US Patent 11940851 Hinge mechanism for foldable devices with flexible displays

In one embodiment, a hinge apparatus includes two curved rack apparatuses, each curved rack apparatus defining an arcuate surface and an arcuate set of gear teeth concentric with the arcuate surface, where the radius of curvature of the arcuate set of gear teeth being non-uniform. The hinge apparatus further includes a gear assembly that includes a first gear, a second gear, a third gear coupling the first and second gears, a fourth gear coupling the first gear and the arcuate set of gear teeth of the first curved rack apparatus, and a fifth gear coupling the second gear and the arcuate set of gear teeth of the second curved rack apparatus.