Reed Kyle B, Okamura Allison M, Cowan Noah J
Department of Mechanical Engineering at The Johns Hopkins University.
IEEE Int Conf Robot Autom. 2009 May 12:3476-3481. doi: 10.1109/ROBOT.2009.5152749.
A flexible needle can be accurately steered by robotically controlling the orientation of the bevel tip as the needle is inserted into tissue. Here, we demonstrate the significant effect of friction between the long, flexible needle shaft and the tissue, which can cause a significant discrepancy between the orientation of the needle tip and the orientation of the base where the needle is controlled. Our experiments show that several common phantom tissues used in needle steering experiments impart substantial frictional forces to the needle shaft, resulting in a lag of over 45° for a 10 cm insertion depth in some phantoms; clinical studies have reported torques large enough to could cause similar errors during needle insertions. Such angle discrepancies will result in poor performance or failure of path planners and image-guided controllers, since the needles used in percutaneous procedures are too small for state-of-the-art imaging to accurately measure the tip angle. To compensate for the angle discrepancy, we develop a model for the rotational dynamics of a needle being continuously inserted into tissue and show how a PD controller is sufficient to compensate for the rotational dynamics.
当柔性针插入组织时，通过机器人控制斜面尖端的方向可以精确地操纵柔性针。在此，我们展示了长柔性针杆与组织之间摩擦力的显著影响，这可能导致针尖方向与控制针的基部方向之间出现显著差异。我们的实验表明，在针操纵实验中使用的几种常见模拟组织会对针杆施加相当大的摩擦力，在某些模拟组织中，对于10厘米的插入深度，会导致超过45°的滞后；临床研究报告称，在针插入过程中，扭矩大到足以导致类似的误差。这种角度差异将导致路径规划器和图像引导控制器性能不佳或失效，因为在经皮手术中使用的针太小，无法通过最先进的成像技术准确测量尖端角度。为了补偿角度差异，我们建立了一个针连续插入组织时旋转动力学的模型，并展示了比例微分（PD）控制器如何足以补偿旋转动力学。
