Orange plate performs planar motion without rotation. Its upper edges are kept always horizontal thanks to a parallelogram mechanism driven by brown cylinder. Distance between two revolute joints on the orange plate is equal to length of the violet conrod.

Change of popcorn fixed cam profile gives various trajectories of a point on the orange plate.

The mechanism has an unstable position when viollet conrod is perpendicular to the rockers. So avoid it or use measures to overcome it.