Research On Offline Programming For Industrial Robot Based On Digital Twin

Offline programming is a technique to perform the path planning task of a robot in a virtual environment and automatically generate robot language programs.This research mostly focuses on improving the trajectory tracking accuracy of industrial robots,but ignores the loss of end-effector tracking accuracy caused by the generated code during migration,which leads to collision accidents as well as machining node positional offsets.In this paper,the above problems are solved by introducing digital twin technology.In this paper,an offline programming framework based on digital twin for industrial robots is proposed,which is implemented in Siemens NX software by secondary development,and the effectiveness of the digital twin-based offline programming scheme for industrial robots is verified in the virtual model and physical system of a small-scale Industry 4.0 production line.The specific work is as follows.1.For the end-effector tracking accuracy errors caused by code migration in offline programming,this paper presents an offline programming framework based on digital twin for industrial robots.The trajectory completed in the simulation and the trajectory completed by the robot model driven by the virtual teaching pendant are called "simulation trajectory" and "debug trajectory",and the generated code is verified by software-in-the-loop(SIL)using the virtual teaching pendant.The experimental results show that the error between the simulation trajectory and the debug trajectory is within the allowable range of engineering practice,which proves the correctness of the code generation module.The solution integrates the debugging verification process of trajectory planning into the virtual environment without causing damage to the real equipment and avoiding possible engineering accidents.2.An offline programming framework based on digital twin for industrial robots is implemented using a secondary development approach based on CAD software.The KUKA KR6R700 six-axis industrial robot is used as the research object,and the trajectory planning module and code generation module are designed and packaged based on NX Open API in the MCD(Mechanical Concept Design)simulation environment of Siemens NX software,and the humanmachine interaction interface and menus are designed to constitute the offline programming toolbox of NX software.Among them,the trajectory planning module integrates joint space and Cartesian space planning algorithms.The former one takes the poses of key path points as inputs,which are transformed into joint angles after kinematic expression analysis of the robot and used to fit polynomial interpolation trajectories.While the latter one uses the end-effector pose under the path constraint as the control target,and designs a nodal pose extraction scheme for the spatially intersecting curved paths incorporating the geometric features of the workpiece surface.The extracted path node poses are discretized by B-Spline curve and spherical linear interpolation to achieve the position and pose of the end-effector,respectively.The experimental results of trajectory planning show that the path node extraction scheme designed in this paper is applicable to different shapes of workpiece models and can effectively avoid the collision between the end-effector and the workpiece surface.3.The above offline programming framework is applied in the small-scale Industry 4.0production line system to realize the trajectory planning simulation of the robot virtual model and the validation of the physical system.The robot trajectory was planned and the trajectory planning simulation was completed in the virtual environment in combination with the top cover inbound and assembly outbound processes,and the generated code was migrated to the real teaching pendant after validation to complete the small-scale Industry 4.0 production line verification experiments.The experimental results show that the real robot can pass through the specified key points according to the planned trajectory,and its position and posture remains the same as that in the virtual simulation,which proves the practical value of the offline programming method for industrial robots proposed in this paper in the production line application.