U ovom radu predstavljen je metod za eksperimentalno određivanje parametara pogonskog mehanizma obrtne platforme hidrauličnih bagera sa dubinskim manipulatorom. Definisan je matemetički model kojim se određuju kinematički i dinamički parametri pogonskog mehanizma obrtne platforme hidrauličkih bagera, na osnovu mrenih veličina stanja rada bagera u eksploatacionim uslovima. Dobijeni eksperimentalni rezultati pokaziju da su najveća opterećenja aksijalnog lezaja pogona okretanja platforme pri operaciji kopanja. Osim toga izrazite dinamičke promene parametara hidrostatičkog sistema pogonskog mehanizma obrtne platforme javljaju se pri operaciji prenosa materijala.
The paper presents the results of a numerical and experimental analysis of the dynamic stability of hydraulic excavators. The analysis has employed the software developed on the basis of a defined general dynamic mathematical model of an excavator grounded in Newton-Euler equations as well as the measured quantities of the excavator operating state in exploitation conditions. The defined model is used to model the members of the excavator kinematic chain using rigid bodies while the actuators (hydraulic cylinders and hydraulic motors) of the excavator drive mechanisms are modeled with elastically dampened elements. The elastically dampened characteristics of the actuators are defined with regard to the size of the actuator as well as to the compressibility and temperature of the hydraulic oil used in the excavator hydrostatic drive system. To illustrate the analysis, the paper provides the results of the analysis of the dynamic stability of a 16000 kg tracked excavator equipped with a manipulator digging bucket of 0.6 m3 in capacity.
Background: Menstruation was presented as a result of inflammatory process. The total and relative numbers of the endometrial immunocompetitive cells vary during the different phases of the menstrual cycle. The aim of this morphological study is to make a contribution to understanding different distribution of leukocyte types during proliferative and secretory phase of normal menstrual cycle. Materials and methods: The study included 40 women (20 in proliferative and 20 in secretory phase of the menstrual cycle). Exploratory curettage performed as preoperative preparation due to uterine myomas. Immunophenotyping was performed by immunoalkaline phosphatase (APAAP) using monoclonal antibodies: CD15, CD20, CD30, CD45RO, CD56, CD57 and CD68. The results were statistically analysed using SPSS 20.0 software. Results: Natural killer (NK) cells are dominant during secretory, and CD45RO T lymphocytes are dominant during proliferative phase of the menstrual cycle. During the secretory phase of menstrual cycle, leukocytes make 30% of total endometrial cells. NK cells (CD56+ bright subpopulation), activated T lymphocytes, macrophages and B lymphocytes significantly increase in their number during the secretory phase of menstrual cycle. Conclusions: Significant changes in endometrial leukocyte populations during proliferative and secretory phase of the menstrual cycle are emphasized. Changes in dominance of different leukocyte subpopulations are determined by hormonal and microenvironmental changes in modulatory factors that have not yet been fully explained.
The paper defines the general mathematical model of hydraulic excavators for determining the boundary and possible digging resistances and equivalent loads of the axial bearing of the slewing platform drive mechanism throughout the excavator’s working area. Using a developed mathematical model and program, in the case of a 100000 kg hydraulic excavator with a shovel manipulator bucket volume of 6,5 m3, a detailed analysis was performed to examine the influence of the position and digging resistance on the loading of the axial bearing of the excavator slewing platform drive mechanism. The results of the performed analysis show that the equivalent loads, relevant for the selection of axial bearing of the excavator slewing platform, occur in the zone of the working area when the kinematic chain of the excavator has positions in which the manipulator mechanisms have coordinated interaction when they can overcome the greatest resistance forces in the stable operation of the excavator.
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