angular contact bearings 15 these preloaded bearings can provide for piston rotation but not for linear motion a pulley can be mounted at the top end of the bearing shaft the pulley its associated belt 32 and a motor pulley 31 can provide a means for coupling the rotary stepper motor 30 to the piston the pulley can have inlet and outlet alignment notches so that an optical switch can sense rotary position on a lower pulley flange is usually at least one notch that represents a home position for the rotary drive the movable upper support 29 can provide for the rotary bearing mounting rotary drive components and a mounting surface for the linear ball screw nut 28 a movable upper support 29 can be coupled to the linear ball guide 35 the figures show the upper support shifted relative to the ball guide 35 so that the piston can be seen outside of the cylinder normally these two surfaces are aligned and the upper support fastened to the ball slide carriage using mechanical fasteners shown attached to the carriage are upper and lower limit magnetic switches a home magnetic switch and an optical scale the renishaw optical head 34 can be fixed to the frame where it can sense the position of the ball guide carriage a ball guide rail 33 is shown attached to the base frame an upper support 29 can be moved up.