Stability Analyzing And Path Planning For Robot-assisted Needle Insertion

In the procedure of needle insertion, the accurately prediction of target’s position is usually strongly expected. However, the target not only leaves away from its original position, but also vibrates. For the vibration of target, it is very hard to accurately predict the position of target in real time. Reducing the amplitude of target, namely improving insertion stability, has great significance to the accurately prediction of target’s potion. The vibration of target results from the interaction between needle and soft tissue. As a result, the vibration of insertion force can reflect target’s vibration. The effects of tissue properties and insertion velocities on insertion stability are analyzed and the velocity relevant stability model is established. The model can be used to choose a suitable velocity with the purpose of improving insertion stability.The D-H(Denavit-Hartenberg) method is used to model the forward kinematics of flexible bevel-tip insertion needle. When the distance between the needle tip and target is less than or equal to 2r(r is the radius of track), the tip’s motion is limited by reachability. Therefore, a geometric approximation model is proposed which can guarantee the reachability of needle tip corresponding to target in real time. The model applies to the case that the distance between the insertion point and target is less than or equal to 2r. All feasible paths can be obtained by using the model. Simulation results show that the proposed model can accurately predict a feasible path between the insertion point and target, so it can supply the theoretical base for path planning.When the distance between the needle tip and target is greater than 2r, the tip’s motion isn’t limited by reachability. The needle tip can arbitrarily move forward in principle. However, the purpose of needle insertion is to make the needle tip reach target. We hence provide a kind of path planning algorithm that can guide the needle tip toward to target. The algorithm also allows some intermediate steps not to decrease the distance between the needle tip and target. Accordingly, the algorithm makes the needle insertion have strong ability of obstacle avoidance. Meanwhile, the proposed algorithm and geometric approximation model are combined to meet the path planning needs of the case that the distance between the insertion point and target is greater than 2r. Finally, the simulation experiments are done. Simulation results reveal that the combination of proposed algorithm and geometric approximation model can accurately plan a feasible path between the insertion point and target. Therefore, when the proposed method is used to perform optimal path planning, the needle tip can certainly reach target theoretically. Consequently, the proposed method can supply the theoretical base for optimal path planning.