Pinion 1 rotates about axis A. The shaft of pinion 1 slides along fixed slot a. Complex rack 2 reciprocates in fixed guides B-B. The rack is composed of two straight portions b and two semicircular portions d. When pinion 1 rotates continuously in one direction its teeth mesh successively with the various portions of rack 2, imparting a sliding motion to rack 2 in the left and right directions. The semicircular portions d of the complex rack provide for smoother transition from the upper portion b to the lower portion b of the rack and vice versa.
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