Papers by Author: Janis Rudzitis

Abstract: The problem of evaluating the life period of different mechanisms is of great importance nowadays. This could be explained by the fact that the wear process is very complex and very many factors take place simultaneously. During the history a variety of theories that offered different methods of wear calculation models were developed. However still there is no exact wear calculation model that could be applied to all cases of wear processes. The offered method is dealing with the calculation of rough surface peaks that make the contact between two surfaces. Taking into account the number of these peaks and applying fatigue wear model based on 3D surface micro-topography, assessing the materials physical and mechanical characteristic quantities and considering definite service conditions of sliding friction pair it is possible to make the wear calculation of friction pair under definite working conditions.

Abstract: The common measurement error when measuring the component geometrical dimensions using universal contact measurement instruments is caused by different factors, such as error of the measurement instrument, personal reading errors, effect of surface roughness on the measuring line deviation, influence of contact deformation measurement force, and others. The present article examines one of these factors, i.e. contact deformations under the influence of measurement force. To make precise measurements it is essential to find out the effect of roughness of measured components. High roughness creates additional measurement errors. It is particularly important in the measurement of thin components, flexible materials and films, as well as for components with nanocoating. Flexible bodies in the meaning of this article are components of different shape and sizes made of rubber or soft plastic. This article studies principles of error formation based on the deformation of surface roughness and basic material.

Abstract: One of the main surface coating quality indexes of details of mechatronic systems is surface roughness. And the surface roughness is described by surface roughness parameters. Nowadays characterization of surface roughness using three-dimension (3D) methods and parameters become more and more important. This type of surface quality characterization, unlike the two-dimension (2D) methods, provide a more complete view on the surface qualities, since the surface roughness is viewed as a spatial object. Within the last ten years intensive work is being carried out on the development of 3D roughness standards, therefore it is necessary to agree on a unified approach in the assessment of surface roughness 3D parameters. To make possible application of the ISO/DIS 25178 standard being developed one needs information on the determination of 3D surface roughness parameter precision, such as number of measurements, dimensions of measurement areas and their disposition on the measured surface.

Abstract: High-precision mass measurement equipment is required in some areas of science and technology. Physics, chemistry, pharmaceutics and high precision mechanics are common examples. In metrology, high-precision scales are used for verification and calibration of lower precision mass measurement equipment (weights and scales). Mass comparators are the most accurate mass measurement instruments available today. It is a special type of electronic scales designed to compare mass of two weights. They can be automatic or manual, with various measurement ranges and accuracy classes. This article discusses principles of operation of mass comparators and practice of high-precision mass measurement. There are special computer programs that can be used in conjunction with these instruments, which may significantly improve measurement accuracy (when mass comparator is controlled remotely) as well as simplify calculations and reporting procedures. This article describes one of these programs – ScalesNet32 – which can be used with mass comparators produced by Sartorius (Germany).

Abstract: For perfect surface roughness description is not enough to know characteristics of surface profile. It is necessary to use topography methods, so called microtopography. Thereby, surface roughness in microtopographycal understanding must be described with three coordinates, whose in Cartesian coordinates system compose point under consideration height h, abscissa and ordinate, determines point position in the plane. Most efficient methods in irregular surface roughness research are random function theory methods. Therefore, microtopography, analogically to profile, may consider as random function, but two dimensional function, i.e. two variable x and y random field h(x,y). From analogy with random process, random field can be normal – ordinates are distributed by normal (Gaussian) distribution. Moreover, random field can be homogeneous and heterogeneous. Random field is deemed homogeneous if its mean value is discretionary and correlation function depends only from distance between surface points. Important characteristic of random field is correlation function, whose depends of two variables t1 and t2 – orthogonal Cartesian coordinates of vector t. Random field is homogeneous and isotropic when its characteristics are equivalent in any direction. There are three types of surface anisotropy: • General event of surface anisotropy. Characteristics of this event roughness parameters are depend of surface split direction. • Surface roughness with direct anisotropy. Those surfaces are with typical traces of tool and they proper two mutually perpendicular surface roughness directions. • Extended anisotropy area – special event of anisotropy roughness. Of analytical opinion, gainfully anisotropy roughness see as extended occasional isotropy area. This let easy cross from anisotropy surface to isotropy and contrariwise, thereby embrace amount class of surface roughness. Let’s formulate microtopography model of rough surface [1]. Surface roughness is described with homogeneous normal random field h(x,y) that has uninterrupted correlation function and uninterrupted deriviates. We may consider that E{h(x,y)}=0. The mean random field value is plane called mean plane. For describing random field we must know mathematical expectation and field correlation function, what in fact reduces on determining dispersion and rationed correlation function r(t1, t2). Homogeneous random field dispersion D{h} doesn’t depends of direction and can be founded in any surface split. Given model of rough surface let inspect surfaces produced by abrasive instruments and friction surfaces after wear-in period.