Angular vertical comb actuators assembled on-chip using in-plane electrothermal actuators and latching mechanisms

We have designed, fabricated and tested self-aligned angular vertical comb-drive (AVC) actuators by on-chip assembly using in-plane electrothermal actuators and latching mechanisms. The on-chip assembly process is carried out by engaging latching mechanism connected to the torsion bars through the off-centered thinned down silicon beams. When the latching mechanism is fully engaged, the assembled AVC actuator forms permanent initial tilt angle by the retraction force of electrothermal actuators. The AVC actuators and latching mechanisms are fabricated on a silicon-on-insulator (SOI) wafer using three photomasks and three times of deep etch steps. The maximum optical scan angle of 30.7° is achieved at 4.56 kHz under the sinusoidal driving voltage of 0–80 V applied to the AVC actuator. After the reliability test performed by operating the actuator for 1.6 × 10⁸ cycles at its resonance, the measured optical scan angle variation and resonant frequency change were within 1.1% and 8 Hz, respectively, and the robustness of the latched mechanism was ensured.     

Air damping of high performance resonating micro-mirrors with angular vertical comb-drive actuators

Microsystem Technologies - The maximum scan angle amplitude of resonating micro-mirrors, intended for micro-projection display applications is limited by air damping. Three-dimensional transient...     

A micromachined impact microactuator driven by electrostatic force

This paper presents a novel micromachined actuator which is developed to produce precise and unlimited displacement. The actuator is driven by impact force between a silicon micro-mass and a stopper. The suspended silicon micro-mass is encapsulated between two glass plates and driven by electrostatic force. When the mass hits the stopper which is fixed on glass plates, impact force is generated to drive the whole actuator in a nano size step (/spl sim/10 nm). The overall dimension of the device is 3 mm /spl times/3 mm. The driving voltage is 100 V and average speed is 2.7 /spl mu/m/s. The total thickness is 600 /spl mu/m.     

A fish robot driven by piezoceramic actuators and a miniaturized power supply

In this paper, we have introduced a prototype of a fish robot driven by unimorph piezoceramic actuators. To improve the swimming performance of the fish robot in terms of tail-beat angle, swimming speed, and thrust force, we used four light-weight piezo-composite actuators (LIPCAs) instead of the two LIPCAs used in the previous model. We also developed a new actuation mechanism consisting of links and gears. Performance tests of the fish robot were conducted in water at various tail-beat frequencies to measure the tail-beat angle, swimming speed, and thrust force. The tail-beat angle was significantly better than that of the previous model. The best tail-beat frequency of the fish robot was 1.4 Hz and the maximum thrust force was 0.0048 N. A miniaturized power supply, which was developed to excite the LIPCAs, was installed inside the fish robot body for free swimming. The maximum free-swimming speed was 3.2 cm/s. Recommended by Editorial Board member Hyoukryeol Choi under the direction of Editor Jae-Bok Song. This work was supported by the Korea Research Foundation under grant KRF-2004-005-D00045. Quang Sang Nguyen received the BS (2001) and MS (2006) from Hochiminh City University of Technology, Vietnam. Formerly an assistant lecturer of Naval Architect and Marine Engineering, Hochiminh City University of Technology, Vietnam (2001-2006), he is currently a Ph.D. student at the Department of Advanced Technology Fusion, Konkuk University. His specialty is biomimetic system design and smart material application. Seok Heo received the B.S., M.S. and Ph.D. degrees in Mechanical Engineering from Dongguk University in 1998, 2000, and 2003, Respectively. Currently he is a Research Professor at the Artificial Muscle Researcch Center, Konkuk University, Seoul, Korea. His research interests include biomimetics, vibration analysis, system design and control, and smart materials and structures. Hoon Cheol Park received the B.S. (1985) and M.S. (1987) from Seoul National University in Seoul, Korea and Ph.D. (1994) from the University of Maryland at College Park, MD, USA. He joined the Department of Aerospace Engineering, Konkuk University in Seoul, Korea, in 1995, and he is currently a Professor in the Department of Advanced Technology Fusion. His professional experience includes Kia Motors (1986–1988) and Korea Aerospace Research Institute (1994–1995). His specialty is finite element analysis and his recent research has focused on biomimetics. Nam Seo Goo graduated with honors in 1990 from the Department of Aeronautics Engineering of Seoul National University, and he got a masters degree and Ph.D. from the Department of Aerospace Engineering at the same university in 1992 and 1996, respectively. His Ph.D. thesis was on the structural dynamics of aerospace systems. As soon as he obtained the Ph.D. he entered the Agency for Defense development as a senior researcher. In 2002, after four years of service, he joined the Department of Aerospace Engineering at Konkuk University, Seoul, Korea, where he is currently serving as an Associate Professor of the Department of Advanced Technology Fusion. His current research interests include structural dynamics of small systems, smart structures and materials, and MEMS applications. Taesam Kang is a Professor of the Department of Aerospace and Information System Engineering, Konkuk University. He received the B.S., M.S. and Ph.D. degrees from Seoul National University in 1986, 1988 and 1992, respectively. His current research areas are robust control theories and the application of those theories with regard to flight control, development of micro-aerial vehicles and fish robots. Kwang Joon Yoon was awarded the BS (1981) and M.S. (1983) in Aeronautics Engineering from Seoul National University and Ph.D. (1990) in Aeronautics and Astronautics Engineering from Purdue. Since 1991 he has been a Professor at Konkuk University in Korea, where he is currently a Professor of Aerospace Engineering, the Director of the National Research Laboratory for Active Structures and Materials, the Director of the Artificial Muscle Research Center, and the Director of the Smart Robot Center. His current research interests include smart structures and materials, micro-aerial vehicles, and insect-mimetic micro-robot systems. Seung Sik Lee received the B.S. (1996) and M.S. (1998) in Civil Engineering from Hongik University in Seoul, Korea and Ph.D. (2003) in Civil Engineering from Georgia Institute of Technology, GA, USA. Currently he is a Senior Researcher at Korea Institute of Marine Science & Technology Promotion.     

Non-linear adaptive robust control of electro-hydraulic systems driven by double-rod actuators

This paper studies the high performance robust motion control of electro-hydraulic servo-systems driven by double-rod hydraulic actuators. The dynamics of hydraulic systems are highly non-linear and the system may be subjected to non-smooth and discontinuous non-linearities due to directional change of valve opening, friction and valve overlap. Aside from the non-linear nature of hydraulic dynamics, hydraulic servosystems also have large extent of model uncertainties. To address these challenging issues, the recently proposed adaptive robust control (ARC) is applied and a discontinuous projection based ARC controller is constructed. The resulting controller is able to take into account the effect of the parameter variations of the inertia load and the cylinder hydraulic parameters as well as the uncertain non-linearities such as the uncompensated friction forces and external disturbances. Non-differentiability of the inherent non-linearities associated with hydraulic dynamics is carefully examined and addressing strategies are provided. Compared with previously proposed ARC controller, the controller in the paper has a more robust parameter adaptation process and may be more suitable for implementation. Finally, the controller guarantees a prescribed transient performance and final tracking accuracy in the presence of both parametric uncertainties and uncertain non-linearities while achieving asymptotic tracking in the presence of parametric uncertainties.     

Micro robot system with moving micro-car driven by electrostatic comb-drive actuators

This paper describes a silicon micro robot system (MRS) that is capable of driving micro-cars in different directions based on a ratchet mechanism and electrostatic comb-drive actuators. Lateral movement of the ratchet racks makes the micro-car move in the perpendicular direction with different velocities. Based on MEMS technology, the MRS described in this article was fabricated from a silicon on insulator wafer by using only one photo mask. In our experiments, various driving frequencies ranging from 1 to 20 Hz were used to accelerate the micro-car up to 200 μm/s. It was observed that the velocity of the micro-car was proportional to the driving frequency used in the experiments. This relation was also confirmed with our theoretical calculation. When combined with microscopes, this MRS can be applied in bio-medical analysis for transportation and classification of small samples.     

Micro cam system driven by electrostatic comb-drive actuators based on SOI-MEMS technology

Microsystem Technologies - This paper reports a design and fabrication process of a micro cam system (MCS) with a flat-faced translating follower. The cam rim with cover diameter of 2.4 mm...     

Motion error correction for non-contact ultrasonic motor driven by multi-layered piezoelectric actuators

An active non-contact ultrasonic motor with the micro positioning abilities of a rotor was proposed and performances were tested. The stator had a simple cylindrical form, which enabled low manufacturing costs. A resonant frequency of 22.2 kHz at eighth flexural mode of vibration was observed. With appropriate assembly and operation of piezoelectric actuators, the flexure vibration of the stator travels in the circumferential direction. The component of the stator deformation in radial direction creates an air film pressure higher than ambient thereby suspending the rotor. Simultaneously, the component that propagates in the circumferential direction rotates the rotor based on acoustic viscous flow. It was experimentally confirmed by electrical conduction test that the rotor rotated with levitation from stator. In addition, piezoelectric actuators around the stator exciting the deflective vibration could make contact-free micro positioning abilities of the rotor with a minimum step width of 0.15 μm.     

Design, modeling, fabrication, and performances of bridge-type high-performance electroactive polymer micromachined actuators

Bridge-type high- performance polymer micromachined actuators (PMATs) based on an electroactive polymer, modified poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer had been designed, modeled, fabricated, and characterized. The results show that the material enables the PMAT to exhibit a high stroke level (60 /spl mu/m displacement with 1 mm lateral dimension microactuator) with high-load capability and high-displacement voltage ratio (DVR) over a broad frequency range (>100 kHz). The stroke reduction in fluid (Silicone oil) is less than 5% comparing with the displacement in air. Impedance analysis and displacement measurement indicate that the PMAT has strong resonance behavior and the resonance frequency can be tuned by varying the dc bias field. Furthermore, the resonance peak, as expected by theoretical study, shifted to 6.5 times lower in fluid than in air with the mechanical Q value reduction less than 40%. In addition, the performance of the PMAT was modeled based on the elastic and electromechanical properties of the materials utilized in the PMAT and the configuration of the device. The comparison between the model and the experimental result shows a good agreement and validates the model as an effective method for the future development of PMAT for various applications. The high frequency response and respected performance in fluid medium demonstrate that the PMAT has potential for high performance MEMS components in the applications of microfluid systems, air dynamic control, under water transducers, and mass sensors, etc.     

A three-axis SOI accelerometer sensing with both in-plane and vertical comb electrodes

A three-axis capacitive accelerometer based on silicon-on-insulator is designed and fabricated. In the accelerometer, totally eight groups of capacitors are compactly arranged around an octagonal proof mass. The four groups of capacitors along orthogonal direction with in-plane comb electrodes detect XY acceleration, while the other four groups of capacitors along diagonal direction with vertical comb electrodes detect Z acceleration. Measurements of in-plane and vertical motion by the respective in-plane and vertical comb electrodes enable direct detection for all the three axes with differential capacitive sensing scheme. For the fabricated accelerometer in the size of 4 × 4 mm², the capacitance sensitivities of in-plane and out-of-plane accelerometers are 145.3 and 9.1 fF/g, respectively.     

Design and fabrication of a resonant scanning micromirror suspended by V shaped beams with vertical electrostatic comb drives

A scanning micromirror suspended by a pair of V-shaped beams with vertical electrostatic comb drives was designed, modeled, fabricated and characterized. The dynamic analyses were carried out by both theory calculation and FEM simulation to obtain frequency response, stiffness characteristics, oscillation modes and their resonance frequencies. The device was fabricated using the silicon-on-insulator process by only two photolithography masks. Some problems during the process such as the micromirror distortion and the side sticking of the comb fingers were effectively solved by thermal annealing and alcohol-replacement methods, respectively. Based on the fabricated device, the typical scanning patterns for 1-D and 2-D operation were obtained. The experimental results reveal that the micromirror can work in resonant mode with the resonant frequency of 2.38 kHz. The maximum deflection angles can reach ±4.8°, corresponding to a total optical scanning range of 19.2° at a driving voltage of 21 V.     

Torque multiplication and stable range tradeoff in parallel plate angular electrostatic actuators with fixed DC bias

The nonlinear torque-voltage characteristics in two-terminal electrostatic actuators can be utilized to magnify the torque generated by a drive voltage applied to one electrode if a fixed dc bias is applied to the other. The resulting torque is enhanced by torque gain factor G/sub /spl tau//>1, and the drive voltage is effectively multiplied by voltage gain factor G/sub V/>1 compared to that of an actuator with no dc bias. These gain factors are generated at the expense of a reduced stable range. In this paper, we study and determine experimentally the tradeoff between torque and voltage gains versus stable range for one-dimensional (1-D), three-terminal, parallel-plate angular electrostatic actuators under dc bias. Simple approximate analytical relations are derived for voltage and torque gain as functions of applied dc bias voltage. We demonstrate that for voltage gains of 2-4, the angular range is marginally reduced. [1361].     

A new MEMS based variable capacitor using electrostatic vertical comb drive actuator and auxiliary cantilever beams

We have proposed a new wide tunable MEMS variable capacitor. In the proposed structure, an electrostatic vertical comb drive actuator is used to extend the tuning range. Moreover, the auxiliary cantilever-beams are used in the electrostatic comb drive actuator to delay the front sticking (Pull in) and increase the tunability. The effect of lateral gap distance between the fingers in the capacitance tunability is investigated. Not only a full review of electrostatic actuator portion is done but also the electric fields related to lateral gap changes are simulated by COMSOL software and its results are compared with theoretical results as well. The structure is calculated using MATLAB software. To verify, the calculated results are compared with simulated results using Intellisuite software. According to calculation and simulation results the achieved tuning range is 285%.

     

Fabrication of comb structure with vertical sidewalls in Si (110) substrate by wet etching in boiling KOH solution

Microsystem Technologies - This paper discusses about the fabrication of comb-structure with vertical sidewall profile by wet chemical etching of Si (110) substrate in boiling KOH solution. Etch...     

Integration of two degree-of-freedom magnetostrictive actuation and piezoresistive detection: application to a two-dimensional optical scanner

A novel two-dimensional (2-D) optical-scanner device is presented. This device incorporates a highly magnetostrictive thin film with anisotropic properties, so that it can produce 2-D-actuation corresponding to bending and torsion vibrations. The magnetostrictive material is a TbFe-CoFe multilayer film, which has optimized properties for micro-actuators operating at low excitation magnetic fields. The new scanner also integrates an original 2-D piezoresistive detector realized in an easy fabrication process using integrated circuit (IC)-compatible technology. The detectors are able to selectively measure bending and torsional vibrations. This new device enables the synchronization of actuation and sensing for 2-D position control.     

Modeling and simulation of powered hip orthosis by pneumatic actuators

In this study, a simulation model for a powered hip orthosis (PHO) with air muscles to predict the gait of paraplegics is presented which can be used as a design tool for hip orthoses. Before simulation, mathematical models for a human dummy with an orthosis and a pneumatic muscle actuator were generated. For the air muscle, coefficients required were obtained by static and dynamic experiments of the air muscle and experiments for the valve controlling the air pressure. The computation was conducted on the ADAMS package together with MATLAB. Computer simulation of the flexion of hip joints by the pneumatic muscle results in similar values to those from gait analysis. With the development of a simulation model for a PHO, the gait simulation model using pneumatic muscles can be used to analyze and evaluate the characteristics and efficiency of a PHO by setting the input and boundary conditions.     

Placing actuators on space structures by genetic algorithms and effectiveness indices

Genetic algorithms are a powerful tool for the solution of combinatorial problems such as the actuator placement problem. However, they require a large number of analyses with correspondingly high computational costs. Therefore, it is useful to tune the operators and parameters of the algorithm on simple problems that are similar to more complex and computationally expensive problems. The present paper employs an easy-tocalculate measure of actuator effectiveness to evaluate several genetic algorithms. Additionally, the effects of population size and mutation rates are also investigated for a problem of placing actuators at 8 of 1507 possible locations. We find that even with the best of the algorithms and with optimum mutation rates, tens of thousands of analyses are required for obtaining near optimum locations. We propose a procedure that estimates the effectiveness of the various locations and discards ineffective ones, and find it helpful for reducing the cost of the genetic optimization.     

Airborne discrete-return LIDAR data in the estimation of vertical canopy cover, angular canopy closure and leaf area index

Remote sensing of forest canopy cover has been widely studied recently, but little attention has been paid to the quality of field validation data. Ecological literature has two different coverage metrics. Vertical canopy cover (VCC) is the vertical projection of tree crowns ignoring within-crown gaps. Angular canopy closure (ACC) is the proportion of covered sky at some angular range around the zenith, and can be measured with a field-of-view instrument, such as a camera. We compared field-measured VCC and ACC at 15° and 75° from the zenith to different LiDAR (Light Detection and Ranging) metrics, using several LiDAR data sets and comprehensive field data. The VCC was estimated to a high precision using a simple proportion of canopy points in first-return data. Confining to a maximum 15° scan zenith angle, the absolute root mean squared error (RMSE) was 3.7-7.0%, with an overestimation of 3.1-4.6%. We showed that grid-based methods are capable of reducing the inherent overestimation of VCC. The low scan angles and low power settings that are typically applied in topographic LiDARs are not suitable for ACC estimation as they measure in wrong geometry and cannot easily detect small within-crown gaps. However, ACC at 0-15° zenith angles could be estimated from LiDAR data with sufficient precision, using also the last returns (RMSE 8.1-11.3%, bias -6.1-+4.6%). The dependency of LiDAR metrics and ACC at 0-75° zenith angles was nonlinear and was modeled from laser pulse proportions with nonlinear regression with a best-case standard error of 4.1%. We also estimated leaf area index from the LiDAR metrics with linear regression with a standard error of 0.38. The results show that correlations between airborne laser metrics and different canopy field characteristics are very high if the field measurements are done with equivalent accuracy.