Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: simonbos on December 28, 2009, 01:15:36 AM
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I am just finishing my DIY router and am having some trouble with the homing process. I have seperate home and limit switches (which work fine). The "ref all home" works ok. but if I enter "G0 X0" it goes too fast near the home switch and overshoots. I tried setting soft limits at mn 0 and max = travel (-ve for Z) and 0.5 for the slow zone but this did not help. Can someone help?
Thanks,
Simon
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Sounds like your switches could be inaccurate, what kind are they?
When you do a homing move the axis will move to the switch then back off and will set the zero position when the switch again closes, if you then move away and return to zero your switches should not be triggered. If however your switches are not accurate the closed position may vary considerably and cause the problems you are experiencing.
Hood
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Hi Hood,
I read his problem differently, in that his machine homes OK
But if he then enters "G0 X0" presumably from the MDI line his machine overshoots.
Maybe he will come back and explain more fully
Phil
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Yes the machine homes OK but if the switches are inaccurate then the X0 position will be different every time and when commanding a move back to X0 the switch may open sooner than it previously closed.
As for setting soft limits and the slow zone, that will all depend on what acceleration your axis have, if fairly low accel then you will need a larger slow zone so that Mach can decel from full rapid in time not to hit the switch.
Hood
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Phil had it right...The home switches work fine when doing a "ref all home" which goes slowly. The G28 (entered from MDI) does not appear to slow down at all before hitting the home switch and then going past to the limit switch.
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So exactly what are you commanding from the MDI?
Hood
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G28 X0
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And what does the DRO read in Machine coords when the limit is hit?
Hood
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Simon from the MDI line you enter "G28 X0"
Doing G0X0 will take you at full speed the same as "G28 X0"
Only jogging near limits does the machine obey the slow zone
Your issue maybe that you have not set the motor tuning correctly maybe acceleration as the likely cause as either the two lines above you should end at Zero
Phil
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Maybe I am using the wrong command to home the axis. What I was trying to do was get to the home switch a bit quicker than the "ref all", which takes a while. Is there a better way to home a single axis? Also is there a way to have the homing go faster until close to the switch and then slow down?
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When homing, I manually jog at full speed to within an inch or so from the switch, then let mach home the axis from there.
Fastest way I know of, if the axis knows not where it is.
In "Homing / Limits" you can set the speed up a bit, but then check for consistency.
Ray has a cool macro for probing that could possibly be incorporated into the reference button where it HOMES once fast, then again slowly for greater precision and accuracy/repeatably.
Are you using servos by chance with a closed following loop ?
Some of them allow an amount of overshoot that can give you a similar problem.
Russ
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You can home each axis individually if you wish, buttons are on the Diagnostics page but you could modify your screenset and put them on the main page if you wanted.
There is no way to move faster than what you have as the homing speed. Reason is because until you have homed Mach doesnt know where you are so how would it know how to go to the slower speed.
You could manually jog until close then press the Ref All button.
Some people have altered the RefAll button to include a G53G0X*Y*Z* move before the actual homing move but this relies on the last homing move you did still being accurate and the table not being moved while switched off and to me it is not safe practice but thats just my opinion. Maybe I am just used to heavy powerful machines but still not something I would like to do.
Hood