機(jī)械外文翻譯---機(jī)構(gòu)介紹-wenkub
2023-05-19 00:05:54 本頁(yè)面
【正文】 (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”。 Other forms of four bar mechanisms exist in which a slider is guided on a moving link rather than on a fixed link. These are called inversions of the slidercrank， produced when another link（ the crank， coupler， or slider） is fixed link。 The fist step in the motion analysis of more plicated mechanisms is to sketch the equivalent kinematic or skeleton diagram。 for convenient reference， the links are numbered（ starting with ground link as number 1）， while the joints are lettered。 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。 Therefore， singledegreeoffreedom mechanisms are the forms used most frequently。 Kinematic synthesis， on the other hand， is the proess of designing a mechanism to acplish a desired task。 Movement analysis One of the simplest and most useful mechanisms is the fourbar linkage。 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。 Notice that the same fourbar linkage can be a different type， depending on which link is specified as the frame（ or ground）。 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。 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。 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 mech
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