Editor’s choice
Is roller screw technology still under appreciated?
Mark Moore of Moore International examines the performance of roller screws and highlights their advantages.
E
ven though the very first patent for a roller screw was granted in 1949, why is roller screw technology a less
recognised option, when compared to other mechanisms for conversion of rotary torque into linear motion? When designers consider the options for
controlled linear motion, do they fully examine the benefits that the roller screw offers in performance in relation to hydraulic or pneumatic cylinders, as well as ball or lead screws? Roller screws have distinct advantages over these four other rivals in all of major selection considerations. Of course, each designer may have differing selection criteria,
The RV screw is a high precision, robust assembly where the rollers do not recirculate, thus enabling a very stable driving torque.
which will be determined by the application. So, in examining the major selection concerns, here is how the roller screw performs ... If we take efficiency as primary criterion for
selection, the roller screw is over 90 per cent efficient, and only the ball screw out of the five recognised choices can compare. Life expectancy is very long for a roller screw, typically 15 times longer than a ball screw, and only the hydraulic or pneumatic cylinder options give similar service life, however, they both need maintenance to retain long life. When it comes to maintenance itself, the
roller screw requires very little maintenance as the friction created by the rolling screw
design is minimal compared to that generated by sliding friction. However, the roller screw should still be lubricated to minimise wear and to dissipate heat. Providing sufficient protection against contaminants is also critical to long functional life, so wipers can be added to the front or back of the nut to scrape par ticulates from the threads throughout the screw stroke. Maintenance intervals will depend on two main factors, the operating conditions and the screw diameter. By comparison, both hydraulic and pneumatic cylinders need much higher levels of attention, and ball screws can suffer from pitting in the ball groove and the ball bearings can be lost or need replacing. The load ratings of a roller screw can only
be matched by a hydraulic cylinder. In performance, roller screws have, in some specific applications, been able to move up to 20,000 times its own weight, so are capable of carrying greater loads in relation to their size. They are also very suitable to carry heavy loads for continuous duty and in the most arduous of conditions. The combination of speed and acceleration can only be equalled by that of a pneumatic cylinder. Both the stiffness and the effects of shock loading also make the roller screw an attractive option. Automated industrial production lines are
being designed to be more compact systems that take up less space. One of the biggest
10 June 2021 Instrumentation Monthly
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