Chinese scales to position the tool

[Robin Hewitt]

I thought rather than just display the co-ordinates I should use the scales to locate the tool on the fly, so I made a computer to read them and move the table and everything else I could think of

Rather than burden the processor reading the scales directly I decided to do it in hardware. When the scale report comes in I just read 3 bytes on an interrupt and I have it. Only one scale wired in so far but it's reading and I have the result coming out on a serial line and it agrees with the scale

The prototype is looking a bit moth eated with all the modifications, but it works. It all wires up with cheap 8 pin patch cords so no problem if they get crunched.

The scales have pcb's screwed to them so the flea squeak signal only has to make it half an inch before it becomes a good solid 5 volts. They also have optical end detectors so I know where to zero it should the battery go flat.

Just got it reading the scale and felt like a quick whoopy doo because it's taken me weeks, thank you for reading to

[Oldmanandhistoy]

Hardly understood a word of that but nice job; sounds very useful

John

[ataxy]

yep same here not sure what you mean

[Hans_G]

I think Robin is explaining how he gets the measurement from the scale into his PC, meaning that the scale can be used as a cheap feedback device for closed loop position control. Neat idea to have the translation done w/ a separate micro. What is the update rate?

[Robin Hewitt]

Not really sure I know what I mean either

Here's the idea I had...

I've been positioning the milling table by turning the leadscrews very precisely and trying to minimise backlash, it works okay.

I had a notion that if the milling machine could read the table and quill positions independantly of the screws, it could position it a lot better.

So I'm making a computer board that accepts g-code, reads the scales, turns the handles, plus a few other things that I think might be fun such as a pendant, tool height and X,Y absolute position gauges.

It's okay to tell me that it's already been done and is available for 50 bucks from Geekware Inc. I won't mind

[Oldmanandhistoy]

Originally Posted by Robin Hewitt So I'm making a computer board that accepts g-code, reads the scales, turns the handles, plus a few other things that I think might be fun such as a pendant, tool height and X,Y absolute position gauges.

I understood what it does, it was just the how to build a computer board to do it that's beyond me. The words smart a** come to mind lol.

John

[Robin Hewitt]

Originally Posted by Hans_G IWhat is the update rate?

The scales normally update about 3 times a second but you can flip them in to "fast" mode which is about 50 per second. Step on report would give me a feed rate of about 0.25mm/s, not entirely useless I usually cut at around 1.2mm/s.

[Robin Hewitt]

Originally Posted by Oldmanandhistoy beyond me. The words smart a** come to mind lol.

Electronics is what I do for a living so I like what you're saying. If everyone thought it was easy I wouldn't make so much money

[Oldmanandhistoy]

Originally Posted by Robin Hewitt Electronics is what I do for a living so I like what you're saying. If everyone thought it was easy I wouldn't make so much money

It most certainly was not meant as an insult; you have my repect

[Robin Hewitt]

Originally Posted by Oldmanandhistoy It most certainly was not meant as an insult; you have my repect

In that case I'll let you in to the secret.

You use circuits you already know work where ever possible. If you have to break new ground you rough out a prototype and then bodge it until it works, cursing your stupidity at every silly mistake you find.

Then you re-make it perfect with the benefit of hind sight and never show anyone the original

[blades]

Very nice! I can certainly appreciate the benefit of reading table position directly, as opposed to taking table position for granted from the stepper motors.

[MIKE JEFFERS]

some people are far to clever enough