Homng moving away from home
05 Sep 2011 10:25 #12975
by ArcEye
Replied by ArcEye on topic Re:Homng moving away from home
TarheelTom :
Now it looks as though you are homing on the negative limit switch, not the positive one.
I don't know if there is a specific standard on it, but I have always homed at the positive limit and all the machines I have converted had their home switches at that end.
As far as I am aware, EMC expects the initial home move to be towards the positive limit, which is why you had to reverse the sign to get it to move the way you wanted.
Why don't you try using the positive limit switch as your combined home / limit and removing the minus sign in front of HOME_SEARCH_VEL.
It seems like that will give you a jog which goes the right way and homing which moves towards the correct switch and off again to latch.
regards
Going right back to the beginning, you were describing the homing as heading away from the the home switchNow my X axis moves in the right directions when jogging, but when I ask it to home, it moves away from the homing switch, instead of towards it.
Creeps down toward the negative limit switch, hits it, then rapids out a bit, then creeps down again until it hits it a second time.
Now it looks as though you are homing on the negative limit switch, not the positive one.
I don't know if there is a specific standard on it, but I have always homed at the positive limit and all the machines I have converted had their home switches at that end.
As far as I am aware, EMC expects the initial home move to be towards the positive limit, which is why you had to reverse the sign to get it to move the way you wanted.
Why don't you try using the positive limit switch as your combined home / limit and removing the minus sign in front of HOME_SEARCH_VEL.
It seems like that will give you a jog which goes the right way and homing which moves towards the correct switch and off again to latch.
regards
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05 Sep 2011 10:33 #12976
by andypugh
Replied by andypugh on topic Re:Homng moving away from home
ArcEye wrote:
[quoteI don't know if there is a specific standard on it, but I have always homed at the positive limit and all the machines I have converted had their home switches at that end.
As far as I am aware, EMC expects the initial home move to be towards the positive limit, which is why you had to reverse the sign to get it to move the way you wanted.[/quote]
EMC2 doesn't "expect" anything, you can home in any direction, and have the switch at any end, or in the middle (If he switch is in the middle then you need a long "flag" so that EMC2 knows which side of the switch it is, and clearly then it can't also be a limit switch.
My machine has Z on the negative limit and X on the positive when it is being a lathe, then when it is being a mill that becomes all axes homing positive. (This is exactly the same hardware and two configurations on a dual-purpose machine)
[quoteI don't know if there is a specific standard on it, but I have always homed at the positive limit and all the machines I have converted had their home switches at that end.
As far as I am aware, EMC expects the initial home move to be towards the positive limit, which is why you had to reverse the sign to get it to move the way you wanted.[/quote]
EMC2 doesn't "expect" anything, you can home in any direction, and have the switch at any end, or in the middle (If he switch is in the middle then you need a long "flag" so that EMC2 knows which side of the switch it is, and clearly then it can't also be a limit switch.
My machine has Z on the negative limit and X on the positive when it is being a lathe, then when it is being a mill that becomes all axes homing positive. (This is exactly the same hardware and two configurations on a dual-purpose machine)
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05 Sep 2011 10:45 #12978
by ArcEye
Replied by ArcEye on topic Re:Homng moving away from home
OK for 'expect' read 'default behaviour'.
I was merely suggesting that setting up in such a way that the defaults worked as expected, might be a simpler way to work.
I was merely suggesting that setting up in such a way that the defaults worked as expected, might be a simpler way to work.
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17 Sep 2011 03:52 #13224
by TarHeelTom
Replied by TarHeelTom on topic Re:Homng moving away from home
After much tweaking, finally got all three axes to home correctly, more or less.
Big problem was the the max feedrate was set at 180 ipm, and that was causing a joint feed error after the limit switch was found the second time and the table moved toward the home offset position.
Lowering the feedrate to 30 ipm solved all those problems. Sometime in the future I'll play with it a little more and do some increases to figure out was the actual practical max feedrate is.
But I'm under the impression that homing an axis should set the position in the window for that axis to zero, but that doesn't occur. Is my thinking wrong on this?
Thanks
Tom
Big problem was the the max feedrate was set at 180 ipm, and that was causing a joint feed error after the limit switch was found the second time and the table moved toward the home offset position.
Lowering the feedrate to 30 ipm solved all those problems. Sometime in the future I'll play with it a little more and do some increases to figure out was the actual practical max feedrate is.
But I'm under the impression that homing an axis should set the position in the window for that axis to zero, but that doesn't occur. Is my thinking wrong on this?
Thanks
Tom
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17 Sep 2011 05:03 #13225
by jmelson
Replied by jmelson on topic Re:Homng moving away from home
TarHeelTom wrote:
the LAST offset you set last time you ran EMC. So, after homing, you should set the right offset
to the part using the Axis touch off button.
Jon
Homing sets the MACHINE position to zero. The workpiece position is arbitrary, generally using
But I'm under the impression that homing an axis should set the position in the window for that axis to zero, but that doesn't occur. Is my thinking wrong on this?
Thanks
Tom
the LAST offset you set last time you ran EMC. So, after homing, you should set the right offset
to the part using the Axis touch off button.
Jon
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17 Sep 2011 08:30 #13229
by ArcEye
The behaviour of displaying the last G54 offsets when you re-home the machine after a new start-up, is actually very useful.
If you have accurate, repeatable home switches, you can pick up where you left off the previous session.
Might not work for cheapo roller arm switches but for good quality short travel switches or proximity sensors, which is what I have, works very well.
I usually leave a reference point against which I can double check, the exact co-ordinates of a hole or a scribed line etc. but 99.9% of the time I find I am back spot on where I was before.
regards
Replied by ArcEye on topic Re:Homng moving away from home
Glad you got there in the end, as you say you can fine tune as you go along.After much tweaking, finally got all three axes to home correctly, more or less.
The behaviour of displaying the last G54 offsets when you re-home the machine after a new start-up, is actually very useful.
If you have accurate, repeatable home switches, you can pick up where you left off the previous session.
Might not work for cheapo roller arm switches but for good quality short travel switches or proximity sensors, which is what I have, works very well.
I usually leave a reference point against which I can double check, the exact co-ordinates of a hole or a scribed line etc. but 99.9% of the time I find I am back spot on where I was before.
regards
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02 Oct 2011 14:22 #13603
by TarHeelTom
Replied by TarHeelTom on topic Re:Homng moving away from home
Saw somewhere recently an inexpensive USB pendant, maybe $30 or so, but stated that it was setup only for Mach3.
Can EMC2 be configured to watch the USB port for incoming "keystrokes" and then translate them into the keystrokes EMC2 needs to do the same function.
Tom
Can EMC2 be configured to watch the USB port for incoming "keystrokes" and then translate them into the keystrokes EMC2 needs to do the same function.
Tom
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02 Oct 2011 15:04 - 02 Oct 2011 15:06 #13604
by BigJohnT
Replied by BigJohnT on topic Re:Homng moving away from home
Here is how I used a common usb game pad with my plasma cutter.
wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Simple_Remote_Pendant
Do you have a link?
John
wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Simple_Remote_Pendant
Do you have a link?
John
Last edit: 02 Oct 2011 15:06 by BigJohnT.
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03 Oct 2011 08:00 #13620
by TarHeelTom
Replied by TarHeelTom on topic Re:Homng moving away from home
BigJohnT wrote:
At the moment, I don't have a link. I'll have to dig back through a bunch of old email and search for the right message, but not tonight.
Tom
Here is how I used a common usb game pad with my plasma cutter.
wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Simple_Remote_Pendant
Do you have a link?
John
At the moment, I don't have a link. I'll have to dig back through a bunch of old email and search for the right message, but not tonight.
Tom
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