Trouble with dual motor gantry setup

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06 Jan 2021 11:17 #194205 by tommylight
I did check the files last night, or this morning as it was 5:45AM, but was to tired to reply.
In the ini file X axis has 0 velocity for search and latch so that will not work. The files are set for a normal 3 axis machine, not for a tandem axis, so there should not be a need for two limit switchesH.
As for holes, they seem big so should do the job if the search velocity is low, i would set it to 5 and test, then 10 and i would leave it at that.
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06 Jan 2021 19:51 #194271 by peterdownunder
Thanks for the advice, and will probably go that way. The construction of your system is similar and you are correct, we could easily implement something similar.

One advantage of the current sensor setup is that if something screws up, ether one motor stopping causing severe racking, or something is on the rails causing the X-Axis to lift, it triggers a limit, which is nice.

We have a lot going on at the moment, but I will probably take you up on that Mesa offer. We would like to install on a small Lenovo thinkcentre that will fit in the control cabinet, but has no slots, so an ethernet connection would solve that (or allow us to install elsewhere with easy cabling).

Also have some safety concerns about the system and would like to put as many safety interlocks as possible, given the use by not so experienced users.

We currently limit the X speed as that is an exposed area and is driven by dual Nema 34 at 5.6 amps, so can move at a frightening speed considering the mass of the gantry.

As part of this SW upgrade we are also replacing the spindle, which has suffered too many crashes and main bearing are a bit sad. The new one has an ATC so we need to drive all the pneumatics for that as well.

Currently running off an old PC that has 2 parallel ports, but that is for testing only.

Add to that we are moving premesis in a couple of weeks time. Not looking forward to that.

Fun local fact: this is an Australian CNC that the previous owner used to make surfboard blanks (how very Australian :) )

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06 Jan 2021 19:52 #194273 by peterdownunder
Thanks tommy will try that today. Lots of work, so little time ...
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06 Jan 2021 20:29 #194281 by peterdownunder
Rod, what is the cost of the Mesa card

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07 Jan 2021 01:17 #194315 by peterdownunder
Ok got this working. I realised that the files I gave you were the ones in the middle of me testing.

The problem ended up being an IO Error (as in Idiot Operator). At the start of the linuxcnc change we decided to fix an issue of the previous setup, in that the longest axis was Y, not X, which is not particularly intuitive. I switched this round every where in the hal/ini files but forgot the wiring diagram from before still had the old parallel port pin setup.

Therefore it was hitting the X-Limit when trying to home Y

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07 Jan 2021 06:06 #194322 by peterdownunder
All homing seems to work Ok now, thanks for all the help.

Am now moving on to the vfd using the hy_vfd over modbus.

All the comms seem to work ok but when the spindle starts to spin I get joint limit errors on all 3 joints
I have look at halshow and dont see anything strange. What I have done is to disable the pwmgen stuff in the main hal and added the attached custom.hal.

Will research it tonight but thought I would post this to be sure that I am not doing something stupid
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07 Jan 2021 08:29 #194335 by tommylight


All the comms seem to work ok but when the spindle starts to spin I get joint limit errors on all 3 joints

That is a grounding/shielding issue, make sure the PC and the machine electronics and the cabinet are properly grounded.
Do not continue without fixing that, it usually adds another PC to the dump.

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07 Jan 2021 17:20 #194378 by peterdownunder
yeah that makes a lot of sense. Will check it today.

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08 Jan 2021 14:31 #194495 by andypugh


All the comms seem to work ok but when the spindle starts to spin I get joint limit errors on all 3 joints

That is a grounding/shielding issue, make sure the PC and the machine electronics and the cabinet are properly grounded.
Do not continue without fixing that, it usually adds another PC to the dump.


Add an input filter to the VFD. That is almost always needed, and they are not expensive.

(Look on eBay for "Rasmi", one of the cheaper manufacturers)
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08 Jan 2021 23:29 #194552 by peterdownunder
Found the problem. it was an earthing problem between the probe and the DIN relays. They were not using the same earth as the PDMX BOB. Surprised they worked at all.

Now to get tool touchoff to work.


Thanks for the help guys.
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