The motion can be seen here.
The housing has two side L-cam tracks (grooves). In it three bearings per side are moving: The front bearing is fixed in the valve plate at a place where it guides the plate in its exact motion. Two other bearings are fixed in a directly driven plate and break through the side-walls of the valve plate (in a bent groove). The result is a very smooth motion of all parts, and a track guiding with no usage of any spring.
