I try to animate a pantograph just for fun, but it doesn'nt work. I have try lot of ideas particularly with the observation of this pages :

How can a mechanical linkage with a closed loop be rigged? https://blenderartists.org/t/animating-a-rigid-linkage/685592

The best result i obtain is this one :

But there is still a mistake, the pantograph bow does not keep a vertical position.

I search the solution to give the blend file in attachment, i come back in few minutes

Thank's !