Flexible Assembly Cell Research Articles

A new redundancy strategy for enabling graceful degradation in resilient robotic flexible assembly cells

The development of resilience in manufacturing systems has drawn more attention than ever. Using redundant components is one of the key strategies for building and enhancing the resilience of a manufacturing system. However, current redundancy strategies require duplicated machinery employed either in active or in standby status. This in turn causes extra costs in designing and achieving resilience. Achieving an efficient deployment of the redundant component in the face of failures is also challenging. In this paper, we introduce a novel redundancy strategy, called adaptive standby redundancy (ASR), to achieve resilient performance for discrete manufacturing systems while reducing the cost of employing the duplicated components that are typically used in traditional systems. This novel strategy permits achievement of high levels of utilisation of the system and graceful degradation in case of failure, keeping the system functional. The strategy is then validated in a developed robotic flexible assembly cell (RFAC), which is tested and results on its efficacy and performance enhancement are discussed.

Fault Detection Algorithm for Pneumatic Measuring and Sorting Station

The aim of this paper is to present basic hardware components of a Flexible Assembly System (FAS) and investigate possible faults, classify the errors and implement real diagnosis. The mentioned system offers professional training according to the industrial reality, simulating a real assembly process and including different technologies from Industry 4.0. This equipment consists of an automated flexible assembly cell with five different stages: assembly, handling, quality inspection, transfer and warehouse. The pneumatic system repeats the identical programmed sequence during it operation. The data was collected when the pneumatic system worked perfectly and had some generated faults including empty magazine, zero vacuum, inappropriate material, no pressure, closed manual pressure valve, missing drilling stroke, poorly located material, not vacuuming the material and low air pressure. The faults are simulated according to developed algorithms in this investigation. The case study with fuzzy logic is used to develop a new sequence for one pneumatic module diagnosis. The analysis of the simulated faults is discussed and the obtained results can be applied in the similar pneumatic systems in industry.

Software for Animation and Graphic Visualization of Mechatronic Elements and Control Process of FMS

The issue of graphical visualization of the simulation, animation and design of mechatronic elements and control process in the example of the mechanical assembly shop of the flexible manufacture system (FMS), which is considered a complex technical system, is set. The purpose of the work is the development of graphics-mode software that provides computer experiments of 2D, 3D designer-modeling, animation and graphic visualization of the interface for evaluating the feasibility of the design process of the flexible mechanical assembly cell (FMAC) As the main research issues, the construction of the 2D and 3D grouping scheme of the static and dynamic elements of the research object, the development of 3D software for the animation models of the activities of its active elements, and the development of the generalized software for the graphic visualization of the interface for the design of the management system were set. Based on the issues raised, the 3D grouping scheme of static and dynamic elements of the FMAC was established, the positioning coordinates of the 2D static and dynamic elements of the FMAC were determined in the PROOF Animation system, the analysis of the technological process of the FMS was carried out to build an animation model, and the animation movements of technological operations were MOVE (management unguided movement) or PATH (guided movement) operators. An animation model of the static and dynamic active elements of the FMAC was built, experiments were conducted, and as a result, it was possible to calculate a technological cycle in the research object and determine the productivity of the workshop. The software for the graphic visualization of the design of the control system of the FMAC was developed, and the procedures and operations of each software module of the interface were planned.

INDUSTRIAL ASSEMBLY LINE OPERATION

The idea of this paper is to present basic components of a flexible assembly system (FAS), discuss it characteristics, classify the systems and describe an application. This equipment offers professional training according to the industrial reality, simulating a real assembly process and including different technologies from Industry 4.0. The FAS consists of an automated flexible assembly cell with five different stages: assembly, handling, quality inspection, transfer and warehouse. It is the ideal answer to research and training in industrial automation. The main advantage is that it has fully modularity in keeping with industrial reality. The technologies included in its different assembly modules, as well as the assembly process with several variants, allow the user to develop the professional skills required by advanced automation. In this work the conventional control approach is presented with programmable logic controllers (PLC) and SCADA level.

Achieving batch-size-of-one production model in robot flexible assembly cells

Manufacturing industry is facing new challenges in that fast-changing demands for products and services from customers push manufacturers to be more flexible and adaptive. The concept of batch-size-of-one production is presented in this paper, which defines a fully automated, highly customised, and short lead time production model. The desired batch-size-of-one production model is a promising solution for the above challenges in manufacturing industry, especially for highly customised or families of similar products like in the mobile phone industry. Along with the concept, we introduce a novel control method that enables the desired batch-size-of-one production model in operation of robots in manufacturing and assembly systems. The strategy was developed for robot control based on a distributed system to enable industrial robots to receive job commands on the fly and to conduct different jobs without the need for reconfiguration and reprogramming and without overheads. The aim of the research is to create the basis for a fully automated robot flexible assembly cell to perform batch-size-of-one assembly tasks with minimal human involvement by eliminating interruptions from the reconfiguration and reprogramming processes. The proposed strategy has been validated in practice in a multi-robot, multi-product flexible assembly cell.

Methodological Approach for Developing Reconfigurable Automation Systems

One challenge for the designers of the current industrial control systems consists of assuring the system reconfiguration at runtime, envisaged at system design time. This article focuses specifically on the fault tolerance to controller failures (as it is the most complex challenge) aiming at redistributing the responsibilities at runtime in order to finish the current production plan. Its applicability is illustrated by means of a case study that consists of a reconfigurable control application based on the IEC 61131-3 for a flexible assembly cell. A prototype software tool guides the developer during the development process. This approach contributes to develop more flexible control systems because they can react in case of a controller failure, to increase the system availability during its operation and to reduce the production downtimes to perform the maintenance tasks.

Digital twin driven human–robot collaborative assembly

This paper discusses an object-oriented event-driven simulation as a digital twin of a flexible assembly cell coordinated with a robot to perform assembly tasks alongside human. The digital twin extends the use of virtual simulation models developed in the design phase of a production system to operations for real-time control, dynamic skill-based tasks allocation between human and robot, sequencing of tasks and developing robot program accordingly. The methodology combines lean methods of manual assembly in human–robot collaboration paving path towards flexible human–robot work teams. The study is validated with an industrial case study involving dexterous assembly tasks.

Dynamic and Static Characteristics Analysis for Flexible Assembly Cell

A flexible assembly cell has been designed for precision microstructures. In this paper, the static analysis and dynamic characteristics of the assembly cell are analyzed respectively. Through the finite element static analysis and simulation, we optimized the assembly cell’s structure design. Through the modal analysis, the first six nature frequencies and nature mode shapes are obtained. The overall oscillation of the first two sections, shows that the asssembly cell has a better dynamic performance. Meanwhile a modal test on assembly cell structure was also conducted. The first-order natural frequency has been obtained. The critical rotating speed is much higher than the maximum speed of the motor in the assembly cell, and no resonance phenomenon can be generated. The simulative results are consistent with the experimental results, and the correctness and adaptability of the simulation method are verified, ensuring the accuracy and reliability of the assembly cell.

Distributed multi-agent scheduling and control system for robotic flexible assembly cells

This paper deals with the development of a distributed multi-agent system (DMAS) for scheduling and controlling Robotic Flexible Assembly Cells (RFAC). In the proposed system, an approach for solving one of the most challenging decisional problems in RFAC is proposed and implemented. This problem is related to the products operations scheduling which requires their allocation and sequencing on the robots, while satisfying products and robots constraints under makespan minimization. The proposed DMAS addresses this challenge by using a cooperative approach supported by three kinds of autonomous control agents: supervisory agent, local agents, and remote agents. These agents interact by a negotiation protocol based on common dispatching rules for coordinating their individual decisions, satisfying their local objective and providing an optimized global solution. Moreover, because of the dynamic nature of the assembly systems, it is imperative to consider external disturbances on production scheduling and to solve the related issues. Consequently, DMAS has the ability to respond and manage some dynamic events that may occur in the cells such as unexpected robot breakdown or dynamic products arrivals. Computational results on benchmarks show the effectiveness and the robustness of the proposed system.

Dual arm robot in cooperation with humans for flexible assembly

This paper discusses a flexible assembly cell, including a dual arm robot in cooperation with humans for assembly tasks typically performed by operators. The robot performs these tasks both in isolation and cooperation with the human. Sensor data are used for programming the robot’s motion and controlling the program’s execution in a fenceless setup. Safety is ensured with the use of 3D sensing devices, while the tasks’ coordination is managed by the so-called station controller. The programming approach combines both offline and on-line methods, in an intuitive manner. The proposed assembly cell is demonstrated in an automotive industry case.

Multi-objective optimisation of dynamic scheduling in robotic flexible assembly cells via fuzzy-based Taguchi approach

This paper presents Taguchi method coupled with fuzzy logic for dealing with multi-objective optimisation problems for dynamic scheduling in robotic flexible assembly cells (RFACs). This is the first study to address these particular problems. In this study, Taguchi optimisation method has been applied to reduce the number of experiments required for scheduling RFACs. The experiments are implemented with four different scheduling factors, namely sequencing rule, dispatching rule, cell utilisation and due date tightness. These factors are difficult to optimise considering the objectives of multiple functions instead of a single objective. Therefore, a multiple performance characteristics index (MPCI) based fuzzy logic approach has been developed to derive the optimal solution. The predicted results of MPCIs have been verified via a confirmation test. Results of the confirmation test show significant improvement in MPCI using the optimal levels of the scheduling factors.

Optimal Selection of the Workpiece Recognition Parameters by Minimizing the Total Error Cost

Workpiece recognition is crucial in many flexible assembly cells, in automatic unmanned workstations and in robotic cells for human-robot collaborative scenarios. It allows for variability in the workpiece location & pose, and timing of the various operations. Automatic object recognition systems often rely on supervised machine learning methods, their parameters have to be chosen before training and cannot be changed later in runtime. In many machine learning applications the parameters are chosen in order to optimize the measures of relevance: accuracy, precision and recall. Usually these conflicting performance metrics are optimized independently from production costs. The innovation of present study is the introduction of a new metric to be optimized, a dimensionless total cost. It is a linear combination of the false positive and the false negative rates which are directly proportional to the real-life costs of errors. The presented case study, an object recognition system for reflective workpieces, is applied the proposed parameter selection to achieve optimal results with minimum production costs.

Handling of Frequent Design Changes in an Automated Assembly Cell for Electronic Products

This paper presents a prototype flexible assembly cell used for the assembly of electronic products. The cell is the first prototype version of the coming assembly system for fire sensors at Autronica. It is developed specifically for testing different concepts to reduce development time for design changes and introduction of new variants. The cell consists of a robot, grippers, sensors, vision systems and fixturing systems which have been selected for in-line adaptivity and reconfiguration. The topics of developing generic vision programs and reducing programming time for vision and robot have been central. The aspects needed to be addressed during development are presented together with considered and chosen solutions. These solutions are also discussed and compared to other systems presented in recent publications on flexible assembly.

Layout Redesign and Material Flow Analysis at a Flexible Assembly Cell Supported by the Use of Simulation

This paper essentially emerges from scientific and teaching needs of a university institute while trying deepen into a more formal analysis and/or design process of the material flow and associated manufacturing decisions, e.g.: the layout. Fulfilling such needs, the paper makes allusion to key manufacturing decisions associated to the material flow, while stressing the fact of their mandatory consideration when integrally addressing the primary problem. A partial application of the ideas takes place at a flexible assembly cell of the institute; some of the main results of it are: (1) a more formal description of the whole cell including alternative material flow scenarios, (2) the proposal of a new scenario implying the redesign of the cell conception, i.e.: the layout and thus material flow itself, (3) the simulation and comparison of material flow scenarios selecting the best one in terms of both the MF and layout, among others. At the end, the integration of all these previous elements clearly contributed to the solution of the research’ problem and objectives traced within the frame of the research.

Chain of refined perception in self-optimizing assembly of micro-optical systems

Abstract. Today, the assembly of laser systems requires a large share of manual operations due to its complexity regarding the optimal alignment of optics. Although the feasibility of automated alignment of laser optics has been shown in research labs, the development effort for the automation of assembly does not meet economic requirements – especially for low-volume laser production. This paper presents a model-based and sensor-integrated assembly execution approach for flexible assembly cells consisting of a macro-positioner covering a large workspace and a compact micromanipulator with camera attached to the positioner. In order to make full use of available models from computer-aided design (CAD) and optical simulation, sensor systems at different levels of accuracy are used for matching perceived information with model data. This approach is named "chain of refined perception", and it allows for automated planning of complex assembly tasks along all major phases of assembly such as collision-free path planning, part feeding, and active and passive alignment. The focus of the paper is put on the in-process image-based metrology and information extraction used for identifying and calibrating local coordinate systems as well as the exploitation of that information for a part feeding process for micro-optics. Results will be presented regarding the processes of automated calibration of the robot camera as well as the local coordinate systems of part feeding area and robot base.

The Methods for Increasing of the Efficiency in the Intelligent Assembly Cell

Efficiency of industrial production lines is crucial as it results in an improved production and utilization of available resources. Industry companies are constantly looking for new ways to improve workplace efficiency. Manufacturing industry trends to employ more flexible assembly cells with changes in programs and configurations for robots, and to achieve a high manufacturing efficiency. The various problems inherent in current mechanized product assembly are outlined, and potential organizational, technological, and engineering measures aimed at increasing the efficiency of product assembly are examined. Future developments in automated assembly are predicted. In order to improve the effectiveness of the cell, it is important to recognize measure and reduce losses in the assembly cell. The most effective method is to analyze the OEE (Overall Equipment Effectiveness) of the cell. It is developed design of assembly system under the project an intelligent assembly cell at the Institute of Production Systems and Applied Mechanics where after process running and debugging, based on the process analysis was evaluated, it is necessary to increase the efficiency of the cell. Deployment of monitoring, visualization and simulation are predicted defects that reduce overall system effectiveness. The project is aiming to develop an efficient intelligent manufacturing system integrating real time data collection, simulation, optimization and synthesis.

Simulation modelling and analysis of scheduling in robotic flexible assembly cells using Taguchi method

Due to increasing competition in the developing global economy, today’s companies are facing greater challenges than ever to employ flexible manufacturing systems (FMS) capable of dealing with unexpected events and meeting customers’ requirements. One such system is robotic flexible assembly cells (RFACs). There has been relatively little work on the scheduling of RFACs, even though overall scheduling problems of FMS have attracted significant attention. This paper presents Taguchi optimisation method in conjunction with simulation modelling in a new application for dynamic scheduling problems in RFACs, in order to minimise total tardiness and number of tardy jobs (NT). This is the first study to address these particular problems. In this study, Taguchi method has been used to reduce the minimum number of experiments required for scheduling RFACs. These experiments are based on an L9 orthogonal array with each trial implemented under different levels of scheduling factors. Four factors are considered simultaneously: sequencing rule, dispatching rule, cell utilisation and due date tightness. The experimental results are analysed using an analysis of mean to find the best combination of scheduling factors and an analysis of variance to determine the most significant factors that influence the system’s performance. The resulting analysis shows that this proposed methodology enhances the system’s scheduling policy.

DEVELOPMENT OF A FUZZY-SIMULATION MODEL OF SCHEDULING ROBOTIC FLEXIBLE ASSEMBLY CELLS

Due to the complexity of scheduling flexible manufacturing systems, the generation of production schedules requires an intelligent technique. Many artificial intelligence techniques such as fuzzy logic, genetic algorithms and neural networks have been successfully applied to the scheduling of advanced manufacturing systems. One such system is Robotic Flexible Assembly Cells (RFACs). Few studies have addressed the problem of scheduling RFACs. The major limitation is that these studies are limited to the assembly of only one product type. The objective of this study is to propose a new intelligent model of scheduling RFACs in a multi-product assembly environment, using fuzzy logic.

APPLICATION OF A FUZZY-SIMULATION MODEL OF SCHEDULING ROBOTIC FLEXIBLE ASSEMBLY CELLS

This study describes the application of the develop ed model to the scheduling of the Robotic Flexible Assembly Cells (RFACs). The present study is a continuation of the paper titled “Development of a Fuzz ySimulation Model of Scheduling Robotic Flexible Assembly Cells”. This new model for multi-objective scheduling problems in RFACs was based on combining a fuzzy-based mathematical model with simulation software tools. In this study, a hypothetical case study of RFACs is presented to demonstrate the effectiveness of the developed model and then compare the results that are obtained by the new methodology with the common scheduling rules. The simulation results show that the performance of the proposed methodology outperforms the most popular scheduling rules from previous research.

Flexible Assembly Cell Optimization by Operational Analysis

Operation analysis one of the system scientific disciplines closely related to system engineering. This discipline is part of praxeology. Praxeology deals with the research effectiveness of the procedure methods for all areas of human activity. The aim of this analysis is creating solved situation model and their optimization. Optimization is model extremes finding. There are model parameters values that output achieved minimum or maximum. Competitive environment is the reason for finding optimal solutions in the production process.