Arūnas Jakštas

Overhead crane anti-swing system based on the Pontryagin’s maximum principle

Overhead cranes are widely used at industrial enterprises for transportation of materials and products. They are successfully adaptable to technological processes used at an enterprise and their exploitation is inexpensive; in addition, the price of cranes is relatively low. However, extension of requirements set for technological processes results in shortened time for transportation and stiffened requirements for accuracy of cargo delivery and cargo safety. In the attempts to satisfy the latter requirements, particular attention is paid to swings of the cargo-holding rope. There is a number of factors that cause increased requirements for the control system of the crane drive. The slewing movement affects the total system of the crane and aggravates the crane movement control. In modern overhead cranes, the abilities and qualification of an operator (who is assisted by a certain anti-swing system) predetermine the cargo swings and the accuracy of its positioning. The said circumstance latterly caused a particular attention to computerisation of overhead crane control. However, a nonlinearity of the mechanical system of a crane and complicated control of swings often cause undesirable swings, in particular in the beginning and the end of cargo transporting process, thus reducing the efficiency of usual crane control systems. In addition, it should be taken into account that the parameters of a crane, as a controlled mechanical system, depend on the cargo and the conditions of its transportation. Consequently, a development of an effective cargo swing reduction system is a currently topical engineering problem.

Dynamic Reaction Forces of an Overhead Crane on Lifting

Abstract In the recent period, girder bridge cranes are replaced with double-beam overhead cranes with a rectangular cross-section of the beams. In addition, new materials are used for producing them thus applying other values of allowable loads and deformations. The paper focuses on two overhead cranes working for JSC Vilniaus kranai (Vilnius Cranes). The presented mathematical model provides an opportunity to assess the structural peculiarities of the above introduced cranes. The calculated results of dynamic loads appearing in the beginning and the end of the lifting process and having an impact on the lifting mechanism and metal structure are provided in the article.

An Investigation Into Fault Diagnosis in a Rotor-Bearing System with Dampers Used in Centrifugal Milk Separators

This paper deals with the problems encountered in the fault diagnosis in damped rotorbearing systems used in centrifugal milk separators. It is shown that direct bearing vibration measurements are more reliable than indirect (through rotor housing) vibration measurements. However, in most cases it is not possible to measure bearing vibrations directly. The factors causing large diagnostic measurement errors, such as the influence of the vibration damping system, step-up gear and electric motor noise are discussed in the paper. It is established that vibration measurements of the damping system are noninformative and cannot be used to diagnose faults in bearings. It is proposed to use the vibration spectra correlation to predict bearing failures in rotor-bearing systems of this type.

The Dynamic Errors of Mechatronically Controlled Lifting Equipment

Upon striving to ensure the cargo safety and precizity of its delivery, mechatronic control systems are more and more widely applied in lifting mechanisms. They get information from various sensors, including those involved in registering the rope’s deformations. The got information may be distorted because of the appearance of cargo swinging that’s level depends on the mode of operation of the lifting mechanism and the rope’s elasticity. The latter varies dependently on the length of the unwound rope and the way of deformation of rope’s wires. In the paper, a mathematical model of a lifting mechanism that describes its dynamics on lifting when both the cargo and the rope swing in respect of a vertical axis is provided. The model was examined by a special program developed upon using MATLAB and SIMULINK program packages. The obtained dependences of the swing parameters on the mode of operation of the lifting mechanism and the rope’s parameters enable assessing a possible application of the lifting mechanism.

COUPLINGS WITH VARIABLE CHARACTERISTICS OF VEHICLES

Abstract Couplings abruptly changing their torsional rigidity and carrying capacity when the transmitted torque reaches a particular value are considered. This state is achieved either changing the conditions of the deformation of a flexible member or by excluding it from torque transmission. In the presented paper the conditions of mode variation are determined and some relationships for determining major parameters of couplings are given.

Universal Coupling for Shaft of Actuators in Mechatronic Systems

The design of shaft coupling ensuring serviceability of an actuator under varying conditions is presented in this paper. The driving half coupling is an eccentric balanced over the axis of rotation. The torque of the coupling is determined by the parameters of the flexible ring and eccentricity. When the parameters of coupling are properly selected, the transfer coefficient of vibration can be reduced markedly.