This is an example of a six-link (one fixed) and seven-joint compound mechanism with one degree of freedom similar to Model S-30 of Chebyshev (1821-1894). It is another example of an approximate straight-line mechanism. Chebyshev spent several decades trying to find a theorem that would establish whether any linkage mechanism could draw an exact straight line. It was a French engineer, Peancellier, and later Chebyshev’s student, Lipkin, who found an eight-line exact straight-line mechanism. Reuleaux discussed briefly compound mechanisms in his Kinematics of Machinery (1876), but it was a follower of Reuleaux, Grübler, who wrote extensively on the criteria for degrees of freedom in a linkage given the number of links and joints.

Francis Moon 2004-11-16