realtime independent motor control with linuxcnc

Hello,

I haven't tried linuxcnc yet, but I'm trying to figure out if it will be helpful.
in my understandings, linuxcnc commands the motors move around by pre-defined G-codes. In my situation, when the motors follow a series 2 D trajectory in a plane, I need to control in realtime a third dimention of the trajectory (random by situation, but cannot be pre-defined).

To ahieve this, I will need realtime the position of the moving point under linuxcnc's command, (and the status if the moving point is following a trajectory or it's moving around in prepartion to follow a trajectory. ) Then I need to tell the motors controlled by linuxcnc wait until ready to follow a trajectory at the start and at the end of the trajectory.

Is my intention feasible with linuxcnc?

Many thanks in advance for your time to read my question

Thanks for your quick reply! that's fast

my z offset data will come from calculated values based on visual feedbacks.

btw i pushed my question further a bit:

"To ahieve this, I will need realtime the position of the moving point under linuxcnc's command, (and the status if the moving point is following a trajectory or it's moving around in prepartion to follow a trajectory. ) Then I need to tell the motors controlled by linuxcnc wait until ready to follow a trajectory at the start and at the end of the trajectory."

is it still possible?

Hi Andy, Thanks so much for your detailed instructions.
I'm planning to ask for further help on this and planning to pay some cahs for it.
Please read if you have time:

I’m planning to make my standard 4-axis（X Y Z A） workstation cut a series of lines(curves) according to my inputs. The non-trivial part of my goal is that while cutting curves in the X-Y plane I need to use a visual sensor to control the Z axis in real-time. The work-flow(path) of my end tool will be: go to the start point of the first curve in an open space, start spinning the blade(always tangent to the cutting point) , go down until visual sensor feedback says ok, follow the first curve (while my visual sensor adjust the height of the tool in real-time) to the last point, then cut the next curve the same way and so forth.

The control board I’m using is a BeagleBone-black with Cramps 2.2. There is a config file available from Machinekit ( see attachment). And I’m instructed to use HAL pins (motion and offset in particular to achieve my goal.

Here is the plan I came up with: Design a HAL logic which includes motion pins (to parse the cutting movement) and offset pins( to control the Z axis), integrate the HAL logic into a python script, say main.py, that imports pygtk and linuxcnc. ( The main.py will receive the cutting-curves in the machine coordinate system from ROS (robotics operating system) topics, either in the form of a series of sets of coordinates or an depth image, I can do this part myself.) After receiving the cutting-curve, the Linuxcnc will start generating G-codes, and start cutting the curves in the way I described above.

Unfortunately I find it hard to write the HAL logic and integrate everything to my main.py ( I have 0 experience with linuxcnc and HAL, I’m looking for someone who find this easy please help me with some sample scripts or help me to write the frame of my main.py (without the ROS part) .

I’m really grateful for your time and help, and I’m willing to pay some cash for your help.
Please leave a message if you would like to do me a favor.

Can you give us a real world example of what you are trying to accomplish? For instance I use an optical tracing plasma cutter but have to make adjustments to the torch height by visually watching the arc distance due to warped metal. Sometimes getting the basic conversation on the same page is the biggest challenge.

ok, sorry to talk about cash here
I need ROS to receive the cutting curves from another machine,
I will check the plasma cutter system thanks for your help again

Hi Badger, your optical tracing plasma cutter sounds infinitely similiar to what I'm trying to do.
I'm building a fur cutter, and I have to make adjustment to the blade height by visually watching the blade cutting-depth as well, otherwise the tool may drag the fur around(in a long run for certain it will). could you please teach me how you did it? will you be willing to open-source your code?
thanks very much for your help =D

With the optical tracer plasma torch the torch height is adjusted with a knob on a gear rack. I literally reach over and turn the knob as needed. It may be that what you need is something independent from linuxcnc controls since you need to control it, not LNC. It maybe something as simple as a RC servo hooked up to a potentiometer?

If you are dealing with a variable surface where you need to keep the blade in a certain depth you may be able use a proximity sensor to follow the surface. You could have a two stage "Z" axis where the g-code commands the blade to lower and then the proximity sensor would move secondary motor or take over the Z axis motor?

I used quite a few cheats on my Rugbot with help of this forum. The answers are out there, you just have to have the right question.

Good luck.