An empirical nonlinear viscoelastic model of reflective force by a layer of soft tissue

Abstract

Haptic sensation delivered to doctor's hands during CT-guided needle intervention complements insufficient visual information. Exploitation of the haptic information is to be trained using simulation. A model is necessary to compute the reflective forces occurring when the needle tip contacts with layers of soft tissues such as skin, membrane, and other layers of tissues. This paper proposes a nonlinear viscoelastic model based on measurements using porcine soft tissues. A 6-axis force-torque sensor and a needle are attached to the end of a 6-DOF articulated robot to measure the layer forces. The measurement results show that the layer forces increase nonlinearly with displacement of the needle. The force is affected by change of the velocity. It is also shown that the reflective force is relaxed when the needle stops. A standard linear solid model which can describe the relaxation phenomena is modified to describe nonlinear damping and stiffness forces. Accuracy of the developed model is verified through comparison between the model and measured data using porcine tissues. The proposed model can describe the nonlinear stiffness and relaxation phenomena with relative error less than 3.8 %.