Feature Averaging

Introduction

Feature Averaging provides the user with the tools to evaluate a critical form dimension during the part inspection run and determine if it exceeds the upper or lower tolerance band. Features that are supported are: Circle, Sphere and Cylinder.

During the part inspection, Geomet will review the Diameter or Radius and compare it against the tolerance band. If it exceeds the tolerance band and remains within the established evaluation zone, Geomet will automatically rerun the feature up to the cycle limit and average all the reported form values.

Establishing the Default Settings for Feature Averaging

You can establish basic guidelines for the two parameters that Feature Averaging will use. To create the defaults, go to the System Options by pressing the < F9 > key. Locate the two setting keys:

Feature Averaging default cycles
Feature Averaging default limit

Set defaults for these two averaging characteristics. The default cycle instructs Geomet to rerun the same feature up to this entered cycle count. The default limit establishes a zone outside the tolerance limits that if the measured feature falls in this zone, then a rerun will automatically take place. For example: if you are measuring a diameter with a nominal value of 1.000” and a tolerance of ± .001 your limits would be 0.999 - 1.001. The evaluation zone entered as 0.0002" would be 0.9988 - 0.999 and 1.001 - 1.0012 or .0002 outside tolerance limits. The default values entered here are only a starting point, you can change the values on a feature by feature basis through the tagging operation listed below.

Feature Average Tagging

figure 2, Tagging

To start the feature tagging process, measure a qualifying feature complete with motion. Apply tolerance to the feature size. Highlight the feature and right-click your mouse to pop-up the feature menu. Choose Configure Feature Averaging and the Feature Averaging dialog will appear.

Note: If you do not see a Configure Feature Averaging in the menu, it can be caused by two conditions. First, the feature must have a tolerance applied to the size attribute. The second reason is that this tool requires Direct Computer Control (DCC).

Feature Averaging Setup Dialog

This setup dialog establishes the operating parameters for Feature Averaging on a qualifying Circle, Sphere or Cylinder. There are three settings which you can set to control the rerun characteristics.

figure 3, Feature Average Setup Dialog

Evaluation Limit
The zone outside the tolerance limits where Geomet will determine whether to rerun a feature. As previously mentioned, this applies only to the Diameter or Radius of the feature.

Maximum Rerun Tries
The number of ReRun cycles Geomet will try to do on the feature. When Geomet enters a rerun cycle it retains the previous actual dimension and adds it to the final record. Once it completes the rerun cycle, Geomet will average out all runs to determine if it falls inside the tolerance zone.

If the average falls inside the tolerance zone, Geomet will cease the reruns at the current cycle and report the feature. If the average falls outside the evaluation zone, Geomet will consider the feature out-of-tolerance and cease the rerun cycles.

Auto Reverse to SO
This check box is used to force the direction of motion back to the first Stand Off (SO). The first SO is the starting point for the first measurement point in the motion map for the feature. On most external features (OD / OR) you should check this box. When Geomet completes the feature and determines that a retry is required it will backup though the motion map through all SOs and IPs to the start of the first measurement point and then rerun the feature.

If the check is not in place, Geomet will drive from the current locate directly to the first SO. On most internal features, this will not cause a problem.

Measurement Values
All currently stored actual measurements will be displayed here for review.

Activate in Feature
When this is checked, Feature Averaging is active for this feature.

Feature Averaging during a Part Inspection

During a part inspection, Geomet constantly monitors every feature for the Feature Averaging tag. After completing gathering the required number of data points, Geomet will calculate the diameter or radius and compare it to the evaluation zone. If it is found that the result falls inside the evaluation zone, Geomet will return store the actual value and display it on the monitor and return to the first SO and rerun the feature.

Once the rerun is completed, Geomet will then average the first and second actual values and perform on of the following:

  1. Average falls inside tolerance zone: The feature is completed and the results are added to the report.
     

  2. Average falls inside evaluation zone: Geomet adds the new actual to the list and attempts another rerun. This cycles continues until either a) or c) conditions exist or until maximum allowed cycles is reached. If maximum cycles is reached, the feature is reported as out-of-tolerance.
     

  3. Average falls outside evaluation zone: The feature is completed and added to the report as a feature out-of-tolerance.

The results shown in the report for the Diameter or Radius is the average of all runs. However, the location reported is that of the last run. The averaging feature is designed for use on critical size not for position.