Customised planetary roller screws from LTK
Our roller screws are available for all types of design
How does a roller screw work?
A planetary roller screw (also known as a planetary screw drive or threaded roller screw drive) is a drive screw that uses rollers or so-called planets to convert a rotational force into a translational movement. Its functional principle combines the features of a roller bearing and a planetary gearbox (see illustration). The planetary rollers are firmly guided in the nut and transmit the rotary motion of the spindle rod.
The resulting advantage is that high forces can be converted at high dynamics (speed and acceleration). By using rollers as rolling elements to transmit the movement and load, a high load capacity, precision and a longer service life can be achieved.
There are three basic types of roller screw drives:
- Roller screw drives with roller feedback
- Roller screw drives without roller feedback
- Inverted roller screws
In roller screw drives without roller feedback, the spindle is synchronised with the nut via the planetary gearring. This eliminates the need to reposition the planetary roller, which allows higher speeds. The gearing means that the position of all components is determined at all times. The spindle can therefore also be developed without slippage or backlash.
In roller screw drives with roller feedback, the planetary roller is moved to the next ‘thread’ at the end of a lead. This design enables smaller pitches and a more compact design, but is subject to slippage due to the design.
Inverted roller screws differ fundamentally in their design from all other mechanical drive screws. This design consists of a nut tube, planetary rollers and a push rod. All components are inverted; the thread is located in the nut tube and the push rod moves instead of the nut. This is ideal for applications in the hygiene sector, where installation space is limited and as a replacement for hydraulic lifting cylinders.
The performance of roller screws exceeds that of ball screws many times over due to the higher number of contact points. The roller screw drive can therefore move higher forces in the same installation space and impresses with a longer service life. The roller screw drive is also particularly suitable for smaller pitches or when only very little installation space is available. The drive types therefore differ in terms of load capacity, speed, precision, efficiency and price. In order to make a measurable statement in facts and figures, the respective application must be considered in detail. Ground ball screws, for example, are very precise drives, but this also has a direct influence on the price.
Explanation: KGT = ball screw drive; GRT = roller screw drive; PWG = planetary screw drive
With regard to modern production possibilities, it is worth considering the use of a roller screw drive as soon as one of the following cases applies:
- Small available installation space
- High power density required
- High forces & dynamics
- High ambient temperatures
- High safety requirements (failsafe application)
Roller screws are used in various high-precision and heavy-duty applications, such as in the machine tool industry, in the aerospace industry, in robotic systems or in medical and measurement technology. Roller screws are particularly suitable for pressing and punching tasks or as a replacement for hydraulic drives/hydraulic cylinders. Common processes include welding, sealing, joining, pressing, assembling and positioning.
