Serial Lines Research Articles

Transient analysis and real-time control of geometric serial lines with residence time constraints

Residence time constraints are commonly seen in practical production systems, where the time that intermediate products spend in a buffer is limited within a certain range. Parts have to be scrapped or reworked if their maximum allowable residence time is exceeded, while they cannot be released downstream before the minimum required residence time is reached. Such dynamics impose additional complexity onto the production system analysis. In order to optimize the production performance in a timely manner, the transient behavior of the production system and a real-time control strategy need to be investigated. In this article, we develop a Markov chain model to analyze the transient behavior of a two-machine geometric serial line with constraints on both maximum allowable residence time and minimum required residence time being. Compared with the simulation, the proposed analytical method is shown to estimate the system’s transient performance with high accuracy. Structural properties are investigated based on the model to provide insights into the effects of residence time constraints and buffer capacity on system performance. An iterative learning algorithm is proposed to perform real-time controls, which improves the system performance by balancing the trade-off between the production rate and scrap rate. Specifically, a control policy derived from Markov Decision Processes is implemented as an initial control policy, and the Bayesian method is then applied to the run time data to improve the control policy.

Serial production line performance under random variation: Dealing with the ‘Law of Variability’

Many Queueing Theory and Production Management studies have investigated specific effects of variability on the performance of serial lines since variability has a significant impact on performance. To date, there has been no single summary source of the most relevant research results concerned with variability, particularly as they relate to the need to better understand the ‘Law of Variability’. This paper fills this gap and provides readers the foundational knowledge needed to develop intuition and insights on the complexities of stochastic simple serial lines, and serves as a guide to better understand and manage the effects of variability and design factors related to improving serial production line performance, i.e. throughput, inter-departure time and flow time, under random variation.

A Polynomial Algorithm For Balancing a Sequence of Operations in Reconfigurable Transfer Lines

We consider the problem of balancing reconfigurable transfer lines. The problem is quite recent and motivated by the growing need of reconfigurability in the industry. The problem consists into allocating a set of operations (necessary to machine a single part) to different workstations placed into a serial line. The workstations can contain multiple machines operating in parallel. The machines considered are mono-spindle head CNC machines which imply setup times between operations in order to perform tool changes. Therefore, the operations allocated to a workstation should be sequenced. Besides, accessibility, inclusion, exclusion and precedence constraints between operations are considered. In this article, we suggest a polynomial exact algorithm that balances the transfer line provided the overall sequence of the operations (called sequence) is given. This balancing subproblem was dealt with in the literature by means of ILP and heuristics. We use this algorithm to solve the balancing problem independently from the overall sequence of operations by embedding it in a simple local search within the giant sequence space. Experimentation show significant improvement compared to literature.

Throughput Analysis of Manufacturing Systems with Buffers Considering Reliability and Cycle Time Using DES and DOE

The complexity of manufacturing systems makes the accurate prediction of production throughput difficult because of many variables. Continuously developing and implementing scientific methods can advance the understanding of the throughput of complex manufacturing systems.This throughput study addresses the main factors of manufacturing systems in the setting of a serial line. The factors include the reliability and cycle time of workstations, the length of a manufacturing line, and the capacity and locations of internal buffers in a manufacturing line. To effectively study these factors, the authors propose and use Design of Experiments (DOE) and Discrete-Event Simulation (DES) to analyze and predict the throughput of a manufacturing system under different settings.The study results provide a new understanding of the impacts of these factors on the production throughput of serial manufacturing lines. The study outcomes can be a valued reference for the development of such complex manufacturing systems to achieve the desired throughput.

Condition-based Maintenance Policy Optimization Using Genetic Algorithms and Gaussian Markov Improvement Algorithm

Condition-based maintenance involves monitoring the degrading health of machines in a manufacturing system and scheduling maintenance to avoid costly unplanned failures. As compared with preventive maintenance, which maintains machines on a set schedule based on time or run time of a machine, condition-based maintenance attempts to minimize the number of times maintenance is performed on a machine while still attaining a prescribed level of availability. Condition-based methods save on maintenance costs and reduce unwanted downtime over its lifetime. Finding an analytically-optimal condition-based maintenance policy is difficult when the target system has non-uniform machines, stochastic maintenance time and capacity constraints on maintenance resources. In this work, we find an optimal condition-based maintenance policy for a serial manufacturing line using a genetic algorithm and the Gaussian Markov Improvement Algorithm, an optimization via simulation method for a stochastic problem with a discrete solution space. The effectiveness of these two algorithms will be compared. When a maintenance job (i.e., machine) is scheduled, it is placed in a queue that is serviced with either a first-infirst- out discipline or based on a priority. In the latter, we apply the concept of opportunistic window to identify a machine that has the largest potential to disrupt the production of the system and assign a high priority to the machine. A test case is presented to demonstrate this method and its improvement over traditional maintenance methods.

Serial production lines with geometric machines and finite production runs: performance analysis and system-theoretic properties

A production run is typically referred to as a group of identical goods that is produced by a particular manufacturing process. In many discrete manufacturing practices, the manufacturing activity is carried out by deploying a series of production runs of different products according to customer orders. If the volume of a production run is relatively small and process changeovers are necessary, the production system operates partially (or entirely) in the transient regime, especially at the beginning and near the end of a production run. In this case, the traditional steady-state analysis approach may become inapplicable. In this paper, we consider finite production run-based manufacturing in serial lines with machines obeying the geometric reliability model and buffers having finite capacity. Exact Markovian analysis is first used to derive the closed-form formulae to calculate the transient performance of the production line during a production run as well as the distribution, mean, and standard deviation of its completion time in one- and two-machine lines. For multi-machine lines, an aggregation-based approach is proposed to approximate the system performance measures with high accuracy and computational efficiency. In addition, system-theoretic properties of production run completion time with respect to machine and buffer parameters are discussed.

Design and Implementation of a Three-Section Transmission Line Transformer

New formulations of fundamental load impedance circuit in the Z-plane are employed to study transformers. Transformer configuration consists of three-section serial lines. The design procedures employ prototypes of transfer function, parametric modeling techniques, and optimization methods; dual-band uncorrelated frequencies of transfer function at the normalizing frequency (π) are studied. This transformer was designed on a PCB FR4 substrate featuring a permittivity er = 4.4, a loss tangent tanδ = 0.0245, and a thickness of h = 1.6 mm. The results of simulation and measurement show that complex load impedance can be matched at two uncorrelated frequencies. The values of characteristic impedances of transmission lines synthesizing the transformers are adjusted according to the autoregressive process by optimization algorithms. The experimental results are in good agreement with theoretical values.

FEATURES OF PROCESSING OF SPECIAL SITUATIONS IN HIGH SPEED RECEIVERS OF SERIAL CHANNELS

The review and comparison of the ways of handling special situations, occurring at the input of high-speed signal receivers from serial communication lines, is presented. Particular attention is paid to the situation when the amplitude of the input signal is below a predetermined threshold and the problem of early detection and indication of this situation at the physical level (in the interface part of the receiver) is solved. The handling of special situations is provided in popular serial transmission standards, but its practical implementation for high-speed transceivers at the physical level is difficult due to the lack of ready-made solutions that take into account the entire set of requirements for the special situations processing subsystem. Proceeding from the formulated requirements, the analysis of possible solutions is justified and the structure of the special block for detecting a special situation of this type that produces the appropriate signal in real time is justified. The proposed special situation detection unit is an auxiliary range comparator that operates in parallel with the comparator in the main channel, does not affect the duty cycle of the signals in this channel and is built on the basis of asymmetric differential stages in the composition of two modified comparators. It is shown that such a solution, in combination with the envelope detector at the output of the auxiliary channel, makes it possible to provide stable thresholds for the operation of the receiver and the generation of a correct (non-destructive) signal indicative of the occurrence of a special situation.The results of modeling such a block in the CML receiver made using 90 nm CMOS technology and operating at a speed of not less than 3 Gbit/s are presented.

Abstract A74: Identification of novel targetable resistance mechanisms and candidate clinical response biomarkers in drug-resistant ovarian cancer, following single-agent and combination chemotherapy

Abstract The aim of our translational research program in Dundee is to develop innovative experimental models to understand the molecular basis of adaptive drug resistance in ovarian cancer patients, extending our findings to the development of novel drug targets, combination chemotherapy approaches, and predictive clinical response biomarkers. Ovarian cancer is a deadly gynecologic malignancy, frequently diagnosed when the disease is already advanced. First-line treatment options in the UK mandate combination carboplatin and paclitaxel chemotherapy, with olaparib and additional PARP inhibitors under evaluation in patients with specific molecular signatures. While treatment is initially effective in many patients, development of drug resistance frequently limits clinical response to chemotherapy. Our understanding of the underlying molecular mechanisms is limited by lack of cell line models that appropriately mimic typical drug choices and commonly prescribed drug combinations in ovarian cancer patients. To address this issue, we have developed a series of novel drug-resistant cell lines, following treatment of A2780 and additional chemotherapy-naïve parental cells with clinically relevant doses of cisplatin (A2780cisR), carboplatin (A2780carboR), paclitaxel (A2780pacR), olaparib (A2780olapR), and combination carboplatin and paclitaxel chemotherapy (A2780cpR), and have used these cell lines to describe a common ABCB1 (MDR1)-mediated drug resistance mechanism common to A2780pacR and A2780olapR cells (Vaidyanathan et al., Br J Cancer 2016;115:431-41). More recently, we have used RNASeq (Ion Ampliseq Targeted Sequencing Technology) and Reverse Phase Protein Array (RPPA) analysis to compare the expression of whole-genome mRNA and more than 300 protein and phosphoprotein targets in pairwise comparisons of drug-sensitive and drug-resistant cells—unsupervised hierarchical clustering of these datasets revealed marked differences in expression between paclitaxel, olaparib, and platinum drug-resistant cells, and significant differences in cisplatin and carboplatin-selected cells. Consistent with improved clinical response, our combination A2780cpR line has a unique phenotype, which is distinct from both A2780carboR and A2780pacR cells. Importantly, we have identified significant increases in the expression of targetable phosphoproteins, for example, pATM (Ser1981), pAKT (Tyr308 and Ser473), pCHK1 (Ser296), and pGSK3b (Ser9/Ser21) in A2780cpR cells. In complementary experiments, we have used Taqman Low Density Arrays (TLDAs) to compare the expression of 377 miRNAs in our cell line panel, and have identified multiple differentially expressed miRNAs, both common to all resistant cells and unique to individual drug-resistant phenotypes. To validate our prioritized candidate phosphoprotein targets and miRNA biomarkers, we have created a unique clinical study, the Dundee Ovarian Cancer Study (DOCS), in which we are creating serial ascites-derived primary cell lines from initially drug-sensitive and subsequently drug-resistant ovarian cancer patients. We are currently using MTT cytotoxicity and colony formation assays in these cell lines to evaluate combination chemotherapy approaches with pathway specific inhibitors to each of our targetable resistance mechanisms, and developing quantitative PCR and immunohistochemical-based methods for evaluation of candidate drug resistance biomarkers in matched serum and plasma samples from DOCS patients. Our combined laboratory and clinical studies therefore provide a “bench to bedside” approach to molecular characterization and prioritization of novel strategies to combat drug resistance, the major treatment-limiting complication in the clinical management of ovarian cancer patients. Citation Format: Aparajitha Vaidyanathan, Lynne Sawers, Probir Chakravarty, Susan E. Bray, K. Wendy McMullen, Michelle J. Ferguson, Gillian Smith. Identification of novel targetable resistance mechanisms and candidate clinical response biomarkers in drug-resistant ovarian cancer, following single-agent and combination chemotherapy. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A74.

Analytical Solution of the serial Bernoulli production line steady-state performance and its application in the shipbuilding process

The modern shipbuilding industry is faced with numerous challenges urging abiding improvement of the shipbuilding process and its management. Such a demanding problem is usually approached using complex production management models involving large data basis handling. The same problem can be solved using simpler, intuitive and mathematically transparent models developed within production system engineering. For these purposes, the analytical solution of the serial Bernoulli production line steady-state performance involving an arbitrary number of machines and buffers of arbitrary occupancy is developed based on Markov chain approach and eigenvalue problem including formulation of the generalised transition matrix as a key novelty. Performance measures in case of general serial Bernoulli production line are developed and the theory is validated using serial Bernoulli lines composed of two, three, four and five machines. The obtained results are compared to those determined using a semi-analytical approach. In order to further demonstrate the applicability of the developed theory, performance measure analysis is performed in cases of longer lines composed of 6, 7, 8, 9 and 10 machines with non-equal buffer capacities. Application of the developed procedure in the analysis of the shipbuilding process is illustrated in a case of the plate prefabrication line usually placed in each shipyard.

A multi-objective hybrid evolutionary approach for buffer allocation in open serial production lines

The buffer allocation problem is of particular interest for operations management since buffers have a considerable impact on capacity improvement in production systems. In this study, the buffer allocation is solved to optimize two conflicting objectives of maximizing the average system production rate and minimizing total buffer size. A hybrid evolutionary algorithm-based simulation optimization approach is proposed for the multi-objective buffer allocation problem (MOBAP) in open serial production lines. As a search methodology, the Pareto optimal set is derived by hybrid approach using elitist non-dominated sorting genetic algorithm (NSGA-II) and a special version of a multi-objective simulated annealing. As an evaluative tool, discrete event simulation modeling is used to estimate the performance measures for the production systems. To demonstrate the efficacy of the proposed hybrid approach, a comparative study is provided for the MOBAP in various serial line configurations. The comparative results show that the hybrid method has a considerable potential to minimize the total buffer space by appropriately allocating space to each buffer while maximizing average production rate.

Configuration selection for a reconfigurable manufacturing flow line involving part production with operation constraints

Configuration selection for reconfigurable manufacturing systems (RMS) is one of the key issue that needs to be addressed to transform RMS implementation from its nascent stage to a mature one. The problem is of vital importance because of the fact that the selection of machine configurations for operations to be performed on any job/part is based on multiple objectives, which often conflicts each other. In the present work, a framework for configuration selection for a manufacturing flow line (MFL) is proposed and demonstrated using non-dominated sorting genetic algorithm-II (NSGA-II). The proposed framework is explained with the help of a mathematical illustration. Results are presented in the form of non-dominated solutions obtained for machine configurations encompassing manufacturing of a product using a multi-tage reconfigurable serial product flow line (RSPFL). The outcome of this work would help in improving the performance of RMSs while considering multiple objectives as the selection criterions. The findings are finally discussed in detail in the light of previous works on the topic.

Scheduling policies in flexible Bernoulli lines with dedicated finite buffers

This paper is devoted to studying scheduling policies in flexible serial lines with two Bernoulli machines and dedicated finite buffers. Priority, cyclic and work-in-process (WIP)-based scheduling policies are investigated. For small scale systems, exact solutions are derived using Markov chain models. For larger ones, a flexible line is decomposed into multiple interacting dedicated serial lines, and iteration procedures are introduced to approximate system production rate. Through extensive numerical experiments, it is shown that the approximation methods result in acceptable accuracy in throughput estimation. In addition, system-theoretic properties such as asymptotic behavior, reversibility, and monotonicity, as well as impact of buffer capacities are discussed, and comparisons of the scheduling policies are carried out.

Serial production lines with waiting time limits: Bernoulli reliability model

Production systems with waiting time constraints are frequently encountered in semiconductor, automotive, battery, food, and many other manufacturing industries. Under the waiting time constraints, the residence time of in-process inventories is constrained by a predetermined time limit. A part exceeding the maximal time limit has to be inspected for quality assurance and it is subject to be scrapped with a certain probability. In this paper, performance evaluation of Bernoulli serial lines with waiting time limits is studied. Analytical formulas are derived to predict the system performance of two-machine lines in steady state. For longer lines, direct analysis is no longer viable due to high complexity, thus an aggregation-based iterative procedure is introduced. Based on extensive numerical studies, the convergence of the procedure can be observed and high accuracy in performance estimation is achieved. In addition, to design such lines, an efficient procedure for near optimal buffer assignment to maximize production rate is also proposed. Analogously, we first propose an exact algorithm for two-machine lines and then extend it to a recursive procedure for longer lines. We then numerically verify that the procedure provides a near optimal solution within a very short computation time. Finally, the impacts of relaxing waiting time constraints on line performance and buffer design are discussed, and operational strategies to achieve better performance are also presented.

The Robotic Assembly Line Design (RALD) problem: Model and case studies with practical extensions

Abstract Spot welding assembly lines are widely present in the automotive manufacturing industry. The procedure of building the vehicle’s body employs several robots equipped with spot welding tools. These robots and tools are a quite costly initial investment, requiring an efficient and conscious line design that meets product demands and minimises implementation expense at the same time. In this paper, the Robotic Assembly Line Design (RALD) problem is proposed and studied based on practical characteristics from an automotive company located in Brazil. A Mixed-Integer Liner Programming (MILP) formulation is developed allowing: (i) station paralleling, (ii) equipment selection, and (iii) multiples robots per workstation. The mathematical model aims at minimising the total cost at the desired production rate, which involves robots, tools and facilities. The proposed model considers dead time during a cycle, space constraints, task assignment restrictions, and parallelism possibilities. Dead time is an unproductive and fixed work-piece handling time included in the capacitated transporter robots’ movement time. Computational experiments were performed in order to evidence the parameters’ influence over the optimal line design solution. In addition, practical case studies were conducted with parameters collected from a real-world robotic welding assembly line located on the outskirts of Curitiba-PR (Brazil), reaching optimality. Compared to the strictly serial lines, the model led to great advantages by allowing parallel stations in the production system, making it possible to evaluate an expected trade-off between the production rate and the total cost; reductions of several hundred thousand dollars on the production layout cost can be achieved by the company, as indicated by the studied cases.

Implementation of ISLIP scheduler for NOC router on FPGA

Network on chip (NoC) effectively replaces a traditional bus based architecture in System on chip (SoC). The NoC provides a solution to the communication bottleneck of the bus based interconnection in SoC, where large numbers of Intellectual modules are integrated on a single chip for better performance. In NoC architecture, the router is a dominant component, which should provide contention free architecture with low latency. The router consists of input block, scheduler and crossbar switch. The design of scheduler leads the performance of the NoC router in terms of latency. Hence the starvation free scheduler is paramount importantin the NoC router design. iSLIP (Iterative serial line internet protocol) scheduler has programmable priority encoder which makes it fast and efficient scheduler over round robin arbiter. In this paper 2x4 NoC router using iSLIPscheduler is proposed. The proposed design is implemented using the Verilog programming on Xilinx Spartan 3 device.

Implementation of ITER Fast Plant Interlock System Using FPGAs With CompactRIO

Interlocks are the instrumented functions of ITER that protect the machine against failures of the plant system components or incorrect machine operation. Regarding instrumentation and control, the interlock control system (ICS) ensures that no failure of the conventional ITER controls can lead to a serious damage of the machine integrity or availability. The ICS is in charge of the supervision and control of all the ITER components involved in the instrumented protection of the tokamak and its auxiliary systems. It is constituted by the central interlock system (CIS), different plant interlock systems (PISs), and its networks. The ICS does not include the sensors and actuators of the plant systems, but it is in charge of their control. The ITER interlock system shall be designed, built, and operated according to the highest quality standards. The international standard IEC-61508 has been chosen as the reference. In both CIS and PIS cases, two main architectures are used: 1) a slow architecture, for those functions with response time requirements slower than 100 ms (300 ms for central interlock functions), based on programmable logic controller technologies and 2) a fast architecture, based on field programmable gate array (FPGA) technologies, for the functions with faster requirement times. The proposed design for fast PIS is based on the use of reconfigurable input/output (RIO) technology from National Instruments (NI CompactRIO platform). In order to provide a high integrity solution, failure modes, effects, and diagnostic analysis (FMEDA) has been conducted to analyze the component behavior. According to the output of the FMEDA, a set of diagnostics has been defined and additional redundancy was added to the architecture to improve the integrity figures. The defined configuration has been called the “double-decker solution,” with two chassis running in parallel, communicated between them using a synchronous high-speed serial line, and using redundant modules to implement the input and output measurements/excitations and redundant analog and digital modules to implement the diagnostics of these input/output modules. The integrity figures for the “double-decker” solution are obtained from the classification of the failure rates, obtaining for different configurations a safe failure fraction of 85% and a probability of dangerous failure per hour of less than 1E−07. The FPGA design includes all the hardware to support the data acquisition from the input modules, the implementation of the diagnostic functionalities for analog and digital modules, the voting schema, and the activation/deactivation of digital outputs. The platform includes an external test platform, also based on NI CompactRIO technology, to perform the validation of the system and to register the performance of different interlock functions implemented. The response time obtained for the transistor–transistor logic (TTL) input to TTL output interlock function ranges from 5 to $20~\mu \text{s}$ ; for the analog input to TTL output, the response time is in the range of 41– $90~\mu \text{s}$ , and for interlock functions using 24-V digital input to 24-V digital output, the time can rise up to $643~\mu \text{s}$ .

Profit-oriented partial disassembly line design: dealing with hazardous parts and task processing times uncertainty

This paper addresses the problem of profit-oriented disassembly line design and balancing considering partial disassembly, presence of hazardous parts and uncertainty of task processing times. Few papers have studied the stochastic disassembly line balancing problem and existing approaches have focused on heuristic and metaheuristic methods. Most existing work has concentrated on complete disassembly where task times are assumed to be normal random variables and where AND/OR graphs are not considered. The objective of this paper is the design of a serial line that obtains the maximum revenue and then balances the workload under uncertainty. The processing time of a disassembly task is assumed to be a random variable with any known probability distribution. An AND/OR graph is used to model the precedence relationships among tasks. Stochastic programming models and exact-based solution approaches combining the L-shaped algorithm and Monte Carlo sampling techniques are proposed. The relevance and applicability of the proposed models and solution methods are shown by solving efficiently a set of disassembly problem instances from the literature.

Software development kit for a compact cryo-refrigerator

This paper introduces a Software Development Kit (SDK) that enables the creation of custom software applications that automate the control of a cryo-refrigerator (Quantum Design model GA-1) in third party instruments. A remote interface allows real time tracking and logging of critical system diagnostics such as pressures, temperatures, valve states and run modes. The helium compressor scroll capsule speed and Gifford-McMahon (G-M) cold head speed can be manually adjusted over a serial communication line via a CAN interface. This configuration optimizes cooling power, while reducing wear on moving components thus extending service life. Additionally, a proportional speed control mode allows for automated throttling of speeds based on temperature or pressure feedback from a 3rd party device. Warm up and cool down modes allow 1st and 2nd stage temperatures to be adjusted without the use of external heaters.

Taking a Look at Capacitive Power Conversion [White Hot

Recently, I wrote about the workshops and presentations at APEC 2017 that talked about the challenges of magnetics in high-frequency power conversion. Those challenges include losses at high frequency, a lack of good data and models on losses in magnetic materials and devices, and lack of standardization of data from manufacturers. But there were also two other presentations that got me thinking in an entirely different direction: capacitive power conversion. By capacitive power conversion, I generally mean the use of “charge pump” techniques. For example, I am sure many of us have used the charge pump in RS-232 serial line driver ICs to convert +12 Vdc to –12 Vdc. Or maybe we have used a simple charge pump to create a +12 V or +15 Vdc from a +5 Vdc rail to power some small amount of analog circuitry.