Design and implementation of real-time scheduling algorithms for flexible manufacturing systems

A new FMS simulator with object-oriented-programming techniques

This paper describes the ways of using program tools for design and simulation of flexible manufacturing systems (FMS) for the purpose of teaching the undergraduate course Flexible Manufacturing Systems. The concept of the course is based on the synergism of theoretical knowledge and practical hands-on experience gained by studying numerous problem cases, using common tools for description of FMS (Petri nets, max-plus algebra and matrix modeling) and by working with more specialized program tools for FMS design and simulation. An emphasis is given to the description o the program tool FlexMan that enables elegant setting of an FMS configuration, supports automatic generation of a matrix-based FMS description and consequently, enables effective off-site design and simulation of the FMS by using virtual reality models and Internet-related technologies.

A flexible manufacturing system (FMS) is designed to achieve good productivity and low cost. The success of an FMS depends largely on effective production scheduling and control. However, it has been found that current manufacturing scheduling and control algorithms lack the flexibility to handle interruptions or resource breakdowns; hence, system performance drops dramatically and abruptly when interruptions occur. This research develops a computer-simulation-based framework of FMS scheduling and control system using the holonic concept. This framework can maintain stability and flexibility while accommodating system disturbance, increase throughput, reduce part flow-time and work-in-process inventory, and balance workload among identical workstations. The significance of this research is the investigation of an innovative approach to revolutionary advances of control technologies for advanced manufacturing systems, and to the revitalisation of control and scheduling algorithms used by existing FMSs. A case study has been provided to substantiate the effectiveness of this proposed framework.

The LTE specification provides Quality of Service (QoS) of multimedia services with fast connectivity, high mobility, and security. However, 3GPP specifications have not defined scheduling algorithms to support real-time and non-realtime application services, this has led to the development of a variety of scheduling algorithms in the recent years. Performance is a key factor for assessing the scheduling algorithms. However, the performance analysis and evaluation for existing scheduling algorithms are limited to QoS parameters (e.g. in terms of throughput, packet loss and delay) and/or fairness metrics. It is not clear how these scheduling algorithms perform in terms of Quality of Experience (QoE) metrics (e.g. MOS score) which are more closely linked with end user experience or user perceived quality. In this paper, we investigate and evaluate the performance of three popular LTE downlink schedulers (proportional fairness (PF), exponential proportional fairness (EXP-PF), and modified largest weight delay first (M-LWDF)) in terms of QoE metric (i.e. MOS score) in addition to normal QoS metrics (e.g. packet loss and delay) for VoIP applications. Simulation results (based on LTE-Sim) show that the best suitable downlink scheduling algorithm is MLWDF, which has short end-to end delay (less than 50ms) and allowing maximum number of user access (more than 50 users) at acceptable MOS score (MOS over 3.5). The widely used scheduling algorithm (PF) will increase its end-to-end delay over 200ms, when number of user access is over 30. This will limit its application for VoIP when user access number increases. This work would help to assist the design and development of QoE-driven scheduling algorithms for mobile multimedia applications in the future.

Although a significant amount of simulation research has been carried out for design and analysis of flexible manufacturing systems (FMS), it does not provide optimal solutions. In this research, we employ two optimum-seeking methods to design and optimize a manufacturing system. The first method is a Taguchi approach, which uses robust design concept to reduce the output variation. The second method is the response surface methodology (RSM), which combines mathematical and statistical techniques to study the geography of the response surface. The results show that throughput of a selected FMS system can be maximized when both methods are employed.

Layout design for flexible manufacturing systems considering single-loop directional flow patterns

With the advance of research, design and operation of flexible manufacturing systems (FMS) which are designed to produce a variety of different part types with high machine utilization, short lead times and little work-in-progress inventory, new requirements like high modeling efficiency, high model validity and credibility and effectiveness and correct analysis of results are defined. Simulation is an efficient tool to verify design concepts, to select machinery, to evaluate alternative configurations and to test system control strategies of an FMS, etc. This paper presents a useful tool for simulating the behavior of random FMSs. This simulator is used for real time alternative routing selection based on a group of metaheuristics principles which include in particular simulated annealing (SA), genetic algorithm (GA), taboo search (TS), ant colony algorithms (ACO), particle swarm optimization (PSO) and electromagnetism like method (EM). This software is also can used for performance and sensitivity analysis of theses techniques jugged by the production rate, machines and material handling utilization rate, the cycle time and the work in process.

As the penetration level of plug-in hybrid electric vehicles (PHEVs) increases, the stress on the distribution system will become more pronounced. In this paper, we concentrate on PHEV charging in public infrastructures, such as shared parking lots in commercial office campuses and shopping malls. In such clustered scenarios, PHEV charging demand can vary significantly and stochastically with time, and the overall system performance is a result of a trade-off between the peak load on the distribution system and the consumer specified charging deadlines that are met successfully. However, unlike distributed residential charging, those scenarios can benefit from centralized algorithms to schedule the charging of vehicles. This paper considers the design of such scheduling algorithms. We show that through proper design of the scheduling algorithms, the parking lot owner can balance distribution system load with quality of charging service.

Capturing urgency and parallelism using quasi-deadlines for real-time multiprocessor scheduling

Scheduling algorithms are fundamental components in the process of resource management in mobile communication networks with heterogeneous QoS requirements such as delay, delay jitter, packet loss rate or throughput. The random characteristics of the propagation environment and the use of complex physical layers in order to combat this random behavior further complicates the design of simple, efficient, scalable and fair scheduling algorithms. This paper presents the main criteria used in the design of scheduling algorithms for 3G/4G mobile communications networks and provides a survey of scheduling mechanisms proposed for use in TDMA and CDMA based systems.Keywordsscheduling4GGPSutility functions

Scheduling algorithm design is a critical and challenging issue in multiuser wireless networks with dynamic flows. The well-known Queue-length-based MaxWeight (QMW) scheduling algorithm can achieve throughput-optimality if there only exist persistent flows that are long-lived with infinite traffic arrival. In this paper, we propose a head-of-line access delay (HAD)-based scheduling algorithm and show that it is throughput-optimal when the flows are dynamic, i.e., they are short-lived with finite data to transmit. HAD is an online algorithm and does not require prior knowledge of the statistics of the arrival traffic and channel information. We also develop the Markov analytic model to study system performance and reveal important properties of the proposed HAD scheduling algorithm. To reduce the complexity of the analysis, we further study two approximation methods corresponding to different arrival traffic intensity. Performance evaluation shows that the HAD scheduling algorithm can outperform the classic QMW and stabilize the system at the presence of flow-level dynamics. Compared to the other existing algorithms, HAD is practical to implement with a better delay performance.

We describe here a systematic method for the design and modeling of flexible manufacturing systems, using object-oriented concepts and Petri nets. We first define the system components in terms of an object model consisting of hierarchical sets of classes and associations. Then, we model the dynamic aspects of the system using statecharts, including exceptions and abnormal behavior. As a third step, we derive Petri nets from those statecharts to realize the concurrency present in the system. Finally we develop a hierarchy of controllers, corresponding to the layers of the object model, for the independent components of the system based on the Petri nets obtained in the previous step. The approach is systematic and relatively easy to apply. It is illustrated through a realistic example. >

The formation of machine–part families is an important task in the design of cellular and flexible manufacturing systems. The formation results in the creation of many benefits for manufacturing systems. Among the many methods utilised in machine–cells formation, the similarity coefficient method (SCM) is most widely used. When SCM is used, the rearrangement of machine and part components is required to form machine–part families. This process of rearrangement has been considered as being subjective and difficult, may result in improper assignments to parts families, resulting in a negation of benefits promised. This paper presents an effective algorithm to identify part–families and bottleneck parts, given machine groupings, rather than addressing the machine grouping problem in general.

The design and operation of flexible manufacturing systems (FMS): Paul Ránky

Justification of multiple circuit lines in automatic test pattern generation (ATPG) is exponential in complexity in the presence of reconvergent fanout. Reconvergent fanout consequently is a chief source of increased complexity in the ATPG process. Reconvergence also degrades the pseudo-random test by producing correlation between inputs of the same combinational logic block. Consideration of reconvergence during synthesis can result in its elimination at minimal area or performance cost. The high regularity of DSP architectures facilitates reconvergence reduction, when, it is addressed during synthesis. We present a design-for-testability approach to remove reconvergence during high-level synthesis. We have developed a method for estimating the degree of reconvergence, based on an estimate of the existence of paths between each pair of hardware units. We have designed and implemented scheduling and binding algorithms which use the proposed reconvergence estimate to consistently direct synthesis to RTL datapaths with reduced reconvergent fanout. The experimental results shown demonstrate the effectiveness of the proposed methodology.