Configuring two-servo gantry with separate home/limit switches

More
02 Jun 2019 06:00 #135611 by JetForMe
Hi. I've got two questions about setting up a two-servo axis.

I've got a CNCRouterParts gantry table whose Y-axis is driven by two steppers (Teknic SDSK servos that take step & direction inputs). I'm using a Mesa 7i76e to generate the signals. Each side of the gantry also has a homing switch.

1) I'd like to configure LinuxCNC to drive the two sides in tandem, but to home them independently. I'm not sure if this is possible.

2) I'm also not really sure how to set up the slaved drive. The examples I've found seem to just send the step & direction signals to two sets of pins, but that would preclude driving them independently.

Suggestions are much appreciated. Thanks!

Please Log in or Create an account to join the conversation.

More
02 Jun 2019 06:51 #135612 by pl7i92
Hi
as you run your servos in Step Dir mode
it is very easy as it is the same as Stepper like systems
you can use the Gantry component for a real eaays setup
linuxcnc.org/docs/html/man/man9/gantry.9.html

so eatch joint got its own homeswitch

2)
This is the way to do it
Quick setup -> forum.linuxcnc.org/38-general-linuxcnc-q...69-7i76e-quick-setup
GANTRY config -> forum.linuxcnc.org/47-hal-examples/34072...ranch-gantry-example

And Norbert's connection sheet is also required reading
forum.linuxcnc.org/forum/search?query=my...catids=all&start=240
The following user(s) said Thank You: JetForMe

Please Log in or Create an account to join the conversation.

More
02 Jun 2019 06:53 #135613 by JetForMe
Perfect, thank you for pointing out those posts. I had seen one before and couldn't find it again.

Please Log in or Create an account to join the conversation.

More
02 Jun 2019 11:59 #135626 by rodw
Just be aware that the gantry config linked to is written for master branch (V2.8). The change to support multi spindles in master branch since I shared that example requires changes to the pins used for the spindle.

The Gantry component also shared with you is no longer relevant in Master branch as it has independent axes. (Joint axes) This has changed the homing configuration linuxcnc.org/docs/devel/html/config/ini-homing.html so it is now much easier to align both sides of the gantry by simply changing the homing offsets in your ini file. eg. If you measure that one side is out of square by 1mm, you just need to add or subtract 1mm from the offset for that joint in your ini file.

So if you have a XYYZ machine, you should set the homing sequence on joints 1 and 2 (YY) to be -1 to tell Linuxcnc that these joints should be homed jointly in unison and thats it. Simple as!
The following user(s) said Thank You: JetForMe

Please Log in or Create an account to join the conversation.

More
02 Jun 2019 12:58 - 02 Jun 2019 12:58 #135629 by JetForMe
Thanks for that heads-up.

You bring up a question I was going to make a separate post about. My spindle’s VFD can be driven via RS-485. Is it possible to use the RS-485 output on the 7i76e to control the VFD? It uses MODBUS.
Last edit: 02 Jun 2019 12:58 by JetForMe.

Please Log in or Create an account to join the conversation.

More
02 Jun 2019 15:01 #135637 by bevins
Yes I believe there is a modbus component. I have never used it.

Does your VFD have 0-10v input? POT input? The 7i76E card has a spindle output or that.

Please Log in or Create an account to join the conversation.

More
02 Jun 2019 20:38 #135656 by rodw
I think this is it for master branch
linuxcnc.org/docs/devel/html/man/man1/mb2hal.1.html

DUnno where the docs are though.

Please Log in or Create an account to join the conversation.

More
02 Jun 2019 22:51 - 02 Jun 2019 22:52 #135666 by bevins
There used to be sample on github but I cannot find it.
There is a wiki though. wiki for modbus
Last edit: 02 Jun 2019 22:52 by bevins.

Please Log in or Create an account to join the conversation.

More
02 Jun 2019 23:58 #135675 by tommylight
To answer your 1 question, yes it is possible to have more than one joint per axis, or motors driving the same axis. Note the more than one, so it is not only 2, but can be more.
The homing is also separate so you can make changes to the INI file regarding the home position separately for each joint, this makes squaring the gantry very easy and does not require any intervention in hardware.
As for slaving axis, this is not mach3 as mach3 can not have separate home switches for the same axis.
Your VFD most probably uses RS485, mesa uses RS422, but I think I read somewhere they can be also used as RS485, but that would probably need other firmware, and aslo probably already exists, so a bit of searching is in order.
You can also use serial RS232 to RS485 converter for that, and that is the existing config some have referee to in this thread, but do have a read as some of those converters do not work and some do.
Personally I use the existing -+10V spindle control on the mesa boards to wire VFD, it is about 3 to 5 wires and it always works.

Please Log in or Create an account to join the conversation.

More
03 Jun 2019 00:40 #135679 by rodw
It is maybe possible to use the MESA RS422 to talk to RS485 if it is a 4 wire interface but you would need to write a driver for it... With the correct firmware there are transmit and receive functions enabled that can be accessed from your component

Please Log in or Create an account to join the conversation.

Time to create page: 0.126 seconds
Powered by Kunena Forum