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나언주(Uhn Joo Na),부민훙(Vu Minh Hung) 한국생산제조학회 2011 한국생산제조시스템학회 학술발표대회 논문집 Vol.2011 No.4
This paper presents force control systems of a new 5-DOF haptic interface for a 5-DOF serial robot. The haptic interface was designed to operate with three translations and three rotations. First open loop force control is implemented to demonstrate the feed forward static force control based on Jacobian matrix. The error of open loop control can be reduced by a PD controller. However this controller does not show good performance if the forces change directions rapidly. In addition the joint frictions and dynamics degrades the controller performance. A master-slave control system for the haptic interface and serial robot is presented.
나언주(Na, Uhn Joo) 한국소음진동공학회 2013 한국소음진동공학회 논문집 Vol.23 No.5
A new linearization model for MR dampers is analyzed. The nonlinear hysteretic damping force model of MR damper can be modeled as a hyperbolic tangent function of currents, positions, and velicities, which is an algebraic function with constant parameters. Model parameters can be identified with numerical method using experimental force-velocity-position data obtained from various operating conditions. The nonlinear hysteretic damping force can be linearized with a given slope of damping coefficient if there exist corresponding currents to compensate for the nonlinearity. The corresponding currents can be calculated from the inverse model when the given linear damping force is set equal to the nonlinear hysteretic damping force. The linearization controller is realized in a DSP controller such that the corresponding currents to satisfy a given damping coefficient should be calculated. Experiments show that the current inputs to the MR damper produce linearized damping force with a given slope of the damping coefficient.
전자석 바이어스 Diskless반경방향-축방향 일체형 자기 베어링 해석
나언주(Na, Uhn-Joo) 한국소음진동공학회 2012 한국소음진동공학회 논문집 Vol.22 No.10
The theory for a new electromagnetically biased diskless combined radial and axial magnetic bearing is developed. A typical magnetic bearing system is composed of two radial magnetic bearings and an axial magnetic bearing. The axial magnetic bearing with a large axial disk usually limits rotor dynamic performance and makes assembling and disassembling difficult for maintenance work. This paper proposes a novel electromagnet biased integrated radial-axial magnetic bearing without axial disk. This integrated magnetic bearing uses two axial coils to provide the bias flux to the radial and axial air gaps of the combined bearing. The axial magnetic bearing unit in this combined magnetic bearing utilizes reluctance forces developed in the non-uniform air gaps such that the axial disk can be removed from the bearing unit. The 4-pole homopolar type radial magnetic bearing unit is also designed and analyzed. Three dimensional finite element model for the bearing is also developed and analyzed to illustrate the diskless combined magnetic bearing.
자속 분리법을 이용한 동극형 자기베어링의 고장강건 제어
나언주(Na, Uhn-Joo) 한국소음진동공학회 2007 한국소음진동공학회 논문집 Vol.17 No.11
The theory for a fault-tolerant control of homopolar magnetic bearings is developed. New coil winding law is utilized such that control fluxes are isolated for an 8-pole homopolar magnetic bearing. Decoupling chokes are not required for the fault tolerant magnetic bearing since C-core fluxes are isolated. If some of the coils or power amplifiers suddenly fail, the remaining coil currents change via a distribution matrix such that the same magnetic forces are maintained before and after failure. Lagrange multiplier optimization with equality constraints is utilized to calculate the optimal distribution matrix that maximizes the load capacity of the failed bearing. Some numerical examples of distribution matrices are provided to illustrate the theory. Simulations show that very much the same dynamic responses (orbits or displacements) are maintained throughout failure events while currents and fluxes change significantly.
전자석 바이어스 반경방향-축방향 일체형 자기베어링 해석
나언주(Na, Uhn-Joo) 한국소음진동공학회 2010 한국소음진동공학회 논문집 Vol.20 No.11
The theory for a new electromagnetically biased combined radial and axial magnetic bearing is developed. This combined magnetic bearing uses two axial coils to provide the bias flux to the radial and axial air gaps of the combined bearing. One dimensional magnetic circuit model for this combined magnetic bearing is developed and analyzed such that flux densities and magnetic forces can be obtained. Three dimensional finite element model for the bearing is also developed and analyzed. Numerical analysis shows that the calculated magnetic forces from 1D model are well matched with those from the finite element model.
나언주(Uhn Joo Na) 한국소음진동공학회 2016 한국소음진동공학회 논문집 Vol.26 No.7
A new hybrid permanent magnet biased magnetic levitation actuator (maglev) is developed. This new maglev actuator is composed of two C-core electromagnetic cores separated with two permanent magnets. Compared to the conventional hybrid maglev actuators, the new actuator has unique flux paths such that bias flux paths are separated with control flux paths. The control flux paths have minimum reluctances only developed by air gaps, so the currents to produce control fluxes can be minimized. The gravity load can be compensated with the permanent magnet bias fluxes developed at off-centered air gap positions while external disturbances are controlled with control fluxes by currents. The consumed power to operate this levitation system can be minimized. 1-D magnetic circuit model is developed for this model such that the flux densities and magnetic forces are extensively analyzed. 3-D finite element model is also developed to analyze the performances of the maglev actuator.