Re: Accumulating position error with servo system

[Jon Elson <elson-at-pico-systems.com>]

Kurtis Martineau wrote:

>7. The STGII 8 axis board was replaced with a 4 axis board.
>  
>
This eliminates the board, itself, but may not completely eliminate 
everything around it
(although this one isn't too likely).  I'm just wondering if something 
else in the computer
may be interfering with the I/O address of the Y axis encoder counter. 
 This is a pretty
long shot.

>8. The last thing I did was swap the X and Y axis wiring to the STGII board.
>ie: The X axis on the Gui now controlled the position of the real world Y
>axis, and vice-versa.
>    At this point the position error moved to the real world X axis and the
>actual position control of the Y axis was +/- 1.5/1000 inches.
>  
>
This really seems to implicate either the STG or the software.  Check 7 
seems to get the STG
off the hook, so software begins to look very suspect.

There was a problem some time ago, when using certain values of backlash 
compensation.
Turn all the backlash values to 0.0 and try it again.  It may have also 
reared its head in
relation to homing, so it gets more suspicious.  One thing I might try 
is to move the
machine manually, while in estop, and compare a dial indicator with the 
screen display.
If there is no problem when manually moving, but you get errors when 
moving under
computer control, then there are only a couple of possibilities.  One is 
a software
problem (and the backlash bug did exactly this, I recall) or there is 
some electrical
problem from servo amp noise that only affects the Y axis encoder counter.

You might also try STG's DOS diagnostic programs and see if they give an 
error.

Jon