Improving machining accuracy with robot deformation compensation

Industrial robots offer a cheaper yet more flexible alternative to the CNC machines in the cleaning and pre-machining applications of automotive aluminum castings. But the low stiffness has limited the application of industrial robots to the machining tasks with very low precision requirement. This paper presents a practical method to compensate the robot deformation caused by the machining force. A constant joint stiffness model based feed forward compensation scheme is implemented in the robot controller. The compensation scheme is shown to be able to reduce the position error by more than 60%. Application test in milling a standard aluminum block has demonstrated the effectiveness of the proposed deformation compensation method. The surface error is reduced from 0.5 mm to 0.1 mm.