Brian wrote:
> Dave,
>
>   I simply want axis to be able to utilize my scale feedback as actual
> joint position.  Thats all.
>   
And that's what I SIMPLY don't understand.  I have two servo-controlled 
machines.
One is a converted manual Bridgeport mill, the other a converted 150Lb 
minimill.
The Bridgeport has no handwheels, but you can turn the pulleys by hand.  
The minimill still has the X and Y handwheels, but I took the crank 
handles off for safety reasons.  On both machines, when I hit E-stop, I 
can turn the screws/handles and the DRO display on Axis (or TkEMC, Mini, 
Touchy, or whatever GUI you choose) updates with the current position.  
When you hit F1-F2 it goes back to CNC mode, and picks up at the 
position the machine is now at.  The location of the encoder is not 
important, it is just a position measuring encoder with so many counts 
per linear inch (or mm, your choice).

So, as far as I can see, it DOES work, and has worked just like this 
since 1988!  Now, in all these cases, I am using external hardware to 
read encoder position.  HAL does offer an encoder counter component, but 
it uses up a lot of parallel port pins.  But, this should also work, as 
long as encoder counts are not coming in too fast to be counted.  Your 
use of the stepgen component requires some changes to the typical 
configs files that would be used with stepgen, and you can pretty much 
forget using stepconf to compose your configs files.

Now, the backlash is an added complication.  I am maybe getting the idea 
that your problem is the classic servo setup won't work due to excessive 
backlash, and you want to have backlash compensation when in servo mode, 
and screw error compensation when in manual/DRO mode.  Now, there I see 
a contradiction.  Without a lot of fudging and kluging, I don't think 
this will work, and fixing the backlash would be the best solution.


Jon

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