The lengths of the links comply with the conditions: A͞B=P͞C, B͞C=A͞P and D͞B:B͞Q=D͞A:A͞P=P͞C:C͞Q=E͞P:F͞Q. Figure ABCP is a parallelogram linkage. Points D, P and Q lie on a straight line. Link 1 turns about fixed axis D and is connected by turning pairs A and B to links 4 and 3. Link 2 rotates about fixed axis E and is connected by turning pairs P to links 4 and 5. When link 2 rotates about axis E, point P describes circle p-p of radius E͞P and point Q of link 3 describes circle q-q of radius F͞Q. Therefore, by adding link 6, shown by dash lines, the mechanism can be made to transmit rotation with constant transmission ratio i₂₆ between links 2 and 6 equal to i₂₆=ω₂/ω₆=1. Directions EP and FQ of links 2 and 6 are always parallel. Links 2 and 6 rotate in the same direction.
$687$LW,GI$