Research on the Sheepdog Problem Using Cellular Automata

A ratchet bearing is provided for mounting the slats in a shutter frame which incorporates directly into the bearing, by virtue of a trunion pin having a ribbed surface which rotates within a bearing collar having inwardly directed detents, a multiple detention action such that when the slat is rotationally opened or closed, the bearing will seat in one of a multiplicity of detent positions so that the shutter will not sag shut or otherwise move after it has been set.