The industry 4.0 concepts are moving towards flexible and energy efficient factories. Major flexible production lines use battery-based automated guided vehicles (AGVs) to optimize their handling ...processes. However, optimal AGV battery management can significantly shorten lead times. In this paper, we address the scheduling problem in an AGV-based job-shop manufacturing facility. The considered schedule concerns three strands: jobs affecting machines, product transport tasks’ allocations and AGV fleet battery management. The proposed model supports outcomes expected from Industry 4.0 by increasing productivity through completion time minimization and optimizing energy by managing battery replenishment. Experimental tests were conducted on extended benchmark literature instances to evaluate the efficiency of the proposed approach.
In job-shop manufacturing systems, an efficient production schedule acts to reduce unnecessary costs and better manage resources. For the same purposes, modern manufacturing cells, in compliance with ...industry 4.0 concepts, use material handling systems in order to allow more control on the transport tasks. In this paper, a job-shop scheduling problem in vehicle based manufacturing facility that is mainly related to job assignment to resources is addressed. The considered job-shop production cell has two types of resources: processing resources that accomplish fabrication tasks for specific products, and transporting resources that assure parts’ transport to the processing area. A Variable Neighborhood Search algorithm is used to schedule product manufacturing and handling tasks in the aim to minimize the maximum completion time of a job set and an improved lower bound with new calculation method is presented. Experimental tests are conducted to evaluate the efficiency of the proposed approach.
At the operational level of Flexible Manufacturing Systems (FMS), several research works have developed solutions not fully realizable considering the operational constraints, which can be difficult ...to model. One of the well-known problems in FMS is the Job-Shop Scheduling Problem (JSSP) with transportation tasks. Indeed, this problem is addressed by many researchers, but most of their studies do not consider operational constraints such as collision avoidance between transporters. Moreover, optimized scheduling may contain deadlock situations due to often neglected geometric constraints. Therefore, in this paper, we propose a simulation approach based on a multi-agent system to test the optimized results known in the literature in more realistic conditions, where collision avoidance between transporters is considered. We propose as well a sim-optimization approach to explore suitable solutions considering collision avoidance constraints. In addition, an algorithm is proposed to solve deadlocks. The obtained results highlight the impact of collision avoidance on the performance of the literature solutions while being more realistic. Furthermore, these results demonstrate the efficiency of the proposed algorithms, since all identified collisions are avoided and all deadlocks are also solved. The proposed approach is expected to be more attractive to the industries as it ensures a small gap between the theoretical and actual results.
•Simulator based on multi-agent system of flexible manufacturing system.•Feasibility test of known benchmark of job shop scheduling problem by simulation.•Consideration of collision avoidance between Autonomous guided vehicles.•Development and test of a fixing deadlock algorithm using simulation.•Proposition of solution of the job-shop-scheduling problem with transport.
This work discusses a Finite Control Set Model Predictive Control (FCS-MPC) with delay compensation approach using field-programmable gate array (FPGA). This study mainly focuses on the ...implementation of a two-step FCS-MPC strategy for a grid-tied inverter with LCL filter capable of injecting high quality current with minimal total harmonic distortion (THD). A detailed description of the proposed digital implementation is provided. The entire system is simulated through MATLAB®/Simulink®, and then implemented on Digilent BASYS 3 evaluation and development FPGA kit with Vivado 2017.2 and Xilinx system generator.
This work presents an FPGA implementation Based of sliding-mode control (SMC) and a proportional-resonant (PR) scheme for grid-connected three-phase voltage source inverter (VSI) based LCL-filter. ...The proposed strategy necessitates generating three-phase reference voltage of the filtering capacitors. However, their calculation involves a derivative operation, which is commonly avoided in control algorithms due to its complexity. To circumvent this issue, the generation of the capacitor voltage is accomplished through the application of a PR controller, eliminating the need for derivatives while achieving accurate tracking reference currents. The digital implementation of the PR based SMC controller is detailed and evaluated through MATLAB/Simulink and Xilinx system generator (XSG) integrated platform. The hardware-in-the-loop (HIL) co-simulation via Digilent BASYS 3 evaluation and development FPGA kit aids in controller performance evaluation.
Elastomeric materials are well-known for their ability to dissipate mechanical energy into heat. Under cyclic loading, this dissipated energy, combined with the low thermal conductivity of these ...materials causes heat storage in the sample resulting in a rise of the material temperature. As this phenomenon induces negative effects on fatigue life, this heat build-up has been widely studied in recent years but a few for multiaxial loadings. In this paper, we propose to investigate the self-heating induced by multiaxial mechanical loading of Natural Rubber (NR). The goal of this research work is to find a suitable modeling to predict the heat build-up of elastomers under multiaxial cyclic loadings. The proposed model, based upon a weak coupling approach and which only requires an estimation of the energy dissipation during a cycle of loading, is used to predict the heat build-up evolution of 3 different specimen geometries under multiaxial cyclic mechanical loading for 2 materials: a natural rubber (NR) experimentally investigated in this work allowing to develop the model and a styrene-butadiene rubber (SBR) which heat build-up data are taken from the literature for further model validation. A satisfactory agreement between simulations and experiments is found, making this approach a useful tool for temperature evolution estimates during fatigue loading.
•An experimental study of heat buildup of rubbers subjected to fatigue loading.•A weak coupling model to predict temperature evolution.•Accounting for multiaxiality using tension and twist loadings.•Good capability of the FE model to capture the experimental results.
Cellular networks (CNs) continue to evolve by implementing several technologies such as nonorthogonal multiple access and device-to-device communication, accommodating thereby the high data traffic ...demand. By leveraging these technologies, in this article, we propose a novel scheme to integrate public safety (PS) networks in CNs. This integration enhances the performance of PS users (PSUs) that rely on low-rate technologies. We formulate a mixed integer nonlinear programming problem for sum throughput maximization, to optimize the channel allocation and achieve the required rate of PSUs. This optimization takes into account power budget, users required rates, and successful interference cancellation constraints. Since the maximization problem is computationally challenging, we design a heuristic algorithm that selects the appropriate cellular users to share their resources with PS clusters. Then, given this selection, we compute the optimal power allocation in each PS cluster using the Lagrange multiplier method. Evaluation results demonstrate that our approach improves spectral efficiency and provides higher sum throughput compared to other works in the literature. We also conduct extensive simulations to compare our throughput maximization approach with the fairness maximization approach. Finally, we compute the outage probability to reassign PSUs groups to new resource blocks if necessary.
Thermo-oxidative aging (TOA) significantly impacts the fatigue life of rubbers by reducing the fatigue strength and modifying the slope of the Wöhler curve, rendering traditional time-temperature ...superposition methods inadequate. In this work, we aim to develop a model capable of predicting the effect of TOA on the fatigue properties of rubbers. For this purpose, dumbbell specimens of natural rubber (NR) were subjected to aging in an air-vented oven at different temperatures prior to mechanical testing. Tensile tests were conducted to quantify the aging effects on a microscale network parameter known as elastically active chains (EAC) density, along with determining ultimate properties such as the stress and strain at break. By using a time-temperature equivalence and the Arrhenius shift factor, master curves were constructed for both EAC density and ultimate properties. Subsequently, the fracture properties of the aged material were predicted using an energy limiter approach whose evolution follows that of EAC density. Furthermore, a relationship between the parameters of the continuum damage mechanics (CDM) approach (specifically, the power law parameters of the Wöhler curve) and the fracture properties was proposed, resulting in accurate estimates of the fatigue life regardless of the aging conditions. Satisfactory agreement was observed between the model predictions and the data for nine aging conditions encompassing four different temperatures. The CDM approach also allows assessing the evolution of mechanical damage within the material influenced by TOA. The novelty of this approach lies in establishing a direct relationship between fatigue and fracture properties. Moreover, this is the first time to the best of our knowledge that TOA has been explicitly incorporated into a fatigue life prediction model via the evolution of the EAC density.
•An experimental study of aging effects on fatigue life of natural rubber reaffirms observations made in the literature.•The Continuum Damage Theory is extended to account for thermo-oxidative aging effects on fatigue life.•The fracture properties are predicted using an energy limiter approach based on the chain network evolution.•The service life is predicted based on the knowledge of fracture properties which makes the model fully predictive.
•A new fatigue indicator based upon the maximal deviatoric stress is developed in this work.•An analytical explicit expression of an equivalent stress as a fatigue loading parameter, is ...proposed.•Coupled with continuum damage mechanics, the developed model account for multiaxiality effects on fatigue life of rubbers.•This new indicator can be computed analytically for some loading paths as uniaxial tension, equal biaxial tension, pure shear and compression.•A good correlation between the proposed model and a wide set of experimental data for 2 kinds of rubbers is found.
The continuum damage mechanics approach allows quantifying the degradation of a material via a damage variable D. By developing a new equivalent stress, a novel way is proposed to analyze the multiaxial fatigue of rubbers. Fatigue experiments under multiaxial loading paths were carried out on a Natural Rubber. Moreover, data on a Styrene Butadiene Rubber available in the literature were also used to check the validity of this approach. The comparison between the experimental data and the model estimates in terms of fatigue life leads to a nice agreement making this approach a robust tool for designing rubber parts.
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