Real time pose control of an industrial robotic system for machining of large scale components in aerospace industry using laser tracker system

The high demand of efficient large scale machining operations by concurrently decreasing operating time and costs has led to an increasing usage of industrial robots in contrast to large scaled machining centers. The main disadvantage of industrial robots used for machining processes is their poor absolute accuracy, caused by the serial construction, resilience of gearings and sensitivity for temperature changes. Additionally high process forces that occur during machining of CFRP structures in aerospace industry lead to significant path errors due to low structural stiffness of the robot kinematic. These errors cannot be detected by means of motor encoders. That is why calibration processes and internal control laws have no effect on errors caused by elastic deformation. In this research paper an approach for increasing the absolute accuracy of an industrial milling robot with help of a Laser Tracker system during machining tasks will be presented. To measure the position and orientation of the robot tool center point (TCP) a specific adapter is mounted on the milling spindle near the TCP to provide a 6DoF measurement. Via a real time interface pose data can be obtained in millisecond cycles and is used for calculating the current path errors of the robot. The implementation of an additional controller in the manufacturers CNC allows the correction of the programmed trajectory so that the machining path will match its specifications.