Encoder Issues, Help!

Over the holidays I powered up my Bridgeport Interact mill refit. Great progress, all of the controls work, servos tuned and no smoke or crashes.

I decided to check the encoder scaling and bad news. I discovered that the scaling is way off. A distance of 1" on the DRO ended up being an actual distance of only 0.6". I re-calculated the encoder scaling again and again and could not find an error. With nothing better to do I multiplied my calculated encode scale by 0.6 and tried it again. To my dismay the scaling is now quite close but it is not consistent. Every time I check it is off 0.003 to 0.010" . I determined that all 3 axis have the same problem and essentially the same magnitude of error. Each axis a stoke of +- 1" ends up causing the position to drift about 0.001" for each round trip. The actual stroke is sometimes spot on and sometimes it's off by up up to 0.003". Everything else is working perfectly. No following errors and motion is smooth and quiet.

It seems that the only way this could happen is if there are extra, spurious encoder pulses. It could be noise, but the results seem too consistent. The results are consistently off, but only by a little. I tried turning off the encoder filters and if there were noise issues that should have made things worse, but there was no change.

Here are a few details about my setup.
Heidenhain ERO-115 encoders
Heidenhain EXE 602D interpolators (configured for 5 fold interpolation)
Mesa 7i77

The encoders have 115 pulses per rev, and with 5 fold interpolation it should have 625 pulses per rev. There a 2:1 motor to ballscrew ratio and I have 5mm ball screws. According to my calculations the encoder scale should be 25400. 15377 is what gets me close to the right scaling.

I am out of ideas and would appreciate any suggestions.

if you can do a very slow move, (and you are running LinuxCNC 2.7.X) I would plot the actual A,B signals from the interpolator.
sounds like the quadrature output is funky somehow (wrong interpolator input settings?)

You can also enable and check for quadrature state transition errors by setting each active encoder channels
quadrature-error.enable bit true and monitoring the quadrature-error bits

Thanks PCW for the suggestion. I set the quadrature-error.enable bit to true and monitored for errors and there were none. I did a very slow move and monitored the A B signals and they are clearly bogus, see the attached halscope screenshot. It's odd that no errors were triggered. Since all 3 of the EXE602's are showing the same symptoms it must be a configuration issue. I carefully read the manual and made the settings, but obviously something is not correct. Thanks for getting me on the right track.

Chris

I ran in to this while I was doing some heidenhain research of my own. From the post it doesn't sound like your dealing with a standard interface signal

www.practicalmachinist.com/vb/cnc-machin...oders-anyone-120852/

I re-checked the documentation and blindly played with the 5 jumpers in one of the exe 602s. The first two jumpers are suppose to select 1 or 5 fold interpolation. Selecting what should be 1 fold should work but the scale would be off, but I get an immediate following error so the manual may not be correct. I am going to connect a scope and use the handwheel for input to really pin down what is going on. I'll post my findings.

Tonight I got my interpolators working.
I blindly changed jumper combinations and scoped the outputs and found a few combinations that work correctly. The combinations that work are wrong according to the manual so this is a documentation issue. I'll call Heidenhain tomorrow and see if they some better information.

now the question is Make Notes !, and dont loose it .

So what was the "correct" settings for you? Was Heidenhain able to help you out?

I heard back from Heidenhain and they provided the correct settings. These settings match up with my blind experimenting. The settings in the manual titled EXE 602D EXE 604C EXE 605S dated 2/2003 are absolutely incorrect and do not work. Here is what Heidenhain tech support sent me:

Awesome! I'm glad it worked out for you. Thanks for posting the correct settings.