What an astonishing device, Joe

Being dim … I am struggling with the concept of:

[quote]

Incremental movements are indicated on a set of ABI signals

with a maximum resolution of 4096 steps / 1024 pulses per

revolution. The resolution of ABI signal is programmable to

4096 steps / 1024 pulses per revolution, 2048steps / 512 pulses

per revolution or 1024steps / 256 pulses per revolution.

[/quote]

…. being available from four Hall sensors and one rotating magnet.

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If you can spare the time; could you please explain that, in easy words of few syllables.

Meanwhile I will try reading the data-sheet again

MichaelG.

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Thanks for that

Yes, I am sure you are correct … 'though it still boggles my mind to think of 1024 steps being extracted from four analog sensors on that physical scale.

MichaelG.

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Thanks, Joe … Whilst I can accept the explanation, I must admit it's more a matter of blind faith than actual comprehension

I really can't get my old head around the idea of the 'virtual pitch' of this encoder being whatever tiny circumference, divided by 1024

MichaelG

Thanks again, Joe

I actually found that document late last night, but haven’t yet done it justice.

The ‘sensor radius’ for the 5147 version is given as 1.1mm

I am fine with the principle of operation, but; even as a microscopist, I find the ‘circular pitch’ of that virtual index wheel quite astonishing.

I calculate it as just under 6.75 microns … from a rotating magnet !

MichaelG.

Michael, maybe think of it in a different way. Imagine that the chip is a compass and the magnet the earth. We are quite blase about the idea that direction can be read to 1 degree from a compass scale, but the needle is doing exactly the same resolving of the magnetic field components as this chip. You could calibrate the compass to 0.1* and have a resolution of 3600 steps using a magnifier to read it. Or even have a vernier and read to 100th of a degree.

The same principle is used in the old "synchro resolver" system. This measured an angle with a rotor coil picking up a signal from two drive coils excited in phase quadrature, so the phase of the induced signal is essentially equal to the angle between the pickup coil and the "in-phase" stator coil. Analog Devices for one (used to?) make chips that could translate between the phase and a precision digital angle measurement.

This is also used in the Newall DRO system. The reference "scale" is a tube tightly packed with a row of precision steel balls, which is surrounded by a pair of pickups that are essentially differential transformers
( "LVDTs" ) excited in quadrature and generating sine and cosine signals that vary in relative amplitude depending on linear relative position. Though the ball diameter is say 5mm, a resolver can convert these into a micron-level position measurement.

The resolution all comes down to the number of bits used to digitise the amplitude measurement, so it's relatively easy in principle to resolve very small movements. The precision and accuracy however depends on many other factors, like the linearity of the sensors and A/D converters, electronic noise, geometry of the magnet and so on. Quite a lot of these depend on good design of the signal processing electronics in the chip. Given that the device will incorporate a processor and non-volatile memory, there is probably a calibration step in the manufacture where some parameters that affect accuracy and measured and compensation parameters stored.

Also think about your optical mouse: this can resolve a movement of 1/3000 inches for an LED type, or 1/15000 inches for a laser mouse, on any old desktop surface. The resolution in this case comes from the patterning of the optical sensor on the chip.

But if you looked at it with a x100 microscope?

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We are obviously at cross purposes, John

… I was trying to understand how they achieve it, with that device, and magnet rotating on a shaft.

Other methods are, of course, available but not at the size, convenience, and price of that chip.

I will quietly ponder, and refrain from further comment or question on the matter.

MichaelG.

I imagine the most critical properties are the alignment of the magnet and chip and how accurately the magnetic field is aligned in the magnet itself.

That's not bad, more than enough for a control and probably as good as using a potentiometer for servo applications, obviously less ideal as a precision position sensor although you could easily calibrate it against a conventional rotary encoder.

Does it just give a quadrature output or can it give an absolute one as well?

Neil

Edit … once the printer is working you could print a jig to hold the IC central whilst you solder it. Another use for 3D printing – custom index wheels and (relatively low-resolution) opto encoders (I once made an absolute 4-bit rotary encoder by photocopying the design onto acetate, for a wind vane, I used IR diodes from two dead computer mice).

Edited By Neil Wyatt on 09/09/2020 16:45:16

Sorry to resurrect a somewhat old thread but I just found this and it seems pretty impressive and also nice and small. I also see that RS sell a board with one already mounted (including a magnet).

I do have a question… I'm looking for something that can tell me the rotational position of a shaft on power up. Can these things do that or must they first be rotated to a zero position in order to 'find themselves' after power up?

Excellent, thank you Joe.

I think something like the AS5040 will fit the bill… a resolution of 1/1024 of a turn which is probably a good deal more resolution than I need for this project.

I will buy one to experiment with in my next RS order.