Thanks for all your input guys,
Sorry about the calculations as Iam a metric man
and seem to think anything after the forth decimal place doesn't matter
which it dose in inch calc`s ie 0.0001968498=0.002 I rounded down instead
of up.
carbidebob,all very interesting ,things are starting to make sense but I don't think Iam ready to travel down
the electronic path just yet "control the integrator on the PID loop Etc"but I might have too soon.
Answer to your some of your questions,
"Please explain how you are checking the accuracy"The only way so far that I have been checking the accuracy is purely mechanical ,through
the use of a dial indicator and jogging the axis ,short steps and long steps eg .02mm (0.00078`) to 150mm(5.90549`) .G0 x0.002 etc
And the best I could do in a single jog would be .05mm (0.002`) ,the axis wouldn't move for anything less.
Then when repeating a longer move eg 150mm (5.905`) it would be out by 0.04mm (0.00156`) to 0.15mm (0.00590`).on returning to 0
I have since pulled the machine apart as I think there might be a binding issue going on,and so in the coming weeks
will knock up a basic oiling system. Can only help and should of been done to start with.
However
Pulled the z axis apart and couldn't even move the section that holds the motor/gearbox ,I think I did the gibs up
to tight? whoops.
The x and y axis I cant explain.
Did you retune the servos after changing encoders?
I didn't retune the servos after changing encoders as I thought by halving the encoder count (500 to 250 )and then putting them
on the motors was the same thing ,since I have 2 to 1 pulley ratio,maybe I should have,retune that is.
Have you ever done a servo size/inertia analysis on this machine ?
No, all with trial and error(with lots of error).
High encoder counts may be a problem if we run into a pulse speed limit from Mach 3
Iam thinking of going with the g100 grex from gecko drives ,it seems it will provide the pulses I require.
With a maximum of 45Khz from Mach 3 at the moment and 2048 cpr encoders on the motors ,by calculation the best I WILL get is
about 60 or so inches per minute,any thoughts.
With those nice ballscrews you should be able to achieve a .0001 inch repeatability but it will take some work. (and probably some different encoders and a lot of testing)
Are there any encoders that you recommend.
From what I have read I think 2048 cpr ,mounted on the motors should get the required accuracy. Testing I can handle pulling the machine down
again ,I cant.
Thanks again for your info.  |