Modeling and Simulation of the Drug Delivery Function

for a Magnetic Driven Capsule Robot

Zixu Wang*1, Shuxiang Guo*2*3 Wei Wei*1 *1Graduate School of Engineering, Kagawa University,

Takamatsu, Kagawa 761-0396, Japan

*3Department of Intelligent Mechanical Systems Engineering,

Kagawa University, Takamatsu, Kagawa 761-0396, Japan

s18d501@stu.kagawa-u.ac.jp

*2Key Laboratory of Convergence Medical Engineering

System and Healthcare Technology, The Ministry of Industry

and Information Technology, School of Life Science and

Technology, Beijing Institute of Technology,

Haidian District, Beijing 100081, China

guo@eng.kagawa-u.ac.jp

Abstract – The capsule robot was developed to detect various

intestinal diseases and mainly used in the minimally invasive

procedures. Among them, commercial capsule robots can already

suit the general inspection requirements. But just having the

inspection function is increasingly unable to keep up with the pace

of the new era, so developers are working hard to integrate some

functional modules into traditional endoscope robots. In this

research, we proposed a new type of robot capable of delivering

drugs in the affected area, and analyze the rationality of structural

design in combination with Ansys Fluent simulation, some

improvements in drug delivery structure will be proposed. Finally,

the experiment will be carried out for motion stability evaluation

of the new type microrobot movement by a custom 6-DOF interial

measurement unit. Through the above methods to improve the

structural design of the robot and finally get a robot with high

performance and stable operation.

Index Terms - Magnetic driven capsule robot, Magnetic

electronic field, Drug delivery.

I. INTRODUCTION

Capsule microrobot is widely used in the modern clinical

medicine fields, such as clinical operation or examination. Due

to the great potential of a micro capsule robot, its mechanism

and motion have developed for decades. Specifically, these

microrobots can be used to remove blood clots or transport

drugs to the desired location of the wound, and even the type of

larger pipe robots can clean pipes under the road. The

development of it is helpful for medical staff to find the exact

position without scar, especially in recent years, with the

development of the hardware and integrated technology, some

of the volume and size limitation problems of capsule robot

have been solved very well. The volume challenges in the

process of robot development are the main problems faced by

researchers. The maximum length is no more than 30mm. These

wireless-capsule microrobots can reach narrow areas such as

blood vessels and small intestine, which is impossible under the

traditional endoscope [1]-[3]. Therefore, the size and volume of

each part of the robot limits the development of functional

modules. In the previous research, various kinds of micro robots

have been put forward before. Propeller or screw propulsion is

a promising new method of laminar motion [4]-[7]. The

electromagnetic module is driven and the robot rotates in the

patient's tissue. Most of these microrobots are controlled by

wireless. The robot has stable motion performance, including

multi-directional motion. Then a hybrid micro robot is

proposed, which can change their motion types according to the

complex environments. Besides, these microrobots also have

some limitations. Most of the microrobots are driven by cables

that are difficult to realize long-distance treatment and

experiment in the human body, which will make patients feel

the discomfort caused by cables. As for the structure design of

wireless micro robots in past research, when patients enter the

human body, they may cause harm to their intestines [8]-[10].

However, due to the limitations of mechanical structure, the

development of functional modules is limited, and these

microrobots cannot achieve multi-function in working time.

Therefore, our research is aimed at the development of active

motion microrobot and keep the safety, which can avoid the risk

factor for capsule retention. So this research will propose a

novel electromagnetic micro robot with space to design the

internal functional modules of the robot, and the protection of

patients' tissues is also one of the main aims of this research.

II. ELECTROMAGNETIC OPERATION SYSTEM

The microrobot driven by the magnetic force is driven by

the electromagnetic field. During previous studies, various

types of electromagnetic drive systems have been proposed to

manipulate magnetic microrobots in human tissues, such as

intestines, blood vessels and stomach. Due to the structure of

the electromagnetic drive system, the application range of

micro robot is limited. Therefore, we propose a new

electromagnetic drive system [11]-[15]. Fig. 1 is the total

electromagnetic drive system. On the operation side, the camera

monitors the visual image in the pipe and displays it on the

monitor. The control command is transmitted to the control unit

through the amplifier, DC power module and control circuit.

After receiving the command, the driving mechanism (three-

axis Helmholtz coil) will generate an external rotating magnetic

field to control various movements of the magnetic controlled

microrobot. Fig.2 shows the monitor can also display the real-

time position of the robot obtained by the magnetically sensor

array. The function of the positioning module is to complete the

closed-loop control and ensure the robot to complete the task.

Therefore, doctors seem to be able to precisely control the

position and posture of wireless micro robots in the human body

[16].

In the detection process, to ensure that the robot moves in

different directions under the same force and magnetic moment,

a controllable magnetic field module needs to be set in the

three-dimensional space. Therefore, we propose to use robot

Three-axis Helmholtz coil as the driving system to drive the

robot. Its function is to provide the rotating power of the

magnetic robot. The structure of the three-axis Helmholtz coil,

there is a pair of coils on each axis, and the center distance of

each pair of coils is represented by L. When L is equal to the

coil radius R, the current in each pair of coils is the same. The

formula for magnetic flux density is shown in equation (1):

𝐵 = ( 4

5 )

3

2𝜇0𝑁𝐼

𝑅 ⑴

where B is the flux density at any point between the coupling

axes of Helmholtz coil, 𝜇0 is the vacuum permeability, R is the

coil radius, n is the number of turns per coil, and I is the coil

current. By operating the control signal of the three-axis

Helmholtz coil, a rotating or fluctuating magnetic field will be

generated to control the permanent magnet inside the micro

robot, so that it can drive in any desired direction [17]-[20].

In the micro robot, there is a permanent cylinder magnet

as the actuator, which is driven by the external magnetic field

in the pipeline. The driving force and magnetic torque are

provided by the external magnetic field. The microrobot can

rotate by force transmission of the magnetic moment T. The

magnetic force F and magnetic torque T acting on the magnet

inside the external magnetic field generated by the three-axis

Helmholtz coils is given by the equations (2) and (3):

𝐹 = 𝑉(𝑀 ∙ 𝛻) × 𝐵 ⑵

𝑇 = 𝑉𝑀 × 𝐵 ⑶

where M is the magnetization of the magnet and V is the volume

of the permanent magnet.

III. Structural DESIGN

The experiments in this paper were carried out in a 20mm

diameter pipe, and the microfluidic conditions were not

considered, so the analysis was performed according to the

macroscopic fluid motion. As shown in Fig.3.

𝑓𝑟𝑜𝑏𝑜𝑡 = 1

𝜌𝑔 (𝑃1 − 𝑃2) +

1

2 𝑔𝑣2 (4)

When the microrobot moves in the horizontal direction,

Conservative Bernoulli equation (5) as:

1

2𝜌𝑣2 + 𝜌𝑔ℎ + 𝑝 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 (5)

where ρ is the density of liquid, v is the velocity of flow, g is gravity acceleration, h is the height of the microrobot, p is the pressure of the liquid. In practice, in addition to the

influence of gravity and fluid pressure, friction and fluid

viscosity will also affect the moving micro robot, resulting in

the loss of mechanical energy. Therefore, the Bernoulli

equation should be changed as equation (6):

𝑊1+𝑃1

𝜌𝑔+

𝑣12

2𝑔 = 𝑊2+

𝑃2

𝜌𝑔+

𝑣22

2𝑔 +𝑊𝑤𝑎𝑡𝑒𝑟+𝑊𝑟𝑜𝑏𝑜𝑡 (6)

where W is mechanical energy, p is the pressure on each part, v

is the velocity of the inlet and outlet part.

So that the dynamic pressure can be written as the equation

(7):

𝑃𝑑 = 1

2𝐶𝐷 × 𝜌(𝑣𝑓𝑙𝑜𝑤

2 − 𝑣𝑟𝑜𝑏𝑜𝑡2) (7)

where 𝐶𝐷 is the drag coefficient, v is the speed on the section

plane of inlet and outlet. Once the capsule robot moves forward.

The drag force increases as the axial velocity increases. So

considering the friction force of the robot moving in the pipe,

the total resistance can be expressed as (8):

𝐹𝑓 = 𝐶𝐷1

2𝜌𝐴𝑣𝑟

2 + 𝜇𝑓(𝑁1 − 𝜌𝑔𝑉𝑟) (8)

where μ𝑓 is the coefficient of friction, N1 is the normal force

between the microrobot and the surface of the pipe which is

equal to gravity, ρ is liquid density, g is gravity acceleration, 𝑉𝑟

is the microrobot volume immersed in the liquid. Then the

Fig. 3 Microrobot in horizontal direction

Fig. 1 The total experimental operation system.

Fig. 2 Electrical magnetic field density of three-axis Helmholtz coils

relationship of propulsive force and total resistance satisfies the

equation (9)

𝐶𝐷1

2𝜌𝐴𝑣2 ≥ 𝐶𝐷

1

2𝜌𝐴𝑣𝑟

2 + 𝜇𝑓(𝑁1 − 𝜌𝑔𝑉𝑟) (9)

When the microrobot moves in a vertical direction (upward

motion), it is mainly affected by three kinds of the resistance

force, pressure drag of liquid, friction caused by contact with

the pipe and gravity.

𝐶𝐷1

2𝜌𝐴𝑣2 + 𝜌𝑔𝑉𝑟 ≥ 𝐶𝐷

1

2𝜌𝐴𝑣𝑟

2 + 𝜇𝑓𝑁2 + 𝐺 (10)

where N2 is the contact normal force between the pipe and the

robot. Meanwhile, the direction of N2 is determined by the

motion direction. Besides, the friction between the robot and

the pipe wall is negligible in the case of smooth operation when

the robot moves in the vertical direction. In this condition, the

propulsive force of the propeller can be calculated according to

the known parameter.

IV. HYDRODYNAMIC SIMULATION

The fluid mechanic’s simulation based on ANSYS can help

us evaluate the parameters of the robot in the flow environment,

and modify the physical model based on the obtained data. In

addition, in order to optimize the dynamic structure of the robot,

considering the different dynamic characteristics of different

actions, a transient model is needed for the simulation of each

detail. A series of vital hydrodynamic parameters of the

motions can be obtained through the analysis of the simulations.

In this article, we will simulate the process of the capsule robot

discharging medicine in still water flow. In this process, we will

consider the fan and the external water flow as a stationary

situation. We set up a cylindrical water tank with a length of

250mm and a radius of 11mm in the fluid domain. The next step

is Boolean subtraction. We will use the water tank for the

Boolean subtraction operation except for the drug cell. Then

select only the model that retains the O-type magnet, in this

way, you can choose to set the O-type magnet as a dynamic

mesh in the subsequent steps to achieve transient simulation.

The next step is to build the mesh, the meshing results of the

geometry model and the flow field are shown in Fig. 5, the total

number of nodes was 12788, and the total number of elements

was 186880. After the whole geometry is meshed, the meshing

results are imported into the establishment step of ANSYS

FLUENT. The calculation model used in this paper is a double

precision k-ε realizable model. In the element region condition

section, we set the rotor as a frame motion rotating around the

y-axis. Then, the boundary of the inlet is the pressure inlet.

Finally, the default divergence coefficient is selected, and the

convergence standard is set to 0.0001. The above three different

settings, due to the convergence requirements, automatically

stop about 80 steps of 20-time steps. After the hydrodynamic

analysis and simulation, in the static flow field, the flow

streamline of the drug flow inside the drug cell is shown in the

Fig. 6 (a), then the with the moving of the O type magnet, the

drug flow transient motion vector can be seen in the Fig. 6 (b)

and Fig. 6 (c) respectively. The structure design can effectively

make the drug flow smoothly through the cell at the rear of the

robot. Combined with the results in the simulation, the

calculated discharge per second is basically consistent with the

experimental data, at 0.02ml/s.

V. EXPERIMENT AND RESULTS

The experiment was carried out to verify the stability of the

movement, we set the electromagnetic field rotating frequency

changed from 1Hz to 10Hz and each step for 10 seconds. As

shown in Fig. 7, the deflection angle of the robot in the forward

direction which was measured in a φ20mm PVC pipe and the

robot was always immersed in water.

When the robot was manipulated at a lower rotational

frequency (1-2 Hz), the resistance was larger than the axial

direction propulsive force. Thus the start frequency of the robot

is 3 Hz, it can be seen in Fig.8, when the robot starts moving at

3 Hz, the static friction becomes dynamic friction. The flutter

of the microrobot is obvious when it overcomes the static

friction and just starts to move forward. After that, the robot has

a relatively stable movement when the frequency at 4-7 Hz.

With the increasing of the frequency, the rotating velocity of

the blades also was increased, and its effect on the balance of

the robot began to emerge. In general, the deflection angle and

stability of the movement during the experiment are

controllable before 11 Hz, which is the step-out frequency of

this type of capsule microrobot.

Fig. 4 Geometry model of the microrobot

Fig. 5 Meshed model of the microrobot with pipe

VI. CONCLUSION

In this paper, we first introduced the operating system and

shown the simulation results of magnetic field density based on

COMSOL software. After that, we systematically introduced

the geometry modelling and related settings in the simulation

process such as the meshing step and how to monitor drag

coefficient changes. A series of parameters such as the drug

discharge speed can be seen in the streamline velocity results,

and then the required parameters such as drug discharge quality

can be calculated in combination with the theoretical formulas

given. Since our simulation is a transient model simulation, the

position of the O-type magnet is different at different times, we

have given the first, 10th step and the last step screenshots of the

results at three different times. Combined with the simulation

results, we can get the effect of the tail hole on the drug

discharge. Finally, we use 6 DOF IMU to evaluate the

movement stability of the robot in the horizontal state and it is

concluded that the robot moves most smoothly at 4-7 Hz. This

also provides valuable basic research for our subsequent

development of robots.

ACKNOWLEDGMENT

This research was supported by National High-Tech.

Research and Development Program of China (No.

2015AA043202), and SPS KAKENHI Grant Number

15K2120.

REFERENCES

[1] S. Guo, T. Fukuda and K. Asaka, “Fish-like underwater microrobot with

3 DOF”, in Proceedings 2002 IEEE International Conference on Robotics

and Automation, Vol. 1, pp. 738- 743, 2002. [2] S. Guo, T. Fukuda and K. Asaka, “A new type of fish-like underwater

microrobot”, IEEE/ASME Transactions on Mechatronics, Vol. 8, No. 1,

pp.136-141, 2003. [3] Sehyuk Yim, “Design and Rolling Locomotion of a Magnetically,

Actuated Soft Capsule Endoscope”, IEEE Transactions on Robotics, Vol.

28, No.1, pp. 183-194, 2012. [4] Wonseo Lee, Jaekwang Nam, Jongyul Kim, Eunsoo Jung, and Gunhee

Jang, “Effective Locomotion and Precise Unclogging Motion of an Untethered Flexible-Legged Magnetic Robot for Vascular Diseases”,

IEEE Transactions on Industrial Electronics, Vol. 65, No. 2, pp. 1388-

1397, 2017. [5] Qiang Fu, Shuxiang Guo, “A Control System of the Wireless Microrobots

in Pipe”, in Proceedings of 2014 IEEE International Conference on

Mechatronics and Automation, pp. 1995- 2000, 2014.

(a) The first time step of O-type magnet moving towards to the tail

(b) The 10th time step

(c) The last time step

Fig. 6 Simulation result of velocity on different time steps

Fig, 7 Experiment result of motion stability evaluated by 6-DOF IMU

[6] Shuxiang Guo, Qiang Fu, “Characteristic Evaluation of a Wireless

Capsule Microrobotic System”, in Proceedings of 2013 IEEE

International Conference on Mechatronics and Automation, pp. 831- 836, 2013.

[7] Qiang Fu, Shuxiang Guo, Songyuan Zhang, “Characteristic Evaluation of

a Shrouded Propeller Mechanism for a Magnetic Actuated Microrobot”, Micromachines, Vol. 6, No.9, pp.1272- 1288, 2015.

[8] Qiang Fu, Shuxiang Guo, “Development and Evaluation of Novel

Magnetic Actuated Microrobot with Spiral Motion Using Electromagnetic Actuation System”, Journal of Medical and Biological

Engineering, Vol. 36, No. 4, pp. 506-514, 2016.

[9] Qiang Fu, Shuxiang Guo, Songyuan Zhang, “Performance Evaluation of a Magnetic Microrobot Driven by Rotational Magnetic Field”, in

Proceedings of 2015 IEEE International Conference on Mechatronics and

Automation, pp.876-880, 2015. [10] Qiang Fu, Shuxiang Guo, “Design and Performance Evaluation of a

Novel Mechanism with Screw Jet Motion for a Hybrid Microrobot Driven

by Rotational Magnetic Field”, in Proceedings of 2016 IEEE International Conference on Mechatronics and Automation, pp.2376- 2380, 2016.

[11] Arcese, L., Fruchard, M., Ferreira, A, “Adaptive controller and observer

for a magnetic microrobot”, IEEE Transactions on Robotics, Vol. 29, No.4, pp. 1060- 1067, 2013.

[12] Peyer, K. E., Zhang, L., Nelson, B. J., “Bio-inspired magnetic swimming

microrobots for biomedical applications”, Nanoscale, Vol.5, No.4, 2013. [13] Kim, S. H., Ishiyama, K., “Magnetic Robot and Manipulation for Active

Locomotion with Targeted Drug Release”, IEEE/ ASME Transactions on

Mechatronics, Vol. 19, No.5, 2014. [14] Shuxiang Guo, Zixu Wang, Qiang Fu, “Motion Performance and

Evaluation of a Magnetic Actuated Screw Jet Microrobot”, in Proceedings

of 2017 IEEE International Conference on Mechatronics and Automation, pp. 2000-2004, 2017.

[15] Qiang Fu, Shuxiang Guo, Jian Guo, “Conceptual Design of a Novel

Magnetically Actuated Hybrid Microrobot”, in Proceedings of 2017 IEEE International Conference on Mechatronics and Automation, pp.1001-

1005, 2017.

[16] Shuxiang Guo, Qiuxia Yang, Luchang Bai, Yan Zhao, “Development of Multiple Capsule Robots in Pipe”, Micromachines, Vol. 9, No. 6, 2018.

[17] J. Nam, W. Lee, E. Jung and G. Jang, “Magnetic navigation system

utilizing a closed magnetic circuit to maximize magnetic field and a

mapping method to precisely control magnetic field in real time,” IEEE

Transactions on Industrial Electronics, Vol. 65, no. 7, pp. 5673-5681, 2018.

[18] Zixu Wang, Shuxiang Guo, Qiang Fu and Jian Guo, “Characteristic

Evaluation of a Magnetic-actuated Microrobot in Pipe with Screw Jet Motion” Microsystem Technologies, Vol.24, No.7, pp.1272-1288, 2018.

[19] Zixu Wang, Shuxiang Guo, Wei Wei, “Characteristic Evaluation of the

Shell Outlet Mechanism for a Magnetic-actuated Screw Jet Microrobot in pipe”, in Proceedings of 2018 IEEE International Conference on

Mechatronics and Automation, pp.1688-1692, 2018.

[20] Shuxiang Guo, Qiuxia Yang, Luchang Bai and Yan Zhao, “Magnetic Driven Wireless Multiple Capsule Robots with Different Structures”, in

Proceedings of 2018 IEEE International Conference on Mechatronics and

Automation, pp. 626-630, 2018. [21] Zixu Wang, Shuxiang Guo and Wei Wei, “Motion Performance of a

Novel Fan Type Magnetic Microrobot in Pipe”, in Proceedings of 2019

IEEE International Conference on Mechatronics and Automation, pp.

1409-1413, 2019.

[22] W. Lee, J. Nam, B. Jang and G. Jang, “Selective motion control of a

crawling magnetic robot system for wireless self-expandable stent delivery in narrowed tubular environments,” IEEE Transactions on

Industrial Electronics, Vol. 64, no. 2, pp. 1636-1644, 2017.

[23] B. Jang, J. Nam, W. Lee and G. Jang, “A crawling magnetic robot actuated and steered via oscillatory rotating external magnetic fields in

tubular environments,” IEEE/ ASME Transactions on Mechatronics, Vol.

22, no. 3, pp. 1465-1472, 2017. [24] Zhou. H. and Gursel. A, “A novel magnetic anchoring system for wireless

capsule endoscopes operating within the gastrointestinal tract,”

IEEE/ASME Transactions on Mechatronics, Vol. 24, no. 3, pp. 1106-1116, 2019.