Research And Implementation Of Force Feedback In Virtual Surgery

Virtual Surgery Simulation is a reality application of virtual reality technology in thefield of medicine, aiming at simulating various situations that may be happened in surgicalprocedures, which has become the frontier and challenging problem researched byInternational Biomedical Engineering currently.Researches of virtual surgery are mainly focused on virtual and haptic. Through visualfeedback, a direct and realistic surgery scene is created; through haptic feedback, the force ofvirtual object can be felt, which allow users to make timely operation and correct judgment.Starting from the virtual technique, this thesis selects the typical as well as difficult humanliver tissue as the research object and conducts an in-depth research on force/haptic feedbackof virtual surgery simulation. The main work is as follows:Firstly, achieving force feedback based on mesh technique: the mass-spring volumemodel was selected to make the physical model of the liver. It had better physical realism,while it also has disadvantages such as large amount of data, complex calculation, so animproved Euler algorithm was proposed to solve the process of soft tissue deformation, usingexplicit Euler method for solving the particles’ velocities to as the initial value and usingimplicit Euler method to solve the displacements. This method combines the advantages ofexplicit and implicit Euler methods with better stability and higher real-time performance;Based on PHANTOM Omni force feedback device, calculating force feedback withspring-damper model, then stable and smooth force was outputted.Secondly, achieving force feedback based on mesh-less technique: Mesh-less methoddoes not depend on the mesh and will not require mesh reconstruction and division. It isself-adaptive and highly precise and has shown good prospects in the field of virtual surgerysimulation. In this paper, SPH method based on mesh-less was applied to calculate forcefeedback of virtual surgery: Voigt viscoelastic model was selected to describe thebiomechanical characteristics of soft tissue, which adequately considers the constitutiveequations and has higher accuracy; SPH method was used to solve deformation equations andforce feedback generated during the interaction, then outputting the force to haptic device toachieve tactile interaction.Thirdly, SPH method is highly precise, however, when it was used in whole model, thecalculation cost was so large that force feedback was not stable and the arm of haptic device bounced up and down. Smooth tactile force feedback requires the refresh rate is not less than300HZ, in order to meet the requirement, a local SPH method based on dynamic deformationarea was proposed. Soft tissue was divided into two parts: deformation area andnon-deformation area. Assuming that deformation of soft tissue was just determined by theparticles in deformation area, so the deformation was considered to not occur innon-interaction area. The deformation area included two parts: interaction region andtranslation region. In local region, every physical quantity of particles was solved by SPH; Intransmission region, physical quantities were obtained by decaying the same physical quantityof the contact point. This method has advantages such as changeable position and extendablearea, at the same time reduced the number of particles involved in calculation and greatlyimproved computational efficiency. Ultimately, the force feedback was stable and hapticinteraction was realistic.Finally, achieving force feedback based on SPH has not been reported by now, thereforeit is necessary to validate the validity and real-time of SPH. In the aspect of validity, with thesame liver data as the test sample, we compared the simulate results of SPH method withresults based on mass-spring model and real pig liver, the result shows that the SPH is suitablefor the calculation of force feedback; In the aspect of real-time, we made statisticalcomparison of the real-time of the mass-spring model, SPH method and the local SPH basedon dynamic interaction area, in the meantime, we also discussed the impact of smooth radiuson the real-time of SPH method.