Abstract— Welding is very difficult and dangerous for manual welders. The double hull structures found in ships are very hazardous environments, and as such the shipbuilding industry demands a safer, autonomous system to perform the welding rather than deploy manual welders. This paper describes the design of a new mechanism, called the ‘Rail Runner’, which is able to autonomously travel within the double hull structure. The design of a 3P3R serial manipulator for welding is also described in this paper. As an application of the ‘Rail Runner’ mechanism, we combine the ‘Rail Runner’ platform and the 3P3R serial manipulator for autonomous welding. The mechanical system of this robot is composed of a six-axes (3P3R) manipulator for achieving the welding function and a six-axes mobile platform for traveling within the double hull structure. This robot is able to autonomously travel between longitudinal structures, with transverse direction, and is capable of welding in double hull structures. The ‘Rail Runner’ can raise the efficiency of the welding process, as compared to manual welders. This in turn raises the international competitiveness of the shipbuilding industry.

I. INTRODUCTION ecently , the need for autonomous welding operations has increased in shipyards as a way to improve both

productivity and the working environment. Autonomous welding using multi-joint robots has been used in many applications since the 1990’s. However, because these robots are able to work only at a fixed place, they need a worker’s support to enable them to be moved to another work site. Therefore, a crane is usually used to move the welding robot

Donghun Lee is with the School of Mechanical and Aerospace

Engineering, Seoul National University, Shilim-Dong, Kwanak-gu, Seoul, 151-742, Korea, (e-mail: dhlee@rodel.snu.ac.kr).

Sungcheul Lee is with the School of Mechanical and Aerospace Engineering, Seoul National University, Shilim-Dong, Kwanak-gu, Seoul, 151-742, Korea, (e-mail: sclee@rodel.snu.ac.kr).

Nam-kug Ku is with the Department of the Naval Architecture and Ocean Engineering, Seoul National University, Shilim-Dong, Kwanak-gu, Seoul, 151-742, Korea, (e-mail: knk80@snu.ac.kr).

Chaemook Lim is with the School of Mechanical and Aerospace Engineering, Seoul National University, Shilim-Dong, Kwanak-gu, Seoul, 151-742, Korea, (e-mail: cmlim@rodel.snu.ac.kr).

Kyu-Yeul Lee is with the Department of the Naval Architecture and Ocean Engineering, Seoul National University, Shilim-Dong, Kwanak-gu, Seoul, 151-742, Korea, kylee@snu.ac.kr

Taewan Kim is with the Department of the Naval Architecture and Ocean Engineering, Seoul National University, Shilim-Dong, Kwanak-gu, Seoul, 151-742, Korea, taewan@snu.ac.kr

Jongwon Kim is with the School of Mechanical and Aerospace Engineering, Seoul National University, Shilim-Dong, Kwanak-gu ,Seoul, 151-742, Korea, jongkim@snu.ac.kr

to another site in the shipyard. However, such multi-joint robots are not able to work in a double hull structure because a crane cannot be fitted into them. This paper describes the development of an autonomous welding robot, using a novel mechanism that is able to travel in a double hull structure, which does not require a crane, or a gantry device, for its mobility.

A. Double Hull Structure of the Ship For safe operation at sea, a ship must have the required

structural stability to withstand a sea change or a sudden reef. As commercial ships carrying liquid cargo such as LNG (Liquefied Natural Gas), LPG (Liquefied Petroleum Gas) and crude oil can cause serious environmental pollution, ships such as VLCC (Very Large Crude oil Carrier), B/C (Bulk Carrier) and LNGC (Liquefied Natural Gas Carrier) incorporate a double hull structure which prevents outflow of cargo following an accidental collision or stranding (Fig. 1).

Fig. 1. Double hull structure in a ship

Due to the inherent advantages of such a double hull

structure, its use has become increasingly common. However, its construction is more time-consuming and expensive due to its greater complexity than the single hull structure. In addition, it is difficult to weld, or paint, in a double hull structure due to it being an enclosed area and other associated working environment problems this creates. For these reasons, research has focused on autonomous work methods for the shipyard construction of double hull structures [1, 2, and 3].

Development and Application of a Novel Rail Runner Mechanism for Double Hull Structures of Ships

Donghun Lee1, Sungcheul Lee, Namkuk Ku, Chaemook Lim, Kyu-Yeul Lee, Taewan Kim, and Jongwon Kim

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2008 IEEE International Conference onRobotics and AutomationPasadena, CA, USA, May 19-23, 2008

978-1-4244-1647-9/08/$25.00 ©2008 IEEE. 3985

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II. DE

A. Working A ‘Rail Run

autonomously directions, in thongitudinal st

movement needFig. 6) and trashown in the Fi

The phases oRail Runner’ m

Runner’ platfo(top), a lower s(below) (Fig. 8wo longitudinwo points.

Fig. 7. M

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paper, a ‘Rail Rusly traveling in the double esented is able talso able to wemanipulator.

ESIGN OF ‘RAIL

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CHANISM

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III. DESIGN O

Design of ‘3P3Roverall ‘3P3R 9. This manipurevolute axes. with the moti

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nal, and transvemechanism use

structure, like.

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OF MANIPULAT

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shown in matic axes AC servo

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3987

micro switches as well as for calibration at start-up. The arrangement of the degree of freedom, and the kinematic parameters, are shown in Figure 10.

The motors for all joints drives each joint via harmonic drive systems for reducing backlash and these operational ranges are shown in Table 2.

Fig. 9. Overall 3P3R manipulator

This manipulator has been designed to be able to carry a payload of up to 5kg for the welding operations. There is some equipment needed for performing this welding, such as welding wire spools and hence the manipulator is designed to be able to carry all the equipment needed so that workers only need to replace the welding wire spool when it has been depleted.

B. Kinematic Analysis This section presents the architecture of the 3P3R

manipulator, followed by the procedures describing the inverse and forward kinematics. As shown in Figure 10, the 3P3R manipulator consists of a PPRPRR serial chain that is fixed on the ‘Rail Runner’ platform. Here, P and R denote prismatic and revolute joints respectively. The manipulator has six degrees of freedom and six actuated joints. All the six actuated joints can be seen in Figure 10, and are indicated by arrows. The operational ranges of all the joints are shown in Table 2.

Fig. 10. Schematic diagram of the 3P3R manipulator (d is for the prismatic,

and θ is for the revolute joint).

We have used the Denavit-Hartenberg parameters for solving the kinematics of the 3P3R manipulator (Table 1).

{T} is the tool frame of the welding torch and α is the torch

angle relative to the 6th axis. The problem of inverse kinematics is to determine the values of the actuated joints from the world position and orientation of the tool frame {T} attached to the moving platform. For the 3P3R manipulator, the inverse kinematics can be solved by successively solving the serial chain. The transformation matrix in this case is the following:

0 0 1 2 3 4 5 67 1 2 3 4 5 6 7

3 6 3 5 6 3 5 6 3 6 α 3 5 α

3 6 3 5 6 3 5 6 3 6 α 3 5 α07

5 6 5 6 α 5 α

3 5 6 3 6 α 3 5 α 3 4 3 5 3 3 2 3 4 1

3 5 6 3 6 α 3 5 α 3 4

( )( )

0 0

( )( )

T T T T T T T Ts c c s s c s c s s c c c sc c s s s s s c c s c s c s

Tc s c c c s s

c s c s s s c c c s L c c L c L c d Ls s c c s s s c c c L s

= ⋅ ⋅ ⋅ ⋅ ⋅ ⋅+ − +⎡

⎢ − − − −⎢=⎢ −⎢⎣

− + + + + + ++ − − 3 5 3 3 2 3 4 1

5 6 α 5 α 5 3 2

11 12 13 14

21 22 23 24

31 32 33 34

41 42 43 44 1

0 1

c L s L s d dc c s s c s L d

r r r rr r r rr r r rr r r r

⎤⎥− − − ⎥⎥− − − −⎥⎦

⎡ ⎤ ⎡ ⎤⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥= =⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥

⎣ ⎦⎣ ⎦

R P

0

(1)

1) The 5th joint value is calculated from the transformation

matrix as follow: ( )5 32 33arcsin r s r cα αθ = − + (2)

2) Calculate the revolute joint values, 3θ and 6θ (see Fig. 10), as follows:

22 233

5

( )arcsin r s r cc

α α⎛ ⎞+θ = ⎜ ⎟−⎝ ⎠

(3)

31 32 56

5 5

arctan2 ,r r s sc c c

α

α

⎛ ⎞+θ = ⎜ ⎟⎝ ⎠

(4)

TABLE 1 DENAVIT-HARTENBERG PARAMETERS OF 6-DOF MANIPULATOR

JOINT I 1−iα 1−ia id iθ

1 2π 0 1d 0

2 2π

1L 2d 0

3 0 0 0 32π θ+

4 2π

0 2 4L d+ 2π−

5 2π 0 0 5θπ +

6 2π 0 3L

62π θ+

T α 0 0 0

α=30°, L1 = 0, L2 = 124.6, L3 = 400

3988

3) Determine the prismatic joint values, 1d , 2d and 4d [see Fig. 10], as follows:

1 3 4 3 5 3 3 2 3 4 24d c L s c L s L s d r= − − − − (5)

2 34 5 3d r s L= − − (6)

14 3 4 3 5 3 3 2 14

3

r s L c c L c L Ldc

⎛ ⎞− − − −= ⎜ ⎟⎝ ⎠

(7)

where, 3 3 3 3

5 5 5 5

6 6 6 6

cos( ), sin( )cos( ), sin( )cos( ), sin( )cos( ), sin( )

c sc sc sc sα α

θ θθ θθ θα α

= == == == =

(8)

The problem of forward kinematics is to determine the position and orientation of the world coordinates of the moving frame given the actuated joint values. The position and orientation values of the moving frame are found in the matrix of equation (1). The position values are:

14 24 34, ,x y zp r p r p r= = = (9)

C. Workspace Analysis The workspace of a robot mechanism is defined as; the set

of all positions and orientations that are reachable by the moving platform. The workspace analysis of the 3P3R manipulator begins with a description of the moving frame and its orientation. Many parameterizations exist for describing the orientation; e.g., Euler angles, fixed angles, exponential coordinates, etc. Due to the simple architecture of the 3P3R manipulator, it was decided to describe the orientation of the mechanism using the z-y-x Euler angles. In terms of these, the rotation matrix is given by;

( ) ( ) ( )Z Y XR Rot α Rot β Rot γ= ⋅ ⋅ where α, β, and γ are the rotation angles, in succession,

about the z, y, and x axes. The actual Cartesian workspace is restricted by the following physical constraints on the mechanism:

1. Stroke limit of the linear prismatic joints; 2. Interference between the vertical columns; 3. Rotation limit of the revolute joints;

The operational range of each joint is shown in Table 2.

The results of workspace analysis are shown in Fig. 11. The “reachable workspace’ is the larger area enclosing the other two workspaces, namely; “task-oriented workspace” and “task workspace.” The reachable workspace is a set of positions that the welding torch tip can approach without considering the possible orientation angle. This means that, in certain positions, the orientation can be limited. The task-oriented workspace is a set of positions that the welding torch tip can approach with the capability of the orientation angles whose orientation axis can be confined to a cone with its aperture angle of 60°. Finally, the task space is a set of required welding tip positions to weld the U-shape path.

Fig. 11. Result of the workspace analysis in the y-x and z-x planes

IV. APPLICATION OF ‘RAIL RUNNER’ MECHANISM

As above, the 3P3R manipulator is designed for welding, and the ‘Rail Runner’ mechanism is designed for autonomously traveling in the double hull structure. Figure 12 shows the combination of these two assemblies together with an overview of the mobile welding robot. The first axis of the 3P3R manipulator is coupled by an LM (Linear Motion) guide at the top plate of the ‘Rail Runner’ platform. Two rails of the LM guide are attached to the top plate of the ‘Rail Runner’ platform, and four blocks of the LM guide are attached under the plate of the 1st axis (Fig. 12).

Fig. 12. Combination of ‘Rail Runner’ platform and ‘3P3R’ manipulator for

welding

TABLE 2 OPERATIONAL RANGE OF EACH JOINT

JOINT I MAXIMUM VALUE MINIMUM VALUE

1 220.0 mm -220.0 mm

2 870.0 mm 0 mm

3 π21 π

21−

4 229.5 mm 0 mm

5 π21 π

21−

6 π π−

3989

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msTcecwi

in

Figure 12 showelding robot. ATable 3.

Fig. 13

SPECIF

Size

Weight

Payload

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VI. VERIFICATION OF THE DEVELOPED ROBOT ON A TEST BLOCK

To verify the motion ability and welding quality of the developed ‘Rail Runner’ robot, a test block was constructed, made of longitudinal stiffeners, and other stiffeners, to reinforce the longitudinal stiffeners. Fig. 18 shows the results of the self-driving movement in the transverse direction of the ‘Rail Runner’ to verify its motion capability. The ‘Rail Runner’ stretches its sliding arms to the next longitudinal stiffener (Figs. 18-1 and 18-2), then moves on the next longitudinal stiffener (Figs. 18-3 and 18-4), and then draws in its sliding arms (Figs. 18-5 and 18-6). It takes the ‘Rail Runner’ approximately 1.5 minutes to move to the next longitudinal stiffener, while it takes ‘DANDY’ approximately 1 minute. Moreover, the ‘Rail Runner’ moves autonomously while ‘DANDY’ requires manual operation of a gantry crane, in order to be moved as already explained.

1 2

3 4

5 6 Fig. 18. Test results of the movement in the transverse direction of ‘Rail

Runner’

Fig. 19. Welding test results from using the ‘Rail Runner’

VII. CONCLUSION This paper describes the development of a new design of

self-driving mobile welding robot, called the ‘Rail Runner’, which can move, and weld, in double hull ship structures. To verify the motion capability and welding quality of the developed robot, the longitudinal, and transverse, movements of the robot, as well as the welding quality, were tested on a test block, and were determined to be satisfactory. The major limitation of the ‘Rail Runner’ is that it cannot be easily handled due to its excessive weight (353kg). Future research will be focused on reducing its weight and also developing a device for placing the ‘Light Rail Runner’ into double hull ship structures.

This work was supported by the second phase of the Brain Korea 21 projects in 2007.

REFERENCES [1] Niels Jul Jacobsen, 2005, “Three Generation of Robot Welding at

Odense Steel Shipyard”, Proc. of ICCAS 2005, Pusan, Korea, 289-300., No. 1

[2] Roger Bostelman, Adam Jacoff, Robert Bunch, 1999, “DELIVERY OF AN ADVANCED DOUBLE-HULL SHIP WELDING SYSTEM USING ROBOCRANE”, Third International ICSC Symposia on Intelligent Industrial Automation and Soft Computing, Genova, Italy, June 1-4, No. 1

[3] Marcelo H. Ang Jr, Wei Lin, Ser-Yong Lim, 1999, “A walk-through programmed robot for welding in shipyards”, Industrial Robot: An International Journal, 26(5), 377-388, No. 1

[4] J. H. Lee, H. S. Hwang, et al., 1998, “Development of Robot Welding System for Panel Block Assemblies of Ship Hull”, Okpo Ship Technologies, 46(2), 32-40., No. 2

[5] Tatsuo Miyazaki, et al., 1999, “NC Painting Robot for Shipbuilding”, Proc. of ICCAS’99, Boston, USA, 1-14., No. 2

[6] Kyu-Yeul Lee, Jongwon Kim and Tae-wan Kim, 2007, DEVELOPMENT OF A MOBILE WELDING ROBOT FOR DOUBLE HULL STRUCTURE IN SHIPBUILDING, Robotics and applications 2007, No. 2

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