CHARACTERIZATION AND RESULTS
4.2. Characterization of an Electro-Thermally Microactuator for Multi-Level Conveying
It is observed that the ends of the conveying finger and the height adjuster curled up about 18 µm and 5 µm from the substrate, respectively, due to the residual stresses in bimorph beams. In testing, various dc voltages are applied to the contact pads to generate different actuation modes.
Figure 4-5 shows comparison of the simulation and testing results of the finger-tip displacements under various input voltages. In testing, the downward displacement up to 18 µm are achieved at input voltage of 2 V. The maximum deviation between simulation and testing results is within 10%. In
addition, the simulation and testing results of the height adjuster are shown in Figure 4-6. In testing, 5 µm downward displacement is achieved at 1 V before touching the substrate, and the deviation between the simulation and measurement results is within 20%. The approximate maximum load per microactuator is about 0.196 mg., which is estimated by calculating the elastic-mechanical stiffness of the adjuster/fingers structures. According to experimental results, the lateral displacement of the conveying finger at output vertical displacement of 13-15 µm is about 0.2-0.3 µm. Hence, the estimated maximum velocity for conveyance is about 1.0-1.5 µm/sec at maximum operating frequency of 5 Hz.
Further, thermal coupling effect of the height adjuster and the conveying fingers are examined by multi-dimensional motion testing. First, the height adjuster is actuated at 1 V, and then different voltages are applied to the conveying fingers to observe whether the conveying finger is affected by the height adjuster. The height adjuster deflects 5 µm in downward direction at one volt while the conveyor fingers are not actuated. Figure 4-7 shows the measured displacements of the height adjuster at 1 V while applying different voltages to the conveying fingers simultaneously. As shown in Figure 4-7, the deviations on positions of height-adjuster end are negligible and that are all within measurement resolution of 1 µm. It is also found that the tips of conveying fingers deflect 18 µm at 2 volts while the height adjuster still delivers 5 µm downward displacement at 1 volt. Testing results indicate that the displacements of height adjuster are not affected by operating conveying
fingers. Similar testing processes are also performed to the conveying fingers.
Figure 4-8 shows the load-position curves of the conveying finger tip with simultaneous actuation of height adjuster. Different curves in Figure 4-8 represent different dc driving voltages of the height adjuster. From this testing, it is observed that the downward deflection of the conveying finger tip relative to the end of the height adjuster is affected by the actuation of height adjuster slightly. For instance, the downward displacements of conveying finger actuated at 1.5 volts with height adjuster actuated at 0.75 volts and 0 volt are 14.5 µm and 10.5 µm respectively. However, the height adjuster produces about 3 µm downward displacement at 0.75 volts. Hence, the absolute downward displacement of conveying finger affected by thermal crosstalk from height adjuster is actually around 1 µm. In testing, the increased downward displacements of conveying finger are all below 10% of the displacements without actuating the height adjuster.
Figure 4-5. The simulated and calibrated downward displacements of the conveying finger under different input dc voltages.
Figure 4-6. The simulated and calibrated downward displacement of the height adjuster under different input dc voltages.
Figure 4-7. The measured displacements at the end of height adjuster in coupling test, where the height adjuster is actuated firstly, and then different input voltages are applied to the conveying fingers.
Figure 4-8. The measured displacements of finger tip in coupling test, where the finger is actuated first, and then different input voltages are applied on the height adjuster.
Chapter 5 CONCLUSIONS
5.1. Summary
Two kinds of electro-thermally driven microactuators with multi-dimensional motions are designed, fabricated, and tested. Some features of electro-thermally driven microactuator with two dimensional motions are summarized below: (Ⅰ ) This microactuator is shown to be able to deflect in two dimensions and nearly uncoupled. (Ⅱ ) This microactuator is self assemblied and does not need any locking structures or external manipulation. ( Ⅲ ) Modified releasing processes is helpful in fabricating this microactuator.
As about the microactuator for multi-level conveyance, beside the conventional horizontal conveying, a height adjuster is included to enhance the conveying range from single-plane to multi-level conveying. It is also shown that the proposed device can be operated at input voltage below 3 volts. The simulation results agree with the test results. From thermal coupling tests, this device is shown to have little cross talking while heating the height adjuster and two conveying fingers. It means that the height adjuster and two fingers can be operated almost independently. The material selections and dimension designs of this microactuator can be further investigated to improve the performance.
5.2. Discussions
The multi-dimensional motions microactuators proposed here are all basically consisted of two actuation parts. The deflecting directions of each actuation part of the same microactuator are different so as to exhibit spatial motions. However, actuation principles are all based on electro-thermal joule heating, therefore, thermal-coupling problems may be encountered and should be minimized as possible in design. In current research, the use of low thermal conductivity materials such as polyimide or polymers and configurations with reduced thermal-flow cross section areas results in larger thermal resistance between actuation parts. From the experimental results, the proposed microactuator of two-dimension motions and microactuator for multi-level conveying showed little thermal-coupling or displacement-coupling problems.
REFERENCES
1. S. Fatikow and U. Rembold, “Microsystem Technology and Microrobotics”, Springer, ch. 3, 1997.
2. W. S. N. Trimmer, “Microrobots and Micromechanical System“, Sensors and Actuators A, vol. 19, pp.267-287, 1989.
3. Gad el Hak Mohamed, “The MEMS Handbook”, CRC press, ch. 2, 2001.
4. C. C. Lee and W. Hsu, “Method on Surface Roughness Modification to Alleviate Stiction of Microstructures”, J. Vacuum Science and Technologies B, vol. 21, no.
4, pp.1505-1510, 2003.
5. K. E. Petersen, “Silicon as a Mechanical Material”, Proc. IEEE, vol.70, no.5, p.420-457, 1982.
6. K. D. Wise, T. N. Jackson, N. A. Masnari, and M. G. Robinson, “Fabrication of Hemispherical Structures Using Semiconductor Technology for Use in
Thermonuclear Fusion Research”, American Vacuum Society, pp. 936-939, 1979.
7. C. H. Lin, Y. C. Lo, and W. Hsu, “Micro-Fabrication of Hemispherical Poly-Silicon Shells Standing on Hemispherical Cavities”, SPIE’s New Millennium‘03, Gran Canaria (Canary Islands), Spain, 2003.
8. L. S. Fan, Y. C. Tai, and R. S. Muller, “IC-processes Electrostatic Micromotors,”
Sensors and Actuators A, vol.20, pp. 41-48, 1989.
9. M. Mehregany, P. Nagarkar, S. D. Senturia, and J. H. Lang, “Operation of Microfabricated Harmonic and Ordinary Side-Drive Motors,” Proc. 3rd. IEEE MEMS Workshop, Napa Valley, CA, pp. 1-8, 1990.
10. W. C. Tang, T. U. Chong, H. Nguyen, and R. T. Howe, “Laterally Driven Polysilicon Resonant Microstructures,” Sensors and Actuators A, vol.20, pp.
25-32, 1989.
11. T. Akiyama, and K. Shono, “Controlled Stepwise Motion in Polysilicon
Microstructures,” J. Microelectromechanical Systems, vol.2, no.3, pp. 106-110,
1993.
12. A. J. L. Yeh, H. Jiang, and N. C. Tien, “Integrated Polysilicon and DRIE Bulk Silicon Micromachining for an Electrostatic Torsional Actuator,” J.
Microelectromechanical Systems, vol.8, no.4, pp. 456-465, 1999.
13. A. M. Flynn, L. S. Tavrow, S. F. Bart, R. A. Brooks, D. J. Ehrlich, K. R.
Udayakumar, and L. E. Cross, “Piezoelectric Micromotors for Microrobots,” J.
Microelectromechanical Systems, vol. 1, pp. 44-51, 1992.
14. I. J. B, Vishniac, “The Case for Magnetically Driven Microactuators,” Sensors and Actuators A, vol.33, pp. 207-220, 1992.
15. M. Ataka, A. Omodaka, N. Takeshima, and H. Fujita, “Fabrication and Operation of Polyimide Bimorph Actuators for a Ciliary Motion System”, J.
Microelectromechanical Systems, vol.2, no.4, pp. 146-150, Dec. 1993.
16. S. P. Timoshenko, “Analysis of Bi-Metal Thermostats”, J. Opt. Soc. Am., vol. 11, pp. 233-255, 1925.
17. W. Riethmuller, and W. Benecke, “Thermally Excited Silicon Microactuators”
Electron Devices, IEEE Transactions on, vol. 35, pp. 758-763, June 1988.
18. H. Guckel, J. Klein, T. Christenson, K. Skrobis, M. Landon, and E. G. Lovell,
“Thermo-magnetic metal flexure actuators”, Tech. Digest, IEEE Solid State Sensor and Actuator Workshop, pp. 73-75, 1992.
19. C.H. Pan, and W. Hsu, “An electro-thermally driven polysilicon microactuator”, J. Micromech. Microeng., vol. 7, pp. 7-13, 1997.
20. M. Kohl and K. D. Skrobanek, “ Linear microactuators based on shape memory effect”, Sensors and Actuators A, vol. 70, pp. 104-11, 1998.
21. S. Ashley, “Getting a microgrip in the operating room”, Mechanical Engineering, pp. 91-93, 1996.
22. W. C. Tang, T. C .H Nguyen, and R. T. Howe, “Laterally Driven Polysilicon Resonant Microstructures”. Proc. of IEEE Micro Electro Mechanical Systems:
53-59, 1989.
23. A. A. Yasseen, J. Mitchell, T. Streit, D. A. Smith, and M. A. Merhergany,
“Rotary Electrostatic Micromotor 1x8 Op tical Switch”, Proc. of Micro Electro Mechanical Systems, MEMS 98, The 11th Annual International Workshop on. pp 116-120, 1998.
24. J. R. Reid, V. M. Bright, and J. T. Butler, “Automated Assembly of Flip-up Micromirrors”, Sensors and Actuators. A66: 292-298, 1998.
25. T. Ebefors, E. Kälvesten, and G. Stemme, “Dynamic Actuation of Polyimide V-Groove Joints by Electrical Heating”, Sensors and Actuators. A67: 199-204, 1998.
26. G. Lin, C. J. Kim, S. Konishi, and H. Fujita, “Design, Fabrication and Testing of a C-shape Actuator”, Tech. Digest, 8Pt hP International Conference. Solid-State
Sensors and Actuators(Transducers ‘95/ Eurosensors Ⅸ ) Stockholm, Sweden. pp.
416 –419, 1995.
27. R. S. Fearing, “Powering 3-Dimensional Microrobots: Power Density
Liminations”, IEEE Int. Conf. on Robotics and Automation, Tutorial on Micro Mectronics and Micro Robotics, 1998.
28. S. Konishi and H. Fujita, “A Conveyance System Using Air Flow Based on the Concept of Distributed Micro Motion Systems”, Journal of
Microelectromechanical Systems, Volume: 3, No, 2, pp. 54-58, 1994.
29. K. S. J. Pister, R. S. Fearing, and R.T. Howe, “TA Planar Air Levitated Electrostatic Actuator SystemT”,T Proc. IEEE 5Pt hP Workshop on Micro Electro Mechanical Systems, Napa Valley, CA, pp. 67-71, T1990T.
30. Y. Mita, S. Konishi, and H. Fujita “Two Dimensional Micro Conveyance Systems with Through Holes for Electrical and Fluidic Interconnection”, Int. Conf. Solid State Sensors and Actuators (Transducers '97), Chicago, Volume: 1, pp. 16-19, 1997.
31. C. Liu, T. Tsai, Y. C.Tai, W. Liu, P. Will, and C.M. Ho, “A Micromachined Permalloy Magnetic Actuator Array for Mmicro Robotics Assembly Systems”,
Int. Conf. Solid-State Sensors and Actuators (Transducers '95), Volume: 1, pp.
328-331, 1995.
32. H. Nakazawa, Y. Watanabe, O. Morita, M. Edo, and E. Yonezawa, “The
Two-Dimensional Micro Conveyer: Principles and Fabrication Process of the Actuator”, Int. Conf. Solid State Sensors and Actuators (Transducers '97), Chicago, Volume: 1, pp. 33 –36, 1997.
33. T. Furuhata, T. Hirano, and H. Fujita “Array-Driven Ultrasonic Microactuators”, Int. Conf. Solid-State Sensors and Actuators (Transducers '91), pp.1056 –1059, 1991.
34. M. Edo, Y. Watanabe, O. Morita, H. Nakazawa, and E. Yonezawa,
“Two-Dimensional Micro Conveyer with Integrated Electrostatic Actuators”, 12Pt hP IEEE International Conference on Micro Electro Mechanical Systems (MEMS '99), pp. 43-48, 1999.
35. D. Koester, R. Majedevan, A. Shishkoff, K. Marcus, “Multi-User MEMS Processes (MUMPS) Introduction and Design Rules, rev.4”, MCNC MEMS Technology Applications Center, Research Triangle Park, NC 27709, USA, July 1996.