The machine does not position consistently, and when reversing the direction of motion, a short delay occurs. This phenomenon is known as backlash or reversal play. It is a major source of uncertainty for both the operator and the designer. At LM Systems, we understand that accuracy forms the foundation of a reliable production process. In this article, we take a deep dive into the subject of play within linear systems. We analyze the causes and present the technical solutions that we, as an engineering partner, provide to guarantee your accuracy.
Undesired backlash (play)
In practice, backlash is often noticed through dimensional deviations in the final product. For example, when milling a circle, a slight flattening appears at the quadrant transitions. This occurs because the drive rotates the spindle, but the carriage does not immediately follow. In addition to positioning errors, excessive play leads to instability in the servo motor control loop. The motor attempts to correct the position, but due to the dead zone, a vibration occurs, commonly referred to as “hunting.” This results in additional wear on components and shortens the lifespan of the entire machine.
Wear is a well-known culprit in existing systems. However, the cause often already lies in the initial selection of components. Under heavy loads or high speeds, raceways or balls deform if the stiffness of the construction is insufficient. Without the proper countermeasures, this results in an inaccurate machine that does not meet the specified tolerances.
Preload for backlash-free linear motion
The most effective method to prevent backlash is the application of preload. In a ball screw, this is achieved by equipping the nut with balls that are a fraction larger than the space between the raceways. This creates a controlled internal load. This preload ensures constant contact between the balls and the spindle, completely eliminating play.
There are various levels within this technique. A single nut with oversized balls provides a solution for medium loads. For applications requiring extremely high stiffness, we use double nuts that are tensioned against each other. The result is a linear motion that responds immediately to every rotation of the motor without any delay or hysteresis.
Extremely tight tolerances
At LM Systems, we do not supply standard off-the-shelf products—we provide certainty. Our components distinguish themselves through extremely tight tolerances and high material purity. Where the standard market often stops at acceptable accuracy, we go further by considering dynamic load ratings and stiffness under varying temperatures.
Our focus is on reducing the Total Cost of Ownership. A spindle with the correct preload and proper lubrication interval will last for years without loss of accuracy. We demonstrate our quality through technical specifications based on actual load diagrams and calculations. With us, you are guaranteed that the selected solution will perform under the demanding conditions of your specific application.
Examples of backlash-free systems in high-end machine building where LM Systems can provide support:
- In CNC machining centers where every micrometer counts for component fit. High stiffness is required here to absorb cutting forces without tool deflection.
- In pick-and-place robots in the electronics industry. These applications involve extremely high accelerations, and the head must stop immediately at the correct position to place small components.
- In medical technology, such as MRI scanners or surgical robots. Absolute reliability and smooth, shock-free motion are required for patient safety.
- In precision dosing systems in the pharmaceutical industry, where spindle displacement directly determines the exact amount of liquid dispensed.
This added value lies in translating a technical challenge into a working machine. Our engineers at LM Systems act as sparring partners for your designer. We implement modifications in our own workshop, ranging from adapting spindle ends to applying special coatings for corrosive environments.
Collaborating with our engineers
When do you choose zero backlash?
Is backlash always a problem? In simple adjustment systems where only manual positioning is required, a small amount of play is often acceptable and more cost-effective. The choice for a backlash-free solution becomes necessary under the following criteria:
When repeatability in both directions must be below 0.02 millimeters, a preloaded system is unavoidable. In dynamic processes with frequent direction changes, eliminating play is essential to prevent vibrations. If the machine must operate in an automated environment with closed control loops, we always recommend a system with defined preload to guarantee control stability.
Working together towards results
You have seen how important it is to limit backlash for any machine that must perform at the highest level of accuracy. By choosing the correct preload and high-quality components, you eliminate design risks and increase the reliability of your installation. LM Systems is ready to support you with in-depth technical knowledge and customized solutions that precisely match your challenge. Contact us and discover what customization means for your application.