Abstract— This paper discusses a casting device for search and

rescue operation to aid higher and faster access for mobile

robots. To realize higher performance, the design concept of the

device is examined from the following three aspects. First, after

the arrangements of the stored tether are categorized, the

method of selecting the optimal one is considered to maximize

the kinetic energy on the tether. Second, to minimize the

resistance caused by the tether, a tapered case for the storage is

proposed, expected to mitigate the friction between the tether

and the case and to prevent the twist on the tether. Third, the

way of anchoring the end of the cast tube is proposed. Finally,

experimental results show the validity of the device designed on

the proposed concepts, after the device is combined with an

unmanned vehicle and a ropeway type robot.

Index Terms— Tether Casting, Search and Rescue,

Pneumatic Actuator, Fluid Power

I. INTRODUCTION

TETHER is effective for mobile robots as a tool to aid

traversing and collecting information on hard access

area. For example, in case of a steep slope that cannot be

climbed by a robot solely, if it can cast a tethered anchor and

fix it to the external environment, it enables the robot to move

without slippage [6]. As another example, in case of rescue

operation in dangerous buildings, it would be helpful to cast a

child machine attached to a tube through an opened window

to collect the gas in order to analyze the harmfulness, before

the rescue parties go into there, as shown in Fig.1(a). The

traverse ability of Ropeway type robot [19], which can let the

gondola with cameras slide along the tube, would be

enhanced by casting the tube with an adhesive ball, as shown

in Fig.(b).

Furthermore, aiming to enhance the performance of mobile

robots, various researches have been reported regarding the

carrying or handling operation by tethers [1-10]. Fukushima

et al. [1] proposed a hyper-tether concept including

communicating function, which provides intelligent tethering

among different mobile robot types, such as a robot with the

environment and a robot with humans and animals. Minor et

al. [4] proposed a smart system for the improvement of

extravehicular activity efficiency by using a remotely

releasable robotic gripper and a retractor controlling the

length of tether. These research results would become more

applicable for the robots which is required to approach the

separated point as fast as possible, if a tether can be casted

farther and higher by the installed actuator .

Hence, in this paper, a one-dimensional casting motion

generated by a pneumatic cylinder with high-speed

performance is focused, which has also the advantage of

being mounted on a manipulator or the robot body simply.

The design concept of the casting device for a tethered

payload is discussed in the following order. To begin, it is

shown that casting heights vary with the arrangements of the

stored tether. Second, a tube-retrieving device is investigated

to mitigate the resistance that occurs when releasing the tether.

Third, how to fix the end of the cast tube is shown, supposing

the casting device is used for the application of Fig.1(b).

Finally, the effectiveness of the proposed methods is verified

experimentally by using a prototype.

(a) Sampling of the gas (b) Search by Ropeway type robot

Fig. 1. Examples of using a casted tube at disaster site.

II. COMPOSITION AND CLASSIFICATION OF CASTING

A. Basic Composition and Configuration

In this research, a pneumatic cylinder is used as the actuator

to generate the casting motion. By relying on the expansion

energy of compressed air, it features the facility of generating

high speed motion with a composition of high power to

weight ratio. In addition, it is explosion proof, differing from

gunpowder based shooter involving ignition, and it does not

generate water aspersion as a plastic bottle rocket does.

In this section, a cylinder composed of a cylinder tube and

of a piston-rod with stroke length L is placed at the ground in

a vertical position facing towards the sky. The end-effector on

the tip of the rod has a cup like form, enabling containment of

an object. On the other hand, the tether to be casted has a

linear density of σ, and length of Y, and a child machine of

mass mK is attached to one of its ends. Here, the child machine

considered in this paper is a payload that represents one or

either of the functions of fixating into the external

environment, inspecting, manipulating, cushioning impact,

and others.

Casting Device for Search and Rescue

Aiming Higher and Faster Access in Disaster Site

Hideyuki Tsukagoshi, Eyri Watari, Kazutaka Fuchigami Ato Kitagawa, Member, IEEE

A

2012 IEEE/RSJ International Conference onIntelligent Robots and SystemsOctober 7-12, 2012. Vilamoura, Algarve, Portugal

978-1-4673-1736-8/12/S31.00 ©2012 IEEE 4348

In the initial state before pressurization, the rod is stored

into the cylinder tube at its minimum extension. Also, the

tether is stored spirally into a case without entangling itself.

Next, by pressurizing the inner of the cylinder with

compressed air, the rod extends to its most in the instant of

casting, and the center of mass of the child machine transits

through the point of height h0 from the ground. At this

moment, the velocity with reference to the ground of the

center of mass of the child machine and of the rod achieves

the maximum velocity of v0, and it will be called final velocity

of the rod. Furthermore, after the casting, the instant that the

velocity of the center of mass of the child machine reaches 0

is considered the maximum casting height. In other words, the

height at this moment is the casting height h (which is a

generalized parameter of ha, hb, hc1, hc2 on section 2.2) based

on h0 of the child machine. Accordingly, the tether satisfies

𝑌 > ℎ0 + ℎ.

B. Classification of Casting the Tether

(a) Fixed Storage Type

The casting method in which the storage case stays onto the

ground with the cylinder will be called ―fixed storage type‖

(Fig.2). This is the most commonly used method for casting

tethers, such as water rescue operation, and others.

Considering the fact that kinetic energy is applied only to

the length h0 of the tether, the relationship between the kinetic

energy just before casting and the potential energy after the

casting of both child machine and tether is described as

equation (1). Here, the resistance that occurs when releasing

the tether from the case is considered to be 0.

𝑚𝐾𝑔ℎ0 + 𝜎ℎ0 𝑔ℎ0

2+

𝑚𝐾+𝜎ℎ0 𝑣02

2= 𝑚𝐾𝑔 ℎ0 + ℎ𝑎 +

𝜎 ℎ0 + ℎ𝑎 𝑔ℎ0+ℎ𝑎

2 (1)

Hence, the casting height of ha can be derived as in equation

(2).

ℎ𝑎 =− 𝑚𝐾+𝜎ℎ0 𝑔+ 𝑚𝐾+𝜎ℎ0 𝑔 2+𝜎 𝑚𝐾+𝜎ℎ0 𝑔𝑣0

2

𝜎𝑔 (2)

Fig. 2 Casting process by Fixed Storage Type.

(b) Unified Type

The casting method, in which the storage case with the child

machine is casted into the air with it combining with the

whole tether from the initial condition until the maximum

height, will be called ―unified type‖ (Fig.3). In the initial

condition, the case is contained by the end-effector. The

kinetic energy of 𝑚𝐾 + 𝜎𝑌 𝑣02/2, applied to both the child

machine and the whole tether length, is assumed to be

transformed to potential energy of 𝑚𝐾 + 𝜎𝑌 𝑔ℎ𝑏 , and

thereby the casting height of hb can be derived as in equation

(3).

ℎ𝑏 =𝑣02

2𝑔 (3)

From the magnitude relationship of equations (2) and (3),

and considering the same v0 (with v0>0), then ℎ𝑏 > ℎ𝑎 is true.

The reason of this difference is that the kinetic energy

generated by the cylinder is applied to the whole tether length

within the unified type casting method, over the fact that it is

applied only to a small portion of the tether length within the

fixed storage type casting method.

In the meantime, it is assumed within this method that the

child fixates somehow to the external environment at its

maximum casting height, and it drops the tether in the

direction of the gravity by opening the case. Hence, although

it loses versatility as a tethered casting method, it is

considered as a basis for comparison since it is an ideal form

which is not being subject to the influence of the motion of

the tether.

(c) Discharge Type

The casting method, in which the storage case with the child

machine is casted into the air with one of the ends of the tether

fixed to the cylinder and with other parts kept inside the case,

will be called ―discharge type.‖ Despite the fact that in the

initial state, the case is contained in the end-effector in the

same way as the unified type, the tether is discharged

(released) in mid-air after the casting until the child machine

reaches its maximum casting height. The procedure of

discharging the tether can be sub-categorized into two ways.

Fig. 3 Casting process by Unified Type.

Fig. 4 Casting process by Gradual Discharge Type.

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c1: Gradual Discharge Type

By casting the child machine unified with the case, the

tether is gradually discharged to mid-air while ascending.

This method will be called ―gradual discharge type,‖ and the

casting height of the child machine is set to be hc1 (Fig.4).

Since the kinetic energy applied to the child machine and to

the tether within this method can be considered as the same as

within the unified type, in the ideal situation in which there

are no losses, hc1 = hb can be thought. Nevertheless, in the real

situation, since there is the influence of the resistance

generated when the tether is drawn out from the case, hc1 is

lower than hb

c2: Instantaneous Discharge Type

By fixating the case inside the end-effector and casting the

child machine and the tether together, the whole tether is

instantaneously discharge to mid-air while ascending. This

method will be called ―instantaneous discharge type,‖ and the

casting height of the child machine is set to be hc2 (Fig.5). For

the same reason as in the gradual discharge type, in the ideal

situation which there are no losses, hc2 = hb can be thought.

Although resistance to draw out the tether from the case is not

generated in this method, i) friction is generated between the

tether and the case in the instant of casting; ii) the increase of

dynamics (including air drag) of the tether is caused by its

diffusion in mid-air. Since such acting losses occur, hc2 is

lower than hb.

Since the magnitude of the losses in both of the above

discharge types depends on the material of the tether and of

the case, as well as their structures, and other individual

elements of design, it is complex to determine the magnitude

relationship between them. In this paper, by introducing a

structure of the storage case which mitigates the losses

showed in section 4, it is assumed the casting heights hc1 and

hc2 can be generated close to hb, and thereby proceeding the

discussion.

The right side of Fig.6 shows the result of the comparison

via simulation of the feature of the MB Cylinder (Magnetic

Brake Cylinder) [12, 13] and the conventional cylinder (used

in a conventional pneumatic circuit). The mass mall of the

horizontal axis represents the total of the mass of the rod

alone mr, the mass of the child machine mK, and the mass of

the tether that acts onto the end-effector. Table 1 shows the

parameters of the cylinder used in the simulation. In the

simulation, the final velocity of the rod is obtained

considering also the variance of temperature and internal

pressure of the cylinder. As constraints of the conditions, the

tank, the internal diameter and stroke length of the cylinder,

and the total mass of the system of both systems are the same.

For this reason, within the conventional cylinder system, the

valve used has a larger effective cross-sectional area than of

the MB Cylinder. As result, as seen in Fig.6, the MB Cylinder

is capable of generating a final velocity of the rod 1.3~1.9

times higher than the one with the conventional cylinder.

Therefore, it is assumed the use of MB Cylinder for the

casting hereafter.

C. Selection of the Casting Method

The basis of selection of the method which provides a high

casting height when using MB Cylinder to cast a tethered

child machine is shown.

First, a comparison of the casting height ha of the fixed

storage type, and hb of the unified type is performed

considering the difference of the total mass mall acting on the

rod. The mall within each method is as follows.

Fixed storage type:

𝑚𝑎𝑙𝑙 = 𝑚𝑟 +𝑚𝐾 + 𝜎 ℎ0 − 𝐿/2 (4)

Unified type and discharge type:

𝑚𝑎𝑙𝑙 = 𝑚𝑟 +𝑚𝐾 +𝑚𝑄 + 𝜎𝑌 (5)

Fig. 5 Casting process by Instantaneous Discharge Type.

Fig. 6 Final velocity of the rod due to payload and the casting height

Table 1. Parameters for obtaining theoretical casting heights.

Parameter Value

v0 for fixed storage type (m/s) 10.75

v0 for unified type (m/s) 10.5

σ (kg/m) 9×10-3

Y (m) 8

mK (kg) 56×10-3

mr (kg) 198×10-3

L (m) 163×10-3

h0 (m) 292×10-3

Internal diameter of cylinder tube (m) 29.9×10-3

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Here, mQ represents the mass of the storage case alone. In

addition, a portion of the total mass acting on the rod within

the fixed storage type is the mass of the tether that moves

along with the end-effector. However, in order to simplify the

analysis, this mass is considered to be an average between the

length of the tether in the initial state and the length of tether

of when the rod is extended at its most.

Next, in the left side of Fig.6, the relationship between the

final velocity of the rod of v0 and the casting heights of ha and

of hb is shown. The parameters of the tether are also showed

in Table 1.

With the above preparations, the requested casting method

is selected following the procedures bellow. For instance,

assuming that the total mass acting on the rod within the fixed

storage type is represented by the point of A1, the final

velocity of the rod is predicted to be the point of B1

(consequently C1 too), and the casting height of ha becomes

the point of D. On the other hand, to generate the casting

height of hb within the unified type casting method, the final

velocity of the rod must satisfy such to be the same as the

point of C2 (consequently B2 too). Hence, the condition for

the casting height of the unified type to be higher than the one

of the fixed storage type must satisfy the following equation

with the mass of mall calculated from equation (5).

𝑚𝑎𝑙𝑙 < 𝑚𝑎𝑙𝑙 A2 (6)

where mall(A2) is the value of mall at the point of A2.

III. STORAGE CASE TO MITIGATE RESISTANCE

In order to attempt the enhancement of the casting height of

a tethered child machine, the existence of losses that occur

with the tether cannot be ignored. In this section, by carefully

elaborating the structure of the storage case, a way to mitigate

the resistance generated when the tether is drawn out of the

case is found.

A. Introduction of a taper case

As a structure for: i) drawing out the tether without moving

the whole tether at once; ii) not twisting the tether; iii) and

retrieving the tether ordered so that there are no interference

between the tether; the tapered form hollow case structure is

introduced. Furthermore, a flexible tether is assumed to be

used, which is able to produce a small restoring force when

curved with small radius. In the initial state which the tether is

not retrieved, one of the ends of the tether is fixed at the

bottom of the case in a way to trace along the internal wall.

From this state, by pushing the tether towards the bottom of

the case and into it, the tether is retrieved spirally along the

internal wall of the case gradually. At this moment, no space

is generated between the spiral form of the tether, and twist to

the tether cannot be observed. On the other hand, when the

tether is drawn out, it is kept still in its spiral form inside the

case, and since it is drawn out of the case sequentially from

the top, there are no friction occurring between the tether

itself, and the resistance generated when drawing out the

tether from the case can be restrained to a minimum.

Fig. 7 Comparison of how to store the tether .

Fig. 8 Tether stored into a tapered form case.

This phenomenon occurs particularly within the tapered

form case, and cannot be observed with a cylindrical form one.

This can be explained by the following. Focus is set to the

cross section of the wound up tether inside the case, including

its maximum line of inclination. The restoring force of Wt of

the tether pushes the internal wall of the case in a direction

inclined with an angle of the maximum inclination of φt of the

wound up tether against the horizontal line. Assuming a

cylindrical form case (Fig.7(a)), the component of Wt towards

the direction of the internal wall of Wtsinφt, acts in the

downward direction in the lowest point of D aiding to retain

the tether into the case, but it acts in the upward direction at

the highest point of U and the spiral form can be easily

collapsed. In contrast, assuming a tapered form case

(Fig.7(b)) with inclination of φs (with φs>φt) from its central

axis, in the lowest point of D the component Wtsin(φs+φt), and

in the highest point of U the component Wtsin(φs-φt), both act

in the downward direction along the internal wall of the case,

and so the spiral form of the wound up tether can be easily

kept in a stable way.

B. Split-opening storage case

The introduced structure consists of a tapered case with a

split-opening function fixed to the end-effector (Fig.9). In

other words, the tapered case is split into two halves along its

central axis. Each of them is connected to a frame, which is

able to swing passively through a pivot fixed at the

end-effector. On the other hand, a roller is placed to the tip of

the each of the arms which are attached to the cylinder tube.

With this structure, the end tip of the frame is pushed by the

rollers when the rod extends to its most, opening the tapered

case. Not only can this split-opening function mitigate the

resistance occurred when releasing the tether in the instant of

the casting, but it is also expected to minimize the air drag

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suffered by the tether since the whole tether is casted in a

tapered spiral form at the beginning. Additionally, to avoid

the opening of the case during the extension of the rod, a

rubber band is set at the tip of the case, which keeps it closed.

C. Results and discussion

As for the comparison of the casting methods, the casting

heights obtained for the 3 methods are higher than the fixed

storage type one, in accordance to the prediction. Hence, the

selection method proposed in section 3.2 can be considered

validated. Furthermore, the reason of both discharge type

methods having a lower casting height than the unified type

one is inferred to be due to still having some resistance to

draw out the tube from the case, although the tapered case is

introduced.

IV. DEFORMABLE ANCHOR BALL WITH SUCTIONS

To fix the end of the cast tube on the outer environment

stably, a new type of anchor device is installed with reference

to an octopus’s sucker. In the case of the octopus, after the

outer line of the sucker is temporarily fixed by the adhesive

force, the suction force is generated by enlarging the inside of

the sucker. The temporal adhesion helps to increase the

adaptability of the sucker against various shape of the

environment, while the enlargement of the inside is effective

to generate negative force easily at each sucker individually.

To utilize these advantages for anchoring the cast tube,

Deformable Anchor Ball with Suctions (DABS) is proposed,

as shown in Fig.11. DABS is covered with adhesive skin,

whose inside is filled with Styrofoam and cylindrical suckers.

After the cast DABS is collide with the wall, it is temporarily

fixed on the wall by the adhesive force first. Second, it can be

tightly fixed by decompressing the inside of the ball. Since

the each Styrofoam particle is compressed and space among

them is reduced, DABS itself becomes stiff, which is helpful

to increase the robustness against the large traction.

The developed DABS was shown in Fig.12 and Table 2,

The outer skin was made of Thermoplastic Elastomer (TPE),

whose adhesive force per square is 0.03MPa against the

concrete wall, generating 21N as the suction force.

Fig. 11 Principle of DABS

Table 2 & Fig. 12 Developed DABS

V. EXPERIMENTS

Searching operation described in Fig.1(b) was demonstrated

by using an unmanned vehicle equipped with the casting

devices and Fluid Powered Ropeway[14], as shown in Fig.13.

First, the vehicle remotely operated by an operator from15m

far distance, approached the building. Second, the adhesive

ball with a tube was casted to the point with 7m height and 8m

horizontal distance by MB cylinder, sticking to the targeted

window. Third, after the tension of the tube was adjusted by

the retrieving device, the gondola carrying the radio camera

slid along the tube at the speed of 2m/s, while the inside of the

tube was pressurized by 0.4MPa compressed air. The picture

capturing the inside of the window could be successfully sent

to the operator, as shown in Fig.14. Basic driving principle of

the gondola was explained in detail in [14].

Fig. 9 Structure of a tapered case with split-opening function.

Fig. 10 Simulated and experimental results of casting for each method.

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(a) Device for casting and retrieving (b) Unmanned vehicle equipped with

casting device and its power unit

Non pressurized condition Pressurized condition

(c) Principle of driving the gondola by fluid power in the tube

(d) Structure of the gondola (d) Gondola to carry the camera

Fig.13. Developed devices to collect information remotely.

Fig.14. Demonstration of search operation in the building using the

unmanned vehicle with the casting device and the ropeway robot.

VI. CONCLUSIONS

Aiming at casting a tethered child machine higher with a

pneumatic cylinder, a novel knowledge regarding casting

methods is presented. To begin, while using effectively the

kinetic energy generated by the cylinder, the casting methods

focusing on how to set the tether is divided into 4 categories.

Next, a tapered form retrieving case, which mitigates the

resistance that occurs when drawing out the tether form the

case, is proposed. Furthermore, the deformable anchor ball to

fix the end of the cast tube was proposed. And finally, the

efficacy of these is validated through experiments using a

prototype. As future works, a control method of the tethered

child machine casting methods will be verified.

ACKNOWLEDGMENT

This work was performed under the support of the Fire and

Disaster Management Agency of Japan. The

acknowledgement is presented here.

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