E-Journal of Advanced Maintenance Vol.7-2 (2015) 145-153
Japan Society of Maintenology

Development of an Augmented Reality Based Simulation System for
Cooperative Plant Dismantling Work
Hirotake ISHII1,*, Zhiyuan MAN1,†, Weida YAN1,††, Hiroshi SHIMODA1 and Masanori
IZUMI2
1

Graduate School of Energy Science, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto
606-8501, Japan
2
Fugen Decommissioning Engineering Center, Japan Atomic Energy Agency, Tsuruga, Fukui,914-8510, Japan
ABSTRACT
An augmented reality-based simulation system for cooperative plant dismantling work has been developed andevaluated. In the system, behaviors of virtual objects such as the dismantling target, chain blocks, and trolleys
are physically simulated. Their appearance is superimposed on camera images captured with cameras on users’
tablet devices. The users can manipulate virtual objects cooperatively via touch operation. They can cut thedismantling targets, lift them on the trolleys using chain blocks, and convey them through narrow passages toascertain whether the dismantling targets can be conducted without colliding with the passages. During thesimulation, collisions between the virtual objects and real work environment are detected based on theirthree-dimensional shape data measured in advance. The collided parts are visualized using augmented reality
superimposition. Four evaluators assessed the simulation system. Results show that the simulation system canbe useful for prior examination of dismantling works, but some points were also found to need improvement.
KEYWORDS

ARTICLE INFORMATION

Decommissioning, Physics simulation, Three-dimensional scanner, Point
cloud, CSCW

Article history:
Received 4 November 2014
Accepted 3 June 2015

1.

Introduction

Nuclear power plants that have completed their operational lifetime must be decommissioned
safely. Such dismantling work must be completed by many workers in narrow spaces. The work often
includes dangerous tasks such as conveyance of heavy objects using cranes. Therefore, producing awork plan carefully and conducting sufficient training are important. Especially when dismantlingwork is conducted by multiple workers, it is necessary to decide how the work is divided and how thedivided work is conducted cooperatively. However, it is difficult to decide and share the cooperative
work plan appropriately because the nuclear power plant is a complicated work environment.
Moreover, the cooperative work procedures are much more complicated than those of the solo work:
workers must understand not only each work step but also the timing of the work because some tasks
must be conducted simultaneously with other workers.
Currently, dismantling work is planned and evaluated mainly referring the past records of thesimilar works [1][2]. Institute of Energy Technology proposed a system called the Halden Planner,which is useful to evaluate dismantling works using virtual reality technology [3]. With this system,
cooperative dismantling work can be planned and visualized using 3D computer graphics. The amountof radiation exposure can be estimated for each worker. The system is actually used to make a plan for
dismantling work, but it cannot be used on-site. It must be used in an office, which means that thefield workers must associate objects appearing in the plan with real objects in a real environment
during the work. This association sometimes fails and might even lead to incorrect operations.
*

Corresponding author, E-mail: hirotake@ei.energy.kyoto-u.ac.jp
Present address: Panasonic Corp. Eco Solutions Company, 1048, Kadoma, Osaka 571-8686, Japan††
Present address: NTN Corp., 1-3-17 Kyomachibori, Nishi-ku, Osaka 550-0003, Japan†

ISSN-1883-9894/10 © 2010 – JSM and the authors. All rights reserved.

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Based Simulation System for Cooperative Plant Dismantling Work

Augmented reality (AR), an interface design scheme, is applicable to realize intuitive system forprior investigation and training for the dismantling work [4]. In this design scheme, users’ views aresuperimposed with three-dimensional (3D) computer graphics of virtual objects aligned with the real
work environment to make the users feel that the virtual objects exist in front of them. Using thisdesign schema, it becomes possible to present the 3D position and orientation in an intuitive manner,which reduces human error and the time necessary for a task.
For this study, the authors developed an AR-based simulation system with which the workers caninvestigate dismantling work on-site to assess whether a dismantling target can be located in a small
space and be conveyed through a narrow passage without colliding with the surroundings. The
system’s unique characteristic is that the multiple workers can use the simulation systemsimultaneously and can conduct the dismantling simulation cooperatively to share the dismantlingwork image. It is expected that the system is useful for both prior investigation and training for thedismantling work.
The remainder of the paper is organized as follows. In Section 2, the developed system
configuration is described with subsequent details of the 3D scanner for obtaining 3D shape data used
for the dismantling simulation, and the user interface of the cooperative simulation system with which
the workers can conduct dismantling simulations cooperatively in a real work environment. Section 3
presents a description of a subjective evaluation conducted to evaluate the acceptance of thedeveloped system and to ascertain points that demand improvement. Finally, the study is summarized
and future works are described in Section 4.

2.

Developed System

2.1. Design requirements
Design requirements (DR) of the developed system were decided based on interviews of theworkers employed at the Fugen Decommissioning Engineering Center, which has a retired nuclear
power plant in its preliminary dismantling stage, as shown below:
DR1
It is possible to understand the current situation of a dismantling target and equipment
such as chain blocks.
DR2
It is possible to understand the current situation of work environment.
DR3
It is possible to place virtual equipment easily in a real work environment.
DR4
It is possible to move virtual equipment easily in a real work environment.
DR5
It is possible to conduct special operations for equipment such as pulling chains.
DR6
It is possible to understand positions where a virtual dismantling target and equipment
collided with the surrounding real environment.
DR7
It is possible to support cooperative work by multiple workers.
DR8
It is possible for workers to recognize all workers’ operations.
DR9
It is possible to cancel and redo operations.
DR10 It is possible to record and play operations.
DR11 It is easy to bring to and from the work environment.
DR12 It is easy for workers to understand how to use the system.
2.2. Configuration of the developed system
As depicted in Fig. 1, the developed system consists of a 3D scanner and a cooperative
simulation system. The 3D scanner scans a work environment including the dismantling target. Thenit generates their textured 3D shapes. The 3D shapes are used in the cooperative simulation system bywhich the users can locate and manipulate virtual objects cooperatively to conduct conveyance ofdismantling target virtually in a real work environment.
2.3. 3D scanner
The 3D scanner consists of a 2D laser range finder (LMS100-10000; SICK Inc.), which provides
distance measurements in 2D polar coordinates, a color camera (CMLN-13S2C-CS; Point Grey146

H. Ishii, et al./ Development of an Augmented Reality
Based Simulation System for Cooperative Plant Dismantling Work

Research Inc.), which obtains the appearance of the work environment and a motion base
(PTU-D46-70; FLIR Systems Inc.), which rotates the 2D laser range finder and the camera to realize
an omnidirectional scan to obtain a point cloud representation of the environment. The scan was
repeated at different places in a target work environment. Their scans are integrated using an Iterative
Closest Point (ICP) algorithm to reduce the unscanned area caused by occlusion. Then a point cloudthat corresponds to a dismantling target is abstracted manually using a GUI software tool. Polygon
models (3D shapes) of the dismantling target and the work environment are generated using Delaunay
triangulation. Textures for the dismantling target are also generated using the images obtained using
the camera. The 3D shapes and the textures are used to show the current position and orientation(pose) of the dismantling target during the simulation. The 3D shapes are also used to detect collisions
between the real work environment and the dismantling target, and to calculate its motion using thephysics simulation. Physical properties of the dismantling target necessary for the physics simulationsuch as the weight and friction coefficient are set manually in advance.
The accuracy of the generated 3D shapes depends on the work environment complexity and the
distance separating the scanner and the work environment. When the 3D scanner was used to scan awater purification room in the Fugen Decommissioning Engineering Center, which includes several
cylinder tanks and many pipes, the maximum error was approximately 0.2 m when the average
distance between the 3D scanner and the environment was about 3 m.
To simulate the complete behavior of the dismantling target, it is necessary to ascertain theaccurate shape, weight distribution, and coefficient of restitution of the dismantling target and work
environment. However, the obtained shape of the dismantling target and work environment using the
3D scanner invariably contains some errors. It is difficult to ascertain the accurate weight distribution
and coefficient of restitution because the special knowledge and equipment are necessary to measurethem. Moreover, it is also difficult to conduct an accurate simulation because it requires muchcomputational power. Therefore, in this study, models which contain errors are used as it is, and it isassumed that the weight distribution and coefficient of restitution are uniform. Accordingly, thesimulated behavior of the dismantling target is definitely an approximation. However, it will be
sufficient if the worker can observe the rough movement of the dismantling target for priorinvestigation of the dismantling work.
2.4. Cooperative simulation system
Functions implemented in the cooperative simulation system were chosen based on an interview
of the workers employed at the Fugen Decommissioning Engineering Center.
The cooperative simulation system forms a server-client structure to enable employment oflightweight devices as client’s hardware by a load distribution. The server (MacBook Pro 15 inch
Early 2011) collects information from clients via a wireless network such as the current pose of eachclient and operations made by users, then conducts heavy calculations such as a physics simulationand collision detection between the dismantling target and the work environment. For the physics
simulation, Bullet Physics library [5] was used. Clients (iPad2 Wi-Fi 16GB) obtain the current pose of

Fig. 1. Configuration of the developed system.

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H. Ishii, et al./ Development of an Augmented Reality
Based Simulation System for Cooperative Plant Dismantling Workthe dismantling target, other clients’ poses, and collided parts on the dismantling target and the work
environment from the server. The client’s camera captures the work environment and estimates thecurrent pose of the client using a marker-based tracking method [6]. Markers are pasted in advance inthe work environment and are thereafter measured by the Marker Automatic Measuring System [7].
Fig. 2 depicts the client interface of the cooperative simulation system. The interface consists of acamera view, object icons and a room top view. The user operates the interface via touch operation.
The camera view shows live images captured with a client’s camera. Virtual objects such as thedismantling target, chain block, and trolley are superimposed on the image according to the estimationof the client’s camera pose so that the users can feel that these virtual objects exist in front of them.
The collided parts of the dismantling target and the work environment are also superimposed on theimage (collided parts of the dismantling target and the work environment are painted, respectively,
with blue and red) so that the users can ascertain whether the dismantling target collides with the work
environment.
The room top view shows a bird’s eye view of the work environment, by which the user canrecognize a positional relation among the work environment, virtual objects, and other users.
The object icons are used to place virtual objects such as a chain block, trolley, and tripod in thework environment. The users drag and drop the icon from the icon list to the room top view. The
chain blocks are attached to the ceiling and used to lift the dismantling target up and down. The
tripods are used when a ceiling is not available for fixing a chain block. In this system, another chain
block is attached at the top of the tripod in advance. The heights of the chain block and the tripod
were set in advance as the default. The users can choose virtual objects by tapping the icon on theroom top view. The chosen icon’s color is changed to enhance the selection. The chosen object can be
moved using the buttons which appear when a movable object is chosen on the room top view.
After the user chooses a chain block, a chain can be connected to the dismantling target bytapping a location at which the user wants to connect on the camera image. When the user chooses a
chain block that is already connected to the dismantling target, a slider bar appears on the side of theinterface. The user can pull and loosen the chain by sliding the bar to lift the dismantling target up anddown. The dismantling target can be conveyed with the trolley. The users lift the dismantling target
using chain blocks over the trolley, put it down on its side, and convey to the objective location. All
the behaviors of the virtual objects are simulated using the physics simulation. It is also possible toundo, redo, record, and replay the operations using the function buttons displayed on the interface.

3.

Preliminary Evaluation

3.1 Objective
The system is expected to be useful. However, it remains unknown how acceptable the developed
system is for actual field workers, and what problems arise in practical use. An evaluation experiment
was conducted to answer these questions.

Fig. 2. Client interface on a tablet device.

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3.2 Method
In the experiment, only the cooperative simulation system was evaluated. The system wasassessed by four evaluators (two Fugen nuclear plant decommissioning workers (Evaluators A and B),
one regular plant worker (Evaluator C), and one human interface expert (Evaluator D)). The
evaluation was conducted in an experimental room (4 m × 6 m) in which some obstacles were locatedto simulate the complicated characteristics of the actual work environment. The results might bedifferent from the results that will be obtained if the evaluation is conducted in a real dismantlingwork environment, but the results obtained in this simulated environment are expected to be useful for
future improvement.
The evaluation was structured along the following steps.
1. An experimenter explained how to use the system for about 40 min (including practice).
2. Evaluators used the system along with a scenario for about 50 min.
3. Evaluators answered a questionnaire mainly related to the usability of the system.
4. A group interview was conducted to ascertain reasons underlying the questionnaire responses.
The evaluators were asked why they gave the response for every questionnaire item.
Four evaluators formed one team and used the simulation system simultaneously. Evaluator B
was designated as the team leader. The three other evaluators played roles of regular workers. The
scenario was constructed so that all system functions were used. The scenario was as follows.
Step 1. All regular workers place a chain block around the dismantling target according to thedirection of the leader. In all, three chain blocks are placed.
Step 2. All regular workers attach a chain on the dismantling target.
Step 3. Cut the base of the dismantling target and put the dismantling target down on its side byoperating the chain cooperatively.
Step 4. The leader moves a trolley to the side of the dismantling target.
Step 5. Lift the dismantling target on the trolley using the chains.
Step 6. Detach all chains.
Step 7. Convey the dismantling target to the objective place by moving the trolley.
Step 8. Repeat steps 1-7 above. This time, tripods are placed instead of chain blocks.
The evaluators were asked to use the undo, redo, record, and replay functions occasionally.
3.3 Questionnaire and Results
The questionnaire includes 32 items for system function and usability. The questions were
designed to evaluate whether the design requirements explained in section 2.1 are fulfilled or not.
Evaluators answered each questionnaire item as 1–5 (1. completely disagree; 2. disagree; 3. neither
agree nor disagree; 4. agree; 5. completely agree). In addition, a free description was added to the endof the questionnaire. Respondents described other problems and points to be improved.
For the function and usability of the simulation system, positive responses were obtained such as“The interface is easy to understand.” and “The simulation system is useful to examine work
procedures.” Table 1 shows the questionnaire items to which all evaluators answered with a response
4 or 5. However, some questionnaire items elicited negative responses. Table 2 shows questionnaire
items to which at least one evaluator answered with a response worse than 4. The indication (DR--) at
the end of each question shows the design requirements which are intended to be evaluated.
The reasons each questionnaire item in Table 2 did not get a 5 response were investigated withthe free description and the interview.
Evaluator B gave response 3 to Q20, 22, 24, and 26–31. Evaluator B explained that he gave these
responses because he was assigned to be a leader and has few chances to use functions related to thesequestionnaire items. Therefore, he could not offer a judgment. Evaluators A, B, and C gave responses
3 and 4 to Q1. They commented that the captions of some buttons were not easy to understand.
Evaluators A, C, and D respectively gave response 2, 3, and 4 to Q8. Evaluator A was unable torecognize who placed the equipment. Evaluators C and D were unable to recognize what and where
the other workers were going to place. Evaluator D gave response 3 to Q12. He commented that hehad difficulty when trying to choose one object from an object cluster. Evaluators B and D
respectively gave responses 3 and 4 to Q15. Evaluator B wanted to rotate the equipment with smaller149

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Based Simulation System for Cooperative Plant Dismantling Work
Table 1 Questionnaire results to which all evaluators responded 4 or 5

EvaluatorA B C D
Q2 It is easy to recognize the 2D position of the dismantling target by watching the 5 4 5 5bird’s eye view. (DR1, DR2)
Q3 It is easy to recognize the 2D position of the chain block by watching the bird’s 5 4 5 5eye view. (DR1, DR2)
Q4 It is easy to recognize the 2D position of the tripod by watching the bird’s eye 5 4 5 5view. (DR1, DR2)
Q5 It is easy to recognize the 2D position of the trolley by watching the bird’s eye 5 4 5 5view. (DR1, DR2)
Q6 It is easy to recognize the other workers’ 2D positions and orientation by 5 5 4 5watching the bird’s eye view. (DR2, DR7)Q7 It is easy to place the equipment such as chain blocks on the bird’s eye view. 5 5 5 4(DR3)Q9 It is easy to understand the spatial correspondence between the real environment 5 4 4 4
and the bird’s eye view. (DR2)Q10 It is easy to recognize the position and orientation of 3D models superimposed 4 4 5 4on the camera view. (DR1)
Q11 It is easy to recognize what the 3D models superimposed on the camera view 5 5 4 5represent. (DR1)Q13 Making the equipment green when it is chosen by the other workers is good 5 5 5 5support to recognize it. (DR8)Q14 It is easy to translate the equipment using the bird’s eye view. (DR4)4 4 5 5Q18 It is easy to switch the camera view and the bird’s eye view. (DR2)5 5 5 5Q19 It is effective that the camera view can be posed when connecting the chains to 4 4 4 5
the dismantling target. (DR3, DR5)
Q21 It is easy to enlarge, reduce, and translate the bird’s eye view. (DR2)5 4 5 5
Questionnaire(DR: Design Requirement)
steps. Evaluator D wanted a function to rotate the equipment using a stylus pen instead of using
buttons. Evaluators A and C gave responses 3 and 4 to Q16 and Q17 because they were unable torecognize who was operating virtual objects. Evaluators A and C respectively gave responses 2 and 3
to Q20. Evaluator A sometimes was unable to attach a chain to the intended location. Evaluator C
wanted a function to enlarge the camera image to make it easy to attach the chain at the intended
location more accurately. Evaluators A and C gave response 3 to Q22. It was difficult for them topredict how fast the dismantling target would move when they operated the chain blocks using theslider bar to pull and loosen the chain. Evaluators A, C, and D gave response 3 to Q23 because they
were unable to recognize who operates the chain. All evaluators gave negative responses to Q25 andQ26. They explained that it was difficult to recognize the collided parts accurately. Evaluators A andC gave responses 3 and 4 to Q28 and Q29. They explained that it was difficult to recognize which
operation will be canceled and redone using redo and undo functions.
Whether the system fulfills the design requirements or not was also investigated. DR1 and DR2
were fulfilled because the positive responses were obtained to the questions corresponding to DR1
and DR2 as shown in Table 1. The reason these questions received positive responses will be (1) the
design of bird’s eye view is technically established and easy to be implemented, (2) Augmented
Reality representation (superimposition of 3D computer graphics over camera view) is appropriate torepresent the positional relation between virtual objects and real environment. Because Q7 and Q20

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Table 2 Questionnaire results to which at least one evaluator responded worse than 4

EvaluatorA B C D
Q1 It is easy to identify each button’s function.(DR12)4 3 4 5Q8 It is easy to recognize the other worker’s operation of the equipment. (DR8)2 5 3 4Q12 It is easy to choose equipment on the bird’s eye view. (DR4)4 5 5 3Q15 It is easy to rotate the equipment on the bird’s eye view. (DR4)5 3 5 4Q16 It is easy to recognize the other worker’s operation for translating the equipment. 3 5 4 5(DR8)Q17 It is easy to recognize the other worker’s operation for rotating the equipment. 3 5 4 5(DR8)Q20 It is easy to connect the chain to the dismantling target on the camera view. (DR3, 2 3 3 5
DR5)Q22 It is easy to pull up and loosen the chain. (DR5)
3 3 3 5
Q23 It is easy to understand the other worker’s operation of the chain. (DR8)3 5 3 3
Q24 Making the chain pink when it is chosen by you is useful to recognize it. (DR5)5 3 4 5
Q25 It is easy to recognize the collided position on the dismantling target by making 2 1 3 4
the collided position blue. (DR6)Q26 It is easy to recognize the collided position on the environment by making the 2 3 3 4collided position red. (DR6)Q27 It is easy to use the button to remove all chains from the dismantling target. 4 3 5 5(DR5)Q28 The function is effective to undo the previous action. (DR9)
3 3 4 5
Q29 The function is effective to redo the undone action. (DR9)
3 3 4 5
Q30 The function is effective to record the current situation. (DR10)5 3 5 5
Q31 The function is effective to replay the recorded situation. (DR10)5 3 5 5
Q32 The system is useful easily even at the first use. (DR12)4 3 4 4
Questionnaire(DR: Design Requirement)
were positively and negatively responded respectively, it seems that placing large objects such as
chain blocks, tripod, and trolley is easy but connecting a chain which requires the operation of small
object is not easy, which means that DR3 is partially fulfilled. Because Q14 was responded positively
but Q12 and Q15 were responded negatively, DR4 is partially fulfilled. As discussed above, it will bepossible to fulfill DR4 by making the step smaller to rotate objects and introducing a new interface tochoose one object from an object cluster. DR5 was fundamentally fulfilled except that it is difficult topredict how fast the dismantling target would move (Q22). DR6 was not fulfilled because Q25 andQ26 responded negatively. Further improvement is necessary to make it easy for the workers torecognize the collided position. For DR7, it was only confirmed that recognizing the other workers’
position and orientation is easy (Q6), but the positive comments such as “I want to use the system forthe real work”, “I feel that it is effective to investigate the conveyance of the dismantling target by
multiple workers” were obtained. Therefore, at least the system is effective to support cooperative
work by multiple workers. For DR8, as discussed above (Q8, Q16, Q17, Q23), it is difficult torecognize who is going to do and what is going to be done. Further improvement is necessary torepresent this information. For DR9, it is necessary to make what will be canceled clearer (Q28, Q29).
DR10 and DR12 are basically fulfilled (Q30, Q31, Q32). For DR11, the portability of the system was
not investigated this time because the evaluation experiment was conducted in the experimental room.
It is necessary to conduct another evaluation in a real plant as future work.

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4.

Conclusion and Future Works

For this study, an augmented reality-based simulation system for cooperative plant dismantlingwork was developed and evaluated. Four evaluators assessed the system. Positive responses wereobtained from the evaluators, but some points were also found to need improvement.
The evaluators commented that it was difficult to recognize the collided parts accurately. The
reason would be that they were unable to move their device freely to see details of the collided parts
because marker-based tracking was used and the superimposed image is apparent only when thecamera captures the markers. A possible improvement for this issue is to use markerless tracking, as
described later, because the markerless tracking method is useful in a larger area than marker-based
tracking is. Another reason is that there is no depth cue to signal the position of the collided parts
because a single camera was used to capture the environment and a monaural image was displayed ona small screen. A possible improvement is to draw shadows of the painted parts to represent theirdepth.
The evaluators requested that the workers’ current situation and intentions be easily
understandable by the other workers. The current poses of the other workers were displayed as abird’s eye view, but it was insufficient to ascertain the other workers’ current circumstances andintentions. A possible improvement is to enable a worker to see other workers’ operational history,
which can be helpful for workers to ascertain the other workers’ circumstances and intentions.
However, the problem is that if the dismantling work is conducted on-site, information of this kind isunavailable. In some cases, they must work without understanding the other workers’ circumstances
and intentions. Even if the system includes a function to show the other workers’ operational history,
it will be better to make it possible to disable the function as necessary.
Some other requests originate from the inaccurate and clumsy tracking of the client devices. The
current system uses a marker-based tracking method to measure camera poses, which is unacceptablefor practical use. Several markerless tracking methods have become available in recent years: PTAM
[8] and LSD-SLAM [9]. These new markerless tracking methods seem promising because they aremuch more stable than conventional markerless tracking methods. However, for actual use, several
issues must be addressed. First, almost all of these markerless tracking methods assume that theenvironment will not change or that only a small part of the environment will change, which is nottrue of a real work environment. If a large part of the environment changes rapidly, then the tracking
becomes unstable very quickly. Second, if the camera view is occluded, then the tracking must be
terminated. It happens frequently when another worker or instrument is moved around the worker. A
possible countermeasure is to use an omnidirectional camera with a 360-degree field of view. The
larger the camera view angle becomes, the more stable and accurate the tracking will be. Moreover, it
will be rare that all fields of view of the omnidirectional camera are occluded by obstacles such asother workers.
After completing these improvements and confirming the effect of the improvements, further
subjective evaluations will be conducted in a real work environment to evaluate the acceptability andthe effectiveness of the developed system.

Acknowledgement
This work was partially supported by KAKENHI (No. 23240016).

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