| With the development of Distributed Virtual Environment, haptic simulation is becoming a popular research field. However, time delay issue is always an obstacle in haptic simulation because this lag over the network-based haptic display violates the stability and performance of haptic display. In the research of teleoperations, some delay prediction methods have been introduced already; however, the performance requirements have been decreased to obtain the stability reducing the total loop gain. The design of virtual coupling, an artificial link between the haptic display and virtual environment, has been introduced into haptic interaction. However, in the traditional design, virtual coupling is always coupled with the virtual environment; as a result, stability condition for the haptic simulation becomes too tight because zero order hold has the phase lag over frequency. To guarantee the stability in the presence of unpredictable time delays new control design strategies are required.; In this thesis, two-port network theory is introduced to design the virtual coupling to guarantee stability of haptic display in time-delayed Distributed Virtual Environments. By decoupling the hatpic display control problem from the design of virtual environments, the use of a virtual coupling network frees the developer of haptic-enabled virtual reality models from the issues of mechanical stability. Passivity criteria in two-port networks are introduced to guarantee stability of haptic interface with a unit time delay. Furthermore, two kinds of virtual environments models---""spring"" and ""spring-damping"" have been simulated. Steady state error and transient response for the interaction between haptic displays and above virtual environments models are investigated. This technique overcomes the influence of time delay to violate the stability of the system and reduces the human risk involved. |
