This paper presents a design method of transparency optimized feedback controller with robustness for a parallel 6-DOF haptic system. A disturbance observer is employed to eliminate coupling effects that exist in a mechanically coupled structure. A performance index for the transparency is defined by admittance matching, and by solving the H/sub 2/ optimal problem. The optimal solution that minimizes the performance index is obtained.

In this paper, a new 6-DOF parallel haptic master device is proposed. Many existing haptic devices require large power due to having floating actuator and also have small workspaces. The proposed new mechanism is relatively light, as it employs nonfloating actuators and has large workspace. Kinematic analysis and kinematic optimal design problem is performed for this mechanism. Dexterous workspace, global isotropic index, and global maximum force transmission ratio are considered as kinematic design indices. To deal with such multicriteria optimization problem, composite design index is employed. Actuator sizing for this mechanism is also carried out.

Underwater robotic vehicles (URV) have been employed for mobility, and robot manipulators attached to the underwater vehicle play the role of manipulation. URV motions are determined by inherent dynamic couplings between active and passive joints. Furthermore, the control problem becomes complex since there should be considered many hydrodynamic terms as well as intrinsic model uncertainties. To cope with these difficulties, we propose a disturbance observer-based robust control algorithm for underwater manipulators with passive joints. The proposed control algorithm is able to treat an underactuated system as a pseudo-active system in which passive joints are eliminated. Also, to realize a robust control method, a nonlinear feedback disturbance observer is applied to each active joint. A four-jointed underwater robotic system with one passive joint is considered as an illustrative example. Through simulation, it is shown that the proposed control algorithm has good position tracking performances even in the presence of several external disturbances and model uncertainties.

A transparency-optimized feedback controller with robustness is designed for a multi-axis haptic device, where a disturbance observer is employed to decouple the coupling effect existing in the multi-axis haptic device. A performance index for the transparency is defined from the viewpoint of admittance matching, and the optimal solution minimizing the performance index is obtained by solving an H/sub 2/ optimal problem. To implement a stabilizing haptic controller robust to parametric uncertainties of the haptic device, a robust stable condition using an H/sub /spl infin// norm derived from small gain theorem is proposed. The effectiveness of the proposed haptic control scheme has been experimentally verified for a virtual wall characterized by stiffness and damping properties.

In this paper, a force estimation method is proposed for force control without force sensor. A disturbance observer is applied to each joint of an n degrees of freedom manipulator to obtain a simple equivalent robot dynamics being represented as an n independent double integrator system. To estimate the output of disturbance observer due to internal torque, the disturbance observer output estimator (DOOE) is designed, where uncertain parameters of the robot manipulator are adjusted by the gradient method to minimize the performance index which is defined as the quadratic form of the error signal between the output of disturbance observer and that of DOOE. When the external force is exerted, the external force is estimated by the difference between the output of disturbance observer and DOOE. A force controller is designed for force feedback control employing the estimated force signal. Several numerical examples and experimental results are illustrated for a 2-axis direct drive robot manipulator.

In this paper, a fuzzy force control algorithm is suggested for commercialized industrial robots equipped with the position servo drives, where control rules of the proposed fuzzy controller are changed according to the magnitude of environmental stiffness in such a way that good force response is maintained regardless of changes of environmental stiffness. Specifically, some fuzzy control rules are designed for several representative environmental stiffness values, and then a control action for a given arbitrary environmental stiffness value is decided by a fuzzy interpolation method. To show the validity of the proposed fuzzy controller, several experimental results are illustrated, where a 5-axis articulated robot manipulator equipped with the wrist force/torque sensor system and our prototype dual robot controller are employed.>