Tolerance Specification Across Sensing, Design, and Manufacturing
Faculty
A Consistent Framework for Tolerance Specification Across Sensing, Design, and Manufacturing
In this project we address the problem of tolerance representation and
analysis across the domains of industrial inspection using sensed data,
CAD design, and manufacturing. Instead of using geometric primitives in
CAD models to define and represent tolerances, we propose the use of
stronger methods that are completely based on the manufacturing knowledge
for the objects to be inspected. We guide our sensing strategies based on
the manufacturing process plans for the parts that are to be inspected
and define, compute, and analyze the tolerances of the parts based on
the uncertainty in the sensed data along the different toolpaths of
the sensed part. We believe that our new approach is
the best way to unify tolerances across sensing, CAD, and CAM, as
it captures the manufacturing knowledge of the parts to be inspected,
as opposed to just CAD geometric representations.
We address the problem of recovering manufacturing
tolerances and deformations from the uncertainty in sensing machine
parts. In particular, we utilize the sensor uncertainty to recover
robust models of machine parts, based on the probabilistic measurements
recovered, for inspection applications. We design and implement
a spline-based model that captures manufacturing tolerancing based
on uncertain sensed data and knowledge of possible manufacturing process plans.
We design and implement our sensing strategies and tolerance determination
algorithms based on interval splines. We believe this is the best way to
define a unifying framework, as it captures both parameterizable manufacturing
tolerancing errors, and non-easily-parameterizable ones (toolpaths that produce
a surface definition, for example). This method is also suitable for our
purposes as our CAD modeler (The Alpha_1 system, designed at the University
of Utah) is based on spline representation, and it is used to produce process
plans and toolpaths for NC milling machines to manufacture the actual parts
from CAD models. Our tolerancing method captures the mechanical way in
which the manufacturing tool moves and actually makes a feature,
surface or curve in a manufacturing process.
The standard representations for Computer Aided Design include volumetric,
boundary and CSG models. Current advanced modelers, can produce
process plans for specific machines in order to manufacture the object. We
believe that the process plan and associated information (e.g., the tool
path, the tool to be used, its speed, etc.) provide a strong basis
for analyzing the manufacturing and inspection steps with respect to
tolerances.
A tolerance specification on the shape geometry must be transformed into the
corresponding tolerance on the machining operation and vice versa.
This in turn can be
used to select an appropriate manufacturing process, given knowledge of the
manufacturing accuracy of the process. This yields direct methods for
deciding on sensing strategies both to monitor the manufacture of the part,
as well as for post-manufacturing inspection. These sensing strategies are
derived from an analysis of where the toolpath is most likely to deviate
from the tolerance specification.
These must all be done as efficiently as possible; in particular, it must be:
- straightforward to choose the cheapest manufacturing process, to go as fast as possible on that machine,
- to make as few sensed measurements as possible, and
- to perform as little computation as possible.
The keys to our approach are:
- have/use knowledge about each feature and machining process for that feature, and
- exploit the tool path representation to guide analysis and sensing.
The usual approach to validation is to simply measure the geometry resulting
from the manufacturing process and compare it to the nominal geometry from
the CAD model. We believe that a stronger approach, exploiting knowledge of
the process plan and the particular manufacturing process, is possible, and
that this approach permits the automatic synthesis of sensing strategies.
To achieve this requires a tolerance specification which:
- specifies design geometry tolerance as well as toolpath tolerances, and
- helps locate high payoff (i.e., maximal information gain) inspection regions.
We are working with the Alpha_1 Computer Aided Geometric Design system
and exploiting its ability to generate process plans for 3 and 5-axis
NC milling machines. For these machines, the process is a set of
toolpaths with appropriate tools, speeds, etc., specified. Thus, a
sensing strategy is a set of sensing operations carried out at particularly
high risk parts of the toolpath or places on the completed part.
Selected Publications:
- Books and Book Chapters:
-
- -
- T. M. Sobh, ``Techniques in Reverse Engineering of Machined Parts in
Manufacturing Systems,'' in Computer Aided and Integrated Manufacturing
Systems Techniques and Applications. Gordon and Breach International
Series in Engineering, Technology and Applied Science, to appear in 1997.
- Journal Papers
-
- -
- T. M. Sobh, X. Zhu, and
B. Bruderlin, ``Analysis of Tolerance for Manufacturing Geometric Objects
from Sensed Data'', Accepted for publicaton in Applied Mathematics
and Computer Science, October 1995, In the Journal of Intelligent and
Robotic Systems, 30: 143-153, 2001.
- -
- T. M. Sobh, T. C. Henderson, and F. Zana, ``A Consistent Framework for
Tolerance Specification across Sensing, Design, and Manufacturing.'' Under
Revision, IEEE Transactions on Robotics and Automation.
- Conference Papers
-
- -
- M. Dekhil and T. M. Sobh, ``Embedded Tolerance Analysis for Sonar Sensors.''
Invited paper to the special session of the 1997 Measurement Science Conference:
Measuring Sensed Data for Robotics and Automation, Pasadena, California,
January 1997.
- -
- T. M. Sobh, T. C. Henderson, and F. Zana, ``A
Unifying Framework for Tolerance Analysis in Sensing, Design, and Manufacturing''.
In proceedings of the IEEE International Conference on Robotics and
Automation, Nagoya, Japan, May 1995.
- -
- T. C. Henderson, T. M. Sobh, F. Zana, B.
Bruderlin, and C. Hsu, ``Sensing Strategies Based on Manufacturing Knowledge'',
In Proceedings of the ARPA Image Understanding Workshop, September
1994.
- Technical Reports
-
- -
- T. M. Sobh, ``Tolerance Analysis for Sensing, Design, and Manufacturing,''
Technical Report UBCSE-96-004, Department of Computer Science and Engineering,
University of Bridgeport, November 1996.
sobh@bridgeport.edu