Research On Two-robot Symmetrically Cooperative Control Based On Impedance Model

In the field of arc welding,the traditional welding station consisting of a welding robot,a part positioner and a part fixture can no longer meet the current demand for small-volume,customized flexible automated production.The multi-robot cooperative welding system has stronger operating capability,a wider range of working space and a more flexible system structure and organization,which can overcome the shortcomings of traditional welding stations.And it is the development direction of welding automation and has broad market application prospects.The multi-robot cooperative welding system includes workpiece-handling robots and welding robots,which brings many advantages as well as more complicated control problems.For a multi-robot welding system with two workpiece-handling robots and one welding robot,how to control the cooperative motion of two workpiece-handling robots is the key to the success of multi-robot welding.The main difficulties and key problems include:(1)the trajectory planning of the two cooperative robots;(2)the modeling of the two-robot cooperation system;(3)the position/force coordination control of the two cooperative robots.Therefore,to study and solve the key problems in the two-robot cooperation system and conclude the theoretical method is the basis for realizing multi-robot cooperative welding.It is of great significance to the development of the theory and practice of multi-robot cooperative control.In order to solve the aforementioned problems,the research approach of this paper is: For the trajectory planning of the cooperative motion of two robots,the study of saddle curve welding seam formed by steel pipes clamped by two robots is focused on,and an object-oriented trajectory planning method is adopted;For the modeling of the two-robot cooperation system,a symmetric architecture model is used to improve the response speed of the system.In view of the position/force coordination of the two robots,the position-based impedance control method is used to adjust the position/force between the two robots.The goal is to achieve a coordinated motion of the two robots gripping steel pipes,so that the saddle curve welding seam meet the ship-shaped welding posture,and the contact force/torque between workpieces is controlled within a reasonable range during the cooperative motion.Firstly,the trajectory planning of the saddle curve welding seam formed by steel pipes clamped by two robots is studied,and an object-oriented trajectory planning method is adopted.A simulation platform based on MATLAB/SimMechanics is built to verify the proposed trajectory planning method.Secondly,a symmetric architecture is used to mathematically model the object of the two robots gripping steel pipes,and the mapping relationship of force,position,velocity,etc.between the clamped workpieces is established.A control diagram for the two-robot cooperation system is built.Then,the position-based impedance control method is used to adjust the position/force relationship in the process of the two-robot cooperation.The principle and implementation method of impedance control are analyzed in detail.Next,the design idea of the two-robot cooperation system is introduced in detail.Based on the open-bus controller developed by the laboratory,an efficient and stable two-robot cooperative control system is designed and implemented.Finally,two Eston ER16 universal six-joint robots are used as the control objects to complete the joint motion of the two robots.The experimental results show that the two robots complete the planned trajectory motion.And through the regulation of the impedance control,the contact force/torque between workpieces is controlled within a reasonable range,which verifies the real-time performance,high efficiency and reliability of the two-robot cooperation system.The research results of this paper lay a solid foundation for realizing the cooperative welding of three robots.