Attachment6_SCOOPVAL_Information.pdf

FAQ.txt Frequently Asked Questions and Common Problems ScoopVal Version 2.1.3 Demian Nave (dnave@propulsor.net) 05/02/2010

Scoop bar analysis:

1. If I only input datum surface inspection points, why does ScoopVal report points for the Inner Surface (I-Point 3)?

A: This happens when inspection points are close to two or more surfaces; e.g.

when a touch probe is used to inspect a bolt hole stud, and the probe touches both the stud and the inner surface. Both RMS alignment (most likely) and roundoff error (less likely) can result in this effect.

Because RMS alignment changes the positions of the inspection points, it is impossible to guarantee correct handling of such ambiguous points.

However, the effect can be ameliorated by (1) using a small-diameter probe or a high-accuracy laser scanner, and by (2) maintaining a "buffer" area near the meeting of two surfaces that is larger than the clearance of the scanning device (e.g. the probe radius, if using a touch probe).

2. ScoopVal is reporting outrageous deviations; is this a program bug?

A: Possibly, but it could also be the result of a poor RMS alignment. RMS alignment does not typically "fail gracefully"---a bad alignment will usually be obvious from the position of the points displayed on the report pages. Make sure that:

... there are few or no outliers in the datum surface inspection points, particularly near the aft stud, on the forward face, or near the projection of the aft stud through the outer (hub) surface. Points in these areas are used to compute a rough initial alignment of the datum points prior to computing the final RMS alignment. RMS alignment is notoriously sensitive to the initial position of the pointset, so a good initial alignment is needed to help ensure a good result.

... the aft stud, forward face, and outer (hub) surface have been inspected with relatively even point density. This is especially important for the aft stud inspection points, since the initial alignment procedure uses these points to find the stud centerline.

... the bolt hole studs are inserted during the inspection of the inner surface. Otherwise, points near the bolt holes may be assigned to the studs rather than to the inner surface, resulting in higher than expected deviations. This is especially true when using a large-diameter probe or laser tracker ball.

3. ScoopVal is reporting plausible---but unexpectedly large---deviations; is this a program bug?

A: As in FAQ 2, a bug is certainly possible. The guidelines from the answer to FAQ 2 apply here also. In addition:

... if the deviations are consistently large, make sure that the right probe offset was selected for each inspection point file.

... if the stud deviations are consistently large, make sure that the right version of ScoopVal is being used. ScoopVal 2.1.3 is distributed in two "microversions", 2.1.3-NFPC and 2.1.3-NSWC. The NFPC microversion is

FAQ.txt setup to use 1.25in diameter bolt hole studs and defaults to a 1.5in laser tracker ball diameter, while the NSWC microversion is setup to use 1in diameter bolt hole studs and defaults to a 6mm probe diameter. (The functionality to select the stud diameter will be included in a future release.)

ScoopBarAnalysisUserNotes.txt Scoop Bar Analysis User's Notes ScoopVal Version 2.1.3 Demian Nave (dnave@propulsor.net) 05/02/2010

1. Scoop Bar Analysis Inspection Configuration

a. The "Select datum point files" list

- This list is used to enter paths to files for each of the scoop bar datum surfaces. In particular, a file must be selected for:

. the outer (hub) surface.

. the forward face . the forward bolt hole (stud) . the middle bolt hole (stud) . the aft bolt hole (stud)

The "Continue" button will not be available unless each datum surface has a file assigned.

- Clicking '+' will bring up a file browser which can be used to select files to be added. The browser allows multiple files to be selected at once. The browser will start in the most recently accessed folder, if available, otherwise it will start in a default location depending upon the local machine's Windows configuration.

- Clicking '-' will remove all currently hilited items from the list.

b. The "Datum inspection ball radius" combobox

- This combobox can be used either to select a preset probe radius from the drop-down list (currently No Ball, 3mm, 1/4", 7/16", or 3/4"), or to enter a custom probe radius (e.g. .5 for a 1/2" radius probe).

Note: Fractional values (e.g. 1/2) are not currently supported; the radius must be set in decimal form.

WARNING: A custom probe radius can affect both the execution time and the accuracy of the report. See "General Notes" for more information.

c. The "Select inspection point files" list

- This list is used to enter paths to inspection point files for non-datum surfaces.

- If "Include datum points as inspection points" is checked, then no inspection point files are required. Otherwise, the "Continue" button will be disabled until at least one inspection point file has been selected. (See "Options" below.)

- Clicking '+' will bring up a file browser which can be used to select files to be added. The browser allows multiple files to be selected at once. The browser will start in the most recently accessed folder, if available, otherwise it will start in a default location depending upon the local machine's Windows configuration.

- Clicking '-' will remove all currently hilited items from the list.

- The inspection ball radius can be set for each data file individually by clicking once on the file to be modified to hilite its line, then by clicking on the hilited line under "Ball Radius". This will display a combobox to either select one of the preset radius entries (currently No Ball, 3mm, 1/4", 7/16", or 3/4"), or to enter a specific ball radius in decimal form (e.g. ".5" for a 1/2" ball radius).

Note: Fractional values (e.g. 1/2) are not currently supported; the radius must be set in decimal form.

In particular, a file can be selected for:

. the inner surface . the aft face . the seal goove

2. Report Configuration

a. Setting the report output directory and report file prefix

- The report output directory can be entered directly into the "Report directory" edit field, or the ellipsis button ('...') can be clicked to show a directory browser with which to select the output directory.

- The report file prefix is prepended to the names of the output files. For example, if the prefix is "ScoopBarReport", then the PDF report file will be called "ScoopBarReport.pdf".

Note: if the directory shown in the "Report directory" edit box does not exist, the "Continue" button will be disabled.

Note: Both the report output directory and the report file prefix are saved between runs of ScoopVal.

b. Configuring the output

- If "Summary only" is selected, only the analysis summary page will be generated. The per-view report pages will not be generated or output into the report file.

- The remaining fields on the dialog can be used to tailor certain information on the report pages:

i. The "Inspection date" and (if enabled) the "Report date" items will display a calendar to allow selection of the date that the inspection data was taken and the date to assign to the report on the summary page.

Note: The inspection date defaults to the date that the most recently generated inspection data file was modified. If there is only one inspection file selected, its file modification time is used. If no inspection files are selected, the inspection date defaults to the current date.

ii. The report classification can be set to "Unclassified" or "Confidential", depending upon the expected report classification.

Note: The classification defaults to "Unclassified", and can only be changed if the "Classification:" checkbox is checked. Furthermore, the classification is NOT saved between runs of ScoopVal.

WARNING: Please consult OPNAV INST S5513.56 Enclosure 56 for classification requirements.

iii. "Document number", "Drawing number", "Scoop bar serial number", and "Inspected by" should be set to the values implied by the names of the fields.

Note: The values of these four fields are saved between runs of ScoopVal.

iv. The "Notes" field can be used to record text under the "Notes" section of the report summary page.

Note: Notes are NOT saved between runs of ScoopVal.

WARNING: The notes should be limited to around 100 characters (2 lines), otherwise the PDF version of the Summary Report page may be truncated (the text version of the page is unaffected, though).

3. Options

a. "Include datum points as inspection points"

- If this box is checked, datum points will be included in the analysis as inspection points. Otherwise, datum points will be used only for alignment, and only the points from files in the "Select inspection point files" list will be included in the analysis.

b. "No RMS alignment"

- If this box is checked, no RMS alignment will be performed. Only use this option if the inspection points are already in the design coordinate system, and RMS alignment is not required.

b. "No initial alignment"

- If this box is checked, the current position of the datum points is used as the starting point for RMS alignment. Otherwise, features extracted from the datum points are used to compute a transformation that approximately aligns the datum points to the design coordinate system prior to computing an RMS alignment. Only use this option if the datum points are already (approximately) aligned to the design coordinate system.

Note: The "No initial alignment" option is available only if "No RMS alignment" is unchecked (i.e. RMS alignment is enabled).

4. Performing the analysis

Once the inspection and report configuration fields have been set, the "Continue" button will be made active (see "General Notes" for more information). Clicking "Continue" will close the setup dialog and will show a progress dialog for the analysis process. The "Cancel" button can be clicked on the progress dialog to stop the analysis, but no report will be generated in this case.

If the analysis completes successfully, the "Exit" button will be enabled.

Clicking the "Exit" button will close ScoopVal, and will automatically open a Windows Explorer window with the PDF report selected.

Note: If there is already a Windows Explorer window open to the folder containing the report, then the PDF report will not automatically be selected.

5. Viewing the results

All results can be found in the folder entered into the "Report directory" edit box. Also, most output files are prefixed with the value of the "Report file prefix" edit box. The output includes:

- The report configuration in <Report prefix>_Report.svcf (this file is currently not used, and is only for information purposes).

- The text version of the summary in <Report Prefix>_Report_Summary.txt.

- Image files for each report page in JPEG format. The first page is the report summary, the next 12 pages report in-tolerance points, and the last 12 pages show out-of-tolerance points. If no out-of-tolerance points were found, only 13 pages are produced.

- A PDF version of the report in <Report prefix>_Report.pdf.

- Several files containing the aligned points used in the analysis:

. <Report prefix>-aft-bolt-hole.asc . <Report prefix>-mid-bolt-hole.asc . <Report prefix>-fwd-bolt-hole.asc . <Report prefix>-aft-face.asc . <Report prefix>-fwd-face.asc . <Report prefix>-datum-surfaces.asc . <Report prefix>-seal-groove.asc . <Report prefix>-aft-bolt-hole-no-offset.asc . <Report prefix>-mid-bolt-hole-no-offset.asc . <Report prefix>-fwd-bolt-hole-no-offset.asc . <Report prefix>-aft-face-no-offset.asc . <Report prefix>-fwd-face-no-offset.asc . <Report prefix>-datum-surfaces-no-offset.asc . <Report prefix>-seal-groove-no-offset.asc

The no-offset versions contain measured points, while the others contain ball-center/probe-offset points.

- Several files in DesignLab minimum distance (DIST) format containing the distance fields for the aligned points:

. <Report prefix>-aft-bolt-hole.DIST . <Report prefix>-mid-bolt-hole.DIST . <Report prefix>-fwd-bolt-hole.DIST . <Report prefix>-aft-face.DIST . <Report prefix>-fwd-face.DIST . <Report prefix>-datum-surfaces.DIST . <Report prefix>-seal-groove.DIST . <Report prefix>-aft-bolt-hole-no-offset.DIST . <Report prefix>-mid-bolt-hole-no-offset.DIST . <Report prefix>-fwd-bolt-hole-no-offset.DIST . <Report prefix>-aft-face-no-offset.DIST . <Report prefix>-fwd-face-no-offset.DIST . <Report prefix>-datum-surfaces-no-offset.DIST . <Report prefix>-seal-groove-no-offset.DIST

The no-offset versions contain measured points, while the others contain ball-center/probe-offset points.

WARNING: The DIST files currently do not contain valid surface information, but the distance information can still be viewed with RepVal.

- Zero or more ASCII and DesignLab DIST formatted files containing aligned points that could not be included in the analysis. Dropped points originating in an inspection file will be saved to a file with the same name and a "-dropped" suffix. Dropped datum points are all saved to a file with the name "datum_surfaces-dropped"; e.g.:

. <Report prefix>-oring_groove-dropped.asc . <Report prefix>-oring_groove-dropped.DIST . <Report prefix>-datum_surfaces-dropped.asc . <Report prefix>-datum_surfaces-dropped.DIST

These files contain ball-center/probe-offset points only.

WARNING: The DIST files currently do not contain valid surface information, but the distance information can still be viewed with RepVal.

General Notes:

- Tooltips (windows containing short help text) are available for most fields on the setup dialog. To show a tooltip for a particular field, point the mouse cursor at the field and do not move it for a short time (about 1 second). If the field has a tooltip, it will be displayed near the cursor.

- The "Continue" button will not be available unless each datum surface has a file assigned. If "Include datum points as inspection points" is checked, then no inspection point files are required. Otherwise, the "Continue" button will be disabled until at least one inspection point file has been selected. The "Continue" button will also be disabled if the report output directory does not exist.

- Clicking the "Cancel" button will exit the program immediately. However, no field values entered in the dialog will be remembered for the next run.

Field values are remembered only if "Continue" is clicked.

- Using a custom inspection ball radius for the datum points can both increase the amount of time spent in the alignment step and reduce the accuracy of the alignment. This is because the alignment algorithm must include the user-supplied ball radius as an extra variable to be minimized, thus increasing the error and the number of iterations required to compute the alignment. On the other hand, each preset radius is associated with a set of surfaces that are already offset by the radius from the design-of-record scoop bar datum surfaces. Using these offset surfaces eliminates the extra variable with a corresponding improvement to both the runtime and the accuracy of the alignment.