578
�KINEMATICS OF MACHINERY.
�(5.) By making^ the length 3'4 less instead of greater than 4'5
we obtain in the chain a motion differing very greatly from any
occurring in either of the former cases. Fig 438 shows this
arrangement. While in Figs. 436 and 437 the whole motion of
b relatively to a was equal to twice the distance 4'5, that is twice
the length e, it is now equal to twice the distance 4' 3. I have
formerly suggested this mechanism as a leading train for punching,
riveting or stamping-machines, and given it the name of toothed-
eccentric* (cf. also p. 300).
����Fro. 439.
�FIG. 440.
�FIG. 441.
�(6.) Leaving still the links a and b infinite, hut giving to 1/5 some
finite value, we obtain a chain represented in a general form in
Fig 439. If we here make 3'4 <^e, we have the chain represented
in Fig. 440, which I formerly called the general case of the
toothed-eccentric. Placing this chain on a we obtain a mechanism
which may serve to give to a link (b) reciprocations of varying
stroke. We obtain an interesting case if we make the toothed-
wheels equal and the lengths 1*5 and 3 - 4 also equal, and at the same
time place the latter symmetrically to a, as in Fig. 441. I have
- See Civil Ingeniemr, 1858, p. 4 ; " Das Zahnexzentrik, ein neuer Bewegungs-
mechanisimis. " In this article I examined the whole series of these mechanisms. I had not then recognised their connection, above explained, with the planet-wheel trains. R.
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