What is a trapezoidal screw drive (TR) and how does it work?

Robust screw drives for safe position-holding and high loads.

A trapezoidal screw drive (TR) converts rotary motion into linear motion by means of sliding friction – and vice versa. Compared to a ball screw drive (KGT), the focus is less on maximum dynamics and more on robustness, cost efficiency and – depending on lead and coefficient of friction – (conditional) self-locking. This makes trapezoidal screw drives the preferred choice when loads must be held securely in position, for example in ZIMM screw jacks (ZE and GSZ series) or ZA actuators.

Operating principle: Sliding instead of rolling

In trapezoidal screw drives, the screw and nut slide on the thread flanks. As a result, friction is higher than in ball screw drives; efficiency and achievable speed are lower.

This is how the mechanism works

• Motion: When the screw rotates, the nut moves linearly along the trapezoidal thread.
• Self-locking (principle): Whether a trapezoidal screw drive is self-locking depends largely on the coefficient of friction (material pairing, surface quality, lubrication) and on the lead angle. If the lead angle is smaller than the friction angle, the drive is (statically) self-locking and holds loads without running back. Important: There is a distinction between static and dynamic self-locking.

Main characteristics and advantages

The change from rolling to sliding friction results in decisive advantages:

• Robust and economical: Trapezoidal screw drives are considered a cost-effective, robust solution for “classic” adjustment tasks. The screw and nut are subject to sliding wear, so correct lubrication is essential.
• Suitable for moderate cycles (duty cycle): A typical specification for trapezoidal screw drive versions at ZIMM is use up to approx. 20 % duty cycle – suitable for many lifting and adjustment applications with moderate speeds.
• High static loads – easy integration: Trapezoidal screw spindles cover high rated loads and are available in numerous ZIMM sizes. This allows them to be integrated modularly into the system kit (couplings, shafts, etc.).

In ZIMM systems, trapezoidal screw drives are mainly used in screw jacks (ZE and GSZ series) and ZA actuators with trapezoidal screw when robust, economical lifting and adjustment movements are required. They are particularly suitable for suspended or vertical loads that must remain safely in position when the drive stops thanks to (conditional) self-locking.