The last step towards the fully automatic grab unloader has now
been made at the Port of Hamburg.
Three years ago Hansaport decided to strive for a fully
automatic (yes, this means ‘operatorless’) grab unloader and
awarded the contract to the German bulk automation specialist
iSAM AG, which had already completed the same task for the
company’s five stacker/reclaimer and two train loading stations.
Last year all four 35t grab unloaders at the terminal were
equipped with an advanced automation system and on 1 January
2010 the actual operation from the integrated control room
started without anybody present on the machine itself.
Teaching a machine how to unload the hatches was a difficult
task but the basic data needed is the same as for a human
operator: the position of the ship, the location of the hatches,
the material distribution and, of course, the position of the grab.
The first three tasks were accomplished with the same 3-D laser
scanner, which has already proven itself during the automation of
the stacker/reclaimers, by being able to reliably measure black
coal from 100m distance whether it was bright sunshine or
heavy rain in the middle of the night.
The positioning of the grab was a much more difficult task.
GPS could not be used and even the most advanced microwave
positioning systems did not work once the grab was in the hatch
with all the ship’s metal around. Finally the problem was solved
using advanced laser-ring gyros as part of an inertial
measurement system (INS) — a technology that sounds
complicated, but has the huge advantage of not having any
moving parts and therefore is practically maintenance-free. The
INS is attached directly to the grab and a radio link transmits
the data to the grab unloader’s control system.
The INS was also the key to overcoming one of the most
demanding control tasks — the oscillation of the grab. Most
significant is the oscillation in the direction of the boom, which is
also the main working direction of the machine. There are
several systems for sway compensation solely based on
mathematical models, but only the direct measurements by the
INS provides sufficient accuracy and reliability to operate very
closely at the ship’s hatches. Wind and uneven load distributions
can cause a second movement orthogonal to the boom, which
can not be detected by any model-based approach, but which
can be easily compensated using the INS data and the crane’s
travel gear. Last but not least there is a third movement, the
rotation of the grab itself. Again, this can be
compensated for by combining the data from the
3D scanner and the INS to put down the grab on
the material in the fraction of a second where it is
perfectly aligned with the boom.
A lot more problems had to be solved on the
way to an ‘operatorless’ unloader, many of them
relating to the safety of the equipment, the ship
and the persons on board. However, since the
beginning of this year the system has been in use
at Hansaport’s control room and grab after grab is
landing in the bunkers taking up to 25 tonnes of
material each time with 0.5m precision
independent of wind, weather, ship’s movement or
the flow of the tides.
THE GRAB UNLOADER— INITIAL CHALLENGES
- What exactly is the position and the orientation
- (attitude) of the grab?
- Where exactly are the ship and the hatches?
- How is the material distributed in the hold?
- How to handle ‘steep’ materials?
- How to handle grab oscillations?
- How to handle safety issues?
- Real-time measurement of grab position and attitude.
- Measurement of hatch position with automatic compensation
- of ship movements.
- Measurement of cargo distribution within hold.