Design and fabrication of novel micro electromagnetic actuator

This study designs, fabricates, and characterizes a novel micro electromagnetic actuator comprising a PDMS diaphragm, a polyimide-coated copper micro coil, and a permanent magnet. When an electrical current is passed through the micro coil, a magnetic force is induced between the coil and the magnet which causes the diaphragm to deflect, thereby creating an actuation effect. The experimental results demonstrate that the diaphragm deflection can be accurately controlled by regulating the current passed through the micro coil. It is shown that the maximum diaphragm deflection within elastic limits is 150 μm; obtained by passing a current of 0.6 A through a micro coil with a line width of 100 μm. The micro actuator proposed in this study is easily fabricated and is readily integrated with existing bio-medical chips due to its planar structure.     

Micromanipulation system using scanning electron microscope

In this study, we aimed to develop a micromechanism in which constituent parts of μm order are used and to establish the handling technology required to achieve this. On the basis of the results of previous studies, we fabricated end effectors driven by a small piece of shape memory alloy (SMA) and succeeded in grasping microobjects on the order of 10–40 μm. However, when the size of an object is 10 μm or smaller, because this size is equivalent to the resolution of optical microscopes, it is necessary to improve and change the design of observation technology to manipulate much smaller objects. In this study, an SEM was used as the observation system and the manipulation system was modified to be compatible with this observation system. A manipulation system for grasping much smaller objects was designed and developed.     

A sub-micron metallic electrothermal gripper

We report the design, fabrication, and characterization of a multiple bent beam, sub-micron metallic electrothermal gripper. A bottom electroplating mold for electrodes was patterned using electron beam lithography in an SU-8, followed by nickel electroplating. A top electroplating mold for a sub-micron metallic gripper with high aspect ratio bent beams (thickness of 1 μm, width of 350 nm) was prepared using electron beam lithography in a polymethyl methacrylate (PMMA), followed by nickel electroplating and dry release of the top and bottom molds. The sub-micron gripper was characterized using a nanomanipulator system installed in a dual column scanning electron microscopy/focused ion beam system. The ability of the jaw to close up to 1.39 μm displacement with high precision and reliability has been reproducibly observed at an applied current of 28 mA, corresponding to the maximum power consumption of 11.2 mW. Finite element modeling displacement results performed using ANSYS for effective bent beam widths of 370 nm showed a good agreement with the measured displacement results. The sub-micron gripper demonstrated herein will enable the reproducible manipulations with nano-scale resolution displacement and could provide an effective means of interface between nano-scale objects and the micro/macro scale robotic systems.     

Easily manageable, electrothermally actuated silicon micro gripper

This paper presents a new batch process to fabricate thermally driven silicon micro grippers for handling and manipulation objects smaller than 25 μm. To achieve a robust gripper gearing with fine gripping tips, silicon on insulator (SOI) technology is used. The flexure gearing is driven by two integrated thermal expansion actuators that are moving in opposite directions and are actuated by Joule heating. In addition, a customized gripper mounting mechanism is presented, which offers fast and easy gripper handling, resulting in reduced tooling time and lower costs for the user. Finally, the experimental results and electrical characteristics for the sophisticated gripper design are presented.     

Micro actuators on the basis of thin SMA foils

Three innovative micro actuator concepts on the basis of the differential SMA principle are presented in this paper: a high adaptive multi-actuator system, which is driven by numerous identical single actuators connected in parallel and in series, a micro gripper for handling and assembling of complex hybrid micro systems and a micro actuator system in medical tools for the percutaneous resection of aortic valves. The SMA material is used in the form of 50 μm thin NiTi foils because of their well-defined properties and high strength. In order to integrate them into micro systems, different manufacturing methods have been applied and improved at the Institute for Microtechnology. Laser cutting and wet chemical etching are used for example to microstructure the actuator elements. Different methods for electrical and mechanical connections of the actuators are employed like soldering by the use of an additional gold layer. A batch fabrication process of SMA actuators is realized by embedding NiTi foil elements into SU-8 structures. To optimize the design of SMA actuator elements according to its application different simulation procedures are used.     

Design, implementation and testing of electrostatic SOI MUMPs based microgripper

This paper presents a detail modeling, finite element analysis and testing results of MEMS based electrostatically actuated microgripper. Interdigitated lateral comb pairs have been used to actuate the microgripper. The microgripper is optimized using standard SOI-MUMPs technology in L-Edit of MEMS-Pro with dual jaws actuation at low voltages. Coupled electromechanical finite element analysis performed in COVENTOR-WARE shows total displacement of 15.5 μm at jaws tip at 50 V, which is quite comparable to experimental result of 17 μm displacement at the tip of gripper jaw for the same voltage. Micromanipulation experiments have successfully demonstrated the gripping, holding micro-objects between 53 and 70 μm in size. The simulated model is used to study detail profile of Von Mises stresses and deformations in the model. It is noted that maximum stress in microgripper is 200 MPa which is much smaller than yield stress of 7 GPa. The slight difference between finite element analysis and experimental results is because of small variations in process material parameters. The total size of gripper is 5.03 × 6.5 mm².     

Design and testing of a microgripper with SMA actuator for manipulation of micro components

The extremely high work-to-volume ratios of the SMA actuators make them suitable to be used as a powerful actuator in micro-scale manipulation. In this study, an easily manufacturable micro-gripper with shape memory alloy (SMA) wire actuator was designed and manufactured. The concept of the designed micro-gripper was based on flexible hinge structures to increase the deflection efficiency and strength. The size of microgripper was a significant criterion in our design. Also, innovative layout in locating of SMA wire caused the microgripper to gripe and manipulate a boarder range of objects. The finite element method was used to analyze and calculate the stress distribution and jaw’s deflection in the gripper. In order to verify the modeling results, an experimental analysis by building a set-up for micro-gripper and running tests were implemented and it showed a good agreement with the modeling results. The approximate size of the micro-gripper is about 12 × 10 mm and its maximum achievable deflection is 200 μm which is perceptibly higher than SMA actuated micro-grippers with the same size.

     

Design and manufacturing of mobile micro manipulation system with a compliant piezoelectric actuator based micro gripper

This paper presents a new design of mobile micro manipulation system for robotic micro assembly where a compliant piezoelectric actuator based micro gripper is designed for handling the miniature parts and compensation of misalignment during peg-in-hole assembly is done because piezoelectric actuator has capability of producing the displacement in micron range and generates high force instantaneously. This adjusts the misalignment of peg during robotic micro assembly. The throughput/speed of mobile micro manipulation system is found for picking and placing the peg from one hole to next hole position. An analysis of piezoelectric actuator based micro gripper has been carried out where voltage is controlled through a proportional-derivative (PD) controller. By developing a prototype, it is demonstrated that compliant piezoelectric actuator based micro gripper is capable of handling the peg-in-hole assembly task in a mobile micro manipulation system.     

Modeling and analysis of a 2-DOF bidirectional electro-thermal microactuator

In this paper, a four hot-arm U-shape electro-thermal actuator that can achieve bidirectional motion in two axes is introduced. By selectively applying voltage to different pairs of its four arms, the device can provide actuation in four directions starting from its rest position. It is shown that independent in-plane and out-of-plane motions can be obtained by tailoring the geometrical parameters of the system. The lumped model of the microactuator was developed using electro-thermal and thermo-mechanical analyses and validated using finite element simulations. The device has been fabricated using PolyMUMPs and experimental results are in good agreement with the theoretical predictions. Total in-plane deflections of 4.8 μm (2.4 μm in either direction) and upward out-of-plane deflections of 8.2 μm were achieved at 8 V of input voltage. The large achievable deflections and the higher degree-of-freedom of the proposed device compared to its counterparts, foresee its use in diverse MEMS applications.     

3-D manipulation of millimeter- and micro-sized objects using an acoustically excited oscillating bubble

This communication describes novel 3-D manipulations of objects using an acoustically excited oscillating bubble deposited on a hydrophobic rod tip. The oscillating bubble captures various millimeter- and micron-sized neighboring objects including glass and polystyrene beads (~100 μm), fish egg, and live water flea (~1 mm). The captured objects are carried in a 3-D space by traversing the bubble tip, and released at desired positions by simply turning off the oscillation. Carrying performance is characterized along with high-speed imaging of oscillating bubbles by varying the frequency and amplitude of the acoustic excitation and the carrying speed. The higher the oscillation amplitude, the higher the carrying efficiency. The maximum carrying speed is measured at over 3 mm/s. This method is effective with a low-level acoustic excitation (bubble oscillation amplitude relative to the diameter ≤5%), possibly providing a cost-effective, soft-contact manipulating tool for handling biological objects.     

Fabrication of three-dimensional hemispherical structures using photolithography

A photolithography technique using SU-8 and PDMS was developed to fabricate three-dimensional hemispherical structures. This technique utilized a mask-aligner and normal binary coded photomasks to generate hemispherical pits on SU-8, followed by PDMS molding to obtain an array of dome-shaped structures. Using this technique, a microfluidic device was fabricated with a patterning area that consisted of an array of 5 μm wells and dome-shaped structures with 10 μm diameter and 6 μm height. Encoded microbeads, 6 μm in size, were immobilized and patterned in the microfluidic device under flow conditions and a DNA hybridization experiment was performed to demonstrate the incorporation of encoded beads that would enable a high level of multiplexing in bioassays.     

Ultra thin ICs and MEMS elements: techniques for wafer thinning,stress-free separation,assembly and interconnection

 Ultra thin chips with a thickness below 30 μm offer low system height, low topography and show enhanced mechanical flexibility. These properties enable diverse use possibilities and new applications. However, advanced wafer thinning, adapted assembly and interconnection methods are required for this technology. A new process scheme is proposed that allows manufacturing of ultra thin fully processed wafers. Secure handling is achieved by means of carrier substrates using reversible adhesive tapes for connection of support and device wafers. Well established backgrinding and etching techniques are used for wafer thinning. To avoid mechanical damage of thin ICs the “Dicing-by-Thinning” (DbyT) concept is introduced to process flow. Best results are obtained when preparing dry etched chip grooves at front side of device wafer and opening these trenches during backside thinning. The new process scheme was also applied to wafers with highly topographic surfaces. Results of 40 μm thin wafers with 15 μm high Nickel bumps are presented. Three different assembly methods are described, interconnection through the thin chip, face down assembly and isoplanar contacting. Received: 6 July 2001/Accepted: 26 February 2002 The authors would like to thank M. Küchler (IZM Chemnitz) for preparing and performing trench etching process and A. Ostmann (IZM Berlin) for performance of nickel bumping process. This paper was presented at the Conference of Micro System Technologies 2001 in March 2001.     

High aspect ratio electrostatic micro actuators using LIGA process

High-power electrostatic microactuators using LIGA process have been fabricated. Comb drive type actuators and a wobble motor were designed and fabricated. A basic structure of the microactuators was composed of movable and fixed electrodes of Ni, a sacrificial layer of SiO₂ and a Si substrate, and carried out by one mask process. As design rules, a minimum resist width of 2 μm, resist height of 120 μm, maximum width of movable parts of 10 μm, minimum width of fixed parts of 40 μm and driving voltage of about 100 V, were decided. A 120 μm-thick PMMA resist was formed on a Si substrate by a casting method. The PMMA was exposed using a compact SR source “AURORA”, using an X-ray mask with 7 μm-thick Au absorber on a 2 μm-thick poly-Si membrane. The exposed PMMA was developed by a developer. Ni microstructures with 100 μm-height, 2 μm-minimum width, 2 μm-minimum gap, and then maximum aspect ratio of 50, were made by electroforming. Ni microstructures used for movable electrodes were separated from the substrate by lateral etching of SiO₂. After lateral etching of SiO₂, Au wires were bonded to electrodes. Actuation of the comb drive type actuator and rotation of the wobble motor were confirmed. The applied voltage to the comb drive actuator and the wobble motor were 65 and 125 V.     

Particle streaming and separation using dielectrophoresis through discrete periodic microelectrode array

This study presents a particle manipulation and separation technique based on dielectrophoresis principle by employing an array of isosceles triangular microelectrodes on the bottom plate and a continuous electrode on the top plate. These electrodes generate non-uniform electric fields transversely across the microchannel. The particles within the flowing fluid experience a dielectrophoretic force perpendicular to the fluid flow direction due to the non-uniform electric fields. The isosceles triangular microelectrodes were designed to continuously exert a small dielectrophoretic force on the particles. Particles experiencing a larger dielectrophoretic force would move further in the perpendicular direction to the fluid flow as they traveled past each microelectrode. Polystyrene microspheres were used as the model particles, with particles of ∅20 μm employed for studying the basic characteristics of this technique. Particle separation was subsequently demonstrated on ∅10 and ∅15 μm microspheres. Using an applied sinusoidal voltage of 20 V_pp and frequency of 1 MHz, a mean separation distance of 0.765 mm between them was achieved at a flow rate of 3 μl/min (~1 mm/s), an important consideration for high throughput separation capability in a micro-scale technology device. This unique isosceles triangular microelectrodes design allows heterogeneous particle populations to be separated into multiple streams in a single continuous operation.     

Electrothermoelastic modeling of MEMS gripper

The design of many thermal Microelectromechanical (MEMS) actuators is often based on finite element analysis, but lacks analytical insight. In this paper we report a novel electro-thermal microgripper and a comprehensive thermal modeling of a general 5 lineshape microbeam’s actuator using 1-D steady state heat equations. Because of the variety of microgripper fabrication technologies and their applications, different thermal boundary conditions are considered for lifted off and attached grippers. Parametric and nonparametric electrothermomechanical identification models for silicon on insulator microgripper, fabricated on 100 μm device layer, are obtained.     

Effect of dispersed phase viscosity on maximum droplet generation frequency in microchannel emulsification using asymmetric straight-through channels

Uniformly sized droplets of soybean oil, MCT (medium-chain fatty acid triglyceride) oil and n-tetradecane with a Sauter mean diameter of d _3,2 = 26–35 μm and a distribution span of 0.21–0.25 have been produced at high throughputs using a 24 × 24 mm silicon microchannel plate consisting of 23,348 asymmetric channels fabricated by photolithography and deep reactive ion etching. Each channel consisted of a 10-μm diameter straight-through micro-hole with a length of 70 μm and a 50 × 10 μm micro-slot with a depth of 30 μm at the outlet of each channel. The maximum dispersed phase flux for monodisperse emulsion generation increased with decreasing dispersed phase viscosity and ranged from over 120 L m⁻² h⁻¹ for soybean oil to 2,700 L m⁻² h⁻¹ for n-tetradecane. The droplet generation frequency showed significant channel to channel variations and increased with decreasing viscosity of the dispersed phase. For n-tetradecane, the maximum mean droplet generation frequency was 250 Hz per single active channel, corresponding to the overall throughput in the device of 3.2 million droplets per second. The proportion of active channels at high throughputs approached 100% for soybean oil and MCT oil, and 50% for n-tetradecane. The agreement between the experimental and CFD (Computational Fluid Dynamics) results was excellent for soybean oil and the poorest for n-tetradecane.     

Development of Multi Micro Manipulation System Using IPMC Micro Grippers

This paper presents a new design of multi micro manipulation system using ionic polymer metal composite (IPMC) micro grippers for robotic micro assembly where IPMC is used as a light weight actuator for developing the micro grippers. It has the potential of large displacement, low mass force generation and misalignment compensation ability during micro manipulation. These capabilities are utilized for handling of miniature parts like pegs. The analysis of IPMC micro gripper and manipulator are carried out for developing a multi micro manipulation system that can handle pegs in micro assembly operation for shifting one to another hole position in a large work space (100 mm × 100 mm). By developing a prototype, it is demonstrated that IPMC based micro grippers are capable of handling the peg-in-hole assembly tasks in a multi micro manipulation system.     

Intelligent robotic gripper with adaptive grasping force

The on-off control robot gripper is widely employed in pick-and-place operations in Cartesian space for handling hard objects between two positions. Without contact force monitoring, it can not be applied in fragile or soft objects handling. Although, an appropriate grasping force or gripper opening for each target could be searched by trial-and-error process, it needs expensive force/torque sensor or an accurate gripper position controller. It has too expensive and complex control strategy disadvantages for most of industrial applications. In addition, it can not overcome the target slip problem due to mass uncertainty and dynamic factor. Here, an intelligent gripper is designed with embedded distributed control structure for overcoming the uncertainty of object’s mass and soft/hard features. A communication signal is specified to integrate both robot arm and gripper control kernels for executing the robotic position control and gripper force control functions in sequence. An efficient model-free intelligent fuzzy sliding mode control strategy is employed to design the position and force controllers of gripper, respectively. Experimental results of pick-and-place soft and hard objects with grasping force auto-tuning and anti-slip control strategy are shown by pictures to verify the dynamic performance of this distributed control system. The position and force tracking errors are less than 1 mm and 0.1 N, respectively.

     

Grasping and in-hand manipulation: experiments with a reconfigurable gripper

This paper addresses the problem of grasping and manipulating three-dimensional objects with a reconfigurable gripper equipped with two parallel plates whose distance can be adjusted by a computer-controlled actuator. The bottom plate is a bare plane and the top one carries a rectangular grid of actuated pins that can translate in discrete increments under computer control. We propose to use this gripper to immobilize objects through frictionless contacts with three of the pins and the bottom plate, and to manipulate an object within a grasp by planning the sequence of pin configurations that will bring this object to a desired position and orientation. A detailed analysis of the problem geometry in configuration space was used in a previous paper to devise simple and efficient algorithms for grasp and manipulation planning. We have constructed a prototype of the gripper and this paper presents our experiments.     

Viable cell handling with high aspect ratio polymer chopstick gripper mounted on a nano precision manipulator

This paper presents the development of an optimized contact technique for viable cell manipulation utilizing a high aspect ratio polymer chopstick gripper. The gripper consists of a 2 μm thick metal heater layer and a 60 μm thick SU-8 layer and is fabricated by a typical UV-LIGA process using SiO₂ as sacrificial layer. The grippers were completely released, de-tethered and assembled as end-effectors on to a nano precision manipulator to perform cell manipulation. Successful pick-and-place of a suspended normal rat kidney cell in phosphate buffered saline solution was demonstrated. The major cell-damage mechanisms associated with contact techniques were identified and alleviated by optimizing the handling force and operating temperature of the polymer gripper. The viability of cells handled with this optimized contact technique was demonstrated by labeling cells with a fluorescent dye. The developed technique will enable incorporation of simple, viable, and repeatable cell handling capabilities into the generic micromanipulators used in the biological laboratories.