Research On The Friction And Cutting Model Of Bevel-tip Flexible Needle Insertion

Recently, the research on robot-assisted minimally invasive surgery systems isa hot and difficult research issue of medical robot technology. The percutaneousminimally invasive surgical robot systems are demonstrating a potential applicationperspective in tissue biopsies, anesthesia-drug injection, and cancer brachytherapyetc for the diagnosis and therapeutic purposes, which is becoming the focus andcutting edge of minimally invasive surgical robot systems. As a core technique ofpercutaneous minimally invasive surgery, a bevel-tip flexible needle can replace thetraditional rigid needle in many clinic percutaneous treatments.When a needle is inserted into the soft tissue along the needle axis, a lateralforce on the tip is generated due to the bevel of the needle tip, which will conductthe bending of needle since the stiffness of the needle is relatively low. The needletrajectory inside of the tissue is controlled by two motion inputs completely, i.e.needle feeding and shaft rotating. In order to guarantee the needle to track a plannedspatial trajectory, the rotation of needle shaft should be controlled to change thedirection of the bevel-tip during the needle feeding. In view of this, the paper firstanalyses the factors which have impact on the flexible needle bending curvature andthe friction between the needle and tissue. Based on the assumption that the needle astraight line, the basic principle of mechanics is employed to analyse the forcesgenerated on the needle and bevel-tip when the needle is linear feeding and axialrotating. Finally, the forces distributed on the whole needle shaft is considered.As the flexible needle inserts into the tissue, in order to make the needle tipreach the target lesion more precise ly, the study of needle tip cutting process is quiteimportant. The research on the mechanism of bevel-tip needle cutting the tissuedepends on the breaking mechanism of materials and the law of conservation ofenergy. In order to make the body out of the track reserved, the steering at the baseshould be rotated a certain angle. Since the needle tip size is smaller than the needlebody’s which leads to the tip is clamped by tissue, and the tissue putting the force onthe bevel-tip. Axial rotation makes the blade of flexible needle do split the tissuewhich make the tissue have serious deformation and even destruction. Meanwhile,the complexity of the forces make the precision of the axial rotation be difficult tocontrol. In order to reduce the rotation error, retracted for some distance of theneedle is carried out, then rotate the flexible needle axially, the accuracy will beeasier to control relatively. Combine with the time-delay characteristics of thematerial, the effective value of the flexible needle retracted distance is obtained.Finally, the experimental platform is built, combined with the experiments corresponding contrast is made about the forces generated on the flexible needleaccording to body bending and straight track. Verify the forces application on theneedle during the process of needle linear feeding and shaft rotating, and alsoconfirm the measure to reduce the axial rotation error.