Shared Haptic Virtual Environments (SHVEs) are often realized using a client–server communication architecture. In this case, a centralized physics engine, running on the server, is used to simulate the object-states in the virtual environment (VE). At the clients, a copy of the VE is maintained and used to render the interaction forces locally, which are then displayed to the human through a haptic device. While this architecture ensures stability in the coupling between the haptic device and the virtual environment, it necessitates a high number of object-state update packets transmitted from the server to the clients to achieve satisfactory force feedback quality. In this paper, we propose a perception-based traffic control scheme to reduce the number of object-state update packets by allowing a variable but not perceivable object-state error at the client. To find a balance between packet rate reduction and force rendering fidelity, our approach uses different error thresholds for the visual and haptic modality, where the haptic thresholds are determined by psychophysical experiments in this paper. Force feedback quality is evaluated with subjective tests for a variety of different traffic control parameter settings. The results show that the proposed scheme reduces the packet rate by up to 97%, compared to communication approaches that work without data reduction. At the same time, the proposed scheme does not degrade the haptic feedback quality significantly. Finally, it outperforms well-known dead reckoning, commonly used in visual-only distributed applications.

Telepresence and teleaction (TPTA) systems enable humans to operate in a remote, hostile, or inaccessible environment. The performance of these systems strongly depends on the deployed sensors and actuators and the quality of the feedback to the user. Spatial perception plays an especially important role when handling dangerous and fragile objects. Stereoscopic cameras and displays can be deployed to improve spatial perception. However, in networked TPTA scenarios with limited transmission capacity on the communication link, the additional bandwidth required for sending two separate video streams is often infeasible. Furthermore, stereoscopic displays are known to have limitations in quality that affect spatial orientation when navigating within the remote environment. In this work, we present methods for displaying remotely measured distance between a teleoperator and a target object through visual and vibrotactile displays in order to improve spatial perception in TPTA systems. Furthermore, we propose to exploit human sensory illusions of the vibrotactile sense to overcome limitations of vibrotactile displays. Psychophysical experiments are conducted to investigate the performance of our proposed display methods. Our experiments show that our proposed vibrotactile feedback methods can compete with visual distance displays.

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.

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.