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THE POTENTIAL OF SMART CLIMBING ROBOT COMBINED WITH A WEATHERPROOF CABIN FOR ROTOR BLADE MAINTENANCE

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The rapid development in the wind energy market is exhausting the capability for upcoming maintenance needs. [1] While the reliability of mechanical parts, e.g. main bearing, generator, gears and main shaft evolved, rotor blade maintenance and improvement turn more and more into focus [2]. Since September 2014 University of Applied Sciences Aachen and industrial partners develop SMART (Scanning, Monitoring, Analyzing, Repair and Transportation) maintenance platform for wind turbines. Ongoing research and development is focused on a prototype, scale one to one for a 2.5 MW plant, including a weatherproof cabin. Employing a weatherproof cabin for rotor blade maintenance extends the annual maintenance period from 8 to 12 month and 3 to 24 hours a day. One challenge for SMART is sealing the cabin top and bottom against the rotor blade surface. Therefore, a complex structure will be attached to cabin bars. The weight of this structure will influence the climbing process.
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ECCM17 - 17th European Conference on Composite Materials
Munich, Germany, 26-30th June 2016 1
J. Schleupen, H. Engemann, M. Bagheri, S. Kallweit
THE POTENTIAL OF SMART CLIMBING ROBOT COMBINED WITH
A WEATHERPROOF CABIN FOR ROTOR BLADE MAINTENANCE
Josef Schleupen1, Heiko Engemann2, Mohsen Bagheri3 and Stephan Kallweit4
1MASKOR Institute, Faculty of Mechanical Engineering and Mechatronics,
FH Aachen University of Applied Sciences, Goethestraße 1, Germany
Email: schleupen@fh-aachen.de, Web Page: http://www.fh-aachen.de
2MASKOR Institute, Faculty of Mechanical Engineering and Mechatronics,
FH Aachen University of Applied Sciences, Goethestraße 1, Germany
Email: engemann@fh-aachen.de, Web Page: http://www.fh-aachen.de
3Faculty of Mechanical Engineering and Mechatronics, FH Aachen University of Applied Sciences,
Hohenstaufenallee 6, Germany, Email: bagheri@fh-aachen.de, Web Page: http://www.fh-aachen.de
4MASKOR Institute, Faculty of Mechanical Engineering and Mechatronics,
FH Aachen University of Applied Sciences, Goethestraße 1, Germany
Email: kallweit@fh-aachen.de, Web Page: http://www.fh-aachen.de
Keywords: SMART, robot, maintenance, climb, rotor blade, wind turbine
Abstract
The rapid development in the wind energy market is exhausting the capability for upcoming
maintenance needs. [1] While the reliability of mechanical parts, e.g. main bearing, generator, gears and
main shaft evolved, rotor blade maintenance and improvement turn more and more into focus [2]. Since
September 2014 University of Applied Sciences Aachen and industrial partners develop SMART
(Scanning, Monitoring, Analyzing, Repair and Transportation) maintenance platform for wind turbines.
Ongoing research and development is focused on a prototype, scale one to one for a 2.5 MW plant,
including a weatherproof cabin. Employing a weatherproof cabin for rotor blade maintenance extends
the annual maintenance period from 8 to 12 month and 3 to 24 hours a day. One challenge for SMART
is sealing the cabin top and bottom against the rotor blade surface. Therefore, a complex structure will
be attached to cabin bars. The weight of this structure will influence the climbing process. The following
study is analyzing the influences in a pratical test with a 1:3 scaled demonstrator based on motion and
force tracking.
1. Introduction
SMART (Scanning, Monitoring, Analyzing, Repair and Transportation) successfully completed proof-
of-concept milestone by demonstrating the climbing process in December 2015. The SMART
demonstrator (see figure 1), a scaled model by one to three, is based on chain-drives to perform continues
climbing and weighs around 400 kg. The first figure features several QR-Marker for motion tracking.
ECCM17 - 17th European Conference on Composite Materials
Munich, Germany, 26-30th June 2016 2
J. Schleupen, H. Engemann, M. Bagheri, S. Kallweit
Figure 1. SMART Demonstrator (scaled 1:3).
Ongoing research and development is focused on a prototype, scale one to one for a 2.5 MW plant,
including a weatherproof cabin. Employing a weatherproof cabin for rotor blade maintenance extends
the annual maintenance period from 8 to 12 month and 3 to 24 hours a day. SMART increases quality
of inspections and repairs. State of the Art technology for inspection, like ultrasonic- and terahertz-
spectroscopy, X-ray, and thermography, can be established to support the engineers and technicians.
Technology, used during the rotor blade manufacturing process, may be scaled down and integrated into
the platform, too, in order to avoid, expensive and inefficient dismounting of rotor blades for full-
inspection, repair and replacement. The structure and surface of rotor blades is highly complex. Figure 2
shows a SMART modell, scaled 1 to 20, with open sealing at the cabin top and bottom. The sealing is
based on several adjustable disks that can be arranged to fit to the rotorblade. The kinematics of the
modell are re-engineered based on the force and motion tracking of the demonstrator (see subchapter
5. Conlusions).
Figure 2. SMART Modell (scaled 1:20).
Weatherproof cabin
Circular arranged
tracked drives
Wind turbine tower
Rotorblade
Support tracked drive
Cabin arms
ECCM17 - 17th European Conference on Composite Materials
Munich, Germany, 26-30th June 2016 3
J. Schleupen, H. Engemann, M. Bagheri, S. Kallweit
Maintenance processes, like inspection, milling, grinding, bonding and painting require a clean, dry and
warm environment. The cabin construction consists of a carbon fiber multi-disk system combined with
a flexible sealing lip. This system is sealing the rotor blade on a certain height and is able to move up-
and downward with the climbing robot. Inside any technician, eventually without a positive attitude to
climbing high structures, can savely perform quality work. Further research and development is
evaluating the possibilities to employ a cooperative or stand-alone robot system for inspection and repair
duties. Regarding this prospects SMART maintenance platform attempts to meet all industrial needs.
Customization of the platform for special applications, e.g. RBE - rotor blade extensions
(Energiekontor), full-autonomous inspection and turbine tower maintenance, are part of the challenging
development.
The following subchapters focus on the analyses of the climbing process under a loaded condition. The
estimated payload for the one to one prototype will be around 20 % of total system weight. This defines
the goal for the following investigation. In numbers a weight of at least 100 kg must be lifted by the
demonstrator.
2. Motion Analysis of climbing process
The 6D visuell tracking system is based on the ROS (Robot Operating System) tool ar_track_alvar, like
described in [3, 4]. In total eight Markers are attached to the SMART Demonstrator. Four markers are
circular distributed over the main body. They reflect the position of the nearby track drives A1 A4. In
addition four other markers are attached to the extension arm, later referred to as MarkerA MarkerD
(see figure 7). These four markers are mounted in different distances to the main body of the climbing
robot. In a later analysis the height of each specific marker is used to determine the bending occurring
at the extionsion arm, caused by the weight dummy. The weight dummy is mounted in a distance of
2.5 m to the horizontal rotation axes between the extension arm and the main body. The main body is
tracked by four high resolution cameras at 15 fps. Furthermore a camera with a resolution of 1936 x 1216
and an effective fps of 160 is used to track the extension arm.
Figure 3. Marker and weight dummy attached to extension arm.
This setup is used for the following measurements. Figure 1 shows the setup in the laboratory.
A2
A3
ECCM17 - 17th European Conference on Composite Materials
Munich, Germany, 26-30th June 2016 4
J. Schleupen, H. Engemann, M. Bagheri, S. Kallweit
2.1. Bending from initial load case
Experimental analyses of the motion are essential to validate the results based on calculation and
simulation of the robot system. The weight and payload of the weatherproof cabin describes a significant
parameter in terms of the climbing process. To determine the influence a weight dummy of 140 kg is
attached to the extension arm (see figure 1 and figure 3). Figure 4 shows the bending of the cabin arms
at four positions distributed along the arms. The total weight is added seven times in steps of 20 kg. In
multiple test drives the data of a set of 6D force sensors and a 6D visual tracking system will be traced
during the climbing process in the following subchapters.
Figure 4. Initial bending of the cabin arms.
The goal is to implicate the results in the implementation of an advanced controller to reduce slip and
unbalanced forces. In addition the simulation modell of SMART can be verified and compared to the
measurement results. This step is necessary to scale the climbing robot up into a one to one prototype.
Table 1. Measured bending results based on figure 4.
Gw
(kg)
Bending
(m)
DA
DB
DC
DD
20
0.016
0.014
0.009
0.006
40
0.031
0.030
0.018
0.012
60
0.049
0.046
0.031
0.017
80
0.067
0.062
0.042
0.022
100
0.086
0.078
0.055
0.028
120
0.104
0.100
0.068
0.036
140
0.125
0.123
0.082
0.044
The measured bending results displayed in table 1 correlate with the estimated results from FEM
analyses in ANSYS (see figure 5).
DA for Gw = 140 kg
ECCM17 - 17th European Conference on Composite Materials
Munich, Germany, 26-30th June 2016 5
J. Schleupen, H. Engemann, M. Bagheri, S. Kallweit
Figure 5. FEM Analyses of cabin arms (bending scaled 10:1).
The bending in table 1 is measured at distances DA DD to the main body, which correspond to the
mounting points of MarkerA MarkerD. Therefore a force Fw, which represents the weight of the
weatherproof cabin is attached to the traverses. The distance between the main body and the impact
point of the force correlates with the mounting point of the weight dummy.
2.2. Measurement results from motion tracking
Figure 6 displays the height of the four circular distributed track drives during two test drives. The time
depending heights reflect the motion of the main body. The left figure shows a normal lifting procedere
with the current state of the demonstrator. On the right the motion behavior is displayed for a 140 kg
weight dummy attached to the extension arm.
Figure 6. Test drive without load (left) and a weight dummy (right).
3. Force analyses of climbing process
In each drive, a 6D force sensor, K6D68 10kN/500 Nm from ME-Systems, is implemented to measure
the individual lifting force in relation to the orientation of the drive and the normal force. Hence, the
system is based on frictional engaged climbing process, a higher normal force allows higher lifting
forces. The maximum lifting force is limited by the motors torque. This customized sensor can measure
loads of up to 20 kN normal forces. In the current design a ball joint is mounted on top of the 6D sensor.
Payload Fw: 140 kg
Permanent weight
DA = 120 mm
ECCM17 - 17th European Conference on Composite Materials
Munich, Germany, 26-30th June 2016 6
J. Schleupen, H. Engemann, M. Bagheri, S. Kallweit
3.1. Measurment results from force tracking
The following figures show the results, regarding the normal forces, from a climbing process without
load (left) and on the right hand the results with a weight dummy of 140 kg. The normal forces on drives
A4 and A5 raise by 2000 N due to the momentum of the weight dummy. Figure 7 displays the normal
forces with a negative signature. During the climbing process several unlinearities occure due to the
slipping of drives, as discovered from the data of the motion tracking.
Figure 7. Test drive without load (left) and a weight dummy (right)
3.2. Cabin load sensor
Figure 8 shows the load sensor of the cabin bars. The system consist of two traverses, which form an
extension arm. The used traverse model features a low weight in relation to bending and torsion stiffness.
The link between the extension arm and the base body of the climbing robot includes a horizontal
rotation axes. The vertical support of the extension arm is coupled to the climbing robot by use of a 1D
force sensor.
Figure 8. Load sensor for cabin.
ECCM17 - 17th European Conference on Composite Materials
Munich, Germany, 26-30th June 2016 7
J. Schleupen, H. Engemann, M. Bagheri, S. Kallweit
Figure 9. Measurments of the initial load with force sensor.
The measured force depends directly on the momentum acting to the climbing robot. Further research
and development will include the momentum into the control mechanism for the climbing process.
4. Results
The results show that SMART climbing robot can lift a 140 kg payload. The maximum is not reached,
yet. 140 kg payload are 25 % to 540 kg total system weight. The estimated goals for the system are
achieved. This study shows that the mechanism is as efficient as expected. The payload of SMART can
be extended to up to 350 kg regarding the maximum torque of the drives. In addition the tensioning
system must be supported to create a higher normal force and the controller must be adjusted to reduce
slipping. Comparing the results from motion and force tracking during the climbing process shows that
slipping of the drives occurs. Combined with the slipping of the tracked drives the normal forces change
rapidly and cause a non-linear pressure distribution on the wind turbine tower.
Despite the pressure distribution on the tower the slipping also causes an unbalanced weight situation
and vibrations. Vibrations of cabin arms cause an even higher momentum on the turbine tower.
Therefore, a system must be established to compensate the cabin arm vibration to minimum.
The optimization of the tensioning system begins with interface between tensioning system and the
tracked drives in the next subchapter.
5. Conclusion
The kinematics for the SMART modell presented in figure 2 are more complex than in the previous
version, the 1:3 scaled demonstrator (figure 1). SMART is a novel mobile robot design. One application
for this kind of robotic system is maintenance for tower and rotor blades of wind turbines. Giving all
circumstances there are two possible solutions to climb a wind turbine either by employing ropes from
the top, or by frictionally engaged climbing.
Robotic system SMART is a frictionally engaged climbing robot. Such mechanism can be split into two
subsystems. The tensioning system and the climbing system. A tensioning system intention is to provide
the essential normal force for static friction between the tower surface of the wind turbine and the
climbing system. The climbing system can either be intermittently or continuously.
-50
50
150
250
350
450
550
650
750
050 100 150
Force [N]
Time [s]
1D Force sensor for cabin load
Vibrations
ECCM17 - 17th European Conference on Composite Materials
Munich, Germany, 26-30th June 2016 8
J. Schleupen, H. Engemann, M. Bagheri, S. Kallweit
The research of this study shows that the absolut movement of certain key-points during operation of
SMART is hardly predictable. A major reason for this is that the tracked vehicles have no individual
connection to the tensioning system. Instead they are both connected via one single ball joint. Therefore,
instead of having one centre ball joint for a tracked drive, the required degrees of freedom for movement
are represented on both, the left and the right drive, with individual ball joints. Additionally, a joint rod
is implanted to restrict the motion capability and enable the tracked drive for skid-steering
(see figure 10). This development is yet realized for the SMART modell in scale 1:20, only.
Figure 10. Optimization of tracked drive kinematics (scaled 1:20).
The cabin construction must be lightweight and for example consist of a carbon fiber multi-disk system
combined with a flexible sealing lip. This system is sealing the rotor blade on a certain height and is
able to move up- and downward with the climbing robot. Further research and development is evaluating
the possibilities to employ a cooperative or stand-alone robot system for inspection and repair duties.
Regarding this prospects SMART maintenance platform attempts to meet all industrial needs.
The motion and structural analysis show that the climbing process under weight requires an advanced
controller strategy for the tracked drives. The cabin weight causes the drives to slip. Still the system can
take high payloads, but the slipping must be compensated to balance the SMART climbing system
horizontally. On the other hand the bending of the cabin arms is relatively high
References
[1] Global Wind Energy Council (GWEC): Global Wind Statistics 2015, www.gwec.net, 10.02.2016
[2] 2. Deutsche Windtechnik: On- and Offshore Services, www.deutsche-windtechnik.de, 01.03.2016
[3] Wiki: ar_track_alvar, http://wiki.ros.org/ar_track_alvar, Oktober 2015
[4] Robot Operating System, http://www.ros.org/, 2015
Interface for
tensioning-system
Servomotors (2 Nm, 40 rpm)
Batteries (7.4V, 520 mAh)
Ball
joints
Joint rod
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