Abstract— This paper discusses a method of locomotion called

the “fluid powered ropeway”. It aims to collect information in

dangerous buildings as rapidly and safely as possible. The device

is mainly composed of a flexible flat tube and a gondola probe

driven by fluid power using the buckling phenomenon of the

tube. The big advantage is the gondola has the potential to

traverse rocky terrains that wheeled and crawler-type vehicles

have difficulty in crossing over. This is because the drive force of

the gondola is not against the ground but against the tube. In this

paper, first, how to operate fluid powered ropeway in a disaster

site is illustrated. Next, how to increase the drive force, how to

enhance the ability of the gondola to travel over obstacles, and an

analysis of the performance are discussed. Finally, the feasibility

of the proposed method is verified through an experiment that

uses the prototype developed.

I. INTRODUCTION

Unmanned mobile robots with search functions have

capability of collecting information in dangerous buildings in

a safe and rapid manner. Above all, in such operations as

lifesaving searches while aftershock continues immediately

after a great earthquake or estimating the locations of

dangerous objects after terrorism, such unmanned mobile

robots that can move around smoothly and rapidly through

scattered obstacles would be promising to reduce the damage.

A number of methods have been studied on the mobility of

robots used in the above-mentioned environments: i) a method

of moving on the ground through the use of floor reaction

forces, as in infinite rotational locomotion with wheels or

crawlers, or as in a jumping style of locomotion using a kick

out mechanism [1, 2, 3]

; ii) a method of moving sticking to walls

or ceilings [4]

; iii) a method of moving floating through the air

like mini helicopters or blimps [5,6]

. Since each of them has

both advantages and disadvantages, we need to select a

method appropriate for the target area.

For example, the above-mentioned method i), which is

principally based on movements along the ground, is more

effective than methods ii) and iii) in collecting information by

approaching close to buried survivors or to dangerous objects

on the floor. It is much easier in terms of energy supply with a

cable or in terms of the rapid collection of target objects by

means of traction. On the other hand, mobility tends to

become far worse under unfavorable ground conditions, such

as bumpy, slippery, or weak ground. This tendency is

unavoidable as long as ground reaction forces are used. Hence,

efforts have been made to find solutions to introduce a robot

into such unfavorable ground conditions.

*Hideyuki Tsukagoshi, Yotaro Mori, and Ato Kitagawa are with Tokyo

Institute of Technology, Tokyo, JAPAN (e-mail:

htsuka@cm.ctrl.titech.ac.jp).

Therefore, we introduced the method of locomotion called

the ―fluid powered ropeway‖ shown in Fig.1 as one of the

solutions for the above-mentioned issues while retaining the

advantages of method i). The proposed method is aimed at

adapting mobility of the probe to a variety of ground

conditions so that the probe can move forward along the

flexible tube laid on the ground, even in the situations where

floor reaction forces may not be available.

In this paper, we first review the basic configurations and

operational procedures for the introduced locomotion, and

then we illustrate the mechanism to move smoothly along the

tube based on the drive principle ―Λ(lambda)-drive‖ shown in

Fig.2. Next, we discuss some improvements in performance of

the probe as well as its capability to traverse obstacles. Finally,

the paper descries the verification through experiments by the

prototype and discusses the effectiveness of the introduced

method.

Fig.1. Image of the fluid powered ropeway at disastrous site.

Fig.2. Basic principle of Λ-drive.

II. CONCEPT OF FLUID POWERED ROPEWAY

A. Basic Configurations and Operation

The introduced ―Fluid Powered Ropeway‖ consists of the

following three basic components: a flexible tube to supply

fluid energy; a gondola mounted with probing device; and a

ball of adequate shape and mass to ensure easy throwing-in of

the tube as well as its capability to remain still. The tube is

attached to the ball in such a way that an operator can

pressurize the tube at the both ends to let it make a U-turn at

the ball.

Fast Accessible Rescue Device by Using a Flexible Sliding Actuator

Hideyuki Tsukagoshi*, Yotaro Mori*, and Ato Kitagawa*

2012 IEEE International Conference on Robotics and AutomationRiverCentre, Saint Paul, Minnesota, USAMay 14-18, 2012

978-1-4673-1405-3/12/$31.00 ©2012 IEEE 1175

The fluid powered ropeway is basically operated in the

following three procedures (Fig.1); i) an operator outside the

building throws the ball attached to the tube toward the

probing target; ii) fluid energy is supplied into the tube to

enable the gondola to slide along the tube, and probing is

conducted based on information sent from the gondola; iii)

soon after probing operation is finished, the gondola returns to

the operator and the tube is pulled at the one end, leaving

behind the ball at the site. Unlike the previously proposed

method of throwing in a ball mounted with the probe [6]

, this

operation helps to reduce impacts working on the probe.

B. Features

The fundamental differences between the introduced fluid

powered ropeway and the conventional methods to move the

probe along the cables may be summarized as follows:

(1) General ropeways move the gondola by pulling the cable

with a drive source (such as a motor) installed in the external

environment (Fig.3 (a)). To carry the gondola far inside the

building, tension acts on the whole pathway between the

gondola and the drive source, which increases the

opportunities for the cable to contact convex regions of the

external environments, causing excessive sliding frictions.

(2) We can see another general method in which a motor on

the gondola generates the drive force against the cable (Fig.3

(b)). It is not necessary to move the cables together with the

gondola in this method; sliding frictions can be reduced more

easily than in the above-mentioned method (1). However, the

increase of drive force of the motor generally results in the

gain of the whole weight of the gondola, which means the

payload cannot be efficiently increased.

(3) Compared to above two, the biggest advantage of the

fluid powered ropeway is that the gondola is driven not by the

drive source on the gondola but by fluid energy inside the tube,

which leads to be a lightweight structure with large power and

fast velocity. Besides, the tube stays still with no friction

against the outer environment. A slider in the gondola can cut

off the flow inside the tube and slides smoothly along the tube

(Fig.3 (c)). Unlike the motor-driven method, there are no

concerns about burning up due to overloads.

Fig.3 Comparison of the drive methods of the gondola.

III. INTRODUCTION OF Λ-DRIVE

A. Basic Configurations of Slider

There are several candidate configurations available for the

slider to drive the gondola. Among them, we have selected a

Λ-drive [10]

, in which frictional losses between the tube and the

slider can be reduced to allow smooth movements of the slider

along the long tube. The greatest features of the Λ-drive lie in

that, unlike the cutoff methods that employ pinch-rollers [8]

or

flexible rod-less cylinders [9]

, the use of the buckling

phenomenon of the tube in Fig.2 allows cutting off the flow

without strong force.

A basic configuration to obtain the stable driving force using

the Λ-drive is shown in Fig.4 (a). The components are a holder

to retain the tube locally buckled into a Λ-shape, rollers which

enable the slider to glide smoothly, stoppers which prevent the

tube from being pulled out, and a cover to prevent the tube

from jumping out. The stoppers are supported by passive

swing arms to avoid disturbing the expansion of the tube when

the tube is pressurized either from the left or the right side. In

the state shown in Fig.4 (a), when the tube is pressurized on

one side, fluid flows to the buckling point, where the flow is

cut off to prevent fluid from flowing into the downstream side

of the buckling point. Then, the stiffness of the tube is

increased on the upstream side to incline the slider in the

direction of movement. Continued pressurization of the tube

moves the buckling point, pulling the rollers on the

downstream side (Roller D) and then moving the whole slider

to the downstream side (Fig.4 (b)).

(a) Structure of the slider in non-pressurized condition

(b) Drive principle when one side of the tube is pressurized

Fig.4 Basic structure of the slider in Λ-drive

For flexible tubes as a component of the Λ-drive, flat tubes

are used. They are in flat sectional shapes in the

non-pressurized condition and are changed into increasingly

circular sectional shapes while maintaining a nearly constant

sectional circumference in the pressurized condition. Unlike

the general cylindrical tubes, flat tubes are already crushed flat

on the downstream side of the buckling point so that the

buckled part of the flat tube can be moved easily and smoothly.

All of the tubes described below are all flat tubes.

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B. Internal Configurations of Gondola

1) Installation of Slider

In order to reduce the counter-force working from the

upstream roller, in addition to the improvements in the

configurations of the slider, the slider’s mounting position in

the gondola needs to be properly selected. How to select such

positions for the slider is discussed as follows, using Fig.5.

Fig.5 Ideal position of the slider to connect with the gondola

The position of installation of the slider inside the gondola

case should be somewhere on the center line C of the holder in

order to secure symmetry in motion, even in the operations

switched over between upstream and downstream. Then, one

of such positions on the center line C should be selected as an

optimum position for the installation of the slider as described

below.

With tension dF acting on the downstream side tube (tube

D) of the slider taken into consideration, it will be found an

effective design in terms of reduction of the counter-force uF

to install the holder to the gondola at the intersection O

between the acting line of tube D and the center line C. This is

because such design produces zero moment around the

intersection O regardless of different magnitudes of dF ,

making the retroflex phenomenon of tube U less likely to

occur.

Such design will only be found effective if the acting line of

tube D is fixed in a certain direction. The following section

describes the tube guide mechanism.

2) Tube Guide Mechanism

The mechanism considered herein is one in which the acting

direction of tube D is always kept parallel to the longitudinal

directions of tube U and the gondola. This ensures identity

between the directions of the drive force and the direction of

movement of the slider, hence improvements in drive

efficiency. In order to ensure such parallel conditions, we have

introduced a tube guide mechanism as described below.

In the introduced mechanism, supporting rollers (pivot

rollers) are fitted at the inlet and outlet of the gondola, and

then swing rollers are fitted around these pivot rollers. The

pivot rollers at the inlet and outlet are interconnected with

linkage so that swing can be conveyed to the opposite side

(Fig.6 (a)). With such a mechanism, pressurization on one side

inclines the slider toward the downstream side, and, at the

same time, lifts up the swing roller on the upstream side.

These motions are conveyed to the downstream side through

the linkage to get the swing roller on the downstream side to

push down the tube so that the tube on the downstream side is

always kept parallel to the direction of the drive force (Fig.6

(b)). This mechanism of such symmetric configurations is

expected to function as well even if the direction of

pressurization is reversed.

(a) Non-pressurized condition

(b) Pressurized condition

Fig.6 Structure of the gondola with the tube guide mechanism

IV. INTRODUCTION OF Λ-DRIVE

A. Propulsion Forces at Buckling Point and Classification

of Drive Modes

As shown in Fig.7, the slider is driven by the propulsion

force bF at the buckling point of the tube or by the traction

force tF acting on the downstream side of the tube. With the

cross-sectional area of the tube denoted by A and internal

pressure by p , it is already known that bF and

tF can be

expressed by the following equations [10]

. The relationships

between bF and

tF as expressed by these equations are also

inferable from the fact that the traction speed of the tube

become twice as fast as the propulsion speed at the buckling

point.

ApFb (1)

2)(2 ApFF bt (2)

Fig.7 Buckling point of the flat tube

Since force-transmitting pathways vary with the contact

conditions between the buckling point and the slider, the

slider’s drive force will be varied even when bF and

tF are

identical. Drive modes that vary with the contact conditions

can be classified into the following three modes (Table.1): A)

Buckling mode, in which the buckling point does not contact

to either the stopper nor the cover; B) Stopper mode, in which

the buckling point contacts the stopper; and C) Cover mode, in

which the buckling point contacts the cover. The said

classification is determined by the fastening conditions

between the upstream and downstream sides of the tube and

the external environments or by the length relationships

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between the distance of the fixed points and the tube length [10]

.

Table.1 Drive modes of slider

In the buckling mode shown in Table.1-A), tension tF acts

on the downstream-side roller to produce drive force tF2 .

This mode is limited to the conditions in which the tube is

fixed to the external environments on both the upstream and

downstream sides, and the buckling point does not contact the

cover or the stopper. Since the buckling mode is very rare with

the fluid powered ropeway, we will only refer to B) stopper

mode and C) cover mode in the following sections.

B. Movement Conditions and Propulsion Forces of the

Gondola

The fastening conditions of the tube and external

environments can vary depending on the movement status of

the gondola along the tube. The conditions of movement of the

gondola can largely be divided into the following: 1) the

condition in which the gondola contacts the ground when it

moves (contact condition), and 2) the condition in which the

gondola does not contact the ground but is kept suspended

when it moves (suspended condition). In the case of 1), no

tension acts on the tube, causing the tube to sag on both the

upstream and downstream sides, and the drive modes vary

with the fastening conditions of the tube on the upstream side.

In the following subsections, we will define the drive modes of

the slider in each of the above-mentioned conditions of

movement of the gondola, and then we will define the

propulsion force produced in the gondola

1) Grounded Condition with the Tube Fixed on the Upstream

Side

Since no tension acts on the tube when the gondola contacts

the ground, drive modes of the slider are determined by the

conditions in which the tube is supported by the external

environments on the upstream side.

First, we consider the case (Fig.8) in which the tube is fixed

to the external environments on the upstream side; the tube

does not sag or move against the external environments on the

upstream side when the gondola moves. In this case, the slider

moves while remaining in the cover mode, because the

buckling point moves to downstream side while the upstream

Fig.8 Cover mode drive when the gondola is on the ground and the upstream

tube does not move against the ground

side tube does not move with respect the external environment.

A pushing force is generated for the slider only when the

buckling point comes into contact with the cover.

In the above-mentioned case, output force of the slider outF

is expressed by Equation (3), taking into account the

propulsion force of the buckling point bF with relation to the

bend of the tube on the upstream side and the friction force R

created when the buckling point slides inside the cover.

ccbout RFF sincos (3)

bFR (4)

where c denotes bend angle of the direction of movement of

the buckling point against the center line of the tube on the

upstream side, and , friction coefficients between the cover

and the tube.

2) Grounded Condition with the Tube Unfixed on the

Upstream Side

In the conditions (Fig.9) in which the tube on the upstream

side cannot support reaction forces produced when the

gondola is propelled, the buckling point of the tube cannot

push the slider. On the other hand, as soon as the tube is

pressurized, the buckling point moves toward the downstream

side of the tube, drawing into the slider the tube on the

downstream side and pulling out the tube on the upstream side.

Such phenomenon continues until tension acts on the tube on

the downstream side to get the buckling point to contact the

stopper.

Fig.9 Stopper mode drive when the gondola is on the ground and the

upstream tube moves against the ground

In such a stopper mode, the downstream side roller is pulled

toward the downstream side by the force tF to drive the slider

toward the downstream side. In such a condition, no tension

acts on the tube on the upstream side, hence there is no

counter-force working from the upstream roller. The output

force outF can be expressed as follows:

tout FF (5)

3) Suspended Condition

When the gondola moves along the tube stretched between

obstacles, as in Fig.10, tension is applied to the tube. The

Fig.10 Stopper mode drive when the gondola is suspended by a tube

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tension affects the tube inside the slider to take the shortest

pathway, and, as a result, the buckling point contacts the

stopper, i.e., stopper mode. Furthermore, since the

counter-force is produced on the upstream tube inside the

slider, the drive force generated in the slider is lower than

Equation (5).

Fig.11 Drive principle of the slider in the stopper mode

Output force outF of the slider in such a condition can be

derived as follows: uT denotes tension on the upstream-side

tube; dT

denotes tension on the downstream- side tube;

uF

denotes the counter-force acting on the upstream-side roller;

and u2 denotes the retroflex angle of the upstream side tube.

Then, the relationships of balancing forces shown in Fig.11

lead to the following equation:

uuudout FTTF sin (6)

On the other hand, as the traction force tF acts on the tube on

the downstream side of the buckling point, the relationships of

tensions between the upstream side and the downstream side

of the tube are expressed by the following equation:

2/ApTFTT utud (7)

The above-mentioned relationships are also derived by

substituting wire for the tension-transmitting tube and the

pushing-up motion of the cylinder for the movement

phenomenon of the buckling point due to fluid pressure inside

the tube. In addition, the following equation is derived from

Equations (6) and (7):

uuout FApF sin2/ (8)

V. EXPERIMENTS

A. Prototype Gondola

In order to verify the effectiveness of the proposed fluid

powered ropeway, we have prototyped a gondola, as shown in

Fig.12.

Fig.12 Overall view of the developed gondola prove unit

The prototype gondola is equipped with two compact

cameras (RF Inc.: RC-12; mass: 14.7 g) capable of radio

transmission up to 30 m. In order to expand the probing range,

these cameras can be rotated using the inclining movements of

the slider; the configurations are such that torque to be created

when the slider gets inclined can be transmitted to the cameras

via the gear mounted on the rotating shaft of the slider. Such

configurations enable the gondola to move backward and

forward with the cameras looking in the same direction. In this

research, we have set the gear ratio so that the cameras should

rotate 180° against the 100° inclination of the slider; in this

way the cameras can always capture images in the direction of

movement. In addition, heavy items such as cameras are all

placed below the gondola so that the center of gravity of the

gondola is below the tube. This allows the gondola to move

along the tube in a stable posture.

B. Experiments in Test Field

We conducted experiments in an environment simulating a

dangerous building similar to Fig.1. The experiments are

aimed at the rapid collection of information in situations in

which the operator cannot look straight inside the building

because of a gap of 4m between the operator and the building.

A ball with a low rebound-characteristic and a mass of 520 g

was attached to the tube and then thrown inside the building

(Fig.13-1). We first pulled back on the tube to remove any

sagging so that the only buckling that would occur in the tube

would be in the slider. The tube was then internally

pressurized with a pneumatic pressure of 0.4 MPa to make the

gondola approach the building at the velocity of about 2.0 m/s

(Fig.13-2). When the gondola advanced to the inside of the

building, it hit the corner of the desk and got stuck there

(Fig.13-3). The tension of the tube was around 10 N, so we

loosened the tube until its tension reached around 5 N, and

increased the velocity of the gondola to 2.5 m/s. The gondola

then succeeded in getting over the corner.

Fig.13 Demonstration of Fluid Powered Ropeway aiming to find the victim

(doll) lying inside the building

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While the velocity of the gondola was adjusted to between

0.0 m/s and 1.0 m/s by the operator controlling the flows in the

tube on the upstream side, the radio cameras mounted in the

gondola captured the head of a person (doll) to be rescued

(Fig.13-4). After that, we continued probing in detail by

moving the gondola backward and forward at a velocity of 0.7

m/s. Finally, we reversed the direction of the pressure in the

tube to get the gondola to return to the operator (Fig.13-5,6),

and we then recovered the tube by pulling the one end of it.

E. High-powered System for Plant Monitoring

The introduced fluid powered ropeway can be applicable for

the system which requires much higher force and power.

Figure 16 indicates the image of the application for

monitoring the inside of a nuclear power plant for preparation

for emergency. To monitor the density of hydrogen or leaked

condition of radioactivity, some sensors with heavy mass are

needed to move smoothly inside the plant surrounded by the

rugged ground and the complex pipes. To satisfy these

requests, the fluid powered ropeway with high power is

expected to be remodeled by replacing the flat tube with a fire

hose. The prototype of the slider with 2.7 kg in weight could

climb up 4m in height perpendicularly, generating 1.28kN

under the water pressure of 1.2 MPa, which suggests us that

the proposed driving method would be also applicable for the

wide designing range of size (Fig. 14, 15).

Fig.14 Structure of the high-powered slider driven by water hydraulics in a

fire hose

Fig.15 Developed slider and the demonstration of climbing up 4m hill by

water hydraulics

Fig.16 Images of monitoring the inside and the outside of the plant by using

the fluid powered ropeway

VI. CONCLUSIONS AND DISCUSSIONS

In this paper, we have proposed a new method of locomotion,

a fluid powered ropeway, as a means of moving, in a rapid and

safe manner, an unmanned probing robot inside a dangerous

building in order to collect information. We have also

described the operating procedures as well as the features of

the fluid powered ropeway. The proposed fluid powered

ropeway, therefore, can travel even in unfavorable

environments where floor reaction forces cannot be relied on.

For the drive method for the gondola, we have introduced the

fluid driving principle, using the buckling phenomenon of the

tube, we call a Λ-drive. We have also studied design methods

for the gondola and analyzed its performance and methods of

traversing obstacles. In the future, we plan to study the

methods of informing the operator of the position of the

gondola when it is in locations that are not visible to the

operator.

References

[1]Toshio Takayama and Shigeo Hirose ―Development of "Souryu I & II"

-Connected Crawler Vehicle for Inspection of Narrow and Winding

Space‖ Journal of Robotics and Mechatronics, Vol.15, No.1 (2003)

[2]Hideyuki Tsukagoshi, Yotaro Mori, Masashi Sasaki, Takahiro Tanaka,

and Ato Kitagawa ―Development of Jumping & Rolling Inspector to

Improve the Debris-traverse Ability― Journal of Robotics and

Mechatronics, Vol.15, No.5 (2003)

[3]Richard M.Voyles, Roy Godzdanker ―Side-Slipping Locomotion of a

Miniature, Reconfigurable Limb/Tread Hybrid Robot‖, Proceedings of

the IEEE International Workshop on Safety, Security and Rescue

Robotics, p.58-64(2008)

[4]Hideyuki Tsukagoshi, Hiroyuki Chiba, Ato Kitagawa ‖Gel-type Sticky

Mobile Inspector to Traverse on the Rugged Wall and Ceiling‖ IEEE

International Conference on Robotics and Automation, FrA2.5 (2009)

[5]Kevin S.Pratt, Robin R.Murphy, Jennifer L.Burke, Jeff Craighead,

Chandler Griffin, Sam Stover ―Use of Tethered Small Unmanned Aerial

System at Berkman Plaza II Collapse‖, Proceedings of the IEEE

International Workshop on Safety, Security and Rescue Robotics,

pp.134-139(2008)

[6]M.Onosato, H.Nakanishi et al. ―Aerial Robots for Quick Information

Gathering in USAR‖, Proceedings of SICE-ICASE International Joint

Conference, p.3435-3438(2006)

[7]Eyri Watari, Hideyuki Tsukagoshi, Takahiro Tanaka, Daichi Kimura, Ato

Kitagawa: ―Development of a Throw & Collect Type Rescue Inspector, ‖

Proceedings of the 2007 IEEE International Conference on Robotics and

Automation ThC12.3 (2007)

[8]Shigeo Hirose, Ryo Yoshida,―Development of Pinch Roller lifters‖, 14th

Annual conference of the Robotics Society of Japan p.889-900(1997)

[9]T.Akagi, S.Dohta et al, Development of Flexible Pneumatic Actuator with

a Flexible Tube, Proc INTERMAC2001 Joint Tech. Conf, F-1093,1-10

(2001)

[10]Yotaro Mori, Hideyuki Tsukagoshi, Ato Kitagawa ―Fluid Powered

Actuator Sliding Along Flexible Flat Tube (1st Report: Proposal of

Λ–drive and Its Driving Analysis)‖, Journal of the Japan Fluid Power

System Society, vol.41, No.5 (2010)

[11]Yotaro Mori, Hideyuki Tsukagoshi, and Ato Kitagawa, ―Flexible Sliding

Actuator Using A Flat Tube And Its Application To The Rescue

Operation,‖ 2010 IEEE International Conference on Robotics and

Automation, ThA2.3 (2010)

[12]Yotaro Mori，Hideyuki Tsukagoshi，Ato Kitagawa, ―Fluid Powered

Ropeway: Self-propelled Probe Sliding Along Flexible Tube‖, Journal of

Robotics and Mechatronics, Vol.23, No.2, 215-224 (2011)

Hose: Φ50mm Fire hose

Roller:Φ60mm with V groove

and Φ90mm Flange

Stopper:Φ8mm

Weight:2,700g

160

V groove

50

Slip on stopper

Head roller

1180