Flexible Assembly Systems Research Articles

Optical scanner assisted robotic assembly

PurposeThis paper aims to propose the method of automatic robotic assembly of two or more parts placed without fixing instrumentation and positioning on the pallet.Design/methodology/approachAssembly tasks performed by industrial robots are usually based on a constant program, extensive tooling, fixing objects in a given place and a relatively limited sensory system. In this study, a different approach is presented. The industrial robot program is adjusted to the location of parts for assembly in the work space. This leads to a transition from a clearly defined assembly sequence realized by the industrial robot to the one in which the order of execution of the assembly operations can be determined by the mutual position of parts to be assembled.FindingsThe method presented in this study combines many already known algorithms. The contribution of the authors is to test and select the appropriate combination of methods capable of supporting robotic assembly process based on data from optical 3D scanners. The sequence of operations from scanning to place the parts in the installation position by an industrial robot is developed. A set of parameters for selected methods is presented. The result is a universal procedure that determines the position of the preset models in partial measurements performed at a fixed relative position of the sensor, the measurement object.Originality/valueThe developed procedure for determining the position of the parts is essential to develop a flexible robotic assembly system. It will be able to perform the task of assembly on the basis of appropriate search algorithms taking into account the selected and implemented sequence of assembly position and orientation of parts, particularly the base unit freely placed on an assembly pallete. It is also the basis of a system for testing different algorithms to optimize the flexible robotic assembly.

Agility in assembly systems: a comparison model

PurposeThis paper aims at analyzing different possible assembly systems, including innovative potential configurations such as the fully flexible assembly systems (FAS), by defining a novel analytical model that focuses on the concept of agility and its impact on the whole system performance, also evaluating the economic convenience in terms of the unit direct production cost.Design/methodology/approachThe authors propose a comparison model derived by Newton’s second law, introducing a quantitative definition of agility (acceleration), resistance of an assembly system to any change of its operative state (inertia) and unit direct production cost (force). Different types of assembly systems (manual, flexible and fully FAS) are analyzed and compared using the proposed model, investigating agility, system inertia and their impact on the unit direct production cost.FindingsThe proposed agility definition and the proposed comparison model have been applied considering different sets of parameters as independent variables, such as the number of components to assemble (product model complexity) and the target throughput of the system. The main findings are a series of convenience areas which either, for a given target unit direct production cost (force), defines the most agile system to adopt or, for a given target agility (acceleration), defines the most economical system to adopt, as function of the independent variables.Originality/valueThe novelty of this work is, first, the analytical definition of agility applied to assembly systems and contextualized by means of the definition of the new comparison model. The comparison between different assembly systems on the basis of agility, and by using different sets of independent variables, is a further element of interest. Finally, the resulting convenience areas represent a desirable tool that could be used to optimally choose the most suitable assembly system according to one or more system parameters.

Polynomial-complexity supervisory control for flexible assembly systems based on Petri nets

ABSTRACTFlexible assembly systems (FASs) are a class of resource allocation systems with assembly processes as their inevitable components. Deadlock resolution and liveness enforcement play important roles in the supervisory control of FASs. Design of deadlock avoidance policies (DAPs) for FASs has received significant attention recently. The computational feasibility of real-time DAPs is of great importance for the policies’ online implementation in practical applications. However, there are difficulties brought by the existence of assembly processes. So far, nearly all known DAPs with polynomial-time complexity apply only to systems without assembly operations. This study focuses on the deadlock-avoidance control problem of a broader class of FASs as compared to those discussed in the existing work. Specifically, for an FAS addressed in this paper, each resource can be shared by any two operations, and it also allows multiple resource acquisition at each processing step. This work develops a novel DAP for such FASs, which is based on their Petri-net models and actually an improved Banker’s algorithm that consists of three executable algorithms. Moreover, the computational time complexity of the DAP is polynomial in the size of the system model. The application of the proposed method to some examples illustrates its effectiveness and efficiency.

Linking product design to flexibility in an assembly system: a case study

PurposeThe recent shift towards accommodating flexibility in manufacturing companies and the complexity resulting from product variety highlight the significance of flexible assembly systems and designing products for them. The purpose of this paper is to provide insight into the requirements of a flexible assembly system for product design from the assembly system’s standpoint.Design/methodology/approachTo fulfil the purpose of the paper, a literature review and a case study were performed. The case study was conducted with an interactive research approach in a global market leader company within the heavy vehicle manufacturing industry.FindingsThe findings indicate that common assembly sequence, similar assembly interfaces, and common parts are the main requirements of a flexible assembly system for product design which reduce complexity and facilitate various flexibility dimensions. Accordingly, a model is proposed to broaden the understanding of these requirements from the assembly system’s standpoint.Research limitations/implicationsThis study contributes to the overlapping research area of flexible assembly systems and product design.Practical implicationsThe proposed model is largely based on practical data and clarifies the role of product design in facilitating flexibility in an assembly system. It can be used by assembly managers, assembly engineers, and product designers.Originality/valueThe key originality of this paper compared to the previous studies lies in presenting a novel assembly-oriented design model. The model enhances understanding of a flexible assembly system’s requirements for product design with regard to reducing complexity and managing variation in a flexible assembly system. These requirements can be applied to product design across various product families within a company’s product portfolio.

A Simulator for Event-oriented Data in Flexible Assembly System Fault Prediction

We present an open source discrete event simulator, FAS Simulator, for generating interleaved process traces of Flexible Assembly Systems. The simulation includes plausible faults creating anomalies in the output. The generated outputs can be used as a benchmark for evaluating novel anomaly detection methods.

Analysis of overtaking in M/M/c queues

Overtaking events can occur in parallel processing systems when customers are served simultaneously by multiple servers. We say that one customer overtakes another when the customer leaves the system after having been served ahead of another customer(s) who arrived earlier. Overtaking events are an important issue in flexible assembly systems or packet switched communication networks. Although materials (or packets) can be processed by different servers simultaneously, there is a designated order for the assembly of final products (or data). If overtaking occurs, then additional time and money may be required to rearrange materials (or packets) to the original order (called resequencing). We investigate overtaking in an M/M/c queueing system. Two distributions were considered to describe the amount of overtaking: the number of customers that an arbitrary (tagged) customer overtakes and the number of customers who overtake the tagged customer. Explicit forms of these distributions are provided for some cases. Finally, we apply our results to practical issues in flexible assembly systems and telecommunication systems.

Assembly line balancing problem with task learning and dynamic task reassignment

This paper addresses an existing but unsolved problem: dynamic task reassignment under changing task performance times. This situation is relevant to automated flexible assembly systems with collaborative learning. The length of the line can be reduced during the period of production by dynamically rebalancing the assembly line because of the changing task times. A task reassignment procedure is designed to balance such an assembly line where task times are being reduced during small lot size production. Backward induction rules, which can be combined with prevalent algorithms, are proposed to form such a procedure. A case study is provided to show that the procedure significantly increases the efficiency of the assembly line in terms of the length of the production line and system idle times.

Drivers of Complexity in a Flexible Assembly System- A Case Study

Various ever-changing market demands have propelled manufacturing companies to offer product variety in an efficient and timely manner. Assembly as a key stage of manufacturing operations is used to realise product variety through establishing mixed-product assembly lines. Although establishing a flexible mixed-product assembly system which both offers product variety and absorbs market demands fluctuation is pivotal for maintaining competitive edge in certain industries such as vehicle manufacturing, it is also considered an elaborate task which calls for further investigation. In this paper, complexity in a flexible mixed-product assembly system is investigated and the key drivers of complexity are identified. To fulfil the research objective, a case study during the pilot implementation of a flexible mixed-product assembly concept in a heavy vehicle manufacturing company has been conducted. The results indicate the key factors concerning assembly operation, product design, and information and communication technology (ICT) which contribute to complexity in the flexible assembly system. The paper concludes with an outlook for possible future research.

Requirements for the Design of Flexible and Changeable Manufacturing and Assembly Systems: A SME-survey

Increasingly complex market dynamics due to unpredictable forecasts and shorter innovation cycles require maximum flexibility from production companies and their manufacturing systems. A manufacturing system should not only produce high-quality products at the lowest possible price; it should also be able to react quickly to market changes and consumers preferences. After the implementation in large enterprises belonging to the automotive sector and other related sectors, the concept of flexibility and changeability has been introduced in small and medium-sized enterprises (SME). In recent years, the concept of flexibility and changeability was object of research and industry. Current research in manufacturing pays great attention to flexibility and changeability in manufacturing and assembly systems. Therefore, research and investigations are needed to analyze the requirements for the design of flexible and changeable manufacturing and assembly systems in SMEs in order to define simple and practically suitable design guidelines. This research analyzes the nature of environmental changes, which SMEs are currently facing, due to a questionnaire-based survey. This research paper summarizes the results of the survey, executed with 27 SME companies in North Italy, showing the main requirements for the design of flexible and changeable manufacturing and assembly systems.

Planning of Workstations in a Modular Automotive Assembly System

In a turbulent market environment an assembly system with a high level of flexibility and changeability is necessary. Especially in the automotive industry the developments towards product differentiation and shorter product lifecycles require highly flexible and changeable assembly systems. One basic enabler to reach this goal is modularization. In a modular assembly system having uncoupled workstations and a flexible transportation of products, however, the methods of production planning need to be adapted as well.In this paper, the well-established methodology of assembly line balancing for the planning of workstations in an assembly line production is analyzed. However, it is shown that this methodology as well as other methods to plan workstations in an assembly system are not applicable for a modular assembly system due to its different characteristics. For this reason, a new planning method to assign assembly tasks to workstations is developed, based on the different targets and restrictions of a modular assembly system.In this method, the assignment of assembly tasks to workstations is primarily based on their position in the assembly priority chart of the products being assembled. The application of the described method is shown in an example of a product-based modular automotive assembly system developed by the authors. In this context, the method is one main aspect of planning and operating a modular assembly system, which is supposed to handle the further increasing diversity and dynamics of the automotive industry by its high level of flexibility and changeability.

Interoperability for a Dynamic Assembly System

There are many challenges for the manufacturing industry when building and maintaining interoperable information systems. Automation and related information systems are often implemented in controlled and secure environments that lead to autonomous disconnected islands. This study presents two innovative solutions that exemplify both horizontal and vertical systems integration. The solutions have been implemented and tested on a flexible and mobile assembly system with equipment from different suppliers.

Using Machine Vision for Flexible Automatic Assembly System

Flexible automatic assembly systems become the useful automation system for high mixed production lines of manufacturing processes. This research was aimed to design the primary prototype of the flexible automatic pick and place assembly system. We integrated the machine vision system with the robotic system to conduct a pick and place process. The product models consisted of a main part and an assembly part. The main parts were transferred to the mechanical system through a conveyor belt. When the main parts were held at the specific location, the images of the main parts were captured. Using the image processing of LabVIEW NI vision software and NI vision builder and image calibration method, we could obtain the shape, and orientation of assemble space in the main part which were used to control selective compliance articulated robot arm (SCARA). The SCARA was used to pick the assembly parts from the storage station and place them into the assembly spaces on the main parts. As the results of the prototyping, we evaluated the coordinate conversion factors from the image calibration and used them to control the movement of the SCARA. We finally obtained the reliable flexible automatic assembly system that could detect and identify the shape, and orientation of the assembly space correctly. The SCARA could also pick the correct assembly parts and place them into the assembly space perfectly.

An open distributed architecture for flexible hybrid assembly systems: a model-driven engineering approach

Assembly systems constitute one of the most important fields in today’s industry. The need for flexibility in the assembly process imposes several challenges in the development of this kind of systems. Model-driven engineering (MDE) has been successfully used to alleviate the complexity of platforms and express domain concepts effectively. In this paper, an open distributed architecture for the engineering of evolvable flexible hybrid assembly systems is described. The proposed architecture is based on the model-driven development paradigm. Models are used to represent in a formalized way the structure, the behavior, and the requirements of the assembly systems. A domain-specific engineering tool is defined to facilitate the assembly system engineer in the engineering process of assembly systems. Specific meta-models are defined to capture domain knowledge and guide the engineer in the construction of the models required to construct the assembly system. The proposed approach imposes a correct-by-construction approach and is based on an architecture that exploits the benefits of Cyber Physical paradigm utilizing web technologies, Internet of Things, and Cloud computing.

Confusion diagnosis and avoidance of discrete event systems using supervisory control

Nondeterministic firing of concurrent transitions in Petri nets (PNs) may lead to the disappearance of conflicts. The disappearance implies that the partial conflicting transitions in a conflict become disabled before the resolution of the conflict. The phenomenon is called confusions that are caused by the interlacement of conflicting and concurrent transitions in PNs, which generates incomplete and faulty system conflicting behavior such that conflicts cannot be correctly resolved. In this paper, conflict‐increasing confusions (CICs) and conflict‐decreasing confusions (CDCs) in a PN are investigated. The relation graph of conflicts and confusions (RGC2) in a PN is proposed to detect the structure of confusions. To avoid the occurrence of confusions in a PN, an algorithm based on generalized mutual exclusion constraints (GMECs) is proposed, which can generate confusion‐avoidance supervisors such that the occurrence of conflicts can be ensured in a PN. Finally, an example of confusion detection and avoidance in a flexible assembly system is presented. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Hybrid fexible assembly systems (H-FAS): bridging the gap between traditional and fully flexible assembly systems

Automation can be a valid way to reduce production costs. Considering medium/low volumes and a wide set of different models, a mixed model assembly work cell is a proper automated production system. The authors have recently introduced a new class of flexible assembly systems (FAS), the F-FAS, in which highly flexible feeding systems are used to improve the flexibility and reduce the set-up times at batch change. Such systems, guaranteeing a higher level of flexibility than traditional automated FAS, show some limitations in terms of productivity, due to the stochastic process of feeding and reorientation of parts and to the time spent for image acquisition and processing. The aim of this paper is to introduce an innovative automated assembly work cell, called the hybrid flexible assembly system (H-FAS), that merges the traditional FAS bowl feeder utilisation with the innovative F-FAS feeding concepts. The paper analyses the main factors influencing the H-FAS design, productivity and cost. Moreover, through a comparative analysis between the different single cell assembly systems, it defines the working conditions in which they can be preferable.

Efficiency improvement of automatic assembly in automotive and tractor engineering

Results of selecting of optimal number of technological equipment for the automatic assembly of gearboxes are given. A method for items grouping is presented; selecting of optimal configuration of flexible assembly system is substantiated mathematically.

Online programming technique for flexible assembly of fuselage

In order to meet the deep flexible demands of "one fixture with more models"and "one fixture with more states"for digital assembly of fuselage,enable the "bridge-frame"flexible tooling to have better capacity for independent adaptability,its kinematic model must be set up and its movement controls strategy must be planned properly by online programming technique. For the locating styles of fuselage and the characteristics of flexible tooling,the kinematic model of flexible tooling was set up,then simulation model-based online programming disciplines,the way of building reference points for assembly and the technology of movement controls strategy planning were studied. The way of building a process-driven simulation environment based on structure function was proposed. In order to generate the codes quickly to control motion,the online programming system for flexible assembly of fuselage was developed. With the assembly of rear fuselage,for example,the accuracy,high efficiency and strong independent adaptability of this system were verified.

Dokładność pozycjonowania robotów w elastycznych systemach montażowych

Dokładność pozycjonowania robotów w elastycznych systemach montażowych

The Essential Constituents of Flexible Assembly Systems: A Case Study in the Heavy Vehicle Manufacturing Industry

The major challenge of today’s manufacturing industry in tackling demands for a wider range of products with short life-cycle times and meeting customisation requirements has drawn considerable att ...

Implementation framework for a fully flexible assembly system (F-FAS)

Purpose – This paper aims to provide a framework for the choice, design, set-up and management of a fully flexible assembly system (F-FAS). Many industrial applications for small batch productions require highly flexible automated manufacturing systems. Moreover, some extensions of the F-FAS concept are provided. Design/methodology/approach – The paper reviews recent findings regarding the F-FAS with a top-down approach, and defines an integrated implementation framework. This framework is structured into three strictly correlated phases, and the presented procedure is organized to be readily used for new industrial applications. Practical applications are presented to show how the system can satisfy flexibility demands in a variety of cases. Findings – The proposed framework is organized in three steps: convenience analysis of the F-FAS compared to a traditional flexible assembly system; an optimal design of the feeder; a choice of the set-up and sequencing algorithm yielding the highest throughput. Following these steps, the F-FAS can become an effective solution for small batch productions with frequent reconfigurations. However, due to the limited throughput, the system is not well suited for large batches. Originality/value – The presented framework allows to implement an F-FAS for a given industrial application, and to evaluate its efficacy with respect to other assembly technologies. Moreover, with the same implementation framework, the F-FAS concept can be applied to production fields that are different from assembly, as shown by the provided examples. This represents an important element of originality and of interest for its strong practical implications in different production environments.