Boring bars with a large length-to-diameter ratio chatter under productive cutting conditions, which leads to poor surface finish and violation of part tolerances. This paper presents an active damping method of boring bars with an in-house designed magnetic actuator. The actuator has been designed to have a linear force output relative to the input current, and instrumented to control boring bar vibrations. Four different H ∞ optimal controllers are designed to shape the boring bar dynamics and improve the chatter stability. The proposed active damping method is experimentally tested on a CNC lathe. The dynamic stiffness of the boring bar is increased considerably, leading to a significant increase in the chatter-free material removal rates.
This paper proposes an application of the switching gain-scheduled control technique to the flexible ball-screw drive servo system with a wide range of operating conditions. The wide operating range is caused by the change of the table position and the workpiece mass during the machining operation, and leads to plant dynamics variations. To achieve high tracking performance of the table position against the dynamics variations and the cutting force disturbance, a set of gain-scheduled controllers is designed so that each controller damps out the resonance of the ball-screw system and increases the closed-loop bandwidth for a local operating range, and tracking performance is guaranteed under the switching between these controllers. Experimental results with a laboratory-scale ball-screw drive setup demonstrate that the switching gain-scheduled controller outperforms the nonswitching one by up to 52% in tracking accuracy.
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