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Reverse engineering industrial applications
Computers md Engng Vol 26, No 2, pp 381-385, 1994
Pergamon
REVERSE
0360-8352(93)F_~19-5
ENGINEERING
INDUSTRIAL
Copyright © 1994 Elsevier Science Ltd Pnnted m Great Britain All rights reserved 0360-8352/94 $7 00 + 0 00
APPLICATIONS
ROBERT J. ABELLA, JAMES M . DASCHBACH a n d ROGER J. M c N I C H O L S Department of Industrial Engmeenng, The University of Toledo, Toledo, OH 43606-3390, U S.A AMtraet--Reverse Engmeenng is being applied to generate CAD files Speclahzed software ~s used wroth CMM and a touch probe m two demonstration experiments. Advantages of the technique include ~mmedmte feedback, data reduction, d~rect generauon of geometry and htgher precision of the final product.
INTRODUCTION
A machine part fails and the production line stops due to the essential character of this machine. No spare parts are available. The broken part is given to a machinist, a new part is made and the machine resumes service maintaining productivity. This situation is not new, it happens often. The basic concept of producing a part based on an original or physical model without the use of engineering drawings is called "Reverse Engineering". Reverse engineering has changed from a skilled manual process to an engineering tool using sophisticated computer software and modern measuring instruments. It has rapidly expanded from its origin in maintenance into the areas of design and production. This expansion is the result of both a change in the basic design process and the development of specialized equipment to support reverse engineering. Graphite drafting and blueprints are being replaced by CAD systems. As computers take over the drawing function, engineers have developed new ways to utilize the computer model in the design process. Finite element analysis and other engineering methods which previously took weeks to perform can now be completed in minutes. Analysis of designs with these mathematical tools has become an integral part of many design processes. Advanced CAM systems (1), which also utilize these computer models, have been incorporated into the product development phase. Along with the utilization of CAD systems has come a trend in many companies to use customized physical models in their design process. These models are made early in the design phase of a product and modified to incorporate functional improvements in meeting customer requests and requirements. Rapid prototyping [2] and other advances in model processing have developed to support these activities. When final design approval is obtained, the customized specifications of the part are often reflected in the model and not in the initial drawings, if they ever existed. Thus, design concepts developed with the model's evolution are being captured physically, but too often not incorporated back into the engineering process. Through reverse engineering, the optimized geometry and part dimensions can be the means to complete the integration of design updates and manufacturing 'polishing' with the necessary 'drawings' and historical records. Engineers working in production increasingly look toward reverse engineering to meet the higher demands for quality and efficiency in today's competitwe environment. One of the most common problems that industry faces is to maintain up-to-date drawings on the production floor. Changes in part designs and tooling made on the production floor to meet quality requirements are often not reflected in the drawings. Stamping dies, for example, are ground and reshaped after they are put in the press. Changes are made to part contours to optimize manufacturing processes. Through the use of reverse engineering, these changes can be captured and used to update production drawings. To support the new requirements of today's engineers, advances in digitizing equipment and software to perform reverse engineering are rapidly being developed. Coordinate measuring machines, long recognized as a quality control tool, are being marketed with sophisticated digitizing software. Laser's and specialized equipment capable of both 2-D and 3-D are being c^tE 26/2--L
381
382
ROBERT J ABELLAet al
introduced [3]. Industry standards such as IGES [4] have simplified the transfer of informauon to CAD systems, making reverse engineering a much more generally applicable tool for most "systems" of equipment. Companies are adapting the basic concepts and equipment available to perform reverse engineering to meet their own special requirements. The two applications discussed below are examples of how reverse engineering can be applied to solve specific industrial problems. APPLYING REVERSE ENGINEERING TO SOLVE REAL PROBLEMS When designing a product, engineers typically utilize standard geometric shapes such as lines, circles and arcs. These features are combined to form parallel faces, perpendicular intersections, and symmetrical surfaces. An existing part, however, has been subjected to forces introduced in the process used to manufacture the part which formed slight to major deviations from the design. In many reverse engineering applications it is not desirable to copy these deviations. The goal of reverse engineering in these applications is to capture the engineering principles used in the design of the part, rather than to make an exact copy of the physical part. To successfully use reverse engineering in these applications, specialized software and engineering analysis ~s required. The standard practice in utilizing reverse engineering has been to digitize points on the part and transfer the points to a CAD system to generate the model. This procedure can be difficult for the CAD operator since it may not be obvious which points should be connected nor ~s the sequence of connections well defined. To circumvent this problem and to reduce the quantity of information that must be transmitted to the CAD system, it is desirable to develop the geometry of the part while the digitizing is being performed. Commercial reverse engineering systems [5] can be purchased which perform the digiuzmg and fitting at the same time. Private companies and research institutions have developed their own specialized reverse engineering systems. The reverse engineering system used for the applications discussed here is an example of this specialized software. The software was developed at The University of Toledo Industrial Engineering Department [6]. The system utilizes a CMM with a touch probe and has all fitting functions resident in the same computer that controls the CMM. Control over the diglttzing and fitting functions is through a menu driven window. Direct construction of the geometry at the C M M or other digmzlng method has a number of advantages over simply recording points on the part surface. First, the CMM operator has immediate feedback as to the adequacy of the digitizing operatmn. That is the operator can determine the number of points and their spacing to insure that the reqmred accuracy ~s being achieved. Second, the amount of information that must be transferred to the CAD system ~s reduced significantly. For example, an axis direction and location together w~th a radius ~s all that is needed to represent a cylinder which would otherwise require a large number of points for its description. Third, having geometry rather than point data greatly speeds and s~mphfies the CAD operator's job of constructing the CAD model. A fourth and major advantage of using geometry over point data ~s that the resultmg model can be a more accurate representation of the desired part. Unless compensated for, the manufacturing deviations, or wear, may introduce inaccuracies in the physical part. For example, part features that should be parallel, perpendicular or co-linear, etc., may not have the desired property if points are fit at the CAD system interface. When geometry is determined at the time the digitizing takes place, the operator can note the desired part features and incorporate desired relationships among surfaces as the digitizing takes place--provided the necessary software is available. Such software has been developed at The University of Toledo and two of the applications it was applied to are described in the following sections.
Spray gun handle A local manufacturer of spray equipment for the painting industry produced a line of manual equipment. Marketing conditions required that a robotic spray unit be developed. A critical
Industrial apphcations
383
z
Fig. 1. Three dimensional model of spray gun handle.
component of the spray equipment is the spray gun handle. The handle used on the manual unit required modifications for use on the robotic unit. The manual equipment had been produced for many years and drawings of the handle were no longer available. However, it was known that manufacturing and user operating constraints required that certain part features be parallel or perpendicular to each other. A drawing of the manual handle was obtained by reverse engineering one of the spray gun handles taken from production. The reverse engineered drawing is shown in Figs 1 and 2. The reverse engineering process is described following the figure. The handle was digitized on a manual coordinate measuring machine using the specialized software described above at The University of Toledo. Individual geometric entities on the part were visually identified, digitized on the CMM, and geometric functions fit to the digitized data. The specialized software was used to fit planes, lines and cylinders with parallel and perpendicular constraints as dictated by the design. The routines which were developed calculated the best fit geometry using both the digitized data and the added constraints. The final model consisted of the following entities: (a) Twenty one planes (b) Thirty-six lines (c) Four cylinders and (d) Four circular arcs su7
SUl]
\
N~
¢:y6
\ m16
x
sttl0
m15 L
ey2
\
tatl3
. ©yl ~ s u l 4
The position on CMM "~" Fig. 2 Geometry reqmred to model spray gun handle.
384
ROBERT J ABELLAet al
F~g 3 Isometric view of v~brator} bowl
Fig 4 Top ~te~x of ~lbratory bowl
Fillet radii were added to blend intersecting surfaces where required and the resulting CAD model used to make dies and produce parts in the established production system.
Vibratory bowl A manufacturer of vibratory bowls used to separate, align, and feed small parts to an on-line production operation provides the second application of reverse engineering. The bowls are round with an internal helical ramp running on the circumference of the bowl from the bottom to the mouth, located at the top edge the bowl's largest diameter. In operation, the bowl is vibrated, causing the parts inside to climb the helix in a single line and be delivered individually at the mouth at a given rate. The bowls had been in production for many years. The original design was developed by making a prototype modified at the shop floor level until the desired performance was achieved. Casting molds were made from the final prototype and used to produce the aluminum production bowls. Because of the design process, drawings of the bowls did not exist. Over time, the original casting patterns had deteriorated and worn and needed to be replaced. In addition, the company began to experience performance problems with the bowls as new equipment demanded higher feed rates. The company contacted The University of Toledo to obtain drawings by reverse engineering castings taken from production. The original scope of the project involved digitizing a bowl and makmg drawings reflecting the actual measured dimensions. The reverse engineering software described earlier was modified to include fitting functions for a hehx and used to create a CAD model directly from the digitized mformat~on. Examination of the CAD model revealed significant deviations from what company engineers perceived as the correct design These deviations were not detected m normal quality control functions which concentrated on individual dimensions. The deviations were apparent, however, by observmg the CAD model which displayed the relationships among the dimensions. Three major deviations found are as follows 1. Material wall thickness varied throughout the bowl. 2 The bowl's major diameter became smaller moving from base to top edge, whereas the design specified an increasing diameter serving as a draft angle for proper foundry processing. 3. The bowl's helical ramp was not described by one hehx as expected. It was actually a series of seven identifiable helixes blended together, each with individual descriptive parameters The final CAD model is shown m Figs 3 and 4. The model is correct mathematically in that the geometry fits standard formulae. Improvements in the design such as describing the ramp with two helixes rather than seven are incorporated. The part's critical dimensions such as the start and end points of the helixes and the overall size dimensions of the bowl re-established by design analysis during the reverse engineering process are integrated. These changes resolved some of
Industrial applications
385
the performance problems and provided a firm foundation for any further design modifications needed. CONCLUSIONS
Reverse engineering has changed from a manual procedure to a sophisticated engineering process utilizing modern digitizing equipment and advanced CAD systems. As a result, the applications of reverse engineering have been greatly extended from the original concept of making an exact copy of a part. Reverse engineering can now be utilized to assist the engineers in identifying and correcting design and manufacturing deficiencies. REFERENCES 1. 2. 3. 4. 5 6.
P M Noaker. 'CAM at the outer hmlts.' Manufact Engng, November 45-49 (1991). T T. Wohlers The real cost of rapid prototypmg. Manufact. Engng, November 77-79 (1991) R. R. Schreiber. The dynamics of digmzing. Manufact Engng March 59-63 (1992). U. S. Department of Commerce, Imtial graphics exchange specification (IGES) Version 4 0, June (1988) Brown & Sharp Manufactunng Company, Precision Park, North Kingston, R.I 02852. R. J Abella, I. Angulo and J. M Daschbach. Development of genenc software mgeneratton of IGES data with coordinate measuring machine. Final report Edison Industrial Systems Center, September (1989).
Pergamon
REVERSE
0360-8352(93)F_~19-5
ENGINEERING
INDUSTRIAL
Copyright © 1994 Elsevier Science Ltd Pnnted m Great Britain All rights reserved 0360-8352/94 $7 00 + 0 00
APPLICATIONS
ROBERT J. ABELLA, JAMES M . DASCHBACH a n d ROGER J. M c N I C H O L S Department of Industrial Engmeenng, The University of Toledo, Toledo, OH 43606-3390, U S.A AMtraet--Reverse Engmeenng is being applied to generate CAD files Speclahzed software ~s used wroth CMM and a touch probe m two demonstration experiments. Advantages of the technique include ~mmedmte feedback, data reduction, d~rect generauon of geometry and htgher precision of the final product.
INTRODUCTION
A machine part fails and the production line stops due to the essential character of this machine. No spare parts are available. The broken part is given to a machinist, a new part is made and the machine resumes service maintaining productivity. This situation is not new, it happens often. The basic concept of producing a part based on an original or physical model without the use of engineering drawings is called "Reverse Engineering". Reverse engineering has changed from a skilled manual process to an engineering tool using sophisticated computer software and modern measuring instruments. It has rapidly expanded from its origin in maintenance into the areas of design and production. This expansion is the result of both a change in the basic design process and the development of specialized equipment to support reverse engineering. Graphite drafting and blueprints are being replaced by CAD systems. As computers take over the drawing function, engineers have developed new ways to utilize the computer model in the design process. Finite element analysis and other engineering methods which previously took weeks to perform can now be completed in minutes. Analysis of designs with these mathematical tools has become an integral part of many design processes. Advanced CAM systems (1), which also utilize these computer models, have been incorporated into the product development phase. Along with the utilization of CAD systems has come a trend in many companies to use customized physical models in their design process. These models are made early in the design phase of a product and modified to incorporate functional improvements in meeting customer requests and requirements. Rapid prototyping [2] and other advances in model processing have developed to support these activities. When final design approval is obtained, the customized specifications of the part are often reflected in the model and not in the initial drawings, if they ever existed. Thus, design concepts developed with the model's evolution are being captured physically, but too often not incorporated back into the engineering process. Through reverse engineering, the optimized geometry and part dimensions can be the means to complete the integration of design updates and manufacturing 'polishing' with the necessary 'drawings' and historical records. Engineers working in production increasingly look toward reverse engineering to meet the higher demands for quality and efficiency in today's competitwe environment. One of the most common problems that industry faces is to maintain up-to-date drawings on the production floor. Changes in part designs and tooling made on the production floor to meet quality requirements are often not reflected in the drawings. Stamping dies, for example, are ground and reshaped after they are put in the press. Changes are made to part contours to optimize manufacturing processes. Through the use of reverse engineering, these changes can be captured and used to update production drawings. To support the new requirements of today's engineers, advances in digitizing equipment and software to perform reverse engineering are rapidly being developed. Coordinate measuring machines, long recognized as a quality control tool, are being marketed with sophisticated digitizing software. Laser's and specialized equipment capable of both 2-D and 3-D are being c^tE 26/2--L
381
382
ROBERT J ABELLAet al
introduced [3]. Industry standards such as IGES [4] have simplified the transfer of informauon to CAD systems, making reverse engineering a much more generally applicable tool for most "systems" of equipment. Companies are adapting the basic concepts and equipment available to perform reverse engineering to meet their own special requirements. The two applications discussed below are examples of how reverse engineering can be applied to solve specific industrial problems. APPLYING REVERSE ENGINEERING TO SOLVE REAL PROBLEMS When designing a product, engineers typically utilize standard geometric shapes such as lines, circles and arcs. These features are combined to form parallel faces, perpendicular intersections, and symmetrical surfaces. An existing part, however, has been subjected to forces introduced in the process used to manufacture the part which formed slight to major deviations from the design. In many reverse engineering applications it is not desirable to copy these deviations. The goal of reverse engineering in these applications is to capture the engineering principles used in the design of the part, rather than to make an exact copy of the physical part. To successfully use reverse engineering in these applications, specialized software and engineering analysis ~s required. The standard practice in utilizing reverse engineering has been to digitize points on the part and transfer the points to a CAD system to generate the model. This procedure can be difficult for the CAD operator since it may not be obvious which points should be connected nor ~s the sequence of connections well defined. To circumvent this problem and to reduce the quantity of information that must be transmitted to the CAD system, it is desirable to develop the geometry of the part while the digitizing is being performed. Commercial reverse engineering systems [5] can be purchased which perform the digiuzmg and fitting at the same time. Private companies and research institutions have developed their own specialized reverse engineering systems. The reverse engineering system used for the applications discussed here is an example of this specialized software. The software was developed at The University of Toledo Industrial Engineering Department [6]. The system utilizes a CMM with a touch probe and has all fitting functions resident in the same computer that controls the CMM. Control over the diglttzing and fitting functions is through a menu driven window. Direct construction of the geometry at the C M M or other digmzlng method has a number of advantages over simply recording points on the part surface. First, the CMM operator has immediate feedback as to the adequacy of the digitizing operatmn. That is the operator can determine the number of points and their spacing to insure that the reqmred accuracy ~s being achieved. Second, the amount of information that must be transferred to the CAD system ~s reduced significantly. For example, an axis direction and location together w~th a radius ~s all that is needed to represent a cylinder which would otherwise require a large number of points for its description. Third, having geometry rather than point data greatly speeds and s~mphfies the CAD operator's job of constructing the CAD model. A fourth and major advantage of using geometry over point data ~s that the resultmg model can be a more accurate representation of the desired part. Unless compensated for, the manufacturing deviations, or wear, may introduce inaccuracies in the physical part. For example, part features that should be parallel, perpendicular or co-linear, etc., may not have the desired property if points are fit at the CAD system interface. When geometry is determined at the time the digitizing takes place, the operator can note the desired part features and incorporate desired relationships among surfaces as the digitizing takes place--provided the necessary software is available. Such software has been developed at The University of Toledo and two of the applications it was applied to are described in the following sections.
Spray gun handle A local manufacturer of spray equipment for the painting industry produced a line of manual equipment. Marketing conditions required that a robotic spray unit be developed. A critical
Industrial apphcations
383
z
Fig. 1. Three dimensional model of spray gun handle.
component of the spray equipment is the spray gun handle. The handle used on the manual unit required modifications for use on the robotic unit. The manual equipment had been produced for many years and drawings of the handle were no longer available. However, it was known that manufacturing and user operating constraints required that certain part features be parallel or perpendicular to each other. A drawing of the manual handle was obtained by reverse engineering one of the spray gun handles taken from production. The reverse engineered drawing is shown in Figs 1 and 2. The reverse engineering process is described following the figure. The handle was digitized on a manual coordinate measuring machine using the specialized software described above at The University of Toledo. Individual geometric entities on the part were visually identified, digitized on the CMM, and geometric functions fit to the digitized data. The specialized software was used to fit planes, lines and cylinders with parallel and perpendicular constraints as dictated by the design. The routines which were developed calculated the best fit geometry using both the digitized data and the added constraints. The final model consisted of the following entities: (a) Twenty one planes (b) Thirty-six lines (c) Four cylinders and (d) Four circular arcs su7
SUl]
\
N~
¢:y6
\ m16
x
sttl0
m15 L
ey2
\
tatl3
. ©yl ~ s u l 4
The position on CMM "~" Fig. 2 Geometry reqmred to model spray gun handle.
384
ROBERT J ABELLAet al
F~g 3 Isometric view of v~brator} bowl
Fig 4 Top ~te~x of ~lbratory bowl
Fillet radii were added to blend intersecting surfaces where required and the resulting CAD model used to make dies and produce parts in the established production system.
Vibratory bowl A manufacturer of vibratory bowls used to separate, align, and feed small parts to an on-line production operation provides the second application of reverse engineering. The bowls are round with an internal helical ramp running on the circumference of the bowl from the bottom to the mouth, located at the top edge the bowl's largest diameter. In operation, the bowl is vibrated, causing the parts inside to climb the helix in a single line and be delivered individually at the mouth at a given rate. The bowls had been in production for many years. The original design was developed by making a prototype modified at the shop floor level until the desired performance was achieved. Casting molds were made from the final prototype and used to produce the aluminum production bowls. Because of the design process, drawings of the bowls did not exist. Over time, the original casting patterns had deteriorated and worn and needed to be replaced. In addition, the company began to experience performance problems with the bowls as new equipment demanded higher feed rates. The company contacted The University of Toledo to obtain drawings by reverse engineering castings taken from production. The original scope of the project involved digitizing a bowl and makmg drawings reflecting the actual measured dimensions. The reverse engineering software described earlier was modified to include fitting functions for a hehx and used to create a CAD model directly from the digitized mformat~on. Examination of the CAD model revealed significant deviations from what company engineers perceived as the correct design These deviations were not detected m normal quality control functions which concentrated on individual dimensions. The deviations were apparent, however, by observmg the CAD model which displayed the relationships among the dimensions. Three major deviations found are as follows 1. Material wall thickness varied throughout the bowl. 2 The bowl's major diameter became smaller moving from base to top edge, whereas the design specified an increasing diameter serving as a draft angle for proper foundry processing. 3. The bowl's helical ramp was not described by one hehx as expected. It was actually a series of seven identifiable helixes blended together, each with individual descriptive parameters The final CAD model is shown m Figs 3 and 4. The model is correct mathematically in that the geometry fits standard formulae. Improvements in the design such as describing the ramp with two helixes rather than seven are incorporated. The part's critical dimensions such as the start and end points of the helixes and the overall size dimensions of the bowl re-established by design analysis during the reverse engineering process are integrated. These changes resolved some of
Industrial applications
385
the performance problems and provided a firm foundation for any further design modifications needed. CONCLUSIONS
Reverse engineering has changed from a manual procedure to a sophisticated engineering process utilizing modern digitizing equipment and advanced CAD systems. As a result, the applications of reverse engineering have been greatly extended from the original concept of making an exact copy of a part. Reverse engineering can now be utilized to assist the engineers in identifying and correcting design and manufacturing deficiencies. REFERENCES 1. 2. 3. 4. 5 6.
P M Noaker. 'CAM at the outer hmlts.' Manufact Engng, November 45-49 (1991). T T. Wohlers The real cost of rapid prototypmg. Manufact. Engng, November 77-79 (1991) R. R. Schreiber. The dynamics of digmzing. Manufact Engng March 59-63 (1992). U. S. Department of Commerce, Imtial graphics exchange specification (IGES) Version 4 0, June (1988) Brown & Sharp Manufactunng Company, Precision Park, North Kingston, R.I 02852. R. J Abella, I. Angulo and J. M Daschbach. Development of genenc software mgeneratton of IGES data with coordinate measuring machine. Final report Edison Industrial Systems Center, September (1989).