Re: [CAD_CAM_EDM_DRO] Re: CNC robotic welding arms

Mark Ehle wrote:

> OOOH! EMC can do that? It has that built in?
>
> Can anybody tell me more?
>
> Mark
>
> >>> thscarince@... 05/17/02 11:38AM >>>
> If your controller software still thinks its driving an XY machine
> instead of a two jointed planar arm, it will not interpolate
> correctly.
>
> For instance, if you want to cut a straight line from a position 45
> degrees to the left of the base to a position the same distance from
> the base but 45 degrees to the right, your G code would command the
> base axis to move +90 degrees and the elbow joint zero degrees.
> Instead of a straight line you would get an arc whose center point is
> the base of the machine.
>
> A way around this is to break things up into very short segments line
> a constant-contouring file. A better way is to use a controller that
> knows what kind of mechanism it is driving ie feed it XY and let it
> do the rectangular to angular conversion itself. I understand that
> EMC can do this easily.

Yes, EMC is a GENERAL CNC program, in that it is not tied to any specific
type of machine construction. It has routines called kinematics
and reverse_kinematics which define the movements the machine's
axes are capable of. EMC was originally designed as a robot program,
so it is built from the ground up for complex kinematics where there is
more than one way to move to a specific XYZ coordinate. Cartesian
machines don't have this complication, so any XYZ position is achieved
by simply moving the X axis to coordinate X, Y axis to Y and Z axis to Z.
That is the totally trivial case. A jointed robot needs to know the length
of the arms between the joints, and the order in which the joints are
stacked to figure out how to get to an XYZ 'there' from the XYZ where
you are, now.

SO, for any jointed robot, you have to supply the equations defining
the motions in these kinematics and reverse kinematics routines.
There are some examples supplied for specific robot machines.
You can look at files in the directory .../emc/src/emcmot for files like :
trivkins.c cartesian machines
puma560kins.c Puma robot
genhexkins.c Generic hexapod (stewart platform)

Jon