Encoders - need REALLY basic info (resolved)

[ScotY]

I saw the Encoder basics thread but it's really kind of over my head. I understand the theory of an encoder (very basic theory) but nothing much beyond that. I'm looking towards the future and want to purchase a second Acorn for my mini lathe. It currently uses a simple Hall sensor for rpm sensing for threading (using Mach3) and it works but I realize it's not ideal. Anyway, I'm hoping someone can educate me regarding the proper type of encoder for use with the Acorn, how to hook it up, and also where one can be purchased (or DIYed) for a reasonable price. I noticed the encoders on the Centroid website but they are quite expensive for just a hobby machine and I believe those are more for servo motors rather than spindles.

Thanks, Scot

[martyscncgarage]

This would work, but would need a cover to help keep dust and liquids out. They sell medium duty ones that are more robust. www.adcpn.com/pn/TRD-SH2000VD
You want inexpensive that works, here you go. You need to belt it at 1:1 with a set of timing pulleys directly to the spindle.
With lathe it will give you the ability to do ACCURATE threading, rigid tapping and constant surface speed. On a mill, you would have the ability to rigid tap.

BUT! Your machine needs to have good tight mechanicals! Typical of a manufactured CNC machine. Can't blame the control for a machine using regular acme screws, no anti backlash nuts etc....

Marty

[762x51]

Marty - You need to edit the link - It isn't working

[ScotY]

I noticed that also but this is where he's sending us to:
www.adcpn.com/pn/TRD-SH2000VD

I'd like to find something smaller as it's for a mini lathe and there's not a lot of room under the cover. There are smaller encoders that are a little over an inch OD but they are maybe ~1000 count or so. What I'd really like to do is have some sort of slotted disk on the back side of the spindle and a sensor that sits on the edge of the disk. That would be much easier to install but it seems there may be no such thing.

I found this thing that appears to have all the right wiring coming out of it...I think. However, I'm assuming it has but one magnet on the part that would attach to the spindle. Somehow it outputs 1024 counts/rev. Experts, please have a look and tell us what you think.

[martyscncgarage]

I noticed that also but this is where he's sending us to:
www.adcpn.com/pn/TRD-SH2000VD

I'd like to find something smaller as it's for a mini lathe and there's not a lot of room under the cover. There are smaller encoders that are a little over an inch OD but they are maybe ~1000 count or so. What I'd really like to do is have some sort of slotted disk on the back side of the spindle and a sensor that sits on the edge of the disk. That would be much easier to install but it seems there may be no such thing.

I found this thing that appears to have all the right wiring coming out of it...I think. However, I'm assuming it has but one magnet on the part that would attach to the spindle. Somehow it outputs 1024 counts/rev. Experts, please have a look and tell us what you think.

Might work. It looks to be an Incremental/Differential encoder.
Try it and report back. I'm curious how you would attach it to the SPINDLE.
Interesting little device.

Marty

[ScotY]

It only costs around $35 so might be worth a try. The mini lathe has a little exposed thread on the back side of the spindle...it's about 28mm or so. My thoughts were to make a threaded cap with a magnet in it and then just mount the circuit board on standoffs above it. This will then make it impossible to pass long stock through the spindle.

I'm not really sure how that encoder works. If it's just a single magnet and a single sensor on the board, I suppose there's no reason why you couldn't make a threaded ring with an embedded magnet and flip the PCB around so only the sensor is over the ring...the majority of the board off to the side. Then long stock can pass through.

I'm hoping the Centroid guys comment on Monday when they return to the office. Would be nice to know what they think. It sounds a little questionable.

[martyscncgarage]

I understand you have space constraints. I would use a regular encoder with timing pulleys belted at 1:1

You should search to see if you can find pictures or video of that encoder you found mounted to a spindle.

Good luck.
Marty

[ScotY]

I've searched a bunch already and seems like no one uses them. But when you're talking about a hobby oriented product like this (and Mach needing just a simple hall sensor for threading), it's no big surprise they aren't being used.

Unless I'm not understanding how that thing works, it's kind of miraculous that it can use one magnet and somehow come up with ~1000 counts.

[762x51]

I've searched a bunch already and seems like no one uses them. But when you're talking about a hobby oriented product like this (and Mach needing just a simple hall sensor for threading), it's no big surprise they aren't being used.

Unless I'm not understanding how that thing works, it's kind of miraculous that it can use one magnet and somehow come up with ~1000 counts.

I agree that you don't see them being used on CNC equipment and this is because of accuracy. I looked at a Omron hall effect encoder and it's rotational accuracy is +/- 0.010" and the Omron is much higher quality than the ENI-1024 sensor. If all you want to measure is RPM then this would probably work OK but for threading then you want as high an accuracy you can get, especially for the index pulse. If the index pulse drifts then your threading results will be poorer.

Yes, I'm sure that the ENI-1024 will work - to an extent.

I also think the ENI-1024's 1000 count output is produced by a pulse generator that is triggered each time the magnet passes the sensor. This is just a guess but I'll bet that is how it works.

Here is a link to the Omron encoder ($27.09) http://www.mouser.com/ProductDetail/Omr ... 7gQAvD_BwE

[martyscncgarage]

Centroid put on a real encoder port on Acorn....for a real encoder. They recommend 2000 line which is 8000 counts per Rev after quadrature.

Anything else is experimental.