Search results

Flexible automated assembly is an emerging need in several industries. The purpose of this paper is to address the introduction of an innovative concept in flexible assembly: the fully flexible assembly system (F‐FAS).

After an analysis of the state of the art, the authors describe the proposed F‐FAS, from a layout, constitutional elements, functioning principles and working cycle point of view. Second, the authors compare the traditional FAS and the manual assembly system versus the proposed F‐FAS according to their throughput and unit production costs, deriving a convenience map as a function of the number of components used in assembly and of the efficiency of the F‐FAS. Finally, using a prototype work cell developed at the Robotics Laboratory of University of Padua, the authors validate the F‐FAS concept.

Results of the research indicate that the concept of full‐flexibility can be exploited to bring automation to a domain where traditional FAS are not competitive versus manual assembly. In fact, the F‐FAS outperforms both traditional FAS and manual assembly, in terms of unit direct production costs, when the size of the batch is small, the number of components used in assembly is large and the efficiency of the F‐FAS is reasonably high. The F‐FAS prototype demonstrated the possibility of working, for certain conditions (models/components/production mix), in the F‐FAS convenience area, highlighting the achievable cost reduction versus traditional assembly systems.

The novelty of the study lies in the F‐FAS concept, its performances in terms of flexibility, compactness, throughput and unit direct production costs. A prototype work cell validated the concept and demonstrated its viability versus traditional assembly systems, thanks to convenience analysis.

The development of a generic flexible assembly system involves the design, selection and integration of a number of different mechanical systems in order to develop an assembly system, which is capable of assembling a wide variety of products having an unknown specification. A specific system configuration being dependent on a variety of factors such as, product size, weight, component insertion direction, and manipulator geometry. This paper examines each of the factors that should be considered when designing a generic flexible assembly system and presents a novel generic flexible assembly system design.

The paper aims to address the modelling and optimization of fully flexible assembly systems (F‐FAS), a new concept in flexible automation recently introduced by the authors.

The paper presents a mathematical model of the F‐FAS, which makes it possible to predict its efficiency, throughput and unit direct production costs, correlating such values with system and production variables. The mathematical model proposed in the paper was derived from experimental and simulation data, which were analysed for a wide range of different productions and system settings.

Correlation analysis revealed that there are three main determinants of the efficiency of the F‐FAS: the number of components (types of parts) used to assemble the models (production variable); the average complexity of the models to be assembled (production variable); the ratio of the average perimeter of components (production variable) over a significant dimension of the working plane (system variable). Such parameters makes it possible to estimate the maximum attainable efficiency of the F‐FAS, and to calculate the optimal setting of the feeder which makes it possible to obtain such efficiency during the execution of the whole production order.

The model presented in the paper makes it possible to quantify in advance the real potential of the F‐FAS, according to the characteristics of the production mix and type of components to be assembled. By using the methodologies presented in the paper, one can first evaluate the convenience of the F‐FAS approach with respect to traditional FAS technology and manual assembly, then identify the optimal design and settings of the F‐FAS, according to the needs of a specific application. As a result, not only can the investment on the automated assembly system be accurately evaluated in advance, but also the return on investment can be maximized.

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.

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.

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.

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.

One of the first steps in designing a flexible assembly system is the selection of an appropriate manipulator. There are a number of different manipulator configurations which can be chosen depending on a variety of factors such as the assembly workspace layout, product size, weight, and component insertion direction.A number of methodologies have been written to help the selection of a manipulator for process cells. However, little work exists to aid the machine designer in the selection of an appropriate manipulator for flexible assembly. This paper examines the factors which affect this process.

A compliance device combining passive and active compliance has been tested and developed for an anthropomorphic robot for use during assembly operations. The device has the ability to correct for angular and lateral misalignments between mating parts, resulting in no equipment or part damage. The method of control, the design features of the device and the modifications made to enable the device to be used by an anthropomorphic robot are described and future modifications which will enable the device to operate more effectively are discussed.

Large gear components widely exist in the transmission system of helicopters, ships, etc. Due to the small assembly clearance of large gear components, using an automatic docking system based on position control will lead to forced assembly. The purpose of this paper is to reduce the assembly stress of large gear components by an active compliant docking technology based on distributed force sensors.

Firstly, aiming at the noise interference in three-dimensional force sensor (TDFS), Kalman filter and Savitzky–Golay filter are used to process the sensor’s output signal. Secondly, the active compliant docking control model is constructed according to the principle of impedance control. Thirdly, the contact force is calculated based on the Euler equation, and the impedance control parameters are tuned by the particle swarm optimization algorithm. Finally, an active compliant docking system of a large gear structure based on distributed force sensor is built in the laboratory to verify the proposed method.

The experimental results show that the contact force and contact torque gradually decrease in all directions and are always in the safe range during the docking process. The feasibility of this method in practical application is preliminarily demonstrated.

The distributed TDFSs are used to replace the traditional six-dimensional force sensor in the active compliant docking system of gear components, which solves the problem of the small bearing capacity of the conventional active compliant docking system. This method can also be used for the docking of other large components.

The purpose of this paper is to carry out a comprehensive study of compressible flow over double wedge and biconvex airfoils using computational fluid dynamics (CFD) and three analytical models including shock and expansion wave theory, Busemann's second‐order linearized approximation and characteristic method (CHM).

Flow over double‐wedge and biconvex airfoils was investigated by the CFD technique using the Spalart‐Allmaras turbulence model for computation of the Reynolds stresses. Flow was considered compressible, two dimensional and steady. The no slip condition was applied at walls and the Sutherland law was used to calculate molecular viscosity as a function of static temperature. First‐order upwind discretization scheme was used for the convection terms. Finite‐volume method was used for the entire solution domain meshed by quadratic computational cells. Busemann's theory, shock and expansion wave technique and CHM were the analytical methods used in this work.

Static pressure, static temperature and aerodynamic coefficients of the airfoils were calculated at various angles of attack. In addition, aerodynamic coefficients of the double‐wedge airfoil were obtained at various free stream Mach numbers and thickness ratios of the airfoil. Static pressure and aerodynamic coefficients obtained from the analytical and numerical methods were in excellent agreement with average error of 1.62 percent. Variation of the static pressure normal to the walls was negligible in the numerical simulation as well as the analytical solutions. Analytical static temperature far from the walls was consistent with the numerical values with average error of 3.40 percent. However, it was not comparable to the numerical temperature at the solid walls. Therefore, analytical solutions give accurate prediction of the static pressure and the aerodynamic coefficients, however, for the static temperature; they are only reliable far from the solid surfaces. Accuracy of the analytical aerodynamic coefficients is because of accurate prediction of the static pressure which is not considerably influenced by the boundary layer. Discrepancies between analytical and numerical temperatures near the walls are because of dependency of temperature on the boundary layer and viscous heating. Low‐speed flow near walls causes transformation of the kinetic energy of the free stream into enthalpy that leads to high temperature on the solid walls; which is neglected in the analytical solutions.

This paper is useful for researchers in the area of external compressible flows. This work is original.

The purpose of this paper is to apply group assembly (GA) considerations to the construction industry and to provide evidence of construction sector industrialization with quantitative results. Moreover, a flexible assembly system is proposed, especially designed to cope with variability: this can be easily extendable to other industrial sectors, especially when dealing with extremely variable environments.

The paper presents a case study conducted at an Italian company leader in the design, manufacture and installation of architectural claddings and lightweight continuous facades.

The research empirically demonstrates how the application of GA and the creation of project families lead to consistent enhancement also within the construction industry. The case study reveals great improvement in terms of both operating and ergonomic performances, agile assembly system reconfiguration design and make span reduction. The possibility of correlating a new project to an identified family gives the opportunity to understand the best assembly line layout configuration which should be assigned to the project, to improve the throughput time and the controllability of the assembly process and to guarantee efficient floor space utilization, lead‐time control, accuracy and reliability.

The novelty of the study lies in the way the assembly layout is designed to cope with variability: the assembly line, which is dedicated to more stable processes, is coupled with pre‐assembly stations, easily reconfigurable, meant to be “variability absorbers”. As far as the authors know, this is also the first time GA is applied to the construction industry. Moreover, a timely topic such as construction sector industrialization is confirmed by quantitative results.

The purpose of this paper is to present a Petri net (PN) model based on assembly plan is presented for modeling a flexible assembly system (FAS) configuration, determining an optimal work‐in‐process (WIP), lead time, throughput, and utilization of each station.

PN model is developed for design, analysis, and performance evaluation of a FAS, keeping in view the assembly line balancing. PN is optimized using weighted WIP. The throughput is bounded by the utilization of the bottleneck machines.

The PN optimization gives minimum WIP corresponding to the maximum production rate. Minimum WIP leads to minimum lead time. The weighted arcs make the model simple and reduce the optimized number of kanbans. Moreover, the PN model pushes more inventory to the initial assembly phase. This reduces the total cost of the WIP.

In the proposed PN model, the transportation times are included in the transitions times. In the future research, the proposed model can be extended for inclusion of transportation times for AGVs.

Using the PN model, the assembly manager may design, analyze, evaluate, and even optimize the layout of the assembly system for minimum WIP, maximum throughput, and reduced lead time. The determination of the total WIP, total number of stations in the assembly system, and the number of servers at each station may be helpful in factory floor management. The same cycle time is managed at each assembly station for the purpose of line balancing. It may result in the highest efficiency and the shortest idling time along with ease of management and supervision.

This paper presents a new PN model for the design and performance evaluation of a dual kanban FAS.