A software architecture for surgical simulation using haptics /

The application of haptic devices to surgery simulation presents many exciting opportunities. For example, medical students could practise surgery without using animals and surgeons could evaluate and plan surgical procedures before making a single real incision. An integral component of these surgical simulator systems is haptic feedback. There are many engineering challenges that must be addressed in order to successfully integrate haptics with the environmental characteristics found in surgery. The most fundamental of these challenges is to achieve update rates of solid nonlinear deformable objects that are acceptable to the human haptic system. This thesis presents a software architecture that is designed to meet these challenges by analysing the task, the haptic, and the hardware constraints of surgery simulation. A new hierarchical finite element mesh structure is introduced that uses an equivalent impedance method to specify parent-child relationships, an idea inspired by Thevenin equivalents in circuits. The mesh hierarchy achieves several important objectives, including mixed-mode simulations, multi-frequency operation, and explicit accuracy-time tradeoffs. After an analysis of the problem constraints, the theoretical framework of the hierarchical mesh structure is presented. Implementation issues and results are presented for three cases: a linear, dynamic, and linear-nonlinear system. These results show that the hierarchical mesh structure can provide low force latency even for nonlinear systems