Links 1 and 2 turn about fixed axes B and A. Links 1 and 2 alternate as driving and driven links. When link 1 turns clockwise, link 2 is stationary as long as lug a of link 1 slides along recess b of link 2. At the extreme position of link 1, lug a slides out of engagement with recess b and link 2 turns clockwise so that lug c of link 2 slides along recess d of link 1.
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