| With the rapid development of industrial robots and ship repairing industry,a number of automatic welding equipment for ships have emerged,including single column welding robot based on horizontal guide rail and gantry welding robot based on truss.But all of them are articulated robotic mechanisms with series structure.Their driving motors are installed on all joints,which will lead to large inertia,large cumulative error and poor dynamic performance of the end-effector.Especially in the complex environment of ports stimulated by fluid load and wind load,they still can not meet the requirements of high-strength and high-precision welding of ships.Aiming at the above problems,based on the related research results of multi-degree-of-freedom(DOF)controllable mechanism and parallel mechanism,the closed-chain welding robot manipulator for shipbuilding is explored.The motors of this kind of low-degree-of-freedom closed-chain actuator are installed on the rotating frame.They are driven by external rotating pairs and closed-chain connecting rods.With large space and flexible output of multi-trajectory,it also avoids the shortcomings of traditional mechanism and can better meet the requirements of shipbuilding welding.The research work in this paper is as follows:Firstly,based on the function analysis of the traditional welding robot,the innovative design of its actuator is carried out.The mechanism configuration is synthesized by combining the traditional regenerative kinematic chain method and the new planar foundation closed-loop substructure replacement method,which changes the traditional single structure form and enriches the configuration of engineering plant for the shipbuilding welding task;Introducing metamorphic mechanism into the field of shipbuilding welding,a variable topology structure welding robot manipulator for shipbuilding is designed.The metamorphic principle and configuration evolution process are obtained through analysis.According to the three effective configurations,they are suitable for different welding operations,which can provide references for the design and research of engineering-oriented metamorphic mechanism.On this basis,based on Assurr groups and Lie group theory,the configuration principle and degree of freedom of one of the closed-chain welding robot mechanisms synthesized are dissected;The kinematics mathematical analytical model of the mechanism is established,and the velocity characteristics of the mechanism are obtained.The singularity of the mechanism is solved by using Jacobian matrix method combined with numerical examples,and the working space of the mechanism is obtained under the condition of no singularity.The kinematics laws and characteristics of the manipulator are revealed.The advantages of the mechanism are obtained by comparing with the 2-DOF closed-chain mechanism.Specifically,the workspace is larger,and it has the functions of positioning and attitude adjustment.Based on the velocity Jacobian matrix of the end output position,the performance analysis is carried out.It has the characteristics of high dexterity,high operability and fast response speed.Then,the force analysis of the mechanism is carried out,and the dynamic and static model of the closed-chain mechanism is established by the dynamic and static method;The rigid body dynamics model is established by the Lagrange method,and the parameters affecting the dynamic performance of the mechanism are determined;The stiffness analysis of the mechanism reveals the influence of the external force,the internal mechanism and the position and posture on the stiffness of the mechanism.All of these can provide some references for the selection of servo motor and the design and research of closed-loop control system.Finally,the virtual prototype model of the closed-chain mechanism is established and imported into ADAMS.Based on the specific working trajectories,the rationality and practical feasibility of the mechanism are further verified by forward and reverse kinematics simulation analysis. |
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