CSMIO/IP-M and slave axis functionality

[Jonathan]

Measuring gantry squareness seems like the biggest issue rather than tweaking switch positions and that's common to all setups. However, I'm not sure that I could use those values in any of the usual solutions, so the straight hardware-based "tweak switch until dual-homing leaves the gantry square" solution seems inevitable.

You can measure the squareness of the gantry as follows:

1. Use the machine to drill 4 holes at the corners of a square (or rectangle), e.g at (x,y)=(0,0);(0,100),(100,100),(100,0).
2. Measure the diagonals of the square/rectangle accurately.
3. If the diagonals aren't equal, your machine isn't square, so either draw the actual dimensions in a CAD program to find how far from perpendicular your axes are, or just calculate it.
4. Offset, and try again... repeat until you deem it square enough.

I find that drilling 4mm holes in a piece of MDF, then pushing 4mm drills into the holes and measuring the center distance with a digital caliper works well and is repeatable. Since I don't have limit switches (a case of a few years ago 'oh it works, time to use the machine now not carry on with wiring'), I just make marks on each rotating nut which align with a mark on the housing when the gantry is square. Then I check that the marks are aligned when I switch the machine on - I can see if the marks are out by about 1/4 of a step, so it's accurate. The machine stays square when switched off unless accidentally knocked...which is fair enough really. If I crash it then I do the above squaring procedure and I do it every 6 months or so just to make sure.

Anyway...

The principle with Arduino's is they provide you with an extensive library of functions that make it very easy to code things as it adds an abstraction layer between the user and setting the microcontroller registers. For that reason I tend to dislike Arduino's because the built in functions limit what you can do to fairly simple stuff, so you end up having to program the microcontroller directly and therefore might as well do that from the start. However in this instance I think it's simple enough for the Arduino language to do what we need. Also, you don't need a programmer (Pickit or whatever) as they program via USB.

The way I envision is for the Arduino to send the step and direction signals to the two X motors and read the limit switch signals, so it takes control of the machine to make it square, then leave the X axis in the home position. The normal machine controller can then take over. We could add potentiometers to set the feedrate and acceleration for homing, or just leave it in software. One extra input for e-stop I guess...

So I think it's worth me acquiring an Arduino and trying it, then I'll post the code and wiring diagram here. Not sure how long it'll be until I have chance to do it, but if someone who already has home switches is willing I'll happily help them wire it up and program it over Skype. One of these should suffice. Jazz could also use it for this.