J.H.D. Luiting Maten
Container-lifting at the front. An introduction to reach stackers and front
lift trucks.
Literature survey,
Report 2000.TT.5358, Transport Engineering and Logistics.
This study is focussed on the role of the reach stacker and the front lift
truck in container and intermodal freight handling. Both machines carry the
loads in front of the truck. Because of this, the load causes a forward moment,
which has to be compensated by a counter balance at the rear of the truck. The
way the load is lifted has a large impact on the stability of the truck. A
front lift truck has a fixed mast and its lift capacity is constant. The
forward moment caused by the load is constant. A reach stacker, with its
extendable boom, can reach beyond the first row. However, the further the load
distance (the distance from front axle till the centre of gravity of the load)
gets, the higher the forward moment, caused by the load, will be. The counter
balance has a constant mass, so the lift capacity will decrease with an
increasing load distance. Because the reach stacker can stack containers in
the second and third row, the stacking density at a terminal served by reach
stackers is higher than terminals served by front lift trucks. However, a
higher stacking density has its effect on the accessibility of the containers,
the so called selectivity. The selectivity refers to the number of moves that
is needed to pick up a certain container. When a large number of moves is
needed, the handling times will increase and the overall productivity will be
lower. The selectivity is also less due to the fact that a reach stacker can
not pick up every container in the second row, because of the decreasing lift
capacity at larger load distances. This means that when a heavy container is
needed, the entire first row has to be removed. With terminal planning software
the situation can be improved, but it will always be difficult to predict when
the shippers will pick up their cargo. Thus a front lift truck scores better on
selectivity, but a reach stacker scores better on stacking density.
To make the machine more competitive with other types of terminal equipment,
manufacturers try to improve handling time and to reduce operation costs. One
of the major exploitation costs is the tyre cost. Tyres are very expensive
and when a tyre has to be replaced, the machine is not productive. If a tyre
fails during operation, the truck can also be damaged. The efforts of the
manufacturers have to lead to longer tyre life, so the cost per kilometre can
be reduced as well as the downtime. Better tyres can also absorb shocks,
which will lead to less damage of the machine and more comfort for the driver.
The comfort of the driver is the next point of attention for the
manufacturers. They have concluded that it is not easy to design faster
machines. Therefore, a lot of effort is put into the design of the interior of
the cabin, to make it more ergonomic, so that the driver can operate it more
easily and can work faster. Furthermore, the manufacturers try to improve the
visibility.
Reports on Transport Engineering and Logistics (in Dutch)
Modified: 2006.01.23;
logistics@3mE.tudelft.nl
, TU Delft
/ 3mE
/ TT
/ LT.