【正文】 gears, chains, sprockets, belts, pulleys, and so on. (spherical and helical joints as well as other connections that allow threedimensional relative motion are not included, as only planar motion in parallel planed are discussed here). Furthermore, imagine the possibility of forming all sorts of linkage types by putting these ponents together. Are there any rules that help govern how these mechanisms are formed? Actually most mechanism tasks require a single used most frequently. For example, it is easy to see intuitively that a fourbar linkage is a singledegreeoffreedom linkage.The process of drawing kinematic diagrams and determining degrees of freedoms mechanisms are the first steps in both the kinematic analysis and synthesis process. In kinematic analysis, a particular given mechanism is investigated based on the mechanism geometry plus possibly other known characteristics (such as input angular velocity, angular acceleration, etc.). Kinematic synthesis, on the other hand, is the process of designing a mechanism to acplish a desired task. Here, both choosing the type as well as the dimensions of the new mechanism can be part of kinematic synthesis. The ability to visualize relative motion, to reason why a mechanism is designed the way it is, and the ability to improve on a particular design are marks of a successful kinematician. Although some of this ability es in the form of innate creativity, much of it is a learned skill that improves with practice.Movement analysisOne of the simplest and most useful mechanisms is the fourbar linkage. Most of the following description will concentrate on this linkage, but the procedures are also applicable to more plex linkage.We already know that a fourbar linkage has one degree of freedom. 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 position, velocities and accelerations.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. The input crank of a crankrocker type can rotate continuously through 360, while the output link just “rocks” (or oscillates). As a particular case, in a parallelogram linkage, where the length of the input link equals that of the output link and the length of the coupler and the ground link are also the same, both the input and output link may rotate entirely around or switch into a crossed configuration called an antiparallelogram linkage. Grashof’s criteria states that the sum of the shortest and longest links of a planar fourbar linkage cannot be greater than the sum of the remaining two links if there is to be continuous relative rotation between any two links.Notice that the same fourbar linkage can be a different type, depending on which link is specified as the frame (or ground). Kinematic inversion is the process of fixing different links of a chain to create different mechanisms. Note that the relative motion between links of a mechanism does not change in different inversions.Besides having knowledge of the extent of the rotations of the links, it would be useful to have a measure of how well a mechanism might “run” before actually building it. Hartenberg mentions that “run” is a term that means effectiveness with which motion is imparted to the output link。 pin joints, slide joints。紡織機械原理[M].北京：紡織工業(yè)出版社，1981.[3] [M].北京：中國紡織出版社，1998.[4] [M].上海：中國紡織大學(xué)出版社，1999.[5] 濮良貴，[M].北京：高等教育出版社，1982.[6] [M].西安：人民教育出版社，1982.[7] [M].上海:上?？茖W(xué)技術(shù)出版社,1982.[8] 羅圣國，李平林，[M].哈爾濱：哈爾濱工業(yè)大學(xué)出版社， 1989.[9] 羅洪田，機械原理課程作業(yè)指導(dǎo)書[M].北京：人民教出版社，1964.[10] ：機械工業(yè)出版社，2002.[11] 戈曉風(fēng)，[M].南京：東南大學(xué)出版社，2000.[12] [M].北京：高等教育出版社，1962.[13] [M].北京：機械工業(yè)出版社，1983[14] [M].北京：機械工業(yè)出版社，1988.[15] [M].北京：機械工業(yè)出版社，1990.[16] 司徒忠，[M].武漢：武漢理工大學(xué)出版社，2001.[17] [M]北京：人民郵電出版社，1997.[18] 黃遠(yuǎn)堯，[M]北京：機械工業(yè)出版社，1997.[19] 梁德潤，[M].北京：外文出版社，1999.[20] 商務(wù)印書館. 牛津高介英漢雙解詞典[M]北京：牛津大學(xué)出版社，1989英文翻譯 Indrotraction to mechanism The function of a mechanism is to transmit or transform motion from one rigid body to another as part of the action of a machine. There are three type of mon mechanical devices that can be used as basic elements of a mechanism. Gear system, in which toothed members in contact transmit motion between rotating shafts. Cam system, where a uniform motion of an input member is converted into a nonuniform motion of the output member. 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, that is, rigid bodies, 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 not cause each of the other links to move to a definite predictable position, then the system is an unconstrained kinematic chain.A mechanism or linkage is a constrained kinematic chain, and is a mechanical device that has the purpose of transferring motion and/or force from a source to an output. A linkage consists of links (or bars), 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 (1) mechanisms if at least two other links remain mobility, or (2)structures if no mobility remains. In other words, a mechanism permits relative motion between its “rigid links”。同時我從