Research on Micro Robot for Colonoscopy YAN Guozheng, WANG Kundong, SHI Jian

(School of Electrical and Information Eng,, Shanghai Jiaotong Univ., Shanghai 200030, China)

Abstract: For diagnosing the colon’s pathologies micro-invasively or non-invasively actively, an autonomous prototype of the

earthworm-like robot for colonoscopy was designed according with the principle of the bionics and manufactured using precision process

technology. In-Vitro experiments in pig colon were made. This micro robot for colonoscopy was drove directly by elecmagnetic linear

driver. The mobile cells were joined with two degree-of-freedom joints and the whole body was flexible. The direction of movement and

the angle of imaging can be controlled by the shape memory alloy (SMA). In experiments, locomotion efficient was analyzed carefully. In-

vitro experiments in pig colon demonstrated that the micro robot can navigate though the colon by itself reliably and freely, which was

useful to the application of robot for colonoscopy in the clinic.

Keywords: elecmagnetic creeping; earthworm-like; robot; colonoscopy; In-vitro experiment;

1 Introduction

If carcinoma of colon or rectum with high fatalrate could be found in its early stage, many patientswould be rescued successfully. So colonoscopy is animportant procedure in diagnosis to colon’spathologies. But because traditional colonoscopy wasquite rigid, patients usually feel very uncomfortable orpain when doctor inserts and rotates it to pass though

, loop with force. Half-autonomous or autonomousrobot for colonoscopy can propel itself in the colon,which reduces above problems of the conventionalcolonoscopy.

There are many reports on half-autonomous or autonomous colonoscopy. Gisela developed a wirelesselectrical capsule which can be swallowed by patients.Capsule transmits the image of colon from inner ofbody to receiver outside body wirelessly. Capsule isdefecated from anus by the squirm of gastrointestinal[1]. Because the motion of capsule is not controlled, itcan not stay in the place interested to doctor. YoungMo Lim manufactured autonomous robot for colonoscopy droved by SMA and pneumatic actuators[2]. Experiments in the rigid tube were made. P. Dario did In-Vitro experiments with pneumatic robot forcolonoscopy successfully [3,4]. Actuators are pressuredon the inner wall of colon as creation of vacuum,which may lead to reject reaction of living tissue.

In this paper we presented a new autonomous

robot for colonoscopy. It is comprised of three lineardrivers which are controlled by signals series tosimulate the squirm of earthworm. Robot propelleditself without any harm to colon and patients will notfeel discomfort. Robot for colonoscopy is controlled totransmit the image to receiver by microimage-forming system under the outside control. It canstay in the place in which doctor is interested.

2 Mechanism of robot colonoscopy

Robot for colonoscopy is comprised of the microimage-forming device, deflection mechanism, sealfilm and three linear drivers as shown in Fig.1.

Fig.1 prototype of robot for colonoscopy

Deflection mechanism, which can control thecamera’s pose, connects the image-forming systemwith first linear driver. Each linear driver is connectedwith two degree-of-freedom joint for adapting itself to curvature colon. Robot’s diameter is 10 mm and itslengthen is 110 mm. We can call reflection mechanism

Proceedings of the 2005 IEEEEngineering in Medicine and Biology 27th Annual ConferenceShanghai, China, September 1-4, 2005

0-7803-8740-6/05/$20.00 ©2005 IEEE. 5050

and image-forming device as head cabin as shown inFig.2. Highlight white lights are arranged around theimage hole to provide camera with illumination inhead cabin. Deflection mechanism is comprised of four shape memory alloy springs. SMA actuatoradjusts the image-forming system’s deflection degreeaccording with the visual feedback from the image toensure direction of advancement is kept in center ofcolon.

Fig.2 image-form and deflection mechanism

3 Locomotion principles

Robot for colonoscopy simulates the squirm ofearthworm which propels itself by difference of friction force between one mobile cell and the otherimmobile cells. This method avoids pressuring to thecolon and the mucous of colon can not be damaged.Four actions will happen when robot advances a stepas shown in Fig.3.

Fig.3 Scheme of locomotion principle

Corresponding signals applied to three lineardrivers are in Fig.4. At t0, colonoscopy is contractedtogether like status 1 in Fig.3. From t0 to t1, driver 1

propels head cabin forward. At t1, colonoscopy is inthe status as 2 in Fig.3. From t1 to t2 and from t2 to t3,driver 2, 3 push the driver 1, 2 forward respectively.Corresponding status is 3, 4 in Fig.3. From t3 to t4,drive 3 is drafted inversely. At t4, colonoscopy is instatus 5 in Fig.3. Now robot for colonoscopy goes astep forward. If above action is repeated, thecolonoscopy can forge ahead continuously. If thecontrol signals are inversed, robot will fall back.

Fig.4 Signals series of three linear motor

4 Result of In-Vitro experiment and discussion

Experiment is did at room-temperature. Fresh pigcolon’s length is 112 cm. Colon is spread out on thedesk as shown in Fig.5. A rigid pipe is inserted intoone end of colon to guide the robot into the colon.Applying signal with certain frequency to robot, robotcrept from the other end of colon after 7.3 minutes. Itcan be found from the motion that robot spent moretime in the curve of colon than in the flat part. Inprevious In-Vitro experiments we found thatnavigating well in the rigid tube can not make sure doing well in colon. Colon with viscoelasticity isdifferent from rigid tube greatly. For example, inmovement from status 1 to status 3 in Fig.3, colon isstretched by friction force between the colon and thehead cabin. Colon will contract after driving forceunloaded because of elasticity, so head cabin isdragged to previous place. Movement like accordionleads to lower locomotion efficiency. Finding outfactors related with locomotion efficiency is very important to improve it.

Soft viscoelastic colon is stretched by friction5051

force, so colon advances together with the robot. In Fig.6, A, B is on the point of robot and colonrespectively. A and B go to biggest deformation Lc ofcolon. A on Colon does not advance any more and Bpoint continues to go forward to L. Here, L is thedesign step of robot, and Lc is the critical step. Thenlocomotion efficiency of robot can be defined asfollow expression:

cL-L=L

(1)

Obviously, if L<Lc, the robot can not advance. Lc

must be determined for improving the locomotionefficiency and providing step design with reference.

Fig.5 In-Vitro experiment of robot colonoscopy

Fig. 6 Step loss of robot

Robot does not touch the surface of colon in fullcircumferential because 10 mm diameter of robot is less than 16-20 mm diameter of colon. In fact touchingpart is curved surface and can be viewed as rectangleexpanded at pitch arc. Friction force F acting on thesurface of colon is equivalent to the force acting on two ends of rectangle. The dimension of rectangle isL10×L20 before deformation and L1×L20 afterdeformation as shown in Fig.7.

Fig.7 Simplified acting force model

Where F=mgµ, m is driver’s mass, µ iscoefficient of sliding friction between driver and colon.Energy function of the viscoelastic colon is expressedas follows:

20

c 'W = exp(aE )2 l (2)

This function is one-dimensional special case oftwo-dimensional viscoelastic strain energy functionexpression[5]. c and a are constant related withmaterials. 0 is density of tissue before deformation.El is Green strain and its expression is:

2l l

1E = -12

(3)

And l is : 1l

10

L=L

(4)

l and Sl is defined under Cauchy—Eulermeaning and Kirchhoff meaning respectively.

l20

F=L h

(5)

0l 2

l

1S = l (6)

is density of tissue after deformation, h isthickness of intestinalis.

Because ll

dS = WdE 0 (7)

Substitute equation (5) into equation (6) then we can get Sl. Sl is substituted into left side of equation(7). Equation (2) is substituted into right side ofequation (7). And equation (7) is simplified as followequation:

2 20l l

2

mgµ c'a= -1 exp -1L h 2

2l (8)

l can be resolved from equation (8), then criticalstep Lc is:

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c 10 lL =L ( -1)

From above equations we can find:(1) Lc is influenced by factors such as L, m, µ;(2)Decreasing Lc is useful to improve locomotionefficiency.

5. Conclusion

Robot for colonoscopy is a new kindcolonoscopy because it can relieve discomfort ofpatients and lower skill’s demand to operator. Based on this, locomotion principles are presented in thispaper and prototype is manufactured to make In-Vitroexperiments in pig colon. Researching finds robot’scritical step is determined by dimension of drivingmechanism, physical characteristics of colon. Morelocomotion efficiency can be got, smaller critical stepis. Robot for colonoscopy based on above analysis canenter into the colon to work reliably and freely. It willplay an important role in early finding of malignancy

tumor.

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New Tech Report NPO-20652,25(2).

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Self-Propelling Endoscopic System. Proceeding of the 2001

IEEE/RSJ, Maui Hawii, USA, Oct 29-Nov. 03,2001,

pp.1117-1122.

[3] Paolo Dario, Maria Chiara Carrozza, Andrea Pietrabissa et

al. Development and In Vitro Testing of a Miniature Robotic

System for Computer-Assisted Colonoscopy. Computer Aided

Surgery, 4,1999, pp.1-14.

[4] L. Phee, A. Menciassi, D. Accoto et al. Analysis of Robotic

Locomotion Devices for the Gastrointestinal Tract. Robotics

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[5]Fung Y.C., Fronek K., Patitucci P. Pseudoelasticity of

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American Journal of Physiology Vol.237,pp.620-631.

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