Research On Active Compliance Control System For Robot Assembly Tasks

With the continuous development of assembly robotics,robots are increasingly required to perform tasks that require extremely high control requirements of their contact with the environment,such as polishing,grinding,and hole-axis assembly.Robot automatic environmental compliance control operation can not only avoid excessive contact force between assembly parts,but also increase the robot's adaptability to inaccurate target environment and reduce the control cost of position accuracy.At present,most domestic industrial assembly robots perform simple position control tasks.For the applications of active contact control with force contact,there are still problems of low applicability and most of them have not been put into practical industrial use,such as assembly and wiping operations.Therefore,the research and application of active compliant control system is an important issue to be solved urgently in intelligent control.In this paper,the position-based force feedback integrated control is realized by admittance control.And the robot assembly system based on active compliaInce control is studied and set up.Thus the main contents are as follows:First,the kinematics and dynamics models of manipulator are established and validated respectively.Based on the kinematic modeling of the manipulator,the correctness of the kinematic model is verified by simulation.Aiming at the problems such as the non-uniqueness of the anti-solution and the non-generalizability of the analytical solution for any robot with arbitrary configuration,a new algorithm of the robot's kinematic inverse solution based on annealing-gradient descent hybrid algorithm is proposed to solve the problem of the anti-solution process In the aspect of dynamics model,the robot dynamic model and ADAMS three-dimensional dynamic simulation model are respectively established and compared.At the same time,a modified mathematical compensation model is proposed to fit the dynamic method error,and improve the accuracy of dynamic model,which provides an effective theoretical basis for the stable control of the control system.Secondly,based on the compliant control principle,different outer loop compliance control algorithms are introduced based on PD control.Then the direct force feedback,impedance control and admittance control are respectively compared and analyzed.And the influence of each parameter on the control index is analyzed,thus the cross-validation method summarizes the control effects of each compliant control algorithm.According to the shortcomings of the control algorithm,the dynamic S-type attenuation factor is introduced and two modified admittance control models are proposed to solve the problem that the admittance control model can not meet the requirements of smaller steady-state errors and overshoots simultaneously.Control dynamic control of the effective regulation,and has strong stability.According to the two correction models,the probability of mutation occurrence and the controllability of parameters are analyzed respectively.Therefore the advantages and disadvantages of the two correction models are analyzed reasonably,thus the correction of the model is realized.Thirdly,aiming at the process of shaft hole assembly,the research on assembly strategy of shaft hole is carried out.After analyzing of the mathematical model,the assembly process is divided into two stages:looking for holes and assembly.According to the direct relationship between contact force and contact torque,a variable step length hole-finding method based on equivalent force arm was designed to solve the hole centering problem and accelerate the hole-finding process.In the assembly stage,the basic stress model is analyzed and the motion state of the assembly process is simulated.Then put forward a control strategy of shaft hole assembly.Finally,according to the control strategy,an active compliance control system experiment platform is set up to carry out compliance testing.The hardware structure,the software framework and the communication system of the active compliance control system are designed and constructed.Three experiments were carried out to verify the proposed theory.The first experiment is the motion following experiment under the action of three dimensional arbitrary force.The second experiment is compliant environmental adaptability experiment in which the end of the manipulator moves along different stiffness and different form of inclined plane.The last experiment is compliant control assembly experiment.These experiments effectively verify the proposed flexibility control algorithm and the shaft assembly strategy.