Centroid Community CNC Support Forum

Checked my linear scale it does have a forth digit about half the size of the first three digits. The scale is only good to a half thousands so the last digit reads a 0 or a 5. When I took my readings it was always a zero

Russ

Well I decided to really clean up all the wiring on the Acorn setup to see if that addresses my accuracy issues. It could be noise impacting the Acorn, because I have been checking everything else and can't figure out why it does not work correctly when cutting a file.
I have been ensuring that I have proper grounds and installed a 1/4" sheet of aluminum that was grounded and mounted the AC servo drives to this plate. Then I installed another EMI filter on the AC power coming to the drivers. I also used shield over the AC line coming to the EMI filter and grounded the shielding and the ground wire to the plate. I have zero ohms to the ground contacts on the drives, but I am still going to hall individual ground wires from the servo drives back to the Star ground connection inside the Acorn cabinet.

What I did not check was if when running my 4KW water cooled spindle if I was getting enough noise to cause additional steps. Strange I can install a parallel port breakout board hanging in mid-air and it never misses a beat. Once I finish cleaning up and shorting all wires I will put on the cabinet door and run the gcode file again cutting plastic to determine if I have found the root cause of my issues. Ugh

Russ

Well after a week of cleaning up all my wiring and putting in braided shield on everything to ensure noise was not impacting the Acorn I still have issues. I currently have EMI filters on my servo drive source power, the Acorn power, and the VFD.
All of the cleanup effort was not a waste of time everything is nice and neat and I have a star ground the system seems very quiet. After the cleanup I decided to run my file that cuts out the plastic security camera adapter plate from 1/4" plastic. Very simple part. If you look at the earlier photos in this thread you will see the part started to skew.
Well as soon as the part started you can see after it drilled the holes it pockets around those holes to allow the screws to be flush with the plastic. You can see the holes are not centered in the pockets, just like before, so I stopped the machine. Chasing issues like this is extremely frustrating. I know the Acorn will work I have watched it on many demos, just something else is wrong.

The next step was to verify if the Gcode posting was causing some kind of strange issue. I decided to use the Centroid Flange.nc file since it comes with the Centroid software, so it should be perfect. Well the gcode does not tell you the size of the tools they used in the demo files so I just let is cut the design into a piece of pine with a 1/8" EM.
Well the stepping issue has not disappeared and is not due to gcode file either.
You can see in this closeup shot each pass the part gets off more and more and more, exactly what the plastic part was doing as well.

The part I do not understand is I can take this exactly machine, exact wiring, and just disconnect the Acorn and attach my old parallel port card to the amplifiers and use all the same power suppliers and all the parts come out perfect. This suggests the machine mechanics are good and accurate.

I have posted my report.zip previously and ran all kinds of tests on movement. I would love to hear some suggestions. Right now I am running 4.07 a developer release, I could update to 4.08. Pretty much at my wits end and I have been doing this kind of stuff many years.

Russ

You said you had a scope. Did you use it?
I don't have the problems you are having. I have 4 or 5 Acorns now.
You seem to be gaining steps. Gotta be coming from somewhere.
I would use your scope, command a move on the offending axis and watch it.
Then command a move on good working axis and compare.

Compare at ACORN terminals and Compare the same move at the drive.

You followed all of Scotts suggestions to a T and reported back?

If you can use the scope, I think it might tell you something?

PROBLEM SOLVED, MACHINE WORKS PERFECT!!! LOVE IT

The problem had absolutely nothing to do with the hardware on my machine. The servo drives and servo motors were perfect. The Panasonic AC servos are expecting either a differential signal for Step and Direction or a Open Collector input, however the differential inputs are highly recommended.

The Acorn outputs at the screw terminals are open collector pulled up to +24V as you can see on the drive interface schematic on page 3 of the Acorn Manual. This hit me while I was taking a nap after two weeks of chasing ghosts. Most breakout board you see in on hobby mills were designed to be driven by the parallel port. The logic out of the computer parallel port is positive logic, so when you hook up a scope to the parallel port and look at the X axis step pulses you will see a stream of positive pulses as you jog a machine. When I hooked up the scope to the Acorn I noticed it was difficult to get a signal to read correctly on the scope, so I looked at the schematic and learned these outputs are open collector. The problem with open collector is it inverts the signal. Now if you try and take the inverted signal and drive a stepper drive or servo drive that is expecting positive logic you will get the valleys not the peaks from the acorn. As the feedrate changes the peeks and valleys are different lengths and you will get the wrong number of pulses.

This made me think of the video of Keith doing a demonstration of the Acorn for a lathe using the G540. The Gecko G540 was designed to interface with the parallel port on a PC, so Acorn had to be using positive logic on their DB25 output connector to the G540. I was certain I was correct so I quickly soldered six wires on a DB25 male connector and then ran those wires into my differential drivers just like I do from a parallel port. The result is I am now getting the positive logic required and guess what it works perfect.
Here is the plastic part that I was making with the Acorn that would skew when cutting, now if you look the drill holes are perfectly centered in the pockets and as it started cutting the circular shape out the cutter remained in the exact same path over and over and over again.

This is really important for people to understand and I will make a dedicated post to explain with some graphics. Many people are coming from the Mach3 world where they used the parallel port to drive stepper drives, servo drivers, etc. If you use the open collector outputs and you do not have drives configured for that situation you will get the wrong outputs to the drives. I could have also reverse the logic in my servo drive, some have that ability and others do not, so this is good to know. Hopefully, my trials and tribulations will help someone save many hours of frustration and maybe some of their hair. LOL

Russ

Russ, glad to hear you got it going. It didn't occur to me that you required inverted signals. Did you see the Advanced tab in the Wizard? You can invert there.
You should he running the latest release too, 4.08

Yay, Congrats! It does feel good when you kill a gremlin dead. I've been watching this thread & pullin' for ya'. There's no way that I fully understand it all but I'm happy for you. Time to open the bar!

DICKEYBIRD wrote: ↑Sat Dec 09, 2017 9:44 pm Yay, Congrats! It does feel good when you kill a gremlin dead. I've been watching this thread & pullin' for ya'. There's no way that I fully understand it all but I'm happy for you. Time to open the bar!

I'll have a Roy Rogers please

martyscncgarage wrote: ↑Sat Dec 09, 2017 9:52 pmI'll have a Roy Rogers please

Had to Google that one. Yuck!

martyscncgarage wrote: ↑Sat Dec 09, 2017 9:52 pm

DICKEYBIRD wrote: ↑Sat Dec 09, 2017 9:44 pm Yay, Congrats! It does feel good when you kill a gremlin dead. I've been watching this thread & pullin' for ya'. There's no way that I fully understand it all but I'm happy for you. Time to open the bar!

I'll have a Roy Rogers please

So glad this worked out Russ!

Since Marty is having a Roy Rogers, I'll chase it with Long Beach Iced Tea.