Spool Servo?

Greetings,

I want to install a spool at each end of my machine so that I can cut fabric as long as the spool of fabric.

Since the diameter of the spool decreases slightly with each revolution, it seems that I will need to put a roller with an encoder that the fabric is feed through to count the length of fabric being fed. I suppose the spool servo would still need an encoder on it.

Is it possible for Axis to rotate a spool to feed fabric before each set of cutting commands? The number of rotations commanded to the servo that controls the spool would be based on readings from the roller encoder measuring the length of fabric fed.

Anyone do anything like this before? Any hints/tips/advice appreciated!

Thanks!

I guess that would work. You don't need an encoder at the servo, tacho+hal or resolver would be enough. Just use the roller with the encoder as the position feedback.
Possible problems:
Tuning the axis might be difficult if the diameter and weight of the spool changes a lot. Not a big problem if there's a gear reduction from the servo to the spool.
Edge cases might need special care. E.g. an empty spool will result in a following error.

Shu wrote:

I guess that would work. You don't need an encoder at the servo, tacho+hal or resolver would be enough. Just use the roller with the encoder as the position feedback.

Thanks for the info. I've never used a tacho+hal before, what does that setup look like? What is the difference between a resolver and an encoder?

If the roller encoder is used as the position feedback, how does the tacho or resolver tie into the configuration?

Shu wrote:

Possible problems:
Tuning the axis might be difficult if the diameter and weight of the spool changes a lot. Not a big problem if there's a gear reduction from the servo to the spool.
Edge cases might need special care. E.g. an empty spool will result in a following error.

Good point, I better gear it down a bit, maybe 4:1? An empty spool following error wouldn't be an issue since at that point the spool is empty.

andypugh wrote:

Typically it would be the feedback for the servo drive, and wouldn't necessarily need to go back to LinuxCNC.

That makes sense, brilliant. Thanks for your help!