류지환 교수

A recently proposed method for stabilizing haptic interfaces and teleoperation systems was tested with a PHANToM commercial haptic device. The passivity observer (PO) and passivity controller (PC) stabilization method was applied to stabilize the system but also excited a high-frequency mode in the device. To solve this problem, we propose a method to use a time-varying desired energy threshold instead of fixed zero energy threshold for the PO, and make the actual energy input follow the time-va

In this paper, modified two-port time-domain passivity approach is proposed for stable bilateral control of teleoperators under time-varying communication delay. We separate input and output energy at each port of a bilateral controller, and propose a sufficient condition for satisfying the passivity of the bilateral controller including time-delay. Output energy at the master port should be less than the transmitted input energy from the slave port with time-delay, and output energy at the slav

We propose new time domain passivity observer (PO) and passivity controller (PC) which removes the constant velocity assumption during one sample time, which was used in our previous PO/PC approach. A new sampled time definition of passivity is introduced, and this new definition is compared with the previous sampled time definition of passivity. Through this comparison, we propose the more accurate PO/PC approach. The proposed new PO/PC approach is applied to "Excalibur" haptic interface system

Parallel manipulators are characterized as having closed-loop kinematic chains. Compared to serial manipulators, which have open-ended structure, parallel manipulators have many advantages in terms of accuracy, rigidity and ability to manipulate heavy loads. Therefore, they have been getting many attentions in astronomy to flight simulators and especially in machine-tool industries.The aim of this book is to provide an overview of the state-of-art, to present new ideas, original results and prac

Inspired from the graphical interpretation of passivity in a position versus force xy graph, this paper proposes a new concept of passivation method to increase the dynamic range of impedance in which a haptic interface can passively interact. The position versus force graph represents the energy behavior in a one-port haptic interface while the haptic interface is traveling in (pressed) or out of (released) a virtual environment (VE). It interprets that to make the one-port system passive, it i

A new bilateral control scheme is proposed to ensure stable teleoperation under a wide variety of operating conditions. To guarantee the stability of a teleoperation system, a previously proposed energy-based method is extended to a two-port network. The issues in implementing the "passivity observer" and "passivity controller" to teleoperation systems are studied. The method is tested with our two-DOF master/slave teleoperation system. Totally stable teleoperation is achieved under conditions s

A general framework to stabilize multilateral teleoperation system over a communication time delay based on the well-known time-domain passivity approach (TDPA) is proposed. The uniqueness of this framework is that it is independent of the amount of communication time delay, the multilateral control architecture, and the number of masters and slaves. The multilateral system was first decoupled into subsystems with respect to each terminal by identifying the input signals' contributions to the ou

Soft growing robots have received considerable attention because of their unique locomotion. However, the use of a single material for their manufacturing causes numerous problems, because each part of the robot requires different characteristics. This study attempts to solve this fundamental problem from a material perspective, rather than integrating independent solutions. A hyperelastic material is proposed for building a soft growing robot. Several problems associated with conventional soft

A virtual fixture (VF) is a constraint built into software that assists a human operator in moving a remote tool along a preferred path via an augmented guidance force to improve teleoperation performance. However, teleoperation generally applies to unknown or dynamic environments, which are challenging for VF use. Most researchers have assumed that VFs are pre-defined or generated automatically; however, these processes are complicated and unreliable in unknown environments where teleoperation

A noisy behavior of the time-domain passivity controller during the period of low velocity is analyzed. Main reasons of the noisy behavior are investigated through a simulation with a one-DOF haptic interface model. It is shown that the PO/PC is ineffective in dissipating the produced energy when the sign of the velocity, which is numerically calculated from the measured position, is suddenly changed, and when this velocity is zero. These cases happen during the period of low velocity due to the