Research Article: Open Access

VIBGYOR

International Journal of

Robotic Engineering

Development of Magnetic Bridge Inspection
Robot Aimed at Carrying Heavy Loads
ISSN: 2631-5106

Yodai Matsumura1, Takehiro Shiba2, Satoshi Ito1, Yuya Kawase1 and Yogo Takada1*
1Department of Mechanical and Physical Engineering, Osaka City University, Japan

2

Industrial Measurement Co., Ltd, Japan

Abstract
This paper presents a bridge inspection robot capable of traveling on inner right-angled paths.
Locomotion of the newly developed robot is achieved via two motor-driven wheels that arecomposed of steel yokes, acrylic plates, and neodymium magnets. When the wheel contacts
a steel plate, it forms a magnetic circuit and generates a strong force. Owing to this force, therobot can move with heavy objects attached. However, when the wheels strongly adsorb on
two surfaces at right-angled junctures, the robot becomes unable to move. To peel the wheels
away from one surface, a mechanism is needed to eliminate the strong magnetic force. To
achieve this, the robot has been equipped with a pushing mechanism that allows for travel on
any inner right-angled path. In this study, the performance of the robot was tested on a steel
box that imitated a box girder. The robot was able to carry heavy objects, and it also showed
an ability to travel along paths that included a right-angled juncture by utilizing the pushingmechanism.

Keywords
Mobile robot, Bridge inspection, Magnetic robot, Pushing mechanism, Two-wheel drive robot

Introduction
In recent years, infrastructure, such as bridges andtunnels, has been aging in Japan. Most of these structures were built during periods of economic growth,
but more than 50 years have passed, which is equivalent to the useful lifespan of most bridges [1]. Therefore, it is necessary to take measures against the aging of these structures [2]. As one of those measures,periodic inspections have been conducted to find andrepair minor damage early [3]. However, this is a costly and time-consuming process that also carries therisk of workers falling from high places. Therefore,
inspections using robots, which lower costs and improve safety, have been attracting attention.
Various robots have been developed to inspect
steel bridges [4-9]. Most of these robots can carryout these inspections while loaded with heavy objects such as cameras and other inspection equipment since they can absorb to bridges via a strong
magnetic force. However, they can examine only asmall portion of the desired inspection area, suchas flat sections or deck sections.

*Corresponding author: Yogo Takada, Department of Mechanical and Physical Engineering, Osaka City
University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka-shi, Osaka, 558-8585, Japan
Accepted: September 18, 2018; Published: September 20, 2018
Copyright: © 2018 Matsumura Y, et al. This is an open-access article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium,provided the original author and source are credited.
Matsumura et al. Int J Robot Eng 2018, 3:010
Citation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010

ISSN: 2631-5106 |Matsumura et al. Int J Robot Eng 2018, 3:010

We have designed and built various magnetic
robots that can inspect a variety of areas [10,11].
These robots can travel on complex three-dimensional paths because they are equipped with magnetic, rimless wheels. The special-shaped wheel
generates a sufficiently large frictional force between itself and the wall surface when it rotates.
As a result, robots such as BIREM-III have exhibited high performance on paths that include inner
right-angled junctures, which imitate the three-dimensional environment of bridges.
However, since these robots have poor loading ca-• Page 2 of 10 •pability, inspection equipment such as cameras andsensors that they can be equipped with is limited.
Therefore, in this study, we aimed to develop amagnetic bridge inspection robot capable of carrying heavy payloads. We confirmed that the robot
was able to travel on paths similar to those found ona bridge, including those with right-angled junctures.

Materials
Figure 1 shows the photograph of the robot wedesigned, Figure 2 shows its structure, and Table 1
shows its specifications. The robot has four main
components: Two front magnetic wheels, a rearmagnetic wheel, a pushing mechanism for peeling the front wheels away from a steel surface at aright-angled juncture, and an arm mechanism supporting the rear wheel.

Front magnetic wheel
A magnetic bridge inspection robot needs totravel on inspection paths with sensors to findcracks or corrosion points. Therefore, its wheels
should be capable of generating a strong adherence force.
Table 1: Specifications of the magnetic-wheeled robot.

Front wheel
Motor

Pushing mechanism
Motor

181 mm
245 mm125.5 mm
118 mm1.75 kgf
44 mm/s

Front wheel

Rear wheel

Rear wheel

245 mm

Arm mechanisma) Front view125.5 mmFigure 1: Photograph of the magnetic-wheeled robot.

LengthWidth
HeightFront wheel diameter
WeightSpeed

181 mmb) Side view

Figure 2: Construction of the magnetic-wheeled robot. a) Front view; b) Side view.
Citation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010

ISSN: 2631-5106 |Matsumura et al. Int J Robot Eng 2018, 3:010

MagnetSignificant leakage ofMagnetSS

Significant
magneticleakage
flux ofmagnetic flux

NN

Minimal leakage ofmagnetic flux

MagnetFe

Fe
MagnetS Fe N Fe• Page 3 of 10 •Minimal leakage ofmagnetic flux

S N

Steel floor

Steel floor

Steel floor

Figure 3: Magnet without yoke adhering to a steel
floor.

Acrylic plate

Steel floor
Figure 4: Magnet with steel yokes adhering to a steel
floor.

MagnetSteel yokea) Illustrationb) Photograph

Figure 5: Construction of the front magnetic wheel. a) Illustration; b) Photograph.

The adherence force generated by a magnet increases as the number of lines of magnetic force
passing through the attracting surface increases.
When a magnet contacts a steel plate, most of themagnetic flux passes through the air, and only a portion of it passes through the plate (Figure 3). This
indicates that the magnetic flux leakage is large. To
generate a strong attractive force, it is necessary to
reduce this leakage.
One of the methods for reducing this leakage
is to sandwich both the left and right sides of themagnet between steel yokes. This causes morelines of magnetic flux to pass through a steel plate(Figure 4) because the permeability of steel is higher than that of air [12]. Therefore, the amount ofleakage flux decreases, and the magnet generates
a strong attractive force.
The front magnetic wheel is composed of twen-ty permanent magnets, a pair of steel yokes, andan acrylic plate (Figure 5). The magnets are ringshaped neodymium magnets with an outer diameter of 12 mm, an inner diameter of 3 mm, and a
thickness of 5 mm. The steel yoke is a ring made ofSS400 with an outer diameter of 118 mm, an innerdiameter of 104 mm, and a thickness of 5 mm. The
acrylic plate is used to arrange the magnets only atthe outer peripheral part, which makes its adherence force stronger while maintaining its weight.
To measure the adherence force of the magnetic wheel, an experiment was conducted. Figure 6
shows the experimental equipment. It is composedof a pre-painted steel plate (thickness 2 mm), a digital force gauge FGP-50 (Nidec-Shimpo Corporation,
Kyoto), and a magnetic wheel (Figure 6a). The measurements were carried out in the following procedure. Firstly, the magnetic wheel was placed in the

Citation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010

ISSN: 2631-5106 |Matsumura et al. Int J Robot Eng 2018, 3:010

Force gauge

Magnet wheel• Page 4 of 10 •Pull upward
0.00

StringSteel platea) Experimental systemb) Steel plate

Figure 6: Environment of the measuring adherence force. a) Experimental system; b) Steel plate.

Steel yoke

MagnetAcrylic platea) Illustrationb) Photograph

Figure 7: Construction of the rear magnetic wheel. a) Illustration; b) Photograph.

inner region of the masking tape of the steel plate
placed on the floor (Figure 6b). Secondly, the string
attached to the wheel was pulled vertically upwardwith a force gauge and the wheel was peeled offfrom the steel plate. Then, the peak value of theforce gauge was recorded. The experiment was
conducted ten times. Then, the value obtained bysubtracting the wheel weight from the average value was used as the adherence force. As a result,
this wheel exhibited a magnetic adherence force of
173.5 N with a mass of only 0.391 kg.

Rear magnetic wheel
The rear magnetic wheel is composed of a permanent magnet, a pair of steel yokes, and an acrylic plate (Figure 7). The magnet is a ring-shaped neodymium magnet with an outer diameter of 25 mm,
an inner diameter of 19 mm, and a thickness of 5mm. The yoke is a ring made of SS400 with an outer
diameter of 45 mm and a thickness of 5 mm. The

Magnetic wheel

Wall
µFmag

Fmag
Right-angle
Floor

Fmag

µFmag

Figure 8: Dynamic model of a magnetic wheel adhering to two surfaces at a right-angled juncture.

acrylic plate fixes the position of the magnet. The
magnetic force of the rear wheel was measured by
the same experiment as the front wheel. The massof the rear wheel is 0.140 kg, and its adherence
power is 61.1 N.

Citation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010

ISSN: 2631-5106 |Matsumura et al. Int J Robot Eng 2018, 3:010

Wall

Wall

µFmag

µFmag

Fmag

Fmag
Floor

Fmag2

• Page 5 of 10 •

F

Floor

a) Demagnetizing

Fmagb) Pushing

Figure 9: Methods of peeling the magnetic wheels away from one surface at a right-angled juncture.
a) Demagnetizing; b) Pushing.

Female thread

Plate

Male thread(shaft)Push roda) Illustrationb) Photograph

Figure 10: Construction of the pushing mechanism. a) Illustration; b) Photograph.

Pushing mechanism
A bridge inspection robot needs to be able to run
through complicated inspection paths that can include right-angled junctures. However, wheel-type
robots cannot travel on such paths using only theirown driving force because their wheels strongly
adhere to two surfaces at right-angled junctures.
Figure 8 shows forces acting on the wheel at aright-angled juncture. To peel the wheels awayfrom one wall to allow the robot to move to another wall, their magnetic force, Fmag needs to at leastsatisfy the following equation:µ Fmag > Fmag			

(1)

However, since the friction coefficient, µ, is lessthan 1, the robot is unable to travel on such paths
by itself.
There are two ways to allow wheel-type robots
to move along paths that include an inner right-an-

gled juncture. One method is to weaken the magnetic force at the right-angled juncture (Figure 9a).
This has the disadvantage of making the structureof the magnetic wheel more complicated. Additionally, it is difficult to weaken only the adherence
force with the intended surface. Another method
is to push away from the wall surface to peel thewheels away from it (Figure 9b). In this method,
the robot pushes away from the wall surface using
a pushing mechanism, making the reaction force
greater than the attraction force. This offers the advantage of a simpler mechanism compared to thefirst method. In this study, therefore, we equipped
the robot with a pushing mechanism.
The pushing mechanism is composed of a trapezoidal screw, a pair of pushing rods, a motor, anda reduction mechanism (Figure 10). First, the rotational motion of the motor is transmitted to the female screw via the reduction mechanism. Second,

Citation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010

ISSN: 2631-5106 |Matsumura et al. Int J Robot Eng 2018, 3:010• Page 6 of 10 •Rotary shaft
Arm supporting rear wheel

Servo motor
Reduction mechanisma) Illustration

Rear wheelb) Photograph

Figure 11: Construction of the arm mechanism. a) Illustration; b) Photograph.

Methodology

Center point of the front wheel

Electronics circuits to control the robot

the push rods contact the wall surface and hinder
the rotational movement of the female screw. As aresult, the entire female screw moves rectilinearly, and the rods push away from the wall surface
strongly. The mechanism mounted on the robot
can push outwards with a maximum force of 490 N.

A control system is mounted outside of the robot. The system is composed of a ZYBO (Digilent,
Pullman, Washington, United States), a motor driver board for driving the front wheels, a regulator
board, a paired transmitter and receiver (Futaba,
Chiba, Japan), and a stabilized DC power supply(Matsusada Precision, Shiga, Japan). The stabilized
DC power supply and the regulator board supply
power to the motor driver board and the receiver.
The transmitter's signal is received at the receiver,and the ZYBO processes it and sends signals to themotor driver board. According to the signals, themotor driver board drives the front wheels andactivates the pushing mechanism. In addition, theZYBO activates the arm mechanism according to
the signal from the receiver. This system enables
remote control of the robot via the transmitter(Figure 13).

Arm mechanism to rotate rear wheel support

Transition method at right-angled juncture

The arm mechanism to rotate the rear wheel
support is composed of a servo motor, a rotary
shaft, a reduction mechanism, and a pair of arms
supporting the rear wheel (Figure 11). This arm
mechanism enables us to change the distance between the front and rear wheels by rotating thearm supporting the rear wheel. The reduction
mechanism has a ratio of 4. The range of the arm
angle, θ is ± 22.5°. When the angle θ is -22.5°, thechassis is horizontal to the surface with which thefront wheels are in contact (Figure 12).

At an inner right-angled juncture, the robot
runs through the following process. First, the robot
is advanced toward the right-angled juncture until both front wheels contact the next wall (Figure14a). Then, the front wheels are peeled away fromthe first wall using the pushing mechanism (Figure
14b, Figure 14c and Figure 14d). Third, the pushingrods are returned to their initial position to prevent
contact with either wall (Figure 14e). Fourth, therobot is advanced forward again. Then, the rear
wheel adheres to both of the walls (Figure 14f).
However, the rear wheel is smoothly peeled awayθCenter point of the rear wheel

Rotary shaft

Figure 12: Relationship between the wheels and thearm mechanism (θ = - 22.5°).

Citation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010

ISSN: 2631-5106 |Matsumura et al. Int J Robot Eng 2018, 3:010• Page 7 of 10 •Robot
ReceiverArmmechanism

ZYBO

Motor driverboard

Front wheel
motor
Pushingmechanism

Transmitter

Figure 13: Signal flow from the receiver to the robot.

Fmf

Pushing mechanism
Front wheel
Chassis
Arm

Fmf
F

Fmf

Fmf

Rear wheelb) Phase 2a) Phase 1

Figure 15: Moving paths including right-angled junctures.

Fmfc) Phase 3d) Phase 4

from the first side since its magnetic force is weak.
Finally, the robot can change walls (Figure 14g).

Discussion
Fmf
Fmr
Fmr

e) Phase 5f) Phase 6

To assess the performance of the robot, twotypes of experiments were conducted. In the firstexperiment, the weight the robot could carry wasmeasured. In the other experiment, the ability of
the robot to travel inner right-angled junctures
such as in paths 1 through 4 was confirmed (Figure15). Both experiments were conducted on a small
steel box within a laboratory environment. The box
was composed of four steel plates with a length of
600 mm, a width of 400 mm, and a thickness is 2.3
mm (Figure 16).

Experiments to measure carrying capacityg) Phase 7

Figure 14: Transition method at a right-angled juncture. a) Phase 1; b) Phase 2; c) Phase 3; d) Phase 4; e)Phase 5; f) Phase 6; g) Phase 7.

In this experiment, the weight that the robot
could carry was measured. First, the robot wasplaced on the steel wall. Next, the plummet was
attached to the robot. Then, the stabilized power supply was turned on, and the robot began to

Citation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010

ISSN: 2631-5106 |Matsumura et al. Int J Robot Eng 2018, 3:010• Page 8 of 10 •ability under different conditions, the locomotive
speed of the robot was measured.
In this experiment, it became clear that the robot was able to carry 2 kg. Table 2 shows the climbing speed of the robot under different conditions.
As the mass of the plummet increased, the climbing speed decreased. However, the robot ran at
sufficient speed even with a plummet of 2.010 kg
attached.

Experiments of traveling on a path that included a right-angled juncture
Figure 16: Steel box used for experiments.

Direction of movement

Wall

StringPlummetFigure 17: Experiment to measure carrying capacityof the robot.
Table 2: Result of experiments to measure the carrying
capacity of the robot.
Mass of plummet Climbing speed
None0.494 kg
1.063 kg
1.494 kg2.010 kg

29.4 mm/s
28.3 mm/s
25.9 mm/s
24.6 mm/s
23.8 mm/s

Ratio to thereference speed
1
0.96
0.88
0.84
0.81

Table 3: Result of experiments of traveling on the paths
that included a right-angled juncture.
Path number
12
3
4

Success rate
100%
100%
90%
100%

move (Figure 17). During this experiment, the power supply voltage was 7.4 V. To compare climbing

In this experiment, the locomotive performanceon a path that included a right-angled juncture wasconfirmed. First, the robot was placed at the startof a path. Next, the robot was advanced along thepath toward a right-angled juncture. At that point,
the pushing mechanism was operated to peel away
the front wheels from the first surface. Then, therobot was advanced farther. Finally, the rear wheel
was pulled away from the first surface, and the robot continued along the path. In this experiment,
an experimenter maneuvered the robot while
viewing it. In addition, the robot was tested without a weight attached. The experiment was conducted ten times for each path. Then, the percentage of travel without incident, such as falling fromthe surface of the wall, was calculated.
Table 3 shows the results of this experiment,
which indicated two things. First, it was confirmedthat the robot was able to cancel the strong adherence between the front wheels and the wall surface by using the pushing mechanism. Second, as
Table 3 indicates, the robot was able to travel witha high success rate on all of the paths. However,
the robot fell one time from the surface of the wallon path 3.
There are two mechanisms that the robot fails
on path 3: Slipping down and rotation (Figure 18).
Firstly, the robot slips down and falls if the friction
force acting between the front wheels and the wall
surface is insufficient (Figure 18a). However, thefront wheels have produced sufficient frictional
force in the experiments to measure carrying capacity. Therefore, we have concluded that the slipping down is not the cause why the robot has failed
traveling on path 3.
Secondly, the robot rotates around the contact
point between the front wheels and the wall surface as the rotation center if the magnetic force ofCitation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010

ISSN: 2631-5106 |Matsumura et al. Int J Robot Eng 2018, 3:010• Page 9 of 10 •RotateContact
point

Slip downa) Slip downb) Rotate

Figure 18: Mechanisms that the robot fails while traveling on path 3. a) Slip down; b) Rotate.

Ceiling

Lr
Fmr

Wall
Mg

Supporting
point

Lg
Figure 19: Dynamic model of robot traveling on path 3.

Ceiling

the rear wheel is insufficient (Figure 18b). Figure 19
shows the dynamic model of the robot traveling on
path 3. In Figure 19, Fmr is the magnetic force of therear wheel, M is the total mass of the robot, g is
the gravitational acceleration, Lr is the distance between the wall surface and the contact point of therear wheel, and Lg is the distance between the wall
surface and the center of gravity of the robot. If theattraction force of the rear wheel is insufficient,
the entire robot rotates around the contact pointof the front wheels and the rear wheel disengages
from the ceiling surface. And, the robot needs tosatisfy equation (2) to prevent this type of rotation.
According to equation (2), this rotation occurs regardless of the frictional force acting between thefront wheels and the wall surface. In addition, therear wheel does not adhere well to the ceiling surface when a roll angle occurs. Then, the magnetic
force of the rear wheel sharply decreases, and theequation (2) comes not to hold. Therefore, we haveconcluded that the lack of the rear wheel is theCeiling
Wall

Rear wheela) Posture of the robotb) Posture of the rear wheel

Figure 20: Posture of the robot with roll angle traveling on path 3. a) Posture of the robot; b) Posture of the rear wheel.
Citation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010

ISSN: 2631-5106 | • Page 10 of 10 •Matsumura et al. Int J Robot Eng 2018, 3:010

cause why the robot has failed traveling on path 3.
Fmr Lr > MgLg 				

(2)The lack of magnetic force in the rear wheel wascaused by the following process. First, the front
wheels were peeled away from the ceiling surface by
the pushing mechanism. At this time, a roll angle α
was caused by the asymmetry of the strength of theattraction force of both wheels or the asymmetry of
the pushing mechanism (Figure 20a). Then, due tothe roll angle α, the contact angle of the rear wheelchanged, and one side of its yoke dropped from theceiling surface (Figure 20b). As a result, the magnetic
force of the rear wheel decreased markedly.
To prevent this rotation from occurring, we propose the following two adjustments. The first is to increase the degree of freedom of the arm mechanism.
Therefore, even when a roll angle α occurs, the rear
wheel can maintain proper contact with the wall surface. However, this method has the disadvantage ofmaking the arm mechanism more complicated, larger, and heavier. Another method is to maintain theroll angle α at zero. Although the robot needs to beequipped with a posture detection sensor, it is unnecessary to otherwise significantly change its structure.
Thus, this method has the advantage of effectively
maintaining the weight of the robot. By adopting thelatter of these methods, the locomotive performanceon path 3 improves.

Conclusion
In this study, we aimed to develop a magnetic
bridge inspection robot that is able to carry heavyloads.
First, we designed a magnet wheel that combined
neodymium magnets and steel yokes. The wheel
forms a magnetic circuit when it contacts a steel plate
and produces a strong magnetic force that allows therobot to carry heavy loads. It was confirmed that the
robot was able to travel vertically upward on a steel
plate even when carrying a 2-kg load.
Second, a pushing mechanism was mounted
on the robot. With the mechanism, the robot wasable to peel away the front wheels when they werestrongly adhering. As a result, the robot was able totravel along paths that included inner right-angled
junctures.
Third, the robot fell one time while traveling on
the path moving from the ceiling to the wall. The
cause of the fall was that the attraction force of therear wheels decreased at the right-angled juncture.

To prevent this from occurring, it is necessary to
maneuver the robot carefully so as not to generateroll angle α. Therefore, maneuvering the robot ismore difficult when traveling on path 3 than whentraveling on other paths.
In the future, we hope to improve the robot sothat it is capable of traveling on paths that include
inner right-angled junctures more successfully andmore easily. For that purpose, a further study ofcontrolling either the robot's posture or the arm
mechanism should be conducted.

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Citation: Matsumura Y, Shiba T, Ito S, Kawase Y, Takada Y (2018) Development of Magnetic Bridge Inspection Robot Aimed at Carrying
Heavy Loads. Int J Robot Eng 3:010