This paper proposes a control method that overcomes the instability arising from both the low update rates of the virtual environment (VE) and the time delay in a communication line. The instability arising from the time delay in a communication line can be overcome using the wave variables since time delay on the wave variables is passive. The so-called multirate control scheme is applied to cope with the problems presented by the low update rates of VE. Since digital sample and hold (rate transitions) can be represented as a series of time delay, the passive nature of time delay on the wave variables is applied. By computing the norm of the scattering matrix, it was verified that rate transitions on the wave variables are passive, thereby deriving a stable haptic interface with the multirate wave transform. Various experiments have shown that a stable force display is achieved with the multirate wave transform.

It is well known that the wave variables are robust to time delay of a system from the viewpoint of passivity. During implementation of the wave transformation on the sampled-data system, a unit time delay arises due to causality of the reflection wave. The unit time delay on the reflection wave occasionally becomes a passive element. From the passivity condition of the sampled-data system, the wave impedance can be designed such that the wave transformation using delayed reflection provides the effect of positive damping and thus the stable haptic interface is achieved on the sampled-data system. Various experiments for a 2-linked passive haptic device show that stable haptic interface can be accomplished for the wall-following task by use of the wave transformation using delayed reflection.

Wave variables have been used to overcome the transmission delay of a system from the viewpoint of passivity. During implementation of the wave transformation for the sampled-data system, a unit delay arises due to causality of the reflection wave. The property of the wave transformation using delayed reflection, which is different from the standard wave transformation, can be verified with the passivity condition of the scattering matrix. The unit delay on the reflection wave occasionally becomes a positive damping. From the passivity condition of the sampled-data system, the wave impedance can be designed such that the wave transformation using delayed reflection wave provides the effect of positive damping. As an example, the wave transformation using delayed reflection wave makes it possible that the stable haptic interface is achieved on the sampled-data system with appropriate wave impedance. The simulation and the experiment results show that the stable haptic interface can be accomplished by use of the wave transformation using delayed reflection.

We propose an energy-based control method of a passive haptic device equipped with electric brakes. Unstable behavior is observed in the passive haptic system due to time delay mainly arising from the slow update rate of the virtual environment. From the passive FME (force manipulability ellipsoid) analysis, a so-called direct force control method is proposed in this paper. Its gain is computed by force analysis at the end-effector of a passive haptic device so that the component of a resultant force at the end-effector causing a pullback motion becomes zero. However, this direct force control scheme requires precise measurement of the hand force input by a human operator. We also propose the indirect force control scheme in which the gain in the direct force control scheme is computed using the notion of passivity without resorting to the high precision force sensor. For the experiments a 2-link passive haptic system was developed in this research. Various experiments have been conducted to investigate the validity of both direct and indirect force control schemes proposed in this paper. It is shown that both schemes produce satisfactory performance in the force display for the wall-following task on the virtual wall.

In this paper, we propose an energy-based stability control of a passive haptic device equipped with passive actuators such as an electric brake. Unstable behavior is observed even in the passive haptic system due to time delay mainly arising from the slow update rate of the virtual environment. The force approximation, one of the major limitations of the passive haptic device, is explained in the passive FME analysis. The ideal force display of passive haptic device is investigated, and it is shown that the passive haptic system frequently obtains the pullback capability due to the force approximation. The indirect force control scheme is proposed in that the change rate of passivity is controlled to simulate the ideal force display. To avoid the increase of the passivity due to the rate controller, which is not correlative to stability, passivity feedback is established. An experiment was conducted with a 2-link passive haptic device equipped with two electric brakes. From the experiment, the proposed control method showed satisfactory performance in displaying a plain virtual wall.

This paper presents a motion planning and control method for the dexterous manipulation with a robotic hand. For a given trajectory of an object, a simulation system calculates the necessary joint displacements and contact forces at the fingertips. These joint displacements and contact forces are the reference inputs to the control loops of the robotic fingers. A task is decomposed into a set of primitive motions, and each primitive motion is executed using the output of the simulation system as the reference. Force sensors and dynamic tactile sensors are used to adapt to uncertainties encountered during manipulation. Several experimental results are presented.

This paper presents an evaluation of joint configurations of a robotic finger based on kinematic analysis. The evaluation is based on an assumption that the current control methods for the fingers require that the contact state specified by the motion planner be maintained during manipulation. Various finger-joint configurations have been evaluated for different contact motions. In the kinematic analysis, the surface of the manipulated object was represented by B-spline surface and the surface of the finger was represented by cylinders and a half ellipsoid. Three types of contact motion, namely: 1) pure rolling, 2) twist-rolling, and 3) slide-twist-rolling are assumed in this analysis. The finger-joint configuration best suited for manipulative motion is determined by the dimension of manipulation workspace. The evaluation has shown that the human-like fingers are suitable for maintaining twist-rolling and slide-twist-rolling but not for pure rolling. A finger with roll joint at its fingertip link, which is different from human fingers, proved to be better for pure rolling motion because it can accommodate sideway motions of the object. Several kinds of useful finger-joint configurations suited for manipulating objects by fingertip surface are proposed.