A Magnetically Driven Linear Microactuator With New Driving Method

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Short Papers

A Magnetically Driven Linear Microactuator

With New Driving Method

Mochimitsu Komori and Takehiro Hirakawa

AbstractElectromagnetically driven microactuators are of interest be-cause they have the potential to generate large deflections. Thus, we havebeen studying magnetically driven microactuators. This time, a magneti-cally driven linear microactuator has been newly developed by using mi-

crofabrication techniques. The microactuator is composed of a mobile mi-croplatform (mover) withsome permanent magnets (PMs)and a statorwitha large number of planar coils. In this paper, two types of microplatformsare fabricated and compared with each other. Furthermore, static and dy-namic characteristics of the magnetically driven linear microactuator arediscussed.

Index TermsLinear drive, linear PM motor, magnetic attractive force,magnetic drive, microactuator.

I. INTRODUCTION

Various kinds of microactuators using electrostatic forces, elec-

tromagnetic forces, and other forces have been studied by many re-

searchers [1][5]. Considering electrostatic forces and electromagnetic

forces, it is said that electrostatic forces are superior to electromagnetic

forces for micro-sized actuators. On the other hand, a magnetically

driven method for millimeter/centimeter-sized actuators is regarded

as promising, because millimeter/centimeter-sized actuators might be

useful for industry, and they typically can be operated at substantially

smaller voltages than electrostatic actuators. Thus, there are a lot of re-

ports on magnetically driven, small microactuators [3][5]. This time,

two types of magnetically driven linear microactuators with a new

driving method have been developed and compared with each other.

II. MICROACTUATOR

A. System

The total system of the magnetically driven linear microactuator is

shown in Fig. 1. The system is composed of the newly developed mi-

croactuator, amplifiers, a digital input and output (DIO) interface, and

a personal computer. Drive signals for the microactuator are generated

by the personal computer with Visual Basic programming language.

The drive signals are applied to the actuator through the DIO interface

and the amplifiers. The amplifiers with a gain of 0.2 A/V generate

driving currents according to the drive signals.

B. Microplatform

Two types of microplatforms with some permanent magnets (PMs)

are fabricated for the linear microactuator as shown in Fig. 2. One

is a microplatform with 2 2 PMs and the other has 2 3 PMs. The

Manuscript received September 8, 2003; revised May 24, 2004. Recom-mended by Technical Editor J. T. Sawicki.

M. Komori is with the Department of Applied Science for Integrated SystemEngineering, Graduate School of Engineering, Kyushu Institute of Technology,Fukuoka 804-8550, Japan (e-mail: komori@ ele.kyutech.ac.jp).

T. Hirakawa was with the Kyushu Institute of Technology, Iizuka, Fukuoka840-8502, Japan. He is now with the Ricoh Company, Ltd., Tokyo 107-8544,Japan.

Digital Object Identifier 10.1109/TMECH.2005.848294

Fig. 1. Total system of the magnetically driven linear microactuator.

Fig. 2. Two types of microplatforms with (a) 2 2 PMs and (b) 2 3 PMs.

microplatform (0.15 g) with 2 2 PMs inFig.2(a)consists ofa Permal-

loy thin plate with a dimension of 8.5 8.5 0.1 mm. The magnets

(1.5 1.5 mm) attached to these thin plates are made from SmCo

with a surface magnetic flux density = 0.16 Wb/m2. The microplat-

form (0.21 g) with 2 3 PMs in Fig. 2(b) consists of a Permalloy thin

plate with a dimension of 8.5 13.5 0.1 mm.

The microplatforms are fabricated by using the photolithography

technique. The fabrication process of the microplatforms is shown in

Fig. 3. First, we make preparations for a Permalloy plate [Fig. 3(a)].A photoresist layer is deposited on the Permalloy plate [Fig. 3(b)].

The photolithography process delivers small holes for PMs [Fig. 3(c)].

Finally, permanent magnets are attached to the Permalloy plate by

putting them into the resist holes [Fig. 3(d)].

C. Stator and Planar Coil Fabrication

The stator is composed of a lot of planar coils for driving the mi-

croplatforms as shown in Fig. 4(a). The stator consists of 36 (6 6)

planar coils and measures 20 20 mm. Each coil has 10 turns, as

shown in Fig. 4(b). The pitch of the coils is 3.4 mm. Each coil has two

copper pads to apply driving currents to the actuators. In this paper, we

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Fig. 3. Fabrication process of the microplatforms by using photolithographytechnique.

Fig. 4. (a) Stator with a lot of planar coils for driving the microplatforms.(b) Coil with 10 turns.

Fig. 5. Fabrication process in which coils are made just by using photolithog-raphy technique.

adopted a process that coils are made just by using photolithography

technique as shown in Fig. 5. First, we make preparations for a poly-

imide film with copperfilm [Fig. 5(a)].Photoresist is spin-coated on the

copper film [Fig. 5(b)]. Photolithography process delivers photoresist

coil patterns [Fig. 5(c)]. The copper without resist is etched by FeCl3[Fig. 5(d)]. Finally, the photoresist on the copper coils is removed as

shown in Fig. 5(e). The cross section of copper wire measures 0.05 mm

in width and =16 m in thickness.

Fig. 6. (a) The microplatform with 2 2 PMs. (b) The stator with 6 6 coils.

Fig. 7. Driving methods for the microplatforms with (a) 2 2 PMs and(b) 2 3 PMs in the right direction.

Fig. 6(a) and (b) show the photos of the microplatform with

2 2 PMs and the stator with 6 6 coils, respectively. In Fig. 6(a) four

permanent magnets attached to the Permalloy plate are seen, because

the microplatform is turned over. A circle around the microplatform in

Fig. 6(a) is a convex lens. The stator with 6 6 planar coils is shown

in Fig. 6(b). These coils are connected to the printed wiring board with

the copper pads.

D. Driving Method

Thestatorcoils areexcited to produceattractive forcesapplied to the

microplatform.Six coils in a lineareexcited atthe same time to drivethe

microplatform. Fig. 7 shows the driving method for the microplatform

with 2 2 PMs in the right direction. The microplatform is illustrated

on the stator in each figure. Each figure shows an exciting pattern of

the stator just before the microplatform does a step motion in the right

direction.

In Fig. 7(a), the upper right-hand magnet with N pole is attractedby two adjacent coils of S pole, and the lower right-hand magnet with

S poleis alsoattracted bya coil ofN pole.As a result, the microplatform

with 2 2 PMs moves in the right direction at a distance of half the

coils pitch (=1.7 mm) asshown in Fig.7(b). Next, upper left and lower

left-hand magnets are attracted by two adjacent coils N and a coil S,

respectively. Then, the microplatform does a step motion in the right

direction as shown in Fig. 7(c). As a result, the microplatform moves

a distance of half the coils pitch (=1.7 mm). The microplatform with

2 2 PMs also moves up and down in the same manner.

With respect to the microplatform with 2 3 PMs, the exciting pat-

tern of thestator is basicallythe same asthe pattern of themicroplatform

with 2 2 PMs.


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Fig. 8. Step responses of the microplatforms with (a) 2 2 PMs and (b) 2 3PMs for various driving currents of 0.15, 0.25, and 0.30 A.

Fig. 9. Displacement of the microplatforms with (a) 2 2 PMs and(b) 2 3 PMs when the microplatforms are driven continuously with a drivingcurrent of 0.15 A.

III. DYNAMIC CHARACTERISTICS

A. Step Response

To investigate dynamics of the microplatforms with 2 2 PMs and

2 3 PMs, step responses were studied. Fig. 8(a) shows step responses

of the microplatform with 2 2 PMs for various driving currents of

Fig. 10. Relationship between final displacement and driving current for themicroplatforms with 2 2 PMs (filled circles) and 2 3 PMs (open circles).

Fig. 11. Relationships between final displacement and driving current for themicroplatforms with (a) 2 2 PMs and (b) 2 3 PMs carrying various loads of0.05, 0.1, 0.2, and 0.3 g.

0.15, 0.25, and 0.30 A. As shown in the figure, step responses with-out overshoots are observed. It is found that the microplatform moves

smoothly on the stator. The step responses have repeatability and accu-

racy to0.1 mm. From the result, final value (displacement) is defined

by using the result in Fig. 8(a). The step responses have different final

values, which are 0.95, 1.24, and 1.38 mm for the driving currents of

0.15, 0.25, 0.30 A, respectively. These final values (displacements) are

a little smaller than an ideal displacement (=1.7 mm). Fig. 8(b) shows

step responses of the microplatform with 2 3 PMs for various driving

currents. The step responses have different final displacements. This

tendency is similar to that of the microplatforms with 2 2 PMs. The

final displacements for the microplatform with 2 3 PMs are larger

than those for the microplatform with 2 2 PMs.


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In addition to the step responses, continuous driving characteristics

of the microplatforms with 2 2 and 2 3 PMs were studied. Fig. 9(a)

shows the displacement of the microplatform with 2 2 PMs with a

driving current of 0.15 A. The continuous step motions are based on

the step response as shown in Fig. 8(a). The final displacement after the

threestep motionsis 5.2 mm, which isequivalent to one and a half coils.

Fig. 9(b) shows the continuous displacement of the microplatform with

2

3 PMs. The step motion for the microplatform with 2

3 PMs issimilar to that for the microplatform with 2 2 PMs.

B. Evaluations

Final values (displacements) are defined by using the experimental

results shown in Fig. 8. Fig. 10 shows the experimental result for the

microplatforms with 2 2 PMs (filled circles) and 2 3 PMs (open

circles). Each final value (displacement) increases with increasing cur-

rent in the range up to 0.3 A. The maximum displacements are about

1.38 and 1.81 mm.

Final displacements of the microplatforms with 2 2 PMs and

2 3 PMs were measured with some loads of 0.05, 0.10, 0.20, and

0.3 g. Theresults for the microplatforms with2 2PMsand2 3PMs

are shown in Fig. 11(a) and (b), respectively. From Fig. 11, the final

displacement for each load increases with increasing driving current.The displacement also increases with decreasing carrying loads. The

final displacements in Fig. 11 are smaller than the displacements with-

out loads in Fig. 10. In general, the displacements in Fig. 11(b) are

larger than those in Fig. 11(a).

IV. CONCLUSION

In this study, the magnetically driven linear microactuator using

microsystem fabrication techniques is successfully developed. From

the results, the driving method is found to be available for driving the

microplatform. The final values of the step responses depend on the

driving currents. From the study on carrying capacity, it is found that

the microplatform carries about the same load as itself. The microplat-

form shows the continuous motion according to the computer signals.As a result, the microactuator mentioned previously is found to be

useful for some kinds of applications such as microconveyer.

REFERENCES

[1] K. S. J. Pister, R. S. Fearing, and R. T. Howe, A planar air levitatedelectrostatic actuator system, in Proc. IEEE MEMS Workshop, NapaValley, CA, Feb. 1990, pp. 6771.

[2] H. Guckel, K. J. Skrobis, T. R. Christenson, J. Klein, S. Ham, B. Choi,E. G. Lovell, and T. W. Champman, Fabrication and testing of theplanar magnetic micromotor, J. Micromech. Microeng., vol. 1, no. 4,pp. 135138, Sep. 1991.

[3] M. Komori and T. Yamane, Magnetically levitated micro PM motors bytwo typesof active magnetic bearings,IEEE/ASME Trans. Mechatronics,vol. 6, no. 1, pp. 4349, 2001.

[4] B. Wagner, M. Kreutzer, and W. Benecke, Permanent magnet micro-motors on silicon substrates, J. Microelectromech. Syst., vol. 2, no. 1,pp. 2329, Mar. 1993.

[5] L. K. Lagorce, O. Brand, and M. G. Allen, Magnetic microactuatorsbased on polymer magnets, J. Microelectromech. Syst., vol. 8, no. 1,pp. 29, Mar. 1999.

Uncoupling Micromachined-Based Piezoelectric

Accelerometer Performance From a Sensor Structure

Transfer Function

Yu-Hsiang Hsu, Chih-Kung Lee, Long-Sun Huang,

Chih-Cheng Chu, and Ta-Shun Chu

AbstractA smart structure technology for autonomous gainand phasetailoring was adapted to develop a new accelerometer that possesses bothan excellent low-frequency response and a high operational bandwidth.

The freedom associated with the uncoupling of the gain and phase tailor-ing to an accelerometer-based structure transfer function can be shown tovastly expand the performance area of traditional accelerometers. We usedfree-fall detection to demonstrate this newly found capability with its wideapplicability to portable devices and which is perceived as extremely dif-ficult to pursue for magnetic disk drives. A micromachined accelerometerwas developed to demonstrate the expanded applicability of this innovativeconcept that integrates smart structuretechnology to accelerometerdesign.Boththeoretical derivations and experimental verification of this new classof accelerometers are detailed in this paper.

Index TermsFree-fall sensors, microsensors, point sensors, smartstructures.

I. INTRODUCTION

Because the performance of an accelerometer is most prominently

demonstrated by its frequency response, the frequency and the damp-

ing factor associated with the first resonant mode becomes the primary

design concern whenever a new potential accelerometer is developed.

In fact, this implicit rule of thumb effectively limits an accelerometer

bandwidth to 1/10 to 1/5 of its first resonant frequency such that the

achieved linearity and accuracy will be better than 510% [1]. Because

accelerometer performance is so tightly linked to the base structure, the

operational bandwidth and the sensitivity required almost immediately

determine the size of the accelerometer. In this article we incorporate

smart structure technology developed over the past two decades [2]

into an accelerometer design. This concept provides us with a method

to vastly expand the design freedom of accelerometers, which was first

reported by Hsu and Lee in 2002 [3]. At that time, to clearly illustrate

the impact of this series of sensors, the concepts of point-distributed

sensors (named PoD sensors) and APROPOS devices (acronym for

autonomous phase-gain rotation/linear piezoelectric optimal sensing)

were described [3]. This study reported that the usable bandwidth of

this newly developed accelerometer can be enhanced by incorporating

an APROPOS device onto a PoD sensor, as gain and phase tailoring

are autonomous [3]. To verify the sensitivity and applicability of this

newly invented piezoelectric accelerometer as a micromachine-based

device and to explore application areas not attainable by previous ac-

celerometers, a free-fall motion was chosen as the metrology target

in this article [4]. It is worth noting that free-fall sensing has been

deemed an important research and development target of the magnetic

Manuscript received October 15, 2003; revised July 12, 2004 and January 17,2005. This work was supported by the National Science Council of Taiwan,R.O.C., under Grant NSC 85-2622-E-002-017R, Grant NSC 86-2622-E-002-023R, Grant NSC 88-2218-E-002-005, and Grant NSC 88-2622-E-002-001.Recommended by Technical Editor J. von Amerongen.

Y.-H. Hsu was with the Institute of Applied Mechanics, National TaiwanUniversity, Taipei, Taiwan, R.O.C. He is now with the University of California,Irvine, CA 92697 USA (e-mail: [email protected]).

C.-K. Lee, L.-S. Huang, C.-C. Chu, andT.-S. Chuare with theInstitute ofAp-plied Mechanics, National Taiwan University, Taipei, Taiwan, R.O.C. (e-mail:[email protected]; [email protected]; [email protected]; [email protected]).

Digital Object Identifier 10.1109/TMECH.2005.848301

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A Magnetically Driven Linear Microactuator With New Driving Method