Efficiency is the ratio of output power to input power. It indicates how much of the energy used is actually converted into useful work, compared to what is lost through friction.
A larger lead angle results in higher efficiency because less force is lost through friction, whereas smaller leads cause more friction and reduce efficiency accordingly. The friction angle, which depends on the friction coefficient of the thread pair, also plays a role. The lower the friction—for example, between the ball, screw, and nut—the more efficiently the screw drive operates. Furthermore, the design significantly influences efficiency. Ball screw drives achieve very high efficiency levels of approximately 0.9 to 0.98 due to rolling friction, while trapezoidal screw drives only reach about 0.3 due to sliding friction.
In principle, due to the lower friction loss, ball screw drives allow for a reversal of the motion—converting linear motion into rotation—even at relatively small lead angles. In installation cases where self-locking is required, appropriate safety devices, such as brakes, must therefore be provided in ball screw drives.