| Redundant parallel robots are widely used in industrial production lines,but when working under variable load conditions,due to the large changes in the force and inertia matrix of each arm of the robot,especially when running at high speed,it will aggravate impact and buffeting,affecting its movement.control precision.This paper takes the four-degree-of-freedom redundant parallel robot as the research object.From the two aspects of optimal trajectory and torque control,its kinematics and dynamic model under variable load conditions,trajectory optimization,torque feedback & feedforward control under variable load are carried out.Research,and strive to solve the impact and buffeting problems caused by the robot running at high speed under variable load conditions.The main research work and results of the paper are as follows:1)Kinematic analysis of four-degree-of-freedom redundant parallel robot and construction of a new dynamic model under variable load.The kinematic model of the four-degree-of-freedom redundant parallel robot is established,and the motion limit position,working space,and singularity of the robot are analyzed,which lays a foundation for its trajectory planning.The influence of variable load on the force/torque of the four-degree-of-freedom redundant parallel robot system is analyzed,and an improved dynamic model under variable load is proposed,that is,the variable load model is simplified by the equivalent method by reflecting the variable load at the end to the coordinates of the center of mass of the end,analyze the energy of each part,and finally use the Lagrangian equation to establish an improved dynamic model of each branch under variable load,to prepare for the subsequent torque control of the robot.2)Joint space trajectory optimization of the four-degree-of-freedom redundant parallel robot under variable load.Aiming at the shock and buffeting phenomenon caused by the four-degree-of-freedom redundant parallel robot running at high speed under variable load,a new type of 12-phase sinusoidal jerk curve is proposed by taking advantage of the characteristic that the sine function has no abrupt change is the the still a sine function after multiple integrations.The trajectory of the joint space of the four-degree-of-freedom redundant parallel robot;and aiming at low energy consumption,the trajectory is optimized by the penalty function method.Through experiments and simulations,the results show that: for the four-degree-of-freedom redundant parallel robot a with small workspace,the 12-phase sinusoidal jerk trajectory is more accurate and stable as a whole;and there is no sudden change in force and speed of each joint,which effectively avoid the phenomenon of mechanism oscillation.At the same time,the force of each joint of the robot is more uniform,each movement amount is closer to the maximum allowable limit value,the operation efficiency is higher,and the movement accuracy is improved from the perspective of trajectory planning.3)Torque hybrid control of four-degree-of-freedom redundant parallel robots under variable load.Aiming at the shock and buffeting phenomenon caused by each branch chain’s high-speed and variable-load operation of a four-degree-of-freedom redundant parallel robot,a hybrid control strategy of fuzzy calculation torque feedback & torque feedforward under variable load is proposed.The feedforward torque includes friction torque and variable load nonlinear disturbance torque.The friction torque is obtained by the parameter identification of the Stribeck friction model,and the nonlinear load disturbance torque is obtained by the real-time calculation of the improved dynamic model under variable load.Through the simulation and experiment of four-degree-of-freedom redundant parallel robot joints,the effectiveness of the robot adaptive fuzzy calculation torque feedback & torque feedforward control method under variable load is verified.The experimental and simulation results show that the motion accuracy of the adaptive fuzzy calculation torque feedback & torque feedforward control of the three drive joints of the robot under variable loads are 49.87%,70.48%,and 50.37% lower than that of the adaptive fuzzy calculation torque feedback;Compared with pure torque feedback control,the speed stability of the three driving joints under adaptive fuzzy calculation torque feedback & torque feedforward control are 23.35%,17.66%,and 25.04% higher,respectively. |
