David Hajdu

Budapest University of Technology and Economics · Department of Applied Mechanics

In this work we present a quantitative measurement-based method to describe the stability behaviour of a periodic dynamical system. In-process response for impulse during milling is analysed to provide operational stability prediction. The proposed method combines chatter detection techniques with the theory of time-periodic delay differential equa...

In this paper, the stochastic dynamical model of a single-degree-of-freedom milling operation is formulated, where a Gaussian white noise process models the high-frequency variation in the cutting force. With the help of this stochastic model, it is shown, that large-amplitude stable vibrations can occur near the critical machining parameters, due...

Chatter vibrations during machining operations are large-amplitude self-excited vibrations, which result in the loss of physical contact between the workpiece and the tool. This paper presents an electric contact sensor, which is used to detect the cutting and noncutting periods during the operation. The spectrum of the signal of the electric conta...

The curved uncut chip thickness model is presented to predict the cutting forces for general uncut chip geometries. The cutting force is assumed to be distributed along a curved path on the rake face of the cutting tool, which makes the solution computable for inserts with nose radius and more complex cutting edge geometries. The curved paths origi...

A stochastic dynamical model is presented to identify the difficulties in chatter detection during cutting processes. The theoretical implications are based on measurements related to the stochastic character of the cutting force. The stochastic model is validated in a Hardware-In-the-Loop (HIL) environment where the multiplicative component of the...

During the milling of thin-walled workpieces, the natural frequencies might change radically due to the material removal. To avoid resonant spindle speeds and chatter vibration, a precise knowledge of the instantaneous modal parameters is necessary. Many different numerical methods exist to predict the changes; however, small unmodelled effects can...

The paper presents a pseudospectral approach to assess the stability robustness of linear time‐periodic delay systems, where periodic functions potentially present discontinuities and the delays may also periodically vary in time. The considered systems are subject to linear real‐valued time‐periodic uncertainties affecting the coefficient matrices...

Connected cruise controllers that utilize motion information of human-driven vehicles must guarantee stability against uncertainties in driver behavior. Here, we present the robustness analysis of such connected vehicle systems using structured singular value analysis. In particular, we consider uncertainties arising from the feedback gains and rea...

This chapter deals with predictor feedback controllers to compensate time delays in feedback loops. The concept and the governing equations of the Smith predictor, the modified Smith predictor and the finite spectrum assignment are discussed in detail. The relationship between the three control strategies is established both in frequency and time d...

This paper presents the robustness analysis for the head-to-tail string stability of connected cruise controllers that utilize motion information of human-driven vehicles ahead. In particular, we consider uncertainties arising from the feedback gains and reaction time delays of the human drivers. We utilize the linear fractional transformation and...

Variable pitch milling cutters intend to increase performance, but off-the-shelf cutters do not ensure this generally. Depending on the milling process they are selected for, they can perform better or even worse than uniform pitch cutters do. Improved performance can be guaranteed by considering the reflected dynamic behaviour of the machine/tool/...

Reliable stability predictions of machine tool chatter have high potential in the optimization of machining processes. Industrial applications can benefit from the corresponding stability lobe diagrams, which can guarantee improvement in the performance. However, predictions and experiments often do not match during cutting tests due to uncertain d...

Reliable prediction of machine tool chatter is an essential problem in efficiency-oriented machine tool centers, since it requires the precise characterization of the dynamics of the machine-tool-workpiece system and the cutting force characteristics. Due to imperfect measurements, noise, uncertain and varying operational conditions, the mathematic...

Chatter detection is usually based on the analysis of measured signals captured during cutting processes. These techniques, however, often give ambiguous results close to the stability boundaries, which is a major limitation in industrial applications. In this paper, an experimental chatter detection method is proposed based on the system's respons...

One of the most significant limitation of the productivity of machining operations is the regenerative machine tool vibration, also called machine tool chatter, which is a self-excited vibration between the tool and the workpiece induced by the chip formation mechanism. Extension of the chatter-free parameters is possible by active chatter control...

The dynamics of connected vehicle systems are investigated where vehicles exchange information via wireless vehicle-to-vehicle (V2V) communication. In particular, connected cruise control (CCC) strategies are considered when using different delay configurations. Disturbance attenuation (string stability) along open chains is compared to the linear...

Prediction of machine tool chatter requires the characterization of dynamic of the machine-tool-workpiece system by means of frequency response functions (FRFs). Uncertainties of the measured FRFs result in uncertainties of the calculated stability diagrams, therefore robustness of stability prediction against parameter perturbations is of high imp...

Prediction of machine tool chatter requires a dynamic characterization of the machine-tool-workpiece system by means of frequency response functions (FRFs). Stability lobe diagrams are sensitive to the uncertainties of the measured FRF, which reduces the reliability of their industrial application. In this paper, a frequency-domain method is presen...

For implementation in real traffic, connected vehicle systems should be designed to be robust against uncertainties arising from human-driven vehicles. Assuming that the bounds of uncertainties are known, we propose a frequency domain approach to guarantee robust string stability and to select optimal control parameters. The method is demonstrated...

The ability of humans to maintain balance about an unstable position in a continuously changing environment attests to the robustness of their balance control mechanisms to perturbations. A mathematical tool to analyze robust stabilization of unstable equilibria is the stability radius. Based on the pseudospectra, the stability radius gives a measu...

Stability prediction of machining operations is often not reliable due to the inaccurate mechanical modeling. A major source of this inaccuracy is the uncertainties in the dynamic parameters of the machining center at different spindle speeds. The measured frequency response functions of the tool are usually loaded by noise and identification of th...

Stability prediction of machining operations is often not reliable due to the inaccurate mechanical modeling. A major source of this inaccuracy is the uncertainties in the dynamic parameters of the machining center at different spindle speeds. The so-called tip-to-tip measurement is the fastest and most convenient method to determine the frequency...

Time-domain representation of the original Smith predictor is presented for systems with feedback delay. Sensitivity to parameter uncertainties is analyzed for a marginally stable, for an asymptotically stable and for an unstable second-order plant. A series of stability diagrams are constructed using the D-subdivision method and Stepan’s formulas....

Time domain representation of the original Smith Predictor is presented for systems with feedback delays. It is shown that if the parameters in the internal model of the predictor are not equal to the parameters of the real system, then the dimension of the closed loop system is double of the dimension of the open-loop system. Furthermore, the time...