[samu]

I have a fanuc 0M-D on a hardinge vmc1000 and i'm sure that it could do better. In circular interpolation, even at low speed or with a great radius, error is abominable. If I cut different diameter with the same tool, I must put different offset for each diameter. Servo software version is 9046-09. I'm reading some fanuc manual about the subject, but all the options that could help me are only available on more recent software version. Any help??

[samu]

I progress! I read about feed-forward function. It was turned off. I began to turn it on, following the procedure. Then, have to set the the feed foward coeficient FALPH according to these formula:

FALPH = α × 4096 ×8192/Position feedback pulses per revolution of the motor

But wath is α ?

After that it's easy, just to set the Velocity feed-forward coefficient (VFFLT)


VFFLT = (− PK2V) ×[(Load inertia +rotor inertia)/Rotor inertia] × 0.04 × 8000/(Position feedback pulses per revolution of the motor)

Where can I find the load inertia and the rotor inertia?

[samu]

one more step. I found that load inertia ration (prm# 8x20) is 256*(load inertia +rotor inertia)/rotor inertia. But i don't know if the value entered in these prm is trustable. I have 64 for all 3 axes. Does it makes sense? I have the same motor on the 3 axes. So i assume it means that the head inertia is the same than the table inertia.

[samu]

i begin to understand. Correct me if i'm wrong. α is Feed-forward coefficient (0 to 1). So if i want a coefficient of 0.7, according to the formula
FALPH = α × 4096 ×8192/Position feedback pulses per revolution of the motor
FALPH=0.7*4096*8192/12500=1879
To konw my Position feedback pulses per revolution of the motor, i check prm #8x24(Number of position detection feedback pulses (PPLS)) Is that o.k.?

[samu]

Something is strange with the inertia ratio. If it is 256*(load inertia+rotor inertia)/rotor inertia i'm supposed to have a value grater than 256. It is impossible that load inertia + rotor inertia be smaller than just the rotor inertia. If anybody have the same machine, please can you give me your parameters back up.

[tc429]

if interpolation is bad, be sure exponential acc/dec for feed is zero- seen a lot of oems throw values in there and toolpath gets distorted really bad. I dont think load inertia will help with interpolation- i usually fudge the ldint values to calm a loose machine down, it can eliminate oscillation at rest if the screw preload is gone, etc...
be sure your gain (517 in a zero) is at default 3000. Weve had some bigger machines with lots of ldint in a compound axis due to excessive mass, it calms the motor, but never noticed any interpolation error changes with the ballbar except maybe quadrant protrusion at reversals.
Suggest programming a 45 degree move and make sure following error matches or is exactly multiplied or divided by a integer value...on the old analog stuff thats how i set tachs, if theyre off even 1% it messes with interpolation accuracy...radii become polygons as one axis will lead/pause- cant really see it, but shows on the ballbar

I know i'm not doing it right, but try to get by...