曲柄(導(dǎo)桿)滑塊機(jī)構(gòu)設(shè)計(jì)分析外文翻譯-其他專業(yè)-文庫(kù)吧資料
2025-01-27 12:21本頁(yè)面
【正文】 ontains the crankshaft bearing at A and the cylinder。 i. e., all points on all of the links have paths on the other links that are fixed and determinate. The paths are most easily obtained or visualized by assuming that, the link on which the paths are required is fixed, and then moving the other links in a manner patible with the constraints. FourBar Mechanisms When one of the members of a constrained linkage is fixed, the linkage bees a mechanism capable of performing a useful mechanical function in a machine. On pinconnected linkages the input (driver) and output (follower) links are usually pivotally connected to the fixed link。 no relative motion between the links is possible. To describe the relative positions of the links in a fourbar linkage it is necessary only to know the angle between any two of the links. This linkage is said to have one degree of freedom. Two angles are required to specify the relative positions of the links in a fivebar linkage。s universal joint is perhaps the most familiar example of a spherical mechanism. Spherical linkages are constituted entirely of revolute pairs. A spheric pair would produce no additional constraints and would thus be equivalent to an opening in the chain, while all other lower pairs have nonspheric motion. In spheric linkages, the axes of all revolute pairs must intersect at a point. Spatial mechanisms, include no restrictions on the relative motions of the particles. The motion transformation is not necessarily coplanar, nor must it be concentric. A spatial mechanism may have particles with loci of double curvature. Any linkage which contains a screw pair, for example, is a spatial mechanism, since the relative motion within a screw pair is helical. Thus, the overwhelming large category of planar mechanisms and the category of spherical mechanisms are only special cases, or subsets, of the allinclusive category spatial mechanisms. They occur as a consequence of special geometry in the particular orientations of their pair axes: If planar and spherical mechanisms are only special cases of spatial mechanisms, why is it desirable to identify them separately?Because of the particular geometric conditions, which identify these types, many simplificatio ns are possible in their design and analysis. As pointed out earlier, it is possible to observe the motions of all particles of a planar mechanism in true size and shape from a single direction.
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