Re: [CAD_CAM_EDM_DRO] Re: machine inaccuracies fixed by software compensation

Smoke wrote:

>
> I think someone should contact the manufacturer(s) to find out exactly what
> the 5% tolerance means and end all the assumptions being made.

Well, looking at my Oriental Motor catalog, they express accuracy of +/-
3 minutes, or .05 degrees. Quoting from the catalog:

"STEP ANGLE ACCURACY
Under no-load conditions the stepping motor can maintain a step angle
accuracy within +/- 3 minutes (.05 deg). This slight error arises from
difference in the mechanical precision of the stator and rotor teeth and
variations in the electrical precision of the DC resistance of the
stator coil.

STOPPING ANGLE ACCURACY
This refers to the difference between the rotor's theoretical stopping
position and it's actual stopping position. A given rotor stopping point
is taken as the starting point, then the stopping angle error is the
difference between the maximum (+) value and the minimum (-) value when
measuring each step of a full rotation.

<actual stopping position>

.745 1.425 2.17 2.885
0----------|-X-----X-|--------|-X-------|X-------(etc)---360
.72 1.44 2.16 2.88

| = Theoretical Stopping Position
X = Actual Stopping Position

The step angle error is +/- 3 minutes, but only under no load. In actual
applications, there is always friction load. The angle precision in such
cases is produced by the angular displacement caused by angle-torque
characteristics based upon the frictional load. If frictional load is
constant, the angle of displacement is constant for rotation in one
direction. When operating from both forward and reverse, however, double
the displacement angle is produced by the round trip. When stopping
precision is required, always position from one direction only."

So, that ought to help settle the debate on stepping accuracy, though I
have to say the issue of doubling the displacement error in
bi-directional applications has me a bit confused.

Jon