How many encoder PPR are too much?

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kenmwallace
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How many encoder PPR are too much?

Post by kenmwallace »

I bought an Acorn, but I have decided my application needs an Oak instead.
I was planning to use SureServo2 amps and motors, but I see they use encoders with 24bit resolution.
That results in 16,777,216 PPR. This seems like total overkill and I doubt the Oak has the bandwidth to read that at 3000 RPM.
Is it typical to run that through a divider to get it down to a reasonable PPR?
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Re: How many encoder PPR are too much?

Post by tblough »

Most servo drives utilize a "pass-through" for the encoder to motion planner. Usually this is configurable in the drive software to set the counts per rev to send to the Oak board.

Check you motor/drive manual before you give up on them.
Cheers,

Tom
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I have CDO. It's like OCD, but the letters are where they should be.
cncsnw
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Re: How many encoder PPR are too much?

Post by cncsnw »

There is nothing wrong with using those drives, motors, and encoders.

As Tom notes, you will configure the drives so that their encoder output to the Oak is divided down to something that the Oak can handle.

If you really need to run them up to 3000 RPM, then you will probably want to send 4096 ppr (16384 quadrature counts/rev) from the drives to the Oak.

If you do not need more than around 2190 RPM, then you can send 8192 ppr (32768 counts/rev) from the drives to the Oak.

This is governed by the 300kHz bandwidth limit going into the Oak encoder inputs (1.2M counts/sec, 72M counts/minute).
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Re: How many encoder PPR are too much?

Post by krissondors »

cncsnw wrote: Wed Jan 18, 2023 8:26 pm There is nothing wrong with using those drives, motors, and encoders.

As Tom notes, you will configure the drives so that their encoder output to the Oak is divided down to something that the Oak can handle.

If you really need to run them up to 3000 RPM, then you will probably want to send 4096 ppr (16384 quadrature counts/rev) from the drives to the Oak.

If you do not need more than around 2190 RPM, then you can send 8192 ppr (32768 counts/rev) from the drives to the Oak.

This is governed by the 300kHz bandwidth limit going into the Oak encoder inputs (1.2M counts/sec, 72M counts/minute).
Not to hijack the thread, but does that mean for a spindle with a 6000 rpm speed, the encoder should have a 2:1 belt drive ratio of the spindle so the oak can process 4096ppr?
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Re: How many encoder PPR are too much?

Post by tblough »

The spibdle only needs a 1000 line encoder. Belting the spindle encoder causes problems if you wish to do peck tapping.
Cheers,

Tom
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Re: How many encoder PPR are too much?

Post by eng199 »

cncsnw wrote: Wed Jan 18, 2023 8:26 pm This is governed by the 300kHz bandwidth limit going into the Oak encoder inputs (1.2M counts/sec, 72M counts/minute).
Technically, this is limited by the pulse output (position request) to the drives. The drives first used with position mode had an input filter that allowed around 1.2MHz, so that limit was used in Centroid's interface hardware and software. The encoder repeat output from drives is also typically limited to less than MPU11 generation encoder inputs' maximum.
Not to hijack the thread, but does that mean for a spindle with a 6000 rpm speed, the encoder should have a 2:1 belt drive ratio of the spindle so the oak can process 4096ppr?
No. Real encoders (not simulated output from drives) will not exceed the frequency that MPU11 generation (Oak, ALLIN1DC, etc.) can handle. You may find some exception, but typically encoders will not output over 1MHz. Often they are 300kHz to 500kHz maximum. Also, parameter 323 may be changed to high speed filters if you did need a higher rate into the Centroid hardware. The encoder output frequency is what needs to be reviewed to see if it can handle that RPM and resolution.
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Re: How many encoder PPR are too much?

Post by tblough »

krissondors wrote: Thu Jan 19, 2023 3:24 am Not to hijack the thread, but does that mean for a spindle with a 6000 rpm speed, the encoder should have a 2:1 belt drive ratio of the spindle so the oak can process 4096ppr?
After you process eng199's response, you might want to have look at this thread regarding the electronic and mechanical bandwidth of encoders: https://centroidcncforum.com/viewtopic. ... dth#p24177

The tl;dr is that you will be hard pressed to find an encoder that is mechanically rated for 6000rpm that will have more lines of resolution than Centroid can process.
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.
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Re: How many encoder PPR are too much?

Post by kenmwallace »

tblough: Thanks for your response.
I am confused at this point.....
The SureServo motors/amps I just bought, advertise an encoder resolution of over 16 million PPR (24 bit), (if I interpreted their specs correctly).
I can't imagine how this is possible. Imagine how small the lines on the encoder disc would have to be. Maybe they use nanometer photo lithography as in making semiconductor chips?
As suggested by some other respondents, I do see that the drive offers "electronic gearing" so I can communicate with it at a more manageable pulse rate.
Are encoders that have digital outputs fundamentally different that the good old quadrature encoders?
Thanks in advance.....
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Re: How many encoder PPR are too much?

Post by krissondors »

eng199 wrote: Thu Jan 19, 2023 9:09 am
cncsnw wrote: Wed Jan 18, 2023 8:26 pm This is governed by the 300kHz bandwidth limit going into the Oak encoder inputs (1.2M counts/sec, 72M counts/minute).
Technically, this is limited by the pulse output (position request) to the drives. The drives first used with position mode had an input filter that allowed around 1.2MHz, so that limit was used in Centroid's interface hardware and software. The encoder repeat output from drives is also typically limited to less than MPU11 generation encoder inputs' maximum.
Not to hijack the thread, but does that mean for a spindle with a 6000 rpm speed, the encoder should have a 2:1 belt drive ratio of the spindle so the oak can process 4096ppr?
No. Real encoders (not simulated output from drives) will not exceed the frequency that MPU11 generation (Oak, ALLIN1DC, etc.) can handle. You may find some exception, but typically encoders will not output over 1MHz. Often they are 300kHz to 500kHz maximum. Also, parameter 323 may be changed to high speed filters if you did need a higher rate into the Centroid hardware. The encoder output frequency is what needs to be reviewed to see if it can handle that RPM and resolution.
tblough wrote: Thu Jan 19, 2023 12:24 pm
krissondors wrote: Thu Jan 19, 2023 3:24 am Not to hijack the thread, but does that mean for a spindle with a 6000 rpm speed, the encoder should have a 2:1 belt drive ratio of the spindle so the oak can process 4096ppr?
After you process eng199's response, you might want to have look at this thread regarding the electronic and mechanical bandwidth of encoders: https://centroidcncforum.com/viewtopic. ... dth#p24177

The tl;dr is that you will be hard pressed to find an encoder that is mechanically rated for 6000rpm that will have more lines of resolution than Centroid can process.
Thank you so much for the replies!

That makes sense and answers my questions. That's one thing I couldn't find in the Oak manual or in the forums when looking, which is how many lines I need for a spindle encoder. Especially how much is enough for rigid tapping and spindle orientation for tool ATC functions.

Thanks agian!
tblough
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Re: How many encoder PPR are too much?

Post by tblough »

kenmwallace wrote: Fri Jan 20, 2023 1:11 am tblough: Thanks for your response.
I am confused at this point.....
The SureServo motors/amps I just bought, advertise an encoder resolution of over 16 million PPR (24 bit), (if I interpreted their specs correctly).
I can't imagine how this is possible. Imagine how small the lines on the encoder disc would have to be. Maybe they use nanometer photo lithography as in making semiconductor chips?
Thanks in advance.....
If it is a glass scale, they do use photolithography. However, it could be magnetic or one of a few different position encoding methods. The 16 million PPR comes from interpolation.
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.
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