Kinematics And Precision Analysis Of Snake Manipulators

The modular super-redundant degree of freedom snake robot arm has an important application prospect in narrow space exploration and other fields due to its excellent dexterity.Due to its unique structural form and kinematic characteristics of super-redundant degrees of freedom,it is challenging in mechanism design,kinematics modeling,and high-precision positioning operation when compared to traditional mechanisms.This paper investigates kinematics modeling,structure design,and high-precision positioning operation to realize high precision inside view operation of a snake robot arm with 20 degrees of freedom.Kinematics analysis is performed on the general model of the snake robot arm,which is divided into three Spaces: drive space,configuration space,and operation space,and four types of mutual mapping relations between them are studied in this paper.For modeling and simulation verification,the numerical method,space vector method,and screw theory were used.The Monte Carlo method was then used to analyze the workspace of the robot arm,which guided the robot arm’s structure design.Second,a new type of snake robot arm with a macro-micro structure is designed using the bionic design concept.The robot is made up of ten 2-DoF joints that are driven in parallel ropes.At the root,the snake robot arm has seven joints in a coupled drive design,allowing for heavy load motion while improving stiffness and support stability.The three head joints use a decoupling design to improve the snake robot arm’s mobility and achieve high-precision operation in a small space.Then,a regularized kinematic calibration method is proposed to improve the kinematic accuracy of the snake robot arm.Aiming at the end position error caused by uncompensable error,the error compensation method and sensitivity evaluation index are introduced to guide the tolerance design of mechanical arm structure parts.To further improve the positioning accuracy of the end of the manipulator,the kinematics calibration of a single joint of the manipulator was carried out,to obtain a smooth solution to solve the problem of ill-posed.By modifying the kinematic model,the precision of the end position of the manipulator is further improved.Then,by analyzing the robotic arm’s statics,a comprehensive stiffness adjustment method is proposed to adjust the compensable error.A serpentine robot arm with 20 degrees of freedom is made up of several 2-degrees-of-freedom joints connected in series,and its stiffness can be adjusted by adjusting each 2-DoF joint.However,the hydrostatic model is affected by gravity,friction,rope tension,and the motion of the coupled joints in addition to the rope drive and external load.To improve the robotic arm’s end position accuracy,an accurate static model of the coupling joints must be established,and the rope tension of the 20-degree-of-freedom joints must be adjusted by analyzing various forces and moments.As a result,the stiffness and motion performance of the robotic arm can be optimized,and it will have improved motion control capability in complex environments.Finally,kinematic control,kinematic calibration,precision testing,and stiffness adjustment of the snake arm were performed to validate the effectiveness of the algorithm and modeling.Point-to-point and continuous trajectory experiments are used to validate the kinematic modeling.The proposed kinematics calibration algorithm’s effectiveness is demonstrated by kinematic calibration experiments on a single joint.The snake robot’s arm stiffness adjustment experiment validates the algorithm’s effectiveness.Finally,the experimental results show that the snake robot arm can operate with high precision.The improvement of the snake manipulator’s accuracy is a multifaceted problem.In the future,the snake manipulator’s dynamics,control system,and trajectory planning can be studied,and a variety of accuracy assurance measures can be proposed to comprehensively improve the snake manipulator’s position accuracy.