Simply genial as always! A new idea from Akiyuky - A Cylindrical Cam made of LEGO elements.
As the "cylinder" cam profile starts to rotate, the follower moves in one direction. When the follower reaches the limit then it moves back without needing to change the direction of the cam rotation.
See how to make one, in the video below.
This was just a great combination of Technic and LEGO SYSTEM elements, used to achieve the intended linear back and forth effect.
These unusual cams are normally composed of a cylinder which has a groove cut out on its surface and it is in this that the follower runs up and down. This type of cam can be seen in some old clock mechanisms and still in modern sewing machines just as an example. Machines that perform repetitive movements often use a cylinder cam profile.