Design of cellular manufacturing systems with assembly considerations

This research proposes incorporating assembly aspects associated with a product into the design of Cellular manufacturing System (CMS). The literature on CMS design implicitly assumes that finished part is the end product by itself. In practice, often, manufacturers produce parts which are assembled into a finished product. The methodology employs a part–subassembly matrix derived from the product structure in addition to the part–machine matrix. A mathematical programming model is developed which determines an assignment of parts, machines and subassemblies to manufacturing cells. The proposed model employs a new similarity coefficient between part, machine and subassembly. The model resulted in a nonlinear program with 0-1 variables. A case study has been analyzed based on a published part–machine matrix and a randomly generated product structure. The analysis reveals that it may be required to forego some of the efficiencies of Group Technology (GT) in order to achieve integration of assembly operations with production of parts. From a practical stand point of view it is preferred to have a system design which has a mix of GT and integration efficiencies, compared to a design which outperforms on GT criteria and completely lacks integration of assembly operations with production of parts.     

Physics-based virtual reality for task learning and intelligent disassembly planning

Physics-based simulation is increasingly important in virtual manufacturing for product assembly and disassembly operations. This work explores potential benefits of physics-based modeling for automatic learning of assembly tasks and for intelligent disassembly planning in desktop virtual reality. The paper shows how realistic physical animation of manipulation tasks can be exploited for learning sequential constraints from user demonstrations. In particular, a method is proposed where information about physical interaction is used to discover task precedences and to reason about task similarities. A second contribution of the paper is the application of physics-based modeling to the problem of disassembly sequence planning. A novel approach is described to find all physically admissible subassemblies in which a set of rigid objects can be disassembled. Moreover, efficient strategies are presented aimed at reducing the computational time required for automatic disassembly planning. The proposed strategies take into account precedence relations arising from user assembly demonstrations as well as geometrical clustering. A motion planning technique has also been developed to generate non-destructive disassembly paths in a query-based approach. Experiments have been performed in an interactive virtual environment including a dataglove and motion tracker that allows realistic object manipulation and grasping.     

Robustness analysis of non-ordinary Petri nets for flexible assembly/disassembly processes based on structural decomposition

Design of robust supervisory controllers for manufacturing systems with unreliable resources has received significant attention recently. Robustness analysis provides an alternative way to analyse a perturbed system to quickly respond to resource failures. Although we have analysed the robustness properties of several subclasses of ordinary Petri nets (PNs), analysis for non-ordinary PNs has not been done. Non-ordinary PNs have weighted arcs and have the advantage to compactly model operations requiring multiple parts or resources. In this article, we consider a class of flexible assembly/disassembly manufacturing systems and propose a non-ordinary flexible assembly/disassembly Petri net (NFADPN) model for this class of systems. As the class of flexible assembly/disassembly manufacturing systems can be regarded as the integration and interactions of a set of assembly/disassembly subprocesses, a bottom-up approach is adopted in this article to construct the NFADPN models. Due to the routing flexibility in NFADPN, there may exist different ways to accomplish the tasks. To characterise different ways to accomplish the tasks, we propose the concept of completely connected subprocesses. As long as there exists a set of completely connected subprocesses for certain type of products, the production of that type of products can still be maintained without requiring the whole NFADPN to be live. To take advantage of the alternative routes without enforcing liveness for the whole system, we generalise the concept of persistent production proposed to NFADPN. We propose a condition for persistent production based on the concept of completely connected subprocesses. We extend robustness analysis to NFADPN by exploiting its structure. We identify several patterns of resource failures and characterise the conditions to maintain operation in the presence of resource failures.     

The effect of lead time variation on the performance of disassembly release mechanisms

A recoverable product environment, which includes strategies to extend product life, is an increasingly important method of waste prevention. A major part of this environment is the recoverable manufacturing system designed to remanufacture products. The recoverable manufacturing system has three distinct subsystems: disassembly, remanufacturing and reassembly. A key characteristic of this environment is the high degree of variability inherent in it. The impact of this variability as represented by highly variable lead times is examined for its effect on the control of parts release from the disassembly area to the remanufacturing area. Various disassembly release mechanisms for releasing the parts are examined. The choice is shown to be more critical for serial number specific parts. Lead time variation is shown to have a significant affect on the choice of disassembly release mechanism. Successful mechanisms for controlling the release of materials from the disassembly area are discussed and recommendations are made.     

基于矩阵运算的虚拟装配体拆卸过程建模方法

现有装配体建模方法在描述虚拟维修训练中装配体拆卸过程时,存在的信息冗余大、建模过程复杂等缺点,在研究现有装配体建模方法和分析装配过程与拆卸过程差异的基础上,提出了一种面向虚拟维修拆卸过程的建模方法。该方法以矩阵描述装配体模型,用矩阵运算描述零部件拆卸过程,简化了建模过程,减少了模型数据量,为虚拟维修训练系统的快速构建提供了一种思路和方法。     

Task-board task for assembling a belt drive unit

ABSTRACT

A task board is a board for assembling parts, developed to test the abilities of a robot system to perform assembly operations associated with a manufacturing process. This study describes a task board that can serve as a basis for developing program modules for assembling a specific product. A properly designed task board can serve as a preliminary template for a specific assembly and can promote robotic assembly. This study analyzes the design of a Task-board task performed at the World Robot Summit 2018 (WRS 2018). The main competitive task at the WRS 2018 was the assembly of a belt drive unit. Analyses showed that the directions of assembly, especially the horizontal direction, were common difficulties in both Task-board and Assembly task competitions. Development of a task board for a specific assembly product requires an increase of its relevance to the assembly product, such as using the same workpieces or using similar assembly orientations.     

Integrated knowledge-based Petri net intelligent flexible assembly planning

Automatic assembly planning is recognized as an important tool for reducing manufacturing costs in concurrent product and process development. A novel knowledge-based Petri net (KBPN) is defined, based on the incorporation of expert systems into the usual Petri nets, and used for a unified assembly knowledge representation scheme. A KBPN-approach integrated with a sequence generation algorithm is proposed for the modeling, planning, simulation, analysis and evaluation of the flexible assembly system (FAS). The developed KBPN-based assembly planning system (KAPS) can automatically adjust the deviations between the theoretical planning parameters and the process parameters of real assembly operations to guarantee the best strategies and plans (sequences) for flexible assembly. The research findings are exemplified with a simple assembly to show the effectiveness of the method.     

Feature-based assembly modeling and sequence generation

A feature-based model is proposed for assembly sequence planning automation. The fundamental assembly modeling strategy for a product is based on the mating features of its components. The objectives of this study are to integrate assembly planning of a product with its CAD model, generate a correct and practical assembly sequence and establish a software system to carry out the planning process. A disassembly approach in assembly planning is used in this study. The degree of freedom information between two mating features is used to characterize their kinematic conditions. Boolean operations of the degrees of freedom on all features of a component provides its local degree of freedom, which is used to set up the functional precedence relation. In some cases, where the functional precedence relation cannot be detected by geometric reasoning, clipping of the known `common sense' relation is applied by a user. A bounding box checking approach is used to ensure no global collision during assembly. Furthermore, a set of criteria based on assembly feasibility, manipulability, assembly direction, cost and stability is used to choose a good assembly sequence.     

An evolutionary simulation-based optimization approach for dispatching scheduling

An effective scheduling decision is one of the key factors towards improving the efficiency of a system’s performance, particularly in the instance of multiple products thus dispatching rules have been widely used for real-time scheduling because they can provide a very quick and pretty good solution. However, deciding how to select appropriate rules is very difficult. In this paper, we develop evolutionary simulation-based heuristics to construct near-optimal solutions for dispatching rule allocation. Our heuristic is easy to use and gives a manager a useful tool for testing a configuration that can minimize certain performance measures. The optimization heuristics are used to determine priority strategies to maximize the performance of a complex manufacturing system with a large number of different products, along with an overtime that changes with a mix of different process types, including assembly and disassembly operations and with different types of internal and external disturbances. Modeling is carried out using discrete-event simulation. Case study analysis is of a commercial offset printing production system.     

Human motion prediction for human-robot collaboration

In human-robot collaborative manufacturing, industrial robots would work alongside human workers who jointly perform the assigned tasks seamlessly. A human-robot collaborative manufacturing system is more customised and flexible than conventional manufacturing systems. In the area of assembly, a practical human-robot collaborative assembly system should be able to predict a human worker’s intention and assist human during assembly operations. In response to the requirement, this research proposes a new human-robot collaborative system design. The primary focus of the paper is to model product assembly tasks as a sequence of human motions. Existing human motion recognition techniques are applied to recognise the human motions. Hidden Markov model is used in the motion sequence to generate a motion transition probability matrix. Based on the result, human motion prediction becomes possible. The predicted human motions are evaluated and applied in task-level human-robot collaborative assembly.     

设备拆装混合现实系统中的拆装逻辑设计

针对机械部件在拆装过程中存在设备投资大、损耗程度高、危险性大、拆装效率低等问题, 本文采用混合现实技术, 设计出一套虚拟拆装系统. 其中, 拆装逻辑是拆装系统的核心, 拆装系统的通用性取决于拆装逻辑的设计. 为了解决虚拟拆装系统通用性差的问题, 本文通过对常见机械模型的连接方式和装配关系进行分析和总结, 设计出一种基于图遍历算法的数据结构来表达各个模型的逻辑关系, 并针对特种阀门、六关节机械臂等设备的拆装进行实验. 实验结果表明: 该拆装逻辑解决了拆装顺序的可定义和通用性等问题, 能够对模型部件按工艺流程进行虚拟拆解和装配, 最终实现虚拟拆装系统的通用性.     

Assembly features in modeling and planning

In recent years, features have been introduced in modeling and planning for manufacturing of parts. Such features combine geometric and functional information. Here it is shown that the feature concept is also useful in assembly modeling and planning. For modeling and planning of both single parts and assemblies, an integrated object-oriented product model is introduced. For specific assembly-related information, assembly features are used. Handling features contain information for handling components, connection features information on connections between components. A prototype modeling environment has been developed. The product model has been successfully verified within several analyses and planning modules, in particular stability analyses, grip planning, motion planning and assembly sequence planning. Altogether, feature-based product models for assembly can considerably help in both assembly modeling and planning, on the one hand by integrating single-part and assembly modeling, and on the other hand by integrating modeling and planning.     

Disassembly sequence structure graphs: An optimal approach for multiple-target selective disassembly sequence planning

Modern green products must be easy to disassemble. Specific target components must be accessed and removed for repair, reuse, recycling, or remanufacturing. Prior studies describe various methods for removing selective targets from a product. However, solution quality, model complexity, and searching time have not been considered thoroughly. The goal of this study is to improve solution quality, minimize model complexity, and reduce searching time. To achieve the goal, this study introduces a new ‘disassembly sequence structure graph’ (DSSG) model for multiple-target selective disassembly sequence planning, an approach for creating DSSGs, and methods for searching DSSGs. The DSSG model contains a minimum set of parts that must be removed to remove selected targets, with an order and direction for removing each part. The approach uses expert rules to choose parts, part order, and part disassembly directions, based upon physical constraints. The searching methods use rules to remove all parts, in order, from the DSSG. The DSSG approach is an optimal approach. The approach creates a high quality minimum-size model, in minimum time. The approach finds high quality, practical, realistic, physically feasible solutions, in minimum time. The solutions are optimized for number of removed parts, part order, part disassembly directions, and reorientations. The solutions remove parts in practical order. The solutions remove parts in realistic directions. The solutions consider contact, motion, and fastener constraints. The study also presents eight new design rules. The study results can be used to improve the product design process, increase product life-cycle quality, and reduce product environmental impact.     

Multi-objective partial disassembly optimization based on sequence feasibility

A sustainable manufacturing system integrates production systems, consumer usage behavior, and End-of-Life (EoL) product value recovery activities. Facilitating multi-objective disassembly planning can be a step toward analyzing the tradeoffs between the environmental impact and profitability of value recovery. In this paper, a Genetic Algorithm (GA) heuristic is developed to optimize partial disassembly sequences based on disassembly operation costs, recovery reprocessing costs, revenues, and environmental impacts. EoL products may not warrant disassembly past a unique disassembly level due to limited recovered component market demand, minimal material recovery value, or minimal functional recovery value. The effectiveness of the proposed GA is first verified and tested using a simple disassembly problem and then applied to the traditional coffee maker disassembly case study. Analyses are disaggregated into multiple disassembly network optimization problems, one for each product subassembly, resulting in a bottom-up approach to EoL product partial disassembly sequence optimization.     

Rule and branch-and-bound algorithm based sequencing of machining features for process planning of complex parts

The machining sequence of machining features is vital to achieve efficient and high quality manufacturing of complex NC machining parts. In most feature-based process planning system, the machining features are sequenced as the lowest level unit. However, a single machining feature of complex parts such as aircraft structural parts is usually machined by multiple machining operations. The one-to-many mappings between the machining features and the machining operations cause the increase of the non-cutting tool path. In order to solve this problem, some types of machining features of complex parts are decomposed into several sub-machining features that are associated with a single machining operation individually according to the rules which are abstracted from the machining process of complex parts. Benefitting from the decomposition, the sub-machining features from different machining feature can be assembled into a sub-machining feature in order to avoid the cutting tool marks. The different types of sub-machining features are sequenced in the light of some rules which are also extracted from the machining process of complex parts. And the branch-and-bound algorithm are employed to sequence the same type sub-machining features to minimum the non-cutting tool path. A pilot feature-based process planning system has been developed based on this research, and has been used in some aircraft manufacturers in China.     

面向PDM的产品及其零部件的EXPRESS模型

对产品及其零部件进行正确建模是PDM系统实现的前提和关键,文中针对现有STEP应用协议存在的局限性进行了合理的扩充,建立了产品及产品版本类、产品定义关系类等产品及其零部件的XEPRESS模型,开发了基于该模型的PDM系统,实现了产品的结构管理、配置管理、以及产品相关信息的集成管理,对所建立的EXPRESS模型进行了验证和应用。     

Linear programming in disassembly/clustering sequence generation

Based on earlier research on optimal disassembly sequence generation, notably graphically supported search methods, a method for solving general optimal disassembly sequence generation problems by linear programming has been developed and described. This method puts no serious restriction to the size of the model. It is adaptable to changes in model structures and constraints, and it is even not restricted to divergent operations, such as disassembly. This is demonstrated by solving the combined disassembly/clustering problem. Clustering is the combination of different disassembly products to categories that can be considered — and sold — as a single product, e.g. steel parts.The theoretical model is validated and clarified by its application to some standard problems from literature.     

A method for computer-aided specification of geometric tolerances

The paper describes a method for the generation of tolerance specifications from product data. The problem is nontrivial due to the increasing adoption of geometric dimensioning criteria, which call for the use of many types of geometric tolerances to completely and unambiguously represent the design intent and the many constraints deriving from manufacturing, assembly and inspection processes. All these issues have to be modeled and explicitly provided to a generative specification procedure, which may thus need a large amount of input data. The proposed approach tries to avoid this difficulty by considering that most precision requirements to be defined relate to the assembly process, and can be automatically derived by analyzing the contact relations between parts and the assembly operations planned for the product. Along with possible user-defined additional requirements relating to function, assembly requirements are used in a rule-based geometric reasoning procedure to select datum reference frames for each part and to assign tolerance types to part features. A demonstrative software tool based on the developed procedure has allowed to verify its correctness and application scope on some product examples.     

Modelling and control of an assembly/disassembly mechatronics line served by mobile robot with manipulator

The aim of this paper is to reverse an assembly line using a mobile platform equipped with a manipulator. By reversibility we mean that the line is able to perform disassembly. For this purpose, an assembly/disassembly line balancing (A/DLB) and a synchronised hybrid Petri nets (SHPN) model will be used to model and control an assembly/disassembly mechatronics line (A/DML), with a fixed number of workstations, served by a wheeled mobile robot (WMR) equipped with a robotic manipulator (RM). The SHPN model is a hybrid type, where A/DML is the discrete part, and WMR with RM is the continuous part. Moreover, the model operates in synchronised mode with signals from sensors. Disassembly starts after the assembly process and after the assembled piece fails the quality test, in order to recover the parts. The WMR with RM is used only during disassembly, to transport the parts from the disassembling locations to the storage locations. Using these models and a LabView platform, a real-time control structure has been designed and implemented, allowing automated assembly and disassembly, where the latter is assisted by a mobile platform equipped with a manipulator.     

A virtual prototyping approach to product disassembly reasoning

An important aspect of Design for the Life Cycle is assessing the disassemblability of products. After an artifact has completed its useful life, it must be disassembled then recycled, remanufactured or scrapped. Disassemblability of a product can be evaluated by performing disassembly activities on prototypes. Virtual prototyping (VP) is an alternative to hardware prototyping in which analysis of designs can be done without manufacturing physical samples. In recent years, disassembly processes have been generated either by using interactive or automated approaches, but these approaches have limitations. Interactive approaches require extensive user input usually in the form of answering questions, whereas automated approaches can only be used to generate disassembly processes for products with simple component configuration and geometry. In this paper automated and interactive techniques are combined, using VP, to generate complete disassembly processes of a product design. To support generation of disassembly processes of a product, a virtual environment and VP method were developed that will support disassembly activities performed by a designer. The product model of the virtual prototype is generated from the CAD model. The disassembly process model for the prototype is generated using automated reasoning techniques and is completed by interactively disassembling the product in the virtual environment. Extensions to automatic reasoning techniques to compute ranges of feasible directions of component removal were developed to facilitate the generation of the disassembly process. A scheme to represent the disassembly process for disassemblability evaluation was developed and implemented. In this paper a Chrysler LHS center console has been used to illustrate our approach of generating disassembly processes via VP.