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Mach4 problems when moving.
« on: July 09, 2018, 02:53:54 AM »
Hi,
I use Mach4 on a laser cutting machine and ran into several problems when moving. The machine has high speed and acceleration. Servo Drives 400W.
1. CycleStop. During operation, if I need to stop the GCode execution, I press CycleStop, the machine stops very quickly and the servo drives issue an overload error. Is it possible to increase the braking from 0 to 1 second, 2 seconds ... ???
2. Jogging. I use the keyboard of the computer for manual movements. If you move one axis, then everything works well. If you move two axes at once, then smooth braking does not work, the axes stop abruptly as with CycleStop and servodrivers issue an overload error. Everything works fine on Mach 3.
3. RunFromHere. If you press this button, the correct position window pops up, select the axes, click Move Select. If you need to move along one axis - then everything works. If two of them - it's moving along a strange trajectory and when one of the axes reaches the required position of the first one, it stops very quickly, as in the case of Jogging, with instantaneous braking and an error of servo overload can appear.

Sorry for my English.
Re: Mach4 problems when moving.
« Reply #1 on: July 09, 2018, 10:18:22 PM »
Sounds like most of the servos havent been tuned yet possibly? Why not increase your decel in tuning? Also depending on how much weight on each axis you might need regen resistors on certain axis depending on how much decel you need also. Your acceleration might need slowing down too.

Re: Mach4 problems when moving.
« Reply #2 on: July 09, 2018, 10:27:04 PM »
Hi,
yes you could  set a max de-acceleration in your servo but with a Cycle Stop command where the
pulse stream stops immediately the servo must overrun a little bit and you end up with a following error
rather than an over current or over voltage fault.

I don't think CycleStop is the correct way to stop Mach, the sudden cessation of movement is effectively
an infinte acceleration and any servo will fault. If there is a means to cause Mach to de-accelerate gracefully
in response to a CycleStop I don't know what it is.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 problems when moving.
« Reply #3 on: July 09, 2018, 11:20:16 PM »
Hi,
I think the correct way is <FeedHold> followed by <CycleStop>.

FeedHold allows the co-ordinated move already committed to complete including its graceful de-accel
phase.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 problems when moving.
« Reply #4 on: July 10, 2018, 01:58:41 AM »
Hi,
Sounds like most of the servos havent been tuned yet possibly?
The servomotors are tuned.
Quote
Why not increase your decel in tuning?
This laser cutting machine, I need high acceleration and deceleration values, and high PID control of servo motors.
Quote
Also depending on how much weight on each axis you might need regen resistors on certain axis depending on how much decel you need also.
Servomotors up to 750 volts have a built-in braking resistor.

Hi Craig, thank you for the constant help.
Quote
Hi,
yes you could  set a max de-acceleration in your servo but with a Cycle Stop command where the
pulse stream stops immediately the servo must overrun a little bit and you end up with a following error
rather than an over current or over voltage fault.
I'm sure it's wrong to stop the impulse step instantly. I use other CNC systems, different manufacturers - there are no problems with braking, there are no problems with manual movements and return to cutting.
Quote
I don't think CycleStop is the correct way to stop Mach, the sudden cessation of movement is effectively
an infinte acceleration and any servo will fault. If there is a means to cause Mach to de-accelerate gracefully
in response to a CycleStop I don't know what it is.
I'm sure the CycleStop is the right way to stop work. The instantaneous stop of the step pulses is incorrect. I have never encountered the error of servomotors at a stop, only in mach3 and mach4.
Quote
I think the correct way is <FeedHold> followed by <CycleStop>.
Craig, watch the video. The laser cutting machine and milling machine are different machines and work differently. If you use a FeedHold, the machine will stop after a long distance, this is not correct.
https://www.youtube.com/watch?v=O0oDtbkMR7A

For the following machines, I want to increase the speed from 30 meters per minute to 50 meters per minute. Problems with stopping, manual movements and returning to the cutting edge will become even greater.
Guys, thanks for trying to help!

Offline Tweakie.CNC

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Re: Mach4 problems when moving.
« Reply #5 on: July 10, 2018, 03:28:48 AM »
Quote
I'm sure the CycleStop is the right way to stop work. The instantaneous stop of the step pulses is incorrect. I have never encountered the error of servomotors at a stop, only in mach3 and mach4.

I agree, however Mach3 requires Feed-Hold then Stop if exact position is not to be lost and this will never change. Mach4 is under development and who knows, future changes may be made to the Stop process to avoid the need for Feed-Hold.

Tweakie.
KEEP SAFE !
Re: Mach4 problems when moving.
« Reply #6 on: July 10, 2018, 03:56:44 AM »
Quote
I'm sure the CycleStop is the right way to stop work. The instantaneous stop of the step pulses is incorrect. I have never encountered the error of servomotors at a stop, only in mach3 and mach4.

I agree, however Mach3 requires Feed-Hold then Stop if exact position is not to be lost and this will never change. Mach4 is under development and who knows, future changes may be made to the Stop process to avoid the need for Feed-Hold.

Tweakie.
If you need to keep the exact position - then I use a Feed-Hold.
In any other situation - CycleStop. But it should not cause errors in the servo system of the machine.

It is not clear that the correct operation of the manual movements and the return to the ...
Re: Mach4 problems when moving.
« Reply #7 on: July 10, 2018, 03:58:47 AM »
Hi,

Quote
I'm sure it's wrong to stop the impulse step instantly.
I agree, if the pulses were to stop immediately it would imply an infinite acceleration. But isn't that exactly what you have described as the fault?
That the deceleration is that violent that the servo faults?

Quote
I use other CNC systems, different manufacturers
That may be so but remember that Mach is not a feedback control system, it can't because Windows is not a realtime environment.

Lets say for example that a move involving the X and Y axes is planned. Mach will plan the trajectory and commit pages of motion data to the motion controller,
one page of position data for every 1 ms of the move. During this move you hit <CycleStop>. If Mach aborts the remainder of the move Mach no longer knows
where it is. It knew where it was at the start of the move and it knows where it was supposed to be by end of the move but it has no idea how far along the move it
got when you hit <CycleStop>. I suppose if the motion controller reported the position of its axis motors then Mach could recover its position, after all this is
exactly how G31 probing works.

Mach is not a feedback control system so the motion controller does not report back to Mach in the normal course of events which includes TO MY KNOWLEDGE
ONLY <CycleStop>.

Lets say that we wanted <CycleStop> to introduce a graceful deceleration phase. First mach would have to abandon the remaining portion of the existing move
and then recalculate the pages of position data required to decelerate the axes. The communication delays  between Mach and the motion controller and back again are
way too slow for that to work.

Quote
If you use a FeedHold, the machine will stop after a long distance, this is not correct.
I agree it is not desirable but I believe it has to work that way. I reason it that because a deceleration phase is built into the planned move and given that Mach cannot go back
and recalculate the move once its already been committed to the controller the ONLY way to decelerate is to allow the current move to complete and THEN stop.

A I said earlier this is based on my understanding of how Mach works, I am by no means sure. I'm interested how you think it works. Its interesting that you claim that
you have had issues with Mach3 and Mach4....could it that this constitutes an explanation why that should be so?

Quote
The laser cutting machine and milling machine are different machines and work differently
I am not convinced this is true. What is true is that Laser requires very VERY high accelerations which make a problem that happens with a mill way WAY worse in a Laser,
but they are both affected by the same phenomenon.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 problems when moving.
« Reply #8 on: July 10, 2018, 04:07:07 AM »
Hi,

Quote
If you need to keep the exact position - then I use a Feed-Hold.
In any other situation - CycleStop. But it should not cause errors in the servo system of the machine.
My misunderstanding, you are not concerned with keeping exact position? You just want to stop?

If that's the case just program your servo to some maximum deceleration. You will have to disable the following error also as there will
be an overrun that will cause a fault.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 problems when moving.
« Reply #9 on: July 10, 2018, 05:13:55 AM »
Hi,
what sort of servos and drives do you have?

I'm thinking of my Allen Bradley AC servo and with that it is possible to limit acceleration and decelerations. I'm wondering if it is so for your
drivers.

I understand you seek to have the highest acceleration you can. Currently however your maximum acceleration on your motor tuning page must be less than
the capability of your servo or otherwise it would cause a fault, either over current or following error on acceleration. When you hit <CycleStop> however the
cessation of pulses implies a much greater acceleration than your maximum allowed under Machs tuning and in fact greater than your servo is capable of and
that does cause a fault.

I think there is some room to move there.....you could limit the servos acceleration somewhat by imposing a current limit but would still allow a slighty greater acceleration
than Machs tuned max acceleration.

What I am proposing is that you limit your servo/drive acceleration to be just a bit more than your max tuned acceleration. Your max tuned acceleration would become the effective
maximum acceleration AND deceleration.

Craig
My wife left with my best friend...
     and I miss him!