OpenPnP with LinuxCNC via linuxcncrsh?

phillc54 wrote:

LinuxCNC would know which direction to home dependent on whether the home switch was activated or not when homing commences.

 

Assuming you had a home switch that stayed in contact the whole time (or at least most of) it was beyond one side of home.  The picture I posted was just an example of the way one side extends while the other retracts. Most of them are belt loops and are hard to add home switches to (like mine)

Definately getting away from the point of the post......lets bring it back now.
 

I had previously mentioned that I was looking for an alternative to the see-saw approach because of the homing problem. With any system, you can't move anything unless you know it is safe to do so and driving Z down on a PNP without knowing where the axes are is unsafe.

plhsystems wrote:

I had previously mentioned that I was looking for an alternative to the see-saw approach because of the homing problem. With any system, you can't move anything unless you know it is safe to do so and driving Z down on a PNP without knowing where the axes are is unsafe.
 

Yeah I spent the last 5 posts trying to explain that. Anyway, the potentiometer approach seemed like such a good idea I changed 2 of the analog inputs on the PCB I'm working on from vacuum sensors to  connectors for a potentiometer.

I think I like your previous idea of having a switch permanently made when the axes is not at home and someway down. That way, you could use two switches (one for each side) and have the centre point where neither switch is made and hence home. So homing would be simply:

• See which switch is made
• Move that side so that it goes up
• Stop when the switch in no longer made

And as long as the switches are at the same height, finding the true centre point wouldn't be too hard, just halve the distance from when the switch on one side releases to when the switch on the other side makes.

1 switch + home_offset will home it anywhere, including in the middle.
As for precission, it uses a stepper with a pulley directly driving heads, so even a cheap microswitch will be more precise than the drive parts.
Using an optical switch and a 0.9 degree motor seems better for accuracy, as there is no need for a lot of torque, and this is for very small parts.

Excuse my lack of knowledge, but I'm not sure what you mean by home_offset, unless you mean you move to the switch and then offset from the switch, but this won't work. In this instance the home switch is in the middle of the axis, if you don't know where you are on that axis, how can you know which direction to move to get to the middle? You can't have the switch at either end of the axis because this risks plunging one of the nozzles into the bed.