Design of Intestinal Modular Robot and Dynamics Analysis of Its

Docking Mechanism

Dasheng Liu

School of Sensing Science and Engineering, School of Electronic Information and Electrical Engineering,

Shanghai Jiao Tong University, Shanghai, China

Keywords: Modular Design, Docking Mechanism, Intestinal Robot, Kinetic Analysis.

Abstract: This paper presents a modular design scheme of intestinal capsule robot, and establishes the analysis model

of multi-module docking mechanisms. Firstly, the overall structure design of the intestinal module robot and

the method of rod-cone docking in the intestinal tract are given. Then, by dividing the modules into installation

module and docking module, the coordinate transformation method and virtual simulation analysis model for

the two modules to realize docking in the intestine are constructed. Finally, the docking process of adjacent

modules is simulated using dynamic analysis software, and the experimental results verify the effectiveness

of the design.

1 INTRODUCTION

In order to overcome the limitations of capsule

endoscopy, many research institutions have carried

out a lot of improvement works in the past 20 years,

and have successively developed two kinds of capsule

endoscopes: magnetic control capsule and magnetic

rotary capsule (Madani et al., 2016; Phan et al., 2021;

Qian et al., 2018; Zhang et al., 2020; Zhang et al.,

2017). The magnetic control capsule endoscope can

realize three-dimensional movement, which is

suitable for diagnosing the expanded gastric cavity,

but its disadvantage is that the positioning of the

capsule in the body is not accurate, and because of the

small magnetic traction, it is difficult to achieve

effective movement in the intestine. The magnetic

rotary capsule endoscope also has some limitations:

for example, when the capsule moves, it needs to fill

the intestine with transparent liquid medium, but

when the liquid is not full, the rotary capsule is easy

to twist the intestine, causing intestinal damage.

Micro gastrointestinal robot is one of the most

potential alternatives to traditional gastrointestinal

endoscopy, and has been a research hotspot in the

field of medical devices in recent years. At the

Liu, D. Design of intestinal modular robot and dynamics

analysis of its docking mechanism. In Proceedings of the

3rd International Symposium on Automation, Information

and Computing (ISAIC 2022).

beginning of gastrointestinal robot research, in view

of the limitations of capsule endoscope, prototypes of

gastrointestinal robots based on many bionic

principles have been designed one after another,

providing them with the function of imitating the

active movement of Inchworm, beetle, cockroach,

fish, etc. (Kosa et al., 2006; Li et al., 2007; Menciassi

et al., 2004; Moglia et al., 2007; Park et al., 2006).

The motion mechanism is the key and difficult point

in the development of gastrointestinal robot. The

ideal motion mechanism should have the ability of

bidirectional movement, expansion and residence in

the intestinal tract, and its principle is simple, easy to

realize and its size is miniaturized (Buselli et al.,

2009; Gao et al., 2016; Gao et al., 2019; Lu et al.,

2018; Wang et al.,2013; Zhang et al., 2020).

The method of adding a motion mechanism to the

capsule increases the number of various parts that

need to be integrated into the capsule, which

inevitably increases the overall size of the robot, so

that it cannot be orally swallowed by the person to be

examined. Therefore, researchers put forward the

design idea of building a modular robot system based

on magnetic self-assembly. The main idea is to

swallow one capsule module each time, and multiple

230

Liu, D.

Design of Intestinal Modular Robot and Dynamics Analysis of Its Docking Mechanism.

DOI: 10.5220/0011918500003612

In Proceedings of the 3rd International Symposium on Automation, Information and Computing (ISAIC 2022), pages 230-235

ISBN: 978-989-758-622-4; ISSN: 2975-9463

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

modules are swallowed in turn, and finally assembled

in the gastrointestinal tract (Li et al., 2018; Nagy et

al., 2010; Zygomalas et al., 2014). At present, the

method of realizing the docking of multiple capsule

modules based on the principle of magnetic

adsorption in the gastric cavity is usually used.

However, the magnetic interaction between modules

is essentially a passive effect, therefore, the docking

process between modules simply relying on it is

uncontrollable. Meanwhile, after multiple modules

are swallowed into the human gastric cavity, their

initial mutual positions and their respective postures

in the three-dimensional space have many

possibilities, thus, it objectively leads to a certain

degree of contingency in achieving successful

assembly.

In this paper, a design of capsule modular robot

based on conical rod docking mechanism is proposed,

and the effectiveness of its docking method is verified

by dynamic analysis.

2 DESIGN OF INTESTINAL

MODULAR ROBOT

2.1 Overall Structure of Intestinal

Modular Robot

The intestinal modular robot mechanism designed in

this paper is shown in Figure 1, which is composed

of three modules, namely module-Ⅰ, module-Ⅱ and

module-Ⅲ. Among them, module-Ⅰ and module-Ⅲ

are of the same structure (Figure 2a, 2b), which is

called installation module, and module-Ⅱ is of

abnormal structure (Figure 2c), which is called

docking module. The installation module mainly

consists of: a radial expansion mechanism, a radial

expansion transmission device and a docking cone

with double symmetrical configuration. The docking

module includes a bidirectional telescopic driving

Figure 1: Overall structure of intestinal modular robot.

device and a bidirectional telescopic docking rod. The

mechanism transmits power to the radial expansion

mechanism to expand the intestinal tract through the

radial expansion drive device of the installation

module, and then drives the telescopic movement of

the docking rod through the telescopic driving device

of the docking module, and completes the connection

between the installation module and the docking

module by using the guidance of the docking cone of

the installation module. Here, the dimension of

installation module is radial diameter Ф14.9mm,

axial length 29mm, and that of docking module is

radial diameter Ф13mm, axial length 24mm.

2.2 Assembly Process of Modular

Robot

Figure 3 shows the docking process of three capsule

modules in the intestine. When the first installation

module (module-Ⅰ) enters the intestinal tract, its radial

expansion mechanism is opened so that module-Ⅰ

resides here; Then, when the second capsule module

(module-Ⅱ) approaches the first capsule module, the

front-end docking mechanism of module-Ⅱ is

controlled to realize docking with module-Ⅰ.

Similarly, when the third capsule module (module-

Ⅲ) enters the intestinal tract and is close to the second

capsule module, its radial expansion mechanism is

opened to make module-Ⅲ stay, and then the action

of the rear docking mechanism of module-Ⅱ can be

Figure 2: Main structure diagram of individual module. (a)Installation module (closed-state), (b) Installation module

(open-state), (c) Docking module.

Design of Intestinal Modular Robot and Dynamics Analysis of Its Docking Mechanism

231

controlled to realize the docking of module-Ⅱ and

module-Ⅲ.

Figure 3: Schematic diagram of capsule module assembly

process.

3 CONE-ROD DOCKING

MECHANISM

Due to the radial deformation of the intestinal tract,

when designing the docking mechanism for module

robot, it is necessary to fully consider that the docking

mechanism has a good deviation correction ability in

the radial position of the intestinal tract. Therefore,

this paper studies and designs a cone-rod docking

mechanism with a certain envelope space in the radial

circumferential direction to ensure that the capsule

module can achieve reliable docking in the flexible

intestinal tract. The premise for the reliable docking

of adjacent capsule modules is that the deviation of

their radial relative posture is maintained in the

envelope space of the docking cone at one end of the

installation module. However, the relative posture of

the capsule module in the intestine shows a certain

range of randomness because of the viscoelastic

deformation of the intestinal wall.

In order to analyze the kinematic characteristics

of the module docking mechanism, the simplified

model shown in Figure 4 is established. Since the

installation module will reside in the intestinal tract

due to the expansion tension during the docking

process, its relative position with the intestinal wall is

fixed during this period. Here, the origin of the global

coordinate system O

-X

is located at the

geometric centre of the installation module, in which

the Y

-axis coincides with its central axis, and the X

plane is taken as the tangent plane of the

installation module passing through the central circle

point and perpendicular to the Y-axis. While the

origin of the local coordinate system O

-X

placed at the center of the docking surface at one end

of the docking module.

Figure 4: Analysis model of docking mechanism.

Euler angle (φ, θ, ψ) is used to define the attitude

of docking module by axis Z

. Assume that the

coordinate of point O

in coordinate system O

is 𝑑



,𝑑



,𝑑



. The formulas of coordinate

rotation and translation compound transformation are

as follows.

𝑇





=𝑇𝑟𝑎𝑛𝑠𝑑



,𝑑



,𝑑



𝑅𝑜𝑡

(

𝑥



,𝜓

)

𝑅𝑜𝑡

(

𝑦



,𝜃

)

𝑅𝑜𝑡

(

𝑧



,𝜑

)

, (1)

where,

𝑇𝑟𝑎𝑛𝑠𝑑



,𝑑



,𝑑



=

100𝑑



010𝑑



001𝑑



0001

 (2)

𝑅𝑜𝑡

(

𝑥



,𝜓

)

=

10 00

0𝑐𝜓−𝑠𝜓0

0𝑠𝜓𝑐𝜓0

00 01

, (3)

𝑅𝑜𝑡

(

𝑦



,𝜃

)

=

𝑐𝜃 0 𝑠𝜃 0

0100

−𝑠𝜃 0 𝑐𝜃 0

0001

, (4)

𝑅𝑜𝑡

(

𝑧



,𝜑

)

=

𝑐𝜑 −𝑠𝜑 0 0

𝑠𝜑 𝑐𝜑 0 0

0010

0001

. (5)

Here, c𝑖,s𝑖,(𝑖=φ,θ,ψ) are the abbreviations of

cos (𝑖),sin (𝑖),(𝑖= φ,θ,ψ).

ISAIC 2022 - International Symposium on Automation, Information and Computing

232

4 DYNAMIC SIMULATION OF

DOCKING MECHANISM

Adams solver is used to simulate the dynamics of the

docking mechanism of the module. Consider that the

expansion mechanism of the installation module

expands and resides in the intestinal tract.

The installation module can be regarded as

relatively fixed with the intestinal pipe-1, and the

docking module in the intestinal pipe-2 can be

regarded as relatively fixed in the docking process

due to the effect of friction as shown in Figure 5.

Figure 5: Virtual prototype analysis model.

In addition, four springs are arranged between

intestinal pipe-1 and pipe-2 at a circumferential

interval of 90° to simulate the flexible deformation of

the intestinal wall. The stiffness and damping

coefficient of each spring are set as 5.8E-006(N/mm)

and 1.5E-006(N·s/mm), respectively.

In order to verify the effectiveness of docking

module in different positions and postures, three

different cases shown in Table 1 are selected to

simulate and analyze the movement of docking rod.

The movement speed of the docking rod along the

axial expansion of the docking module is set to 2mm/s.

Table 1: Simulation parameters.

Case Parameters

(φ

, θ,

ψ)

[de

ree]

(

dx, d

, dz

)

[mm]

Case 1 (-1.736,0.20,0) (-0.44, 20.47, 4.19)

Case 2 (-1.736, -5.192, 0) (-2.44, 20.59, 4.34)

Case 3 (3.265, 1.803, 0.114) (3.70, 20.53, 4.14)

The results of simulation analysis are shown in

Figure 6, in which motion screenshots at different

time points after the start of simulation are taken

respectively. It can be seen from Figure 6 that in

Case-1 (Figure 6a), the docking rod-head smoothly

entered the central circular hole at the top of the

installation module after about 4s under the guidance

Figure 6: Snapshot of docking process in three cases. (a) Case 1, (b) Case 2, (c) Case 3.

Design of Intestinal Modular Robot and Dynamics Analysis of Its Docking Mechanism

233

of the docking cone, while in Case-2 (Figure 6b) and

Case-3 (Figure 6c), the time required for docking

completion is nearly 4.5s and 4.9s, respectively.

Figure 7 shows the trajectory of the docking rod-

head in three-dimensional space during the docking

movement in the above three cases. In Figure 7, the

green square point represents the starting point

coordinate of the docking rod-head, while the red dot

stands for the end point coordinate after docking

process is completed.

Table 2: Coordinates of starting point and ending point of

docking rod-head.

Case Coordinate

Start

oint End

oint

Case 1 (-0.894, 25.086,

4.437)

(-0.173, 16.410,

0.265)

Case 2 (-2.808, 25.088,

4.435)

(-0.525, 15.095,

0.0587)

Case 3 (3.014, 25.168,

4.409

)

(-0.986, 17.439,

0.622

)

The three-dimensional coordinates of the start

point and end point of the docking rod-head in the

three cases are shown in Table 2. It can be seen from

Figure 6 and Figure 7 that in the process of module

docking, even if the position and posture of the

docking module are different from the installation

module within a certain range, the docking rod can

successfully complete the docking of two adjacent

modules under the guidance of the docking cone.

Figure 7: Trajectory diagrams of endpoint in docking rod

with three cases.

5 CONCLUSIONS

This paper presented a design scheme of an intestinal

modular robot based on docking cone and established

the coordinate transformation method and virtual

simulation model for the two modules to realize

docking in the intestine. The dynamics and docking

simulation process of modular docking mechanism

are analyzed emphatically. The simulation results

showed that the modular design of the intestinal robot

proposed in this paper is feasible.

ACKNOWLEDGEMENTS

This work was supported by the Research Project of

Traditional Chinese Medicine of Shanghai Health

Committee under Grant number 2020JP012. The

statements made herein are solely the responsibility

of the authors.

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