PF755 Electronic gearing sync problem

[lftmx3]

I have set up a 755 with dual encoder board to follow a filler drive motor position on a bottle filler and capper machine. The master encoder is mounted to the motor shroud of the filler. The slave encoder is mounted to the shroud of the capper. The 755 drives the slave (capper).

I used RA technote QA13283 as a template in setting up. I have everything running now, but the capper is gradually drifting out of time and has to be corrected by using an HMI button I added that momentarily adds an integer to the position offset velocity parameter in the vfd through a datalink.

If the capper drive is strictly following the position of the master encoder now, what should I be looking for as a cause? Would have to be a mechanical slop issue or could it still be a VFD setting issue? Many thanks

 

[Steve Bailey]

A geared axis "gradually drifting out of time" suggests to me that there is something not quite right in your calculation of the ratio between the master and slave axis.

 

[DarrylR]

Thats correct. You should look at your ratio setting and master/slave encoder counts.

 

[lftmx3]

Ok, looks like we will be changing gearboxes then. The one on the filler has no part# or nameplate, all totally worn off long ago. I was entering my gear ratio based on the part # spec’d in the 25 year old drawings…

 

[lftmx3]

For anyone that may randomly be attempting a similar feat in the future, the solution for me was to avoid rounding the EGR numerator/denominator equations as much as possible (pf755 allows 6 places). That’s param 816 and 817. I had originally rounded to two places and apparently it was not giving the drive the granularity it needed to maintain accuracy.