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Mach3 Homing Algorythm
« on: November 18, 2007, 06:39:56 PM »

I am building a CNC machine of my own design, and plan to run it under Mach3. I am currently working on the home and limit position switch system. To ensure the most effective switch placement, I need to know what to expect from the program using the actuation information (Mach3).

As I understand it, CNC machine homing switches are normally first actuated and then de-actuated to complete the home cycle. That is not a problem, if my understanding is correct.

I am using three mechanical switches per axis, one of which is for homing. Limit switching is not an issue as they are located at the limits of travel. Home switches are not at the end of travels, and so become more problematic. The home switches must be actuated from only one direction during the homeing cycle to be consistently repeatabe.
 
I am assuming that Mach3's homing routine takes this into account and approaches each switch from only one direction, but I am only guessing, and need to know for sure which direction it is for each axis.

So, the problem is in understanding (exactly) how Mach3 determines the home position. For example, From any positive or negative X,Y, or Z location on the table, will the homing travel path go first to a positive (or negative) position, prior to approaching the home switch for its initial actuation?

Hope my question is clear...

Thanks, and Regards,

Roger

 

vmax549

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Re: Mach3 Homing Algorythm
« Reply #1 on: November 18, 2007, 08:54:58 PM »
Yes mach approaches from only one direction to home BUT that direction can be set in config. The problem as you know with a midrange home switch is homing from the backside of the switch position that is opposite from the configured direction. It will just run till it hits the opposite limits.

I " think" an approach PATH  can be configured through the script that runs the home sequence BUT I have not tried it myself. You would want it to run in Machine COOR to ensure it went by way of the exact path each time regardless of fixture or work offsets.

(;-) TP

Offline Greolt

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Re: Mach3 Homing Algorythm
« Reply #2 on: November 19, 2007, 02:31:06 AM »
Roger having a home switch in some position other than one end of axis travel is often desirable and Mach can handle it no worries.

What you need is a system whereby the home switch is activated all the way to one limit of travel.

The principal is simple but my explanations are not always so.  :)

As example I have a mill on which the home switch is toward the middle of the X axis travel.

It is a photo interrupter. So it has a tab that goes through the slot and activates the switch.

Now the thing is that tab extends all the way to one end.  The X zero end.

When Mach is told to find home it knows whether this switch is active or not.

If it is already active Mach seeks home in a positive direction.  If it is not active then it seeks home in a negative direction.

There is a setting on the General Config page called "Home Sw Safety" that needs to be unchecked.

And enter the value you need in the "Home Off" column in the "Homing and Limits"

It works well.  I hope this is what you were asking.    :D

Greg

EDIT:  Just to add if using roller type mechanical switches then you would have a ramp to activate the switch.

      This ramp then needs to extend all the way to one end of travel.
« Last Edit: November 19, 2007, 03:01:31 AM by Greolt »
Re: Mach3 Homing Algorythm
« Reply #3 on: November 19, 2007, 12:17:31 PM »
Greg,
You are to be COMMENDED on your explanation !
Thanks

vmax549

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Re: Mach3 Homing Algorythm
« Reply #4 on: November 19, 2007, 04:53:07 PM »
THERE you go, we learn something new every day(;-)
Thanks Greg,

(;-) TP
« Last Edit: November 19, 2007, 05:44:27 PM by vmax549 »