DCF - Dual Cylinder Fit

About the Feature

DCF (Dual Cylinder Fit) is the major enhancement for VTube-LASER in version 2.8 (April 19, 2017) Because it replicates measuring the tube TWICE in one pass when the user measures the tube the first time. In addition to measuring each cylinder twice, it also now requires 3 additional pass-fail checks for cylinder calculations. The goal is to ensure repeatability of the cylinder measurements on-the-fly using a LASER scanner.

How It Works

When using the LASER scanner*, the UNISCAN DCF feature divides the cylinder surface data into two groups, then calculates the cylinder data and intersection points twice to verify repeatability. *(Note: DCF is not used tactile measurements because it is assumed that there isn't enough data to perform DCF properly with ball probe measurements.) The DCF Point Repeatability value is reported in the Cylinder Fit window (see CHECK 4 below). What happens if the points are too far apart? If the two DCF points are too far apart (the Point Repeatability value is too high), then VTube-LASER will warn you and ask for a remeasure. This allows you to remeasure the straight to guarantee that the measure repeats before moving to the next straight. What happens if the points are close to each other? If the two DCF points are near to each other within tolerance, then VTube uses the average of those two points as the final point. See the illustration on the right.

Introductory Video

Click on the image to see the five-minute video of the feature explained by Michael Cone, the developer of VTube-LASER.

MULTIPLE LEVELS OF CYLINDER FIT CHECKS

As part of the DCF feature, the Cylinder Fit Data window reports cylinder fit values that help you know if the cylinder measurement is good. When using the laser scanner in Uniscan mode, VTube cylinders must pass a total of FOUR checks to be qualified as good cylinder scans. (Versions before 2.8 only required CHECK 1 shown below. This 4-level check is only available in version 2.8 and newer.) CHECK 1 - MAXIMUM WOBBLE PREDICTION The Maximum Wobble value predicts how precise the surface data fits the cylinder. This was in previous versions, but now two cylinders must pass - not just one. And we've created a single new value to display at the top rather than multiple XY values. CHECK 2 - OD SURFACE TO CENTERLINE The new OD Surface to Centerline value reports the low and high points on the measured diameter relative to the centerline. If the values get too far from each other (the "Delta"), then VTube-LASER will warn you. Also, the Out-of-round% is reported and used to qualify the cylinder fit. This is active for both LASER and ball probe. CHECK 3 - INTERSECTION PASS DISTANCE The Intersection Pass Distance shows how near each intersecting 3D centerline comes to each other in 3D space. If the Nearest Pass value is more than the Intersection Error Tolerance, then VTube-LASER will warn you. This is active for both LASER and ball probe. CHECK 4 - DUAL CYLINDER FIT As mentioned above, because the DCF engine creates two cylinders, it always builds and compares the resulting intersection points from both cylinders. It warns you if they don't match well enough.