Assembly Planning System Research Articles

Generating and evaluating stable assembly sequences

High-level assembly planning systems generate plans for the automated assembly of mechanical products by robots. The sequences to be generated underlie several physical and geometrical constraints,...

CAD-directed automatic assembly sequence planning

SUMMARY CAD-directed assembly sequence planning is an essential component of automated robotic assembly task planning. Many research attempts have been made in the past to integrate computer-aided design (CAD) and robot task planning to increase the efficiency and effectiveness of robotic assembly automation. This paper presents a graph-based heuristic approach for automatic generation of assembly sequences from a feature-based data base. A feature-based representation is used to model product assembly. The automatic assembly sequence planning system utilizes four major stages to generate assembly sequences without any user intervention:(1) creates connective graphs based on the product feature representation; (2) decomposes an assembly into sub-groups using the connective graphs; (3) generates the disassembly sequence for each sub-group formed at stage 2; and (4) merges the disassembly sequences of the sub-groups into a complete disassembly sequence, and converts the disassembly sequence into the final assembly sequence. The assembly planning system associated with the feature-based product model has been implemented in Smalltalk-an object-oriented programming language. Several examples are included to illustrate the approach and the heuristic algorithms. The results show that the approach can be used to automatically generate assembly sequences for robot assembly task planning directly from the feature-based database.

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>

Subassembly identification and evaluation for assembly planning

This paper presents a method for the automatic generation of assembly sequences from a liaison graph representation of an assembly through the recursive decomposition of assembly into subassemblies. In order to increase the planning efficiency, the proposed assembly planning system automatically identifies and avoids those decomposition that incur physically infeasible assembly operation. This is achieved by merging those parts that can not be mutually separable at the current stage of assembly planning due to interconnection infeasibility as well as functional dependency. The above merging process transforms the original liaison graph into an abstract liaison graph with smaller number of nodes. Then, weights are assigned to each liaison of abstract liaison graph based on the stability and structural connectivity associated with liaison such that these weights are used to extract the tentative subassemblies. To select preferred subassemblies, the extracted tentative subassemblies are evaluated based on the subassembly selection indices defined in terms of mobility, structural preference, stability, and parallelism. Furthermore, by adjusting the assembly coefficients of subassembly selection indices according to given assembly environment, an optimal assembly sequence can be generated. The application of the proposed planning system to the tabletop vise assembly is illustrated as an example. >

A systematic approach for design and planning of mechanical assemblies

A system that integrates design and planning for mechanical assemblies is presented. The system integrates neural network computing that captures designer's design concept and rule-based system to generate a task-level assembly plan automatically. The design concept is expressed by a standard pattern format representing qualitative assembly information. A neural network model together with feature-based model translates the input pattern into a preliminary boundary representation (B-rep). Based on a refinement B-rep assembly representation, assembly plans are generated for practical use in a single-robot assembly workcell. A feasible assembly plan that minimizes tool changes and subassembly reorientations is generated from the system. A robust part collision detection algorithm to generate the precedence relationships among the assembly's components is included in the system. By contrast with many assembly planning systems that used a prolonged question-and-answering session or required knowledge beyond what is typically available in the design database, an automated assembly planning system presented here draws input relationships directly from the conceptual design and the geometry of the assembly. The system developed under this study extracts all reasoning information from the product model and permits the components to be assembled in a multitude of directions. Several experiments illustrate the effectiveness of the designed assembly planning system.

3D MAPS: Three-dimensional mechanical assembly planning system

3D MAPS: Three-dimensional mechanical assembly planning system

3D MAPS: Three-dimensional mechanical assembly planning system

Abstract 3D MAPS, an acronym for 3-Dimensional Mechanical Assembly Planning System, is an automated system that generates detailed assembly plans for three-dimensional mechanical products. It has three major modules: description of mechanical assembly design, analysis of assembly models, and generation of assembly plans. Both geometric models and nongeometric properties are considered in describing a 3-D assembly design, and the following information is inferred from the system: mating parts, mating faces, mating directions, collision constraints, and nongeometric sequence constraints. The inferred information is then used in the subsequent planning stage for generating detailed assembly instructions. The planning scheme contains two parts: initial assembly planning that considers solely geometric constraints, and plan modification that further considers nongeometric constraints. In this paper, the algorithms developed to implement the above three modules are discussed. Examples of mechanical assemblies are used to illustrate the information flow of the entire planning system, from the assembly design input through the execution of the developed algorithms to the final assembly plan output. Analysis of the results is also included.

An integration of neural network and rule-based systems for design and planning of mechanical assemblies

A case associative assembly planning system (CAAPS), which integrates neural computing techniques and rule-based systems has been developed. The neural network computing captures the designer's design concept and self-organizes similar experienced designs. The CBAPM (CLIPS-based assembly planning module), a component of CAAPS, generates a task-level assembly plan automatically. The design concept is expressed by a standard pattern format representing components' 3D geometry. A feature-based model translates the conceptual design into a preliminary boundary representation (B-rep). Based on a refinement of the B-rep assembly representation, assembly plans are generated for practical use in a single-robot assembly workcell. A feasible assembly plan that minimizes tool changes and subassembly reorientations is generated from the system. The CBCAPM presented draws input relationships directly from the conceptual design and the geometry of the assembly. At all stages of the design process the designer can consult the design cluster memory and plan cluster memory to see what experience knows of similar assemblies. Efficient use of prior experiences is emphasized. >

A knowledge based approach for automatic process plan generation in an electronic assembly environment

SUMMARY In this paper important issues in the automatic generation of process plans are addressed. Since the conventional method of electronic assembly planning is subjective and depends greatly on the skills, memory, knowledge, and experience of the planners, inconsistencies in the plan arise, which in turn create problems in the manufacturing environment. An automatic electronic assembly planning system that would offer advantages over manual systems has been implemented. Due to frequent advances in technology, the electronic industry is a very dynamic one. This affects the effectiveness of the current process plans and the applicability of the system that generates them. The framework of a system which takes into account the dynamic nature of the environment is presented as an example. A network representation of plans that allows for flexibility and modularity in the planning system is being used. A hybrid architecture consisting of production rules, procedural algorithms and a hierarchical database has been implemented using an expert system shell.

Symbol grounding via a hybrid architecture in an autonomous assembly system

We describe the architectural principles of our somass robotic assembly system. It requires little more information than the shape of the desired assembly and the shape of the parts from which to construct an assembly plan, which is executed reliably by a robot system. It is a hybrid system, comprising a careful marriage of a prolog assembly planning system with a plan execution agent designed to control uncertainty (including the use of sensors) by means of behavioural modules which accomplish useful motions of the parts. The key notions are the simplification of the planner resulting from increasing the competence of the plan execution agent, and grounding the planner through a single hierarchy of behavioural modules instead of a twin hierarchy of sensing and action. We develop new terms for this discussion, since the old ones-such as ''subsymbolic''-beg the questions we wish to address.

A case study in cyclic assembly planning and dynamic coordinated component shops' loading in a locks manufacturing plant

This case study arose in a large plant manufacturing locks. The existing production control system involved partially a rudimentary MRP at the assembly level and a pull-system of an informal (r,Q) type for triggering component production. The expressed problem was: component shortages affecting assembly operations and load fluctuations as well as imbalances affecting component shops. Coordination between assembly shop loading and component shops' loading was identified as crucial. The plant happened to have a considerable flexibility in production smoothing. A cyclic assembly planning system was considered, with minor variations from month to month. A policy for monthly joint planning of assembly and component shops' production was obtained. Consideration was given to presence of lead times for component production. For load balancing over time certain bin-packing heuristics were considered. For sequencing in assembly lines certain flow-shop heuristics were used. The component inventory control policy involved a restoration of month-end inventories towards steady state target values. The operational feasibility of the policy was verified on actual data. The study includes approximate quantification of losses that would be caused in the original system due to component stockouts. Certain subproblems concerning component lotsizing under random tool failures were also settled adequately.

Planning and Scheduling of Assembly Systems

In this keynote paper, the state of practice, the state of the art and the state of research concerning planning, scheduling and control of assembly systems are discussed. First, the concepts of planning, scheduling and control are elucidated and put in relation to one another. Next the most important evolutions in computer-aided intuitive and formal assembly planning and scheduling systems are explained. Finally, the important issues of programming, real time control and sensor integration are dealt with.

Knowledge-based process planning for electronic assembly

The conventional method of electronic assembly planning is subjective and depends greatly on the skills, memory, knowledge and experience of the planners. This gives rise to inconsistencies which in turn create problems in the manufacturing environment. Since the computer logics are systematic and consistent, it is conceivable that an automatic electronic assembly planning system would have advances over manual systems. Due to the frequent advances in technology the electronic industry is a very dynamic one. This affects the effectiveness of the current process plans and the applicability of the system that generates them. In this paper important issues which address the automatic generation of process plans will be presented. The framework of a system which takes into account the dynamic nature of the environment will be introduced as an example.

Espfas — A prototype expert system for technological planning in robot-based flexible assembly systems

This paper describes an application of expert systems to the area of technological planning for robot-based flexible assembly systems. The work described in this paper is part of the research being done in the Republic of Ireland as part of the European Strategic Programme for Research and Development in Information Technology (ESPRIT), Project No. 623. The discussion focuses on the role of technological planning, an explanation of the generative approach to planning, the use of robot-based flexible assembly systems, and the need for a planning procedure within these systems. Following this, a description of the logic of the assembly planning system being developed at the University College Galway (U.C.G.) is given, followed by a review of the knowledge which is encoded in the expert system. The final section details some developments, which have been carried out on the system as a result of two case studies.