Modeling mechanism and hand impedances for improved control of haptic interfaces.

摘要

Haptic interfaces to virtual environments have received increasing attention from researchers during the last ten years. Applications in the fields of education, entertainment, and surgery have driven the demand for interfaces that have high fidelity force transmission from machine to user, allowing realistic kinesthetic immersion in the virtual environment through the sense of touch. Whereas stable force transmission up to bandwidths of 175 Hz is possible for interfaces with only one degree of freedom, more complex five or six degree of freedom interfaces suffer from loss of stability related to the interactions within the mechanism. The result is that the performance is compromised in certain directions of force rendered to the user. This thesis presents a novel multivariable modeling and control methodology for parallel haptic interfaces equipped with force sensors close to the contact point between the hand and the mechanism. The method uses a second order matrix polynomial description of the mechanism and hand impedances to create a closed-loop force control law based on inversion of the approximate model. At the frequencies where the model is correct, the performance of the device is largely equalized in all directions of applied force. The new method broadens the range of achievable virtual impedance and improves the transparency of the device to the virtual environment over previous control methods.