Motion Planning And Position/Force Coordination Control Of Multi-robot Cooperative System

The advances in robotics technology have made robots increasingly used in complex industrial production.In order to meet the complexity,operational intelligence,and system flexibility of modern industrial task,dual robots and even robot collaboration technologies have been introduced into the actual industry.It is of great significance to introduce the cooperative technology of dual robot and even multi robot into the actual industrial environment.At the same time,we need to solve the problems such as planning methods,feasible control methods,and interacting with uncertain environments(such as human-robot interaction).The key to multi-robot collaboration system lies in the existence of “collaborative relationship”.The existence of the collaboration relationship concentrates on posture constraints and force constraints during the robot movement.That accurately describe the cooperative relationship and keep these relationships in the process of coordination become the key to motion planning and coordination control of the real multi-robots system.The trajectory planning process of multi-robot system is much more complicated than that of a single robot.Synchronization and coordination of robot trajectories is an important research content.At the same time,robots generate contact forces during the movement of cooperation.The environment also produces forces for robots.Coordinated operation with force control has also become an important research direction in this fieldThis article relies on the multi-robots cooperative welding project in the laboratory to carry out research on multi-robot motion trajectory planning and position force coordination control.The current research and application of multi-robot coordination work is relatively simple,and most of them are focused on dual robots.In terms of force coordination control,impedance control has achieved some results in the area of single-arm control,but due to the uncertainty of the environment,there are still many difficulties in the application of cooperative robot systems.In summary,the key technical problems and difficulties in summarizing the completion of multi-robot collaboration are:(1)A good coordinated motion path,which satisfying the constraints of kinematic,guaranteeing synchronization of trajectories and avoiding problems such as collisions,singularities,etc.,is needed according to a given mission;(2)For some complex coordinated welding tasks,poor initial welding position selection may not be able to plan effective trajectories,even the robot in a different configuration state has a great influence on the flexibility of the robot,so it is necessary to establish a set of automatic selection of the initial welding position and calculate the corresponding trajectory method with high operability;(3)In cooperation,the robot and the object form a closed chain,and the contact between each other will inevitably generate a force,and the presence of the motion pose error will cause a huge internal force.In this case,it is critical that all robots in the system continue to maintain a cooperative relationship and be addressed with force control.First of all,to achieve multi-robot cooperation,we must plan the trajectory of each robot during the entire collaboration process.In this paper,after analyzing the kinematics relationship between different robots in multi-robot collaboration,a mathematical model of multi-robot cooperative system is established.Based on this,a method for evaluating the manipulability of multi-robot cooperative system is proposed,The optimization objective function is further constructed,and the constraints of collision and singular configuration are considered.Genetic algorithm is used to obtain the optimal initial welding position in the multi-robot cooperative space to ensure the optimal position.Multi-robots maintain high transfer and transmission speeds throughout the entire collaboration.Then,for the coordinated operation with force control,the robot and the object form a closed chain system during the robot's joint operation of the object.the statics and dynamics of the system are analyzed,and the impedance model of the position force between the end of the robot and the environment is studied.This paper focuses on the application of impedance control in free space and force tracking in constrained space,and adopts the master-slave robot control architecture.The master-slave architecture has the advantage that the master robot can move in strict accordance with the planned desired trajectory,ensuring that the trajectory does not exhibit large deviations.A six-dimensional force / torque sensor is installed at the end of the robot,which adjusts the position of the robot in real time according to the size of the force feedback and thus indirectly realizes the control of the size of the end forceFinally,the SolidWorks-SimMechanics joint simulation platform of multi(three)robot cooperation system and the physical experiment platform of industrial robot control based on EtherCAT bus are designed and developed.The trajectory planning of the three robots' cooperative welding task is realized on the simulation platform,the three robots' initial welding position layout is optimized,and the synchronism of robot trajectories is performed.The results and experiments show that the multi-robot cooperative trajectory calculation and initial welding position selection presented in this paper change the way the current welding site is selected by teaching and man-made in the industrial site,and the flexibility of the robot during the operation process is improved and optimized.Aiming at the coordinated control of the position force of the dual robot,this paper first simulates the experiment of coordinated motion and force control when the two robots cooperate to carry the object in the simulation platform.Finally,the experiment of carrying the rigid object cooperatively in the dual robot is completed on the physical experiment platform,and the experiments of the human and robot are carried out to carry the object.The experimental results show that the robot can better track the motion of the main robot,show high compliance,improve the security and stability in the cooperation process,and verify the feasibility and effectiveness of the related algorithms,so as to realize the more complex multi robot cooperative system in practice.The application of the industry has laid the foundation.