Event-driven data transmission in variable-delay network

Transparency and stability issues have been a major concern for haptic tele-operation. Researchers in this area have already shown that a minimum refresh rate of 1 kHz is required to achieve smoothness for human perception in force-feedback experiments. This rate requires the highest priority for real-time applications to achieve transparent haptic tele-presence. As a result, this rate leads to a round-trip time delay requirement of less than 1ms, which consequently constrain the transmission delay to less than 500us for sample packets in each direction. On the other hand, emerging haptic cooperative and collaborative applications, such as network gaming are typically implemented on loosely-coupled packet switched networks. However, the transmission delay of UDP packets in such network lower-bounded to 1.5ms, which is higher than haptic applications constraint. This research proposes a new method of event-based haptic data sample transmission, which significantly reduces the number of sample packets required for transparent haptic tele-presence. Prioritizing the events, an event synchronization scheme, and utilization of a haptic-specific PID controller for smooth position adjustment within slave side are the major techniques elaborating this method. Furthermore, an experimental study with a virtual impedance device has been set up, and the results have analyzed. A compression ratio of 94% in the master device, and 97% in slave device has been achieved by the proposed technique.