- Email: [email protected]
A prototype system for early geometric configuration design
ELSEVIER
Computers in Industry 30 (1996) 233-239
A prototype system for early geometric configuration X. Guan * , D.A. Stevenson,
design
K.J. MacCallum
CAD Centre, Departmmt ofDesign, Manufacture and Engineering Management, Unirersiq ofStrathclyde, 75 Montrose Street, Glasgow Gl IXJ, UK Received 15 January 1996
Abstract In this paper, we pnzsent a prototype system that has been developed to support geometric configuration of objects at the early stages of design. Guided by the general principle of minimum commitment, this system assists in the iterative development of alternative geometric configurations based on approximately or precisely defined information. The system has been evaluated in the context of computer enclosure design. Kqvwords: Early geometric design support: Geometric configuration: Computer aided design
1. Introduction A computer aided design system suitable for early stages of design should be an integrated environment that offers a wide range of capabilities in assisting the development and evaluation of early design concepts, as well as their detailing in subsequent stages. This requires the system to support not only functional and other relevant design activities, but also geometric information processing. Our research goal has been to investigate a system that assists in the development of early geometric concepts. At the early stages of geometric design, a designer’s attention and interest is mainly on exploring a variety of possible geometric configurations of a product, where geometric configuration refers to the total geometric structure of the product consisting of the approximate or precise geometry of components
* Corresponding
author. Email: [email protected]
0166.3615/96/$15.00 Cupylight PII SOl66-3615(96)00024-3
of the product and their overall spatial arrangement in forming the structure (Guan, 1993). These altemative configurations are developed at an abstract and approximate level, and are evaluated with respect to certain criteria. As a result, the most suitable ones are selected for further detailed design and evaluation. This development-evaluation-refinement process may iterate many times until the best concept is derived and ready for full design. Geometric information available during the early stages is usually a mixture of both vague and precise information, where vague can be characterised as approximate, abstract, or as incomplete. Free-hand sketches and diagrams are used frequently during the design process for effective expression, communication, and recording of both geometric and non-geometric aspects of or information about the product being designed (Tovey, 1989; Ullman, 1992). These sketches, and their use in the design process, highlight a desire to explore and investigate design options or concepts without commitment to exactness or detail.
D 1996 Elsevier Science All rights reserved.
X. Gum et al. /Computers
234
Although various Computer Aided Design (CAD) systems, such as the traditional and now widely used geometric modelling systems and more advanced parametric, variational and feature based systems, have been developed to support the modelling of product geometry, they usually require complete, concrete and precise definitions on the geometry which are only available at the detail stages of the design process. Thus, by requiring from designers greater commitment than they can make or are willing to make at the early concept design stages, these systems are not well suited to deal with early geometric configuration problems. In contrast, we have adopted a principle of minimum commitment modelling which does not force a designer to make commitments prematurely, i.e. earlier than necessary, desired or appropriate. Here, a commitment refers to a decision regarding components, arrangements, sizes or positions. Any decision which uses vague information is regarded as less committing than precise information. This paper presents a prototype system for supporting the modelling of geometric configurations. Adopting the minimum commitment principle imposes important requirements on the modelling capabilities of the system. These requirements are discussed in Section 2, followed by an overview of the structure of the system in Section 3. We illustrate, in Section 4, the use of the system through examples, and in Section 5 raise issues for further investigation.
2. Modelling
requirements
To support the minimum commitment modelling of geometric configurations, the following basic requirements were established for the system: - Permit the use of various types of geometric information which may be vague or precise; - Support incremental refinement of approximate size and location of components; - Support simultaneous incremental development of multiple approximate or precise geometric configuration models; - Support the handling of conflicting or inconsistent geometric information. A major requirement for the user interface to the system was that it should facilitate, or at least not
in Indctstryv 30 (19961 233-239
hinder, the user’s access to and interaction with the modelling utilities of the system. A graphical user interface (GUI) was deemed appropriate, but with the clear understanding that the user-accessible functionality of the system should not become embedded in, and so dependent on, any one particular user interface front end. Through an examination of the early stages of design, we identified the various types of geometric information involved during the process of geometric configuration and the possible forms in which such information is given by designers (Guan, 1993). During the initial development phase, we decided to concentrate on providing the system with the capabilities of handling primitive shapes, approximate and precise size information given in the form of inequalities (e.g. width I 15.2, depth = 13.41, ranges (e.g. height = i22.5, 23.411, and equalities (e.g. radius = 9.4), as well as abstract and precise location information given in the form of spatial relationships (e.g. above, right and behind) and point position (e.g. (12.0, 22.4, 21.7)).
3. Structure
of the system
Fig. 1 illustrates the various modules of the prototype system. They have been implemented on a SunSparc platform running Sun Common Lisp with the Common Lisp Object System (CLOS). The prototype system also accesses, directly or indirectly, three non-Lisp packages: a geometric modeller ACIS (Spatial Technology Inc., 1992), a constraint solver CLP(R) (Heintze, 1991) and a graph editor EDGE (Paulisch and Walter, 1990). Our approach has been to define an interaction shell around the modelling core (which is also referred to as the application system), consisting in the complete suite of modelling operations by which any outside agent can manipulate and access the models under construction, and to develop a GUI which is linked to this interaction shell. This allows the application system to be accessed in two ways: directly through the interaction shell commands, and, more conveniently, through the GUI. A most significant advantage of this is that it allows the GUI and the application system to develop in parallel.
X. Guan et al. / Computers in Industry 30 (1996) 233-239
A Geometric Configuration Model is a cluster of CLOS objects that are linked to one another as defined by a developed representation framework (Guan, 1993). These objects are instantiated with the known geometric information about a product. The model describes the total geometric structure of a product as a geometric configuration, confined to a geometric configuration space, which consists of geometry objects that represent the components of the product and are spatially related to one another.
235
Based on a comparison of a number of approximation handling techniques, we have chosen the interval based method (Moore, 1966) to represent uniformly the approximate and precise size and location definition of components. Using this method, size information of types, e.g. depth = 30 and height = 40 is captured by ranges as L28.7, 31.31 (assuming the degree of approximation is 2.6) and 140, 401. Here, a range is an interval of real numbers defined by a lower and an upper bound. The location of a compo-
Interaction Shell
Graphical User Interface ‘Front End’ Fig. 1. Modules of the geometric configuration system.
236
X. Gum rt al. / Computers in Industp
nent is characterised in the model by a datum point on the component, which is situated in a 3D uncertain region defined by three ranges capturing the allowable X, y, and z co-ordinates of the datum point. In the present system, we have chosen the geometric centre of a component as its datum point. To handle such information, a reasoning mechanism has been developed based on constraint management technique combined with interval calculation (Guan, 1993). The various modules in Fig. 1 have been designed to provide the necessary handlings based on the mechanism. When using the system, the user establishes the geometric model of a component by specifying ’ its shape type, size constraints, and possibly the location of the component in the configuration through spatial relationships or point position. The Geometric Configuration Manager is responsible for dispatching such information to other modules and managing the established models. The Primitive Shape Handler accesses basic definitions of a set of primitive shapes, currently cuboid, cylinder, sphere, frustum and prism. The Size Constraint Handler manages the processing of the set of size constraints sent down by the Geometric Configuration Manager. It tries to simplify some of them and dispatches the others, in appropriate forms, to the Constraint Solver CLP(R) to solve and to the Range Converter to transform the results into value ranges for the corresponding size parameters. The Conflict/Inconsistency Handler deals with possible syntactical and some semantic errors that may exist in size or location information. The Location Constraint Handler transforms spatial relationships or point positions specified by designers into constraints on the bounds of the uncertain regions of the relevant components and solves these constraints using CLP(R). The results obtained are passed on to the Uncertain Region Modifier to update the uncertain regions of the corresponding objects. Based on the size and location definitions of components, the Boundary Model Manager generates or updates the corresponding boundary geometric models by use of the ACIS geometric modeller. The user’s graphical display requirements on ACIS are set up by the
’ Default values are used for unspecified parameters.
30 (19961 233-239
ACIS View Controller. Supported by the Spatial Relationship Query Handler, a user may inspect the spatial relationships specified for a given geometric configuration, such as finding the relationships between two geometry objects in a configuration and finding all the spatial relationships specified for a configuration. This handler has been implemented using the DAG package (Donaldson, 19931, developed based on the EDGE program, which consists of Lisp based utilities for making and manipulating directed acyclic graphs. A widget-based graphical user interface has been developed using Lispview, a SunCL binding to OpenLook windows, and the MINDER system (Stevenson, 1990). It provides active displays of application objects (i.e. changes in values of displayed objects invoke automatic updates of the displays), form-fill panels for composing and executing modelling operations defined in the interaction shell, and view control panels for the ACIS wire-frame and EDGE graph displays.
4. Examples
of using the system
In this section, we briefly illustrate the use of the system through examples taken from computer enclosure design: the process of spatially interconnecting together various components of a computer system via a mechanical structure to satisfy various requirements - functional, service, ergonomic, safety, environmental, etc. Suppose we have some information about the geometry of a Power Supply Unit and would like to construct a rough model for it (we either are not interested in a precise model or are not yet sure of the exact size). The shape of the component can be approximated by a cuboid with the size of width = 21.08 (expressed as width A= 21.08 in the system), depth in range 114.02, 15.501 (expressed as depth = 14.02 -+ 15.50) and height = 3.05. We do not yet want to consider its location in the whole enclosure design. Fig. 2 shows the use of the system in making this model by issuing the corresponding commands through the GUI. Note that the modelling operations can also be performed by typing directly into the Lisp Listener as Lisp commands.
231
X. Guan et al. / Computers in Industry 30 (1996) 233-239
VACUECEOM~RY
CONTIIOL
IVCI-CON11
G@OlWtrhS:
m
;1
GEOMETRY1
Power
Supply
Unit
creatw80m~trlc-conflg sdlt
g8omtblc
.l.
conflguratlon
,..)
traateqeometry I
Sk
Conrtralntr:
i
-
SIZE-CONSTRAINT3
((HEIGHT
SIZE-CONSTRAINT2
((DEPTH
GEOMETRYI)
- 14 02 ->
SIZE-CONSTRAINT1
((WIDTH
GEOMETRYI)
A- 21.08)
rePresents
shape
!‘ow
supply
.,. ,.,
GEOMETRYI)
*-
3 05)
rpeclfy-locatIon r) 15 5)
m REFRESH “is,,
1 ;ew)
geometry
Ill0
B
_.I
-
edlt
J -EdIt)
m
.
s
REFRESH
adge)
unit
CUBOID I
Fig. 2. Constructing
the geometric
To present the associated size approximation, the system, through the ACIS window, displays two boundaty models of the component, called the minimum envelope and the maximum envelope respectively. The minimum envelope corresponds to the minimum size of the. component and is displayed at a position such that its centre (datum point) is at the left-bottom-front most comer of its uncertain region. The maximum envelope corresponds to the maximum size and is also displayed at this position in order to present the associated size approximation graphically. The space between the two envelopes presents the ranges of possible size for the component and can be interpreted in two ways: (a) the precise boundary of this component will lie somewhere in this space; (b) any cuboid whose boundary
model of the Power Supply Unit.
lies in this space when displayed at the same position satisfies the size requirements of the component. Support for working with such approximate information in the system does not force a user to make commitment to unnecessary or unavailable details, and thus leaves the solution space as open as possible. It is assumed that later incremental refinement or configuration constraints will reduce the uncertain ranges until a precise model is defined. Fig. 2 also shows the main panel of the system which provides menus of commands that allow the user to construct, modify and inspect various geometric configuration models. It also presents active lists (initially empty) of the modelling entities such as geometries, configurations and relations, as they are created by the user during the session.
238
Ghan et al. / Computers
Fig. 3. Geometric-configuration1
Having established the rough model, suppose we now wish to place it on the right of an Electric Fan whose geometric model, geometry2, has also been constructed. This can be achieved by invoking the operation specify-location. As a result, a geometric configuration, geometric-configurationl, will be constructed by the system in which the Power Supply Unit is located on the right of the Electric Fan. The width of the Power Supply Unit has been between 14.02 and 15.50 (Fig. 2). If we at this stage discover or decide that this depth should be 2 14.65, this new information can then be used to refine the value range of the depth from the initial specification of [14.05, 15.501 to [14.65, 15.501. If, however, a new value is supplied that is outside the previous range, say depth 2 16, the system detects and notifies the user of the inconsistency, and disallows the change. If the user does require the change to be made, the existing conflicting constraint must first be deleted. The system is also able to detect certain obvious spatial conflicts. For example, if a Mother Board was specified to be behind a Hard Disk Drive and on the right of the Electric Fan in the configuration in a previous step, then specifying the Mother Board to be in front of the Hard Disk Drive in the same configuration will be detected as a conflict, and the
in Industy
30 t 1996) 233-239
- A preliminary
enclosure design.
user is prompted to either withdraw from the operation, or enforce the new position. Fig. 3 shows a rough computer enclosure design - geometric-configuration1 - with all the defined spatial relationships, incrementally developed using the system. Note that it displays only one of the possible configurations allowed by the location constraints. In this default display, components are shown in the left-low-front comers of the corresponding location uncertain regions. By changing the current configuration being worked on during a modelling session, one can also investigate simultaneously a number of different geometric configurations for the same product. Throughout this approach, the uniform definition of approximate and precise geometry underpins the minimum commitment principle. In particular, it allows commitments to complete and exact size and location specifications to be deferred as desired or necessary.
5. Conclusions In this paper, we have described a prototype system for supporting the development of early geometric configurations following a minimum commit-
X. Guan et al. / Computers in Industry 30 (1996) 233-239
ment modelling principle. The system currently supports a user’s moclelling, incrementally and nonsequentially, of multiple approximate or precise geometric configurations using primitive shapes, simple inequality, range and equality types of size constraints, and abstract primitive spatial relationships. To adapt to various practical configuration problems, further research and development is required to enhance the capacity of the system, in particular for modelling more complex size constraints, spatial relationships, shapes. and different orientation. A sketch-based GUI would further facilitate the use of the system. To fully support the development of early geometric configuration concepts, research should also be carried out to provide utilities for evaluating and conserving geometric configurations. Finally, investigation is proposed to integrate with those systems that deal with other aspects of concept design, such as functional modelling, towards providing an integrated conceptual design support environment.
Acknowledgements The authors wish to acknowledge the support received from EPSRC, U.K. for the work presented in this paper.
References I. Donaldson, “The CCINCEPT FRAME SYSTEM: An objectoriented data representation for concept model@“, Technical Report, CAD Centre, University of Strathclyde, U.K., 1993. X. Guan, “Computational support for early geometric design”, Ph.D. Thesis, CAD Centre, University of Strathclyde, U.K., 1993. N. Heintze et al., The CLPfR) Programmer’s Manual, Version 1.1, IBM Thomas J. Watson Research Centre, USA, 1991. R.T. Moore, Interual Analysis, Prentice-Hall, Englewood Cliffs, 1966. F.N. Paulisch and F.T. Walter, “EDGE: An extendible graph editor”, Sojiware Practice and Experience 20, Sl, 1990. Spatial Technology Inc., ACIS: Inteface Guide, 1992. D.A. Stevenson, “An output-oriented approach to user interface design”, M.Phil T&is, CAD Centre, University of StrathClyde, U.K., 1990.
239
M. Tovey, Drawing and CAD in industrial design, Design Studies, Vol. 10, No. 1, 1989, pp. 24-39. D.G. Ullman, The Mechanical Design Process, McGraw-Hill, Inc., 1992. Xiaohong Guan is a research assistant at the CAD Centre, University of StrathClyde, UK. Her current research interests include early design support systems, geometric reasoning, constraint management and geometric modelling. She obtained a BSc in Radio Electronics Science from University of Sichuan, China, in 1984, an MSc in Information Engineering from Xidian University, China in 1987 and a PhD from University of Strathclyde, UK in 1994. She is a member of IEEE, ACM and AAAI. David A. Stevenson is a research assistant at the CAD Centre, University of Strathclyde, UK. His current research interests include early design support systems and the use of graphical presentation and interaction techniques to support working with computer-based applications, particularly those concerned with design and problem-solving. After many years working as an architectural assistant, he obtained a BSc in Mathematical Sciences as a mature student in 1985 and an MPhil for research into user interface provision for design-related systems in 1990, both from the University of Strathclyde, UK. Ken MacCallum obtained his first degree in Naval Architecture from the University of Glasgow, proceeding to postgraduate study in Imperial College, University of London where he obtained a PhD for research into the application of computer graphics to free-form surface design. After three years with a software company, he joined the University of Strathclyde, establishing the CAD Centre in 1985 as a research and postgraduate centre. He is currently the Head of Design, Manufacture and Engineering Management in the Faculty of Engineering at the University of Strathclyde. Ken MacCallum’s main area of research has been the application of Artificial Intelligence to Engineering Design. He has led projects concerned with intelligent design modelling, data exchange, computer based design coordination, and computer aided learning. He is editor of the International Journal on Artificial Intelligence in Engineering, is a member of IFIP WG 5.2, and has been on the Technical Programme Committees of a large number of Conferences and Workshops concerned with computer aided design.
Computers in Industry 30 (1996) 233-239
A prototype system for early geometric configuration X. Guan * , D.A. Stevenson,
design
K.J. MacCallum
CAD Centre, Departmmt ofDesign, Manufacture and Engineering Management, Unirersiq ofStrathclyde, 75 Montrose Street, Glasgow Gl IXJ, UK Received 15 January 1996
Abstract In this paper, we pnzsent a prototype system that has been developed to support geometric configuration of objects at the early stages of design. Guided by the general principle of minimum commitment, this system assists in the iterative development of alternative geometric configurations based on approximately or precisely defined information. The system has been evaluated in the context of computer enclosure design. Kqvwords: Early geometric design support: Geometric configuration: Computer aided design
1. Introduction A computer aided design system suitable for early stages of design should be an integrated environment that offers a wide range of capabilities in assisting the development and evaluation of early design concepts, as well as their detailing in subsequent stages. This requires the system to support not only functional and other relevant design activities, but also geometric information processing. Our research goal has been to investigate a system that assists in the development of early geometric concepts. At the early stages of geometric design, a designer’s attention and interest is mainly on exploring a variety of possible geometric configurations of a product, where geometric configuration refers to the total geometric structure of the product consisting of the approximate or precise geometry of components
* Corresponding
author. Email: [email protected]
0166.3615/96/$15.00 Cupylight PII SOl66-3615(96)00024-3
of the product and their overall spatial arrangement in forming the structure (Guan, 1993). These altemative configurations are developed at an abstract and approximate level, and are evaluated with respect to certain criteria. As a result, the most suitable ones are selected for further detailed design and evaluation. This development-evaluation-refinement process may iterate many times until the best concept is derived and ready for full design. Geometric information available during the early stages is usually a mixture of both vague and precise information, where vague can be characterised as approximate, abstract, or as incomplete. Free-hand sketches and diagrams are used frequently during the design process for effective expression, communication, and recording of both geometric and non-geometric aspects of or information about the product being designed (Tovey, 1989; Ullman, 1992). These sketches, and their use in the design process, highlight a desire to explore and investigate design options or concepts without commitment to exactness or detail.
D 1996 Elsevier Science All rights reserved.
X. Gum et al. /Computers
234
Although various Computer Aided Design (CAD) systems, such as the traditional and now widely used geometric modelling systems and more advanced parametric, variational and feature based systems, have been developed to support the modelling of product geometry, they usually require complete, concrete and precise definitions on the geometry which are only available at the detail stages of the design process. Thus, by requiring from designers greater commitment than they can make or are willing to make at the early concept design stages, these systems are not well suited to deal with early geometric configuration problems. In contrast, we have adopted a principle of minimum commitment modelling which does not force a designer to make commitments prematurely, i.e. earlier than necessary, desired or appropriate. Here, a commitment refers to a decision regarding components, arrangements, sizes or positions. Any decision which uses vague information is regarded as less committing than precise information. This paper presents a prototype system for supporting the modelling of geometric configurations. Adopting the minimum commitment principle imposes important requirements on the modelling capabilities of the system. These requirements are discussed in Section 2, followed by an overview of the structure of the system in Section 3. We illustrate, in Section 4, the use of the system through examples, and in Section 5 raise issues for further investigation.
2. Modelling
requirements
To support the minimum commitment modelling of geometric configurations, the following basic requirements were established for the system: - Permit the use of various types of geometric information which may be vague or precise; - Support incremental refinement of approximate size and location of components; - Support simultaneous incremental development of multiple approximate or precise geometric configuration models; - Support the handling of conflicting or inconsistent geometric information. A major requirement for the user interface to the system was that it should facilitate, or at least not
in Indctstryv 30 (19961 233-239
hinder, the user’s access to and interaction with the modelling utilities of the system. A graphical user interface (GUI) was deemed appropriate, but with the clear understanding that the user-accessible functionality of the system should not become embedded in, and so dependent on, any one particular user interface front end. Through an examination of the early stages of design, we identified the various types of geometric information involved during the process of geometric configuration and the possible forms in which such information is given by designers (Guan, 1993). During the initial development phase, we decided to concentrate on providing the system with the capabilities of handling primitive shapes, approximate and precise size information given in the form of inequalities (e.g. width I 15.2, depth = 13.41, ranges (e.g. height = i22.5, 23.411, and equalities (e.g. radius = 9.4), as well as abstract and precise location information given in the form of spatial relationships (e.g. above, right and behind) and point position (e.g. (12.0, 22.4, 21.7)).
3. Structure
of the system
Fig. 1 illustrates the various modules of the prototype system. They have been implemented on a SunSparc platform running Sun Common Lisp with the Common Lisp Object System (CLOS). The prototype system also accesses, directly or indirectly, three non-Lisp packages: a geometric modeller ACIS (Spatial Technology Inc., 1992), a constraint solver CLP(R) (Heintze, 1991) and a graph editor EDGE (Paulisch and Walter, 1990). Our approach has been to define an interaction shell around the modelling core (which is also referred to as the application system), consisting in the complete suite of modelling operations by which any outside agent can manipulate and access the models under construction, and to develop a GUI which is linked to this interaction shell. This allows the application system to be accessed in two ways: directly through the interaction shell commands, and, more conveniently, through the GUI. A most significant advantage of this is that it allows the GUI and the application system to develop in parallel.
X. Guan et al. / Computers in Industry 30 (1996) 233-239
A Geometric Configuration Model is a cluster of CLOS objects that are linked to one another as defined by a developed representation framework (Guan, 1993). These objects are instantiated with the known geometric information about a product. The model describes the total geometric structure of a product as a geometric configuration, confined to a geometric configuration space, which consists of geometry objects that represent the components of the product and are spatially related to one another.
235
Based on a comparison of a number of approximation handling techniques, we have chosen the interval based method (Moore, 1966) to represent uniformly the approximate and precise size and location definition of components. Using this method, size information of types, e.g. depth = 30 and height = 40 is captured by ranges as L28.7, 31.31 (assuming the degree of approximation is 2.6) and 140, 401. Here, a range is an interval of real numbers defined by a lower and an upper bound. The location of a compo-
Interaction Shell
Graphical User Interface ‘Front End’ Fig. 1. Modules of the geometric configuration system.
236
X. Gum rt al. / Computers in Industp
nent is characterised in the model by a datum point on the component, which is situated in a 3D uncertain region defined by three ranges capturing the allowable X, y, and z co-ordinates of the datum point. In the present system, we have chosen the geometric centre of a component as its datum point. To handle such information, a reasoning mechanism has been developed based on constraint management technique combined with interval calculation (Guan, 1993). The various modules in Fig. 1 have been designed to provide the necessary handlings based on the mechanism. When using the system, the user establishes the geometric model of a component by specifying ’ its shape type, size constraints, and possibly the location of the component in the configuration through spatial relationships or point position. The Geometric Configuration Manager is responsible for dispatching such information to other modules and managing the established models. The Primitive Shape Handler accesses basic definitions of a set of primitive shapes, currently cuboid, cylinder, sphere, frustum and prism. The Size Constraint Handler manages the processing of the set of size constraints sent down by the Geometric Configuration Manager. It tries to simplify some of them and dispatches the others, in appropriate forms, to the Constraint Solver CLP(R) to solve and to the Range Converter to transform the results into value ranges for the corresponding size parameters. The Conflict/Inconsistency Handler deals with possible syntactical and some semantic errors that may exist in size or location information. The Location Constraint Handler transforms spatial relationships or point positions specified by designers into constraints on the bounds of the uncertain regions of the relevant components and solves these constraints using CLP(R). The results obtained are passed on to the Uncertain Region Modifier to update the uncertain regions of the corresponding objects. Based on the size and location definitions of components, the Boundary Model Manager generates or updates the corresponding boundary geometric models by use of the ACIS geometric modeller. The user’s graphical display requirements on ACIS are set up by the
’ Default values are used for unspecified parameters.
30 (19961 233-239
ACIS View Controller. Supported by the Spatial Relationship Query Handler, a user may inspect the spatial relationships specified for a given geometric configuration, such as finding the relationships between two geometry objects in a configuration and finding all the spatial relationships specified for a configuration. This handler has been implemented using the DAG package (Donaldson, 19931, developed based on the EDGE program, which consists of Lisp based utilities for making and manipulating directed acyclic graphs. A widget-based graphical user interface has been developed using Lispview, a SunCL binding to OpenLook windows, and the MINDER system (Stevenson, 1990). It provides active displays of application objects (i.e. changes in values of displayed objects invoke automatic updates of the displays), form-fill panels for composing and executing modelling operations defined in the interaction shell, and view control panels for the ACIS wire-frame and EDGE graph displays.
4. Examples
of using the system
In this section, we briefly illustrate the use of the system through examples taken from computer enclosure design: the process of spatially interconnecting together various components of a computer system via a mechanical structure to satisfy various requirements - functional, service, ergonomic, safety, environmental, etc. Suppose we have some information about the geometry of a Power Supply Unit and would like to construct a rough model for it (we either are not interested in a precise model or are not yet sure of the exact size). The shape of the component can be approximated by a cuboid with the size of width = 21.08 (expressed as width A= 21.08 in the system), depth in range 114.02, 15.501 (expressed as depth = 14.02 -+ 15.50) and height = 3.05. We do not yet want to consider its location in the whole enclosure design. Fig. 2 shows the use of the system in making this model by issuing the corresponding commands through the GUI. Note that the modelling operations can also be performed by typing directly into the Lisp Listener as Lisp commands.
231
X. Guan et al. / Computers in Industry 30 (1996) 233-239
VACUECEOM~RY
CONTIIOL
IVCI-CON11
G@OlWtrhS:
m
;1
GEOMETRY1
Power
Supply
Unit
creatw80m~trlc-conflg sdlt
g8omtblc
.l.
conflguratlon
,..)
traateqeometry I
Sk
Conrtralntr:
i
-
SIZE-CONSTRAINT3
((HEIGHT
SIZE-CONSTRAINT2
((DEPTH
GEOMETRYI)
- 14 02 ->
SIZE-CONSTRAINT1
((WIDTH
GEOMETRYI)
A- 21.08)
rePresents
shape
!‘ow
supply
.,. ,.,
GEOMETRYI)
*-
3 05)
rpeclfy-locatIon r) 15 5)
m REFRESH “is,,
1 ;ew)
geometry
Ill0
B
_.I
-
edlt
J -EdIt)
m
.
s
REFRESH
adge)
unit
CUBOID I
Fig. 2. Constructing
the geometric
To present the associated size approximation, the system, through the ACIS window, displays two boundaty models of the component, called the minimum envelope and the maximum envelope respectively. The minimum envelope corresponds to the minimum size of the. component and is displayed at a position such that its centre (datum point) is at the left-bottom-front most comer of its uncertain region. The maximum envelope corresponds to the maximum size and is also displayed at this position in order to present the associated size approximation graphically. The space between the two envelopes presents the ranges of possible size for the component and can be interpreted in two ways: (a) the precise boundary of this component will lie somewhere in this space; (b) any cuboid whose boundary
model of the Power Supply Unit.
lies in this space when displayed at the same position satisfies the size requirements of the component. Support for working with such approximate information in the system does not force a user to make commitment to unnecessary or unavailable details, and thus leaves the solution space as open as possible. It is assumed that later incremental refinement or configuration constraints will reduce the uncertain ranges until a precise model is defined. Fig. 2 also shows the main panel of the system which provides menus of commands that allow the user to construct, modify and inspect various geometric configuration models. It also presents active lists (initially empty) of the modelling entities such as geometries, configurations and relations, as they are created by the user during the session.
238
Ghan et al. / Computers
Fig. 3. Geometric-configuration1
Having established the rough model, suppose we now wish to place it on the right of an Electric Fan whose geometric model, geometry2, has also been constructed. This can be achieved by invoking the operation specify-location. As a result, a geometric configuration, geometric-configurationl, will be constructed by the system in which the Power Supply Unit is located on the right of the Electric Fan. The width of the Power Supply Unit has been between 14.02 and 15.50 (Fig. 2). If we at this stage discover or decide that this depth should be 2 14.65, this new information can then be used to refine the value range of the depth from the initial specification of [14.05, 15.501 to [14.65, 15.501. If, however, a new value is supplied that is outside the previous range, say depth 2 16, the system detects and notifies the user of the inconsistency, and disallows the change. If the user does require the change to be made, the existing conflicting constraint must first be deleted. The system is also able to detect certain obvious spatial conflicts. For example, if a Mother Board was specified to be behind a Hard Disk Drive and on the right of the Electric Fan in the configuration in a previous step, then specifying the Mother Board to be in front of the Hard Disk Drive in the same configuration will be detected as a conflict, and the
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- A preliminary
enclosure design.
user is prompted to either withdraw from the operation, or enforce the new position. Fig. 3 shows a rough computer enclosure design - geometric-configuration1 - with all the defined spatial relationships, incrementally developed using the system. Note that it displays only one of the possible configurations allowed by the location constraints. In this default display, components are shown in the left-low-front comers of the corresponding location uncertain regions. By changing the current configuration being worked on during a modelling session, one can also investigate simultaneously a number of different geometric configurations for the same product. Throughout this approach, the uniform definition of approximate and precise geometry underpins the minimum commitment principle. In particular, it allows commitments to complete and exact size and location specifications to be deferred as desired or necessary.
5. Conclusions In this paper, we have described a prototype system for supporting the development of early geometric configurations following a minimum commit-
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ment modelling principle. The system currently supports a user’s moclelling, incrementally and nonsequentially, of multiple approximate or precise geometric configurations using primitive shapes, simple inequality, range and equality types of size constraints, and abstract primitive spatial relationships. To adapt to various practical configuration problems, further research and development is required to enhance the capacity of the system, in particular for modelling more complex size constraints, spatial relationships, shapes. and different orientation. A sketch-based GUI would further facilitate the use of the system. To fully support the development of early geometric configuration concepts, research should also be carried out to provide utilities for evaluating and conserving geometric configurations. Finally, investigation is proposed to integrate with those systems that deal with other aspects of concept design, such as functional modelling, towards providing an integrated conceptual design support environment.
Acknowledgements The authors wish to acknowledge the support received from EPSRC, U.K. for the work presented in this paper.
References I. Donaldson, “The CCINCEPT FRAME SYSTEM: An objectoriented data representation for concept model@“, Technical Report, CAD Centre, University of Strathclyde, U.K., 1993. X. Guan, “Computational support for early geometric design”, Ph.D. Thesis, CAD Centre, University of Strathclyde, U.K., 1993. N. Heintze et al., The CLPfR) Programmer’s Manual, Version 1.1, IBM Thomas J. Watson Research Centre, USA, 1991. R.T. Moore, Interual Analysis, Prentice-Hall, Englewood Cliffs, 1966. F.N. Paulisch and F.T. Walter, “EDGE: An extendible graph editor”, Sojiware Practice and Experience 20, Sl, 1990. Spatial Technology Inc., ACIS: Inteface Guide, 1992. D.A. Stevenson, “An output-oriented approach to user interface design”, M.Phil T&is, CAD Centre, University of StrathClyde, U.K., 1990.
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M. Tovey, Drawing and CAD in industrial design, Design Studies, Vol. 10, No. 1, 1989, pp. 24-39. D.G. Ullman, The Mechanical Design Process, McGraw-Hill, Inc., 1992. Xiaohong Guan is a research assistant at the CAD Centre, University of StrathClyde, UK. Her current research interests include early design support systems, geometric reasoning, constraint management and geometric modelling. She obtained a BSc in Radio Electronics Science from University of Sichuan, China, in 1984, an MSc in Information Engineering from Xidian University, China in 1987 and a PhD from University of Strathclyde, UK in 1994. She is a member of IEEE, ACM and AAAI. David A. Stevenson is a research assistant at the CAD Centre, University of Strathclyde, UK. His current research interests include early design support systems and the use of graphical presentation and interaction techniques to support working with computer-based applications, particularly those concerned with design and problem-solving. After many years working as an architectural assistant, he obtained a BSc in Mathematical Sciences as a mature student in 1985 and an MPhil for research into user interface provision for design-related systems in 1990, both from the University of Strathclyde, UK. Ken MacCallum obtained his first degree in Naval Architecture from the University of Glasgow, proceeding to postgraduate study in Imperial College, University of London where he obtained a PhD for research into the application of computer graphics to free-form surface design. After three years with a software company, he joined the University of Strathclyde, establishing the CAD Centre in 1985 as a research and postgraduate centre. He is currently the Head of Design, Manufacture and Engineering Management in the Faculty of Engineering at the University of Strathclyde. Ken MacCallum’s main area of research has been the application of Artificial Intelligence to Engineering Design. He has led projects concerned with intelligent design modelling, data exchange, computer based design coordination, and computer aided learning. He is editor of the International Journal on Artificial Intelligence in Engineering, is a member of IFIP WG 5.2, and has been on the Technical Programme Committees of a large number of Conferences and Workshops concerned with computer aided design.