How can lead screw backlash be reduced?

The reverse clearance is an inherent characteristic of the lead screw assembly due to the sliding motion between the screw and nut.A degree of clearance or "clearance" may be tolerated for some applications,but applications such as positioning,dispensing or assembly usually require a degree of precision and repeatability that cannot be achieved if clearance is present.

To address these applications,lead screw manufacturers have developed methods to compensate for backlash,despite the disadvantages of reduced or zero backlash designs.First,backlash compensation usually increases the nut diameter and/or length.Secondly,in order to eliminate or reduce the clearance,the clearance between the screws and nuts must be eliminated or reduced.When the clearance is removed,the sliding friction between the components increases,resulting in higher heat generation,reduced efficiency,and shortened life.

Backlash compensation methods usually follow one of two basic designs.However,screw manufacturers have developed variations of these designs to ensure that clearance reduction(or elimination)remains consistent throughout the life of the screw assembly,even as the screw and nut wear out.Anti-backlash nut designs have also recently progressed to minimize friction increases(and increased driving torque)due to backlash compensation.

The most basic way to reduce or eliminate the backlash of the lead screw is to use a spring(or other compliant element,such as a washer)to axially push the two halves of the nut against the opposite sides of the thread.This design is relatively simple,and the use of springs ensures that the backlash is kept small while a certain number of components are worn.

In this backlash compensation design,the spring pushes the two halves of the nut to opposite sides of the thread.

The disadvantage of this method is that the clearance will not be compensated if the load is greater than the force of the spring.Higher loads can be addressed by stronger springs,but stronger springs result in greater friction between nuts and screws,which reduces efficiency and requires more driving torque to be overcome.The use of springs or compliant elements also means that axial stiffness is relatively low.

Variations of this design use nuts with"fingers"or protrusions that can be pushed into the threads by radial force.This radial force is transmitted by springs that press the rings against the fingers,causing them to bend downward into the threads,thereby reducing or eliminating the gap between the screws and nuts.This design reduces or eliminates clearance even if the load is greater than the spring force,and it has less impact on friction and driving torque than conventional designs.

Another design that applies a radial(rather than axial)force to the nut to eliminate the backlash uses a spring that is essentially wound around the outer body of the nut.The design maintains consistent clearance reduction(or elimination)regardless of wear and tear,and can be adjusted to meet the requirements of preload,friction,and operating clearance applications.

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