Chang-Doo Kee

Electrospun Fullerenol-Cellulose Biocompatible Actuators

Though there are many stimuli-responsive polymer actuators based on synthetic polymers, electroactive natural biopolymer actuators are very rare. We developed an electrospun fullernol-cellulose biocompatible actuator with much lower power consumption and larger electromechanical displacement in comparison with a pure cellulose acetate actuator. Morphology of the electrospun membranes resembles the nanoporous structure of extracellular matrix in natural muscles. Presence of minute concentrations of fullerenol leads to sharp increase in the degree of crystallinity and substantial increase in tensile strength of membranes. Chemical interactions between cellulose acetate and fullerenols are confirmed by three shifts in carboxylate, carboxy, and carbonyl linkages from the Fourier-transform infrared spectrometry. Much larger tip displacement, nearly 3-fold even at 0.5 wt % fullerenol content, was observed with much lower power consumption under both alternating and direct current conditions.

Electro-active hybrid actuators based on freeze-dried bacterial cellulose and PEDOT:PSS

We report a high-performance electro-active hybrid actuator based on freeze-dried bacterial cellulose and conducting polymer electrodes. The freeze-dried bacterial cellulose, which has a sponge form, can absorb a much greater amount of ionic liquid, which is a prerequisite for dry-type and high-performance electro-active polymers. In addition, the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conducting layers are deposited on the top and bottom surfaces of the freeze-dried bacterial cellulose using a simple dipping and drying method. The results show that the freeze-dried bacterial cellulose actuator with conducting polymer electrodes has a much larger tip displacement under electrical stimuli than pure bacterial cellulose actuators with metallic electrodes. The large bending displacement of the freeze-dried bacterial cellulose actuator under low input voltage is due to the synergistic effects of the ion migration of the dissociated ionic liquids inside the bacterial cellulose and the electrochemical doping processes of the PEDOT:PSS electrode layers.

Novel electroactive PVA-TOCN actuator that is extremely sensitive to low electrical inputs

A novel electroactive biopolymer actuator was developed based on a cross-linked ionic networking membrane of TEMPO-oxidized bacterial cellulose nanofibers (TOCNs) and polyvinyl alcohol (PVA). Ionic liquids were added to develop an air-working artificial muscle and to enhance the performance of the PVA-TOCN actuator. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conducting layers were deposited on the top and bottom surfaces of the PVA-TOCN membrane via a simple dipping and drying method. The electroactive PVA-TOCN actuator under both step and harmonic electrical inputs shows much larger tip displacements and faster bending deformation than the pure TOCN actuator. The cross-linking reaction between PVA and TOCN was observed in the Fourier transform–near-infrared (FT-IR) spectrum of the PVA-TOCN networking membrane. Scanning electron microscopy (SEM), x-ray diffusion (XRD), thermogravimetric analysis (TGA) and tensile and ion conductivity testing results for the PVA-TOCN membrane were compared with those of pristine TOCN. Most important, the PVA-TOCN actuator shows much larger bending deformation under even extremely low input voltages, and this could be attributed to the cross-linking mechanism and the greater flexibility resulting from the synergistic effects between PVA and TOCN.

Multi-Range Approach of Stereo Vision for Mobile Robot Navigation in Uncertain Environments

The detection of free spaces between obstacles in a scene is a prerequisite for navigation of a mobile robot. Especially for stereo vision-based navigation, the problem of correspondence between two images is well known to be of crucial importance. This paper describes multi-range approach of area-based stereo matching for grid mapping and visual navigation in uncertain environment. Camera calibration parameters are optimized by evolutionary algorithm for successful stereo matching. To obtain reliable disparity information from both images, stereo images are to be decomposed into three pairs of images with different resolution based on measurement of disparities. The advantage of multi-range approach is that we can get more reliable disparity in each defined range because disparities from high resolution image are used for farther object a while disparities from low resolution images are used for close objects. The reliable disparity map is combined through post-processing for rejecting incorrect disparity information from each disparity map. The real distance from a disparity image is converted into an occupancy grid representation of a mobile robot. We have investigated the possibility of multi-range approach for the detection of obstacles and visual mapping through various experiments.

Effect of viscosity-inducing factors on oxygen transfer in production culture of bacterial cellulose

Bacterial cellulose (BC) production culture requires high oxygen transfer rate (representatively kLa) at a low shear force. Considering that oxygen exhaustion is observed at the latter half of the exponential growth phase where BC production actually begins, it is highly probable that the drastic reduction of kLa (oxygen volumetric transfer coefficient) is caused by the drastic increase of the soluble and insoluble viscous materials. Therefore, we examined the apparent viscosity-inducing materials generated during BC culture and investigated their effects on kLa. Using the saccharified liquid from food waste as the culture medium, we discussed the relationship between the concentration of the generated solid matters, especially BC and the viscosity, the relationship between the BC concentration and kLa, and the correlation between the viscosity and kLa. The relationship between the solid matter (BC), which is the insoluble viscosity-inducing material, and kLa showed that the BC concentration and kLa were in exponentially reciprocal proportion with the linear regression equation. In case of using agar as the soluble viscosity-inducing material, the correlation between the viscosity and kLa showed that the viscosity depending on the agar concentration was in exponentially reciprocal proportion with kLa in both tap water and the saccharified liquid medium. The results indicated that the effect of the BC concentration on kLa was not great in the saccharified liquid medium. As the agar concentration increased in tap water and the saccharified liquid medium, the viscosity was increased and kLa was decreased gradually, showing a linear relation between the logarithm of the viscosity as agar and kLa. In conclusion, the effect of the soluble viscosity on kLa was greater than that of solid matter (BC). Also, it was suggested that the soluble viscosity-inducing matters like agar were rather more effective than kLa in BC production.

Development and Evaluation of the Biomimetic Actuator based on Bacterial Cellulose

Bacterial cellulose based actuator with large displacement was developed for biomimetic robots. Bacterial cellulose has 3D nanostructure with high porosity which was composed of the nanofibers. Freeze dried bacterial cellulose was dipped into ionic liquid solution such as 1-butyl-3-methylimidazolium(BMIMCl) to enhance the actuation performance due to increase the ion-exchange capacity and ionic conductivity. And Poly(3,4-ethylenedioxythiophene)-poly (styrnenesulfonate)(PEDOT:PSS) was used for the electrodes of both side of bacterial cellulose actuator by dipping and drying method. The FT-IR and XRD were conducted to examine the electrochemical changes of developed bacterial cellulose actuator. The biomimetic caudal fin was designed using bacterial cellulose actuator and PDMS to verify the possibility for biomimetic robot. The step and harmonic response were conducted to evaluate the performance of developed biomimetic actuator.

Collision-free path planning of stereo vision based mobile robots using power potential approach

This paper describes power potential approach for the collision-free path planning of stereo-vision based mobile robots. This approach relies on an obstacle detection procedure by stereo matching. We construct the potentials for the robot path planning using sources and sink. The proposed potential distributes sources discretely on the boundaries of obstacles and puts a sink at the goal point and then superpose the power potentials which is defined so that the potential for any one of the source points will have more influence on the robot than the potential for the sink point when the robot is near to source point and the total influence of the source potentials on the robot will be less than that of the sink potential when the robot is more than a defense distance away from the obstacle. We also propose the noble method of escaping from local minima by preserving the directional characteristic of the movement of the mobile robots and using the various potentials simultaneously.

Self-validating sensors with application to a flexible link control system

For the satisfying performance of a control system, design of a controller for the system which meets the required specifications, and the role of its supporting hardware that keeps functioning are equally important. Therefore it is inevitable to keep track of accurate and reliable sensor readings for good controller performance. Among the hardware of a control system sensors are most vulnerable to malfunction. Thus it is necessary to provide physical and analytical redundancy for the sensor measurement outputs to increase reliability against sensor failures. In general the task of detection, identification, and accommodation of sensor failures is widely pursued for this need. In case of sensor faults, they are detected by examining the sensor output values and the correlated or relevant values of the system. And then the types of the faults are identified by the analysis of symptoms of faults. If necessary self-validating sensor values are synthesized according to the types of faults, and then they are used for the controller instead of the raw data. In this paper, a self-validating sensor is applied to the control of a flexible link system with the sensor fault problems in the light sensor module for exact positioning to show the applicability. It is shown that the digital controller can provide a satisfactory loop performance even when the sensor faults occur.

Intelligent data processing of an ultrasonic sensor system for pattern recognition improvements

Though conventional time-of-flight ultrasonic sensor systems are popular due to the advantages of low cost and simplicity, the usage of the sensors is rather narrowly restricted within object detection and distance readings. There is a strong need to enlarge the amount of environmental information for mobile applications to provide intelligent autonomy. Wide sectors of such neighboring object recognition problems can be satisfactorily handled with coarse vision data such as sonar maps instead of accurate laser or optic measurements. For the usage of object pattern recognition, ultrasonic senors have inherent shortcomings of poor directionality and specularity which result in low spatial resolution and indistinctiveness of object patterns. To resolve these problems an array of increased number of sensor elements has been used for large objects. In this paper we propose a method of sensor array system with improved recognition capability using electronic circuits accompanying the sensor array and neuro-fuzzy processing of data fusion. The circuit changes transmitter output voltages of array elements in several steps. Relying upon the known sensor characteristics, a set of different return signals from neighboring senors is manipulated to provide an enhanced pattern recognition in the aspects of inclination angle, size and shift as well as distance of objects. The results show improved resolution of the measurements for smaller targets.