Lead screws and nuts are commonly used to convert a rotary movement into a linear movement.

When high precision and long life are required a lot of parameters have to be taken into consideration:

• Materials used, both for the screw and the nut.
• Thread profile
• Backlash
• Stiffness, etc.

No one design can properly cover all the applications. It is common knowledge that trapezoidal screws and matched polymer nuts provide the best performance and the longest life.

Power screw system suppliers offer many more options for the designer to fine tune his equipment: special coatings and lubricants, anti-backlash nuts (adjustable or not), different nut materials, to list a few.

The anti-backlash nuts themselves can be realised in different configurations leading to different balances between drag torque, stiffness and overall cost.

The simplest anti-backlash nut assembly consists in two half-nuts pushed apart by a spring. The preload is thus defined by the spring force. When relatively high preload is required the drag may become unacceptable.

Other types of nut assemblies, like the ‘wedge design’, will provide high degree of stiffness with a low drag torque.

The same design will also compensate when the nut travels between screw portions with different wear conditions.

Nuts using a torsional wear adjustment mechanism can be used for even higher loads and offer the added feature of adjustable preloading in order to further match the specific application.

Haydon Motion Europe is based in Coueron, France. www.hsi-inc.com or www.haydoneurope.com