SIX LINKED CYLINDER CHAINS.
�573
�make the links e and / infinite, and further make the axes of the
pairs in each of the ternary k links (1, 2, 5 and 2, 3, 7,) conplane,
we obtain the combination shown in Fig. 428. If we make the
original chain (6 1 "), a, &, c, d, a parallelogram (as here shown) we
obtain a combined chain which has some remarkable properties,
although they have not yet been utilised. The line 7'4' parallel to
a is always=2'l, and the length 1*4' is constant, the lines 5'6 and
1*4 therefore always intersect in the same point 0. If we place
the chain on d we obtain a mechanism in which the bar e will
��move so that its axis passes always through a fixed point beyond
the mechanism, and which therefore may be itself inaccessible.
If we make e finite and therefore / and 3*7 infinitely long, we obtain the chain shown in Fig. 429, which is essentially different from the last.
��FIG. 429.
The combination of cylinder-pairs already described in 60, which is again represented in Fig. 430, is a combined chain. The closure of the links 4*7 and 3'6 of the (C" 4 ') chain makes the other- wise incompletely closed five-linked chain 1. 2. 3. 4. 5 constrained. This chain finds several useful applications in " parallel motions/ 1 trains in which one or more points move in (accurately or ap- proximately) straight paths. One of these, for instance, given by Tchebyscheff, * and another by Harvey,^ are formed on this
- Dingler's Journal, 1862, vol. 163, p. 403.
t Practical Mechanic 1 & Journal, 1850, volil, p. 174.
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