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Author Topic: Jogging and DRO errors  (Read 3191 times)

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Re: Jogging and DRO errors
« Reply #10 on: February 04, 2018, 06:27:46 PM »
do you even read the post? This is the MACH4 dro showing the error. I'm not trying to impress anyone with 1/16 excitation, I'm trying to meet the thumbrule for 5000 steps per unit. The Mach4 thumbrule.
In my case 1/8 just didn't work, but 1/16 does. For whatever reason. The machine isn't even built yet.
THE PROBLEM IS THAT MACH4 DOES NOT SEND THE CORRECT NUMBER OF STEPS PER UNIT.
It's supposed to be a digital control system, but it's doing fuzzy math figuring number of steps per command. The steppers are doing exactly what is commanded. They are not slipping, skipping or stalling.
Mach4 is not requesting the correct number of steps to achieve one unit.
GRBL on an Arduino is more precise.
Re: Jogging and DRO errors
« Reply #11 on: February 04, 2018, 06:44:08 PM »
Hi,
yes I did read your post, did you read mine? Try full steps, ie NO microstepping.

That would correspond to a steps per value of 40 steps per if in millimeters or 1016 steps per if in inches.

My machine is accurate to 5um and I can operate it all day without it deviating from its programmed position
by more than 5um. Is that accurate enough for you?

Craig
My wife left with my best friend...
     and I miss him!
Re: Jogging and DRO errors
« Reply #12 on: February 04, 2018, 07:17:51 PM »
OK I did try  1:1, and the error is worse. Jogging one unit five times gives 4.985" dro change.  The motor tuning is set to 1016 steps per unit in mach4 config. Pretty simple. 5.08 x 200.
Jog an axis one unit. Mach4 does not send 1016 steps. The digital read out in mach4 shows less than an inch travel. I expected it to be precise.
Why does mach4 not send 1016 steps when told to jog one unit? Isn't precision the target here? How does it not follow a command?

I don't have a pulse counter hooked up to it yet, but it is possible it's sending 1016 steps and it's the dro that doesn't count right.
« Last Edit: February 04, 2018, 07:26:41 PM by Roaster »
Re: Jogging and DRO errors
« Reply #13 on: February 04, 2018, 07:26:59 PM »
Hi,
not sure whats going on. Mach doesn't send pulses, it sends numbers, its up to your motion controller
to produce the right number of pulses.

What motion controller are you using?

If mach were faulty there would be many people who suffer this problem but there isn't. Thats not to say that
your copy could be faulty but it seems unlikely.

It could also be your steppers but more likely the drivers. Is it possible to drive two drivers with the same signals,
if they behave identically you could pretty much say the the steppers/drivers are OK.

That leaves the motion controller. I can't really think of anyway to test short of substituing a known good one.

Craig
My wife left with my best friend...
     and I miss him!
Re: Jogging and DRO errors
« Reply #14 on: February 04, 2018, 07:46:30 PM »
I get you, but like I said, I'm not measuring the steppers travel or anything. This is strictly an error showing up on the digital readouts of Mach4 Mill application.
It gets worse if I raise the acceleration value, and it got worse when I changed from 16256 steps per unit to 1016.
To me that means the math formula for determining what to send to the motion controller is fuzzy. And yes, everybody should be seeing it, based on what I have here.
The original poster of this thread brought it up first, so call it a known problem.
The fact that the error changes with motor tuning specifics would seem to indicate that the math could be improved. In the interest of digital precision.
I'll settle for this kind of accuracy, but it just isn't right, analy speaking.

My motion controller is a piece of work, I can tell you, but I'm not able to measure the output yet.

Hold on. What you said about the software not sending pulses, it sends a number.  So what drives the dro values? Is it feedback from the motion controller??
« Last Edit: February 04, 2018, 07:58:59 PM by Roaster »
Re: Jogging and DRO errors
« Reply #15 on: February 04, 2018, 07:58:39 PM »
Hi,
if you are not measuring an axis travel distance how do you know Mach is sending wrong info?

May I suggest to start with use MDI at a very slow rate, I guess you use inch units so;
g1 x1 f5

followed by;
g1 x0 f5

ie just sending the x axis back and forth 1 inch at 5 in/min. If that works ok up the speed. I think the trajectory
planner in Mach, which is in itself quite an advanced breed, incoperates max accelerations and velocities when it plans
a move.

It is not my experience that anything about Mach4 is fuzzy, thats more a description of me rather than Mach.

Craig
My wife left with my best friend...
     and I miss him!
Re: Jogging and DRO errors
« Reply #16 on: February 04, 2018, 08:00:08 PM »
see above post re the feedback. It could be the f ing motion controller.
Re: Jogging and DRO errors
« Reply #17 on: February 04, 2018, 08:53:15 PM »
Hi,
no Mach is not a feedback controller.

It can read MPGs and encoders, the motion controller actually receives and counts the pulses and sends the numbers
back to Mach. Mach can display them if you wish. What it won't do, or at least do well, is alter the output to a motor
to cause the encoder to go to a specific place.

Unless you have encoders hooked up then the DROs are a reflection of whats going on inside Mach.

Are you using work coordinates or machine coordinates, machine coordinates are most direct and preferred for testing
despite being a little confusing.

Craig
My wife left with my best friend...
     and I miss him!
Re: Jogging and DRO errors
« Reply #18 on: February 04, 2018, 09:20:02 PM »
Hi Craig
I'm a total noob at this and just learning the system.
I'm building a machine and just now setting up the control box and configuring the motors.
I expected that giving a command to move 1 inch would cause the dro to go to 1.0000. It does not. It's always a bit less, and with the steps per inch set to 1016 it changes to .9995" It's cumulative and after a couple jogs it's off pretty good.
If it's not reacting to feedback from the motion controller then mach4 is not following orders.  
I have to get the motors on the rig and do some motion and measure it now, just to see what's real.
I'll get back when I have data.
Thanks for your help
 Mike
Re: Jogging and DRO errors
« Reply #19 on: February 04, 2018, 09:27:51 PM »
Hi Mike,
that is unusual. I use metric but if I MDI 100mm say, the DRO goes 100mm and my actual machine is that close
to 100 mm Ii can't measure the error with verniers.

If you have metric basllscrews why use inch native units?

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