Shape Estimation of Soft Manipulators using Piecewise Continuous Pythagorean-Hodograph Curves
Shape Estimation of Soft Manipulators using Piecewise Continuous Pythagorean-Hodograph Curves
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DOI：
10.23919/acc53348.2022.9867270
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发表时间：
2022-06
期刊：
影响因子：
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通讯作者：
Harish Bezawada;Cole Woods;V. Vikas
中科院分区：
文献类型：
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作者：
Harish Bezawada;Cole Woods;V. Vikas
近年来，在包括外科手术和农业机器人在内的不同领域中使用软连续体操纵器引起了极大的兴趣。因此，研究人员设计了开环和反馈控制算法，这样的系统。在这里，知识的机械手的形状是至关重要的有效控制。机械手形状的估计是具有挑战性的，由于其高度可变形和非线性的性质。研究人员探索了感应、磁性和光学传感技术来推断操纵器形状。然而，它们是侵入性的并且经济上昂贵。替代的非接触感测方法可以涉及使用沿着操纵器以已知间隔沿着放置的视觉或惯性测量单元（伊穆斯）。这里，相机提供标记的位置，而斜率（旋转矩阵或方向余弦）可以使用伊穆斯来确定。在本文中，我们数学模型的机械手形状使用多个分段连续的五次Pythogorean-Hodograph（PH）曲线。PH曲线具有连续的斜率，并且是具有恒定长度的曲线的方便的参数模型。我们研究使用多个分段连续曲率PH曲线来估计软连续体操纵器的形状。该曲线对恒定长度的操纵器段进行建模，同时假定节点处的斜率是已知的。对于具有（4 N + 8）个未知数的N个曲线段，形状估计被公式化为最小化曲线弯曲能量的约束优化问题。该算法施加了（4 N + 3）对应于连续性，斜率和段长度的非线性约束。与传统的三次样条不同，优化问题是非线性的，对初始猜测敏感，并有可能提供不正确的估计。我们研究的鲁棒性的算法，通过增加变化的方向余弦，并比较输出的形状。五段机械臂的仿真结果表明了该算法的鲁棒性。在柔性张拉整体脊柱机器人上的实验结果验证了该方法的有效性。在这里，估计误差的末端执行器的位置归一化为机械手的长度为6.53%和6.2%的两个实验位姿。
In recent years, there has been significant interest in use of soft and continuum manipulators in diverse fields including surgical and agricultural robotics. Consequently, researchers have designed open-loop and feedback control algorithms for such systems. Here, the knowledge of the manipulator shape is critical for effective control. The estimation of the manipulator shape is challenging due to their highly deformable and non-linear nature. Researchers have explored inductive, magnetic and optical sensing techniques to deduce the manipulator shape. However, they are intrusive and economically expensive. Alternate non-contact sensing approaches may involve use of vision or inertial measurement units (IMUs) that are placed at known intervals along the manipulator. Here, the camera provides position of the marker, while the slope (rotation matrix or direction cosines) can be determined using IMUs. In this paper, we mathematically model the manipulator shape using multiple piecewise continuous quintic Pythogorean-Hodograph (PH) curves. A PH-curve has continuous slope and is a convenient parametric model for curves with constant length. We investigate the use of multiple piecewise continuous-curvature PH curves to estimate the shape of a soft continuum manipulator. The curves model manipulator segments of constant lengths while the slopes at the knots are assumed to be known. For N curve segments with (4N + 8) unknowns, the shape estimation is formulated as a constrained optimization problem that minimizes the curve bending energy. The algorithm imposes (4N + 3) nonlinear constraints corresponding to continuity, slope and segment length. Unlike traditional cubic splines, the optimization problem is nonlinear and sensitive to initial guesses and has potential to provide incorrect estimates. We investigate the robustness of the algorithm by adding variation to the direction cosines, and compare the output shapes. The simulation results on a five-segment manipulator illustrate the robustness of the algorithm. While the experimental results on a soft tensegrity-spine manipulator validate the effectiveness of the approach. Here estimation error of the end-effector position normalized to the manipulator length are 6.53% and 6.2% for the two experimental poses.