Ukrainian Journal of Mechanical Engineering and Materials Science

8

Authors: Serhii Hromniuk, Ihor Hrytsai

The relevance of the problem which is solved in this article has been substantiated. In modern machines and equipment, rotary motions which cannot be implemented without gear wheels and gear trains are always present. Attainment of high performance of a machine – increase in loading with simultaneous increase in speed, increase in transmitted forces and moments, decrease in noise during operation, ensuring high indexes of failure-free performance and longevity of a machine – depends on precision in manufacturing the gear wheels and gear trains. These requirements to modern machines are put simultaneously with improvement of technology of their manufacturing and with creation of new effective methods of machine parts working. A new effective method of radial-circumferential (RC) gear cutting by disk-type cutting tool under the conditions of continuous generation (revolving) around is described; this way enables us to considerably reduce the expenditures for expensive and complicated cutting tools, to increase productivity of the process, and to increase precision of gear wheels. However, for application of this method in the course manufacturing, it is necessary to develop a technique of prediction of the precision of the gear cutting; such a technique being able to serve as a basis of substantiation of the choice of regimes of gear cutting. Principles of the mathematical model of cutting force of gear cutting, i.e. a model which is based on modelling of parameters of shearings made by a disk-type milling cutter, are presented in this article. This mathematical relation takes into account the intensity of deformation of the layer which is being removed and the strength of the material which is being machined; the model also enables us to determine the force on individual blades and its total value on all the active teeth in RC-method at any instant of time of milling as a function of the turn angle of the cutting tool. Analysis of cutting force has indicated that in one revolution of a milling cutter the cutting force varies according to aperiodic regularity, and its peak values are considerably less than the force of gear-tooth milling by a hobbing cutter under the same initial conditions. Since the disc-type gear milling cutter, as compared with the hobbing cutter, is considerably more sensitive to elastic deformations, the cutting force can essentially influence the error of gear cutting of ring gears. Proceedings from this, the influence of primary errors and that of elastic deformations which are caused by variable cutting force in the cycle of revolution of the milling cutter and formation of gears on the error of the working is investigated. Laws of the influence of radial, axial, and torque deformations of the elastic system of a machine on the deviations of parameters of the teeth from their rated ones and on the error of profiles in the process of gear milling according to radial-circumferential method are presented. The enhance of precision of tooth cutting and reduction of the total error becomes possible due to the choice of such regimes of cutting (first of all, axial feed) under which the necessary precision of the chosen parameter of precision, in particular, profile error, can be attained.

10

Authors: Volodymyr Malashchenko, Oleh Strilets, Volodymyr Strilets

The article deals with problem of speed change management in engineering, i.e., hoisting, building, road and land reclamation machines, cars and tractors, machine tools and other equipment. The review of the methods and devices for stepped, steppless and combined speed change process management have been performed. Their major disadvantages have been identified. Among others, main disadvantages of stepped speed management devices are the complexity of design, their large material consumption, the emergence of dynamic loads during the transition from one speed to another, even in case of synchromesh using. Continuously variable speed devices have intense components wear due to the use of friction connections like brakes or lock-up clutches. The authors lead to the conclusion about the need for new devices of speed change management to remove, or at least decrease, identified deficiencies. New devices suggested for speed changes management via epicyclic gear trains with a closed circuit hydrosystem. Those new constructions are supposed to remove abovementioned shortcomings and can be the basis and foundation for new devices creation and their further research.

14

Authors: Vitaliy Korendiy

Problems and prospects of using the walking mode for producing motion of robotic systems are considered. Advantages and spheres of the use of mobile robotic systems equipped with walking movers are substantiated. Preferences of cyclic (lever) walking mechanisms are analyzed. The kinematic parameters of four-bar crank-rocker walking mechanism, constructed on the basis of Chebyshov-Umnov mechanism, are accepted as the subject of research. The process of motion of the supporting foot of the walking mechanism is accepted as the object of research. The main aim of the investigation consists in carrying out structure and kinematics analysis of the mentioned mechanism with further derivation of analytical dependencies for calculating kinematic parameters of the supporting foot motion. The special features of the structure of four-bar walking mechanism and theoretical foot loci (paths) are considered. The form of the most reasonable path for further research is established. As a result of carried out structure analysis, it is ascertained that the mechanism consists of two structural groups: that of the first class and that of the second class second order first type. As a result of kinematics analysis, the analytical expressions for calculation of coordinates of the supporting foot hinge of the walking mechanism depending on geometric parameters of the mechanism and the angle of the crank rotation are deduced. The prospects of further investigation under the themes of the paper are analyzed. In particular, the goal function, which may be used for further optimization of structural parameters of the mechanism, is considered and the use of applied software for solving optimization problem is suggested. The optimization problem consists in evaluating such geometric parameters of the walking mechanism which allow the motion of the supporting foot in accordance with the prescribed (specified) path.

16

Authors: Bohdan Diveyev

Passive, broadband targeted energy transfer refers to the one-way directed transfer of energy from a primary subsystem to a nonlinear attachment; this phenomenon is realized in damped, coupled, essentially nonlinear impact or particle dynamic vibration absorber (DVA). An impact damper is a passive control device which takes the form of a freely moving mass, constrained by stops attached to the structure under control, i.e. the primary structure. The damping results from the exchange of momentum during impacts between the mass and the stops as the structure vibrates. A particle-based damping system can overcome some limitations of ordinary DVA by using particles as the damping medium and inter- particle interaction as the damping mechanism. Large damping at such family constructions of DVA’s does not bring to destruction an elastic DVA element over in critical cases, when working frequency approaches own frequency of DVA, or when the transitional process of acceleration of rotating machines is slow enough and DVA’s has time to collect large amplitudes of vibrations. The primary structure is modelled as a spring-mass system. In this paper, an efficient numerical approach based on the theoretical-experimental method is proposed to maximize the minimal damping of modes in a prescribed frequency range for general viscous tuned-mass systems. Methods of decomposition and numerical synthesis are considered on the basis of the adaptive schemes. The influence of dynamic vibration absorbers and basic design elastic and damping properties is under discussion. A technique is developed to give the optimal DVA’s for the elimination of excessive vibration in sinusoidal forced rotating system. It is found that the buffered impact damper not only significantly reduces the accelerations, contact force and the associated noise generated by a collision but also enhances the level of vibration control. The interaction of DVA’s and basic design elastic and damping properties is under discussion. One task of this work is to analyze parameters identification of the dynamic vibration absorber and the basic structure. The discrete-continue models of machines dynamics of such rotating machines as water pump with the attachment of particle DVA’s and elongated element with multi mass impact DVA’s are offered. A technique is developed to give the optimal DVA’s for the elimination of excessive vibration in harmonic stochastic and impact loaded systems.