A virtual environment comprises three components: a human operator, a computer, and an interface linking the human operator to the computer. Modern computers are generally very good at visual and auditory interactions. However, they are not yet able to sense and reflect forces well. The focus of this dissertation is to develop a sense of touch by which a human operator will be able to manually sense and manipulate virtual objects.; In order for an operator to manually interact with a virtual surface, a contact model is needed. The contact models developed so far by other researchers treat the virtual contact without regard to the existence of the operator. Inclusion of the operator's model, specially a model of the fingertip, would allow perception of forces very close to those in the real world.; In the virtual environment, we need to interact with virtual objects in normal and tangential directions. Contacts in these two directions are analyzed separately. For the normal direction, it is shown that it feels more natural if there is no finger pad contact with the force-reflecting device before reaching a virtual surface. Besides rigid virtual objects are felt more rigidly. In addition, only a low-power, small, and inexpensive interface is needed because the haptic interface is preactuated just before reaching the virtual surface. For the tangential direction, a stick-slip friction model is developed. The parameters of such model are derived from the fingertip characteristics.; Finally, an application of interaction with virtual surfaces—manipulation of virtual mechanisms—is presented. Formulations for interaction with both open-chain and closed-chain virtual mechanisms are developed.
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