Vytautas Bučinskas

Modelling of Mechanical Structure of Atomic Force Microscope

This paper dedicated of introduction of dynamic model of improved mechanical system of sensor of atomic force microscope. The subject of the research is enhancement of dynamic characteristics of cantilever - main mechanical part of sensor. These characteristics defines frequency of oscillations of mentioned cantilever and are main limitations of the speed of scanning procedure of the microscope. Modification of original dynamic system of atomic force microscope made adding nonlinear additional stiffness, created by stream of compressed air. In order to determine dynamic characteristics of modified system there are necessary to create corresponding dynamic model. Parameters of such model were defined using experimental research and theoretically from 3-D model of microscope cantilever. Solution of this model brings dependencies between air gap, pressure of compressed air and oscillation frequency of cantilever. Finally, results there are presented and conclusions are drawn.

Research of Modified Mechanical Sensor of Atomic Force Microscope

Atomic force microscope (AFM) is a remarkable device for nanoscale surface scanning. Among several positive features, speed of a scanning limits implementation of AFM. This paper proposes method that enables to increase a speed of scanning by modifying some features of mechanical sensor by adding a nonlinear force to lever of a mechanical sensor of AFM. Proposed method is modeled theoretically, using Simulink features by realizing original algorithm, and researched experimentally, using original modification of AFM sensor. Original results are obtained after a research is performed. Finally, comparison of results of original and modified AFM scans is made and corresponding conclusions are drawn.

Application of Frequency Method for Defining Threaded Joint Tightening Degree

There is a big variety of machines and equipment – internal combustion engines, aviation parts, building frames - joined by threaded joints, realized as bolt, nut and pin ones. For successful and safe exploitation of such equipment, it is required to check the tightening degree of threaded joints. There are few known methods of such control and one is presented in this paper. The proposed method is based on contact stiffness and friction change from thread tightening degree. At the same time, tightening changes with sufficient significance the dynamical properties of such a system - natural and resonance frequencies, amplitude – frequency and amplitude-phase characteristics, so, that it is possible to evaluate the tightening degree of the investigated joint. Dynamic properties are defined by exciting transient process between bolt head and tightened by this bolt detail using as short as possible force impact. Sensors register analogical signal of transient process and transmit it to a special computer card. The computer card converts analogical signal to code. Code is saved in the computer file for further processing. Processing data is saved in this file, and we find desired dynamical characteristics. Using special experimental bench proved that dynamic characteristics are sensitive enough to threaded joint tightening degree and the method is applicable to practice.

The Research of Wire Rope Defect Using Contactless Dynamic Method

This paper is intended to reveal possibilities of defects finding in the wire ropes using dynamic properties of the tensed wire rope using specially designed test rig. The subject of the research is the tensioned wire rope with broken wires, located on surface of the rope.Fragment of steel rope (4 mm diameter and 1.35 m length) was tested experimentally in order to find mentioned defects. A measurement of vibrations of the wire fragment on this test rig was performed using contactless vibration sensors. Fragment of the rope, installed in the test rig was excited with electrodynamics vibrator, which created sinusoidal excitement indirectly, i.e. through own frame. Research of vibrations of the rope was performed in wide ranges of frequencies and desired dynamic properties of the rope fragment as a dynamic system was obtained. Finally, results of the experimental research are presented and conclusions are drawn.

Investigation of quality change in locomotive lubricant

This paper describes experimental investigation of lubricant properties used in locomotive engines. The workbench for experimental investigation is described, and experiment technique is presented. Results and their interpretation show direction for further investigation. Conclusions of results are made.

Dynamics of a mechatronic system with flexible vertical rotor

The paper is dedicated to research on flexible rotor systems with anisotropic rotor material properties. In addition, the anisotropy of rotor supports alters the rotor system resonance frequencies and the machine has to pass till it attains the operating angular speed. This phenomenon of rotor vibration is observed in vertical rotors. The aim of this work is to compare experimental vibration measurements and results of theoretical modeling. In the paper theoretical model, created from physical one of really existing rotor system is described. Collected experimental data of rotor vibrations in bearings are compared with results of theoretically derived equations. The results of theoretical modeling and research enables for estimation of a more precise technical condition of the rotor system both after the overhaul and during the maintenance and thus to avoid unexpected breakdowns, especially concerning the fatigue development in ball bearing elements.

Modification of the AFM Sensor by a Precisely Regulated Air Stream to Increase Imaging Speed and Accuracy in the Contact Mode

Increasing the imaging rate of atomic force microscopy (AFM) without impairing of the imaging quality is a challenging task, since the increase in the scanning speed leads to a number of artifacts related to the limited mechanical bandwidth of the AFM components. One of these artifacts is the loss of contact between the probe tip and the sample. We propose to apply an additional nonlinear force on the upper surface of a cantilever, which will help to keep the tip and surface in contact. In practice, this force can be produced by the precisely regulated airflow. Such an improvement affects the AFM system dynamics, which were evaluated using a mathematical model that is presented in this paper. The model defines the relationships between the additional nonlinear force, the pressure of the applied air stream, and the initial air gap between the upper surface of the cantilever and the end of the air duct. It was found that the nonlinear force created by the stream of compressed air (aerodynamic force) prevents the contact loss caused by the high scanning speed or the higher surface roughness, thus maintaining stable contact between the probe and the surface. This improvement allows us to effectively increase the scanning speed by at least 10 times using a soft (spring constant of 0.2 N/m) cantilever by applying the air pressure of 40 Pa. If a stiff cantilever (spring constant of 40 N/m) is used, the potential of vertical deviation improvement is twice is large. This method is suitable for use with different types of AFM sensors and it can be implemented practically without essential changes in AFM sensor design.

Modification of the AFM Sensor by the Precisely Regulated Air Stream to Increase the Imaging Speed and Accuracy

Increasing of the imaging rate of conventional atomic force microscopy (AFM) is almost impossible without impairing of the imaging quality, since the probe tip tends to lose contact with the sample. We propose to apply the additional nonlinear force on the upper surface of a cantilever, which will help to keep the tip and surface in contact. In practice this force can be produced by the precisely regulated airflow. Such an improvement affects the AFM system dynamics, which were evaluated using a mathematical model presented in this paper. The model defines the relationships between the additional nonlinear force, the pressure of the applied air stream and the initial air gap between the upper surface of the cantilever and the end of the air duct. It was found that the nonlinear force created by the stream of compressed air (aerodynamic force) prevents the contact loss caused by the high scanning speed or higher surface roughness, and at the same time has minimal influence on the interaction force, thus maintaining stable contact between the probe and the surface. This improvement allows to effectively increase the scanning speed by at least 10 times using a soft (spring constant of 0.2 N/m) cantilever by applying the air pressure of 40 Pa. If a stiff cantilever (spring constant of 40 N/m) is used, the potential of accuracy improvement reaches 92 times. This method is suitable for use with different types of AFM sensors and can be implemented practically without essential changes in AFM sensor design.

Research of the New Type of Compression Sensor

Measuring process of physical parameters for mechatronic system well developed and available sensors covers vast amount of interest area. Nevertheless, there are areas with some requests for sensors with special properties. Many applications require sensors, able to operate in harsh conditions.

Implementation of Different Gas Influence for Operation of Modified Atomic Force Microscope Sensor

This paper presents modelling of various gas application to modified atomic force microscope sensor in order to change its existing dynamic characteristics. This paper represents part of continuous research, which is focused on improvement of scanning speed of atomic force microscope (AFM) sensor. Subject of our research is enhancement of dynamic characteristics of Atomic force microscope sensor. Natural frequency of AFM sensor is the main factor influencing max scanning speed of atomic force microscope. In case of working range of frequencies approaches to the resonant frequency of cantilever, scanning results becoming inaccurate and unreliable. Improvement of properties of atomic force sensor made by adding additional nonlinear aerodynamic force to the AFM sensor. This force would act as additional controllable stiffness element, which allows shift resonant frequency to higher side. In this paper is presented research of additional nonlinear force behavior using different gasses as well as compressed air. Research covers factor of humidity of compressed air. Our research performed using 3D atomic microscope cantilever model in SolidWorks flow simulation software. Results of simulation delivered as dependencies of additional stiffness in the AFM sensor in all modelled cases. Finally, results presented in graphical form and conclusions are drawn.