In the previous article, it was explained that ball screws "can be moved more smoothly with the same force". This article is a simplified explanation of the reason of such feature.
First, when an object can be moved more smoothly with the same force, it indicates high mechanical efficiency; that is, mechanical efficiency and thrust are closely related. This is due to a feature of the ball screws.
A trapezoidal screw and a triangular screw are a type of slide screw consisting of a screw shaft and nut. When the screw shaft is rotated, the external thread and internal thread of the shaft and nut, which have some contact, move by rubbing against each other. (Left side of Figure 1)
In a ball screw, the screw shaft and nut are both internal threads. When the screw shaft is rotated, it can move more smoothly converting more energy into thrust because the rolling balls in between the two internal threads act as a guide. (Right side of Figure 1)

Fig.1