Page:The Kinematics of Machinery.djvu/310

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KINEMATICS OF MACHINERY.

If the mechanism be placed on d, as in Fig. 205, its formula runs (C" 2 ' || G v 2 ') d . It falls into the same class whether it be placed on & or c or a ; so that all the four mechanisms with which the chain furnishes us are similar. We shall call them Parallel Cranks.

FIG 207

We have already seen that in the dead positions 2' 1 3' 4 and 1 2" 4 3" the chain is not constrainedly closed. If then it is to be used so that the points 2' and 2'.' can be passed some special closure must be arranged. We have found ( 46) that this could be done by the addition of another similar chain in the two ways, among others, shown in Figs. 206 and 207. We have now to find means for indicating these in our kinematic notation.