Simultaneous Control of Translational and Rotational Motion

for Autonomous Omnidirectional Mobile Robot

Report: Robot Model Considering Moving Parts

and Evaluation of Movable Area by Heights

Ayanori Yorozu, Takafumi Suzuki, Matsumura Tetsuya and Masaki Takahashi

Department of System Design Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan

Keywords: Service Robot, Obstacle Avoidance, Omnidirectional Platform, Fuzzy Potential Method.

Abstract: This paper presents a real time collision avoidance method for an autonomous omnidirectional mobile robot

considering shape of the robot and movable area by heights based on simultaneous control of translational

and rotational motion. Service robots which have been developed in recent years have arms to work and

execute tasks. In these robots, the size of width is sometimes not equal to that of length by heights. In order

to avoid obstacles considering safety and mobility for the robots, it is necessary to evaluate shape of the

robot and movable area by heights. To evaluate them, the robot model is defined in heights of each moving

part. Evaluating of the robot model and the movable area for each height, if the robot is unable to move

keeping a safe distance from the obstacles, the robot determines the suitable orientation angle considering

the minimum length from the center of the robot model to that outer shape. In this paper, the novel control

method based on the Fuzzy Potential Method is presented. To verify the effectiveness of the proposed

method, several numerical simulations are carried out.

1 INTRODUCTION

Recently, autonomous mobile robots work in human

living space have been studied and developed. Some

cases of these robots installation to public facilities

have been reported (Tiejun et al., 2005). These

robots sometimes have two arms so these robots can

be used for manipulation and human-robot

interaction (Kuindersma et al., 1999), (Mehling et al.,

2007). In these robots, the size of width is not equal

to that of depth by heights. In order to avoid

obstacles considering safety and mobility, it is

necessary to consider moving parts and evaluate

shape of the robot and movable area by heights.

Various obstacle avoidance methods and their

availabilities for mobile robots have described

(Borenstein and Koren, 1991), (Minguez and

Montano, 2004). Most of these studies regard the

robots as points or circles and control methods of the

translational movements in two-dimensional plane

are discussed. However, depending on the shape of

the robot, this approach reduces and wastes available

free space and can decrease the possibility that the

robot reaches the goal. To enable wide robots to

avoid obstacles safely and efficiently, it is necessary

to control not only a translational motion but also a

rotational motion. Several studies have focused on

the orientation angle of the robot (Kavraki, 1995),

(Wang and Chirikjian, 2000). However, these

methods require an environmental map and the

studies have not shown the effectiveness for

avoidance of unknown obstacles by autonomous

mobile robots. Therefore, in our current research, to

avoid unknown obstacles reactively for wide robots,

simultaneous translational and rotational motion

control method is presented (Suzuki and Takahashi,

2011). In addition, there are obstacles of various

heights in the human living space and the relation

between the robot and the surrounding environment

Figure 1: Proposed robot model considering moving parts.

Robot

Obstacle

451

Yorozu A., Suzuki T., Tetsuya M. and Takahashi M..

Simultaneous Control of Translational and Rotational Motion for Autonomous Omnidirectional Mobile Robot - 2nd Report: Robot Model Considering

Moving Parts and Evaluation of Movable Area by Heights.

DOI: 10.5220/0004035804510454

In Proceedings of the 9th International Conference on Informatics in Control, Automation and Robotics (ICINCO-2012), pages 451-454

ISBN: 978-989-8565-22-8

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

Figure 2: Trajectory of the robot with two motion control method: (left) considering footprint at the height of wheeled

platform, (right) evaluating shape of the robot and movable area by heights with robot model considering moving parts.

changes depending on shape of the robot. Therefore,

in order to avoid obstacles more safely and

efficiently, it is necessary to evaluate shape of the

robot and movable area by heights. Moreover, the

relation between the robot and the surrounding

environment is changed depending on the shape of

the robot by moving parts. Consequently, this study

proposes the following two points.

 Robot model considering moving parts.

 Simultaneous control of translational and

rotational motion considering shape of the

robot and movable area by heights.

With the proposed method, if the robot is unable to

move keeping a safe distance from the obstacles, the

robot determines the suitable orientation angle

considering the minimum length from the center of

the robot to that outer shape in real time. To verify

the effectiveness of the proposed method, several

simulations are carried out.

2 CONCEPT

For the robot which the size of width is not equal to

that of depth by heights according to moving parts,

in order to achieve obstacle avoidance considering

safety and mobility, it is necessary to evaluate shape

of the robot and movable area by heights.

2.1 Robot Model

To consider the changes of the shape of the robot by

moving parts, a new robot model with multi-circle

shown in Figure 1 is proposed. The modeling

method is as follows.

 The model is defined at the heights that the

occupied area of each moving part is

maximum.

 The robot body is enclosed by a circle.

 The moving parts are enclosed in each circle.

With proposed robot model, changing the position of

the moving parts, the relation between the robot and

the environment is changed. Thus, performing the

motion control considering that point, as well as

translational and rotational motion control, the robot

can respond flexibly to various situations.

2.2 Motion Control Considering Shape

of the Robot and Movable Area by

Heights

Evaluating of the shape of the robot and the movable

area by heights, if the robot is unable to move

keeping a safe distance from the obstacles, the robot

determines the suitable orientation angle considering

the minimum length from the center of the robot to

that outer shape. Then, evaluation of the shape of the

robot and the movable area is used the width of the

robot model and the movable area measured with

range sensor like Laser Range Finder (LRF) by

heights. Considering the orientation angle in real

time based on the evaluation of the shape of the

robot and the movable area by heights, the robot can

move smoothly without unnecessary rotational

motion keeping a safe distance from obstacles like

Figure 2 (right).

In this study, the novel control method based on

the fuzzy potential method (FPM) (Tsuzaki and

Yoshida, 2003) is proposed. In the FPM, element

actions are represented as potential membership

functions (PMFs). The vertical axis of PMF

indicates the grade for the direction of the robot. The

PMFs for translational and rotational motion are

respectively designed by evaluating the shape of the

robot and movable area by heights. Finally,

translational and rotational velocity commands,

which are calculated by defuzzification of PMFs, are

realized by an omnidirectional drive system. (Suzuki

and Takahashi, 2011).

Robot

Obstacle

Wall

Safety area

Goal

Safety area

Start

Goal

Start

Safety area

Goal

Baggage

Start

ICINCO 2012 - 9th International Conference on Informatics in Control, Automation and Robotics

452

(a) Situation A

(b) Situation B

(d) Situation D

Figure 3: Aspects of the translational PMF and the traveling direction depending on the robot model and rotational motion.

3 SIMULATION

The robot has an omnidirectional drive system, and

can measure 4.0 m in

120deg

range at 0.23 m

height of the wheel platform and 0.60 m height of

arms with two LRFs. A safe distance for obstacles is

0.20 m. In situations A-D, the positions of two

obstacles that radius is 0.35 m were immobilized at

each point (-1.0 m, 1.0 m) and (1.0 m, 1.5 m) and

the robot transports baggage with arms, as shown in

Figure 3. On the other hand, in situations E and F,

the obstacles were immobilized (-0.5 m, 1.5 m) and

(0.5 m, 1.5 m) and the robot can open the forearms

at the height 2, as shown in Figure 4.

3.1 Effectiveness of Evaluation Shape

of the Robot and Movable Area by

Heights

In situations A-C, the height of obstacles is lower

than the robot arms. In situation A shown in Figure

(a), the robot cannot go through between the

obstacles keeping the safe distance from the

obstacles. As the result, the robot selected the

traveling direction toward the outside of the

obstacles to the goal. In situation B shown in Figure

3 (b), the rotational motion of the robot changes the

relation between the robot and the environment from

situation A. As the result, the robot can select the

traveling direction to go through between the

obstacles keeping the safe distance from the

obstacles. In situation C shown in Figure 3(c),

(a) Situation E

(b) Situation F

Figure 4: Verification of the effectiveness of the proposed

robot model in a symmetrical environment.

Baggage

(1.0 m)

Height 1 (0.60 m)

Height 2 (0.23 m)

Baggage

(0.60 m)

Height 2

0.20 m

0.40 m

0.20 m

0.35 m

0.40 m

0.15 m0.15 m

Height 2

0.20 m

0.40 m

0.20 m

0.35 m

0.40 m

0.15 m0.15 m

70 deg

Height 1

Height 2

0.35 m

0.20 m

0.40 m

0.20 m

0.35 m

0.40 m

0.15 m0.15 m

Height 1 Height 2

0.35 m

0.20 m

0.35 m

0.20 m

0.15 m

1.0

-1.0

2.0-2.0

0.0

3.0

-1.0

0.0

1.0

2.0

x-coordinate [m]

y-coordinate [m]

Goal

PMF

Robot

Selected direction

Obstacle Obstacle margin

1.0

-1.0

2.0-2.0

0.0

3.0

-1.0

0.0

1.0

2.0

x-coordinate [m]

y-coordinate [m]

Goal

PMF

Robot

Selected direction

Obstacle Obstacle margin

1.0

-1.0

2.0-2.0

0.0

3.0

-1.0

0.0

1.0

2.0

x-coordinate [m]

y-coordinate [m]

Goal

PMF

Robot

Selected direction

Obstacle Obstacle margin

1.0

-1.0

2.0-2.0

0.0

3.0

-1.0

0.0

1.0

2.0

x-coordinate [m]

y-coordinate [m]

Goal

PMF

Robot

Selected direction

Obstacle Obstacle margin

Height 1 Height 2

0.35 m

0.20 m

0.35 m

0.20 m

0.15 m

Height 1

Height 2

0.35 m

0.20 m

0.40 m

0.20 m

0.35 m

0.20 m

0.15 m

1.0

-1.0

2.0-2.0

0.0

3.0

4.0

-1.0

0.0

1.0

2.0

x-coordinate [m]

y-coordinate [m]

Goal

t = 12.4 s

Obstacle

1.0

-1.0

2.0-2.0

0.0

3.0

4.0

-1.0

0.0

1.0

2.0

x-coordinate [m]

y-coordinate [m]

t = 12.4 s

Obstacle

-100

-60

-20

100

0.0 2.0 4.0 6.0 8.0 10.0 12.0

Traveling direction [deg]

Time [s]

Situation E Situation F

Simultaneous Control of Translational and Rotational Motion for Autonomous Omnidirectional Mobile Robot - 2nd Report:

Robot Model Considering Moving Parts and Evaluation of Movable Area by Heights

453

evaluating the shape of the robot and the movable

area by heights, the robot can select the traveling

direction to go through between the obstacles

keeping the safe distance from the obstacles without

unnecessary rotational motion like situation B. In

situation D shown in Figure 3(d), the height of

obstacles is higher than that of the robot arms. If the

shape of the robot at the height 1 is horizontally long

according to the baggage, the robot can go through

between the obstacles by rotational motion as well

as situation B. By contrast, in situation D that the

robot closes arms according to the size of the

baggage, the robot can select the traveling direction

to go through between the obstacles without

unnecessary rotational motion keeping the safe

distance from obstacles by evaluating the shape of

the robot by heights.

These results showed that it is possible for the

robot to select the traveling direction that makes a

short route to the goal keeping the safe distance from

obstacles by the evaluation of the shape of the robot

and the movable area by heights.

3.2 Effectiveness of Consideration of

Moving Parts

In situation E shown in Figures 4(a) and 4(c), the

robot cannot get to the goal because it is difficult to

determine the traveling direction uniquely only

using reactive motion control method in situation

that the surrounding environment of the robot is

completely symmetrical. By contrast, in situation F,

the robot changed the position of the moving part.

As shown in Figures 4(b) and 4(c), the robot can

deal with this problem by changing the relation

between the robot and the surrounding environment

depending on the position of the moving parts.

These results show that the robot becomes

possible to respond flexibly to various situations by

the proposed robot model because the choices of

method for motion control to change the relation

between the robot and the environment increase.

4 CONCLUSIONS

In this paper, toward the realization of motion

control for autonomous mobile robots that can be

flexible in various situations, the robot model

considering moving parts has been proposed. In

addition to translational and rotational motion, using

this robot model, it was verified that the changes of

the moving parts can change the relation between

the robot and the environment. Furthermore, the real

time collision avoidance method based on the fuzzy

potential method considering the shape of the robot

and the movable area by heights has been proposed.

Evaluating of the robot and the movable area for

each height, if the robot is unable to move keeping a

safe distance from the obstacles, the robot

determines the suitable orientation angle considering

the minimum length from the center of the robot

model to that outer shape. The effectiveness has

been verified by numerical simulations. It has been

shown that the robot becomes possible to respond

flexibly to various situations by proposed robot

model and control method.

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