Roller screw drive with roller return

A roller screw drive with roller return is a linear technical drive with roller-shaped rolling elements .

functionality

In contrast to the planetary roller screw drive, the rollers of the roller screw drive with roller return do not have a thread, but circumferential grooves. They therefore move faster in the axial direction than the spindle nut and must be lifted off the spindle and set back due to a special geometry on the nut.

Since the rollers move radially and axially relative to the nut, they cannot be guided through a ring as with the planetary roller screw drive. Instead, they are held in place radially by a kind of cage.

The decisive advantage of the roller screw drive with roller return is the minimum possible pitch, which is even less than that of the planetary roller screw drive. Since the thread of the rollers has no pitch, the pitch of the spindle can be selected even more finely - up to 1 mm pitch for a 50 mm spindle diameter. The resulting large number of contact surfaces creates a very rigid system with a high load rating . However, the feedback mechanism limits the maximum permissible speed of the screw drive to a peripheral speed of 1.5–2.5 m / s at the center circle diameter.

lifespan

The service life of a roller screw drive is calculated using the dynamic load rating, analogous to roller bearings and ball screws . Since only axial forces are permitted anyway, the radial and axial coefficients are omitted. The following applies to the characteristic fatigue life of the roller screw drive with roller return: ${\displaystyle C_{a}}$

${\displaystyle L_{10}=\left({\frac {C_{a}}{F}}\right)^{3}\cdot 10^{6}[Umdrehungen]}$

As with rolling bearings , this is the service life that has a 90% probability of being reached or exceeded.

application

The properties of the roller screw drive with roller return - great rigidity and high load rating with a low gradient - allow extremely precise positioning of large loads at rather low speeds of maximum 50-100 mm / s in conjunction with a high-resolution measuring system and a corresponding controller .

See also

• Ball screw
• Planetary roller screw drive
• Coilover suspension

Web links

• Roller screw drives (accessed January 15, 2016)
• Linear technology (accessed on January 15, 2016)
• Mechatronik-News-Issue-9-September-2009 (accessed on January 15, 2016)