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Dong-Il Dan Cho,Hyung Jung Yoo Institute of Electrical and Electronics Engineers 2015 Journal of microelectromechanical systems Vol. No.
<P>A drug delivery system is used for targeting drugs to specific cells. Various drug carriers, that also reduce the side effects of unbound drugs, have been introduced and commercialized in the pharmaceutical field. Among them, synthetic biodegradable polymers have received much attention attributed to their low toxicity, controllable biodegradation rates, manufacturability, and low costs. This paper reviews the salient characteristics of biodegradable polymers as drug carriers and their microfabrication methods. The reviewed microfabrication methods include laser micromachining, rapid prototyping, replication, emulsification, microfluidic fabrication, and X-ray-lithography-based methods. For these microfabrication methods, critical dimensions, feature variety, solvent compatibility, production throughput, and tooling requirements are also summarized.</P>
IEEE 2015 IEEE Transactions on Biomedical Engineering Vol.62 No.1
<P>Retinal prosthetic devices stimulate retinal nerve cells with electrical signals proportional to the incident light intensities. For a high-resolution retinal prosthesis, it is necessary to reduce the size of the stimulator pixels as much as possible, because the retinal nerve cells are concentrated in a small area of approximately 5 mm × 5 mm. In this paper, a miniaturized biphasic current stimulator integrated circuit is developed for subretinal stimulation and tested in vitro. The stimulator pixel is miniaturized by using a complementary metal-oxide-semiconductor (CMOS) image sensor composed of three transistors. Compared to a pixel that uses a four-transistor CMOS image sensor, this new design reduces the pixel size by 8.3%. The pixel size is further reduced by simplifying the stimulation-current generating circuit, which provides a 43.9% size reduction when compared to the design reported to be the most advanced version to date for subretinal stimulation. The proposed design is fabricated using a 0.35 μm bipolar-CMOSDMOS process. Each pixel is designed to fit in a 50 μ m × 55 μm area, which theoretically allows implementing more than 5000 pixels in the 5 mm × 5 mm area. Experimental results show that a biphasic current in the range of 0 to 300 μA at 12 V can be generated as a function of incident light intensities. Results from in vitro.</P>
Dong-Hoon Yi,Tae-Jae Lee,Dong-Il “Dan” Cho 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10
This paper presents an improved inverse perspective mapping (IPM) technique based on a virtual-vertical plane model for obstacle detection. The conventional IPM based obstacle detection has a problem that it is difficult to determine whether the IPM based detected pixels are from real obstacle or caused by noise. Small errors in model, unknown camera motion, and colorful patterns of ground cause noises which are actually the ground region that is detected as an obstacle. It can be interpreted as false positives. Furthermore, there are few detections on homogeneous patterned obstacles such as an unicolor box. This work proposes a new simple method for distinguishing the noise and real obstacle in an image when IPM based detection method is used. A vertical plane model based detected pixel is checked after the IPM based detection. The results show that the real obstacles including a homogeneous patterned unicolor box are detected as obstacles, and A4-size black paper on a floor which is not an obstacle is not detected as an obstacle.
Afocal Optical Flow Sensor for Mobile Robot Odometry
Dong-Hoon Yi,Tae-Jae Lee,Dong-Il “Dan” Cho 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10
This paper presents an application of an afocal optical flow sensor (AOFS) for mobile robot navigation. The OFS-based odometry is advantageous for mobile robots because it is not affected by wheel slippage. However, the changes in vertical height result in systematic errors when estimating the moving distance of robots moving on uneven surfaces. This paper presents an application of an AOFS module to improve this vertical-height sensitivity. To evaluate the proposed system performance, two kinds of experiments are performed: on a bare laminate floor and on the laminate floor that is partially covered with an area carpet. The test area is 150 cm x 150 cm size. For the bare laminate floor case where no slip occurs, the localization error of the developed system is 0.2%. The error using a conventional OFS module, encoders, and gyroscope combination is also 0.2%. For the case where the laminate floor is partially covered with an area carpet, the localization error of the developed system is 0.7%. The error using a conventional OFS module, encoders, and the gyroscope is 2.9%.
Tae-il Kim,Ji-Seok Han,Tae-Ho Oh,Young-Seok Kim,Hyun-Taek Lim,Sang-Hoon Lee,Dong-Il “Dan” Cho 제어로봇시스템학회 2019 제어로봇시스템학회 국제학술대회 논문집 Vol.2019 No.10
This paper presents an application of a discretization method with a new phase compensation technique for adaptive-notch-filter (ANF) based resonance suppression in an actual industrial servo system. The ANF includes a frequency estimator which estimates the frequency of the vibration in the input signal in real time and automatically filters it out. Because the ANF is designed in the continuous-time domain, a discretization process is required for digital implementation. However, the discretization error may restrain the performance of the ANF, especially when the resonance frequency is near the Nyquist frequency. This paper develops the discretization method for the ANF that combines a modified bilinear transform method with a compensation method for the frequency and damping ratio warping, and a phase compensation technique. The proposed method reduces the magnitude and phase error near Nyquist frequency, and thus the discretized ANF can suppress the resonance in relatively high-frequency. Experiments using an industrial servo system are performed to show the improved frequency estimation performance of the developed ANF.
A new accurate discretization method for high-frequency component mechatronics systems
Kim, Tae-Il,Han, Ji-Seok,Oh, Tae-Ho,Kim, Young-Seok,Lee, Sang-Hoon,Cho, Dong-Il “Dan” Pergamon Press 2019 Mechatronics Vol.62 No.-
<P><B>Abstract</B></P> <P>Modern mechatronics systems are implemented digitally. However, the magnitude and phase errors caused in the discretization process severely restrain the control performance in systems with high-frequency components where only a few sampled data points are available per period. This paper presents a new accurate discretization method for mechatronics systems that provide good performance even when intrinsic frequency components are close to the Nyquist frequency which is one-half of the sampling frequency. The bilinear transform method is most commonly used, but it causes oscillations when the initial state error of the output is not zero or when rapid changes occur in the input signal. Several variations of the bilinear transform method have been proposed to improve these problems, but as a tradeoff, they introduce large magnitude and/or phase errors at high frequencies. In this paper, a more accurate discretization method is developed, which combines a modified bilinear transform method with a new method to compensate for the frequency and damping ratio warping caused by approximate discretization. The proposed method reduces the magnitude and phase errors over the entire frequency range. The proposed method is experimentally evaluated in a mechatronics system with a mechanical resonance frequency that is about 0.6 times the Nyquist frequency.</P>
Satnesh Singh,Dong-il “Dan” Cho 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.11
This paper investigates the problem of a decoupled disturbance compensator (DDC) based stochastic sliding mode control (SMC) design for discrete linear time-invariant systems. In the developed method, the actual disturbance is estimated using the DDC method to design the control input and stabilize the system. The proposed method allows the disturbance compensation to be modified separately from the control input, since the two inputs of system are completely decoupled. To demonstrate the effectiveness of the DDC based discrete-time stochastic SMC, its performance is compared with that of the existing methods using the simulation results. Finally, experimental results are presented to demonstrate the effectiveness of the proposed method.
Hyun-Taek Lim,Tae-il Kim,Ji-Seok Han,Tae-Ho Oh,Young-Seok Kim,Sang-Hoon Lee,Dong-Il “Dan” Cho 제어로봇시스템학회 2019 제어로봇시스템학회 국제학술대회 논문집 Vol.2019 No.10
This paper develops an overshoot enhancement method of discrete-time sliding mode control (DSMC) with a decoupled disturbance compensator (DDC) subject to ramp-type disturbances. The original DSMC with DDC method has several features such as excellent trajectory tracking, easy implementation, and robustness to disturbances. However, when the system suffers from ramp-type disturbance such as viscosity friction, position error remains and overshoot arises at the end of motion. They are highly undesirable in position control applications such as robot manipulators and manufacturing systems. In this paper, a new structure of DSMC with DDC is developed to reduce the overshoot. An outer loop is added to the original DSMC with DDC structure, which provides asymptotic convergence of the error state subject to ramp-type disturbance. A transfer function is derived to analyze the overshoot performance. Experiments are performed on an industrial linear motor system to demonstrate the improved overshoot performance.
Ji-Seok Han,Tae-Il Kim,Ji-Ho Park,Tae-Ho Oh,Ji-Hyung Lee,Sang-Oh Kim,Sang-Sub Lee,Sang-Hoon Lee,Dong-Il “Dan” Cho 제어로봇시스템학회 2017 제어로봇시스템학회 국제학술대회 논문집 Vol.2017 No.10
This paper presents a method to enhance robustness in sliding mode control (SMC) combined with decoupled disturbance compensator (DDC). More specifically, a gain selection method for the DDC in industrial servo systems with unknown inertia is developed. The SMC with DDC method is a well-known robust control method which is effective for slowly-varying and bounded disturbances. However, when the gain of the DDC is improperly selected, a large error of the inertia parameter can lead to poor performance such as a large overshoot in the motor position. This paper shows that the disturbance caused by an uncertain inertia can produce a pair of complex conjugate eigenvalues of the error dynamics in the z-domain, which results in the overshoot in both position and velocity. In addition, utilizing this analysis, a gain selection method of DDC is proposed when the ratio of the actual inertia to the nominal inertia is assumed to be bounded. The analytical results are further supported using experiments performed on industrial servo systems with a ball-screw load and a belt load.