The successful implementation of the robot teleoperation system has greatly improved the ability of remote robots. The force feedback technology is applied to the teleoperation system. On the one hand, the main operator manipulates the operator's related movement information to the target robot; on the other hand, the main hand feeds back the force situation of the target robot in the remote control to the operator. From the robot under the control of the system can more accurately complete the task, with a higher work efficiency. Teleoperation system with force feedback function generally adopts bilateral control, the master and slave end of the system have a certain delay in the transmission process, it makes the stability of the system destroyed. This paper uses a two-port network to simulate the communications link of the teleoperation system as a lossless transmission line, solves the stability problem of teleoperation systems with force feedback in the presence of time delay effectively. Experimental simulation results show that this method can guarantee a higher stability of the system..
- Force Feedback
Teleoperation system enables local operators to manipulate smart devices such as remote robots, Complete designated tasks in hazardous, human-inaccessible, or human-unfriendly environments. But communication delays when the system operator and the remote robot are far apart. Experiments have shown that if there is a delay of 0.25s, it may cause instability in the teleoperation system which affects work efficiency and safety seriously .
Teleoperation system adopts master-slave control mode, the operator interacts with the master, feels the force generated by slave robot and environment. The operator's instructions are sent to the slave robot by signal transmission, makes it follow the instructions of the operator, at the same time, the feedback information is returned to the master through a signal transmission process and fed back to the operator. Treating teleoperational transmission modules as two-port networks, the system structure is shown in Figure 1. There is a correspondence between the force F of the teleoperation system and the speed v and the voltage V and current I in the circuit, which is F->v, V->I. .
In the theory of electric networks, passivity reflects the energy dissipation characteristics of the system during movement. Stability is the basic structural characteristic of a dynamic system, shows the boundedness of system output.
The two-port network shown in Figure 3, it can be described with different parameters. When
The master and slave dynamic equations of the teleoperation system with force feedback after neglecting the influence of gravity are as follows:
Constructing the following energy storage function based on the definition of passivity:
As shown in Figure 3, when there is a delay of T in the communication link of the teleoperation system, the relationship between the input and output of the system is as follows:
So the mixing matrix is:
The transmission line shown in Figure 4 is a lossless transmission line. When
According to the theorem of the scattering matrix:
According to the definition of the scattering matrix, when the lossless transmission line is used to simulate the communication link, the time delay communication link is passive, so that the entire teleoperation system is passive, that is, the system is stable. The passive control algorithm for the communication link is:
The above formula is a control algorithm for the communication link, so that the communication link remains passive.  When the communication link of the teleoperation system with force feedback has a time delay of T=0.5 seconds, the position, velocity and force variation curves of the system master and slave ends are shown in Figure 5 to Figure 7. It can be seen that the system is convergent when it is in an autonomous state, that is, the system is stable. 
According to the structure of the teleoperation system, the influence of time delay on the stability of the system is pointed out, and the connection between the passiveness and the stability is analyzed. Through the analysis of the stability of the time-delay force feedback teleoperation system, it is pointed out that the transmission line theory based on the two-port network is an effective means to solve the poor stability of the teleoperation system due to the delay in the communication link.