New initiatives in stacking crane configurations

Ports around the world continue to take heed in order to retain their levels of competitiveness. In order to handle an increase in containerized cargo, ports could benefit from new container handling technologies with higher capacity. One of the newest technologies available is the revolutionary concept of having two gantry cranes cooperating in yards, which has already been implemented in several container terminals in an effort to improve yard operations efficiency. In this article we describe different types of two-crane technologies and discuss control issues that should be addressed during implementation.

Introduction
Since its introduction in the early 1960s, the containerized market has been growing significantly. In 2007, it was estimated that 485 million TEUs were handled around the world [1].

Container terminals are constantly seeking new ways to increase their transshipment and storage capacity. Investing in new types of technologies and equipment seems to be a necessity to keep up with the increased volume of containers to be handled. This article describes two-crane technologies for the yard (stack), which is one of the areas in a container terminal that is highly affected by an increase in the demand of containers.

The design of the yard should be selected carefully to ensure an efficient interface with all other processes in the terminal and to make sure that turn-around times of both sea-going vessels and trucks is minimised. Yard design issues include selecting the equipment to handle containers, determining the layout of the yard, and defining the appropriate methods to sequence requests and assign them to cranes. Two new stacking crane configurations have been developed to improve the throughput of the yard. In this article we will explain each configuration in more detail by describing their specifications and control issues.

Revolutionary concept of multiple cranes operating in the same block
Consider a yard equipped with Automated Stacking Cranes (ASCs) where storage and retrieval requests are transferred from and to the cranes at the far ends of each row (lane) as illustrated in Figure 1a.

Commonly, a single ASC handles requests in each block. Recently, the container terminals in Rotterdam and Hamburg introduced the revolutionary concept of having two automated stacking cranes in operation in a single block. However, there is an important difference in the technologies used at these terminals. The ASCs used in Hamburg are capable of passing each other and as a result each of them is able to operate in the entire block. On the other hand, in Rotterdam the ASCs cannot pass each other and as a result each serves a separate part of the block. If a container needs to be transported from one side of the block to the other, then the container will be transferred in an interchange zone to the other crane or the entire track should be cleared out by the other crane. Both configurations are illustrated in Figure 1b/c. We will describe the difference between both configurations in more detail below. Recently, a three crane configuration has been introduced that includes two identical small cranes and a large one that can pass the other two. However, we do not discuss it in this article as we consider it to be a combination of the configurations described below.

Hector J. Carlo, Assistant Professor, Department of Industrial Engineering, University of Puerto Rico-Mayagüez, PR, USA and Iris F.A. Vis, Associate Professor of Logistics, VU University Amsterdam, The Netherlands
Edition: Edition 44

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