No abstract

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.

This paper presents an innovative system determining machine tool quasi-static stiffness in machining space, so-called Stiffness Workspace System (SWS). The system allows for the assessment of the accuracy of a machine which has become a vital aspect over past years for machine tool manufacturers and users. Since machine tools static stiffness is one of the main criteria using to evaluate the machines' quality, it is crucial to highlight the relevance of experimental and analytical stiffness determination methods. Therefore, the proposed method is applied to estimate the spatial variation of static stiffness in the machine tool workspace. This paper describes the SWS system—its design, working principle, mounting conditions and signal processing. The major advantage of the system is the capability to apply forces of controlled magnitude and orientation as well as simultaneously measure the resulting displacements. The obtained results give possibility to estimate and evaluate static stiffness coefficients depending on the position and direction under loaded conditions. The results confirm the validity of the analyses of spatial stiffness distribution in the machine workspace.

This article describes the experimental studies of a preloaded asymmetric multi-bolted connection in the exploitation state. The construction of two stands were introduced: for bolt calibration and for evaluating the bolt forces in a multi-bolted connection. The bolts were tightened in a specific optimal sequence, in three passes, monitoring the force values in the bolts using a calibrated strain gauge measuring system. The studies were conducted for the selected multi-bolted connection on an Instron 8850 testing machine. The measurement data were saved in MATLAB R2018b Simulink. The measurement results were analysed statistically and are presented via charts showing the distributions of the normalised values of the bolt forces as a function of the linearly increasing and decreasing exploitation loads. We show that the forces in individual bolts, after unloading the multi-bolted connection, change in relation to the initial values of their preload.

Hepatic drug metabolizing enzymes (DMEs), whose activity may be affected by liver diseases, are major determinants of drug pharmacokinetics. Hepatitis C liver samples in different functional states, i.e., the Child–Pugh class A (n = 30), B (n = 21) and C (n = 7) were analyzed for protein abundances (LC-MS/MS) and mRNA levels (qRT-PCR) of 9 CYPs and 4 UGTs enzymes. The protein levels of CYP1A1, CYP2B6, CYP2C8, CYP2C9, and CYP2D6 were not affected by the disease. In the Child–Pugh class A livers, a significant up-regulation of UGT1A1 (to 163% of the controls) was observed. The Child–Pugh class B was associated with down-regulation of the protein abundance of CYP2C19 (to 38% of the controls), CYP2E1 (to 54%), CYP3A4 (to 33%), UGT1A3 (to 69%), and UGT2B7 (to 56%). In the Child–Pugh class C livers, CYP1A2 was found to be reduced (to 52%). A significant trend in down-regulation of the protein abundance was documented for CYP1A2, CYP2C9, CYP3A4, CYP2E1, UGT2B7, and UGT2B15. The results of the study demonstrate that DMEs protein abundances in the liver are affected by hepatitis C virus infection and depend on the severity of the disease.