Need help Linuxcnc homing sequence in H-bot system

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Need help Linuxcnc homing sequence in H-bot system

Сообщение jhlee98y » 02 окт 2014, 04:58

Dear CNC club members,
I'm from KOREA and this is my first post.

It's a long story.
Since 2 years ago, I have made my Micro-CNC adopted H-bot(CoreXY) system. Actually, my machine was built for 3D printer. So its controller was Marlin firmware based on Arduino.
Because I wanted PCB milling and simple AL routing, I had changed my machine to CNC milling machine with H-bot system.
Then since 2 months ago, I have adopted my control system from Arduino to Linuxcnc, because Arduino based firmware has many leakages for CNC motion.

Regarding H-bot(Core-XY) system,
as you know, it has coupled joint of X and Y axis by one timing belt. If you want to move tool head in X or Y direction, it should drive X and Y motor at the same time. If not, it's tool head will move diagonally. Simply, it need to drive 2 motor(X and Y) at the same time.
For this reason, I already installed the core_xy kinematics component to Linuxcnc system as refer this topic.(viewtopic.php?f=15&t=2154, CoreXY + LinuxCNC (PopFab).)
Finally I've got the proper movement of tool head using Core-XY kinematics with Linuxcnc controller. (only world mode)
Thank you cnc-club members for offering Core-XY kinematics.

However, the problem is that, before homed all axis (joint mode), Linuxcnc allow to move only one axis movement.
In case of H-bot(CoreXY), at start of operation, when I press X home button, H-bot machine's X and y axis move diagonally because Linuxcnc drive only X motor.
So, machine's gantry will press the unwanted homing switch, Linuxcnc shut down the machine with Error message.
Currently, I've only driven my machine in world mode with No homing sensors. This mean is that my machine don't know the tool's exact point in XY work area.
I plan to adopt tool change and length measurement automatically during PCB milling, so my machine needs to know the tool head's exact position.

I would like you to share your ideas that solved this H-bot system's homing problem.
- Is there method to allow to follow the kinematics in joint mode?
- Is there method to find the exact XY point using home or limit switch after homing in arbitrary point?

( Googling youtube about Linuxcnc delta kinematics robot, also some delta bot performs homing sequence in joint mode!!
But I don't know how they can..)

I'm looking forward your reply and comments.
Thanks in advance.

P/S: As reference, in my blog page ( http://dreammakercnc.blogspot.kr/ ), you can see my Micro-CNC machine.
Korean blog page: http://blog.naver.com/jhlee98n
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Need help Linuxcnc homing sequence in H-bot system DSC_1835수정.jpg
my H-bot system
jhlee98y
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Re: Need help Linuxcnc homing sequence in H-bot system

Сообщение PKM » 02 окт 2014, 05:16

Hello and welcome!
You can use HOME_SEQUENCE in each [AXIS] section to home both joints simultaneously. Did you try that?
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Re: Need help Linuxcnc homing sequence in H-bot system

Сообщение jhlee98y » 03 окт 2014, 00:48

Dear PKM, Thank you for attention and kind reply.

Just now, I tried to set HOME_SEQUENCE = 1 for [AXIS_0] and [AXIS_1] and then I pushed "Home All".
ONLY X axis was moved toward Min Limit SW and STOP!! GOOD!! Linuxcnc drived X and Y axis motor at the same time!!

Although "AXIS" displayed the same value for X and Y posion during only X movement, my machine successed homing to its Limit.
(I don't know, while motor driving is correctly follow the kinematics, why AXIS don't know the kinematics in homing sequence.)

Currently X limit homing was success but Y axis went wrong direction( Y goes to MAX direction).
So I need more try and investigation.

Again thank you for your replay and help.
jhlee98y
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Re: Need help Linuxcnc homing sequence in H-bot system

Сообщение Nick » 10 окт 2014, 17:31

jhlee98y писал(а): but Y axis went wrong direction( Y goes to MAX direction)

just change sign of the home search velocity to negative.
Use the Console, Luke.
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