The Virtual Crane
Author: Silvano de Gennaro
This document proposes the developement of a web-based general purpose crane simulator
within the contest of
Based upon technology similar to aircraft
and vehicle simulators, the Virtual Crane would reproduce realistically
the movements, operations and limits of the bridge cranes to be
installed in the LHC premises. Using a hardware and/or software
reproduction of the future control interfaces, the Virtual Crane
operators would be able to interactively drive one or several Virtual
Cranes simultaneously, moving objects in the
LHC virtual prototypes, and
simulating detector assembly phase by phase. These simulations, stored
as VRML animations, can later be played back, modified, filmed from
different viewpoints, and finally they may eventually be used to
digitally control the real cranes during detector assembly.
This document consists of an introduction to simulator
technology, followed by a thourough description of the Virtual Crane idea and
its implementation phases,
and concludes with the its possible future development in the domain of
- An introduction to simulators
Machine simulators are today widely used in educational, industrial and military
applications, mainly with the purpose of training operators and exploring
alternative mechanical strategies at no risk for equipment and humans.
With the falling costs of computing equipment and the breakthrough of
Virtual Reality applications, these simulators become more and more
affordable, and their application is expanding to all fields, with
surprisingly high investment return.
- Aircraft simulators
Since the first rocket simulators built at
NASA during the Space
Programme in the mid '60s, aircraft simulators have progressed to a
impressive level of realism. Most air companies own these sophisticated
and expensive machines, which play a fundamental role in pilot training.
Aircraft simulators behave so much like real aircrafts that pilots have
a lifelike flight experience.
A great part of the pilot training programme is performed in simulators,
particularly concerning reaction to emergency situations, which the computer
reproduce at no risk. One particularly risky excercise, impossible to
train in real life is air combat. Military requirements have pushed research in
Virtual Reality further than ever thinkable. This technology is today mature
to be transferred to all sorts of industrial sectors.
- Vehicle simulators
Once more it was the US Departement Of Defense that opened the road with
the first tank simulators. When the first commercial packages became
available, the automotive industry followed. Today most car
manufacturers include a "virtual car" simulator as part of product
conception. Because all car design is performed in CAD, and prototyped in
Virtual Reality, the simulator is an easy and natural step to
accomplish. Car simulators allow engineers to drive the car before it is
built, evaluate its ergonomy, its interior design and even its road
behaviour. The simulator cabin is usually mounted on telescopic
hydraulic legs that reproduce the feel of suspensions, tyre elasticity
and sometimes also acceleration. Sided by high tech realistic graphics,
these simulators give designers an excellent immersive experience of
their product. Ford and Mercedes use a VR
accessiblity and driver's visibility. Volvo go as far as simulate crash test.
But cars are not the only vehicles for which simulators are built. John
Deere simulate escavators, Caterpillar have buldozzers and lorry
simulators, a Swedish copany, ADtranz, use VR to simulate trains.
At CERN, we could enormously improve the LHC detectors assembly strategy by
developing a Virtual Crane simulator.
Figure 1: The Caterpillar buldozzer simulator
- The Virtual Crane
- Environment and needs
Detectors assembly brings enormous space management problems, which are
most critical in the case of ATLAS, where the detector will be assembled
in its extremely tight pit. In order to avoid space contention and deadlock,
each phase of assembly must be carefully planned. CAD models and Virtual
Prototypes are already useful to visualize static situations and
eventual collisions and intersections. The Robcad software is also being
used for path finding within the accelerator modules. However none of these technologies and tools can go as far as
simulating appropriately the cranes operations needed to lower and place
each part of the detector and its infrastructure.
The VENUS project produced
in May '96 some graphical animations which, using the i3D software,
demonstrated the possibility of reducing the diameter of the ATLAS main
shaft from 26mt to 18mt. This reduction involves pivoting the 200T
toroid magnets to descend
vertically in the shaft, then pivoting them again in the pit to be placed
and assembled horizontally. This pivoting in performed by simultaneous
actions by two bridge cranes, both at the surface and in the pit.
Available software today cannot reproduce the physics involved in this
In order to carefully plan and simulate the complex operations needed
for the assembly of each detector part, the VENUS project intends to
develop a crane simulator tool.
- The crane simulator
If aircraft and vehicle simulators are mainly intended to train a human's
piloting skills, or to evaluate ergonomic appreciation of the vehicle
before construction, a crane simulator would go even further, becoming
a central part of the detector assembly. Designed as a general,
configurable toolkit, the simulator could easily impersonate all the kinds of
cranes to be used in the LHC complex. Equipped by software and hardware
control interfaces, the simulator would give the operator the look and
feel of the real crane, operating within the detector's CAD representation.
The simulator could offer several degrees of immersion in the virtual
- A web based "on screen" interface directly available
through any VRML2 plugin browsers
(Cosmoplayer, Live3D, i3D etc.),
controlled through the standard mouse/spaceball interface.
- A specialized "immersive" environment based on a
set of large screens surrounding the user (cube style technology) and
driven through a hardware buttons/joysticks control board.
The basic "on screen" version consists of a functional crane simulation
layered over the Virtual Prototypes as available
from the VENUS website. It could be developed in 6 months at the most.
The "immersive" cabin will be equipped by a real
control board, identical to the wearable radio control desks that will be
used in the pits. Coupled with the use of large stereoscopic screens,
this is the equivalent of a proper high-end vehicle simulator (see picture above). The
crane driver thinks he/she is operating within the real experimental
areas, displacing and assembling objects like in reality. In order to
enhance this feeling of immersion, the Virtual Crane must react like the
real one, considering collisions, weights, elasticity, cable stretch and
hook swing. These features can be implemented progressively, according to the
"implementation plan" below.
The deeper the immersion,
the easier and more realistic will be the manipulations and their
We have no doubts that such a tool will become immediately useful to the
experimental areas assembly planning, even in its earliest phases.
The Virtual Crane will be implemented in the VRML2 (Moving Worlds) and
Java standards. This means that it will be immediately available over Netscape
or Internet Explorer to anybody who wishes to use it. For the later
phases we will need to add some C++ modules, particularly for joystic
and large screen drivers. This means that the "on screen" version will be
independent (although its usability in a geometry crowded environment will
greatly depend upon the host's 3D graphics performance) whereas the
"immersive" simulator must be implemented upon a powerful graphic
processor (eg. SGI Onyx2 InfiniteReality).
speaking, the user will be able to play back the animations over the web satisfactorily
on most PowerPC equipped Windows or Mac platform,
or modern UNIX workstation, whereas to run the simulator with a likely feel of
immersion you will
need a very fast interactive response, hence an Onyx.
The Virtual Crane can be implemented in three phases:
- Phase 1: "on screen" crane simulation
As said above, this implementation phase is relatively easy and it will allow
exploring immediately the first and basic assembly strategies. It will use
essentially VRML2 scripts for the functional simulation, and JAVA
scripts to represent a button/sliders virtual control board outside the 3D window.
This allows free navigation without the risk of "loosing" the control board
in the Virtual environment. Navigation will be restrained essentially to
the metaphore offered by the local 3D browser. Adaptation of i3D to VRML2
(already started by JF. Balaguer before leaving) will allow
the use of a Spaceball and stereoscopic glasses. Apart from the basic
crane movements, this phase will feature:
- interactive path recording, playback and editing
- hook collision and grab/release
- floor recognition
- objects stacking by bounding box
Manpower estimate: 6 man/month (tech. student) + 10 days consultancy
- Phase 2: physical behaviour
This phase consist mainly of a dynamics and kinematics study. Objects in
the database will be assigned physical properties, such as as weight and
elasticity. The crane cable stretch, bounce and pendulum will also have to be
computed interactively. Finally we should consider multipoint force and
momentum, to cope for natural and controlled rotations and swing. This
will push the Virtual Crane into a barely explored field, as most
CAD simulation packages (CATIA, Robcad, Megavision) today are limited to
simple inverse kinematics. Work in this field should be done by an
expert of dynamics and IK simulation.
should be a one or two year fellowship. Most likely he/she will use and extend
an existing collision detection toolkit, then plug the results of calculations
into the VRML2 graphic interface.
This phase is independent, therefore
can be overlapped at any time with phase 3.
Manpower estimate: 18 man/month (fellow or associate) + 18 days consultancy
- Phase 3: immersive cockpit
Probably the best way to implement this effectively is to contract it to
a specialized company. Technology in this field is very well advanced,
and interfacing any sorts of joysticks, buttons, sliders etc. to a
computer is no longer a matter of alchemy. The same goes for large
screens, stereoscopic or not. Developing an immersive cockpit may take a
specialist a couple of months.
Manpower estimate: contract
- Robots and Teleoperations
At this point we have a flexible tool, consisting of cabin that "moves"
within the LHC experimental areas, even before we start digging the
pits. Sitting in this cabin we can control the bridge cranes through a
natural interface, and create assembly strategies for each part of the
LHC detectors. These "strategies" are recorded as a path disk files, which can
be associated to VENUS' VRML Virtual Prototypes, therefore they
can be played back on any computer on the planet. All this is very useful to
LHC engineers, for the assembly planning and space management, to the collaboration
members, to "watch" their detector being put together, and finally to the crane
drivers to train to do their job in a realistic environment. But this is not all.
By pushing the project a little bit further, we could at this point capitalize on
the work done so far, using these precomputed paths to
actually drive the real cranes.
- Real time vs delayed teleoperation
the analog era, robots could be driven in real time using mechanical
arms that could sense the pilot's arm and hand movements and replicated
them by the robot. Alternatively, robots could be programmed to repeat a
certain movement. The first technique (telecontrol) has been used mostly for
interventions in hostile envirments, the second (programming) was usually
destined to a production chain. However "often robotics has failed to
meet industry expectations because programming or telecontrolling robots is
tedious, requires specialists and often does not provide enough real
flexibility to be worth the investment.
Virtual Reality has introduced a totally new way of using robots. By the
intermediate of a Virtual Prototype, the operator only works on
graphic representations of objects, using "Virtual Tools".
The action performed in the Virtual Environment, is then transitted
on line (Telepresence) or after validation
(Delayed Teleoperation) to a robot, which is programmed
automatically as a byproduct
of using the Virtual Tool. The result is the elimination
(or at least minimization)of the human
error factor from the construction budget.
- The human factor
This does not mean elimination of the
human, but just laying a safety net under him/her.
By driving the bridge cranes via paths tested in the
simulator, we will reduce considerably the manouvering risks. Instead of
handling manually extremely fragile and expensive magnets, often through complex
manouvers, which sometime involve more than one crane, the crane drivers
could do all the work in the simulator, then let the computer operate the real crane.
Human drivers will be there during the real assembly, but they will
carry the much lighter responsibility of a START/STOP button.
- Technology Transfer
The Virtual Crane is undoubtely an extremely appealing product to a
crane manufacturer. The ability to simulate "in vitro" hazardous
manouvers, to be later performed in real life by a computer with its
digital precision, is a major argument, and could make a real marketing
difference. It is quite likely that we will find partners and collaborations
within the heavy transport industry. Third party or European funding is
also very probable.
The project presented in this paper is consistent and general. Its technology
is available, acquired and mature for implementation.
Like machines have replaced tedious, heavy or hazardous manual work in
industrial environments, simulators are today being used to program
these machines effectively and safely. Effectiveness and safety are the two
major keys to the successful assembly of the LHC experimental halls. The
Virtual Crane implements both.
 Cannon DJ. & Thomas Geb - Virtual Tools for Supervisory and
Collaborative Control of Robots. Presence Vol. 6, No 1, Feb 1997, 1-28.
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Comments and suggestions
Last update June 12, 1997.
This document is available from http://www-venus.cern.ch/VENUS/virtual_crane.html