Spindle encoder options

[escott]

I am in the planning stages of upgrading a Denford Easiturn lathe from a parallel port BOB to the Acorn board. I want to use a Zettlex Incoder as the spindle encoder. This is available with two RS422 ABZ variants. The only difference appears to be the width of the Z index pulse (90 or 180 degrees). Would either choice be preferable for use with the Acorn?

The second choice is the resolution of the sensor. The 11 bit sensor will give me 2048 counts per rev. For a small additional cost I could obtain a 12 bit/4096 count sensor. My question is would there be any noticeable benefit from the higher resolution?

Thanks.

[Dave_C]

Do a search for Encoder Basics on this forum. It will save you a lot of trial and error!

Acorn boards have to have an encoder that gives quadrature pulses, uses 5 vdc, and has one z pulse per rev.

There just isn't any reason to try and get around it!

Dave C.

[escott]

Thank you for the response Dave. I have read the Encoder Basics thread and I believe the Incoder would be suitable. There is probably no real difference between the options I outlined. However, it is quite expensive so I want to pick the best option if I can.

[Dave_C]

Having spent months in "Encoder HELL", even after I bought a compatible encoder, I discovered that the cable on some encoder are not shielded twisted pair and I spent a lot of wasted time getting to the bottom the issue. I finally just bought the encoder and cable from Centroid and I never had any more issues!

I wish I had made that decision from the get go and life would have been much sweeter.

Anyway, the machine turned out to be a great CNC mill and I'm very happy with the Acorn board and the Centroid Software.

Centroid techs will talk to you if you need advice! Cheap is not always the lowest cost solution! Spend once and be happy!

Just my 2 cents worth.

Dave C.

[tblough]

Centroid recommends at least 1024 line encoder for spindles. From Incoder's data sheet:

10bits 1,024counts per rev 1265.6arc-seconds 6144micro-radians 256pulses per rev
12bits 4,096counts per rev 316.4arc-seconds 1536micro-radians 1024pulses per rev
14bits 16,384counts per rev 79.1arc-seconds 384micro-radians 4,096pulses per rev
16bits 65,536counts per rev 19.77arc-seconds 96micro-radians 16,384pulses per rev
18bits 262,144counts per rev 4.94arc-seconds 24micro-radians 65,536pulses per rev
19bits 524,288counts per rev 2.47arc-seconds 12micro-radians 131,072pulses per rev
.
.
.
10, 12 or 14bits = 6,000r.p.m. 16bits = 3,600r.p.m. 18bits = 900r.p.m. 19bits = 450r.p.

So you need at least 12 bits which also limits you to a max 6000rpm on the spindle. 11Bits is not an option for the RS422 output options. I looked at Incoders as well but ended up going with RLS magnetic ring encoders https://www.rls.si/eng/ring-encoders. Good luck.

[escott]

Thank you tblough. I read your excellent write up of the Bridgeport spindle encoder. It is a cheaper and easier to implement solution than the Incoder. You can add me to the list of people copying the idea.