Loader Cranes Research Articles

ИССЛЕДОВАНИЕ НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ МАТЕРИЛА В ОБЛАСТИ ВЕРШИНЫ ТРЕЩИНЫ, РАСПОЛОЖЕННОЙ В ЗОНЕ КОНСТРУКТИВНОГО КОНЦЕНТРАТОРА

The influence of the stress concentrator is studied due to the design features of the welded metal structure of a loader crane on the stress-strain state of the material in the fracture process zone. Within the framework of the research, a physical criterion using the basic mechanical properties of the material is applied. A normal tear-off crack is considered under uniaxial loading conditions. FEM analysis of T-joint and lap welded joint models, as creating the highest stress concentration in metal structures of loader cranes, is carried out. A comparative analysis of calculation results for models with a crack in the concentrator area and models with a crack in a smooth plate is performed. The influence of the concentrator and its several parameters on the stress stiffness at the crack tip is shown. A general averaged estimation of the concentrator influence on the material stress state in the fracture process zone is proposed. Recommendations on taking into account the presence of the concentrator in analytical calculations are given.

Modeling the swing of mobile loader cranes with anchor outriggers when operating on weak soils

The paper presents a dynamic model illustrating the swing of a mobile machine on a wheeled chassis equipped with a loader crane and anchor outriggers during loading and unloading operations. The model regards the interaction effect of the outrigger anchoring device with weak soil within the system “load – loader crane – chassis – outriggers – anchor devices – soil”. Possible variants of single and multiple step soil compaction and changes in its deformation characteristics in the area of the outrigger anchor device implementation are considered. The impact of the gaps formed during soil compaction on the swing parameters of a mobile machine during the swing of the boom of the loader crane is demonstrated as applied to a full-scale crane-manipulator. The rate of chassis tilt angle and swing period of the mobile machine increase during the loader crane operation with an increase in the gaps in the ground. The swing parameters during the initial stage of crane operation gradually increase for soils characterized by multiple compaction until these parameters reach some steady-state values determined by soil stiffness. Awareness of the steady-state value of the crane tilt angle amplitude achieved at the end of the process of weak soil compaction enables to reasonably assess the risk of a mobile machine overturning.

Dynamic Processes of Loader Cranes Manipulators with Excessive Backlashes and Elastic Damping in Their Hinges

This research is aimed at developing a mathematical model and the methodology for computer simulation of hydraulically driven manipulators of mobile cranes having excessive backlashes in cylindrical joints. The authors proposed a structural design and considered the mechanism of reducing the additional impact load in the hinges by means of elastic damping of oscillatory processes. This method allows estimating the degree of influence of the backlash and stiffness of the elastic damper on the change in the quantitative characteristics of the dynamic loading of the manipulators metalwork and the motion parameters of the transported load. While in operation, the excessive backlashes may cause an increase in the level of dynamic loading of manipulators up to 2 times or more. However, the rational choice of the elastic dampers stiffness allows an effective solution to this problem to the point of complete elimination of the additional impact load.

Universal Mathematical Model of a Hydraulic Loader Crane

The paper presents the modeling technique of working processes of loader cranes installed on mobile machines using the developed universal mathematical model that considers complex interaction between the elements of a dynamic system ‘Working Body – Loader Crane – Basic Machine – Base Surface and Substructure – Control System – Environment’. The model considers the developed feedbacks between subsystems. The paper proposes the technique of imitating modeling of a loader crane loading during the entire operation period using the Monte-Carlo method and the universal mathematical model. The application of the developed approaches is shown on the example of a task concerning the general buckling of a mobile machine ACT-4-A equipped with a loader crane in the conditions of ground subsidence under a caterpillar.

Increasing operating life of hinge lugs in manipulators of mobile transportation and production machines

The article deals with the issues of increasing the reliability of hinge lugs in manipulators of mobile transportation and production machines (loader cranes). At present, the actual operating life of hinges in heavily loaded cranes amounts to not more than 3000 operating hours, with the estimated value being 6000…8000 operating hours. The paper provides technical solutions of how to increase the operating life of hinge lugs. The first way consists in providing crack resistance in bimetallic compositions with specified crack resistance which allows increasing the operating life of hinge lugs by up to 50%. The second way involves equipping hinge joints with damper devices having elastic and dissipative elements. The damper devices allow reducing or completely eliminating the impact loads which occur due to the presence of a backlash in a worn-out hinge. The rational values of damper device elasticity and viscosity coefficients, which allow attaining the maximal reduction of impact loads, were determined. To prove the effectiveness of the proposed technical solutions, a mathematical modeling approach to the dynamic processes in loader cranes was employed

ОПТИМАЛЬНЫЙ СИНТЕЗ ПРИВОДНЫХ ШАРНИРНЫХ СОЕДИНЕНИЙ ГИДРАВЛИЧЕСКИХ МАНИПУЛЯЦИОННЫХ СИСТЕМ МОБИЛЬНЫХ КРАНОВ

Рассмотрены конструкция, особенности работы и методика оптимального проектирования приводного шарнирного соединения, предложенного в качестве альтернативного конструктивного варианта шарнирного соединения смежных звеньев гидравлических манипуляционных систем мобильных стреловых кранов-манипуляторов. Конструкция устройства позволяет совместить две функции: обеспечить постоянную неразрывную кинематическую связь между смежными звеньями манипуляционной системы путем создания цилиндрического шарнира для выполнения возвратно-поворотного относительного движения смежных звеньев и сформировать встроенный поворотный гидродвигатель шиберного типа. Разработана математическая модель, сформулирована и решена задача оптимального синтеза приводного шарнирного соединения на основе минимизации массы устройства при соблюдении нелинейной системы конструкторских, монтажных, силовых, прочностных и кинематических ограничений. Анализ результатов выполненных оптимизационных расчетов показал, что масса оптимального варианта устройства возрастает с ростом преодолеваемого момента от перемещаемого груза и снижается с увеличением числа камер шарнирного соединения. Рабочее давление гидросистемы не оказывает практического влияния на оптимальную массу, что позволяет использовать для обеспечения движения звеньев манипуляционной системы насосный агрегат меньшей мощности. Оптимальные значения основных конструктивных размеров приводного шарнирного соединения определяются как величиной эксплуатационной нагрузки, так и условиями монтажа устройства с учетом размеров поперечных сечений смежных звеньев манипуляционной системы. При проектировании манипуляционных систем приводные шарнирные соединения позволяют отказаться от выносных силовых гидродвигателей, исключить эксплуатационные отказы вследствие изнашивания и усталостного разрушения элементов шарниров, а также повысить энергоэффективность кранов-манипуляторов путем перевода гидросистемы на более низкие уровни рабочего давления при сохранении требуемых грузо-высотных характеристик.

Modeling the Dynamic Load of Loader Cranes Metal Structure with Excessive Backlashes in Sections Hinge Joints

The research objective presented in this paper is working out the mathematic model and methods of computer modeling the performance of hydraulic loader cranes with excessive backlashes in sections hinge joints. The mechanism for generating the additional impact load in joints is illustrated. It is based on analyzing the hinge pin displacement within the backlash and its periodic collisions with the limiting elements of a hinge joint. This method allows evaluating the degree of influence of the backlash value on the changes in the qualitative characteristics of the dynamic load of the cranes metal structure and the motion parameters of the conveying load. The computer modeling of the loader crane dynamics in its turning motion was performed. The excessive backlash at the point of connection of a load-handling device and a boom was analyzed. The comparative evaluation of the dynamic load of the crane metal structure was performed for two controlling cases: 1) the absence of a backlash; 2) the presence of a backlash (the backlash variation range is 0…2 mm). While the crane is in operation, some excessive backlashes may result in increasing the dynamic load of loader cranes metal structure twofold and more.

A Local Positioning System for Loader Cranes Based on Wireless Sensors—A Feasibility Study

This paper presents a feasibility study that deals with a local positioning system for a loader crane based on battery-powered wireless sensors and consists of two joint angular sensors and one telescopic boom length ranger. The practical challenges associated with using conventional sensors are described in order to provide the motivation behind the choice to use the sensing methods proposed in this paper. A novel method is tested using microelectromechanical system inertial sensors mounted around the crane joints to indirectly measure the joint angles, as well as an ultrasound time-of-flight ranging method to measure the telescopic boom length. The local positioning system's wireless sensor prototype designs are described in detail. Data from the angular sensor experiments conducted on a loader crane and the ultrasound ranging experiments conducted both in the laboratory and on the loader crane are presented and analyzed. The preliminary results from these experiments show that the performance of the new sensors is promising. The conclusion is drawn from the experimental results, and future work for this local positioning system is also described.