Roland Jollivet wrote: > > Thanks. And a curved ball; > Does the rotary encoder really have to be in sync with the linear scale? > I'm thinking of a small encoder that is geared up, off the motor shaft > (tenshioned/no backlash) > > No, it really can't be. You would never be able to sync up a linear scale and a shaft encoder on a ballscrew. Even minute variations in a precision ballscrew would get it out of sync at some point. > So now you have the rotary resolution, but the software would need to keep > zero-ing this counter, as it will have a poor tracking relation to the > linear sclae, but always yield maybe 5x the linear scale in resolution. > That is why you don't do it that way. You use the shaft encoder mostly for velocity feedback, and the linear for position feedback. The dual PID scheme that was worked out some years ago does this nicely. It would be nice to somehow merge the higher resolution of the shaft encoder with the accuracy of the linear, and maybe some makers do that. I think you'd need to map the shaft encoder against the full travel of the linear, and then have some sort of interpolated table to do the merge. As the leadscrew warmed up, this alignment could drift, too! It could, of course, be done in a new HAL component.
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