Each point or scan within SA is traceable back to the instrument that measured it and that link is fundamental to geometry fitting and instrument alignment. SA has always made it easy to measure and fit geometry, analyzing the deviations and reporting the statistics individually. However, part inspection is all about streamlined comparisons between nominal and measured geometry, reporting measured locations within specified tolerances and effectively reporting those results.
SA uses Geometry Relationships to effectively link nominal and measured geometry position and location information, and dynamically update and report on these comparisons. These features can be built in advance or after measurements are made and, once built, provide a template for future measurements.
Geometric measurement is an essential part of any inspection process. SA uses the idea of a Geometry Relationship to build a measurable element within SA that can be configured as a template. This allows measurement settings as well as reporting to be setup in advance of a measurement process and as soon as the measurements are available all the results update dynamically.
Adding a new feature from the Features tab creates a placeholder geometry relationship within the SA tree bar:
An important thing to notice is that both a circle named GR-Circle is added to the tree and under the circles category and another with the same name is listed within the Relationship. This is because a Geometry Relationship is an additional dynamic element that is added that controls and links together other elements within the tree. As soon as measurements are taken of this circle feature the relationship will use these measurements to update the size and position of the circle:
Additional references can be added such as a nominal circle and a projection plane:
Now this single Geometry relationship is dynamically using the 9 points and the projection plane to compute the position and size of the GR-Circle. It is also using the nominal circle as a reference for comparison and report building. The advantage of this architecture is that the relationship dynamically compares each element but they are each also independent. This allows any element to be exchanged or modified at any point and as needed, and everything will update automatically.
The status of features in the toolkit can vary depending of if tolerances are set or if measurements have been made of particular features. To more clearly identify the status of these features different icons are used in both the tree and in the Inspection Tab of the Toolkit. This includes 4 states:
A gray feature icon indicates that it is a placeholder and does not have measurements assigned yet in order to determine its position and orientation.
A colored icon indicates that the feature has valid measurements but no tolerances are set.
A green check mark indicates that the feature has both valid measurements and all of the position and size tolerances are within specifications
A red X icon indicates that at least one specification is out of tolerance.
The Inspection Bar offers an alternative perspective on the SA Treebar, offering a focused ordered list of items with Trapping capabilities for inspection. This list can be rearranged and items can be hidden from view as needed to provide a list of features to inspect. The status of the features are displayed using the appropriate status icons.
Geometry can also be inspected using our ASME and ISO compliant Standardized GD&T inspection process. The datums and feature checks will also appear as stand along inspection features that also will updated dynamically. In fact both GR-Features and feature checks can be included for the same circle feature and feature checks can also be build by directly referencing the GR-feature.
This may seem redundant but there are important reasons to separate and clearly identify the inspection method used. The primary reason these evaluation processes are separate in SA are:
GD&T feature checks use the built in datum references to perform an internal alignment and then evaluate with respect to that alignment. GR features display deviations using the current job alignment which provide greater visual feedback and flexibility.
GD&T feature use either ASME or ISO inspection processes that are designed to establish if a part is within specification. This means that it optimizes fits using bounding thresholds in its mathematical evaluation. GR features use an RMS fit to help identify measurement error.
Therefore, the following guidelines can be used as a rule of thumb:
If an inspection is to be performed strictly following an ASME or ISO guideline then GD&T inspection is the standardized approach.
If analysis of measurement quality and a deeper understanding of the influence of the alignment are desired then relationships are often the better approach.
GD&T checks can be build directly from GR-Feature which allow both approached to be used together.