Encoder

I have a 5125 and a 7177 board. Has anyone used these encoders
www.digikey.com/product-detail/en/AMT103...08-ND/827016?cur=USD ?

Good, Bad? Recommendations? .

Thanks

Jeff

I think they are good, inexpensive, and flexible but are not the best choice for very high accuracy or high acceleration systems.

The limitations of this type of encoder are due to the fact that they generate their high resolution quadrature counts by interpolating from a relatively coarse code wheel. This causes two problems: 1. the angular accuracy is not as high as standard optical encoders, and 2. the interpolator has a slight delay in count outputs (in the order of a millisecond or two) during fast acceleration.

All that said, for a normal lathe or mill where accelerations are moderate
they are probably more than adequate.

Thank you for the information. This is all a learning curve for me. Is there one you would recommended?

PCW wrote:

I think they are good, inexpensive, and flexible but are not the best choice for very high accuracy or high acceleration systems.

The limitations of this type of encoder are due to the fact that they generate their high resolution quadrature counts by interpolating from a relatively coarse code wheel. This causes two problems: 1. the angular accuracy is not as high as standard optical encoders, and 2. the interpolator has a slight delay in count outputs (in the order of a millisecond or two) during fast acceleration.

I put up a comparison plot of the CUI AMT-103 against an old HP HEDS encoder,
where the scale is set to compensate for the encoder resolution.
pico-systems.com/images/compare_encoders.png
The red trace is the CUI, and it is in the servo loop. The white trace
is the HP encoder, which is giving the true reading. These traces are
velocity derived from the raw encoder counts. The horizontal scale is
20 ms/div. You can often see the CUI encoder is several ms late in
reporting velocity changes. This can cause major difficulties in
servo tuning.

Jon

So my next question. Incremental or Absolute encoder? Pro's Con's?

jeffie_3 wrote:

So my next question. Incremental or Absolute encoder? Pro's Con's?

What absolute encoder are you thinking about? What is the system
for reading this encoder into the computer?

Many absolute encoders have low update rates or limited spatial
resolution, while incremental encoders may not have those
problems. Also, incremental encoder are VERY standard, while
there is no standard at all for absolute. To be useful, an
absolute encoder pretty much needs to either be sent a sample
pulse to give valid data, or provide gray code data, which then needs
to be deciphered by the program. (The gray code only changes
one bit at a time, so you can't misread the code when several bits
change at almost the same time, as when a binary number
generates a carry.)

Where would you get an absolute encoder?

Jon

Thank you John. I don't have any particular encoder in mind. Over the past few years I have been reading and trying to understand all of this with the Linux cnc. I have an old mill I want to get running but seem to run into road blocks. Mostly my understanding on how all of this works. I'm just now taking a more active hands on approach to getting it running. So I am taking each step of it and reading thru it. I have bought the 5i25 and the 7i77 board. 1) 1200 oz 90 volt 6.6 amp servo d.c. motor, 3) 30A8T servo drivers. Now I am exploring the encoder part. 1 step at a time so to speak.
If any of you have suggestions or can point me in a direction. Please do. Someday I need all the help I can get.

Thank you,

Jeff