INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 10, No. 4, pp. 143-146 OCTOBER 2009 / 143

DOI 10.1007/s12541-009-0082-4

1. Introduction

In order to produce a large structure such a ship, we need safety

equipments for working on inclined or vertical plane which results

in excessive hours and costs. Thus, researchers had been developing

several devices enabling mobile robots to operate on inclined or

vertical walls. To attach the wall-climbing robots on the wall,

suction types had been widely used. Luk et al. developed a 4-legged

articular “Nuro robot”, whose legs and body had suction cups and

Bahr et. al. measured attaching force of suction cup on horizontal

and vertical walls.1-3 Wang et al. introduced new suction plates with

improved efficiency and tolerance loads.4 Also, Nishi reported

various types of suction cups.5 These types can be utilized

regardless of the materials of walls. Furthermore, they have good

attaching force-weight ratio and the attaching force can be easily

controlled. The fast motion of the robots, however, cannot be

obtained when suction cups are adhered on the wall. In addition,

supplementary devices are required to adhere and control the

suction cups. On the other hand, Hirose introduced a robot named as

“Disk Rover”.6 It has inclined magnetic disks attached and rotated

on the wall which produces driving force to move forward.

Furthermore, Lee et. al. developed a magnet-wheel robot to inspect

cracks in the coolant pathway of nuclear reactor and Schempf

developed an endless track type to inspect the inside of a storage

tank.7,8 Zhang et. al. investigated the effect of magnetic strength of

three-dimensional arranged barrel machine on polishing

characteristics and saitov built the effective map using a wave

algorithm in multi-robot system.9,10 Lim et. al. proposed a new

driving mechanism to allow a rescue robot to climb stairs.11

This paper aims to introduce a new design of permanent magnet

wheel to obtain effective movement and detachment of permanent

magnetic wheel for mobile robot application. In newly suggested

design, the magnetic flux enhances the adhesive force during the

attachment while induction pins redirect magnetic flux in order to

achieve an easier detachment. 3-D finite element analysis (FEA) is

performed utilizing commercial FE software “MAXWELL” and the

experiment apparatus is constructed to investigate the character-

istics of the attaching force of magnetic wheels.

2. Permanent Magnet Wheel

2.1 Structure and operating principle

Fig. 1 shows the structure and the operation principle of newly

suggested permanent magnet wheel for mobile robot. It consists of

permanent magnets, steel-made wheels and pins. The magnetic flux

from permanent magnet generates attaching force acting on the

wheel as shown in Fig. 1(a). If we insert the induction pins to the

A Novel Design of Permanent Magnet Wheel with Induction Pin for Mobile Robot

Seung-Chul Han1, Jinho Kim2,# and Hwa-Cho Yi2

1 School of Automobile Engineering, Yeungnam College of Science & Technology, Daegu, South Korea, 705-7032 School of Mechanical Engineering, Yeungnam University, Gyeongsan, Gyeongbuk, South Korea, 712-749

# Corresponding Author / E-mail: jinho@ynu.ac.kr, TEL: +82-53-810-2441, FAX: +82-53-810-4627

KEYWORDS: Attaching force, Finite element analysis, Induction pin, Mobile robot, Permanent magnet, Wheel

Robots are utilized to automate works on a vertical plane of a large structure such as a ship and permanent

magnet wheels have been utilized to make possible the robots to be attached to vertical plane and be in motion. In

this paper, we propose a new design of the permanent magnet wheel for mobile robots to improve the adhesive

force and facilitate the detachment of the wheel. In newly suggested design, the magnetic flux enhances the

adhesive force during the attachment while induction pins redirect magnetic flux in order to achieve an easier

detachment. To characterize the performance, finite element analysis is executed and experiment apparatus is

constructed. The results show that the adhesive force is reduced effectively by using induction pins.

Manuscript received: May 13, 2008 / Accepted: June 22, 2009

© KSPE and Springer 2009

144 / OCTOBER 2009 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 10, No. 4

hole of wheel, the part of magnetic flux from permanent magnet is

induced to flow through the pins, which results in weakening of

attaching force as shown Fig. (b).

N S

Inducing Pin

PM

Magnetic

Flux

N S

Steel Plate

(a) (b)

Fig. 1 Structure and operation principle of proposed permanent

magnet wheel (a) attaching mechanism (b) detaching mechanism

using induction pins

2.2 Finite element analysis

To demonstrate proposed detaching mechanism using induction

pin, we perform 3-D static finite element analysis using commercial

FE program “MAXWELL”.

The goal of this device is to obtain easy detachment with high

attaching force i.e. we needs to minimize the ratio of detaching

force to attaching force. For high attaching force, more permanent

magnet is utilized while more pin-holes are created for easy

detachment. Therefore, the magnet size, the magnet arrangement,

number of magnets, number of pin hole and size of pin hole are

considered to be design variables. Accordingly, three different types

of wheels shown in Table 1 are modeled and we investigate two

cases of magnetic force using each model. One is to measure the

magnetic force without induction pins and the other is measure

magnetic force with induction pins. Table 1 shows the

specifications of permanent magnet wheel models and Fig. 2 shows

the schematic diagram respectively. Fig. 3 shows 3-D model and

mesh of wheel 2. For FE modeling, the magnetic properties of

Ceramic magnet material in Table 2 is assigned to permanent

magnets and the nonlinear magnetization curve of 1010 steel shown

in Fig. 4 is assigned to wheels and pins.

Inducing

Pin

WheelMagnet

(a) (b)

Fig. 3 Wheel (2) (a) 3-D model (b) mesh model

Table 2 Magnetic properties of ceramic magnet

Residual Induction (Br) 0.4 (T)

Coercivity (Hc) -8.9*105 (A/m)

0 50000 100000 150000 200000 250000 300000

0.0

0.5

1.0

1.5

2.0

2.5

Flu

x d

ensity (

T)

Magnetizing field strength (A/m)

Fig. 4 Initial magnetization curves of 1010 steel

Fig. 5 shows the side view plot of magnetic field vector of

wheel (1). When the pins are put into the holes, we can verify that

the parts of magnetic flux from permanent magnets are guided to

flow through induction pins and the amount of magnetic flux

flowing from wheels to steel plate become decreased. Fig. 6 shows

the results of finite element analysis calculating maximal attaching

force according to type of wheels without and with induction pins.

Table 1 Specifications of permanent magnet wheels

Wheel type Magnet Wheel Pin

Diameter 10 mm 40 mm 9 mm

Length 10 mm 10 mm 30

Wheel (1)

Number 4 2 4

diameter 20 mm 40 mm 9 mm

Length 10 mm 10 mm 30

Wheel (2) Number 1 2 4

diameter 15 mm 50 mm 11 mm

Length 10 mm 10 mm 30

Wheel (3) Number 3 2 4

Fig. 2 Schematic diagrams of permanent magnet wheels

(a) Without pins (b) With pins

Fig. 5 Magnetic field vector plot of wheel (1)

INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 10, No. 4 OCTOBER 2009 / 145

In fact, the magnetic attaching force of permanent magnet wheel

oscillates because of changes of positions of permanent magnets

and inserting holes as the wheels rotates. Three wheels have

maximal force at the status as shown Fig. 2. In case of wheel (1)

that has four magnets of small size, the attaching force is 78 N, but

it is reduced to 15 N when four induction pins are inserted. In case

of wheel (2) which has one magnet of large size, the attaching force

is 99 N, but it is reduced to 16 N when four induction pins are

inserted. In case of wheel (3) which has three magnets of medium

size, the attaching force is 297 N, but it is reduced to 124 N when

four induction pins are inserted.

0

50

100

150

200

250

300

Wheel(1) Wheel(2) Wheel(3)

Newton

w/o pins

w/pins

Fig. 6 Attaching force calculated by FEA according to types of

wheels

2.3 Experiments

To compare the performance of induction pin with FEA results,

we manufacture the sample model of permanent magnet wheels

according to the specification in Table 1. Fig. 7 shows the picture of

sample model of wheel 3. In addition, the experimental apparatus is

constructed, which consists of a computer to acquire data and

control a motor, an oscilloscope to analyze values of attaching force

and a load cell (50kgf). Fig. 8 shows the schematic diagram and the

picture of experiment setup. Using load cell, we measure the

attaching forces of three wheels respectively.

Fig. 7 Manufactured permanent magnet wheel (2)

Fig. 9 shows the results of experiments according to types of

wheels without pins and with pins. In case of wheel (1), the

attaching force is 72 N, but it is reduced to 13 N when four

induction pins are inserted. In case of wheel (2), the attaching force

is 76 N, but it is reduced to 13 N by when four induction pins are

inserted. In case of wheel (3), the attaching force is 283 N, but it is

reduced to 103 N when three induction pins are inserted.

Table 3 compares the results of FEA and experiments. The

attaching forces of FEA are slightly larger than one of experiment

overall, but they are all much the same in the ratio of detaching

force with pins to attaching force without pins. The wheel (2) has

the smallest ratio of detaching force to attaching force and the

wheel (2) is considered to be the best design among three wheels.

(a)

Load Call

Magnet Whee

Load Call

Magnet Whee

Load Cell

Magnet Wheel

(b)

Fig. 8 Experiment setup of magnet wheel (a) schematic diagram (b)

picture

0

50

100

150

200

250

300

Wheel(1) Wheel(2) Wheel(3)

Newton

w/o pins

w/ pins

Fig. 9 Attaching force according to types of wheels measured by

load cell

Table 3 Comparison of FEA and experiment

Wheel type FEA Experiment

w/o pin 78 N 72 N

w/ pin 15 N 13 N

Wheel (1)

ratio 0.19 0.18

w/o pin 99 N 76 N

w/ pin 16 N 13 N

Wheel (2)

ratio 0.16 0.17

w/o pin 297 N 282 N

w/ pin 124 N 103 N

Wheel (3)

ratio 0.42 0.36

2.4 Mobile robot with proposed wheels

Fig. 10 shows the mobile robot manufactured with proposed

magnet wheels. This device can move upward and downward on

vertical wall in a speed 3 m/min without slip carrying the total load

of 6 kgf weight including 4 magnet wheel of type (2), motor and

146 / OCTOBER 2009 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 10, No. 4

other supplementary part using two AC motors of 15 kg-cm torque

each. Each motor is coupled to the wheel by the chain shown in Fig.

10(c). The maximum speed when moving upward is 3.7 m/min

while it is 5.7 m/min. The main problem on the performance is the

handling and the slip. The handing trouble of robot in right and left

is due to magnetic force between wheel and steel plate. In addition,

the slip and the idling of wheel happen sometimes when the rotation

of the first row wheel does not coincide with that of the second row

wheel.

137 mm

300 mm

137 mm

300 mm

(a) (b)

(c)

Fig. 10 Mobile robot with proposed magnet wheels (a) 2-D

schematic diagram (b) picture (c) 3-D schematic diagram

3. Conclusions

This paper presents new design of permanent magnet wheel

using induction pins for easy detachment. To demonstrate enhanced

performance of newly suggested mechanism, we execute finite

element analysis and experiment with three different models of

wheels. The results show that the induction pins reduce the

magnetic attaching force efficiently. Thus, this new design of

magnetic wheel using induction pins for easy detachment may be

suitable for application in mobile robots. The manufactured mobile

robot with proposed magnet wheels has the problem in the handling

and the slip. In future research, the study about it will be performed.

It is expected that the less magnet wheels make the handling easer

and the coating of urethane to wheel lessens the slip.

ACKNOWLEDGEMENT

This research was supported by Yeungnam University research

grants in 2008.

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