A structure of bilateral control system with time delay considering improvement of stability

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.

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.

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.

In this paper, the method which eliminates the reactive operational force in bilateral control system under time delay is proposed. In bilateral control system under time delay, an operator feels large operational force. In addition to that, amplitude of response increases and it makes system unstable. In this paper, the proposed method eliminates this increasing. Therefore, operationality in free motion is improved. To solve this problem, reactive operational force is introduced which is calculated by using power factor in mechanical system. Power factor in mechanical system is derived from power factor in electrical system. Then, the concept of power factor is explained. In this research, only free motion is considered. Then, contact motion should be considered in future work. The performances of the previous method and the proposed method are evaluated through experiments.

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.

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.

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.

As haptic technology has advanced in the past decade, many sensor devices have been built and commercialized for providing the sense of action/reaction forces or moment feedback to the human operator. In the ideal bilateral control of the haptic system, the force and position control should achieve with the same actions of force and motion movements. An external force should be sensed quickly after contact with an unknown environment. This paper presents formulation and application of a Kalman filtering technique for control of master-slave robots contacting environment in a bilateral control. The different types of motion sensors are mounted on each robot to provide the position and acceleration data in the horizontal dimension. A Kalman-filter-based state observer and a Kalman-filter-based disturbance observer have been designed to estimate action/reaction forces. This paper also deals with the construction of bilateral control with the use of data provided by the different types of motion sensors. Compared to the other conventional disturbance observer or state observer, the bilateral control system based on the proposed method offers the advantages of wider bandwidth, faster response, and free from sensor noise. Thus, it is possible to provide high transparency and good perception of the environmental stiffness. The experimental results are provided to illustrate the performance of the proposed algorithms.

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.

Haptic sense is indispensable for skillful operation in a telerobotic system. Bilateral control attracts considerable interest because it transfers the haptic sense to a remote place. Although it is simply composed of two manipulators, its design is complicated. This study proposes an idea that provides a new framework on design of a bilateral control system. The idea is to design the bilateral control system based on a “function”, a minimum component of a system role. It enables simple and explicit design for various tasks. The features of the proposed method provide a way to design an adjustable system, Experimental results show the validity of the proposed method.

Recently, in the medical care, in order to achieve micro manipulation, many robots are researched. This paper focuses macro-micro bilateral control system which is one of the micro manipulation robots. Macro-micro bilateral control system consists of position control and force control. Therefore, in this paper, in order to achieve high accuracy macro-micro bilateral control system, high accuracy position control and force control is implemented. Firstly, the high resolution encoder is used. A low friction structure is used to force control. In addition, nominal mass is important for accurate force observation. Therefore, identification of mass is proposed. Macro-micro bilateral control system is implemented with proposed structure and identified nominal mass.

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.

In this paper, mathematical models for the management of biological resources based on a given predator-prey relationship are proposed, and two types of control strategies, unilateral and bilateral control with impulsive state feedback, are studied. The existence of the order-1 homoclinic orbit, order-1 periodic solution, and bifurcation of homoclinic of the unilateral control system are obtained, and the attraction region of this system is also discussed. Besides, sufficient conditions for the existence and stability of the order-1 and order-2 periodic solutions of the bilateral control system are also gained. A series of numerical simulations including bifurcation diagrams of periodic solution are performed, which not only verify the theoretical results we get but also reveal some peculiar dynamical phenomena, such as the appearance of high-order periodic solutions and existence of parameter intervals with drastic order change of periodic solution. By comparing the two management strategies, our study encourages bilateral control rather than unilateral control for the risk of predator extinction.

A Design Method of Bilateral Control of Teleoperators with Uncertain Communication Time-Delay

Precise force control and position control is essential for many robotic applications. During unilateral or bilateral object handling remote applications, human operators apply excess forces on the actuators with the intention of better grip and it is possible to damage the handled objects. This paper proposes position control and force control techniques when human applies excess force. The controllers consist of predefined force and equilibrium position which are correspond to remote environmental object safety. The operator applied excess force is modeled as a spring force through a virtual stiffness model. The paper introduces proportional derivative position control loop to conventional virtual stiffness controller. The force control loop and the position control loop references are combined in the common dimension of acceleration to produce current reference to the actuator. The sensorless sensing techniques of disturbance observer and reaction force observer are utilized to disturbance suppression and external force estimation. In the force controller, estimated reaction force is reduced to desired value by introducing virtual force loop between reaction force observer output and reaction force feedback input. The position control is achieved by introducing a scaling factor to reaction force feedback path. The switching between force control and position control is possible with scaling factor value. The performances of proposed methods are compared with conventional method and validity of the proposed methods is verified by simulations and experiments.