為了使小齒輪產生齒輪換位(小齒輪由一側繞至另一側)，所以採用針齒輪以達到此種效果，進而使針齒輪產生等速的往復運動。

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in order to produce the gear transposition (i.e. the gear involves from one side to the other side) ， we take advantage of the pin gear , therefore , it moves back and forth in the uniform velocity