A ball screw assembly having a ball screw nut including an outer surface, an inner surface defining a central bore, and a ball track defined by the inner surface, a ball screw shaft including an outer surface defining a ball track, the ball screw shaft being disposed in the central bore so that the two ball tracks form a ball raceway, a first stopper disposed at a first end of the ball screw nut within the ball raceway, a plurality of main balls forming a ball train disposed in the ball raceway, a main spring assembly disposed in the ball raceway between a first end of the ball train and the first stopper, and a strain sensing element affixed to a flat surface portion defined by the outer surface of the ball screw nut.