A point on red slider draw a trapezoid of small height.
Blue slider moves in rear runway.
Green slider moves in front runway.
Two red pins of the pink slider move in groove of the green slider.
Violet pin of the pink slider moves in 45 deg. oblique groove of the blue slider.
Green pin fixed to the green slider restricts motion of the pink slider in vertical direction when it contacts with the two red pins.
Input: yellow crank gives the blue slider reciprocating linear motion via a coulisse mechanism (violet lever of two slots).
When the blue slider goes to the right, first it pushes up the pink slider (due to its 45 deg. oblique groove) then moves the green slider to the right. The green slider can not move first because of its large inertia and its large friction with the runway.
When the blue slider goes to the left, first it pushes down the pink slider (due to its 45 deg. oblique groove) then moves the green slider to the left.