Abstract: The invention relates to an ion implantation apparatus comprising a vacuum chamber, an ion beam generator generating an ion beam in the vacuum chamber and an implant wheel in the vacuum chamber. The wheel has a plurality of circumferentially distributed wafer support elements. A scanning arm is mounted for reciprocal movement about a scan axis and has a free end supporting the implant wheel for rotation about a wheel axis, so that rotation of the implant wheel about the axis brings the wafer support elements successively to intercept the ion beam and reciprocation of the scanning arm about the scan axis scans the ion beam across the wafer support elements. A motor drives the scanning arm, the motor having a drive shaft connected directly to a cycloid type gearbox, the output of which directly drives the scanning arm.