Model predictive force control for multi-axis rough milling

力是铣削过程中最重要的过程变量，因为它决定生产率(通过进给速度)、产品质量(通过刀具的位移)和过程安全(关于刀具破损)。模型预测控制(MPC)使用显式的过程和机器模型来确定短时间范围内的未来机器行为，并相应地控制过程。它能够在工艺的技术极限下实现安全、无超调的最佳控制。这种系统已经作为双轴铣削加工的原型被开发出来。本课题旨在开发一套多轴联动铣削控制系统，并对其进行了系统的研究。为此，台式测功机的测量信号必须在过程中进行校正，例如，其惯性和工件质量变化的测量信号。这引入了额外的不确定性，应通过对工艺模型的连续校准(“识别”)加以考虑。由于MPC使用模型系数作为反馈环，因此能够实现稳健控制。MPC控制沿刀具路径的进给，但机器的行为沿该路径变化。这是因为一个运动涉及不同的机床轴--尤其是在多轴铣削中。在控制中还必须考虑这种非线性行为。本项目的目的是开发和研究一种多轴粗加工的闭环力控制系统。假设控制器在不超过力的任何参考力的情况下操作多轴铣削过程--与刀具的条件无关。该系统的基准是一种已经在切割技术研究中确立的控制方法。

Force is the most important process variable in the milling process, because it determines productivity (via the feed rate), product quality (via the displacement of the tool) and process safety (with regard to tool breakage). A model predictive control (MPC) uses an explicit process and machine model to determine the future machine behavior for a short time horizon and controls the process accordingly. It enables for a safe, overshoot-free, optimal control at the technological limit of the process. Such a system has been developed as a prototype for the biaxial milling process. In this project, a control system for multi-axis milling is to be developed and systematically examined. For this purpose, the measurement signal of a table dynamometer must be corrected during the process, e.g. of its inertia and of the change in the mass of the workpiece. This introduces additional uncertainties, which should be considered through a continuous calibration ("identification") of the process model. Since the MPC uses the model coefficients as the feedback-loop, this enables for a robust control. The MPC controls the feed along the tool path, but the behavior of the machines varies along this path. This is because different machine axes are involved for a movement - especially in multi-axis milling. This nonlinear behavior must also be taken into account in the control. The aim of the project is to develop and research a closed-loop force control system for multi-axis roughing. It is assumed that the controller is operates a multi-axis milling process at any reference of the force without exceeding it - independent of the condition of the tool. The system is benchmarked to a control method, which is already established in the research of cutting technology.