An empirical model of friction force between a needle and soft tissue

Experienced doctors complement insufficient visual information during CT-guided needle intervention by using haptic sensation delivered to their hands. Training simulation with haptic feedback can enhance effect of the training. A model is necessary in such simulation to compute the friction force between the inserted needle and surrounding tissue in real-time. This paper proposes a mathematical model of the friction force based on the experiment results using porcine soft tissue. The friction force is measured by inserting a needle into the tissue using a 6-DOF articulated robot. The results show that the friction force increases gradually up to kinetic friction due to deformation of surrounding tissue. This is in contrast with friction force between rigid objects where kinetic friction appears immediately after movement. Deformation of the tissue also results that the friction has hysteresis over the velocity of the needle. Magnitude of the friction varies according to the moving direction of the needle. Dahl friction model is adopted and modified by adding a term for linear viscous friction based on the characteristics confirmed through experiments. Accuracy of the model is verified through comparison between the model and measured data from porcine tissue. The proposed model can describe friction force of various porcine tissue with root-mean-square error less than 0.13 N.