Research article
Tele-operated climbing and mobile service
robots for remote inspection and mainte nance
in nuclear industry
B.L. Luk and K.P. Liu
Department of Manufacturing Engineering and Engineering Management, City University of Hong Kong, Hong Kong,
People’s Republic of China
A.A. Collie
Climbing Robot Company Ltd, Hants, UK
D.S. Cooke
BOC Edwards, HSM, Burgess Hill, UK, and
S. Chen
Department of Electronics and Computer Science, University of Southampton, Southampton, UK
Abstract
Purpose – Aims to report on the various types of tele-operated mobile service robots for remote inspection and maintenance, especially in the field of
nuclear industry.
Design/methodology/approach – Describes nuclear electric robot operator (NERO), Sizewell A duct inspection equipment (SADIE), Robug-IIs (all leg-
based) and Roboslave (wheel-based).
Findings – That these robots can handle a significant portion of inspection and maintenance tasks in a typical nuclear plant, though, given that they
are primarily tailor-made, they are still too expensive for ordinary industries.
Originality/value – As the interests of health and safety and paramount, this study sees the use of such robots expanding and diversifying,
irrespective of cost.
Keywords Remote handling devices, Robotics, Nuclear technology
Paper type General review
1. Introduction
Inspecti on and maintenance is essential in the nuclear
industry. Failure in carrying out proper maintenance could
increase the chance of accidents which could result in severe
casualty not only inside the nuclear plant but also in the
nearby community. However, it is not easy to carry out such
maintenance tasks since the environments are usually highly
radioactive, and unsafe for human workers to work in such
locations. The usual way of car rying out the inspection and
maintenance task in a hazardous environment is to use long-
reach and fixed-base manipulators. However, the manipulator
will suffer from low payload capacity and relatively large end
point deflection. Also, the installation and the storage of these
long manipulators can be costly. An alternative solution is to
use the mobile service robot installed with appropriate tool
package or manipulator, which can overcome the problems
encountered by the long-reach manipulator.
Over the years, a number of service robots, especially the
climbing ones, have been developed for various applications
(Wang and Shao, 1999; Grieco et al., 1998; Sato et al., 1991;
Bahr and Yin, 1994; Pack et al., 1997; Nishi, 1996; Hirose
et al., 1991; Kroczynski and Wade, 1987; Briones et al., 1994;
Guo et al., 1994; Tso et al., 2000; 2001; Zhang et al., 2001;
Hillenbrand et al., 2001; Sattar et al., 2001). These robots are
mainly engineering prototypes for the purpose of proof of
concept. This paper will report the various types of tele-
operated mobile service robots which are developed by the
authors. They include nuclear electric robot operator
(NERO) series, Sizewell A duct ins pection equipment
(SADIE) series, Robug IIs and Roboslave. These robots are
designed for the remote inspection and maintenance tasks,
especially applied to the field of nuclear industry.
NERO and SADIE are two series of walking and climbing
service robots which have been applied successfully to inspect
two Magnox reactors in the UK. In order to overcome the
The current issue and full text archive of this journal is available at
www.emeraldinsight.com/0143-991X.htm
Industrial Robot: An International Journal
33/3 (2006) 194– 204
q Emerald Group Publishing Limited [ISSN 0143-991X]
[DOI 10.1108/01439910610659105]
194
difficulty in launching these climbing service robots in
confined environments, Robug-IIs, an articulated legged
walking-and-climbing servic e robot, is developed. It is
designed to work in a relatively unstructured and rough
terrain. Practically, it is capable to walk on rough floor, climb
up vertical surface, and perform autonomous floor to wall
transfer. On the contrary, Roboslave is a general-purpose
wheel-based mobile service robot applied to flat floor area.
The distinct feature of Roboslave is being tele-operated by a
pair of hand-held robot end-effector representatives (REERs)
that helps to apply the robot to a nuclear plant for tasks such
as handling radioactive substances, and turning off emergency
valves inside a hazardous area. Human operator performs the
task with the REERs in a safe control room while the remote
robot follows the operator motion and executes the
demonstrated task.
2. NERO series of climbing robots
Magnox type nuclear reactors form the early generation of
commercial nuclear reactors in the UK. In order to extend the
life of an early-built reactor, a non-destr uctive test (NDT)
programme is set-up to inspect part of the reactor pressure
vessel (RPV) at the Trawsfynydd nuclear power station.
Since, the design of this reactor provides only limited access
for engineer ing ser vicing, fixed-base manipulators with
multiple linkages cannot reach all the required areas of the
RPV. As a result, NEROs are designed to carry out various
tasks of the NDT programme. NERO is a pneumatically
driven non-articulated legged vehicle. It uses vacuum gripper
feet to hold on the RPV surfaces. It is originally designed to
assist the installation of additional thermocouples onto the
RPV surface. However, for the later designs of NERO II and
NERO III, they are, respectively , fitted with wire brush and
metal cutter for the preparation of obstacle-free access and
robot movement. For small obstacles, NERO is capable to
step over them, and crawl under low overhangs.
2.1 Design constraints
NERO is designed to work on the outside surface of an RPV.
The RPV is an 18.7 m diameter welded steel sphere structure.
The vehicle has to cope with this curvature and with any local
variations. A cooling hood is situated over the top of the vessel
to direct a flow of cooling air over the crown of vessel
(Figure 1). The gap between the cooling hood and the vessel
is approximately 250 mm (Figure 2). This gap restricts the
heigh t of the mobile vehicle. There are a number of
thermocouples installed on the surface which are up to
25 mm high and which the mobile vehicle is required to step
over. Owing to the prohibited access to the RPV because of
the radiation hazard, the vehicle has to be driven remotely by
an operator at the end of a 100 m umbilical cable. Since, the
RPV surf ace is potentially covered with contaminated
substances, it is an important design constraint that the feet
do not collect loose material in order to allow the operators to
service the vehicle. The surface preparation tools are heavy
and together with the weight of the umbilical power and
communication cable, NERO has to be powerful.
2.2 Mechanical system
All the NERO type of tele-operated vehicles shares the same
basic drive mechanism consisting of two rectangular
structures – a frame and a shuttle. The frame is the outer
moving structure and the shuttle is the inner moving
structure. Each structure carries four specially designed
vacuum gripper feet which are attached onto pneumatic “leg”
cylinders. This arrangement allows the vehicle to step over
25 mm obstacles without the need of excessive headroom. In
order to ensure that the vehicle can be operated on uneven
and rough surfaces, redundancy has been built into the
system. The whole robot can be held onto the surface with
only two front feet or a diagonal pair gripping. Compliance is
obtained by feedback control of the leg cylinder pressures and
also by ball joints between the “leg” cylinders and the gripper
feet.
The translation movement of the structures is achieved by a
double acting pneumatic cylinder. The ends of the cylinder
rods are attached to frame whilst the cylinder body is attached
to a metal plate on the shuttle. This metal plate is connected
to the shuttle rotary centre column. Rotary actuation is
achieved by a further double acting cylinder which is mounted
on the shuttle plate and linked to the shuttle rotary centre
column. Both translation and rotation pneumatic cylinders
are controlled by solenoid valves. A pulse width modulation
method is used to drive the cylinders in a force and position
servo control system. The choice of pneumatic actuation gives
the vehicle the high power to weight ratio and inherent
compliance which has been found essential for climbing
vehicles.
Motion is achieved by sequences of stepping, sliding and
rotating movements. In order to move the vehicle, one
structure will stand with its feet gripping on the surface whilst
the feet of the other structure will be lifted and free to move.
This allows the structure with its feet lifted to rotate or
translate. Movement in the same direction is achieved by
swapping the raised structure with the gripping structure. An
all 8 ft gripping stage is implemented between swapping
gripping structure to ensure maximum safety while walking
on the RPV surface.
In order to avoid picking up contaminated substances from
the surface, the g ripper foot develops its vacuum from a
compress air ejector pump. By reversing the flow, the air
ejector cleans the filter in the foot and at the same time clears
loose material on the surface prior to gripping.
Safety is one of the important considerations in the design
stage of NERO system. The pneumatic control valves are
arranged so that in the event of electrical power failure, the
system will be fail-safe by lowering the vehicle on to the
surface so that it grips with all eight feet in its lowest profile
mode. The pneumatic supply system uses two compressors
and one automatic selection valve to protect the NERO
system from pneumatic supply failure. Wherever possible a
safety wire is taken up to avoid damaging force in the event of
a fall.
Three NERO type vehicles have been built. NERO I carries
a special tape feeder for installing additional thermocouples
(Plate 1). NERO II has a rotating wire brush for removing
loose materials from the RPV surface. NERO III (Plate 2) has
a 1.3HP rotary disc grinder fitted on a swing arm and is
mainly used for removing unwanted studs and welding
splatter from the surface.
2.3 Operational experience
Owing to the limited access to the RPV, all the mobile vehicles
have to enter the void containing the RPV from the four
entrances at the base of the biological shield. Vehicles have to
Tele-operated climbing and mobile service robots
B.L. Luk, K.P. Liu, A.A. Collie, D.S. Cooke and S. Chen
Industrial Robot: An International Journal
Volume 33 · Number 3 · 2006 · 194 – 204
195
be hoisted up around the equator of the RPV before it is
possible to place them onto the RPV surface. The 250 mm
diameter vessel viewing stand-pipe is found suitable for
feeding a steel cable from the charge face to hoist the vehicles.
The umbilical cable of each vehicle is also fed through the
vessel viewing stand-pipe. This arrangement allows the
operator to manoeuvre the position of the umbilical cable
on the RPV surface and reduce the weight of the cables that
the vehicle has to carry. Because of the convenience for
hoisting NERO from this position, the vehicle control stations
are placed on the charge f ace. Since, the radiation level at the
entrance of the void is high, conveyor belts are set-up at each
entrance for transporting the vehicles into the void. Several
ground mo bile vehicles are also used to assist vehicle
launching. Flat metal plates are installed on top of these
ground mobile vehicles and the wall-climbing vehicle is placed
on this plate during launching. The whole unit is then placed
onto the conveyor. Once the ground mobile vehicle is
transported inside the void by the conveyor, it carries the wall-
climbing vehicle to a suitable location inside the void and the
wall-climbing vehicle is then hoisted up onto RPV. Wires are
attached at the rear side of the wall-climbing vehicle. These
wires are also connected to ground mobile vehicles and are
used to manoeuvre the wall climbing vehicles onto the
surface.
Figure 1 Reactor pressure vessel
Figure 2 RPV cooling hood
Plate 1 NERO robot and its control console
Tele-operated climbing and mobile service robots
B.L. Luk, K.P. Liu, A.A. Collie, D.S. Cooke and S. Chen
Industrial Robot: An International Journal
Volume 33 · Number 3 · 2006 · 194 – 204
196
Closed-circuit television cameras and lights are installed
inside the void to monitor all the launching operations.
Cameras can also be inserted through the vessel viewing
stand-pipe. However, all these cameras can only provide
images around the equator area. As soon as the wall climbing
vehicle climbs above the vessel viewing stand-pipe, the
monitoring will solely depend on the on-board cameras
attached to the robot.
Once the vehicle has been launched onto the RPV surface,
there is one operator required to drive the vehicle, one worker
needed to handle the umbilical cable and one supervisor
asked to oversee the operation. All the actions need to be
conducted with extreme care to ensure the safety of the
operations.
3. SADIE series of climbing robots
The SADIE robot is commissioned by Magnox Electric plc to
perform non-destructive testing of various welds on the main
reactor cooling gas ducts at Sizewell “A” Power Station. It has
been determined that a vehicle similar in size
(640 £ 400 £ 180 mm) and concept to NERO will be able
to carry the necessary equipment for the range of tasks
required, including pre-inspection preparation and ultrasonic
weld inspection. The actual robot and its control console are
shown in Plates 3 and 4, respectively. As an important part of
the requirements, the robot is required to climb upside down
at the top of the duct to inspect some of the welds. It is
therefore necessary to develop a force controlled foot change
over sequence in order to prevent the robot from pushing
itself off the duct surface by exerting excessive force.
The welds which required preparation and inspection are
RC24, RC25, RC26, SC12, M1, L1 and L2. These are
shown in Figure 3.
3.1 Grinding application
During the initial design of the SADIE robot, it has been
identified that some of the welds which require inspection are
obscured by ladder brackets. As a result, SADIE is required to
carry a specially designed grinding package to remove those
ladder brackets. Since, the ducts are connected directly to the
reactor core, it is essential that the ladder brackets should not
be allowed to fall down the duct to endanger the reactor. A
special grab mechanism is therefore incorporated on to the
cutting tool for recovering the cut ladder-brackets. A
schematic drawing is shown in Plate 5.
The ladder bracket removal package (LBRP) is mounted on
the front frame of the vehicle and consists of two main
elements – an air powered disk grinder mounted on a cross-
Plate 2 NERO III
Plate 3 SADIE robot and its tool packages
Plate 4 SADIE control console
Tele-operated climbing and mobile service robots
B.L. Luk, K.P. Liu, A.A. Collie, D.S. Cooke and S. Chen
Industrial Robot: An International Journal
Volume 33 · Number 3 · 2006 · 194 – 204
197
feed mechanism, and a pneumatically ope rated g rab
mechanism.
The grinding tool and the cross-feed mechanism are hinged
on the axis of the cross feed. A pivot allows the grinding tool
and the cross feed to rotate on the cross feed axis. These
degrees of freedom allow the grinder to follow the curves in
the duct, providing compliance with the contours of the
surface. This compliance is stabilised by ball transfer units on
either side of the grinder disk and a centrally positioned
pneumatic cylinder applying a steady force ensuring the
transfer balls stayed on the surface. The pneumatic cylinder
also provides lift to allow the grinder to be raised off the
surface when manoeuvring into position. The cross feed is
driven by a force controlled pneumatic cylinder.
The grab mechanism is positioned above the cross feed.
The ladder bracket is held in a U bracket with a spring return
piston actuating a bolt through the hole in the ladder bracket.
The arm is actuated using additional pneumatic cylinder s to
provide a lift/lower and extended/retract functions.
The mechanism uses a camera for primary observation and
micro-switches to indicate the ends of the cross fed travel.
The cross feed actuators utilises a differential pressure sensor
to provide force sensing.
To allow more than one ladder bracket to be removed per
deployment a ladder bracket box is designed. This box is
mounted on the deployment scoop. Its design incorporates a
hinged lid which is kept shut with a spring. The lid traps the
ladder bracket within the box.
3.2 Non destructive testing application
To inspect the welds ultrasonic scanning is used. An
inspection tool has been designed by Magnox Electric for
SADIE which could carry the ultrasonic transducers. An array
of sensors are used in what is known as the probe pan. The
probe pan uses a gimbal joint to ensure a good contact with
the surface and it scans across the weld by a servo controlled
linear axis mounted across the front of the vehicle.
The probe pan contains a system for squirting ultrasonic
couplant around the transducers so that good quality signals
are produced. The ultrasonic couplant is a water-based gel to
avoid the need for cleaning the gel after the inspection.
3.3 Deployment
A major part of the operation is the deployment of the vehicle.
A specially designed deployment system is constructed which
comprises of a framework and a radiation containment unit.
This car ries the vehicle deployment scoop, deployment cable
and its associated winch and the umbilical management
system. The vehicle deployment scoop is a four-sided box
structure, on which the vehicle is positioned prio r to
deployment. Its angle is controlled by a winch drive and cable.
The vehicle is placed on the deployment scoop and the
vacuum is applied to the gripper feet. Having moved the
frame towards the duct, the platform and vehicle are inserted
through the duct access port and when the appropriate
position is reached, the platform will be rotated to a vertical
axis. The vehicle is then either be driven off or lifted off
(having first removed the gripper feet vacuum) by the
umbilical/retrieval wire onto the landing zone, at the sloping
surface of the duct bend.
Retrieval is a reverse of this sequence, driving the vehicle up
the duct until it is positioned on the scoop. Vacuum is then
applied to cause the vehicle to attach itself onto the plate. A
rotation of the scoop when it reaches the man door is
executed to allow retrieval of the vehicle.
Figure 3 Sizewell “A” air cooling duct
Plate 5 Ladder bracket removal tool package
Tele-operated climbing and mobile service robots
B.L. Luk, K.P. Liu, A.A. Collie, D.S. Cooke and S. Chen
Industrial Robot: An International Journal
Volume 33 · Number 3 · 2006 · 194 – 204
198
