LinuxCnc and Industrial Robot?

I have/had KUKA industrial robots welding and paletizing bricks and sacks with sand, but they used a stripped down version of winxp.
And there are some robots here on this forum running LinuxCNC, just search for Scara robot. Also there should be some configs included with LinuxCNC so you can download the ISO, write it to a USB and boot from it, then run LinuxCNC in sim mode, some sim configs also have visualization so you can see on screen the machine moving.
As for toolpaths, it depends on what you need, some stuff can be done as simple as for a normal router/engraver/plotter, some might need specialized CAM software.

See the config
sim/axis/vismach/puma
for an example config including a graphical representation of the simulated robot.

Note that getting the Denavit-Hartenberg parameters exactly right is not a trivial task if they are not provided. (and there are two different conventions for them)

There are a few examples out there. Look on YouTube.
For example:

The Melfa seems to be all in-line so that makes the kinematics somewhat simpler.

It is possible to use LinuxCNC to run cartesian (ie xyz) gcode on an industrial robot. However, since the planner has no information about the kinematics used and 'assumes' a cartesian joint/axes configuration you will not get uniform velocities over the robot's work space.
If accurate path velocities are important for your application then you are going to have a hard time using LinuxCNC with a manipulator.

heaven wrote:

One more problem, LinuxCNC is using 3-axis (xyz) readahead, so if you are using xyz+(abcuvw) axis blending in G-code command, the speed will be very slow

That will depend on the G-code. The slow motion in combined moves is to do with the requirement in the simple path planner that the system can stop in the next segment (if it turns out to be the last segment, because without lookahead it can't know what the allowed exit speed is for the current segment) 
If the G-code is very short segments, this becomes a limit to the speed. But if the moves are long, the system can run at full speed.