1

Akira HeyaKatsuhiro Hirata

Osaka University, Japan

Experimental Verification of Three-Degree-of-Freedom Electromagnetic

Actuator for Image Stabilization

19th International Symposium on Electromagnetic Fields in Mechatronics, Electrical and Electronic Engineering29-31 August 2019, “Prouvé” Congress Center Nancy – FRANCE

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Outline

Introduction

Proposed 3DOF actuator

Experimental verification

Conclusion

3

Introduction

Environment recognition for autonomous systemusing camera

Phantom 4 (DJI Co., Ltd.) ibuki (Nakata et al., 2018)

Recognition accuracy deteriorations due to vibrations

Development of small robotic eye which has high kinematical performance

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Lens for camera Image sensor

Relationship of eye and camera

Lens-unit-swing system

Consists of lens (crystalline lens) and image sensor (retina)

Application of 3DOF actuator for downsizing

AdvantageCorrect wide range around 3-axis

DisadvantageIncrease in size and weight

Crystalline lens RetinaCrystalline lens Retina

Lens for camera Image sensor

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Experimental verification of proposed 3DOF actuator

Conventional Proposed*

3DOF actuator

Wang et al., 2003 Nishiura et al., 2016

* A. Heya et al., “Dynamic Analysis of High-Speed Three-Degree-of –Freedom Electromagnetic Actuator for Image Stabilization”, IEEE Transactions on Magnetics, Vol. 53, No. 11, 2706942, 2017

ApplicationRobot wrist, machine tool etc.

RequirementHigh torque, wide-angle drive

Large in sizeComplicated control device

ApplicationImage stabilizationfor eye system

RequirementSmall sizeHigh responsivenessSimple control device

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Contents

Introduction

Proposed 3DOF actuator

Experimental verification

Conclusion

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Based on a MM type VCM

Size：Φ28×25 mm (Magnetic circuit part)

About human’s eye size

Basic structure

X/Y-axis Z-axis

Cover

Bass plate

Coil

Rotor

Support parts

Outeryoke

Spherical bearing

Permanentmagnet

Mover

Rotor and bearing

Movable range

X : ±25 deg.

Y : ±25 deg.

Z : ±5 deg.

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X

Y

Z

B

FI

SN

SN

Rotation around X/Y-axis

XY

Z

B

FI

SN

N NS S

CoilLorentz force

Outer yoke A

Rotation around Z-axis

Operating principle

Controlled by 3-phase : simple control system

Outer yoke B

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z

y xX

Magnetic circuit

Magnetic path of the proposed actuator

xy

z

z

x

Magnetization

Reduction of magnetic flux leakage from 3-D structure

Detent torque works as magnetic spring

Y

Z

Y X

Z

X

Z

Outer yoke A

Outer yoke BOuter yoke B

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Contents

Introduction

Proposed 3DOF actuator

Experimental verification

Conclusion

11

Prototype

Overview

Coil for driving around X/Y-axis

Side view

Overview

Base plate

Coil for driving around Z-axis

Supportparts

Top view

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Overview

Outer yoke A

Single coil for driving around X/Y-axis

Yoke

Rotor

20 mm

Permanentmagnet (Br = 1.3 T)Overview

Prototype

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Without the coil Aand rotor

Overview Except for the support parts

Outer yoke B

Overview

Prototype

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Operating verification

Experimental setup

• H-bridge circuit×3 (MAX14870, Maxim Integrated corp.)

• PWM frequency : 20 kHz

• Input voltage: 12 V

mbedLPC1768

(ARM Cortex-M3)

H-bridge driver

X-axis

Y-axis

Z-axis

Micro computer

System configuration for drivingProposed actuator

×3

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動作検証

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Torque characteristics

Experimental setup

Rotation around the X-axis Rotation around the Z-axis

Force sensor（MAF-3, WACOH-TECH Co.)Servo motor

Servo motor

Torque sensor（TCF02N, Tohnichi Co.)

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Measured results

Rotation around the X-axis Rotation around the Z-axis

Generated torques in each axis

-6

-4

-2

0

2

4

6

-25 -20 -15 -10 -5 0 5 10 15 20 25

Dete

nt

torq

ue [

mN

m]

Angle [deg.]

-6

-4

-2

0

2

4

6

-5 -4 -3 -2 -1 0 1 2 3 4 5

Dete

nt

torq

ue [

mN

m]

Angle [deg.]

02468

101214

To

rqu

e co

nst

an

t

[mN

m/A

]

05

101520253035

To

rqu

e co

nst

an

t

[mN

m/A

]

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Frequency characteristics

Ratio of input voltage and amplitude

Rotation around the X-axis Rotation around the Z-axis

Laser displacement sensor（LK-G35, KEYENCE Co.)

Multi functiongenerator

Bipolar amplifier

3DOF actuator

Voltage

Sine wave

System configuration

Linear stage

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Operating verification

Rotation around the X-axis Rotation around the Z-axis

0

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80 90 100

Gain

[d

eg./

V]

Frequency [Hz]

0

1

2

3

0 10 20 30 40 50 60 70 80 90 100

Gain

[d

eg./

V]

Frequency [Hz]

Measured results

Proposed actuator can be drivenover wide frequency range

* Speed and Accuracy of Saccadic Eye Movements : Characteristics of Impulse Variability in the Oculomotor SystemRichard A. Abrams , David E. Meyer and Sylvan Kornblum

Max. angular acceleration: 60.2 × 104 [deg./s2]

Human’s eye motion*: 4.4 × 104 [deg./s2]

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Conclusion

Experimental verification

• Operating verification using prototype

• Torque generation by proposed principle

• Driving over wide frequency range

Future work

Proposal of Attitude sensor-less control method

Proposed magnetic structure and operating principle are valid