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BULGARIAN ACADEMY OF SCIENCES NATIONAL COMMITTEE OF THEORETICAL AND APPLIED MECHANICS Journal of Theoretical and Applied Mechanics
Print ISSN: 0861-6663 Online ISSN: 1314-8710
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JTAM, Sofia, vol. 24 Issue 4 (1993) |
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Myths in Control of Robots D. Dontchev Institute of Mechanics, Bulgarian Academy of Sciences, Sofia
This paper is conserned with an investigation on some wrong, yet common ideas on the application of classical control theory to servo-control of manipulating robots. Two main problems are commented. The first one is the real necessity of stability of the closed-loop control system. It is shown that the stability is neither a sufficient nor a necessary condition for a good performance of the trajectory tracking task. An analysis of the real deviations from a desired trajectory is provided and the tracking error is evaluated.
The second problem is connected with the applicability of PD and PID control laws to servo-control of robots. The results obtained in [8] are weighted and the limits of its application are pointed out.
JTAM, Sofia, vol. 24 Issue 4 pp. 017-022 (1993), [Full Article]
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Parallel Robot with Controlled Compliance D. Chakarov Institute of Mechanics, Bulgarian Academy of Sciences, Sofia
In this paper are presented the investigations carried out on a parallel robot with controlled compliance according to patent of Bulgaria No 97141, 1992. A model for a robot compliant control is presented, which is used in the execution of a number of technological operations associated with kinematic and force constrains on robot motion. The relations for specifying of the end effector compliance and for robot control are carried out. The mechanical parameters of the robot are studied by the ALASKA Software Package. The change of the generalized coordinates and reaction forces and torques in the robot joints are analyzed with positioning and with technological movements. The computer pictures of the robot structure and of the change of mechanical parameters are shown.
JTAM, Sofia, vol. 24 Issue 4 pp. 023-029 (1993), [Full Article]
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Two and Three Arms Manipulator Systems with Special Structure for Belt-Grinding A. Ananiev Institute of Mechanics, Bulgarian Academy of Sciences, Sofia
The experiments and successful application of robotics in the solution of belt-grinding and polishing problems is extending in industry. This paper discusses some of the advantages, adaptation, integration, design and problems encountered in these types of operations. The utilization of robots offers yet another alternative to automation of grinding, which sometimes is still dangarous for human health.
Robots can improve the finishing operations by providing more consistency in the finished parts, often processing parts faster than if hand-made. Robots can work in the noisy, dusty environment that humans find unsuitable or harmful. The savings by automation of manual off-hand belt-grinding and off- hand buffing can be substantial.
Robots for belt-grinding and buffing of details with complex shapes with CNC have been designed in Bulgaria. The paper includes a short survey of the previous results for belt-grinding robots.
JTAM, Sofia, vol. 24 Issue 4 pp. 030-034 (1993), [Full Article]
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Predictive Adaptive Control of Robot Manipulators with Unknown Dynamics V. Balavessov Institute of Mechanics, Bulgarian Academy of Sciences, Sofia
The paper treats decentralized control of robotic manipulators when a priori information about the robot dynamics is not available. Two theorems concerning stability issues are proven. The approach is based on a novel decentralized inverse dynamics model. The control includes compensation of the disturbances using predictive adaptive tuning of the model parameters. A similar approach is proposed for feed-back gains tuning. Numerical simulation results are appended.
JTAM, Sofia, vol. 24 Issue 4 pp. 035-045 (1993), [Full Article]
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A Study on Non-Stationary Processes in the Transmision of an Automobile St. Bachwarov, L. Kunchev, St. Poulev Technical University, Sofia
The subject of this paper is to study the non-stationary processes in the transmission of an automobile starting off from a repose position. The mechanical model includes four-stroke internal combustion engine and three rotating masses, taking into account the inertia of the crankshaft, the gear box, the drive wheels and the reduced mass of the automobile. It is assumed that the driving moment from the clutch increases after an exponential law. The obtained system of nonlinear differential equations is solved numerically and the results from the calculation procedure for a concrete type of automobile are presented as computer graphs. Some experiments are made on the real automobile transmission. The comparison between theoretical and experimental results shows good convergence with their functional features.
JTAM, Sofia, vol. 24 Issue 4 pp. 046-051 (1993), [Full Article]
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Vibrations of a Robocrane in a Vertical Base Plane Considering the Variable Load Mass S. Nikoloff1, Z. Popova1, Al. Kazakoff2 1Technical University, Sofia 2Institute of Mechanics, Bulgarian Academy of Sciences, Sofia
Vibration characteristics of a robocrane are investigated in a vertical base plane with simultaneous linear travelling movement and lifting load movement. Robocrane is a mechanical system of a crane with the following three components: Mechanical construction, electrical driving, and computer control. The investigation carried out is a basis for defining optimal solutions for crane control in different working modes.
JTAM, Sofia, vol. 24 Issue 4 pp. 052-056 (1993), [Full Article]
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Nonlinear Vibrations of a Rigid Body with Combined Excitement in the Field of Elastic Forces Z. Tcherneva-Popova1, D. Vassilev2 1Technical University, Sofia 2High Military Transport School, Sofia
The properties of the spatial movement of a rigid body with excitations of self excited parametrical and forced vibrations in the field of an elastic hanging forces are described in the article. The model could be applied for example, in the case of the railway vehicle system. The investigation of the dynamics of this model is a condition for the creation of active vibroisolation of transport vehicles. This model provides a great variety of different vibrational regimes – stationary and transient, resonance and nonresonance, periodical and nonperiodical, stable and unstable, with mutual influence between the coordinates. The model realizes different forms of the resonance zones with transmission of energy from one coordinate to the other, exciting and declining of the resonance, etc.
JTAM, Sofia, vol. 24 Issue 4 pp. 057-064 (1993), [Full Article]
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Mechanical Design and Software System of a Six Degree-of-Freedom Parallel Robot V. Balavessov1, P. Cholakov2, D. Nenchev2, Z. Sotirov2 1Institute of Mechanics, Bulgarian Academy of Sciences, Sofia 2Technical University, Sofia
In the paper the mechanical design of a six degree-of-freedom parallel robotic system is described. The robot has been designed for educational purposes and later on commercialized as an inexpensive educational robot. The kinematic relationships and the inverse kinematic solution which is used in real-time continuous path planning are developed. The software concept is greatly influenced by the position and trajectory error analysis performed. The results show, that better positioning accuracy is obtained when Cartesian coordinates are used instead of joint coordinates. The software system is highlighted and the TOROL high-level programming language designed and used for the control of this robot is illustrated in a simple programme.
JTAM, Sofia, vol. 24 Issue 4 pp. 065-080 (1993), [Full Article]
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Basic Thesis for Formal Force Analysis of Real Mechanical Parts M. Leparoff Technical University, Sofia
The purpose of this work is to create a data base which will permit to do the formal force analysis. Force analysis of mechanical assembly is intended to solve the problem of discovering all the forces and moments in their quantitive and qualitive aspects, which load up all the parts of the assemblies, when the incoming forces are known.
Nine statemens and IO consequences resulting from them were proved in order to solve the problem.
JTAM, Sofia, vol. 24 Issue 4 pp. 081-086 (1993), [Full Article]
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On the Formal Force Analysis of Real Mechanical Parts M. Leparoff Technical University, Sofia
The purpose of this work is to create a data base which will permit to do the formal force analysis. Force analysis of mechanical assembly is intended to solve the problem of discovering all the forces and moments in their quantitive and qualitive aspects, which load up all the parts of the assemblies, when the incoming forces are known.
Nine statemens and IO consequences resulting from them were proved in order to solve the problem.
JTAM, Sofia, vol. 24 Issue 4 pp. 087-092 (1993), [Full Article]
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Computing Added Masses for Dynamic Analysis of Dams Using Finite Element Method St. Grigorov, Sv. Tashev, St. Tasev Institute of Water Problems, Bulgarian Academy of Sciences, Sofia
The interaction in the system foundation-dam-water, subjected to seismic effect is computed.
A procedure for determining the dynamic characteristics introducing added masses matrix for the threedimensional case is suggested. The integration procedure is simplified by means of shape functions on the contact surface and as a consequence some labor-consuming stages drop out. A complete earthquake analysis can be performed on the basis of the achieved numerical values of the dynamic characteristics and after applying the Spectral Method.
JTAM, Sofia, vol. 24 Issue 4 pp. 093-098 (1993), [Full Article]
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Nonlinear Wave Motion in a Magnetic Thermo Elastic Solid with Small Deformations St. Dimitrova, L. Vulkov Technical University of Rousse, Rousse
This paper investigates the wave propagation in a thermoelastic solid placed in a magnetic field. It is proved that the governing quasilinear system is hyperbolic although the eigenvalues change their ordering in the hodograph (solution) space. The type of the characteristic fields (genuinely nonlinear, exceptional) is established. Then, the propagation of weak discontinuities, that are acceleration waves, are studied. The time and position of occurence of shock when they do form are examined.
JTAM, Sofia, vol. 24 Issue 4 pp. 099-104 (1993), [Full Article]
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Numerical Simulation of Contaminant Transport in a Settle Tank O. Iliev1, V. Naydenova2 1Institute of Mathematics, Bulgarian Academy of Sciences, Sofia 2University of Sofia
The backward-facing step flow, when part of the domain is occupied by a porous medium, is numerically studied. Extended 2D Navier-Stokes equations with an introduced Darcy term are solved simultaneously in liquid and porous media. Convection-diffusion contaminant transport in liquid and porous media is numerically investigated. Raection-convection-diffusion processes of the settle tank purging are numerically studied, too.
JTAM, Sofia, vol. 24 Issue 4 pp. 105-113 (1993), [Full Article]
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Mathematical Modelling of Filling and Crystallization of Two-Dimensional Casting Processes G. Georgiev, K. Daskalov Institute for Metal Science, Bulgarian Academy of Sciences, Sofia
This work consists a brief exposing of some methods and devices, used in the mathematical modelling of fundamental processes during the forming of axisymmetric castings. Hydrodynamics of the filling is based on the assumption of laminar flow and incompressible Newtonian fluid. The chosen approach treats all the necessary conditions for casting with counter-pressure, low pressure casting, vacuum casting and etc. The problem of heat and mass-transfer in the casting-mold system is solved during the process of filling, taking into account the evolution of the liquid-solid zone. For practical needs a communicable software product for PC and VAX is created.
JTAM, Sofia, vol. 24 Issue 4 pp. 114-121 (1993), [Full Article]
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On the Integral Statement of the Stress-Strain State of Cylindrical Shell under External Loading J. Ivanova, V. Valeva Institute of Mechanics, Bulgarian Academy of Sciences, Sofia
The singularity of the stress state of cylindrical shell under normal concentrated force P, apllied to the free edge of a shell is investigated. As a base the simplified differential equation of the cylindrical shell written in a complex form is taken. The functions of the complex solution, we search, are expanded into the trigonometric Fourie's series; the respective arbitrary constants are determined from the boundary conditions at the free edge of the shell.
As a result the asymptotic formulae in the neighbourhood of the point of the concentrated load are obtained. The integral equations of the considered cylindrical shell are obtained and solved numerically by BEM. The numerical results for the stress-strain state of a shell with given geometric parameters are illustrated.
JTAM, Sofia, vol. 24 Issue 4 pp. 122-129 (1993), [Full Article]
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Spatial Numerical Model of the Thermal Stress State of Elastic – Creeping Concrete Blocks L. Kolarov, O. Santurjian Institute of Water Problems, Bulgarian Academy of Sciences, Sofia, Sofia
A mathemathical model of the spatial thermal stress state of incremental concrete blocks is discussed accounting for the creep. It is done on the basis of FEM and the theory of the elastic-creeping body. A solution, developed, is employng the relaxation function, which is always convergent. The relaxation
function can be determined by direct experimental tests or on the basis of a known creep function. Studies have been done for an assesment of the inaccuracy in the results, when the modelling is performed by a two-dimensional model.
JTAM, Sofia, vol. 24 Issue 4 pp. 130-134 (1993), [Full Article]
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Insolation Effect Consideration in Dam Block's Thermal Regime Modelling I. Etimova, O. Santurjian Institute of Water Problems, Bulgarian Academy of Sciences, Sofia
A method for consideration of the solar radiation effect in modelling of concrete dam blocks temperature field is reported. The insolation heat flux, comprising a considerable part of the heat transfer through the blocks boundary surfaces, is calculated on the basis of the solar radiation intensity, measured on surfaces with defferent exposure and expected duration in months. Determined in this way, the insolation flux is included in the boundary condition of III type of the temperature field mathematical model of concrete dam blocks, as well as in the algorithm of the computer programme "THERM". Numerical results are presented.
JTAM, Sofia, vol. 24 Issue 4 pp. 135-140 (1993), [Full Article]
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On the Form of the Weakly Conservative Forces Ts. Ivanov1, R. Savova2 1University of Sofia, Sofia 2Institute of Mechanics, Bulgarian Academy of Sciences, Sofia
We consider a deformed elastic body subject to additional weakly conservative body forces and surface tractions. It is supposed that the total potential energy functional is Gateaux differentiable, whereas the body forces and surface tractions and their corresponding potentials are differentiable functions depending on the additional displacement and its gradients. The restrictions on the form of these functions due to their conservativeness as well as the balance equations are obtained.
JTAM, Sofia, vol. 24 Issue 4 pp. 141-144 (1993), [Full Article]
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Stress Smoothing, in the Ritz Method Using Isoparametric Finite Elements I. Stefanov University of Architecture, Civil Engineering and Geodesy, Sofia
The Ritz method is combined with the finite element method for plane elasticity problems. In a numerical example the displacements and stresses obtained by different clasgical solutions and by Ritz method are compared. A stress smoothing, based on Boubnov-Galerkin averaging is also applied.
JTAM, Sofia, vol. 24 Issue 4 pp. 145-150 (1993), [Full Article]
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Big Constructions Displacement and Deformation Measurement of by White Light Speckle Photography V. Kavardjikov, A. Dimitrova Institute of Mechanics, Bulgarian Academy of Sciences, Sofia
A methodical study of white-light speckle photography potentiality for a remote and noncontact control and measurement of the field deformations of some types of constructions – frames, cranes, bridges, etc., and their elements is made.
Two types of difficulties are synthesized. In the case of illumination of these diffusers by noncoherent light (for instance – Sun light) and the creation of their images by conventional photo objectives of focus lenght respectively &nadash; 58 mm, 135 mm and 186 mm, good quality speckle images are obtained.
Applying some possible combinations of a diffuser, an objective and the distance between them, the lower and upper measurement limits are defined.
JTAM, Sofia, vol. 24 Issue 4 pp. 151-156 (1993), [Full Article]
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Axisymmetric Problems of Elasticity for a Transversely Isotropic Body with Cracks M. Savruk Karpenko Physico-Mechanical Institute, Academy of Sciences of Ukraine, Ukraine
The axisymmetric deformation of a transversely isotropic medium with an arbitrary system of axisymmetric cuts on smooth surfaces of revolution is investigated by the boundary integral equation method under the action of body forces and boundary traction or displacement. This approach involves the use of the theory of generalized functions, and in particular of the surface delta function. The closed-form solutions are presented for the case of an internal or external circular crack with faces under arbitrary tractions or displacements.
JTAM, Sofia, vol. 24 Issue 4 pp. 157-162 (1993), [Full Article]
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