Joon-wan Kim

Elastic Inflatable Actuators for Soft Robotic Applications

The 20th centurys robotic systems have been made from stiff materials, and much of the developments have pursued ever more accurate and dynamic robots, which thrive in industrial automation, and will probably continue to do so for decades to come. However, the 21st centurys robotic legacy may very well become that of soft robots. This emerging domain is characterized by continuous soft structures that simultaneously fulfill the role of robotic link and actuator, where prime focus is on design and fabrication of robotic hardware instead of software control. These robots are anticipated to take a prominent role in delicate tasks where classic robots fail, such as in minimally invasive surgery, active prosthetics, and automation tasks involving delicate irregular objects. Central to the development of these robots is the fabrication of soft actuators. This article reviews a particularly attractive type of soft actuators that are driven by pressurized fluids. These actuators have recently gained traction on the one hand due to the technology push from better simulation tools and new manufacturing technologies, and on the other hand by a market pull from applications. This paper provides an overview of the different advanced soft actuator configurations, their design, fabrication, and applications.

ECF Micropump-Integrated Micro Hand by MEMS Technology

On purpose to realize a novel flexible micro-hand for biological and medical applications, this paper presents a major step forward in this direction by directly integrating micropumps into eccentric tube type micro-fingers driven by the ECF (Electro-Conjugate Fluid) jet. ECF is a functional fluid which can generate the strong jet by applying high DC voltage between the electrodes. The ECF eccentric tube type micro-hand (ECF-ETMH) comprises three elastic PDMS micro-fingers with eccentric void and their corresponding MEMS-fabricated ECF micropumps. Because of the geometrical asymmetry created by an eccentric void in a cylindrical elastic body, this micro-finger acts bending motion upon the pressurization of the eccentric void by the ECF jet. Each ECF micropump has 41 pairs of a triangular prism and slit electrodes (TPSEs) that are designed to generate maximum pressures of 300kPa at the applied voltage of 3.5kV. We successfully fabricated eccentric tube type micro-fingers (ETMF) by high aspect ratio micromolding. Although we could not succeed in integrating the ECF micropumps and ETMFs due to the leakage, we experimentally proved the feasibility of this micro-hand system by investigating the characteristics of them separately.Copyright

MEMS-based tube-type micropump by using electro-conjugated fluid (ECF)

This paper proposes and presents an electro-conjugate fluid (ECF) micropump whose pumping sources are mounted on the inside of flow channels and are serially located through the flow channels. ECF is a kind of functional and dielectric fluid. A strong and active jet flow of ECF is generated between electrodes surrounded by ECF when high DC voltage is applied to the electrodes. To combine easy fabrication and high performance, we propose a novel ECF-jet generator that consists of a triangular prism electrode and a slit electrode for the tube-type ECF micropump. In order to determine the main parameters of MEMS-based ECF micropump, this research performs the experimental optimization of the prototype fabricated by mechanical machining, by changing the following parameters: slit width; electrode gap; and tip angle. Experimental results by the prototype show that the optimal values are 200µm in slit width, 200µm in electrode gap, and 19° in tip angle. Based on these values, MEMS-based tube-type ECF micropump is successfully fabricated. The maximum output pressure obtained is 19 kPa at 2 kV of the applied voltage. The result shows that the tube-type ECF micropump can be a good candidate as a driving source for forced liquid cooling systems, new microactuators and so on.

ECF micropump fabricated by electroforming with novel self-aligned micro-molding technology

This paper proposes and presents a novel ECF (electro-conjugate fluid) micropump with TPSEs (triangular prism and slit electrode pair) fabricated by electroforming process using newly developed self-aligned micro molds. ECF is a kind of functional and dielectric fluid. ECF micropump is based on the principle of ECF jet, which is a powerful and active jet flow generated between electrodes immerged in ECF, when high DC voltage is applied to the electrodes. Our previous research experimentally demontrated that the ECF micropump had high power density thanks to the 2D-integraton (serialized integration and paralleled integration) of our proposed MEMS fabrication method by using micro-molding and electroplating. Moreover, it was also proved that higher aspect ratio of TPSEs by the multilayer fabrication process resulted in higher flow rate of the ECF micropump. However, the multilayer fabrication has demerit to require precise alignment that is time-consuming and extremely difficult to be met. In order to improve alignment accuracy and alleviate fabrication difficulty, this paper proposes a novel self-aligned MEMS fabrication process for high aspect ratio TPSEs. The ECF micropump by this newly-proposed MEMS process was successfully fabricated and the feasibility was proved by experimentally investigating output performance of the ECF micropump.

New Microactuators Using Functional Fluids

An electro-conjugate fluid (ECF) generates jet flow in inhomogeneous electric field. Electro-rheological fluid (ERF) and magneto-rheological fluid (MRF) change their apparent viscosities in electric or magnetic field. Such functional fluids are expected to realize new promising actuators with simple and miniaturizable structure without sliding part. The paper describes objective and outline of our research on new microactuators using functional fluids. Then, as some results of our research, ECF micromotors, ECF gyroscopes, soft actuators using pressure due to ECF jet, forced liquid cooling systems using ECF jet, microactuators using ERF/MRF, and high output power piezoelectric micropumps are described briefly.

One-step fabrication of a tunable nanofibrous well insert via electrolyte-assisted electrospinning

The integration of the Transwell® assay with an electrospun nanofiber membrane shows a significant potential in chemotactic assays and co-culture models, but the complicated integration processes often limit its utilization. Here, we present a one-step fabrication process of a nanofibrous well insert by adopting electrolyte-assisted electrospinning, named ELES. The utilization of ELES, which introduced the electrolyte solution as a temporal collector, enabled the facilitation of not only the fabrication of a free-standing electrospun polycaprolactone (PCL) nanofiber on the bottom opening of a well insert wall but also the spontaneous integration between the nanofiber membrane and the well insert wall in a one-step process. The versatility of this approach was demonstrated by modulating the diameter of PCL nanofibers and thickness of the membrane. The indentation test revealed stable integration between the membrane and the well insert wall. The fabricated nanofibrous well inserts were confirmed as an in vitro cell culture platform with promising cell culture results of mouse brain endothelial cell line (bEnd.3).

Proposal of a peristaltic micropump using dielectric elastomer actuators fabricated by MEMS technology

A peristaltic micropump using dielectric elastomer (DE) actuators is proposed and developed. The peristaltic micropump is designed so that diaphragm-type DE actuators are placed serially on a microchannel and volume changes due to diaphragm-type DE actuators can transfer fluid and pressure. In this report, we propose a novel MEMS process that enables us to place multiple DE actuators on the microchannel. In order to fabricate a DE actuator using a MEMS technology, ultraviolet (UV) curable materials for both compliant electrodes and DE were selected. Poly(3, 4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was used for compliant electrodes. PEDOT:PSS is a polymer mixture of two ionomers and a conductive, transparent polymer. As a DE material, polydimethylsiloxane (PDMS) was used. PDMS is a silicon-based organic polymer and is widely used for the DE. In this research, both PEDOT:PSS and DE modified to have an UV curable property were used. In order to verify the proposed fabrication process, we developed a diaphragm-type DE actuator using UV curable PEDOT:PSS and PDMS. The DE actuator is a disk shape with 10 mm diameter and 0.8 mm thickness. A diaphragm-type DE actuator was fabricated in the order of (1) a bottom cover, (2) a bottom compliant electrode, (3) a DE, (4) a top compliant electrode, and (5) a top cover by using UV curable material patterning. In the driving experiment, we measured an out-of-plane displacement of 55 μm when 2.5 kV was applied to the DE actuator.

Development of a MEMS-based electro-rheological microfinger system with an alternating pressure source

This paper presents a novel MEMS-based electro-rheological (ER) microfinger system with an alternating pressure source for multiple microactuator systems. Based on rectifying alternating flow by the ER microvalves, the ER microfinger system enables half number and small size of supply and return pipes, which is suitable for multiple microactuator systems. The MEMS-based finger part was realized by newly developed PDMS micromolding process featuring high-aspect-ratio and three-dimensional structures. This is the first time demonstration of bi-directional, large-displacement of 1.1 mm and high-speed (rise time of 1.1 s) bending motion of the fabricated 1.6-mm long ER microfinger.

ECF micro hydraulic power source by MEMS-fabricated pentagonal prism electrode arrays

Electro-Conjugate Fluid (ECF) is a kind of functional and dielectric fluid. When a high DC voltage is applied to a pair of electrodes immersed in the ECF, a strong and active jet flow of ECF (ECF jet) is generated between these two electrodes. To satisfy high output power and easy fabrication at the same time, triangular prism and slit electrode (TPSE) pairs for a novel ECF micropump was proposed and developed by MEMS technology based on photolithography with thick photoresist and nickel electroplating. In order to get higher output power density, we propose a novel electrode shape that is called as pentagonal prism electrode array (PPEA) for generating very strong ECF jet with high volume density. Both TPSEs and PPEAs are successfully fabricated by the proposed MEMS technology and ECF micro hydraulic power sources (ECF micropumps) are realized by using them respectively. This paper experimentally investigates ECF jet characteristics of these two kinds of ECF micropumps and compares their performance. The experiment results show that the ECF micropump composed of PPEAs can generate almost same output pressure as that of TPSEs, which means output power density increases two times.

Focus-tunable ECF microlens by MEMS technology

This paper proposes a novel elastomer-based tunable liquid-filled microlens by using an electro-conjugate fluid (ECF) and MEMS technology. The common approach for tuning the elastomer-base microlens is to change the geometry of boundary determined by the control pressure of the chamber by using the external pump, while this paper proposes micropump-inside tunable microlens by using the ECF. ECF is a dielectric fluid that works as a smart fluid, generating a powerful jet flow (ECF jet) when subjected to a high DC voltage. Since ECF jet is generated only with a pair of tiny electrodes, the pumping mechanism can be inside the device. We fabricated the focus-tunable microlens by using the ECF and MEMS technology. The experimental results show us the feasibility of the ECF microlens.