As links 1 and 2 approach each other (upper view), cam 5 causes lever 3 to turn cam 4 clockwise until latch a at the end of lever 6 enters recess b of cam 4. At the same time, latch c at the end of lever 3, operating in the same way as lever 6, enters recess d of cam 5. Cams 4 and 5 are returned to the initial (uncoupled) position by springs 8 and 7 when levers 3 and 6 are disengaged by turning handles 9 and 10 which are rigidly attached to (or integral with) the levers. The lower view shows the coupled position.
$3278$CmL,FD$