LINEAR encoder

[Martin Zarnay]

Hey guys,
I've just been in conversation with one guy, who loves MASSO controller, He´s had his version and I´ve had main.
I´ve been using an offline controller for a while, and it is a great system, but still believe in PC base as batter choice, with a LOT of expansion.

I'm using acorn at this time and want to stick with it for a long time as I love it!
BUT
I would love to see some kind of truly closed-loop system on it, I know that you cant plug linear encoder to the board, but it is possible to
connect the linear encoder to DB25 ( with some kind expansion board ) or to Ethernet ( similar as 16IN 16OUT board ) ????

If you guys in centroid would designe something like that, I would jump on it like crazy!!

[Muzzer]

Closing the loop like this sounds like the answer to lots of problems but if you are actually trying to overcome nonlinearities such as backlash (wear), it's no miracle solution. Introducing hysteresis into a linear control system makes it almost impossible to stabilise, so unless your mechanical system is well set up, I suspect you'd be disappointed.

I believe it's possible to close the loop externally like this using the Oak(?) but for most of us, minimising mechanical backlash and then closing the loop at the motor spindle is perfectly adequate. Perhaps Keith will tell us about the requirements and limitations of such a system?

From what I've seen, the latency (speed) of the Ether1616 inputs would be FAR too slow to be useful in a servo system.

[martyscncgarage]

It's called Oak....
Its not likely to happens with Acorn.
If you want closed loop at the Acorn price range, buy closed loop drives and motors that accept step and direction(there are a lot of them out there). Much better than an open loop drive/motor system.

Marty

[tblough]

Centroid has already designed that. Both the Oak and AllIn1DC do full closed loop with linear scale feedback. I am running an Oak with glass scales on my lathe, and a AllIn1DC with scales on my mill.

[martyscncgarage]

Just to clarify, OAK drives external stand alone motor drives while All in One has 3 DC brush servo drives built on.

[kevincnc]

Martin, have you seen this drive? You can have an encoder on the motor plus a linear scale for better accuracy/performance (according to them.)
https://www.machdrives.com/bra.aspx
Kevin

[martyscncgarage]

Martin, have you seen this drive? You can have an encoder on the motor plus a linear scale for better accuracy/performance (according to them.)
https://www.machdrives.com/bra.aspx
Kevin

As far as I am concerned, DC Brush servos are old technology. At the price point of $349 per axis, I would much rather buy the Centroid All in One DC if I had to drive DC Servos. AC servos are current technology.
Marty

[kevincnc]

I think you're right, it would depend on what you already have.

[Martin Zarnay]

Hi guys
Thank you for your messages I do have closed-loop hybrid steppers on my machine and I'm good with backlash too,
Why i was considering true closed loop is that my ball screws are just rolled ones. and when I tell a machine to go 15cm it goes 15.00
but when I tell it to go 40 cm it goes 40.02

And also I thought Centroid could do some more money to release new products for Acorn users...

[tblough]

If every thing else is working, just implement ball screw error compensation and that will take care of the errors in a rolled ball screw.