpm with its max speed parameter set to 8300rpm, it outputs 8000/8300 times 10V. With the VFD / servo drive set to 10V = 10,000rpm, you get 9600rpm. No surprise there, surely? That takes care of the top end.

Quite why you have set min speed at 600rpm isn't obvious unless you like making life difficult for yourself. The Acorn will only start to output a (0V) voltage when you ask for 600rpm. However, at this point, the servo will be seeing zero volts, so it will spin the motor at 0rpm(!). I'm not sure how the graph you show is inconsistent with the settings we see.

Set Acorn to give min speed = 0 and max speed = 10krpm. Then set the servo back to factory settings and scale the input to 10V = 10krpm. Even a really basic Chinesium servo drive will observe those basic parameters.

You might be overthinking this.
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Re: Rls encoder and vfd calibration

Post by tblough »

You are not missing anything unless your BLDC drive has some hidden parameters. The PLC program does a linear fit to the spindle speed with 0V = 0rpm. If you set your max rpm at 10,000 and your minimum at 600 then the DAC will output 10V when 10K rpm is commanded. When S5000 is entered the DAC output will be 5V. When you command 600 rpm you will get 0.6V. And if you command anything between 0rpm and 600rpm, you will get 0.6V.

If you cannot change the analog input bias on the drive and the precise control of the spindle is important, then you'll need to edit the spindle output section of the PLC.
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
Muzzer
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Re: Rls encoder and vfd calibration

Post by Muzzer »

If you want to do the sums more accurately, at 8000rpm demand with 8300rpm set as max speed and 600rpm as min speed, the output of Acorn will be

(600/8300)*10 + (7400/7700)*9.28V = 9.64V.

With 10krpm set in the servo, that would result in 9640rpm. That looks pretty close to what you are seeing.
cncsnw
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Re: Rls encoder and vfd calibration

Post by cncsnw »

Muzzer,

Standard MPU11 and Acorn PLC programs do not scale the 10V analog range from min to max. They scale the 10V analog range from zero to max, but at the bottom end, they do not put out an analog value less than that for minimum speed. So the minimum analog voltage, with spindle on, will be greater than zero.

For what it's worth, the earlier CNC10 and CNC7 architecture scaled the analog linearly from min to max, to make better use of the limited resolution (because the hardware on those systems initially had only 8-bit DACs). However, that turned out to be too confusing for most installers, so with the MPU11 system Centroid migrated to a simple cutoff.

It would be possible for a mathematically-inclined installer to change the calculations in the PLC program to provide for a true bias/offset value, but that is not the standard behavior.
nicolasjolliet
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Re: Rls encoder and vfd calibration

Post by nicolasjolliet »

Again, many thanks to you folks for help and patience.
From what I read, and think I understand, the minimum spindle speed in acorn does not have an effect on the motor/encoder ratio (confirmed by cncsnw). It is the same for the dead band width parameter in my vfd, these are only hipass filters, not scaling points.
At least, this is what I experience while testing.
As tblough suggest, there is a hidden parameter in my VFD, as I am able to tune the top range but not the minimum range.
to make sure I understand all what you guys are saying, I will start from the beginning again, reset everything, and write it all down.
instead of looking for a hidden parameter, I'm hoping that I'm doing something obviously wrong somewhere.
nicolasjolliet
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Re: Rls encoder and vfd calibration

Post by nicolasjolliet »

Ok, here is what i did in exact details, see if it looks right:

acorn voltage 0-10 values have been tested and are accurate

Motor maximum speed is rated at 5400 rpm.
set vfd max speed to 5400 rpm

Pulley diameter on motor is 3.116, pulley diameter on spindle (encoder) is 1.816, the gear ratio is then 1.715

5400 rpm of max speed on motor gives me a 9261 rpm max speed in Acorn
So I set max spindle speed in Acorn to 9261, minimum speed to 0 rpm,

run the test:

1k=840 rpm
3k=2872
5k=4940
7k=7002
8k=8065


This shows me that these settings work well for 7k rpm, at 7k rpm the encoder matches the motor.
the low range is below the commanded values, and the high range goes above

Lets try to tune this a bit, so my 5k is better tuned:
Change acorn maximum speed from 9261 rpm to 9000 rpm:

1k=870
3k=2968
5k=5096
7k=7230
8k=8308

the 5k is closer now, below 5k the values are under, above 5k the values are above.

I can lower the acorn max speed to tune the 1k range ( I was hoping to do rigid taping), and guess what? all values above 1k will be too high.

Does this make sense? Does it show that I'm missing a bottom scale parameter somewhere hidden in the VFD?
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