- Email: [email protected]
Microvibromotor for Precision Microrobot
Copyright ro IFAC Infonnation Control in Manufacturing, Nancy - Metz, France, 1998
MICROVIBROMOTOR FOR PRECISION MICROROBOT Philippe Helin, Veronique Sadaune, Christian Druon
Institut d'Electronique et de Microelectronique du Nord Departement Opto-Acousto-Electronique Avenue Poincare, BP 69 59652 Villeneuve d'Asq Cedex, France E-Mail : [email protected]
Abstract : This paper reports an ultrasonic driven microvibromotor. An angular and linear microvibromotor is obtained from a motorization by surface acoustic waves generated from interdigital transducers on a substrate LiNb0 3 • The linear and rotational movements are obtained according to the position of the slider with regard to acoustic beam. The displacement of the slider is controlled from the burst duration applied across the interdigital transducer. This device is capable of nanometer resolution, for a travel area of over 40 mm square and rotation until 360 0 with a resolution better than 0.10. A number of possible applications are discussed. Copyright © 1998 IFA C Keywords : Motor, Actuator, Positioning systems, Ultrasonic transducers, Friction.
1. INTRODUCTION
waves to move a slider with frictional drive. In this paper, this concept of motorization is enlarged to the fabrication of a new angular and linear microvibromotor which well corresponds needs of precision engineering industry.
Considering the reduction of size in the production of semiconductors or microengineering products, the sector of micro-manipulation is expected to be a key task. For example, the micromanipulation by radiation pressure is crucial in biotechnology. Wu (1991) demonstrated the trapping and moving of the latex particle (270 /lm diameter) using two collimated ultrasound beams radiating from focusing PZT transducers. Moroney et al. (1990) also observed the movement of 2.5 /lm diameter polystyrene spheres in the flow of water using 4 MHz flexural waves traveling in 4 /lm thick silicon nitride membrane. Takeuchi et al. (1994) performed a two dimensional manipulation of 50 /lm diameter glass spheres using two pairs of leaky wave transducers at frequency of 48.5 MHz. In the other hand, the micromanipulation by friction drive is important in microsystem industry. Kurosawa et al. (1996) demonstrated the possibility to use Rayleigh
2. DESIGN
This microvibromotor is based on the conversion, through frictional contact, of a retrograde elliptical motion of surface particles due to the traveling wave propagation into slider displacements (Helin et aI. , 1997a). Interdigital transducer (IDT) can be used for Rayleigh wave excitation. Eight IDT's have been fabricated, patterned through photolithography step on a 1 mm thick substrate, on the X cut of 3 inches LiNb0 3 substrate, arranged as shown in Figure 1. The IDT electrodes consist of 1000A of Ti followed by 5000A of Au. The IDT's are facing each other to
249
obtain the two-way motion. All the fabricated transducers have the following characteristics : 100 ~m strip width and 15 mm aperture size. The operation area is about 40 mm square. Each IDT has 10 strip electrodes pairs. From geometrical considerations, the x- and y- direction resonance frequencies are 8.75 MHz and 9. 10 MHz, respectively. They are not the same due to anisotropy of the substrate material. To prevent a standing wave excitation, acoustical absorbent is pasted between the IDT's and the wafer edge. Concerning the surface strain amplitude, it is worthwhile mentioning that it has to be large enough for having a sufficient coupling between acoustic wave and slider. To this aim and by impedance matching consideration, the geometrical capacitance of IDT is matched with an inductance to increase the strain amplitude. A slider with three contact points is used in order to obtain a high contact pressure with a weak contact surface to avoid the wave attenuation. This slider consists of a washer (diameter 5 mm) stuck over three tungsten carbide balls (diameter 1 mm) in order to obtain a large friction coefficient.
16- IDT 115- IDTI Fig. 2. Operation principle of the angular and linear microvibromotor.
3. VIBROMOTOR PERFORMANCE The theory of the piezoelectric Rayleigh generation is well know and the components of the ideal IDT equivalent circuit can be calculated by using formulas of reference (Feldrnann et aI. , 1986). The ideal IDT radiation resistance R(f) and radiation reactance X(f) are thus given by :
Z(f) = R(f) + with
R(f)
j( X(f) - C~)
= Ra( Si:x
r
X(f) = R sin2x - 2x
10':01
a
Fig. 1. The angular and linear microvibromotor.
and
X
2X 2
N-l f-J; = --1t 0
2 The operation principle of this actuator is represented in Figure 2. The linear and rotational movements are obtained according to the position of the slider with regard to acoustic beam. In first case (case a) the three balls of the slider are in the acoustic beam. Then, a linear motion of the slider is obtained along x- or y-directions when, for example, the 8- or 2-IDT is excited, respectively. In second case (case b) only one ball is in the acoustic beam of the 7-IDT and so it is alone affected by the tangential force of acoustic wave which produces a torque hence a rotational motion of the slider. The discrete nature of the slider motion (one pulse per acoustic period) allows us to control the position of the slider according to the burst duration applied across the IDT with a great accuracy.
R = 1.4e a Em W
(I)
(2) (3)
(4)
fo (5)
where N is the fmger number, E is the equivalent dielectric constant , CT is the electrode capacitance, W is the aperture , k2 is the electromechanical coupling coefficient, fo is the excitation frequency, Wo is the angular frequency and f is the frequency . Figures 3 and 4 show the calculated and measured input impedance Z(f) of an IDT oriented for wave propagation along x- and y- direction, respectively. Note that the transducer impedance curves show close agreement in shape. In figure 3, the transducer resistance curve is quasi-symmetric in shape about the IDT center frequency, this is a typical behavior of an IDT for Rayleigh wave generation. In figure 4, the
250
curve shapes are modified due to the leaky wave propagation at 11.5 MHz. The radiation resistance in the y-direction is matched to signal generator impedance, but in the x-direction this radiation resistance is more large on account of geometrical considerations. The differences in the calculated and measured impedances can be attributed to several factors, such as : uncertainty in material constants, crystal cut, alignment of translation stages and of the IDT with the chosen propagation direction.
displacement values for both directions with a driving time from 0.05 to 50 ms in a logaritlnnic scale.
I_
1.E+Ol
t
1.E+oo
! C
1.E-Ol
i
1.E-02
u
i.!! o
~
"x l
0
o ~
1.E-03
El
1.E-04
0
0
-
~ D'"
~
m
c.
0
1.E·Q5
0.1
0.01
1
10
100
Driving time (ms)
Fig. 6. Linear displacement of the slider for both directions. so
se
115
13
BO
.,
i5
103
110
"
The smallest displacement is about 40 nm to 0.05 ms. This time corresponds to about 450 acoustic wave periods. Then, it will be possible to measure a lower displacement down to a few nanometers with a shorter driving time. Concerning the rotation, the angle values are measured under microscope with the help of a vernier. Figure 7 shows the angle values versus driving time. With the previous measurements of displacement (40 nm), it should be possible to obtain lower rotation down 10-3 degree. A rotation of 360 0 has been obtained by applying successive bursts.
(I
Frequency (~)
Fig. 3. Calculated and measured impedance of an IDT oriented along x-direction. JOO
.. _-- - . .
575
-1 '-"
IS
725
e 7S 115 Frequency (~)
102S
11 75
6
5
_4
Fig. 4. Calculated and measured impedance of an IDT oriented along y-direction.
!!...
-
j::
The vibration amplitude of the nonnal direction to the surface is measured using an interferometric probe. The measurements of the vibration amplitude distribution versus distance from the emitted IDT for both directions are shown in Figure 5. The amplitude is on the order of nanometers. The peak-to-peak driving voltage applied across the IDT is 90 Vpp.
3 2
o o
•
10
20
30
40
Driving time (ms)
Fig. 7. Rotational movement of the slider.
30
E
25
...
20
S-
4. CONCEPT OF MICROROBOT AND POSSIBLE APPLICA nONS
O>
'""a.'E"
.
15
0
10
J:l
5
c
~ :>
We designed an integrated microvibromotor unit, that as part of a microconveying station will be able to perfonn certain tasks: locomotion, transportation of objects, operation on objects, and so on (Helin et aI., 1997b). The basic actuator unit could be transfonned into a variety of adaptations, according to the special requirements for different environments or application. Some expected advantages of this method over an electrostatic motor are : inherent stability, independence of the presence of a conducting medium around the motor unit, easy to start because
I I
0 0
10
20
30
Distance (mm)
40
so i I
Fig. 5. Vibration amplitude distribution for both directions. The displacement values are obtained using an optical displacement measuring instrument. Its resolution limit is about 40 nm. Figure 6 shows the
251
no synchronization is required, compatibility with linear and rotational motions; high output force . One can imagine that hordes of small and cheap microrobots could be used in chores too tedious or dangerous for human beings, or requiring skills beyond the dexterity of the human hand. Examples are : maintammg alignment of fiber-optical connections, ultrafme control in reading/writing heads of optical or magnetic storage disks, specific filtering for special objects in large samples, in order to remove the damaged objects from the accurate objects. A microrobot could grab an object, hold it in front of a microscope objective connected to a computer that can recognize the form or features on the object surface, turn it around to give the computer the possibility to look at the object from all directions, and let it decide whether this object should be put in the basket for discarded objects or selected objects. In another application, this microvibromotor is envisioned as being observed under a microscope by an operator who holds joy sticks to control their movements. The slider would be to walk in the direction indicated by the operator and microgrippers that can perform a number of functions .
REFERENCES Feldman M. and J.Henaff (1986) Processing signal by surface acoustic waves (text in French) Mason. Helin P., V.Sadaune and C.Druon (1997a) Angular and linear microvibromotor, Proceedings IEEE Solid State Sensors and Actuators, 16-19 June, Chicago, USA, pp 181-182. Helin P., M.Calin, V.Sadaune, N.Chaillet, C.Druon and A.Bourjault (1997b) Microconveying station for assembly of microcomponents, Proceedings IEEElRJS Intelligent Robots and Systems, 8-12 September, Grenoble, France, pp 1306-1311. Kurosawa M., M.Takahashi and T.Higuchi (1996) Ultrasonic linear motor using surface acoustic waves, IEEE Ultrasonic Ferroelectrics Frequency Control, Vo1.43, N°.5, pp 901-906. Moroney R., R.White and R.Howe (1990) Fluid motion produced by ultrasonic Lamb waves, Proceedings IEEE Ultrasonic Symposium, pp 355-358.
5. CONCLUSION
Takeuchi M., H.Abe and K.Yamanouchi (1994) Ultrasonic micromanipulation of small particles in liquid using VHF-range leaky wave transducers, Proceedings IEEE Ultrasonic Symposium, pp 607-610.
We have demonstrated an angular and linear microvibromotor using surface acoustic waves. These waves are generated from interdigital transducer on a substrate of LiNb03. The linear and rotational movements are obtained according to the position of the slider with regard to acoustic beam. This device is capable of nanometer resolution, for a travel area of over 40 mm square and a rotation until 360 0 with a resolution better than 0.10. This microvibromotor can be insert in a number of possible applications, as discussed.
Wu
252
1. (1991) Acoustical tweezers, Journal Acoustical Society American, Vo1.89, N°.5, p 2140.
MICROVIBROMOTOR FOR PRECISION MICROROBOT Philippe Helin, Veronique Sadaune, Christian Druon
Institut d'Electronique et de Microelectronique du Nord Departement Opto-Acousto-Electronique Avenue Poincare, BP 69 59652 Villeneuve d'Asq Cedex, France E-Mail : [email protected]
Abstract : This paper reports an ultrasonic driven microvibromotor. An angular and linear microvibromotor is obtained from a motorization by surface acoustic waves generated from interdigital transducers on a substrate LiNb0 3 • The linear and rotational movements are obtained according to the position of the slider with regard to acoustic beam. The displacement of the slider is controlled from the burst duration applied across the interdigital transducer. This device is capable of nanometer resolution, for a travel area of over 40 mm square and rotation until 360 0 with a resolution better than 0.10. A number of possible applications are discussed. Copyright © 1998 IFA C Keywords : Motor, Actuator, Positioning systems, Ultrasonic transducers, Friction.
1. INTRODUCTION
waves to move a slider with frictional drive. In this paper, this concept of motorization is enlarged to the fabrication of a new angular and linear microvibromotor which well corresponds needs of precision engineering industry.
Considering the reduction of size in the production of semiconductors or microengineering products, the sector of micro-manipulation is expected to be a key task. For example, the micromanipulation by radiation pressure is crucial in biotechnology. Wu (1991) demonstrated the trapping and moving of the latex particle (270 /lm diameter) using two collimated ultrasound beams radiating from focusing PZT transducers. Moroney et al. (1990) also observed the movement of 2.5 /lm diameter polystyrene spheres in the flow of water using 4 MHz flexural waves traveling in 4 /lm thick silicon nitride membrane. Takeuchi et al. (1994) performed a two dimensional manipulation of 50 /lm diameter glass spheres using two pairs of leaky wave transducers at frequency of 48.5 MHz. In the other hand, the micromanipulation by friction drive is important in microsystem industry. Kurosawa et al. (1996) demonstrated the possibility to use Rayleigh
2. DESIGN
This microvibromotor is based on the conversion, through frictional contact, of a retrograde elliptical motion of surface particles due to the traveling wave propagation into slider displacements (Helin et aI. , 1997a). Interdigital transducer (IDT) can be used for Rayleigh wave excitation. Eight IDT's have been fabricated, patterned through photolithography step on a 1 mm thick substrate, on the X cut of 3 inches LiNb0 3 substrate, arranged as shown in Figure 1. The IDT electrodes consist of 1000A of Ti followed by 5000A of Au. The IDT's are facing each other to
249
obtain the two-way motion. All the fabricated transducers have the following characteristics : 100 ~m strip width and 15 mm aperture size. The operation area is about 40 mm square. Each IDT has 10 strip electrodes pairs. From geometrical considerations, the x- and y- direction resonance frequencies are 8.75 MHz and 9. 10 MHz, respectively. They are not the same due to anisotropy of the substrate material. To prevent a standing wave excitation, acoustical absorbent is pasted between the IDT's and the wafer edge. Concerning the surface strain amplitude, it is worthwhile mentioning that it has to be large enough for having a sufficient coupling between acoustic wave and slider. To this aim and by impedance matching consideration, the geometrical capacitance of IDT is matched with an inductance to increase the strain amplitude. A slider with three contact points is used in order to obtain a high contact pressure with a weak contact surface to avoid the wave attenuation. This slider consists of a washer (diameter 5 mm) stuck over three tungsten carbide balls (diameter 1 mm) in order to obtain a large friction coefficient.
16- IDT 115- IDTI Fig. 2. Operation principle of the angular and linear microvibromotor.
3. VIBROMOTOR PERFORMANCE The theory of the piezoelectric Rayleigh generation is well know and the components of the ideal IDT equivalent circuit can be calculated by using formulas of reference (Feldrnann et aI. , 1986). The ideal IDT radiation resistance R(f) and radiation reactance X(f) are thus given by :
Z(f) = R(f) + with
R(f)
j( X(f) - C~)
= Ra( Si:x
r
X(f) = R sin2x - 2x
10':01
a
Fig. 1. The angular and linear microvibromotor.
and
X
2X 2
N-l f-J; = --1t 0
2 The operation principle of this actuator is represented in Figure 2. The linear and rotational movements are obtained according to the position of the slider with regard to acoustic beam. In first case (case a) the three balls of the slider are in the acoustic beam. Then, a linear motion of the slider is obtained along x- or y-directions when, for example, the 8- or 2-IDT is excited, respectively. In second case (case b) only one ball is in the acoustic beam of the 7-IDT and so it is alone affected by the tangential force of acoustic wave which produces a torque hence a rotational motion of the slider. The discrete nature of the slider motion (one pulse per acoustic period) allows us to control the position of the slider according to the burst duration applied across the IDT with a great accuracy.
R = 1.4e a Em W
(I)
(2) (3)
(4)
fo (5)
where N is the fmger number, E is the equivalent dielectric constant , CT is the electrode capacitance, W is the aperture , k2 is the electromechanical coupling coefficient, fo is the excitation frequency, Wo is the angular frequency and f is the frequency . Figures 3 and 4 show the calculated and measured input impedance Z(f) of an IDT oriented for wave propagation along x- and y- direction, respectively. Note that the transducer impedance curves show close agreement in shape. In figure 3, the transducer resistance curve is quasi-symmetric in shape about the IDT center frequency, this is a typical behavior of an IDT for Rayleigh wave generation. In figure 4, the
250
curve shapes are modified due to the leaky wave propagation at 11.5 MHz. The radiation resistance in the y-direction is matched to signal generator impedance, but in the x-direction this radiation resistance is more large on account of geometrical considerations. The differences in the calculated and measured impedances can be attributed to several factors, such as : uncertainty in material constants, crystal cut, alignment of translation stages and of the IDT with the chosen propagation direction.
displacement values for both directions with a driving time from 0.05 to 50 ms in a logaritlnnic scale.
I_
1.E+Ol
t
1.E+oo
! C
1.E-Ol
i
1.E-02
u
i.!! o
~
"x l
0
o ~
1.E-03
El
1.E-04
0
0
-
~ D'"
~
m
c.
0
1.E·Q5
0.1
0.01
1
10
100
Driving time (ms)
Fig. 6. Linear displacement of the slider for both directions. so
se
115
13
BO
.,
i5
103
110
"
The smallest displacement is about 40 nm to 0.05 ms. This time corresponds to about 450 acoustic wave periods. Then, it will be possible to measure a lower displacement down to a few nanometers with a shorter driving time. Concerning the rotation, the angle values are measured under microscope with the help of a vernier. Figure 7 shows the angle values versus driving time. With the previous measurements of displacement (40 nm), it should be possible to obtain lower rotation down 10-3 degree. A rotation of 360 0 has been obtained by applying successive bursts.
(I
Frequency (~)
Fig. 3. Calculated and measured impedance of an IDT oriented along x-direction. JOO
.. _-- - . .
575
-1 '-"
IS
725
e 7S 115 Frequency (~)
102S
11 75
6
5
_4
Fig. 4. Calculated and measured impedance of an IDT oriented along y-direction.
!!...
-
j::
The vibration amplitude of the nonnal direction to the surface is measured using an interferometric probe. The measurements of the vibration amplitude distribution versus distance from the emitted IDT for both directions are shown in Figure 5. The amplitude is on the order of nanometers. The peak-to-peak driving voltage applied across the IDT is 90 Vpp.
3 2
o o
•
10
20
30
40
Driving time (ms)
Fig. 7. Rotational movement of the slider.
30
E
25
...
20
S-
4. CONCEPT OF MICROROBOT AND POSSIBLE APPLICA nONS
O>
'""a.'E"
.
15
0
10
J:l
5
c
~ :>
We designed an integrated microvibromotor unit, that as part of a microconveying station will be able to perfonn certain tasks: locomotion, transportation of objects, operation on objects, and so on (Helin et aI., 1997b). The basic actuator unit could be transfonned into a variety of adaptations, according to the special requirements for different environments or application. Some expected advantages of this method over an electrostatic motor are : inherent stability, independence of the presence of a conducting medium around the motor unit, easy to start because
I I
0 0
10
20
30
Distance (mm)
40
so i I
Fig. 5. Vibration amplitude distribution for both directions. The displacement values are obtained using an optical displacement measuring instrument. Its resolution limit is about 40 nm. Figure 6 shows the
251
no synchronization is required, compatibility with linear and rotational motions; high output force . One can imagine that hordes of small and cheap microrobots could be used in chores too tedious or dangerous for human beings, or requiring skills beyond the dexterity of the human hand. Examples are : maintammg alignment of fiber-optical connections, ultrafme control in reading/writing heads of optical or magnetic storage disks, specific filtering for special objects in large samples, in order to remove the damaged objects from the accurate objects. A microrobot could grab an object, hold it in front of a microscope objective connected to a computer that can recognize the form or features on the object surface, turn it around to give the computer the possibility to look at the object from all directions, and let it decide whether this object should be put in the basket for discarded objects or selected objects. In another application, this microvibromotor is envisioned as being observed under a microscope by an operator who holds joy sticks to control their movements. The slider would be to walk in the direction indicated by the operator and microgrippers that can perform a number of functions .
REFERENCES Feldman M. and J.Henaff (1986) Processing signal by surface acoustic waves (text in French) Mason. Helin P., V.Sadaune and C.Druon (1997a) Angular and linear microvibromotor, Proceedings IEEE Solid State Sensors and Actuators, 16-19 June, Chicago, USA, pp 181-182. Helin P., M.Calin, V.Sadaune, N.Chaillet, C.Druon and A.Bourjault (1997b) Microconveying station for assembly of microcomponents, Proceedings IEEElRJS Intelligent Robots and Systems, 8-12 September, Grenoble, France, pp 1306-1311. Kurosawa M., M.Takahashi and T.Higuchi (1996) Ultrasonic linear motor using surface acoustic waves, IEEE Ultrasonic Ferroelectrics Frequency Control, Vo1.43, N°.5, pp 901-906. Moroney R., R.White and R.Howe (1990) Fluid motion produced by ultrasonic Lamb waves, Proceedings IEEE Ultrasonic Symposium, pp 355-358.
5. CONCLUSION
Takeuchi M., H.Abe and K.Yamanouchi (1994) Ultrasonic micromanipulation of small particles in liquid using VHF-range leaky wave transducers, Proceedings IEEE Ultrasonic Symposium, pp 607-610.
We have demonstrated an angular and linear microvibromotor using surface acoustic waves. These waves are generated from interdigital transducer on a substrate of LiNb03. The linear and rotational movements are obtained according to the position of the slider with regard to acoustic beam. This device is capable of nanometer resolution, for a travel area of over 40 mm square and a rotation until 360 0 with a resolution better than 0.10. This microvibromotor can be insert in a number of possible applications, as discussed.
Wu
252
1. (1991) Acoustical tweezers, Journal Acoustical Society American, Vo1.89, N°.5, p 2140.