肠道机器人扩张机构设计与优化

Design and optimization of expanding mechanism of intestinal robot

为了满足肠道机器人在肠道中运动和驻留的要求,设计了一种大变径比的新型扩张机构。该机构通过采用双层叠腿式设计,增大了与肠道的接触面积,最大扩张半径达到24.5mm,变径比增加到3.27。为了进一步研究该扩张机构的性能,建立了扩张臂的数学模型,对扩张臂的力学与运动学特性进行了理论分析。然后通过有限元分析,对扩张臂运动过程进行了动力学仿真,研究了不同扩张半径下,扩张臂的应力分布和变化趋势,基于有限元分析结果,对扩张臂进行了优化设计,优化后的等效应力最大值比优化前减小了12.89%。之后通过ADAMS对扩张臂进行运动学仿真,以验证其运动学模型的准确性。最后搭建了力学性能实验台,对其扩张力进行了测试,以验证其力学模型的准确性。实验结果显示:实验值与理论值的变化趋势基本一致,而且实验值小于理论值;机构扩张初始阶段误差较大,扩张半径为7.5 mm时,实验值仅为理论值的14.30%;之后误差急剧减小并趋于稳定,扩张半径为10~23mm时,实验值平均为理论值的73.64%;扩张臂1、2、3的实际扩张半径分别为24.5、24和23mm。结果显示本文设计的肠道扩张机构基本满足肠道安全性和大变径比的设计要求,而且结构优化效果明显。

A new-type expanding mechanism with Variable Diameter Ratio （VDR） is designed to satisfy requirements of intestinal robot movement and anchoring in the intestine tract. With the double-stacked folding design of the mechanism, the contact area with intestine tract is increased. The maximum expanding radius reaches to 24.5 mm, and VDR increases to 3.27. To further study the performance of the expanding mechanism, the mathematical model of the expanding arm is established to analyze the mechanical and kinematic properties of the expanding arm. Then, the dynamics of the expanding arm is simulated by using the finite element analysis （FEA） and the stress distribution and the trend of the expanding arm with different expanding radius are studied. Optimization design of expanding arm is conducted based on the results of FEA, and maximum of equivalent stress after optimization reduced by 12.89% than that before optimization. Subsequently, the kinematics of the expanding arm is simulated by ADAMS and the kinematics model is verified. Finally, the mechanical performance test platform is established to test its expanding force and verify its mechanical model. Experimental result indicates：the variation trend of experimental value and theoretical value is basically the same,and experimental value is less than theoretical value; the error is large in initial stage of mechanism expanding, and experimental value is only 14.30% of theoretical value when expanding radius is 7.5 mm, After that, the error drastically decreases and the mechanism tends to be stable, and experimental value is 73.64% of theoretical value on average when expanding radius is 10 mm-23 mm; Actual expanding radius are respectively 24.5, 24 and 23 mm for expanding arms 1, 2 and 3. Designed expanding mechanism of intestinal tract basically satisfies design requirements of intestinal tract safety and large VDR, and structural optimization effect is significant.