Self-locking

Self-locking refers to the property of a mechanical system in which an applied load does not trigger a reverse movement when the drive is not active. The component or drive therefore remains stationary under load without the need for additional brakes or holding devices.

Self-locking is particularly important for:

• Secure holding of loads
• Energy savings, as no holding torque is required
• Protection against unintentional back-driving in the event of power or drive failure

Development of self-locking

Self-locking results from the ratio of friction to lead in the system: high friction angle, small lead angle.

The following applies to screw drives:
self-locking if

α = lead angle
ρ = friction angle

Examples

• Trapezoidal screw drives: Often self-locking
• Buttress threads: Self-locking in the direction of load
• Worm gears: Often self-locking
• Ball screws: Generally not self-locking due to low friction

Advantages & Disadvantages