Research On Structure Optimization Of Heavy Load Industrial Robot With Joint Flexibility Considered

Currently, heavy load industrial robots have a wide range of applications inmetallurgy, automobile, logistics and palletizing, and many other industries. With theimprovement of production requirements and the complexity of the work environment,a higher load capacity, better stability and better movement speed, acceleration, andother properties are required for the industrial robot. Therefore, it is needed to optimizethe structure of the robot according to the relevant performance index.In the past, the links and joints are considered to be rigid in the structureoptimization of the industrial robot. However, for heavy load industrial robots, jointflexibility is obvious than link flexibility. So, the joint flexibility characteristics must beconsidered in the structure optimization of heavy load industrial robots.The main research purpose of this paper is to improve the robot’s vibrationperformance index and the static stiffness performance index by optimizing thestructure of the robot which is a casting robot researched and developed independentlyby the laboratory considered the joint flexiblity. Firstly the pure rigid robot simulationmodel is established in ADAMS. A method of adding joints flexiblity in the simulationmodel is introduced by using additional virtual object, revolute joint and rotationaltorque. Four experiments are done to compare the pure rigid joint robot model and theflexible joint robot model in order to verify the influence of joints flexiblity on the robotmovement performance. The standard D-H coordinate system is established for therobot model, the robot forward kinematics problems are analyzed and the robot jacobianmatrix parametric form is also derived.Secondly, the robot modle’s dynamic equations which contain flexible jointcharacteristic are established by the Lagrangian method, the link’s dynamic equationand the motor’s dynamic equation are obtained separately. The parametric form of thedynamic inertia matrix is also derived. According to the multi-degree of freedom systemmodal analysis theory, the vibration equation of the robot system which contain theflexible joint is derived. The vibration simulation experiments are tested in thefrequency domain by using the ADAMS/Vibration analysis module to verify thecorrectness of the robot system’s vibration equation.Then, the performance index that measures the vibration characteristics of therobot is proposed. The robot’s optimization objective function model that combines withthe robot’s vibration performance index, static stiffness performance index and speedcomprehensive performance index is build. The optimization variables are determinedthrough sensitivity analysis. The complete robot structural optimization mathematicalfunction model is established based on the practical constraints. Finally, after the coupling analysis of the optimization objective function, theNSGA-Ⅱ multi-objective evolutionary algorithm is used to solve the optimizationfunction model. The robot’s arm length parameters and cross-section parameters areoptimized separately. Then the optimized results are compared to determine the best sizeparameters form. The effectiveness of the structural optimization results are verifiedthrough the simulation experiments.