1. Micro-Robot for Endoscope Based on
Wireless Power Transfer
Guozheng Yan, Dongdong Ye, Peng Zan, Kundong Wang and Guanying Ma
School of Electrical and Information Engineering
Shanghai Jiao tong University
Shanghai, China
{gzhyan, yeddon, zanpeng, kdwang & maguanying}@sjtu.edu.cn
Abstract - This paper proposes a new prototype of wireless
micro-robot system for endoscope. The micro-robot we have
fabricated and tested is able to propel itself in the intestine canal
of pig in an autonomous manner by earthworm locomotion. It is
different from the conventional micro-robot endoscope that
wireless module is used for communicating and power transfer
being up to 480mW of DC power for receiving coil in the
proposed system. The system composes of wireless
communications module, personal computer, micro-robot,
wireless power transfer controller and wireless power transfer
coil. The experimental results show that the driving voltage of
micro-robot is stable which fulfils the need of the micro-robot
system. The micro-robot can creep reliably in the rubber canal
and the intestinal canal of pig.
Index Terms - micro-robot; endoscope; intestinal canal; linear
actuator; wireless power transfer.
I. INTRODUCTION
The diagnosis and therapy of gastrointestinal disease
mainly depend on the medical endoscope which is inserted
into human body equipped with video, sampling tools and
operation tools, etc. But the traditional push endoscope tools
are quit rigid to make the patients very painful and require the
doctor to perform difficult manoeuvres for insertion.
Therefore, the micro-robot for endoscope as a micro-invasive
or non-invasive tool has attracted much attention in the fields
of medical appliance and micro electro mechanical system
(MEMS).
In the past twenty years, many people had researched on
the micro-robot for endoscope. In 1988, Ikuta proposed a
called “Mediworm” robot for large intestinal inspection [1].
The endoscopic robot was actuated by SMA and integrated
with a SMA-actuated miniature gripper. Carrozza et al.
developed an active endoscope driven by pneumatic actuators
and successfully carried out in-vitro experiments [2]. Phee et
al. proposed a robot using corrugated pipe pneumatic actuators
[3]. In these literatures, the SMA actuators have minor
temperature difference to deformation and reversion because
of the low high-temperature tolerance of the intestinal tissue
and have lower speed of the locomotion. On the other side,
either hydraulic or pneumatic actuators may lead to injurious
pressure on the flimsy living tissue because of its pressing
against the inner wall of intestinal canal. In addition, all these
endoscopic robots have trailing cable to transmit power and
control signals. The trailing cable types would cause resistance
to motion of the micro-robot and the resistance increases with
the length of trailing cable deep into body. The resistance
restricts the creeping distance and the rate of micro-robot in
the intestinal canal. Furthermore, the trailing cable may injure
the inner intestine because of its rigidity. Ergo, the wireless
power transfer is desirable.
In this paper we present a novel wireless micro-robot
prototype for endoscope. It is composed of three linear
actuators based on DC motor. Wireless modules with
dimensions of 10.5mm 9.5mm are adopted for
communication and transfer power. The power is up to
480mW of DC power for receiving coil. The micro-robot is
controlled by the VC-program running in the PC to start
entering the intestine canal from the anus and can go forward
and backward with different velocities. The micro-robot also
can rest on where the doctor wanted to observe in the intestine
canal.
II. MICRO-ROBOT SYSTEM
Fig.1 shows the system structure of the micro-robot for
endoscope. It is made up of wireless communications module,
personal computer (PC), micro-robot, wireless power transfer
controller, wireless power transfer coil.
The micro-robot prototype we have fabricated and tested is
composed of a head cabin, three actuators and tectorial
membrane, as shown in the fig.2. The communication control
module and wireless power receiving module are embedded in
the head cabin. Three gimbal joints connect four parts of
micro-robot to ensure that the robot can adjust its poses in the
complex environment of intestinal canal. The tectorial
membrane is used to protect the micro-robot keeping from
water penetration. The dimensions of the robot are 12.1 mm
120.5 mm. The weight is 30g and the designing pace is 8mm.
1-4244-0828-8/07/$20.00 © 2007 IEEE. 3577
Proceedings of the 2007 IEEE
International Conference on Mechatronics and Automation
August 5 - 8, 2007, Harbin, China

2. Fig.1 Photograph of micro-robot system for endoscope
Head cabin Driver1 Driver3Driver2
Tectorial
membrane
Communication
control module
V-Stabilizing
board
Receiving
coil
Fig.2 Photograph of micro-robot system for endoscope
Fig.3 The linear actuator prototype
The linear actuators of micro-robot adopt miniature DC
motors as the driving source (fig.3). Because the output of DC
motor is consecutive rotary motion, corresponding mechanism
is adopted to accomplish controllable rectilinear motion.
The key of design is to confirm the high transfer efficiency
during the conversion from rotary to rectilinear movement.
This paper adopts the nut and leading screw mechanism to
accomplish the conversion. The deceleration is realized at the
same time with increasing force. The linear actuator is made
up of DC motor, reducer box, gasket, leading rails, leading
screw and nut. The reducer box is fixed on the outer shell of
DC motor and the nut can slide forward and backward along
the leading rails. The table 1 shows the parameters of DC
motor used in design.
TABLE I
THE PARAMETERS OF THE DC MOTOR
Driving voltage
(v)
Dimensions
(mm)
Rev
(zero load)
Weight
(g)
Torque
(g-cm)
3.2 6 12 13000rpm 2.2 3
III. LOCOMOTION AND CONTROL PRINCIPLE
The micro-robot for colonoscopy has two typical
locomotion modes according to the different driving
principles. One simulates the squirm of earthworm and another
simulates the inchworm pulling. The locomotion modes of this
paper is based on the first locomotion mode which propels
itself by difference of friction force between one mobile unit
and the other immobile units. Locomotion involves the process
of generating net displacement inside a flexible lumen by
specific sequences of stretching and contracting actions. Such
sequences are controlled without difficulty by using a PC.
A. Locomotion principle
The fig. (a) shows the locomotion principle of the micro-
robot. The micro-robot starts moving under the control signals
as shown in fig. (b). The status 1 is free elongation. At 1
t , the
driver 3 is loaded on positive voltage ,and then it contracted
itself toward the left. The robot is in the status 2 after the diver
3 stops motion. At 2
t , the driver 3 is loaded on negative
voltage and driver 2 is loaded on positive voltage, then the
driver 2 contracted itself toward the left. The robot is in the
status 3 after the diver 2 stops motion. At 3
t , the driver 2 is
loaded on negative voltage and driver 1 is loaded on positive
voltage, then the driver 1 contracted itself toward the left. The
robot is in the status 4 after the diver 1 stops motion. At 4
t ,
the driver 1 is loaded on negative voltage, then the head cabin
is propelled by driver 1 toward the left. The robot is in the
status 5 after the diver 1 stops motion. Thus the robot finish a
pace forward. If the above action is repeated, the robot can
move forward continuously. If the control signals are inversed,
the robot will fall back.
(a) Locomotion principle
(b) Control signal
Fig.4 Scheme of micro-robot locomotion and control signal
B. Control principle
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3. Fig.5 Functional block diagram of micro-robot
The Fig.5 shows the block diagram of control principle of
the micro-robot system. The system includes a man-machine
interaction VC-program that the manipulator can input control
parameters. The input parameters are transmitted by the
RS232-TTL to the wireless communication module (Fig.1).
The communication module broadcast the parameters to the
communication control board embedded in head cabin of the
micro-robot (Fig.2) through radio frequency (RF) 433 MHz
modulated by frequency shift keying (FSK). The parameters
received by micro-robot are compiled by C8051F33 to
generate a certain sequence waveform as shown in Fig. 4(b).
The waveform signals amplified and loaded on the linear
actuators can control the direction of motion, speed and towing
force.
IV. WIRELESS POWER TRANSFER PRINCIPLE
Fig.6 Scheme of wireless power transfer model
Fig.7 Equivalent circuit of wireless power transfer
The transfer coil which is a solenoid will be installed
around the patient’s trunk and has inductive link with receiving
modules embedded in the head cabin for a power-transfer
realization. Fig.6 shows wireless power transfer model.
For describing the degree of coupling of two coils, the
coupling coefficient is defined as follows:
1 2
M
K
l l
= 1
Where: M is mutual inductance between the two coils, 1
l
and 2
l are the self-inductance of two coils, respectively.
In practice, the transfer coil can be driven by a class E
amplifier or a switching circuit and the rectifier may be full
bridge or full wave topology. The inductive links are all the
same and can be generalized as a lumped transfer model as
shown in fig.7.
For a power-efficient realization of an inductive, the
inductance at the receiving side is commonly cancelled by a
parallel-resonant capacitor 2
C . Where 1
R and 1
R are the
respective series-resistances of 1
L and 2
L . L
R the resistor
simulating the load. 1
C the series-resonant capacitor to drive a
sinusoidal high-amplitude electric current 1
I with maximum
current amplitude of 2A through the transfer coil,
corresponding to i
1
V amplitude of 12V. i
2
V the inductive
voltage of receiving coil.
Then the loop equation of above circuit is given by:
i i i
1 1 1 2V Z I j M Iω= − 2
i i
1 2 2j M I Z Iω = 3
Where 1 2
Z Z is the equivalent resistor of the transfer
and receiving circuits, respectively.
The resonance frequency is defined as:
1 1 2 2
1 1
l C l C
ω = = 4
The output voltage at L
R is:
i i
2 2LV R I= 5
Then:
i
i
1
2 2 2
1 2 2 1 2 2 1
2 2
2
(
)
L
L
L
j MR V
V
R R M j C R R R L R
M C R
ω
ω ω
ω
=
+ + +
+
6
The link efficiency achievable with secondary resonance is
expressed as:
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4. 2 2
2 2 2
2 1 2 2( )(1 )
L
L
M R
Z Z Z M j C R
ω
η
ω ω
=
+ +
7
As explained in [4], combining the equality (1) and (4), the
equality (7) can be simplified as:
2
22
1 22 2
2( )
r
r
Q R
K Q Q
Q R
η =
+
8
Where: 1
1
1
l
Q
R
ω
= , 2
2
2
l
Q
R
ω
= ,
2
L
r
R
R
R
= ,
2
2 1Q ,
2
1 2 1K Q Q
When
2
2r
R Q= , the maximum efficiency achievable with
secondary resonance is expressed as
2
1 2
max
4
K Q Q
η = .
As max
η is a monotonically rising function of ω , it is most
important to make ω as large as possible. But if the ω is too
high, the impedance of 1
L and 2
L in a resonant circuit will
increase with frequency. According to the papers [5~7] and the
technology limits, the resonance frequency of operation is
decided at around 36KHZ.
LinkEfficiency(Ș)
Resistor Load (ȍ) Coupling Coefficient (K )
Fig.8 The relationship between the η and K , L
R
Fig.8 shows the calculated results on the K and L
R of the
link efficiency η . It can be known that the micro-robot can
not work normally if the quantity value of coupling coefficient
is too small. The approximate coupling coefficient of two coils
in this paper is 0.005, which the receiving coil is in the middle
of transfer coil and the axes of receiving coil is tangent to the
direction of magnetic field.
The η is rising firstly and then declining with the rising of
L
R . So there is an optimal value L
R to make the link
efficiency maximum. But the dissipative power is varied
during the locomotion of micro-robot. Then the L
R is
designed to vary within a range to fit the varied dissipative
power.
In this paper, the transmitting coil is monolayer structure
and is made up of solid copper line AWG16. The receiving
coil is multilayer structure and is made up of solid copper line
AWG35. The table 2 shows the parameters of two coils.
TABLE
PARAMETERS OF TRANSMITTING COIL AND RECEIVING COIL
Parameters Transmitting coil Receiving coil
Outside diameter mm 400 11.5
Inside diameter mm 360 6
Average diameter mm 380 8.75
Thickness mm 10 0.6
Number of windings 66 232
series-resistances( ) 0.3 7
Self-inductance( ) .476 1.340
V. IN-VITRO EXPERIMENT
Fig.9 Scheme of locomotion current and voltage of micro robot in a
locomotion pace
Fig.10 Photograph of in-vitro experiment
Before the in-vitro experiment, the micro-robot is placed
on the middle of the transfer coil and the wireless power
transfer controller is running. The wireless communication
receiving module embedded in the micro-robot receives the
control command coming from the PC and the micro-robot
start creeping. When the micro-robot creeps along the axial
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5. direction of the transfer coil, that is Į=0o
(fig.6), the
locomotion distance of micro-robot is the farthest 8cm. When
the degree of Į increases to 90o
, the locomotion distance
decrease to zero. The experiment shows that the driving
voltage of micro-robot is stabile when the micro-robot is
creeping within the limits of wireless power transfer. On the
contrary, the driving voltage declines to 0V rapidly and the
micro-robot stop creeping. In the experiment, the transfer
power of the transfer coil is 25W and the maximum dissipative
power of locomotion units is about 400mW, as shown in fig.9.
As shown in fig.10, the micro-robot is placed in a rubber
canal with length of 30cm and a segment of fresh pig intestine
canal with the length of 75cm, respectively, at room
temperature. The micro-robot starts creeping toward the other
end of the rubber canal in 1 minute and the intestine canal in
15 minutes. It can be seen from the experiment that the micro-
robot creeps steadily and almost has no pace lose in the rubber
canal. In the intestinal canal, the micro-robot spent more time
in the curve than in the flat part where the micro-robot loses
the less pace. The pace loss is the result of the firmo viscosity
character of intestine canal.
VI. CONCLUSIONS
A new wireless micro-robot system for endoscope has been
introduced in this paper. The micro-robot is simulating the
squirm of earthworm. The power supplying and
communications control are all wireless which is differ from
the previous trailing cable style. The wireless style reduces the
resisting force that the trailing cable brought and is fitter for
locomotion in the living body than the trailing cable style. The
in-vitro experimental results show that this robot can move
reliably in rubber canal and intestine canal of pig. This
research has laid foundation for the application of the
miniature robot endoscope.
ACKNOWLEDGMENT
The research work was supported by National Natural
Science Fund (305-70-485) the National 863 Programme
(2006-AA-04Z368).
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