Uhn Joo Na

A New 6-DOF Haptic Device for Teleoperation of 6-DOF Serial Robots

A new 6-DOF parallel haptic device is developed and presented in this paper. The haptic device consists of two 3-DOF parallel structures connected with a steering handle. The design satisfies requirements of low inertia, quick motion, large orientation angles, and large applied torques. Kinematics for position and differential motion is analyzed for the 6-DOF haptic device. Static force relation between the user force and motor torque is also analyzed and implemented on the controller. The control system for the teleoperation of 6-DOF serial robot is developed. The closed loop impedance force control system is analyzed and realized on the digital controller. Tele-operation of a 6-DOF serial robot using this haptic device is demonstrated. Experiments show that dynamic forces caused by the haptic device are well compensated with the closed loop force control.

Remote control system of a 6 DOF underwater robot

This paper presents a remote control system of a 6 DOF underwater robot using two acoustic transducers, while radio and optical waves are not used because they are strongly attenuated in a complex environment as water. Underwater robots can be controlled by cables limited by distances, environment conditions, and not flexible. Therefore, it is necessary to develop a remote control system for underwater robots. These robots are used to discover, investigate environment parameters under rivers, canals, and seashores. This paper includes two main parts: underwater communication and control system. The communication is designed with a transmitter and a receiver. The transmitter receives commands from a control station and then generates acoustic wave signals, in which usable frequencies are 8-16 KHz. The receiver receives signals from the acoustic transducer and after processing, they are converted in to pulse signals. Two coding methods for communicating are frequency coding and pulse coding which are proposed and compared to evaluate their advantages and disadvantages. Decoded pulse signals are used to control the underwater robot. Fuzzy P+ID algorithm is proposed to control depths, heading and directions of the underwater robot. Experiment results show that the signal is well processed and the underwater robot can be effectively operated.

Adaptive neural fuzzy control for robot manipulator friction and disturbance compensator

This paper presents an application of an adaptive neuro-fuzzy controller for compensating friction and disturbance effects on robot manipulators. The frictions and disturbances are important parts of the dynamic system of a robot manipulator. However, they are highly nonlinear and not easily modeled. Feedback linearization control combined with PD type fuzzy control and adaptive neural network control are proposed to control robot manipulators with unmodeled frictions. The feedback linearization control is designed to control the trajectory of the robot manipulator while the PD type fuzzy control is added as a parallel controller to control frictions and disturbances. This fuzzy control ensures that good tracking control is maintained even if some modeling error, disturbance, noises exist. The neural network can also be trained with experimental data for the frictions and disturbances. Simulations show that the joint positions are well controlled under wide variation of operation conditions and existences of uncertainties.

Tele-operation of a 6-DOF serial robot using a new 6-DOF haptic interface

This paper presents the kinematic analysis of a new 6-DOF haptic interface and control system analysis for the tele-operation of 6-DOF serial robot. The haptic interface consists of two 3-DOF parallel structures connected with a steering handle. The design satisfies requirements of low mass moment of inertia, quick motion, big rotation, and large applied torques. Kinematics for position and differential motion are developed for the 6-DOF haptic interface. Tele-operation of a 6-DOF serial manipulator using this haptic interface is demonstrated. Experiment results provide comparison of trajectories and forces/torques between 6-DOF haptic interface and 6-DOF serial robot on the Cartesian space.

Fault Tolerant Control of Magnetic Bearings with Force Invariance

A magnetic bearing even with multiple coil failure can produce the same decoupled magnetic forces as those before failure if the lemaining coil currents are properly redistributed This faulttolerant, force invariance control can be achieved with simply leplacing the distribution matrix with the appiopnate one shortly after coils fail, without modifying feedback control law The distribution gain matrix that satisfies the necessary constraint conditions of decoupling linearized magnetic foices is determined with the Lagrange Multiplier optimization method

Adaptive impedance control of a haptic teleoperation system for improved transparency

An adaptive impedance force control model of a haptic device for teleoperation is analyzed. A new force control model of the haptic device is constructed to investigate the dynamic effects of the user hand. Movements of the user hand may work as a force disturbance to the haptic force control system so that it is difficult to realize a good transparency. A model reference adaptive control (MRAC) is proposed to improve the transparency of the haptic device. A third order reference model with relative degree one is selected to satisfy requirements of rise time, settling time and overshoots. Experiments show that the force tracking performances are improved while force disturbances from the user hand are well compensated.

Design and control of energy efficient magnetic bearings

A new energy efficient magnetic bearing is developed. The magnetic forces to current inputs relation for the new bearing is analyzed with both 1-D magnetic circuit and 3-D magnetic field modeling. The test rig for the new magnetic bearing is constructed. A digital controller for stable levitation of rotor-magnetic bearing system is implemented on a dSPACE controller. Energy efficient magnetic bearings may find great use in some applications such as flywheel energy storage systems.

Fault Tolerant Homopolar Magnetic Bearings with Flux Invariant Control

The theory for a novel fault-tolerant 4-active-pole homopolar magnetic bearing is developed. If any one coil of the four coils in the bearing actuator fail, the remaining three coil currents change via an optimal distribution matrix such that the same opposing pole, C-core type, control fluxes as those of the un-failed bearing are produced. The hompolar magnetic bearing thus provides unaltered magnetic forces without any loss of the bearing load capacity even if any one coil suddenly fails. Numerical examples are provided to illustrate the novel fault-tolerant, 4-active pole homopolar magnetic bearings.

Bidirectional homopolar magnetic bearings with fault tolerant capability

A fault tolerant current distribution scheme is presented for a bi-directional magnetic bearing with reduced eddy currents and cross coupled stiffness. The bearing continues to function normally even though one coil among four radial coils and one coil of two axial coils fail. The dynamic properties and load capacity remain unchanged for the suggested fault tolerant control scheme at the cost of additional hardware such as a decoupling choke, additional DSP channels, and power amplifiers. A one-dimensional circuit that represents the bi-directional bearing is utilized to obtain the optimal bearing parameters such as the radial pole face area, number of coil turns, and permanent magnet size.

Design of Flux Invariant, Fault Tolerant Homopolar Magnetic Bearings

The theory for a fault-tolerant 4-active-pole homopolar magnetic bearing is developed. If any one coil of the four coils in the bearing actuator fail, the remaining three coil currents change via an optimal distribution matrix such that the same opposing pole, C-core type, control fluxes as those of the un-failed bearing are produced. The homopolar magnetic bearing thus provides unaltered magnetic forces without any loss of the bearing load capacity even if any one coil suddenly fails