The Acme Screw Backlash Survival Guide
The question constantly being asked is, what's so essential about perfecting backlash design for acme screws? This acme screw backlash survival guide will answer that question and give you the information you need to accommodate backlash in your linear motion design.
What Is Backlash?
Backlash (lash) is defined as the relative axial clearance between a lead screw and nut without rotation of the screw or nut. Backlash can increase wear and stack up over time, resulting in inaccurate positioning.
The Importance of Backlash Design
Backlash consideration is critical in lead screw designs where positioning, power, and accuracy are essential, like syringe pumps, unmanned robots, and other medical, industrial, and defense applications. It is imperative that doctors, defense officers, and industry professionals can rely on precision accuracy in their applications.
Backlash is detrimental in precision positioning applications where small location changes are relevant. If a power transmission system doesn't compensate for backlash, it can add up over many cycles resulting in inaccurate positioning. For example, medical infusion pumps gradually administer intravenous medications to patients. Suppose the design engineer of the pump application doesn't compensate for the correct amount of backlash. A patient could receive the wrong medication dosage in this specific case, resulting in a life-threatening situation.
The image below depicts the difference in force between a standard nut, tension anti-backlash nut, and compression anti-backlash nut.
CAUTION – When uncompensated lash is equal to or greater than the pitch, the assembly should be replaced.
How to Compensate for Backlash
The most basic method for reducing or eliminating lead screw and acme screw backlash is the incorporation of a spring or washer to axially force two nut halves against opposite flanks of the screw thread. Helix Linear Technologies offers multiple anti-backlash nut options, including axial, radial, torsional, and custom anti-backlash nuts and lead screws with centralizing, high-lead threads. Selecting the right anti-backlash option for your project depends on numerous factors, such as; payload, accuracy, repeatability, space constraints, and available torque. Our application engineers will work with you to determine the best solution for your specific system needs.
The design of an accurate lead screw application starts with a backlash consideration. Correct design principles are critical in achieving low friction, minimum wear, long life, and precise positioning.
As the nut's wear and backlash increase, loosen the mounting bolts and readjust the PowerAc™ No-Lash Flange and nut until the lash is minimized.
Helix has developed several unique ways to reduce or remove the lash between the screw and nut.
For screw diameters of 5/8 inch, PowerAc™ No-Lash Flange is identical to a standard flange except for the slotted mounting holes. The backlash can be removed by using a nut with PowerAc™ No-Lash Flange in combination with a standard nut and flange. By rotating the slotted PowerAc™ No-Lash Flange and nut relative to the other, the thread in the second nut advances until the lash is reduced.
For a completed PowerAc™ No-Lash Flange assembly order: two standard nuts, one standard flange, and one No-Lash Flange. For example, a ¾” – 2 assemblies will require the following:
2 – 20072 Standard Nuts
1 – 70262 Standard Flange
1 – 73262 No-Lash Flange
A Word of Caution
When the uncompensated lash is equal to or greater than times the pitch, the assembly should be replaced.
As the nut's wear and backlash increase, loosen the mounting bolts and readjust the PowerAc™ No-Lash Flange and nut until the lash is minimized.
Contact us today to speak to one of our anti-backlash engineering experts about your project requirements and backlash challenges. Let's innovate together.
