Shutter drive

Abstract

An auxiliary drive unit (30) intended for driving a chain (11) in a horizontal track (12) is arranged to operate only when a forward end (33) of the chain passes a predetermined point. A drive sprocket (16) engages with the chain and initially freewheels until the forward end (33) of the chain contacts a switch (34), actuating a drive motor (13) of the auxiliary drive (30). The drive sprocket (16) is normally "parked" in a precisely orientated position so as to engage the forward end (33) of the chain (11) cleanly. The sprocket (16) has a plurality of circumferentially spaced alternating polarity magnetic poles (22, 23) which park the sprocket (16) precisely in position relative to opposite polarity magnetic poles (27) provided on a fixed member of the auxiliary drive unit. The auxiliary drive unit (30) is particularly designed for driving a rolling shutter (10) suspended from a chain (11) running in a horizontally extending track (12).

Dependencies are inferred from the claim text.