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Strange Jogging results
« on: January 25, 2013, 05:52:17 AM »
When I first installed Mach3 I could set the jog increment to
1.0000 ,0.1000 ,0.0100 or 0.0010 and set it for single step then
pressing the jog button it would jog as I would expect it to

setting it to 0.0001 didnt work so obvious. For about every 8 presses
on the jog button it would increase by 0.0005 but I doubt I would want to
jog in steps that small anyway

So far so good .

My lead screws are 3mm pitch and my motor drivers are set to 16 microsteps
and the motor is 200 steps /rev so I calculate that as needing 1066.666667 steps per mm

When I went to motor tuning I changed the original
Steps 2000 , velocity 120  acceleration 4     to my calculated
Steps 1066.7 velocity 120 acceleration 4

The motor moved as expected . Doing G0 X3
made the motor rotate one full turn which with a 3mm pitch screw  gives me 3mm.

Now I went to jog ,

setting step size to 1.0000 and pressing jog it read  0.993 , then 1.9996 , 2.9999 ,4.0002
setting step size to  0.1000 and pressing jog it read 0.0994 ,0.1997, 0.3000
as the step size reduces the problem gets worse

How can I set it to suit my motors required step rate but still work correctly in jog mode ?

Also in Config/General config is a table that will select step size each time you press Alt J
it has 10 lines , but as I dont want to jog in 0.0001 steps I really only need 8 lines.
Is there a way to achieve this without just duplicating a line to fill up the space

Regards
Don

Offline RICH

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Re: Strange Jogging results
« Reply #1 on: January 25, 2013, 06:13:03 AM »
When you microstep the step can be anywhere within a few microstep. Greater than 10 is the limit for steppers unless using mechanical reduction to achieve better resolution. ie; Steps per inch on my engraving machine is 253000, very difficult to see /
actualy check micron movements. I could see 0.0000100" using 400x microscope along with calibrated standard even lower but real PITA.

Back to the real world.........
 Different controllers, motors. screw accuracy, (even belt tension....), backlash, etc all come into play on very small moves. Set your steps per unit based on the longest travel, accurately, that way, small moves will more accurate. Calculated system resolution  for the smallest step is never realy real world.

RICH
Re: Strange Jogging results
« Reply #2 on: January 25, 2013, 06:32:05 AM »
Hi Rich
  and thanks for your reply . I was not questioning the accuracy of the small moves.
it was the fact that it screws up the jog control readout

If I set the jog increment to .1000  for example it steps .0994 .2006 etc
setting the increment to .0100 gives .0094 .0188 etc

yet if I leave the motor tuning as is when you first instal the software ( Steps 2000 velocity 120 acceleration4 )
the jog behaves perfectly and reads out in perfect .1 or .01, .001 steps

Don
« Last Edit: January 25, 2013, 06:34:53 AM by donrecardo »

Offline Hood

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Re: Strange Jogging results
« Reply #3 on: January 25, 2013, 07:13:25 AM »
your min step size is 1/1066.7  = 0.00093747 mm so Mach will only move to the nearest step amount. The standard 2000 is a nice round number so Mach can also jog in nice round step increments.
If you are using metric units then it is best to edit the screenset to remove the extra zeroes in the DROs, 2 are enough in my opinion.

Regarding the step increments, you cant edit the amount but you could enter the values you want in such a way that they repeat.
Hood

Re: Strange Jogging results
« Reply #4 on: January 25, 2013, 08:17:45 AM »
Thank you Hood

That now makes perfect sense .

I think I will also follow your advice and
try to reduce the DROs to show 2 decimal places

Don

 

Offline Hood

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Re: Strange Jogging results
« Reply #5 on: January 25, 2013, 08:25:34 AM »
If you open the screenset in one of the editors available (Screen4 or MachScreen) you can then click on the DROs you want to change and edit the format string. It will be %+.4f and you want to change the number after the decimal point so if you want 3 decimals it would be %+.3f, if you want 2 it would be %+.2f

Hood
Re: Strange Jogging results
« Reply #6 on: January 25, 2013, 09:05:25 AM »
Thanks for the help Hood

I used Screen4 and set 2 decimal places which give me nice round numbers
1.01  1.02  1.03  etc

Regards
Don

Offline Hood

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Re: Strange Jogging results
« Reply #7 on: January 25, 2013, 10:55:24 AM »
Yes Machs DRO display will now show correctly as you are asking it to only show two decimal places and your steps per unit are to 4 decimal places. The true position will still be as before just the display will look better :) Well when I say the true position will be the same, really you will be very unlikely to get anything like that accuracy as, for a start, microstepping is not accurate but when we are talking numbers that small its neither here nor there.
Hood