Upgraded Kalman filtering of cutting forces in milling

Advanced piezoelectric dynamometers with a wide frequency bandwidth are required for cutting force measurement in high-speed milling and micromilling applications. In many applications, the signal bandwidth is limited by the dynamic response of the mechanical system, thus compensation techniques are necessary. The most effective compensation techniques for a full 3D force correction require an accurate and complex identification phase. Extended Kalman filtering is a better alternative for input force estimation in the presence of unknown dynamic disturbances. The maximum bandwidth that can be currently achievable by Kalman filtering is approximately 2 kHz, due to crosstalk disturbances and complex dynamometer\u2019s dynamics. In this work, a novel upgraded Kalman filter based on a more general model of dynamometer dynamics is conceived, by also taking into account the influence of the force application point. By so doing, it was possible to extend the frequency bandwidth of the device up to more than 5 kHz along the main directions and up to more than 3 kHz along the transverse directions, outperforming state-of-the-art methods based on Kalman filtering

Semi-Analytical Estimation for the Escape of Solutions of Linear Differential Equations with Slowly Varying Coefficients

Emerging vibrations are a major and often unpredictable limitation in engineering design. The engineering description of these vibrations is usually based on linear models with constant parameters. However, in reality, this is rarely the case and parameters do vary in engineering systems during operation. Among these systems, we consider the simplest case: a scalar system with two time scales, one fast describing the process dynamics, and another slow for parameter change. It has been noted that at a bifurcation point, going from stable to unstable, dynamical systems are resilient and do not immediately lose stability. However, traditional numerical schemes are not able to handle this situation, and numerical solutions cannot be trusted. We present and test a method for approximating solutions, and we name these approximations \textit{semi-analytical solutions}; we rigorously prove the efficacy of the method. Our main result shows that semi-analytical solutions exist beyond the bifurcation time

Optimum selection of variable pitch for chatter suppression in face milling operations

Cutting capacity can be seriously limited in heavy duty face milling processes due to self-excited structural vibrations. Special geometry tools and, specifically, variable pitch milling tools have been extensively used in aeronautic applications with the purpose of removing these detrimental chatter vibrations, where high frequency chatter related to slender tools or thin walls limits productivity. However, the application of this technique in heavy duty face milling operations has not been thoroughly explored. In this paper, a method for the definition of the optimum angles between inserts is presented, based on the optimum pitch angle and the stabilizability diagrams. These diagrams are obtained through the brute force (BF) iterative method, which basically consists of an iterative maximization of the stability by using the semidiscretization method. From the observed results, hints for the selection of the optimum pitch pattern and the optimum values of the angles between inserts are presented. A practical application is implemented and the cutting performance when using an optimized variable pitch tool is assessed. It is concluded that with an optimum selection of the pitch, the material removal rate can be improved up to three times. Finally, the existence of two more different stability lobe families related to the saddle-node and flip type stability losses is demonstrated

Semi-analytical framework for the study of finite-time stability of forced dynamical systems with time varying parameters

We present a framework to analytically approximate the solution of forced dynamical systems with time varying parameters and to analyse their finite-time stability. The work was inspired by an example in robotic machining, where the mechanical parameters of the system can vary over a wide range during the process, and where there are large forces due to an assumed cutting operation. The simplest possible non-autonomous linear system undergoing dynamic stability loss is studied which serves as a solid foundation to explore the mathematical intricacy behind such systems. After defining the differential equation corresponding to this simple system, the complementary function is studied using a frozen-time approach. The particular integral can be evaluated for this system by the asymptotic expansion of error functions. We present a new approach for the approximation of particular integrals, the iterative integration by parts (IIBP) method, which is then extensively studied and compared to the equations describing the exact analytic solution. The convergence and sensitivity of the IIBP method are discussed. The method is extended to multiple degrees of freedom mechanical systems with time varying parameters. It is shown that standard numerical schemes are not suitable for predicting finite-time stability properties even in the simplest case, because small errors accumulate causing large differences from the analytical solution

ICP-MS determination of trace elements in the serum samples of healthy subjects using different sample preparation methods

The concentration of some trace elements of clinical importance was studied in blood serum samples of healthy subjects (n=19, mean age 22 +/- 4.5 years) to determine reference ranges for the healthy urban population in Eastern Hungary. A sample preparation method has been developed using closed-vessel microwave digestion with an oxidizing acid mixture (nitric acid and hydrogen peroxide) for multielemental analysis and atmospheric wet digestion with the aqueous solution of trimethyl amine (TMAH) for the measurement of aluminum. Contamination of the samples with Al was observed during acidic microwave digestion because of the chemicals used. Trace element concentrations in the samples were measured with ICP-TIS. The reference ranges obtained were (in mug/L): Al 0.98-1.74, Cr 42.8-59.3, Mn 2.27-5.05, Fe 1282-2050, Co 0.22-0.88, Ni 0.03-16.33, Cu 691-1003, Zn 591-1217, Sr 30.37-47.37, Mo 0.73-1.19, Cd 0.02-0.62, and Pb 0.02-2.70. The results were compared to the reference ranges actually used in the clinical practice, some of which are available in the literature. The effect of the applied digestion methods on the obtained individual results and average concentration ranges was also studied

Chatter suppression techniques in metal cutting

The self-excited vibration, called chatter, is one of the main limitations in metal removal processes. Chatter may spoil the surface of the part and can also cause large reduction in the life of the different components of the machine tool including the cutting tool itself. During the last 60 years, several techniques have been proposed to suppress chatter. This keynote paper presents a critical review of the different chatter suppression techniques. Process solutions with design and control approaches are compiled to provide a complete view of the available methods to stabilize the cutting process. The evolution of each technique is described remarking the most important milestones in research and the corresponding industrial application. The selection of the most appropriate technique for each specific chatter problem is also discussed considering various aspects of machining processes

Grid-type transparent conductive thin films of carbon nanotubes as capacitive touch sensors

Abstract Transparent conductive films are used in a wide variety of devices. While solar cell top electrodes as well as tablet and mobile phone screens require high optical transparency and low sheet resistance (>80% and <10 Ω/❑) to maximize power efficiency; other, less demanding applications, such as those in capacitive touch panels and antistatic coatings, in which only small currents are involved, can be managed with coatings of moderate conductivity. In this paper, we show that area-selective argon plasma treated polyethylene terephthalate surfaces are suitable for localized deposition of carbon nanotubes from their aqueous dispersions by a simple dip coating and subsequent drying processes. The as-deposited carbon nanotubes form entangled networks in microscopic patterns over the plasma-treated surface areas with sheet resistance of <1 kΩ/❑ and optical transparency of ~75%. Based on this process, we demonstrate grid-type transparent conductive thin films of carbon nanotubes as capacitive touch sensors. Since each process step is robust, easy to up and downscale, and may be implemented even in roll-to-roll and sheet-to-sheet fabrication, the demonstrated technology is promising to produce grid-type structures even at an industrial scale in the future