End support refers to the way in which the two ends of a threaded spindle (e.g., a ball screw or trapezoidal screw) are supported, guided, and secured within the machine. It ensures that the spindle runs precisely, maintains its position, and safely absorbs the forces that act upon it.
Purpose of end support
- Absorption of axial and radial forces
- Ensuring smooth, backlash-free operation
- Preventing vibrations and deflection of the spindle
- Determining the Permissible Speed (Critical Speed)
- Achieving High Positioning Accuracy
Properly designed end bearings are critical to the system’s service life and the accuracy of the entire axis operation.
Typical Types of Storage
In ball screws, end stops are typically implemented in the following combinations:
- Fixed-Loose Bearing Arrangement
The fixed bearing absorbs axial and radial forces and defines the position, while the loose bearing allows for longitudinal expansion of the spindle. This bearing arrangement is considered the standard solution for most applications. - Two Fixed Bearings
In this configuration, both bearings are fixed, which increases the risk of preload; it is used only for short spindles or symmetrical loads. - Two floating bearings
No axial position is defined here, which is why this configuration is only suitable for radial guidance. - Single-sided bearing / free end
This solution is compact but is only suitable for short spindles or light loads.
Bearing Configurations
The following are typically used in the final bearing housing:
- Angular contact ball bearings (preloaded in pairs): high axial rigidity
- Deep groove ball bearings: simple radial support
- Tapered roller bearings: high load capacity
- Cylindrical roller bearings: high radial loads
In ball screw drives, preloaded angular contact ball bearings are most common because they allow for precise axial positioning.
Practical Implications
The choice of end bearings affects:
- maximum speed
- Stiffness of the entire system
- Positioning Accuracy
- Wear Characteristics
- Vibration and Noise Levels
An improperly designed end stop can cause even a high-quality lead screw to become inaccurate or unstable.