Study the pictures that you yourself have provided and figure out how they work. Then make your own example using the same principles.
If you study the photos you will see that there is a piece at the top hinge point that also retains its orientation as the arms move. And it transfers that fixed orientation to the bar at the end.
Like I said earlier if you have Lego you can easily experiment. Or you could make bars from cardboard with thumbtacks for joints.
...R