| The hybrid welding robot is a kind of industrial robot engaged in welding tasks.Compared with the traditional series mechanism,it has the advantages of high intelligence,good motion output flexibility and high motion precision.It is a kind of nonlinear system with complex nonlinear dynamic behavior.When performing the welding operation,the hybrid welding robot needs to move from the initial position to the specified position according to the predetermined trajectory within a certain period of time,but because of the nonlinear characteristics of the structure,the robot still has serious elastic vibration during and after welding,resulting in the end of the robot can not reach the designated position quickly and accurately,and even cause fatigue damage.For example,the spot welding robot needs to wait for the residual vibration of the working arm to be reduced before it can carry out the next work.The arc welding robot must run continuously and smoothly according to the specific trajectory at the rated speed.Therefore,in order to achieve fast,accurate and high quality welding,it is necessary to study the nonlinear dynamic behavior of this new type of robot and make reasonable trajectory planning to reduce the influence of system vibration on welding operation.This paper takes the series-parallel hybrid welding robot as the research object,in order to improve the vibration suppression effect and tracking and positioning ability,takes the computer technology and mathematical modeling theory as the technical means,and combines theoretical analysis with practical experiments.the following studies are carried out from the aspects of robot kinematics,dynamics,vibration characteristics and trajectory planning:(1)Based on the kinematics theory,the forward and inverse kinematics model of the hybrid welding robot is established by using the Dmurh parameter method,and the validity of the model is verified by the robot toolbox Robotics.On this basis,the effective workspace of the robot is analyzed.Using Lagrange equation,the rigid body dynamics model of hybrid welding robot is established from the point of view of energy,and the control force / torque of the joint is obtained.With the combination of finite element method and dynamic substructure analysis,the motion differential equations of drive system substructure,transmission system substructure,flexible member substructure and bearing substructure are derived respectively.Through the displacement coordination conditions of each substructure,a comprehensive elastodynamic model of hybrid welding robot is established,which provides a theoretical basis for further study of the dynamic performance of hybrid welding robot.(2)Based on the multi-position attitude acceleration frequency response function measured by the robot experiment,a model correction method based on the normalized frequency response function sensitivity is proposed,and the modified elastodynamics(CKED)model of hybrid welding robot is established,which makes the theoretical calculation results closer to the experimental results.Through the hammering test,the natural frequency of the robot system is tested to verify the correctness of the CKED model.According to the shock and vibration phenomena of the welding robot during the welding task,the impulse excitation method is used to test the impact vibration of the robot under different postures,and the vibration characteristic parameters of the midpoint strain of the end bar of the robot are studied.Compared with the theoretical calculation results,the validity of the CKED model is further verified.(3)The terminal trajectory error controller is introduced to improve the end trajectory tracking accuracy of the robot.The dynamic response of hybrid welding robot is solved by the direct integral Newmark method,and the motion law of nonlinear system is analyzed.The time domain diagram,phase diagram,Poincare map,maximum Lyapunov exponent and bifurcation diagram of the robot end effector moving according to the specific welding trajectory are studied,and the chaotic phenomena in the system are identified.The relationship between the maximum Lyapunov exponent and the trajectory radius,trajectory velocity,rod material,rear arm thickness and material elastic modulus of the robot system is revealed,and the dynamic performance design theory of this new type of robot is formed.It is helpful to further obtain the characteristics of the nonlinear dynamic behavior of the system and reveal the causes of the abnormal vibration of the system.(4)According to the task of continuous path tracking of hybrid welding robot,the spatial arc trajectory is planned based on the double S velocity profile interpolation function,and the path planning problem is transformed into the parameter optimization problem in the interpolation function.In order to avoid the sudden change of joint angle,based on the normalized Jacobian condition number,a multi-objective optimization model considering motion time,system energy consumption and terminal amplitude fluctuation is proposed,which is solved by elite non-dominant sorting genetic algorithm(NSGA-II).The optimal solution is determined by defining the weight of the target,and the continuous task with faster time,lower energy and more stable is realized.To achieve the purpose of vibration suppression of hybrid welding robot based on trajectory planning. |
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