The present invention is directed to a scanning apparatus and method for processing a workpiece, wherein the scanning apparatus comprises a wafer arm and moving arm fixedly coupled to one another, wherein the wafer arm and moving arm are operable to rotate about a first axis. An end effector, whereon the workpiece resides, is coupled to the wafer arm. A rotational shaft couples the wafer arm and moving arm to a first actuator, wherein the first actuator provides a rotational force to the shaft. A momentum balance mechanism is coupled to the shaft and is operable to generally reverse the rotational direction of the shaft. The momentum balance mechanism comprises one or more fixed spring elements operable to provide a force to a moving spring element coupled to the moving arm. A controller is further operable to maintain a generally constant translational velocity of the end effector within a predetermined scanning range.