Selection of Anti-Backlash Nuts in Linear Motion Systems

Christopher Nook by Christopher Nook

All lead screws need clearance between the screw and the nut to operate. Backlash is the relative axial movement between the nut and the screw without rotation of either one. Backlash can increase with wear and can be detrimental to your application. If your lead screw system has no way to compensate for backlash, you will experience inaccurate positioning.

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All lead screws need clearance between the screw and the nut to operate. Backlash is the relative axial movement between the nut and the screw without rotation of either one. Backlash can increase with wear and can be detrimental to your application.  If your lead screw system has no way to compensate for backlash, you will experience inaccurate positioning. The solution?  Anti-backlash nuts.

 

There are many styles of anti-backlash nuts. Selecting the right nut style for your project depends on various factors, including; payload, accuracy, repeatability requirements, budget, space constraints, and available torque.  Linear accuracy, often referred to as lead error, is a function of the leadscrew quality.  Repeatability is a function of the nut. In many cases, bi-directional repeatability (returning to the same position each time) is more important than linear point A to point B accuracy. Repeatability can often be compensated for in the system once that value is known.

Axial Anti-Backlash Nuts

Axial anti-backlash nuts consist of two nut halves biased against opposite flank angles with a compression spring. This configuration provides the simplest means of taking up backlash at a low price point.  The disadvantage to this type of design is the resulting higher drag torque that typically occurs. This nut's stiffness is highly dependent on the force of the spring. However, multiple springs options are available and can be sized appropriately depending on the application.

Radial Anti-Backlash Nuts

Radial style anti-backlash nuts have three fingers that close down like a collet to squeeze the threads of the nut into the flank angle of the lead screw, removing the backlash. The accompanying compression spring provides constant pressure to compensate for wear.  This nut style is moderately priced and offers greater stiffness than an axial anti-backlash nut.  This nut style is ideal for higher loads and better repeatability.

Torsional Anti-Backlash Nuts

The anti-backlash nut with the highest design load rating and greatest bi-directional repeatability is a torsional anti-backlash nut.  A spacer that separates the two nut halves automatically adjusts with the use of a torsion spring to lengthen and take up the gap as wear occurs.  This automatic adjustment ensures that the nut maintains zero backlash.  This design has the highest stiffness of any anti-backlash nut while at the same time providing the lowest drag torque.

Custom Anti-Backlash Nuts

When standard anti-backlash nuts do not satisfy all of your project criteria, a custom nut may be the solution.  Modifications can be as simple as a material change (such as PEEK for medical uses or bronze for industrial projects) or a different mounting flange to suit the space and preferred attachment method. Or, your application may warrant a completely custom anti-backlash nut requiring a rework of the axial, radial, and torsional principles. These can be shaped to maximize stroke length, increase life, eliminate other components, and reduce assembly time.

 

 

Whatever the application, anti-backlash nuts play an essential role in enhancing design, improving operating performance, and the overall success of your linear motion project. The innovative engineering team at Helix Linear Technologies can help you select or design anti-backlash nuts for your linear motion application. 

Contact our project engineers today to learn more.

 

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