Мехатроника 1 Бөлім mechatronics
Structural analysis of mechanisms of mechatronic modules
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Мехатроника 1 том Баймухамедов М.Ф., Джаманбалин Қ.Қ.,Ақгул м.К.
| 2.3 Structural analysis of mechanisms of mechatronic modules
Structural analysis of the mechanism is the study of the properties of the mechanism according to its specified structural scheme. It is carried out accor- ding to structural formulas, which relate the number of degrees of mobility of mechanism with the number of links, the number and type of its kinematic pairs, excessive connections and superfluous mobilities [8]. The main task of structural analysis is to find redundant links and excess mobilities in the mechanism and indicate ways of eliminating them, as well as determining its number of degrees of mobility. Mechanisms with flat and three-dimensional closed kinematic circuits contain one or more closed loops, and with open ones can contain local closed contours. Flat and spatial closed mechanisms with flat closed contours require high accuracy of manufacturing and assembly, otherwise due to misalignment of axes of kinematic pairs and deformation of links under forced assembly in kinematic pairs, friction increases, which can lead to jamming of the mechanism. Similarly, jamming can occur in open mechanisms with local flat closed loops. Therefore, such mechanisms are considered as spatial ones with redun- dant (identical, duplicating) contour links, which allows correcting the mecha- nism and get rid of the indicated shortcomings. The number of redundant circuit links of the entire mechanism is defined according to the formula (2.1) [8]: (2.1) where W o – is the number of degrees of mobility of the main circuit of the mechanism; n – is the number of mobile links of the mechanism; i – is the class of the kinematic pair; P i is the number of kinematic pairs of the i -th class in the mechanism. In this equation, two unknown parameters is the number of degrees of mobility W o and the number of excess circuits links S . For it it is necessary to determine one of them. Usually, the number of degrees of mobility of the main 179 circuit is found on the basis of geometric considerations without any analytical calculations or by investigating the position functions of the links, that is, in most cases intuitively. It all depends on the experience of the calculator. Formula (2.1) makes it possible, with the known W o to determine only the total number of excess circuit links of the entire mechanism. But it can consist of several closed circuits and each circuit can have a certain number of redundant circuits links and superfluous mobility (the possibility of links to turn around their longitudinal axes or their common axis without affecting the functionality of the mechanism). This formula does not allow them to be identified and correctly eliminated. There may be cases when, in the calculation, S = 0, and separate closed circuits of the mechanism have excessive circuits links and superfluous mobility. Also, this formula does not make it possible to take into account superfluous links and kinematic pairs that do not affect functional transformation of the mechanism. For the most basic structural schemes of flat mechanisms, the number of degrees of mobility can be determined from formula of Chebyshev (2.2). (2.2) where number 4 refers to higher kinematic pairs, the number 5 is to the lower kinematic pairs. Thus, such an approach to the determination of excess contour links, excess mobilities and the number of degrees of mobility of the mechanism is not entirely correct. Therefore, consider a different approach to their definition. A mechanism containing one closed circuit formed by kinematic pairs of only the 5th class, possesses three redundant circuits links. If the kinematic pairs in a closed circuit other than the 5-th class can be of the 4-th, 3-rd, 2-nd or 1-st grades, i.e. have additional mobilities, then the number of excess circuits links of the жүктеу/скачать 11,25 Mb. Достарыңызбен бөлісу:
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