Boring bar vibration in machine tools during internal turning operations is a pronounced problem in the manufacturing industry. Due to the often slender geometry of the boring bar, vibration may easily be induced by the material deformation process. One approach to overcome such vibration problems is to use active control of boring bar vibration. The design time of an active boring bar depends to a great extent on the knowledge of its dynamic properties when clamped in a lathe for different actuator positions and sizes, crucial for its performance. This thesis focuses on the development of accurate dynamic models of active boring bars with the purpose of providing qualitative information on suitable actuator position for a certain boring bar. The first part of the thesis considers the problem of building an accurate "3-D" finite element (FE) model of a standard boring bar used in industry. Results from experimental modal analysis of the actual boring bar are the reference. The second and the third parts discuss analytical and experimental methods for modeling the dynamic properties of a boring bar clamped in a machine tool. For this purpose, the Euler-Bernoulli and Timoshenko beam theories are used to produce both distributed-parameter system models and corresponding "1-D" FE models. A more complete "3-D" FE model of the system boring bar - clamping house is also developed. Spatial dynamic properties of these models are discussed and compared with adequate experimental modal analysis results from the actual boring bar clamped in a machine tool. The third part also investigates the sensitivity of the spatial dynamic properties of the derived boring bar models to variation in the structural parameters' values. The fourth part focuses on the development of a "3-D" FE model of the system boring bar - actuator - clamping house. Two models are discussed: a linear model and a model enabling variable contact between the clamping house and the boring bar with and without Coulomb friction in the contact surfaces. Based on these FE models fundamental bending modes and control path frequency response functions are discussed in conjunction with the corresponding quantities estimated for the actual active boring bar. In the fifth part, a method based on FE modeling and artificial neural networks for selecting a suitable actuator position inside an active boring bar is presented. Objective functions for selecting an actuator position are suggested. An active boring bar with an actuator position suggested by the method was manufactured and it displays fairly good correlation with the corresponding FE model. The final part focuses on modeling of an active boring bar vibration control system. A simple "1-D" FE model of a boring bar is utilized to simulate the dynamic response and an adaptive digital feedback controller realized by the feedback filtered-x LMS algorithm is used.
展开▼
