Dead Center Synthesis with RRRR Mechanism
Introduction
Dead Center Synthesis with a RRRR Mechanism
Schematic Diagram of a 4 Bar RRRR Linkage
The dead center configuration is achieved when the input link and the coupler become collinear, that is the revolute joints of these two links are in a straight line. Such a configuration also corresponds to a limit or extreme position when the linkage is driven from the output side, that is the current driven or output link is made the input or driver link. Such configurations are important in designing of quick return mechanisms. In this experiment you will be synthesizing a 4 bar RRRR mechanism, given the following input data:
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A specified QRR or Quick Return Ratio (with a constant speed of the input link)
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A given range of angular displacement of the output link (theta_4_2 - theta_4_1).
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4 Bar RRRR Linkage General Configuration |
4 Bar RRRR Linkage Dead Center Configuration |
The ouput link oscillates between theta_4_1 and theta_4_2, but the time taken to move from theta_4_1 to theta_4_2 and back to theta_4_1 from theta_4_2 is different for a constant speed of the input link. The ratio of these two time intervals is the the QRR. The input link completes a full rotation. Thus the synthesized linkage will be a crank rocker.
Dead center configuration is also important in optimizing the transmission ratio of a 4 bar RRRR mechanism, since the transmission ratio is minimum at this configuration.