Does Linux CNC support Closed loop with Steppers?
- Craig E
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02 Feb 2021 14:49 #197430
by Craig E
Does Linux CNC support Closed loop with Steppers? was created by Craig E
Hey everyone I heard from Mesa yesterday that the LinuxCNC does not support Closed loop using Steppers and encoders.
I reached out to Mesa yesterday to get information on 7I95 + encoders and the rep said I should use 7I76 E or 7I96 which are cheaper so that's good but I was hoping to at least stop if I lose steps. Since I am new to this hobby I was assuming It would take some time to get a handle on speeds, and depth of cut and all that other stuff that I don't even know exists yet. I would be nice to stop the machine before destroying the work piece, tool or the machine.
I would appreciate any and all advice on hardware and LinuxCNC capabilities.
I reached out to Mesa yesterday to get information on 7I95 + encoders and the rep said I should use 7I76 E or 7I96 which are cheaper so that's good but I was hoping to at least stop if I lose steps. Since I am new to this hobby I was assuming It would take some time to get a handle on speeds, and depth of cut and all that other stuff that I don't even know exists yet. I would be nice to stop the machine before destroying the work piece, tool or the machine.
I would appreciate any and all advice on hardware and LinuxCNC capabilities.
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- tommylight
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02 Feb 2021 16:03 - 02 Feb 2021 16:04 #197443
by tommylight
Replied by tommylight on topic Does Linux CNC support Closed loop with Steppers?
LinuxCNC and Mesa can do closed loop everything, even dual feedback closed loop (i.e. incremental encoders on motor shaft and linear scales for the same axis), but from your post it is not clear if you mean using closed loop stepper/drive AND closed loop in LinuxCNC = still works on LinuxCNC, or stepper/drives with no feedback and encoders closed in LinuxCNC = also works in LinuxCNC.
The only issue is when using closed loop stepper/drives and using the same encoders for LinuxCNC feedback ( even this will work for sure ) but might need some signal shaping and/or splitting to have the same encoder wired to two inputs on the drive and Mesa board.
BTW, LinuxCNC can do all this with a simple parallel port, although with very limited speed.
EDIT:
Closed loop stepper/drives have a fault output that can be used to stop the machine when the drive detects it's lost position.
The only issue is when using closed loop stepper/drives and using the same encoders for LinuxCNC feedback ( even this will work for sure ) but might need some signal shaping and/or splitting to have the same encoder wired to two inputs on the drive and Mesa board.
BTW, LinuxCNC can do all this with a simple parallel port, although with very limited speed.
EDIT:
Closed loop stepper/drives have a fault output that can be used to stop the machine when the drive detects it's lost position.
Last edit: 02 Feb 2021 16:04 by tommylight. Reason: more info
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- Hakan
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02 Feb 2021 18:38 #197463
by Hakan
Replied by Hakan on topic Does Linux CNC support Closed loop with Steppers?
Don't know if linuxcnc officially supports it but I have it, use it and it works great.
The 7i95 should work but I guess the guy didn't have that one since he tried to sell you a 7i96.
The 7i96 should work together with a 7i85 for encoder input. The 7i76e + 7i85s is what I have
since a couple of years and yes it works fine, wouldn't use the milling machine without the linear scales.
The 7i95 should work but I guess the guy didn't have that one since he tried to sell you a 7i96.
The 7i96 should work together with a 7i85 for encoder input. The 7i76e + 7i85s is what I have
since a couple of years and yes it works fine, wouldn't use the milling machine without the linear scales.
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- PCW
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02 Feb 2021 19:17 - 02 Feb 2021 19:18 #197464
by PCW
Replied by PCW on topic Does Linux CNC support Closed loop with Steppers?
I think I replied to your question at Mesa. My point was that using a closed loop
step drive and tapping off the drives encoder is not recommended for electrical
reasons. If you have linear scales for feedback, there are real gains possible.
but not so much if you are just reading the rotary encoder on the motor.
If you are mainly concerned about lost steps or stalling, its much simpler to use
closed loop step drives and monitor their fault output that indicate a motion problem
step drive and tapping off the drives encoder is not recommended for electrical
reasons. If you have linear scales for feedback, there are real gains possible.
but not so much if you are just reading the rotary encoder on the motor.
If you are mainly concerned about lost steps or stalling, its much simpler to use
closed loop step drives and monitor their fault output that indicate a motion problem
Last edit: 02 Feb 2021 19:18 by PCW.
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- jbraun
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02 Feb 2021 19:53 - 02 Feb 2021 20:01 #197466
by jbraun
Replied by jbraun on topic Does Linux CNC support Closed loop with Steppers?
The way I understanding of how these drives are used...based on no experience, is it's like this:
The attempt to correct lost steps is done between the encoder and the drive. Linuxcnc is unaware of what happens there.
The shut-down alarm can be sent to Linuxcnc like an e-stop.
I think that's what PCW is saying (I'm no tech guy)
Someone here must be using these things ? A search of the forums might return something.
The attempt to correct lost steps is done between the encoder and the drive. Linuxcnc is unaware of what happens there.
The shut-down alarm can be sent to Linuxcnc like an e-stop.
I think that's what PCW is saying (I'm no tech guy)
Someone here must be using these things ? A search of the forums might return something.
Last edit: 02 Feb 2021 20:01 by jbraun.
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- rodw
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02 Feb 2021 20:43 #197470
by rodw
Replied by rodw on topic Does Linux CNC support Closed loop with Steppers?
Not estop but connect tofor the joint the motor is driving.
joint.N.amp−fault−inPlease Log in or Create an account to join the conversation.
- tommylight
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02 Feb 2021 21:04 #197475
by tommylight
www.google.com/search?source=hp&ei=-r0ZY...WQBskQ4dUDCAY&uact=5
Replied by tommylight on topic Does Linux CNC support Closed loop with Steppers?
Correct and correct.The attempt to correct lost steps is done between the encoder and the drive. Linuxcnc is unaware of what happens there.
The shut-down alarm can be sent to Linuxcnc like an e-stop.
www.google.com/search?source=hp&ei=-r0ZY...WQBskQ4dUDCAY&uact=5
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- Craig E
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03 Feb 2021 12:57 #197546
by Craig E
Replied by Craig E on topic Does Linux CNC support Closed loop with Steppers?
Thanks everyone,
This is very helpful. My stepper drivers have encoder inputs and alarm out if I understand correctly I should just wire the alarm out to Mesa board for LinuxCNC?
or am I misunderstanding and it would it be better to just wire the encoders to Masa directly and not the drivers?
This is very helpful. My stepper drivers have encoder inputs and alarm out if I understand correctly I should just wire the alarm out to Mesa board for LinuxCNC?
or am I misunderstanding and it would it be better to just wire the encoders to Masa directly and not the drivers?
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- bevins
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03 Feb 2021 13:54 #197548
by bevins
Your drive requires the encoders as you just mentioned. You cant just disconnect them from the drives and add them to linuxcnc.
Do what the guys are telling you. leave the encoders connected to the drives and alarm out to linuxcnc.
Replied by bevins on topic Does Linux CNC support Closed loop with Steppers?
Thanks everyone,
This is very helpful. My stepper drivers have encoder inputs and alarm out if I understand correctly I should just wire the alarm out to Mesa board for LinuxCNC?
or am I misunderstanding and it would it be better to just wire the encoders to Masa directly and not the drivers?
Your drive requires the encoders as you just mentioned. You cant just disconnect them from the drives and add them to linuxcnc.
Do what the guys are telling you. leave the encoders connected to the drives and alarm out to linuxcnc.
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- tommylight
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03 Feb 2021 16:41 #197571
by tommylight
Forget the encoders for now, leave them wired to the drive and let the drives do it's thing, first lets get the machine moving.
Replied by tommylight on topic Does Linux CNC support Closed loop with Steppers?
Yes, namely wire it to the "joint.N.amp−fault−in" as Rod mentioned in the hal file, but the actual wire from the fault output can be connected to any of the Mesa field inputs. It literally needs a single line added for each of the drive/motors used in hal.My stepper drivers have encoder inputs and alarm out if I understand correctly I should just wire the alarm out to Mesa board for LinuxCNC?
Forget the encoders for now, leave them wired to the drive and let the drives do it's thing, first lets get the machine moving.
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