Encoder Basics

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bilorn
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Re: Encoder Basics

Post by bilorn »

Does anyone have info on Sequential encoders?
I have a 25 GN, but have no docs on it.
There are 8 colored wires coming out of it, I have no clue as to their assignment.
Thank you
bilorn
Andrew-UK
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Re: Encoder Basics

Post by Andrew-UK »

Hi,
Does anyone know the maximum "pulse per revolution" value the Acorn will accept?

For a lathe conversion I have bought a 5000ppr incremental quadrature encoder which I want to use on the spindle motor. I have entered the 20,000 count value for the required parameter (5000 x 4) and it sort of works but the DRO spindle speed on the main screen is rather erratic and the pulse count shown in the PID view continues to show pulses being counted for 1 or 2 seconds after the spindle stops suggesting there is a delay in processing the encoder signal. I'm just wondering if there is an upper limit to the ppr the Acorn can manage and if I've exceeded it!

Thanks,
Andrew
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Re: Encoder Basics

Post by eng199 »

ACORN will accept a higher frequency than any normal rotary encoder can output. The frequency is not specified because some filtering may be added in a future revision to bring it down to 1-5MHz. It is unlikely that your encoder is rated to output more than 1MHz.

If your encoder is rated 1MHz, you are good to almost 12000 RPM, or more likely whatever the mechanical RPM rating is.

If the encoder count changes after the encoder stops, there is likely noise on the signal lines. The most common cause for this is high voltage switching on the motor wires crossing over to the encoder wires. Ideally, the motor power cable will be shielded as well as the encoder cable. The encoder cable should be routed away from power cables. It is most important to keep hard switched high voltages like drive to motor cables away from signals.
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Re: Encoder Basics

Post by Andrew-UK »

Hi,

Thanks for your comments.
The encoder I have is rated to 6,000rpm and has 5000 pulses per revolution. Although I doubt I'll ever run it that fast, theoretically it could be pushing out four quadrature pulses, each at 30MHz.

When I was testing, I did not have any stepper motors or spindle motor running. I was using a battery powered brushless DC electric drill to turn the spindle at around 400rpm. What I noticed was a lag in the display of RPM such that when the drill stopped the RPM display continued to count for a second or two before it stopped at zero. It is not picking up noise, it just seems the controller/PC is still processing the incoming counts.

I am some way off getting all the parts of this lathe conversion running and I'll know more in the coming weeks.

Thanks,
Andrew
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Re: Encoder Basics

Post by Toysrfun »

Curious. Can these encoders be added to existing steppers? I imagine it would improve accuracy in some way. I have a couple mills with dual shaft Nema 34’s I would like to add encoders if it’s possible and of course if it is beneficial. I’d be more than willing to experiment if it’s worth the effort. I haven’t had anything to date with encoders and just in process of ordering actual servos for another machine 2500ppr. I could just as well go and sell off the steppers and buy servos but it seems it would be less work adding encoders to existing motors and calling it a day. As far as speed they are fine for those two machines but they do lose steps periodically. That may change when my acorn system arrives it is yet to be seen.
Centroid_Tech
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Re: Encoder Basics

Post by Centroid_Tech »

Can these encoders be added to existing steppers?
As long as the drives that are moving those steppers can support the encoder feedback, I don't see a reason why you can't use them. You will need to check the drive's manual for the encoder specifications that it requires. The ACORN does not have any axis encoder feedback. The only encoder port on the ACORN is for the spindle encoder which needs to be geared 1-to-1 with the spindle as the CNC12 software needs to know what the spindle is doing for such things as rigid tapping and threading cycles.
When requesting support, please ALWAYS post a current report. Find out how to take a report from your Acorn, CNC11 or CNC10 system here: https://www.youtube.com/watch?v=Ecvg0VJp1oQ.

If your question is PLC, Macro or program related, please also post a copy of the program or macro as well.

Without the above information we may not be able to help and/or reply until the required information is posted..
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Re: Encoder Basics

Post by cut2cut »

For the spindle I am looking at a hollow shaft encoder, mostly for rigid tapping but also to verify the rpm is accurate for generally milling. I am a bit unsure of the specifications so I'm looking for some help specifying the model I need.

This is my thought : GHH100-40-G-2000-B-M-P-5
( see the attachment )
I am concerned with "output phase" and "index" options but also P likely being Push Pull for differential ? I am assuming B is quadrature and the index I hope can be either M or N and still provide the necessary index signal for rigid tapping. I chose M as it is the default, assuming its more of a standard. The P designation should provide differential type wiring ?

Also, I chose 2000pr because I assume the Acorn will not be pushed hard and noise could conceivably be less an issue at a lower frequency signal?

Thanks in advance for any help,

Jake
Attachments
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Re: Encoder Basics

Post by tblough »

Output phase just reverses the "positive" direction and does not matter for a spindle encoder because the steps/rev can be entered as a negative number in CNC11/12 to reverse the spindle direction. You want an "M" index signal option because you want the index signal to go high when the encoder is on the index mark. For output form, you want "L" for line driver (RS422).

The output resolution you choose will also set the maximum spindle RPM the encoder will work at. Therefore, you need to determine your maximum spindle RPM and choose an output resolution that will work at that RPM. The maximum frequency for that encoder looks like 300kHz. Line Count = (300000 X 60/RPM) or RPM = (300000 X 60/Line Count). A 2000ppr encoder would be good to 9000RPM electrically but the max mechanical RPM is 6000 so you should be good.

Looks like you want GHH100-40-G-2000-A-M-L-5

One other benefit of a spindle encoder is you can use feed/rev for feedrates.
Cheers,

Tom
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I have CDO. It's like OCD, but the letters are where they should be.
cut2cut
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Re: Encoder Basics

Post by cut2cut »

tblough wrote: Tue Sep 04, 2018 2:06 pm Output phase just reverses the "positive" direction and does not matter for a spindle encoder .....

Looks like you want GHH100-40-G-2000-A-M-L-5

One other benefit of a spindle encoder is you can use feed/rev for feedrates.
Tom, Thank you for the explanation. Much appreciated !

Jake
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Re: Encoder Basics

Post by ballsop123 »

Hello All...

Has anybody done this before ?

Here is my situation .... I recently bought a 400W BLDC Spindle motor that has a built in encoder with the motor.... It also came with a spindle controller drive that is 3 ph (UVW) to the motor and receives the quadrature signals A /A, B /B, C /C phase signals back to the the supplied spindle drive. I believe the encoder informs the spindle drive of the RPM when the spindle comes under load and the controller will attempt to maintain the commanded RPM under load until it just simply cannot respond if the load becomes greater than the spindle specification permits.

My question is this..... Can I "piggy back" the encoder connections from the Spindle controller in a parallel connection, and feed those signals to Acorn's DB9 encoder port to get the actual RPM of the motor to be displayed on the screen of the CNC12 software package for mill? I would figure the 6 phase wires A /A, B /B, C /C would be plausible, but the +5VDC and GND are my question....

Does the Acorn DB9 Pin on the board supply +5VDC or receive 5VDC on that pin ? I would figure it would supply +5VDC to an external encoder unit if I weren't using the built in encoder on the spindle. Correct ?

So I am thinking I would connect all encoder wires to the DB9 port with the EXCEPTION of the +5VDC from the DB9 port on Acorn's board. Let the power to the encoder come directly from the supplied spindle drive controller... so contrary to the connection schematics for quadrature encoders I would connect 7 wires instead of the 8 wires.

Same question with GND .... I figure I must make this connection to the GND or COM of the DB9 port to work correctly....

Assuming all of this works as planned, I would then need to figure out the encoder line counts on the spindle drive .... no information on that was supplied.... I figure i would start with 2000 and work up or down from there.... Accuracy could be tweaked with a digital tachometer as needed.

Does this sound like it would be do-able ?

Your thoughts and or comments appreciated.
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