Hierarchical Optimal Force–Position Control of Complex Manufacturing Processes

A hierarchical optimal controller is developed to regulate the cutting force and tool position, simultaneously, in a micro end milling process. The process is divided into two levels of decision making. The bottom level includes the measurable states, which in this work comprise the servomechanism positions. The top level includes the higher order objectives which can be derived from the bottom level objectives by an aggregation relationship. In this work the top level objective is concerned with cutting force regulation. The aggregation relations are linearized to fit into a linear optimal control problem to reduce the computational efforts. Reference velocity is calculated based on the force model, using the desired depth-of-cut and spindle speed. The proposed method is compared to a normal optimal controller without considering the top level objectives. Comparison between the two methods reveals the advantages of considering the top level objectives.