Research On Tracing The Source Of Dynamic Error For Five-axis CNC Machine Tool Based On RTCP

With increasing machining speed of machine tool, dynamic performance is already one of the most important influence factor of machining precision of high-grade CNC machine tool. However testing standards is still unsatisfactory. RTCP function is necessary for high-grade CNC machine tool. It is used to directly program the displacement of the tool tip in the workpiece coordinate system, and could decrease the nonlinear errors. What’s more, by setting the tool tip staying still in the workpiece coordinate system, the motion errors could be measured conveniently. Nowadays equipment based on the theory is already evented and used on the measurement of the geometric error of CNC machine tool. In this article, efforts are focus on how the parameters of the servo system and the machine tool influence the trajectory error of the tool tip for five-axis CNC machine tool and how to analysis and compensate the trajectory error of the tool tip while it is already measured.The main contents are:1. According to the feature that the tool tip is still relatively to the workpiece, trajectories of the rotation center of the tool are planned. Then the motion instruction series of each axis is calculated. Besides, the constraint in the velocity and acceleration between the translational axis and rotation axis is analyzed.2. The model of driving system is built for the translation axis and rotation axis. By combining the control system and driving system together, the model of servo system is built. Then a math expression describing the relationship of the motion instructions, the actual motion and the parameters is simplified from the model, which is optimized.3. The kinematic model and the position error of the tool tip are established by the multi-body theory. Then the simplified model of the position error is presented by ignoring the higher order error.4. The model of motion error is established by combining the model of tracking error and position error together. Then, with the designed RTCP trajectory, simulation is used to show the correspondence between each parameter of the servo system model and the error trajectory.5. By assuming the motion instructions and the motion error were known, the way to separate the dynamic error from the position error is suggested. And then simulation is shown to verify the method of dynamic error analysis and compensation.