Martina Calzavara

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.

A comparative analysis of different paperless picking systems

Purpose – Warehouse picking is often referred to as the most labour-intensive, expensive and time consuming operation in manual warehouses. These factors are becoming even more crucial due to recent trends in manufacturing and warehousing requiring the processing of orders that are always smaller and needed in a shorter time. For this reason, in recent years more efficient and better performing systems have been developed, employing various technological solutions that can support pickers during their work. The purpose of this paper is to introduce a comparison of five paperless picking systems (i.e. barcodes handheld, RFID tags handheld, voice picking, traditional pick-to-light, RFID pick-to-light). Design/methodology/approach – Warehouse picking is often referred to as the most labour-intensive, expensive and time consuming operation in manual warehouses. These factors are becoming even more crucial due to recent trends in manufacturing and warehousing requiring the processing of orders that are always ...

Analysis of economic and ergonomic performance measures of different rack layouts in an order picking warehouse

Abstract Manual order picking ranks among the most time- and cost-intensive activities in warehouses, and it has frequently been studied in the past. The aim of existing studies was to improve the operational efficiency of order picking processes mainly by developing planning models that help to reduce the time that is needed for order picking. As order picking is still performed manually with technical support in most warehouses, human workers play an important role for order picking performance. Although it is recognized that manual material handling activities in warehouses expose workers to a high risk of developing musculoskeletal disorders, integrated planning approaches that consider both economic and ergonomic objectives in order picking design are still rare. This paper contributes to closing this research gap by developing economic and ergonomic performance measures for the case where orders are picked from pallets, half-pallets and half-pallets equipped with a pull-out system. The comprehensive analysis of the different rack layouts shows that there are opportunities to replace the traditional pallet storage system by half-pallets with a pull-out system on the lower rank to improve both ergonomics and economic performance.

Additional effort estimation due to ergonomic conditions in order picking systems

Within a warehouse, the picking activity often relies on human operators. Therefore, when designing and evaluating a manual picking system, it is important to consider that, besides the high flexibility the pickers are able to warrant, they inevitably require an additional effort due to their ergonomic working conditions. In this paper, the authors propose a new model to consider such additional effort, starting from the concepts of human availability and rest allowance. The new method allows the evaluation of the current configuration of a certain warehouse, considering two different operative situations (directly employed operators and indirectly employed ones). Moreover, it makes it possible to estimate and to understand the benefits that can be achieved by introducing some ergonomic improvements. The proposed procedure has also been applied to a real industrial case study.

Preventing ergonomic risks with integrated planning on assembly line balancing and parts feeding

In this paper, we advise to perform assembly line balancing simultaneously with decision-making on parts feeding. Such integrated planning may open additional potential to reduce labour costs. Additional planning flexibility gained with the integrated planning may be used to mitigate ergonomic risks at workplaces. We formulate the integrated assembly line balancing and parts feeding planning problem, propose a mixed-integer model and compare integrated planning to a common hierarchical planning approach in a detailed case study on the assembly of a self-priming pump. Our case study illustrates that workplaces with high ergonomic risks may emerge even in productions that involve handling parts and workpieces of low weights and avoid static and awkward postures. We also show that the proposed integrated planning approach may eliminate excessive ergonomic risks and improve productivity indicators simultaneously.

A device to monitor fatigue level in order-picking

In order-picking activities, the performance of the system can be influenced by different variables such as the order to be fulfilled, the distance to be covered or the experience of operators. Usually, this kind of activity is performed by operators rather than machines to assure flexibility. Consequently, their fatigue accumulation can decrease the performance of the overall system. The purpose of this paper is to define the kind of device to be used in an order-picking context, to obtain data which can be utilized for the evaluation of the level of fatigue and to improve the performance of the picking system.,The paper presents a comparison between existing fatigue methods which can be applied in a picking context. In addition, an analysis of the physiological literature for the evaluation of a new device for the monitoring of fatigue level is carried on and its practical use is shown.,The proposed research identifies in the heart rate monitor the device that, thanks to its advantages, can be the best one to be used in an industrial context for monitoring the physical fatigue of operators.,This study considers the importance of human factors in picking activities such as physical fatigue of operators and the need to have validated tools to monitor and to define the level of fatigue accumulation in each activity of different rate and duration.

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.

A model for rest allowance estimation to improve tasks assignment to operators

Manual activities are still present in production systems, such as order picking in warehouses, material handling in production systems, loading and unloading of work centres. Many scientific contributions have widely demonstrated production system efficiency is strictly linked to the operator wellbeing. In fact, activities at different pace and duration imply different productivity but also different effects on the fatigue accumulation acquired by the operators, with consequently required resting period. It is necessary to integrate operator fatigue and recovery analysis into traditional decision support models for the design and management of production systems. This paper aims to present an analytical model for setting the time necessary for operators to recover from the performed activity. According to previous research, the exponential trend of fatigue accumulation and recovery alleviation is studied. The energy expenditure rate, predicted with heart rate monitoring, is used to model the fatigue/recovery level, varying the physiological factors of the operators and the characteristics of the analysed manual activities. The model is limited to the activities where the whole body is used rather than a specific part stressed continuously. Finally, it is applied to optimise the scheduling of activities among operators in a manual order picking system. It is demonstrated that its use improves performance in terms of productivity.

ECONOMIC AND PERFORMANCE ANALYSIS OF DUAL-BAY VERTICAL LIFT MODULES (VLMS)

Warehouse picking is one of the most time and cost consuming activities in a warehouse, often requiring the presence of human operators, who travel within the aisles to retrieve the items needed by the customers. Several studies demonstrate that the travelling activity can represent even the 50% of the total picking time, with a subsequent creation of a separate storage and picking area for small objects. In the last years, new solutions for order picking systems have been developed, especially for small items. One of these solutions requires Vertical Lift Modules (VLMs), storage columns with extractable trays. In this paper, the employ of dualbay VLMs, compared to a traditional bin-shelving warehouse, has been analysed from an economic point of view. Some mathematical formulations have been developed, to estimate the total annual cost and the respective convenience limits of both systems, according to their productivity. Moreover, some useful guidelines for practitioners are derived.

A method to choose between carton from rack picking or carton from pallet picking

Abstract In a manual picker-to-parts picking warehouse, a usual approach is to divide the whole stocking area in two different zones, the reserve and the forward areas. The dimensioning of the forward area, which is dedicated to picking activities, has an important impact on the overall performance of the picking system. Indeed, its size as well as the item allocation deeply influence the travel time of the operators on one side and the frequency of the refilling activities on the other. The present paper aims to provide a new method that can be easily used to assess the most suitable way of storing a product in the forward area, considering the possibility of keeping a product directly in a pallet or storing it in racks. Starting from simple data, such as the picking orders of the items to pick and their physical dimensions, as well as the characteristics of the warehouse, the method focuses on the comparison of the total times to define the Carton Pick from rack Convenience Condition (CPCC). The CPCC formulation and its application methodology allow to quickly establish which items should be stored on pallets and which on racks, with interesting impacts on space and time savings. This is shown also in the reported case study, the results of which prove the effectiveness as well as the easy and full applicability of the methodology, also in different warehouse contexts.