Combating Latency in Haptic Collaborative Virtual Environments

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Abstract
Haptic (force) feedback is increasingly being used in surgical-training simulators. The addition of “touch” is important extra information that can add another dimension to the realism of the experience. Progress in networking these systems together over long distances has been held back, principally because the latency of the network can induce severe instability in any dynamic objects in the scene. This paper describes techniques allowing long-distance sharing of haptic-enabled, dynamic scenes. At the CSIRO Virtual Environments Laboratory, we have successfully used this system to connect a prototype of a surgical-simulation application between participants on opposite sides of the world in Sweden and Australia, over a standard Internet connection spanning 3 continents and 2 oceans. The users were able to simultaneously manipulate pliable objects in a shared workspace, as well as guide each other's “hands” (and shake hands!) over 22,000 km (13620 miles) of Internet connection. The main obstacle to overcome was the latency-induced instability in the system, caused by the delays and jitter inherent in the network. Our system involved a combination of an event-collection mechanism, a network event-forwarding mechanism and a “pseudophysics” mechanism. We found that the resulting behavior of the interconnected body organs, under simultaneous-user manipulation, was sufficiently convincing to be considered for training surgical procedures.