This paper proposes a 6 degree of freedom (DoF) manipulator for haptic application. The proposed haptic device, named GHap, is designed based on the four-bar-linkage mechanism for linear motion with the ring-type gimbal mechanism. To improve the force display ability, the device is designed to compensate the gravity force of the manipulator by its own weight. The conceptual mechanical design is compared by placing the third joint, which controls the four-bar mechanism, in two different configurations. The forward kinematics and the jacobian of GHap are presented. Finally, the gravity compensation method and open-loop force display performance of the proposed haptic device are validated by an experiment with the GHap prototype.

This paper revisits computed torque method for robot manipulators and aims at developing its new framework based on the$L_{1}$robustness, in which the$L_{\infty}$norm together with its induced norm is employed to characterize model uncertainties and a performance measure. More precisely, we consider the$L_{1}$robust stability and performance for a given robot manipulator with a computed torque controller. We first show that the modelling errors in the computed torque method can be divided into an exogenous disturbance and a multiplicative model uncertainty, which are bounded in terms of the$L_{\infty}$norm and its induced norm, respectively. It is next shown that the robot manipulator with the computed torque controller can be equivalently represented by an interconnection of a continuous-time linear time-invariant (LTI) nominal plant and a stabilizing controller together with the$L_{\infty}$-induced norm bounded model uncertainty. Based on the interconnected representation, the$L_{1}$robust stability condition and an upper bound of the$L_{1}$performance against the exogenous disturbance with respect to all model uncertainties in a class of a bounded$L_{\infty}$-induced norm are dealt with by using the small-gain theorem. Finally, the effectiveness of the theoretical results is demonstrated through some experiment results.

In this paper, we consider the L1optimal proportional-derivative (PD) controller synthesis by which the L∞gain of trajectory tracking systems can be reduced. The notion of input-to-state stability (ISS), which has been equipped with the L2norm of a vector-valued signal, plays important roles in evaluating the effect of disturbances on the system states. In connection with this, we first redefine the conventional ISS with the L∞norm to deal with bounded persistent disturbances because the disturbances should be mathematically regarded as elements of the L∞space. A tractable model for trajectory tracking control of robot systems is then given by using ideas of extended disturbance and composite error. We next introduce a design method of the L1optimal PD controller for such a model, by which the trajectory tracking system satisfies the redefined ISS and the L∞gain is less than a performance level γ. Finally, we examine the effectiveness of the design method through experimental results for a typical robot manipulator.

This paper presents a novel haptic device, named VirtuaPower, having abilities of 6 degrees of freedom (DOF) position measurement with a high-force display capability and wide workspace. The VirtuaPower is designed as a parallel mechanism with double in-parallel supporting chains. The mechanical design is presented with constraints and space Jacobians. The workspace and force display capability are computed via kinematic analysis. The VirtuaPower has a wide workspace up to 1 m3 (semicylinder, diameter 1.8 m × height 1.0 m). Moreover, the force display capability is enhanced compared to any existing haptic device, i.e., approximately 100 N of linear force and 10 Nm of torque. The force display ability is validated by an experiment with a 6 DOF force/torque sensor. Finally, a simple virtual reality environment is experientially realized with the VirtuaPower to show its utility as a haptic device.

This paper addresses a control method for friction-existing robot manipulators and safe motion with its environment. In order to control the robot manipulator with unknown effects, a time-delay control(TDC) method that eliminates the nonlinear effects is used to control the joint torque servo. Although the TDC is very adaptive in nonlinear systems, there is limitation of the TDC in a high friction robot manipulator; hence, a friction model is considered. A collision detecting method is proposed to secure safety for human and robot-interacting environment. Using the torque sensor attached at the joints of the robot arm, the collision is detected more effectively. After detecting collision, a safety reaction method is applied. A torque sensor based 3-joints robot arm is used to verify the performance of the proposed methods.

This paper addresses a torque control method in a high friction robot manipulator. A stiction feed-forward compensator is proposed to eliminate the control problem caused by the nonlinear friction and disturbance. In order to control a robot manipulator with unknown effects, a time-delay control method is used to control the torque. One degree of freedom flexible joint robot manipulator with a joint torque sensor is used to show the performance of the proposed control method.