Realistic Force Rendering For Virtual Hand Interactions

The force rendering for virtual hand interaction is a hot research issue in the field of virtual reality. While manipulating virtual objects by virtual hands, users hope virtual reality systems could not only provide vivid visual scenes but also feed back realistic interaction force to improve the immersion and authenticity of virtual environments. However, it is still a strong challenge because VE is unable to provide physical constraints necessary for interaction as the real world does. In this dissertation, we conduct the realistic haptic rendering for virtual hand interaction.The main contents of this dissertation are as follows:We present models and algorithms that can be used to render realistic contact force for virtual hand interaction in virtual environments. Based on some research results of the human hand haptics, we firstly construct a measuring apparatus to measure the human fingers' contact forces and contact areas. Then we describe some experiments that were performed on in-vivo fingertips, and analyze the experimental datum. From the experimental datum, a contact force model is deduced to describe the real contact force properties of the human fingertips. Finally an algorithm for calculating the virtual fingertips' contact areas, which is based on the kinematics model of a virtual hand, is proposed. Based the contact force model and the contact area algorithm, Experiments are carried out to generate the contact force of virtual hands.A physically-based method for generating and feed-backing virtual hand grasp force in virtual environments is proposed. Based on the theory of robot's hand grasp, a physically-based general force model of virtual hand grasp is presented and analyses are performed for solving the model. To overcome the uncertainty in the solution of the general model and produce realistic force feedback for virtual hand grasp, optimized model with minimum force spiral are presented and solution schemes are discussed. By the minimum force spiral optimized model, we realize the grasp force generation for virtual hand interaction.We propose a method for rendering the realistic grasp force of the virtual hand grasping an object and moving in virtual environments. By tracking the position of the grasped object, the pose change of the grasped object is detected. If it's true, an algorithm is used to calculate the distribution of the external force (e.g. the gravity of virtual object) imposed on the grasped object in the new pose, and the grasp force of the virtual hand is regenerated according to the physically-based general force model of virtual hand grasp. Based on the theory of kinematics and dynamics, the resultantforce which causes the motion state's change of grasped object can be obtained. Further, the grasp force of the virtual hand is regenerated through combining the pose of grasped object and the resultant force.A method of rendering and feed-backing collision force with friction for virtual hand interaction in virtual environments is proposed. Based on impulse theorem and coefficient of elastic recovery, the motion rules for virtual objects collided are deduced. By coulomb's friction model, we put forward an approach to generating collision force in planar space which can be extended to 3D virtual space. The means that the collision force is imposed on a hand is also discussed, and impulsive force for each finger is calculated by optimized virtual hand grasp models with minimum force spiral.Finally, conclusions are given and future work is discussed.