机械外文翻译---机构介绍(编辑修改稿)

机械外文翻译---机构介绍(编辑修改稿)内容摘要：

this linkage， but the procedures are also applicable to more plex linkages。 We already known 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 positions， 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 crankrocher type can rotate continuously through 3600 ，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 lengths 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 黄石理工学院 毕业设计 (论文 ) 外文文献翻译 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 indifferent inversions。 Besides having knowledge of the extent 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 ； it implies smooth operation， in which a maximum force ponent is available to produce a force or torque in an output member。 The resulting output force or torque is not only a function of the geometry of the linkage， it is generally the result of dynamic or inertia force which is often several times as large as the static force。 For the analysis of lowspeed operations or for an easily obtainable index of how any mechanism might run， the concept of the transmission angle is extremely useful。 During the motion of a mechanism， the transmission angle changes in value。 A transmission angle of 0 degree may occur at a specific position， on which the output link will not move regardless of how large a force is applied to the input link。 In fact， due to friction in the joints， the general rule of thumb is to design mechanisms with transmission angle of large than a specified value。 Matrixbased definitions have been developed which measure the ability of a linkage to transmit motion。 The value of a determinant（ which contains derivatives of output motion variables with respect to an input motion variable for a given linkage geometry） is a measure of the mova。