In telepresence and teleaction (TPTA) systems, the transmission of haptic signals puts high demands on the applied signal processing and communication procedures. When running a TPTA session across a packet-based communication network (e.g., the Internet), minimizing the end-to-end delay results in packet rates of up to the applied sampling rate of the local control loops at the human system interface and the teleoperator. The perceptual deadband data reduction approach for haptic signals successfully addresses the challenge of high packet rates in networked TPTA systems and satisfies the strict delay constraints. In this paper, we extend the underlying perceptual model of the deadband approach by incorporating psychophysical findings on human force-feedback discrimination during operators' relative hand movements. By applying velocity-dependent perception thresholds to the deadband approach, we observe further improvement in efficiency and performance due to improved adaption to human haptic perception thresholds. The psychophysical experiments conducted reveal improved data reduction performance of our proposed haptic perceptual coding scheme without impairing the user experience. Our results show a high data reduction ability of up to 96% without affecting system transparency or the operator's task performance.

Time delay is recognized as an important issue in haptic telepresence systems as it is inherent to long-distance data transmission. What factors influence haptic delay perception in a time-delayed environment are, however, largely unknown. In this article, we examine the impact of manual movement frequency and amplitude in a sinusoidal exploratory movement as well as the stiffness of the haptic environment on the detection threshold for delay in haptic feedback. The results suggest that the detection of delay in force feedback depends on the movement frequency and amplitude, while variation of the absolute feedback force level does not influence the detection threshold. A model based on the exploration movement is proposed and guidelines for system design with respect to the time delay in haptic feedback are provided.

Limited communication resources represent a major challenge in networked tele-presence and teleaction systems. Video and audio compression schemes are well advanced employing models of human perception. In contrast to that haptic data reduction schemes are rather poorly treated in the known literature. This article introduces a novel approach to reduce network traffic in haptic telepresence systems exploiting limits in human haptic perception. With the proposed deadband control approach, data packets are transmitted only if the signal change exceeds a signal amplitude dependent perception threshold. Experimental user studies show that an average network traffic reduction of up to 85% can be achieved without significantly impairing the perception of the remote environment. The assumption throughout this article is that there is no communication time delay.

Two of the major challenges in networked haptic telepresence and teleaction systems are the time delay associated with the data transmission over the network and the limited communication resources. Sophisticated control methods are available for the stabilization in the presence of time delay. The reduction of haptic network traffic, however, is only poorly treated in the known literature. Data reduction approaches for time delayed haptic telepresence are not available at all. This article presents a novel approach to reduce the network traffic in haptic telepresence systems with constant (unknown) time delay. With the proposed deadband control approach data are sent only if the signal to transmit changes more than a given threshold value. In order to guarantee stability with time delay and data reduction a well-known time delay approach, the scattering transformation, is extended. Experimental user studies show that an average network traffic reduction up to 96% is achieved without significantly impairing the perception of the remote environment compared to the standard approach with time delay.