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Re: dangerous malfunction of a machine driven by Mach4
« Reply #40 on: March 03, 2022, 05:27:54 PM »
Hi Craig,

Yes i slow it down to 5m/min, its still very fast for the size.

Do u have any advice for the manual servo tuning? I know that linuxcnc has an internal oscilloscope so that u can check the actual movement and commanded movement and try to bring them closer in a graphic window by tuning the driver parameters but Mach4 has no such an option, so any advice?

Hakan
Re: dangerous malfunction of a machine driven by Mach4
« Reply #41 on: March 03, 2022, 05:32:34 PM »
Hi,
that is usually provided by the servo tuning software.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: dangerous malfunction of a machine driven by Mach4
« Reply #42 on: March 04, 2022, 11:58:41 AM »
> If you want true closed loop performance, don't waste your money on closed loop steppers, get servos. A servo will eat any stepper ever made.

While I agree that servos are vastly better than steppers - my ongoing PM25-class mill conversion will use ClearPath servos - closed-loop steppers are WAY better than open loop:

1. The driver will pick up on a missed step and "try again", meaning when you are getting marginal on power you get some backstop; and

2. Outright failure to reach the commanded position errors out and stops the machine - which is a HUGE safety feature.
Re: dangerous malfunction of a machine driven by Mach4
« Reply #43 on: March 04, 2022, 01:48:27 PM »
Hi,

Quote
1. The driver will pick up on a missed step and "try again", meaning when you are getting marginal on power you get some backstop; and

The problem with that is that IF a stepper misses a step its because it is marginally overloaded, so any extra step inserted to catch up is likely to be missed as well.
The manufacturers claim that closed loop increases the power, pure BS.  Closed loop steppers are no more powerful than their open loop counterparts
of the same spec.

Quote
2. Outright failure to reach the commanded position errors out and stops the machine - which is a HUGE safety feature.

This is correct, and is a distinct and clear advantage of closed loop steppers over open loop steppers.

One feature that you did not mention was that closed loop steppers can interpolate between full steps whereas open loop steppers can do
1/2 steps reliably but no finer. Thus closed loop steppers have genuinely better resolution than open loop steppers.

These two features are to my knowledge the only two genuine advantages that closed loop steppers enjoy. My contention is that the premium
paid for closed loop steppers is not justified by these two features alone. Others may have a different opinion.

Genuine AC servos are still quite a bit more than closed loop steppers, say 25% or so, and if you are going to pay a premium then servos are  worth
the extra. There again that is my opinion, others may differ with that. The principle advantage that a servo has is overload capacity.
When a stepper (open or closed loop) gets overloaded it misses steps or stalls, no ifs or buts, it just stalls, whereas a servo just 'digs' into
its overload capacity, typically 3-4 times its rated output, and just does the job. The short term overload capability of a servo means that it
seems to have MUCH greater output than the specs suggest whereas steppers never seem to quite live up to their specs.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: dangerous malfunction of a machine driven by Mach4
« Reply #44 on: March 04, 2022, 08:04:39 PM »
Hi,

The problem that i thought we fixed by decreasing the microstepping came back today while machining a wood mold, this time i was touching to the ballscrew because cv_feedrate was not on so that the machine was shaking while turning the corners and i was touching the ballscrew to see if it is because of the X axis motor, so i felt the stall by chance when it did it. But this time it was for a very short period of time like a second or so and machine miss aligned the gcode by 1cm(or so) on the x axis.

This happens when i play with the FRO, because today the tip of the endmill was not touching to the part so i didnt want to loose time and increased the feedrate by %150 and in one of the sharp corners machine did this error.

obviously decreasing the microstepping 10 times fixed the error to some extend but x, y and zth axis are all within the range of pulse frequency of pmdx bob, ess and motor drivers so i dont know what mach4 does when u increase the FRO but thats what is causing this error(as it seems microstepping was exaggerating it).

In actual feedrate(the feedrate embedded in the gcode) there is no error what so ever but when u increase the FRO this happens once in a while, hard to say when exactly.

Hakan
Re: dangerous malfunction of a machine driven by Mach4
« Reply #45 on: March 05, 2022, 02:00:02 PM »

The manufacturers claim that closed loop increases the power, pure BS. 


Agreed - although the "try again" feature adds a little fault-tolerance for transitional spikes. This won't let you routinely run hard up against the motor's power limit, but it can save a job that would have missed a step or two on a transient load.

Quote
This is correct, and is a distinct and clear advantage of closed loop steppers over open loop steppers.

And it's the primary reason why I recommend them over open-loop steppers. "Can't get there" immediately stops that axis, and you can connect the error line so the driver can notify Mach and stop the whole machine.

Open loop steppers just keep pushing and trust you to notice the problem and e-stop. Unsat!


Quote
One feature that you did not mention was that closed loop steppers can interpolate between full steps whereas open loop steppers can do
1/2 steps reliably but no finer. Thus closed loop steppers have genuinely better resolution than open loop steppers.

I haven't seen this play out in my application - I changed my lathe X axis from open loop to closed loop - but that might be me not recognizing the error in the first place, or misattributing the source.

Quote
My contention is that the premium paid for closed loop steppers is not justified by these two features alone.

There really is not much of a price premium to pay, something on the order of $50 per motor/driver combo to get closed loop. And they can be had in integral driver/motor packages (like a ClearPath servo) where the motor driver is built into the motor housing. You run power and logic-level step and direction out to the motor, and take a logic-level alarm signal back.

Honestly, there's no good reason to ever use an open-loop stepper any more.

Servos are better than steppers, but the price differential is substantial.

My lathe was a good candidate for steppers, because the max axis speeds I need are well within stepper ranges, and the weak link is the spindle power (I will stall the spindle before I stall an axis).

https://www.youtube.com/watch?v=wnsZTu_pA9s

But the mill will be servos.
Re: dangerous malfunction of a machine driven by Mach4
« Reply #46 on: March 05, 2022, 02:08:32 PM »
Hi,

The problem that i thought we fixed by decreasing the microstepping came back today while machining a wood mold,

Hakan

I feel like this is a motor tuning problem, either in max motor speed, max motor acceleration, or maybe both.

It isn't that there's a problem in the FRO, it's that you are using FRO to push the motor into an unstable state.

I'd set up a pair of dial indicators and ping-pong between them at ever-increasing rapid speeds to see what max rapid you can get away with before you start losing steps, and then a similar test in sacrificial material, cutting first straight lines (in each axis) then squares, then circles, and see if you can isolate a motor speed at which the trouble starts. Then play with the acceleration tuning and see if that changes anything.
Re: dangerous malfunction of a machine driven by Mach4
« Reply #47 on: March 05, 2022, 04:27:03 PM »
Hi RecceDG,

This does not happen when u move the x alone, this happens when couple or more axis move simultaneously, i decreased the speed and acceleration and go on working like that after this happens last time but i am not sure thats the problem(it was already adjusted to half speed that 3phase 16nm motor can drive)

and when this happened the feedrate in gcode was 300mm/min i increased it to 750mm/min or so with the FRO, 750mm/min is not fast, actual speed that x can do with the 16nm stepper(keeping the 10-15um accuracy) is 3000mm/min in my case.
Re: dangerous malfunction of a machine driven by Mach4
« Reply #48 on: March 05, 2022, 04:31:26 PM »
It is not a good idea to push feed rate up more than 20% or so with FRO because the trajectory planning was done at the original speed. If you really want to do 100% or more speed change, code it for maximum speed and turn it down to 50% for regular run.
Steve Stallings
www.PMDX.com
Re: dangerous malfunction of a machine driven by Mach4
« Reply #49 on: March 05, 2022, 04:47:02 PM »
Hi Steve,

That is the problem i am facing with i think too, increasing FRO %100 messes up the control, u explained it technically of course, i am gonna do it like that by manipulating the gcode from now on, thanks.

Hakan