The grey disk with an Archimedean rib is fixed.
The green disk with the same rib receives motion from a pink eccentric shaft. Due to a Oldham mechanism with the orange disk the orientation of the green disk does not change during motion.The eccentricity of the pink shaft e = (p – 2a)/2
p: pitch of Archimedean spiral
a: thickness of the Archimedean rib
Instead of Archimedean spiral, other spirals can be used, for example, involute one.