Abstract: A forward and reverse chain drive systems for a scanner has a one-way clutch mounted on the drive shaft for the scanner cable pulley. The clutch has a sprocket wheel linked by a chain drive to a reverse motor to turn the drive shaft in a first rotation direction when the reverse motor is energized. The sprocket wheel is free to rotate in the other rotation direction independently of the drive shaft so that when the reverse motor is de-energized at the end of the scanner reverse movement, the chain drive may move the clutch sprocket wheel in that other direction, as the chain reacts to reverse motor turn-off, without changing the position of the drive shaft.