G76 problem

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14 Dec 2022 16:02 #259471 by Ismacr63
G76 problem was created by Ismacr63
Hi, after a lot of struggling I have managed to make something similar to a bagel.
 The problem I have is that each pass the cut is brought forward a bit.
I have an A-B encoder with 600ppr and a 1ppr rate sensor. the encoder is connected to phase A and the index sensor is connected to the spindle index.

I would really appreciate if someone can tell me what is going on.
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14 Dec 2022 17:00 #259476 by tommylight
Replied by tommylight on topic G76 problem
Scaling is not correct, or to fast spindle speed if using a parallel port, or encoder cable not shielded so interference causes erratic counts.
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14 Dec 2022 17:04 #259477 by Ismacr63
Replied by Ismacr63 on topic G76 problem

Scaling is not correct, or to fast spindle speed if using a parallel port, or encoder cable not shielded so interference causes erratic counts.

Thanks for your reply. the encoder cable has a mesh that is connected to gnd, I don't know if that is enough to prevent interference.

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14 Dec 2022 17:31 #259480 by tommylight
Replied by tommylight on topic G76 problem
Having a scope would help, but sometimes using a simple DVM can be enough to spot interference.
Set spindle to run at say 200RPM, measure the voltage betwen gnd and one of the encoder inputs, it should not fluctuate, measure the other chanel, also should be no fluctuations in voltage reading.
Set at 400 and measure again, no fluctuations, vut voltage might be different value.
Set at 600 and measure again.
The voltage vill be diferent value for diferent speeds by a bit, should be same for encoder A and B.
You still did not mention what is counting the encoder.
If it is a parallel port, do not bother measuring, just try lower speed..
Still, if the error distance is the same after every start of threading operation, it is a scaling issue.
Then again, it can be the Z axis is skipping. Does it return to the same starting point after the operation is complete?
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14 Dec 2022 18:08 #259482 by Ismacr63
Replied by Ismacr63 on topic G76 problem

Having a scope would help, but sometimes using a simple DVM can be enough to spot interference.
Set spindle to run at say 200RPM, measure the voltage betwen gnd and one of the encoder inputs, it should not fluctuate, measure the other chanel, also should be no fluctuations in voltage reading.
Set at 400 and measure again, no fluctuations, vut voltage might be different value.
Set at 600 and measure again.
The voltage vill be diferent value for diferent speeds by a bit, should be same for encoder A and B.
You still did not mention what is counting the encoder.
If it is a parallel port, do not bother measuring, just try lower speed..
Still, if the error distance is the same after every start of threading operation, it is a scaling issue.
Then again, it can be the Z axis is skipping. Does it return to the same starting point after the operation is complete?

It is controlled by parallel port. I have done all the tests at 250rpm.
when the operation ends it does not return to the same point, I put a mark in Z0 and when the operation ends Z0 stays a little further forward.
when it makes a pass, the Z axis moves to the beginning for a new pass very quickly, but I don't know how to lower that speed. the general speed setting in Z is set slower than it travels in threading.

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14 Dec 2022 20:41 - 14 Dec 2022 20:41 #259498 by andypugh
Replied by andypugh on topic G76 problem
It travels at the G0 speed (MAX_VELOCITY from the INI file, in general)

Try lowering that a bit. But first try lowering the MAX_ACCELL

Also, do you have backlash compensation turned on?
 
Last edit: 14 Dec 2022 20:41 by andypugh.
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14 Dec 2022 20:50 #259502 by Ismacr63
Replied by Ismacr63 on topic G76 problem

It travels at the G0 speed (MAX_VELOCITY from the INI file, in general)

Try lowering that a bit. But first try lowering the MAX_ACCELL

Also, do you have backlash compensation turned on?

 

I'll try to slow down like you said.
I don't know if I have the backlash compensation activated because I don't know how to activate it.
This is the code I'm using:

G76 P1.5 Z-10 I-0.2 J0.02 K1.3

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15 Dec 2022 19:06 #259571 by Ismacr63
Replied by Ismacr63 on topic G76 problem
I have corrected the backlash compensation and it was not the problem.

From the tests that I have been doing, the problem is that I lose steps in Z.

I have tried to lower the maximum speed in stepconf wizard, but whatever I put the motor moves just as fast with the G76 (very fast). with Z+ or Z- the motor moves much slower.

In the INI file the MAX_VELOCITY value is always = 36.5384615385 no matter what you put in the stepconf wizard.

The motor I use in the Z is nema 23 closed loop configured as a servo at 800 pulses per revolution. the pitch of the spindle is 2mm (I don't know if it's a good configuration). I'm hoping to mount a sfu1605 spindle.

I have attached some photos of the motor and controller. also the INI file.
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17 Dec 2022 23:11 #259777 by andypugh
Replied by andypugh on topic G76 problem
if the Stepconf Wizard is not doing what you want, you should feel free to edit your INI file. The INI and HAL files are intended to be human-readable and user-edited.

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17 Dec 2022 23:26 #259778 by Ismacr63
Replied by Ismacr63 on topic G76 problem

if the Stepconf Wizard is not doing what you want, you should feel free to edit your INI file. The INI and HAL files are intended to be human-readable and user-edited.

 

As you say, I have slowed down and it seems that I no longer lose steps and it makes a decent thread. but how is it possible to lose steps with a closed loop motor?

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