So you power over Vneg/Vpos and use a cap as the battery?
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My first mill is a First mill
- Thread starter PaulL
- Start date
Yes. And to avoid electrical interference, inside the DRO-350 is this regulator circuit (power.pdf) which produces the 1.5V needed for the scales. Here are the fake batteries.
The DRO-350 was only capable of working with this type of scale protocol. Not even sure these types are available anymore. Scott did have a module that converted quadrature to the Chinese format.
The DRO-550
Can handle either type of scale.
Oh and there are a number of circuits using PIC processors to combine two Z axis. Essentially wind the knee up creates pulses similar to bringing the quill down. And the other way too.
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The scale protocols do seem to be pretty straightforward - very much possible even bit-banging on a low-end Arduino.
That said, I went searching, and of course this is all integrated now, including the Hall sensor array and amplifiers: https://ams.com/en/as5306
So there's nothing left to do, and I'm discharged from having to think about how to build one ;-) Unless I find myself short on projects.
Very interesting. Thanks for this Paul. I had wondered about a chip vs discrete components. This answers that. Of course, it's a Block Diagram of the AS5304/6 chip function. I will have to see if I can find an Applications Guide to go with it.
The accuracy and repeatability of my 1 uM scales is nothing short of hard to believe. It does tend to give one very high confidence in the output though.
My readout box can be programmed for different scale resolutions but not scale size. This makes me suspect that the AS5304/6 chip itself is in the read head and the read head is matched to the scales and the output is universal. But I don't know that for sure. The magnetic scales and magnetic heads might be interchangeable too.
The gain feedback explains the relatively high tolerance to the gap between the strip and the read head. It either works or it doesn't and no adjustment other than the gap itself is possible. I had wondered how that was possible if there were no smarts in the read head itself. Now I know that there probably is.
I assume that the purpose of the sine and cos functions in the chip is to calculate and linearize the phase of the input signals from the hall sensors.
I'm just guessing here from experience that the over-reaching objective was to always have access to a fast changing signal sensitive to displacement. This is much more easily done from a phase measurement than raw amplitude. But again I'm just volunteering an educated guess.
Like you, I'm not sure its really worth any more digging. I don't plan to make scales or read heads.
But if anyone finds additional info, I'm interested in learning.
Edit - never mind. All the application info is available at the link you provided above. Lots of reading. Thanks again Paul.
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Dabbler
ersatz engineer
One of the guys on HM builds his own DRO for each machine, by buying the components separately. Apparently there is only one place that makes all the magnetic rubberized tape, and it is adhesive, so he sticks it to a flat part of the machine itself. He buys read heads from a second place and the head units elsewhere.
He has been in the CNC/retrofit workspace doing this professionally for 35 years, so he's kinda got it down pat. If I do my 60" LeBlond, I'll be getting his help, as it will save me a lot of money.
He has been in the CNC/retrofit workspace doing this professionally for 35 years, so he's kinda got it down pat. If I do my 60" LeBlond, I'll be getting his help, as it will save me a lot of money.
Very elegant. My magnetic strips are indeed just taped into an extruded aluminium channel with double sided adhesive tape. As long as the base machine is truly flat, that should work great! Way easier than mounting an aluminum channel.