Unmanned turning force control with selecting cutting conditions

While the rough turning process is machining a workpiece at various cutting depth, the feedrate is usually selected based on the maximum depth of cut. Even if this selection can avoid power saturation or tool breakage, it is very conservative compared to the capacity of machine tools and can reduce the productivity significantly. Many adaptive control techniques have been reported that can adjust the feedrate to maintain the constant cutting force. However, these controllers are not very widely used in manufacturing industry because of the limitations in measuring the cutting force signals and selecting the appropriate cutting force level. In this paper, an unmanned turning process control system is proposed based on the spindle drive characteristics. A synthesized cutting force monitor is used to estimate the cutting force as accurately as a dynamometer does. The reference cutting force level as well as the feed-rate is selected considering the spindle motor characteristics. Because the cutting process is highly nonlinear, a fuzzy logic controller is applied to maintain the desired cutting force level. The experimental results demonstrate that the proposed system can be easily realized in CNC lathe with requiring little additional hardware.