|Place of Conferral||北京，中国科学院自动化研究所|
|Keyword||超冗余机械臂 绳索驱动 多自由度关节 张力建模、优化 避障路径规划 几何误差辨识|
With the development of robotics, currently, in the industrial field, traditional manipulators have been able to replace humans to perform simple and repetitive tasks. However, there are still some operation scenarios with complex and narrow space that is difficult for traditional industrial robots to work within it, such as nuclear facility inspection, aircraft assembly, and power equipment maintenance. At the same time, in these cases, for manual work, either it is difficult to guarantee the quality and safety or because of the high temperature, high radiation, and toxic and harmful gases in the environment, it is impossible to conduct on-site operations at all. The common characteristics of these scenes are the complex and narrow working space, the disorderly distribution of obstacles, the harsh working environment, and the working point is located deep in the space. Therefore, the study of robots suitable for complex and narrow spaces has very important theoretical significance and application value. This paper takes the manipulator with a large aspect ratio and hyper redundant degrees of freedom as the object and conducts research in the aspects of mechanism design and realization, kinematics modeling, tension modeling and optimization, and obstacle avoidance path planning. The main contents are as follows:
Firstly, in response to the work requirements in complex and narrow spaces, a hyper-redundant cable-driven snake-like manipulator based on multi-degree-of-freedom joints was developed. The multi-degree-of-freedom design of the joints improves the flexibility of the manipulator. Through the modular joint and link structure, the flexible configuration of the manipulator under different operating scenarios is achieved. For the requirements of high precision, high load, and small size of the cable driver, a linear cable driver based on a trapezoidal screw has been developed. Due to the narrow space, the cable drivers' layout is optimized, and they are arranged in a cylindrical structure in two circles inside and outside. Finally, a snake-like manipulator control system was built to form a 10-joint snake-like manipulator experimental platform.
Secondly, aiming at the motion control of cable-driven hyper-redundant manipulators, a kinematics modeling method from driving space to pose space is proposed. The kinematics model was established by analyzing the relationship between the manipulator's posture, joint angle, cable length, and motor position. Due to the difficulty in solving inverse kinematics, a workspace solution model based on the Monte Carlo method is established by using forward kinematics. On this basis, the mechanical parameters of the manipulator were optimized by analyzing the influence of the link length, the maximum steering angle of the joint, and the number of joints on the working space.
Thirdly, aiming at the problem of tension estimation and optimization under cable drive, a cable tension modeling and optimization method is proposed. Based on the principle of rigid body torque balance, a cable tension model is established, and the torque is decomposed according to the mechanical constraints of the joints to solve the cable tension. A tension optimization evaluation function is constructed according to the tension model in the path planning and by the redundant degrees of freedom of the robotic arm, the optimization of the rope tension is realized.
Fourthly, aiming at the obstacle avoidance path planning problem of the hyper-redundant manipulator, a path planning method based on the fusion of improved artificial potential field method and joint following obstacle avoidance is proposed. By decomposing the path planning process into two stages, the complexity of planning is reduced. In the first stage, aiming at the search for the end-guided trajectory of the manipulator, an improved artificial potential field method based on the passive repulsion mechanism is proposed, which avoids the problem caused by the mismatch of the gravity function and the repulsion function. In the second stage, in order to plan the other links' poses when the end of the manipulator is advancing along the guiding trajectory, a joint following method based on the optimal search is proposed and the fitness function is constructed through the geometric constraint between the joint and the link. At the same time, in order to avoid the obstacle, a collision detection method based on the angle between obstacles and links is proposed, which improves the efficiency of collision detection.
Fifthly, aiming at the geometric parameter calibration of the cable-driven snake-like manipulator, a parameter identification method based on the rotation angle of the joint is proposed. The use of the measurement of the rotation angle instead of the measurement of the posture of the joint end overcomes the problem of the complex measurement processes and expensive equipment. Taking the joint angle as the intermediate variable, the relationship between the geometric parameters and the rotation angle is analyzed and the identification model is established, and the joint geometric parameter calibration is realized. For the rotation angle measurement, the information of the monocular camera and the acceleration sensor is fused through the extended Kalman filter, and an easy and low-cost method of rotation angle measurement is proposed. The calibration process based on the above identification method and measurement method has high operating convenience and environmental adaptability.
Finally, the research work of this paper is summarized and pointed out the work that needs to be carried out in the future.
|徐大伟. 复杂狭窄空间中超冗余蛇形机械臂设计与规划控制技术研究[D]. 北京，中国科学院自动化研究所. 中国科学院大学,2021.|
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