Strange homing behavior

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06 Jan 2022 18:17 - 06 Jan 2022 18:20 #230975 by johnbl
Hi all,

So I'm trying to home the first axis of my machine with the following settings:
[AXIS_X]
MIN_LIMIT = 0
MAX_LIMIT = 600

[JOINT_0]
MIN_LIMIT = 0
MAX_LIMIT = 600
...
HOME_SEQUENCE = 0
HOME_USE_INDEX = YES
HOME_IGNORE_LIMITS = NO
HOME_SEARCH_VEL = -15
HOME_LATCH_VEL = 1
HOME_FINAL_VEL = 30
HOME_OFFSET = 1
HOME = 0
 

When homing, the axis travels in the correct direction, detects the homing switch correctly, index pulse also works. But for the final phase (HOME_OFFSET, HOME), instead of staying where it is and setting the machine origin to 0 (as I would expect), the axis moves back where it was at machine power on ?!
Last edit: 06 Jan 2022 18:20 by johnbl.

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06 Jan 2022 19:34 #230979 by Todd Zuercher
What the values for HOME= and HOME_OFFSET= do are this.
The number you set for HOME_OFFSET= is the value given to the position where Linuxcnc detects the index pulse (or homeswitch latch without index), In your case that position is given the value of 1.0. After that Linuxcnc will then make a rapid move to position specified by HOME=, In your case 0, so the home position and where your machine will park after homing will be -1.0 away from your home index detection point.

If you want your the home index detection point to be = 0 and have the machine park there at the end of homing, change HOME_OFFSET = 1 to 0.

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06 Jan 2022 19:41 - 06 Jan 2022 19:44 #230980 by johnbl
Replied by johnbl on topic Strange homing behavior

In your case 0, so the home position and where your machine will park after homing will be -1.0 away from your home index detection point.
 

And this is exactly what I want, but the machine does not park at this position, it goes straight back to where it was before homing, and applies the HOME value relative to that position.

Let's say the table is in the middle of the axis before homing (so for a 600mm travel it would be at X=300), and HOME=0. Homing switch is at X=0. During homing the axis moves to 0, triggers the homing switch and looks for index, then goes straight back to the middle!

By the way I'm using git master from around October 2020.
Last edit: 06 Jan 2022 19:44 by johnbl.

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06 Jan 2022 19:47 - 06 Jan 2022 19:48 #230981 by Todd Zuercher
I moves after homing when both HOME_OFFSET = 0 and HOME = 0?

Are you sure the ini config file you are opening when you start Linuxcnc is the same one that you are editing?
Last edit: 06 Jan 2022 19:48 by Todd Zuercher.

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06 Jan 2022 20:04 - 06 Jan 2022 20:05 #230983 by johnbl
Replied by johnbl on topic Strange homing behavior
Affirmative to both questions.
I just double-checked everything and all is correct config wise.

Could this be a weird bug in AXIS? I don't use the "Home All" button as the other 2 axes are not yet configured, but I click on Machine menu -> homing -> X homing
Last edit: 06 Jan 2022 20:05 by johnbl.

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06 Jan 2022 21:25 #230989 by tommylight
Replied by tommylight on topic Strange homing behavior
Does the machine have indexes ?
Or encoders wired to LinuxCNC in any way ?

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07 Jan 2022 16:40 #231036 by johnbl
Replied by johnbl on topic Strange homing behavior
Yes I use encoder index for homing, but the index pulse detection seems to work just fine.

Today I tried with a fresh build from git master and the behavior is exactly the same.

After homing LinuxCNC always sets the 0 origin where the axis was at first power on!!
I can then unhome, jog the axis manually somewhere else and re-home. Same thing, goes back to where it was at power on.

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07 Jan 2022 17:19 - 07 Jan 2022 17:39 #231037 by johnbl
Replied by johnbl on topic Strange homing behavior
Here's a quick screen capture:


Encoder scaling seems way off, but it shouldn't affect homing right?
Last edit: 07 Jan 2022 17:39 by johnbl.

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07 Jan 2022 18:19 #231040 by arvidb
Replied by arvidb on topic Strange homing behavior
You get an error at the end of the move: "Exceeded NEGATIVE soft limit (0.00000) on joint 1". Perhaps that's got something to do with it, i.e. the homing process is aborted due to hitting the soft limit? Just a guess...

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07 Jan 2022 18:31 #231042 by tommylight
Replied by tommylight on topic Strange homing behavior
It is not homing anything, it is exceeding the limits without ever getting triggered by index or home switch.

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