Servo -> Gear -> Spindle

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Daniel_turning
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08 Mar 2020 19:20 #159496 by Daniel_turning

Servo -> Gear -> Spindle was created by Daniel_turning

Hello there,

First of all sry for my bad english.

Back in the days I was designing my cnclathe, I think I was super smart. *irony*
I want to use a ac-servo-motor hook up to the spindle. Using timing belts with pullys 48:32 to get more speed on the spindle.

Now I have build everthing up and notice that I am not able to synchronize the spindle.
The velocity of the servo-encoder is 1.5 slower than the spindle. Same problem with the index signal.

Now I am asking me, can I solve this issue with linuxcnc software encoder or linuxcnc sofware gearchange?
Or is it not worth it and should I change pullys to 1:1 ratio?

Kind regards
Daniel

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cmorley
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08 Mar 2020 19:43 #159499 by cmorley

Replied by cmorley on topic Servo -> Gear -> Spindle

Can you add an encoder or an index to the spindle shaft?

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Daniel_turning
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08 Mar 2020 21:26 #159513 by Daniel_turning

Replied by Daniel_turning on topic Servo -> Gear -> Spindle

I think that should be possible!

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andypugh
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09 Mar 2020 00:41 #159542 by andypugh

Replied by andypugh on topic Servo -> Gear -> Spindle

Daniel_turning wrote:
Now I am asking me, can I solve this issue with linuxcnc software encoder or linuxcnc sofware gearchange?
Or is it not worth it and should I change pullys to 1:1 ratio?

The best answer might be to add an index flag of some sort to the actual spindle and use that as the spindle index.
You can continue to use the A and B phases from the motor encoder, with the scale corrected to allow for the gearing.
The index could be anything, such as a proximity sensor detecting a keyway or a reflective opto-sensor detecting a target on a drive pulley.

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Daniel_turning
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10 Mar 2020 18:11 - 10 Mar 2020 18:13 #159679 by Daniel_turning

Replied by Daniel_turning on topic Servo -> Gear -> Spindle

Thank you both for your information.

Today I take a look at my machine. Unfortunatly I don't have enougth space for another pully on the spindle shaft.
So I have to struggle witch A and B phase from servo and add seconde index signal.

So if I am using A and B phase from servoencoder I have to use Linuxcnc-software-encoder module?

somethink like?

loadrt encoder num_chan =1;
addf encoder.update-counters base-thread
addf encoder.capture-position servo-thread

setp encoder.0.position-scale 6666.66  #servo-encoder counts 10.000 units/rev  == spindle turns 1.5 times more

# set the HAL encoder to quadrature counting using A and B.
setp encoder.0.counter-mode false

# connect the HAL encoder outputs to LinuxCNC.
net spindle-position encoder.0.position => motion.spindle-revs
net spindle-velocity encoder.0.velocity => motion.spindle-speed-in
net spindle-index-enable encoder.0.index-enable <=> motion.spindle-index-enable

# connect the HAL encoder inputs to the real encoder.
net spindle-phase-a encoder.0.phase-A <= myMesaPin.xy.fromServoEncoder
net spindle-phase-b encoder.0.phase-B <= myMesaPin.xy.fromServoEncoder
net spindle-index encoder.0.phase-Z <= myMesaPin.xy.fromSecondeIndexSource

Is that the right way to get lucky?

Kind regards
Daniel

By the way, thanks for your time!

Last edit: 10 Mar 2020 18:13 by Daniel_turning.

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PCW
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10 Mar 2020 18:33 - 10 Mar 2020 18:34 #159681 by PCW

Replied by PCW on topic Servo -> Gear -> Spindle

You can use a hardware encoder with a independent index source
The only disadvantages I can think of (which also apply to the software
encoder)
are:

1. The index is not synchronized with A or B so you may have a count or so
of uncertainly in index position. You might be able to adjust the index sensor
so index is in sync with counts on a low resolution encoder where a 1 count uncertainty matters.

2. The index is likely to be wider than 1 count so the index position will be
different depending on direction. I don't think this makes any practical difference to LinuxCNC.

Last edit: 10 Mar 2020 18:34 by PCW.

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andypugh
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10 Mar 2020 18:59 - 10 Mar 2020 18:59 #159688 by andypugh

Replied by andypugh on topic Servo -> Gear -> Spindle

My suggestion for an index would be to drill a hole in one of the spindle pulley flanges and then mount an opto-sensor (fork / slot type) in the area where the belt is not wrapped round the pulley.

Last edit: 10 Mar 2020 18:59 by andypugh.

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Daniel_turning
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10 Mar 2020 19:39 #159692 by Daniel_turning

Replied by Daniel_turning on topic Servo -> Gear -> Spindle

I will try it. Thank you

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Daniel_turning
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05 Apr 2020 09:21 #162749 by Daniel_turning

Replied by Daniel_turning on topic Servo -> Gear -> Spindle

Hello,

I tinker around and put another pully on the spindle shaft.
Now I have a new 2000 line encoder hooked up 1:1 to the spindle shaft. Not beautiful but it seems to works.

Thanks for your help!

Kind regards
Daniel