About homing and limit switches .

[stragenmitsuko]

I'm designing a 3 axis stepper controller to be used on a gantry router
and controlled by Mach3 . It has full manual control with jog buttons for
each axis , and an array of PLD inputs wich are wired to each stepper driver and to the DB25 . I can virtually program any logic function between any input and output . The idea is to make it all fit an eurocard size pcb , wich is ideal for pcb drills and small routers .

Now , I've got inputs for two limit switches on each axis , and if needed an extra optical home switch .

The limit switches are combined into the pld , and will halt stepper motion on their axis , and only for the concerned direction . Example X+ limit switch activated will block further motion in X+ direction , but will not affect X- direction or the other 2 axis .

So far so good .
But what I don't know is : what do I tell mach3 , and how do I do that .

5 inputs are available on the db25 .
One for the e-stop
One for the z-axis optical home switch .
wich leaves only 3 .


I could wire all six switches into an or function , and mach 3 will know when a limit is reached . But then I can't use them as homing switches . Because teher's no way to tell wich axis has reached the home position first .

I could also wire them into two combined and functions , then the homing will work , but then mach 3 won't know if a single limit is reached .

The extra home on the Z-axis is a highly precise optical device , wich I would like to use to determine tool height relative to the T-slot table after a tool bit has been changed .
Tool bit change would require the machine to move to a predefined position , X+ and Y+ limit , raise the tool to maximum height ( Z- limit ) and then wait .
After the tool change , the z-axis should move very slowly , without the spindle activated , until it presses the optical Z home .


Does that sound OK ? I have no experainace with mach or any other cnc software .

Thx for any advice .


Pat

[Torchhead]

You can actually wire all of the switches to one pin. MACH does a home sequence in a specific order and predefined direction so it see's the first switch closure as the first axis in the homing sequence, etc. Conversely if you are not doing a Homing move and have the switches all mapped to the one pin, if you hit one (any) it assumes a limit and stops all motion (Flips reset button).

Manual buttons for jog control (outside the control software) are counter productive. The machine has no position feedback and loses position. All of the tool height stuff can be done in MACH with macro's or if you are handy with C++ a custom plug in.

[stragenmitsuko]

I see .
So the Z-axis could move first until it hits the switch , then back off a few steps until it deactivates . This way the tool bit will be in a safe position .
Then move the Y-axis , same procedure , and finally the x-axis .

Do I understand correctly that the home and toolchange
protocols can be written or customized by the user ?
That ofcourse would open a lot of perspective .

Thx for the reply
Pat

[ger21]

Originally Posted by stragenmitsuko Do I understand correctly that the home and toolchange protocols can be written or customized by the user ? That ofcourse would open a lot of perspective . Thx for the reply Pat

The tool change could be completely customized via a macro. You can't change the homing routine itself, but you could call individual axis in any order via a macro.