Elimination of reactive operational force in bilateral control system under time delay

Position error between master and slave occurs in bilateral control system under time delay and it is undesirable for delicate works. To solve this problem, this paper proposes a compensation method of position error in bilateral control under time delay. Firstly, the cause of position error is expressed. After that, it is shown that 3-channel bilateral control system, which is the conventional method, compensates position error. However, 3-channel bilateral control system is known to be unstable in contact motion. In 3-channel bilateral control system, a compensation term is added in master. In contrast, in the proposed method, a compensation term is added in slave. Moreover, stable contact motion and compensation of position error are realized. The validity of the proposed method is verified through experiments.

Time delay in bilateral control system seriously deteriorates stability. Conventional acceleration based bilateral control method has stabilized position control. But, force control is not stabilized. This paper proposed a stability improved structure for bilateral control system. Position control and force control of proposed bilateral control system are stabilized. The validity of the proposed method is shown by numerical and experimental results.

SUMMARY This paper proposes a method of decoupled bilateral control based on a modal space observer. In a conventional bilateral control system, the structures of master-slave systems are not considered. This paper shows that a force controller and a position controller in a bilateral control system interfere with each other when the structures of the master-slave systems are different. In order to solve this problem, a bilateral control system based on a hybrid matrix has been proposed. However, the computational process for calculating the hybrid matrix becomes complicated as the numbers of degrees of freedom in the master-slave systems increase. In the proposed method, a nominal equivalent mass matrix with respect to the modal space is used, and the interfering terms are estimated and compensated using a modal space observer. Therefore, a simple control structure is realized using the proposed method. The performance of the proposed method is compared to that of the conventional methods through simulations and experiments, and the validity of the proposed method is confirmed.

Recently, there are many researches of a system which has implemented a bilateral control system which can touch an environment in distant place. However, a singular configuration due to the inverse Jacobian matrix becomes the problem in a bilateral control with different configurations. In this paper, the problem of a singular configuration regarding the inverse Jacobian matrix is avoided by singularity-consistent method. In addition, an error observation method of a torque regarding the singularity-consistent method is proposed. And, the bilateral control system consists of a parallel link manipulator and a serial link manipulator. When the direct kinematics of the parallel link manipulator is derived, mode decoupling method is introduced. Finally, proposed method and sc method are applied to the bilateral control system with different configurations, its system is realized and the error of the torque due to singularity-consistent method is observed. The experimental results of the bilateral control with different configurations are shown.

This paper shows behavior of power factor in mechanical system in the case of work space motion. XY table and two link manipulator are employed to demonstrate the difference between work space power factor and joint space power factor. It turns out that power factor in work space and joint space becomes different even though the same motion is performed. In addition, power factor during free motion is investigated. Experimental results supports that structure of the system is relevant to the efficiency of the motion.

The paper proposes a method to reduce an operational force in a bilateral control system that realizes simultaneity property under communication delay. A bilateral control that realizes simultaneity property is previously proposed, which is achieved by delaying the own force information. It focused on the fact that the force information is the pure information that actuates the motor, therefore, timing of the force information input is corrected. However, the control system requires large force when operator tries to operate the system. In this paper, the problem is solved by utilizing the delayed position information of the own system. The proposed control system is designed to mix present and buffered position information to reduce the operational force. The delayed information can easily affect the stability problem, therefore, phase compensator and the velocity feedback is used. The validity of the proposed method is confirmed by experiments.

ABSTRACTThis paper aims at developing an estimation method of end-point impedance. Human operators are constantly changing their end-point impedance for adapting to the surrounded environment and executing some complicated tasks, and it is highly meaningful to investigate these variations for the further understanding of human motion. Most of the conventional researches, however, have considered non-contact-point impedance or tasks that is only holding the vibrated sticks due to the experimental constraints. This paper proposes the estimation method of end-point impedance by using bilateral control system. The extra signal is added to the force controller for the impedance estimation. In addition, the effect of the bilateral controller is estimated and removed from the impedance estimation process for securing the applicability of moving tasks. The proposed method was validated through simulations and an experiment. The experimental result showed that the end-point stiffness can be estimated properly even if the operator robot was moving and changed its end-point impedance.

A comparison between optimization algorithms applied to synchronization of bilateral teleoperation systems against time delay and modeling uncertainties

Passivity theory is a very useful tool for the stability analysis of bilateral teleoperation with communication delay. Many researchers use passivity-based stabilization method such as those based on scattering theory or wave variables. However, passivity-based stabilization is too conservative for the design of a high-performance teleoperation system. The term “high-performance” implies that people who operate this system can experience a highly accurate reaction force from environments. In this study, we analyze the L2-stability of some bilateral control systems with time-varying communication delay by using the small-gain theorem. The small-gain theorem is known to be a stability condition for multi-input multi-output feedback systems. Additionally, a novel control structure for the bilateral control system with communication delay is proposed. The bilateral control system with the proposed structure satisfies the L2-stability condition of the small-gain theorem. The experimental results show the utility of the proposed control structure.

Passivity-based bilateral teleoperation control systems can offer robust stability against arbitrarily large communication delays at the expense of poor transparency. In fact, most passive control frameworks are designed for a particular task and do not adjust transparency when transitioning between different environments. This paper presents a bilateral control strategy that passively compensates transparency when transitioning between free motion and hard contact motion scenarios. The proposed control framework exploits the effect that the wave impedance (a design parameter of the passivitybased scattering transformation) has on transparency without compromising closed-loop stability regardless of time-varying communication delays. To adjust transparency, the control scheme smoothly switches the wave impedance between a low value, ideal for free motion, and a sufficiently large value, suited for hard contact scenarios. We show, by rigorous mathematical treatment and simulations, that the proposed control strategy can effectively adjust the transparency of the system without compromising stability.

The control problem for bilateral teleoperation systems using only one controller is studied in this paper. In the proposed control framework, the remote robot transmits position/velocity signals to the controller located with the local robot. The corresponding control inputs for local and remote robots are obtained from the same controller. The individual control signal is sent to the local robot directly, and transmitted to the remote robot over a network subject to communication delays. Two control algorithms, P-like and PD-like controllers, are considered in the novel bilateral teleoperation system framework. Stability and tracking performance can be guaranteed if control gains are contingent to time delays when the external force are passive or both robots are in free motion. Numerical examples are presented to validate the performance of the proposed bilateral teleoperation control systems.

To address the problem of internet based communication delay in bilateral control systems, numerous methods have been proposed. This study is among the few recent studies taking a disturbance observer approach to the problem of time delay, and introduces a sliding-mode (SM) observer to overcome specifically the effects of communication delay in the feedback loop. The observer operates in combination with a PD+ controller which controls the system dynamics, while also compensating load torque uncertainties on the slave side. To this aim, an EKF based load estimation algorithm is performed on the slave side. The performance of this approach is tested with computer simulations for the teleoperation of a 1-DOF robotic arm. Experimental results are also presented to test the performance of the approach under constant and random measurement and control input delay for no load.

Recently, network-based control systems attract a lot of attentions. One of the applications of such control systems is haptic transmission using a bilateral control system. In order to construct the bilateral control system over the time delayed-network, many researchers have proposed many methods and succeeded to improve the stability and performance of the system. By assuring the system’s passivity, some of conventional methods have succeeded to stabilize the system even when the communication blackout occurs. However, the passivity-based methods are conservative and deteriorate the performance. In this paper, the mode shifting method is proposed to deal with the communication blackout without considering the system’s passivity. In the proposed method, the bilateral controller is shifted to a local controller when the communication blackout occurs. By shifting to the local controller, the system is not destabilized by the blackout. Moreover, when the communication recovers, the bilateral controller is gradually restored to regulate the robot’s output power. Owing to the power regulation, the robots never damage environmental objects during and after the communication blackout. Therefore, the proposed method realizes stable and safe control even under the blackout. The validity of the proposed method is confirmed by simulations and a experiment.

In this paper, a sliding-mode-based design framework for fully actuated mechanical multibody system is discussed. The framework is based on the possibility to represent complex motion as a collection of tasks and to find effective mapping of the system coordinates that allows decoupling task and constraint control so one is able to enforce concurrently, or in certain time succession, the task and the constraints. The approach seems naturally encompassing the control of motion systems in interaction, and it allows application to bilateral control, multilateral control, etc. Such an approach leads to a more natural interpretation of the system tasks, simpler controller design, and easier establishment of the systems hierarchy. It allows a unified mathematical treatment of task control in the presence of constraints required to be satisfied by the system coordinates. In order to show the applicability of the proposed techniques, simulation and experimental results for high-precision systems in microsystem assembly tasks and bilateral control systems are presented.

This paper presents a novel zero-crossing point detection method for boundary current mode PFC converter. In the conventional boundary current mode, the zero-crossing point is detected by observing the inductor voltage. When the digital controller is used in the conventional method, the detection of the zero-crossing point is delayed due to the delay time caused by the processing of DSP. And the detection of the zero-crossing point is also delayed by the effect of the parasitic capacitance of main components in the PFC converter. As a result, the boost converter operates under the discontinuous mode. The harmonic currents occur and the power factor becomes low when the boost converter operates under the discontinuous mode. In order to make the boost converter to operate under the boundary current mode, it is necessary to reduce the delay time caused by the DSP's processing and the parasitic capacitance. The proposed zero-crossing detection circuit is formed by the differentiation circuit and the differential amplifier circuit and the RS-FF. In the proposed method, the delay time of zero-crossing point detection can be reduced and the boost converter can operate under the boundary current mode with high accurate. Simulation results show that compared with the conventional method, the zero-crossing point detection delay time characteristics are improved in the proposed method.