| M. Fotoohi, Quanser Consulting Inc., 80 ESNA Park Drive, Markham,
Ontario L3R-2R6, Canada, S. Sirouspour, Department of Electrical and
Computer Engineering, McMaster University
1280 Main St. W., Hamilton, Ontario L8S-4K1, Canada and D. Capson Department of Electrical and Computer Engineering
McMaster University, 1280 Main St. W., Hamilton,
Ontario L8S-4K1, Canada, |
| This paper is concerned with multi-user haptic simulation environments
in which users can interact across an Ethernet-based Local
Area Network (LAN) or a Metropolitan Area Network (MAN). Using
network protocols such as the UDP and TCP/IP under normal
network traffic conditions, the achievable real-time packet communication
rate can be well below the 1 kHz update rate suggested in
the literature for high fidelity haptic rendering. However by adopting
a multi-rate control strategy, the local control loops can be executed
at a much higher rate than that of the data packet transmission
between the user workstations. Within such a framework, two control
architectures, namely centralized and distributed are presented.
Mathematical models of the controllers are developed and used in a
comparative analysis of their stability and performance. The results
of such analysis demonstrate that the distributed control architecture
has greater stability margins and outperforms the centralized controller.
It is also shown that the limited network packet transmission
rate can degrade the haptic fidelity by introducing a viscous damping
into the perceived impedance of the virtual object. Using the proposed
models, this damping value is calculated and compensated by active
control. Experiments conducted with a dual-user/dual-finger haptic
platform confirm the analytical results. |
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