This is a example from Robert L. Norton's books on machinery: "Design a fourbar Grashof crank-rocker to give 45° of rocker rotation with equal time forward and back, from a constant speed motor input.(adsbygoogle = window.adsbygoogle || []).push({});

Solution

1)Draw the output link O_{4}B in both extreme positions, B_{1}and B_{2}in any convenient location, such that desired angle of motion O_{4}is subtended

2)Draw the chord B_{1}B_{2}and extend it in either direction.

3)Select a convenient point O_{2}on line B_{1}B_{2}extended.

4)Bisect line segment B_{1}B_{2}, and draw a circle of that radius about O_{2}

5)Label two intersection of the circle and B_{1}B_{2}extended, A_{1}

and A_{2}

6)Measure the lenght of the coupler as A_{1}to B_{1}or A_{2}to B_{2}

7)Measure ground length 1, crank length 2, and rocker lenght 4.

8)Find the Grashof condition. If non-Grashof, redo steps 3 to 8 with O_{2}farther from O_{4}

9)make a model of the linkage and check its function and transmission angles.

Here is what the mechanism seems

I understand the steps but I can't understand by what step does the mechanism have equal time forward back and forth and how can we understand this mechanism has equal time forward and back. Is there any criteria or formula which show mechanims' back and forth time.

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# Rocker Output-Two Positions with Angular Displacement

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