Robotics in order picking: evaluating warehouse layouts for pick,place, and transport vehicle routing systems

Motivated by recent technological advances in mobile robotics, this paper explores a novel approach for warehouse order picking. In particular, this work considers two types of commercially available mobile robots – one that can grasp items from a shelf (a picker) and another (a transporter) that can quickly deliver all items from the pick list to the packing station. A new vehicle routing problem is defined which seeks to minimise the time to deliver all items from a pick list to the packing station, a problem termed the pick, place, and transport vehicle routing problem. A mixed integer linear programming formulation is developed to answer three related research questions. First, what combination of picker and transport robots is required to obtain performance exceeding traditional human-based picking operations? Second, how should the composition of the robot fleet be altered to affect the greatest performance improvements? Finally, what are the impacts of warehouse layout designs when coordinated mobile robots are deployed? An extensive numerical analysis reveals that, (1) increasing the number of cross aisles decreases system performance; (2) centrally located packing stations improve system performance; and (3) the average distance from each pick location to the packing station and the average distance between pick locations are effective metrics for identifying specific fleet modifications that are likely to yield system improvements.     

A generalized design and performance analysis model for end-of-aisle order-picking systems

In this paper we present an analytical design algorithm to determine the near-minimum number of pickers required in an end-of-aisle order-picking operation based on a miniload automated storage/retrieval system. The algorithm is based on an approximate analytical model we developed to estimate the expected picker utilization (and the storage/retrieval machine utilization) for general system configurations with two or more pick positions per aisle and/or two or more aisles per picker. For systems with two pick positions, we also investigate the possibility of improving the picker utilization by sequencing container retrievals within each order.     

A method for the concurrent design and analysis of networked manufacturing systems

Multistage manufacturing processes (MMPs) require multiple stations and operations. Traditionally, analysis of MMPs focused on material planning and control strategies. For a given MMP, the effect of the strategy on the volume and rate of production, ability to handle product type variability, and the effects of process variability on production rate, on-process inventory, etc., have been studied individually. Such approaches, while necessary, do not address the combined effects of MMP design choices on the final product quality. In this article, a method based on the compromise decision support problem and stream of variation model is proposed to provide a way to evaluate suitable designs for the implementation of MMPs. Using the dimensional quality of the product as a measure of quality, the proposed method is illustrated using a three-stage MMP in an automobile panel stamping process while considering the conflicting requirements of diagnosability and controllability.     

截齿截割煤岩的LS_DYNA仿真模拟

研究应用LS_DYNA软件进行煤岩截割破碎仿真的程式与方法,对悬臂式掘进机截割头上镐形截齿截割煤岩进行仿真模拟,在hypermesh中建立有限元网格模型,调用LS_DYNA971求解器进行求解,研究不同切削角对截齿截割阻力的影响以及切削厚度与比能耗之间的关系,并与常用的截齿截割阻力公式计算结果相比较,仿真结果证明了建模...     

滚筒式采煤机截齿排列参数化设计系统的研究

为解决采煤机滚筒截齿排列设计水平低、研发周期长、截割性能差等问题,给出了截齿排列方式及其参数确定方法.利用MATLAB GUIDE语言编程,开发了采煤机滚筒截齿排列参数化设计系统.该系统通过输入设计参数便可设计出滚筒的多种截齿排列方案,利用截割顺序图、切屑图以及滚筒载荷图可判断设计方案的合理性.通过实例,对常用三头螺旋滚筒的2种截齿排列方式进行模拟分析,结果显示:畸变1式截割性能优于畸变2式.研究表明,该系统可提高滚筒设计质量,设计方案直观,设计结果可定性、定量分析,为设计质量好、性能佳的采煤机滚筒奠定了基础.     

A computer-aided design procedure for flyback step-up DC-to-DC converters

A flyback step-up dc-to-dc power converter is modeled utilizing a linear magnetic core, transistor switch, diode, filter capacitance, and load resistance. Assuming constant voltage drops across the semiconductor elements when conducting, the circuit is analyzed to obtain an equation for the required number of turns, subject to the constraints of specified output voltage, operating frequency, maximum winding factor, maximum and minimum input voltage, output power, and flux density. Using an interpretive language, a program has been written to run on a minicomputer which searches a data base of magnetic core characteristics obtained from commercial core catalogs and prints a list of windable cores. In an evaluation section of the program, a core from the windable core list is selected by the designer and the losses in the various elements, along with maximum and minimum transistor current are computed. Another program is used to display on a computer graphics device the loci of maximum and minimum flux density in a selected core as functions of input voltage and output power in a perspective plot. Converter circuits derived from this computer-aided design procedure when tested in the laboratory have yielded data in close agreement with that predicted by the program.     

A practical fab design procedure for wafer fabrication plants

Facility design is crucial to the performance of wafer fabs in the semiconductor industry. This research proposes a practical Fab Design Procedure (FDP) to conduct quick calculations to develop and evaluate initial fab design alternatives. A series of practical formulae are presented to sequentially determine the following design parameters from an interbay point of view: the required number of machines; machine grouping and allocation; interbay flow matrix; bay dimension and location; interbay distance matrix; the required number of vehicles in an interbay material handling system; and the average wafer moving distance. Rules-of-thumb for wafer fab design on the basis of FDP are also suggested. A case study is used to demonstrate the effectiveness and efficiency of FDP. Results indicate that FDP is able to quickly calculate the required number of machines and related fab design parameters. With this tool, fab designers would be able to evaluate design alternatives and conduct what-if analysis in the initial phase of fab design.     

A decomposition procedure for large-scale optimum plastic design problems

A decomposition procedure is proposed in this paper for solving a class of large-scale optimum design problems for perfectly-plastic structures under several alternative loading conditions. The conventional finite element method is used to cast the problem into a finite dimensional constrained nonlinear programming problem. Structures of practically meaningful size and complexity tend to give rise to a large number of variables and constraints in the corresponding mathematical model. The difficulty is that the state-of-the-art mathematical programming theory does not provide reliable and efficient ways of solving large-scale constrained nonlinear programming problems. The natural idea to deal with the large-scale structural problem is somehow to decompose the problem into a collection of small-size problems each of which represents an analysis of the behaviour of each finite element under a single loading condition. This paper proposes one such way of decomposition based on duality theory and a recently developed iterative algorithm called the proximal point algorithm.     

A participatory systems design methodology for changeable manufacturing systems

The ability to adapt to changes in products, processes and technologies is a key competitive factor. Changeable manufacturing paradigms have emerged to address this need, but the industrial implementation remains challenging. In this paper, a participatory design methodology for changeable manufacturing systems is proposed, including requirements specification, selection of appropriate manufacturing paradigm and suitable physical and logical enablers. The methodology supports companies in determining the potential for and mechanisms of transitioning towards changeable manufacturing systems, based on knowledge of products, production, technologies and facilities. The developed methodology is applicable to both new and existing manufacturing systems. It is demonstrated in two industrial cases which highlight its applicability and differences in the appropriate recommended manufacturing systems transition towards changeability as a result of differences in manufacturing characteristics, change requirements and enablers.     

Adaptive colour classification for structured light systems

The authors present an adaptive colour classification method as well as specialised low-level image processing algorithms. With this approach the authors achieve high-quality 3D reconstructions with a single-shot structured light system without the need of dark laboratory environments. The main focus of the presented work lies in the enhancement of the robustness with respect to environment illumination, colour cross-talk, reflectance characteristics of the scanned face etc. For this purpose the colour classification is made adaptive to the characteristics of the captured image to compensate for such distortions. Further improvements are concerned with enhancing the quality of the resulting 3D models. Therefore the authors replace the typical general-purpose image preprocessing with specialised low-level algorithms performing on raw photo sensor data. The presented system is suitable for generating high-speed scans of moving objects because it relies only on one captured image. Furthermore, due to the adaptive nature of the used colour classifier, it generates high-quality 3D models even under perturbing light conditions.     

An analysis of safety-critical digital systems for risk-informed design

This paper quantitatively presents the results of a case study which examines the fault tree analysis framework of the safety of digital systems. The case study is performed for the digital reactor protection system of nuclear power plants. The broader usage of digital equipment in nuclear power plants gives rise to the need for assessing safety and reliability because it plays an important role in proving the safety of a designed system in the nuclear industry. We quantitatively explain the relationship between the important characteristics of digital systems and the PSA result using mathematical expressions. We also demonstrate the effect of critical factors on the system safety by sensitivity study and the result which is quantified using the fault tree method shows that some factors remarkably affect the system safety. They are the common cause failure, the coverage of fault tolerant mechanisms and software failure probability.     

The effects of pick density on order picking areas with narrow aisles

The cost and service performance of an order fulfillment center are determined partly by how workers are organized into an order picking system. One common approach is batch picking, in which workers circumnavigate a picking area with other workers, gathering items on a pick list. In some systems with high space utilization, narrow aisles prohibit workers from passing one another when in the same aisle, and this leads to congestion. We build analytical and simulation models of these systems to investigate their behavior under different levels of activity. Among other things, our results suggest that when the system is busier and pick density is high (that is, when workers stop often to make picks) congestion is less of a problem and workers are more productive.     

A heuristic procedure for loading problems in flexible manufacturing systems

The loading problem in a flexible manufacturing system (FMS) is viewed as selecting a subset of jobs from a job pool and allocating the jobs among machines. In this paper a heuristic solution to the loading problem has been suggested by developing the concept of essentiality ratio for the objective of minimizing the system unbalance and thereby maximizing the throughput. The proposed heuristic is tested on ten problems and the results show that the algorithm developed is very reliable and efficient.     

A cost-benefit analysis for the design and implementation of reverse logistics systems: case studies approach

Reverse logistics (RL) has created new and innovative opportunities for academic researchers and business communities to explore the strategic, economic, environmental, and regulatory implications of recycled, remanufactured, and disposed products. This paper considered and analysed the relevant literature in RL and identified the present state of theory in RL regarding cost-benefit. The research methodology used is exploratory case study approach. The cost-benefit is analysed and evaluated in terms of specific sub-factors associated with it by use of two in-depth case studies. Two companies from different industries engaged in RL operations are considered. The analysis of these case studies resulted in propositions and insights regarding RL operations. Based on these insights, the cost-benefit sub-factors, propositions, and a framework for effective design and implementation of RL operations are provided. This framework determines the appropriate sub-factors and how the return process of products/parts with respect to cost-benefit works. In conclusion, the managerial implications and future research directions were provided.     

A simplified procedure for the economic design of X¯ -charts

A simple procedure for selecting the optimal economic design of an X¯ control chart for a single assignable cause system is presented that can be applied at the workshop level. The procedure only consists of solving an explicit equation for h (sampling interval) in terms of n (sample size) and k (control limit factor). We conclude that our model is not only more accurate, more applicable, and more flexible, but also simpler to solve than those of Duncan's model (1956), Goel et al.'s model (1968) and Chiu and Wetherill's model (1974).     

Proposal for a multi-material design procedure

This paper describes a proposal for a multi-material design procedure. First, the context of the study and the requirements of the multi-material must be clearly defined in order to specify the parameters that the designer must select or optimise in order to produce the design: the components and their volume fraction, the architecture and morphology at different scales, etc. The general design procedure proposed here starts with the reasons why the designer has turned to multi-materials, from which a multi-material concept with fixed parameters can be defined. In this first stage the design problem can be made less complex by reducing the number of unknown parameters and guiding the designer towards the appropriate selection or optimisation tools: (i) subdivision of requirements, guided by applying statistical analysis tools to the materials database to search for appropriate multi-material components, (ii) tools to filter the materials database and search for multi-material components and their volume fraction, (iii) optimisation tools to search for the appropriate architecture when components are known or to search for architecture and components simultaneously. The paper demonstrates how these tools can be applied to different design concepts.     

Use of the manufacturing system design decomposition for comparative analysis and effective design of production systems

The focus of this paper is on the use of the Manufacturing System Design Decomposition (MSDD) to make effective cost and production system design decisions. A comparative study is conducted to illustrate how and why the total cost is reduced when the functional requirements defined by the MSDD are achieved. The ultimate goal of this research was to advance manufacturing and production system development to being guided by engineering science and design rather than the common practice of duplicating another person’s or entity’s notion of the best physical implementation.     

Reanalysis procedure for large structural systems

An efficient procedure is presented for repetitive analysis of structures, with large numbers of degrees of freedom and design variables, as they are progressively modified during the automated optimum design process. The three key elements of the procedure are: (a) lumping of the large number of design variables into a single tracing parameter; (b) operator splitting or additive decomposition of the different arrays in the governing finite element equations of the modified structure into the corresponding arrays of the original structure plus correction terms; and (c) application of a reduction method through the successive use of the finite element method and the classical Bubnov-Galerkin technique. The reanalysis procedure is applied to the linear static and free vibration problems of framed structures. Changes in both the sizing and shape (configuration) design variables are considered. For static problems the similarities between the proposed procedure and the preconditioned conjugate gradient technique are identified and are exploited to provide a physical meaning for the preconditioned residual vectors. The effectiveness of the proposed procedure is demonstrated by means of numerical examples.