Geometric Design of Planar Four-Bar Mechanisms.

摘要

Outstanding issues concerning systematic design procedures for planar four-bar mechanisms, specifically three aspects hitherto not addressed, are treated in this thesis. These include (1) Advance-retire crank angle ratio for crank-rockers, (2) angle ratio for double-rockers and, (3) lead-lag angle ratio for double-cranks.;This thesis aims to introduce a systematic method to determine parameters of planar four-bar mechanisms which specify a unique mechanism design. The design procedures introduced are based on the geometric properties of mechanisms. The symmetry of these geometric formulations makes it easy to find a unique mechanism design for defined design parameters. Moreover, the relations derived can be conveniently programmed and implemented in "Computer Aided Design (CAD)" algorithms.;The equations, which are revealed for the first time in this thesis, can be used to determine a unique planar linkage design for specified design parameters. These design parameters are such characteristics of the mechanisms which are of particular importance to the designer, i.e., link lengths, assembly sequence and choice of fixed link. All design parameters and design formulations are dimensionless, giving this opportunity to the designer to select ratios instead of size.;Crank-rocker, slider-crank, double-rocker, and double-crank mechanisms are studied in this thesis. The design parameters are: The ratio of coupler length to crank throw radius and the time ratio for crank-rocker and slider-crank; oscillating angles of two rockers and the ratio of two rocker link lengths for double-rocker; and specified minimum and maximum leads and the angles at which the driver link has these extreme leads relative to the driven link for crank-crank mechanisms.;Each chapter is devoted to the design of one of three types of planar four-bar mechanisms. Crank-rocker and slider-crank mechanisms are studied in one chapter since their design procedures are mainly the same. Double-rocker and double-crank mechanisms are the others. For each type of mechanism, the design parameters are introduced, then the design process and design equations are provided and clarified with proper figures and plots. Finally, the design process is illustrated with numerical examples and validated by Grashof's criterion. Explanation of the step-by-step process to obtain each mechanism design is clearly illustrated with appropriate diagrams.