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The Mirror Model Comparator (MMC) is a proprietary patent
pending geometry verification system that ensures a high-level of accuracy in
the feature-based translation of a CAD file from one commercial CAD/CAM system
to another. Although the MMC is a module of the Acc-u-Trans translation engine,
it has been designed with the ability to compare models that were not
translated using Acc-u-Trans. This technology is confidential to Translation Technologies.
1. What does the MMC do?
The MMC 1) detects, 2) reports, and 3)
displays differences in geometry between the original source model and the
newly created target model.
The analysis for detection can be run in two
modes:
- Forward mode: extract analysis data from the source model and compare it to
the target model
- Reverse mode: extract analysis data from the target model and compare it to
the source model
Although the MMC can be run
in just one of these modes, some categories of discrepancies could go undetected
in forward analysis only, but would be detected by a subsequent reverse
analysis process and vice versa.
Running the analysis consecutively in the two modes provides additional
confidence that the translation was accomplished correctly.
Once the differences are detected, this data
is then presented in an analysis report.
In addition the information is visually displayed in the target model
for both forward and reverse analysis.
This enables the discrepancies to be observed in a very quick and effective
manner. In addition, changes can be
made in the target model very easily with this displayed information as a
guide.
2. How does it do it?
Step 1:
During the extraction phase of the translation process, analysis data in the form of
point cloud data is extracted from the source model and stored in the TTI
Proprietary file. Acc-u-Trans extracts
two different types of analysis data for use by the MMC:
Step 2:
The MMC then superimposes the points from the surface and edge data onto the target
model and measures the distance between each point and its respective surface
or edge. Any distance that is greater
than the pre-specified analysis tolerance is deemed an error and is presented
as such in the analysis report.
Additionally, the MMC leaves each point representing the error in the
target model, so that an operator can investigate the nature and magnitude of
the error, as well as perform any corrective action.
This
analysis is run independently as a final QA step after the complete model is
translated. This assures that the
completed target model geometrically matches the source model.
3. User
controlled Mirror Model Comparator Functionality:
The MMC accepts user input and the user has
the ability to set a number of options.
- Resolution of the analysis data - a qualitative setting of High, Medium and
Low. One can think of this as setting the mesh grid resolution for the model.
- Analysis tolerance - The analysis tolerance can be set as a function of the source model
tolerance or to an absolute value.
Setting the analysis tolerance too tightly relative to the source model
tolerance can result in a number of false errors being reported by the
MMC. However, theoretically the
operator can set the analysis tolerance as tightly as desired.
- Full analysis, or only reanalyze items that were detected as out of
tolerance previously. The user can analyze using
forward mode only, reverse mode only, or both.
Reanalysis options for reverse are also available.
Figure 1 - Analysis Results (source Pro/E, target CATIA V4)
4.
Advantages of the Mirror Model Comparator over a simple mass properties
comparison of the source and the target models:
For
many years designers have relied on comparing the mass properties of the source
and target models to determine if the translation is accurate. TTI’s Acc-u-Trans technology uses mass
properties comparison during the translation process to assist in detecting
certain types of errors. While this
methodology has it’s merits and is certainly better than not checking at all,
it does suffer from certain limitations.
These limitations fall into three main areas:
- Lack of
Information about the position of the discrepancy - Just as important as knowing that an error
exists is to know the location and magnitude of the individual
discrepancies. A mass properties
comparison does not indicate to a user where the error is, nor how much. The user cannot determine precisely where
the error is, or its magnitude is.
- Lack of
precision in mass property calculations - A mass properties analysis of a 3D CAD model is an
approximation. The accuracy of the
approximation depends entirely on the calculation techniques used in the CAD
system to output the values and the modeling precision available in the CAD models. The most precise CAD systems only
approximate these measurements to an accuracy of 0.03 to 0.1 percent of the
value being measured. When a model has
a volume of 200055.39 cubic millimeters (approximately the volume of the
example model used in the illustrations) the accuracy of the measurement ranges
from +/- 60 to 200 cubic millimeters.
The error displayed in Figure
1 above causes a difference of 2.16 cubic
millimeters. This error is
significantly less than the analysis precision of the volume measurement (by as
much as 2 orders of magnitude) and therefore would likely go unnoticed in a
mass properties comparison analysis.
- Cancellation
effects from multiple discrepancies -
In the inevitable event that there is more than one error, it is just as likely
that the errors will occur in locations that cancel or reduce the resultant
effects on the differences of center of mass and moments of inertia values
reported. For example, if two errors
exist in the translated geometry and they are located on opposite sides of the
center of mass, they will tend to cancel each other. Mass properties comparison
is a useful tool for providing roughindications of the degree to which
two different CAD models are geometrically the same. But in order to be sure that the two models are geometrically the
same, one would have to overlay the models on top of each other and scan for
differences. This is precisely the
underlying philosophy of the TTI Mirror Model Comparator. The MMC surmounts all of these limitations
in an effective manner and provides a very accurate comparison of the source
and target models.
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