Improving surface roughness in turning using optimal control of tool's radial position

Abstract

Vibration suppression of the tool results in improved surface texture, dimensional accuracy and enhanced productivity in machining operations. Vibrations of the machine-tool structure, as well as the tool-workpiece interaction are the main contributors to the tool vibration. In light of this, abating the tool vibration can be approached by isolating the tool from the machine structure in the presence of a random process representing the tool-workpiece interaction. An active tool holder capable of isolating the cutting tool from the vibration of the machine-tool structure is constructed. Vibration isolation is accomplished by means of a Kalman estimator-based control strategy, a high bandwidth magnetostrictive actuator, and two accelerometers. The proposed control technique focuses on lowering the transmitted force to the tool that is subject to the machine structure vibration (base excitation) in presence of cutting process disturbance. The important aspect of this control strategy is that, while it is designed based on a full order model of the plant, its implementation is reduced to the realization of a second order estimator irrespective of the order of the plant model. Machining experiments showed that an average of 25% improvement in surface roughness of the workpiece has been achieved using the proposed technique.