Kinematic analysis and synthesis of four-bar mechanisms for straight line coupler curves

Mechanisms are means of power transmission as well as motion transformers. A fourbar mechanism consists mainly of four planar links connected with four revolute joints. The input is usually given as rotary motion of a link and output can be obtained from the motion of another link or a coupler point. Straight line motion from a four bar linkages has been used in several ways as in a dwell mechanism and as a linkage to vehicle suspension. This paper studies the straight line motion obtained from planar four-bar mechanisms and optimizes the design to produce the maximized straight line portion of the couplerpoint curve. The equations of motion for four different four-bar mechanisms will be derived and dimensional requirements for these mechanisms will be obtained in order to produce the straight line motion. A numerical procedure will be studied and computer codes that generate the coupler curves will be presented. Following the numerical results study, a synthesis procedure will be given to help a designer in selecting the optimized straight line motion based on design criteria. CONTENTS 1 . Introduction 1 2. Mechanism And Its Components 6 3. Four-BarMechanism And Its Classifications 1 0 4. Special Four-Bar Linkages For Approximate Straight Line Output 1 9 5. Position Analysis Of A Basic Four-Bar Mechanism 28 6. Equation Of Coupler Curve For A Generic Four-Bar Linkage 35 7. Four-Bar Linkages That Generate Symmetrical Coupler Curves 38 8. Analysis Of Four-Bar Linkages Generating Straight Line Coupler Curves 47 9. Numerical Generation of Coupler Point Curves 58 10. Synthesis Procedure For Designing A Four Bar Linkage 68