Because of the the strongly increased national and international trade flows the performance requirements for storage and distribution centers have grown. Therefore, in the planning phase of a warehouse, the objective is to achieve the optimum performance of storage and retrieval operations per hour by selecting a suitable warehouse configuration. The warehouse configuration describes a warehouse system with regard to the depth of the shelf compartments as well as the number of load receiving means on the shelf operating device and has a decisive influence on the performance of a warehouse.

The SpieDo research project deals with the cycle time calculation for a double deep storage system, in which two load-receiving devices can transport loading units during working cycles. Over the mean cycle time for a working cycle the average throughput capacity can be calculated by means of the reciprocal value for warehouse operations (storing or retrieving) per observation period. Due to the widespread application in industrial practice, the double depth storing using two load-bearing devices can already be counted as standard solutions for warehouse systems. However, there is so far a lack of general cycle time formulas for the warehouse configuration under consideration, which is to be addressed by the research project SpieDo.

The double depth storage with two load-bearing devices offers advantages as well as challenges, just like other warehouse configurations: the double-depth storage of load units in a high bay warehouse can increase the space utilization rate. In comparison to the single-depth storing, a shorter aisle length is required for the same number of places, which leads to a shorter traveling time of the shelf operating device in the horizontal direction. Conversely, double depth storage means that rearrangements occur as soon as a aisle-close load unit blocks access to a aisle-far load unit to be retrieved. However, this challengeof a possible increase in the cycle time can be minimized with appropriate strategies for storage space allocation as well as rearrangements. Furthermore, the possibility of performing quadruple games is obtained by means of the double-load receiving means on the shelf operating device. Thus, two storages as well as two retrievals can be carried out within one working cycle. By combining the orders to quadruple games, time for empty runs is also eliminated. Furthermore, the cycle time per order can be further optimized by means of so-called operating or movement strategies.  

In order to be able to realize the research project, the state of science and technology are analyzed at the beginning and the required parameters for the cycle time model are defined. Operating strategies include, among other things, the way of storage, the movement of the shelf operating device during the quadruple play, and the sequence of the rearrangement. The selected operating strategies thus influence the achievable cycle time results. Therefore, suitable storage strategies are formulated within the research project. In a further step, a model for the simulation of the cycle time in the case of double depth storage with the use of two load receiving means is created. Within the scope of the analysis of the simulation results, the results can be evaluated and suitable warehouse operating strategies can be identified for the application. Then the formula for the analytical cycle time model is derived and representative subjects for an average working game are determined.

The goal of SpieDo is to present a general formula for the cycle time with double depth storage using two load bearing devices. Since previous cycle time models for the warehouse configuration under consideration only provide results for the mean cycle time, the created cycle time model is intended to ensure a more accurate calculation of the cycle time. The results of the research project are aimed particularly at small and medium-sized enterprises (SMEs), either as manufacturers, planners or users of a storage system. An improved calculation of the cycle time can both avoid costly mis-planning and determine the effective performance of a warehouse. Similarly, SpieDo is intended to identify representative storage units for a work cycle within the framework of the examined inventory configuration, e.g. in a norm. In addition, recommendations for action are derived from the research results obtained for companies, which are intended to provide support for possible efficiency improvements through suitable operating strategies.

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The objectives of SpieDo at a glance:

• Presentation of a general formula for the cycle time calculation for double-depth storage using two load-bearing devices
• Determination of representative storage units for a work cycle in the warehouse configuration under consideration
• Recommendations for the economic operation of a double-depth storage with two load-bearing devices