Aviator System as an Alternative to Warehouse Handling Devices Peter Bindzár 1,a, Martin Straka 1,b, Thomas Thate 2,c and Michal Balog 3,d

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1 Applied Mechanics and Materials Submitted: ISSN: , Vol. 683, pp Revised: doi: / Accepted: Trans Tech Publications, Switzerland Online: Aviator System as an Alternative to Warehouse Handling Devices Peter Bindzár 1,a, Martin Straka 1,b, Thomas Thate 2,c and Michal Balog 3,d 1 Technical University of Košice, Faculty of Mining, Ecology, Process Control and Geotechnology, Logistic institute of industry and transport, Park Komenského 14, Košice, Slovak Republic 2 Dresden University of Technology, Faculty of Transport and Traffic Sciences, Hettnerstraße 3, Gerhart-Potthoff-Bau, Germany 3 Technical University of Košice, Faculty of Manufacturing Technologies, Institute of Advanced Technologies, Department of Production Management, Bayerova 1, Prešov, Slovak Republic a peter.bindzar@tuke.sk, b martin.straka@tuke.sk, c tomas.thate@gmx.net, d michal.balog@tuke.sk Keywords: warehouse vehicle, material handling, manipulation, floor-free warehouse system Abstract. The Aviator is a floor-free working warehouse vehicle, which gives a third alternative to the market of stacker cranes that consist also of the narrow aisle stacker and the rack feeder. Officially introduced as Transfaster in 2002, this full-automatic working system has been realized several times. This article will give an overview concerning the structure of the system and its functionality, and will compare it to conventional systems regarding advantages, disadvantages and performance. Therefore ways of calculating cycle times are introduced. Introduction to the Aviator system In recent time a new kind of warehouse trucks has been available on the market. This device is called Aviator (AV) (Fig. 1) and it consists of a positioning unit (1), moving horizontally by the means of rails (5). These are attached at the inside of the rack at the adjusted shelf level. Via four steel wire ropes (4) the lift platform (2) - including the load suspension device (3) - is connected to cable winches placed on the positioning unit that realize the vertical movement. Fig. 1 The Aviator system and its parts Due to this construction the Aviator becomes a floor-free working warehouse vehicle. Since the lift platform is moving freely in the shelf aisle, a collision free movement and an oscillation that has All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (# , Pennsylvania State University, University Park, USA-16/09/16,01:30:42)

2 16 Research, Production and Use of Steel Ropes, Conveyors and Hoisting Machines been reduced to a minimum at the point of arrival have to be ensured to afford charge exchange. Therefore a new regulation is used that specifically has been developed for the Aviator and will be explained shortly in the following. The warehouse management system generates driving points for the Aviator that is used to calculate a trajectory which will be converted into a time function up to the fourth derivative. These data will be transmitted as a reference variables vector to the curved path regulation module and are minimal in regard to driving time due to the given boundary conditions. These regulations occur adaptively and separately for the horizontal and vertical direction. Since this data is only an abstraction, sensors - which are fixed on the Aviator are used to detect the actual position. With an adaptive working state feedback to the control input the remaining oscillation can be prevented at the point of arrival. To ensure a save charge exchange between the load suspension device which can be for example a telescopic fork, a satellite vehicle or even every pull- and push device - and the storage shelf, the lift platform is connected to the storage rack via two bolts [1,2,3]. Aviator system description and its properties With respect to the special features of the Aviator-system, some advantages yield in comparison to the narrow aisle stacker (NAS) and the rail bounded rack feeder (RF), which will be listed below. The floor free working warehouse vehicle with a total weight of about 7.2 tons is three times lighter than a rail bound rack feeder, and a narrow aisle stacker weighs about twice as much. From this follows that it is not necessary to include an extra enhanced bottom panel into the warehouse. The Aviator technology also allows during maintenance or malfunction via forklift the operation in the aisle can continue. The infeed and outfeed conveyor system can be installed in any height reachable by the Aviator reachable height, as well as crosswise to the rack. As it is possible to negotiate such obstacles, there are also other functions conceivable, like a passage way for warehouse personnel or a crosslink between order-picking areas, which are placed in the lower levels of the rack. Another advantage offers the possibility to extend the rails for the positioning unit, so that the Aviator can reach the pre-storage area. This allows a direct integration of the warehouse into the production processes of a company. Due to the system structure of the Aviator the possibility of installing two or three of these warehouse vehicles in one shelf aisle exists. Related to the throughput, increases up to 130% respectively 150% are possible, which makes this alternative of warehousing interesting for high dynamic processes. On the other hand stores that only need one warehouse vehicle for two or more shelf aisles can make use of a conversion unit that realizes the moving of the Aviator between the shelf aisles. This happens within 50 to 60 seconds. In comparison, the narrow aisle stacker needs 40 to 60 seconds, depending on where it is situated. The rack feeder requires up to 120 seconds. This argument further supports the use of the Aviator system. But there are also some disadvantages. As the steel cables have a limited bearing capacity, the maximum weight of the load is 1 ton. Furthermore the system limits the maximum height of a warehouse using the Aviator technology to 20 meters. In comparison to a narrow aisle stacker system this is five meters more, but rail bounded rack feeders reach up to 45 meters. It is also not possible to store units that include a high amount of liquid, because of the relatively natural oscillation, which causes changes of the focal point during the Aviator is driving. Thus a forecast of the driving way is not possible. Another disadvantage results out of the oscillation of the lift platform at the destination, which extends every cycle time about six seconds [4,5,6]. Comparison of cycle time and throughput for the warehouse vehicles To compare the different types of warehouse vehicles, it is necessary to calculate single or double cycle times. Based on this data it is possible to calculate the according throughput. Simulation approach should be also used in some cases [7,8]. The single cycle consists of the drive of the load suspension device in z-direction at the in- and output location and back, to carry the charge onto the lift platform. It follows the drive to the

3 Applied Mechanics and Materials Vol intended shelf to which the charge is delivered by the load suspension device. Accordingly the Aviator moves to the in- and output location again to pick up the next charge. During double cycles, the warehouse vehicle performs an additional transverse drive after delivering the load into the stock. It takes another load out of a shelf and transports it to the in- and output location. Because of this, an additional dead and two more movements in z-direction are necessary. With this strategy the amount of empty runs can be reduced. One way to calculate the single cycle time (SCT) works by using a shelf parameter. It is used to adjust the ratio between the warehouse height and length to the maximum speed in x- and y- direction of the warehouse vehicle. Calculations for the work cycle are expressed in the following equations [9,10,11,12]: The average single cycle time. follows out of (1) The shelf entry- respectively exit movement is calculated with the following equation: (2) The shelf parameter indicates the ratio between the warehouse dimensions and the speed in x- and y-direction. (3) On this depends the kind of equation used for the average moving time. (4) (5) (6) Another way for calculating the average single cycle time follows, which is also valid for warehouse vehicles that are able to move synchronous in horizontal and vertical direction. (7) needs to be calculated with the following formula: (8) It dues to the maximum of the time for the movements in horizontal and vertical direction in dependency to the stock dimensions. According to this, and are calculated as follows. true for (9)

4 18 Research, Production and Use of Steel Ropes, Conveyors and Hoisting Machines true for (10) Due to this method it is possible to calculate the average double cycle time the following equation:, which results out of (11) Formula symbol Unit Explanation, [m/s²] Acceleration generally, in x-, y-, z-direction [m/s²] Brake acceleration [m] Storage height [m] Storage length [m] brake-, acceleration distance, distance in x-, y-, z- direction [s] Brake-, acceleration time, [s] Average single cycle time, average driving time [s] Dead time [s] Average driving time [s] Moving time of the load suspension device in z-direction, [s] Average single cycle time for a retrieval cycle respectively storage cycle [s] Average double circle time - Shelf parameter [m/s] Speed general, in x-, y-, z-direction, [m/s] Maximum speed, speed to the time [m] Distance in z-direction Performance data of the warehouse vehicles (WHV) The following Table 1 represents the performance data for progressive Aviator-system and classic Rack feeder and Narrow aisle stacker [13,14,15,16,17]. Table 1 Performance data of the warehouse vehicles Parameter Aviator Rack feeder Narrow aisle stacker x-direction speed [m/s] acceleration [m/s²] y- direction speed [m/s] acceleration [m/s²] z- direction speed [m/s] (loaded) acceleration [m/s²] z- direction speed [m/s] (unloaded) acceleration [m/s²] Dead time [s] As shown in Table 1, the Aviator has the best performance in most directions. Compared to the rack feeder it has a higher dead time, which results out of the oscillation of the lift platform. The narrow aisle tracker has the lowest performance and the highest dead time, so it is expected to have the highest cycle times. The performance data of the Aviator were received from its manufacturer; the data of rack feeder is more a collection of experienced data.

5 Applied Mechanics and Materials Vol Results and discussion The single cycle time (SCT) for warehouse vehicles is calculated in Table 2. As expected, the narrow aisle stacker takes the longest time to complete one cycle, even though this data is calculated for a height of 15 meters, which is the maximum for this kind of warehouse vehicle. It can also be seen that the difference between the Aviator and the rack feeder is very little. SCT Arnold [s] Table 2 Results of cycle times for the WHV SCT Gudehus SCT Gudehus Length [s] [s] [m] Aviator Rack feeder Narrow aisle stacker Height [m] What can be said is that with a shorter length of the warehouse the rack feeder is the more efficient machine. But with growing dimensions in the horizontal way, the Aviator can improve its throughput. This can also be seen in the diagram below (Fig. 2). Fig. 2 Comparison of WHV in terms of throughput Reasons for this improvement are the higher acceleration and speed, which balances the dead time. This Fig. 2 shows how many single cycles the specific warehouse vehicle can realize within

6 20 Research, Production and Use of Steel Ropes, Conveyors and Hoisting Machines one hour, which is equal to the throughput. The diagram also shows which performance is possible if two or three Aviators are used in one shelf aisle. Therefore the quantity of single cycle trips per hour for one Aviator has been multiplicated with the factor 1.3 and 1.5, respectively. This is a new way of warehousing, because before this multiple use, a comparable throughput could not be achieved. Until now only systems including two Aviators in one shelf have been realized. So the question remains when the highly profitable version including three Aviators will be produced and used. Costs analysis Cost analysis is present in the works of many authors [18,19,20,21]. The following short costs analysis is based upon a warehouse model with a capacity of pallets and a rate of inventory turnover of 10 per year. A comparison of the running costs per year showed that the use of the Aviator technology is about respectively more profitable than operating a rack feeder respectively a narrow aisle stacker. The investment costs for a rail bounded stacker crane are higher than for an Aviator. The narrow aisle stacker, on the other hand, is even cheaper. Summary The Aviator should be used in warehouses over the many industries like manufacturing or logistics centres [22]. The Aviator offers a new, automatically working alternative in the field of warehousing vehicles. Due to its floor-free functioning, new ways of building and designing stores are possible. As the performance of this unit is nearly the same to the rack feeder, and also the costs are lower, up to a warehouse height of 20 meters the Aviator should be the preferred system. But for increased heights the rack feeder remains the unbeatable system. Since the technical development for such systems continues as well, stacker cranes will probably soon be able to reach higher performances. Finally, the narrow aisle stacker can be the preferred solution for a warehouse that is at most 15 meters high and does not need a very high throughput. By the way, the Aviator is not a system that is always the optimum, but complements the field of warehouse vehicles. Acknowledgements This paper was created within the VEGA grant project No. 1/0216/13 Methods and new approaches study to measurement, evaluation and diagnostic performance of business processes in the context of logistics management company and VEGA grant project No. 1/0036/12 Methods development and new approaches to design of input, interoperable and output warehouses and their location in mining, metallurgy and building industries. References [1] O. Sawodny, H. Aschemann, Webcontrol for the Transfaster, Lifting and handling equipment. 4 (2002) (original in Deutsch). [2] M. Hompel, V. Heidenblut, Taschenlexikon Logistik, Springer-Verlag Berlin and Heidelberg GmbH & Co. KG, Berlin, [3] Information on [4] R. Hricova, Importance of the optimal batch size, in: proc. TEAM th int. scientific and expert conf., Presov, Slovakia 2013: pp [5] V. Modrak, P. Semanco, Developments in Modern Operations Management and Cellular Manufacturing, in: V. Modrak, R.S. Pandian, Operations Management Research and Cellular Manufacturing Systems-Innovative Methods and Approaches, IGI Global, Hershey, 2011, pp

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