Torque control for a form tool drilling operation

This paper presents the dynamic modeling and real-time torque control for a form tool drilling process. The form tool produces a desired shape in a workpiece through a drilling process. In this study, the form tool drilling process resembles the combination of drilling, reaming, counter-boring, and chamfering operations. The machining process is modeled as a linear system with variable gain due to the form tool geometry. The process is also subject to unknown disturbances such as unpredictable chip jamming and tool-workpiece friction. Spindle motor power and speed measurements were used to estimate drilling torque for cost effective practical implementation. An input-output pole placement controller with previewed gain scheduling was designed and implemented. Through experimental studies, this controller was shown to effectively regulate tool torque and hence avoid tool breakage, by manipulating the feed during drilling, and reduce cycle time compared to current practice.