config two motor on gantry axis (Y) to square the machine

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13 Jan 2020 18:46 #154779 by rogerxue
Hi, I've read that you can use gantrykins to link two joints to a single axis, but also read that with the latest, it's no longer needed.

So what should I do? I use 2.7.15, and willing to upgrade to any version if necessary.

I have two limit switch on Y, and I want to take advantage of that to square gantry to the table

thanks

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13 Jan 2020 18:52 #154780 by Clive S
You will need to update to V2.8/2.9 as that will give you the ability to have more than one joint on an axis

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13 Jan 2020 20:47 - 13 Jan 2020 21:55 #154781 by AgentWD40
Can you set the zero offset to be different for each *joint's* limit switch?

eg. to rack the gantry to square the left side of the gantry needs to zero at the limit switch while the right side of the gantry needs to back off the limit switch by a couple mm. Is that possible in the software or do the switches need to be physically adjusted?

[Edit]
Doing some research. Please tell me if I have this correct:
Each joint will have it's own HOME and HOME_OFFSET values in the ini file. These correspond to pncconf's "Home Position Location" and "Home Switch Location" axis config fields respectively. To accomplish racking of the gantry one only needs to adjust the HOME_OFFSET for the appropriate joint. That sound right? HOME needs to be the same value for joints on the same axis, right?

linuxcnc.org/docs/html/config/ini-homing.html#_home_offset

[Edit #2]
The docs note that something to watch out for is that the HOME_OFFSET has to be between MIN_LIMIT and MAX_LIMIT. Is this the joint or axes' min/max limits? In the example above if the right side of the gantry needs to back off 2mm to rack square, the HOME_OFFSET for that joint needs to be -2mm and the MIN_LIMIT = -2mm + -0.001 ? What about the axis' min_limit?
Last edit: 13 Jan 2020 21:55 by AgentWD40.

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13 Jan 2020 21:55 #154787 by Todd Zuercher
Yes
and
Yes

Home (or home position) sets the point where the axis will rapid to and park at the end of the home cycle. Home Offset sets the value given to the point where the home switch is triggered.

So if your switch is at the negative end of travel, and you set the Home Offset = -10
and Home = 0 the joint will home to the switch and rapid move to 10 units away from the switch and that point will = 0.

If two slaved joints are set up, one with a Home offset of -10 the other with -10.253. Both joints will move to their switches, touch off, (which ever one finishes it's touch first will then wait for the other), then both joints will rapid together to the Home = position.
The following user(s) said Thank You: AgentWD40

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13 Jan 2020 22:34 #154790 by rogerxue
Thanks, how do I update to 2.9? do I need to compile myself?

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13 Jan 2020 22:52 #154792 by Clive S

rogerxue wrote: Thanks, how do I update to 2.9? do I need to compile myself?


This might help you forum.linuxcnc.org/38-general-linuxcnc-q...s/34817-updating-2-8

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14 Jan 2020 09:50 #154808 by CNCFred

If two slaved joints are set up, one with a Home offset of -10 the other with -10.253


Is this a setting or hardware switches setup differently?

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14 Jan 2020 10:15 #154809 by bevins

CNCFred wrote:

If two slaved joints are set up, one with a Home offset of -10 the other with -10.253


Is this a setting or hardware switches setup differently?


Its a setting in your ini file.

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15 Jan 2020 00:47 #154868 by andypugh

rogerxue wrote: Thanks, how do I update to 2.9? do I need to compile myself?


Simplest way is via the buildbot.
buildbot.linuxcnc.org

(point Synaptic at the buildbot repository and install the pre-built packages)

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