Lőrinc Márton

Communication delay and jitter influence on bilateral teleoperation

One of the most challenging problems during the design of bilateral teleoperation systems implemented over Wide Area Networks is to assure the stability and transparency in the presence of time varying communication delay between the master and the slave. In this work the influence of the delay and jitter on the passivity controller - passivity observer type stabilizers is analyzed. This control design approach does not require the explicit knowledge on the communication delay. In spite of this fact in this work it is shown that time varying the delay influences the teleoperation performances. Firstly, the relation between the delay and the dissipated energy by the controller was studied. Secondly, it was shown that in the presence of jitter the passivity controller can induce undesired oscillations into the received signals, affecting the transparency of the teleoperation. To handle this problem an extended passivity controller was proposed which assures better performances in the presence of jitter. Experimental measurements, including teleoperation experiments between two universities situated in different countries, are performed to validate the theoretical results.

Detection of overload generated faults in electro-hydrostatic actuators

This paper proposes a method for detecting faults generated by increased loads in a class of mechanical control systems. It is considered that the load (input disturbance) is unmeasurable, only its bounds corresponding to normal operation are known. To solve the fault detection problem, a detector was proposed for a class of linear control systems that can be implemented with low computational costs. The method is applicable for electro-hydrostatic actuators (EHA) with unknown load. The proposed fault detection approach is validated through simulations for jamming detection of aircraft control surfaces driven by EHA.

Network Controller for Teleoperated Mobile Robotic Agents

In the communication channels of bilateral teleoperation systems it is critical to keep the delay and delay variation under prescribed limits. Otherwise, the stability and transparency of the teleoperation are compromised. In this paper a network controller is proposed for video supported teleoperation systems implemented over WLANs (Wireless Local Area Networks). The algorithm controls the transfer rates in the video channels which serve for online monitoring of the teleoperation task. The video transfer rate controller was developed using multi-objective optimization and it assures the best achievable video transmission quality for a prescribed delay or jitter in the communication channels of the teleoperator. The performed real-time experimental measurements show that, with the proposed rate control algorithm, the delay and its fluctuation can be substantially reduced in the teleoperation systems implemented over WLAN.

Data transfer regulator for wireless teleoperation

To achieve stability and transparency in bilateral teleoperation systems, it is critical to have reliable communication channels between the master and slave robots. Efficient data transmission algorithms have to be developed which take explicitly into consideration the characteristics of the applied communication medium. This paper introduces a new data transfer rate adjustment algorithm for bilateral teleoperation systems that includes video transmission from the slave side to the master side and uses wireless local area networks (WLANs) as a communication medium. If a high amount of data is transmitted over the wireless network which is used by the teleoperation system, significant delay, jitter and packet loss can be expected in the channels of the teleoperation system. Based on application layer measurements performed in the communication channels with variable delay, the proposed regulator adjusts the video transfer rate. The algorithm is designed using two cost functions which define the transmission quality in the teleoperation channels and the quality of the video displayed to the human operator, respectively. The obtained algorithm is able to maintain the expected value of the delay and delay variation in the communication channels of the bilateral teleoperation system at a predefined level. The performed real-time experiments show the proper behavior of the data transfer regulator on the teleoperation even in the presence of independent network load.

Bilateral Teleoperation in the Presence of Jitter: Communication Performance Evaluation and Control

In this study the influence of the communication channels with time varying delays on the networked robot control systems is treated. The first part of the work focuses on communication performance evaluation of such applications that are developed to support bilateral teleoperation over wireless local area networks. Detailed experimental investigations are performed to analyze the communication performances in wireless teleoperation systems. It is shown that the jitter is a good indicator of the communication performances in wireless networked control systems. In the second part of the work it is shown that in the presence of large communication delay variation (jitter) the transparency of the teleoperation is compromised. To handle this problem an extended teleoperation controller was proposed which assures better performances in the presence of jitter. Control experiments are presented to validate the theoretical results.

Passive bilateral teleoperation with bounded control signals

In this study a new approach is proposed for time domain passivity based control of bilateral teleoperation systems in the presence of communication delay. According to the time domain passivity framework a Passivity Observer monitors the behavior of the teleoperation system. Whenever it is necessary, a Passivity Controller is switched on to assure the passivity of the teleoperation system. In this work a method is introduced according to which the rate (first order derivate) of the velocity and force signals, which are sent through the communication network, are limited with known bounds. In this case Passivity Controllers with bounded outputs can guarantee the stable behavior of the teleoperation system. Real-time experimental measurements are provided to show the efficiency of the proposed technique.