Factors impacting manual picking on assembly lines: an experiment in the automotive industry

Manual picking on assembly lines is an important part of the assembly operator's work. In the automotive industry, alternative material exposure strategies are continually evaluated in order to facilitate the assembler's work and minimise non-value-adding time, resulting in increased use of smaller bins or containers at workstations, instead of large pallets. The assembly operator's retrieval of components from bins, containers or pallets is known as manual picking. Previous work in this area has focused on picking from pallets placed on the floor; therefore, there is a need to include other forms of material exposure. The purpose of this paper is to explain what material exposure factors have an impact on manual picking times on assembly lines. A full factorial experiment, testing seven factors in 128 experiments, was conducted in an automotive assembly line setting. The factors with the greatest impact on manual picking time were packaging type; angle of exposure; height of exposure; and part size. This study contributes by addressing the importance of six factors influencing manual picking times, enhancing knowledge derived from MTM and elsewhere. The results from this study can be useful for designing manual picking operations, not just at assembly lines but also other situations where discrete manual picking occurs such as at workstations or bench assembly. Managerial contributions are evident in the examination of factors important in designing new production systems, including materials supply processes and assembly processes. A further managerial application is the use of the results in managing assembly lines.     

An integrated storage assignment method for manual order picking warehouses considering cost,workload and posture

This paper presents an integrated storage assignment method for low-level picker-to-parts order picking warehouses taking into account economic and ergonomic objectives. Three different pallet rack layouts are studied in this paper, namely (a) picking from full pallets on the floor, (b) picking from half-pallets on the floor, and (c) picking from half-pallets on the upper rank of the shelf. First, cost functions are developed to assess the total order picking performance impact of these different pallet rack layouts. Second, with regard to workload, the metabolic cost and energy expenditure rates for picking from the different rack layouts under study are derived. Third, for assessing the working posture during order picking, the Ovako Working Posture Analysing System index is used where the required data is collected using a motion capturing system. The developed models are combined to propose a heuristic storage assignment procedure that supports the decision of which item to store on which pallet. The developed storage assignment method is then applied to an industrial case study. The results of the paper support warehouse managers in assessing the order picking storage assignment from an ergonomics viewpoint and in estimating its impact on financial order picking performance.     

面向“货到人”拣选系统的一种随机调度策略

通过“货到人”拣选系统作业流程分析,提出了在分批下发订单任务的情况下的一种随机调度策略。以AGV (automated guided vehicle)完成所有任务的总时间最短为目标函数,以任务分配为决策变量,考虑进行调度时AGV所处的状态以及在完成任务过程中AGV在拣选台的排队等待时间,建立随机调度策略的数学规划模型。利用遗传算法进行求解,通过实例仿真,验证了随机调度策略较调度空闲AGV策略具有更高的拣选效率,同时解决了AGV调度与拣选序列问题,对AGV数量配置具有指导作用。     

基于NSGA-Ⅱ算法的分区拣选优化

电商背景下的客户订单呈现出多品种、小批量、高频次等特点,给仓库拣选工作带来很大的挑战。为提高拣选效率,在订单完全拆分的分批策略和组合优化的行走策略下,设计了以总服务时间最小、分区工作量平衡度最优和二次分拣效率最高的多目标分区拣选模型。由于3个目标函数之间存在矛盾,设计了NSGA-II算法对多目标优化模型进行求解。通过数值实验,与传统的不拆分订单的分区拣选系统对比,发现在订单批量环境为[1,4]时,分别使总服务时间减少了43.88%,平衡度改善了84.61%,并分析了区域个数、订单总数和订单批量环境对系统效率的影响。     

Exploring the role of picker personality in predicting picking performance with pick by voice,pick to light and RF-terminal picking

Order pickers and individual differences between them could have a substantial impact on picking performance, but are largely ignored in studies on order picking. This paper explores the role of individual differences in picking performance with various picking tools (pick by voice, RF-terminal picking and pick to light) and methods (parallel, zone and dynamic zone picking). A unique realistic field experiment with 101 participants (academic students, vocational students and professional pickers) is employed to investigate the influence of individual differences, especially the Big Five personality traits, on picking performance in terms of productivity and quality. The results suggest that (PbV) performs better than RF-terminal picking, and that Neuroticism, Extraversion, Conscientiousness and the age of the picker play a significant role in predicting picking performance with voice and RF-terminals. Furthermore, achieving higher productivity appears to be possible without sacrificing quality. Managers can increase picking performance by incorporating the insights in assigning the right pickers to work with a particular picking tool or method, leading to increased picking performance and reduced warehousing costs.     

Enhancing the order picking process through a new storage assignment strategy in forward-reserve area

This paper reexamines the order picking process in a warehouse facing the challenges that e-commerce brings about and which are characterised by a very large number of small sized orders and returns. Implementing effective storage assignment strategies combined with efficient batching, in this context, is very fundamental to keep the warehouse’s responsiveness and order completion times up to the standards. This paper investigates a new storage assignment strategy, initially implemented by a large shoes and footwear wholesaler, to enhance the performance of the order picking process in its warehouses. The impact of this new storage assignment strategy on the performance of the order picking process is analysed via simulation. The performance of the system, measured in terms of total picking time as well as order lead time while taking congestion into account, is compared to the cases where conventional storage assignment strategies are implemented. A full factorial design is set up and the simulation output is statistically analysed. The results of this analysis are reported and thoroughly discussed. Attending to the results, the proposed strategy presents a remarkable potential to shorten total picking travel distances and order completion time and consequently customer satisfaction.     

Dynamic order batching in bucket brigade order picking systems with consecutive batch windows and non-identical pickers

The blocking mitigation mechanism contained in a batching and sequencing model improves order picking performance in bucket brigade order picking systems by adjusting the batch formation in a given batch window. The batch formation of a given batch window affects the transition to the next batch window and limits the batch formation’s structure in the next window. In addition, imbalance in picker capability increases the variation of batch formation while mitigating blocking delay. Our paper proposes a dynamic indexed batching model to smooth the transition between consecutive batch windows and give a better approximation of non-identical pickers’ capability. We develop a mixed integer programming solution for a dynamic indexed batching model in a bucket brigade order picking system (DIBMB). Simulation experiments show that the DIBMB smooths the transition between batch windows as measured in the delay experienced by the first batch in each batch window. Comparisons to the available batching models show that under DIBMB, the blocking delay gradually increases throughout the sequence of batches.     

The use of time series forecasting in zone order picking systems to predict order pickers’ workload

In order to differentiate from competitors in terms of customer service, warehouses accept late orders while providing delivery in a quick and timely way. This trend leads to a reduced time to pick an order. This paper introduces workload forecasting in a warehouse context, in particular a zone picking warehouse. Improved workforce planning can contribute to an effective and efficient order picking process. Most order picking publications treat demand as known in advance. As warehouses accept late orders, the assumption of a constant given demand is questioned in this paper. The objective of this study is to present time series forecasting models that perform well in a zone picking warehouse. A real-life case study demonstrates the value of applying time series forecasting models to forecast the daily number of order lines. The forecast of order lines, along with order pickers’ productivity, can be used by warehouse supervisors to determine the daily required number of order pickers, as well as the allocation of order pickers across warehouse zones. Time series are applied on an aggregated level, as well as on a disaggregated zone level. Both bottom-up and top-down approaches are evaluated in order to find the best-performing forecasting method.     

Optimal order picker routing in a conventional warehouse with two blocks and arbitrary starting and ending points of a tour

This paper investigates manual order picking, where workers travel through the warehouse to retrieve requested items from shelves. To minimise the completion time of orders, researchers have developed various routing procedures that guide order pickers through the warehouse. The paper at hand contributes to this stream of research and proposes an optimal order picker routing policy for a conventional warehouse with two blocks and arbitrary starting and ending points of a tour. The procedure proposed in this paper extends an earlier work of Löffler et al. (2018. Picker routing in AGV-assisted order picking systems, Working Paper, DPO-01/2018, Deutsche Post Chair-Optimization of Distribution Networks, RWTH Aachen University, 2018) by applying the concepts of Ratliff and Rosenthal (1983. “Order-picking in a Rectangular Warehouse: a Solvable Case of the Traveling Salesman Problem.” Operations Research 31 (3): 507–521) and Roodbergen and de Koster (2001a. “Routing Order Pickers in a Warehouse with a Middle Aisle.” European Journal of Operational Research 133 (1): 32–43) that used graph theory and dynamic programming for finding an optimal picker route. We also propose a routing heuristic, denoted S*-shape, for conventional two-block warehouses with arbitrary starting and ending points of a tour. In computational experiments, we compare the average order picking tour length in a conventional warehouse with a single block to the case of a conventional warehouse with two blocks to assess the impact of the middle cross aisle on the performance of the warehouse. Furthermore, we evaluate the performance of the S*-shape heuristic by comparing it to the exact algorithm proposed in this study.     

The use of bucket brigades in zone order picking systems

As the transactions through electronic commerce and TV home shopping increase, the warehouses often receive a large amount of small orders to be picked within tight time windows. One of the important warehousing activities is order picking, the process of retrieving a number of items from warehouse storage to meet a number of independent customer orders. This paper examines a new order picking method, bucket brigade order picking (BB picking). Bucket brigade is a way of coordinating workers who progressively perform a set of operations on a flow line. In the BB picking system, a worker performs operations on an order until the next worker downstream takes it over; then goes back to the previous worker upstream to take over a new order. We discuss distinct characteristics in order picking systems when bucket brigades are applied. We identify some efficiency losses under the BB picking and present a new BB picking protocol to improve the performance of order picking systems. The new BB picking is compared with the existing BB picking and zone picking through simulation experiments.     

可变路径人工拣货系统动态货位调整研究

考虑在线零售企业的时变需求,基于逐步求精、渐进式优化的思路,通过实时、动态调整商品在仓库中的存储位置来响应需求的快速变化,并允许拣货员改变其行走路线,在订单拣货的同时进行货位调整。构建了可变路径下动态货位调整框架模型;提出前进和返回交替进行的回转路径策略,并对路径调整策略及商品选择策略两个关键进行研究;通过实验验证模型的有效性。结果表明,在订单规模中等,需求偏度较大时,动态货位调整可节约25%左右的拣货距离,货位优化效果明显,可为在线零售企业科学实施动态货位调整提供理论指导。     

Order Picking In An Aisle

A classical order picking problem is the case where items have to be picked from both sides of an aisle and the picker cannot reach items on both sides without changing position. Hence the picker must cross the aisle one or more times. An efficient optimal algorithm is developed and shown to yield policies with up to 30% savings in travel time over commonly used policies. It is also shown that, for most practical aisle widths, it is significantly more efficient to pick both sides of the aisle in the same pass (a traversal policy) rather than pick one side and then pick the other side (a return policy) unless the pick densities are greater than 50%. All the algorithms presented here can be implemented in real time on a microcomputer.     

拣货方式、存储策略与路径策略协同研究

对拣货方式、路径策略与存储策略进行协同研究,设计了具有代表性的策略组合。推出了不同路径策略下,实际拣货路径长度的计算公式。通过对各种策略组合仿真结果的比较分析,确定了3种策略的相对重要性:1）分批策略对减少拣货作业总时间影响最大;2）分类存储策略比随机存储策略所需的行走路径缩短很多;3）路径策略对拣货行走的时间的减少明显小于分批拣货方式和分类存储策略带来的拣货作业时间的减少。具体决策时,应优先考虑分类存储策略和分批拣货方式,在确定其已经有效的情况下再考虑路径策略,以使拣货效率达到整体最优。     

Modelling and performance evaluation of explosive storage policies in internet fulfilment warehouses

Internet Fulfilment Warehouses (IFWs) are designed to exclusively process online retail orders. An observational study reveals that IFW operating and design attributes are significantly different from traditional warehouses in their storage and fulfilment policies. Specifically, we identify six IFW differentiators: explosive storage, very large number of beehive storage locations, bins with commingled SKUs, immediate fulfilment, short picking routes with single unit picks and high transactions with total digital control. Explosive storage of incoming bulk allows for faster fulfilment of customer orders often within a few hours. A new IFW control model is developed. This describes the associated receiving and fulfilment flows. Two decision algorithms for generating (i) a stocking list and (ii) an order picking list are presented. A simulation model was built to evaluate the fulfilment performance of the explosive policy. Experimental runs on a problem with 400 SKUs, 3240 bins and 22,000 customer orders over nine days are reported. Results show that increasing levels of explosion reduce the linear fulfilment time by as much as 16%, confirming the IFW storage policy is advantageous. The results also show that fulfilment time behaviour is convex as a function of the maximum number of stops allowed by the picking algorithm parameter.     

基于改进遗传算法的自动拣选系统 拣选位分配建模与优化

针对某自动拣选系统建立了拣选位分配优化模型,以拣选时间模型作为适应度函数,并通过判断海明距离添加一个惩罚函数对遗传算法进行了改进,对算例进行仿真实验,可以得到货位排序优化后,总拣选时间明显降低了27.85%。结果表明,货物拣选位的分配对自动拣选系统的拣选效率有很大的影响。要想降低总拣选时间,提高自动拣选系统的拣选效率,不能只考虑个别种类货物的位置分配,要从全局的方向去考虑。该研究对配送中心如何提高自动拣选系统的效率提供了理论支持。     

Determining the number of zones in a pick-and-sort order picking system

In this study we consider a pick-and-sort order picking system, in which batches of orders are picked simultaneously from different (work) zones by a group of order pickers. After picking, the orders are transported by a conveyor to a next station for consolidation and packing. Packing can only occur when an order has been picked completely. For a given number of workers, each assigned to a single zone, a larger number of zones reduces pick time (since travel time reduces), but increases waiting time for completion at the packing stations, because more partial batches needing assembly arrive at the packing stations. Our aim is to determine the optimal number of zones such that the total (picking and packing) time to complete a batch is minimised. We solve this problem by optimally assigning items to pick routes in each zone. We illustrate the method with data taken from a distribution centre of one of the largest online retailers in The Netherlands.     

Examining the use of dedicated and general purpose pallets in a dedicated flexible manufacturing system

This research describes one example of how the failure to understand the relationships between the flexibility associated with all resources within an FMS can be critical to overall performance. The need for such understanding is clearly spelled out by Jaikumar (1986). This research illustrates that even in situations where the demands placed upon the system are very well defined, tooling resources, such as pallets, may constrain overall system flexibility and subsequent system performance. In this paper, we simulate the operational performance of an existing FMS designed to manufacture a relatively small set of agricultural equipment components (only eight part types) over a known planning horizon using general purpose pallets and dedicated pallets. The simulation model is run under experimental conditions that include levels of: demand mix variability, number of each type pallet available to the system, and incremental loading time and scrap rate when general purpose pallets are used. In most cases, the results indicate a significant increase in system performance when using general purpose pallets. In general, while system performance decreases as the level of demand mix variability increases, relatively higher throughput is obtained using general purpose pallets except where the assumed incremental loading times and scrap rates associated with assembling the pallets are highest. System performance also improves as additional pallets are made available. In addition, overall system investment is impacted as fewer general purpose pallets are required to achieve a given level of performance compared to the use or dedicated pallets. As the overall system investment and scheduling restrictions associated with dedicated pallets would be expected to increase with the number of part types made in the system, the results found in this analysis for a dedicated FMS producing a small number of parts on a regular basis form a relative ‘lower bound’ on the scheduling and investment benefits of using general purpose pallets.     

Evaluating order throughput time with variable time window batching

Given increased pressure to provide short delivery times, minimising customer order throughput time is a very important objective in warehousing operations. There are many factors that may affect the performance of an order picking system, such as layout of the warehouse, the storage strategy, the routing policy, the zoning method and the batching policy. In this study, we propose a simple travel time model and analyse the effect of order batching on the expected customer order throughput time with variable time window batching. In addition, we discussed the impact of some parameters on the batch size and the expected customer order throughput time. In the practice of Wuhan Dong Hon Logistics co. Ltd, the storage rack in the warehouse has two levels: the low storage level and the high storage level. These two levels are visited by pickers and forklifts, respectively. The classification improves the performance of order picking. In this study, we build the model based on this practice.     

Order picking system design: the storage assignment and travel distance estimation (SA&TDE) joint method

Of all the warehouse activities, order picking is one of the most time-consuming and expensive. In order to improve the task, several researches have pointed out the need to consider jointly the layout of the warehouse, the storage assignment strategy and the routing policy to reduce travelled distances and picking time. This paper presents the storage assignment and travel distance estimation (SA&TDE) joint method, a new approach useful to design and evaluate a manual picker-to-parts picking system, focusing on goods allocation and distances estimation. Starting from a set of picking orders received in a certain time range, this approach allows to evaluate the combinations of product codes assigned to storage locations, aisles, sections or warehouse areas and to assess the most relevant ones, for the best location and warehouse layout, with the aim of ensuring optimal picking routes, through the application of the multinomial probability distribution. A case study is developed as well, in order to clarify the concept that underlies the SA&TDE joint method, and to show the validity and the flexibility of the approach, through the calculation of the saving at different levels of detail.     

柑橘类水果采摘机器的设计与研究

目的 设计并制作一款柑橘类水果采摘机器,对柑橘等水果进行采摘和装箱。方法 对整机的机械和控制部分进行设计,机械部分包括末端执行器、机械臂、移动平台、上升机构、存储机构和运输机构;控制部分基于OpenMV系统对指定颜色的柑橘进行扫描,通过串口通信将坐标值传输给STM32单片机,基于STM32单片机对各模块进行控制,利用Altium Designer软件对各模块的控制电路图进行设计与仿真。结果 制作出实物样机且在果园试验成功,采摘1次的平均时间为5.4 s,采摘的最大高度是1.85 m。结论 该机器能够完成对柑橘识别、采摘、分拣和装箱一体化功能,满足使用要求。