The lengths of the links comply with the conditions: A͞B+B͞C<A͞D+D͞C and A͞B<B͞C<C͞D<A͞D. Link 3 is a circular slider moving along circular guides a-a of radius D͞C and with the centre at point D. When link 1 oscillates about fixed axis A, slider 3 oscillates in guides a-a. The mechanism is equivalent to four-bar double-swing linkage ABCD in which AB and CD are rocker arms and BC is the connecting rod.
$1492$SC,4L$