Collision Detection And Force Feedback Algorithm For Virtual Surgery Training System Based On Point Cloud Model

The concept of virtual reality is a comprehensive interdisciplinary technology, which has been widely used in military, movies, health and games currently. Virtual reality can simulate the objective world by the way of visualization and immersion. Virtual surgery provides a reusable surgical training platform for surgeons, helps pre-operative preview and surgical outcome prediction and avoiding risks. Collision detection and force feedback control algorithm are the premise to guarantee immersive and transparency of virtual surgery system.In order to ensure real-time collision detection, the paper structures "octree" to store "point cloud data" and presents "bounding sphere with simplified point collision" algorithm and " bounding sphere with simplified line collision" algorithm for different virtual surgical instruments on the basis of bounding sphere algorithm, and improves the detection efficiency. In order to ensure that the system stability won’t be affected by interaction of surgery instruments and soft tissue, the paper designs the adjusting Output-Limiter algorithm to ensure the continuity and stability of Output-Force.Collision detection is the indispensable key part of the virtual surgery and the rapidity and veracity of collision detection algorithm premises the real time performance of virtual surgery. The paper adopts Hierarchical bounding sphere algorithm which utilizes space subdivision to structure "octree" to store "point cloud data". In order to improve the real-time performance of collision detection, edge and cutting line of surgical instrument are simplified to a small ball or a straight line respectively, but the visual presentation will remain unchanged so the collision detection speed will be greatly promoted while the visual effects won’t be affected. The experimental results show that the average detection time is reduced by more than the conventional method 70%.Force feedback control algorithm is the key to guarantee system stability. Virtual surgery system is composed of four two-port networks as the operator, force feedback device, the sample holder and the virtual environment. This paper adopted Output-Limiter algorithm, which must meet the passive theory, to ensure the system stability. According to passive theory the system predicts the maximum output-force of the next sampling time to ensure that the system stability as the current robot output limits, the output-force was corrected in real-time. The experimental results show that the algorithm can ensure the system stability effectively.