Re: Backlash problem? - Solved

Art (of Mach2 fame) suggested I not use the multiplier on the Gecko
G210. I took his suggestion and it worked. I also removed the pll
from another G210 and it also worked. Art said that this error had
been reported to him before. It was something about the quick change
of direction?
Kevin

--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
wrote:

> As I wrote yesterday, I intended to run the program today when I

got a chance as the original poster presented and it works perfect. I
set the handwheels on zero and it returns to the exact same position
every time. There must be something wrong with the machine. It isn't
Mach2 or a programming error.

>
> Ron
>
> Tom Hubin <thubin@e...> wrote:
>
> > Well, You are in absolute per the G90 command. So it is

irrelevant what moves you make when you tell the machine to return to
X0Y0 it should return to the same spot every time.

>
> Agreed.
>
> > The only time you can build program end position errors on

repitition is in Incremental G91 programming and miscalculating the
move to go back to the starting point. Never use Incremental.

>
> As far as what you say about incremental and absolute, you can

switch

> back and forth as often as you wish. If you start in absolute at

(0,0)

> and end in absolute at (0,0) then you should end up where you

started

> with no accumulated error. As you suggest, you cannot accurately

move

> incrementally to a calculated position.
>
> The thing that can mess you up is if you change your coordinate

system,

> using G92 for example, then you effectively redefine x0y0 as

someplace

> new. I do not see that anywhere in the poster's short program so

that is

> clearly not the problem.
>
> > However, I'm looking at the code more closely. Are you sure Mach2

produced that code exactly like that? You start out in Absolute but
your commands are in Incremental then it goes back to absolute??.

>
> I don't see anyplace where G91 sets up incremental mode. As it sits

it

> is all in absolute mode.
>
> > In absolute the radii are always called out with "I" and "J"

values.

>
> Not true. I often use X, Y, and R in absolute mode. The arc must be

less

> than a semicircle to use R reliably. For arcs greater than a

semicircle

> you need to use I, J to specify center and not R to specify radius.
>
> In some Gcode interpreters I and J are always incremental values. In
> other interpreters I and J are absolute or incremental according to

the

> G90, G91 mode in effect. In still other interpreters, the user

chooses

> from a menu to interpret I and J as incremental or absolute. I think
> Mach2 allows the user to choose. But there are no I and J values in

the

> poster's Gcode program so this should be academic.
>
> > If thats not it and you are using servos I'd be looking at

possible encoder/motor lead cross-talking. It could be lost steps due
to a certain place in the machining process that inducing a heavy
load on the axis drive.

>
> Steps are being lost someplace. Could be a software bug. Try

sending the

> program to the appropriate software folks and see if they can fix

their

> software or tell you what is wrong with your Gcode.
>
> Try running the Gcode with a different Gcode interpreter like

TurboCnc

> or EMC.
>
> > If it were a mechanical backlash issue it would still be out the

same .033" every time from zero. Not .033" then .066" then .099".

>
> Agreed.
>
> Tom Hubin
> thubin@e...
>
>
>
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