Iulian Popescu

Position analysis in polynomial form of planar mechanisms with Assur groups of class 3 including revolute and prismatic joints

This paper presents the position analysis in analytical form of the Assur group of class 3 and order 3 with four links and six revolute/prismatic joints (triad). The aim of this position analysis is to determine all possible configurations of the Assur group, for a given position of its external joints. Four kinds of the Assur group of class 3, with one, two and three prismatic joints are investigated. The analysis leads to a nonlinear system of three equations with three unknown parameters. Using a successive elimination procedure, a final polynomial equation in one unknown is obtained. The real solutions of the polynomial equation correspond to assembly modes of the Assur group. Three numerical applications of the proposed methods are presented. Finally, a numerical application for position analysis of a planar mechanism with eight links including a triad with three external prismatic joints is also given.

The structure of planar mechanisms with dyads

The structural synthesis of planar mechanisms with dyads is presented. A classification of dyads is elaborated. New planar mechanisms are constructed using this classification of dyads. The trajectories for different mechanisms are studied. The advantage lies in the classification of the kinematic chains. The solution of the whole system can then be obtained by composing partial solutions.

Curves with Special Aesthetics Generated by an Original Mechanism

Our goal is to create artificial beauty by generating new plane figures—curves not known in Geometry. The paper deals with an original mechanism that generates curves featuring special aesthetic properties. The mechanism synthesis was achieved starting from relations known from Trigonometry for multiple arcs. The angles considered for the aforementioned arcs are represented by the angles of the leading elements, correlated through a coefficient n. The mechanism has two leading elements and two dyads of type RPP, rotation-translation-translation. In the extended paper the cinematic schema of the mechanism is provided. Its structure is analyzed, the associated equations are introduced along with the obtained plots (many curves with special aesthetic properties). Comments are made with respect to the influence of the coefficient n used to correlate the angles of the leading elements over the shapes of the generated curves and over the number of close contours. The obtained curves are analyzed for both possible distinct cases: when both leading elements are rotating clockwise, respectively in opposite senses. The continuity of these curves is studied as well, close or open curves being obtained. Some mathematical properties of the curves generated by the above mechanism are studied (the curvature and the curvature radius in a current point of the curve, the equation of the tangent and the equation of the normal to the curve in a current point and the symmetries of the curve with respect to the coordinate axes (Ox axis and Oy axis) and with respect to the origin O).

Rolling with and without Slipping during Orthocycloids Generation

The starting point consists in the modality to generate epicycloids when two external circles are considered. The mobile circle is rolling on the fix circle without slipping, such as two arcs belonging to these circles are equal. The specialty literature presents an example with a simple planetary gear in which the “satellite porting” arm provides the rolling of the mobile circle on the fix circle. Our original idea, not approached in the specialty literature, considers the rolling with slipping of the mobile circle on the fix circle. Instead of the gears providing the rolling without slipping, two wheels with smooth surfaces are used now. The case when the two involved arc are no longer equal is analysed. Between them appear either frictions generating braking or “skating like” rolling when the lubricant layer is too thick. An analysis of the theoretical case when the slipping has a sense opposite to that of a normal rolling is also performer. A significant class of curves was obtained. Some are even epicycloids obtained with slipping, with other parameters.

Geometric Aesthetic Locus Generated by a Mechanism

It starts from an issue of locus that generates Rhodonea curves . It is found the equivalent mechanism, having two driving links and one dyad, RRT type, that generates series of curves with special aesthetic shapes. The process is useful in mechanical toys, at commercials where curves are generated successively on a screen, and in kinetic art. Numerous examples of curves are given.

Trajectories and Laws of Motion for a Mechanism with Two Leading Elements and Two RRP Dyads

The paper deals with the trajectories and lows of motion of a mechanism of type T-RRP that was buil by using the properties of Cardano circles. It has two slides moving along the axis of the system xOy. A second leading element and another T-RRP dyad were added to this mechanism, the resulting mechanism, of type T-RRP-R-RRP. The trajectories of three points of interest were determined, for various (linear) correlations between the movements of the leading elements. The obtained trajectories are similar, but not identical, to the loops of epicycloides, wrapping ellipses. The generated laws of movement were also determined, variable oscillations of the final slide being obtained.

Paths and Laws of Motion of a Mechanism with Two Successive Conductive Elements and a Triad

It starts from a structural scheme of a mechanism with a triad and two successive conductive elements, and a kinematic scheme with ternary element and another element with void lengths is made. The relations to calculate the positions by contour method are written and the nonlinear algebraic system is solved by the method of successive elimination of the unknowns. There are determined the successive positions, the paths of some points and the variations of lifts, for different correlations between the laws of motion of the two conductive elements. It appears that there result paths and interesting laws.

Research about Surface Quality of Polytetrafluoroethylene (Teflon) after Inner Turning

For this study with high originality, a teflon bushing with outer diameter of 58 mm and 32 mm internal diameter has been turned. After inner turning with various cutting feeds, the part has been cut in half to measure roughness. The roughness parameters Ra, Rz and Rq have beeen measured with an electronic roughness tester Mitutoyo, Japan, SJ-201 P. The micro-asperity images for each of the 6 samples performed are presented in the paper. Diagrams with the variations of roughness parameters are also given in this study. The trend is the increasing of roughness values with feed increasing, but some abnormalities also appear in samples 3 and 4 for Ra and Rz. At sample 5 for Rz parameter and sample 6 for Rq parameter a decreasing of values occurs, although geometrically there should be with ascending tendencies. It follows that in teflon turning the cutting process is not uniform, although there are no marks on the blade. However, because this material is not metallic, it does not have a uniform structure, which influences the resulted roughness. This is the cause of the anomalies established by these experiments.

RESEARCH ABOUT 18CrNi5 STEEL MACHINABILITY BY CUTTING

There have been made experiments on 18CrNi5 steel by external cylindrical turning, collecting the resulted chips. In this paper the shapes and sizes of the resulted chips, explaining their correlation with channel dimensions on the front face of cutting tool, according to and chip deformation sections are analyzed. Also, the forms of resulted chips in relation with parameters of cutting process are explained. Keywords— chips forms, chip section, 18CrNi15 steel, turning.

Studies Regarding the Movement on the Cochleoid

There are given details about the cochleoid geometry and there are traced, based on equations, different areas of cochleoid, based on a supporting mechanism. They are shown the laws of variation of the curvature radius and of the tracer point coordinates. It is studied the material point movement on the cochleoid and there are presented relationships and diagrams for speeds and accelerations.