A Multi-rate Control Approach to Haptic Interaction in Multi-user Virtual Environments

High-fidelity haptic interaction in multi-user environments over general Ethernet-based Local Area Networks (LAN) and Metropolitan Area Networks (MAN) can be challenging but has promising applications. Under typical network traffic conditions, the 1kHz real-time control rate suggested in the literature for stable haptic simulation is well above that achievable by conventional network protocols such as the UDP and TCP/IP. To overcome this limitation, a decentralized multirate control approach is proposed in which local force-feedback loops are executed at higher rates than data packet transmission between the user workstations. Mathematical models for stability and performance analysis of such multi-rate haptic control systems are presented. Analytical and experimental results demonstrate improved performance and stability for the distributed control architecture when compared with a centralized controller.