JOURNAL OF SCIENCE <& TECHNOLOGY • No. 94 - 2013
DESIGN AND FABRICATION OF THE MICRO BI-DIRECTIONAL MOTOR DRIVEN BY ELECTRO-THERMAL ACTUATORS
THIET KE CHE TAO MICRO MOTOR HAI CHIEU DAN DONG BANG BQ KICH HOAT NHIET Nguyen Tuan Khoa*, Dang Bao Lam, Dinh Khac Toan, Pham Hong Phue
Hanoi University of Science and Technology Received March 07, 2013; accepted April 25,2013
ABSTRACT
This paper presents a novel micro linear motor with simulation and measurement of electro- thermal actuators based on thermal expansion of V-shape silicon beams when applying a voltage. The processes have been carried out with three types of motors with different numbers of thermal expansion beams, i.e. 3, 6 and 10in U = 5-^ 30V voltage range. t\/leasured displacements of the motor shuttle are from 12 to 18 pm and driving force can reach tens of millinewton (mN). By measurement of the step displacement with dnving frequency from 1 to 30 Hz. it can be seen that the optimal range of applied voltage is from 15 to 30 V The displacements increase with the larger number of actuator beams. The advantages of the motor are small size, simple fabrication process with only single mask, high accuracy control
Keywords: MEMS, micro linear motor, electro-thermal actuator TOM TAT
Sa; bio niy trinh bay thiit ki mpt lo^i vi motor tuyin tinh mdi cung v&i cac kit qui md phdng va do dac thi/c nghiem cho bd kfeh ho^t nhi$t dan ddng h$ thong bai biin d^ng nhi$t cua dim silicon d^ng cha V khi cho ddng di$n ch^y qua. Tinh toin, md phdng va do dac tht/c nghi$m a diin ip U = 5 + 30V, v&i tdng h$ dim khic nhau vi so luvng c^p dim li 3. 6 vi 10, thu duvc chuyin vi bu&c cOa thanh tCr 12 din 18 pm va li/c diy cua bp kich ho?t c& hing chtjc mill nev\/ton (mN). Kit qui do d$c chuyin vi v&i dii tin so tif 1 din 30 Hz chf ra ring cic bd l<ich boat nfji^t ho$t ddng tot trong dai di$n ip tir 15 din 30V Chuyin vi cOa dim diy vi thanh truvt ting theo sd c^p dim cua bd kich hoat. Wu diem cua motor nhiet din dgng bai dim V li kich thu&c gpn, dan giin trong gia cdng, diiu khiin tin ciy, dat dp chinh xic cao v&i vi$c chi su' di^ng mpt mat n?.
1. INTRODUCTION
Electro-thermal actuators (ETAs) in MEMS have many advantages such as low driving voltage, simple fabrication process, They can also generate larger force and displacement in comparison with electrostatic comb actuators (ECA) [1-3]. However, ETAs waste more energy than others and only work well in low frequency range. The effect of electro-thermal expansion has been used widely in MEMS technology in order to design ETA, for example, V-shape beam actuators [4-6], thermal bimetal actuators [7-8], cascade beam actuators [9], spring beam actuator [10] and complex spring and anchor beam actuators [11], dual beam actuator [12], etc.
The ETA in this paper is used for driving shuttle in a micro linear motor. It contains couples of parallel V-shape beam (Fig. 1) with slope angle a = 2° defining movement direction
^
i
Fig. 1 V-shape beam of the peak of the beams. The number of V- shape beams in each type is 3, 6 or 10, respectively. Each separate beam has length L = 750 |im, width b = 6^im and depth A = JO (im.
2. CONFIGURATION AND WORKING PRINCIPLE
Fig. 2 describes design of the micro linear motor with shuttle ®, four ETAs © and, two clamp actuators ®, which can move fortl', and back in both directions by activation o'
JOURNAL OF SCIENCE & TECHNOLOGY * No. 94 - 2013 each couple of actuators alternately. When
square waveform voltage Vi is applied to two left ETAs, in the driving period with Vi >0, thermal expansion of the beams ® of couple actuators caused the peak of V-shape move forward following planned direction with slope angle a. Each driving beam ® is arranged with slope angle ^ to shuttle direction so that after overcoming gap g/ with shuttle, beams of ETAs (D clamp and push the shuttle to move to the left direction.
In the next segment, when Vi decreases to zero, beams of ETAs ® contract to initial dimension, the shifted phase voltage V2 is
applied to the couple of clamp actuators ® ^ caused the clamp beams expand and prevent Ihe shuttle from moving backward. In the nea voltage period, driving actuators expand and push shuttle move forward to the left once again. Movement of shuttle is linear and step- by-step by inchworm method. Anchors ® are there to guide shuftle to move in planned direction. The gap g2 between the anchors and shuftle is designed for allowing free movemat of the shuttle as well as assuring linear movement direction. When the shuttle moves to the right, whole process repeats.
v
Vt V l
! 1
' ; 1 ! 1
' . ^ • • • • ^ • ^ • • • • • • • • r a • • • • • • • • • • • • » » » • - —— - — _ - _ J^
3. DISPLACEMENT ANALYSIS 3.L Temperature and displacement of single beam
Expansion of beams can be express by:
AL = a„^[T(x)-T,]dt (I)
0
T(x) is temperature at x (fLtt\) of single beam, oo is expansion coefficient (a„ is considered as a constant), T, is the temperatuis of the air.
Differential conduction equation [13];
Fig. 2 Configuration of linear motor driven by ETAs
Fig. 3 Displacement calculation
JOURNAL OF SCIENCE & TECHNOLOGY * No. 94 - 2013 Resistivity of silicon p = pti(\+X{T-Tr)), >l
is linear temperature coefficient, J = — is pL current density, and k is thermal conduction coefficient, we have:
, d^T U'
(i-/i(r-r,)) = o
dx' Vp,
We have boundary condition:
T ( x ) = T + ^ + C,e B
(3)
(4)
c,-
A' e"+e'''Consequently, the displacement of single beam can be calculated as:
AL = a.J^L + ^e"- -'^e"- - ^ + ^ 1 (5)
° A' A A A A-' ^ ' 3.2. Displacement of driving beams
As showing in fig. 3, displacement of driving beams can be calculated:
AD =FF' = GF'-GF
= Vi
EF -EG -EFsina (6) - i/(L + AL)^ - ll cos^ a - Lsin a 3.3. Step displacement of the shuttleConsidering driving beams only deformed at elastic point as showing in fig.4 and there is no sliding between the driving beams and the shuttle, we have:
AS = ^d^ -(d'sin^f -d' cos^, (7) d = A'B\d' = A'B = AB-AD + g.
sinP With U= \5\ (voltage in half side of V-shape beams), cto = 4x10-^, A = 5x10'^ V , / J o = 2x10'^
Qm, k^ 1.5x10'' Wjim''K"', step displacements of the shuttle is calculated in table I.
Table 1. Step displacement of the shuttle (AS [pm])
Couples of beams a = 2»
3 AS =18.3
S AS =18.3
10 AS =18.3
4. SIMULATION
The micro linear motor has been simulated by muhi-field finite element model with number of couples of beams n = 3, 6 and 10, respectively, depth of structure h = 30|im, width of the beam b = 6jim, length of the beam L = 750nm, slope angle of the beam a = l".
4.L Simulation result of displacement of the actuators
Simulation of displacement of ETAs is carried out with three cases of 3, 6 and 10 couples of beams and slope angle 2". Fig.5 shows displacement of actuator with 10 couples of beam at voltage U=30V. It can be determined that the largest displacement is at the peak of the beams.
The relation between displacement of the driving beam in cases of 3, 6 and 10 couples of beams and applied voltage is showed in Fig.6.
4.2. Simulation result of temperature of V- shape beam
The temperature of V-shape beams is showed in fig. 7. The highest temperature is found at the peak of beams t^ax ~ 395°C.
Fig. 8 shows relation between the highest temperature and voltage of actuators in the cases of 3, 6 and 10 couples of beams.
4.3. Simulation result of driving force In the case of 10 couples of beams, at voltage t/=30V, the generated force in x- direction Fx = 58 mN. It is determined that thermal actuators generate large forces about ten of millinewton (much larger than those generated by the ECAs, which have values of hundreds of micro Newton).
5. EVALUATION TEST RESULT OF ACTUATORS AND MOTOR
S.L Test result of displacement of driving beams
The ETA works well in 5-30V voltage range. When applied voltage reached 40V, The ETA has been short-circuited.
Test resuh shows step displacement at same voltage increases with the higher value of number of beams.
39
JOURNAL OF SCIENCE & TECHNOLOGY • No. 94 - 2013
••(g. 4 Step elisiilacen
fM 1
unl of shuttle
20 [-
^ 1 5 1 ^—3 beams
^ I * •• 6 beams
£ j - • — 10 beams
L
Fig 5 Displacement of V-shape beams
T 5 10 15 20 25 30 Voltage (V) Fig 6 The relation between displacement i applied voltage of ETA
450 -
— 400 i
^ 3 5 0
§ 300 I
™ 250 I
£200 1150 • r 100 I 50 .S" 0
r 3 beams
—6 beam 10 beams
— —r>-
10 15 20 25 Voltage (V) Fig. 7 Distribution of temperature in V-shape
beams
Fig. 8 The relation between displacement i applied voltage of ETA
- 1 6
=.14
¥12 g i o
15 20 25 30 Voltage (V) ,^
Fig. 10 Simulation and test result_of displacement of actuators with 10 eoi^les of beams
JOURNAL OF SCIENCE & TECHNOLOGY • No. 94 - 2013 Actuator with 10 couples of beams has the
largest displacement. At i7=30V, shuttle moves toward 17fim.
The deviation of step displacement of the shuttle when comparing calculation and testing results (fig. 10) occurred because of elastic bending of the driving beams and sliding when the driving beams push the shuttle, abatement of voltage at contact point of probes.
In testing process, positions of driving beams are compared in video frames in order to find the displacements of driving beams following driving voUage.
Test result showed relation between displacements and voltages of driving beams in case the ETAs have 3, 6 and 10 couples of beams at IHz frequency, square pulse in 15- 30V voltage range (fig. 11-12)
15 20 25 30
Voltage (V)
Fig. II Test resuh of displacement and voltage of driving beams
5.2. Test the moving of the shuttle In the evaluating process, it can be seen that in returning period, elastic force of V-shape pulls shuttle to move backward so that displacement of shuttle actually lower than theoretical calculation (fig. 13).
Table 2 Step displacement of shuttle at voltage 30V, frequency I Hz
Couples o f beams Displacement(nni)
3 12
6 14
10 17
16
r i 2
| i o S 8
Dis
2 0
— • k K . . ^
' ' * 7-- '^,
1 3 beams ^ .
\
• 6 beams 10 beams
1 i 10 15 20 Frequency(Hz)
Fig. 13 Step displacement of shuttle at voltage 30V in 1-20 Hz frequency range
5.3. Test of driving force
In order to determine values of the force generated by the motor, the strength calculation model is used in fig. 14-15 with two clamped heads
a. V, = OV b. Vl = 30V Fig. 14 Video captured pictures of bending beam lo figure out generated force of the motor
Following [14], driving force can be calculated as:
^ 2AEJ 2AEb^h F,cose = —^ = —-^
^d ^d
^ 2AEb^h 2x15x169x10^x6^x30 Fig. 12 SEM images of largest displacement of
driving beams
L]cose 300^xcos35''
=5U22ipN)=^S^.\mN
JOURNAL OF SCIENCE & TECHNOLOGY * No. 94 - 2013
• FdCosBj^\^
l\
I FdSinG Fd Fig. 15 Generated force of the motor 6. CONCLUSION6.L Displacement of the driving beams The motor works well in voltage range of 15-30V. Up to 40V, the motor has been stopped due to short-circus occurence.
Displacement at the same voltage increases with the higher number of beams of the motor. The motor with 10 couples of beams, can generate the largest displace-ment (about IT^im when the applied voltage is 30V).
6.2. Working process of tbe motor The motor with 10 couples of beams of actuators generates the largest displacement of shuttle.
The motor works well in voltage range 15-30V. The slide between driving beams anj the shuttle happened in the frequency range o[
lO-lSHz in case of 3 and 6 couples of beami, and higher 20Hz in case of 10 couples of beams.
Forces generated by the ETA are mud) larger than those by ECAs at the same voltage, But The ETA can only work well with low driving frequencies.
6.3. Applied capability of ETAs This paper reports the main advantages of the motor driven by the ETAs as follow: small size and large generated force. But it also caa be seen that the generated temperature is ratlw high, which is up to 400''C at 30V voltage. BE motor can be applied in driving micro robot, micro container in micro transportation systems, etc.
ACKNOWLEGDEMENT This work is supported by the Projeci B20I2-OI-32 of Ministry of Education and, Training of Vietnam.
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thor 's address: Nguyen Tuan Khoa - Tel: (+84) 982.864.246, Email: [email protected] Hanoi University of Science and Technology
No.l Dai Co Viet Str., Ha Noi, Viet Nam
