The lengths of the links comply with the conditions: A͞B=D͞C and B͞C=A͞D. Thus four-bar mechanism ABCD is a crossed-crank linkage, and links 1 and 3 rotate completely about fixed axes A and D. Links 4 and 5 are connected by turning pairs E and G to cranks 1 and 3. Upon rotation of crank 1, point F describes the connecting-rod curve shown in the drawing. Uncertainty of motion of the mechanism is eliminated by the provision of lugs a and b and slots c and d on cranks 1 and 3. In the extreme positions of crossed-crank linkage ABCD, lug a enters slot d and lug b enters slot c. This enables the mechanism to pass through its extreme positions.
$591$LW,6L$