- Email: [email protected]
A compact and quick-response dynamic focusing lens
A
ELSEVIER
Sensors and Actuators
PHYSICAL
A 70 ( 1998) 92-97
A compact and quick-response dynamic focusing lens Takashi Kaneko *, Takuhiro Ohmi ‘, Nobuyuki Ohya 2, Nobuaki Kawahara 3 Research
Laboratories,
DENS0
CORPORATION,
500-l
Minamiyama,
Komenoki-cho,
Nisshin-shi,
Aichi 470-0111,
Japan
Abstract A dynamic focusing lens with a completely new mechanism that can be miniaturized and allows for a quick-response has been developed. This lens is structured to directly transform the lens shape as a crystalline lens of the human eye. The lens is comprised of two thin glass diaphragms as a refracting surface, with a transparent working fluid sealed between them, and a new type of piezoelectricbimorph actuator. The displacement of theactuator is enlargedby thebimorphstructure.Thegenerated force is determined by thelayer numberof thebimorph cells.Whenthe actuator is drivento pushor pull the glassdiaphragm at theactuatorside,theotherglassdiaphragm istransformedinto a lens shape(convexlensor concavelens)havingvariouscurvatures.Thefocal lengthof thelensiscontrolledby theappliedvoltageto theactuator. The dynamicfocusinglensshowsquick response up to 150Hz. When the lensis operatedover 60 Hz, humanvisualperceptioncannot recognizethechangeof thefocallength,andwecanobservemanyi,mages havingdifferentfocallengthssimultaneously. 0 1998Elsevier ScienceS.A. All rightsreserved. Keywords:
Dynamic focusing lens; PZT bimorph actuator
1. Introduction An optical device such as a camera or a microscope requiresa focalizing mechanismto provide a clear image.As a conventional optical element, i.e., lens or mirror, contains no focalizing function in itself, this shouldbe doneby moving the optical element or the object for observation. The conventional focalizing mechanismof these optical devices is complicated and consistsof many gears,motors, andsliders, making it difficult to realize high speedoperation. The technology of increasing the operation speedof the focalizing mechanismand miniaturizing the lenssize hasbeenstrongly demandedin the courseof developing various types of optical devices. We have developed an innovative dynamic focusing lens that can momentarily change the lens shape.This lens is structured to directly transform the lens shapesimilar to a crystalline lensof the humaneye. Therefore, the massmovement can be minimized compared with the conventional * Corresponding author. Tel.: +81-5617-5-l 149; fax: + 81-5617-5-1193; e-mail: [email protected],co.jp 1 Tel.: +81-5617-5-1043; fax: + 81-5617-5-1194; e-mail: toomi@ fp.denao.co.jp ’ Tel.: i 81-5617-5-1876; fax: +81-5617-5-1193; e-mail: nooya@ rlab.denso.co.jp 3 Tel.: +81-5617-5-1822, fax: +81-5617-5-1193; e-mail: nkawaha@ rlab.denso.co.jp 0924-4247/98/$ - see front PIISO924-4247(98)00119-8
matter
0
1998 Elsevier
Science
method of moving the lensposition. This dynamic focusing lens is expected to be applied not only to the high speed focalizing for a cameraor a microscopebut also to various techniquesto developthe focalizing mechanismfor an optical pick-up of the ultrahigh density recording media andthe like. This paper discussesthe principle and construction of the newly developed dynamic focusing lens and the multilayered piezoelectric bimorph actuator that has also been developed to realize the high speedoperation up to 1.50Hz. The dynamic focusing lenswasattachedto an objective of amicroscope,andthe focal planeat the object sidewasmoved at a cycle of 60 Hz or more. This experiment indicates that the depth of field was apparently expandeddue to the afterimage of the human eye causedby the aforementionedhigh speedoperation, providing an imageof the whole object that has been focalized. The evaluation of the resultant optical characteristicsis alsoreportedherein.
2. Structure
2.1. Sfrucfure of dynamicforming lens Fig. 1 showsa schematiccross-sectionalview of the present dynamic focusing lens. Fig. 2 comprisesphotos showing an appearanceof the lens. The dynamic focusing lens is comprisedof two glassdiaphragmshaving a thicknessof 50
%A. All rights reserved.
T. Kaneko et al. /Sensors
and Actuators
PZT Bimorph Actuator Stainless Steel Plate
/ I Transparent /’’ lTIF$mm Working Fluid ‘1 h1 GlassDiaphragm Glass Diaphragm (thickness50w m) ( 6 14 mm,thickness50pm) Fig. 1. Schematic view of dynamic focusing lens.
pm (each having different diameters, 10 and 14 mm, respectively ) , silicone oil exhibiting refractive index of 1SO sealed between them as the transparent working fluid, and multilayered piezoelectric bimorph actuator mounted thereon. The optical characteristics of the lens can be changed to a greater extent by adjusting the pressure of the transparent working fluid through push/pull operation of the actuator to the glass diaphragms. As Fig. 3a shows, when the actuator presses the diaphragm at the actuator side to compress the transparent working fluid, the diaphragm at the incident side transforms into a convex shape that will serve as the convex lens. As Fig. 3b shows, when the diaphragm at the actuator side is pulled to decompress the working fluid, the diaphragm at the incident side transforms into a concave shape that will serve as the concave lens. 2.2. Multi-layeredpiezoelectric bimorph actuator
To transform the lens, a large displacement and quickresponse actuator is needed. A piezoelectric actuator is well known as a quick-response actuator. However, the displace-
Glass Diaphragm
A 70 (1998)
92-97
93
ment is quite small, approximately l/1000 of its length. To enlarge the displacement, unimorph and bimorph structures have been proposed. We have newly developed a multi-layered piezoelectric bimorph actuator for the dynamic focusing lens. This actuator is in the shape of a ring, and a ray can pass through it. The generating force is determined by the layer number of the bimorph cells [ I]. Fig. 4 shows the structure of the actuator. The bimorph cell consists of a stainless steel plate and two piezoelectric plates. The piezoelectric plates have a thickness of 50 ym, and the stainless steel plates have a thickness of 40 km. The piezoelectric plates are polarized in the same direction as shown in Fig. 4. A feature of the actuator is that each bimorph cell is mechanically and electrically connected to the output pipe and outside pillars to reduce the length of the actuator. The electrodes of the piezoelectric plates are connected to the power source through the output pipe, and the stainless steel plates are connected to the ground through the outside pillars as shown in Fig. 4. The laser welding method was used to assemble the actuator. 2.3. Principle of the new type of optical microscope
A new type of optical microscope has been developed as one of the applications using the quick response of the dynamic focusing lens for expanding depth of field. For three-dimensional observation by optical microscope, we can observe only one focalized image because the depth of field of microscope is confined. In order to observe the whole image of the object, or to expand the depth of field, some methods using special optics or computer image processing have been studied [ 2,3]. As Fig. 5 shows, the dynamic focusing lens is provided as the mechanism to shift a focal plane of the objective. The focal plane is rapidly and continuously shifted along the optical axis in order to focalize each part of the object. When the focal plane is moved at a cycle of 60 Hz or more, all images are overlapped due to the afterimage effect seen by the human eye, thus obtaining real-time image of the whole object that
PZT Bimorph Actuator
Fig. 2. Photos of dynamic focusing lens.
94
T. Kaneko
et al. /Sensors
and Actuators
PZT Bimorph Actuator
A 70 (1998)
92-97
Dynamic Focusing Lens (inside) Close Up Lens \
CCD Camera
Pull
-//A
y
fi/ Glass Diaphragm
-
-
\ Transparent Working Fluid
(a) Convex Lens (b) Concave Lens Fig. 3. Principle of dynamic focusing. Elastic Plate (Stainless Steel) Direction of :
Metal Spacer !
Fig. 6.
Photo of microscope.
set to 64.5 mm wasusedas the objective. The diaphragm at the incident side was set at a position about 14 mm in front of the close-up lens.The lateral magnification of the microscopewas approximately 50 on a 15 in. monitor. The range of movement of the focal plane was calculated through geometrical opticswith respectto the characteristics of the dynamic focusing lens. According to the calculated result, movement in the rangefrom - 4 to + 4 mm wasfound to be possible.
3. Experimental results 3.1. Static characteristics of actriator Fig. 4. Structure of multi-layered piezoelectric bimorph actuator.
Fig. 5. Structure of microscope witb dynamic focusing lens.
has been focalized. As a result, the depth of field of the microscopecan be apparently expanded. Even when the object is observedby a CCD camera,the imagewith anexpandeddepth of field canbe takenby moving the focal plane at 1 cycle or more during l-frame scanning of the CCD camera.
The static characteristicsof the piezoelectric bimorph actuator were measured.The measurementwas done asfollows: (1) the applied voltage to the actuator was changed from - 30 to + 30 V; (2) the generatingforce and the displacement were measuredby the load cell and the laser displacement meter. The piezoelectric bimorph actuatorgeneratesthe displacement for the glassdiaphragmat the actuator sidein the range from - 15 to + 15 p,rn with the force ranging from - 0.67 to + 0.67 N at the applied voltage from - 30 to + 30 V as shownin Fig. 7. The displacementof the diaphragmat the incident sidewas expanded approximately from - 30 to + 30 p,rn by increasing each arearatio of the respective glassdiaphragms. Required Load to transform Glass Diaphragm
2
2.4. Srructure of microscope Fig. 6 showsthe appearanceof the thus preparedmicroscope. The dynamic focusing lens is attached to the top of the close-uplensof the CCD camera.A close-uplenshaving focal length cf, set to 25 mm and object spacefocal length
-2 20 0 10 Displacement (p m) Fig. 7. Generated force-displacement relations of actuator. -20
-10
T. Kaneko
et al. /Sensors
and Actuators
A 70 (1998)
92-97
3.2. Frequency and indicial response of dynamic focusing lens
The frequency response and the indicial response of the dynamic focusing lens were measured for confirming its quick response. The experiments for measuring the frequency response were done as follows: (1) the dynamic focusing lens was oscillated under different frequencies; (2) vibration of the glass diaphragm at the incident side was measured by a laser displacement meter. The experiments for measuring the indicial response were done as follows: ( 1) a step voltage in the range from 0 to + 20 V was applied to the actuator; (2) displacement of &heglass diaphragm at the incident side was measured by a laser displacement meter. The dynamic focusing lens generates a flat response until 150 Hz and resonant points at around 350 and 1400 Hz as shown in Fig. 8. The step voltage generates overshoot and vibration of the glass diaphragm at a cycle of 13 15 Hz near the resonant point as shown in Fig. 9. The settling time of the vibration is approximately 18 ms. These results indicate that the lens part acts as a mass to the actuator; the lens part consists of two glass diaphragms and the transparent working fluid. 3.3. Optical characteristics
100 Frequency (Hz)
Frequency (Hz) Fig. 8. Frequency response of dynamic focusing lens.
of microscope
The optical characteristics of the microscope were evaluated by measuring the modulation transfer function (MTF) of the lens system including the dynamic focusing lens and the close-up lens. The resolution of the lens system was evaluated with a spatial frequency where the contrast became 0.5. The measurement was done as follows: (1) the actuator was driven by the sinusoidal voltage at a cycle of 60 Hz to shift the focal plane from - 4 to + 4 mm; (2) the object was shifted in the direction of the optical axis; (3) at each position of the object, the spatial frequency that can be resolved by the lens system was measured. Fig. 10 shows the result of the optical characteristics. For example, iE the spatial frequency that can be resolved by the lens system is 10 cycle/mm, the lens system can resolve a stripe pattern of approximately 100 pm pitch on the object. The black square symbols represent optical characteristics under the condition where no voltage was applied to the actuator, In this case, high resolution was obtained on the focal plane indicating a similar value to that of the close-up lens. As the object is shifted away from the focal plane, however, the resolution sharply declined. The white square symbols represent optical characteristics under the condition where a suitable voltage was applied to the actuator for focalizing each object positioned at different heights. The data show that 12 cycle/mm or more resolution can be obtained for the object positioned at various heights in the range from - 4 to + 4 mm. As the absolute value of the object height becomes larger, optical characteristics deteriorate. This is caused by an aher-
0
4
8 12 16 Time (msec) Fig. 9. Indicial response of dynamic focusing lens.
0 : Dynamic Focusing Lens statically -O- : Focal Plane was rapidly moved
-4
-2 0 2 Height of Object (mm)
4
Fig. 10. Optical characteristics of microscop&
96
T. Kaneko
et al. /Sensors
and Actuators
A 70 (1998) 92-97
show, pins on both sides were able to be observed when the dynamic focusing lens operated, while only one side on the highest position was observed when it did not operate.
4. Conclusions A miniaturized dynamic focusing lens using a newly developed multi-layered piezoelectric bimorph actuator shows a quick response up to 150 Hz. The dynamic focusing lens has been attached to the objective of the microscope for quick focalization. Furthermore, when the focal plane was shifted at a cycle of 60 Hz or more, whole images of the object were simultaneously obtaineddue to the afterimage effect. As a result, the depth of field of the microscope can be apparently expanded.
Acknowledgements A part of this work was performed under the management of the Micromachine Center as the Industrial Science and Technology Frontier Program ‘Research and Development of Micromachine Technology’ of MIT1 supported by the New Energy and Industrial r‘&nology Development Organization.
References Fig. 11. Example of observation. (a) Dynamic focusing lens was rapidly operated. (b) Dynamic focusing lens did not work.
ration which is generated accompanied with the transformed shape of the glass diaphragm having constant thickness used for the present dynamic focusing lens. Such a drawback can be solved by providing a specific thickness profile to the diaphragm so as to control the transformed shape, leading to improved resolution [ 41, When operating the dynamic focusing lens at a high speed, 4 cycle/mm or more resolution can be maintained over a wide range at the depth from - 4 to + 4 mm on the object as shown by the white round symbols. This indicates that the depth of field has been apparently expanded due to the high speed movement of the focal plane. The resolving power has declined because defocused images are overlapped on properly focused images. However, it is important to focalize the whole object for real-time observation, so the obtained characteristics will be useful for observation. For example, Fig. 11 shows an example of an observation using the microscope. The object was a DIP type of IC package with I/O pins on the left and right sides. These pins were observed from their sides. The interval of the pins was about 8 mm. As the photos
[ 11 S. Kawakita, T. Isogai, N. Ohya, N. Kawahara, Multi-layered piezoelectric bimorph actuator, Proc. of 1997 Int. Symposium on Micromechatronics and Human Science, Nagoya, Japan, Oct. 5-8, 1997, pp. 73-78. [2] T. Shiraishi, K. Miifitsui,Image processing systemfor expanding depth of focus of optical microscope-composition of expanded depth of focus image and three-dimensional expression of shape, JSPE 60 (8) (1994) 1112-1116. [3] G. Indebetown, H. Bai, Imaging with Fresnel zone pupil masksextended depth of field, Appl. Opt. 23 (23) ( 1984) 42993302. 141 T. Kaneko, Y. Yamagata, T. Idogaki, T. Hattori, T. Higuchi, S-dimensional specific thickness glass diaphragm lens for dynamic focusing, LEICETrans. Electron. E 78-C (2) (1995) 123-127.
Biographies TakashiKnneko received the BE and ME degrees in mechan-
ical engineering from Waseda University, Japan, in 1987 and 1989, respectively. He joined DENS0 CORPORATION in 1989, and has been engaged in the research and development of micromachines. He is currently researching optical micromachines and micromanipulators. Takuhim Ohmi received the BE degree in materials engi-
neering from Tokyo Denki University, Japan, in 1988. He joined DENS0 CORPORATION in 1988 and has been
T. Kaneko
et al. /Sensors
and Actuators
engaged in the research departments. His research interests include the micromachine, micromachining and flat panel display technologies, Nobuyyuki Ohya received the BS and MS degrees in nuclear
engineering from Nagoya University, Japan, in 1982 and 1984, respectively. He joined DENS0 CORPORATION in 1984, and has been engaged in the research departments. He
A 70 (1998)
92-97
91
is currently researching microactuators. His interest is micromachining technologies. Nobuaki Kuwaham received the BE, ME and PhD degrees from Kyushu University in 1981, 1983 and 1993, respectively. He joined DENS0 CORPORATION in 1983 and has been engaged in the research departments. His research interests include micromachines, micromachining, microactuators and energy supplies for microsystems.
ELSEVIER
Sensors and Actuators
PHYSICAL
A 70 ( 1998) 92-97
A compact and quick-response dynamic focusing lens Takashi Kaneko *, Takuhiro Ohmi ‘, Nobuyuki Ohya 2, Nobuaki Kawahara 3 Research
Laboratories,
DENS0
CORPORATION,
500-l
Minamiyama,
Komenoki-cho,
Nisshin-shi,
Aichi 470-0111,
Japan
Abstract A dynamic focusing lens with a completely new mechanism that can be miniaturized and allows for a quick-response has been developed. This lens is structured to directly transform the lens shape as a crystalline lens of the human eye. The lens is comprised of two thin glass diaphragms as a refracting surface, with a transparent working fluid sealed between them, and a new type of piezoelectricbimorph actuator. The displacement of theactuator is enlargedby thebimorphstructure.Thegenerated force is determined by thelayer numberof thebimorph cells.Whenthe actuator is drivento pushor pull the glassdiaphragm at theactuatorside,theotherglassdiaphragm istransformedinto a lens shape(convexlensor concavelens)havingvariouscurvatures.Thefocal lengthof thelensiscontrolledby theappliedvoltageto theactuator. The dynamicfocusinglensshowsquick response up to 150Hz. When the lensis operatedover 60 Hz, humanvisualperceptioncannot recognizethechangeof thefocallength,andwecanobservemanyi,mages havingdifferentfocallengthssimultaneously. 0 1998Elsevier ScienceS.A. All rightsreserved. Keywords:
Dynamic focusing lens; PZT bimorph actuator
1. Introduction An optical device such as a camera or a microscope requiresa focalizing mechanismto provide a clear image.As a conventional optical element, i.e., lens or mirror, contains no focalizing function in itself, this shouldbe doneby moving the optical element or the object for observation. The conventional focalizing mechanismof these optical devices is complicated and consistsof many gears,motors, andsliders, making it difficult to realize high speedoperation. The technology of increasing the operation speedof the focalizing mechanismand miniaturizing the lenssize hasbeenstrongly demandedin the courseof developing various types of optical devices. We have developed an innovative dynamic focusing lens that can momentarily change the lens shape.This lens is structured to directly transform the lens shapesimilar to a crystalline lensof the humaneye. Therefore, the massmovement can be minimized compared with the conventional * Corresponding author. Tel.: +81-5617-5-l 149; fax: + 81-5617-5-1193; e-mail: [email protected],co.jp 1 Tel.: +81-5617-5-1043; fax: + 81-5617-5-1194; e-mail: toomi@ fp.denao.co.jp ’ Tel.: i 81-5617-5-1876; fax: +81-5617-5-1193; e-mail: nooya@ rlab.denso.co.jp 3 Tel.: +81-5617-5-1822, fax: +81-5617-5-1193; e-mail: nkawaha@ rlab.denso.co.jp 0924-4247/98/$ - see front PIISO924-4247(98)00119-8
matter
0
1998 Elsevier
Science
method of moving the lensposition. This dynamic focusing lens is expected to be applied not only to the high speed focalizing for a cameraor a microscopebut also to various techniquesto developthe focalizing mechanismfor an optical pick-up of the ultrahigh density recording media andthe like. This paper discussesthe principle and construction of the newly developed dynamic focusing lens and the multilayered piezoelectric bimorph actuator that has also been developed to realize the high speedoperation up to 1.50Hz. The dynamic focusing lenswasattachedto an objective of amicroscope,andthe focal planeat the object sidewasmoved at a cycle of 60 Hz or more. This experiment indicates that the depth of field was apparently expandeddue to the afterimage of the human eye causedby the aforementionedhigh speedoperation, providing an imageof the whole object that has been focalized. The evaluation of the resultant optical characteristicsis alsoreportedherein.
2. Structure
2.1. Sfrucfure of dynamicforming lens Fig. 1 showsa schematiccross-sectionalview of the present dynamic focusing lens. Fig. 2 comprisesphotos showing an appearanceof the lens. The dynamic focusing lens is comprisedof two glassdiaphragmshaving a thicknessof 50
%A. All rights reserved.
T. Kaneko et al. /Sensors
and Actuators
PZT Bimorph Actuator Stainless Steel Plate
/ I Transparent /’’ lTIF$mm Working Fluid ‘1 h1 GlassDiaphragm Glass Diaphragm (thickness50w m) ( 6 14 mm,thickness50pm) Fig. 1. Schematic view of dynamic focusing lens.
pm (each having different diameters, 10 and 14 mm, respectively ) , silicone oil exhibiting refractive index of 1SO sealed between them as the transparent working fluid, and multilayered piezoelectric bimorph actuator mounted thereon. The optical characteristics of the lens can be changed to a greater extent by adjusting the pressure of the transparent working fluid through push/pull operation of the actuator to the glass diaphragms. As Fig. 3a shows, when the actuator presses the diaphragm at the actuator side to compress the transparent working fluid, the diaphragm at the incident side transforms into a convex shape that will serve as the convex lens. As Fig. 3b shows, when the diaphragm at the actuator side is pulled to decompress the working fluid, the diaphragm at the incident side transforms into a concave shape that will serve as the concave lens. 2.2. Multi-layeredpiezoelectric bimorph actuator
To transform the lens, a large displacement and quickresponse actuator is needed. A piezoelectric actuator is well known as a quick-response actuator. However, the displace-
Glass Diaphragm
A 70 (1998)
92-97
93
ment is quite small, approximately l/1000 of its length. To enlarge the displacement, unimorph and bimorph structures have been proposed. We have newly developed a multi-layered piezoelectric bimorph actuator for the dynamic focusing lens. This actuator is in the shape of a ring, and a ray can pass through it. The generating force is determined by the layer number of the bimorph cells [ I]. Fig. 4 shows the structure of the actuator. The bimorph cell consists of a stainless steel plate and two piezoelectric plates. The piezoelectric plates have a thickness of 50 ym, and the stainless steel plates have a thickness of 40 km. The piezoelectric plates are polarized in the same direction as shown in Fig. 4. A feature of the actuator is that each bimorph cell is mechanically and electrically connected to the output pipe and outside pillars to reduce the length of the actuator. The electrodes of the piezoelectric plates are connected to the power source through the output pipe, and the stainless steel plates are connected to the ground through the outside pillars as shown in Fig. 4. The laser welding method was used to assemble the actuator. 2.3. Principle of the new type of optical microscope
A new type of optical microscope has been developed as one of the applications using the quick response of the dynamic focusing lens for expanding depth of field. For three-dimensional observation by optical microscope, we can observe only one focalized image because the depth of field of microscope is confined. In order to observe the whole image of the object, or to expand the depth of field, some methods using special optics or computer image processing have been studied [ 2,3]. As Fig. 5 shows, the dynamic focusing lens is provided as the mechanism to shift a focal plane of the objective. The focal plane is rapidly and continuously shifted along the optical axis in order to focalize each part of the object. When the focal plane is moved at a cycle of 60 Hz or more, all images are overlapped due to the afterimage effect seen by the human eye, thus obtaining real-time image of the whole object that
PZT Bimorph Actuator
Fig. 2. Photos of dynamic focusing lens.
94
T. Kaneko
et al. /Sensors
and Actuators
PZT Bimorph Actuator
A 70 (1998)
92-97
Dynamic Focusing Lens (inside) Close Up Lens \
CCD Camera
Pull
-//A
y
fi/ Glass Diaphragm
-
-
\ Transparent Working Fluid
(a) Convex Lens (b) Concave Lens Fig. 3. Principle of dynamic focusing. Elastic Plate (Stainless Steel) Direction of :
Metal Spacer !
Fig. 6.
Photo of microscope.
set to 64.5 mm wasusedas the objective. The diaphragm at the incident side was set at a position about 14 mm in front of the close-up lens.The lateral magnification of the microscopewas approximately 50 on a 15 in. monitor. The range of movement of the focal plane was calculated through geometrical opticswith respectto the characteristics of the dynamic focusing lens. According to the calculated result, movement in the rangefrom - 4 to + 4 mm wasfound to be possible.
3. Experimental results 3.1. Static characteristics of actriator Fig. 4. Structure of multi-layered piezoelectric bimorph actuator.
Fig. 5. Structure of microscope witb dynamic focusing lens.
has been focalized. As a result, the depth of field of the microscopecan be apparently expanded. Even when the object is observedby a CCD camera,the imagewith anexpandeddepth of field canbe takenby moving the focal plane at 1 cycle or more during l-frame scanning of the CCD camera.
The static characteristicsof the piezoelectric bimorph actuator were measured.The measurementwas done asfollows: (1) the applied voltage to the actuator was changed from - 30 to + 30 V; (2) the generatingforce and the displacement were measuredby the load cell and the laser displacement meter. The piezoelectric bimorph actuatorgeneratesthe displacement for the glassdiaphragmat the actuator sidein the range from - 15 to + 15 p,rn with the force ranging from - 0.67 to + 0.67 N at the applied voltage from - 30 to + 30 V as shownin Fig. 7. The displacementof the diaphragmat the incident sidewas expanded approximately from - 30 to + 30 p,rn by increasing each arearatio of the respective glassdiaphragms. Required Load to transform Glass Diaphragm
2
2.4. Srructure of microscope Fig. 6 showsthe appearanceof the thus preparedmicroscope. The dynamic focusing lens is attached to the top of the close-uplensof the CCD camera.A close-uplenshaving focal length cf, set to 25 mm and object spacefocal length
-2 20 0 10 Displacement (p m) Fig. 7. Generated force-displacement relations of actuator. -20
-10
T. Kaneko
et al. /Sensors
and Actuators
A 70 (1998)
92-97
3.2. Frequency and indicial response of dynamic focusing lens
The frequency response and the indicial response of the dynamic focusing lens were measured for confirming its quick response. The experiments for measuring the frequency response were done as follows: (1) the dynamic focusing lens was oscillated under different frequencies; (2) vibration of the glass diaphragm at the incident side was measured by a laser displacement meter. The experiments for measuring the indicial response were done as follows: ( 1) a step voltage in the range from 0 to + 20 V was applied to the actuator; (2) displacement of &heglass diaphragm at the incident side was measured by a laser displacement meter. The dynamic focusing lens generates a flat response until 150 Hz and resonant points at around 350 and 1400 Hz as shown in Fig. 8. The step voltage generates overshoot and vibration of the glass diaphragm at a cycle of 13 15 Hz near the resonant point as shown in Fig. 9. The settling time of the vibration is approximately 18 ms. These results indicate that the lens part acts as a mass to the actuator; the lens part consists of two glass diaphragms and the transparent working fluid. 3.3. Optical characteristics
100 Frequency (Hz)
Frequency (Hz) Fig. 8. Frequency response of dynamic focusing lens.
of microscope
The optical characteristics of the microscope were evaluated by measuring the modulation transfer function (MTF) of the lens system including the dynamic focusing lens and the close-up lens. The resolution of the lens system was evaluated with a spatial frequency where the contrast became 0.5. The measurement was done as follows: (1) the actuator was driven by the sinusoidal voltage at a cycle of 60 Hz to shift the focal plane from - 4 to + 4 mm; (2) the object was shifted in the direction of the optical axis; (3) at each position of the object, the spatial frequency that can be resolved by the lens system was measured. Fig. 10 shows the result of the optical characteristics. For example, iE the spatial frequency that can be resolved by the lens system is 10 cycle/mm, the lens system can resolve a stripe pattern of approximately 100 pm pitch on the object. The black square symbols represent optical characteristics under the condition where no voltage was applied to the actuator, In this case, high resolution was obtained on the focal plane indicating a similar value to that of the close-up lens. As the object is shifted away from the focal plane, however, the resolution sharply declined. The white square symbols represent optical characteristics under the condition where a suitable voltage was applied to the actuator for focalizing each object positioned at different heights. The data show that 12 cycle/mm or more resolution can be obtained for the object positioned at various heights in the range from - 4 to + 4 mm. As the absolute value of the object height becomes larger, optical characteristics deteriorate. This is caused by an aher-
0
4
8 12 16 Time (msec) Fig. 9. Indicial response of dynamic focusing lens.
0 : Dynamic Focusing Lens statically -O- : Focal Plane was rapidly moved
-4
-2 0 2 Height of Object (mm)
4
Fig. 10. Optical characteristics of microscop&
96
T. Kaneko
et al. /Sensors
and Actuators
A 70 (1998) 92-97
show, pins on both sides were able to be observed when the dynamic focusing lens operated, while only one side on the highest position was observed when it did not operate.
4. Conclusions A miniaturized dynamic focusing lens using a newly developed multi-layered piezoelectric bimorph actuator shows a quick response up to 150 Hz. The dynamic focusing lens has been attached to the objective of the microscope for quick focalization. Furthermore, when the focal plane was shifted at a cycle of 60 Hz or more, whole images of the object were simultaneously obtaineddue to the afterimage effect. As a result, the depth of field of the microscope can be apparently expanded.
Acknowledgements A part of this work was performed under the management of the Micromachine Center as the Industrial Science and Technology Frontier Program ‘Research and Development of Micromachine Technology’ of MIT1 supported by the New Energy and Industrial r‘&nology Development Organization.
References Fig. 11. Example of observation. (a) Dynamic focusing lens was rapidly operated. (b) Dynamic focusing lens did not work.
ration which is generated accompanied with the transformed shape of the glass diaphragm having constant thickness used for the present dynamic focusing lens. Such a drawback can be solved by providing a specific thickness profile to the diaphragm so as to control the transformed shape, leading to improved resolution [ 41, When operating the dynamic focusing lens at a high speed, 4 cycle/mm or more resolution can be maintained over a wide range at the depth from - 4 to + 4 mm on the object as shown by the white round symbols. This indicates that the depth of field has been apparently expanded due to the high speed movement of the focal plane. The resolving power has declined because defocused images are overlapped on properly focused images. However, it is important to focalize the whole object for real-time observation, so the obtained characteristics will be useful for observation. For example, Fig. 11 shows an example of an observation using the microscope. The object was a DIP type of IC package with I/O pins on the left and right sides. These pins were observed from their sides. The interval of the pins was about 8 mm. As the photos
[ 11 S. Kawakita, T. Isogai, N. Ohya, N. Kawahara, Multi-layered piezoelectric bimorph actuator, Proc. of 1997 Int. Symposium on Micromechatronics and Human Science, Nagoya, Japan, Oct. 5-8, 1997, pp. 73-78. [2] T. Shiraishi, K. Miifitsui,Image processing systemfor expanding depth of focus of optical microscope-composition of expanded depth of focus image and three-dimensional expression of shape, JSPE 60 (8) (1994) 1112-1116. [3] G. Indebetown, H. Bai, Imaging with Fresnel zone pupil masksextended depth of field, Appl. Opt. 23 (23) ( 1984) 42993302. 141 T. Kaneko, Y. Yamagata, T. Idogaki, T. Hattori, T. Higuchi, S-dimensional specific thickness glass diaphragm lens for dynamic focusing, LEICETrans. Electron. E 78-C (2) (1995) 123-127.
Biographies TakashiKnneko received the BE and ME degrees in mechan-
ical engineering from Waseda University, Japan, in 1987 and 1989, respectively. He joined DENS0 CORPORATION in 1989, and has been engaged in the research and development of micromachines. He is currently researching optical micromachines and micromanipulators. Takuhim Ohmi received the BE degree in materials engi-
neering from Tokyo Denki University, Japan, in 1988. He joined DENS0 CORPORATION in 1988 and has been
T. Kaneko
et al. /Sensors
and Actuators
engaged in the research departments. His research interests include the micromachine, micromachining and flat panel display technologies, Nobuyyuki Ohya received the BS and MS degrees in nuclear
engineering from Nagoya University, Japan, in 1982 and 1984, respectively. He joined DENS0 CORPORATION in 1984, and has been engaged in the research departments. He
A 70 (1998)
92-97
91
is currently researching microactuators. His interest is micromachining technologies. Nobuaki Kuwaham received the BE, ME and PhD degrees from Kyushu University in 1981, 1983 and 1993, respectively. He joined DENS0 CORPORATION in 1983 and has been engaged in the research departments. His research interests include micromachines, micromachining, microactuators and energy supplies for microsystems.