Extracting Articulation Models from CAD Models of Parts With Curved Surfaces (original) (raw)
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Assembly modelling by geometric constraint satisfaction
Computer-Aided Design, 1996
A new approach for representing and reasoning about assemblies of mechanical parts has been developed. The approach combines a formalism for representing relationships among features with a new method for geometric constraint satisfaction. The method employs symbolic reasoning about the geometric structure of parts to solve spatial constraints between the parts, in contrast to other approaches that reduce the geometric relationships to a set of non-linear equations to be solved. The system characterizes over-, under-, and fullyconstrained assemblies. For under-constrained assemblies, the remaining degrees of freedom are automatically coalesced into a set of kinematic joints that capture some of the functionality of the assembly. For over-constrained situations, redundant constraints are identified and checked for consistency, and degenerate cases are handled; this allows multiple feature relationships between two parts to be handled. A computer implementation in a limited feature domain is described and used to illustrate the approach with an example. Copyright 0 1996 Elsevier Science Ltd
Generation of assembly models from kinematic constraints
The International Journal of Advanced Manufacturing Technology, 2005
In this paper, we propose a new joint-based assembly modeling method. In joint-based assembly modeling, the assembly constraints are specified on the components, but not on the geometric elements of the components. The proposed method generates assembly models from kinematic joint constraints by applying three procedures (1) to extract all feasible JMFs (Joint Mating Feature) for each mating component using information on joint constraints, (2) to derive mating alternatives for each pair of mating components after reducing the number of JMFs using the pruning criteria, and (3) to generate an assembly model by choosing the intended one from the mating alternatives for each pair of mating components and solving the JMF constraints. Since the joint constraints are expressed in terms of the relations between components rather than relations between geometric elements, the proposed method is more intuitive and natural for assembly modeling and supports modeling activities effectively by minimizing user interactions. By using joint mating constraints for assembly modeling, moreover, the kinematic behaviors of assemblies determined in the conceptual design stage can be directly applied and consistently maintained up to the detailed design stage. In the proposed method, it is also not necessary to re-input the mating constraints even when the component topology is changed.
Computer-Aided mechanical Assembly Design Using Configuration Spaces
1997
We describe a. unified approach to computer-aided mechanical assembly design in which all design tasks are performed within a single computational paradigm supported by integrated design software. We have developed a prototype design environment for planar assemblies, called HIPAIR, that automates dynamical simulation and provides novel support for tolerancing and parametric design. We organize design tasks around the fundamental task of contact analysis, which we automate by configuration space computation. Configuration space is a complete, concise, and explicit representation of rigid body interactions and contains the requisite information for design tasks involving contacts. We describe algorithms for dynamical simulation, kinematic tolerancing, and parametric design of planar assemblies based on configuration space computation. HIPAIR allows designers to perform computations that lie outside the scope of previous software and that defy manual analysis. It allows them to visualize assembly function under a range of operating conditions, to find and correct design flaws, and to evaluate the functional effects of part tolerances. It has been tested on hundreds of pairs and on a dozen assemblies. HIPAIR performs at interactive speed on assemblies of ten pa.rts with tens of thousands of contacts.
Journal of Mechanical Design, 2010
This research presents a novel approach to virtual assembly that combines dynamic modeling with geometric constraint-based modeling to support low clearance manual assembly of CAD models. This is made possible by utilizing the boundary representation solid model data available in most contemporary CAD representations, which enables (a) accurate collision/physics calculations on exact model definitions, and (b) access to geometric features. Application of geometric constraints during run-time, aid the designer during assembly of the virtual models. The feasibility of the approach is demonstrated using a pin and hole assembly example. Results that demonstrate the method give the user the ability to assemble parts without requiring extensive CAD preprocessing and without over constraining the user to arrive at predetermined final part orientations. Assembly is successful with diametral clearance as low as 0.0001 mm, as measured between a 26 mm diameter hole and pin.
Computer-aided mechanical design using configuration spaces
Computing in Science & Engineering, 1999
We describe a. unified approach to computer-aided mechanical assembly design in which all design tasks are performed within a single computational paradigm supported by integrated design software. We have developed a prototype design environment for planar assemblies, called HIPAIR, that automates dynamical simulation and provides novel support for tolerancing and parametric design. We organize design tasks around the fundamental task of contact analysis, which we automate by configuration space computation. Configuration space is a complete, concise, and explicit representation of rigid body interactions and contains the requisite information for design tasks involving contacts. We describe algorithms for dynamical simulation, kinematic tolerancing, and parametric design of planar assemblies based on configuration space computation. HIPAIR allows designers to perform computations that lie outside the scope of previous software and that defy manual analysis. It allows them to visualize assembly function under a range of operating conditions, to find and correct design flaws, and to evaluate the functional effects of part tolerances. It has been tested on hundreds of pairs and on a dozen assemblies. HIPAIR performs at interactive speed on assemblies of ten pa.rts with tens of thousands of contacts.
Qualitative and quantitative mechanical assembly design
1997
We describe a unified approach to computeraided mechanical assembly design in which all design tasks are performed within a single computational paradigm supported by integrated design software. We have developed a prototype design environment for planar assemblies, called HIPAIR, that supports diverse design tasks. We organize the design tasks around the fundamental task of contact, analysis, which we automate by configuration space computation. Configuration space is a complete, concise representation of rigid body interactions that contains the requisite qualitative and quantitative contact information for all design tasks. We describe practical algorithms for the key tasks of dynamical simulation and kinematic tolerancing. HIPAIR allows designers to perform computations that lie outside the scope of previous software and that defy manual analysis. It computes qualitative and quantitative functional changes, allowing designers to study assembly function under a range of operating conditions, to find and correct design flaws, and to evaluate the functional effects of part tolerances. HIPAIR has been tested on hundreds of pairs and on a dozen assemblies. It performs at interactive speed on assemblies of ten parts with tens of thousands of contacts .
A CAD-Based Methodology for Motion and Constraint Analysis According to Screw Theory
The need for a designer to have a tool able to do motion and constraint analysis, to check for the under-constrained and/or over-constrained status of an assembly, is strategic in a design contest where several changes are made during the design process by using CAD. Traditional kinematic tools provide little information on over-constraints at 3D level. Screw theory has been already used in mechanical assemblies, in a top-down design, to do motion and constraint analysis. This theory is here used to analyze mechanical assemblies in the contest of a feature-based CAD system. The structure of the CAD assembly is captured and described as assembly graph, similar to Datum Flow Chain, through which the motion or constraint status of any part (in terms of twist and wrench matrices), can be obtained. The underlying algorithm is based on the Kirchoff's rules successfully applied by Davies to mechanisms. How to automatically create the assembly graph, detect the useful loops and then write the loop kinematic equations is described. Three case studies are presented related to CAD assemblies of mechanisms built up in SolidWorks® CAD system by Dassault Systemes from which assembly constraints have been acquired.
Solving 3D geometric constraints for closed-loop assemblies
The International Journal of Advanced Manufacturing Technology, 2004
In the design activity, part geometry is assembled to create an assembly model. The number of parts may range from a few tens to a few million and typically the relationship among them constructs closed-loops with under-constrained states. In this paper, a 3D constraint solving method is proposed for closed-loop assemblies with under-constrained states. The proposed constraint solving method determines assembly configurations by applying the following procedures: 1. Transform the geometric mating relations into the kinematic joint relations, 2. Convert the closed-chain kinematic assembly to an open kinematic assembly by removing a joint, 3. Compute an open kinematic configuration by solving the open kinematic problem and 4. Obtain the closed-loop kinematic configuration by pasting the 'cut' links of the open assembly. The cut and paste operations minimise the number of constraint variables that have to be solved simultaneously. Thus, it can maximise the efficiency and robustness of an assembly constraint solver. The proposed constraint solving method combines the simplicity of a sequential solving approach with the universality of a simultaneous solving approach.
Toward a Theory for Design of Kinematically Constrained Mechanical Assemblies
The International Journal of Robotics Research, 1999
This paper summarizes a theory to support the design of assemblies. It describes a top-down process for designing kinematically constrained assemblies that deliver geometric key characteristics (KCs) that achieve top-level customer requirements. The theory applies to assemblies that take the form of mechanisms (e.g., engines) or structures (e.g., aircraft fuselages). The process begins by creating a kinematic constraint structure and a systematic scheme by which parts are located in space relative to each other, followed by declaration of assembly features that join parts in such a way as to create the desired constraint relationships. This process creates a connective data model containing information to support relevant analyses such as variation buildup, constraint analysis, and establishment of constraint-consistent assembly sequences. Adjustable assemblies, assemblies built using fixtures, and selective assemblies can also be described by this theory.