【正文】 osition。 Are there any more that are useful to know about fourbar linkage？ indeed there are！ these include the Grashof criteria， the concept of inversion， deadcenter position（ branch points）， branching， transmission angle and their motion feature， including positions， velocities and accelerations。 There are hundreds of thousands of different linkage types that one could invent。 黃石理工學(xué)院 畢業(yè)設(shè)計 (論文 ) 外文文獻(xiàn)翻譯 Introduction to mechanism The function of mechanism is to transmit or transform motion from one rigid body to another as part of the action of a machine. There are three types of mon mechanical devices that can be used as basic elements of a mechanism. (1) Gear system, in which toothed members in contact transmit motion between rotating shafts. (2) Cam system, where a uniform motion of an input member is converted into a nonuniform motion of the output member. (3) Plane and spatial linkages are also useful in creating mechanical motions for a point or rigid body. A kinematic chain is a system of links, which are either jointed together or are in contact with one another in a manner that permits them to move relative to one another. If one of the links is fixed and the movement of any other link to a new position will cause each of the other links to move to definite predictable position, the system is a constrained kinematic chain. Otherwise, the system is an unconstrained kinematic chain. A mechanism or linkage is a constrained kinematic chain, and is a mechanical divice that has the purpose of transferring motion and force from a source to an output. A linkage consists of links (or bar),generally considered rigid,which are connected by joints, such as pin (or revolute) or prismatic joints, to form open or closed chains (or loops). Such kinematic chains,with at least one link fixed, bee (i) mechanisms if at least two other links remain mobility, or (ii) stuctures if no mobility remains. In other words, a mechanism permits relative motion between its “rigid links”。 Envision a bag containing a large variety of linkage ponents： binary， ternary， quaternary， and so on， links ； pin joints，slide joints； cams and cam followers； gears， chains， sprockets， belts， pulleys， and so on。 The fourbar linkage may take form of a socalled crankrocker or a doublerocker or a doublecrank（ draglink） linkage， depending on the range of motion of the two links connected to the ground link。 If a mechanism has one degree of freedom (. a fourbar linkage), then prescribing one position parameter, such as the angle of the input link, will pletely specify the position of the rest of the mechanism (discounting the branching possibility). We can develop an analytical expression relating the absolute angular positions of the links of a fourbar linkage. This will be much more useful than a graphical analysis procedure when analyzing a number of positions and /or a number of different mechanisms, because the expressions will be easily programmed for automatic putation. The relative velocity or velocity polygon method of performing a velocity analysis of a mechanism is one