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References From Application Programs to Geometric Computer Models

IP.com Disclosure Number: IPCOM000121475D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 4 page(s) / 160K

Publishing Venue

IBM

Related People

Fitzgerald, WJ: AUTHOR

Abstract

Disclosed are novel references from an application program to a geometric computer model. First, a novel geometric reference is described that is still correct for some changes which invalidate a logical reference. Then the combination of the two references is shown to approach a single error correction system. For these cases references can be automatically updated to reflect changes in the model, even when the application program is not running at the time of the change.

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References From Application Programs to Geometric Computer Models

      Disclosed are novel references from an application
program to a geometric computer model.  First, a novel geometric
reference is described that is still correct for some changes which
invalidate a logical reference.  Then the combination of the two
references is shown to approach a single error correction system.
For these cases references can be automatically updated to reflect
changes in the model, even when the application program is not
running at the time of the change.

      The ability to build 2D and 3D computer models of geometric
objects is well established, as demonstrated by the CADAM* modeling
system.  There are now many efforts to build application programs to
analyze and utilize various aspects of these models, such as
programming numerically controlled machines to cut the part being
modeled and analysis of the tolerances associated with dimensions.

      These application programs bring up a new problem in accessing
data which will be illustrated using an example involving two types
of dimensions.  Dimensions applied directly to a part can be filed
with the part, are present when changes are made to the part, and can
comply with these changes.  A tolerance-analysis application program
is applied to an assembly of parts, and it is desirable to add
dimensions to the assembly for the analysis.  These assembly
dimensions refer to the parts, but are not filed with the parts.  Any
simple pointers from an assembly dimension to a part are invalidated
when the assembly is filed.  When the assembly is modeled again,
there is not only the problem of reestablishing the pointers, but it
is possible that the parts have been changed since the assembly was
filed.

      A typical model of an assembly is a tree whose leaves can be
models of parts.  Each node in the tree has a system or user-defined
name.  If an object in the assembly includes multiple copies of the
same object, the name of each copy is augmented by an instance
number.  This is done so that a list of the names of a part and
its Dads is unique.

      This unique naming system was specifically established for
references from a tolerance loop to dimensions in the assembly.  A
full word TOD (time of day) stamp can be given to each dimension when
it is created.  Because of the great range of numbers that can be
represented, the chance of duplication for different dimensions is
extremely small. This stamp and the unique name of the part in which
a dimension exists provide a logical reference from the tolerance
loop to the dimension.  If the name of an object or any of its
ancestors is changed or the object or its ancestors moved in the
hierarchy, of course, any references using that name will be invalid.

      A new geometric reference was developed to avoid these
limitations.  This reference will be described for a 3D modeling
system, but applies also to 2D modeling, w...