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공경철,최현진,오세훈 제어·로봇·시스템학회 2016 International Journal of Control, Automation, and Vol.14 No.4
The robotic manipulators which are actively interacting with humans should be able to emulate the characteristicsand performance of human body systems. Among various approaches to this end, this paper introduces anovel coordination system to control a two link manipulator in a more intuitive and human-friendly way: the polarcoordinate system to describe the motions of a two-link manipulator and a biarticular actuation mechanism. Thekinematics and dynamics of the two-link manipulator are analyzed utilizing the biarticular actuation mechanismand the polar coordinate system for an effective and convenient expression of the equation of motion inspired bythe musculoskeletal structure of humans, which enables the sophisticated and intuitive control of an end-effector ofa two-link manipulator. The dynamic equation with the proposed coordinate system and biarticular actuation mechanismis formalized into a state space equation, and the state feedback controller is designed based on the derivedstate space dynamics (1) to reject undesired dynamic couplings caused by the inherent mechanical structure and (2)to realize the desired dynamic characteristics at the end-effector. As applications of the proposed method, a positiontracking controller is designed for the end-effector. In addition, for implementation of the proposed method, akinematic Kalman filter is utilized for the best estimation of state variables. The experimental verifications of theproposed method are given in this paper.
공경철,Masayoshi Tomizuka 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.1
Disturbance observer-based control systems often encounter the stability problem due to modeling un-certainties. In such cases, the disturbance observer (DOB) may have to be re-designed by narrowing the bandwidth of the Q-filter to enhance stability robustness, but this approach to stability enhancement deteriorates the performance of DOB. In order to improve robust stability while main-taining the performance of DOB, this paper proposes a method that manipulates the nominal plant model in the DOB; the parameters of the discretized nominal model are optimized to improve robust stability in the discrete time domain. For the optimization of nominal model, it is assumed that the closed-loop poles of DOB are subjected to multiplicative uncertainties, and the maximum allowable magnitude of uncertainties is utilized as the measure of stability robustness. Then, the proposed method changes the location of closed-loop poles to maximize the robustness margin. This paper pro-vides a case study that includes experimental results.
Real-Time Nonlinear Programming by Amplitude Modulation
공경철,Masayoshi Tomizuka 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.4
The nonlinear programming (NLP) is an optimization technique that minimizes arbitrary nonlinear cost functions. To apply the NLP to real-time applications, however, the estimation of the gradient of the cost function is remained as a challenge. The extremum-seeking control (ESC) optimizes the cost functions in real-time, but it involves the complicated design of filters for simultaneous estimation of the gradient. In this paper, a complementary method that optimizes an arbitrary multi-variable cost function in real-time is proposed. Taking the advantages of both NLP and ESC, the variables are updated by the steepest descent method of NLP, while the gradient of the cost function is continuously estimated by the amplitude modulation as in ESC. Unlike the ESC, the proposed method does not require the design of complicated filters. The optimization performance is verified by simulations on time-varying and noisy cost functions, as well as automatic controller tuning applications.
공경철(Kyoungchul Kong),전도영(Doyoung Jeon) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
This paper proposes a tendon-driven exoskeletal power assistive device to reduce the problem of the existing exoskeletal power assistive equipment. In addition, this paper suggests a caster walker, which can be moved by pushing, in order to carry heavy peripheral devices and maintain stable balance of the user at the same time. A muscle fiber expansion signal is used to control this proposed tendon-driven exoskeletal assistive device in order to compensate for the delay time of a motor and perform an easy assistance by sensing the user's action in advance. The muscle fiber expansion signal has the characteristics that the signal is ahead of the action and in proportion to joint torque.
공경철(Kyoungchul Kong),차진훈(Jinhoon Cha),전도영(Doyoung Jeon),조동일(Dong-il Dan Cho) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Recently the technology of capsule endoscopy has been developed dramatically and many researchers are making efforts to combine surgical function into the capsule endoscope. In this paper, the micro biopsy device which is a part of the capsule endoscope is proposed. The proposed device consists of a trigger with paraffin block, rotational tissue-cutting razor with a torsion spring, and controller. They are designed to operate sequentially so that the tissue sampling, sealing, and fixing are achieved in one operation. It becomes possible for the capsule endoscope to get sample tissue inside the small intestine which can not be reached by a conventional biopsy device. Experiments were performed with the small intestine of a cow and rabbit. In conclusion, the tissue samples of 1.0㎜ long were extracted successfully by the proposed biopsy device of the capsule endoscope.
공경철(Kyoungchul Kong),전도영(Doyoung Jeon) 한국정밀공학회 2005 한국정밀공학회 학술발표대회 논문집 Vol.2005 No.10월
Though the technology on the ultra-precise machining has been developed intensively, the high speed and high precision for large machining range is still very hard to achieve. The linear motor system for the universal machining center is proper for high speed and high precision, but it has drawback of sensitivity to disturbance. In this research, two degrees of freedom controller based on the zero phase error tracking controller (ZPETC) and disturbance observer are proposed to improve the tracking performance and dynamic stiffness of linear motor system. The proposed controller is verified in simulations and experiments on a nano-positioner system, and the experimental result shows that the tracking performance improved. In addition, the PID optimization method is proposed for the commercialized controller such as the PMAC based system. The tracking as well as impedance is included in the cost function of optimization.