A driven nut, also known as a driven spindle nut, is a type of threaded drive in which the nut—rather than the spindle—is set in rotation. Linear motion is generated in two ways: If the nut’s bearing housing is mounted in a fixed position, the spindle is displaced axially and, in a sense, pushed out of the nut, as is the case, for example, in presses. If, on the other hand, the spindle is firmly clamped, the rotating nut, together with its bearing housing, moves along the spindle and carries the load attached to it—for example, the ram of a machine tool.
Structure and Functioning
For long travel distances, the conventional ball screw drive with a rotating spindle reaches its limits sooner than one would expect based on power transmission alone. The limiting factor is the critical bending speed: Starting at a certain combination of spindle length and rotational speed, the rotating spindle begins to oscillate. This compromises positioning accuracy and service life and limits the achievable travel speed. The driven nut reverses this principle: Because the spindle is fixed in place, it cannot reach its critical bending speed. As a result, spindle length is no longer a limiting factor.
Advantages
- A key advantage of the driven nut is that there is no critical bending speed. Since the spindle does not rotate, there is no upper speed limit dictated by the critical bending speed of a rotating spindle. However, the natural bending frequency must still be taken into account even for stationary spindles. Resonance is less critical due to the low energy input from the driven nut.
- In addition, the driven nut optimizes radial and axial runout. This allows the system to operate at maximum speed. However, the natural frequency range should be passed through quickly to avoid placing unnecessary stress on the system.
- This special nut also reduces the moments of inertia. Since the spindle does not need to be rotated, the moments of inertia in the system are reduced. This enables a simpler and more cost-effective end bearing arrangement for the non-rotating spindle.
- Another advantage stems from the compensation for temperature effects. The fixed spindle can be easily preloaded to compensate for changes in length caused by temperature effects, which are further minimized by the use of a hollow spindle with cooling.
Limitations and Disadvantages
One drawback of this system is the motor, which must be moved along with the table, requiring additional installation space and the corresponding power supply.
Applications
- CNC machines and machine tools with high dynamic performance requirements
- 3D printers or handling systems
- Actuators with Integrated Linear Drive
- Presses
- Pipe Bending Machines
- Sheet Metal Fabrication and Sheet Metal Bending Machines
- Clinching Machines
- Die-cutting machines