| During machining, the factors such as change in the depth of cut, material hardness variation and tool wear may result in the conservative feed rate selected and therefore insufficient use of NC machining tools. It is the important way to increase productivity by real-time monitoring and adaptive adjusting the machining process. At present, the cutting force supervisory control is a research field. However, the method in which the cutting force is measured by the dynamometer can't be applied in industry, but only in laboratory. As a result, this thesis aims to the research of monitoring the cutting force indirectly using spindle motor currents.An experimental platform is established to measure the cutting force and motor currents. After analyzing the cutting force and spindle motor currents in both time and frequency domain, it is found that the amplitude change of spindle motor currents can represent the cutting force. In the thesis, the RMS value of spindle motor three-phase current is given as the current characteristic to represent the cutting force. It is found that the RMS value contains the frequency of cutting force by PSD analysis. Furthermore, the cutting force can be extracted from the RSM value.The process of power conversion between machine and electric power is studied in theory. On the base of the study, the relationship of spindle motor current and milling force is modeled as a state space equation using system identification. The experimental data has been used to prove that the model is reasonable.Using the established model, an adaptive controller based on the embedded PC and real-time operate system is designed and implemented. The controller monitors and controls the cutting force by monitoring the spindle motor current. In the end of the thesis, the controller is applied on the HCNC-21M and Siemens 840D system. The performance is testified by controlling the machining of the blade of large-scale water turbine.
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