Help Needed: Cracking the Code on LinuxCNC Servo Homing Setup!

Nevermind. I will figure out a workaround to use custom/default homing with automatic homing enabled.
Like this:
Usually using auto home, and when needed just toggle on custom homing, do homing, toggle off, then using auto homing by default.

Thanks again for the very efficient help!

After speaking to Delta, the Gantry functionality only works with their motion controllers.

Donb9261 wrote:

After speaking to Delta, the Gantry functionality only works with their motion controllers.
 

Which Delta series? A2? A3? B3?

The A3 manual is 1373 pages long but only has brief mentions of the gantry function (I have 4x Delta A3 servos for a planned build with a gantry and was expecting to be able to use the gantry function)

All of them. The reason is that tandem axis control is the domain of the master. The master must issue commands for each motor. The same would be present if using a MESA card with S/D.

Tandem axis control using ECAT in LCNC isn't functional if I understand correctly. I am still digging.

Delta explained what I already knew to be true, that an ECAT servo must derive all commands via the master who is fed commands via the controller. They said, that with the setup they have the position loop is closed for both drives and the encoder output for D1 is fed into D2. The D1 drive uses the standard RS422 encoder output and D2 uses the external encoder interface IN as the position FB for D2. From there, D2 will be placed in follow me mode where it follows the pulse train from D1. While novel, much of the position calculations must be done by the master to ensure the following error of each drive remains as low as possible. Hence the reason it only works with their controllers.

I am just the messenger here. But what they said makes sense based on how their drives are designed. What they have provided as a solution is not ideal even by their standards. Tandem axis control should be the domain of the controller/master not the drive.

The engineer was going to reach out to his counterpart in Taiwan but DeltaTW is off next week so it would be W1 of July before a response is possible. He will forward any white papers if any are available.

So really the gantry function is not needed / helpful when we have a full controller (such as LinuxCNC)

And what we need is to be able to configure 'home offset' whether homing is done fully in LinuxCNC or in a servo drive

Possibly. I work with Siemens and Fanuc extensively. Daily in fact. For a myriad of reasons all motion for any purpose is controlled by the controller/master domain. It makes sense if you think about it.

In the Delta scenario, D1 drives the motion of D2. If D1 sends erroneous commands to D2 the controller would not know which violates the Functional Safety standards used internationally.

On both Siemens and Fanuc the gantry or tandem control is done fully closed loop per drive. Both use active position control to maintain the sync between the 2 axis positions. All commands for both are mirrored but the net motion is constantly being updated to keep error aka following error as close to zero as possible. The drives are set to Torque mode over the bus using the drives ABS position feedback and direct scale feedback(connected directly to the controller not the drive) or simply use the drives ABS FB POS.

Essentially, this makes the drives although ECAT based a dumb terminal that just does what it is told. For CNC where high precision is required at high velocity this makes perfect sense. If I am simply controlling a Pick and Place machine then precision is required but within a wider error spectrum.

I am thinking the best solution for the entire LCNC and ECAT is to do the same as what Siemens/Fanuc have done and find a solution for homing that makes sense based on true ABS encoder technology. There is a net savings in cost in doing this as well as ensuring the precision required. The cost savings comes in the wiring and reliability aspect. Less wires less cost and less chance for things to break. And it maintains proper separation of concerns with a true master slave setup.

I will be looking at how to change LCNC to act more like the CNC ECAT standard vs. trying to reinvent the wheel. Currently LCNC has a single mode for positioning. Command Position Mode. Which is the same as S/D mode using a Mesa. The drive is in follow my lead more or less. This creates some questions as to whether the ECAT interface in LCNC can use the same functionality of the standard interface within the ECAT interface. Can LCNC use the ABS POS FB as the FB to close the loop on the LCNC side? Will the driver do an actual tandem control? Can LCNC custom homing work with a "home in place" "update position to current ABS POS FB, then assume homed?

These are all questions that need to be answered. I will try to do so, but the documentation on the LCNC ECAT interface is lacking a bit. Once you figure out the best practice for how to control the axis over ECAT in the available mode, then how to tandem and how to home become less obtuse. In my honest opinion, using the drives as a dumb terminal similar to Siemens/Fanuc is the best course to take if one wants a gantry axis setup with homing and sync.

I wonder if we could use the ECAT to move the servo and a Mesa for scale feedback simply for a gantry axis to close the loop allowing LCNC to provide the requisite sync/error control along with the homing to index/ABS case? It works in S/D mode...???