This article presents a numerical study of the stability of a hydraulic excavator during performing lifting operations. A planar dynamic model is developed with six degrees of freedom, which considers the base body elastic connection with the terrain, the front digging manipulator links, and the presence of the freely suspended payload. Differential equations describing the excavator dynamic behavior are obtained by using the Lagrange formalism. Numerical experiments are carried out to study the excavator dynamic stability under different operating conditions during the motion along a vertical straight-line trajectory. It is shown that the arising inertial loads during the movement of the links along the vertical trajectory, combined with the payload swinging and the motion of the base body, decreases the excavator stability. It was found that the excavator stability during following vertical straight-line trajectory decreases considerably in the lower part of the vertical trajectory. If the stability coefficient is close to 1, the payload swinging can cause the separation of a support from the terrain; nevertheless, the excavator stability can be restored. A method for tire stiffness and damping coefficients estimation is presented. The validation of the dynamical model is performed by the use of a smallscale elastically mounted manipulator.
The present paper introduces a cloud-based expert system for synthesis and evolutionary optimization of planar linkages. The kinematic structure of the linkage is composed by the modular approach based on Assur’s groups. The dyads are represented as functional blocks with input and output variables. The applied approach for obtaining the geometrical relationships between the input and the output variables of the dyads is based on the use of homogeneous transformation matrices. The developed software system allows a dimensional synthesis of planar linkages by using genetic optimization algorithms. One feature is remote creation of the models of genetic algorithms as well as the receiving of the results by means of a user-friendly interface. By exploiting the application, the user can produce and edit the initial information about the synthesized or optimized linkage; thus he can receive the calculation results as a web page and/or as MS Excel file. An additional mutation of the best chromosome genes by scanning of every gene within its searching space improves the optimal solution. The analyzed numerical case studies show the applicability of the developed software system for mechanism analysis, synthesis and optimization. Because the number of genes is not limited, the linkages with a very big number of design variables can be synthesized by exploiting the developed approach.
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