Graphic and haptic rendering of a 4-DOF virtual finger interacted with the virtual object at multiple contact points

This paper investigates the simulation of a virtual index finger interacted with an object for a virtual rehabilitation system of human hand. Corresponding to the anatomy of human hand, the virtual finger is modeled as three phalanges which are connected by three joints, which is essentially a 4-Degree-of-Freedom (DOF) open chain mechanism. The special characteristic of the virtual finger poses the special issues on graphic rendering, collision detection, and haptic rendering, which is investigated in this paper. Since the interaction only occurs on the surfaces of the fingers and objects in the rehabilitation application, triangle mesh representation is used to build the geometry model of the virtual hand and the object which are both simplified as rigid bodies for the preliminary research. A graphic rendering method based on the sequence of priority of collision detection is proposed to deal with the various contact situations at which the finger contacts the object with different phalanges. The non-penetration graphic rendering is realized by displaying the virtual finger at the position which is closest to the contact point. This position is searched out from the recorded motion trajectory of the finger. The virtual contact forces are modeled upon the spring-mass model and the joint torques are calculated according to the equilibrium equation of moment. The system experiment result demonstrates that the proposed method can provide the satisfactory graphic and haptic display for various contact situations.