Active Bending Electric Endoscope Using

Shape Memory Alloy Wires

Takumi Kobayashi1, Tadao Matsunaga2 and Yoichi Haga3 1) Graduate School of Engineering, Tohoku University

2) Micro System Integration Center, Tohoku University

3) Graduate School of Biomedical Engineering, Tohoku University

1

International Workshop and Summer School on Medical and Service Robotics

July 2014, EPFL Lausanne

1. Background

Endoscopy

Previous study

Method

2. Multidirectional bending mechanism

Outline

Multi bending device

4. Conclusion

5mm

Principle, Structure, Measurement

2

3. Active bending electric endoscope Structure

Measurement of bending angle

Measurement of surface temperature

Active bending electric endoscope system

Motion

Discussion

5mm

Active bending electric endoscope

Endoscopy is widely used as minimally invasive therapy

・Disposable

・High insert ability

・Ability to observe and bend

・Reusable

・Infection due to lack of cleaning

・Disinfection and sterilization time

Bending part

Wire

Shaft

Background 1:Endoscopy

Shaft

Inserting endoscope from nose

Pylorus Endoscope

Stomach End

osco

pe

Work

ing

chan

nel

Invo

lved

area

Field lens Light

Stomach

Endoscope Snare

Involved part

Conventional endoscope structure

Angle knob

3

For upper digestive

＊W. Makishi et al., The Institute of Electrical Engineers of Japan E, 2011

5 mm

Background 2: Previous study Active bending device using SMA(Shape memory alloy ; Ti-Ni) coils

External diameter : 3.9mm

Bending part : 35mm

・Complex circuit for CCD imager ・Need to dispose CCD imager ・Expensive SMA coils → Difficult to be disposable

4

Background 3 : Method

・Easily inserting to small bowel

－Ability to observe and bend

・Disposable endoscope

・Miniaturized endoscope

CMOS imager (mounted lens)

・Mounted CMOS imager

・Using SMA(Shape memory alloy ; Ti-Ni) wires as actuators

5

Purpose

Background 3 : Method

CMOS imager (mounted lens)

・Mounted CMOS imager

・Using SMA wires as actuators

Medigus 1.2mm Camera

Outer diameter : 1.2mm

Rigid part : 5.0mm

Pixel : 49280 pixels

Field of view : 100,130 deg.

Working distance: 4,8,10,20,30

Medigus Co.

・Less heat generation

・Lower cost

・Avoiding overheat

・Better controllability

・Small contraction

Characteristic compared to SMA coil

6

𝑥 = 1 − 2𝐿

𝜃− 𝑎

𝑠𝑖𝑛𝜃2

𝐿

Arc type

𝑎

𝜃

𝐿

𝑙′

Straight type

SMA wire

Bending device

𝑎

𝜃

𝐿

𝑙

𝑥；Contraction of SMA wires

𝑥 =𝑎𝜃

𝐿

Relationship between bending angle

and strain

Straight；

Arc；

Background 3 : Method

7

・Actuation ・Initial state

SMA wire

Inner tube

Stopper

Link

𝑙 = 2(𝐿

𝜃+ 𝑎)2 1 − cos 𝜃

Minimum route of SMA wire

Maximum extended SMA wire ＝0.2%

When one SMA wire is driven, the others shift inward without strain.

Background 3 : Method

8

Outer diameter； 1.7mm

Bending length；35mm

Bending angle；59, 53, 51 degree

Radius of curvature ; 34, 37, 39 mm

(280mA)

T. Kobayashi et al., Sensors, Micromachines and Applied System,

5AM2-B-6, 2013 9

Bending motion (Current:280mA)

5mm 5mm

Actuation mechanism of Our device

Multidirectional bending device

1mm 5mm Outer tube

(b) (c)

Structure of Active bending electric endoscope

Observation part Bending part

5mm

CMOS imager

Bending mechanism

Lead wires for LEDs and SMA wires Links (a)

Inner tube

O.D. of SMA wires：150 μm

O.D.：4.1 mm

Bending angle：35 mm

LEDs 10

LED

Size : 1.6×0.8× 0.68mm

Luminous intesty : 556-723 mcd

Driven one SMA wire

Driven two SMA wires

・Bending angle：50 deg

・Radius of curvature：40 mm

・Bending angle：37 deg

・Radius of curvature：54 mm

Measurement of bending angle

11

5mm

5mm

Observation method； ・Input static current in a thermostatic oven(38℃)

・observe bending angle to not increase temperature

・observe bending angle using a camera

Measurement of surface temperature

Supply current of SMA wire: 300 mA

Bending angle : 43 degree

Maintaining the surface temperature of the device under 41℃

Achievement

*Limitation temperature of protein denaturation

*

Driven one SMA wire

12

Active bending electric endoscope system

Video unit

Monitor

Controller for

bending device

Controller for

LEDs

Endoscope

Joy stick

13

10 mm

Motion of active bending electric endoscope

5 mm 2 mm

Motion of actuation device using

controller

Observation using CMOS

imager in small intestine model

14

・Controlling bending angle

・Observation of circular folds (2 mm) in small intestine model

Discussion

15

556-723 mcd

High illumination intensity

Size :

Luminous intensity :

1.6×0.8× 0.68mm

61.7 cd

1.6×1.6× 1.44mm

Cree Inc. LED paradise

(Store)

Cardia

Pylorus

Stomach model

inspection of stenosed lesion of

the small intestine

Observation of circular folds

(2 mm) in small intestine model

Application

navigation from cardia to pylorus

×85

Conclusion

・Active bending electric endoscope

－Outer diameter：4.1 mm

－Bending angle：50 deg (300 mA)

・Controlled Bending angle using controller

・Observed Small bowel model

5mm 1mm

Small bowel model

Active bending mechanism (a) (b)

16

Conclusion

－In the future－ ・Insertion test from cardia to duodenum using stomach model

－Confirmation of observational function

－Appropriate rigidity of shaft part

・Drug delivery using working channel

Stomach model

Working channel

Duodenum

Cardia

Tip of active bending

electric endoscope 17

Conclusion

－In the future－

・Feedback control using electrical

resistance of SMA wires

－Prevention of overheat

－Precise position control

45℃

50℃

(b) Feedback (a) Without feedback

45℃

50℃

18

47.5℃

52.5℃

45℃

50℃

47.5℃

52.5℃

Bending mechanism

Thermocouple (T type)