Computer-aided Assembly Planning Research Articles

Minimizing geometric tests in CAAP-systems

The article is devoted to modeling geometric obstacles in the assembly of complex products. The problem of minimizing the number of geometric tests is considered. Two assertions about geometric inheritance in the assembly of technical systems are introduced. Based on these assertions, a game-theoretic model has been developed. The model made it possible to minimize the number of geometric tests. It is a game of decision-maker and nature by coloring the vertices of an ordered set in two colors. A classification of ordered sets is proposed. The computational experiment on coloring of ordered sets of each class using different criteria is carried out. The experiment made it possible to determine the optimal criteria for the coloring ordered sets of each class. The use of these criteria allows minimizing the labor intensity of geometric analysis in computer-aided assembly planning.

Computer Aided Assembly of Buildings

This article presents an interactive method of computer-aided assembly planning. It is estimated that such planning will be more and more desirable due to the increasing use of prefabrication in construction. Prefabrication meets the trends of sustainable development and digitization as it enables the application of intelligent control systems at the stage of highly specialized production, assembly and facility maintenance. The presented planning method is based on the Monte Carlo simulations and logical algorithms for assembly work planning. It was determined on the basis of the literature studied and our own observations. The paper introduces a detailed model of assembly works planning and is an example of using a computer application developed on the basis of the described model. The example confirms the correctness of the algorithm and indicates its usefulness in the scope of analyzing many decision variants. Further research on labor productivity rates for assembly works, implementation of digital databases of assembly machines and prefabricated elements, as well as integration of the proposed application with the BIM environment should make it easier to commercialize the developed application.

Analysis of Geometric Obstacles Avoidance in Assembling Complex Products as a Decision-making Problem

Computer aided assembly planning (CAAP) of complex products is an important and urgent problem of state-of-the-art information technologies. A configuration of the technical system imposes fundamental restrictions on the design solutions of the assembly process. The CAAP studies offer various methods for modelling geometric constraints. The most accurate results are obtained from the studies of geometric obstacles, which prohibit the part movement to the appropriate position in the product, by the collision analysis methods. An assembly of complex technical systems by this approach requires very high computational costs, since the analysis should be performed for each part and in several directions.The article describes a method for minimizing the number of direct checks for geometric obstacle avoidance. Introduces a concept of the geometric situation to formalize such fragments of a structure, which require checking for geometric obstacle avoidance. Formulates two statements about geometric heredity during the assembly. Poses the task of minimizing the number of direct checks as a non-antagonistic two-person game on two-colour painting of an ordered set. Presents the main decision criteria under uncertainty. To determine the best criterion, a computational experiment was carried out on painting the ordered sets with radically different structural properties. All the connected ordered sets are divided into 13 subclasses, each of which includes structurally similar instances. To implement the experiment, a special program has been developed that creates a random ordered set in the selected subclass, implements a game session on its coloration, and also collects and processes statistical data on a group of the homogeneous experiments.The computational experiment has shown that in all subclasses of the partial orders, the Hurwitz criterion with a confidence coefficient of 2/3 and that of Bayes-Laplace demonstrate the best results. The Wald and Savage criteria have demonstrated the worst results. In the experiment, a difference between the best and worst results reached 70%. With increasing height (maximum number of levels) of an ordered set, this difference tends to grow rapidly. In the subclass of pseudo-chains, all criteria showed approximately equal results.The game model of geometric obstacles avoidance allows formalizing data on geometric heredity and obtaining data on the composition and the minimum number of configurations, the test of which objectifies all existing-in-the-product geometric constraints on the movements of parts during assembly.

Structural Analysis of Product and Computer-Aided Assembly Planning in AssemBL Software Package

Computer-aided design of assembly processes (Computer aided assembly planning, CAAP) of complex products is an important and urgent problem of state-of-the-art information technologies. Intensive research on CAAP has been underway since the 1980s. Meanwhile, specialized design systems were created to provide synthesis of assembly plans and product decompositions into assembly units. Such systems as ASPE, RAPID, XAP / 1, FLAPS, Archimedes, PRELEIDES, HAP, etc. can be given, as an example. These experimental developments did not get widespread use in industry, since they are based on the models of products with limited adequacy and require an expert’s active involvement in preparing initial information. The design tools for the state-of-the-art full-featured CAD/CAM systems (Siemens NX, Dassault CATIA and PTC Creo Elements / Pro), which are designed to provide CAAP, mainly take into account the geometric constraints that the design imposes on design solutions. These systems often synthesize technologically incorrect assembly sequences in which known technological heuristics are violated, for example orderliness in accuracy, consistency with the system of dimension chains, etc.An AssemBL software application package has been developed for a structured analysis of products and a synthesis of assembly plans and decompositions. The AssemBL uses a hyper-graph model of a product that correctly describes coherent and sequential assembly operations and processes. In terms of the hyper-graph model, an assembly operation is described as shrinkage of edge, an assembly plan is a sequence of shrinkages that converts a hyper-graph into the point, and a decomposition of product into assembly units is a hyper-graph partition into sub-graphs.The AssemBL solves the problem of minimizing the number of direct checks for geometric solvability when assembling complex products. This task is posed as a plus-sum two-person game of bicoloured brushing of an ordered set. In the paradigm of this model, the brushing operation is to check a certain structured fragment for solvability by collision detection methods. A rational brushing strategy minimizes the number of such checks.The package is integrated into the Siemens NX 10.0 computer-aided design system. This solution allowed us to combine specialized AssemBL tools with a developed toolkit of one of the most powerful and popular integrated CAD/CAM /CAE systems.

Generation of AR-enhanced Assembly Instructions based on Assembly Features

Writing assembly manuals for workers is a tedious and time-consuming task. After discussing some of the challenges in the field of Computer-Aided Assembly Planning, we introduce our approach to alleviate the burden of this task. We use different methods to firstly determine the assembly sequence of a product and second to assign each edge in the graph the appropriate assembly feature. Using a library of animation templates, AR-enhanced instructions are instantiated for each edge and positioned in the real world using the anchoring feature of the HoloLens. Our approach is showcased and evaluated using the Cranfield Assembly Benchmark.

Augmented reality aided interactive manual assembly design

Augmented reality (AR) is a novel technology which overlays computer-generated information seamlessly on the real-world environment. AR technologies have opened up a powerful set of tools for computer-aided assembly planning. This paper presents a manual assembly design system using AR technologies. An assembly data structure is devised for assembly information management. Algorithms for assembly constraint recognition and assembly location refinement have also been proposed. A hybrid approach based on these methods has been formulated and implemented to allow the users to simulate a manual assembly without the need for auxiliary computer-aided design information in assembly design. This would result in enhanced user experience and reduced preparation time. A methodology for 3D bare-hand interaction is integrated with this interactive manual assembly design system for the users to manipulate the virtual components in a natural and effective manner. A prototype system for interactive manual assembly design has been developed. An example has been provided to demonstrate the developed prototype system.

A pragmatic system to support interactive assembly planning and training in an immersive virtual environment (I-VAPTS)

Assembly planning for complex products is a difficult task requiring both intensive knowledge and experience. Computer aided assembly planning (CAAP) systems have been the subject of considerable research in recent years without achieving a wide application in manufacturing industry. In this paper an alternative approach to the generation of an optimal assembly planning scheme is presented based on the adoption of immersive virtual reality. A product is assembled from CAD models by providing a CAD interface to transfer assembly constraint information from the CAD system to a virtual environment. In the virtual environment an efficient dynamic recognition and management method based on surface geometry is employed, and a process-oriented assembly task model is established to support interactive assembly planning and evaluation. The system is implemented using an object oriented methodology, and has been successfully applied to train and guide the assembly workers in a pump assembly process.

A novel approach to the geometric feasibility analysis for fast assembly tool reasoning

A product assembly or disassembly is completed by means of proper tools. The selection of feasible tools is an important process in planning a complete assembly or disassembly sequence. A key tooling consideration in assembly or disassembly planning is to reason the available space for a tool application during the assembly or disassembly of a product. Currently, assembly tool reasoning about space mainly depends on simulation-based or user-interactive approaches because of its computational complexity. These approaches are inappropriate in dealing with various what-if scenarios regarding assembly or disassembly planning in a rapid product development. They also depend on users’ expertise or experience in assembly or disassembly. This paper presents a novel approach to the geometric feasibility analysis for fast assembly tool reasoning. Techniques described in this paper are advantageous not only in the aid of generating a complete assembly or disassembly plan but also in the efficient support of such systems as computer-aided assembly planning (CAAP), design for manufacturing (DFM), design for assembly (DFA), design for disassembly (DFD), and computer-aided tool selection (CATS).

A technology-driven architecture for developing highly configurable CAx software

Developing software for computer aided ‘x’ (CAx), where ‘x’ stands for design, manufacturing, engineering, etc., is a programming- and research-intensive process. Over the years, advances in software technology and tools have made the process of development easier, but expectations of the user have also risen accordingly. Software like computer aided process planning (CAPP) and computer aided assembly planning (CAAP) systems require extensive configuration and development by the user. This problem of user configuration and user development of the system poses a challenge to the software developers and researchers. This paper presents a case study of system development, which uses the state-of-the-art software technologies to overcome some of the problems.

Integrated Computer Aided Design for Assembly Systems

Assembly being the last step of the production cycle of a product, it is normally submitted to the constraints of the precedent step. Techniques like Design for Assembly have been developed to try to take into consideration the peculiarities of the assembly process and reduce costs. The paper present the research and development of an integrated computer aided design for assembly system. The project main aim is to obtain methodologies and tools to design and manage a complete flexible assembly system but in this paper we will describe a CAAP (Computer Aided Assembly Planning) for the determination of gripping features, gripper and finger configuration, assembly sequence, simulation of the assembly system for the design of management rules, three dimensional simulation of robots (serial and parallel) for the design of each single assembly and control cell. The results of the project is tested in a specifically designed and implemented system for the assembly of electro-mechanical components.

The generation and practical use of plans for manual assembly using immersive virtual reality

The preparation of assembly plans for manufactured goods is a major bottleneck in the time it takes to bring many new products to market. Computer aided assembly planning (CAAP) systems have been the subject of considerable research in recent years without achieving significant up-take in manufacturing industry. This paper proposes an alternative approach based on the adoption of immersive virtual reality, which is used here to produce practical downstream manufacturing information. The product is assembled from computer aided design (CAD) models of its components by experienced assembly operators working in a virtual environment. The operators' actions are monitored and assembly sequence plans are automatically generated by the system. In the research described in this paper, the plans produced for an advanced electromechanical product were then used by a second group of participants to demonstrate the functionality of the system in an industrial environment. The development of virtual reality-based assembly planning carries with it the opportunity not only to shorten the product innovation cycle but also to capitalize on the experience of assembly operators and bring this to bear much earlier in the design process.

A Method of Generating Optimal Subassemblies from Assembly Drawings by Disassembly Equations.

Computer aided assembly planning raises several issues such as the combinatorial explosion of information required for describing intermediate plans, a representation method of movable deirections of parts with respect to the other parts, and a representation method of assembly methods. This paper describes a method of using disassembly equations that represent movable directions of parts and distances with respect to the other parts, and assembly methods. Giving assembly criteria such as costs to assembly methods and solving the set of disassembly equations generate an optimal set of subassemblies under the given criteria. The solving of the equations does not employ a mechanism of generating every possible combination of subassemblies for searching for an optimal combination, and avoids the combinatorial explosion of the information. Furthermore, our method is able to represent motion steps sometimes required for assembling parts.

On constraints in assembly planning

Constraints on assembly plans vary depending on product, assembly facility, assembly volume, and many other factors. Assembly costs and other measures to optimize vary just as widely. To be effective, computer-aided assembly planning systems must allow users to express the plan selection criteria that apply to their products and production environments. We begin by surveying the types of user criteria, both constraints and quality measures, that have been accepted by assembly planning systems to date. The survey is organized along several dimensions, including strategic versus tactical criteria; manufacturing requirements versus requirements of the automated planning process itself; and the information needed to assess compliance with each criterion. The latter strongly influences the efficiency of planning. We then focus on constraints. We describe a framework to support a wide variety of user constraints for intuitive and efficient assembly planning. Our framework expresses all constraints on a sequencing level, specifying orders and conditions on part mating operations in a number of ways. Constraints are implemented as simple procedures that either accept or reject assembly operations proposed by the planner. For efficiency, some constraints are supplemented with special-purpose modifications to the planner's algorithms. Fast replanning enables an interactive plan-view-constrain-replan cycle that aids in constraint discovery and documentation. We describe an implementation of the framework in a computer-aided assembly planning system and experiments applying the system to a number of complex assemblies, including one with 472 parts.

AUTOMATIC LIAISON MODEL GENERATION FROM 3-D SOLID MODELS

Computer Aided Assembly Planning (CAAP) is characterized by the manual generation of a liaison (or graph) model used to represent explicitly mating information among parts. This paper describes an automatic method for generating such relational information. It is based on an exhaustive and systematic surface-level analysis of the Boundary Representation (B-Rep) file of the solid modeled product. Simple mathematical tests performed on pairs of surfaces each on a different part enable the identification of mating surfaces. The system which performs this analysis also enables a visual display of the mating information in the form of a graph model This paper describes how mating surfaces are identified from more elemental information found in the B-Rep file and also provides examples of the automatically generated graph model for some products.

Minimizing user queries in interactive assembly planning

This paper describes an interactive computer-aided assembly planning system that greatly reduces the human input required to construct assembly plans. The system takes a dual approach. First, most assembly operations are validated automatically from the CAD models of the assembly's parts using simple, fast techniques. Second, with each query the user is allowed to identify a set of parts that constrain a subassembly; the system uses this information to answer future queries automatically. This dual approach has proven quite powerful in experiments on real assemblies, reducing the number of queries by orders of magnitude over previous systems without sacrificing accuracy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Development of a CAD-based intelligent manufacturing system

Abstract This research proposes a CAD-based manufacturing system that embraces computer-aided design, design for manufacturing and assembly (DFMA), computer-aided process planning (CAPP), computer-aided assembly planning (CAAP), and vision-robot integration. The proposed system starts with the design of products using a commercial CAD software, Autocad. The design data is then extracted from the CAD database and organized into a standardized product model. Interface programs are used to translate the geometrical and topological information in the model into DFMA, CAPP, CAAP and vision image representations. Based on the results generated by the interface programs the applications using artificial intelligence techniques can automatically generate redesign advises, CNC part programs, assembly sequence and instructions for robots.