Page:The Kinematics of Machinery.djvu/493

 LOOSE COUPLINGS.

471

"We thus see that these loose couplings, looked at as mechanisms, are click-trains or brakes, but that instead of combining a moving with a stationary piece, they are used to unite two moving pieces. As to their action in the mechanism as a whole we notice that when the parts to be coupled are engaged, or put in gear with each other, they become kinematically one piece only. The shafts A and B become in this way a single shaft C ... | ... C, while before they are coupled each one separately forms such a shaft. The engagement therefore forms A and B into one link of a chain, while the disengagement again separates the parts or elements of this link. Disengagement and engagement then, by such methods as

FIG. 343.

have been described, are respectively the separation, and re- union of the elements of a link of a kinematic chain. The various couplings used in this way may be subdivided ac- cording to the manner in which the parts of the link move, or are compelled to cease motion, after their separation ; as may also the couplings before described. It is the province of Applied Kine- matics to examine all these matters, here we must be content with the establishment of the general principles of their construction. I need only further mention that many of the contrivances used to prevent the loosening of nuts or keys are click-trains of the kind here described.