Jaewook Ryu

A ciliary motion based 8-legged walking micro robot using cast IPMC actuators

In this paper, we present a micro robot using IPMC (Ionic Polymer Metal Composite) actuators. The IPMC actuator usually has been fabricated with commercially available ion-exchange polymer with the typical thickness of 100-300 /spl mu/m. By the casting of liquid ion-exchange polymer solution, the thickness of the IPMC actuator could increase up to a few millimeters. Based on the casting method, we could achieve the IPMC actuator that has larger stiffness and produces more generative tip force than the IPMC actuator fabricated with the commercially available solid ion-exchange polymer. A ciliary type 8-legged micro robot using the casting based IPMC actuators is constructed. The ciliary type 8-legged micro robot is 6.5 cm in length and 4.2 cm in width, and 1.5 cm in height and the total weight is 4.4 g with the actuators installed. The IPMC actuators used in this robot have a dimension of 20 mm in length, 4 mm in width and 1.15 mm in thickness. The input voltage to the IPMC actuator is set to /spl plusmn/4 V and the frequencies to the IPMC actuator is varying from 0.2 Hz to 1.0 Hz; with the increment of 0.2 Hz. The walking speed of the micro robot is changed from 3 mm/min to 17 mm/min with the variation of the frequencies.

A ciliary based 8-legged walking micro robot using cast IPMC actuators

We have proposed a prototype model of walking micro robot using IPMC (Ionic Polymer Metal Composite) actuators. The stiffness of IPMC actuator is a key parameter to implement a walking robot. Therefore, the casting process is developed to increase the stiffness of the actuator by controlling thickness of ion-exchange polymer film. The process of fabricating a solid film front liquid state of ion-exchange polymer is difficult since any process parameter and handling material are not disclosed and has to be set by trial and error. The bending characteristics and generative tip force of IPMC actuator under variation of thickness and length of the actuator and voltage input are investigated. Also, mechanical model is derived to predict the generative tip force and displacement of IPMC actuator according to the variation of thickness. With cast film based IPMC actuators, a ciliary type 8-legged micro robot, which can be operated in aqueous surroundings like inside of human body, is constructed and tested. The robot shows good reliability and can reach up to 17 mm/min in speed.

Analysis of mechanical characteristics of the ionic polymer metal composite (IPMC) actuator using cast ion-exchange film

IPMC (Ionic Polymer Metal Composite) is a promising candidate actuator for bio-related applications mainly due to its biocompatibility, soft properties and operation in wet condition. The widely used and commercialized ion-exchange polymer film has limitation in thicknesses, but more various film thicknesses are required for extensive applications. Especially for the enhanced force as an actuator, acquisition of thick film is essential. Various ion-exchange polymer films with thickness of 0.4-1.2 mm have been prepared by casting of liquid ion-exchange polymer. As well, IPMC actuators using cast ion-exchange polymer films have been fabricated and the basic mechanical characteristics such as stiffness, displacement and force were measured and analyzed. These results can be used for the optimized design of actuators for different applications.

Fabrication and Mechanical Characterization of Micro Electro Mechanical System Based Vertical Probe Tips for Micro Pad Measurements

As a result of new developments in semiconductor technology, the number of pads per unit area is increasing and pad arrays are becoming irregular. Therefore, there is an increased need for a versatile probe card to address these issues. We developed a vertical micro electro mechanical system (MEMS) probe tip that is usable in a small pad (approximately 100 µm) and a two-dimensional pad array. The main process used to produce the tip was wafer bonding, silicon etching by deep reactive ion etcher (RIE) and electro-plating. The material of the electro-plated probe tip was an Ni–Co alloy. To optimize the design of the vertical probe tip, we designed various models and measured them in a micro compression and tensile tester. The structural analyses of the probe tip were accomplished using finite element method (FEM) and compared with actual measurement values. In this study, we demonstrated the potential of the vertical probe tip applied to a small area with the over drive (O.D.) of 10–40 µm and the contact force of 1–8gf.

Potential of Thermo-Sensitive Hydrogel as an Actuator

To use poly-N-Isopropylacrylamide (PNIPAAm) as an actuator, we investigated its general characteristics such as swelling/deswelling ratio, response time and swelling force. Through out the variation, a change in volume of over 600% of PNIPAAm and a force generation of gram force order was obtained. Furthermore, we measured the significant change of friction caused by phase transition phenomena that is hydrophobic and hydrophilic. Surface condition that influences friction force can be reversed from swelling phase to deswelling phase by controlling the temperature of PNIPAAm. To verify the potential application of PNIPAAm using this characteristic, we compared its friction force under glass and small-intestine tissue of a pig. It was found that the level of friction differs significantly depending on phase change of PNIPAAm. Based on this knowledge, we could conclude that PNIPAAm can be applied to the stopping mechanism of in-body locomotion in order to replace the clamping mechanism of in body robot for locomotion on the gastrointestinal tract.

Thickness Characteristics and Improved Surface Adhesion of a Polypyrrole Actuator by Analysis of Polymerization Process

Characterizing electrochemical polymerization of polypyrrole film on a substrate depends on many parameters. Among them, potential difference and cumulative charges play important role. The level of potential difference affects the quality of the polypyrrole. On the contrary, cumulative charge affects the thickness of the polypyrrole. The substrate surface is adjusted physically and chemically by treating with sandblasting and the addition of thiol for surface adhesion improvement. Experimental results show that the sandblasted and thiol treated substrate provides better adhesion than non-sandblasted and non-thiol treated substrate.

Contractile force measurement of cardiomyocytes using a hybrid biopolymer microcantilever array

This paper reports a method for quantitative and real-time contractile force measurement of cardiomyocytes using a hybrid biopolymer micracrocantilever array. We designed and fabricated a hybrid biopolymer microcantilever array made of PDMS (polydimethylsiloxane) elastomer to overcome the above problems. Culturing primary cardiomyocytes on PDMS microcantilever array leads to self-organization of cells on the structure, which enables to make massively paralleled arrangement of cells in the hybrid system.

Design and fabrication of a large-deformed smart sensorized polymer actuator

The demands for actuators featuring biomimetic properties, such as high power density, large strain, and biocompatibility are growing in microrobotics and bioengineering. PPy is one candidate for biomimetic actuator since it is biocompatible, easy to be fabricated by MEMS technique, has large strain, and consumes low energy. In this paper, a novel sensorized polymer actuator which can measure its bending motion precisely with real-time is presented. It is fabricated by integrating polypyrrole(PPy) actuator with polyvinylidenefluoride(PVDF) sensor. Since PVDF is also biocompatible, stable to chemical, flexible, and polymer sensor, it could be well combined with PPy actuator. In experimental results, the proposed actuator shows the feasibility which can not only be actuated with large strain (a few mm) but also produce meaningful signals which made from bending motion and vice versa.