Robotics Engineering Department, DGIST, Daegu, 42988, Republic of Korea.
Convergence Research Center for Collaborative Robots, DGIST, Daegu, 42988, Republic of Korea.
Int J Comput Assist Radiol Surg. 2019 Aug;14(8):1365-1377. doi: 10.1007/s11548-019-01976-4. Epub 2019 Apr 17.
One of the main factors that affect the rigidity of flexible robots is the twist deformation because of the external force exerted on the end effector. Another important factor that affects accuracy is the fact that such robots do not have a constant curvature. The conventional kinematic model assumes that the curvature is constant; however, in reality, it is not. To improve the rigidity and accuracy of flexible robots used in minimally invasive surgery via preventing the twist deformation while ensuring a constant curvature, we propose a novel flexible manipulator with ball-constrained spherical (BCS) joints and a spring.
The BCS joints are used to prevent the twist deformation in the flexible robot. The joints have two degrees of freedom (DOFs), which limit the rotation about the axial direction. The rotation is limited because the ball that is inserted into a BCS joint can move only along the ball guide. To obtain a constant curvature, springs are installed among the BCS joints. The springs receive the uniform compression force generated among the joints, thus achieving a constant curvature. The proposed BCS joint is designed based on the diameter of the forceps, desired workspace, and desired bending angle.
To evaluate the proposed mechanism, three experiments were performed using a 20-mm-diameter prototype consisting of 13 BCS joints with a two-DOF motion. The experimental results showed that the prototype can realize a constant curvature with a mean error of 0.21°, which can support up to 5 N with no apparent twist deformation.
We developed a flexible manipulator with BCS joints for minimally invasive surgery. The proposed mechanism is anticipated to help prevent the twist deformation of the robot and realize a constant curvature. Accordingly, it is expected that rigidity is improved to ensure accuracy.
影响柔性机器人刚度的主要因素之一是由于末端执行器受到外力而产生的扭曲变形。另一个影响精度的重要因素是，此类机器人的曲率不是恒定的。传统的运动学模型假设曲率是恒定的；然而，实际上并非如此。为了通过防止扭曲变形同时确保恒定曲率来提高微创手术中使用的柔性机器人的刚度和精度，我们提出了一种具有球约束球形（BCS）关节和弹簧的新型柔性机械手。
BCS 关节用于防止柔性机器人的扭曲变形。关节有两个自由度（DOF），限制了沿轴向的旋转。由于插入 BCS 关节的球只能沿球导槽移动，因此限制了旋转。为了获得恒定的曲率，在 BCS 关节之间安装了弹簧。弹簧接收关节之间产生的均匀压缩力，从而实现恒定的曲率。提出的 BCS 关节是根据钳子的直径、所需工作空间和所需弯曲角度设计的。
为了评估所提出的机构，使用由 13 个具有两自由度运动的 BCS 关节组成的 20 毫米直径原型进行了三项实验。实验结果表明，原型可以实现曲率恒定，平均误差为 0.21°，可以支撑高达 5N 的力而没有明显的扭曲变形。
我们为微创手术开发了一种具有 BCS 关节的柔性机械手。所提出的机构有望帮助防止机器人的扭曲变形并实现恒定的曲率。因此，预计可以提高刚度以确保精度。
