Bartosz Powałka

Active vibration control in milling flexible workpieces

During milling of flexible workpieces a regenerative chatter vibration may become a critical factor that limits productivity. It is shown in this paper that a selection of cutting parameters based on a stability lobes diagram may not always be a remedy for low productivity due to increased forced vibration level. Additionally, other factors such as tool wear may limit the selection of stable spindle speeds. This paper presents an active control system that counteracts the development of chatter vibration. The proposed active control system employs Linear Quadratic Gaussian (LQG) algorithm and piezoelectric actuator to suppress vibration during cutting. The Kalman filter is used to estimate the state of the system required by LQG algorithm. The active control introduces damping into the system, thereby raising the critical depth of cut and reducing forced vibration amplitude. It enables stable cutting under a much wider range of cutting parameters than for the uncontrolled system. Cutting tests are performed to demonstrate an effectiveness of the control system. Practical issues limiting applications of the proposed technique are discussed.

Vibrostability of the Milling Process Described by the Time-Variable Parameter Model

This paper presents a method for vibrostability prognosis using a non-stationary model of the machine tool-cutting process system. The method employs Liapunov-Floquet theory. The method is illustrated by the example of the determination of limit cutting parameters using appropriate model reduction methods.

Method of Reducing the Number of DOF in the Machine Tool-Cutting Process System from the Point of View of Vibrostability Analysis

The model of the mass-damping-spring (MDS) system of a machine tool is multi-degree of freedom model. The model of the cutting process (CP) has to correspond structurally to the MDS system model constituting the machine tool-cutting process (MT-CP) system model. This is often a model of time-variant parameters. Therefore, forecasting the vibrostability, i.e. resistance to the occurrence of self-excited vibrations, in the MT-CP system is a complicated task. To simplify analysis it is justified to reduce the number of degrees of freedom. The method presented simplifies significantly the computational model while the interpretation of the results applies to the whole construction. The reduced model carries information concerning vibration modes that determine vibrostability loss. The paper presents the mathematical fundamentals of the reduction of the machine tool MDS system model, analysis and selection of vibration modes considered in the reduced model and analysis of reduction errors.

Accuracy and repeatability positioning of high-performance lathe for non-circular turning

Abstract This paper presents research on the accuracy and repeatability of CNC axis positioning in an innovative lathe with an additional Xs axis. This axis is used to perform movements synchronized with the angular position of the main drive, i.e. the spindle, and with the axial feed along the Z axis. This enables the one-pass turning of non-circular surfaces, rope and trapezoidal threads, as well as the surfaces of rotary tools such as a gear cutting hob, etc. The paper presents and discusses the interpretation of results and the calibration effects of positioning errors in the lathe’s numerical control system. Finally, it shows the geometric characteristics of the rope thread turned at various spindle speeds, including before and after-correction of the positioning error of the Xs axis.

Object’s optical geometry measurements based on Extended Depth of Field (EDoF) approach

The authors propose a method of using EDoF in macro inspections using bi-telecentric lenses and a specially designed experimental machine setup, allowing accurate focal distance changing. Also a software method is presented allowing EDoF image reconstruction using the continuous wavelet transform (CWT). Exploited method results are additionally compared with measurements performed with Keyence’s LJ-V Series in-line Profilometer for reference matters.

Assessment of Modal Parameters of a Building Structure Model

This paper relates to the field of vibrations of contemporary building structures. The aim of this study is to develop methods to estimate the safety of use of buildings subjected to dynamic loads. Calculations are carried out based on selected computational models of the column-beam-plate system used at the design stage of monolithic building structures. For modeling, the finite element method (FEM) is used. The results of calculations are compared with laboratory tests of the special model mapping of a building structure.