| Under the influence of the industrial policies of Made in China 2025 and Industry 4.0,smart warehousing and automated logistics have gradually emerged in recent years.The movable assembly robot has a large working space and high flexibility,which is more in line with the application requirements of modern factories.At present,tandem articulated robots are mostly used in the field of industrial assembly.This type of robot has a small load-bearing capacity and can only be applied to the assembly of small and light workpieces.Compared with series robots,parallel robots have some unique advantages.For example,parallel robots can carry larger weight workpieces,have high position control accuracy,and have small inertia of workpieces at their ends.In this paper,the Stewart parallel robot is used as the experimental platform,and the force compliance control based on dynamic feedforward compensation and the position-based impedance control strategy are designed,and the simulation and experiment of the control system are completed.The main research contents of this article are:First,the structure of the Stewart parallel six-degree-of-freedom platform was simplified and the world coordinate system and dynamic coordinate system were established.The derivation process of Stewart platform inverse kinematics formula is briefly introduced and the derivation formulas of linear velocity,acceleration,angular velocity and angular acceleration of six branch chains are given.The inertia moments of the moving platform and 6 branch chains of the Stewart parallel robot are deduced to prepare for the inverse dynamic modeling of the platform.The Newton-Euler method is used to establish the inverse dynamics theoretical calculation model of the Stewart platform.Using Matlab and Adams built a simulation model to verify that the theoretical model of inverse kinetics is correct.Secondly,researched and analyzed the servo motion system with the motor and the ball screw as a whole,and established the dynamic equation of the servo motion system.In order to complete the force compliance control of the Stewart parallel robot based on dynamic feedforward compensation,the friction force of the servo motion system cannot be ignored.In this paper,a model based on Coulomb-viscous friction is established,and the unknown parameters in the friction model are identified through experiments.This paper proposes an external force estimation method based on a dynamic model,which allows the Stewart platform to detect the external force and estimate the magnitude of the external force.Since it is difficult to guarantee the position accuracy of the robot in the torque mode,this paper designs the position-based impedance control algorithm of the Stewart platform.Finally,the composition of the hardware control system of the experimental platform is introduced in detail,and the structural parameters of the Stewart platform studied in this paper are given.Using the C++ programming language in the programming environment of Vs2015+Qt5.8,the software control interface,the communication function between the host computer and the hardware system,and the control algorithm function are programmed.On this basis,the experiments of force compliance control based on dynamic feedforward compensation and position-based impedance control are completed.The experimental results of the two control methods are compared and analyzed,and the control method with fast response speed and better control accuracy is selected to complete the workpiece assembly task of the platform. |
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