[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 :wave:

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 :cheers:

John

[ataxy]

yep same here not sure what you mean

[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]

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]

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]

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

[turmite]

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

It's already been done and available for 50 bucks from Geekware Inc.

I'm sorry, but I just couldn't pass that one up. I can tell you that not only what you have planned has already been done, but done using dual encoder feedback on 6 axis with position correction on the fly! It is not 50 bucks though! I will tell you this though, I have seen a video where the developer places his hand on his mill and pushes on an axis and you can hear the steppers moving to correct the position, then when he takes his hand off, you can hear them correct again.......or I should say, you can hear them end correction!

BTW nice work!

Mike

[cozymkiv]

It's already been done and available for 50 bucks from Geekware Inc.


Mike

Do you have a link to the website you mention above?

hennie

[turmite]

Do you have a link to the website you mention above?

hennie

I do, but I don't have permission to post it since it will be announced here hopefully early this week. I will try to get permission to post a video but that will strictly be the developer's call.

Mike

[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]

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.

[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

[Pres]

Congratulations Robin on accomplishing what you have.

I particularly like the caliper extension board that gives a decent cable connection.
-Much needed.
Would you provide details on how it was done? (like a pic w/cover off or ??)

Keep up the good work.

Pres

[Robin Hewitt]

Would you provide details on how it was done? (like a pic w/cover off or ??)

Pic with scale in upside down attached.

The scale connects top left hand corner, if you use fine wire you can snap the plastic cover back over the top so it all looks neat and tidy.

The chip nearby is a high impedance input comparator which buffers the clock and data lines.

Lower down a pair of opto slots do the end detection.

I'm reworking this one to

[Oldmanandhistoy]

high impedance input comparator

Oh the old "high impedance input comparator", if you said that in the first place no one would have gotten confused. :wee::drowning:

Nice job mate, now how much do they cost?

[Robin Hewitt]

Oh the old "high impedance input comparator", if you said that in the first place no one would have gotten confused. :wee::drowning:

Nice job mate, now how much do they cost?

A comparator is a very simple device. Basically it has two input pins and one output. It compares the input pins. If the plus input has more volts on it than the minus input then the output is high. If the minus input has more volts then the output is low. High impedance means it doesn't draw any current on it's input pins so it doesn't flatten the battery in the digital scale.

I used an expensive TLC372CD dual comparator (two comparators in one pack), £0.45 plus tax from Rapid Electronics, cheaper if you buy ten

[Oldmanandhistoy]

A comparator is a very simple device. Basically it has two input pins and one output. It compares the input pins. If the plus input has more volts on it than the minus input then the output is high. If the minus input has more volts then the output is low. High impedance means it doesn't draw any current on it's input pins so it doesn't flatten the battery in the digital scale.

I used an expensive TLC372CD dual comparator (two comparators in one pack), £0.45 plus tax from Rapid Electronics, cheaper if you buy ten

Thanks for the explanation; I’ve learnt at least one new thing today. :cheers:When I mentioned cost I was asking the total cost for the set up not just the comparators

John

[mikehg1]

Is that some type of universal proto board ? Seems like a LOT of connectors on there!
I did about the same for my mill just for the readout. I used an 8pin AVR chip for each one that did away with the need for any extra circuitry for reading the signal. The AVR has a built in analog comp with a 1.1V ref available, works like a charm!

I just soldered the wire connections directly on mine, but have been meaning to make some real plug-in connectors since I now have PCB making capabilities.