may meshingly engage the geared portion 74 of the drive shaft 60 in this manner the drive shaft 60 and the drive member 66 may cooperate to form a rack and pinion mechanism accordingly rotation of the drive shaft 60 may cause corresponding linear motion of the drive member 66 relative to the drive shaft 60 and the frame 12 the drive member 66 may be slidably mounted to the frame 12 such that some portion of each of the first and second arcuate slots 80 82 may be aligned with some portion of the corresponding guide slots 30 as the drive member 66 moves between the open and closed positions in this manner each of the guide pins 46 may be in slidable engagement with the corresponding guide slot 30 and the corresponding one of the arcuate slots 80 82 and movement of the drive member 66 forces the guide pins 46 to move relative to the guide slots 30 and the first and second arcuate slots 80 82 thereby causing the shutters 14 15 to rotate between the open and closed positions configuring the guide pins 46 such that they extend from the midpoints of the shutters 14 15 i e halfway between opposing edges 40 may.