Experimental Internet Haptic Collaboration using Virtual Coupling Schemes

In this paper we present the results from several global-scale haptic collaboration experiments that were performed using the Internet. These experiments consist of three virtual coupling schemes proposed to maintain position coherency in a networked haptic virtual environment (NHVE). We compared two of our virtual coupling schemes - which represent a peer-to-peer architecture - to the third - with a client-server architecture. We set up a packet reflector network at our collaborator servers (Italy, Canada and North Carolina, USA) to perform the experiments with subjects located within the same laboratory. Our largest one-way latency was in the order of 200 ms for the packet reflector situated in Italy. The virtual coupling parameters were chosen so that it resulted in stable operation for all the delay values that were tested. User datagram protocol (UDP) was used for haptic data communication because of the high transmission rate requirement for NHVEs. There were three experiments carried out in total: two of them at the packet transmission rate of 1000 Hz with a change in the virtual coupling parameters in scheme 2, and the third one, which tested the three virtual coupling schemes at two fixed transmission rates of 500 Hz and 100 Hz. Locally, the haptic update rate was maintained at 1000 Hz during all the experiments. Our results demonstrate that the peer-to-peer virtual coupling schemes can be used for maintaining position coherency in a NHVE. We also show that the position error and the force rendered to the users increase with the reduction in the packet transmission rate. Given that these experiments were performed through the actual Internet, this work proves valuable for global-scale stable haptic collaboration using the Internet.