design of a voice coil motor used in the focusing systerm of

IEEE TRANSACTIONS ON MAGNETICS,VOL.41,NO.10,OCTOBER20053979 Design of a V oice Coil Motor Used in the Focusing System of a Digital Video Camera Hsing-Cheng Yu1,Tzung-Yuan Lee2,Shyh-Jier Wang1,Mei-Lin Lai1,Jau-Jiu Ju1,Der-Ray Huang1,and

Shir-Kuan Lin2

OES/ITRI,Hsinchu310,Taiwan,R.O.C.

Department of Electrical and Control Engineering,National Chiao Tung University,Hsinchu300,Taiwan,R.O.C.

This paper raises a valid method to design a voice coil motor(VCM)used in the focusing system of a digital video camera(DVC).

A better VCM performance,such as lower battery consumption,higher ef?ciency,and shorter focusing time,can be achieved by turning the diameter of a winding coil,the thickness of the magnet,and the winding spaces in a VCM.

Index Terms—Battery consumption,digital video camera,focusing,voice coil motor.

I.I NTRODUCTION

R ECENTLY,digital video cameras(DVCs)have been very

popular,and better performance of focusing is always

asked.In order to attract more customers,the conventional

focusing actuators,steppers,in a DVC are gradually replaced

with a voice coil motor(VCM),whose focusing time is shorter.

Most works concerning VCMs considered mainly the dynamic

response[1].However,both the battery consumption and the

ef?ciency of a VCM are also important factors to be taken into

account in a DVC system,since DVCs are portable apparatuses.

This paper tries to introduce a design procedure for a VCM that

meets the strict requirements of low power consumption,high

ef?ciency,and fast focusing.

II.P ROBLEMATIC F ORMULATIONS

A typical VCM used in a DVC consists of a permanent

magnet,a moving coil,a yoke,and a steel plate as shown in

Fig.1.The design problem of a VCM restricted in a limited

space can be formulated to?nd the diameter of

one coil in the

windings and the thickness

ratio

(1)

where is the thickness of the permanent magnet

and is

the thickness of the windings.Indeed,the magnetic?eld in the

VCM is constructed by

determining.Furthermore,the number

of turns of the moving

coil can be estimated

as

(2)

where is the width of the windings

and is a function

of

and.

The design philosophy for a high-quality VCM used in a DVC

is to de?ne three performance indexes,namely:1)the rising

time;2)the battery consumption

energy;and3)the ef-

?ciency.The rinsing time is a measure of the focusing time

of a DVC,while the battery consumption energy is that of the

Digital Object Identi?er

10.1109/TMAG.2005.855161

Fig.1.Structures of the VCM in DVC.

battery duration.The ef?ciency is used to estimate the copper

loss of the VCM.These indexes are formulized

as

(3)

(4)

(5)

where is the maximum stroke of the

VCM,is the speed of

the VCM moving part,is the current of the windings per

turn,

is the terminal voltage,

and is the coil resistance.Equations

(3),(4)and(5)show

that

,,

and are all functions

of

and

.The design goals are to

decrease

and and to

increase

to obtain a better VCM.

It is known[2]that the dynamic equations of the VCM can

be written

as

(6)

(7)

where is the coil

inductance,is the voltage

constant,is

the mass of the VCM moving

part,is the damping

constant,

is the electric

force,is the loading force,

and is the

force constant.If ,

,

,

,

,

,

,,

and are

0018-9464/$20.00?2005IEEE

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